Major, trace and platinum-group element geochemistry of harzburgites and chromitites from Fuchuan, China, and its geological significance

Abstract

Abstract The Fuchuan ophiolite, one of the oldest ophiolites in southern China, is located in the northeasternmost segment of the Jiangnan Orogen. It mainly consists of harzburgites, with minor dunites, pyroxenites and gabbro veins. To investigate the origin of the Fuchuan ophiolite and its related chromite ore deposit, bulk-rock major and minor element and platinum-group element (PGE) studies have been carried out. Major and trace element analyses show dual features of mid-ocean ridge basalt (MORB) and supra-subducted zone (SSZ) peridotites and high degrees of partial melting. The chondrite-normalized rare earth element (REE) patterns of the Fuchuan harzburgites are “U” shaped, reflecting the influence of light REE-enriched subducted melts or fluids. The Fuchuan chromitites originate from MORB-like melts and are enriched in IPGE and depleted in PPGE, which are basically consistent with high-Al chromitites worldwide, and the low PGE concentrations of chromitites reflect a lack of sulfur saturation of the parental melts during an early stage of their crystallization. Combining with the tectonic setting of the Jiangnan Orogen, we suggest that the Fuchuan peridotites and chromitites are believed to be formed in a back-arc spreading ridge between the Yangtze and Cathaysia blocks during 860–820 Ma.