| 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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| 作者姓名： | QIAN Ye SUN Fengyue LI Bile LI Shijin and ZHAO Junwei |
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| 作者单位： | 1 College of Earth Sciences, Jilin University, Changchun 130061, Jilin, China
2 Qinghai Geological Survey, Xining 810000, Qinghai, China
3 No.5 Geological and Mineral Survey Institute of Qinghai Province, Xining 810000, Qinghai, China |
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| 基金项目： | This work was funded by the work programs of the China Geological Survey (1212011086020) and the National Natural Science Foundation of China (41272093). |
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| 摘 要： | 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 suture. Our aim is to constrain the Early Permian–Late Triassic tectonic evolution of the region. Zircons from the magmatic rocks of the Tuotuohe region are euhedral–subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios(0.4–4.6), indicating a magmatic origin. The 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 magmas. They 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 fluids. Taking 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 Triassic, and post-collisional extension from the Late Triassic.
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| 关 键 词： | zircon U–Pb chronology zircon Hf isotopes geochemistry tectonic setting Tuotuohe region Jinshajiang suture Qinghai–Tibet Plateau |
| 收稿时间： | 2013/11/20 0:00:00 |
| 修稿时间： | 2014/1/19 0:00:00 |
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