The Northern Section Of Helan Mountain Mesozoic Magmatic Hydrothermal Activies And Its Oil And Gas Significance

Helanshan is located in the northwestern margin of the Ordos basin, the area has experienced many tectonic evolutions from Meso-Cenozoic to Mesoproterozoic. And Mesozoic was the key period for the formation and evolution of the Helanshan tectonic belt and the large basin in the Ordos Basin. At present, Indosinian movement, Yanshan movement exists widely of the Ordos Basin, for the large lacustrine basin formation, high-quality hydrocarbon source rock evolution and oil and gas migration, aggregation produced an important influence.But the magmatie-hydrothermal activity related to the Mesozoic tectonic activity did not appear to be strong, and there are only sporadic distribution in the basin margin, which has not been paid much more attention. And Mesozoic strata in northern Helanshan is widespread, the strata was including the residual Mesozoic basalt and a large number of dikes, which is an important area to explore the magmatic hydrothermal activity of Mesozoic, it’s important theoretical significance to reveal the Mesozoic tectonic environment. In addition, there arce hydrocarbon source rock and coal seam of Mesozoic in Helanshan, magma-hydrothermal activity were discussed which is a reference for the exploration of oil and gas in the area.In the paper, the basalt and quartz vein, calcite vein and epidote veins of Mesozoic are discussed based on the basis of detailed field profile observation and sampling, combined with rock section identification, geochemistry, wrapped body temperature, zircon LA-ICP-MS U-Pb dataing, Ro values test, on behalf of the Helanshan magmatie-hydrothermal activity characteristics, temporal and spatial distribution of oil and gas significance are discussed.According to the field observation data, the development scale, stages, forming period, microscopic feature of widespread veins in Mesozoic strata were researched, pointing out the main types of veins were quartz vein, calcite veins, and a small amount of epidote veins. The distribution direction of veins was mainly NNE, followed directions were NNW and NEE. The combinations of vein are parallel, mesh, echelon, radial, and so on. The vein distribution strata were from Mid-Triassic Zhifang Group to Mid-Jurassic Anding Group. From cross-section, as a old formation to new, development degree of the veins weakened gradually; from plane, development degree of the veins weakened from rujigou Syncline to the two wings; At the same time, the veins development was related to the tectonic position, lithology. The sources of the veins were mainly from magmatic hydrothermal; the veins formation was approximately in the Late Jurassic-Early Cretaceous.Field geological survey and observation show that Helanshan Mesozoic Magmatic activity is mainly reflected in Rujigou Gugutai and Erdaoling area basalts. Wherein the distribution of large basalt bulging station launched a detailed field geological characteristics, geochemistry and zircon LA-ICP-MS dating analysis. Studies suggest that:This is a high iron basalt tholeiitic basalts, dasalt was formed in the plate extensional environment Zircon U-Pb dating of 2 basalt samples, a total of 94 reliable age. Through the age distribution, the age distribution is relatively dispersed, and the ages were three peaks:early proterozoic, middle proterozoic and Mesozoic, the peak of Mesozoic (the youngest age) were about 194-234Ma. Zircon grains morphology and cathode luminescence characteristics show that older zircons genetic were complex, these zircons may represent inherited or captured zircon, most young zircon magmatic band with clear, these zircons may magmatic zircons, and represent the Mesozoic magmatic eruption age. According to the formation and the results of previous studies, this paper argues that bulging of basalt formation age of late Triassic to early Jurassic (194Ma-234Ma).Comprehensive regional geological setting and Mesozoic Helanshan magmatic-hydrothermal activity analysis, the paper argues that there are at least two magmatic hydrothermal events in Mesozoic of Helanshan, respectively Late Triassic-Early Jurassic and Late Jurassic-Early Cretaceous.The Mesozoic Magmatic activities in the Helan mountains have a certain performance. Through the analysis of the Helan Mountain Paleozoic-Mesozoic dark mudstone, coal reflectance of vitrinite and coal rank, indicating that the Helan Mountain layer has higher thermal evolution degree. Based on the analysis of hydrocarbon source rock type and organic carbon, it is pointed out that the magmatic hydrothermal activity promoted the hydrocarbon source rock to oil and gas, so the area may have a certain prospect of oil and gas exploration.