Abstract
Relevance of the work. The Western Siberian megabasin is the main source of oil and gas in Russia. Therefore, the study of geological structure and evolution of the development of sedimentary cover rock complexes and the basement of the region is important for estimating the oil and gas potential of this vast territory. The object of this paperis the mineralogical and petro-geochemical study of volcanites from the pre-Jurassic basement of the Lakyuganskaya area (well no. 101) of the Longyugansk exploration acreage within the territory of the Nadym megadepression of the Western Siberian megabasin. Scope of work. This work can be useful when constructing geological maps of the basement of the northern part of the Western Siberian Plate. Results and conclusions. We have studied and described the mineralogy of strongly altered volcanites from the pre-Jurassic basement of the Lakyugansk area (well no. 101) of the Western Siberian Plate. According to chemical composition, the studied volcanites are classified as moderate and high potassic basalts, andesite-basalts and andesites. The rocks were subjected to significant secondary changes in the mineral composition, such as greenschist metamorphism and propylitization. Only titanomagnetite has been preserved from primary minerals in volcanites; all other minerals were subjected to changes. In general, we have determined the following minerals – albite, clinochlore, titanite, calcite, goethite, titanomagnetite (magnetite, ulvospinel), fluorapatite, and rutile. For the first time, ferroaluminoceladonite (dioctahedral mica) and three relatively rare secondary copper sulfides – spionkopite, yarrowite, and geerite – were identified and described in basalts from the basement of Western Siberia. Sulfide coppery mineralization in the studied basalts was due to overlapped propylization processes. The rocks have features of volcanites of island arcs, as well as evidence of calc-alkali and intraplate basalts. The petrological and geochemical characteristics of the studied volcanites are similar to basalts composing the Koltogorsko-Urengoysky rift of the Western Siberian Plate.
Highlights
A large number of publications have been devoted to the study of basaltoids from the basement of the Western Siberian Plate [1–18, etc.]
It was found that rocks from the basement of the Western Siberian megabasin were subjected to a multistage evolution
Compression replaced sublatitudinal trending with formation of rifts or grabens as a result [3, 8, 15, etc.]. It is assumed [5 et al.] that superplume was present in the Late Permian Triassic within the territory of Western Siberia; it was in the form of basic and acid magmatism
Summary
Is necessary in order to create a database of the structure of this vast region for its further development. Сlinochlore contains an admixture of Cr2O3 from 0.6 to 4.1 wt.%; such a high content of isomorphic impurity of chromium in the mineral would affect its color, which is not observed. Most likely, this is a mechanical admixture of chromium oxide, which is used in polishing thin sections. Fluorapatite up to 5 microns in size in the form of single grains of hexagonal section was found in the rock among chlorite aggregate. 8 V.S. Ponomarev et al Сomposition of volcanites from pre-Jurassic basement of the Western Siberian megabasin (Lakyuganskaya oil exploration area, YNAD)//Известия УГГУ.
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