CONTINENTAL BREAKUP
Geometric aspects of continental breakup: How do continents break ?
Rift modes: Narrow, wide, core complex: The role of pre-existing heterogeneity.
The continental crust contains numerous mechanical heterogeneity in a large variety of form: pre-existing faults and fratures; high-pore pressures lenses; lateral and vertical compositional discontinuities; elastic heterogeneity, variation of radiogenic heat production and or heat capacity etc, all contributing to stress concentration and potentially to strain localization. What role may initial weakness potentially play in controlling the rifting mode? We examine here a range numerical models in which localized (punctual and planar) and diffuse rheological heterogeneities are embedded within homogeneous but layered models (Dyksterhuis et al., 2006).

Single localized weak seed: Single weak seeds: square regions of low viscosity material are included in the lithosphere possibly representing regions of higher radiogenic heat production (if anomaly is located in the crust), regions of locally reduced viscosity due to thermal/pressure perturbations or regions of weakness caused by a material inhomogeneity.

Upon extension, strain focuses around the weak seed resulting in the development of a narrow rift. By placing the weak seed at increasing depth we are locally increasing the depth to the effective base of the brittle layer (the top of the weak seed) and subsequently increasing the width of the resulting rift basin.