A model of Palaeozoic obduction and exhumation of high-pressure/low-temperature rocks in the southern Urals

Abstract

A new evolutionary geodynamic model of Devonian continental subduction and exhumation of high-pressure/low-temperature metamorphic rocks in the southern Urals is proposed based on the results of physical modelling, geological and geophysical data, and on the comparison of this belt with other orogens. The model includes the following principal phases. (1) Closure of the western Uralian ocean by eastward intraoceanic subduction associated with the Magnitogorsk volcanic arc. (2) Subduction of the European continental margin, causing failure of the overriding plate in the arc area along a fault dipping eastward under the arc. (3) Subduction into the mantle of the fore-arc block together with the underlying continental crust and sedimentary layer. The sedimentary cover, as well as the crustal and mantle fragments of this block, are scraped off and accreted in front of and under the arc. The continental crust, shielded from the hot mantle by the fore-arc block, subducts to depths of more than 150 km, remaining at a relatively low temperature. The crust then fails at depths of several tens of kilometres. (4) The subducted crustal slice starts to rapidly rise and intrude the interplate zone, scraping and pushing up the sediments and slivers of the oceanic fore-arc block previously dragged down to different depths. (5) Exhumation of the rising high-pressure/low-temperature rocks within the Uraltau dome, separating the subduction accretionary complex from the Magnitogorsk arc. The eastern border of the Uraltau dome coincides with the Main Uralian Fault. This fault represents a complex suture zone which at the stage of deep crustal subduction was associated with a major thrust (subduction) fault, and at the exhumation stage with a major normal fault corresponding to the upper surface of the rising crustal/sedimentary body.