DOI: 10.18710/6cv6c1
title: Replication Data for: Coupling crustal-scale rift architecture with passive margin salt tectonics: a geodynamic modelling approach

description: Geodynamic Numerical model outputs (animations) of paper "Coupling crustal-scale rift architecture with passive margin salt tectonics: a geodynamic modelling approach". Submitted for Review.

These novel numerical models are generated by arbitrary Lagrangian‐Eulerian (ALE) thermo-mechanically coupled finite element method for the solution of plane strain, incompressible viscous‐plastic creeping flows. The method solves the force balance equations of equilibrium for quasi‐static incompressible flows (Stokes) in two dimensions coupled with time-dependent heat conservation equations. The mechanical and thermal evolution is coupled through nonlinear temperature- and pressure-dependent rheologies in addition to the temperature dependence of buoyancy.

The models are designed using a rheologically layered lithosphere comprising a 35 km‐thick crust and a 90 km mantle lithosphere above a sublithospheric mantle in a 600 km‐high and 1,200 km‐wide model domain. The Eulerian grid consists of 2,400 in horizontal and 290 elements in vertical directions. The distribution of the elements in the vertical direction is irregular, allowing for high resolution in the upper crust of Δz=200 m in the shallowest 20 km, Δz=625 m between 20 and 70 km, Δz=1,100 m between 70 and 120 km, and Δz=7,917 m between 120 and 600 km of depth. The resolution in the horizontal direction is 500 m for the entire model domain. Extensional horizontal velocity conditions (v = ±0.5 cm/year) are applied to the lithosphere, and the corresponding exit flux is balanced by a low-velocity inflow in the sublithospheric mantle. The top of the model is a free surface, and the sides and base are free slip boundaries.

The crust follows a wet quartz (WQ) rheology with different scaling factors (fc) as a way to test variable crustal strength. We use four contrasting crustal with variable fc from 30, 1, 0.1, and 0.02 for strong, intermediate, weak, and very weak crusts, respectively. These results in distinct thicknesses of the frictional‐plastic upper crust that range from 25 km, 15, 11, to 8 km. The densities of crust, mantle lithosphere, and sub-lithospheric mantle are calibrated so that the depth of the modelled mid-ocean ridge spreading system fits with global observations of average mid-ocean ridge depth. Salt is treated as a linear viscous material and all models have a constant salt viscosity (see ReadMe). Sedimentation occurs by filling all accommodation between the model surface and a defined base(sea)-level with sediments at each time step. We implement two different styles of sedimentation in our models, aggradation for syn-rift clastics and salt, and post-rift progradation using a dynamic depositional profile. We also apply a new novel tracking method based on Lagrangian surface descriptions that allow resolving the internal stratigraphic architecture of the salt and post-salt intervals with greater detail than in previous studies. 

Models demonstrate the genesis and evolution of salt-bearing rifted margins and investigate the interplay between rifted margin architecture, late syn-rift salt deposition, and post-rift salt tectonics. We focus on four different types of continental margins: i) narrow, ii) intermediate, iii) wide, and iv) ultra-wide margins. We evaluate the: 1) interplay between laterally variable syn-rift extension, salt deposition and deformation, 2) influence of syn-rift basin architecture on post-rift salt flow, 3) spatial and temporal distribution of salt-related structural domains, and 4) contrasting styles of salt tectonics for different margin types. Narrow and intermediate margins form partially-isolated salt basins associated with prominent base-salt relief, limited translation but significant diapirism, and minibasin development. Wide and ultra-wide margins form wide salt basins with subtle base-salt relief that results in significant seaward salt expulsion and overburden translation. These wide margins demonstrate significant updip extension with the development of post-rift normal faults and rollovers, mid-margin translation associated with complex diapirism and downdip diapir shortening. All margins contain a distal salt nappe that varies in width and complexity. We also test the effect of different salt viscosities, relative post-salt progradation rates, and pre-salt sediment thicknesses. The results can be directly compared to several examples of salt-bearing rifted margins and provide an improved understanding of their dynamics and controls on the variability of salt tectonics.
description: FANTOM (Thieulot, 2011)