volcanic rocks of the Nanpengxia Formation-complex Mineralogy, petrology and geochemistry of the Neoarchean metasedimentary-volcanic rocks at Jixichong, northeastern Hunan

Abstract： Through regional geological investigation and research, the authors found a metasedimentary-volcanic series in the original Mesoproterozoic Lengjiaxi Group at Jianxichong Village, Wenjia City, northeastern Hunan. Mineralogical, petrological and geochemical studies indicate that this metasedimentary-volcanic series is a metamorphic series consisting of metavoIcanic rocks with metamorphosed clayey sedimentary rocks. The metamorphism is of greenschist-high greenschist farcies. The protolith of the metavolcanic rocks is a volcanic-subvolcanic rock series composed chiefly of low-K tholeiite with subordinate low-K basaltic andesite formed in an oceanic extensional environment. The provenance was the depleted mantle. Whole-rock Sm-Nd isochron dating of the metavolcanic rocks indicates a Neoarchean age. Therefore, they are notably different from the traditional Mesoproterozoic Lengjiaxi Group in rock association, formation environment, formation age and metamorphism-deformation. So the original Lengjiaxi Group should be disintegrated.