Late Carboniferous crustal evolution of the Chinese Central Tianshan microcontinent: Insights from zircon U-Pb and Hf isotopes of granites

The Central Tianshan microcontinent (CTM) in the southern Central Asian Orogenic Belt is characterized by Precambrian crustal basements and widespread Palaeozoic granitic rocks. However, the Palaeozoic tectonic process and associated crustal evolution of the CTM have not been well constrained. In this paper, we report whole-rock geochemistry, zircon U-Pb ages, Hf isotopes, and trace elements for the Late Carboniferous granodiorite and monzogranite from the Hongliujingbei area of the eastern CTM. These data were further integrated with previously published whole-rock geochemistry and zircon Hf isotopic data of the intensive Late Carboniferous (327-300 Ma) magmatic rocks in the CTM in order to gain more insights into the crustal and tectonic evolution of the CTM during the Late Carboniferous. LA-ICP-MS zircon U-Pb dating results indicate that the granodiorite and monzogranite from the Hongliujingbei area were emplaced at ~320 Ma. Their highly variable zircon epsilon(Hf)(t) values (-0.1 to +12.9) suggest that the magmas of these rocks were formed by the mixing of mantle- and crustal-derived magmas. The Late Carboniferous magmatic rocks from the CTM, as a whole, show a wide range of zircon epsilon(Hf)(t) values (-3.7 to +13.4) and geochemical characteristics typical for magma evolution in an active continental margin setting. Therefore, we suggest that the Late Carboniferous magmatic rocks in the CTM were probably generated in a continental arc formed by the southward subduction of the North Tianshan Ocean Plate beneath the CTM, and their mostly depleted zircon Hf isotopic compositions indicate that juvenile crustal growth was a dominant process in the CTM during the Late Carboniferous.