Middle–late permian I-type granitoids from the Diaobingshan region in the northern margin of the North China Craton: insight into southward subduction of the Paleo–Asian Ocean

Abstract

ABSTRACT An integrated study of the petrology, zircon U–Pb geochronology, whole–rock geochemistry, and in situ zircon Hf isotopic compositions of middle–late Permian granitoids from the Diaobingshan region in the northern margin of the North China Craton (NCC) has been implemented, with the aim of investigating their geochronological framework, petrogenesis, and tectonic significance. The studied granitoids are widely distributed on the southern side of the Changchun–Yanji suture zone and comprise mainly monzogranite and syenogranite, with minor quartz monzonite. New zircon U–Pb data measured by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) yield emplacement ages of 262–256 Ma, reflecting middle–late Permian magmatism. Geochemically, the rocks contain 60.53–73.33 wt.% SiO2, 12.60–18.35 wt.% Al2O3, 3.50–8.10 wt.% K2O, 0.18–0.91 wt.% TiO2, and 0.22–1.01 wt.% MgO, and exhibit weakly peraluminous (A/CNK = 0.86–1.01) and high-K calc–alkaline and shoshonitic characteristics, indicating I-type granite affinities. They are also characterized by low Sr and high Yb contents, reflecting low-pressure magma source conditions with residual plagioclase (i.e. amphibolite facies). These granitoids also exhibit geochemical characteristics typical of arc–type magmatic rocks, with enrichment in large ion lithophile elements (LILEs; e.g. Rb, Ba, and K) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs; e.g. Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating that they were formed in a subduction-related setting. Moreover, magmatic zircons from the studied rocks have relatively homogeneous Hf isotopic compositions (εHf(t) = – 1.4 to +15.1) and corresponding two–stage model (TDM2) ages of 1839–348 Ma, indicating that they were generated by partial melting of Paleoproterozoic–Phanerozoic accreted lower crust, with minor contributions of ancient crustal materials. Their geochemical characteristics and specific lithological assemblage, together with the temporal–spatial distribution of Permian granitic magmatism, indicate that the formation of middle–late Permian granitoids in the northern margin of the NCC was related to southward Paleo–Asian oceanic subduction. Data from this and previous studies lead us to favour a double-sided, early–late Permian subduction model, with the Paleo–Asian Ocean closing after the late Permian.