Petrogenesis and tectonic implications of Late Jurassic – Early Cretaceous granitic magmatism in the Xing’an Block, Northeast China: geochronological, geochemical, and Hf isotopic evidence

摘要

This study presents new geochronological, whole-rock geochemical, and zircon Hf isotopic evidence for the age, petrogenesis, and source of Mesozoic granitic rocks of the Xing’an Block, Northeast China. This evidence reveals the Late Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt. Laser-ablation inductively coupled plasma – mass spectrometryzircon U–Pb age data indicate that the syenogranite, monzogranite, and alkali feldspar granite units, as well as their associated diorite microgranular enclaves, were emplaced between 150–142 Ma, providing evidence of Late Jurassic to Early Cretaceous magmatic events within the Xing’an Block. The granites contain high concentrations of SiO2 (65.24%–75.73 wt.%) and K2O (3.94%–5.30 wt.%), low concentrations of MgO (0.10%–1.30 wt.%), and A/CNK values of 0.92–1.06. In addition, Hf isotopic analysis of zircons from the 150–142 Ma granites yields εHf(t) values of +4.54 to +12.16 and two-stage Hf model aged from 906 to 423 Ma, indicating that they formed from magmas generated by partial melting of a juvenile Neoproterozoic–Phanerozoic accreted crustal source. The basic magma source for the diorite microgranular enclaves most likely formed from partial melting of a depleted mantle that had been metasomatized by subduction-related fluids. Combining these new geochemical data with the geology of this region, Late Jurassic to Early Cretaceous magmatism in the Xing’an Block most likely occurred in an extensional environment associated with closure of the Mongol–Okhotsk Ocean.