摘要
The Maylashan area is situated in the southern part of the West Junggar Basin, NW China. The Middle-Upper Silurian Maylasha Formation consists of grayish green tuffaceous siltstone and fine-grained sandstone, sandstone and conglomerate, with intercalated beds of chert and basalt, and fault contacts with the Maylashan ophiolitic mélange. The basalts are of sub-alkaline tholeiitic showing geochemical characteristics similar to those of island arc basalt (IAB). It can be deduced that the volcanic rocks were derived from partial melting of spinel iherzolite mantle source (2%~10% partial melting) with the participation of small amount of subducted fluid, under back-arc basin setting different from that of the Maylashan ophiolitic mélange. Thus, an intra-oceanic subduction model was proposed for the Silurian-Carboniferous evolution of the West Junggar.