MAZARIEGOS, RUBEN A., The University of Texas-Pan American, Edinburg, TX; NEVILLE L. CARTER, Salt Micromechanics Inc., Crescent City, CA, and JAMES E. RUSSELL, Texas A&M University, College Station, TX

Abstract: Modeling Allochthonous Salt Structures Integrating Microstructural Observations and Laboratory-Derived Salt Rheologies

The evolution of allochthonous salt sheets of different geometries and at different depths were analyzed by means of a 2D finite-volume numerical model. The model incorporated two laboratory-derived rheological laws for rocksalt, a low-stress, dislocation-creep power law (PL) (<strain rate> varies as s^3.4) and a fluid assisted diffusion creep law (FAL) (<strain rate> varies as s/Td³), in which <strain rate> is the strain rate, s is the equivalent stress, T = the absolute temperature, and d = the grain size.

Salt sheets, buried at depths of 1 km and 3.3 km in sediments of 3.0 x l0¹⁷ to 3.0 x 10¹⁹ Pa<dot>s viscosity, subjected to differential loading were modeled for a time evolution of 2 My to 5 My. At the end of the simulation, for the shallow salt sheet, the PL model developed a well defined "depressed salt zone;" by contrast, the FAL model developed two well defined "depression zones" or intra-salt basins and the salt sheet extended a total of 12.4 as compared to 6 km for the PL. For the deeper sheet, deformation is primarily lateral at the two lower sediment viscosities and vertical at m_sed = 3.0 x 10¹⁹ Pa<dot>s.

Using microstructural observations made on rotary sidewall cores from a salt sheet in the Gulf of Mexico, stresses within the salt were estimated using the relation d= 214s^-1.15, where d is the salt subgrain diameter (in mm) and s is the differential stress in megapascals. A stress function was obtained and incorporated into the model to predict the velocity field within the salt sheet. Significantly, a highly localized velocity anomaly was identified on one flank of a highly deformed allochthonous salt structure.

See page 1358 of PDF for this abstract.

AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana