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Rejuvenation and Subsidence of Salt Diapirs by Regional Extension
Hongxing Ge (1,2), Martin P. A. Jackson (1), Bruno C. Vendeville (1)
Because salt is much weaker than its surrounding sedimentary rocks, buried salt diapirs are sensitive to regional extension. To investigate extensional reactivation of salt walls and stocks, we conducted physical experiments using dry quartz sand to simulate brittle sedimentary rocks and a silicone polymer to simulate viscous salt. Initially, salt walls had triangular profiles and their height decreased along strike. Salt stocks had circular planforms.
In experiments, diapiric walls widened by extension. The diapiric roof first extended where it was thinnest, forming a graben over the crest of the walls. The crestal graben then propagated along strike to the lower parts of the wall, where the roof was thicker. Along strike off the diapirs, the graben broadened in an array of widely spaced faults. Where the diapir was initially oblique to the regional extension, crestal faults formed en echelon arrays above the diapir, and their traces deflected sharply above the ends of the walls. Where the source layer was thick and extension was slow, walls were rejuvenated to form reactive and even emergent, passive diapirs. Conversely, where the source layer was depleted or where extension was rapid, the walls subsided. Salt stocks were even more modified than were salt walls. Regional grabens formed above the stocks and propagated laterally but were not significantly deflected beyond the salt stocks. Salt eventually pierced the thinned roofs of the diapirs and extruded to form salt sheets above foundered roof blocks surrounded by salt. Grabens above the stocks were connected by an oblique transtensional zone.
We apply the model results to the Paradox Basin, Utah and Colorado, where salt structures were affected by regional extension during Cenozoic time.
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