Study On The Volcanic Rocks Of The Baishan Formation In The Carboniferous In The Guaizi Lake Area Of The Inner Mongolia

Guaizi Lake area of the Ejina County in the Inner Mongolia Autonomous Region is located in the northwest of our country,which bengs to the northern region of our country.It is an important metallogenic prospect areas in China. The Basic research of theVolcano rocks has important significance of geological prospecting and geological evolution. The Volcanic Rocks of the Baishan Formation in the Carboniferous are widespread the nourth-center of the guaizi lake area in the Inner Mongolia. Therefore, some basic research on the volcanic rocks of the BaiShan Formation has important sientific meaning for better understanding the early Paleozoic magmatic evolution process of the area. At the same time, it also provides basic geologic information on later Paleozoic volcanic metallogenic background. this paper take the volcanic rocks of Baishan Formation in the Carboniferous exposed in the whole egion as an object of study, by systematically studying the aspects of Petrology,geochemical and so on. we determined the rock association, stratigraphic sequence and its variation. and then discussed the petrogenesis of the volcanic rocks and its tectonic setting. Made the following understanding: 1.The Volcanic Rocks of the Baishan Formation in the Carboniferous in the area are on the top of the volcanic rocks of the Green Mountain Formation in the Carboniferous, the top boundary of which is contact with the gravel beach in the Quaternary. We have not find weathering surface and basal conglomerate on the contact position. 2.The volcanic rocks of the Baishan Formation in the area are overall composed of andesite, dacite, rhyolite and intermediate-acid pyroclastic rock. 3. The volcanic rocks of the Baishan Formation in the area are mainly classified into the calc alkaline series.They are generally enriched in the sodium and potassium,and have high content of alkali metals,and are enriched in the aluminum, and contain a small amount of titanium,They belong to Andean type arc. 4. volcano rock samples’ REE chondrite normalized distribution maps of the Baishan Formation in the area shows the weak right type. The samples show they have the relative concentration of LREE, the relative loss of HREE,and different degree of fractionation of LREE and HREE.The total of REE is moderate.The samples show they have Weak anomalies of negative Eu.The samples may exist in the fractional crystallization of plagioclase in the process of magmatic evolution. Study on trace elements of primitive mantle rocks volcano spider diagram, we can see that the trace element spidergram show obviously right leaning curves, They are generally enriched in the LILE such as Rb,Ba,U,Pb and so on, and relatively depleted in HFSE such as Nb,Ta,Ti and so on.5. The magmatic source of the volcanic rocks of the Baishan Formation is not primitive mantle. The magmatic source maybe the enriched mantle wedge which are reformed through fluids in subduction zones. 6. The volcanic rocks of the Baishan Formation in the area are Andean-type continental margin arc in the tectonic environment,which are formed in the subtractive subduction zone, with characteristics of tectonic environment of the continental margin arc.