Evaluating controls on deformation patterns and styles in the salt-detached Sureste Basin, southern gulf of Mexico: Insights from physical models

Abstract

The Sureste Basin forms the southern portion of the Isthmian Salt Province in the southern Gulf of Mexico. This basin is unique in this region as it is both part of a passive/divergent margin and also part of an active/convergent margin due to its proximity to Pacific margin plate tectonics. As a result it has experienced both orogenic and gravity-driven deformation resulting in a complex array of deformation styles and patterns. Our goal is to understand some of the structural patterns and impact of various driving forces in this basin using a series of regional-scale physical models. In particular the Sureste Basin illustrates five major complexities that we explore using our models.1) Sureste narrows from south to north — models with a trapezoidal shape illustrate heightened complexities on their margins where constrictional strains associated with convergent basin margins form transpressional systems.2) Entire basin has been shortened — unlike typical salt detached gravity-driven deformation where shortening is focused at the downdip margin of the salt basin, a combination of a gravity driven and tectonically induced shortening in our models produces shortening structures spanning the entire basin.3) Sureste is full of diapirs and allochthonous salt bodies — the presence of a major diapir network coupled with gravity-driven and moving-endwall induced shortening rejuvenates diapirs all the way to the distal pinchout, with diapir linkage forming complex, composite, curvilinear fold and thrust structures encompassing the basin.4) Sureste has been affected by non-parallel driving forces — in models where the shortening direction is 45° oblique to the regional dip direction this results in major transpression against the western margin of the basin, and initial transtension on the eastern margin as the salt flows down this regional dip. Structures display an asymmetric curvature in structural grain from east to west due to these non-parallel driving forces. Introducing thicker model salt and a multi-stage history to our model formed major diapir and canopy systems, a variety of thrust welds, roho extension down the regional dipslope, as well as major structural curvature, partly matching gross structural patterns seen in Sureste, and.5) Variable salt isopach in Sureste — in our final model the salt isopach thinned across the basin towards the East. The presence of this variable salt isopach controlled where major canopies and isolated salt bodies formed in the basin with these locations being a close match to those seen in Sureste.