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Abstract: Rejuvenation of Salt Diapirs by Regional Extension

Hongxing Ge, Martin P. A. Jackson, Bruno C. Vendeville

Salt diapirs stop rising and are buried by sedimentary rocks when the source layer is effectively depleted, when the overburden becomes too thick to be pierced, or when regional tectonics stops. However, salt diapirism can be subsequently rejuvenated by regional extension. Because salt is much weaker than the surrounding rocks, strain is concentrated within the salt diapir and its relatively thin roof.

We conducted physical experiments, using dry sand to simulate brittle sedimentary rocks and a silicone polymer to simulate viscous salt, to investigate extensional rejuvenation of salt walls and stocks. Initially, salt walls had triangular profiles and varied in height along strike. Salt stocks had circular planforms.

Regional extension widened diapiric walls. A crestal graben first formed where the roof was thinnest then propagated along strike to lower parts of the wall, where the roof was thicker. Where diapirs were initially oblique to the direction of regional extension, crestal faults formed in relay or en echelon patterns above the diapir and were deflected sharply in strike above the ends of the walls. Where the source layer was thick and extension was slow, pre-existing walls were rejuvenated as reactive and even passive, emergent diapirs. Conversely, walls subsided where the source layer was depleted or where extension was rapid. During regional extension, grabens formed above the stocks and propagated laterally beyond the stock with no significant deflection. Stocks extruded through their thinned roofs to form salt sheets above foundered roof blocks.

We apply the model results to the Paradox basin, Utah and Colorado, where buried salt structures were rejuvenated by regional extension during Cenozoic time.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana