关于滇西地质的一些新认识

SOME NEW RESEARCH ON THE GEOLOGICAL CHARACTERISTICS IN THE WESTERN YUNNAN

本文依据对云南西部保山、腾冲地区晚古生代丁家寨组、勐洪群含砾地层的研究,认为含砾地层属冰川成因,时限为中、晚石炭世的Baskirian期—Kasimovian期。其层位与西藏珠穆朗玛峰、阿里、拉萨地区及印度次大陆、泰国西部和马来西亚西部的冰成岩系均可对比。根据云南西部及邻区深部地质构造及澜沧江断裂的资料,论述了澜沧江断裂是一条超壳深的压性、压扭性深断裂,是冈瓦纳板块与扬子板块的结合带。结合带以西属于冈瓦纳大陆,以东均属扬子大陆。两大板块的最终敛合时间可能在古新世末期。

The stratigraphy of Gondwana facies with glacial marine sediments and the cold water fauna of Lytvolasma and Stepanoviella are widely distributed and well developed in Middle and Late Carboniferous in Baoshan and Tengchong areas of the western Yunnan. The Dingjiazhai Formation and Menghong Group is represented by glacio-marine sedi- ments. Its lower part is littoral diamictite, some of which show striations on gravel sur- faces. the middle part is marked by glacio-marine sediments, containing the cold water fau- na of Stepanoviella. and the glacial gravels show strlations, pits and compressive fractures on their surfaces. The upper part yields fusulinids such as Triticites and the cold water fau- na of Lytvolasma , which are of Late Carboniferous age. The glacio--marine sediments with the cold water fauna of Stepanoviella and Lytvolas- ma are also well developed in Pakistan, India, Tibet of China, Thailand, Malaysia and Aus- tralia. From a plate tectonic perspective, the Baoshan and Tengchong areas should belong to Gondwana land.