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Along Passive Continental Margins Such as Northern Gulf of Mexico, Fluids from Ocean and Mantle May Ascend and Descend from one to Another

Allen Lowrie
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Major normal and growth faults are known to extend from seafloor through to base of sediment wedge, with origins generally occurring along the then shelfbreak/uppermost slope with overall less contemporary tectonics farther landward. Loci of extensional tectonics proceeds basinward as entire sediment mass migrates offshore, also incorporating lesser sediment depocenters due to sealevel oscillations. These wedge-transiting faults appear to often terminate into semi-plastic salt. Unconsolidated clay deposition is dominated by electromagnetics and create breakage zones along which extruded fluids from dewatering can migrate. Thus, seafloor expression of significant faults can range from well-defined fault-breaks to varying concentrations of clays. Granting a continental margin under extension from rifting while deepening into a new ocean basin, normal faults seemingly occur within subsiding crust. Given synchroneity of extension and subsidence in sediments and crust, breakage zones might coincide in both. The upper crust is brittle. Lower crust temperatures and pressure suggest semi-plasticity, with dislocations between separate masses. Between upper and lower crust would be transitional crust, possibly with fluid-injection along brittle breakages. As measured by earthquake seismology, crust maintains constant densities of 3.3 km/sec for oceanic and 2.7 km/sec for continental crust with a transition between them; such density transition mandates the Airy-Pratt controversy is unresolved. Mantle, plastic and heterogeneous, contains convective cells with lateral extents from 10-100 km to basin-spanning within a hierarchy of vertical to horizontal flows. Ocean and mantle fluids could traverse from one to another.

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013