--> ABSTRACT: Active Diapirism Affected by Extension, Contraction, or Interlayer Slip: Results from Finite-Element Modeling, by D. D. Schultz-Ela; #91021 (2010)

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Active Diapirism Affected by Extension, Contraction, or Interlayer Slip: Results from Finite-Element Modeling

SCHULTZ-ELA, DANIEL D.

Active diapirism reflects a balance between the impetus of salt pressure and the resistance of overburden weight and strength. Factors that change these forces influence the evolution of active diapirs. Finite-element modeling demonstrates the effects of regional extension or contraction, interlayer slip in an anisotropic overburden, regional slope, diapir tilt, and changes in source-layer thickness.

A vertical active diapir rising beneath an isotropic overburden deforms the roof into a crestal graben flanked by rigid flaps that rotate upward and outward along curved reverse faults above the shoulders of the diapir. Active rise of a tilted diapir is similar, but the crestal graben tends to shift away from the overhanging side of the diapir. Regional contraction laterally compresses the diapir and increases its rise rate and ultimate height. The faults at the base of the flaps become shallower-dipping thrust faults. The crestal graben shrinks. Regional extension has the opposite effects to contraction. The roof rises more slowly, or may even subside for sufficiently fast extension. The flap faults tend to disappear as extension concentrates in the crestal graben. A thinner source layer slows active rise. It enhances the effects of contraction and extension by inhibiting flow out of or into the diapir, respectively. A regional slope causes effects similar to contraction if the upslope flank of the diapir can slide basinward. A roof composed of freely slipping layers markedly modifies the roof structures. Folds replace faults. Rather than lifting above a pointed diapir, the roof covers a flat or rounded diapir crest. Uplift is faster and higher than for isotropic roofs.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.