Pleistocene-Holocene deformation and seismic history of the Kalabagh Fault in Pakistan using OSL and post-IR IRSL dating

Abstract

The Kalabagh Fault forms a lateral offset in the Main Frontal Thrust in the Sub-Himalayan area of Pakistan, forming a push-up block within the stepover zone of its segments. Deformed sediments along the frontal part of this push-up block have cross cutting relations with morphotectonic and paleoseismic features. These sediments are dated using luminescence dating methods. The post-infrared infrared stimulated luminescence (post-IR IRSL) of K-feldspar was used for samples representing these sedimentary units. For stratigraphically younger sediments with partially-bleached pIRIR signal, optically stimulated luminescence (OSL) of quartz was applied with the minimum age model (MAM). These ages are used to illustrate the timing of development of the push-up block, the westward diversion of the Indus River and Holocene earthquakes along the Kalabagh Fault (KBF). The deformed sediments from the mountain front at Larkakki are older than those of Khairabad and Ghundi. These age estimates are consistent with the chronological order of the tectonic deformations in the stepover zone of the Kalabagh Fault. Age estimates and correlation of the sedimentary units suggest the emergence of the push-up block in the stepover zone during the past ∼0.5 Ma. Active faulting and development of the ramp along the Kalabagh Fault has diverted the course of the Indus River towards the west at a displacement rate of 12–15 cm/a during last ∼140 ka. Luminescence data indicate Holocene timing for the earthquakes along the Kalabagh Fault, which are diachronous and suggest differential movements along the segments of the fault. The earthquake recurrence interval at Khairabad is 10 ± 2 ka on average. The younger earthquakes at the foreland in the south of the stepover indicate seismically active zone.