The Genetic Research Of Linear Granites In The Shangdan Suture Zone In Eastern Qingling

The Qinling orogen belt divided the north China block and the Yangtze block in our country.The ShangDan suture zone as main plate suture zone of qinling orogenic belt, which record the history of interaction of these two blocks,Keeping a lot of material records.The linear granites in the Shangdan suture zone in Eastern Qingling is important geological carrier which can discussed the tectonic evolution of ShangDan suture zone. Currently tectonic setting of these linear granites, there are still different views,such as syntectonic granite, collision granite and subduction period granites. And linear distribution for the granite formation has not been a reasonable explanation. Formation time and tectonic background and tectonic deformation of these linear granites have important geological significance for understanding and explanation the tectonic evolution of ShangDan tectonic belt. In the system on the basis of summarizing predecessors'research, this paper has carried out detailed field geology, petrology,geochemistry,geochronology and related research of these linear granites, get the following conclusion:(1) Linear granite nearly east-west distribution in plane, and intrusive contact relationship to the surrounding rock (the Danfeng group),granite in the development of structural surface into the permeability,deformation is stronger. According to the structure deformation of the granite can be divided into the mylonitization granite and granitic protomylonite.Mylonite plane direction about 110°, southward dipping, Structure phenomenon of outcrop scales which can be observed indicate space distribution of the linear granites under left shear control, consistent with the structure characteristics of the ShangDan ductile shear zone over the same period. Granitic protomylonite mineral combination for new substrate:Mc+Pl+Qtz+Bt,corresponding to the low amphibolite facies metamorphism temperature pressure condition.(2) Field observation and indoor rock studies show that linear granite body for monzonitic granite and biotite monzonitic granite. LA-ICP-MS Zircon U-Pb dating results indicate monzonitic granite formed 409.8±2.2Ma(MSWD=0.21),beginning of the early Devonian. LA-ICP-MS Zircon U-Pb dating results indicate monzonitic granite formed 397.4±2.1Ma (MSWD=0.072), at the end of the early devonian-the early middle Devonian.(3) Detailed geochemical studies show that the linear granite with the characteristics of high silicon,low titanium, low calcium and high aluminum, aluminium saturation index A/CNK mostly less than 1.1,showing aluminum-weakly peraluminous I-type granite. The linear granite is enriched in LREE and poor in HREE,as well as enrichment of Rb?Th?K and loss of Nb?Ti.It is result of the partial melting of metamorphic basic rocks in middle and lower crust in the stage of syn-collision.(4) Comprehensive petrology, geochemistry,geochronology and Eastern QinLing's metamorphism and granitic magma activity records in early Paleozoic, we think that the linear granite is the product of the Danfeng group's partial melting.It is indicate that the subduction alone ShangDan suture zone has ended in the early Devonian.Eastern QinLing has gradually turned into the phase of syn-collision.