The 401–409 Ma Xiaodonggou granitic intrusion: implications for understanding the Devonian Tectonics of the Northwest China Altai orogen

摘要: AbstractPalaeozoic granitoids in the Chinese Altai are important for understanding evolution of Central Asian Orogenic Belt (CAOB). The Xiaodonggou granitic intrusion, situated (southern CAOB), is composed two intrusive phases, medium-grained granite intruded by porphyritic granite. Zircon LA-ICP-MS U–Pb analyses and yield ages 409 ± 2 Ma 400 ± 1 Ma, respectively, indicating that these formed Early Devonian time. Medium-grained have similar geochemical features Nd–Hf isotopic compositions. Arc-like characteristics (e.g. enrichment LILEs negative anomalies Nb, Ta, Ti, P) show both phases volcanic arc granites (VAGs). Geochemical suggest magmas originated from melting older crust. Based on their near-zero or eNd(t) values (−1.4to 0) positive eHf(t) (+1.4 to +7.8), together with Nd model ...