The Study Of Wulanhada Volcanic Petrology And Lava Surface Structure In Inner Mongolia

Wulanhada volcano group was the only found Plateau Quaternary volcanic group in the southern margin of the Mongolian. It was a natural volcanic "museum." Volcanic activity can be divided into both the late Plewastocene and Holocene epoches. Rock types are volcanic clastic rocks and lava, the development of lava clastogenic rocks of this area is one of the important features. Late Plewastocene lava was Alkaline olivine basalt, Holocene was tephrite. The Mg # value of basalt was 0.48-0.57, which was less than 0.6; NiO content was below 0.036%, Petrochemical and geochemical characteristics indicate that the magma was low degree partial melting of enriched mantle, underwent a certain amount of AFC during ascent, it was the evolutional magma. The mantle xenoliths was not found, but it has many granite xenoliths. Basalt tectonic environment was the early stages of rift. This has important implications of the deep activities of the modern Mongolian Plateau southern edge.Wulanhada Quaternary volcanic lava flow has large volume, lava flow types include pahoehoe lava and aa lava. Lava flow surface structure develops, and it includes smooth raft-like structure of large streamline, rope-like structure, tumuli, jet cone, extrusion slag-like ridges and uneven slag-like lava stone sea, etc., these structures reflect the physical property of lava flow, the flow velocity, the boundary conditions, positioning environment and cooling processes. This paper suggest wulanhada lava flows was P-type lava flows; tumuli includes tumuli along the main line, lava flows wetlands tumuli and flow-lobe tumuli. Different lava tumuli with a different genetic mechanism, this paper focuses on the formation causes of flow-lobe tumuli and simulates the formation process of flow-lobe tumuli, the formation of flow-lobe tumuli might have relatively low, uniform and stable in the magma supply rate; It needs lava overpressure 183-458MPa in the formation of Wulanhada flow-lobe tumuli, the surface tensile strength of the lava crust was 0.2-0.3MPa, the elevation difference between the surface of the lava lake (which was the source of the tubes) and the flow-lobe tumuli was 7-12m, magma supply rate was 95-372 m3/h, the appearance of the flow-lobe tumuli marked the end of the scope.