Growth and evolution of salt canopies on a salt-detached slope; insights from physical models

Salt canopies form the most spectacular and complex structures in the realm of salt tectonics. In this study, we use two physical models to examine salt-canopy growth and evolution on a salt-detached slope. A series of 14 feeders were seeded in our models and grew upward as passive diapirs. Eventually, these passive diapirs spread as salt sheets, with motion vectors skewed down the imposed regional dip slope. Sutures between individual sheets were bowed in the direction of override and became dismembered as the canopy system matured. Feeders in the interior of the array faced increasing competition for salt due to drawdown and primary welding. In contrast, feeders on the canopy peripheries faced less competition and rose more vigorously, generating local elevation-head gradients and imparting salt-flow directions that were highly oblique to the regional dip slope. Finally, our model canopies were loaded by prograding sediments. Canopy formation is strongly controlled by the salt budget, among other factors, and our less mature model formed a series of small canopies and isolated salt sheets. During sedimentary loading, this model displayed intrasheet and intracanopy inflation-deflation flow cells as salt was driven downdip. Sutures were further dispersed, and some were everted. Loading of our mature model deflated the originally continuous canopy, driving salt seaward up a series of base-salt ramps to form a shallow distal canopy. Suture fragments were carried all the way to the toe of this shallow canopy. Our more mature model was also shortened before loading, which resulted in canopy remobilization, thickening, and enhanced suture deformation. Salt flow during shortening was channeled by feeders, forming salt streams with orientations commonly oblique to regional dip. Canopy salt responded to shortening primarily by thickening, whereas the sediments below the canopy displayed a contrasting story. Here, a complex network of thrusts and tear faults linked the variably welded feeders.