Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 1. Structure, Kinematics, and Salt Tectonics in the Tajik Fold‐and‐Thrust Belt of the Western Foreland of the Pamir

Abstract

AbstractSurface, seismic, and borehole data characterize the Neogene‐Recent Tajik fold‐and‐thrust belt of the Tajik basin. The basin experienced little sub‐detachment basement deformation, acting as a rigid foreland plate during the Pamir orogeny. The Tajik fold‐and‐thrust belt contains variable thin‐skinned structural styles, changing along and across strike as a function of the thickness and facies of Upper Jurassic evaporites, which constitute the basal detachment, and the influence of the surrounding thick‐skinned belts. The southern Tajik fold‐and‐thrust belt shows regularly spaced, salt‐cored, thrusted detachment anticlines that transition northward into imbricated thrust sheets grouped in oppositely verging stacks facing each other across a common footwall syncline. The width of the fold‐and‐thrust belt decreases northeastward accommodated by the Ilyak fault, a lateral ramp developed over a seismically active dextral basement fault. The southeastern Tajik fold‐and‐thrust belt contains massive subaerial salt sheets, formed by squeezing of preexisting salt diapirs. The salt‐tectonic domain originates from a local depocenter within the Late Jurassic Amu Darya‐Tajik evaporitic basin. Serial cross sections, integrating the structural geometries, yielded minimum thin‐skinned shortening oriented at ~90° to the India‐Asia convergence direction, increasing from ~93 km in the south to ~148 km in the center, and dropping to ~22 km in the northeast; total shortening—including the foreland buttress—is ≥170 km. Most of the shortening in the central‐southern Tajik fold‐and‐thrust belt occurred by hinterland‐vergent, high‐displacement back thrusts. The Pamir played a dominant role in the transfer of shortening to the sedimentary infill of the Tajik basin with the Tian Shan acting as a semi‐passive buttress.