Diapiric and tectonic geomorphology of the river-damming Jahani salt extrusion associated with the strike-slip Kareh Bas Fault, including DInSAR displacement data (Zagros Mountains, Iran)

Abstract

The Fars Arc of the Zagros Fold-and-Thrust Belt hosts the most remarkable examples of salt extrusions worldwide, within a context of rapid collision-related deformation and high seismic activity. Hormuz salt extrusions in the western Fars Arc form rows associated with >200 km long dextral strike-slip faults, which constitute major seismic sources. This work is focused on the Jahani salt fountain and the associated Kareh Bas Fault. The Kareh Bas Fault is interpreted as a supra-salt tear fault controlled by thickness variations in the Hormuz salt detachment and associated rows of precursor diapirs. The precursor Jahani diapir likely induced the segmentation of the S-propagating Kareh Bas Fault, generating a releasing stepover that facilitated salt emergence. OSL dating of +40 m terrace deposits of the Shur River deformed by the Kareh Bas Fault reveals that the fault sourced two paleoearthquakes before and around 14.7–13.8 ka, and indicates a long-term fluvial incision rates of 2.7–2.9 mm/yr. The emerged Jahani diapir (68 km2, 918 m in local relief) is a salt fountain comprising a protruding summit dome and laterally spreading salt glaciers (i.e., namakiers). The northern namakier has been trimmed by the Shur River, generating an exceptional salt escarpment 6 km long and >400 m high. Masses of disconnected Hormuz rocks on the opposite margin of the valley and paleolake deposits found upstream and dated by OSL at 28 ± 5 ka, indicate that the Shur River has experienced multiple damming episodes, likely during dry periods. This work documents for the first time the damming of a major drainage by a salt glacier and the creation of a lake. DInSAR data reveal an overall progressive displacement pattern in the Jahani salt fountain characterised by a rising summit dome (1–2 cm/yr) and laterally spreading namakiers with distally decreasing horizontal displacement rates (1–2 cm/yr) and some uplift in the frontal sectors. This general pattern is altered in the northern sector, where the debuttressed salt extrusion rapidly flows towards the deeply entrenched Shur valley at horizontal and vertical rates of around 10–15 cm/yr. The presented displacement data invalidate a previous work, that based on inadequate theodolite displacement measurements of the order of m/yr, suggested that the is one of the most vigorously rising salt extrusions on Earth.