Polybaric partial melting in the continental mantle:Evidence from mantle xenoliths from Qilin,Guangdong Province  

作　　者：XU Yigang VAN Wen SUN Min LIU Ying HE Zaicheng SHI Lanbin 

机构地区：[1]Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China [2]Institute of South China Oceanography,Chinese Academy of Sciences,Guangzhou 510240,China [3]Department of Earth Sciences,The University of Hong Kong,China [4]Institute of Geology,State Seismological Bureau,Beijing 100029,China

出　　处：《Chinese Science Bulletin》2001年第20期1732-1736,共5页

基　　金：This work was supported by the National Natural Science Foundation of China (Grant Nos. 49925308 and 49733110); the Ministry of Science and Technology of China (pre-selected 39 project) ;and the Chinese Academy of Sciences (Grant Nos. KZ951-B1-406-04 a

摘　　要：The extremely low Ti content (160-245μg/g) in clinopyroxene in some spinel peridotites from Qilin, South China is indicative of high degree of partial melting, inconsistent with their relatively high clinopyroxene modes (7.4%-12.4%). These clinopyroxenes show fractionated HREE patterns ((Gd/Yb)n【0.2), suggesting the involvement of garnet in the melting regime. These REE patterns can be modeled as residues of 22%-23% fractional melting from a primitive mantle, first in garnet stability field (12%) then continuing in spinel stability field (10%-11%) after breakdown of garnet to pyroxenes and spinel. Such a polybaric melting suggests the lithospheric thinning and rapid mantle upwelling in south China during the Cenozoic. This is consistent with the dominant MORB-OIB isotopic signature and high thermal gradient of the lithospheric mantle in this region, and supports the contention that the formation of South China Sea basin is related to southward migration of continental lithosphere extension, ratherThe extremely low Ti content (160–245 μg/g) in clinopyroxene in some spinel peridotites from Qilin, South China is indicative of high degree of partial melting, inconsistent with their relatively high clinopyroxene modes (7.4%–12.4%). These clinopyroxenes show fractionated HREE patterns ((Gd/Yb)n<0.2), suggesting the involvement of garnet in the melting regime. These REE patterns can be modeled as residues of 22%–23% fractional melting from a primitive mantle, first in garnet stability field (12%) then continuing in spinel stability field (10%–11%) after breakdown of garnet to pyroxenes and spinel. Such a polybaric melting suggests the lithospheric thinning and rapid mantle upwelling in south China during the Cenozoic. This is consistent with the dominant MORB-OIB isotopic signature and high thermal gradient of the lithospheric mantle in this region, and supports the contention that the formation of South China Sea basin is related to southward migration of continental lithosphere extension, rather than passive back-arc basin.

关 键 词：MANTLE XENOLITHS TRACE element polybaric MELTING Qilin. 

分 类 号：P59[天文地球—地球化学]