Post-collisional Potassic–Ultrapotassic Magmatism of the Variscan Orogen: Implications for Mantle Metasomatism during Continental Subduction
Post-collisional Potassic–Ultrapotassic Magmatism of the Variscan Orogen: Implications for Mantle...
G, Soder, Christian;L, Romer, Rolf
2018-06-01 00:00:00
Abstract Mantle-derived potassic to ultrapotassic magmatism is a typical feature of collisional orogens. Potassium-rich magmas recurrently formed across the European Variscides during a period of 50 Myr, following the peak of the orogeny at 340 Ma. Lamprophyre dykes are part of this magmatism and have crust-like trace element patterns, as well as elevated initial 87Sr/86Sr and 207Pb/204Pb and low 143Nd/144Nd along with high mantle-compatible trace element concentrations. This hybrid nature requires at least two source components: subducted continental crustal material and mantle peridotite. Sampling of dyke rocks across tectonic zones of contrasting development reveals two groups of K-rich mantle-derived rocks with distinct trace element patterns and isotopic compositions. The dataset covers a wide range of magma compositions, reflecting their multi-stage petrogenesis. Many of the geochemical characteristics of ultrapotassic magmas, such as very high K2O/Na2O, are already features of the high-pressure crustal melts. Whether the trace element signature is transferred unchanged into these liquids or not largely depends on the behaviour of accessory phases. For instance, high Th/La is related to residual allanite during partial melting of subducted felsic crust. The silica-rich liquids migrate from the slab into the overlying lithospheric mantle. Reaction with peridotitic wall-rocks during channelized flow crystallizes orthopyroxene ± garnet at the expense of olivine, resulting in depletion in Al2O3 and garnet-compatible trace elements in the coexisting melt. Progressive wall-rock interaction causes enrichment in incompatible trace elements and may produce peralkaline melt compositions. These metasomatic agents eventually freeze in the lithospheric mantle, forming non-peridotitic lithologies rich in hydrous minerals such as phlogopite. Variable degrees of melting during post-collisional and later lithospheric extension preferentially affect the heterogeneously metasomatized mantle domains, which results in a broad range of lamprophyre compositions, including amphibole lamprophyres, mica lamprophyres and peralkaline lamproites. INTRODUCTION Mantle-derived potassic and ultrapotassic rocks are widespread in many collisional belts and their emplacement is typically related to stages of post-collisional extension, which cause partial melting of metasomatized lithospheric mantle domains (e.g. Peccerillo, 1999; Williams et al., 2001; Altherr et al., 2004; Prelević et al., 2012). One of the most striking features of these rock associations is their strong trace element enrichment, coupled with continental crust-like isotopic signatures. This feature is indicative of the contribution of high amounts of subducted continental material (e.g. sediments) to their source regions (e.g. Thompson et al., 1984; Conticelli & Peccerillo, 1992; Nelson, 1992; Peccerillo, 1999). Partial melts derived from subducted sediments are highly fertile components and may control the trace element budget of calc-alkaline arc magmas (e.g. Elliott, 2003; Hermann & Spandler, 2008; Skora & Blundy, 2010). Compared with ultrapotassic rocks, however, the sedimentary contribution to arc basalts is minor. Here, dehydration of subducted altered oceanic lithosphere causes flux-melting of the mantle wedge, which produces high amounts of basaltic magma, thereby diluting the sedimentary signal (e.g. Grove et al., 2002; Singer et al., 2007). The generation of ultrapotassic rocks is favored during subduction of continental crust (e.g. during continental collision), where dehydrating altered mafic–ultramafic lithologies are largely missing as a fluid source. The small volumes of silica-rich melt released from subducted continental crust are in chemical disequilibrium with peridotite and become entrapped within the lithospheric mantle (Sekine & Wyllie, 1982a, 1982b). Hydrous minerals in the resulting metasomatic domains may cause preferential melting during later decompression and heating in connection with regional extension (Foley, 1992). Ultrapotassic magmatism, therefore, should be one of the typical consequences of deep subduction and ultrahigh-pressure (UHP) metamorphism of continental crust. This is supported by the occurrence of ultrapotassic rocks in many collisional belts, such as the Alpine–Himalayan range or the European Variscides (e.g. Schreyer et al., 1987; Parkinson & Kohn, 2002; Janoušek & Holub, 2007; Zhao et al., 2009; Ersoy & Palmer, 2013). The Variscan Orogen is the ideal site for studying the effect of crustal recycling in collision zones. Here, felsic high-pressure rocks are widely distributed and are commonly associated with garnet peridotites, garnet pyroxenites and eclogites, and locally may contain micro-diamonds, providing evidence for deep continental subduction (e.g. Becker & Altherr, 1992; Massonne, 2003; Medaris et al., 2006; Kotková et al., 2011, 2016; Perraki & Faryad, 2014; Haifler & Kotková, 2016). Low-volume potassic to ultrapotassic magmas are present throughout the internal zones of the orogenic belt, repeatedly emplaced during phases of lithospheric extension, covering a time span of at least 50 Myr (e.g. Schaltegger & Corfu, 1992; Laurent et al., 2017). Lamprophyre dykes are a manifestation of this magmatism and were mostly emplaced between 325–315 Ma and 300–285 Ma (e.g. Turpin et al., 1988; von Seckendorff et al., 2004; Abdelfadil et al., 2014; Dupuis et al., 2015; Krmíček et al., 2016). We present a comprehensive set of whole-rock geochemical and Sr–Nd–Pb isotope data from several lamprophyre dyke swarms of SW Germany and eastern France. The study covers the type lamprophyre areas Spessart (spessartite) and Vosges (vogesite, minette). We also provide the first report on lamproite-like minette dykes for this classical area. The dyke swarms studied constitute suites of cogenetic magmas that are interpreted to represent several independent melting events within the metasomatized mantle. The resulting chemical heterogeneity allows us to investigate their multi-stage petrogenesis: (1) selective mobilization from the subducted crust, whereby partial melts and restite may show different trace element signatures; (2) reactive melt transport within the mantle; (3) partial melting of the metasomatized mantle; (4) modification of these melts during fractional crystallization, crustal assimilation and/or magma mixing. Although later processes obliterate to some extent the original nature of contributions from the subducted material, sampling along the traverse across various Variscan tectonic units allows the tracing of two distinct continental signatures. GEOLOGICAL SETTING The Variscan Orogen is the result of the Palaeozoic convergence of Laurussia and Gondwana during the closure of the Rheic Ocean, eventually leading to the assembly of Pangaea (e.g. Matte, 1986; Franke, 2000; Kroner & Romer, 2013). In SW Germany and easternmost France, Variscan basement is exposed in two belts (i.e. the Vosges and Palatine to the west and the Schwarzwald, Odenwald, and Spessart to the east) that are separated by the Cenozoic rift of the Upper Rhine Graben (Fig. 1). The study area includes several tectonic zones: Rheno-Hercynian Zone (RHZ), Northern Phyllite Zone (NPZ), Mid-German Crystalline Zone (MGCZ), Saxo-Thuringian Zone (STZ) and Moldanubian Zone (MZ). The RHZ was part of Avalonia (Laurussia), whereas the STZ and MZ were part of Gondwana (Franke, 2000). The MGCZ probably hosts the obscured Rheic suture (Zeh & Gerdes, 2010). Fig. 1. View largeDownload slide (a) Map showing the exposed Variscan basement of Europe, palaeogeographical affinities of crustal domains and the location of the Rheic suture zone (after Franke, 2000; Linnemann et al., 2007). BM, Bohemian Massif; FMC, French Massif Central. (b) Simplified geological map of the study area (modified after Lahner & Toloczyki, 2004) with sample localities indicated within the basement units (Taunus, Odenwald–Spessart, Palatine, Schwarzwald and Vosges) exposed along the Cenozoic Upper Rhine Graben (URG). SNB, Permo-Carboniferous Saar–Nahe Basin. In cases of high density of sample locations, only representative ones are shown. Fig. 1. View largeDownload slide (a) Map showing the exposed Variscan basement of Europe, palaeogeographical affinities of crustal domains and the location of the Rheic suture zone (after Franke, 2000; Linnemann et al., 2007). BM, Bohemian Massif; FMC, French Massif Central. (b) Simplified geological map of the study area (modified after Lahner & Toloczyki, 2004) with sample localities indicated within the basement units (Taunus, Odenwald–Spessart, Palatine, Schwarzwald and Vosges) exposed along the Cenozoic Upper Rhine Graben (URG). SNB, Permo-Carboniferous Saar–Nahe Basin. In cases of high density of sample locations, only representative ones are shown. The MGCZ is exposed in the Odenwald–Spessart area and represents a basement wedge within the STZ, dominated by granitoid plutons framed by medium- to high-grade schists and gneisses (Altherr et al., 1999a; Zeh & Will, 2010). Orthogneisses with Silurian–Devonian protolith ages are possibly remnants of the Rheic magmatic arc (e.g. Dombrowski et al., 1995; Reischmann et al., 2001; Franke, 2000). They additionally contain relict eclogites (Will & Schmädicke, 2001). The MGCZ separates very low- to low-grade metasediments and volcanic rocks from the NPZ and RHZ in the NW and low- to medium-grade metamorphic rocks of the STZ in the SE. The Saxo-Thuringian volcano-sedimentary succession in the northern Vosges and northern Schwarzwald area comprises a SE-dipping wedge of lower Palaeozoic metasediments and meta-igneous rocks and Upper Devonian to Lower Carboniferous synorogenic volcanic rocks and clastic sediments. The Lalaye–Lubine/Baden Baden shear zone separates the STZ–MGCZ from the MZ, where a basement wedge of dominantly medium- to high-grade gneisses and granitoids is exposed in the Vosges and the Central and Southern Gneiss Complexes of the Schwarzwald (e.g. Eisbacher et al., 1989; Skrzypek et al., 2014). Relict mafic and felsic granulites, as well as retrogressed eclogites and Spl-, Grt–Spl- and Grt-peridotites, are present within the metamorphic basement of the Vosges and Schwarzwald (e.g. Altherr & Kalt, 1996; Marschall et al., 2003; Janoušek et al., 2004; Skrzypek et al., 2012). Zircon U–Pb dating of gneisses and granulites has yielded ages of ∼335–342 Ma (Schaltegger et al., 1999; Kober et al., 2004; Skrzypek et al., 2012). UHP conditions (about 4–6 GPa and 1000–1100°C; Altherr & Kalt, 1996) are recorded in garnet peridotites enclosed in gneisses of the Vosges and they indicate that continental crust was subducted to mantle depths during the final stages of the Variscan collision. Additionally, abundant syn- to postkinematic granitoid magmatism affected both domains during the Late Visean (e.g. Schaltegger et al., 1996; Altherr et al., 1999b, 2000; Tabaud et al., 2014, 2015). K-rich Variscan magmatism Although the collisional development of the Variscan belt is highly diachronous and different crustal blocks collided at different times, the post-collisional (after 340 Ma) development of the Variscan belt is largely coeval and broadly corresponds to periods of reorganization of the stress field (e.g. Kroner et al., 2016) that culminated in the development of the Permian Oslo Rift and volcano-sedimentary basins in Variscan Europe (Wilson et al., 2004). Variscan K-rich mantle-derived magmatism is directly related to these tectonic processes. It recurrently formed during c. 60 Myr following the peak of the Variscan Orogeny at 340 Ma, clustering in three major intervals. The first pulse of potassic–ultrapotassic magmatism occurred around 340–335 Ma, synchronous with and shortly following the exhumation of (U)HP units. The second and third pulses occurred during post-collisional and post-orogenic regional extension between 325–315 Ma and 305–280 Ma, respectively (see below and Fig. 2). Fig. 2. View largeDownload slide Compilation of age information on Variscan potassic and ultrapotassic magmatism. Sources of geochronological data: Alps: Schaltegger & Corfu (1992); Bussy et al. (2000), Rubatto et al. (2001) and Bussien et al. (2008); Armorican Massif: Caroff et al. (2015) and Ballouard et al. (2017); Balkan region: Buzzi et al. (2010); Bohemian Massif: Wemmer & Ahrendt (1997), Janoušek & Gerdes (2003), Siebel et al. (2003), Kotková et al. (2010) and Kusiak et al. (2010); Corsica: Paquette et al. (2003) and Rossi et al. (2009); Erzgebirge: Werner (1998), von Seckendorff et al. (2004) and Seifert (2008); French Massif Central: Pagel et al. (1992) and Laurent et al. (2017); Harz: Goll et al. (1998); Iberia: López-Moro et al. (2018, and references therein); Odenwald–Spessart: Hess & Schmidt (1989) and von Seckendorff et al. (2004); Schwarzwald: Hegner et al. (1998); Sudetes: Marheine et al. (2002), Żelaźniewicz et al. (2006) and Jokubauskas et al. (2018); SW England: Dupuis et al. (2015, and references therein); Thuringian Forest: Goll & Lippolt (2001); Vosges: Hess et al. (1995), Schaltegger et al. (1996) and Tabaud et al. (2015). Fig. 2. View largeDownload slide Compilation of age information on Variscan potassic and ultrapotassic magmatism. Sources of geochronological data: Alps: Schaltegger & Corfu (1992); Bussy et al. (2000), Rubatto et al. (2001) and Bussien et al. (2008); Armorican Massif: Caroff et al. (2015) and Ballouard et al. (2017); Balkan region: Buzzi et al. (2010); Bohemian Massif: Wemmer & Ahrendt (1997), Janoušek & Gerdes (2003), Siebel et al. (2003), Kotková et al. (2010) and Kusiak et al. (2010); Corsica: Paquette et al. (2003) and Rossi et al. (2009); Erzgebirge: Werner (1998), von Seckendorff et al. (2004) and Seifert (2008); French Massif Central: Pagel et al. (1992) and Laurent et al. (2017); Harz: Goll et al. (1998); Iberia: López-Moro et al. (2018, and references therein); Odenwald–Spessart: Hess & Schmidt (1989) and von Seckendorff et al. (2004); Schwarzwald: Hegner et al. (1998); Sudetes: Marheine et al. (2002), Żelaźniewicz et al. (2006) and Jokubauskas et al. (2018); SW England: Dupuis et al. (2015, and references therein); Thuringian Forest: Goll & Lippolt (2001); Vosges: Hess et al. (1995), Schaltegger et al. (1996) and Tabaud et al. (2015). Potassic–ultrapotassic magmatism around ∼340–335 Ma resulted in the emplacement of amphibole–biotite quartz-melasyenites to melagranites (durbachites) and subordinate two-pyroxene melasyenites to melagranites, forming independent intrusive bodies or co-magmatic enclaves within granitoids of the Bohemian Massif, Vosges, Schwarzwald, the External Massifs of the Alps, and the Balkan segment, for instance (e.g. Schaltegger & Corfu, 1992; Holub, 1997; Gerdes et al., 2000; Janoušek & Holub, 2007; Buzzi et al., 2010; Kotková et al., 2010; von Raumer et al., 2014; Tabaud et al., 2015). Similar to durbachites, the vaugnerites of the French Massif Central (FMC) are K-rich monzodiorites and quartz monzonites, which are typically associated with more voluminous granites (Sabatier, 1991). Although the FMC vaugnerites dominantly fall into the youngest age group of Variscan K-rich mafic magmatism, they are present during all three stages (Laurent et al., 2017). Similar to the FMC, vaugnerites were emplaced in Iberia (e.g. Scarrow et al., 2009; López-Moro et al., 2017) and redwitzites in the West Bohemian Massif/Erzgebirge (e.g. Siebel et al., 2003). Lamprophyre dyke swarms were emplaced throughout the internal zones of the orogen during both the post-collisional and post-orogenic stages of lithospheric extension (e.g. Oberhänsli, 1986; Hess & Schmidt, 1989; Hess et al., 1995; Hegner et al., 1998; von Seckendorff et al., 2004; Awdankiewicz, 2007; Abdelfadil et al., 2014; Dupuis et al., 2015; Krmíček et al., 2016). K-rich mafic magmatic rocks, such as lamproites, lamprophyres, shoshonites and latites, also occur in the Upper Carboniferous–Permian basins of SW England, the Saar–Nahe area, the Thuringian Forest and the Erzgebirge foreland (Velde, 1971; Goll & Lippolt, 2001; von Seckendorff et al., 2004; Dupuis et al., 2015). The earliest K-rich, mantle-derived melts within the study area are amphibole–biotite quartz melasyenite intrusions (durbachites), which are present in the central and southern Vosges (as part of the Crêtes and Ballons intrusions), dated around 340 Ma, and the Schwarzwald (Schaltegger et al., 1996; von Raumer et al., 2014; Tabaud et al., 2015). Following Late Visean post-collisional granitoid magmatism, countless lamprophyre dykes were emplaced throughout the study area between 325 and 315 Ma (Turpin et al., 1988; Hess & Schmidt, 1989; Hess et al., 1995; Hegner et al., 1998; von Seckendorff et al., 2004). It is also likely that younger dykes and lavas are present; however, age data are mostly lacking. This study focuses on lamprophyre dykes. ANALYTICAL TECHNIQUES A total of 143 lamprophyre dyke rocks with minimal visible secondary alteration were sampled, examined in thin section and analyzed for whole-rock major and trace elements (Table 1 and Supplementary Data 1; supplementary data are available for downloading at http://www.petrology.oxfordjournals.org). A total of 36 representative samples were analyzed for Sr, Nd and Pb isotopes (Table 2). For whole-rock analysis, specimens were processed in a steel jaw crusher and powdered in an agate ring-and-puck mill. Rock powders were then dried at 105°C for 24 h. Major elements were determined by wavelength-dispersive X-ray fluorescence spectrometry (XRF) using lithium borate fusion disks. International reference samples were used for calibration. Measurements were performed with a Bruker AXS S4 Explorer instrument at the Institute of Earth Sciences at Heidelberg University. Loss on ignition (LOI) was determined from mass loss after heating of 2 g sample powder to 1050°C for 8 h. Table 1: Representative major (wt %) and trace element (μg g–1) analyses of Variscan lamprophyres Group I Odenwald-N Spessart Sample: OD153B OD154 OD169R OD175 OD178 OD043 OD064 OD151C OD156B SP12 SP15 SP19 SiO2 54·2 55·9 55·9 57·0 55·9 45·9 51·5 53·9 55·6 55·9 57·1 56·5 TiO2 2·04 2·06 2·30 2·08 2·17 1·18 1·14 0·96 1·05 2·28 0·82 0·97 Al2O3 12·2 12·0 11·2 11·4 11·5 11·1 14·7 14·1 14·7 11·3 15·3 14·5 Fe2O3 5·39 5·09 4·60 4·81 4·60 9·71 10·2 6·54 7·15 4·98 7·90 7·31 MnO 0·080 0·088 0·069 0·081 0·084 0·150 0·130 0·096 0·100 0·080 0·120 0·100 MgO 5·18 4·18 5·49 4·84 3·82 12·3 7·49 6·84 6·48 5·53 5·70 6·49 CaO 5·27 5·98 6·35 4·53 6·17 8·01 6·89 4·94 5·90 4·64 5·75 5·02 Na2O 0·92 0·28 0·31 1·11 0·20 2·57 3·14 3·20 3·31 1·15 3·32 3·57 K2O 10·1 9·30 8·80 10·0 10·5 3·33 1·03 4·62 3·87 9·72 2·90 3·62 P2O5 1·72 1·28 1·56 1·45 1·50 0·46 0·21 0·58 0·34 1·56 0·14 0·39 LOI 1·91 3·15 2·98 1·77 2·56 4·21 3·29 3·42 1·02 1·59 0·70 1·03 Sum 99·9 99·9 100·1 100·0 99·7 99·5 99·9 99·7 99·9 99·7 100·0 100·0 Sc 23 23 21 22 21 29 23 22 20 21 23 20 V 161 146 121 129 148 202 190 138 149 125 140 142 Cr 173 239 223 196 335 885 254 262 280 236 163 222 Co 20 20 20 20 15 47 41 26 28 21 29 27 Ni 95 121 134 136 185 273 148 162 150 150 98 140 Ga 21 18 19 22 23 15 19 18 19 20 17 18 Rb 245 369 292 408 411 182 49 107 108 366 93 99 Sr 1050 340 580 810 510 1330 630 930 970 710 570 940 Y 30 29 24 30 29 25 20 25 20 27 19 23 Zr 1510 1500 2140 2300 2330 164 152 440 341 2070 175 247 Nb 71 59 62 76 80 21 7·9 24 19 68 16 15 Cs 2·0 3·4 2·3 2·0 6·2 7·5 5·3 3·6 2·7 3·1 5·0 4·6 Ba 3930 2090 1120 3890 2690 2590 730 2680 1830 4560 1110 1900 La 219 115 173 182 171 77 37 117 67 172 32 99 Ce 425 239 317 355 354 178 77 224 130 323 63 191 Pr 55 30 38 41 43 23 8·8 27 15 37 7·3 23 Nd 214 121 144 160 164 93 35 101 59 142 28 89 Sm 30 20 22 24 25 13 6·1 15 9·1 21 4·9 13 Eu 6·4 4·2 4·3 5·0 5·1 3·0 1·7 3·4 2·2 4·4 1·4 3·0 Gd 16 12 12 15 14 7·7 4·8 9·0 6·5 13 4·5 8·8 Tb 1·54 1·34 1·28 1·50 1·56 0·92 0·67 1·00 0·76 1·24 0·63 0·99 Dy 7·4 6·6 6·0 7·3 7·7 5·2 3·9 5·4 4·2 6·0 3·8 5·1 Ho 1·16 1·13 0·91 1·21 1·21 0·90 0·70 0·92 0·76 0·98 0·78 0·86 Er 2·7 2·8 2·3 2·9 3·1 2·5 2·0 2·4 1·9 2·4 2·1 2·1 Tm 0·34 0·39 0·30 0·40 0·40 0·32 0·28 0·31 0·28 0·33 0·31 0·29 Yb 2·3 2·4 1·7 2·4 2·4 2·1 1·8 2·1 1·7 2·2 2·0 2·0 Lu 0·35 0·33 0·24 0·33 0·33 0·34 0·26 0·30 0·23 0·31 0·28 0·26 Hf 41 42 55 69 67 4·2 4·0 12 9·1 57 6·3 6·6 Ta 3·6 3·1 3·4 3·9 4·2 1·0 0·4 1·6 1·2 3·4 1·1 1·0 Pb 24 89 7 91 35 18 19 29 23 151 15 26 Th 63 42 67 85 69 14 11 39 22 63 18 33 U 9·4 8·2 11 13 13 2·7 2·0 5·6 3·0 10 3·4 4·8 Group I Odenwald-N Spessart Sample: OD153B OD154 OD169R OD175 OD178 OD043 OD064 OD151C OD156B SP12 SP15 SP19 SiO2 54·2 55·9 55·9 57·0 55·9 45·9 51·5 53·9 55·6 55·9 57·1 56·5 TiO2 2·04 2·06 2·30 2·08 2·17 1·18 1·14 0·96 1·05 2·28 0·82 0·97 Al2O3 12·2 12·0 11·2 11·4 11·5 11·1 14·7 14·1 14·7 11·3 15·3 14·5 Fe2O3 5·39 5·09 4·60 4·81 4·60 9·71 10·2 6·54 7·15 4·98 7·90 7·31 MnO 0·080 0·088 0·069 0·081 0·084 0·150 0·130 0·096 0·100 0·080 0·120 0·100 MgO 5·18 4·18 5·49 4·84 3·82 12·3 7·49 6·84 6·48 5·53 5·70 6·49 CaO 5·27 5·98 6·35 4·53 6·17 8·01 6·89 4·94 5·90 4·64 5·75 5·02 Na2O 0·92 0·28 0·31 1·11 0·20 2·57 3·14 3·20 3·31 1·15 3·32 3·57 K2O 10·1 9·30 8·80 10·0 10·5 3·33 1·03 4·62 3·87 9·72 2·90 3·62 P2O5 1·72 1·28 1·56 1·45 1·50 0·46 0·21 0·58 0·34 1·56 0·14 0·39 LOI 1·91 3·15 2·98 1·77 2·56 4·21 3·29 3·42 1·02 1·59 0·70 1·03 Sum 99·9 99·9 100·1 100·0 99·7 99·5 99·9 99·7 99·9 99·7 100·0 100·0 Sc 23 23 21 22 21 29 23 22 20 21 23 20 V 161 146 121 129 148 202 190 138 149 125 140 142 Cr 173 239 223 196 335 885 254 262 280 236 163 222 Co 20 20 20 20 15 47 41 26 28 21 29 27 Ni 95 121 134 136 185 273 148 162 150 150 98 140 Ga 21 18 19 22 23 15 19 18 19 20 17 18 Rb 245 369 292 408 411 182 49 107 108 366 93 99 Sr 1050 340 580 810 510 1330 630 930 970 710 570 940 Y 30 29 24 30 29 25 20 25 20 27 19 23 Zr 1510 1500 2140 2300 2330 164 152 440 341 2070 175 247 Nb 71 59 62 76 80 21 7·9 24 19 68 16 15 Cs 2·0 3·4 2·3 2·0 6·2 7·5 5·3 3·6 2·7 3·1 5·0 4·6 Ba 3930 2090 1120 3890 2690 2590 730 2680 1830 4560 1110 1900 La 219 115 173 182 171 77 37 117 67 172 32 99 Ce 425 239 317 355 354 178 77 224 130 323 63 191 Pr 55 30 38 41 43 23 8·8 27 15 37 7·3 23 Nd 214 121 144 160 164 93 35 101 59 142 28 89 Sm 30 20 22 24 25 13 6·1 15 9·1 21 4·9 13 Eu 6·4 4·2 4·3 5·0 5·1 3·0 1·7 3·4 2·2 4·4 1·4 3·0 Gd 16 12 12 15 14 7·7 4·8 9·0 6·5 13 4·5 8·8 Tb 1·54 1·34 1·28 1·50 1·56 0·92 0·67 1·00 0·76 1·24 0·63 0·99 Dy 7·4 6·6 6·0 7·3 7·7 5·2 3·9 5·4 4·2 6·0 3·8 5·1 Ho 1·16 1·13 0·91 1·21 1·21 0·90 0·70 0·92 0·76 0·98 0·78 0·86 Er 2·7 2·8 2·3 2·9 3·1 2·5 2·0 2·4 1·9 2·4 2·1 2·1 Tm 0·34 0·39 0·30 0·40 0·40 0·32 0·28 0·31 0·28 0·33 0·31 0·29 Yb 2·3 2·4 1·7 2·4 2·4 2·1 1·8 2·1 1·7 2·2 2·0 2·0 Lu 0·35 0·33 0·24 0·33 0·33 0·34 0·26 0·30 0·23 0·31 0·28 0·26 Hf 41 42 55 69 67 4·2 4·0 12 9·1 57 6·3 6·6 Ta 3·6 3·1 3·4 3·9 4·2 1·0 0·4 1·6 1·2 3·4 1·1 1·0 Pb 24 89 7 91 35 18 19 29 23 151 15 26 Th 63 42 67 85 69 14 11 39 22 63 18 33 U 9·4 8·2 11 13 13 2·7 2·0 5·6 3·0 10 3·4 4·8 Group I Group II Taunus Vosges-N Odenwald-S Palatine Schwarzwald Sample: TA01 VO33A VO36 VO86 VO37 OD152 OD157B OD163 PF01 PF04 SCH06 SCH09 SiO2 49·6 50·8 49·3 48·1 52·5 53·8 55·5 51·0 52·8 46·1 52·9 58·7 TiO2 1·16 1·28 1·79 1·73 1·93 0·98 1·35 1·14 1·30 1·52 0·96 1·27 Al2O3 14·0 13·8 12·8 10·8 13·4 13·3 13·0 11·2 14·8 11·6 13·5 14·4 Fe2O3 8·04 7·70 7·83 7·15 6·55 7·87 7·71 7·24 8·25 10·4 7·00 6·74 MnO 0·130 0·130 0·120 0·096 0·072 0·120 0·110 0·140 0·120 0·170 0·110 0·063 MgO 10·4 7·46 8·94 6·97 6·63 8·10 5·64 11·5 5·80 10·8 8·52 5·88 CaO 6·63 7·66 6·37 7·86 4·50 5·86 5·30 4·11 5·90 8·05 5·59 1·93 Na2O 2·17 4·00 2·74 1·57 1·33 2·55 2·54 1·10 2·41 2·27 1·70 2·95 K2O 2·66 1·79 5·84 7·10 7·75 4·63 6·14 6·54 5·67 3·47 4·26 5·20 P2O5 0·47 0·84 1·35 2·14 1·11 0·57 0·82 1·02 0·79 0·96 0·70 0·96 LOI 3·32 4·96 1·78 4·17 4·18 1·55 1·13 4·18 2·36 4·14 4·87 1·11 Sum 99·1 100·8 99·8 99·4 100·6 99·7 99·7 99·9 100·6 100·0 100·4 99·8 Sc 29 21 24 21 17 28 30 23 31 33 29 23 V 192 160 175 171 126 187 203 182 212 247 160 170 Cr 543 213 406 238 188 550 230 482 204 586 600 215 Co 39 27 33 32 23 34 25 37 29 46 31 26 Ni 231 143 207 156 130 137 37 334 43 269 183 120 Ga 15 17 19 21 20 17 17 16 17 19 16 20 Rb 95 26 126 196 153 167 335 224 265 154 174 177 Sr 1120 1470 1100 2430 910 730 560 670 720 810 440 910 Y 25 26 33 36 27 26 35 43 34 29 34 30 Zr 225 322 609 1040 1050 273 532 352 394 322 350 545 Nb 11 27 40 52 112 15 28 19 26 32 26 25 Cs 3·9 0·7 4·7 7·2 1·6 4·5 4·8 11 20 21 9·2 60 Ba 3300 1150 5270 10600 2560 2190 1490 4950 2120 2710 1910 2560 La 77 139 154 305 127 37 57 81 53 65 35 67 Ce 164 263 326 644 251 79 132 159 114 140 74 139 Pr 20 31 40 74 29 10 18 20 15 17 10 17 Nd 75 120 162 287 109 42 81 80 66 69 45 72 Sm 11 17 25 40 16 8·4 15 17 13 12 10 13 Eu 2·7 3·9 5·8 8·1 3·5 1·9 3·0 4·1 2·9 3·0 2·1 2·8 Gd 7·6 10 15 20 10 6·7 10 14 9·4 9·0 8·1 9·2 Tb 0·90 1·09 1·55 1·97 1·14 0·87 1·18 1·70 1·20 1·11 1·08 1·08 Dy 5·0 5·5 7·5 8·7 6·1 5·1 6·8 8·8 7·0 6·2 6·7 5·9 Ho 0·86 0·97 1·23 1·34 0·99 0·94 1·25 1·43 1·28 1·09 1·26 1·08 Er 2·3 2·4 3·0 3·0 2·4 2·6 3·5 3·6 3·4 2·8 3·4 2·9 Tm 0·33 0·32 0·38 0·38 0·31 0·38 0·50 0·47 0·50 0·37 0·49 0·38 Yb 2·2 2·1 2·3 2·4 1·8 2·4 3·4 2·9 3·2 2·4 3·1 2·6 Lu 0·32 0·31 0·34 0·34 0·27 0·35 0·48 0·43 0·47 0·33 0·44 0·36 Hf 5·7 7·5 15 27 25 7·3 15 8·8 11 8·4 10 15 Ta 0·69 1·5 2·4 2·9 7·4 1·0 1·9 1·2 1·7 1·8 1·9 1·6 Pb 18 21 23 34 24 30 17 12 21 26 29 10 Th 16 33 31 65 29 17 40 21 29 19 36 27 U 2·8 5·8 4·0 5·9 5·4 4·2 8·1 4·7 4·8 2·9 10 6·0 Group I Group II Taunus Vosges-N Odenwald-S Palatine Schwarzwald Sample: TA01 VO33A VO36 VO86 VO37 OD152 OD157B OD163 PF01 PF04 SCH06 SCH09 SiO2 49·6 50·8 49·3 48·1 52·5 53·8 55·5 51·0 52·8 46·1 52·9 58·7 TiO2 1·16 1·28 1·79 1·73 1·93 0·98 1·35 1·14 1·30 1·52 0·96 1·27 Al2O3 14·0 13·8 12·8 10·8 13·4 13·3 13·0 11·2 14·8 11·6 13·5 14·4 Fe2O3 8·04 7·70 7·83 7·15 6·55 7·87 7·71 7·24 8·25 10·4 7·00 6·74 MnO 0·130 0·130 0·120 0·096 0·072 0·120 0·110 0·140 0·120 0·170 0·110 0·063 MgO 10·4 7·46 8·94 6·97 6·63 8·10 5·64 11·5 5·80 10·8 8·52 5·88 CaO 6·63 7·66 6·37 7·86 4·50 5·86 5·30 4·11 5·90 8·05 5·59 1·93 Na2O 2·17 4·00 2·74 1·57 1·33 2·55 2·54 1·10 2·41 2·27 1·70 2·95 K2O 2·66 1·79 5·84 7·10 7·75 4·63 6·14 6·54 5·67 3·47 4·26 5·20 P2O5 0·47 0·84 1·35 2·14 1·11 0·57 0·82 1·02 0·79 0·96 0·70 0·96 LOI 3·32 4·96 1·78 4·17 4·18 1·55 1·13 4·18 2·36 4·14 4·87 1·11 Sum 99·1 100·8 99·8 99·4 100·6 99·7 99·7 99·9 100·6 100·0 100·4 99·8 Sc 29 21 24 21 17 28 30 23 31 33 29 23 V 192 160 175 171 126 187 203 182 212 247 160 170 Cr 543 213 406 238 188 550 230 482 204 586 600 215 Co 39 27 33 32 23 34 25 37 29 46 31 26 Ni 231 143 207 156 130 137 37 334 43 269 183 120 Ga 15 17 19 21 20 17 17 16 17 19 16 20 Rb 95 26 126 196 153 167 335 224 265 154 174 177 Sr 1120 1470 1100 2430 910 730 560 670 720 810 440 910 Y 25 26 33 36 27 26 35 43 34 29 34 30 Zr 225 322 609 1040 1050 273 532 352 394 322 350 545 Nb 11 27 40 52 112 15 28 19 26 32 26 25 Cs 3·9 0·7 4·7 7·2 1·6 4·5 4·8 11 20 21 9·2 60 Ba 3300 1150 5270 10600 2560 2190 1490 4950 2120 2710 1910 2560 La 77 139 154 305 127 37 57 81 53 65 35 67 Ce 164 263 326 644 251 79 132 159 114 140 74 139 Pr 20 31 40 74 29 10 18 20 15 17 10 17 Nd 75 120 162 287 109 42 81 80 66 69 45 72 Sm 11 17 25 40 16 8·4 15 17 13 12 10 13 Eu 2·7 3·9 5·8 8·1 3·5 1·9 3·0 4·1 2·9 3·0 2·1 2·8 Gd 7·6 10 15 20 10 6·7 10 14 9·4 9·0 8·1 9·2 Tb 0·90 1·09 1·55 1·97 1·14 0·87 1·18 1·70 1·20 1·11 1·08 1·08 Dy 5·0 5·5 7·5 8·7 6·1 5·1 6·8 8·8 7·0 6·2 6·7 5·9 Ho 0·86 0·97 1·23 1·34 0·99 0·94 1·25 1·43 1·28 1·09 1·26 1·08 Er 2·3 2·4 3·0 3·0 2·4 2·6 3·5 3·6 3·4 2·8 3·4 2·9 Tm 0·33 0·32 0·38 0·38 0·31 0·38 0·50 0·47 0·50 0·37 0·49 0·38 Yb 2·2 2·1 2·3 2·4 1·8 2·4 3·4 2·9 3·2 2·4 3·1 2·6 Lu 0·32 0·31 0·34 0·34 0·27 0·35 0·48 0·43 0·47 0·33 0·44 0·36 Hf 5·7 7·5 15 27 25 7·3 15 8·8 11 8·4 10 15 Ta 0·69 1·5 2·4 2·9 7·4 1·0 1·9 1·2 1·7 1·8 1·9 1·6 Pb 18 21 23 34 24 30 17 12 21 26 29 10 Th 16 33 31 65 29 17 40 21 29 19 36 27 U 2·8 5·8 4·0 5·9 5·4 4·2 8·1 4·7 4·8 2·9 10 6·0 Group II Schwarzwald Vosges-C Vosges-S Sample: SCH12 SCH17 SCH29 SCH32A SCH38 VO10 VO14 VO52 VO05 VO64B VO66 VO83 SiO2 60·0 57·5 62·2 64·2 52·4 51·9 54·0 52·3 56·9 63·7 50·4 60·5 TiO2 1·19 0·95 0·85 0·75 0·91 1·13 1·35 1·31 1·01 0·81 0·93 1·25 Al2O3 12·1 12·8 13·2 14·0 13·1 16·3 15·1 14·8 12·4 12·4 14·1 12·7 Fe2O3 5·26 5·82 4·84 4·19 7·45 7·70 7·55 9·45 6·13 4·13 8·33 3·87 MnO 0·087 0·100 0·089 0·066 0·120 0·120 0·110 0·120 0·100 0·060 0·130 0·120 MgO 5·74 5·37 5·53 4·61 9·73 7·07 7·73 6·97 8·58 4·99 7·15 5·71 CaO 3·93 4·81 3·03 2·92 5·70 5·61 4·90 3·97 4·60 2·55 6·43 3·41 Na2O 1·51 1·63 2·29 2·76 1·82 2·41 2·77 3·71 2·02 1·82 2·46 1·49 K2O 7·38 6·33 5·60 5·22 3·96 2·41 3·93 4·47 6·34 7·53 4·73 7·90 P2O5 1·55 1·10 0·59 0·53 0·73 0·23 0·47 1·02 0·97 1·02 0·85 1·02 LOI 1·21 3·17 1·68 0·73 3·16 5·12 1·76 1·46 0·63 0·61 4·63 1·83 Sum 100·5 100·0 100·2 100·5 99·5 100·1 100·0 100·0 100·1 100·1 100·6 100·3 Sc 22 23 16 14 31 25 24 21 24 18 40 20 V 130 136 102 93 172 151 158 179 138 99 229 117 Cr 235 152 427 230 762 298 313 224 548 341 331 247 Co 20 22 20 16 33 47 27 18 26 19 32 21 Ni 125 66 93 131 209 248 93 101 188 98 90 111 Ga 18 19 16 20 15 17 17 22 16 18 16 21 Rb 219 286 229 167 175 87 168 328 335 407 230 426 Sr 660 480 440 840 520 360 680 880 460 430 750 260 Y 35 28 26 22 31 23 27 30 24 32 35 32 Zr 600 377 306 358 329 210 309 331 393 465 237 649 Nb 33 27 27 22 24 9·4 13 38 35 35 17 39 Cs 5·3 16 24 8·9 19 16 33 19 39 34 12 20 Ba 3050 2410 1750 2890 2390 1100 2130 2550 2460 2230 2120 2750 La 59 49 52 59 62 32 72 124 35 42 37 75 Ce 153 114 116 120 135 68 151 233 87 106 78 179 Pr 26 18 15 15 17 8·1 19 27 13 17 11 28 Nd 133 88 66 61 71 32 74 100 63 87 48 134 Sm 28 20 12 11 13 6·0 12 14 15 23 10 30 Eu 4·5 3·5 2·1 2·3 2·5 1·5 2·9 3·3 2·5 3·5 2·2 4·1 Gd 15 11 8·2 8·0 9·2 4·8 8·2 10 8·8 12 8·1 15 Tb 1·49 1·18 0·99 0·90 1·13 0·72 0·98 1·16 0·98 1·28 1·05 1·54 Dy 7·6 6·1 5·4 4·6 6·4 4·5 5·6 6·4 5·1 6·5 6·5 7·3 Ho 1·24 1·02 0·91 0·85 1·22 0·86 1·02 1·09 0·85 1·13 1·21 1·15 Er 3·1 2·7 2·4 2·1 3·2 2·5 2·7 2·7 2·2 2·9 3·4 2·9 Tm 0·43 0·39 0·36 0·28 0·45 0·37 0·38 0·38 0·32 0·43 0·52 0·40 Yb 2·8 2·3 2·1 1·7 3·0 2·4 2·4 2·2 2·0 3·0 3·5 2·4 Lu 0·41 0·33 0·31 0·26 0·42 0·35 0·36 0·33 0·30 0·43 0·47 0·32 Hf 16 11 9·4 10 10 5·5 8·0 7·7 12 13 6·4 19 Ta 1·9 1·9 2·4 2·4 1·5 0·6 0·8 2·1 2·9 2·4 1·2 2·8 Pb 10 19 15 123 18 48 20 9·3 18 387 22 108 Th 115 69 43 35 43 11 19 40 68 82 26 95 U 20 18 6·6 7·8 9·3 2·2 3·5 6·6 22 27 11 25 Group II Schwarzwald Vosges-C Vosges-S Sample: SCH12 SCH17 SCH29 SCH32A SCH38 VO10 VO14 VO52 VO05 VO64B VO66 VO83 SiO2 60·0 57·5 62·2 64·2 52·4 51·9 54·0 52·3 56·9 63·7 50·4 60·5 TiO2 1·19 0·95 0·85 0·75 0·91 1·13 1·35 1·31 1·01 0·81 0·93 1·25 Al2O3 12·1 12·8 13·2 14·0 13·1 16·3 15·1 14·8 12·4 12·4 14·1 12·7 Fe2O3 5·26 5·82 4·84 4·19 7·45 7·70 7·55 9·45 6·13 4·13 8·33 3·87 MnO 0·087 0·100 0·089 0·066 0·120 0·120 0·110 0·120 0·100 0·060 0·130 0·120 MgO 5·74 5·37 5·53 4·61 9·73 7·07 7·73 6·97 8·58 4·99 7·15 5·71 CaO 3·93 4·81 3·03 2·92 5·70 5·61 4·90 3·97 4·60 2·55 6·43 3·41 Na2O 1·51 1·63 2·29 2·76 1·82 2·41 2·77 3·71 2·02 1·82 2·46 1·49 K2O 7·38 6·33 5·60 5·22 3·96 2·41 3·93 4·47 6·34 7·53 4·73 7·90 P2O5 1·55 1·10 0·59 0·53 0·73 0·23 0·47 1·02 0·97 1·02 0·85 1·02 LOI 1·21 3·17 1·68 0·73 3·16 5·12 1·76 1·46 0·63 0·61 4·63 1·83 Sum 100·5 100·0 100·2 100·5 99·5 100·1 100·0 100·0 100·1 100·1 100·6 100·3 Sc 22 23 16 14 31 25 24 21 24 18 40 20 V 130 136 102 93 172 151 158 179 138 99 229 117 Cr 235 152 427 230 762 298 313 224 548 341 331 247 Co 20 22 20 16 33 47 27 18 26 19 32 21 Ni 125 66 93 131 209 248 93 101 188 98 90 111 Ga 18 19 16 20 15 17 17 22 16 18 16 21 Rb 219 286 229 167 175 87 168 328 335 407 230 426 Sr 660 480 440 840 520 360 680 880 460 430 750 260 Y 35 28 26 22 31 23 27 30 24 32 35 32 Zr 600 377 306 358 329 210 309 331 393 465 237 649 Nb 33 27 27 22 24 9·4 13 38 35 35 17 39 Cs 5·3 16 24 8·9 19 16 33 19 39 34 12 20 Ba 3050 2410 1750 2890 2390 1100 2130 2550 2460 2230 2120 2750 La 59 49 52 59 62 32 72 124 35 42 37 75 Ce 153 114 116 120 135 68 151 233 87 106 78 179 Pr 26 18 15 15 17 8·1 19 27 13 17 11 28 Nd 133 88 66 61 71 32 74 100 63 87 48 134 Sm 28 20 12 11 13 6·0 12 14 15 23 10 30 Eu 4·5 3·5 2·1 2·3 2·5 1·5 2·9 3·3 2·5 3·5 2·2 4·1 Gd 15 11 8·2 8·0 9·2 4·8 8·2 10 8·8 12 8·1 15 Tb 1·49 1·18 0·99 0·90 1·13 0·72 0·98 1·16 0·98 1·28 1·05 1·54 Dy 7·6 6·1 5·4 4·6 6·4 4·5 5·6 6·4 5·1 6·5 6·5 7·3 Ho 1·24 1·02 0·91 0·85 1·22 0·86 1·02 1·09 0·85 1·13 1·21 1·15 Er 3·1 2·7 2·4 2·1 3·2 2·5 2·7 2·7 2·2 2·9 3·4 2·9 Tm 0·43 0·39 0·36 0·28 0·45 0·37 0·38 0·38 0·32 0·43 0·52 0·40 Yb 2·8 2·3 2·1 1·7 3·0 2·4 2·4 2·2 2·0 3·0 3·5 2·4 Lu 0·41 0·33 0·31 0·26 0·42 0·35 0·36 0·33 0·30 0·43 0·47 0·32 Hf 16 11 9·4 10 10 5·5 8·0 7·7 12 13 6·4 19 Ta 1·9 1·9 2·4 2·4 1·5 0·6 0·8 2·1 2·9 2·4 1·2 2·8 Pb 10 19 15 123 18 48 20 9·3 18 387 22 108 Th 115 69 43 35 43 11 19 40 68 82 26 95 U 20 18 6·6 7·8 9·3 2·2 3·5 6·6 22 27 11 25 Table 1: Representative major (wt %) and trace element (μg g–1) analyses of Variscan lamprophyres Group I Odenwald-N Spessart Sample: OD153B OD154 OD169R OD175 OD178 OD043 OD064 OD151C OD156B SP12 SP15 SP19 SiO2 54·2 55·9 55·9 57·0 55·9 45·9 51·5 53·9 55·6 55·9 57·1 56·5 TiO2 2·04 2·06 2·30 2·08 2·17 1·18 1·14 0·96 1·05 2·28 0·82 0·97 Al2O3 12·2 12·0 11·2 11·4 11·5 11·1 14·7 14·1 14·7 11·3 15·3 14·5 Fe2O3 5·39 5·09 4·60 4·81 4·60 9·71 10·2 6·54 7·15 4·98 7·90 7·31 MnO 0·080 0·088 0·069 0·081 0·084 0·150 0·130 0·096 0·100 0·080 0·120 0·100 MgO 5·18 4·18 5·49 4·84 3·82 12·3 7·49 6·84 6·48 5·53 5·70 6·49 CaO 5·27 5·98 6·35 4·53 6·17 8·01 6·89 4·94 5·90 4·64 5·75 5·02 Na2O 0·92 0·28 0·31 1·11 0·20 2·57 3·14 3·20 3·31 1·15 3·32 3·57 K2O 10·1 9·30 8·80 10·0 10·5 3·33 1·03 4·62 3·87 9·72 2·90 3·62 P2O5 1·72 1·28 1·56 1·45 1·50 0·46 0·21 0·58 0·34 1·56 0·14 0·39 LOI 1·91 3·15 2·98 1·77 2·56 4·21 3·29 3·42 1·02 1·59 0·70 1·03 Sum 99·9 99·9 100·1 100·0 99·7 99·5 99·9 99·7 99·9 99·7 100·0 100·0 Sc 23 23 21 22 21 29 23 22 20 21 23 20 V 161 146 121 129 148 202 190 138 149 125 140 142 Cr 173 239 223 196 335 885 254 262 280 236 163 222 Co 20 20 20 20 15 47 41 26 28 21 29 27 Ni 95 121 134 136 185 273 148 162 150 150 98 140 Ga 21 18 19 22 23 15 19 18 19 20 17 18 Rb 245 369 292 408 411 182 49 107 108 366 93 99 Sr 1050 340 580 810 510 1330 630 930 970 710 570 940 Y 30 29 24 30 29 25 20 25 20 27 19 23 Zr 1510 1500 2140 2300 2330 164 152 440 341 2070 175 247 Nb 71 59 62 76 80 21 7·9 24 19 68 16 15 Cs 2·0 3·4 2·3 2·0 6·2 7·5 5·3 3·6 2·7 3·1 5·0 4·6 Ba 3930 2090 1120 3890 2690 2590 730 2680 1830 4560 1110 1900 La 219 115 173 182 171 77 37 117 67 172 32 99 Ce 425 239 317 355 354 178 77 224 130 323 63 191 Pr 55 30 38 41 43 23 8·8 27 15 37 7·3 23 Nd 214 121 144 160 164 93 35 101 59 142 28 89 Sm 30 20 22 24 25 13 6·1 15 9·1 21 4·9 13 Eu 6·4 4·2 4·3 5·0 5·1 3·0 1·7 3·4 2·2 4·4 1·4 3·0 Gd 16 12 12 15 14 7·7 4·8 9·0 6·5 13 4·5 8·8 Tb 1·54 1·34 1·28 1·50 1·56 0·92 0·67 1·00 0·76 1·24 0·63 0·99 Dy 7·4 6·6 6·0 7·3 7·7 5·2 3·9 5·4 4·2 6·0 3·8 5·1 Ho 1·16 1·13 0·91 1·21 1·21 0·90 0·70 0·92 0·76 0·98 0·78 0·86 Er 2·7 2·8 2·3 2·9 3·1 2·5 2·0 2·4 1·9 2·4 2·1 2·1 Tm 0·34 0·39 0·30 0·40 0·40 0·32 0·28 0·31 0·28 0·33 0·31 0·29 Yb 2·3 2·4 1·7 2·4 2·4 2·1 1·8 2·1 1·7 2·2 2·0 2·0 Lu 0·35 0·33 0·24 0·33 0·33 0·34 0·26 0·30 0·23 0·31 0·28 0·26 Hf 41 42 55 69 67 4·2 4·0 12 9·1 57 6·3 6·6 Ta 3·6 3·1 3·4 3·9 4·2 1·0 0·4 1·6 1·2 3·4 1·1 1·0 Pb 24 89 7 91 35 18 19 29 23 151 15 26 Th 63 42 67 85 69 14 11 39 22 63 18 33 U 9·4 8·2 11 13 13 2·7 2·0 5·6 3·0 10 3·4 4·8 Group I Odenwald-N Spessart Sample: OD153B OD154 OD169R OD175 OD178 OD043 OD064 OD151C OD156B SP12 SP15 SP19 SiO2 54·2 55·9 55·9 57·0 55·9 45·9 51·5 53·9 55·6 55·9 57·1 56·5 TiO2 2·04 2·06 2·30 2·08 2·17 1·18 1·14 0·96 1·05 2·28 0·82 0·97 Al2O3 12·2 12·0 11·2 11·4 11·5 11·1 14·7 14·1 14·7 11·3 15·3 14·5 Fe2O3 5·39 5·09 4·60 4·81 4·60 9·71 10·2 6·54 7·15 4·98 7·90 7·31 MnO 0·080 0·088 0·069 0·081 0·084 0·150 0·130 0·096 0·100 0·080 0·120 0·100 MgO 5·18 4·18 5·49 4·84 3·82 12·3 7·49 6·84 6·48 5·53 5·70 6·49 CaO 5·27 5·98 6·35 4·53 6·17 8·01 6·89 4·94 5·90 4·64 5·75 5·02 Na2O 0·92 0·28 0·31 1·11 0·20 2·57 3·14 3·20 3·31 1·15 3·32 3·57 K2O 10·1 9·30 8·80 10·0 10·5 3·33 1·03 4·62 3·87 9·72 2·90 3·62 P2O5 1·72 1·28 1·56 1·45 1·50 0·46 0·21 0·58 0·34 1·56 0·14 0·39 LOI 1·91 3·15 2·98 1·77 2·56 4·21 3·29 3·42 1·02 1·59 0·70 1·03 Sum 99·9 99·9 100·1 100·0 99·7 99·5 99·9 99·7 99·9 99·7 100·0 100·0 Sc 23 23 21 22 21 29 23 22 20 21 23 20 V 161 146 121 129 148 202 190 138 149 125 140 142 Cr 173 239 223 196 335 885 254 262 280 236 163 222 Co 20 20 20 20 15 47 41 26 28 21 29 27 Ni 95 121 134 136 185 273 148 162 150 150 98 140 Ga 21 18 19 22 23 15 19 18 19 20 17 18 Rb 245 369 292 408 411 182 49 107 108 366 93 99 Sr 1050 340 580 810 510 1330 630 930 970 710 570 940 Y 30 29 24 30 29 25 20 25 20 27 19 23 Zr 1510 1500 2140 2300 2330 164 152 440 341 2070 175 247 Nb 71 59 62 76 80 21 7·9 24 19 68 16 15 Cs 2·0 3·4 2·3 2·0 6·2 7·5 5·3 3·6 2·7 3·1 5·0 4·6 Ba 3930 2090 1120 3890 2690 2590 730 2680 1830 4560 1110 1900 La 219 115 173 182 171 77 37 117 67 172 32 99 Ce 425 239 317 355 354 178 77 224 130 323 63 191 Pr 55 30 38 41 43 23 8·8 27 15 37 7·3 23 Nd 214 121 144 160 164 93 35 101 59 142 28 89 Sm 30 20 22 24 25 13 6·1 15 9·1 21 4·9 13 Eu 6·4 4·2 4·3 5·0 5·1 3·0 1·7 3·4 2·2 4·4 1·4 3·0 Gd 16 12 12 15 14 7·7 4·8 9·0 6·5 13 4·5 8·8 Tb 1·54 1·34 1·28 1·50 1·56 0·92 0·67 1·00 0·76 1·24 0·63 0·99 Dy 7·4 6·6 6·0 7·3 7·7 5·2 3·9 5·4 4·2 6·0 3·8 5·1 Ho 1·16 1·13 0·91 1·21 1·21 0·90 0·70 0·92 0·76 0·98 0·78 0·86 Er 2·7 2·8 2·3 2·9 3·1 2·5 2·0 2·4 1·9 2·4 2·1 2·1 Tm 0·34 0·39 0·30 0·40 0·40 0·32 0·28 0·31 0·28 0·33 0·31 0·29 Yb 2·3 2·4 1·7 2·4 2·4 2·1 1·8 2·1 1·7 2·2 2·0 2·0 Lu 0·35 0·33 0·24 0·33 0·33 0·34 0·26 0·30 0·23 0·31 0·28 0·26 Hf 41 42 55 69 67 4·2 4·0 12 9·1 57 6·3 6·6 Ta 3·6 3·1 3·4 3·9 4·2 1·0 0·4 1·6 1·2 3·4 1·1 1·0 Pb 24 89 7 91 35 18 19 29 23 151 15 26 Th 63 42 67 85 69 14 11 39 22 63 18 33 U 9·4 8·2 11 13 13 2·7 2·0 5·6 3·0 10 3·4 4·8 Group I Group II Taunus Vosges-N Odenwald-S Palatine Schwarzwald Sample: TA01 VO33A VO36 VO86 VO37 OD152 OD157B OD163 PF01 PF04 SCH06 SCH09 SiO2 49·6 50·8 49·3 48·1 52·5 53·8 55·5 51·0 52·8 46·1 52·9 58·7 TiO2 1·16 1·28 1·79 1·73 1·93 0·98 1·35 1·14 1·30 1·52 0·96 1·27 Al2O3 14·0 13·8 12·8 10·8 13·4 13·3 13·0 11·2 14·8 11·6 13·5 14·4 Fe2O3 8·04 7·70 7·83 7·15 6·55 7·87 7·71 7·24 8·25 10·4 7·00 6·74 MnO 0·130 0·130 0·120 0·096 0·072 0·120 0·110 0·140 0·120 0·170 0·110 0·063 MgO 10·4 7·46 8·94 6·97 6·63 8·10 5·64 11·5 5·80 10·8 8·52 5·88 CaO 6·63 7·66 6·37 7·86 4·50 5·86 5·30 4·11 5·90 8·05 5·59 1·93 Na2O 2·17 4·00 2·74 1·57 1·33 2·55 2·54 1·10 2·41 2·27 1·70 2·95 K2O 2·66 1·79 5·84 7·10 7·75 4·63 6·14 6·54 5·67 3·47 4·26 5·20 P2O5 0·47 0·84 1·35 2·14 1·11 0·57 0·82 1·02 0·79 0·96 0·70 0·96 LOI 3·32 4·96 1·78 4·17 4·18 1·55 1·13 4·18 2·36 4·14 4·87 1·11 Sum 99·1 100·8 99·8 99·4 100·6 99·7 99·7 99·9 100·6 100·0 100·4 99·8 Sc 29 21 24 21 17 28 30 23 31 33 29 23 V 192 160 175 171 126 187 203 182 212 247 160 170 Cr 543 213 406 238 188 550 230 482 204 586 600 215 Co 39 27 33 32 23 34 25 37 29 46 31 26 Ni 231 143 207 156 130 137 37 334 43 269 183 120 Ga 15 17 19 21 20 17 17 16 17 19 16 20 Rb 95 26 126 196 153 167 335 224 265 154 174 177 Sr 1120 1470 1100 2430 910 730 560 670 720 810 440 910 Y 25 26 33 36 27 26 35 43 34 29 34 30 Zr 225 322 609 1040 1050 273 532 352 394 322 350 545 Nb 11 27 40 52 112 15 28 19 26 32 26 25 Cs 3·9 0·7 4·7 7·2 1·6 4·5 4·8 11 20 21 9·2 60 Ba 3300 1150 5270 10600 2560 2190 1490 4950 2120 2710 1910 2560 La 77 139 154 305 127 37 57 81 53 65 35 67 Ce 164 263 326 644 251 79 132 159 114 140 74 139 Pr 20 31 40 74 29 10 18 20 15 17 10 17 Nd 75 120 162 287 109 42 81 80 66 69 45 72 Sm 11 17 25 40 16 8·4 15 17 13 12 10 13 Eu 2·7 3·9 5·8 8·1 3·5 1·9 3·0 4·1 2·9 3·0 2·1 2·8 Gd 7·6 10 15 20 10 6·7 10 14 9·4 9·0 8·1 9·2 Tb 0·90 1·09 1·55 1·97 1·14 0·87 1·18 1·70 1·20 1·11 1·08 1·08 Dy 5·0 5·5 7·5 8·7 6·1 5·1 6·8 8·8 7·0 6·2 6·7 5·9 Ho 0·86 0·97 1·23 1·34 0·99 0·94 1·25 1·43 1·28 1·09 1·26 1·08 Er 2·3 2·4 3·0 3·0 2·4 2·6 3·5 3·6 3·4 2·8 3·4 2·9 Tm 0·33 0·32 0·38 0·38 0·31 0·38 0·50 0·47 0·50 0·37 0·49 0·38 Yb 2·2 2·1 2·3 2·4 1·8 2·4 3·4 2·9 3·2 2·4 3·1 2·6 Lu 0·32 0·31 0·34 0·34 0·27 0·35 0·48 0·43 0·47 0·33 0·44 0·36 Hf 5·7 7·5 15 27 25 7·3 15 8·8 11 8·4 10 15 Ta 0·69 1·5 2·4 2·9 7·4 1·0 1·9 1·2 1·7 1·8 1·9 1·6 Pb 18 21 23 34 24 30 17 12 21 26 29 10 Th 16 33 31 65 29 17 40 21 29 19 36 27 U 2·8 5·8 4·0 5·9 5·4 4·2 8·1 4·7 4·8 2·9 10 6·0 Group I Group II Taunus Vosges-N Odenwald-S Palatine Schwarzwald Sample: TA01 VO33A VO36 VO86 VO37 OD152 OD157B OD163 PF01 PF04 SCH06 SCH09 SiO2 49·6 50·8 49·3 48·1 52·5 53·8 55·5 51·0 52·8 46·1 52·9 58·7 TiO2 1·16 1·28 1·79 1·73 1·93 0·98 1·35 1·14 1·30 1·52 0·96 1·27 Al2O3 14·0 13·8 12·8 10·8 13·4 13·3 13·0 11·2 14·8 11·6 13·5 14·4 Fe2O3 8·04 7·70 7·83 7·15 6·55 7·87 7·71 7·24 8·25 10·4 7·00 6·74 MnO 0·130 0·130 0·120 0·096 0·072 0·120 0·110 0·140 0·120 0·170 0·110 0·063 MgO 10·4 7·46 8·94 6·97 6·63 8·10 5·64 11·5 5·80 10·8 8·52 5·88 CaO 6·63 7·66 6·37 7·86 4·50 5·86 5·30 4·11 5·90 8·05 5·59 1·93 Na2O 2·17 4·00 2·74 1·57 1·33 2·55 2·54 1·10 2·41 2·27 1·70 2·95 K2O 2·66 1·79 5·84 7·10 7·75 4·63 6·14 6·54 5·67 3·47 4·26 5·20 P2O5 0·47 0·84 1·35 2·14 1·11 0·57 0·82 1·02 0·79 0·96 0·70 0·96 LOI 3·32 4·96 1·78 4·17 4·18 1·55 1·13 4·18 2·36 4·14 4·87 1·11 Sum 99·1 100·8 99·8 99·4 100·6 99·7 99·7 99·9 100·6 100·0 100·4 99·8 Sc 29 21 24 21 17 28 30 23 31 33 29 23 V 192 160 175 171 126 187 203 182 212 247 160 170 Cr 543 213 406 238 188 550 230 482 204 586 600 215 Co 39 27 33 32 23 34 25 37 29 46 31 26 Ni 231 143 207 156 130 137 37 334 43 269 183 120 Ga 15 17 19 21 20 17 17 16 17 19 16 20 Rb 95 26 126 196 153 167 335 224 265 154 174 177 Sr 1120 1470 1100 2430 910 730 560 670 720 810 440 910 Y 25 26 33 36 27 26 35 43 34 29 34 30 Zr 225 322 609 1040 1050 273 532 352 394 322 350 545 Nb 11 27 40 52 112 15 28 19 26 32 26 25 Cs 3·9 0·7 4·7 7·2 1·6 4·5 4·8 11 20 21 9·2 60 Ba 3300 1150 5270 10600 2560 2190 1490 4950 2120 2710 1910 2560 La 77 139 154 305 127 37 57 81 53 65 35 67 Ce 164 263 326 644 251 79 132 159 114 140 74 139 Pr 20 31 40 74 29 10 18 20 15 17 10 17 Nd 75 120 162 287 109 42 81 80 66 69 45 72 Sm 11 17 25 40 16 8·4 15 17 13 12 10 13 Eu 2·7 3·9 5·8 8·1 3·5 1·9 3·0 4·1 2·9 3·0 2·1 2·8 Gd 7·6 10 15 20 10 6·7 10 14 9·4 9·0 8·1 9·2 Tb 0·90 1·09 1·55 1·97 1·14 0·87 1·18 1·70 1·20 1·11 1·08 1·08 Dy 5·0 5·5 7·5 8·7 6·1 5·1 6·8 8·8 7·0 6·2 6·7 5·9 Ho 0·86 0·97 1·23 1·34 0·99 0·94 1·25 1·43 1·28 1·09 1·26 1·08 Er 2·3 2·4 3·0 3·0 2·4 2·6 3·5 3·6 3·4 2·8 3·4 2·9 Tm 0·33 0·32 0·38 0·38 0·31 0·38 0·50 0·47 0·50 0·37 0·49 0·38 Yb 2·2 2·1 2·3 2·4 1·8 2·4 3·4 2·9 3·2 2·4 3·1 2·6 Lu 0·32 0·31 0·34 0·34 0·27 0·35 0·48 0·43 0·47 0·33 0·44 0·36 Hf 5·7 7·5 15 27 25 7·3 15 8·8 11 8·4 10 15 Ta 0·69 1·5 2·4 2·9 7·4 1·0 1·9 1·2 1·7 1·8 1·9 1·6 Pb 18 21 23 34 24 30 17 12 21 26 29 10 Th 16 33 31 65 29 17 40 21 29 19 36 27 U 2·8 5·8 4·0 5·9 5·4 4·2 8·1 4·7 4·8 2·9 10 6·0 Group II Schwarzwald Vosges-C Vosges-S Sample: SCH12 SCH17 SCH29 SCH32A SCH38 VO10 VO14 VO52 VO05 VO64B VO66 VO83 SiO2 60·0 57·5 62·2 64·2 52·4 51·9 54·0 52·3 56·9 63·7 50·4 60·5 TiO2 1·19 0·95 0·85 0·75 0·91 1·13 1·35 1·31 1·01 0·81 0·93 1·25 Al2O3 12·1 12·8 13·2 14·0 13·1 16·3 15·1 14·8 12·4 12·4 14·1 12·7 Fe2O3 5·26 5·82 4·84 4·19 7·45 7·70 7·55 9·45 6·13 4·13 8·33 3·87 MnO 0·087 0·100 0·089 0·066 0·120 0·120 0·110 0·120 0·100 0·060 0·130 0·120 MgO 5·74 5·37 5·53 4·61 9·73 7·07 7·73 6·97 8·58 4·99 7·15 5·71 CaO 3·93 4·81 3·03 2·92 5·70 5·61 4·90 3·97 4·60 2·55 6·43 3·41 Na2O 1·51 1·63 2·29 2·76 1·82 2·41 2·77 3·71 2·02 1·82 2·46 1·49 K2O 7·38 6·33 5·60 5·22 3·96 2·41 3·93 4·47 6·34 7·53 4·73 7·90 P2O5 1·55 1·10 0·59 0·53 0·73 0·23 0·47 1·02 0·97 1·02 0·85 1·02 LOI 1·21 3·17 1·68 0·73 3·16 5·12 1·76 1·46 0·63 0·61 4·63 1·83 Sum 100·5 100·0 100·2 100·5 99·5 100·1 100·0 100·0 100·1 100·1 100·6 100·3 Sc 22 23 16 14 31 25 24 21 24 18 40 20 V 130 136 102 93 172 151 158 179 138 99 229 117 Cr 235 152 427 230 762 298 313 224 548 341 331 247 Co 20 22 20 16 33 47 27 18 26 19 32 21 Ni 125 66 93 131 209 248 93 101 188 98 90 111 Ga 18 19 16 20 15 17 17 22 16 18 16 21 Rb 219 286 229 167 175 87 168 328 335 407 230 426 Sr 660 480 440 840 520 360 680 880 460 430 750 260 Y 35 28 26 22 31 23 27 30 24 32 35 32 Zr 600 377 306 358 329 210 309 331 393 465 237 649 Nb 33 27 27 22 24 9·4 13 38 35 35 17 39 Cs 5·3 16 24 8·9 19 16 33 19 39 34 12 20 Ba 3050 2410 1750 2890 2390 1100 2130 2550 2460 2230 2120 2750 La 59 49 52 59 62 32 72 124 35 42 37 75 Ce 153 114 116 120 135 68 151 233 87 106 78 179 Pr 26 18 15 15 17 8·1 19 27 13 17 11 28 Nd 133 88 66 61 71 32 74 100 63 87 48 134 Sm 28 20 12 11 13 6·0 12 14 15 23 10 30 Eu 4·5 3·5 2·1 2·3 2·5 1·5 2·9 3·3 2·5 3·5 2·2 4·1 Gd 15 11 8·2 8·0 9·2 4·8 8·2 10 8·8 12 8·1 15 Tb 1·49 1·18 0·99 0·90 1·13 0·72 0·98 1·16 0·98 1·28 1·05 1·54 Dy 7·6 6·1 5·4 4·6 6·4 4·5 5·6 6·4 5·1 6·5 6·5 7·3 Ho 1·24 1·02 0·91 0·85 1·22 0·86 1·02 1·09 0·85 1·13 1·21 1·15 Er 3·1 2·7 2·4 2·1 3·2 2·5 2·7 2·7 2·2 2·9 3·4 2·9 Tm 0·43 0·39 0·36 0·28 0·45 0·37 0·38 0·38 0·32 0·43 0·52 0·40 Yb 2·8 2·3 2·1 1·7 3·0 2·4 2·4 2·2 2·0 3·0 3·5 2·4 Lu 0·41 0·33 0·31 0·26 0·42 0·35 0·36 0·33 0·30 0·43 0·47 0·32 Hf 16 11 9·4 10 10 5·5 8·0 7·7 12 13 6·4 19 Ta 1·9 1·9 2·4 2·4 1·5 0·6 0·8 2·1 2·9 2·4 1·2 2·8 Pb 10 19 15 123 18 48 20 9·3 18 387 22 108 Th 115 69 43 35 43 11 19 40 68 82 26 95 U 20 18 6·6 7·8 9·3 2·2 3·5 6·6 22 27 11 25 Group II Schwarzwald Vosges-C Vosges-S Sample: SCH12 SCH17 SCH29 SCH32A SCH38 VO10 VO14 VO52 VO05 VO64B VO66 VO83 SiO2 60·0 57·5 62·2 64·2 52·4 51·9 54·0 52·3 56·9 63·7 50·4 60·5 TiO2 1·19 0·95 0·85 0·75 0·91 1·13 1·35 1·31 1·01 0·81 0·93 1·25 Al2O3 12·1 12·8 13·2 14·0 13·1 16·3 15·1 14·8 12·4 12·4 14·1 12·7 Fe2O3 5·26 5·82 4·84 4·19 7·45 7·70 7·55 9·45 6·13 4·13 8·33 3·87 MnO 0·087 0·100 0·089 0·066 0·120 0·120 0·110 0·120 0·100 0·060 0·130 0·120 MgO 5·74 5·37 5·53 4·61 9·73 7·07 7·73 6·97 8·58 4·99 7·15 5·71 CaO 3·93 4·81 3·03 2·92 5·70 5·61 4·90 3·97 4·60 2·55 6·43 3·41 Na2O 1·51 1·63 2·29 2·76 1·82 2·41 2·77 3·71 2·02 1·82 2·46 1·49 K2O 7·38 6·33 5·60 5·22 3·96 2·41 3·93 4·47 6·34 7·53 4·73 7·90 P2O5 1·55 1·10 0·59 0·53 0·73 0·23 0·47 1·02 0·97 1·02 0·85 1·02 LOI 1·21 3·17 1·68 0·73 3·16 5·12 1·76 1·46 0·63 0·61 4·63 1·83 Sum 100·5 100·0 100·2 100·5 99·5 100·1 100·0 100·0 100·1 100·1 100·6 100·3 Sc 22 23 16 14 31 25 24 21 24 18 40 20 V 130 136 102 93 172 151 158 179 138 99 229 117 Cr 235 152 427 230 762 298 313 224 548 341 331 247 Co 20 22 20 16 33 47 27 18 26 19 32 21 Ni 125 66 93 131 209 248 93 101 188 98 90 111 Ga 18 19 16 20 15 17 17 22 16 18 16 21 Rb 219 286 229 167 175 87 168 328 335 407 230 426 Sr 660 480 440 840 520 360 680 880 460 430 750 260 Y 35 28 26 22 31 23 27 30 24 32 35 32 Zr 600 377 306 358 329 210 309 331 393 465 237 649 Nb 33 27 27 22 24 9·4 13 38 35 35 17 39 Cs 5·3 16 24 8·9 19 16 33 19 39 34 12 20 Ba 3050 2410 1750 2890 2390 1100 2130 2550 2460 2230 2120 2750 La 59 49 52 59 62 32 72 124 35 42 37 75 Ce 153 114 116 120 135 68 151 233 87 106 78 179 Pr 26 18 15 15 17 8·1 19 27 13 17 11 28 Nd 133 88 66 61 71 32 74 100 63 87 48 134 Sm 28 20 12 11 13 6·0 12 14 15 23 10 30 Eu 4·5 3·5 2·1 2·3 2·5 1·5 2·9 3·3 2·5 3·5 2·2 4·1 Gd 15 11 8·2 8·0 9·2 4·8 8·2 10 8·8 12 8·1 15 Tb 1·49 1·18 0·99 0·90 1·13 0·72 0·98 1·16 0·98 1·28 1·05 1·54 Dy 7·6 6·1 5·4 4·6 6·4 4·5 5·6 6·4 5·1 6·5 6·5 7·3 Ho 1·24 1·02 0·91 0·85 1·22 0·86 1·02 1·09 0·85 1·13 1·21 1·15 Er 3·1 2·7 2·4 2·1 3·2 2·5 2·7 2·7 2·2 2·9 3·4 2·9 Tm 0·43 0·39 0·36 0·28 0·45 0·37 0·38 0·38 0·32 0·43 0·52 0·40 Yb 2·8 2·3 2·1 1·7 3·0 2·4 2·4 2·2 2·0 3·0 3·5 2·4 Lu 0·41 0·33 0·31 0·26 0·42 0·35 0·36 0·33 0·30 0·43 0·47 0·32 Hf 16 11 9·4 10 10 5·5 8·0 7·7 12 13 6·4 19 Ta 1·9 1·9 2·4 2·4 1·5 0·6 0·8 2·1 2·9 2·4 1·2 2·8 Pb 10 19 15 123 18 48 20 9·3 18 387 22 108 Th 115 69 43 35 43 11 19 40 68 82 26 95 U 20 18 6·6 7·8 9·3 2·2 3·5 6·6 22 27 11 25 Table 2: Sr, Nd and Pb isotopic composition of Variscan lamprophyres Sample Region 87Sr/86Sr 87Sr/86Sri 143Nd/144Nd 143Nd/144Ndi εNdi 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Group I lamprophyres OD153B Odenwald 0·709845±8 0·70698 0·512203±2 0·51202 –3·9 19·069 15·652 39·349 OD154 Odenwald 0·724709±7 0·71150 0·512262±6 0·51205 –3·4 18·864 15·724 39·114 OD169R Odenwald 0·714681±5 0·70841 0·512327±6 0·51212 –2·1 22·605 15·845 43·881 OD175 Odenwald 0·713785±9 0·70753 0·512294±8 0·51211 –2·3 18·854 15·682 39·087 OD178 Odenwald 0·718006±6 0·70809 0·512293±4 0·51210 –2·5 19·305 15·710 39·573 OD043 Odenwald 0·707055±7 0·70537 0·512349±3 0·51217 –1·1 18·690 15·634 38·862 OD064 Odenwald 0·706322±7 0·70535 0·512386±4 0·51216 –1·2 18·574 15·632 38·715 OD151C Odenwald 0·707766±3 0·70634 0·512310±2 0·51212 –2·0 18·780 15·652 39·132 OD156B Odenwald 0·707798±3 0·70642 0·512315±3 0·51212 –2·1 18·823 15·649 39·107 SP12 Spessart 0·714355±8 0·70798 0·512297±4 0·51211 –2·2 18·594 15·636 38·709 SP15 Spessart 0·708091±6 0·70610 0·512363±7 0·51214 –1·6 18·779 15·656 39·039 SP19 Spessart 0·707852±5 0·70656 0·512306±3 0·51211 –2·2 18·703 15·627 38·949 TA01 Taunus 0·710476±3 0·70943 0·512295±5 0·51210 –2·4 18·881 15·674 39·080 VO86 N Vosges 0·707850±5 0·70685 0·512246±3 0·51207 –3·1 18·566 15·603 39·149 VO33A N Vosges 0·705679±4 0·70546 0·512325±3 0·51214 –1·6 18·890 15·619 38·967 VO36 N Vosges 0·707814±5 0·70641 0·512284±4 0·51209 –2·7 18·592 15·601 38·907 VO37 N Vosges 0·707554±5 0·70549 0·512376±8 0·51219 –0·7 18·797 15·635 38·857 Group II lamprophyres OD152 Odenwald 0·709997±8 0·70716 0·512326±4 0·51207 –3·0 18·725 15·649 38·761 OD157B Odenwald 0·717790±6 0·71037 0·512208±8 0·51197 –5·0 19·620 15·702 39·941 OD163 Odenwald 0·711949±8 0·70781 0·512276±3 0·51201 –4·1 18·929 15·655 39·137 PF01 Palatine 0·712907±6 0·70836 0·512288±6 0·51204 –3·7 18·860 15·659 39·147 PF04 Palatine 0·708332±7 0·70599 0·512372±5 0·51215 –1·5 18·686 15·645 38·912 SCH06 Schwarzwald 0·715629±9 0·71071 0·512227±3 0·51195 –5·5 19·315 15·692 39·252 SCH09 Schwarzwald 0·708423±8 0·70603 0·512336±2 0·51212 –2·2 19·675 15·681 39·562 SCH12 Schwarzwald 0·716534±4 0·71244 0·512130±5 0·51186 –7·1 26·834 16·081 50·608 SCH17 Schwarzwald 0·720344±9 0·71292 0·512182±4 0·51190 –6·4 20·483 15·739 40·603 SCH29 Schwarzwald 0·716851±6 0·71044 0·512208±6 0·51198 –4·9 19·292 15·706 39·859 SCH32A Schwarzwald 0·712485±4 0·71004 0·512236±3 0·51200 –4·4 18·499 15·669 38·482 SCH38 Schwarzwald 0·713737±5 0·70954 0·512205±2 0·51197 –5·0 20·103 15·735 40·527 VO10 C Vosges 0·710602±8 0·70765 0·512296±4 0·51206 –3·3 18·733 15·622 38·644 VO14 C Vosges 0·709658±4 0·70664 0·512264±3 0·51206 –3·3 18·936 15·643 39·090 VO52 C Vosges 0·711017±4 0·70641 0·512314±4 0·51213 –1·9 20·373 15·712 40·246 VO05 S Vosges 0·719062±4 0·70997 0·512225±5 0·51192 –5·9 20·681 15·726 40·117 VO64B S Vosges 0·726743±8 0·71506 0·512174±5 0·51184 –7·5 18·962 15·694 38·882 VO66 S Vosges 0·711987±8 0·70819 0·512291±4 0·51202 –4·1 19·345 15·618 38·781 VO83 S Vosges 0·736281±4 0·71636 0·512181±3 0·51190 –6·4 19·550 15·665 39·357 Sample Region 87Sr/86Sr 87Sr/86Sri 143Nd/144Nd 143Nd/144Ndi εNdi 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Group I lamprophyres OD153B Odenwald 0·709845±8 0·70698 0·512203±2 0·51202 –3·9 19·069 15·652 39·349 OD154 Odenwald 0·724709±7 0·71150 0·512262±6 0·51205 –3·4 18·864 15·724 39·114 OD169R Odenwald 0·714681±5 0·70841 0·512327±6 0·51212 –2·1 22·605 15·845 43·881 OD175 Odenwald 0·713785±9 0·70753 0·512294±8 0·51211 –2·3 18·854 15·682 39·087 OD178 Odenwald 0·718006±6 0·70809 0·512293±4 0·51210 –2·5 19·305 15·710 39·573 OD043 Odenwald 0·707055±7 0·70537 0·512349±3 0·51217 –1·1 18·690 15·634 38·862 OD064 Odenwald 0·706322±7 0·70535 0·512386±4 0·51216 –1·2 18·574 15·632 38·715 OD151C Odenwald 0·707766±3 0·70634 0·512310±2 0·51212 –2·0 18·780 15·652 39·132 OD156B Odenwald 0·707798±3 0·70642 0·512315±3 0·51212 –2·1 18·823 15·649 39·107 SP12 Spessart 0·714355±8 0·70798 0·512297±4 0·51211 –2·2 18·594 15·636 38·709 SP15 Spessart 0·708091±6 0·70610 0·512363±7 0·51214 –1·6 18·779 15·656 39·039 SP19 Spessart 0·707852±5 0·70656 0·512306±3 0·51211 –2·2 18·703 15·627 38·949 TA01 Taunus 0·710476±3 0·70943 0·512295±5 0·51210 –2·4 18·881 15·674 39·080 VO86 N Vosges 0·707850±5 0·70685 0·512246±3 0·51207 –3·1 18·566 15·603 39·149 VO33A N Vosges 0·705679±4 0·70546 0·512325±3 0·51214 –1·6 18·890 15·619 38·967 VO36 N Vosges 0·707814±5 0·70641 0·512284±4 0·51209 –2·7 18·592 15·601 38·907 VO37 N Vosges 0·707554±5 0·70549 0·512376±8 0·51219 –0·7 18·797 15·635 38·857 Group II lamprophyres OD152 Odenwald 0·709997±8 0·70716 0·512326±4 0·51207 –3·0 18·725 15·649 38·761 OD157B Odenwald 0·717790±6 0·71037 0·512208±8 0·51197 –5·0 19·620 15·702 39·941 OD163 Odenwald 0·711949±8 0·70781 0·512276±3 0·51201 –4·1 18·929 15·655 39·137 PF01 Palatine 0·712907±6 0·70836 0·512288±6 0·51204 –3·7 18·860 15·659 39·147 PF04 Palatine 0·708332±7 0·70599 0·512372±5 0·51215 –1·5 18·686 15·645 38·912 SCH06 Schwarzwald 0·715629±9 0·71071 0·512227±3 0·51195 –5·5 19·315 15·692 39·252 SCH09 Schwarzwald 0·708423±8 0·70603 0·512336±2 0·51212 –2·2 19·675 15·681 39·562 SCH12 Schwarzwald 0·716534±4 0·71244 0·512130±5 0·51186 –7·1 26·834 16·081 50·608 SCH17 Schwarzwald 0·720344±9 0·71292 0·512182±4 0·51190 –6·4 20·483 15·739 40·603 SCH29 Schwarzwald 0·716851±6 0·71044 0·512208±6 0·51198 –4·9 19·292 15·706 39·859 SCH32A Schwarzwald 0·712485±4 0·71004 0·512236±3 0·51200 –4·4 18·499 15·669 38·482 SCH38 Schwarzwald 0·713737±5 0·70954 0·512205±2 0·51197 –5·0 20·103 15·735 40·527 VO10 C Vosges 0·710602±8 0·70765 0·512296±4 0·51206 –3·3 18·733 15·622 38·644 VO14 C Vosges 0·709658±4 0·70664 0·512264±3 0·51206 –3·3 18·936 15·643 39·090 VO52 C Vosges 0·711017±4 0·70641 0·512314±4 0·51213 –1·9 20·373 15·712 40·246 VO05 S Vosges 0·719062±4 0·70997 0·512225±5 0·51192 –5·9 20·681 15·726 40·117 VO64B S Vosges 0·726743±8 0·71506 0·512174±5 0·51184 –7·5 18·962 15·694 38·882 VO66 S Vosges 0·711987±8 0·70819 0·512291±4 0·51202 –4·1 19·345 15·618 38·781 VO83 S Vosges 0·736281±4 0·71636 0·512181±3 0·51190 –6·4 19·550 15·665 39·357 87Sr/86Sri, 143Nd/144Ndi and εNdi were calculated for the emplacement age of 320 Ma using λ87Rb = 1·3972E – 11 a–1 (Villa et al., 2015) and λ147Sm = 6·54E – 12 a–1, (147Sm/144Nd)0CHUR = 0·1967 and (143Nd/144Nd)0CHUR = 0·512638, respectively, and the concentration data given in Table 1. Table 2: Sr, Nd and Pb isotopic composition of Variscan lamprophyres Sample Region 87Sr/86Sr 87Sr/86Sri 143Nd/144Nd 143Nd/144Ndi εNdi 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Group I lamprophyres OD153B Odenwald 0·709845±8 0·70698 0·512203±2 0·51202 –3·9 19·069 15·652 39·349 OD154 Odenwald 0·724709±7 0·71150 0·512262±6 0·51205 –3·4 18·864 15·724 39·114 OD169R Odenwald 0·714681±5 0·70841 0·512327±6 0·51212 –2·1 22·605 15·845 43·881 OD175 Odenwald 0·713785±9 0·70753 0·512294±8 0·51211 –2·3 18·854 15·682 39·087 OD178 Odenwald 0·718006±6 0·70809 0·512293±4 0·51210 –2·5 19·305 15·710 39·573 OD043 Odenwald 0·707055±7 0·70537 0·512349±3 0·51217 –1·1 18·690 15·634 38·862 OD064 Odenwald 0·706322±7 0·70535 0·512386±4 0·51216 –1·2 18·574 15·632 38·715 OD151C Odenwald 0·707766±3 0·70634 0·512310±2 0·51212 –2·0 18·780 15·652 39·132 OD156B Odenwald 0·707798±3 0·70642 0·512315±3 0·51212 –2·1 18·823 15·649 39·107 SP12 Spessart 0·714355±8 0·70798 0·512297±4 0·51211 –2·2 18·594 15·636 38·709 SP15 Spessart 0·708091±6 0·70610 0·512363±7 0·51214 –1·6 18·779 15·656 39·039 SP19 Spessart 0·707852±5 0·70656 0·512306±3 0·51211 –2·2 18·703 15·627 38·949 TA01 Taunus 0·710476±3 0·70943 0·512295±5 0·51210 –2·4 18·881 15·674 39·080 VO86 N Vosges 0·707850±5 0·70685 0·512246±3 0·51207 –3·1 18·566 15·603 39·149 VO33A N Vosges 0·705679±4 0·70546 0·512325±3 0·51214 –1·6 18·890 15·619 38·967 VO36 N Vosges 0·707814±5 0·70641 0·512284±4 0·51209 –2·7 18·592 15·601 38·907 VO37 N Vosges 0·707554±5 0·70549 0·512376±8 0·51219 –0·7 18·797 15·635 38·857 Group II lamprophyres OD152 Odenwald 0·709997±8 0·70716 0·512326±4 0·51207 –3·0 18·725 15·649 38·761 OD157B Odenwald 0·717790±6 0·71037 0·512208±8 0·51197 –5·0 19·620 15·702 39·941 OD163 Odenwald 0·711949±8 0·70781 0·512276±3 0·51201 –4·1 18·929 15·655 39·137 PF01 Palatine 0·712907±6 0·70836 0·512288±6 0·51204 –3·7 18·860 15·659 39·147 PF04 Palatine 0·708332±7 0·70599 0·512372±5 0·51215 –1·5 18·686 15·645 38·912 SCH06 Schwarzwald 0·715629±9 0·71071 0·512227±3 0·51195 –5·5 19·315 15·692 39·252 SCH09 Schwarzwald 0·708423±8 0·70603 0·512336±2 0·51212 –2·2 19·675 15·681 39·562 SCH12 Schwarzwald 0·716534±4 0·71244 0·512130±5 0·51186 –7·1 26·834 16·081 50·608 SCH17 Schwarzwald 0·720344±9 0·71292 0·512182±4 0·51190 –6·4 20·483 15·739 40·603 SCH29 Schwarzwald 0·716851±6 0·71044 0·512208±6 0·51198 –4·9 19·292 15·706 39·859 SCH32A Schwarzwald 0·712485±4 0·71004 0·512236±3 0·51200 –4·4 18·499 15·669 38·482 SCH38 Schwarzwald 0·713737±5 0·70954 0·512205±2 0·51197 –5·0 20·103 15·735 40·527 VO10 C Vosges 0·710602±8 0·70765 0·512296±4 0·51206 –3·3 18·733 15·622 38·644 VO14 C Vosges 0·709658±4 0·70664 0·512264±3 0·51206 –3·3 18·936 15·643 39·090 VO52 C Vosges 0·711017±4 0·70641 0·512314±4 0·51213 –1·9 20·373 15·712 40·246 VO05 S Vosges 0·719062±4 0·70997 0·512225±5 0·51192 –5·9 20·681 15·726 40·117 VO64B S Vosges 0·726743±8 0·71506 0·512174±5 0·51184 –7·5 18·962 15·694 38·882 VO66 S Vosges 0·711987±8 0·70819 0·512291±4 0·51202 –4·1 19·345 15·618 38·781 VO83 S Vosges 0·736281±4 0·71636 0·512181±3 0·51190 –6·4 19·550 15·665 39·357 Sample Region 87Sr/86Sr 87Sr/86Sri 143Nd/144Nd 143Nd/144Ndi εNdi 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Group I lamprophyres OD153B Odenwald 0·709845±8 0·70698 0·512203±2 0·51202 –3·9 19·069 15·652 39·349 OD154 Odenwald 0·724709±7 0·71150 0·512262±6 0·51205 –3·4 18·864 15·724 39·114 OD169R Odenwald 0·714681±5 0·70841 0·512327±6 0·51212 –2·1 22·605 15·845 43·881 OD175 Odenwald 0·713785±9 0·70753 0·512294±8 0·51211 –2·3 18·854 15·682 39·087 OD178 Odenwald 0·718006±6 0·70809 0·512293±4 0·51210 –2·5 19·305 15·710 39·573 OD043 Odenwald 0·707055±7 0·70537 0·512349±3 0·51217 –1·1 18·690 15·634 38·862 OD064 Odenwald 0·706322±7 0·70535 0·512386±4 0·51216 –1·2 18·574 15·632 38·715 OD151C Odenwald 0·707766±3 0·70634 0·512310±2 0·51212 –2·0 18·780 15·652 39·132 OD156B Odenwald 0·707798±3 0·70642 0·512315±3 0·51212 –2·1 18·823 15·649 39·107 SP12 Spessart 0·714355±8 0·70798 0·512297±4 0·51211 –2·2 18·594 15·636 38·709 SP15 Spessart 0·708091±6 0·70610 0·512363±7 0·51214 –1·6 18·779 15·656 39·039 SP19 Spessart 0·707852±5 0·70656 0·512306±3 0·51211 –2·2 18·703 15·627 38·949 TA01 Taunus 0·710476±3 0·70943 0·512295±5 0·51210 –2·4 18·881 15·674 39·080 VO86 N Vosges 0·707850±5 0·70685 0·512246±3 0·51207 –3·1 18·566 15·603 39·149 VO33A N Vosges 0·705679±4 0·70546 0·512325±3 0·51214 –1·6 18·890 15·619 38·967 VO36 N Vosges 0·707814±5 0·70641 0·512284±4 0·51209 –2·7 18·592 15·601 38·907 VO37 N Vosges 0·707554±5 0·70549 0·512376±8 0·51219 –0·7 18·797 15·635 38·857 Group II lamprophyres OD152 Odenwald 0·709997±8 0·70716 0·512326±4 0·51207 –3·0 18·725 15·649 38·761 OD157B Odenwald 0·717790±6 0·71037 0·512208±8 0·51197 –5·0 19·620 15·702 39·941 OD163 Odenwald 0·711949±8 0·70781 0·512276±3 0·51201 –4·1 18·929 15·655 39·137 PF01 Palatine 0·712907±6 0·70836 0·512288±6 0·51204 –3·7 18·860 15·659 39·147 PF04 Palatine 0·708332±7 0·70599 0·512372±5 0·51215 –1·5 18·686 15·645 38·912 SCH06 Schwarzwald 0·715629±9 0·71071 0·512227±3 0·51195 –5·5 19·315 15·692 39·252 SCH09 Schwarzwald 0·708423±8 0·70603 0·512336±2 0·51212 –2·2 19·675 15·681 39·562 SCH12 Schwarzwald 0·716534±4 0·71244 0·512130±5 0·51186 –7·1 26·834 16·081 50·608 SCH17 Schwarzwald 0·720344±9 0·71292 0·512182±4 0·51190 –6·4 20·483 15·739 40·603 SCH29 Schwarzwald 0·716851±6 0·71044 0·512208±6 0·51198 –4·9 19·292 15·706 39·859 SCH32A Schwarzwald 0·712485±4 0·71004 0·512236±3 0·51200 –4·4 18·499 15·669 38·482 SCH38 Schwarzwald 0·713737±5 0·70954 0·512205±2 0·51197 –5·0 20·103 15·735 40·527 VO10 C Vosges 0·710602±8 0·70765 0·512296±4 0·51206 –3·3 18·733 15·622 38·644 VO14 C Vosges 0·709658±4 0·70664 0·512264±3 0·51206 –3·3 18·936 15·643 39·090 VO52 C Vosges 0·711017±4 0·70641 0·512314±4 0·51213 –1·9 20·373 15·712 40·246 VO05 S Vosges 0·719062±4 0·70997 0·512225±5 0·51192 –5·9 20·681 15·726 40·117 VO64B S Vosges 0·726743±8 0·71506 0·512174±5 0·51184 –7·5 18·962 15·694 38·882 VO66 S Vosges 0·711987±8 0·70819 0·512291±4 0·51202 –4·1 19·345 15·618 38·781 VO83 S Vosges 0·736281±4 0·71636 0·512181±3 0·51190 –6·4 19·550 15·665 39·357 87Sr/86Sri, 143Nd/144Ndi and εNdi were calculated for the emplacement age of 320 Ma using λ87Rb = 1·3972E – 11 a–1 (Villa et al., 2015) and λ147Sm = 6·54E – 12 a–1, (147Sm/144Nd)0CHUR = 0·1967 and (143Nd/144Nd)0CHUR = 0·512638, respectively, and the concentration data given in Table 1. Trace element analyses were carried out at the GeoZentrum Nordbayern (GZN), University of Erlangen-Nuremberg, with a single-collector quadrupole Agilent 7500i inductively coupled plasma mass spectrometry system equipped with a New Wave UP193Fx argon fluoride laser ablation system. Measurements were performed on the lithium borate fusion disks along four 1200 µm long lines with a velocity of 40 µm s–1 using a spot diameter of 50 µm and a laser frequency of 20 Hz. Bulk-rock SiO2 concentrations from XRF were used as internal standards. For external calibration, the glass reference material NIST SRM 612 with the values of Pearce et al. (1997) was used. Element concentrations were calculated using the GLITTER software (Macquarie University, Sydney, Australia). Details on the accuracy and analyses of international standards using this method have been given by Soder et al. (2016). Sr, Nd and Pb isotope analyses were performed at the Deutsches GeoForschungsZentrum, Potsdam, using splits of the powders used for whole-rock element analyses. Samples were digested in concentrated HF in Savillex beakers on a hotplate for 4 days, dried, taken up in 2N HNO3 to convert fluorides to nitrates, slowly dried again, and eventually redissolved in 6N HCl. The clear solutions were aliquoted for Sr–Nd and Pb isotope analysis. Strontium, Nd and Pb were separated using standard ion-exchange procedures (e.g. Romer & Hahne, 2010, and references therein). To avoid interferences of BaO on mass 146Nd, Ba was removed before elution of the rare earth element (REE) fraction (using an additional washing step with 2·5N HNO3). The Sr and Nd isotopic compositions were measured on a Triton thermal ionization multi-collector mass spectrometer operated in dynamic multi-collection mode, using Ta single filaments and Re double filaments, respectively. Strontium and Nd isotope ratios were normalized to 86Sr/88Sr = 0·1194 and 146Nd/144Nd = 0·7219. During the measurement period, NBS-987 Sr reference material and the La Jolla Nd standard gave average 87Sr/86Sr and 143Nd/144Nd values of 0·710249 ± 12 (2SD of 20 measurements) and 0·511850 ± 7 (2SD of 11 measurements), respectively. The Pb isotopic composition was measured on single Re filaments using static multi-collection. Instrumental fractionation was corrected by 0·1% per a.m.u. as determined from the long-term reproducibility of Pb reference material NBS-981. The accuracy and precision of the reported Pb isotope ratios are better than 0·1% at the 2σ level of uncertainty (Romer & Hahne, 2010). Mineral analyses (representative mineral analyses and formula calculations are given in Supplementary Data 2) were carried out at the Institute of Earth Sciences at Heidelberg using a CAMECA SX51 electron microprobe in wavelength-dispersion mode. Operating conditions were 15 kV accelerating voltage, 20 nA beam current and a beam diameter of ∼1 µm. To minimize loss of alkalis during measurement, the electron beam was defocused for analyzing feldspar (10 µm) and phlogopite/biotite (5 µm). Peak counting times were 20 s for major elements (except 10 s for K, Na) and 40 s for minor elements (Ba, Zr, Sr). Background counting times were half the counting times of the peak. The standards used were albite (Na), anorthite (Ca and Al in feldspar), K-feldspar (K), corundum (Al), periclase (Mg), wollastonite (Ca, Si), hematite (Fe), rhodonite (Mn), TiO2 (Ti), Cr2O3 (Cr), celestine (Sr), barite (Ba) and ZrO2 (Zr). The raw data were corrected with the ‘PAP’ software (Pouchou & Pichoir, 1985). RESULTS Petrography Lamprophyre dykes from the Variscan basement massifs along the shoulders of the Cenozoic Upper Rhine Graben are typically steeply dipping, with a thickness in the decimetre to metre range. The dykes include a range of petrographically and mineralogically different rocks (Fig. 3). In the southern Vosges and the Schwarzwald, mica lamprophyres (minettes and kersantites) prevail, whereas in the northern outcrop areas, amphibole lamprophyres (spessartites) are common and even dominate in some areas (e.g. Spessart). Vogesites, although originally defined in the Vosges (Rosenbusch, 1887), were not observed. The lamprophyres are mostly melanocratic to mesocratic. Some dykes classified as ‘normal’ lamprophyres have lamprophyre-like mineralogy, but are leucocratic [semi-lamprophyres according to Wimmenauer (1973)]. Furthermore, we identified peralkaline minettes in the Spessart–Odenwald and Vosges areas, previously described as minettes with blue–green hornblende from the Odenwald (Klemm, 1924) and with crocidolite (fibrous riebeckite) from the northern Vosges (Delesse, 1856). Based on mineralogy, mineral chemistry and whole-rock geochemistry, these peralkaline dykes are lamproites as defined by Mitchell & Bergman (1991) and are similar to orogenic lamproites, which occur along the Alpine–Himalayan belt (e.g. Conticelli et al., 2009). Minette dykes are cut by kersantites and spessartites in the Odenwald area. Fig. 3. View largeDownload slide Photomicrographs of lamprophyres (plane-polarized light). (a) Peralkaline minette (sample OD153) with phlogopite (phl), diopside-rich clinopyroxene (di), apatite (ap), aegirine (aeg), zoned alkali amphibole (amph; dirty violet–blue arfvedsonite core rimmed by blue magnesio-riebeckite–winchite), embedded in a groundmass of K-feldspar ± quartz and tiny euhedral titanite. (b) Peralkaline minette from northern Vosges (sample VO03) with phlogopite and blue–violet magnesio-riebeckite (rieb; ‘crocidolite minette’ from Delesse, 1856). (c) Minette (sample VO64B) with phenocrysts of clinopyroxene and phlogopite (with dark Fe-rich rims) embedded within a fine-gained quartzo-feldspathic matrix; southern Vosges. (d) Peralkaline minette (sample OD153) with interstitial (late-stage) allanite (aln), quartz and blue amphibole (magnesio-riebeckite–winchite). (e) Spessartite–kersantite (sample PF04) with large amphibole phenocrysts along with clinopyroxene and some biotite/phlogopite. (f) Minette (sample OD157) with fine-grained matrix showing quench textures (dendritic mineral growth). Fig. 3. View largeDownload slide Photomicrographs of lamprophyres (plane-polarized light). (a) Peralkaline minette (sample OD153) with phlogopite (phl), diopside-rich clinopyroxene (di), apatite (ap), aegirine (aeg), zoned alkali amphibole (amph; dirty violet–blue arfvedsonite core rimmed by blue magnesio-riebeckite–winchite), embedded in a groundmass of K-feldspar ± quartz and tiny euhedral titanite. (b) Peralkaline minette from northern Vosges (sample VO03) with phlogopite and blue–violet magnesio-riebeckite (rieb; ‘crocidolite minette’ from Delesse, 1856). (c) Minette (sample VO64B) with phenocrysts of clinopyroxene and phlogopite (with dark Fe-rich rims) embedded within a fine-gained quartzo-feldspathic matrix; southern Vosges. (d) Peralkaline minette (sample OD153) with interstitial (late-stage) allanite (aln), quartz and blue amphibole (magnesio-riebeckite–winchite). (e) Spessartite–kersantite (sample PF04) with large amphibole phenocrysts along with clinopyroxene and some biotite/phlogopite. (f) Minette (sample OD157) with fine-grained matrix showing quench textures (dendritic mineral growth). The lamprophyres have typical porphyritic textures with a fine-grained groundmass owing to high cooling rates during shallow-level emplacement (Rock, 1991). Larger dykes are texturally zoned with a submicron-sized matrix along chilled margins and a fine-grained matrix with conspicuous quench textures. These include spherulitic to sheave-like crystallization of the feldspathic matrix and dendritic growth of mafic minerals (Fig. 3f), with a coarsening towards the center of the dyke, where poikilitic textures may be developed. Major phenocryst phases are clinopyroxene and phlogopite/biotite (Fig. 3a–d) and/or Ca-amphibole (Fig. 3e). Many dykes additionally contain phenocrysts of (altered) olivine with tiny octahedral inclusions of Cr-rich spinel. Some also have apatite (micro-) phenocrysts. The groundmass is made up of K-feldspar and plagioclase, titanite, magnetite (more rarely ilmenite), apatite and interstitial precipitates of calcite, REE-bearing epidote-group minerals and, in many cases, interstitial quartz. Peralkaline minettes in the Odenwald–Spessart and northern Vosges areas are porphyritic with phenocrysts of up to 1 cm long phlogopite laths, clinopyroxene, apatite, and alkali amphibole (Fig. 3a, b and d). Numerous tiny crystals of titanite are present in the Odenwald–Spessart dykes. The matrix is dominated by mostly euhedral, lath-shaped or sheave-like alkali feldspar. Plagioclase is absent or occurs in subordinate amounts within a late-stage interstitial mass of alkali feldspar, quartz, allanite/REE-rich epidote, extremely U-rich and metamict zircon, and some calcite. The alkali amphiboles are overgrown by a second generation of chemically heterogeneous Na- and Na–Ca- to Ca-amphiboles (magnesio-arfvedsonite, magnesio-riebeckite, K-richterite, winchite, actinolite) that also form acicular interstitial grains. Clinopyroxene phenocrysts are rimmed by Zr-rich aegirine. Autometasomatic processes, owing to exsolution of volatiles (Rock, 1991), affected all dykes to variable degrees. Olivine phenocrysts are always completely transformed to secondary phases (calcite–chlorite, calcite–chlorite–actinolite, talc). Clinopyroxene is replaced by calcite-rich pseudomorphs in some lamprophyres. Subordinate amounts of late magmatic to hydrothermal minerals including chlorite, albite, actinolite, epidote, prehnite, analcime, phengite, calcite, barite, fluorite and hematite may be present in the groundmass. Upper mantle and crustal xenoliths rarely occur in the lamprophyres studied. Fragments of gneiss, granitoid, felsic high-pressure granulite, amphibolite, retrogressed eclogite, hornblendite, phlogopite-clinopyroxenite, phlogopite-orthopyroxenite and possibly retrogressed dunite are present in some dykes from the Odenwald. Such contaminated samples were not analyzed in this study. Mineral chemistry Minettes, kersantites and spessartites Phlogopite phenocrysts in kersantites and ‘normal’ minettes are characterized by high Al2O3 contents (∼14–18 wt%), typical of orogenic lamprophyres (Rock, 1991; Fig. 4). Clinopyroxene phenocrysts have diopsidic compositions and show Fe-enrichment towards the margins (XMg = 0·89–0·62; Ca = 0·812–0·963 a.p.f.u.). Oscillatory and sector zoning is locally present. Some dykes contain reversely zoned crystals (with Fe-rich cores and more Mg-rich rims), commonly with sieve textures partly replacing more Fe-rich domains. Chromium concentrations are typically below 0·1 wt% Cr2O3, but values of up to 1·6 wt% can be found. Titanium increases towards the margins and ranges between 0·26 and 2·20 wt% TiO2. Amphibole is present as a phenocryst and a groundmass phase in spessartites and some kersantites. The composition of Ca-amphiboles mostly ranges from magnesio-hastingsite to pargasite. Additionally, late-stage actinolitic amphibole may be present. Fig. 4. View largeDownload slide Mineral chemistry diagrams for (a) clinopyroxene and (b) mica illustrate that peralkaline minettes show deficiencies in Al compared with metaluminous spessartites, kersantites and minettes. The mineralogy and mineral chemistry of peralkaline minettes resemble those of orogenic lamproites. (a) Clinopyroxene compositions are given in atoms per formula unit (a.p.f.u.). (b) Phlogopite phenocrysts of Group I peralkaline minettes have higher Ti compared with those of Group II. The latter overlap with phlogopite phenocryst cores from Mediterranean lamproites (Fritschle et al., 2013). Analyses are reported in Supplementary Data 2. Fig. 4. View largeDownload slide Mineral chemistry diagrams for (a) clinopyroxene and (b) mica illustrate that peralkaline minettes show deficiencies in Al compared with metaluminous spessartites, kersantites and minettes. The mineralogy and mineral chemistry of peralkaline minettes resemble those of orogenic lamproites. (a) Clinopyroxene compositions are given in atoms per formula unit (a.p.f.u.). (b) Phlogopite phenocrysts of Group I peralkaline minettes have higher Ti compared with those of Group II. The latter overlap with phlogopite phenocryst cores from Mediterranean lamproites (Fritschle et al., 2013). Analyses are reported in Supplementary Data 2. Peralkaline minettes Phlogopite phenocrysts in peralkaline minettes differ from those in metalduminous minettes/kersantites by their lower Al2O3 contents (∼10–14 wt%) and fall in the compositional range known from lamproitic rocks (Mitchell & Bergman, 1991). Although these micas have elevated Si contents, there is not sufficient Al present to fill the tetrahedral sites and some Fe3+ may compensate for this deficiency (as the tetra-ferriphlogopite component). Phlogopite shows a rimward decrease in the Mg# that is accompanied by decreasing Al and increasing Ti and Ba. Phlogopite phenocrysts usually contain 0·2–0·4 wt% BaO, 3·5–3·9 wt% TiO2 and up to 1·3 wt% Cr2O3. Rim compositions are more heterogeneous. Clinopyroxene in peralkaline minettes is Al-poor diopside (Fig. 4a) in which Fe3+ may occupy the tetrahedral site. Aegirine–aegirine-augite is present in some samples as a late rim around diopside phenocrysts with 26–92% aegirine component. These late-stage pyroxenes show variable but high contents of TiO2 and ZrO2, with maximum values of 3·9 wt% and 4·2 wt%, respectively. Peralkaline minettes contain microphenocrysts and late-stage sodic to sodic–calcic amphiboles. These Si-rich amphiboles fall in the compositional range of arfvedsonite–richterite–winchite–riebeckite. Most peralkaline minettes contain two generations of alkali amphibole (Fig. 3a). The North Vosges minettes contain microphenocrysts of magnesio-riebeckite, which is also a late-stage phase and replaces clinopyroxene. A minette from the southern Vosges contains microphenocrysts of arfvedsonite. Peralkaline minettes contain no or only very little plagioclase. Alkali feldspar (Or88–93Ab2–8) in the Odenwald–Spessart dykes is characterized by elevated concentrations of Fe3+, increasing from core to rim to a maximum of 5·0 wt% Fe2O3 (18% Fe-orthoclase component). These alkali feldspars are surrounded by small amounts of late-stage, interstitial alkali feldspar with <0·3 wt% Fe2O3. The composition of alkali feldspar from the northern and southern Vosges peralkaline minettes is in the range of Or72–93Ab17Fe-Or1–5·5 to Or72–93Ab17Fe-Or1–5·5, respectively. The Ba content of alkali feldspar is variable and may in some cases reach 4 wt% BaO. Minerals in peralkaline lamprophyres (lamproites) show deficiencies in Al (e.g. Al-poor clinopyroxene; phlogopite with tetrahedral Fe3+). Similarly, peralkalinity may result in crystallization of Cr-rich spinel with very high Cr/(Cr + Al), commonly reported for peralkaline lamprophyres and lamproites (Wagner & Velde, 1985; Mitchell & Bergman, 1991) and should not be genetically confused with refractory Cr-rich spinel known from ultramafic mantle rocks. Major and trace element geochemistry The lamprophyres span a wide range in major and trace element compositions (Figs 5 and 6). The samples dominantly have high Mg# [= molar Mg/(Mg + 0·9 × Fetot) ×100] but show highly variable MgO (5–14 wt%), SiO2 (45–64 wt%) and K2O concentrations (1·0–10·1 wt%; Fig. 5). Most of the dykes plot in the shoshonitic field of Peccerillo & Taylor (1976). About half of the samples are ultrapotassic (with K2O > 3 wt%, MgO > 3 wt% and K2O/Na2O > 2; Foley et al., 1987). The remaining samples predominantly fall in the shoshonitic field (Fig. 5). Most of the dykes are metaluminous, whereas some Si–Al-rich lamprophyres are peraluminous. The most K-rich dykes are mildly peralkaline with a maximum peralkalinity index of 1·11 [= molar (K2O + Na2O)/Al2O3] and Na2O contents as low as 0·2 wt% (Fig. 5b; maximum K2O/Na2O of 52). Fig. 5. View largeDownload slide (a) K2O vs SiO2 content of Variscan mantle-derived lamprophyres with fields from Peccerillo & Taylor (1976). (b) Samples show a rough negative correlation in the diagram of K2O vs Na2O. Ultrapotassic, shoshonitic and calc-alkaline fields (not labelled) are from Turner et al. (1996). Fig. 5. View largeDownload slide (a) K2O vs SiO2 content of Variscan mantle-derived lamprophyres with fields from Peccerillo & Taylor (1976). (b) Samples show a rough negative correlation in the diagram of K2O vs Na2O. Ultrapotassic, shoshonitic and calc-alkaline fields (not labelled) are from Turner et al. (1996). Fig. 6. View largeDownload slide Chondrite-normalized rare earth element patterns for (a) Group I and (c) Group II lamprophyres, and average primitive mantle-normalized trace element concentration patterns for regional varieties of (b) Group I and (d) Group II lamprophyres; normalization values are from McDonough & Sun (1995). The grey reference fields give the total variation of each group. Additional chondrite-normalized rare earth element patterns and primitive mantle-normalized element concentration diagrams for individual regions are given in Supplementary Data 3. Fig. 6. View largeDownload slide Chondrite-normalized rare earth element patterns for (a) Group I and (c) Group II lamprophyres, and average primitive mantle-normalized trace element concentration patterns for regional varieties of (b) Group I and (d) Group II lamprophyres; normalization values are from McDonough & Sun (1995). The grey reference fields give the total variation of each group. Additional chondrite-normalized rare earth element patterns and primitive mantle-normalized element concentration diagrams for individual regions are given in Supplementary Data 3. Two geochemically defined lamprophyre groups are present in the study area. Unambiguous distinction between the two groups is possible based on a combination of isotopic composition and trace element ratios, although some overlap between the groups exists for most ratios (Table 3). Most characteristic features are the contrasting shapes of the REE patterns and different Sr–Nd isotopic compositions. Group I lamprophyres occur mainly in the NW (i.e. in the Odenwald–Spessart, the Taunus, and the northern Vosges). Group II predominantly occur in the SE (i.e. the Schwarzwald and the central and southern Vosges) but they also show a spatial overlap with Group I lamprophyres at the southern margin of the MGCZ (i.e. the southern Odenwald and the northern Vosges–Palatine areas) (Fig. 1). Group II lamprophyres are predominantly mica lamprophyres whereas Group I dykes also comprise abundant amphibole lamprophyres. Table 3: Geochemical characterization of Group I and Group II lamprophyres Group I Group II 87Sr/86Sri 0·70535–0·71150 0·70599–0·71636 εNdi –0·7 to –3·9 –1·5 to –7·5 Th/La 0·15–0·55 0·22–1·96 Eu/Eu* 0·89 ± 0·07 0·74 ± 0·16 Nb/Ta 17·2 ± 3·9 14·4 ± 3·9 K/Rb 307 ± 152 187 ± 70 Cr/Ni 1·8 ± 0·4 4·0 ± 3·1 Group I Group II 87Sr/86Sri 0·70535–0·71150 0·70599–0·71636 εNdi –0·7 to –3·9 –1·5 to –7·5 Th/La 0·15–0·55 0·22–1·96 Eu/Eu* 0·89 ± 0·07 0·74 ± 0·16 Nb/Ta 17·2 ± 3·9 14·4 ± 3·9 K/Rb 307 ± 152 187 ± 70 Cr/Ni 1·8 ± 0·4 4·0 ± 3·1 Mean values given ±2σ SD. Eu/Eu* = EuN/(SmN × GdN)0·5. Table 3: Geochemical characterization of Group I and Group II lamprophyres Group I Group II 87Sr/86Sri 0·70535–0·71150 0·70599–0·71636 εNdi –0·7 to –3·9 –1·5 to –7·5 Th/La 0·15–0·55 0·22–1·96 Eu/Eu* 0·89 ± 0·07 0·74 ± 0·16 Nb/Ta 17·2 ± 3·9 14·4 ± 3·9 K/Rb 307 ± 152 187 ± 70 Cr/Ni 1·8 ± 0·4 4·0 ± 3·1 Group I Group II 87Sr/86Sri 0·70535–0·71150 0·70599–0·71636 εNdi –0·7 to –3·9 –1·5 to –7·5 Th/La 0·15–0·55 0·22–1·96 Eu/Eu* 0·89 ± 0·07 0·74 ± 0·16 Nb/Ta 17·2 ± 3·9 14·4 ± 3·9 K/Rb 307 ± 152 187 ± 70 Cr/Ni 1·8 ± 0·4 4·0 ± 3·1 Mean values given ±2σ SD. Eu/Eu* = EuN/(SmN × GdN)0·5. Lamprophyres of both groups are enriched in lanthanides (ΣLa–Lu of 150–1500 µg g–1 and 165–530 µg g–1 for Group I and Group II, respectively). The chondrite-normalized REE patterns (Fig. 6) are characterized by high LaN/YbN (11–109 for Group I and 7–38 for Group II) and flat heavy REE (HREE) patterns between Er and Lu. Group II lamprophyres additionally show a conspicuous flattening in their light REE (LREE) patterns, becoming more pronounced with increasing trace element enrichment. Furthermore, Group II lamprophyres have clear negative Eu-anomalies [Eu/Eu* = EuN/(SmN × GdN)0·5 = 0·59–89]. Primitive mantle-normalized element abundance patterns of all lamprophyres are characterized by strong enrichments in large ion lithophile elements (LILE), positive Pb anomalies and negative anomalies of the high field strength elements (HFSE) Nb, Ta and Ti (Fig. 6). Peralkaline minettes show similar patterns, but have higher contents of trace elements compared with other petrographic varieties of cogenetic dykes. However, they differ in having strongly positive anomalies of Zr and Hf and less pronounced negative Ti-anomalies (Fig. 6b). Both lamprophyre groups and their regional varieties are on average equally enriched in Pb and some outliers are related to secondary mobilization of highly fluid-mobile Pb. Some differences are present between the various dyke swarms of each group. Group I lamprophyres from the northern Vosges, for instance, show on average higher concentrations of Sr, Ba, P or Zr, compared with those from other regions. Northern Vosges dykes are furthermore characterized by the lowest SiO2 concentrations and contain some exotic members (e.g. VO91 with high Nb/Ta and Zr/Hf, or VO37 with high Nb/U). Sr–Nd–Pb isotopic composition The lamprophyres have negatively correlated initial 143Nd/144Nd and 87Sr/86Sr isotopic compositions (Fig. 7). The εNd320 values of the lamprophyres range from slightly negative to distinctly negative. They show compositions similar to the local post-collisional Variscan granitoids. Group I lamprophyres show only small variations in 87Sr/86Sri (0·70535–0·71150) and εNdi (–0·7 to –3·9) or 143Nd/144Ndi (0·51202–0·51219). Odenwald–Spessart and northern Vosges samples define two slightly different trends. Group II lamprophyres extend to more radiogenic 87Sr/86Sri (0·70599–0·71636) and have a broader range in εNdi (–1·5 to –7·5) or 143Nd/144Ndi (0·51184–0·51215). Fig. 7. View largeDownload slide 87Sr/86Sri–εNdi isotopic composition of lamprophyres corrected for post-emplacement radiogenic growth based on an average age of 320 Ma (see the section ‘Geological setting’). (a) Saxo-Thuringian and Moldanubian crustal fields are drawn for granitoids from the study area (Liew & Hofmann, 1988; Altherr et al., 1999a, 1999b, 2000; Siebel et al., 2012; Tabaud et al., 2015). Data for orthogneisses from the MGCZ are from Reischmann et al. (2001). Data for Moldanubian HP granulites from the Bohemian Massif are from Becker et al. (1999) and Janoušek et al. (2004). HP granulites from the Vosges Mountains plot in the same range as the Moldanubian HP granulites (Hasalová et al., 2015). The 360 Myr old Frankenstein Gabbro Complex (FGC) of the northern Odenwald possibly represents the best estimate for the isotopic composition of the mantle prior to metasomatism by continental subduction. (b) Detailed Sr–Nd isotopic compositions of the lamprophyre groups. Symbols used are as in Fig. 6. Fig. 7. View largeDownload slide 87Sr/86Sri–εNdi isotopic composition of lamprophyres corrected for post-emplacement radiogenic growth based on an average age of 320 Ma (see the section ‘Geological setting’). (a) Saxo-Thuringian and Moldanubian crustal fields are drawn for granitoids from the study area (Liew & Hofmann, 1988; Altherr et al., 1999a, 1999b, 2000; Siebel et al., 2012; Tabaud et al., 2015). Data for orthogneisses from the MGCZ are from Reischmann et al. (2001). Data for Moldanubian HP granulites from the Bohemian Massif are from Becker et al. (1999) and Janoušek et al. (2004). HP granulites from the Vosges Mountains plot in the same range as the Moldanubian HP granulites (Hasalová et al., 2015). The 360 Myr old Frankenstein Gabbro Complex (FGC) of the northern Odenwald possibly represents the best estimate for the isotopic composition of the mantle prior to metasomatism by continental subduction. (b) Detailed Sr–Nd isotopic compositions of the lamprophyre groups. Symbols used are as in Fig. 6. The Pb isotopic compositions of Group I and Group II lamprophyres define overlapping fields, and therefore show no regional differences. The Pb isotopic composition of both groups falls in the range of typical crustal rocks (Fig. 8). As most radiogenic 207Pb formed early in Earth’s history (owing to the relatively short half-life of 235U), the high 207Pb/204Pb ratios at a given 206Pb/204Pb of Group I and Group II lamprophyres indicate that the lead in these rocks is derived from old continental crust (or sediments derived from an old continent). Thus, the contribution of mantle Pb must be subordinate. The lead of lamprophyres from the Saxo-Thuringian Zone, including all samples from this study, has higher 207Pb/204Pb values than lamprophyres from the Moldanubian Zone of the Bohemian Massif. This indicates that there are regional differences in the Pb isotopic composition of the metasomatized mantle beneath different zones of the Variscan Orogen. Fig. 8. View largeDownload slide The Pb isotopic composition of the lamprophyres is not corrected for post-emplacement (in situ) growth, as some samples were affected by late alteration, possibly during Jurassic–Early Cretaceous hydrothermal activity that affected the entire study area (e.g. Pfaff et al., 2009). Alteration of feldspar releases Pb, which may be redistributed by fluids and results in an overcorrection of in situ Pb growth (i.e. the calculated initial Pb isotopic composition yields too low values) if the alteration does not represent a late magmatic autometasomatic alteration, but reflects a much younger process. Samples OD169R and SCH12 are not shown because of strongly radiogenic lead with 206Pb/204Pb of 22·60 and 26·83, respectively. Reference fields for lamprophyric dykes from the Bohemian Massif (BM) are given [including lamprophyres from the Moldanubian Zone (Krmíček et al., 2016) and the Saxo-Thuringian Zone (Abdelfadil et al., 2014)]. Lead evolution curves for mantle (M), orogen (O) and upper crust (UC) are from Zartman & Doe (1981). Fig. 8. View largeDownload slide The Pb isotopic composition of the lamprophyres is not corrected for post-emplacement (in situ) growth, as some samples were affected by late alteration, possibly during Jurassic–Early Cretaceous hydrothermal activity that affected the entire study area (e.g. Pfaff et al., 2009). Alteration of feldspar releases Pb, which may be redistributed by fluids and results in an overcorrection of in situ Pb growth (i.e. the calculated initial Pb isotopic composition yields too low values) if the alteration does not represent a late magmatic autometasomatic alteration, but reflects a much younger process. Samples OD169R and SCH12 are not shown because of strongly radiogenic lead with 206Pb/204Pb of 22·60 and 26·83, respectively. Reference fields for lamprophyric dykes from the Bohemian Massif (BM) are given [including lamprophyres from the Moldanubian Zone (Krmíček et al., 2016) and the Saxo-Thuringian Zone (Abdelfadil et al., 2014)]. Lead evolution curves for mantle (M), orogen (O) and upper crust (UC) are from Zartman & Doe (1981). DISCUSSION Orogenic lamprophyres (and lamproites) generally are characterized by high contents of potassium and incompatible trace elements, with Sr–Nd–Pb isotopic compositions reflecting the involvement of continental crust. These features are coupled with high magnesium numbers (Mg#) and high concentrations of mantle-compatible elements (e.g. Cr and Ni). This hybrid geochemical signature is indicative of melting of a lithospheric mantle source contaminated by liquids derived from subducted continental material (e.g. Peccerillo, 1999; Altherr et al., 2004; Conticelli et al., 2009; Prelević et al., 2012). Silica-rich melts released from the subducting slab may be highly heterogeneous, depending on the age of the subducted material (reflected by the Sr, Nd, and Pb isotopic composition) and its chemical composition. The latter controls the stable phase assemblage during melting and, thus, the trace element signature of the melt. The geochemical signature of these melts may be modified during the formation of a hybrid mantle that later melts to produce lamprophyres. In the following, we discuss some of the key aspects of the various processes in the sequence in which they occur in nature, except for AFC processes (assimilation and fractional crystallization), being aware that several processes affect the trace element signatures. Fractional crystallization and crustal contamination Some dykes contain xenocrystic material (e.g. cpx-rimmed undulatory quartz) indicating at least some crustal contamination. Minor crustal assimilation, however, does not significantly change the trace element patterns of the lamprophyres because of their high primary incompatible trace element contents (Conticelli, 1998; Hegner et al., 1998). Some composite dykes from the Schwarzwald with a granite porphyry core grading into lamprophyre margins may reflect hybridization (Wimmenauer, 1973). The leucocratic ‘semilamprophyres’ described by Wimmenauer might be related to strong fractional crystallization and/or hybridization with other crustal melts. As it is difficult to distinguish between the recycled, mantle-derived crustal component and a possible additional component of admixed crustal melt, more evolved samples (semilamprophyres) were not used for the discussion of source signatures. High-Mg varieties of all petrographic lamprophyre groups show petrographic evidence for a crystallization sequence starting with olivine, containing inclusions of Cr-spinel, followed by clinopyroxene and finally phlogopite and/or amphibole. Some dykes rich in phosphorus (mostly minettes) additionally contain phenocrysts of apatite. Fractional crystallization of olivine, spinel and clinopyroxene is indicated by covariations between MgO and Cr, Ni and Sc (Fig. 9). It is difficult to evaluate the effect of fractionation of amphibole or phlogopite as primary melt compositions are not uniform and may show considerable variability in both mantle-compatible and -incompatible elements, complicating the evaluation of the effects of fractional crystallization or assimilation on magma compositions. Fig. 9. View largeDownload slide Variation diagrams to illustrate major and compatible trace element variability. Data for intraplate basalt reference fields in (g) are from Lustrino & Wilson (2007). Fig. 9. View largeDownload slide Variation diagrams to illustrate major and compatible trace element variability. Data for intraplate basalt reference fields in (g) are from Lustrino & Wilson (2007). Group I and Group II lamprophyres show striking differences in their Cr/Ni ratios. Group I lamprophyres have nearly constant Cr/Ni (Fig. 9g), unaffected by fractional crystallization, similar to alkaline intraplate basalts. In contrast, Group II lamprophyres typically show high and variable Cr/Ni. These higher ratios are the result of lower Ni contents in Group II lamprophyres at similar Cr contents. Constant Cr/Ni during fractional crystallization might result from the coupled removal of olivine with inclusions of spinel, which are the major hosts of Ni and Cr, respectively. Nickel is chalcophile and early removal of sulfide phases (e.g. pyrrhotite) enclosed in fractionating olivine or clinopyroxene might fractionate Cr/Ni ratios. Early sulfide saturation in Group II lamprophyres could be related to higher sulfur contents or, alternatively, more reducing conditions, as the solubility of sulfur depends on its speciation and increases with increasing sulfate content (Jugo et al., 2005). Nature of the subducted crustal material Sampling of lamprophyres across the tectonic zones of the Variscan Orogen in SW Germany and eastern France has revealed two chemically different crustal signatures within the lithospheric mantle. Partial melting of these mantle domains produced lamprophyres that have comparable major element characteristics, but different trace element and Sr–Nd isotope signatures (Table 3). Group I lamprophyres are primarily distributed across the northern crustal segment (STZ–MGCZ) and those of Group II along the southern segment (MZ), although some spatial overlap between the two groups exists (Fig. 1). The presence of two distinct continental crust-derived metasomatic signatures that are spatially separated in the lithospheric mantle is indicative for mantle enrichment during two stages of subduction. The Moldanubian (Group II) lamprophyres have Sr–Nd isotopic compositions similar to Moldanubian HP–HT granulites (Fig. 7). In the Bohemian Massif, these granulites show close spatial and temporal relationships as well as chemical affinities to ultrapotassic intrusions (durbachites) and might be related to their mantle source enrichment (Becker et al., 1999; Janoušek & Holub, 2007). The granulites are dominated by felsic (metagranitic) lithologies with subordinate metasedimentary and mafic material (e.g. Marschall et al., 2003; Kotková, 2007; Skrzypek et al., 2012). A similar model for source enrichment has been applied to durbachites from the Vosges (Tabaud et al., 2015) and might also hold for Group II lamprophyres of this study. The age of HP metamorphism, and therefore the timing of mantle metasomatism for Group II lamprophyres, is around 340 Ma (Schaltegger et al., 1996, 1999). The tectonic framework and timing of metasomatism of the mantle source of Group I lamprophyres is less clear, as the MGCZ has a long-lived history and a wide range of different rocks may have been deeply subducted, producing melts that enriched the lithospheric mantle. A ∼360 Myr old calc-alkaline gabbroic complex in the northern Odenwald (MGCZ) is interpreted to have originated from a depleted, subduction-modified mantle source (Altherr et al., 1999a). The post-collisional lamprophyres, however, exhibit a much stronger trace element enrichment than the gabbros and distinctly more continental crust-like Sr–Nd isotopic compositions. This indicates that either the lamprophyres and gabbros were derived from different mantle sources or that metasomatism of the lamprophyre mantle source post-dated the extraction of the parental magmas of the gabbros. Mantle source contamination for Group I lamprophyres possibly occurred during closure of the Rheic Ocean or during the final Variscan collision at c. 340 Ma. Group I lamprophyres are characterized by lower 87Sr/86Sr320 and higher εNd320 compared with Group II lamprophyres. In addition, they inherited only a weak negative Eu-anomaly from their enriched mantle source. These characteristics argue for source enrichment by a relatively primitive and juvenile crustal component. The MGCZ, which was intruded by the lamprophyres, has a comparable primitive average elemental and Sr–Nd isotopic crustal composition. This might be related to rejuvenation of this crustal segment by the addition of mantle-derived melts along the Silurian to early Devonian magmatic arc of the Rheic Ocean (Franke, 2000). Post-collisional granitoids have similar Sr–Nd isotopic compositions and relatively weak negative Eu-anomalies (Altherr et al., 1999a). Furthermore, orthogneisses enclosing relics of medium-grade HP metamorphic rocks, interpreted as remnants of this arc, have comparable Sr–Nd isotopic compositions (Fig. 7). Similar rocks are possibly responsible for the contamination of the mantle source of the lamprophyres. The subducted material, however, is heterogeneous, as indicated by compositional differences among the dyke swarms. The northern Vosges and Odenwald–Spessart dyke swarms define distinct mixing arrays in a 87Sr/86Sri–εNdi diagram (Fig. 7). Lamprophyre samples from the northern Vosges have remarkably higher abundances of P2O5, Sr, Ba and LREE than samples from the Odenwald–Spessart area. In addition, they have higher amounts of calcite. Melting of subducted continental crust During continental subduction, hydrous silicate melts may be released from a wide variety of lithologies and cause metasomatism of the overlying mantle rocks. At low to medium pressures, and in the temperature range suitable for partial melting, amphibole, biotite, muscovite and epidote/zoisite are the dominant hydrous phases in crustal rocks. These minerals, however, become unstable at UHP conditions where phengite is present. Crustal material of mafic, pelitic or granitic composition subducted to a depth >100 km shows uniform parageneses consisting of garnet + clinopyroxene + phengite + coesite ± kyanite ± rutile in variable modal proportions (Schmidt & Poli, 1998; Hermann & Green, 2001; Schmidt et al., 2004). At pressures of 3–4 GPa, fluid-saturated melting takes place at around ∼700–800°C, whereas fluid-absent melting owing to phengite dehydration occurs at temperatures above 900–1000°C. As phengite is the only hydrous mineral present at relevant temperatures, melting reactions, temperatures, and initial melt compositions are similar in the various crustal lithologies (Schmidt et al., 2004). Liquids extracted from such lithologies are characterized by high K/Na owing to consumption of phengite and the stability of jadeite-rich clinopyroxene, retaining Na (Schmidt et al., 2004). Highly potassic compositions are, therefore, a typical feature of melts derived from subducted continental crust and, thus, the occurrence of ultrapotassic magmatic rocks might be indicative of UHP metamorphic processes. The production of highly potassic melts at high pressures has also been observed in exhumed felsic HP metamorphic terrains, such as in the Bohemian Massif (Vrána, 1989). The crustal component of the lamprophyres is responsible for their high K/Na signature, as indicated by the correlation between this ratio and the crustal fingerprint as defined by the Sr–Nd isotopic compositions (Fig. 10a). Fig. 10. View largeDownload slide Variations between εNdi and major and trace element ratios indicate mixing between components with contrasting trace element signature and isotopic compositions. A mixing relationship is most obvious for Group II lamprophyres owing to a more evolved Sr–Nd isotopic composition of the crustal endmember, which furthermore has a distinctive trace element signature; for example, high Th/La or a marked negative Eu anomaly [Eu/Eu* = EuN/(SmN × GdN)0·5]. Fig. 10. View largeDownload slide Variations between εNdi and major and trace element ratios indicate mixing between components with contrasting trace element signature and isotopic compositions. A mixing relationship is most obvious for Group II lamprophyres owing to a more evolved Sr–Nd isotopic composition of the crustal endmember, which furthermore has a distinctive trace element signature; for example, high Th/La or a marked negative Eu anomaly [Eu/Eu* = EuN/(SmN × GdN)0·5]. Hydrous silicate melts that formed at high pressures from phengite-bearing crustal lithologies are enriched in those trace elements that are predominantly hosted in mica (e.g. Be, Rb and Ba). Other trace elements may be dominantly sequestered by phases such as garnet, zircon, rutile, monazite or epidote-group minerals. Such phases in the melting residue may strongly influence the trace element inventory of the metasome-forming melts released from the subducting slab (e.g. Klimm et al., 2008; Skora & Blundy, 2010). Exceptionally high Th/La ratios compared with average continental crust are a typical feature of some Variscan lamprophyres (Group II lamprophyres in this study; Fig. 11), similar to ultrapotassic rocks from the Alpine–Himalayan belt (e.g. Tommasini et al., 2011). Importantly, elevated Th/La ratios are signatures of the continental crust-like geochemical components, as identified by covariations with Sr–Nd isotope ratios (Fig. 10b). High Th/La is related to selective depletion of LREE relative to similarly incompatible elements, increasing Th/La, Sm/La or Nb/La. Potential repositories for Th and LREE in continental crust are monazite and epidote-group minerals (zoisite, epidote, allanite). LREE-rich epidote-group minerals form in metagranitoids or metagreywackes and are common phases in (U)HP rocks (e.g. Guo et al., 2017), whereas monazite rather occurs in Ca-poor metapelites (e.g. Finger et al., 1998). Both monazite and LREE-rich epidote-group minerals have DTh/U > 1 and DSm/La <1. Concerning the Th/La ratio, however, monazite and allanite may have contrasting fractionation behavior, with DTh/La > 1 for monazite (Hermann & Rubatto, 2009; Skora & Blundy, 2010; Stepanov et al., 2012) and DTh/La < 1 for allanite (Hermann, 2002; Klimm et al., 2008). Partial melting of subducted crust with residual allanite may produce melts with the typical features of Group II lamprophyres (i.e. high Th/La–Sm/La; Fig. 11). Batch melting of average upper continental crust containing residual allanite generates Th/La ratios like those observed for lamprophyres from the Odenwald (maximum Th/La ∼1), whereas lamprophyres from the southern Vosges are even more strongly fractionated (Th/La up to ∼2). This range in Th/La could be related to variations in solubility, primarily controlled by temperature and melt composition, causing different amounts of restitic allanite, and hence variably strong trace element fractionation. Fig. 11. View largeDownload slide LREE–Th–U systematics of the lamprophyres. Both allanite and monazite cause strong fractionations between La, Sm, Th and U. (a) Residual allanite during partial melting is assumed to explain the positive correlation between Sm/La and Th/La of Group II lamprophyres. The allanite fractionation vectors starting from the composition of average upper continental crust (UC) of Rudnick & Gao (2003) are calculated using a batch-melting model with the partition coefficients of Klimm et al. (2008; run 19). Monazite also fractionates both ratios. Published monazite partition coefficients are not fully consistent (e.g. Hermann & Rubatto, 2009; Skora & Blundy, 2010; Stepanov et al., 2012) but dominantly show DTh/La >1, as represented by the vector. (b) Allanite and monazite incorporate U in preference to Th. Fig. 11. View largeDownload slide LREE–Th–U systematics of the lamprophyres. Both allanite and monazite cause strong fractionations between La, Sm, Th and U. (a) Residual allanite during partial melting is assumed to explain the positive correlation between Sm/La and Th/La of Group II lamprophyres. The allanite fractionation vectors starting from the composition of average upper continental crust (UC) of Rudnick & Gao (2003) are calculated using a batch-melting model with the partition coefficients of Klimm et al. (2008; run 19). Monazite also fractionates both ratios. Published monazite partition coefficients are not fully consistent (e.g. Hermann & Rubatto, 2009; Skora & Blundy, 2010; Stepanov et al., 2012) but dominantly show DTh/La >1, as represented by the vector. (b) Allanite and monazite incorporate U in preference to Th. Temperatures during Variscan continental subduction may have exceeded 1000°C, as documented by exhumed (U)HP–UHT metamorphic rocks (e.g. Massonne, 2003; Kotková & Janák, 2015; Haifler & Kotková, 2016). This makes fluid-absent phengite dehydration melting a possible scenario. Phengite dehydration (above 900–1000°C) results in high melt productivity with as much as 50 wt% melt over a short temperature interval (Schmidt et al., 2004). In such a situation, the preservation of allanite in the residue is unlikely. A strongly trace element enriched source is required, as generally high solubilities at elevated temperatures would even be enhanced by the highly alkaline compositions of UHP melts (Klimm et al., 2008). Partial melting and extraction of liquids with a high Th/La signature probably took place during prograde metamorphism at lower temperatures and required at least a small amount of free fluid. It cannot be ruled out, however, that additional melting occurred during peak temperatures of ∼1000°C. In contrast to Group II lamprophyres, Group I lamprophyres do not show strongly fractionated LREE systematics. In this case, LREE–Th-bearing accessory phases must have been completely dissolved during partial melting of their crustal protoliths. Group II lamprophyres show systematically lower (below average upper continental crust) and less scattered K/Rb ratios compared with Group I lamprophyres (Fig. 12a). Lamprophyres of Group II additionally show a broader range and on average higher Cs/Rb compared with those of Group I (Fig. 12b). The LILE systematics of Group II lamprophyres is in accordance with the buffering effect of mica during (U)HP anatexis, as relative compatibilities are given as K > Rb > Cs (e.g. Wunder & Melzer, 2003; Stepanov et al., 2016). The budget of the HFSE5+ in partial melts from Ti-poor felsic crust may also be controlled by phengite. Phengite has DNb > DTa and, therefore, lowers Nb/Ta ratios in coexisting melts during partial melting, as observed in Group II lamprophyres (Fig. 13). In contrast, relatively high Nb/Ta ratios in some Group I lamprophyres may reflect restitic Ti-oxides during partial melting (Stepanov & Hermann, 2013). Which phases control the trace element composition of the (U)HP melts eventually depends on the composition of the subducted crust (and possibly earlier melting). A more differentiated subducted crust is indicative for Group II lamprophyres compared with Group I. The differing LILE systematics between the two groups might suggest contrasting protolith compositions, similar to the inheritance of negative Eu-anomalies (Fig. 6c, Table 3). Fig. 12. View largeDownload slide LILE systematics of Group I and II lamprophyres. (a) The compositions of average upper continental crust (UC) and lower continental crust (LC) are from Rudnick & Gao (2003). Reference fields are based on whole-rock data for post-collisional granitoids from the study area (Henes-Klaiber, 1992; Altherr et al., 1999a, 1999b, 2000; Tabaud et al., 2014, 2015). (b) Lamprophyres of Group II show scattered but on average higher Cs/Rb compared with those of Group I. Fig. 12. View largeDownload slide LILE systematics of Group I and II lamprophyres. (a) The compositions of average upper continental crust (UC) and lower continental crust (LC) are from Rudnick & Gao (2003). Reference fields are based on whole-rock data for post-collisional granitoids from the study area (Henes-Klaiber, 1992; Altherr et al., 1999a, 1999b, 2000; Tabaud et al., 2014, 2015). (b) Lamprophyres of Group II show scattered but on average higher Cs/Rb compared with those of Group I. Fig. 13. View largeDownload slide The lamprophyres of Group I and II differ with respect to their Nb/Ta–Zr/Hf compositions (samples with Mg# <70 are excluded because of the effect of cpx fractionation on Zr/Hf). The silicate differentiation line in the diagram is taken from Münker et al. (2003) and indicates first-order coupling of Nb/Ta–Zr/Hf owing to fractionation of the silicate mantle by melting processes. The average composition of the continental crust (CC) is taken from Barth et al. (2000). Vector for garnet (Grt) is shown to illustrate fractionation during melt–peridotite interaction, using partition coefficients from Rubatto & Hermann (2007; 1000°C run). Vector for phengite (Phe) is given to illustrate the effect of buffering by mica on Nb/Ta during partial melting of subducted continental crust (Stepanov & Hermann, 2013; 1000°C run). Rutile may counteract the decrease in Nb/Ta caused by fractionation of mica. However, the unknown primary composition of subducted crustal material hinders an evaluation of the respective processes. Fig. 13. View largeDownload slide The lamprophyres of Group I and II differ with respect to their Nb/Ta–Zr/Hf compositions (samples with Mg# <70 are excluded because of the effect of cpx fractionation on Zr/Hf). The silicate differentiation line in the diagram is taken from Münker et al. (2003) and indicates first-order coupling of Nb/Ta–Zr/Hf owing to fractionation of the silicate mantle by melting processes. The average composition of the continental crust (CC) is taken from Barth et al. (2000). Vector for garnet (Grt) is shown to illustrate fractionation during melt–peridotite interaction, using partition coefficients from Rubatto & Hermann (2007; 1000°C run). Vector for phengite (Phe) is given to illustrate the effect of buffering by mica on Nb/Ta during partial melting of subducted continental crust (Stepanov & Hermann, 2013; 1000°C run). Rutile may counteract the decrease in Nb/Ta caused by fractionation of mica. However, the unknown primary composition of subducted crustal material hinders an evaluation of the respective processes. Metasomatism of the lithospheric mantle High-pressure silicate liquids from the subducted crust may have many major and trace element features typical for post-collisional (ultra-)potassic magmas (see above). Silica-rich liquids, being out of equilibrium with the overlying mantle rocks, will react with the latter (e.g. Sekine & Wyllie, 1982a, 1982b), which increases the concentrations of mantle-compatible elements such as Mg, Fe, Ni or Cr in the melt and lowers SiO2, resulting in hybrid melt compositions (e.g. Campbell et al., 2014). These hybrid melts may be completely consumed by reaction with peridotite, creating metasomatized domains in the lithospheric mantle, which contain hydrous phases such as phlogopite. Later, these domains may be preferentially mobilized—owing to their lower solidus compared with ambient peridotite—and produce trace element-enriched lamprophyres (e.g. Foley, 1992). The metasomatized domains may be texturally and mineralogically heterogeneous, depending on the composition of the melt and ambient mantle and the degree of interaction between them. Porous flow may result in complete reaction and forms a homogeneous, hybrid mantle (e.g. Mallik et al., 2015), whereas focused flow results in vein-like structures (Foley, 1992). Both endmember models probably are relevant for mantle enrichment during subduction of continental material. The major and trace element composition of melts derived from these mantle domains, however, strongly depends on the interaction process (Pirard & Hermann, 2015). Peralkaline dykes are crucial for understanding the hybridization process in the lithospheric mantle. Potassium contents of up to 10 wt% K2O and extremely high K2O/Na2O in peralkaline minettes clearly demonstrate the presence of a potassic phase in their source region, most probably phlogopite. Such K-rich compositions, however, have not been reproduced in experiments using homogeneous, phlogopite peridotite (e.g. Condamine & Médard, 2014; Mallik et al., 2015, 2016; Condamine et al., 2016). Instead, a veined mantle source may be required, at least for the production of these particular melts (Foley, 1992). The presence of a veined mantle is supported by the occurrence of phlogopite-rich veins hosted within ultramafic mantle rocks of the Bohemian Massif that have been interpreted to result from hybridization between high-pressure silicate liquids released from subducted felsic lithologies and peridotite (e.g. Becker et al., 1999). Depletion in aluminum relative to alkali metals (i.e. peralkalinity) is a peculiar feature of primary, mantle-derived magmas. Although silica-rich partial melts from continental material (pelitic and granitic/granodioritic in composition) formed at high temperatures and (ultra)-high pressures have very high K2O contents (and K2O/Na2O), they still are peraluminous to metaluminous (Schmidt et al., 2004; Auzanneau et al., 2006; Hermann & Spandler, 2008). Peralkalinity may result from the production of the hybrid mantle and/or its partial melting. Phlogopite melts incongruently in peridotites and pyroxenites, producing peritectic olivine or orthopyroxene, causing only a slight increase in the alkali to aluminum ratio in the melts relative to the protolith (Modreski & Boettcher, 1973; Sweeney et al., 1993; Foley et al., 1999; Funk & Luth, 2013; Mallik et al., 2015; Condamine et al., 2016). Some vein assemblages within the lithospheric mantle, however, already have peralkaline compositions, such as phlogopite-rich MARID rocks exhumed by kimberlites (e.g. Grégoire et al., 2002). These veins are unlikely to represent liquid compositions, but may be produced by flow differentiation resulting in accumulation of liquidus crystals on vein walls (Irving, 1980; Harte et al., 1993). Reaction zones consisting of orthopyroxene and garnet have been shown to develop between silica-rich melt and peridotite (e.g. Sekine & Wyllie, 1983; Johnston & Wyllie, 1989; Rapp et al., 1999; Pirard & Hermann, 2015). Removal of an aluminous phase such as garnet during reactive transport through the lithospheric mantle eventually may result in peralkaline residual melts in vein centers. In support of this process, garnet-compatible trace elements show systematic variations with alkalinity. A variable degree of garnet fractionation explains the covariations between alkalinity and Dy/Yb observed for the studied lamprophyres (Fig. 14). Garnet fractionation also affects Zr and Hf that have solid–liquid partition coefficients of ∼1 with DZr/Hf >1 (e.g. Pertermann et al., 2004; Rubatto & Hermann, 2007). Removal of garnet may explain why peralkaline dykes are shifted towards lower Zr/Hf ratios in Nb/Ta–Zr/Hf space compared with non-peralkaline dykes (Fig. 13). Fig. 14. View largeDownload slide Formation of orthopyroxene + garnet as a result of melt–peridotite interaction during channelized flow increases (Dy/Yb)CN and removes Al2O3 from the melt, and thereby increases the peralkalinity index [molecular (Na2O + K2O)/Al2O3]. Only samples with Mg# >70 are shown. Symbols used are as in Fig. 12. Chondrite normalization values (CN) are from McDonough & Sun (1995). Fig. 14. View largeDownload slide Formation of orthopyroxene + garnet as a result of melt–peridotite interaction during channelized flow increases (Dy/Yb)CN and removes Al2O3 from the melt, and thereby increases the peralkalinity index [molecular (Na2O + K2O)/Al2O3]. Only samples with Mg# >70 are shown. Symbols used are as in Fig. 12. Chondrite normalization values (CN) are from McDonough & Sun (1995). Trace elements that are incompatible in the fractionating phases (orthopyroxene + garnet) may passively increase during reactive transport, in addition to the enrichment during the double-stage melting process (of continental crust first and overprinted mantle second). Compared with cogenetic dykes, peralkaline lamprophyres show the strongest trace element enrichment, several times higher than average continental crust. In general, the whole-rock concentration of K2O is roughly positively correlated with many incompatible trace elements for cogenetic dykes. For peralkaline compositions, however, some trace elements deviate from the linear trend towards exceptionally high concentrations, which is most pronounced for HFSE4+ (Fig. 15a). The solubility of HFSE in depolymerized, peralkaline melts strongly increases with increasing alkalinity owing to complexation with excess alkalis (Watson, 1979). The excess alkali ions generate non-bridging oxygen atoms (NBO), which may speciate HFSE in the melt. To dissolve one excess cation of HFSE4+ and HFSE5+, four and five excess alkali ions are needed by stoichiometry, respectively. Consequently, solubilities increase differently with increasing alkalinity and may cause increased HFSE4+/HFSE5+ (Linnen & Keppler, 1997, 2002). The solubility of LREE also is affected by alkalinity (e.g. Duc-Tin & Keppler, 2015). This process explains the strongly fractionated trace element ratios, such as Hf/Sm, Zr/Nb or Lu/Hf, of peralkaline lamprophyres (Fig. 15b). Therefore, the trace element signatures of peralkaline lamprophyres (or lamproites) may not be suitable for inferring the nature of slab input to the mantle. Furthermore, owing to the involvement of garnet during reactive transport, HREE signatures may be misleading when used to derive information on the depth of partial melting (e.g. spinel peridotite vs garnet peridotite signature). Fig. 15. View largeDownload slide Influence of metaluminous–peralkaline transition on geochemical trace element signatures observed in lamprophyres. (a) Zirconium (like other HFSE) is strongly enriched in peralkaline lamprophyres. (b) HFSE ratios, such as Zr/Nb or Hf/Sm, are significantly fractionated in peralkaline rocks. Fig. 15. View largeDownload slide Influence of metaluminous–peralkaline transition on geochemical trace element signatures observed in lamprophyres. (a) Zirconium (like other HFSE) is strongly enriched in peralkaline lamprophyres. (b) HFSE ratios, such as Zr/Nb or Hf/Sm, are significantly fractionated in peralkaline rocks. An extensive system of veins may be produced by crystallization following variable degrees of flow differentiation. Reaction walls formed early during channelized flow may shield later melts from reacting with the mantle, as these melts react only with older reaction rinds. The vein assemblages are likely to be mineralogically and chemically zoned and may also contain accessory phases that are not in equilibrium with the surrounding peridotite. Even felsic rocks are possible (e.g. Beccaluva et al., 2004; Shimizu et al., 2004). Rocks ranging from peraluminous to metaluminous or to peralkaline compositions may be stored within the vein network. Consequently, metasomatism of the lithospheric mantle is responsible for a considerable diversification. Later, a low degree of partial melting affecting these domains results in chemically and mineralogically heterogeneous lamprophyre melt compositions. Partial melting of the metasomatized mantle Variscan (ultra-)potassic magmatism occurred during post-collisional and post-orogenic regional extension (see the section ‘Geological setting’). Partial melting of the metasomatized mantle occurs in response to lithospheric thinning, as decompression results in dehydration melting owing to breakdown of hydrous phases such as phlogopite (e.g. Conceição & Green, 2004). Additionally, thinning may move the asthenosphere–lithosphere thermal boundary to higher levels, thereby increasing the temperature within the lithospheric root and providing a heat source for partial melting (e.g. Turner et al., 1996). Material input from the asthenosphere is not necessary, but is possible (e.g. Prelević et al., 2012; Soder et al., 2016). In most samples studied, a chemical signal for an asthenospheric contribution is not visible. The Nb/U ratios of Group I and Group II lamprophyres are <10 (6·1 ± 2·3 and 3·2 ± 1·5, respectively). They fall in the range of continental crust and are significantly lower than average ocean island basalt (Nb/U = 47 ± 10; Hofmann et al., 1986). Increased Nb/U values of up to 21 (northern Vosges/Palatine samples PF04, VO37, VO88, VO91) may indicate contributions of material from an undepleted, anorogenic mantle source to some lamprophyres. Partial melting of the lithospheric mantle returns crustal material that was subducted to mantle depths back to the crust. The manifestation of this magmatism covers a broad range of different magma compositions, ranging from calc-alkaline to shoshonitic, ultrapotassic and lamproitic with increasing K2O content. Lamprophyre varieties of these compositions are present in the study area and range from spessartite to kersantite, minette and peralkaline minette. All these types may contribute to a single dyke swarm. Similar associations are known from other orogens (e.g. Owen, 2008; Conticelli et al., 2009). Covariation between Sr and Nd isotope ratios and K2O/Na2O (Fig. 10a) reflects variable contributions from at least two reservoirs to the two lamprophyre groups: subducted continental crust and peridotite. Variable proportions of both components probably are introduced during both metasomatism of the lithospheric mantle and its partial melting. Metasomatism creates hybrid mantle domains, ranging from a modally metasomatized but homogeneous peridotite to chemically and mineralogically zoned veins. This mantle may be affected by variable degrees of melting. High degrees of melting might be achieved in the veins, although still below the solidus of peridotite. Phlogopite, whose stability is shifted towards higher temperature by the incorporation of fluorine, melts over a considerable temperature interval and may buffer the melt in potassium, but also in Rb and Ti (e.g. Foley et al., 1986; Foley, 1989). During progressive melting of the veins, material from phlogopite-poor wall-rock pyroxenites or the ambient peridotite may be increasingly introduced, owing to either partial melting or dissolution by melts originating within the veins, eventually resulting in less enriched, less K-rich lamprophyres (Foley, 1992; Foley et al., 1999). Higher degrees of melting and, hence, stronger influence of wall-rock material may be related to partial melting of Ca-amphibole. Calcium-amphibole has a lower upper thermal stability than phlogopite and may cause relatively high degrees of melting at low temperatures (e.g. Conceição & Green, 2004; Condamine & Médard, 2014; Mallik et al. 2015). Less K-rich lamprophyres (e.g. spessartites) are more abundant among Group I lamprophyres and may have had higher amounts of amphibole in their source. In any case, re-melting of the metasomatized mantle should further increase the concentration of most trace elements. CONCLUSIONS Subduction of continental crust during Variscan continental collision resulted in metasomatism of the lithospheric mantle. Thinning of the lithosphere during post-collisional and post-orogenic extension triggered partial melting of enriched mantle domains, resulting in recurrent pulses of potassic–ultrapotassic magmatism. Lamprophyre dykes are part of this magmatism and show considerable chemical and mineralogical heterogeneity, comprising amphibole lamprophyres, mica lamprophyres and lamproites. Lamproites (or peralkaline mica lamprophyres) are particularly important for understanding the recycling of crust during continental subduction. Highly potassic crustal melts were introduced into the Variscan lithospheric mantle during continental subduction. Melts released from most crustal lithologies at high pressure have high K2O/Na2O, owing to preferential melting or dissolution of phengite, whereas jadeite-rich clinopyroxene remains stable. The trace element signature of melts released from the subducted crust may be strongly affected by the stability of phases that sequester particular groups of elements and thereby control the trace element budget of the subducted material. High Th/La and Sm/La and low Th/U are indicative of residual allanite, for instance. Interaction between silica-rich melts derived from the slab and mantle peridotite during focused flow causes reaction zones of orthopyroxene and garnet. Reactive transport removes garnet-compatible elements (e.g. Al, HREE) from the coexisting melt and eventually may result in the crystallization of peralkaline metasomes. Variable degrees of melting affecting the lithospheric mantle that hosts chemically and mineralogically zoned veins results in a broad spectrum of primary lamprophyre compositions. Peralkaline lamprophyres are selectively enriched in some trace elements with high solubilities in peralkaline magmas, most strongly in HFSE4+, but also HFSE5+ and REE. This enrichment occurs during melt–peridotite interaction, partial melting of metasomes and magma evolution. The mineralogy of the K-rich magmas is strongly controlled by alkalinity. Mineral phases in peralkaline lamprophyres (lamproites) are Al-poor (e.g. diopside, Fe3+-rich phlogopite and K-feldspar, highly chromian spinel). The contrasting chemical signatures of lamprophyres (Group I in the Moldanubian Zone and Group II in the Mid-German Crystalline Zone) allow us to chemically map the lithospheric mantle of the Variscan orogen. These regional variations are related to the nature and source of the subducted continental material, but also to the conditions of partial melting and the nature of residual phases. ACKNOWLEDGEMENTS The authors would like to thank Helene Brätz (University of Erlangen-Nuremberg), Bettina Hübner (Potsdam) and Hans-Peter Meyer (Heidelberg) for analytical assistance. Special thanks are due to Ilona Fin and Oliver Wienand for preparing large numbers of high-quality thin sections. This paper benefited from discussions with Rainer Altherr and Michael Hanel. We gratefully acknowledge constructive and helpful comments from reviewers Vojtěch Janoušek and Dejan Prelević, as well as the editorial work of Marjorie Wilson. REFERENCES Abdelfadil K. M. , Romer R. L. , Glodny J. ( 2014 ). Mantle wedge metasomatism revealed by Li isotopes in orogenic lamprophyres . Lithos 196–197 , 14 – 26 . Google Scholar Crossref Search ADS Altherr R. , Kalt A. ( 1996 ). Metamorphic evolution of ultrahigh-pressure garnet peridotites from the Variscan Vosges Mts. (France) . Chemical Geology 134 , 27 – 47 . Google Scholar Crossref Search ADS Altherr R. , Henes-Klaiber U. , Hegner E. , Satir M. , Langer C. ( 1999a ). Plutonism in the Variscan Odenwald (Germany): from subduction to collision . International Journal of Earth Sciences 88 , 422 – 443 . 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