Midu Himalayan Magmatic Rock Geochemical Characteristics And Magmatic Evolution

The study area is located in the northern section of the Red River fault zone, the exposed Himalayan period magmatic rocks of this area are part of the Ailaoshan-Jinsha River alkali-rich magmatic belt.From the early 80s,a lot of research were doing by many people about the structure environment,rock characteristics and causes of the rocks that exposed in the alkali-rich magmatic belt,and achieved fruitful results; a number of alkali-rich igneous rocks related to the deposit were found meanwhile.Deep geological and geochemical studies about the Himalayan alkali-rich magmatic rocks, not only can reveal formation and evolution of these rocks and related mineralization process of great value, as an important window to understand the upper mantle,it also reveal the upper mantle features of the Himalayan period and geodynamic processes. Based on these, the author selected the alkali-rich intrusive rocks(mainly including Caiyuan pluton,Changpolin plutons, Juli plutons, Jixiangzhuang plutons,Duogu plutons, and Dalinghuashan plutons, plus a small amount of lamprophyre veins), and extrusive rocks (mainly including basalt) in the petrology, geochemistry and geochronology research and discussed the formation of the environment and magma evolution of the pluton (plutons), progress made as follows:Chemical research about the intrusive rocks of the area shows that, in addition to biotite granodiorite-porphyry, the other samples are alkali-rich intrusive rocks. From trace elements in ocean ridge basalt normalized spider diagram shows that the intrusive rocks in almost the same distribution pattern, that is rich Rb, K, Th, Ce and light rare earth elements such as LILE, depleted Ti, Nb, Ta, Sr, etc.. The Nb/U are less than the value of mid-ocean ridge basalt, these features indicate that a subduction zone magma source material contamination, indicating the rock's material comes from the same magma chamber the product of different period, with the igneous characteristics. REE showed significant enrichment of LREE, Eu weak loss of the right inclined REE patterns. Biotite granodiorite-porphyry light REE enrichment is more obvious, showing the distribution pattern of steep slope. Alkali-rich intrusive rocks from the collision of tectonic environment in the post-orogenic uplift to the trend of the late transition. The Dalongtang plutons were formed in the collision of the same.Alkaline Basalt is characterized by AI was 0.73, indicating more involvement of mantle materials. And ocean ridge basalt compared to alkali-rich volcanic rocks obviously enriched Rb, K, Ba, Th, Ce and other large ion lithophile elements, poor Ti, Nb, Ta, Sr and other elements, showing a significant negative anomalies; Cr obviously rich set. The REE characteristics and the chondrite-normalized patterns of the alkali-rich volcanic rocks show that there is no significant loss of Eu, relatively enrich LREE. The alkaline basalt tectonic discrimination explanation is the magmatism product of post-orogenic.Samples from porphyritic rich-biotite sanidine quartz syenite of the Caiyuan pluton, trachyte of the Jixiang zhuang plutons and porphyritic hornblende-quartz syeniteof the Dalinghuashan plutons were selected to do LA-ICPMS U-Pb test. The results prove that all these three products formed in Himalayan period.Combined with the petrology, geochemistry, chronology of evidence of the pluton and plutons in the study area, we believe that the igneous rocks in this area have the same sources. After analysising the spatial and temporal distribution,we found that the evolution of magmatic rocks in the study area has a certain regularity.