Petrogenesis of Jingxia Diabase Dykes, Eastern Tianshan Orogenic Belt and Its Geological Implication

The diabase dykes are sparsely distributed in the Aqishan-Yamansu belt of eastern Tianshan and have received little attention. This paper reports the petrography, geochronology, and geochemistry of the Jingxia diabase dykes to provide important information for understanding tectonic evolution of eastern Tianshan. The geochemical characteristics reveal that Jingxia diabase dykes have low SiO2, medium K2O, MgO, and high Na2O. They are calc-alkaline basaltic rocks. The U–Pb SHRIMP age of magmatic zircon from the Jingxia diabase dyke in Aqishan-Yamansu belt of Eastern Tianshan Orogenic Belt is 347 ± 6 Ma, indicating that the diabase formed in the early Carboniferous. The Jingxia diabase dykes are enriched in LREEs relative to the HREEs with depletion of Nb, Ta, Zr, and Ti, which indicates that they crystallized from the melt derived from mantle source and experienced fractional crystallization and crustal contamination. The mantle source had undergone metasomatism induced by the fluid released from the subduction slab. Combined with previous studies, we propose that the Jingxia diabase dykes formed in an immature island arc setting and they were products of southward subduction of Paleo-Kangguer oceanic slab in the early Carboniferous.