International Geology Review

Zeng, Linlin; Zheng, Han; Zhang, Dexian; Han, Shibo; Peng, Heng; Kang, Peixuan; Ma, Shuya

doi: 10.1080/00206814.2025.2546417pmid: N/A

Comprehensive field, petrographic, mineral chemical, zircon U-Pb geochronological, phase equilibrium modelling, and microstructural and crystallographic preferred orientation (CPO) analyses of garnet gneisses and garnet amphibolites from the eastern Shangdan Shear Zone (SSZ) in the Qinling Orogen reveal a three-stage Early Paleozoic P-T-t-D evolution. The garnet-bearing lithologies collectively define a clockwise P-T trajectory within the mid- to lower-crust, characterized by progressive burial heating, near-isothermal decompression, and subsequent near-isobaric cooling. The three metamorphic-deformational stages are as follows: Stage 1 (ca. 510–480 Ma) records high- to ultrahigh-pressure metamorphism ( ≥30 kbar, ≥700°C) in mantle-depth slivers triggered by northward subduction of the Shangdan oceanic plate, coeval with high-pressure granulite-facies metamorphism (14–15 kbar, 755–775°C) in the lower crust. A steeply dipping penetrative S1 foliation developed during this stage, consistent with NNE–SSW compressional tectonics. Stage 2 (ca. 480–450 Ma) exhibits rapid exhumation-driven retrograde paths characterized by near-isothermal decompression (14–15 kbar → 5.8–7.6 kbar at 725–758°C), with tectonic quiescence facilitating vertical transport of metamorphic complexes along the SSZ. Stage 3 (ca. 420–400 Ma) marks near-isobaric cooling to amphibolite-facies conditions (4.5–6.8 kbar, 550–620°C) during continental collision between the north and south Qinling belts, where syn-kinematic sinistral shearing was dynamically coupled with retrograde metamorphism under transpressional regimes. This study establishes genetic linkages between discrete metamorphic stages and regional deformation events, reconstructs a coherent Early Palaeozoic metamorphic-deformational chronology, and elucidates the coupling mechanisms between deformation and metamorphism during the evolution of the SSZ.

Chattopadhaya, Soumi; Talukdar, Debojit; Rao, N. V. Chalapathi; Ghosh, Biswajit

doi: 10.1080/00206814.2025.2547394pmid: N/A

Nephelinite, the earliest derivation of the rift-related magmatism, is distributed across diverse global tectonic settings, including the end-Cretaceous Deccan Large Igneous Province, India. Two contrasting global models are in vogue, favouring the genesis of the nephelinites, viz. (i) low-degree partial melting of a volatile-rich, metasomatized subcontinental lithospheric mantle or (ii) mantle transition zone. We compile all the available Deccan-nephelinites data and compare it with the global datasets. Our observation shows – i) a substantial latitudinal trend in the chemical variation of the Deccan nephelinites from north to south; ii) the nephelinites of the Sarnu-Dandali and the Kutch alkaline complexes show the most primitive signature and match with that of the eastern China variants, while the remaining fraction shows evolved character; iii) a conspicuous similarity in the trace element patterns between Mesoproterozoic kimberlites and HIMU type OIB. We therefore conclude that, despite being a by-product of the contemporaneous Deccan magmatism, a distinct difference exists amongst the earliest derivative of the Reunion plume caused by Deccan magmatism. We further highlight that the source heterogeneity existed in the earliest stages beneath the western Indian subcontinental lithospheric mantle. A much deeper origin, along with a carbonated peridotite source, can be invoked for the genesis of these Deccan nephelinites.

Du, Yilun; Cao, Yi; Zhang, Zhaonian; Lou, Yuang

doi: 10.1080/00206814.2025.2555272pmid: N/A

The Xiong’er volcanic rocks (XVRs) on the North China Craton (NCC)’s southern margin are vital for understanding the NCC’s late Proterozoic evolution. This study focuses on the Xiong’ershan area’s volcanic rocks and performs detailed investigations on their petrology, chronology, and geochemistry, coupled with re-evaluation of prior geochemical data. Zircon U – Pb dating indicates their eruption ages of 1806–1764 Ma. These volcanic rocks are classified into basic – intermediate and felsic groups. Abundant quartz-filled vesicles and amygdales appear in basic – intermediate volcanic rocks, which can lead to an overestimation of SiO2 content in geochemical analyses. To remove this bias, the SiO2 content of the basic – intermediate rocks were re-evaluated by subtracting the quartz contributions from vesicles and amygdales. Our corrected data reveals a clear bimodal distribution (basalt + rhyolite/dacite), contradicting prior interpretations of continuous intermediate compositions. This supports that the XVRs formed in an intracontinental extensional environment, likely to have occurred due to the Columbia supercontinent’s break-up in the late Paleoproterozoic. All volcanic rocks have similar Sr-Nd-Hf isotope ratios and trace element patterns, indicating a common origin. The consistent isotopes and incompatible element ratios imply little crustal contamination during magma ascent. The relationships between MgO and other elements agree with the fractionation of clinopyroxene, olivine, and plagioclase before MgO decreases to ~2 wt%, and then the fractionation of ilmenite and apatite. Additionally, the rocks have lower water content and oxygen fugacity than arc magmas, and contain numerous inherited zircons with ages close to those of the Taihua group’s basement rocks. These results indicate that the XVRs originated from the reworking of the late Paleoproterozoic lithospheric mantle on the NCC’s southern margin, which was enriched by contamination of delaminated lower crust materials and metasomatism of subducted slab fluids before the late Proterozoic.

Lei, Wan-Shan; Duan, Yu; Liu, Zhi-Qiang; Wang, Ran; Zhang, Hai-Dong; Li, San-Zhong

doi: 10.1080/00206814.2025.2555274pmid: N/A

A series of metamorphic core complexes, including the Xiaoqinling, Xiong’ershan, and Dabie Mountains, span from west to east within the Qinling-Dabie Orogen of Central China. Despite their similar formation timelines and tectonic trends, they exhibit distinct geochemical signatures and exhumation processes. In the Xiaoqinling region, magmatic source temperatures initially increase with depth from approximately 606°C, reaching a peak around 847°C, and then decrease to approximately 660°C at greater depths, whereas in the Xiong’ershan area, they consistently decrease (811→609°C). The Dabie Mountains show consistent source temperatures (~800°C) across depths, suggesting their location above the ‘kink’ of Late Mesozoic Pacific subduction mantle wedge. Multi-method thermochronological analysis indicates that from 139 Ma to 85 Ma, the Xiaoqinling region cooled at 15.1°C/Ma initially, followed by deceleration to 2.7°C/Ma. Similarly, the Xiong’ershan and Dabie Mountains experienced two-stage exhumation processes, with cooling rates of 10.2°C/Ma, 3.7°C/Ma, and 20.3°C/Ma, 3.2°C/Ma, respectively. High-angle subduction and rollback of the ancient Pacific Plate during the Jurassic–Cretaceous transition facilitated the formation and rapid exposure of these metamorphic core complexes. Subsequent Pacific subduction reorientation during the Late Cretaceous reduced regional extension and thereby decreased the uplift and exhumation rates of these complexes.

Koroleva, Olga V.; Kamo, Sandra L.; Polyansky, Oleg P.; Prokopiev, Andrei V.; Ernst, Richard E.; El Bilali, Hafida

doi: 10.1080/00206814.2025.2555277pmid: N/A

New geochronological and geochemical data are reported for the Yakutsk-Vilyui Large Igneous Province (YV-LIP) of the Siberian Craton. We report a high-precision U-Pb zircon CA-ID-TIMS age of 366.14 ± 0.28 Ma for the felsic Olekminsk Stock, located within the Chara-Sinsk mafic dyke swarm of the Vilyui paleorift. The age falls within the broader ~ 390–360 Ma timeframe of the YV-LIP magmatic event. Two magmatic pulses (stages) have been previously distinguished through geological mapping and based on a limited set of high-precision geochronology, their ages are ~378–373 Ma for Stage 1 and ~366–362 Ma for Stage 2 (with inclusion of our new U-Pb age for the Olekminsk Stock). Both magmatic stages are plume-derived and Stage 2 is associated with maximum rifting. Geochemical data link the felsic Olekminsk Stock with the YV-LIP and the formation of the Vilyui paleorift, and indicate involvement of both mantle and lithospheric sources in the formation of the felsic rocks. During Stage 2, mafic melts generated in the upper mantle (from the plume) ascended to form an intermediate chamber at the base of the crust. This induced partial melting of the lower crust (including melting of mafic underplate produced during Stage 1), and emplacement of felsic massifs in the upper-middle crust. The 366.14 ± 0.28 Ma age for the Olekminsk Stock suggests a temporal coincidence with Late Devonian extinction events, particularly the ~365 Ma Annulata Event.