Neoproterozoic And Paleozoic Magmatic Events And Mesozoic Cold Collisional Orogen Of South Qinling,Central China

China Central Orogen(CCO), located in the middle of China, is W-E extending for nearly 5000Km which was called the "backbone" of China continent. From west to east, CCO is comprised of Kunlun, Qilian, Qinling, Dabie and Sulu orogens. CCO is a composite orogen experiencing a long and multi-stage evolution including Neoproterozoic and Paleozoic oceanic subducting, mico-continents amalgamating and collision, Indosinian convergence and collision between South China block and North China Block and Yanshanian intracontinent orogeny, uplifting and exhumation. Thus, this dissertation chose South Qinling as the target and study the long evolution of South Qinling (SQL).The 705-716 Ma granitoid rocks and ca.630Ma A-type granite, syenite, monzodiorite intruding into the Wudangshan group are reported in the research. The magmatic events during late Neoproterozoic can be classified into two stages, ie. the 800-700 Ma subduction-related magmatic event and the ca.630 Ma within plate rifting probably due to slab-rollback. Because of the long-subduction around the northern and western of South China Block, it is suggested that the SCB located in periphery of the Rodinia supercontinent. In Neoproterozoic, Yangtze block and Tarim block experienced similar evolutional process, which imply that they might be very close to each other or even once connected with each other as a united continent located in the western or northwestern periphery of Australia.A Paleozoic alkaline intrusive belt which is composed by mafic rocks, quartz syenite, syenite, nepheline syenite, carbonate et al. is existed in the southern part of SQL. In this reseach, the zircons of mafic rocks, quartz syenite-syenite and nepheline syenite were dated and yielding a weighted age of ca.440 Ma. All these rocks were formed under the background of within plate rifting. Consequently, the evolutional model of the Paleozoic magmatic rocks is proposed. Regional extension gave rise to the thinning of lithosphere and uprising of asthenosphere, and the OIB-like mafic rocks were formed by partial melting of upper mantle. Meanwhile, the decompression and dehydration of lithospheric mantle generated the parent magma of the syenite-quartz syenite and nepheline syenite. Because the lithospheric mantle was metasomated by melts and fluids from the asthenosphere, the rocks are enriched in incompatible elements.South China Block collided with North China Block during Indosinian movement. As the passive margin of the South China Block, SQL is featured by Indosinian deep d6collement between the basement rocks and cover rocks, showing ramp-flat structure, multi-layers dexollement deformation and thin-skinned structure and indicating the northward subduction of South China Block. Our research reveal that deollement occurred not only in the Wudang uplift, but also in Ankang and Pingli uplift. And in Ankang uplift two deollements are discovered between basement rocks and cover rocks. Controlled by the top-to-the-south shearing-decollement, the basement rocks were uplifted in the form of detachment fold, duplex or antiformal stack. Syn- or post-erosion made the basement rocks exhumed.The greenschist facies basement rocks of SQL were low-grade metamorphed. Quartz fabrics reveal that the decollement-shearing belt was formed with low-medium temperature, implying that decollement was formed in the upper crust with a relatively low-temperature condition. Besides, there was no Indosinian and Yanshanian magma in SQL. Consequently, SQL is a classic cold collisional orogen, quite different from the Greater Himalayan hot collisional orogen with high-grade metamorphed, high-temperature-ductile deformation and extensive partial melting.Dabashan structural belt, located in the southern margin of the Qinling orogenic belt, has attracted much attention by its remarkable geometric shape of salient. The mechanics of the salient has long been discussed. Using the numerical modelling method, the formation mechanism of the Dabashan salient is studied in the article. Modelling results show that the pre-existing salient-shaped boundary originated in extensional setting and a pair of indenters in the front control the trajectory of the maximum horizontal principal stress during intra-continental orogeny. Considering the background and the former work done by the author, decollement is also considered to be a key role in the process. It is proposed that Dabashan salient resulted mainly from pre-existing salient-shaped boundary formed in extensional setting, a pair of indenters in the front and decollement.