Geochemical Evidences and Tectonic Significances of Dalabute SSZ-type Ophiolitic Mélange,Western Junggar Basin

The serpentinite of Dalabute ophiolitic melange shows low TiO2,Al2O3,CaO and total alkali,high MgO,Mg#; and has low ∑REE,is enriched in LREE,the rare earth element distribution patterns appear "凹" or "U". It is a depletion pyrolite form primitive mantle which had undergone partial melting. The geochemical of gabbo and basalt characteristics of low ∑REE,depleted in LREE and unfractionated in HSF elements indicate that it is similar to a normal mid-ocean basalt (N-MORB),meanwhile,the samples are enriched in large-ion lithophile elements(LILE),depeleted in Nb and Ta on different degrees. It is indicated that the Dalabute ophiolitic melange is a typical SSZ-type ophiolite,associating with the new isotope age (391±6Ma),it is concluded that the main Western Junggar oceanic basin has begun to eliminate,and the continental plate has begun to converge in Middle Devonian.