An intensive magnetic anomaly within the limits of West Siberia Danilov graben-rift indicates magnetic rocks while numerous wells encountered only weakly magnetized Triassic basalts and liparites in the basement covered by thick loose Jurassic and younger sediments. The wells penetrated only the first tens meters of the basement and could not tell us about the liparites structure at depth where supposedly they may form a big single body and magnetic rocks may be situated deeper. Geological ideas on a graben-rift structure may be proved (or rejected) by a computer modeling of its magnetic properties. For the anomalous geomagnetic field interpretation, a method of volume integral equations taking into account demagnetization effect was employed. To fit a model a trial-and-error procedure was utilized. The results show that 1) at the depth some rocks are magnetized in opposite direction to the present field; 2) highly magnetized rocks (magnetic susceptibility 0.06-0.1SI) coming up continuously from the bottom of the model and situated under the graben; 3) the studied structure is not a graben but the rift because the continental light crust is absent.

An additional comprehensive study of the west Siberia Karabash zone basement has been conducted. Core samples from more than 300 wells that opened the rocks of the basement were analyzed by different methods. A new map of the pre-Jurassic basement of Karabash zone of the west part of the Khanty-Mansi Autonomous Okrug (KhMAO) has been made. For the first time for the West Siberia megabasin U-Pb dating was made for samples from Shaim-Kuznetsovsk meganticlinorium and late to middle Devonian ages were obtained. The Devonian ages was obtained for metamorphic complexes of the region and, in general, for the basement of West Siberia. The complexes considered as Precambrian before that. The obtained results enable significantly to clarify more exact history of pre-Jurassic rock forming for the basement of the west part of West Siberia craton and its structure in the limits of Karabash zone. Thus, obtained data testify that in pre-Jurassic basement of the west part of the West Siberia (Karabash zone), filling grabens basalt effusion began during Permian time (probably at the end of early Permian) at sublatitudinal compression, that is, at collision, possibly immediately after or subsynchronously with the origin of the granite. On the edge of Permian and Triassic (or in early Triassic), sublatitudinal compression changed into stretching, and submeridional grabens came to existence and basalt effusion came up to the maximum.

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