11/2/2016 - Flexural bending of the Zagros Foreland basin


12:00 PM - 12:50 PM
Geology 1707

Presented By:
Mortaza Pirouz - Caltech


Flexural bending of the Zagros Foreland basin

Flexural deflection of the Arabian plate is modeled using point load distribution and convolution technique. The results are compared to the constrained flexural depression of the Zagros foreland obtained from subsurface data from Iran, Iraq and Syria for the entire northern edge of the Arabian plate. The Oligo-Miocene Asmari Formation, and its equivalents in Iraq and Syria are used to estimate Arabia-Eurasia post-collisional subsidence. This extensive rigid carbonate platform limestone separates passive margin sediments from the younger foreland deposits. In order to obtain geometry of the Asmari limestone in the Zagros foreland, we compiled a large database of well logs, seismic profiles and structural sections to track Asmari depth beneath the Mesopotamian basin and the Persian Gulf. Our results show that the foreland depth is not constant along strike of the Zagros wedge and varies between 1 and 6 km. The deepest part of the foreland is located beneath the Dezful embayment in Iran and becomes shallower towards both ends. The resulting geometry is clearly consistent with the interpretation of the basin as a simple flexural foreland loaded by the Zagros orogenic wedge. In this study, we investigate how the geometry of the foreland relates to loading by the range topography focusing on the eastern sector. We then show the observed geometry and gravity data over the foreland and range topography can be well reproduced with a simple flexural model which only assumes loading due to sediments, topography and crustal thickening. The equivalent elastic thickness of the flexed Arabian lithosphere is estimated to be 52km, and decreases beneath the range. We find no evidence for any other main source of loading of the lithosphere, either related to the density variations or dynamic origin. The model also implies about 120 km of mean crustal shortening across the entire Zagros, which represents shortening in both the basement as well as the sedimentary cover. Furthermore, predicted Free-Air anomaly using our Moho depth model shows much better agreement with the observed Free-Air anomaly than the Free-Air anomaly derived from other published seismic Moho depths.

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