[1] Three primary salt tectonic structural styles of the Scotian Basin are compared with plane strain finite element models in order to investigate their origin. Here, we focus on simplified model salt basins with initial rectangular cross-sectional geometries and follow their evolution in the context of tectonic and parametric thermal subsidence and under various sedimentation regimes. Structural style A, an open-ended roho system with a synkinematic wedge, is reproduced by models including deltaic progradation and seaward spreading/ gliding of sediments above a salt detachment. Structural style B, a linked salt tectonic system with landward regional normal faults and allochthonous salt sheets climbing seaward over Late Cretaceous and Paleogene strata, is shown to be a consequence of early aggradation followed by progradation. Structural style C is characterized by salt diapirs and intervening minibasins and is reproduced by models with Rayleigh-Taylor instabilities requiring compaction driven density inversions, weak sediments, and initial perturbations of the overburden-salt interface.

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[1] The Perdido Fold Belt (PFB) is a prominent saltcored deep water structure in the northwestern Gulf of Mexico. It is characterized by symmetric, kink-banded folds of a $4.5 km thick prekinematic layer and its vicinity to the extensive Sigsbee Salt Canopy. We use 2-D finite element numerical models to study the evolution of the PFB as a gravity-driven fold belt both in a local context and in the context of the larger-scale passive margin, influenced by adjacent allochthonous salt structures. We show that parameters such as overburden strength, salt geometry, or salt viscosity determine timing, extent, and location of the modeled fold belt. Simplified models of the Gulf of Mexico show that toe-of-slope folding is a viable mechanism to develop diapirs in the deep salt basin and to delay folding of the distal overburden. In this scenario, the PFB likely represents the terminal folding of a much larger, diachronously formed fold belt system.

Two-dimensional plane-strain numerical experiments illustrate the effects of variable evaporite viscosity and embedded frictional-plastic sediment layers on the style of salt flow and associated deformation of the sedimentary overburden. Evaporite viscosity exerts a first-order control on the salt flow rate and the style of overburden deformation. Nearly complete evacuation of low-viscosity salt occurs beneath expulsion basins, whereas significant salt is trapped when viscosity is high. Embedded frictional-plastic sediment layers with yield strength partition salt flow and develop transient contractional structures (folds, thrust faults and folded faults) in a seaward salt-squeeze flow regime. Multiple internal sediment layers reduce the seaward salt flow during sediment aggradation, leaving more salt behind to be remobilized during subsequent progradation. This produces more seaward extensive allochthonous salt sheets. If there is a density difference between the embedded layers and the surrounding salt, then the embedded layers fractionate during deformation and either float to the surface or sink to the bottom, creating a thick zone of pure halite. Such a process of ‘buoyancy fractionation’ may partially explain the apparent paradox of layered salt in autochthonous salt basins and pure halite in allochthonous salt sheets.Supplementary material:Animated gif files of the model results are available at http://www.geolsoc.org.uk/SUP18500.

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Finite strain analysis and thermal modeling of magmatically folded leucocratic dikes in the Mount Stuart Batholith, Washington and the Tuolumne Intrusive Suite, California, yield strain rates in the range of 10 −2 to 10 −13 s -1 . Compared to published regional strain rates (10 −13 to 10 −15 s -1 ), wallrock strain rates associated with dike-fed expansion (10 −7 s -1 ), and rates resulting from numerical modeling of crystal-plastic creep in aureoles (10 −11 s -1 ), our fast rates are several orders of magnitude higher.Field and microstructural observations suggest that multiple material transfer processes, including rigid rotation, ductile fl ow, cracking, and potentially melt-assisted granular fl ow operated in the aureoles to accommodate emplacement of these two plutons. Calculated durations of pluton construction and bulk shortening in the aureoles indicate that aureole deformation requires only slow, long-term strain rates of 10 −14 s -1 . Thus our local fast strain rates indicate that aureoles may be characterized by pulsating high strain rate surges. We suggest that magmatically folded dikes in these and other pluton aureoles around the world may be used as evidence for fast host rock strain rates during pluton emplacement.

[1] Having established the first-order controls of the three primary salt tectonic structural styles of the Scotian Basin in paper 1, in this paper (paper 2) we investigate and show that many unexplained structures can be attributed to more complex initial geometries of the autochthonous salt basins than the simple rectangular shapes used in paper 1. Basement highs modify and reduce the efficiency of salt evacuation during sediment aggradation followed by progradation. Lowangle taper (∼3°) of the basin edge slows Poiseuille flow and allows for trapping of salt beneath distal salt sheets. Seaward basement step ups do not necessarily hinder salt flow, and basement step downs can localize diapirs. Midbasin salt sheets can emerge when basement blocks as high as the salt is thick divide a basin into two subbasins. Deep salt basins that form above basement lows are efficiently evacuated. Weak overburden sediments augment the formation of salt sheets. Citation: Albertz, M., and C. Beaumont (2010), An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 2. Comparison of observations with geometrically complex numerical models, Tectonics, 29, TC4018,