Crust-mantle Interaction Of Yanshanian Granitic Magma In Qitianling And Daoxian Area Southern Hunan

The chronology framework was established preliminary in this paper based on collecting relative comprehensive former researches results and information, and focusing on the main basic rock and acid rock of the southern Hunan area, and carrying out the accurate U-Pb zircon isotopic dating of the samples. The granite in study area was named in unified with using the methods of CIPW An-Ab-Or diagram of the O'Conner. Base on that the igneous petrotectonic assemblages was analyzed and redefined That the results was proofed by using the chronology and the lithogeochemistry method, which the Yanshanian granites in southern Hunan was the intermingling results of the crust-mantle rock magma by the asthenosphere oceanic upwelling. And the diagenetic model of the Yanshanian granite was proposed preliminary. Researches have made the following understanding:1. The chronology framework of the Yanshanian igneous rock in study area was proposed based on that the ages of Yanshanian granite of the southern Hunan province, dark dioritic enclave and basic rock was redefined with the unified platform for dating of LA-ICPMS U-Pb.2. The Yanshanian granite in study area was named in unified with useing TAS classification diagram and CIPW An-Ab-Or Triangular diagram of O'Conner(1965) for the foundation date of redefiniting and correcting of the granite name in study area. The rock types of the Yanshanian granite in study area were mainly including granite, granodiorite and adamellite and without TTG association caused by the downgoing process of the oceanic crust to the continental crust. Thereby, the structural setting of the Yanshanian in the study area is not the former general result of the Pacific downgoing westward.3. The five-stage igneous rock association of the Yanshanian in the southern Hunan area: Middle-Late Triassic igneous association, the association of Jurassic igneous rocks, Middle-Late Jurassic igneous composition, Late Jurassic and Early Cretaceous igneous rock composition.4. The Yanshanian granite in study area was the result of the second source rocks intermingling of crust and mantle owing to asthenosphere upwelling through the researches on Petrology, Mineralogy, Geochronology, Geochemistry, Isotope, and Lu-Hf isotope of the granite, basalts, basic rock, ultrabasic dyke and maficmagmatic enclave of granite in the southern Hunan area5. The process of crust-mantle mixing of the mass of rock in Qitianling and Tongshanling were redefined under the back of regional geology and based on the Petrography, Geochronology, Geochemistry and Isotopic studies.6. The diagenetic model of the Yanshanian granite was proposed preliminary based on the above study. The model included three stages:the one stage was that the lithosphere of the southern Hunan area was being cracked and heated then soften effect. And the second stage was that the lithosphere of the Middle Jurassic-Late Jurassic was dismantled and flopped with effect of asthenosphere upwelling. And the third stage was that the lithosphere of the Early Crataceous begun isostatic adjust and stepped in uplift stage.