Abstract:Basic volcanic rocks from Ke-Xia region of northwestern Junggar Basin were inves tigated systematically in such aspects as petrology, mineralogy, trace elements and Nd-Sr-Pb isotope geochemistry. Ke-Xia basic volcanic rocks belong to tholeiitic series and are characterized by low abundance of Ti, poor REE, slight enrichment of LREE, and significant enrichment of LILE relative to HFSE in the spider diagram, consistent with features of island arc tholeiitic melts. Ke-Xia basic volcanic rocks have positive εNd（t)(+7.2～+7.4), low values of （87Sr/86Sr)i(0.703717～0.704520) and HFSE/LILE, and steeper 206Pb/204Pb 207Pb/204Pb correlation gradient than that of MORB and OIB. These data show that Ke-Xia basic volcanic rocks might have been generated from the high-degree partial melting of depleted lithosphere mantle wedge above the subducted oceanic plate in the oceanic island arc, genetically related to the subduction of oceanic crust of western Junggar. It is thus consi_dered that the western Junggar arc-basin system extends eastward into the Jungaer Basin, and that the basement crust in northwestern Junggar Basin is a island arc type accreted block formed by ocean-continent collision.
