东天山雀岭地区中泥盆世侵入岩成因机制及构造意义OA

The Dananhu-Tousuquan island arc belt in the eastern Tianshan represents a pivotal accretionary orogenic belt within the Paleo-Asian Ocean tectonic domain.The genesis and tectonic affinity of its intermediate-acidic intrusive rocks are therefore crucial for deciphering the Late Paleozoic subduction-accretion processes in the eastern Tianshan.The Queling area,situated on the western flank of this arc belt,is geologically characterized by porphyritic granite,granodiorite,and biotite granite based on field investigations.Zircon U-Pb dating constrains the emplacement age of these three rock types to 387.4～382.1 Ma,indicating they are products of Middle Devonian magmatism.Geochemically,all samples exhibit high SiO2(66.60％～72.66％),high Sr,low Y,and low heavy rare earth element(HREE)contents.Their geochemical signatures are transitional between adakite and typical arc granitoids,showing an arc affinity marked by enrichment in large-ion lithophile elements(LILE)and light rare earth elements(LREE),and depletion in high field strength elements(HFSE).Zircon Hf isotopic compositions yield significantly positive εHf(t)values(+9.7～+15.3)and young two-stage Hf model ages(TDM2=0.74～0.40 Ga).Integrated with their moderate Mg#values(43～50),these data collectively indicate that the primary magmas were derived from partial melting of juvenile basaltic lower crust that was newly accreted during the Neoproterozoic to Early Paleozoic,with involvement of mantle-derived components,suggesting a certain degree of crust-mantle interaction.This comprehensive study demonstrates that the Middle Devonian intrusive rocks in the Queling area formed in an island arc setting,under the ongoing subduction of the Paleo-Tianshan Ocean.Their petrogenesis is closely associated with mantle-derived magma underplating,which triggered the melting of the juvenile lower crust,coupled with crust-mantle mixing.This process elucidates an orogenic mechanism featuring vertical crustal growth through mantle-derived material addition,juvenile lower crustal melting,and crust-mantle interaction,providing key petrological evidence for constraining the Late Paleozoic tectonic framework of the eastern Tianshan and the subduction-accretion evolution of the Paleo-Asian Ocean.