Neoproterozoic Sedimentary Formations And Igneous Rock Associations In The Songnen And Jiamusi Massifs

This thesis mainly studies on the geochronology(LA-ICP-MS),whole-rock geochemistry and zircon Hf isotopic geochemistry of the Honglin Formation of the Dongfengshan Group from the Songnen Massif and the Ximashan Formation of the Mashan Group and the Majiajie Group from the Jiamusi Massif,as well as deformed igneous rock associations in the both massifs.Our aims are to(1)constrain the depositional ages,provenance and sedimentary environment of the Honglin Formation of the Mashan Group in the Songnen Massif and the Ximashan Formation of the Mashan Group and the Majiajie Group in the Jiamusi Massif,(2)investigate the chronological framework of the Neoproterozoic magmatism in the Songnen and Jiamusi massifs,(3)analysize the petrogenesis of the Neoproterozoic magmatism and its tectonic setting,and(4)discuss the the tectonic affinity between the Songnen and Jiamusi massifs and their tectonic affiliation,as well as the relationship between the Neoproterozoic magmatism and tectonic evolution of the Rodinia supercontinent.Main achievements are as follows:1.The depositional ages,provenance and tectonic setting of the Honglin Formation of the Dongfengshan Group in the Songnen Massif and the Ximashan Formation of the Mashan Group and the Majiajie Group from the Jiamusi MassifThe depositional age of the Honglin Formation of the Dongfengshan Group in the Songnen Massif is 800–703 Ma,which is formed in a continental island arc.The source rocks experienced moderate degrees of sedimentary sorting,and have a moderate degree of compositional maturity,suggesting that the source rocks were dominated by Meso-Neoproterozoic felsic rocks from the nearly Songnen Massif.The depositional age of the Ximashan Formation of the Mashan Group in the Jiamusi Massif is 929–898 Ma,which is also formed in an active continental margin.The source rocks experienced low degrees of sedimentary sorting,and have a moderate degree of compositional maturity.In contrast,the depositional age of the garnet-bearing carbonaceous phylite from the Majiajie Group is 976–918 Ma,which is also formed in a continental arc.Their source rocks experienced moderate degrees of sedimentary sorting,and have a high degree of compositional maturity,suggesting that their sediments are from far away.Therefore,we conclude that the source rocks of the Ximashan Formation and Majiajie Group are derived from Proterozoic felsic igneous rocks in the Songnen and Jiamusi massifs.2.Neoproterozoic magmatism in the eastern margin of the Songnen Massif and the western margin of the Jiamusi MassifThis study discovered several stages of Neoproterozoic magmatism in the eastern margin of the Songnen Massif and the western margin of the Jiamusi Massif.The Neoproterozoic magmatism in the Songnen Massif can be subdivided into nine stages:(1)?950±4 Ma gneissic monzogranites,(2)?929–927 Ma gneissic syenogranites and gneissic quartz-syenites,(3)?895–894 Ma gneissic monzogranites,(4)?872–871 Ma gneissic syenogranites and granitic pegmatites,(5)?801–787 Ma gneissic biotite monzonites,(6)?767±4 Ma meta-gabbro-diorites,(7)?728±13 Ma granitic pegmatites,(8)?639±4 Ma gneissic monzogranites,and(9)?579–573 Ma gneissic amphibole monzonites and meta-gabbros.In contrast,the Neoproterozoic magmatism in the Jiamusi Massif can be subdivided into four stages:(1)?930±4 Ma monzogranitic gneisses,(2)?774±3 Ma gneissic monzogranites,(3)?740±6 Ma gneissic biotite monzonites,(4)?703±7 Ma gneissic granodiorites.In addition,associated metamorphism recorded by metamorphic zircons can be subdivided into three stages,i.e.,?730 Ma,?527 Ma and?492 Ma.3.Petrogenesis and tectonic setting of the Neoproterozoic magmatism in the eastern margin of the Songnen Massif and the western margin of the Jiamusi MassifThe?950 Ma magmatism in the Songnen Massif was generated in convergent margin related to compressive orogenesis by partial melting of ancient mafic lower crustal material;The?929–927 Ma magmatism in the Songnen Massif was generated in an active continental margin,and their primary magmas most likely originated from enriched mantle sources,which were metasomatized by subducted sediments and underwent fractional crystallization during ascension;The?895 Ma magmatism in the Songnen Massif was generated in convergent margin related to the late stage of compressive orogenesis by partial melting of ancient thickened mafic lower crust;The?872–787 Ma igneous rocks in the Songnen Massif are characterized by intraplate granites,and their primary magmas were generated in an extensional environment after the orogenesis by partial melting of juvenile mafic lower crustal material;The?801–767 Ma igneous rocks in the Songnen Massif are also characterized by intraplate granites,and their primary magmas are similar to 639±4 Ma magmatism,which were generated in an extensional environment related to lithospheric thinning by partial melting of mafic lower crustal material;The?579–573 Ma magmatism in the Songnen Massif consists of a bimodal igneous rock associations,and their primary magmas were generated in extensional environment by assimilation and fractional crystallization(AFC)processes from a basaltic parental magma.In contrast,the?930 Ma magmatism in the Jiamusi Massif was generated in convergent margin related to compressive orogenesis by partial melting of Meso–Neoproterozoic mafic lower crustal material;The?774±6 Ma gneissic monzogranites in the Jiamusi Massif and?767±4 Ma meta-gabbro-diorites in the Songnen Massif belong to bimodal igneous rock associations,which were generated in an extensional environment.The?740 Ma magmatism in the Jiamusi Massif was generated in a low P-T extensional environment related to lithospheric thinning by partial melting of Meso–Neoproterozoic mafic lower crustal material.4.Tectonic affinity between the Songnen and Jiamusi massifsThe chronological studies indicate that the Neoproterozoic sedimentary formations and magmatism occur in the Songnen and Jiamusi massifs.Taking into account the similar age distribution of detrital zircons from the Neoproterozoic strata,the Songnen and Jiamusi massifs have a same Neoproterozoic crystalline basement.Additionally,zircons from the widespread Phanerozoic granites are characterized by Paleo-Neoproterozoic T_DM2,further suggesting that the two massifs have a same Proterozoic crystalline basement,and the Phanerozoic granites are generated by reworking the Proterozoic basement.Moreover,the coeval magmatism in the Songnen and Jiamusi massifs has similar petrogenesis and tectonic setting,and zircons from the?895–891 Ma granitic gneisses record?492±4 Ma metamorphism in the Songnen and Jiamusi massifs,suggesting that the Songnen and Jiamusi massifs have similar tectonic evolution history.Therefore,the same Neoproterozoic crystalline basement and tectonic evolution history indicates that the Songnen and Jiamusi massifs have a close tectonic affinity.5.Tectonic affiliation of the Songnen and Jiamusi massifs and the relationship between tectonic evolution of the Rodinia supercontinent and the two massifsPetrogenesis and age of the Neoproterozoic magmatism in the Songnen and Jiamusi massifs are consistent with tectonic evolution of the Rodinia supercontinent,suggesting that the Songnen and Jiamusi massifs record the key information of the assembly and breakup of the Rodinia supercontinent.The inversion results of detrital zircon ages from sedimentary formations in the Songnen and Jiamusi massifs indicate that the Songnen and Jiamusi massifs experienced similar tectonic evolution history with the Tarim Plate.Taking into account the paleomagnetic data,the Songnen and Jiamusi massifs and the Tarim Plate were all located near to the equator during the Sinian period.Therefore,the Tarim Plate probably has a tectonic affiliation with the Songnen and Jiamusi massifs.Based on the paleomagnetic data of the Tarim Plate and the evolution history of the Rodinia supercontinent,the Songnen and Jiamusi massifs were involved in the assembly and breakup of the Rodinia supercontinent with the Tarim Plate.