LATE QUATERNARY FAULTING AND ENVIRONMENTAL CHANGE IN IRAN INFERRED FROM DATING OF ALLUVIAL FANS, RIVER TERRACES, AND LAKEBEDS

The eastern boundary of the Arabia-Eurasia collision coincides roughly with the eastern border of Iran. North-south right-lateral shear across eastern Iran is distributed across multiple parallel strike-slip faults, and associated thrusts, many of which have a documented history of generating destructive earthquakes. We describe the results of several dating studies, distributed around eastern Iran, in which alluvial fan, river terrace, and lakebed deposits are used to determine the rate of slip on several of the major faults in the region.

An important general result is that the most recent period of alluvial deposition is at 10 +/- 3 ka with subsequent incision and terrace development occurring within the early Holocene. The similarity of results at the few reliably dated locations suggests that the landscape evolution responds to a regional climatic signal. Dry lakebed deposits at Dasht-e-Bayaz in NE Iran and Golbaf in SE Iran provide ages in the early Holocene, coincident with the onset of fan incision and river terrace development, and suggesting a much wetter climate at that time relative to the present. The inferred Holocene climatic changes in eastern Iran may relate to variations in monsoonal intensity (as seen in climate records from Oman and Yemen). Regional correlation of fan abandonment opens the possibility for rapid and cheap determinations of many fault slip-rates averaged over ~10 ka. The potential for being able to produce such rapid slip-rate measurements across wide regions opens up very exciting possibilities in the ability to measure how strain is distributed across wide zones of continental deformation.