关键词: 花岗岩')">

花岗岩, 锆石U-Pb定年, 地球化学, I型花岗岩, 早白垩世, 库中, 大兴安岭北段

Abstract:

The widespread Mesozoic granitoids in the Great Xing’an Range play a pivotal role in deciphering the tectonic-magmatic evolution of Northeast China. To constrain the emplacement age, petrogenesis, and tectonic setting of granites in the northern segment of the Great Xing’an Range, this study conducts integrated petrographic, LA-ICP-MS zircon U-Pb geochronological, zircon Hf isotopic, and whole-rock geochemical investigations on the Kuzhong granitic pluton. Zircon U-Pb geochronology yields a crystallization age of (136.5±1.7) Ma, placing the magmatic event in the Early Cretaceous. Whole-rock geochemical data reveal that the pluton represents a highly fractionated calc-alkaline I-type granite, characterized by high silica (w(SiO₂)=70.40%-73.54%), elevated alkalis (w(Na₂O+K₂O)=8.77%-9.30%), enrichment in large-ion lithophile elements (e.g., Rb, Ba), and depletion in high-field-strength elements (e.g., Nb, Ti, P). Chondrite-normalized rare earth element patterns exhibit right-dipping trends with pronounced negative Eu anomalies. The homogeneous zircon Hf isotopic compositions (εHf(t)=5.1-8.8, mean 6.7) suggest magma derivation predominantly from partial melting of juvenile lower crust. Synthesizing regional tectonic evidence, we propose that the Kuzhong granite formed in a post-orogenic extensional setting following the closure of the Mongol-Okhotsk Ocean, overprinted by lithospheric thinning and asthenospheric upwelling driven by Paleo-Pacific plate rollback. This thermotectonic process facilitated melting of juvenile lower crustal materials, ultimately generating highly fractionated calc-alkaline I-type granites.

Key words: granite')">

granite, ziron U-Pb dating')">ziron U-Pb dating, geochemistry, granite;Early Cretaceous')">I-type granite;Early Cretaceous, Kuzhong')">Kuzhong, Xing’an Range ')">Northern Great Xing’an Range