Rock And Mineral Geochemical Characteristics And Geological Significance Of Monzonitic Granites Of Tuotuohe Saiduopugangri Region In Qinghai Province

Monzonitic granite of Saiduopugangri located approximately50kilometerssouthwest of Yanshiping in Qinghai, its tectonic position located at depression ofYanshiping of edge of Tanggula’s foreland basin which located at the north of Qiangtangbetween Lazhulong-Jinshajiang suture zone and Bangongcuo-Nujiang suture zone. Basedon the studying of monzonitic granite’s petrology, Rock and mineral geochemicalcharacteristics of Saiduopugangri, this paper discusses the source characteristics andtectonic settings of their formation, at the same time accumulated data for theestablishment of mineral typomorphic characteristic from this kind of granite.Studying of petrology of monzonitic granite shows that the SiO2’s content of thegranite is higher(70.89%~71.39%), and the K2O’s content is slightly higher than Na2O,this phenomenon display this granite belongs to Quasi aluminous to peraluminous nature.Major element geochemical characteristics indicate that the granite is I-type granites.Light and heavy rare earths element shows clear differentiation. The REE has aasymmetric and steep curve which turns right, and the δEu values between0.56to0.68,asa weak negative Eu anomaly, indicating that the source region has a small amount ofplagioclase presence of residual or fractional crystallization. Enrichment LREEs,lossHREEs and HFSEs, Sr/Y ratio is between72.47-83.48more than40%, LaN/YbNratio isbetween53.06～107.36,more than20%,all these characteristic exhibits geochemicalcharacteristics of adakiti, which indicates that granite is adakitic rock. We can get theinformation though the discussion that granite forms at the process of partial melting of crustal lies under a thick mafic. Through Zircon U-Pb dating of the stars of the era, wecan get the conclusion that monzonitic granite of Saiduopugangri is formed in PaleogenePaleocene.Plagioclase composition tests show this feldspar belongs to oligoclase and andesinebecause Plagioclase has a higher number and An values between24.83to31.66, Anorder of Plagioclase zone from the core part to the outside is An31.66-An31.12-An24.84-An26.37-An25.23displaying of oscillatory zoning, however, on the contrary, An orderof Plagioclase zone from the core part to the outside is increasing, the phenomenon of thePlagioclase reverse zoning shows magma mixing occurred and we can consider thisgranite is Cenozoic granite. In the Alkali feldspar minerals, Or’s content is67.78%-92.58%, and Ab’s content is the secondary with content is7.32%-31.44%. Hardly is Anmolecule’s content less than1, as a result, is belongs to Orthoclase. Biotite electronmicroprobe analysis indicates that Biotite belongs to high iron magnesium biotite mica.Geochemical test data in the evolution of the orogenic belt Y-Nb diagram indicatedthat sample is both evolved in Arc granite area and Syncollision area. In the R1-R2picture,sample evolved in Syncollision area because Crustal thickening process in the area may becaused by a collision, which suggests that Granite of this epoch may be due to thecollision between the plates leads to the formation of the crust thickened. Biotite riches inmagnesium, aluminum, and lacks of titanium and other features indicate that adamelliteformed in orogenic tectonic setting.The study showed that adamellite geochemical characteristics and mineralgeochemical characteristics can be supported each other, and can provide a theoreticalbasis for the use of mineral geochemical characteristics determine granite petrogenesis,tectonic setting and material source.