The challenge in restoring magma-rich rifted margins: the example of the Mozambique-Antarctica conjugate margins

Abstract Using the example of the conjugate Mozambique-Antarctica rifted margins, we investigate how mantle plume magmatism interacts with extensional processes during lithospheric rifting and breakup. The presence of extensive plume related magmatic additions formed during rifting masks the edges of the continental margins, making it difficult to determine a tight conjugate margin restoration and hindering the evaluation of their pre-breakup evolution. Based on rift domain mapping from seismic reflection interpretation, crustal thickness mapping using gravity inversion, lithosphere thinning from subsidence analysis, and the testing of different plate kinematic scenario, we develop a tight initial fit of the conjugate Mozambique-Antarctica margins and describe their evolution by a three stage model. These three stages consist of: i) during early rifting, the filling of accommodation space created by continental crust thinning with Karoo related magmatism resulting in a hybrid crust that maintains bulk crustal thickness producing shallow bathymetry or emergence and allowing SDR formation; ii) the decrease of magmatic budget relative to extension rates leading to bulk crustal thinning and increased bathymetries; and iii) the transition to seafloor spreading with a steady state magmatic budget resulting in normal thickness (6,5±1km) oceanic crust. This study not only adds new constraints on the regional breakup of Gondwana but also presents a new multidisciplinary methodology for restoring magma rich rifted margins formed in the presence of mantle plumes and for improving the understanding of the nature of such hybrid magma-rich crust.