Propagating rifts and spreading centers

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Abstract
Propagating rifts are extensional plate boundaries that progressively break through rigid lithosphere. If the rifting advances to the sea-floor spreading stage, propagating sea-floor spreading centers follow behind, gradually extending through the rifted lithosphere. The combination of sea-floor spreading and propagation produces a characteristic V-shaped wedge of lithosphere formed at the propagating spreading center, with progressively younger and longer isochrons abutting the pseudofaults that bound this wedge. Figure 1 shows several variations of this geometry. Although conceptually simple, the propagating rift hypothesis has important implications for both large-scale and fine-scale plate tectonic evolution. It explains: (1) the existence of several classes of structures that are oblique to both relative and absolute plate motion and that previously seemed incompatible with plate tectonic theory; (2) why some continental margins are not parallel to sea-floor isochrons and why some continental drift reconstructions are inaccurate; and (3) the large-scale reorganization of some sea-floor spreading systems, including both the onset and termination of many fracture zones as well as the formation of some transient microplates. The hypothesis provides a mechanistic explanation for the way in which many (if not all) spreading center jumps occur and why they occur in systematic patterns, how spreading centers reorient when the direction of sea-floor spreading changes, and the origin of large areas of sea floor with high petrologic diversity, including the major abyssal ferrobasalt provinces.

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