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Durham University

Department of Earth Sciences

Academic Staff

Publication details for Prof Mark Allen

Obaid, Ahmed K. & Allen, Mark B. (2019). Landscape expressions of tectonics in the Zagros fold-and-thrust belt. Tectonophysics 766: 20-30.

Author(s) from Durham

Abstract

This study uses geomorphic indices, including normalized channel steepness index (ksn), integrated relief and hypsometric index (HI), to investigate how landscape responds to tectonic and climatic drivers in the Zagros fold-and-thrust belt, and show how geomorphology can be a sensitive indicator of tectonic processes. There is a broad association of relatively high ksn values (>50 m0.9) with the upper elevation limit for seismogenic thrusting, which occurs regionally at the 1250 m topographic contour. Higher ksn values occur beyond this seismicity cut-off in the Bakhtyari Culmination, but are rare in the Fars region. We measured HI values for 17,380 third order river basins across the Zagros. In many areas the low/high HI transition (0.3) is typically at the elevation limit of seismogenic thrusting. There are two important exceptions. In the Dezful Embayment/Bakhtyari Culmination the low/high HI transition lies at higher elevations than the thrust seismicity cut-off. In the Fars region, the HI transition lies at lower elevations than the seismicity cut-off. We explain these differences by the different climates of the two areas: wetter conditions and vigorous drainage systems in the Dezful/Bakhtyari region retard orogenic plateau growth; drier climate and low power rivers in the Fars region promote plateau growth. Orographic precipitation may itself have a tectonic control; regional basement strength variations have caused intense thrusting and high relief in the Bakhtyari Culmination. Integrated relief of five across-strike Zagros topographic swath profiles is in the range 2.2–2.8 108 m2. We argue that this consistency within ~25% relates to the comparable strain rates across different sectors of the Zagros, regardless of local structural, drainage network or climatic variations.