Seismologic and geologic fault-slip data characterize the active deformation of the intramontane Tajik basin and its margins, the Tian Shan, Pamir, and Hindu Kush at the northwestern tip of the India-Asia collision zone. Within this complexly deforming region, the Tajik basin lithosphere forms the backstop for the north-dipping Indian-slab subduction beneath the Hindu Kush but itself delaminates and retreats west and northward beneath the Pamir. Herein, we link crustal deformation to these lithosphere-scale processes, using data from recently deployed seismic networks and geologic observations. Transpressive strike-slip deformation dominates the bounding fault zones along the basin's northern and eastern margins. Seismicity is most intense in the Garm region/Peter I. range of the northeastern basin, where these bounding faults converge and gain a dominant thrust component. Within the basin, seismically and geologically derived P axes align with the~W-trending GPS velocity vectors. Seismicity is concentrated in and at the base of a southward deepening, ∼9-15-km-thick wedge. Seismic deformation at the basin's southern margin occurs beneath the Afghan platform, where deep crustal earthquakes likely trace the western end of the Hindu Kush subduction zone. Roughly NNE-striking sinistral strike-slip events outline the Hindu Kush-Pamir transfer system, a zone of distributed shear in the crust overlying the transition of the two oppositely dipping slabs at subcrustal depths. Our observations suggest that crustal deformation in the Pamir and Hindu Kush links with lithosphere-scale processes, whereas deformation in the basin is controlled by the westward gravitational collapse of the Pamir and the resultant basin inversion.

Surface, 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 tõ 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.

The Tajik basin and southwestern Tian Shan constitute the northwestern tip of the India-Asia