| Xinlingol area of Inner Mongolia is located in the eastern central Asian OrogenicBelt. Its geotectonic units include the Ergun, Xing’an and Songnen massifs typically.The Upper Paleozoic in the suty area were widely distributed.The lithology is mainlyincluding mudstone, silty mudstone, argillaceous siltstone, metamorphic stiltymudstone,metamorphic argillaceous siltstone, sericite phyllite etc.Affected byHercynian fold systerm views, Dong Shenbao etc(1986),Cheng Yuqi etc(1994)viewpoint considered that study area belongs to the metamorphism of low greenschistfacies.In this paper,we already used D/max-2500X-ray diffraction researched theillite crystallinity, illite(muscovite)type, illite (muscovite) b values,the relative contentof clay minerals in the Upper Paleozoic pelitic rocks.Also discussed the geologicalsignificance of genetic parameters.Using MPV-SP, MPM80microphotometeranalysised Organic matter of vitrinite reflectance,discussed the relasionship betweenvitrinite reflectance and palaeogeothermal.General discussion the diagenetic–verylow-grade metamorphism in the regin of Xinlingol Inner Mongolia.In the study area, Upper Paleozoic pelitic rocks illite crystallinity distributed inthe0.28to0.77, the average value is0.40. Most are found easily in the range of0.31to0.42. However in the range of0.25to0.30or greater than0.42, appears less. Itreflects that the stratum had suffered diagenetic–very low-grade metamorphism.There are three different kinds of illite (muscovite) types existing in the study area. The polytype of illite (muscovite) is featured by1Md,1Md+2M1and2M1types.The popurlar polytype of illite (muscovite) is2M1,represented approximately60%ofthe total. The less are1Md+2M1illite (muscovite) type.1Mdillite (muscovite) typerarely appears.1Mdillite (muscovite) type and1Md+2M1illite (muscovite) type wererepresented approximately30%of the total.Our research demonstrated that clay mineral of argillaceous rock in the UpperPaleozoic,in this area major oppears smectite, illite, chlorite, kaolinite, palm, greenslip layer, illite/smectite mixed layer,chlorite/smectite mixed layer etc. In thedifferent age strata and the intensity of metamorphic belt, the relative contents of clayminerals appears getting changes. Devonian had experienced very low-grademetamorphism. The clay mineral in nearly metamorphic belt mainly composition isillite and chlorite, kaolinite content is relatively less. Carboniferous suffereddiagenetic-very low-grade metamorphism, nearly metamorphic zone of clay mineralis characterized by relatively rich in illite and chlorite.illite average value is74.19%,kaolinite averages5.28%, chlorite averages8.2%. Late diagenetic clay mineralcomposition is characterized with a certain amount of illite/smectite mixed layer.Theaverage value of illite content is63.5%, kaolinite is5.71%, chlorite is5.28%, illite/smectite mixed layer21.4%,rate of illite/smectite mixed layer is16.4%.Carboniferous illite crystallinity have negative correlation with illite,presentingpositive correlation are illite/smectite mixed layer, rate of illite/smectite mixed layer.Clay minerals in Permian anchizone is mainly composed of illite, illite/smectite,chlorite. Clay minerals in the late diagenetic zone mainly consist of illite andchlorite.Permian illite crystallinity have positive correlation with illite, presentingnagetive correlation are illite/smectite mixed layer, rate of illite/smectite mixedlayer.For those illites samples which illite crystallinities are higher than0.42, their illite(muscovite) b is generally a small value, and most of these samples belong to the typeof1Md+2M1or2M1. In contrast, those illites samples which illite crystallinities arelower than0.42, their illite (muscovite) b is usually quite big. And the majority ofthese samples belong to the type of2M1. In other words, there is a relationship between the b dimension of illite (muscovite) and illite crystallinity, and the samerelationship existing between b dimension of illite (muscovite) and the illite(muscovite) polytype.Using the relationgship between palaeogeothermal and vitrinite reflectance canestimate the metamorphic temperature of the Upper Paleozoic pelitic rocks in the area.The Ro value in the study area mainly fluctuates in the range of1.01%~3.67%, theaverage is1.97%. For the Carboniferous samples, Ro value varies in the range of1.22%~1.87%. The average is1.57%. For the Permian samples, the Ro value changesbetween1.01~3.67%and the average is2.10%. Estimated the temperature ofmetamorphism respectively, through adopting the Vitrinite reflectance thermometerthat proposed by Barker and Pawlewicz (1986),Barker and Goldsteinl(1990),Barkerand Pawlewicz(1994),Mullis et al.(2001) and Mullis et al.(2001). Results present thatthe metamorphic temperature of the Upper Paleozoic pelitic rocks in the area isaround180℃~260℃.The average is245℃and the estimated average temperature forthe Carboniferous is194℃. For the Permian, the estimate temperature is216℃.In conclusion, the research of inorganic mineral and vitrinite reflectance in thestudy area shown that the upper palaeozoic mudstone rocks were generally suffered aregion very low-grade metamorphism. However the degree of the metamorphichaven’t reached to a Low greenschist facies. It’s metamorphism belongs to anchizone. |
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