HR: 09:05h
AN: V21B-05    [PDF]
TI: Geochemical constraints on melting proccess in the GLIMPSE region
AU: * Donnelly, K E
EM: donnelly@ldeo.columbia.edu
AF: LDEO, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Langmuir, C H
EM: langmuir@eps.harvard.edu
AF: Harvard University - Dept of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: LDEO, 61 Rt. 9W, Palisades, NY 10964 United States
AB: The GLIMPSE region, where there are cross grain gravity lineaments, has abundant volcanism that permits tests of melting conditions and mantle sources associated with these important off-axis features. The Sojourn and Brown Ridges are extensive linear features, subparrallel to one another and perpendicular to the East Pacific Rise (EPR), which lies to the east. The Brown Ridge lies further to the east of Sojourn, ending $\sim$60 km or less from the EPR. South of the two ridges, Hotu and Matua are central complexes punctuated by dozens of smaller cones. Fresh lava flows with no topographic expression also cover portions of the sea floor in the general area. The recent flows on flat lying terrain include a flow northwest of the Sojourn Ridge, arguing for recent volcanism in the west as well as in the east. Samples from two cruises show that compositions range from highly depleted to strongly enriched. Sojourn Ridge samples show a general increase in enrichment with increasing distance from the EPR. On the Brown Ridge sporadic spikes of enrichment with no systematic geographic distribution occur and are associated with limited isotopic variations that are similar to those observed on the EPR, suggesting very recent enrichment and depletion events near the spreading axis. In contrast Hotu and Matua samples largely consist of incompatible element enriched lavas with isotopic compositions similar to Easter Island. Evidence for recent volcanism is found throughout the region. In the west, SiO$_{2}$ contents are significantly lower, reflecting higher pressures of formation and therefore little lithospheric thinning in the west. On the Brown Ridge in the east, recent volcanism also is apparent, but low SiO$_{2}$ contents are not observed reflecting younger and thinner lithosphere.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 8100 TECTONOPHYSICS
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting