Initiation and growth of salt-based thrust belts on passive margins: results from physical models
T.P. Dooley, M.P.A. Jackson and M.R. Hudec
Journal name: Basin Research
Issue: Vol 19, No 1, January 2007 pp. 165 - 177
Info: Article, PDF ( 4.17Mb )
Scaled sandbox models simulated primary controls on the kinematics of the early structural evolution of salt-detached, gravity-driven thrust belts on passive margins. Models had a neutral-density, brittle overburden overlying a viscous décollement layer. Deformation created linked extension-translation- shortening systems. The location of initial brittle failure of the overburden was sensitive to perturbations at the base of the salt. Salt pinch-out determined the seaward limit of the thrust belt. The thrust belts were dominated by pop-up structures or detachment folds cut by break thrusts. Pop-ups were separated by flat-bottomed synclines that were partially overthrust. Above a uniformly dipping basement, thrusts initiated at the salt pinch-out then consistently broke landward. In contrast, thrust belts above a seaward- flattening hinged basement nucleated above the hinge and then spread both seaward and landward. The seaward-dipping taper of these thrust belts was much lower than typical, frictional, Coulomb-wedge models. Towards the salt pinch-out, frictional resistance increased, thrusts verged strongly seawards and the dip of the taper reversed as the leading thrust overrode this pinch-out. We attribute the geometry of these thrust belts to several causes. (1) Low friction of the basal de¤collement favours near- symmetric pop-ups. (2)Mobile salt migrates away from local loads created by overthrusting, which reduces the seaward taper of the thrust belt. (3) In this gravity-driven system, shortening quickly spreads to formwide thrust belts, in which most of the strain overlapped in time.