The Provenance Analysis Of Triassic Sandstones And Tectonic Significance In Suolun-Linxi Area

Suolun-Linxi area, located in the middle section of Daxing’anling, is surrounded by three plates(north of Siberian plates, east of the Pacific Plate and south of North China plate) and superposed by two tectonic domain(Paleoasiaoceanic tectonic domain and Paleopacificoceanic tectonic domain). Most previous studies mainly focused on the Late Paleozoic and Mesozoic. Due to the less exposed strata of the Triassic, it has been rarely reported. But the Triassic plays an important role in the tectonic evolution of the northeast China. Therefore, the study of the Triassic strata in the northeastern region has always been a hot topic.In this paper, we mainly focus on the Triassic sandstones in Suolun-Linxi area(i.e. the middle section of Daxing’anling).Through a variety of provenance analysis means(analysis of sand matrix component, detrital zircon LA-ICP-MS U-Pb chronology, etc.), the Triassic sandstone provenance area and its tectonic significance have been studied. Combined with the latest research results,we try to discuss the reasons why large area missed in Triassic. Main points are as follows:1. The Triassic sediments in the study area(Longjiang area, Zhalute area, Alukeerqin area) are mainly feldspathic lithic sandstone. Microscopy of sample showed that the sand composition included quartz(monocrystalline quartzbased),feldspar, a mica minerals, debris(lithic component based mostly volcanics). It Shows that the Triassic sediments features with lower compositional maturity, rapid erosion, fast moving, near source deposition. The characteristics of a large number of volcanic rock cuttings and magmatic-characterised single crystal quartz which reflects that the source area should be dominated by magmatic arc. In addition, Dickinson triangular diagram clearly reflects the studied Triassic samples tend to be transitional arc source.2. Sandstone detrital zircons show that the zircons are mostly of magmatic crystallization(long columnar features accompanied by oscillatory zoning), and a small portion was metamorphic or captured zircons(development of thin and narrow edge of hyperplasia and incomplete crystal nucleus structure). Their main age peaks are ~242 Ma,~280 Ma, ~310 Ma, ~450 Ma and ~500 Ma. The ~242 Ma peak age is consistent with the age of widely distributed volcanic rocks in this area(Shuang Jingzi rock,, Halatu rock); ~310Ma age peak is consistent with magmatic arc Baolidao era; 450~500Ma peak age is equivalent to the ages of the early Paleozoic Sunit magmatic arc and Erguna massif on the post orogenic granites. In addition, Triassic sandstone detrital zircon has retained the 1800 Ma and 2500 Ma captured zircons, which is the typical ages of the North China Plate, indicating that during the deposition of the Triassic sediment the the northern margin of the North China had been connected to the united micro-continent in the NE China.3. Through field investigation, we found the early Cretaceous strata directly cover on the top of the Late Permian strata with an unconformity. Combined with the latest Triac cover in the NE China. The present scattered Triassic strata was caused by the tectonic uplifting and erosion related to the Yanshanian tectonic movement in the study area.