滇西北石鼓岩群新元古代变质基性岩锆石U-Pb定年及地质意义

Zircon U-Pb Dating and Geological Significance for Neoproterozoic Metabasite of the Shigu Group in Northwestern Yunnan Province

滇西北石鼓岩群位于羌塘-三江造山系中咱-中甸地块南缘丽江地区石鼓-巨甸一带,石鼓岩群变质岩系中发育的新元古代变质基性岩是Rodinia超大陆裂解的重要构造-岩浆记录。通过对石鼓岩群中的变质基性岩岩石学、地球化学的研究表明,其主要为大洋拉斑玄武岩,具有介于EMORB与OIB之间的地球化学特征,岩浆起源于富集地幔区,是尖晶石地幔橄榄岩部分熔融的产物,并经历了地壳的混染作用。LA-ICP-MS锆石U-Pb定年表明石鼓岩群变质基性岩形成于新元古代中期(833.9±3.5Ma),时代与扬子陆块西缘大量分布的新元古代岩浆岩一致,其形成可能与该时期的地幔柱活动有关。

The Shigu group in southern margin of the Zhongzan - Zhongdian block of Qiangtang - Sanjiang orogenic system is located in the Shigu - Judian area of Lijiang. The Neoproterozoic metabasite in metamorphic series of the Shigu group is an important tectonic - magmatic record of the Rodinia supercontiuent breakup. Based on petrology and geochemistry research, it is indicated that the metabasite in the Shigu group is mainly oceanic tholeiite with the characteristics between E - MORB and OIB. The magma was originated from enriched mantle, which is product of spinel mantle peridotite partial melting, with crustal contamination. LA -ICP- MS zircon U -Pb dating indicates that the metabasite in Shigu group was formed during Mid -Neoprot- erozoic （833.9 ± 3.5 Ma）, consistent with the many Neoproterozoic magmatic rocks from the western margin of Yangtze block, which was probably related to mantle plume activity of that time.