HR: 17:10h
AN: U14A-05    [Abstracts]
TI: Preservation of Fertile Mantle Components at Mid-Ocean Ridge
AU: * Montesi, L G
EM: montesi@umd.edu
AF: University of Maryland, Department of Geology, College Park, MD 20742-4211, United States
AU: Behn, M D
EM: mbehn@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hoole, MA 02543, United States
AU: Standish, J J
EM: standish@fas.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA 02138, United States
AU: Dick, H J
EM: hdick@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hoole, MA 02543, United States
AB: Recycled lithosphere is suspected to contribute to the geochemical enrichment not only of Ocean Island Basalts (OIB) but also exceptional Mid-Ocean Ridge Basalts collected at ultraslow ridges. In particular, the chemistry of basalts at volcanic centers along the Southwest Indian Ridge oblique supersegment of 9-16°E is best explained by an exceptionally strong contribution from an enriched mafic component mixed in the upwelling mantle. Why this component is so strong at these volcanic centers can be understood in at least two ways. 1) The mantle underneath each volcanic center is anomalous. Such an explanation is equivalent to appealing to small plume-like features underneath each volcanic center. 2) The fertile component is present everywhere but melt migration gathers the resulting magma toward the volcanic centers. In this contribution, we test the second hypothesis using a numerical melt migration model in which magma rises vertically until it encounter the base of the thermal lithosphere. In the SWIR 9-16°E area, variations in ridge axis azimuth produce a strong relief to the base of the lithosphere, which focuses magma towards the location of the observed volcanic centers. Magma produced off-axis, which is dominated by the fertile component, is focused even more strongly than near-axis magma, explaining the relative enrichment of the surface lava. We compare the expected enrichment pattern with the geochemistry of collected lava and show that, were the ridge straighter or spreading faster, this signal would be more difficult to observe.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1037 Magma genesis and partial melting (3619)
DE: 3035 Midocean ridge processes
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8434 Magma migration and fragmentation
SC: Union [U]
MN: 2007 Fall Meeting