کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4726835 1640142 2014 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Early Jurassic high-pressure metamorphism of the Amdo terrane, Tibet: Constraints from zircon U–Pb geochronology of mafic granulites
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات زمین شناسی
پیش نمایش صفحه اول مقاله
Early Jurassic high-pressure metamorphism of the Amdo terrane, Tibet: Constraints from zircon U–Pb geochronology of mafic granulites
چکیده انگلیسی


• The Amdo terrane, central Tibet, has experienced an Early Jurassic HP metamorphism.
• The exhumation rate of the HP granulites was ca. 3 mm/year.
• The Amdo terrane is not a part of the Mid-Qiangtang Suture zone.

The Amdo terrane holds one of the important keys to understand the tectonic evolution of Central Tibet. Here we report the results from a combined study of Cathodoluminescence imaging, LA–ICPMS U–Pb dating, and trace element analysis of zircons from high-pressure (HP) mafic granulites from the Amdo terrane. Zircons from the mafic granulite are rounded or anhedral and show sector or planar domains with low Th/U ratios, low REE contents, and flat HREE patterns, and can be divided into two types. The first type of zircons shows negative Eu anomalies, indicating that they coexisted with garnet and symplectitic plagioclase during the retrograde stage of metamorphism, whereas the second type possesses positive Eu anomalies, implying that they formed during the peak-metamorphic stage of the HP granulite. U–Pb data yielded a weighted mean 206Pb/238U age of 190.7 ± 3.0 Ma (MSWD = 2.8, n = 8) for zircons with positive Eu anomalies, interpreted as the time of the peak metamorphism, and a mean age of 181.4 ± 1.8 Ma (MSWD = 2.2, n = 16) for zircons with negative Eu anomalies corresponding to the amphibolite-facies retrogression. Combining with previous data, we suggest that the Amdo terrane became a microcontinent in the Tethys Ocean during the Permian–Triassic rifting between the Lhasa and Qiangtang terranes, and then the Amdo terrane subducted to about 50-km-depth beneath the Qiangtang terrane experiencing HP granulite-facies metamorphism in the Early Jurassic at 190 Ma. The region was then uplifted to the mid-crustal levels (~ 20 km) with an exhumation rate of ca. 3 mm/year. The presence of Early Jurassic HP granulite shows that the Amdo terrane is related to the Bangong–Nujiang Suture zone instead of with the Mid-Qiangtang Suture zone.

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ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Gondwana Research - Volume 26, Issues 3–4, November 2014, Pages 975–985
نویسندگان
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