Late Pleistocene Basaltic Volcanism Of The Lamayinwusu Area,Xilin Hot, Inner Mongolia

A large area of the Cenozoic volcanic rocks distribute along northwest-southeast direction in Xilinguole league, Inner Mongolia, the north of which is connected wi th the one of aliganjia area in the southeast of the Republic of Mongolia. They are the largest intraplate basalts in Asia. Based on the previous research, this article in vestigated the Cenozoic volcanic rocks of the Lamayinwusu area in Xilinhot, Inner Mongolia. As a result, this article has found out the volcanic edifice types, the vole anic facies and the time of volcanic eruption, classified the volcanic eruptive period s, studied the lithogeochemical characteristics and tectonic environment and achieved meaningful results and understanding finally.According to field line survey and section measurement, the Late Pleistocene basalts can be divided into four eruption sub-cycles and each of them can be further divided into more than two different erupting sequences. The main facies of the Cenozoic volcanic rocks are effusion facies, volcanic explosion-collapse facies, eruption-sedimentary facies, surge facies and volcanic conduit facies. A large area of lava plateau, independent cone-shape, shield-shape and Maars volcano are reserved, and 15 volcanic apparatus are classified. Basaltic agglomerate, pumice, volcanic breccia containing volcanic bombs, basaltic tuff breccia, dense block olivine basalt and vesicular olivine basalt are near the crater, lava flow which formed from olivine basaltic lava is far from the crater, the occurrence of which is gentle with partially spherical weathering. Basalts have olivine, pyroxene and plagioclase xenocrysts and a small amount of granite xenoliths, and phenocrysts mainly have olivine, diopside and plagioclase.Based on geochemical analysis, Ti, Y of basalt was "V" shape, which indicated loss; Ba, Nb, La was the peak shape, whcih indicated enrichment; but part of the samples loss Sr and Hf, others enriched, reflecting strong enrichment of incompatible elements overall. The mean of ΣREE is 214.5×10-6, LREE / HREE is between 2.05-4.56,δEu between 0.94-1.13, abnormal is not obvious, CeN / YbN between 4.99-13.20, belonging to LREE enrichment type. The Cenozoic basalts formed at the edge of the continental plate and the side near the extensional environment within the plate, belonged to the intraplate rift basalts and had a relationship with the mantle plume activity.Optically stimulated luminescence (OSL) age of 116.4±5.6Ka and 123.2±5.5Ka are obtained in the eruption-sedimentary facies, showing that the Cenozoic volcanic rocks erupted in the Late Pleistocene era.