Asymmetric rifts due to asymmetric Mohos: An experimental approach

Large-scale asymmetries in structures, and in the uplift, width and volcanism of pairs of conjugate passive margins have been documented in various parts of the world; these asymmetries reflect the dominant mode of extension preceding the break-up of the continental lithosphere. Of the many parameters involved, the pre-rift crustal structure has been shown to play a fundamental role in controlling the process of continental rifting. In this work, we have used analogue models to show how initial asymmetric Moho configurations are prone to produce asymmetric rifting, with prominent asymmetries in the amount of extension accommodated by boundary faults, in the patterns of lithospheric thinning/asthenospheric upwelling, and in the trajectories of magma migration. After continental break-up, these deformative patterns are expected to lead to the development of a pair of asymmetric passive margins, with one narrow, strongly volcanic margin and a wider, less volcanic (or with areas of concentrated volcanic activity) counterpart.