Geochronology, Geochemistry and Geological Implications of Early Carboniferous A-Type Granites in Harlik Area from East Tianshan

Study of A-type granites is critical for understanding the crust-mantle interaction and tectonic evolution in the Tianshan orogenic belt. Here it reports a detailed petrologic, geochemical and geochronologic data for the alkali-feldspar granite and syenogranite from Harlik in East Tianshan, to constrain their petrogenesis and tectonic setting. LA-ICP-MS zircon U-Pb ages indicate that the granites were emplaced at early Early Carboniferous (350.7±2.0 Ma and 351.8±2.0 Ma). The rocks contain abundant alkali feldspar and biotite with little sodium amphibole. The granites are characterized by high silicon and alkali, low CaO and MgO contents, and enriched in Rb, Th, K (LILE), and Zr, Hf (HFSE), but depleted in Ba, Sr, and Eu. The chondrite-normalized REE patterns show slight enrichment in LREE with (La/Yb)N from 3.23 to 5.55, and great negative Eu anomalies (δEu=0.19-0.28). These feactures indicate the geochemical characteristics of high-K meta- to per-aluminous A-type granite. They have positive ϵNd(t) (+4.2 to +4.8) values, and the Neoproterozoic two stage Nd model ages (tDM2=0.71-0.75 Ga), suggesting that the A-type granitic magma was probably generated from partial melting of a juvenile crustal source produced by depleted mantle-derived basaltic magmas and a few marine sediments. Combining with the previous works in this region, our study reveals that Harlik and Bogda are constrained by the same tectonic setting in Early Carboniferous, and the A-type granites from Harlik were genetically linked to the initial extensional stage of the Bogda back-arc rift. © 2022 China University of Geosciences. All rights reserved.