HR: 17:15h
AN: V22H-06    [PDF]
TI: Varieties of Melt-Rock Interactions in Abyssal Peridotites
AU: * Ross, K
EM: kross@soest.hawaii.edu
AF: Geology and Geophysics, SOEST, Univ. of Hawaii, Honolulu, HI 96822 United States
AU: Elthon, D
EM: elthon@uh.edu
AF: Dept. of Chemistry, Univ. of Houston, Houston, TX 77204 United States
AB: Ocean Drilling Program cores of abyssal peridotite from Hess Deep (Leg 147) and near the Kane Fracture Zone (Leg 153) exhibit features suggesting that a variety of melt-rock interaction processes can influence their compositions. Shallow intrusion into peridotite by melt veins can produce small gabbroic intrusives, with local interaction with the host peridotite, leading to local enrichments in peridotite incompatible element budgets and changes in peridotite modes. This process reveals nothing about proposed reactive porous flow or melt-entrapment processes that might be influencing peridotite geochemistry at greater depth. Given the limited extent of our `outcrop' (one core diameter), it is possible that the gabbroic intrusive could be un-sampled, but that the chemical effects could be present in the core and mistaken for some other type of melt-rock reaction. The presence of these gabbroic veins in both suites of drilled peridotites shows that this type of process has demonstrably changed the geochemistry of parts of these cores. Other processes that could influence the geochemistry of these rocks include: 1. Melt-entrapment; the effects this have on the mode of peridotite will depend on the pressure at which the melt is entrapped and crystallizes and on the composition of the melt; if this occurs at shallow levels, then plagioclase will be present and the occurrence of melt-trapping will be obvious, but if it occurs at greater depths, then the melt will crystallize no plagioclase and the process will be cryptic. 2. Reactive porous flow; this process could also be cryptic, because in the absence of a set of samples that clearly represents simple melt-residues, the baseline against which modal and geochemical changes have occurred is lacking. Both suites of peridotites studied show evidence for Na enrichments, but in different styles. The Kane suite is pervasively enriched in Na above the amount that should be present based on fractional melting models, in samples that are distal from shallow gabbroic intrusives. The Hess Deep suite shows local enrichments in Na by a factor of $>$ 30 over baseline Na levels. The causes of these different enrichment styles are being investigated and we are determining abundances of strongly incompatible trace elements in CPX by ion probe to constrain the histories of these suites.
DE: 1025 Composition of the mantle
DE: 1065 Trace elements (3670)
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting