| 西藏班公湖—怒江结合带南缘革吉地区晚侏罗世流纹斑岩的成因——锆石U-Pb定年、地球化学和Hf同位素约束 |
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| 关键词:rhyolite porphyry zircon U-Pb dating geochemical characteristics Hf isotopes Geji area Bangong–Nujiang metallogenic belt northern Lhasa terrane |
| 基金项目:中国地质调查局二级项目(编号: DD20160026);国家自然科学基金项目(编号: 41403040) |
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| The Discovery of Late Jurassic Rhyolite Porphyry in Geji Area, Southern Bangong Co–Nujiang Suture Zone, Tibet: Constraints from Zircon U-Pb Geochronology, Geochemistry and Hf Isotopes |
| Zircon U-Pb age, geochemistry and zircon Hf isotopes of the Naibuzhakangba rhyolite porphyry in Geji area of Tibet are reported in this study. LA-ICP-MS zircon U-Pb dating indicates that the Naibuzhakangba rhyolite porphyry was emplaced at (151.6±1.2) Ma (MSWD=0.9). Geochemical data show that the rhyolite porphyry rocks are weakly peraluminous and have high content of SiO2 (73.93%~74.71%) and Na2O+K2O (6.73%~7.30%), and low content of TFe and MgO, belonging to high-K calc-alkaline series. These rhyolite porphyry rocks are enriched in LREE and show obvious negative Eu anomalies in the chondrite-normalized di-agram and significant negative Nb, Ta, Ti and P anomalies in the primary mantle-normalized diagram. These rocks have LREE/HREE ratios of 9.71~12.38, (La/Yb)N values of 10.64~14.42, and δEu values of 0.65~0.73. The rhyolite porphyry rocks have geochemical features of subduction-related I-type granitoids and have negative zircon εHf(t) values (–3.1 on average). The wide range of zircon εHf(t) values (up to 11ε units) indicates that the rhyolite porphyry has a mixture source region. Hf isotopes and whole-rock Zr saturation temperature of these rocks (750~791℃) indicates that the mantle magma played an important role in the formation of the parent magma. In combination with the regional geology, the results obtained by the authors indicate that the rhyolite porphyry was formed in the southward subduction setting of the Slainajap Ocean. Thus, the mantle-derived magma provided the heat and materials for the partial melting of ancient mafic lower crust and was mixed with it, and then the mixed magma moved upward and experienced the fractional crystallization process to form the Naibuzhakangba rhyolite porphyry. |
| WANG Yong,WANG Li-qiang,DANZHEN Wang-xiu,LI Zhuang,LI Shen.2017.The Discovery of Late Jurassic Rhyolite Porphyry in Geji Area, Southern Bangong Co–Nujiang Suture Zone, Tibet: Constraints from Zircon U-Pb Geochronology, Geochemistry and Hf Isotopes[J].Acta Geoscientica Sinica,38(5):723-733. |
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