Tectonic Evolution And Assembly Of The East Segement Of Northern Boundary Of Proto-tethys Ocean

From the Rodinia supercontinent rifting to the end of the Caledonian, theProto-Tethys is an EW-striking ancient ocean, developing between north of theBurma and the Thailand/Baoshan micro-continental blocks, and south of theTarim-the North China Craton. There exists the North China Block, theYangtze Block, Qaidam Block, the Qilian Block, the Indosinia block, theNorth Qinling Micro-continental Block and many other continentalblocks/micro-continental blocks. But it is unclear of the boundary of theProto-Tethys Ocean, the tectonic attributes and ocean-land configuration ofdifferent continental blocks/micro-continental blocks. Therefore, this thesismainly focus on the North Qinling Tectonic Belt and the north of the TongbaiTectonic Orogenic Belt, intensively analyzing the field-based geometry andkinematics structures and utilizing LA-ICPMS,40Ar/39Ar dating methods, andintegrating the previous data of igneous tectonics, sedimentary tectonics,geochemistry, geochronology, lithofacies, paleogeography information andmuch more research data for innovation. The study will determine the easternboundary of the north of the Proto-Tethys Ocean to confirm the property,rifting timing and processes, to reconstruct ocean-land configuration of theeastern segment of the north of the continental blocks/micro-continentalblocks, to discuss the tectonic evolution of the eastern segment of the north ofProto-Tethys Ocean. The reseach will make a solid foundation of the globalreconstruction of the Pangea supercontinent.(1) Based on comparison of sedimentary strata, detrital zircon agespectrum, magmatism, tectonic deformation-metamorphism and other aspectson both sides of the old Luonan-Luanchuan Fault, this thesis reveals that thereis a huge difference of geological features between the south margin of theNorth China Block as passive continental margin and the North Qinling as active continental margin at early Paleozoic, so this thesis proposes that theeast of northern boundary of the Proto-Tethys Ocean is the oldLuonan-Luanchuan Fault.(2) Episodes and features of tectonic deformation: based on the detailedstructural deformation analysis and geochronological data, this paper dividesthe Palaeozoic structural deformation of study area into three episodes. Thefirst stage of the deformation time is characterized by the development ofregional penetrative foliation and top-to-the north thrust faults; the secondstage of deformation embodys the near-NW-striking tight folds; the thirdstage of deformation time should be featureded by the near-NWW-strikingopen folds.(3) The timing and processes of assembly： at540Ma, southwardsubduction of the oceanic crust of the Kuanping Ocean following the reversionof the subduction polarity at about460Ma, and northward subduction ofoceanic crust of Shangdan Ocean. It resulted in the arc-continent collisionbetween the island arc of the North Qinling and the southern edge of the NorthChina Block at450Ma.(4) Tectonic units of the north margin and its adjacent areas of the NorthQinling-Tongbai Orogenic Belt can be divided into the following tectoniczones from north to south. The southern margin of the North China Block isNeoproterozoic-Early Paleozoic passive continental margin; the KuanpingGroup is volcanic rift to ocean basin nearby island arc shelf, its clastic materialsources mainly came from the North Qinling Island Arc; the Erlangping Groupis wide forearc basin caused from southward subduction of the KuanpingOcean, and later transforming into the island arc; the Qinling Group is anancient independent micro-landmass, at the early Paleozoic transforming intoa continental island arc and at the end of its collision with the North ChinaBlock collision as a whole; the Shangdan Ocean is a separate ocean basin or isthe back-arc basin caused from southward subduction of the Kuanping Ocean;the Guishan complex and the Nanan flysch are forearc accretionary wedge system and the tectonic melange belt resulting from northward subduction ofthe Shangdan Ocean in the late Paleozoic, but the South Qinling and the northmargin of the Yangtze Block are passive continental margins in the earlyPaleozoic.