Transcurrent segmentation within rifted continental margins: examples from the West Iberian Margin

Abstract

The West Iberian Margin (WIM) is a type-example of a magma-poor rifted margin that underwent prolonged multiphased extension prior to continental breakup. It also records main extensional events on both the northern Central and the southernmost North Atlantic Ocean (e.g. Tucholke et al., 2007; Pereira and Alves, 2012). Notwithstanding widespread evidence for oblique rifting and transcurrent tectonics during the evolution of the margin, these events are still poorly investigated and a comprehensive study is yet to be achieved.

Based on the analysis of extensive multichannel seismic data tied to outcrop, dredge and well data, the geometry and kinematics of the first-order transcurrent zones is investigated and their role in accommodating pre-, syn- and post-rifting strain on the distinct segments of the WIM is described. The focus is on the Messejana-Plasencia (MPFZ) and the Nazaré Fault Zones (NFZ), main structures that are used to explain depositional and structural controls throughout the WIM, as well to provide a broad context in relation to an oceanic triple junction. These transfer zones are characterised on seismic data by presenting a predominant negative flower-structure geometry that extends over 150 km West and Southwestwards across the margin. The transfer zones are 5 to 15 km wide, and are the locus of significant seismogenic activity.

Evidence of the importance of the transcurrent zones can be observed not only by the control they impose on sediment deposition and bypass (e.g. Alentejo, Peniche and Lusitanian Basins), but also on the decoupling of strain and the accommodation of conspicuous and prolonged lateral displacement during syn- and post-rift. In addition, the MPFZ and the NFZ bound important crustal hinge zones that act as oceanic divide throughout West Iberia, important features to the evolution of petroleum systems that may exist on each side of these zones.

The analysis of the geometry and kinematics of these transcurrent zones additionally explains how the geometry of West Iberian changes from a lower to an upper-plate architecture, an observation that can be used to understand the relations with its conjugate margins and additionally provide indications for characterising other rifted continental margins worldwide. Understanding the geometry, the extent and the timing of such transcurrent areas ultimately bear implications on the understanding of how elastic palaeogeographic reconstructions are elaborated.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015