HR: 1330h
AN: B12A-0736    [PDF]
TI: A proposal for drilling to the base of a Lamont Seamount at 9$\deg$50 N EPR
AU: * Lundstrom, C
EM: lundstro@uiuc.edu
AF: Dept of Geology University of Illinois Urbana Champaign, 245 NHB, 1301 W Green St, Urbana, IL 61801 United States
AB: The Lamont Seamount chain intersects the East Pacific Rise at 9$\deg$50N and is a significant feature within the RIDGE2000 program integrated study site at 8-10$\deg$N. However, the origin of this, as well as all near-ridge seamount chains, remains unresolved. Geochemically, Lamont Seamount lavas form an excellent depleted end-member magma which mix with more enriched magmas to form typical 9$\deg$N EPR NMORB. Here I present the case for an IODP project to obtain a drill core to the base of a Lamont Seamount in order to gain fundamental insight into mantle melting processes. Drilling into the oldest Lamont Seamount will test the hypothesis that seamount chains reflect the presence of dunite melt conduits in the upper mantle feeding magma to near-ridge locations. If these conduits are created by the passage of reactive melts derived from melting of enriched mantle heterogeneities, the base of the oldest seamount should contain geochemically enriched melts. Seamount chains like Lamont aligned along absolute plate motion would reflect a melt conduit in the upwelling asthenosphere while relative motion hotspot chains would reflect dunite in the lithosphere. A stratigraphic sequence of seamount lavas in a core will also allow an assessment of whether melt compositions are chromatographically modified during ascent. This would also allow quantification of melt porosities in the melting column, complimentary to geophysical tomography efforts. A final hypothesis is that once established, dunite conduit systems lead to a melting process whereby diffusion of alkali elements into the surrounding mantle flux melts the mantle at shallow depths. This process might explain the production of anorthitic plagioclase in MORB, the creation of anomalous Cl rich melt inclusions in MORB, and the production of the volumetric majority of magmas beneath a mid-ocean ridges. Finally, a $>$1km long drill core would also allow other interdisciplinary RIDGE research such as unmatched look at microbial alteration of basalt through time.
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 3035 Midocean ridge processes
SC: Biogeosciences [B]
MN: 2003 Fall Meeting