3-D visualization and. isochore analysis of extensional diapirs overprinted by compression

Palinspastic restorations elucidate geologic and hydrocarbon-migration hist ories 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 bodi es before deformation, which hampers accurate restorations. Three-dimension al computer visualization of a physical model and analysis of isochores pro vide clues to the original shape of allochthonous salt bodies that were emp laced during extension and later compressed. Initially, tabular salt (simul ated by viscous silicone) was regionally extended as synkinematic sediments accumulated. Extension triggered the rise of reactive salt walls that subs equently were shortened coaxially. Contraction produced curvilinear faulted folds, pop-ups, detachment anticlines, and pinched-off salt walls. Salt wa s squeezed to higher levels through fault-bounded vents in the roof. Three generations of stacked salt sheets were extruded and later acted as structu ral detachments. Isochore plots in the overburden show how patterns of sedi mentation, 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 c ontrast, isochores of synkinematic strata recorded mostly deposition on exp osed structures, with thicks recording salt expulsion, block grounding, and roof collapse and thins recording diapir rejuvenation. Synkinematic isocho res also recorded the former shape of subsequently shortened allochthonous salt, showing palinspastically how the weaker salt absorbed much more short ening than the stronger sediments encasing it. Isochore analysis thus impro ves two-dimensional and three-dimensional restorations of salt tectonics.