DInSAR kinematics and long-term dynamics of Mesijune salt fountain in the Zagros Mountains. Terrestrial analogue for the development of supra-namakier and marginal namakier-dammed basins

Abstract

The morphologically degraded Mesijune salt extrusion (137 km2, 650 m local relief), with a summit dome and a multidirectional namakier, is the largest salt fountain in the Zagros Mountains. This work analyses the long-term evolution of the salt extrusion, including the development of associated basins, and characterises its current kinematics with decomposed DInSAR data. The salt fountain displays an alluvium-filled supra-namakier basin associated with an encircling autosuture located downstream of an obstacle of upturned bedrock strata (probable flap). This basin atop the namakier expanded downstream as the salt sheet advanced downslope and experienced rotation, resulting in a sedimentary fill with a general offlap arrangement and backtilted structure. In the Late Pleistocene, the advancing namakier front obstructed drainage creating a marginal namakier-dammed basin with lacustrine-palustrine deposits dated by Optically Stimulated Luminiscence (OSL) at 14.3 ± 2.5 ka. Currently, the highest horizontal displacement rates (140 mm/yr) occur in the steep flanks of the summit dome, and progressively decrease to null values towards the stable fronts of the namakiers. The summit dome is dominated by surface lowering at an average rate of -16 mm/yr, suggesting that it could vanish in around 5 kyr, involving the transition of the salt fountain into salt droplet. The comparison of LOS displacement time series with monthly rainfall data from a nearby station indicates steady salt creep unaffected by the rainfall regime. The Mesijune salt fountain may serve as a terrestrial analogue for unravelling the past evolution of salt sheets and associated features from the geological record.