OTJ-Samoa

Recent work offers tantalizing hints that the Samoan hotspot may be a long-lived hotspot that has been active since the Cretaceous. The 87 to 106 Ma volcanoes in the Magellan Seamount Chain have Samoan geochemical signatures, and their ages and locations match predictions for the Samoan hotspot made using absolute plate motion models for the Pacific. 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 Samoa and Rarotonga plumes would have resulted in lower degree plume melts with stronger enriched mantle (EM) signatures than anywhere else along the Samoa 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 thicker lithosphere and stronger EM signatures. To test whether the OJP passed over the Samoa and Rarotonga plumes, and whether this resulted in generation of extreme EM melts, we propose a 43-day seagoing expedition to sample the seamounts along the modeled traces of these two hotspot tracks on top of the OJP. A combination of geochemical analyses and 40 Ar/ 39 Ar ages will allow us to uniquely identify contributions from these two hotspots.