Geochronology and Genesis of the Diabase-Dykes from Qijiaojing-Balikun Area in Eastern Tianshan Mountain

The diabase-dykesin Carboniferous, featured by relatively higher Al₂O₃ and MgO, lower TiO₂, and deficient P₂O₅ and K₂O, are widespread in Qijiaojing-Balikun area in East Tianshan Mountain, Xinjiang. Analysis on geochemical characteristics show that REE patterns is right ward oblique characterized by LREE enrichment and HREE depletion;trace elements distribution curve demonstrates LILE enrichment in Cs and K, and HFSE depletionin Nb, Ta, Zr and Hf;uniform abundance of SiO₂ and LILE fluctuate in significantly;the magma formatting temperature is close to the interface temperature between asthenosphere and lithosphere, all of the above indicate that the original magma of the diabase-dykes derives from partial melting of enriched mantle wedge, which is metasomated by liquid or melt; the high Mg^#(0.64—0.67), low Ce/Y (1.55—1.79) and Dy/Yb (1.97—2.02), and the La/Sm-La diagram shows that the primitive magma of the diabase-dykes with a low evolution may come out of high degrees of partial melting from garnet-phase peridotite; lazy elements such as Zr, Hf and Y, and discrimination diagrams suggest that the diabase-dykes are probably formed in an intraplate environment.The LA-ICP-MS zircon ²⁰⁶Pb/²³⁸U age of 314.7±1.5 Ma indicates that Bogda orogenic belt should be extensional environment from late Carboniferous.