Petrology Geochemistry?Chronology Characteristics And Their Significances Of Early Paleozoic Granite In Yunxian West Yunnan

The Biluoxueshan-Lincang granite belt is the largest outcropped composite batholith in the“Sanjiang”area of west Yunnan-an important part of the Proto-paleotethys tectonic unit,which plays an important role in correctly understanding the evolution and extinction of Proto-paleotethys.Previous researches on Lincang granite batholith mainly focus on the Indosinian Triassic monzogranite and Yanshanian monzogranite which is its main part,and there are few reports on early Paleozoic magmatic rocks.In this paper,with the support of the regional geological survey project of China Geological Survey,the early Paleozoic granitic rocks were newly disintegrated in the Mayidui area of Yunxian county in the south section of Lincang granite.Through detailed field geological investigation,and comprehensive study in petrology?and petrochemical?,geochemical characteristics and high precision Zircon U-Pb chronology,combining with the research achievements in recent years of the study area,did a further study of the rock mass of emplacement age,genetic types and sources of material,provided a new insights to comprehensive understanding of western Yunnan Yunxian county of early Paleozoic granite rock formation and tectonic background.The main lithology of early Paleozoic granites in Yunxian county,west yunnan is monzonite granite and?weekly gneissic?granodiorite.The Si O₂ content of the rock is between 66.04%and 76.97%,K₂O/Na₂O=1.32-8.97,with the characteristics of potassium rich,high silicon,aluminum rich,high potassium characteristics,mainly belongs to the high potassium calcium alkaline series,showing the characteristics of stronger than aluminum granite,which is a typical s-type granite.The light rare earth elements were relatively enriched,while the heavy rare earth elements were relatively deficient??Eu=0.27-0.92?,indicating a moderate degree of negative uranium amoraly.The trace elements were enriched with large ionic lithophile elements?U,Th?and Rb,the deficiency of high field strength elements such as Ba,Nb and Sr,and the negative anomaly of Zr and selective enrichment of Ce and Sm indicate that the materials in the source area are from partial melting of continental crust and basic magma,which are mainly composed of argillaceous rocks,supplemented by variable graywacke and variable andesite.The zircon UP-b ages of the rocks were obtained to be435.4±2.1Ma and 454.4±2.3Ma respectively by LA-ICP-MS zircon U-Pb dating to two granite samples,indicating that the rock masses formed in early silurian and late ordovician.A variety of discriminant illustrations show that the rock mass falls into the volcanic arc and the granite area of the anomalous oceanic ridge,indicating that the rock may be formed in the volcanic arc and the collision type dual environment with the characteristics of the anomalous oceanic ridge.In combination with regional geological setting and geochemical characteristics,western Yunnan Yunxian county Paleozoic granitoids are the ant heap area as the original tethys ocean eastward subduction to reduce the product of the oceanic crust dehydration effect and the bottom of the mantle source magma invasion or injection melt in the earth's crust,thus shows the volcanic arc granite and the dual characteristics of collision type granite.The Early Paleozoic granite rocks in the area have great potential for searching for rare earth minerals such as phosphorite and monazite and tin-tungsten ore,but because of its small distribution area,it is easy to be ignored..