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Abstract

Coupled thermal-kinematic finite-element modeling done in 3D is used to study spatial and temporal distribution patterns of the lower crustal viscosity at transform margins during their continent-ocean transform development and passive margin stages. Modelled scenarios combine different pre-rift thermal regimes and lower crustal rheologies. The outcome indicates that substantial parts of the lower crust have the potential to flow at geologically appreciable strain rates. This discovery can lead to our better understanding of lateral variations in uplift/subsidence, upper and lower crustal thicknesses, and Moho depth. Modeled low viscosity zones having effective viscosities below 1018 Pa s make up ductility distributions, which vary spatially and temporally during the entire margin evolution. Thermal history-related ductility patterns can be divided into three categories, including: (1) reduced lower crustal viscosities controlled by continental rifting and break-up in extensional and pull-apart terrains near transforms; (2) reduced lower crustal viscosities along the transform caused be the migrating ridge and oceanic crust; and (3) the background reduced viscosity resulting from the equilibrium temperature field. Superposition of these ductility patterns and the complex interaction of the underlying perturbations of the temperature field result in differences in the potential for lower crustal flow both in space and time. Our modeling results provide templates for the understanding of lower crustal flow at transform margins in general. They await follow-up studies focused on comparing their results with data on thermal regime, maturation history, and uplift/subsidence patterns.

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