Abstract: 3-D Visualization of Extensional Diapirs Modified by Later Compression

Guglielmo Jr, Giovanni, Vendeville, B. C., and Jackson, M. P. A. - Bureau of Economic Geology, The University of Texas at Austin

Palinspastic restorations have been instrumental in unveiling geological and hydrocarbon migration history in salt provinces. However, salt dissolution and salt flow in and out of the section plane make it impossible to determine the shape of salt bodies before deformation, which hampers accurate restorations. 3-D computer visualization of a physical model shows how isochores can establish the original shape of allochthonous salt bodies and illustrates the effects of compression superposed on extensional diapirs in three dimensions.

The model initially comprised a layer of viscous silicone overlain by a prekinematic sand layer. During the experiment, one endwall moved to produce extension then shortening. Sand layers were deposited synkinematically. Salt decoupled adjacent strata. Contraction produced (1) curvilinear fault-bend folds cored by salt, (2) pop-ups that die out along strike, (3) pinched-off salt walls, and (4) reactivated diapirs that created stacked salt extrusions, which, in nature, would seal intervening reservoirs.

Sequential isochore plots in the overburden show how patterns of sedimentation, deformation, and underlying salt changed through time. Isochores of prekinematic strata record only strain: thinned belts record early extension, and paired thickened belts record late shortening. In contrast, isochores of synkinematic strata record mostly thickness variations due to deposition on actively deforming topography: thicks record salt expulsion, block grounding, and roof collapse; thins record diapir rejuvenation. Overburden isochores record the shape of underlying extrusions before deformation, which allows accurate 2-D and 3-D restorations of salt in balanced sections.

The preprint of a full-length article, animations, and color figures related to this abstract will be available in the Web at www.utexas.edu/research/beg/giovanni.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil