GEOLOGY AND GEODYNAMIC EVOLUTION OF THE HIGH-P/LOW-T MAKSYUTOV COMPLEX, SOUTHERN URALS, RUSSIA

Abstract

The high-pressure/low-temperature Maksyutov Complex is situated in the southern Urals between the Silurian/Devonian Magnitogorsk island arc and the East European Platform. The elongated N-S-trending complex is made up of two contrasting tectono-metamorphic units. Unit 1 consists of a thick pile of Proterozoic clastic sediments suggested to represent the passive margin of the East European Platform. The overlying unit 2, composed of Paleozoic sediments, volcanic rocks, and a serpentinite melange with rodingites, is interpreted as a remnant of the Uralian Paleo-ocean. Devonian eastward subduction of oceanic crust beneath the Magnitogorsk island arc resulted in an incipient blueschist-facies metamorphism of unit 2 indicated by lawsonite pseudomorphs in the rodingites. While unit 2 was accreted to the upper plate, subduction of the continental passive margin caused the high-pressure metamorphism of unit 1. Buoyancy-driven exhumation of unit 1 into the forearc region led to its juxtaposition with unit 2 along a retrograde top-to-the-ENE shear zone. Further exhumation of the Maksyutov Complex into its present tectonic position was accomplished by later shear zones that were active as normal faults and are exposed along the margins of the complex. At the western margin a top-to-the-west shear zone juxtaposed a low-grade remnant of a Paleozoic accretionary prism (Suvanyak Complex) above the Maksyutov Complex. Along the eastern margin a top-to-the-east shear zone and the brittle Main Uralian Normal Fault emplaced the Maksyutov Complex against the Magnitogorsk island arc in the hanging wall.