Anomalous Geomagnetic Field Modeling for Crustal Structure of a Graben in West Siberia

Abstract

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.

Geological Structure and Historical Development of Pre-Jurrasic Basement of West Siberia Oil- and Gas-Bearing Megabasin Karabash Zone

“…We consider that there is no need to reduce to the pole the AMF map (Figure 4) at our latitudes. Besides, it is possible that in the area there are geological bodies at the depth of about 10 km with remanent magnetization opposite to the currect AMF [14].…”