Magma Mixing Of The Late Paleozoic Tayuan Complex In The Xing’an Block

This paper reports petrographical,zircon U-Pb ages,whole-rock geochemical and Hf isotope data of the host granodiorites and mafic microgranular enclaves（MMEs）from the Tayuan complex at the northern Xing’an Block in NE China,in order to constrain formation time,petrogenesis and tectonic setting of the complex.LA-ICP-MS zircon U-Pb dating results show that the ages of host granite and MMEs are 319 Ma and 320 Ma,respectively,indicating that the Tayuan complex was formed in the Late Carboniferous.Through field geological survey and petrographic characteristics,we find that the MMEs display igneous-texture,and some of them have quenched margin,back veins and acicular apatite.The disequilibrium mineral associations or disequilibrium textures are developed in both MMEs and host granodiorites.Combined with chronology and geochemistry,excluding restite unmixing and xenolith,we can conclude that the Tayuan complex is the product of Late Carboniferous magma mixing.The host granite suite has high SiO₂（66.16⁷4.18 wt.%）and K₂O（3.89⁴.86 wt.%）,but low MgO（0.07⁰.49 wt.%）,CaO（0.14⁰.60 wt.%）,P₂O₅（0.01⁰.08 wt.%）and yields enriched LILE and depleted HFSE patterns.Most of the zircons in the host granite have two-stage model ages of 899¹382Ma,together with?_Hf（t）values of-0.46⁺7.1.These results indicate that the granitoid magmas were generated by partial melting of young crustal materials.The MMEs suite has a restricted range of SiO₂（46.29⁶1.94 wt.%）together with high Mg^#values（46⁶6）and high concentrations of Ni,Co,and Cr.Zircons from gabbro enclaves samples have single-stage Hf model ages of 748¹076 Ma and?_Hf（t）values of-0.69⁺5.33.These results suggest that the mafic magmas were derived from melting of mantle that had been metasomatized by slab-derived fluids.According to the geochemical data and previous geological investigations,we conclude that the Tayuan complex was emplaced in an active continental margin setting,which was probably related to the northern subduction of the Paleo-Asian oceanic plate between Xing’an and Songnen blocks.