Collaborative Research: Was early Cenozoic Samoa and Rarotonga volcanism suppressed when the Ontong Java Plateau drifted over the hotspots?

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Oceanic hotspot tracks form when plumes of hot rock upwell from the deep mantle and melt. Approximately 60 million years ago the Ontong Java Plateau (OJP) moved over the Samoan and Rarotonga plumes. The OJP is the largest volcanic structure on Earth. This project will sample seamounts on top of the OJP to study the interactions between plumes and the overlying large and thick OJP. Early-career scientists, graduate students, and undergraduate students will take part in the cruise. In port the science team will lead ship tours for local public schools and media. While at sea the PIs will make a training video that outlines how to prepare for and carry out a successful cruise. Recent work offers tantalizing hints that the currently active Samoan hotspot may be a long-lived mantle melting anomaly, or hotspot, that has been active since the Cretaceous. Many of the 87 to 106 Ma volcanoes in the Magellan Seamount Chain, located north of the OJP, have Samoan hotspot geochemical signatures. Critically, their ages and locations match predictions for the Samoan hotspot made using absolute plate motion reconstructions. The implications for identifying a Cretaceous segment (87-106 Ma) of the Samoan hotspot are profound. First, using the same plate motion models, reconstructions of the Samoan hotspot show that the OJP passed over the Samoan plume at ~60-30 Ma, and over the Rarotonga plume—a second, possibly-long-lived hotspot—at ~60-50 Ma. Second, passage of the extraordinarily thick OJP lithosphere over the Samoan and Rarotonga plumes would have resulted in lower degree plume melts with stronger enriched mantle (EM) signatures than anywhere else along the Samoan and Rarotonga hotspot tracks. The hypothesized relationship between thicker lithosphere and stronger EM signatures is supported by the Cretaceous Samoa-related Magellan Seamounts, which exhibit a robust relationship between older (and therefore thicker) lithosphere and stronger EM signatures. A 43-day seagoing dredging expedition to sample the seamounts along the modeled traces of these two hotspot tracks on top of the OJP will test whether the OJP passed over the Samoan and Rarotonga plumes, and whether this resulted in generation of extreme EM melts. A combination of geochemical analyses and 40Ar/39Ar ages will uniquely identify contributions from these two hotspots.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.