Geological And Geochemical Studies On The Regional Magmatism And Mineralization Of Lancangjiang Volcanic And Intrusive Rock Belt Of Yunnan Province

Lancangjiang volcanic-intrusive rock belt lies in the middle southern segment of the western Yunnan province, the middle Lancangjiang River, the western border of the Lanping basin and the Simao basin, whose range includes the narrow and long zone of the stream-valley along the Lancangjiang River form Lanping to Simao of Yunnan province which almost presents the southern-northern direction. The region is complicated in geological structure, magmatism and mineralization conditions, which has the good copper mineralization background. Almost 200 copper-polymetallic ore deposits have been found by now. It is also the important component of the southwestern copper, silver-polymetallic deposits concentration area in China. So it is taken into account by the Ministry of Geology and Mineral Resources of China as the important zone of the mineral resource survey, exploration and developing region.This work for the degree of Doctor of Philosophy was based on the natural geographical conditions of the region and the achievements in scientific research of the former. The field work's method was making the importance clearly and concentrating power to breakthrough difficult questions. The reconnaissance of the field regional geological line and spots as well as the observation and researching of the mineral deposits were carefully carried through. The regional igneous rocks were carefully sampled. And four representative mineral deposits were chosen for emphatic researching, which are Kedengjian, Jinman, Shuixie and Songjiapo. A lot of magmatic rocks and ores specimens were systematically picked up, and the suitable geological samples were chosen for relevant test and analysis. Based on these above, combining the scientific productions for synthetic-theoretical analysis and probing of the former people, the major outcomes and innovational cognitions are as follows:1. In accordance with the lithochemistry and the lithogeochemical studies of the Lancangjiang volcanic-intrusive rock belt of Yunnan province, the regional tectonic-magmatic evolution has carefully discussed in the paper. The author agrees with the standpoints of Zhu Qinwen et al (1991; 1993) and Mo Xuanxue et al (1993; 1998), and mainly considers that the volcanic rocks of the oceanic ridge / oceanic island type and the ophiolites in Changning-Menglian belt and the volcanic-intrusive rocks in the southern Lancangjiang belt (the arc volcanic rock belt in the southern Lancangjiang River and the granite belt in Lincang-Menghai), jointly form the volcanic rocks of oceanic ridge-ophiolite-arc magmatic rock belt distributing in couples. Changning- Menglian belt is the vestiges of the major oceanic basin of the paleo-Tethy, the southern Lancangjiang belt is the product of orogenic movement in intracontinent that the oceanic basin dived to the crust of the east of the basin.2. The middle Triassic volcanic rocks in the volcanic-intrusive rock belt of Lancangjiang River are the acid rocks in majority. The geochemical studies of trace element and the rare earth element indicate the volcanic rocks are similar to island arc volcanic rocks. The research of the stratigraphy and the Sm-Nd isotopic geochronology show that diagenetic age of the volcanic rocks (228±56Ma) and the intrusive epoch of the regional (the western belt) large scale granite batholith (190~240Ma) (Wang Yizhao et al, 2000) are simultaneous roughly. This reflects the Tethyan ocean in the middle Triassic period had closed, the landmass had occurred collision and subduction. At the background of compression in overall, pull-apart in local, the Lancangjiang fault moved again, which made the anatectic magma product, upwelled and erupt along the faulted zone. So the volcanic rocks shouldbe the "post-collision type" island arc volcanic rocks.3. The copper-polymetallic ore deposits are widely distributed in the Lancangjiang volcanic-intrusive rock belt of Yunnan province. Synthetical analysis and constasting of the regional ore deposits geological characteristics and distribution regularities of the belt show that the n...