Research On Origin And Background Of The Silicalite In Permian And Triassic, Zhongdian

Zhongdian is located in the southeast margin of the Qinghai-Tibetan Plateau,thejoint of Eurasian plate and India plate. Combined with tectonic background, thepetrological characteristics and geochemical characteristics, the origin andbackground of the silicalite is researched, which is from Ganzi-Litang suture zone,Zhongdian island arc zone and Yidun back-arc basin.The silicalite of Ganzi-Litang suture zone, mainly exposes in Luoji Formation ofPermian, which is together with pillow basalt.Most samples belong to biogenicsediment silicalite, and a few samples belong to hydrothermal sediment ones. Thebackground of most samples is continental margin, and generally show shallowsedimentary characteristics，which is likely seamount in Ganzi-Litang oceanic basin.The silicalite of Zhongdian island arc zone, generally show Rhythmic beddingwith shale, which reflects the characteristics of deep-water sediment. Some samplesare biological sediment silicalite, and orhers are hydrothermal sediment ones, andmost samples are influenced by hot water, which display that the tectonic activity ofZhongdian island arc zone is active in Triassic. The background of the samples is bothcontinental margin and deep-sea basin. In early Late Triassic, Ganzi-Litang oceanicbasin arrived maximum, and the tectonic activity of study area was relatively stable,as a result, the silicalite showed the feature of deep-water basin. In medium-lateterm of Late Triassic, with the subduction of Ganzi-Litang ocean basin, the silicaliteshowed the feature of hydrothermal sediment, which displayed that the tectonicactivity of study area was active and the source of hot water was extensive during theperiod. The silicalite of deep-water basin may be formed in early Late Triassic, whichwas the sedimentary system of Ganzi-Litang ocean basin.The silicalite of continentalmargin may be formed in medium-late term of Late Triassic, which was the sedimentary system of inter-arc basin.The silicalite of Yidun back-arc basin shows the characteristics of thesedimentary melange bolck. Hagong Formation generally shows the sedimentarycharacteristics of the neritic continental shelf, but the silicalite of melange blockshows the characteristics of the deep-water basin, and it may be why the block ofunderlying strata fell in basin,when Yidun back-arc basin was constantly extensionaltectonic background and edge of the basin continued to collapse.