International Journal of Earth Sciences

Hennig-Breitfeld, Juliane; Hall, Robert; White, Lloyd T.; Breitfeld, H. Tim; Forster, Marnie A.; Armstrong, Richard A.; Kohn, Barry P.

doi: 10.1007/s00531-024-02390-1pmid: N/A

The Sibela Mountains of the island of Bacan in eastern Indonesia contain one of the Earth’s youngest metamorphic complexes that is now exposed at elevations up to 2000 m. New mica 40Ar/39Ar and apatite (U–Th–Sm)/He data from metamorphic and igneous rocks indicate that these rocks were rapidly exhumed in the Pleistocene (c. 0.7 Ma). Exhumation of the metamorphosed Permo-Triassic basement (c. 249–257 Ma) was accompanied by metamorphism (recorded by schists) as well as partial melting (recorded by c. 1.4 Ma granitic dykes). These processes must have occurred at extremely high cooling and exhumation rates. The rapid exhumation on land was associated with significant subsidence in adjacent basins offshore that reach depths up to 2.4 km. Neogene metamorphic core complexes and other metamorphic complexes are well-known from eastern Indonesia, but they usually record much higher exhumation rates than those reported from older classic metamorphic core complexes found in other parts of the world and require a different formation mechanism. Unlike classic metamorphic core complexes that are characterized by low-angle detachment faults, the Bacan metamorphic rocks were exhumed on steep bounding normal faults forming a rectilinear block pattern. We suggest such complexes are termed metamorphic block complexes (MBC). The Bacan MBC is exceptionally young and like the other east Indonesian complexes was rapidly exhumed during subduction rollback. A flexure formed during arc-arc collision as the Sangihe forearc loaded the Halmahera forearc which reactivated steeply-dipping faults in a rectilinear chocolate block pattern.Graphical abstractThe Sibela Mountains of the island of Bacan in eastern Indonesia are formed by one of the Earth’s youngest metamorphic complexes. a Dense rain forest cover and steep flanks of the Sibela Mountains which rise from sea level to more than 2000 m. b Quaternary collision between the Sangihe and Halmahera arcs. Loading of the Halmahera forearc formed a flexure that reactivated steeply-dipping faults, which exhumed the Sibela Mountains metamorphic block. c Rapid cooling paths during exhumation of the Sibela metamorphic complex[graphic not available: see fulltext]

Suryanata, Putu Billy; Bijaksana, Satria; Dahrin, Darharta; Nugraha, Andri Dian; Harlianti, Ulvienin; Putra, Putu Raditya Ambara; Fajar, Silvia Jannatul; Suandayani, Ni Komang Tri; Pratama, Aditya; Gumilang, Mukhamad Fajar; Al Basyarah, Wisandie Syah; Paramartha, I. Komang Agus Aditya;

Dostal, Jaroslav; Solari, Luigi; Ma, Changqian

doi: 10.1007/s00531-023-02375-6pmid: N/A

Late Devonian felsic volcanic rocks of the Grand Beach complex (GBC) of Avalonia from the Burin Peninsula, southeastern Newfoundland (northwestern Appalachians) are part of an overstep sequence overlying the Neoproterozoic basement. The volcanic complex is composed of volcanic and volcaniclastic rocks deposited in a post-tectonic extensional setting proximal to the St. Lawrence granite (SLG), a Devonian pluton associated with a prominent vein-type fluorite mineralization. The volcanic rocks are alkali rhyolites, which are weakly peraluminous and exhibit geochemical characteristics of A-type felsic magmas, such as low FeOt, MgO, CaO, and TiO2 but high contents of alkalis, Nb, Y, and Zr and high Ga/Al and FeOt/MgO ratios. They have positive ɛNd(t) values (~ + 2.5) and their Nd-depleted mantle model ages (~ 0.9 Ga) are consistent with derivation of the parental magma from metasomatized dry Avalonian lower crustal basement via partial melting followed by fractional crystallization. The U–Pb zircon age for the volcanic complex (375.6 ± 1.1 Ma) is closely comparable to the age of the SLG, suggesting that they were emplaced during the same magmatic episode. They also have similar chemical and isotopic compositions, suggesting that the GBC represents a volcanic equivalent of the SLG. The compositional differences between the volcanic rocks and the main phase of the granite pluton, including higher oxidation state of the GBC, reflect the interaction of the parental magma with crustal material and fluids. The close proximity of SLG and GBC suggests that the volcanic complex could host fluorite mineralization.Graphical abstract[graphic not available: see fulltext]

Estrada, Solveig; Koglin, Nikola; Riefstahl, Florian; Nopper, Hannah; Geissler, Wolfram; Spiegel, Cornelia

doi: 10.1007/s00531-024-02389-8pmid: N/A

The Yermak Plateau (YP) north of Svalbard is a prominent bathymetric feature in the Eurasia Basin of the Arctic Ocean, forming the northwesternmost margin of the Eurasian plate. Seismic data indicate that the YP comprises continental basement; however, little is known about its geology. New petrographic, geochemical, Sr–Nd isotopic, and Ar–Ar geochronological data were obtained on rock fragments, which were previously recovered from basement highs of the northeastern and southwestern YP and are dominantly of magmatic origin. These new data combined with available literature data, and comparisons with volcanic and sedimentary rocks from onshore and offshore areas adjacent to the YP indicate that the northeastern YP and the southwestern YP are different regarding their geological evolution. The southwestern YP comprises an alkaline basaltic suite for which an Ar–Ar biotite age of 51 Ma was previously reported. The suite was formed in a continental extensional regime offshore northern Svalbard. Associated sedimentary rocks (sandstone, several limestones) show petrographic similarity with rocks of the Devonian Old Red Sandstone on Svalbard. From the northeastern YP, in contrast, we recovered mildly alkaline basaltic rocks with mid-Cretaceous Ar–Ar ages (102 ± 3 and 98 ± 3 Ma). The rocks show certain geochemical characteristics (partial enrichments of P, Ba, and Eu), which overlap with similar-aged Cretaceous basaltic rocks from northern Ellesmere Island of Canada and North Greenland. We suggest that the northeastern YP is a continental fragment derived from the North American plate, which was separated from the conjugate Morris Jesup Rise and juxtaposed to the geologically distinct southwestern YP by the propagation of the Gakkel Ridge spreading center since the early Oligocene.Graphical Abstract[graphic not available: see fulltext]

Levi, Nicola; Weissl, Michael; Decker, Kurt

doi: 10.1007/s00531-023-02383-6pmid: N/A

Borehole image data and a 1D-stress model built on open hole logs, leak-off tests (LOT) and image logs are used to evaluate the potential of seismicity caused by fault triggering during geothermal heat production in the city of Vienna. Data were derived from a 4220 m deep geothermal exploration well that investigated the geothermal potential of fractured carbonates below the Miocene fill of the Vienna Basin. The well penetrated several normal faults of the Aderklaa Fault System (AFS) that offset Pleistocene terraces at the surface and hence are regarded as active. Stress-induced borehole failures and 1D geomechanical modeling proves that the potential reservoirs are in a normal fault stress regime with Sv > SHmax > Shmin. While stress magnitudes in the upper part of the well (down to about 2000 m) are significantly below the magnitudes that would trigger the rupture of critically oriented faults including the AFS, stresses in the lower part of the drilled section in the pre-Neogene basement (below about 3300 m) are not. Data evidence a rotation of SHmax for about 45° at a fault of the AFS at 3694 m to fault-parallel below the fault suggesting that the fault is active. Critical or near-critical stressing of the fault is corroborated by the stress magnitudes calculated from the 1D geomechanical model. The safety case to exclude unintended triggering of seismic fault slip by developing geothermal reservoirs in close vicinity to one of the branch faults of the AFS may therefore be difficult or impossible to make.Graphical Abstract[graphic not available: see fulltext]

Benito, María P.; Tibaldi, Alina M.; Cristofolini, Eber A.; Barzola, Matías G.; Schwartz, Joshua J.; Molina, José F.; Escribano, Facundo A.

doi: 10.1007/s00531-024-02385-ypmid: N/A

The western Argentinian sector of Gondwana has been the focus of several recent studies related to the Famatinian orogeny; however, the geologic history of arc activity in hinterland areas remains poorly understood. We present new data from the Monte Guazú Complex that reveal arc-related magmatism in the Sierras de Córdoba, which we consider part of the Famatinian hinterland. Igneous rocks comprise a diorite unit which includes an amphibole quartz-gabbro/diorite and a tonalite unit comprising amphibole- and biotite-bearing tonalites to minor granodiorites. Both units constitute a medium-K calc-alkaline series ranging in composition from metaluminous to moderately peraluminous. Trace-element signatures show Ti and Nb depletion and strong incompatible element enrichments (large-ion lithophile elements, Pb, Th, U, and light-rare earth elements) relative to normal mid-ocean ridge basalts, suggesting that they formed in an arc setting. U–Pb zircon geochronology constrains magmatism to 455–498 Ma, while weighted mean ages of 474–489 Ma are mostly synchronous with the Famatinian arc beginning. We demonstrate that fractional crystallization of mantle wedge-derived melts controlled the early magmatic evolution, while country rock assimilation and anatectic melt mixing were prevalent in evolved rock members. These results spatially extend the Late Cambrian–Late Ordovician Famatinian retro-arc to the southern Sierras de Córdoba. Our findings show that magmatism involved coeval anatexis of host rocks, conversely to previous geodynamic models. Our data have fundamental implications for Paleozoic tectonic and magmatic processes operating along the western Argentinian sector of Gondwana, demonstrating the importance of crustal reworking and the addition of mantle material in the Famatinian arc inboard sector.Graphical Abstract[graphic not available: see fulltext]

Miranda-Díaz, Gustavo; Menzies, Andrew; Riveros-Jensen, Karl; Heide, Gerhard; Bußmann, Lena; Härtel, Birk; Tagle, Roald; Medina, Eduardo; Griem, Wolfgang

doi: 10.1007/s00531-024-02391-0pmid: N/A

Portezuelo de Pajas Blancas' primary metasomatic deposits host sapphires that differ in size, colour, and colour distribution through different lithological units. The discovery of sapphire-bearing secondary aeolian placer deposits enabled a detailed analysis of sapphire types to determine the causes of this heterogeneity. Representative single sapphires from the primary and secondary deposits were analysed using various techniques, including SEM-CL, OM-CL, Micro-XRF, Raman spectroscopy, and polarised transmitted light multi-focus optical microscopy. Based on the results, seven sapphire types were identified according to their colours and colour distribution. Fe and Ti concentrations mainly contribute to the colour and micro-textures occurrence. The primary growth textures include cores, progressive, oscillatory, and diffusion zoning, whereas the secondary alteration features correspond to micro-brecciation, re-arrangement, and overgrowth. Inclusions such as euhedral andalusite, anhedral anhydrite, and anhedral rutile were identified in the sapphires. The formation of Portezuelo de Pajas Blancas sapphires can be divided into five genetic stages: (i) core growth development; (ii) chemical imbalance due to open system behaviour that produces progressive and oscillatory zoning; (iii) low-temperature deformations that produce micro-brecciation; (iv) re-arrangement of pre-formed sapphire fragments and subsequent sapphire overgrowth; (v) diffusion zoning that produce Fe- and Ti-enriched outer rims. In conclusion, the Portezuelo de Pajas Blancas' sapphires were formed through at least five stages of oxidised contact metasomatism at varying temperatures and low pressures, where a heterogeneous forming condition predominates during sapphire formation.Graphical Abstract[graphic not available: see fulltext]

Mousa, Fatma A.; El-Hassan, Mohamed M. Abu; Sallam, Emad S.

doi: 10.1007/s00531-024-02395-wpmid: N/A

Hu, Qiaoqing; Wang, Yitian; Wei, Ran; Wang, Jiawei; Liu, Junchen; Chen, Guimin; Chen, Jun

doi: 10.1007/s00531-024-02388-9pmid: N/A

The Aqishan-Caixiashan polymetallic ore cluster, located in the eastern Tianshan Orogenic Belt, is part of the southern Central Asian Orogenic Belt (CAOB) and experienced extensive tectono-magmatic events with polymetallic mineralization during the Carboniferous. However, the Carboniferous tectonic affinity and magmatic evolution of the ore cluster are still controversial, which limits further understanding of the tectonic evolution and regional metallogeny. With the aim of solving these problems, we have carried out geochronological and geochemical studies on Carboniferous intrusive rocks and volcanic rocks from the ore cluster. The samples of the Carboniferous magmatic rocks are enriched in LREEs and LILEs but depleted in HFSEs, which attest to the I-type affinity and are similar to those formed in a continental arc. The early Carboniferous granodiorites and granites (350–343 Ma) in the Central Tianshan Block (CTB), with high Mg# values of 37–66, low Y values of 2.3–17.2 ppm, and high Sr/Y ratios (34–85), show characteristics of adakites that are formed by partial melting of delaminated oceanic crust and/or lower crust. Additionally, they have a wide range of εHf(t) values (5.4–15.9), high εNd (t) values (1.78–6.31) and low ISr values (0.705–0.706), indicating a mixed source of depleted mantle and lower crust for its origin. The Late Carboniferous volcanic rocks (314–306 Ma) in the Aqishan-Yamansu Tectonic Belt (AYTB) north of the CTB have obviously negative Nb–Ta-Ti anomalies, as well as high Y contents (12–20 ppm) and low Sr/Y ratios (5.6–29.9) compared to primitive mantle, which has a relatively flat chondrite-normalized REE pattern, resembling arc-related magmas. Additionaly, they have positive values of εHf(t) values (8.7–14.7), high εNd(t) values (3.04–4.45) and low ISr ratios (0.704–0.707), showing a depleted mantle source, which is weakly affected by the contamination of ancient crustal material. Combining this study and previous works, we suggest that the continuous southwards subduction of the North Tianshan Ocean during the Carboniferous generated the continental arc and forearc basin in the northern part of the CTB. The expansion of the Aqishan-Yamansu forearc basin formed intrusions and volcanic formations along the arc belt. The early Carboniferous intermediate-felsic mantle-derived adakitic magmas in the CTB are probably related to regional Zn-Pb enrichment and mineralization, and the Late Carboniferous intrusions and volcanic formations in the AYTB are related to large-scale Fe-Cu-Zn-Pb-Ag mineralization.Graphical Abstract[graphic not available: see fulltext]

Sun, Shengnan; Song, Zhigang; Han, Zuozhen; Ren, Xiang; Wei, Pengfei

doi: 10.1007/s00531-024-02400-2pmid: N/A

To better understand the geodynamic evolution of northeastern China during the Late Mesozoic, we analyzed zircon U–Pb geochronological, Lu–Hf isotopic, and geochemical data for Early Cretaceous volcanic rocks from the southeastern margin of the Songliao Basin. Newly identified A-type rhyolite and trachyandesite yielded zircon 206Pb/238U ages of ca. 123 Ma and 117 Ma, respectively. The rhyolites are high in SiO2 (72.24–78.89 wt%) and total alkali (K2O + Na2O = 8.81–10.03 wt%), and low in MgO (0.10–0.26 wt%), CaO (0.32–0.36 wt%), Ni (0.08–2.69 ppm), and Cr (0.39–4.87 ppm) concentrations, with negative Nb, Ta, and Sr anomalies. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs); the calculated Zr saturation temperatures are high (828–915 °C). The A-type rhyolites possess variable zircon εHf(t) values ranging from + 5.69 to + 10.49. Petrogenetic analysis leads us to propose that the A-type rhyolites were probably formed by partial melting of a Neoproterozoic–Early Paleozoic juvenile lower crust. The trachyandesites have Nb/Ta (14.9–17.25), Zr/Hf (35.04–42.75), Rb/Sr (0.25–0.40), and Lu/Yb (0.14–0.15) ratios that are similar to those of mantle-derived magma, indicating a mantle source. They have εHf(t) values of + 4.71 to + 7.29 and show enrichment in LILEs and LREEs, and weak depletion in HFSEs, suggesting that the parent magma originated from partial melting of a depleted lithospheric mantle, and was subsequently metasomatized by subduction-related fluids, followed by extensive fractional crystallization during the magma evolution. Combined with the temporal and spatial distribution of Late Mesozoic igneous rocks from the southeastern margin of the Songliao Basin, we propose that Early Cretaceous volcanic rocks formed in an extensional tectonic setting that was closely related to rollback of the Paleo-Pacific (Izanagi) oceanic slab.Graphical abstract[graphic not available: see fulltext]