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Shortening of Diapir Provinces: Translation, Tilting and Rotation of Minibasins in Isolated Minibasin Systems


In this study we use a series of physical models to investigate minibasin mobility, tilt direction and rotation during regional shortening. Our impetus for this modeling investigation was a recent seismic based study on a portion of the Precaspian basin. Minibasins consisted of granular materials (sands and cenospheres) and sank into a sea of model salt (silicone polymer). A moving endwall imposed shortening on the system. During shortening minibasins are propelled basinward by the flow of salt around and beneath them. In general, minibasins in this type of system show few signs of contractional deformation despite the significant shortening strains imposed. Shortening is primarily accommodated by salt inflation, and thus minibasin thickness is not a proxy for original salt thickness. Rare thrust welds formed between the minibasins but this required significant shortening strains, particularly if all the minibasins were mobile. In the absence of any thrust welds minibasin fill architecture does offer some clues about cryptic shortening strains, as minibasins generally tilt toward the shortening direction during contraction. A regionally consistent tilt direction could be indicative of shortening. However, this tilt can be reversed if the minibasin welds to the base of salt or collides with other minibasins. Several factors impact upon the lateral mobility of minibasins: (1) primary welds inhibit translation although remobilization is possible by collision of more mobile minibasins; (2) obstruction by base-salt relief, and; (3) obstruction by intrasalt inclusions or intrasalt minibasins. As noted above minibasins generally tilt during shortening, typically toward the shortening direction. Tilt can be modified or enhanced by: (1) structure or relief at base of salt; (2) primary welding; (3) secondary welding when minibasins collide, and; (4) tilting away from zones of pressurized salt caused by shortening. Minibasin rotation is also driven by the flow of salt around them. Variations in flow strength and direction drive rotations. Flow directions and strengths can be modified by canopy margins, arrays of minibasins and local dips. Minibasin rotation has strong implications for reconstruction of sediment routes, especially where minibasins have rotated significantly and disconnected from the sediment entry points.