Provenance Study For Triassic Sediments In Shulehe Area And Its Tectonic Significance

Center-south Qilian arc-basin system is a vital tectonic unit in Qin-Qi-Kun orogenic system. The strata of Triassic, which distributes along NWW direction and in the shape of bands, located in the southwest of Shule Basin and in the southeast of Shule South Mountain. To the south of study area is the South Qilian Block, on which several small basins and uplift zones distribute. To the north of study area is BengKun-Zhaermage tectonic melange zone and Central Qilian Block, in which Precambrian system strata develops. In order to acquire more information about tectonic evolution of this area, previous studies mostly focused on tectonic activities of main tectonic belts, characteristics of orogenic belts' basements, splitting of tectonic plates and subduction evolution, seldom on provenance study.This study, based on the Dickinson triangular diagram system and combining previous studies on tectonic and strata division and the newest information from this regional geology survey, conducts point-counting on detrital framework grains statistically on samples from study area and tries to discuss the characteristics of the source areas of the Triassic strata in north edge of the South Qilian Block and analyses the basin-mountain structure and the modes of basin sedimentary.Through the sedimentary faces analysis, this study concludes that in Triassic the study area experienced transgression and recession due to the tectonic impaction. The result of statistic analysis on detrital framework grains of the sandstone samples shows that the nature of major source area might be stable continental block, the percentages of different sorts of lithic fragments show that intrusive rock features the earlier major source area,while metasedimentary rock features the later major source area. Based on the newest knowledge acquired from the regional geology survey, this study infers that the major source area transferred from unique northern source area to both northern and southern source area. The relatively uplift of southern source area might started at the early Triassic.