Factors controlling early stage salt tectonics at rifted continental margins and their thermal consequences

Abstract

[1] We use 2-D thermomechanical models to investigate the early evolution of rifted margin salt tectonics in terms of the competition among margin tilt, salt flow, and sediment aggradation. Model experiments include initial geometry of the rifted margin and autochthonous salt basin, subsequent synrift and thermal subsidence, sediment and water loading, and sediment compaction. We also calculate the thermal evolution of the system to investigate the impact of the high thermal conductivity of the salt (halite). Model Set 1 demonstrates a two-phase response to salt deposition: short-term thermal equilibration between the salt and crust and longer-term relaxation in which the salt basin thermal image penetrates to a depth on the order of its width. Set 2 addresses the competition among margin tilt, salt flow, and sediment aggradation. Set 3 examines other factors, the salt basin width and depth, and the rifted margin width, which potentially affect the system evolution. Set 4 shows that sawtooth subsalt topography, representing faulted basement grabens, does not strongly impede salt flow. The model results are discussed in terms of a ternary diagram with apices representing tilt, salt flow, and sedimentation rates. Characteristic styles include the following: (1) tilt and rapid salt flow draining salt to the distal basin before the sediment aggrades, (2) an equivalent system with faster aggradation that captures draining salt as diapirs between minibasins, and (3) rapid sediment aggradation in which diapir-minibasins systems develop before the salt drains. Thermal consequences of these styles are discussed. A preliminary comparison shows that salt structures resembling these styles occur in the southwest Nova Scotian margin.

Allochthonous salt initiation and advance in the northern Flinders and eastern Willouran ranges, South Australia: Using outcrops to test subsurface-based models from the northern Gulf of Mexico

“…Similarly, the Aptian layered evaporite sequence of offshore Brazil contains little to no nonevaporite lithologies, but contains mostly halite with varying amounts of anhydrite, carnallite and other evaporite minerals (e.g., Karner, 2000;Meisling et al, 2001;Gamboa et al, 2008;Fiduk and Rowan, 2012). Despite these differences in composition and, thus, the average viscosity of the salt layer, which might be expected to influence the deformation (e.g., Albertz and Ings, 2012;Goteti et al, 2013), the Callanna Group appears to have mobilized in a similar fashion to the GOM and South Atlantic evaporites. However, the nature of the Callanna Group breccia and the similarity of its clasts to minibasin lithologies in terms of composition may explain in part the apparent absence of slumped material (rubble zone).…”

Continental margin syn‐rift salt tectonics at intermediate width margins

“…Unlike our earlier salt tectonic models (e.g. Albertz et al ., ; Goteti et al ., ), the results presented here provide an improved integrated physical understanding of the development of salt tectonics at rifted margins by not prescribing the salt basin geometry but, instead, allowing it to evolve in a self‐consistent manner during extension of the crust, and by considering the interactions among salt deposition, rifting and ongoing sedimentation. This analysis, therefore, offers insight into the relative importance rifting, timing of salt deposition and sedimentation, in driving salt tectonics at rifted continental margins for particular cases.…”

“…For example, in previous numerical experiments by Goteti et al . (, ), a geometrically defined salt basin was deformed by uneven sediment loading, tilt of the model or some combination thereof. Analogue models of salt tectonics at rifted margins have focused on the role of gravity gliding as a means of mobilizing salt, with gravity spreading generally considered less important (Brun & Fort, ; Adam et al ., ), though the formation of particular structures, such as minibasins, has required differential loading by sediments (e.g.…”

Late‐Syn‐ to Post‐Rift Salt Tectonics on Wide Rifted Margins—Insights From Geodynamic Modeling

“…We implement two different styles of sedimentation in our models, aggradation for syn‐rift clastics and salt (Figure 2b), and post‐rift progradation using a dynamic depositional profile (Figure 2c) (Theunissen & Huismans, 2019). We also apply a new novel tracking method based on Lagrangian surface descriptions that allows to resolve the internal stratigraphic architecture of the salt and post‐salt intervals with greater detail than previous studies (Allen & Beaumont, 2016; Goteti et al., 2013).…”