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The effects of the source composition on the origin of orthopyroxenebearing adakitic granitoid in West Qinling,Central China

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Geoscience Frontiers 2023年第3期14卷 180-200页

作者： Yuanhui Xie Xiaowei Li Xuanxue Mo Guochen Dong Yuqin Sun Wei Shan State Key Laboratory of Geological Processes and Mineral Resources and School of Earth Sciences and ResourcesChina University of Geosciences(Beijing)Beijing 100083China Shandong Institute of Geological Sciences and Key Laboratory of Gold Mineralization Processes and Resource UtilizationJinan 250013China

Orthopyroxene-bearing granodiorite(sometimes referred to as‘charnockite’)with an adakitic affinity is a rare type of granitoid.It is generally accepted that the stabilization of orthopyroxene in igneous charnockites essentially requires low aH_(2)O and/or high temperatures in a closed system.However,orthopyroxene can be an antecryst in a trans-crustal magmatic system.In this regard,orthopyroxenebearing granitoids are somewhat analogous to pseudo-charnockites,where the orthopyroxene stems from a mafic reservoir.On the other hand,the source compositions of continental adakites can vary,which is often ignored in the interpretation of their contribution to the adakitic geochemical signature.In this study,we have investigated a rare orthopyroxene-bearing felsic pluton from the Zhuyuan area of West Qinling,Central China.The Zhuyuan pluton was emplaced in the Middle–Late Triassic(222–217 Ma)and is mainly composed of metaluminous to weakly peraluminous granodiorites belonging to the high-K calc-alkaline series.Moreover,they are characterized by high Mg#values(49.7–60.9)and Sr contents(471–697 ppm),low Y(12.2–15.4 ppm)and Yb(1.03–1.24 ppm)contents,high Sr/Y(33.2–46.2)and(La/Yb)_(N)(15.3–21.4)ratios,and weakly negative Eu anomalies(Eu/Eu^(*)=0.78–0.89).The Zhuyuan adakitic granodiorites exhibit fairly limited Sr–Nd–Pb isotopic ratios and variable zircon initial Hf isotopes,indicating a major contribution from the Neoproterozoic basement of the Qinling Orogenic Belt.There is no evidence of any formation through high-pressure magmatic processes,and we propose that the adakitic signature of the Zhuyuan pluton could have been inherited from its source rocks(i.e.,from the Neoproterozoic basement).The orthopyroxenes in the Zhuyuan granodiorites display poikilitic textures with high MgO,NiO and Cr_(2)O_(3) contents,indicating that they have an antecrystic origin.Studies of regional tectonic evolution have shown that the Zhuyuan granodiorites formed during the tearing stage of the A’nimaque–Mianlue oceanic subduction slab.Therefor

关键词： Qinling Orogenic Belt adakitic rock Orthopyroxene-bearing granodiorite Pseudo-charnockite

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Syn-Faulting Calcite Ages:Constraint for the Late Mesozoic Deformation of the Ningzhen Mountain,Eastern China

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Journal of Earth Science 2021年第6期32卷 1485-1495页

作者： Jinbao Su Hongbing Tan Yuexing Feng Guoxing Qin College of Oceanography Hohai UniversityNanjing210098China School of Earth Sciences and Engineering Hohai UniversityNanjing210098China School of Earth Sciences The University of QueenslandBrisbaneQLD4072Australia

It is difficult to date a brittle fault because of the absence of effective dating methods.Recently,calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the age of brittle deformation.The South China Block(SCB)has experienced multiphase deformations characterized by widespread brittle faults and folds,which has led to significant debate on the Mesozoic dynamic mechanism and deformational phases.A syn-faulting calcite vein that occurred in the Permian limestones of the Ningzhen Mountain region was analyzed using U-Pb dating and geochemistry techniques in this paper.The U-Pb dating results display multiphase activities with two mixed ages of 109.9±5.8 Ma(MSWD=46,n=231)and 117.2±2.4 Ma(MSWD=3.6,n=150).The age of 117.2±2.4 Ma likely represents the timing of the brittle faults.Trace elements and rare earth elements data indicate that these fault-related calcites are mainly derived from host limestones and unrelated to Cretaceous magmatic activity.These faults formed in a tectonic reactive period and dormant time of the adakitic magma in the Lower Yangtze region.

关键词： U-Pb dating calcite South China Block brittle fault adakitic rock

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Geochronology and Geochemistry of Metallogenetic Porphyry Bodies from the Nongping Au-Cu Deposit in the Eastern Yanbian Area, NE China: Implications for Metallogenic Environment

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Acta Geologica Sinica(English Edition) 2012年第3期86卷 619-629页

作者： REN Yunsheng JU Nan ZHAO Hualei WANG Hui HOU Kejun LIU Shen College of Earth Sciences Jilin UniversityChangchun 130061China MRL Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral ResourcesChinese Academy of Geological SciencesBeijing 100037China State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of SciencesGuiyang 550002China

The metallogenetic porphyry bodies in the Nongping Au-Cu deposit, in the eastern Yanbian area, mainly include porphyritic granodiorite and biotite granodiorite porphyry. They are featured with high silicon and enrichment in sodium, and classified into sodic rocks of low-K tholeiitic basalt series. Except slightly low Sr content, the rock basically has the geochemical characteristics of the adakite： relatively high A12O3 content, relatively low MgO content, depletion in Y and Yb; relative enrichment in large ion lithophile elements （LILEs） and light rare-earth elements （LREEs）, relatively low content of high field strength elements （HFSEs）; positive Eu anomaly or weak negative Eu anomaly. In situ zircon dating technology LA-MC-ICP-MS was used to conduct single-grain zircon dating of biotite granodiorite porphyry, and the results show that the age of metallogenetic porphyry body is 100.04±0.88 Ma, indicating that the porphyry bodies were emplaced in the late Cretaceous period. According to the regional tectonic setting and the comparison with the same kind of deposits, we think that the metallogenetic porphyry bodies in the Nongping Au-Cu deposit have a close genetic connection with the subduction of the Pacific plate in the late Yanshanian period. The adakitic magma generated from partial melting of the subducting plate has high formation temperature, high oxygen fugacity, and volatile constituents＇ enrichment, so it is helpful for enrichment of metallogenetic elements and plays an important role in the formation of porphyry Au-Cu deposits in this region.

关键词： porphyry body zircon U-Pb dating adakitic rock Nongping Au-Cu deposit

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