Abstract
AbstractTransform margins are first‐order tectonic features that accommodate oceanic spreading. Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structural complexity is added. This work investigates the evolution of transform margins and associated rift‐transform intersections, using an analogue modeling approach that simulates changing plate motions. We investigate the effects of different crustal rheologies by using either (a) a two‐layer brittle‐ductile configuration to simulate upper and lower continental crust, or (b) a single layer brittle configuration to simulate oceanic crust. The modeled rifting is initially orthogonal, followed by an imposed plate vector change of 7° that results in oblique rifting and plate overlap (transpression) or underlap (transtension) along each transform margin. This oblique deformation reactivates and overprints earlier orthogonal structures and is representative of natural examples. We find that (a) a transtensional shift in the plate direction produces a large strike‐slip principal displacement zone, accompanied by en‐echelon oblique‐normal faults that accommodate the horizontal displacement until the new plate motion vector is stabilized, while (b) a transpressional shift produces compressional structures such as thrust fronts in a triangular zone in the area of overlap. These observations are in good agreement with natural examples from the Gulf of California (transtensional) and Tanzania Coastal Basin (transpressional) shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins.
Highlights
Transform margins and oblique rifts are first‐order structural features present in almost every tectonic plate across the globe
These observations are in good agreement with natural examples from the Gulf of California and Tanzania Coastal Basin shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins
A series of experiments designed to simulate the effects of a change in plate motion on transform margins and rift‐transform intersection (RTI) produces structural patterns and topographic effects that show good agreement with natural examples
Summary
Transform margins and oblique rifts are first‐order structural features present in almost every tectonic plate across the globe. In particular, represent 16% of the cumulative length of continental margins (Basile, 2015; Mercier de Lépinay et al, 2016) and accommodate or have accommodated oceanic spreading motion. These features were first discussed and described in the context of shear margins in the 1960–1970s (e.g., Le Pichon & Hayes, 1971; Mascle, 1976; Scrutton, 1979; Turcotte, 1974; Wilson, 1965). Transform margins remain considerably less studied than their continental divergent and convergent counterparts. Transform margins are areas of active hydrocarbon exploration with significant exploration risk factors such as uncertainty over the postbreakup uplift patterns in space and time, poor knowledge of structural architecture and associated topography, and diachronous timing of the transform fault activity (Nemcok et al, 2016)
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