The Characteristics And Causes Of Monzonite Granite Porphyry In Gejiumu, Nanjian County,Yunnan

Gejiumu pluton located in western Yunnan alkali-rich porphyry banding, whichbelonging Jinsha-Red alkali-rich intrusive plutons’ southern section. Gejiumu plutonis divided into three phases: the inside quartz monzonite porphyry phase, the outsidegranite porphyry phase, and the edge diorite porphyry phase. There is no completelyfacies boundaries, and the pluton possess the transition characteristics.Carried out on pluton’s geochemical characteristics analyzed, and tested theU-Pb isotopic age of rock. Through the analysis of the samples of major elements thatbelong to Gejiumu alkali-rich porphyry pluton. The pluton significantly enriched Rb,Sr, Th, U, K, etc. LILE elements (LILE), loss Ta, Nb, Ce, P, Ti high field strengthelements (HFSE), showed a low left high right smooth curves, all distributionpatterns are very similar, LREE enrichment, HREE, LREE fractionation significantly,Eu negative anomaly is not obvious. For samples XIAO-1(syenite porphyry)zircon’s U-Pb average age is (37.91±0.35) Ma (n=27, MSWD=0.99). For samplesPM14-15(porphyry) zircon’s U-Pb average age is (35.50±0.56) Ma (n=9, MSWD=0.75). Both of they are Paleogene Cenozoic intrusive rocks.Gejiumu pluton and Machangqing pluton possess the similar chemicalcharacteristics through comparative studies. This paper also research the DafoshanCu-Pb mineralization point near the Gejiumu pluton, which mainly have the Cu,Pbelements mineralization. The ore bed is white mid-bed siltstone in the upper TriassicMaichuqing group. Considers that Gejiumu pluton may have some potential ofmineralization, it can form porphyry Cu, Au, Pt and other depositGejiumu pluton should belong to a broad alkaline rocks or alkali-rich porphyryaccording to the chemical characteristics. Alkali-rich porphyry formation mechanismand kinetics background has a close relationship with India-Eurasian plate’s collisionand the forming of the Tibetan Plateau. Gejiumu pluton’s LA-ICP-MS zircon U-Pbisotopic dating results is35~38Ma, is the late stage of Paleogene Eocene, is India-Eurasia late collision tectonic transformation stage, also known as the early stages ofthe after the collision. This paper uses geochemical data analysis and U-Pbgeochronology of research, combined with a large number of predecessors’ research on Dianxi Ailaoshan-Red River fault information Cenozoic potassium-rich magmaticactivity area, and discusses the various causes of the formation to Gejiumu rock ’smechanism and geodynamic background.