Redefinition Of The Manghuihe Group And Its Tectonic Implications For The Southern Lancangjiang Tectonic Zone In Western Yunnan

The Pu’er Jiangqiao region in southwestern Yunnan is located in the Lancangjiang fault zone edge, which is belong to San Jiang tectonicmagmatic belts of volcanic rock. It is in the colliding region of the southern margin of the Eurasian land mass and Gondwana continental blocks. Besides, it’s important area of research the Paleo-Tethys.I join in the work process of "1:250000four areas survey work of Lancang Country, Menghai County, Mengla County, Jinghong City" and "1:50000six areas survey work of Banpo, Guanfang" project. We make a deep research on the Manghuihe group in Pu’er Jiangqiao region. And according to the lithological assemblage characteristics divided it into two stratigraphic sections:the sedimentary rock and volcanic rock, which are unconformable contact between of the vocanic eruption. The volcanic rock is an important part of the South Lancangjiang volcanic rock belts. And there is an important significance for further study of the Paleo-Tethys tectonic evolution to clarify its geochemical characteristics, formaton age, background and oter issues.The field work measured two sections including Jiangqiao Manghuihe group and Nanpahe Manghuihe group. We collect two volcano rock specimens from two places which are20kilometers far away. Then we use the zircon LA-ICPMS to measure their age. And the result is that196.7±2.3Ma and198.1±3.5Ma Isotopes age, which indicate that the area of the volcano rocks formed in early Jurassic, not in Late Triassic. It fills in the record of volcanic-sedimentary in Jurassic’s geological history.We collect volcano rock specimen to make a research about the geochemical characteristics in Manghuihe group two sections. We make sure that volcano rocks in Manghuihe group is rhyodacite and dacite. We analyses from the rock major elements, REE and trace elements, then come to a conclusion that Manghuihe group volcano rocks formed by after the oceans closed extrusion orogenic in the construction phase, protolith is argillaceous crust partial melting. It is a very low Sr and high-Yb granite, and has the feature of post-orogenic granite or "A2" type granite. And it might be related to the dive lithosphere plate or orogenic belt Yamane delimitation after the close of Changxi-Menglian, which is the product of magmatic activity after collision stage.We make an analysis about the geochemical characteristics in Manghuihe group, as well as the zircon U-Pb Isotopes age. The result is that volcanic rock formed in early Jurassic post-collision extensional tectonic background, which has the same tectonic background of Guanfang Laomao country POG in South Lancangjiang zone. Both geological era, rock chemical composition showed the trend of continuous change; implies both is likely to be the product of two closely along the same tectonic evolution magmatism stage. And it indicates the Indo-Chinese cycle end time.