A method to check the structural coherence of magma-poor rifted margins seismic interpretations: application to the Iberian margin

During continental rifting, two main types of faults accommodate crustal extension and thinning, namely high-angle normal faults and large-offset (“low-angle”) detachment faults. Classical interpretations of Atlantic-type rifted margins assume a predominance of high-angle normal faults in the proximal margin and of extensional detachment faults in the most distal domain; however, the structural interpretation of the so-called necking domain in between remains disputed.

Identifying high-angle faults and extensional detachment faults at rifted margins is challenging because: (1) seismic reflection images may not allow interpreters to indisputably locate the top basement and/or recognize syn-tectonic sedimentary sequences; and (2) the interpretation of extensional detachment faults is often debatable due to their faint topographic and stratigraphic expressions and the common overprint of their exhumed footwall by high-angle normal faults or erosion. Yet, the accurate identification of high-angle and extensional detachment faults is crucial for understanding the stratigraphic, thermal and isostatic evolutions of rift systems, all of which are fundamental to successful predictions.

We present a methodology to interpret crustal-scale seismic reflection images of magma-poor rifted margins and test the reliability of structural interpretations via geometrical criteria. We use TGS line 140 located offshore Portugal, north of the Peniche peninsula, as a case study.