Abstract
AbstractThe Salt Range in Pakistan exposes Precambrian to Pleistocene strata outcropping along the Salt Range Thrust (SRT). To better understand the in‐situ Cambrian and Pliocene tectonic evolution of the Pakistan Subhimalaya, we have conducted low‐temperature thermochronological analysis using apatite (U‐Th‐Sm)/He and fission track dating. We combine cooling ages from different samples located along the thrust front of the SRT into a thermal model that shows two major cooling events associated with rifting and regional erosion in the Late Palaeozoic and SRT activity since the Pliocene. Our results suggest that the SRT maintained a long‐term average shortening rate of ~5–6 mm/yr and a high exhumation rate above the SRT ramp since ~4 Ma.
Highlights
Low-temperature thermochronological data coupled to structural data can provide constraints on the structural evolution and long-term exhumation history of relatively shallow (2–5 km deep) crustal levels
We propose that normal faulting observed in published seismic data formed half graben structures that, in combination with regional erosion, could explain the Late Palaeozoic cooling recorded by our samples and formation of the unconformity in the Salt Range (SR) (Figure 5)
We suggest that clastic foreland strata were mostly eroded as the thrust sheet was translated across the Salt Range thrust (SRT) ramp, TA B L E 4 Thermal model parameters of samples from the Salt Range, Pakistan
Summary
Low-temperature thermochronological data coupled to structural data can provide constraints on the structural evolution and long-term exhumation history of relatively shallow (2–5 km deep) crustal levels. Previous thermochronological and magnetostratigraphic studies of the Subhimalaya have used Neogene foreland strata to examine the Cenozoic deformational history The Palaeozoic to Mesozoic strata exposed in the Salt Range (SR; Figure 1) has the potential to record pre-Cenozoic thermal and cooling events from low-temperature thermochronometers because of limited (~2–5 km) burial beneath Cenozoic foreland sediment. The thermal model and structural reconstructions are used to document the Palaeozoic deformational event and long-term thermotectonic evolution of the Salt Range thrust (SRT). The Pakistan Subhimalaya is defined by the Kohat and Potwar (Figure 1). These are bounded to the north by the Main Boundary. The stratigraphy in the SR is subdivided into three major units: (a) Late Neoproterozoic to Lower Cambrian evaporites, (b) Cambrian to Eocene siliciclastic and carbonate sequences, and (c) Miocene to Pliocene foreland strata derived from erosion of the Himalayan orogen (Gee & Gee, 1989; Figure 2, Supplementary material section 1)
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