The Study On Geochemical Characteristics And Tectonic Setting Of Jiaren Granitic Plutons In Yangla Region, Western Yunnan

Jiaren granitoid plutons in Yangla region of western Yunnan is located in the middle part of Jinshajiang suture zone that is in the eastern paleotethys, and it is received much concern because of its special tectonic location and the discovery of Yangla large-type copper deposit in recent years. However, with the poor geographic conditions and the complex geological structure, there are different viewpoints on the tectonic setting of Jinshajiang suture zone. This paper makes the study of geology, petrology, geochemistry and the comparative analysis on the geochemical characteristics between the enclaves and the plutons, on this basis, the interrelationship among the granites and the genetic relationship between the enclaves and the plutons are discussed, and then, a further discussion on petrogenetic type of granites, magma genesis and evolution, tectonic setting and geodynamic significance of Jiaren granitoid plutons is made on the basis of previous results and new study. This thesis mainly obtain the following understanding:1. Through the analysis of regional geology and petrology characteristics, Jiaren granitoid plutons is composed by the Beiwu, Linong, Jiangbian, Lunong, Jiaren and Qulong plutons which are a linear distribution from north to the south. The mineral composition of the plutons are mainly of feldspars, quarts, hornblendes and mior biotites with accessory minerals of zircons, apatites, sphenes and allanites, and there are mass of mafic microgranular enclave (MME) composed mainly of hornblendes in Linong and Jiaren plutons.2. The main elements of Jiaren granitoid plutons shows the high-K and low-P granitoids plutons are high-K calc-alkaline metaluminous-weak peraluminous granite, which is similar to the post-collision high-K calc-alkaline metaluminous-weak peraluminous granitoids. The content of SiO2and other oxide has a good linear relationship, which shows the typical magmatic characteristics of differentiation and evolution, and all the plutons had the consanguineous igneous magma. The good linear relationship and the difference of the content between the enclaves and the plutons indicates there was magma mixing during the formation of the plutons, and the magma mixing was incomplete. 3. The REE and trace elements study shows that the characteristics between the enclaves and the plutons are marked difference, which suggests that the MME and plutons were the products of two different magma sources. The evidences that relative depletion Sr、P in all the samples, the overlapping Rb、Th、U between the enclaves and the plutons and Nb/Ta range from lower crust to depleted mantle indicate the magma source were mainly crust and mantle mixed magma, and the crust-mantle magma mixing was incomplete.4. The mineral composition and geochemistry characteristics of Jiaren granitoid plutons show that the petrogenetic type is post-collision high-K calc-alkaline I-type granite. The difference geochemistry characteristics between the enclaves and the plutons shows that magma source area were mainly crust and mantle mixed magma, and there were crust and mantle magma incomplete mixing in the process of magma evolution.5. By comprehensive researching Jiaren granitoid plutons geology, petrology, geochemistry characteristics, and tectonic setting, previous research on Jinshajiang suture zone, the granites in the studying area have the feature of post-collision granite. The geodynamic significance is that the granites originated in the transition environment from extrusion to extension between Changdu-Simao and Zhongza continental plate during the late period, and the magma was the mixed product of the underplating mantle magma and felsic magma which was partial melting from middle-lower crust.