Does asymmetrical seafloor spreading result from ridge jumps or proximity of single ridges to hotspots?



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In the paradigm of plate tectonics, seafloor spreading is viewed as a perfectly symmetrical process - whereby equal areas of new oceanic crust are created on either side of a single, spreading ridge. Asymmetrical seafloor spreading - recorded by unequal areas of oceanic crust present in the North Atlantic, Gulf of Mexico, and South Atlantic- has been previously explained by three models: 1) the presence of multiple spreading ridges - formed by “ridge jumps” - would produce wider zones of oceanic crust on the side of the main spreading ridge with additional ridges; these earlier extinct ridges can be identified from maps of magnetic anomalies formed at the spreading ridges and from bathymetry; 2) the presence of hotspots are frequently associated with areas of asymmetrical spreading; where the wider zone of oceanic crust is found on the opposite side of the hotspot; and 3) for backarc basins one idea is that trenchward slab rollback provides a mechanism to explain asymmetry in a subduction setting. I use Gplates software to create reconstructions of the most asymmetrical areas of seafloor spreading in both continental breakup and subduction settings in order to better understand the role of nearby hotspots on the spreading ridge.