Relationship Between 3D Tectonic Frame And Metallogenic District: Theory And Implications In The Three Rivers Region, Yunnan

The shallow crust structure, magma activities and metallogenesis are the effect of deep lithosphere evolution, so ore deposit is closely related to the lithosphere structure of various depth. On the basis of this idea, Using the present advanced processing methods, such as tomography of earthquakes, the gradient modules and multi-scale edge analysis of the gravity and magnetic data, as well as reversal calculation, the shallow, middle and deep tectonic background and geometry shape of the Three Rivers region, eastern Tibet, where are of great potential in finding ore deposit, have been imaged. According to"glass earth"idea, that is, transparent three-dimension structure of the crust, in combination with the analysis of geological, geo-chemical and ore deposit data, the tectonic frame of the research region is divided, and several metallogenesic potential areas are marked. The main achievements are as follows:1. The three-dimension model for the pipe-like low velocity and high velocity cylinders are established, respectively. Through the synthetic analysis of the tomography of earthquakes and the velocity structure from deep seismic sounding profile using explosive source, the tectonic background and geometric shape of the shallow, middle and deep levels are revealed. The cylinders with the low p-wave velocity and high p-wave velocity anomalies existed in the different levels of crust in the Three Rivers region. These low p-wave velocity anomalies spreads all over the mantle lid, but distributes as the limited rings in the middle and lower crust. The rings in the different levels can be linked together up and down. These low p-wave velocity anomalies represent the tracks leaved in the ascending process of mantle magma or melted crust material. They are the results of ascending along pipe-like passageway to different depths in the crust, part of them formed the alkalic and dike rocks on the surface. The passageways of ascending outcropped on the surface and formed volcanogenic hot springs in the Tengchong area. And high p-wave velocity anomalies represent fossils leaved after the ascending mantle magma cooled.2. 13 EW tectonic belts are determined. The present EW tectonic belts are the product of multiple tectonic activities and remolding, and result from the reaction of old EW faults in the middle and lower crust. According to the analysis, 13 EW or nearly EW tectonic belts are determined and marked. The main EW tectonic belts include Weixi-Lijiang tectonic belt which located near 27°north latitude, Lanping-Jianchuan-Pur-Mengla tectonic belt which located near 26.5°north latitude,Yunlong-Eryuan tectonic belt which located near 25.5°north latitude, and Luxi-Yongping-Dali tectonic belt which located near 24.5°north latitude.3.A central axial tectonic belt is proposed. It locates in the Lanping-Simao basin and is a large-scale and complex tectonic belt composed of the narrow uplift belt, fault belt, metamorphic belt, alteration belt and marginal fault belt. It starts at Weixi-Qiaohou fault belt, through Lanping, along Bijiang fault southward, via Guoyunlong, Huanglianpu and Zhujie, detouring Gonglang arc, and goes in Wuliangshan-jinggu-Pur-Mengla fault belt. It extends nearly NS direction and is a snake-like shape. Many fault dislocations existed in this tectonic belt. It is similar to oceanic ridge in shape. It is characteristic of both spreading and strike-slip. The central axial tectonic belt system is nearly upright and dips slightly east in the Lanping basin, and dips west in the Simao basin. This fault belt cuts downward the middle crust, is a large-scale deep fault,and locates in the margin.of uplift Under the central axial tectonic belt, Moho reflects the uplift of mantle. There is difference in the fluctuation of Moho along EW direction. The central axial tectonic belt experienced the multiple tectonic events. It provided the passageway for the ascending of deep material to the surface.4. According to"glass earth"idea, Using the present advanced processing methods, such as tomography of earthquakes, the gradient modules and multi-scale edge analysis of the gravity and magnetic data, in combination with the previous tested and verified geological, geo-chemical and ore deposit data, the transparent three-dimension structure frame in the Three Rivers region is imaged.5. The analysis shows that the EW tectonic belts, particularly intersection locations between the EW tectonic belts and the regionally large-scale fault, are the favorable metallogenesic area. The large Pb-Zn ore deposit in the research region is controlled by the low velocity zone where extends along about NE 30-40°direction.6. The apparent 3-dimension Metallogenic pattern is established in the Three Rivers Metallogenic district. According to the deep structure of lithosphere and the model of pipe-like low and high velocity cylinders, in combination with the analysis of 3-dimension structure of the shallow crust, 9 Metallogenic zones and 13 Metallogenic potential areas are marked. 6 of 13 Metallogenic potential areas are researched and discussed. The exploring research on the Metallogenesis pattern of ore deposit district and deep geological process has been done.