Crust-Mantle Interaction Controls the Formation of High-Mg Adakitic Rocks: Evidence from Early Cretaceous Intrusive Complexes in Luxi Terrane, North China Craton

Abstract

High-Mg adakite rocks preserve crucial information about the crust-mantle interactions during the magma evolution. The Luxi Terrane, southeastern North China Craton, stores a set of Early Cretaceous high-Mg adakite rocks; nevertheless, their petrogenesis remains controversial. In this study, we present new whole-rock geochemistry, zircon U-Pb-Hf isotopes in the Tiezhai, Jinxingtou, and Sanshanyu complexes which are composed of gabbroic diorite, diorites, syenites, and monzonites. Field observations and zircon U-Pb dating indicate that all of the rock units crystallized contemporaneously at ca. 125–120 Ma. They are characterized by high Al2O3 and Sr contents, and low MgO, Y, Yb, and heavy rare earth elements contents, coupled with high Sr/Y values (42–163), showing adakitic affinities. The magma mixing process is supported by the following ample evidence: (1) the disequilibrium mineral textures and mafic enclaves; (2) high Mg# values (37–69, Mean = 58); and (3) widely zircons εHf(t) values (−25.6 to +7.8). The signature geochemical characteristics support that the adakites were generated by magma mixing of ancient crust-derived melts and relatively mafic melts from metasomatized mantle source. In combined with regional geology, the Early Cretaceous high-Mg adakites in Luxi Terrane represent the magmatic response of intensive crust-mantle interaction caused by the underplating of voluminous mantle-derived magma in an extension intracontinental setting.