Do seamounts on fossil oceanic spreading centers record triple-junction migration or mantle-plume activity? Guadalupe Island, Mexico as an archetype

Volcanism on Earth is usually focused near boundaries between tectonic plates. This occurs at mid-ocean spreading centers or at subduction zones where plates sink. In some cases, though, volcanism occurs within a tectonic plate. While some intraplate volcanism can be explained by upwelling of a mantle plume, most of Earth's intraplate volcanoes are probably not related to a plume despite such volcanoes being widespread. One possible origin may involve transitions occurring between different types of plates. This project investigates intraplate volcanism offshore of the California Borderlands. This region has a complex plate margin history and unusual types of volcanism. The research team will conduct and video-blog fieldwork on Guadalupe Island offshore Baja California. This island is located along a system of failed mid-ocean spreading centers. It is an ideal location to test ideas related to the formation of non-plume, intraplate volcanism. This project will support a postdoctoral scholar and a PhD student. Together with Mexican collaborators, this project will provide educational opportunities, mentoring, and career development for USA and Mexican students. This project investigates the development of seamounts along failed oceanic spreading centers as a symptom of their interaction with convergent margins. When oceanic spreading centers approach subduction zones, the subducting oceanic plate stalls and subdivides into smaller microplates while the convergent margin evolves into a transform margin bounded by migrating triple junctions. The microplates are eventually captured when their convergent margins become transform margins. This terminates decompression partial melting of depleted mantle along their former divergent margins and initiates the development of alkaline, low-degree partial melting of enriched mantle that produces seamounts along their fossil spreading-center margins. Mantle plumes can produce seamounts with similar chemistry and must also be considered as a potential origin for seamount trails such as the Fieberling–Guadalupe seamount chain that intersect fossil spreading centers. The project intends to determine the origin of oceanic Guadalupe Island, which is an alkaline seamount that emerged above sea level ~270 km offshore of Baja California (Mexico) and is situated along a system of failed oceanic rifts that developed offshore of the California borderlands during the late Cenozoic. The project will test four hypotheses that predict different temporal and geochemical patterns for the transition from tholeiitic, mid-ocean-ridge-basalt (MORB) magmatism to alkaline, fossil-spreading-center-seamount magmatism due to triple-junction instability or mantle-plume magmatism. The approach is to integrate field geology, 40Ar/39Ar geochronology, major–trace-element and isotope geochemistry, and petrological modelling. Investigation of seamount petrology and timing within a regional-tectonic framework may therefore reveal geodynamic relationships among mantle flow, mantle melting, triple-junction migration, microplate capture, and/or mantle-plume activity, in addition to improving our understanding of the evolution of western North America during the late Cenozoic. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.