The Regional Sedimentary Response To The Translation Of Datong Volcanic Activity

During the quaternary period, the strong uplitf of the Tibetan Plateau caused astaged evolution of Shanshan graben system. Under the impacts of tectonic movement,there were violent volcanic activities in the Datong Basin which located at thenorthern end of Shanshan graben system. Volcanic activities are periodic which meansthat volcanic activities are divided into active period and quiet period. Volcaniceruptions will produce a large number of lapilli, cinder, ash and lava. These volcaniceruptions interspersed among the lfuvio-lacustrine strata and loess-paleosol strata. Thedetrital size and the sedimentary thickness of the volcanic eruption falling sedimentsare decreasing regularly as the sediments away from the volcanic crater. Volcanicashes settling in the lakes or loess layer which are at the farther from volcanic craterpresent multilayer distributed phenomenon. In the section or horizon which containrich volcanic ashes, the physio-chemical characteristic parameters are abnormal, suchas the increase of magnetic susceptibility value, the growth and the granularitycoarsening of Fe, Ti, Mn and other metal elements.From comparing the lake depositions which have various distances from thecrater and physio-chemical characteristic parameters of the loess deposit，this articleunderstands the response of the lake deposition and loess deposition to Datongvolcanic activities. Through the analysis of variation characteristics of lake sedimentsrhythmic layering, this thesis proves the coupling between changes in regionallacustrine transgressive and regression, and Datong volcanic activities. Therefore, it reveals the staged history of volcanic activities in the Datong Basin during thequaternary period and also verifies the validity of the corresponding mode betweenregional volcano active-quiet period and the ancient lake large lacustrine regressionstage-small lacustrine transgressive stage. During the ifeld research, the researcherscollects the samples of Jinshan loess deposition proifle，Chenzhuang lacustrinedeposition profile, Xiao Jiayao volcanic cone section from the inside of Datongvolcanic activity zone and Chicun loess deposition profile, Gao Zhenzi lacustrinedeposition proifle from the outside of Datong volcanic activity zone. Atfer takingsamples back into laboratory and conducting data analysis，we come to the followingmain conclusions.(1)Atfer the eruption of Datong volcano, there are related ash deposit recordsin the loess deposition near the volcanic cone region. Atfer comparing thephysio-chemical characteristic parameters of Chicun loess deposition profile withJinshan loess deposition proifle，the results indicate that there are ash deposition in thedepth of555cm from Jinshan loess deposition profile.(2)The granularity of lake deposition becomes ifne gradually from the shoreto the middle of the lake. When volcanic ashes fall into the surrounding lakedeposition, the granularity of sediment becomes coarser. From comparing thephysio-chemical characteristic parameters of Gao Zhenzi lake deposition proifle withChenzhuang lake deposition proifle, the outcomes prove that Datong volcano is activein the depth of65cm from Chenzhuang lake deposition profile.(3)From the analysis of Xiao Jiayao pyroclastic sediments，it is concluded thatthere are four times active period in the Xiao Jiaoyao volcano. Every time atfer thevolcanic activity, lacustrine sediment granularity is changed by the process of coarse-ifne-coarse.during the volcanic activities of Datong, The earth’s mantle on the basinupwarps intensely, Magma upwells, and volcano erupts. Also, Lake deposition andlake sediments rhythmic layering exist, when lake deposits and the upwelling magmaon The earth’s mantle on the basin cool and shrink gradually, Lake deposition and lakesediments rhythmic layering exist, it veriifes verifies the validity of the correspondingmode between regional volcano active-quiet period and the ancient lake large lacustrine regression stage-small lacustrine transgressive stage, that is to say, In theupper mantle strong arch stage lead to "active" datong volcanic eruption, which isconsistent with the ancient lake lake quick back stage sharply, slightly slow and quietperiod and ancient lake lake assault phase is consistent.