Petrogenesis Of The Late Paleozoic Magmatism And Tectonic Evolution Of The Central-western Xing-meng Orogenic Belt

The tectonic evolution of the Xing-Meng Orogenic Belt(XMOB)is characterized by multiple phases of subduction,amalgamation,juvenile crustal growth and voluminous magmatism.The petrogenesis,geodynamic setting and temporal-spatial distribution characteristics of the Paleozoic magmatism can provide key evidence for constraining the tectonic evolution of the Paleo-Asian Ocean and XMOB.Therefore,this dissertation focuses on the origin and petrogenesis of the representative Late Paleozoic intrusive rocks from the Langshan area,Bulitai area and Daqing pasture,new insights into the Paleozoic tectonic evolution of central-western the XMOB were provided based on the temporal-spatial distribution characteristics of the late Paleozoic magmatism,the deep geological structure of main tectonic units revealed by geophysical soundings and the regional research results.The geochemical and Hf isotopic compositions of the Early Carboniferous(325 ~ 338 Ma)quartz diorites,tonalites and mafic–ultramafic rocks from the Langshan area indicate that they were formed during different stages of magma mixing between partial melting of enriched lithospheric mantle wedge and ancient crustal materials in an active continental margin setting.The Middle Permian(261 ~ 272 Ma)biotite granite shows relatively high Sr and low Y contents,which are comparable with the geochemical signatures of adakites,they might be derived from partial melting of the thickened lower crust during the transient period from subduction to amalgamation.The Early Carboniferous(330 Ma)quartz diorite from Daqing pasture shows typical features of HMA and may be formed by melting of the subcontinental lithospheric mantle wedge induced by the fluids released from partial melting of the subducted oceanic crust,while the Early Permian(271 ~ 282 Ma)granodiorite and biotite granite might be related to the low-pressure and water-deficiency fractional crystallization process of the partial melted juvenile crustal materials in a relatively extensional setting.In the MT 2-D version profiles,there are two large-scale high resistivity bodies situated at the deep crust of the Solonker suture zone,the mirror-image arrangement of these two bodies might point out the “double-sided subduction” of the Paleo-Asian Ocean.The large-scale low resistivity zones in upper crust and the large-scale high resistivity bodies under the crust-mantle transitional zone may represent delamination of lower crust and upwelling of asthenosphere after the continent-continent amalgamation,respectively.The Paleo-Asian Ocean persistently subducted under the North China Craton(NCC)and South Mongolian Block(SMB)since Carboniferous,the Carboniferous-Early Permian active continental margin arc magmatism in the northern margin of the NCC and the Early Carboniferous HMA from Suozuoqi-Xilinhot-Xiwuqi area are resulted from the complicated crust-mantle mixing processes in the subduction zone.The opening and closing of the Hegenshan back-arc oceanic basin during latest Early Carboniferous to Late Carboniferous led to the formation of Hegenshan ophiolite-accretion complex and the Early Permian extensional-related magmatism in the northern XMOB.The Permian magmatism in the south side of the Solonker suture zone were related to the latest phases of the Paleo-Asian Ocean subduction and partial melting of the thickened lower crust under the northern margin of the NCC,the final closure of Paleo-Asian Ocean might happened during Early-Middle Permian.