Sm-Nd isotopic constraints on the age of the Bangxi-Chenxing ophiolite in Hainan Island: implications for the tectonic evolution of eastern Paleo-Tethys
海南岛“邦溪—晨星蛇绿岩片”的时代及其构造意义—Sm—Nd同位素制约

SmNd isotopic data are presented for the metabasites that are present as lenses within the Paleozoic metasediments at the Chenxing and Bangxi regions in central Hainan Island, SE China. A SmNd isochron age of 33312 Ma obtained for the metabasites is interpreted as their crystallization age. These metabasites are characterized by varying degrees of depletion in Th, Nb, Ta and LREEs, and show high positive Nd values of ca. 7, similar to those of midocean ridge basalts (MORB). The combined geochemical and SmNd isotopic data suggest that these metabasites were generated by varying degrees of partial melting from a MORBlike mantle source in an oceanic regime. These rocks are therefore regarded as the mafic member of BangxiChenxing ophiolite. It is proposed that the BangxiChenxing ophiolite can be correlated with broadly synchronous ophiolites from the JinshaShuanggouSong Ma. Taken together, these ophiolites probably represent remnants of fragmented oceanic crust of the eastern part of PaleoTethys. The BangxiChenxing ophiolite were obducted onto the continental crust as part of the "Shilu Melange" in earliest Mesozoic time when southern Hainan (part of the Indochina block) collided with northern Hainan (part of South China).