Zircon U-Pb geochronology of high-pressure granulite and its tectonic implications in the Dulan area, North Qaidam Mountains, western China
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    Abstract:

    High-pressure granulite occurs as lenses in muscovite schist, granitic gneiss and amphibolite of Dulan area at the eastern end of North Qaidam HP-UHP metamorphism terrane, Northwest China. The high-pressure granulite could mainly be divided into two types: mafic granulite and acid-intermediate granulite. The dominant mafic granulite is composed of garnet, clinopyroxene, plagioclase and quartz, whereas the peak assemblage of intermediate-acid granulite is composed of garnet, plagioclase, K-feldspar, clinopyroxene, kyanite and quartz. Based on microstructure and reaction textures, the authors have recognized three main metamorphic stages from the high-pressure granulite: ① the estimated p-t conditions for the metamprphic peak stage of high-pressure granulite facies (M1) were 1.4~1.85 GPa and 800~925℃; ② retrogression began at the high amphibolite facies stage (M2) with p-t conditions of 0.8~1.05 GPa and 580~695℃; ③ subsequent retrogression occurred at the green-schist/high-amphibolite facies stage (M3). Combined with cathodoluminescence patterns and mineral inclusions(garnet, clinopyroxene and plagioclase inclusions in zircon), U-Pb dating of zircons revealed that the peak metamorphism age of the high-pressure granulite-facies is 466.9±6.5 Ma. Petrological and chronological studies suggest that the granulite and adjacent eclogite were formed in different thermal environments of the same subduction zone, i.e., the ecolgite was formed in the subduction zone while the high-pressure granulite was formed at the root of the thickened crust above the seduction zone. The high-pressure granulite experienced its unique metamorphic history, and was not associated with the action of thermal relaxation after the eclogite-facies metamorphism recorded in adjacent eclogites.

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于胜尧,张建新,李金平,孟繁聪,2010,柴北缘都兰高压麻粒岩的锆石U-Pb定年及其地质意义[J].岩石矿物学杂志,29(2):139~150. YU Sheng_yao, ZHANG Jian_xin, LI Jin_ping, MENG Fan_cong,2010,Zircon U-Pb geochronology of high-pressure granulite and its tectonic implications in the Dulan area, North Qaidam Mountains, western China[J]. Acta Petrologica et Mineralogica,29(2):139~150.

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