Geochemical Characteristics And Genesis Of Granitoids In Yanbian Area Of Sichuan

Magmatic activities was more active in Neoproterozoic,in Panzhihua area, intrusive rocks were widely distributed. Like ultramafic to felsic rocks, alkaline rocks, from Danba of Sichuan to Eshan of Yunnan, It’s range of thousands of kilometers, The size of rock mass is up to more than 60. To clarify their emplacement age, petrological and geochemical characteristics of granite formation mechanism of Pan Xi rift structure reveals the complex evolutionhistory and dynamic mechanism is very important. Therefore, to carry out the study of granite can not only reveal the crust source petrogenesis, composition, and help to restore the orogenic process and the tectonic movementhistory.The research area is located in the eastern part of Himalaya Tetisisi a tectonic region, the southwest margin of Yangtze block. Influenced by India Ocean plate, the Pacific plate and the Eurasian plate,resulting in the complex geological structure and diversity. According to Pan Guitang et al.(2009) the tectonic facies, tectonic unit division of the China, the area is in the southwestern edge of the Yangtze block area, west of Sanjiang arc basin system, across the Kangdian basement uplift zone and the Yanyuan-Lijiang continental margin rift basin. Since late Archean experienced complex geological evolution process, is a strong tectonic magmaticactivity area. Geological survey area are unique in Sichuan and China, especially the formation and evolution oftectonic basement and Panxi paleorift magmatic sedimentation.In the survey area is mainly Jinning-Chengjiang period and the variscan. Jinning-Chengjiang period mainly include Da Dukou quartz diorite, Da Luxiang quartz diorite,Shui Luxiang quartz diorite, Da Jianshan quartz diorite,Guan Daoshan quartz diorite,Zhang Menzha plagioclase granite,Gan Yu quartz syenite porphyry. The Variscan include Er Tan、San Taipo quartz nepheline syenite rock.In Yanbian of Panzhihua,granitoid rocks are rich, this paper selects the district has representative of several granite,with petrology, major and trace elements and Sr-Nd isotopes, zircon U-Pb chronology method to research.At the same time,to research the rock formation and the formation of tectonic background. The main achievements obtained in the following:From the geochemical characteristics of major elements in the study area granite types can be roughly divided into quartz diorite and plagioclase granite and quartz syenite. Three types of rocks are peraluminous characteristics. The quartz diorite and plagiogranite granite are sub alkaline rock series, with calc alkaline characteristics. The quartz syenite is alkaline rock series. The quartz diorite differentiation index averaged 48.4,of lower degree of differentiation, plagioclase granite and quartz syenite differentiation index average 92.83 and 85.16,of higher degree of differentiation.Performance of quartz diorite Guan Daoshan intrusion syenite in obvious positive Eu anomaly, the REE distribution curve showed right deviation. Remaining Shui Luxiang, Da Dukou, Da Luxiang,Da Jianshan rock REE distribution curve showed to the right deviation,LREE enrichment pattern and a smooth, Eu, Ce values are basically similar. Most of them have not evident or weak negative anomalies that showed homology. Quartz diorite diorite,Shui Luxiang, Da Dukou, Da Luxiang,Da Jianshan rock rare earth microelement overall performance consistent showed homology. Quartz diorite diorite rocks are enriched in large ion prostone elements Rb, Ba, Sr, K etc., lossed high field strength elements such as Nb, Ta, P, incompatible elements such as Hf in rock strongly enriched,except Guan Daoshan.From the LA-ICP-MS zircon U-Pb measured results and collected the age value, can be seen roughly 937.5Ma, 864.3Ma ~ 756.4Ma,211 Ma in the three groups. Rock performance is quartz diorite diorite- plagioclase granite(monzonitic granite)- quartz syenite rock evolution sequence, alkaline to subalkaline series of sequential evolution. The sequence is consistent with neutral- acid- alkaline magmatite evolution.Gan Yu quartz syenite rock is the oldest 937.5Ma, this is one of the important findings of this work, in the alkaline magmatite has not in the Panzhihua region. According to the evolutionary sequence of the magmatite, as a continuation of Green’s magma evolution. From continental rift environment, due to the collision effect of the orogenic phase, The basalt in the group of Huangtian of Qingbaikouan System,was partial melting and formation.864.3 ~ 756.4Ma is the Jinning-Chengjiang period, development of magmatic activity. The period is divided into three sorts of magma, with I type and S type double feature of the Guan Daoshan intrusion, S-shaped Shui Luxiang, Da Dukou, Da Luxiang,Da Jianshan rock. Guan Daoshan intrusion is the formation of the syntectonic lower mantle material Chung, ancient crust become dome. Due to the ancient crust is thin, at the end of the monarch under the action of, mantle material piercing cover layer intrusion, forming a ring integrated rock. It is formed in the mantle and crust source materials together;Shui Luxiang, Da Dukou, Da Luxiang,Da Jianshan rock is Jinning-Chengjing orogeny, the heat generated in the oceanic crust subduction and collision processes the deep crust from the crust partial melting and the formation of granitic magma, and fissures along the shear layer penetration. A piece of A the tie plagiogranite, which formed during 766.7Ma, other than the new age of rock mass. According to the rock mass of the Nb-Y and Rb-Y+Nb diagram, that R1-R2 diagram, Zhang Menzha plagioclase granite is island arc, post orogenic tectonic environment.Late the pre rock mass emplaced in, orogenic extensional environment making deep mantle material along the channel Chung emplacement, in the process of emplacement may makes part of crust derived material melt intrusion.211Ma Er Tan, San Taipo quartz nepheline syenites, Pearce Nb-Y and Rb-Y + Nb diagram, two samples are projected in WPG(intraplate granite type) and its edge. At the late stage of the Variscan orogeny, due to intracontinental rift extensional and Mount Emei basalt Chung in the process of crystallization differentiation because of decompression,so its form of high potassium calc alkaline rock series.