STRUCTURE OF THE HANGING WALL OF THE MAIN URAL FAULT (SOUTHERN URALS): IMPLICATIONS FROM GRAVITY DATA

Abstract

The Urals orogen includes a paleocontinental and a paleo-island arc segments. The paleo-island arc segment of the eastern Urals consists of two major island-arc terrains of different ages: the Tagil terrain in the northern and central Urals and the Magnitogorsk terrain in the southern Urals. The two terrains produce a strong gravity anomaly in their western part known as the Main Ural gravity supermaximum. The axis of the anomaly is delineated by mafic-ultramafic complexes of the Pt-bearing belt within the Tagil terrain, but no such complexes are exposed in the southern terrain. Two-dimensional Bouguer gravity inversion for the region of the gravity step and the supermaximum along seven profiles across the Irendyk zone in the western Magnitogorsk terrain indicates gabbro complexes similar to those in the Pt-bearing belt buried beneath basaltic andesites of the Irendyk island arc at a depth of several kilometers. Inversion was carried out proceeding from the known geometry of the gravity-producing bodies in the Pt-bearing belt, and the results were interpreted taking into account gravity and geological evidence in view of tectonic similarity of the Tagil and Magnitogorsk terrains. The ultramafic complexes in the Magnitogorsk terrain may have remained buried because of a lower-angle dip and shallower erosion of the Irendyk island arc.