کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5784280 | 1638635 | 2017 | 69 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Early Mesozoic deep-crust reworking beneath the central Lhasa terrane (South Tibet): Evidence from intermediate gneiss xenoliths in granites
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
Understanding the rheological behavior of the Tibetan Plateau and its response to geodynamic processes requires a clear knowledge of the composition, evolution and lithological properties of the deep crust. Here we present U-Pb-Hf isotopes of zircons, bulk-rock geochemistry and mineral compositions for seven intermediate gneiss xenoliths and their host Early Mesozoic granites (205 ± 6 Ma) in the central Lhasa terrane to probe the deep crust beneath Southern Tibet. The xenoliths contain plagioclase, amphibole, titanite, allanite, quartz, biotite and muscovite, with accessory Fe-Ti oxides, apatite and zircon. Bulk-rock and mineral geochemistry suggests that these xenoliths have a magmatic origin and experienced deformation and amphibolite-facies metamorphism (equilibration at pressures of 0.46-0.83 GPa and temperatures of ~ 650 °C), before they were captured by the host granite at ~ 205 Ma. Zircons in these xenoliths show complex microstructures, including inherited cores, magmatic or metamorphic bands, and high U-Th hydrothermal rims. Inherited zircon cores record U-Pb ages from 2277 Ma to 517 Ma. Igneous zircons show a range of concordant U-Pb ages, suggesting a protracted magmatism from 236 Ma to 203 Ma. Metamorphic zircon zones record the timing of amphibolite-facies metamorphism from 224 to 192 Ma, while the high U-Th hydrothermal rims show a subsequent fluid activity until ~ 150 Ma. Unradiogenic Hf isotopic compositions of both xenoliths and host granites [xenolith εHf(t) = â 11.2 to 0; host granite εHf(t) = â 17.3 to â 3.3] indicate that the Early Mesozoic deep crust in the central Lhasa terrane originated mainly from ancient (i.e., Proterozoic) crust, with little or no interaction with juvenile magmas. This study suggests a possible continental differentiation mechanism during crustal reworking; progressive melting may initiate from the lower mafic crust (at ca. 236 Ma) and gradually migrate into the sediment-rich upper crust (until ca. 203 Ma). The reworking results in the transition from small fluxes of intermediate magmas to voluminous peraluminous S-type granite in a convergent depth.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volumes 274â275, March 2017, Pages 225-239
Journal: Lithos - Volumes 274â275, March 2017, Pages 225-239
نویسندگان
Xiang Zhou, Jian-Ping Zheng, Qing Xiong, Jing-Sui Yang, Yuan-Bao Wu, Jun-Hong Zhao, William L. Griffin, Hong-Kun Dai,