Petrogenesis and Tectonic Implications of Carboniferous Granites and Its Dark Enclaves in the Western Awulale Mountain, Western Tianshan

The petrogenesis and dynamic background of the magmatic rocks in the West Tianshan Mountains are of great significance to reveal the tectonic evolution history of the restoration area. In this paper, the granite and its dark enclaves in the northwestern area of Kunes Zhongyangchang in the western Awulale Mountain were selected for petrology and zircon U-Pb chronology and petrogeochemical analysis. The results show that the dark enclaves are fine-grained diorite, with K₂O=0.93～2.50, K₂O/Na₂O=0.20～0.21, A/CNK=0.83～0.87 and σ=2.33～3.02, which are quasi-aluminous calc-alkaline rock series. Host granites belong to I type granites with K₂O=2.92～3.48, K₂O/Na₂O=0.60～0.79, Ritman index σ=1.87～2.17, and A/CNK =1.01～1.04, which are weakly peraluminous calc-alkaline rock series. Both of them are enriched in large ion lithophile elements (LILE, e.g. Rb、Ba、Pb) and depleted in high field strength elements (HSFE, e.g. Nb, Ta, Ti), The total amount of rare earth elements is low, accompanied by the relative enrichment of light rare earth elements, and the relative loss of heavy rare earth element. The diorite enclaves have no significant Eu and Sr anomalies, while the granites have obvious negative Eu anomalies and strong loss of Sr, P and Ti elements. Zircon U-Pb dating shows that the formation age of granite is (320.0±2.7) Ma, belonging to the early Late Carboniferous. The diagenetic age of the diorite enclaves is (344.5±1.4) Ma, belonging to the Early Carboniferous. The type of diorite enclaves is xenolith, which were captured during the rising of the host granitic magma. The geochemical and chronological characteristics of the rocks reveal that they have different petrogenesis. The dioritic enclaves were formed during the northern Tianshan Ocean subduction southward, and the granite intrusion was located in the post-collision extension environment, which was formed due to the upwelling of the asthenosphere, leading to the partial melting of the lower crust. Based on regional geological data, it is likely that the early Carboniferous to late Carboniferous is an important stage of tectonic system transformation in the western Tianshan Mountain, that is, the tectonic environment transformed from compression to extension.