Distinctive Seafloor Fabric Produced Near Western Versus Eastern Ridge‐Transform Intersections of the Northern Mid‐Atlantic Ridge: Possible Influence of Ridge Migration

Abstract

Multibeam bathymetry compiled along fracture zones of the northern Atlantic reveals a striking morphological asymmetry. Seafloor fabric produced at western ridge‐transform intersections (RTIs) tends to consist of linear ridges, small in amplitude, and regularly spaced, and oceanic core complexes (OCCs) occur infrequently. In contrast, seafloor fabric produced at eastern RTIs is more irregular and blocky and displays characteristics usually associated with melt‐poor accretion: These include more than double the occurrence of OCCs as well as greater seafloor depths, even where seafloor is younger than that on the opposite side of the fracture zone. We propose that this asymmetry is a consequence of the westward migration of the Mid‐Atlantic Ridge. Such migration is expected to result in an enhanced melt supply at leading (western) RTIs compared to trailing (eastern) RTIs. The morphological asymmetry is observed for ridge offsets of ~40 to ~200 km, a range that may be related to the width of melting regimes that supply ridge segments. At slow spreading ridges, contrasting melt supplies across fracture zones may therefore be best expressed in the distinct seafloor fabrics preserved beyond the dynamically maintained relief of the axial rift valley and walls rather than in the contrasting axial depths documented for faster spreading ridges. Although OCCs appear to form preferentially at spreading rates lower than 30 mm/year, their common occurrence along the northern Mid‐Atlantic Ridge may also reflect the significantly higher rates at which it is migrating compared to the southern Mid‐Atlantic Ridge.

Margin-to-Margin Seafloor Spreading in the Eastern Gulf of Aden: A 16 Ma-Long History of Deformation and Magmatism from Seismic Reflection, Gravity and Magnetic Data

“…However, this feature appears to be at the outside corner of the segment, which is unusual for OCC formation. Moreover, a significant amount of offset on the transform fault is necessary to develop an OCC (Cormier and Sloan, 2019) and the HFZ seems to have a very small offset. Thus, OCC formation seems an unlikely explanation for the post-A5 spreading asymmetry here.…”

Tectonic Evolution of a Sedimented Oceanic Transform Fault: The Owen Transform Fault, Indian Ocean

“…The use of magnetics to follow transform faults tectonics is itself limited since chron identification provides snapshots with a time step of the order of a million years. Beyond plates‐related events, the steady‐state regime of oceanic transform faults is still prone to discussion, with issues such as the tectonic regime (Grevemeyer et al., 2021; Mishra & Gordon, 2016; Ren et al., 2022), the width of the accommodation zone (Ligi et al., 2002), the role of fluid circulation (Kohli & Warren, 2020; Kohli et al., 2021; Prigent et al., 2020), the thermal regime (Behn et al., 2007; Sandwell, 1986; Turcotte, 1974; Wessel & Haxby, 1990), the Ridge‐Transform Intersection (RTI) tectonics (Cann et al., 1997; Fox & Gallo, 1984; Morgan & Parmentier, 1984; Severinghaus & Macdonald, 1988), the variability of the nature of the crust (Guo et al., 2023; Marjanović et al., 2020), the role of the absolute motion with respect to the mantle (Cormier & Sloan, 2019). Little is known about the short‐term evolution of oceanic transform faults at the million‐year timescale, simply because time and tectonic markers are missing.…”