Conjugate margins — An oversimplification of the complex southern North Atlantic rift and spreading system?

Abstract

The prevalence of conjugate margin terminology and studies in the scientific literature is testimony to the contribution that this concept and approach has made to the study of passive margins, and more broadly extensional tectonics. However, when applied to the complex rift, transform, and spreading system of the southern North Atlantic (i.e., the passive margins of Newfoundland, Labrador, Ireland, Iberia, and southern Greenland), it becomes obvious that at these passive continental margin settings, additional geologic phenomena complicate this convenient description. These aspects include (1) the preservation of relatively undeformed continental fragments, (2) formation of transform systems and oblique rifts, (3) triple junctions (with rift and spreading axes), (4) multiple failed rift axes, (5) postbreakup processes such as magmatism, (6) localized subduction, and (7) ambiguity in identification of oceanic isochrons. Comparison of two different published reconstructions of the region indicates the ambiguity in conducting conjugate margin studies. This demonstrates the need for a more pragmatic approach to the study of continental passive margin settings where a greater emphasis is placed on the inclusion of these possibly complicating features in palinspastic reconstructions, plate tectonics, and evolutionary models.

A kinematic reconstruction of Iberia using intracontinental strike‐slip corridors

“…The computed total ~185 km of extension for the Orphan Basin during the Mesozoic (Figures 2 and 4f,g) is compatible with reported observations (MacMahon et al., 2020; Peace & Welford, 2020). Our orthogonal setting has a NAM‐FL pole of rotation far from Flemish Cap, in contrast to previous estimations (Sibuet et al., 2007; see Figure 1).…”

“…Euler stage poles represent relative motions for plates and microplates (different colors) (Angrand et al., 2020; Lundin & Doré, 2019; Reid, 1988; Sandoval et al., 2019; Sibuet et al, 2007). Necking lines outline the boundaries of the rigid continental blocks (Figure 3; Angrand et al., 2020; Gómez et al, 2019; King et al., 2020; Nirrengarten et al., 2018; Peace & Welford, 2020). Symbols refer to our and previous global kinematic models that do not separate Iberia in numerous continental blocks (Barnett Moore et al, 2016; Nirrengarten et al., 2018; Van Hinsbergen et al., 2020).…”

“…This four‐step approach has achieved outstanding results in reconstructing global plate motions at divergent settings (Müller et al, 2019). However, problems arise when obliquely deforming continental regions are considered, as shown for the Iberian case (Angrand et al., 2020; Barnett‐Moore et al., 2016; Peace & Welford, 2020; Tavani et al., 2018). During a large part of its Mesozoic history, Iberia was a continental rigid block delimited by intracontinental deforming regions, 40–200 km wide (Ady & Whittaker, 2019; Angrand et al., 2020; King et al., 2020) and hereafter referred to as strike‐slip corridors.…”

The Rockall and the Orphan Basins of the Southern North Atlantic Ocean: Determining Continuous Basins across Conjugate Margins

“…Several petroliferous Mesozoic sedimentary basins (e.g., the Orphan Basin, the Flemish Pass Basin and the Jeanne d'Arc Basin) are located offshore Newfoundland and Labrador, eastern Canada, which were formed during the Late Triassic to Early Jurassic rifting that proceeded to the opening of the modern North Atlantic Ocean [1][2][3] (Figure 1B). On the conjugate Irish Atlantic margin, several basins were formed at approximately the same time (Late Triassic to Early Jurassic; e.g., the Rockall Basin and the Porcupine Basin; [4][5][6][7][8]; Figure 1C). While separation of the Irish continental margin from its conjugate pair, the Orphan Basin region, through seafloor spreading that occurred during the Mid-extensive, reaching as far north as between Canada and Greenland possibly as early as the Triassic [11][12][13], with simultaneous, intermittent rifting episodes affecting the Rockall [4,14] and Orphan [2,15] basins during the entire Jurassic period.…”

A review of “A reconstruction of Iberia accounting for W-Tethys/N-Atlantic kinematics since the late Permian-Triassic” by Angrand et al.

“…(e.g., Nirrengarten et al, 2018). The importance of including these blocks is shown in Peace and Welford (2020). Essentially, these blocks play an important kinematic role and I do not think that Iberia can be accurately reconstructed without including these blocks.…”