Characteristics Of Sedimentary Rocks In Southern Tibet

The area of study includes from the south to the Jiali fault to the national boundary,the east to Coqin,and the west to the great turn of YarlungZangbo River.The main body of geotectonic position crosses the Gangdise stratum region,the suture zone of YarlungZangboRiver,and the Himalayan block.The research crosses two large stratum regions,including Yunnan-Tibet stratum region and Indian sub-stratum region,but mainly focuses on the Yunnan-Tibet region.This paper analyzes the combined types about sedimentary rocks involved in the Paleozoic,Mesozoic and Cenozoic erathom,summarizes combined characteristics about sedimentary rocks,and then discusses the related questions about the uplifting of the Qinghai-Tibet Plateau and the collision between India and Tibet.At last,the author gets the following results.(1)There are 24 kinds of sedimentary rock associations in the study area,including 5 kinds of rock associations of continental face,2 kinds of rock associations of sea-continent interaction face,8 kinds of rock associations of shallow-sea face,3 kinds of rock associations of platform face,2 kinds of rock associations of semi-deep sea face,and 4 kinds of rock associations of deep sea face.(2)In the Ordovician-Silurian,Gangdise belt and Himalayan belt all developed clastic–carbonate rock association of platform and continent,which was not very thick.In the middle,Qudegong metamorphic rock group and Mabuku metamorphic rock group were developed,whose original rock were the giant sandy slate of semi-deep sea.The all showed that there may exist deep-water shelf or continental slope environment in the northern Himalayan belt and the south of Gangdise,and the eastern part of the YarlungZangbo River might be a deep water basin.(3)In the Devonian-Middle Triassic,Gangdise zone had obvious separated sedimentary belts.In the north of Gangdise belt,there were the clastic-carbonate rock association of shallow sea and platform faces.In the middle of the Gangdise belt,the shallow sea volcanic – carbonate rock association was developed.In the south,sandy slate of semi-deep sea(turbidite-isokinite)association,ophiolite-sand rock association of deep sea and volcano-deposition association of ocean plate were developed.The south of Yajiang belt was clastic-limestone rock association of the shallow sea,platform and basin faces and there was the medium-based volcanic rock association among them,which were of significant sedimentary zoning.The all showed that the Himalaya belt was a passive continental margin.In the Gangdise belt,there appeared volcano arc and forearc basin,which proved that there existed Songduoyang plate in the north of southern Gangdise.(4)In the late Triassic-Cretaceous,there appeared carbonate-clastic rock association of the shallow sea,platform and semi-deep sea in the north of Gangdise belt.There appeared,in the middle,island arc volcanic-clastic rock.There appeared,in the south,carbonate-clastic rock association of shallow sea and platform faces.And in the farther south,there appeared the volcanic-carbonate – clastic rock association.Yajiang belt developed clastic rock of semi-deep sea face,ophiolite-sand rock association of deep sea and volcano-deposition association of ocean plate.In the south of Himalayan belt,there was clastic-carbonate rock association of shallow sea and platform faces,and in the northern part,there was carbonate-clastic rock association of platform,basin and semi-deep sea faces.From the north to south in the study area and according to the sedimentary rock zoning,it can be seen that the Gangdise belt was the active continental margin,the north of Gangdise was the fore-arc basin,the south of the Gangdise was the volcanic arc environment,the middle was the inter-arc basin environment,the farther south was the volcanic arc environment.And the Yajiang belt was the continental slope environment and the ocean plate,and the Himalayan belt was the shelf environment of the passive continental margin.(5)In the Paleocene-the Eocene,The Gangdise belt developed the clastic association of continent and lake faces,the east of Yajiang belt uplifted,the deposition intermitted,and the western part existed clastic rock of the semi-deep sea and deep sea faces.The Himalayan belt was clastic – carbonate rock association of the shallow sea and the platform faces.The India-Asia collision happened during the late Cretaceous-Paleocene,Gangdise belt uplifted,Yajiang belt was the remnant ocean,and Himalayan belt was the forecontinent basin environment.(6)In the Oligocene-Quaternary,the marine environment ended in the study area.The Gangdise belt formed a lot of deposition of continent and lake faces,which were the graben basin environment.And the Himalayan belt formed many submarine fan clastic rock of river and lake faces,which were the forecontinental basin environment.