HR: 0830h
AN: T51F-0219    [PDF]
TI: A Mechanism for Alborz Support and Caspian Subsidence:an Elasto-visco-plastic Model for the Last 10 Ma of Strain Accumulation in Northern Iran
AU: * Guest, B
EM: bguest@ess.ucla.edu
AF: University of California Los Angeles, 595 Young Dr. E., Los Angeles, CA 90095 United States
AU: Guest, A S
EM: alice.slancova@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Grove Oak Dr., Pasadena, CA 91109 United States
AU: Axen, G J
EM: gaxen@ess.ucla.edu
AF: University of California Los Angeles, 595 Young Dr. E., Los Angeles, CA 90095 United States
AB: The Alborz Mountains of northern Iran are a region of 4 km topography adjacent to the south Caspian basin, one of the thickest accumulations of sediment on earth ($\sim$20-25 km of Jurassic and younger sediment). The upper 10 km of south Caspian sediment and the 4 km of Alborz topography accumulated during the last 6 Ma, accounting for 15 km of the $\sim$25 km structural relief that is observed in this region. The mechanism by which this structural relief is accumulated, the nature of south Caspian basement and mechanism by which the isostatically overcompensated (rootless) Alborz can be supported are currently being debated in the earth science community. Two dimensional, elasto-visco-plastic, finite element modeling provides insight into the types of strain distributions that result when an 8 km thick oceanic slab overlain by 10 km of sediment, and an adjacent low lying continental region are subjected to 10% shortening. This configuration mimics the cross-sectional structure of the south Caspian and northern Iran just prior to $\sim$10 Ma. The modeling shows that geometry plays an important role in the strain accumulation: The strong upper crust of Alborz mountains and strong 10 km deep oceanic crust of the south Caspian partially maintain the stresses due to shortening and deform chiefly by crustal scale flexure. On the contrary, the weak hot lower crust of Alborz and weak 10 km thick south Caspian sediments relax much of the stress and accumulate shortening due to the presumably low Young modulus and high Poisson ratio in these layers. This "chessboard geometry" causes the Alborz upper crust to buckle upwards and the Caspian oceanic crust to buckle downwards. The model yields results that are consistent with first and second order observations from the Alborz region implying that the Alborz may have developed by upper crustal buckling over hot, buoyant lower crust and lithosphere which compensates for the lack of a crustal root. Rapid South Caspian subsidence is due to the combination of thermal subsidence and downward buckling of the oceanic slab.
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2003 Fall Meeting