Oblique rifting: the rule, not the exception

Abstract

Abstract. Movements of tectonic plates often induce oblique deformation at divergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2D deformation 10 where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until present-day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension 15 direction and rift trend normal. We find that more than ~70% of all rift segments exceeded an obliquity of 20° demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3D stress and strain fields that cannot be accounted for in simplified 2D plane strain analysis. We therefore highlight the importance of 3D 20 approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation.

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

“…Our analysis of thermochronometric data and magmatism patterns within the RGR rules out rift models involving time progressive propagation of rifting (northward propagation in the case of the RGR). Accordingly, we consider generalized synchronous rifting models—block rotation and oblique strain, as possible mechanisms driving the development of the RGR (Figure ; e.g., Ebinger et al, ; Nelson et al, ; Brune et al, ; Molnar et al, ; Brune et al, ).…”

“…However, this rotation is suggested to have occurred in the middle to late Miocene (i.e., 10–15 Myr after rift initiation as determined by our thermochronometric data analysis). Therefore, we cannot rule out an oblique strain model especially in light of a recent global rifting study which showed that the majority of rifting is accomplished from oblique strain (Brune et al, ). We suggest that rifting is driven by a combination of oblique strain and block rotation, mechanisms which evolve with the changing far‐field plate boundary conditions through time.…”

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

“…In addition, transform faults and systems can become particularly complex when the relative motion of the plates either side changes (Farangitakis et al, 2019), or a component of compression or extension is present, resulting in the development of transpressional and Manuscript under review for Interpretation transtensional systems . In addition to true transform faults and systems, it has been shown that the majority of rifts preceding conjugate margin formation can be considered to be oblique, lying on a spectrum between truly orthogonal rifts and transform-type margins (Brune et al, 2018). Spreading on mid-ocean ridges can also be oblique, and vary through the lifespan of a ridge, such as on the Reykjanes Ridge (Martinez et al, 2019), again complicating plate tectonic reconstructions, and conjugate margin studies.…”

“Conjugate margins” – An oversimplification of the complex southern North Atlantic rift and spreading system?

“…In addition, transform faults and systems can become particularly complex when the relative motion of the plates either side changes (Farangitakis et al, 2019), or a component of compression or extension is present, resulting in the development of transpressional and Manuscript under review for Interpretation transtensional systems (Peace et al, 2018b). In addition to true transform faults and systems, it has been shown that the majority of rifts preceding conjugate margin formation can be considered to be oblique, lying on a spectrum between truly orthogonal rifts and transform-type margins (Brune et al, 2018). Spreading on mid-ocean ridges can also be oblique, and vary through the lifespan of a ridge, such as on the Reykjanes Ridge (Martinez et al, 2019), again complicating plate tectonic reconstructions, and conjugate margin studies.…”