Study Of Rock Southeast Yunnan Fu Ning Regional Mafic Intrusive Rocks

Triassic mafic-ultramafic intrusive rocks widely distribute in southeast region of Yunnan Funing, according to the different types of intrusive relationship, petrology and the main element geochemical characteristics, rocks can be divided into early Banwa Rock and late Anding Rock. However, it is been disputed in the issue of both magma origin, forming age and tectonic setting. Through comprehensive research of petrology, geochemistry, geochronology and other aspects of the two typical rock mentioned above, meanwhile, combined with the development of regional crustal evolution process, a new geological understanding on formation of age, material sources, tectonic setting of Banwa rock and Anding Rock have been proposed and two types of mineralization characteristics of rock has been discussed.The researcher studies on the exposed surrounded basic intrusive rocks of Funing County in the follows three aspects:petrology, geochemistry and geochronology. The result of observation in the field shows that Banwa rock and Anding rock can be interspersed with each other, two stage magma emplacement time is closed which belong to nearly same geological age of emplacement of magma, and it has obtained the evidence of zircon geochronology. Chemical composition of Banwa rock is obvious rich titanium and iron, and there is a close relationship between ilmenite; the Na2O+K2O of rock is higher and it is detected as the alkali basalt series by the discriminant for silicon-alkali diagram. The Banwa rock is with high amount of tombarthite elements (∑REE=168.54-402.90×10-6, with an average of 255.05×10-6), distribution curve of tombarthite exhibited slanting right liner with LREE enrichment obviously. At the same time, the high field strength cations like Zr, Nb, Ta are higher while the strong incompatible elements such as Cr and Ni is low. It is located at the intraplate basalts area of the trace discrimination diagrams. It obtains the age of zircon U-Pb LA-icp-ms:253.8±2.3Ma、 244.8±4.3Ma. About Anding rock, the contents of K2O, Na2O and TiO2 is low, but the MgO and CaO content are higher. According to the analysis of the silicon-alkali diagram, A-F-M graphic discriminant, it is belongs to the tholeiite with low amount of tombarthite elements (55.74-79.15×10-6, the average comes to 68.51×10-6) and the tombarthite distribution curve presents like the slanting right "L". What is more, it is with LREE enrichment and strong incompatibility, the degree of HREE depletion and incompatibility is lower; the content of High-field strength elements (Zr, Nb, Ta, etc.) is low, and content of strong compatible elements (Cr, Ni, etc.) is higher, especially the content of Cu up to 1170×10-6 which indicates it has been a good geological conditions for copper and nickel mineralizing. They are located at the island arc area and volcanic basalt area in the trace discrimination diagram. They obtain the age of zircon U-Pb LA-icp-ms:253.8±2.3Ma244.8±4.3Ma, which the former is the age of magmatic crystallization and the later one probably is the age of the magma source area formed.From the regional geological data analysis, with the plate convergence of the global Rodinia supercontinent in the Qingbaikouan period of late Proterozoic era,the Yangtze plate and cathaysian plate collide with each other and formed into the south China plate. The junction of both is generally accepted in the fault zone of Jiang-Shao to Maitreya-Shizong fault zone. Starting from the late period of Early Devonian, the earth’s crust of study area started cracking and developed into Nandan sedimentation and Xiangzhou sedimentation. With the development of the Emeishan mantle plume in middle-late Permian period of geologic history, crustal cracking is further aggravated in the research area which shows the sedimentary record of late Permian led while group, the early-middle Triassic ShiBao group, plate of bathyal deposit. Magmatic activity records appear as emplacement of Banwa-type and Anding-type. Two types of rock emplaced in the basically same time, but with the different geochemical characteristics which should be the same magma source area formed under different tectonic background. Banwa rock may be rooted in the Emeishan mantle plume activity which caused the upper mantle low degree of molten magma after crystallization differentiation, it is the product of rising and emplacement. Anding rock mass may be originated from the early oceanic crust subduction of the product of high degree partial melting emplacement directly.