The major goals of cruise SO208 with the German research vessel Sonne were to investigate 1) plume-ridge interaction through time at the Cocos-Nazca spreading center (CNS) north of the Galápagos Islands by sampling across axis profiles of the seafloor and 2) off axis volcanism at the East Pacific Rise (EPR) versus far field effects of the Galápagos hotspot documented in seamounts off the coast of N Costa Rica and Nicaragua. Overall the nature of material transfer from the plume to the ridge and its large scale distribution throughout the Eastern Pacific is being investigated by means of major and trace element and Sr-Nd-Pb (double spike) isotope data.
The seamounts on the EPR generated part of the Cocos plate appear to originate on one hand from a depleted MORBlike source consistent with their formation near the EPR axis, while other seamounts formed through lower degrees melting of an enriched OIB source either more distant from the EPR or by intraplate volcanism. Geochemical profiles across the Western and Eastern CNS indicate the participation of two different Galápagos plume components with a change in the amount this material entering the CNS with time. While at the western profile element ratios of more to less incompatible elements show an overall decrease of a plume component, Wolf-Darwin or Northern domain [1], with increasing age, the opposite is observed at the eastern profile. The Central domain component [1] increases with increasing age of the crust in this area. These observations indicate variable flux of specific Galápagos plume components to the CNS over the past 800 000 years. Sr-Nd-Pb isotope data to verify these observations are currently being generated and will be presented at the conference.
[1] Hoernle et al. (2000) Geology 28, 435–43
