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Early Permian–Late Triassic Magmatism in the tuotuohe region of the Qinghai–Tibet Plateau: Constraints on the Tectonic evolution of the Western Segment of the Jinshajiang Suture

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Acta Geologica Sinica(English Edition) 2014年第2期88卷 498-516页

作者： QIAN Ye SUN Fengyue LI Bile LI Shijin ZHAO Junwei College of Earth Sciences Jilin University Qinghai Geological Survey No.5 Geological and Mineral Survey Institute of Qinghai Province

In this paper we present new zircon U-Pb ages,whole-rock major and trace element analyses,and zircon Hf isotopic data for magmatic rocks in the tuotuohe region of the western segment of the Jinshajiang *** aim is to constrain the Early Permian-Late Triassic tectonic evolution of the *** from the magmatic rocks of the tuotuohe region are euhedralsubhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.4-4.6）,indicating a magmatic *** zircon U-Pb ages obtained using LA-ICP-MS are 281 ± 1 Ma,258 ± 1 Ma,244 ± 1 Ma,and 216 ± 1 Ma,which indicate magmatism in the Early Permian-Late Triassic.A diorite from Bashihubei （BSHN） has SiO2 =57.18-59.97 wt％,Al2O3=15.70-16.53 wt％,and total alkalis （Na2O ＋ K2O） =4.46-6.34 wt％,typical of calc-alkaline and metaluminous series.A gabbro from Bashibadaoban （BSBDB） belongs to the alkaline series,and is poor in SiO2 （45.46-54.03 wt％） but rich in Al2O3 （16.19-17.39 wt％） and total alkalis （Na2O ＋ K2O =5.48-6.26 wt％）.The BSHN diorite and the BSBDB gabbro both display an enrichment of LREEs and LILEs and depletion of HFSEs,and they have no obvious Eu anomaly; they have relatively low MgO contents （2.54-4.93 wt％）,Mg# values of 43 to 52,and low Cr and Ni contents （8.07-33.6 ppm and 4.41-14.2 ppm,respectively）,indicating they differentiated from primitive mantle *** have low Nb/U,Ta/ U,and Ce/Pb ratios （1.3-9.6,0.2-0.8,and 0.1-18.1,respectively）,and their initial Hf isotopic ratios range from ＋9.6 to ＋16.9 （BSHN diorite） and ＋6.5 to ＋12.6 （BSBDB gabbro）,suggesting their primary magmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized by subduction *** all the new data together,we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian-Late Triassic：oceanic crust subduction before the Early Permian,continental collision during the Early-Middle T

关键词： zircon U-Pb chronology zircon Hf isotopes geochemistry tectonic setting tuotuohe region Jinshajiang suture Qinghai-Tibet Plateau

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Zircon U–Pb age and geochemical constraints on the origin and tectonic implication of the tuotuohe Cenozoic alkaline magmatism in Qinghai–Tibet Plateau

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Acta Geochimica 2020年第1期39卷 67-84页

作者： Ye Qian Shengnan Tian Yujin Li Fengyue Sun College of Earth Sciences Jilin UniversityChangchunChina Key Laboratory of Mineral Resources Evaluation in Northeast Asia Ministry of Natural Resources of the People's Republic of ChinaChangchunChina

A large number of Eocene-Oligocene alkaline/alkali-rich igneous rocks were developed in the tuotuohe region of the Qinghai-Tibetan *** this study,we present zircon U-Pb ages,Hf isotope data,and major and trace element compositions of the Cenozoic alkaline rocks from the tuotuohe region in order to constraint the petrogenesis and tectonic evolution history of Qiangtang *** U-Pb ages were measured via LA-ICP-MS to be39.6,37.6 and 32.0 *** 39.6 Ma trachyte was characterized by low SiO2 and high K2O and MgO *** 37.6 and 32.0 Ma orthophyres show enrichment in SiO2 and K2O,but deficient in *** of the samples belong to the alkaline *** rocks display enrichment in REE,LREE,and LILE,depletion in HFSE,and no obvious Eu *** and geochemical features suggest that there were two possible mechanisms for the origin of the alkaline rocks in the tuotuohe region:(1)the removed mafic lower crust dropped into the asthenosphere,forming the mix magma(Nariniya trachyte);(2)the upwelling asthenosphere triggered the crustal melting(Nariniya and Zamaqu orthophyre).The Eocene-Oligocene alkaline rocks in the study and adjacent areas are likely to be the result of the same tectonic-magmatic event of deep lithospheric evolution that is the crustal material melting triggered by lithospheric *** conclusion extends the influence scope of lithospheric delamination eastward to the tuotuohe region(*92°E)from Banda Co(*82°E).

关键词： Zircon U-Pb chronology Zircon Hf isotopic Delamination tuotuohe region Qinghai–Tibetan Plateau

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