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

Abstract

We use structural and petrologic data from a cross section through the high-pressure‐lowtemperature Maksyutov Complex to develop a new model for its tectonometamorphic 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 tectonometamorphic units. The core of the antiform exposes wellpreserved eclogites and blueschists in the structurally lower unit 1 that underwent 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 S 1 affected by northwestvergent F 2 folds. F 2 fold axes and S 1 /S 2 intersection lineations trend northeast-southwest, oblique to the present north-south trend of the Maksyutov antiform. The D 1 /D 2 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 D 3 shear zone associated with the retrograde metamorphic evolution. The exhumation of unit 1 occurred in Late Devonian‐Early Carboniferous time, during continuous plate convergence that was accommodated by a thrust that 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 D 4 shear zones exhibiting 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.