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Tectonics of Passive Margin Salt Basins: Crustal Structure of the Gulf of Mexico and South Atlantic during Salt Deposition

Norton, Ian 1; Jackson, Martin 1; Hudec, Michael R.1
1 Univ. Texas, Austin, TX.

New plate reconstructions of the Gulf of Mexico and South Atlantic are used to outline motions of their surrounding major plates during rifting and the transition to ocean crust formation. These plate motions resulted in large amounts of crustal thinning and extension before relative plate motions were accommodated by sea floor spreading. We use plate motions to estimate crustal stretching factors. In the Gulf of Mexico, Yucatan moved over 300 km relative to North America during rifting. Similar magnitudes of synrift horizontal motion are inferred to have occurred in the South Atlantic. These motions must have resulted in formation of large rift basins and extreme crustal thinning, yet basement-involved extensional faulting to accommodate these motions is not seen on seismic data.. It is likely that extension involved large-magnitude low-angle faults and may also have resulted in mantle exhumation. Little is known about present-day crustal structure beneath the thick sediment wedge in the northern GOM. We can, however, infer crustal structure by analogy to the Angola margin, where there is some seismic refraction and deep seismic reflection data that allows for modeling of crustal structure. We use plate motions to estimate crustal stretching factors and hence crustal structure at the end of rifting for both these areas. Sedimentation during the final rifting phase, before initiation of sea floor spreading, consisted of thick salt sections. In both basins salt deposition ceased at the onset of sea floor spreading. The basin in which the salt was deposited was partly floored by extremely thin continental crust or, if mantle exhumation did take place, salt was deposited directly on exposed continental mantle.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009