The discovery of Neoproterozoic pillow lava in spilite-ceratophyre of Lushan area, northern Jiangxi Province, and its geological significance

Abstract：Located on the northern side of the eastern section of Jangnan orogen, Lushan area has outcropped metamorphic rocks of Pre-Sinian Xingzi Group and Shuangqiaoshan Group. Recently, the authors found a suite of spilite-ceratophyre with pillow structure in strata of Shuangqiaoshan Group. An analysis of element geochemistry reveals that the spilite-ceratophyre and the concomitant dacite have the characteristics of oceanic-island basalt, hence their formation environment should have been a back-arc small oceanic basin upside continental crust. The authors thus hold that the suture of southern Jiangxi (Shexian County) had an approximately EW strike, and extended straightforward to Lushan area of northern Jiangxi, whereas the Jiangnan orogen remained not closed from 830 Ma to 850 Ma. It is also held that the Shuangqiaoshan Group is a component part of the basement of “poly-basement with one cover” in the middle-lower Yangtze block.