Abstract
In transform margins, oblique structural inheritance and plate motion vector changes have a direct impact on the margin's morphology and duration of transform activity. We investigate the effect of these two factors using numerical modelling. To simulate oblique inheritance in continental lithosphere, we model an initial rift-transform-rift configuration oriented at a range of angles (−45o to +45o) with respect to the extension direction. In a second suite of calculations, we first extend a rift-transform-rift system orthogonally and then vary the extension direction to simulate rotation of the far-field stress directions, and hence the relative plate motion. We found that transpressional deformation on the transform results in increased duration of fault activity and diffuse, longer transform zones at higher angles, while the opposite is true for the transtensional case. These observations are in good agreement with natural examples such as the Ungava Transform Zone, the Gulf of California and the Gulf of Aden, indicating that relative plate rotation plays an important role in the structural evolution of transform margins. Finally, we present a metric that links current transform margin morphology to past evolution.
Highlights
Transform margins and their accompanying transform faults are a relatively understudied feature of plate boundaries that accommodate predominantly boundary-parallel relative plate motion
We refer to these features as continent-continent transform faults (CCTs), based on the nature of crust being displaced on each side of the margin
Our work focuses on the first case: continental transform margins directly associated with transform faults
Summary
Transform margins and their accompanying transform faults are a relatively understudied feature of plate boundaries that accommodate predominantly boundary-parallel relative plate motion. Continentocean transforms are found in settings where there has been: a) orthogonal extension between oceanic spreading segments (e.g., Gerya, 2013; Basile, 2015); b) oblique extension (e.g., Bellahsen et al, 2013; Brune and Autin, 2013); c) plate rotations (Morrow et al, 2019); or d) combinations of the above (Farangitakis et al, 2019) Transform margins start their life-cycle as transfer faults offsetting rift segments (Bosworth, 1986) or as prototransform faults representing diffuse zones of oblique strike-slip motion that initiate during the later stages of continental breakup (Illsley-Kemp et al, 2018). Our work focuses on the first case: continental transform margins directly associated with transform faults
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