First identification of late Mesozoic intraplate magmatism in the Chinese north Tianshan: implications for the orogenic architecture and crustal evolution

Abstract

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical and Sr–Nd–Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced at c . 145–132 Ma. They have positive ε Nd ( t ) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk-rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are probably inherited from Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were probably triggered by thermal relaxation owing to crustal shortening and thickening. These data further imply that the Tianshan changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Supplementary material: LA-ICP-MS zircon U–Pb dating results, whole-rock major and trace element compositions, whole-rock Sr–Nd isotopic data and zircon Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.7167890 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change