Geochemical Features And Tectonic Significance Of Granites In The North Of West Qinling Orogenic Belt

West Qinling orogenic belt is an important part of the Central Orogenic Belt, which adjoins to North Qilian orogenic belt and East Kunlun orogenic belt. There are many granites in the north of the West Qinling orogenic belt. Four granites from Tianshui area in the West Qinling orogenic belt were selected in this thesis. By the method of systematic geochemical and previous studies, the material source, petrogenesis, tectonic setting and significance of granites of different periods and types are discussed.Tianzishan pluton is a metalumious high-K calc-alkaline I-type granites. Tianzishan pluton is similar to C-type adakitic rocks. It is formed by partly melting of subducting basaltic lower crust (Yaolinghe group metabasic volcanic rocks of Yangtzr Block)under thickened setting. It is the evidence of subduction from Yangtzr Block to North Qinling Block in the Indosinian epoch;Dangchuan pluton isstrongly peraluminous high-K calc-alkaline S-type granites. It has geochemical characteristics of both syn-collision(post-collision) and arc setting. It is formed by partly melting of granulite facies rocks in the lower crust with high pressure, low temperature and liquid. It is the results of the collision between North Qinling Block and North of North China Plate and the subduction of Shangdan oceanic crust in the Early Palaeozoic;Huamiaozi diorite vein is metalumious calc-alkaline to high-K calc-alkaline rocks. It has geochemical characteristics of arc magmas. It is the evidence of the subduction of Shangdan oceanic crust in the Early Palaeozoic;Qinling group biotite gneiss’s virginrock is granite. It is strongly peraluminous high-K calc-alkaline S-type granites. It has geochemical characteristics of syn-collision setting. It is formed by partly melting of Qinling group with the collision of North Qinling Block and Yangtze Block in the Neoproterozoic. It is a response of the assembly of Rodinia.