A “Rolling Hinge” Model of the Incremental Oceanward Development of the S-type Reflector Horizontal Detachment at Magma-Poor Rifted Margins

Abstract

Recent 3D seismic reflection imaging has provided new insights into lithosphere extensional deformation processes in the hyper-extended domain of magma-poor rifted margins where extensional faults penetrate through the thinned continental crust into the topmost mantle. Seismic analysis shows that high-angle extensional faults sole out into a sub-horizontal reflector (the S-type reflector) in the top-most mantle. This reflector is interpreted as a horizontal detachment and has been shown to develop progressively oceanward with the in-sequence extensional faulting above. We examine the evolution of fault geometries during extensional faulting in the hyper-extended domain. We show that the predictions of a recursive flexural rolling-hinge model  of planar faulting of thinned continental crust soling out into a horizontal detachment in the top-most mantle are consistent with the seismic interpretations. Our modelling shows that initially high-angle extensional faults are isostatically rotated to low-angle by oceanward in-sequence faulting and that their deeper segments form a continuous sub-horizontal structure in the top-most mantle corresponding to the S-type reflector imaged by seismic data. Both 3D seismic interpretation and our modelling indicate that the sub-horizontal detachment imaged as the S-type reflector, and forming an apparent regional detachment, is not active simultaneously over its whole length in the dip-direction but that it developed oceanward incrementally together with the in-sequence high-angle extensional faulting above.