Subduction- and exhumation-related fabrics in the Paleozoic high-pressure–low-temperature Maksyutov Complex, Antingan area, southern Urals, Russia

This paper uses structural and petrologic data from a cross section through the high-pressure/low-temperature Maksyutov Complex to develop a new model for its tectono-metamorphic evolution. The Maksyutov Complex is located within the Southern Urals, the only Paleozoic orogen that apparently preserved its collisional architecture without overprinting by late-orogenic extensional deformation. The high-pressure complex constitutes a large antiform in the footwall of the east-dipping Main Uralian fault and is composed of two tectono-metamorphic units. The core of the antiform exposes well-preserved eclogites and blueschists in the structurally lower Unit 1 which experienced peak metamorphic conditions of ~17 kbar and ~570 °C. In contrast, the structurally overlying Unit 2 contains lawsonite-bearing assemblages indicating both lower peak pressure (< 8 kbar) and temperature (< 450 °C). Both units exhibit a composite foliation S1 affected by northwest-vergent F2 folds. F2 fold axes and S1/S2 intersection lineations trend northeast-southwest, oblique to the present north-south trend of the Maksyutov antiform. The D1/D2 fabrics record a progressive northwest-directed shearing under prograde metamorphic conditions and are interpreted as the result of eastward subduction beneath the Irendyk island arc during oblique northwest-southeast directed plate convergence at 370-380 Ma. After their subduction to different depths, the structurally lower Unit 1 was tectonically juxtaposed against the upper Unit 2 by a ductile, top-to-the-northeast extensional D3 shear zone associated with the retrograde metamorphic evolution. The exhumation of Unit 1 occurred in the Late Devonian/Early Carboniferous during continous plate convergence that was accomodated by a thrust which imbricates the basement of the East European Platform and is situated below the high-pressure rocks. Further exhumation of the Maksyutov Complex to a shallow crustal level was accomplished by ductile D4 shear zones with east-west trending stretching lineations present at the margins of the complex. Large-scale folding of the Maksyutov antiform and minor top-to-the-east backthrusting on the western limb took place during a late stage of the Uralian orogeny, coeval with formation of the foreland thrust-and-fold-belt in Permian time.