Age, Petrogenesis and Tectonic Implications of the Kalatage Intrusive Rocks in the Eastern Tianshan, Xinjiang

The Eastern Tianshan (ET) is located at the southernmost part of the Central Asian Orogenic Belt (CAOB) and has recorded the late stage of the subduction-accretion process of the CAOB. However, some key tectonic evolution processes of the ET in the Early Paleozoic remains controversial, such as the tectonic property, the onset of subduction, and the subduction polarity of the Dananhu-Tousuquan belt. In order to reveal the Early Paleozoic tectonic evolution of the Dananhu-Tousuquan belt, we carried out a systematical study on zircon U-Pb age and whole-rock geochemistry of the Kalatage intrusions. Our dating results indicate the granite, granodiorite, and gabbro-diorite were intruded at 434±4 Ma, 442±2 Ma, and 445±4 Ma, respectively. These ages suggest that the Kalatage intrusions were mainly generated in the Early Silurian. The granite and granodiorite samples exhibit characteristics of calc-alkaline I-type granites with low P2O5 (＜ 0.1%), high Na2O (K2O/Na2O ≤ 0.5), and metaluminous to weakly peraluminous geochemistry (A/CNK = 0.57 – 1.24 and 0.91 – 1.03, respectively). They have very low Sr/Y (1.9 – 4.5 and 8.1 – 11.4, respectively) and (La/Yb)N (1.6 – 2.4 and 2.4 – 3.0, respectively), higher εHf(t) (+12.7 – +15.5 and +11.0 – +14.7, respectively) and εNd(t) (+7.0 – +7.5 and +7.1 – +7.7, respectively), and more juvenile two stage Hf (426 – 589 Ma and 485 – 722 Ma, respectively) and Nd model ages (559 – 603 Ma, and 555 – 598 Ma, respectively), indicating that they are the products of partial melting of the juvenile lower crust. Gabbro-diorite is characterized by enrichments in large ion lithophile elements (LILE) and highly incompatible elements, and depletions in high field strength elements (HFSE), displaying typical geochemical features of a subduction-related origin. They have low SiO2 (54.17% – 55.39%) and high MgO contents (5.26% – 5.54%), positive εHf(t) (+12.1 – +15.7) and εNd(t) values (+7.1 – +7.3), together with their relatively young Hf and Nd model ages (429 – 589 Ma and 634 – 669 Ma, respectively), suggesting that their parental magmas were derived from depleted mantle. The gabbro-diorite samples have relatively high Ce/Nb (11.5 – 16.1) and low Th/La (0.11 – 0.13), indicative of a magmatic source metasomatized by slab-derived fluids. Combining with the previous results of the Early Paleozoic magmatic rocks in this area, we suggest that the Dananhu-Tousuquan igneous arc were formed in an intra-oceanic arc environment triggered by the northward subduction of the Kanggur ocean plate, and the initiation subduction of the Kanggur plate is no later than the Early Silurian. © 2023 Science Press. All rights reserved.