Geochronology, geochemical properties and tectonic significance of Baergaiti granitoid in western Tianshan Mountain, NW China

The Baergaiti granitoid is located in the Boluohuoluo tectonic belt in the western Tianshan Mountain of the Yili Basin. LA-ICP-MS zircon U-Pb shows age of 374±7.0 Ma, corresponding to the Late Devonian. Petrogeochemical analyses suggest that the intrusion belong to calc-alkaline metaliferous rocks characterized with high silica, potassium, and alkalinity, low magnesium and titanium. The contents of SiO₂, Al₂O₃, K₂O, Na₂O range 70.72%-79.12%, 9.87%-14.51%, 4.13%-5.54%, 2.87%-4.35%, respectively. Meanwhile, the REE contents show an obvious rich LREE pattern ((La/Yb)_N ranges 7.61-16.31) with negative Eu anomalies. Large ion lithophile elements such as Rb, Th and U are relatively enriched, whereas high strength field elements such as Nb, Ta and Ti are relatively depleted. Geochemical and isotope characteristics show a transition feature of high-K calc-alkaline I-A type granite. The analyses of a regional angular unconformity and sedimentary features suggest that the Baergaiti granitoid was deposited under a post-orogenic intra-continental extensional tectonic setting during the Late Devonian, and formed a complete tectonic evolution cycle coupling with the Carboniferous volcanic-sedimentary strata.