Tibet In Long County, Lang Jie Group Petrology And Tectonic Environment

Writer place unit —Yunnan Province Geology Survey undertook Xizang Autonomous Region 1 :250,000 Linzhi County Sheet(H46C003003) Longzi County Sheet(H46C004002) , Zhariqu Sheet (H46C004003) regional geologies investigate, the relies on 1 :250,000 region geologies investigate, choosing as: Rock characteristic and the earth structure environment analysises of later Triassic period Langjiexue Group on Xizang Langxian County .Later Triassic period Langjiexue Group distribute Langxian County south shore in the Yaluzangbu river with the south, dividing the Songre Formation Jiangxiong Formation , Zhangcun Formation totally 3 Formation. Songre Formation is carnian period; Jiangxiong Formation and Zhangcun Formation is norian period. Langjiexue Group is a set of deep sea to accumulate the rock, showing an outside fan middle fan inside fan development from Songre Format ion Jiangxiong Formation Zhangcun Formation, reflecting to contracts gradually from the basin that attend early the night closing process. Langjiexue Group rock composition contains the deal with the construction a low and mud high, have the near source to sink to accumulate quickly muddy to accumulate the rock characteristic. Pass to 356 diagraph for prognosticating orderings, Langjiexue Group ancient water current be flowed by N S.Later Triassic period Langjiexue Group volcanic rock to distribute primarily in Zhangcun Formation, the rock type has basalt, andesitebasalt etc., showed the basaltic characteristic inside the plate.Part of microelements and rare earth element of the sandstone has the opposite stability, the combination often element characteristic cans used for the thing source district analysis with sink to accumulate the environment explains, reflecting the thing source district to accumulate the background with the geochemistry characteristic that sink ( Bhatia 1983) .Fall into the active continental margin ( Bhatia 1983, Maynard 1982, Fangguoqingl993,Rose 1986)in often element measure. Fall into slot in Blatt etc. (1972) map. Fall into continental islandarc area mostly in illustration of microelements. The rare earth element characteristic compare( Bhatia, 1983) with the element in sandstone in different structure background, is active continental margin structure environment.Sandstone composition statisticses from Langjiexue Group, adopting method of Dickinson(1983), Valloni etc. ang Mengxianghua (1989)the mineral composition statistics, make the average index number in grain in framework in a sandstone, passing to statistics to 120 sandstones mineral composition, their quartz Q50. 40%, feldspar F13. 01%, lithoclast L16. 21%, mud and gum knot thing 20. 36%. The lithoclast is a sharp angle form. In diagram for Dickinson(1983) Q — F — L, fall into the material source district of recurence to build the mountain zone, in diagram for Valloni etc. (1981) and Mengxianghua(1989) Q —F—L, the most fall into the valley and sink the basin area.To study the Langjiexue Group, rock characteristics , sedimentary environment, sandstone quantitative analysis ( rock chemistry and geochemistry), the sandstone composition statisticses and the geogion background , make Langjiexue Group is a slope — basin, that is a Gangdisi active continental margin sinks .the structure background of the material source district is the recurence to build the mountain zone, and with magma and volcano function, material come from northern Gangdisi .