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  • Original Article
    Bin LIN, Juxing TANG, Pan TANG, Yan SUN, Jing QI, M. SANTOSH, Jinling XIE, Shilin DENG, Faqiao LI, Fuwei XIE, Aorigele ZHOU
    Acta Geologica Sinica (English Edition), 2024, 98(1): 83-103. https://doi.org/10.1111/1755-6724.15113
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    Rubidium (Rb) deposits mostly occur in the South China and Central Asia orogenic belts and are often closely associated with highly differentiated granites. This study investigates a newly-discovered giant Rb deposit at Gariatong in the Central Lhasa terrane in Tibet. Detailed field studies and logging data revealed that the Rb mineralization mainly occurs in monzogranite and is related to greisenization. LA-ICP-MS U-Pb dating of zircon yielded ages of 19.1 ± 0.2 Ma and 19.0 ± 0.2 Ma for greisenized monzogranite and fresh monzogranite, respectively. The monzogranites are characterized as strongly peraluminous, with high contents of SiO2, Al2O3, K2O and Na2O as well as a high differentiation index. They are enriched in light rare earth and large ion lithophile elements with significant negative Eu anomalies and depleted high field-strength elements. Petrological and geochemical features of these ore-related monzogranites suggest that they are highly fractionated S-type granites, derived from remelting of crustal materials in a post-collisional setting. The geochemistry of zircon and apatite points to a low oxygen fugacity of the ore-related monzogranite during the magma's evolution. The discovery of the Gariatong Rb deposit suggests that the Central Lhasa terrane may be an important region for rare metal mineralization.

  • Original Article
    Yabo WANG, Lei LIU, Zengxia ZHAO, Xijun LIU, Wenmin HUANG
    Acta Geologica Sinica (English Edition), 2024, 98(3): 617-629. https://doi.org/10.1111/1755-6724.15136
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    The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province. LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8 ± 1.6 and 246.5 ± 1.3 Ma, coeval with peraluminous granites of the Qinzhou Bay Granitic Complex. The studied rhyolites and dacites are characterized by high SiO2, K2O, and Al2O3, and low MgO, CaO, and P2O5 contents and are classified as high-K calc-alkaline S-type rocks, with A/CNK = 0.98–1.19. The volcanic rocks are depleted in high field strength elements, e.g., Nb, Ta, Ti, and P, and enriched in large ion lithophile elements, e.g., Rb, K, Sr, and Ba. Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions (εHf(t) = –29.1 to –6.9), source discrimination indicators and high calculated Ti-in-zircon temperatures (798–835°C) reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S-type silicic magma. The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo-Tethys Ocean in this region, as the associated subduction would have generated an extensional setting in which the mantle-derived upwelling and volcanic activity occurred.

  • Original Article
    Jianchao SU, Xu LIN, Chang'an LI, Jolivet MARC, Lin WU, Feng CHENG, Bin DENG, Zhonghai WU, Xiaokang CHEN, Chengwei HU
    Acta Geologica Sinica (English Edition), 2024, 98(1): 250-264. https://doi.org/10.1111/1755-6724.15117
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    Plate subduction leads to complex exhumation processes on continents. The Huangling Massif lies at the northern margin of the South China Block. Whether the Huangling Massif was exhumed as a watershed of the middle reaches of the Paleo-Yangtze River during the Mesozoic remains under debate. We examined the exhumation history of the Huangling Massif based on six granite bedrock samples, using apatite fission track (AFT) and apatite and zircon (U-Th)/He (AHe and ZHe) thermochronology. These samples yielded ages of 157–132 Ma (ZHe), 119–106 Ma (AFT), and 114–72 Ma (AHe), respectively. Thermal modeling revealed that three phases of rapid cooling occurred during the Late Jurassic–Early Cretaceous, late Early Cretaceous, and Late Cretaceous. These exhumation processes led to the high topographic relief responsible for the emergence of the Huangling Massif. The integrated of our new data with published sedimentological records suggests that the Huangling Massif might have been the watershed of the middle reaches of the Paleo-Yangtze River since the Cretaceous. At that time, the rivers flowed westward into the Sichuan Basin and eastward into the Jianghan Basin. The subduction of the Pacific Plate beneath the Asian continent in the Mesozoic deeply influenced the geomorphic evolution of the South China Block.

  • Original Article
    Kazem KAZEMI, Soroush MODABBERI, Parisa GHARIBNEJAD, Yilin XIAO, Fatemeh SARJOUGHIAN, Ali KANANIAN
    Acta Geologica Sinica (English Edition), 2024, 98(3): 657-678. https://doi.org/10.1111/1755-6724.15118
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    The Hesar pluton in the northern Urumieh–Dokhtar magmatic arc hosts numerous mafic-microgranular enclaves (MMEs). Whole rock geochemistry, mineral chemistry, zircon U-Pb and Sr-Nd isotopes were measured. It is suggested that the rocks are metaluminous (A/CNK = 1.32–1.45), subduction-related I-type calc-alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures. The host rocks yielded an U-Pb crystallization age of 37.3 ± 0.4 Ma for gabbro-diorite. MMEs have relatively low SiO2 contents (52.9–56.6 wt%) and high Mg# (49.8–58.7), probably reflecting a mantle-derived origin. Chondrite- and mantle-normalized trace element patterns are characterized by LREE and LILE enrichment, HREE and HFSE depletion with slight negative Eu anomalies (Eu/Eu* = 0.86–1.03). The host rocks yield (87Sr/86Sr)i ratios of 0.70492–0.70510, positive εNd(t) values of +1.55–+2.06 and TDM2 of 707–736 Ma, which is consistent with the associated mafic microgranular enclaves ((87Sr/86Sr)i = 0.705014, εNd(t) = +1.75, TDM2 = 729 Ma). All data suggest magma-mixing for enclave and host rock formation, showing a complete equilibration between mixed-mafic and felsic magmas, followed by rapid diffusion. The TDM1(Nd) and TDM2(Nd) model ages and U-Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantle-derived magmas in a pre-collisional setting of Arabian–Eurasian plates. Clinopyroxene composition indicates a crystallization temperature of ∼1000°C and a depth of ∼9 km.

  • Original Article
    Limin WU, Touping PENG, Weiming FAN, Guochun ZHAO, Jianfeng GAO, Xiaohan DONG, Shili PENG, Kang MIN, Tin Aung MYINT
    Acta Geologica Sinica (English Edition), 2024, 98(3): 569-584. https://doi.org/10.1111/1755-6724.15164
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    Since the Cenozoic, the Tibetan Plateau has experienced large-scale uplift and outgrowth due to the India–Asia collision. However, the mechanism and timing of these tectonic processes still remain debated. Here, using apatite fission track dating and inverse thermal modeling, we explore the mechanism of different phases of rapid cooling for different batholiths and intrusions in the southeastern Tibetan Plateau. In contrast to previous views, we find that the coeval granitic batholith exposed in the same tectonic zone experienced differential fast uplift in different sites, indicating that the present Tibetan Plateau was the result of differential uplift rather than the entire lithosphere uplift related to lithospheric collapse during Cenozoic times. In addition, we also suggest that the 5–2 Ma mantle-related magmatism should be regarded as the critical trigger for the widely coeval cooling event in the southeastern Tibetan Plateau, because it led to the increase in atmospheric CO2 level and a hotter upper crust than before, which are efficient for suddenly fast rock weathering and erosion. Finally, we propose that the current landform of the southeastern Tibetan Plateau was the combined influences of tectonic and climate.

  • Original Article
    Xiang QIN, Xuanhua CHEN, Zhaogang SHAO, Yiping ZHANG, Yongchao WANG, Bing LI, He SU, Ye WANG, Kui LIU, Lele HAN
    Acta Geologica Sinica (English Edition), 2024, 98(3): 548-568. https://doi.org/10.1111/1755-6724.15157
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    The Tianshan range, a Paleozoic orogenic belt in Central Asia, has undergone multiple phases of tectonic activities characterized by the N–S compression after the early Mesozoic, including the far-field effects of the Cenozoic Indian–Asian collision. However, there are limited reports on the tectonic deformation and initiation of Triassic intracontinental deformation in the Tianshan range. Understanding this structural context is crucial for interpreting the early intracontinental deformation history of the Eurasian continent during the early Mesozoic. Growth strata and syn-tectonic sediments provide a rich source of information on tectonic activities and have been extensively used in the studies of orogenic belts. Based on detail fieldwork conducted in this study, the middle–late Triassic Kelamayi Formation of the northern Kuqa Depression in the southern Tianshan fold-thrust belt has been identified as the typical syn-tectonic growth strata. The youngest detrital zircon component in two lithic sandstone samples from the bottom and top of the Kelamayi growth strata yielded U-Pb ages of 223.4 ± 3.1 and 215.5 ± 2.9 Ma, respectively, indicating that the maximum depositional age of the bottom and top of the Kelamayi growth strata is 226–220 and 218–212 Ma. The geochronological distribution of detrital samples from the Early–Middle Triassic and Late Triassic revealed abrupt changes, suggesting a new source supply resulting from tectonic activation in the Tianshan range. The coupling relationship between the syn-tectonic sedimentation of the Kelamayi Formation and the South Tianshan fold-thrust system provides robust evidence that the Triassic intracontinental deformation of the South Tianshan range began at approximately 226–220 Ma (during the Late Triassic) and ended at approximately 218–212 Ma. These findings provide crucial constraints for understanding the intraplate deformation in the Tianshan range during the Triassic.