Samples of visualization and interpretation of extensional diapirs overprinted by compression (see animations). Hot colors represent structural highs in Figures 7, 8 and 10, and isochore thicks in Figure 9.
Figures 7 and 8 — Map and oblique views of salt body, showing distinct structural levels and generations of salt, such as the deformed autochthonous salt (A); the first generation of allochthonous salt (B); and the second generation of allochthonous salt (C and D). In the authochthonous salt, the more prominent wall (E) actually rose slower than the shorter wall, which was pinched off to form a secondary weld (F). In the absence of regional topography, younger allochthonous flows (B) were vertically stacked above salt pinch-offs (F). The vergence of fault-bend folds (figure 10) determined the final direction of both the dip of the feeder (G) and the flow of overlying allochthonous salt sheets (C). The collapse of sand layers at the roof of the salt sheet produced depressions in the salt sheet (H, visualized by slicing the digital model along the gray horizontal plane). Pinch-out of underlying stems by shortening produced feederless allochthonous salt sheets (D). The diapir (I) was aborted before extrusion.
Figures 9 and 10 — Isochore map (Figure 9), which represents the vertical thickness of a synkinematic layer (brown and structurally contoured in the oblique view in Figure. 10) deposited on top of an allochthonous salt sheet. Blues represent thins and reds, thicks. To facilitate comparison, the isochore map is overlaid by a black outline of the underlying salt (from Figure 7). The isochore thin (blue and purple in A) is wider than the final shape of the underlying salt flow (black outline in A) because it records the shape of the underlying allochthonous salt during deposition. That showed palinspatically how the weaker salt absorbed much more shortening than the stronger sediments encasing it. In contrast, another thin (B) almost perfectly overlies the underlying allochthonous salt sheet (black outline centered in B) indicating no shortening after the emplacement of the salt in the relatively stable foreland. Palinspastic restorations have helped inference of geologic and hydrocarbon-migration history 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. Synkinematic isochores (e.g., Figure 9) recorded the former shape of subsequently shortened allochthonous salt, thus improving 2-D and 3-D restorations of salt tectonics.