The Magmatic Activities And Its Deepth Process Of The Later Yanshannian Granitoids In The Jiangnan Uplift In The Area Of Anhui Province

This Ph.D thesis is supported by the geological survey project of the Ministry of Land and Resources (Grant No.K1.4-2-2). It is "the Mineralization, the depth process and resources potential in Jiangnan Uplift Zone". It is a branch project of "the Mineralization of Cu,Au,Ag,Pb,Zn,Fe in the southeastern part of China (the Dabieshan-Taiwan Profile Zone) and its resources potential and the 4-dimention structure of the Mineralization Zone".After systemic study during two years, and based on the project research, I selected the Jiangnan Uplift Zone (Anhui segment) as the research region, including the north part of the folding and thrusting belt of forland. The major aim is studying on the magmatism, petrology, geochemistry, magmatism, its depth process and regional geodynamic basement of the later stage of Yanshanian. The main contents are such as the tectonic property and its evolution, the characteristic of its physical geography of gravitation and magnetism and seismic structures; the magma distribution, types, evolution of the later stage of Yanshanian. The main progresses in this thesis are as below.1. The stages of the magmatism. It is decided that the main magmatism was happened in the later stage of Yanshanian based on the first accurate isotopic dating. We obtained two isotopic data by the dating of two biotites with the method ⁴⁰Ar/³⁹Ar, they are 133.97±0.48Maof the Kaobeijian biotite-granodiorite and 141.46±0.62Ma of Xiaoyao granodiotite porphyry. After statistically analysis, we can found that the isotopic data of the magmatism in the region are mostly located between 130 142Ma or 120¹30Ma. So it indicated that there were two stages of the magmatism of the region during the later stage of Yanshanian, they are the middle stage and later stage of Cretaceous.2. The time of the lithosphere delamination and extention. After regional correlating, we supposed that the two intrusive bodies of Xiaoyao granodiotite porphyry and Kaobeijian biotite-granodiorite have a certain regional representation of the magmatism. The magmatic activities indicated that the lithosphere delamination, the asthenosphere uplifting and lower crust partly melt and mantle underplating to the crust. The 142Ma isotopic data is the oldest precise age in the region until now, considering the regional geological information; we supposed that age was precise one that it is the representation of the regional magmatism. So it indicated that the beginning time of the lithosphere delamination, i.e. the lithosphere had been delaminated since 142Ma in Jiangnan Uplift Region.3. The magma petrology and its cause of formation. The most of the intrusive bodies of the Later Yanshanian are belong to the HK calc-alkalite granite. The mother sources of the granite-porphyry and granite are from the crust, and mixed with somecomponents of the mantle. They are similar to the crustal rebuilt serials granite, such as CPG type granite. But according to the characteristic of the REE, micro elements, Pb, Nd and Sr isotopes show the type of syntactic magma series, and the diagenetic matter show a mixed pattern of the crust and mantle. It indicated that there were some mantle components in the sources of the magma. According to the Nd model age of the magma, it shows that the granite (except Fencun, Huangshan and Tanshan) and granite-porphyry exhibit younger Nd model ages (<1.6Ga), Fencun, Huangshan and Tanshan granites show elder Nd model ages (>1.6Ga). But if we take the equation of the two stages of Nd model age, all of the granites exhibit younger Nd model ages (<1.6Ga). and also, the granites exhibit that the higher /Sr, above 0.708. Concerning those mentioned above, it indicated that the magmatism was happened mainly in the crust, it was formed by partly molten of the crust, but some mantle components have been put in the petrogenetic processes.4. The evolution of the regional tectonic paleostress field since Yindosinian. It exhibit the compression which strikes NW-SSE, nearly N-S; the inner-continental orogeny developed, it belonged to in the paleo-Tethyan...