3-D Visualization and Isochore Analysis of Extensional Diapirs Overprinted by Compression

Abstract

Palinspastic restorations elucidate geologic and hydrocarbon-migration histories in salt provinces; however, salt dissolution and salt flow in and out of the section plane make it difficult to determine the shape of salt bodies before deformation, which hampers accurate restorations. Three-dimensional computer visualization of a physical model and analysis of isochores provide clues to the original shape of allochthonous salt bodies that were emplaced during extension and later compressed.Initially, tabular salt (simulated by viscous silicone) was regionally extended as synkinematic sediments accumulated. Extension triggered the rise of reactive salt walls that subsequently were shortened coaxially. Contraction produced curvilinear faulted folds, pop-ups, detachment anticlines, and pinched-off salt walls. Salt was squeezed to higher levels through fault-bounded vents in the roof. Three generations of stacked salt sheets were extruded and later acted as structural detachments.Isochore plots in the overburden show how patterns of sedimentation, deformation, and underlying salt changed through time. Isochores of prekinematic strata recorded only strain, with thinned belts recording early extension and paired, thickened belts recording late shortening. In con-1095 trast, isochores of synkinematic strata recorded mostly deposition on exposed structures, with thicks recording salt expulsion, block grounding, and roof collapse and thins recording diapir rejuvenation. Synkinematic isochores also recorded the former shape of subsequently shortened allochthonous salt, showing palinspastically how the weaker salt absorbed much more shortening than the stronger sediments encasing it. Isochore analysis thus improves two-dimensional and three-dimensional restorations of salt tectonics.