Continental rifting and postbreakup evolution of Southwest
\nIberia: Tectono‐stratigraphic record of the first segment of the North Atlantic Ocean

The Southwest Iberia continental margin, located in the south‐eastern North
\nAtlantic Ocean and in proximity of an oceanic triple junction separating the
\nwesternmost Tethys, the Central and North Atlantic Ocean, is part of a world‐class
\nexample of a magma‐poor hyper‐extended rifted margin that records the complete
\nrift‐to‐drift evolution, mantle exhumation and subsequent tectonic inversion.
\nNevertheless, the Southwest Iberian margin remains a poorly investigated province
\nand key uncertainties are yet to be addressed. The current work presents an
\nintegrated analysis of the tectono‐stratigraphic rift‐to‐drift evolution of the Southwest
\nIberian margin and discusses its overall geodynamic implications.
\nThe tectono‐stratigraphic analysis of the continental margin reveals that three
\nmajor extensional pulses controlled the architecture of the discrete tectonic sectors
\nprior to continental breakup. Growth strata within each of these sectors denote
\npersistent tectonic subsidence and demonstrate not only the progressive westwards
\nrift locus migration towards the breakup position, but also conclusive evidence of
\nmultiphased rifting. In such a context, the current geometry of the margin is
\ninterpreted to have resulted mainly from rifting between the conjugate margins of
\nIberia‐Newfoundland, but also from the combined continental extension between
\nNova Scotia and Morocco and the oblique rifting in the westernmost Tethys. The
\nintegrated tectono‐stratigraphic analysis carried out herein shows that eight discrete
\nMegasequences can be assigned to major tectonic events and used for modelling
\nburial history of the discrete rift segments, consequently demonstrating that extension
\nwas significant not only during the transition to seafloor spreading, but also during the
\nEarly to mid‐Jurassic. This analysis additionally reveals that similar depositional
\narchitectures can be grouped into meaningful Tectonic System Tracts, namely, the Rift
\nInitiation System Tracts (RIST), the Rift Climax System Tracts (RCST), and the Late Rift
\nSystem Tracts (LRST). The revised framework proposed in this work demonstrates that
\nsequence stratigraphy can be used to describe and predict sedimentary facies
\ndistribution in continental rifted margins, as it recognises that multiple tectonicstratigraphic
\n(rift) cycles can occur on deep‐offshore rift basins since the onset of riftrelated
\nextension until continental break‐up.
\nviii
\nThe investigation of the tectono‐stratigraphic controls and effects of margin
\ninversion reveal that after a period of relative tectonic quiescence, post‐rift tectonic
\nreactivation affected the margin almost continuously since the latest Cretaceous to the
\npresent day. It is also revealed that the continental crust and their adjacent strata
\naccommodated long‐lived crustal shortening, which was neither synchronous nor
\nsimilar in style. The magnitude and architecture of shortening is shown to be
\nessentially dependent on the inherited syn‐rift geometry and rheological behaviour of
\npreviously extended continental crust, the existence of detachments rooted at viscous
\nearly rifting deposits and the position of the ocean–continent transition zone.
\nMechanisms controlling the location and magnitude of crustal shortening were mainly
\ndominated by the opening of the Gulf of Biscay during the Late Cretaceous, by
\ncontinental collision of the Iberia microplate with North Africa during the Eocene‐
\nMiocene, and by the recent westward convergence with the oceanic domain.
\nThe role of oblique deformation throughout the SW Iberian margin was assessed
\nand is herein revealed to be more significant than anticipated. Transcurrent
\ndeformation, as part of a wider area of strike‐slip tectonics, is thus dominantly
\ncontrolled by first‐order transfer zones, namely by the offshore prolongation of the
\nMessejana‐Plasencia Fault Zone (MPFZ). Here, growth strata reveal the development
\nof a rift‐related dextral releasing bend that accommodated both NW‐SE oblique rifting
\nin the westernmost Tethys and E‐W rifting of the Iberia‐Newfoundland conjugate
\nmargins. Post‐rift change in kinematics of the MPFZ towards a predominant left‐lateral
\nrestraining bend, demonstrate that first‐order transfer zones play a significant role in
\nsegmenting distinct areas of the continental margin and in accommodating noticeable
\nintra‐plate deformation. The MPFZ is also revealed both as a major area of sediment
\nbypass since the Late Cretaceous and the locus of early canyon incision since the
\nPalaeogene, as well as an area where potential destructive earthquakes and tsunamis
\ncan be generated.
\nThe results presented in this work suggests Southwest Iberia is an upper‐plate
\nrifted continental margin, which bears implications for the re‐assessment of evolution
\nof the Iberia‐Newfoundland conjugate margin as a whole.

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