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Title: Continental rifting and postbreakup evolution of Southwest Iberia : tectono-stratigraphic record of the first segment of the North Atlantic Ocean
Author: Sousa Lemos Pereira, Ricardo Nuno
ISNI:       0000 0004 2742 4102
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2013
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The Southwest Iberia continental margin, located in the south‐eastern North Atlantic Ocean and in proximity of an oceanic triple junction separating the westernmost Tethys, the Central and North Atlantic Ocean, is part of a world‐class example of a magma‐poor hyper‐extended rifted margin that records the complete rift‐to‐drift evolution, mantle exhumation and subsequent tectonic inversion. Nevertheless, the Southwest Iberian margin remains a poorly investigated province and key uncertainties are yet to be addressed. The current work presents an integrated analysis of the tectono‐stratigraphic rift‐to‐drift evolution of the Southwest Iberian margin and discusses its overall geodynamic implications. The tectono‐stratigraphic analysis of the continental margin reveals that three major extensional pulses controlled the architecture of the discrete tectonic sectors prior to continental breakup. Growth strata within each of these sectors denote persistent tectonic subsidence and demonstrate not only the progressive westwards rift locus migration towards the breakup position, but also conclusive evidence of multiphased rifting. In such a context, the current geometry of the margin is interpreted to have resulted mainly from rifting between the conjugate margins of Iberia‐Newfoundland, but also from the combined continental extension between Nova Scotia and Morocco and the oblique rifting in the westernmost Tethys. The integrated tectono‐stratigraphic analysis carried out herein shows that eight discrete Megasequences can be assigned to major tectonic events and used for modelling burial history of the discrete rift segments, consequently demonstrating that extension was significant not only during the transition to seafloor spreading, but also during the Early to mid‐Jurassic. This analysis additionally reveals that similar depositional architectures can be grouped into meaningful Tectonic System Tracts, namely, the Rift Initiation System Tracts (RIST), the Rift Climax System Tracts (RCST), and the Late Rift System Tracts (LRST). The revised framework proposed in this work demonstrates that sequence stratigraphy can be used to describe and predict sedimentary facies distribution in continental rifted margins, as it recognises that multiple tectonicstratigraphic (rift) cycles can occur on deep‐offshore rift basins since the onset of riftrelated extension until continental break‐up. viii The investigation of the tectono‐stratigraphic controls and effects of margin inversion reveal that after a period of relative tectonic quiescence, post‐rift tectonic reactivation affected the margin almost continuously since the latest Cretaceous to the present day. It is also revealed that the continental crust and their adjacent strata accommodated long‐lived crustal shortening, which was neither synchronous nor similar in style. The magnitude and architecture of shortening is shown to be essentially dependent on the inherited syn‐rift geometry and rheological behaviour of previously extended continental crust, the existence of detachments rooted at viscous early rifting deposits and the position of the ocean–continent transition zone. Mechanisms controlling the location and magnitude of crustal shortening were mainly dominated by the opening of the Gulf of Biscay during the Late Cretaceous, by continental collision of the Iberia microplate with North Africa during the Eocene‐ Miocene, and by the recent westward convergence with the oceanic domain. The role of oblique deformation throughout the SW Iberian margin was assessed and is herein revealed to be more significant than anticipated. Transcurrent deformation, as part of a wider area of strike‐slip tectonics, is thus dominantly controlled by first‐order transfer zones, namely by the offshore prolongation of the Messejana‐Plasencia Fault Zone (MPFZ). Here, growth strata reveal the development of a rift‐related dextral releasing bend that accommodated both NW‐SE oblique rifting in the westernmost Tethys and E‐W rifting of the Iberia‐Newfoundland conjugate margins. Post‐rift change in kinematics of the MPFZ towards a predominant left‐lateral restraining bend, demonstrate that first‐order transfer zones play a significant role in segmenting distinct areas of the continental margin and in accommodating noticeable intra‐plate deformation. The MPFZ is also revealed both as a major area of sediment bypass since the Late Cretaceous and the locus of early canyon incision since the Palaeogene, as well as an area where potential destructive earthquakes and tsunamis can be generated. The results presented in this work suggests Southwest Iberia is an upper‐plate rifted continental margin, which bears implications for the re‐assessment of evolution of the Iberia‐Newfoundland conjugate margin as a whole.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QE Geology