Zircon U-Pb age,geochemical features of the Shenlin granite,eastern Qinling Orogenic Belt,and its implications for tectonic settings
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    Abstract:

    The Shenlin granite is located in the eastern Qinling Orogenic Belt,which emplaced in Yanshanian.The Shenlin granite provides us an opportunity to revealing the tectonic evolution history in the eastern Qinling Orogenic Belt during Yanshanian.Methods: Based on detailed field observations of the Shenlin granite in the eastern Qinling Orogenic Belt,we have studied the petrology,geochemistry and chronology of the Shenlin granite.The petrogenesis and deep tectonic implications of the Shenlin granite was discussed.Results:The zircon LA-ICP-MS U-Pb dating was used to constrain the formation age of the Shenlin granite.The 27 of 30 zircon spots of the Shenlin granite yield a n(206Pb)/n(238U) age of 130.6±0.7 Ma (MSWD=2.1).The Shenlin granite are characterized by higher in SiO2 and alkali,and lower in MgO and CaO contents.The Shenlin granite belong to high-K calc-alkaline series in the SiO2—K2O diagram, and metaluminous to weakly peraluminous with A/CNK ratios of 0.99~1.03. The Shenlin granite samples are enriched in large ion lithophile elements (e.g.,Rb,Th and K) and depleted in high field-strength elements (e.g.,Nb,Ta and Ti).In chondrite-normalized rare earth element (REE) patterns,the Shenlin granite samples exhibit light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion with δEu values of 0.59~0.72.The linear trend of the Shenlin granite samples in LaN—(La/Yb)N diagram has suggested that the compositional change is controlled mainly by source and degree of partial melting.The Shenlin granite samples are with high Sr,and low Y and Yb contents,with the Sr/Y ratios of 24.3~37. 9 that is indicative of adakite affinity.The Shenlin granite is originated from partial melting of the thickened lower crust with thickness > 50 km,and its residual phases include garnet, rutile and amphibolite,and minor plagioclase.In chondrite-normalized REE patterns of zircons,the characteristics of LREE-depleted,HREE- enriched with Ce positive anomaly are shown, and the zircon formation temperatures are calculated from 624℃ to 701℃. The variation of HREE partition coefficients with ages in the zircon/melts system of the Shenlin granite indicates that it has experienced injection,mixing and activation of the magma/fluids,which is consistent with mafic microgranular enclave in this intrusion.The activated magma/fluids system were intruded along the regional huge fault, and emplacement and consolidation formed the Shenlin granite took place at the fault intersection in the secondary faults.Conclusions:The Early Cretaceous Shenlin granite belongs to adakite,which originated from partial melting of the thickened lower crust with a thickness of > 50 km.It was intruded during intracontinental (intraplate) orogenesis in the eastern Qinling Orogenic Belt,which was triggered by regional lithosphere delamination.

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LIANG Tao, LU Ren, LIU Xiaoli.2021. Zircon U-Pb age, geochemical features of the Shenlin granite, eastern Qinling Orogenic Belt, and its implications for tectonic settings[J]. Geological Review,67(5):1245-1262.

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History
  • Received:October 22,2020
  • Revised:May 31,2021
  • Adopted:
  • Online: September 20,2021
  • Published: September 15,2021