Geochemistry, Zircon U-Pb Dating and Tectonic Significance of Basitein the Middle Section of Bogda Orogenic Belt, Xinjiang

Basic rock is widly distributed in Bogda orogenic belt.Studies on its genesis is of great significance to the regional tectonic evolution. Geochemical characteristics of rocks show that the SiO₂ in Diabases is 47.71%~53.7%, the K₂O is 0.61%~1.87%, and Na₂O is 2.97%~5.14%. are metaluminous, and show transitional characteristics from the calc-alkaline to high-potassic calc-alkaline series, belonging to quasi-aluminous medium-high calc-alkaline series.The Mg^# values range from 29.80 to 47.89, which is much lower than the reference value of the original basaltic magma 65, indicating that the basic rocks in this area may be the product of strong differentiation from the primitive magma.The differentiation index (DI) is higher than 35.00, while the consolidation index is lower than 30, implying that the diabase suffered strong differentiation.The charateristics of rare earth element(REE) show a right-dipping mode with high total contents and intense enrichment of light REEs. Large-ionic lithophilic elements such as Rb, Ba, K, and Th, are relatively enriched and high-field elements such as Nb, Ti, Hf, and Zr are relatively depleted. The diabase zircon U-Pb dating is (305.9±3.1)Ma. Diabase magma may derive from the transitional phase of Depleted spinel peridotite facies and Primitive spinel peridotite facies and is a moderate partial melting of the lithospheric mantle and the evolution of magma differentiation, which is the product of limited extension of Bogda post-arc rift basin in Late Carboniferous.