Research On The Petrographic Characterristics And Provenance From The Uppe Triassic To The Lower Jusrassic Of Shiwandashan Basic In Guangxi

Shiwandashan basin was a continental basin in the Mesozic and Cenozoic after late Triassic Indosinian period. Compared with other regions, Shiwandashan basic research was relatively weak, the relative lack of basic geological information. In recent years, mainly concentrated in the structural geology, sedimentary geology and magmatic activity. The thesis as the Shiwandashan basic was research object, according to the actual field exploration and indoor analysis, by using the theories and methods of sedimentary, petrology, geochemistry, sedimentary basic analysis, trypical clastic rock microscopic characteristics were identified, summed up clastic rocks had 6 categories and 20 types of macroscopic types and 2 categories and 5 types of macro combination type.The comprehensive analysis from the petrology, sedimentology and geochemistry for the Shiwandashan basic clastic rocks provenance from upper Trsssic to lower Jurassic.Quartz grain type was more abundant, cutting type combination for shallow metamorphic rock debris and fine-grained sedimentary rocks fragments, Dickinson diagram shows that the provenance was recycled orogen properties. Geochemical characteristics revealed the contect and characteristics of the trace elements and rare earth elements value were consistent in the Shiwandashan basic from upper Trissic to lower Jurassic, and each section、the age of mudstone samples of REE distribution curve models was consistent, the basin clastic material source is consistent, all come from the southeast side, the provenance area is near the deposition distance, and the chemical composition of the source rocks dominated by sedimentary rocks, may contain or small with granitic rocks supply.And the related parameters and the discrimination diagrams show fulongao formation provenance tectonic background of the passive continental magin and active continential margin,and the lower Jurassic tectonic background of the overall nature of the source region of the active continental margin.Combined with the tectonic evolution history, thought in the late collisional foreland basin stage(T3-K), the qinfang orogenic belt again revival orogeny, provided the source material for the northwest side of Shiwandashan basic. From Devonian to early Permian in the qinfang trough area deposition of large sets of complex of Shi Jianzao, in which case the continuous deposition trough in Late.Paleozoic in the qinfang trough area, and mainly for qin zhou formation(D1q), xiao dong formation(D1-2xd), shi jia formation(D3C1sj) and ban cheng formation(C1P1b) the development of city group in a lot of grey chert, siliceous shale, mudstone. In the end of middle Triassic, due to the subduction and collision of the circum pacific plate, caused the qinfang orogenic revived orogenic, generating a plurality of deep faults occur, occurrence of thrust nappe, Due to the regional metamorphism of clastic rocks in trough in the desposition, including the formation of the phyllite slate and schist-shallow metamorphic rocks, late in the deep faults of transpressional stress, some occurrenced dynamic metamorphism, and many of the deep fracture due to thrusting compressional stress eefect, the crustal remelting, the formation of crust derived granite, becoming the Shiwandashan basic the secondary source of clastic rock from the upper Triassic to lower Jurassic. The evolution process of parent rocks, temperatures and depth of influence less, tectonic action was the important factors resulting in the evolution of the paraent rock.The set of strata from Shiwandashan basic was controlled by the tectonic rhythm from the upper Triassic to the lower Jurassic in Guangxi, The trust and nappe tectonic movement rhthm control of classic detrial content. The conglomerate composition and detrial composition of sandstones in the various parameters indicating indicated the study area the parent rocks of orogenic tectonic activity is stronger in the second、third and the fourth part of fulongao formation. Source area weathering and denudation occurred in front of rapid accumulation basic casued help the sandstone of the third and fourth part of fulongao formation with low maturity, and with reduced orogenic movement, the maturity of sandstones increased relatively from the Wangmen formation and Baixing formation, shows the orogeny after filled in despositon prpcess. And geochemical characteristic reveal also revealed provenance tectonic background characteristics of clastic rock of Shiwandashan basic from the late Triassic was in a stage of transformation of tectonic activity, but the tectonic activity of the clastic provenance was relatively stable in the early Jurassic.