Delaminated lower slab thermal regime before slab break-off in the Pamirs: Implications from 3D kinematic modeling

The intracontinental subduction of a >200-km-long section of the Tajik–Tarim lithosphere beneath the Pamir Mountains is proposed to explain nearly 30 km of shortening in the Tajik fold–thrust belt and the Pamir uplift. Seismic imaging revealed that the upper slab was scraped and that the lower slab had subducted to a depth of >150 km. These features constitute the tectonic complexity of the Pamirs, as well as the thermal subduction mechanism involved, which remains poorly understood. Hence, in this study, high-resolution three-dimensional (3D) kinematic modeling is applied to investigate the thermal structure and geometry of the subducting slab beneath the Pamirs. The modeled slab configuration reveals distinct along-strike variations, with a steeply dipping slab beneath the southern Pamirs, a more gently inclined slab beneath the northern Pamirs, and apparent upper slab termination at shallow depths beneath the Pamirs. The thermal field reveals a cold slab core after delamination, with temperatures ranging from 400 °C to 800 °C, enveloped by a hotter mantle reaching ~1400 °C. The occurrence of intermediate-depth earthquakes aligns primarily with colder slab regions, particularly near the slab tear-off below the southwestern Pamirs, indicating a strong correlation between slab temperature and seismicity. In contrast, the northern Pamirs exhibit reduced seismicity at depth, which is likely associated with thermal weakening and delamination. The central Pamirs show a significant thermal anomaly caused by a concave slab, where the coldest crust does not descend deeply, further suggesting crustal detachment or mechanical failure. The lateral asymmetry in slab temperature possibly explains the mechanism of lateral tearing and differential slab–mantle coupling.