Precise Restriction of Non-UHP Granitic Gneiss from the UHP Metamorphic Belt in the Sulu Terrane, Eastern China: Evidence from Mineral Inclusions,Cathodoluminescence Images and SHRIMP U-Pb Dating in Zircon Domains
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P588.3

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    Abstract:

    A combined study of Laser Raman spectroscopy, cathodoluminescence (CL) image and SHRIMP U-Pb dating reveals that some granitic gneisses distributing in drillhole CCSD-PP1 in the Zhimafang and Fangshan areas of the southwestern Sulu terrane do not have ultrahigh pressure (UHP) metamorphism. Most zircons separated from such granitic gneisses retain inherited cores and mantles with abundant low-pressure mineral inclusions and impurities, and the metamorphic overgrowth rims contain quartz and other low-pressure mineral inclusions. The relative cathodoluminescence image reveals a primary magmatic crystallization pattern in the core and mantle, and an irregular zoning pattern in the rim. SHRIMP U-Pb analyses of zoned zircons were performed to constrain the age and geochronological significance of the non-HP granitic gneisses. In generally, the cores and mantles of zircons from non-HP granitic gneisses recorded 404~748 Ma (238U-206Pb* age) for inherited zircons, implying partial loss of Pb from zircon in the protolith; the protolith age should be older than 748 Ma. While the overgrowth rims of zircons recorded 204 - 214 Ma (238U-206Pb* age) for the late-stage amphibolite facies metamorphism related to rapid exhumation of the Sulu terrane, which is similar to that (the weighted mean age of 238U-206Pb* = 211 ++++++++++ 4 Ma; Liu et al. , 2003a) recorded by the retrogressive rims of the zircons from the analyzed UHP paragneisses and UHP granitic gneisses in the southwestern Sulu terrane. These data indicate that part of the UHP granitic gneisses were intruded into supracrustal rocks prior to UHP metamorphism, but did not experience deep-obduction and UHP metamorphism during the middle Triassic. During the late Triassic, with rapid uplifting of the Sulu terrane, the non-UHP granitic gneisses were put together with the middle Triassic UHP metamorphic slabs and experienced amphibolite facies retrogressive metamorphism.

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LIU Fulai, XU Zhiqin, SONG Biao Laboratory of Continental Dynamics, Institute of Geology, CAGS, Beijing, SHRIMP Laboratory of Beijing, Institute of Geology, CAGS, Beijing,.2003. Precise Restriction of Non-UHP Granitic Gneiss from the UHP Metamorphic Belt in the Sulu Terrane, Eastern China: Evidence from Mineral Inclusions, Cathodoluminescence Images and SHRIMP U-Pb Dating in Zircon Domains[J]. Acta Geologica Sinica,77(4):533-539

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  • Received:
  • Revised:May 23,2003
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