HR: 0800h
AN: U21B-0402    [Abstracts]
TI: Plumes, Superplumes, and Dupal
AU: * Phipps Morgan, J
EM: jp369@cornell.edu
AF: Cornell, EAS, Snee Hall, Cornell, Ithaca, NY 14853, United States
AU: Morgan, W J
EM: wjmorgan@princeton.edu
AF: Harvard, EPS, 20 Oxford St., Harvard,Cambridge, MA 02138, United States
AB: The Dupal anomaly is a prominent low-order spatial pattern in the geochemistry of oceanic basalts. In 1988 Castillo noted an apparent correlation between the Dupal spatial pattern and the large-scale structure of seismic velocity anomalies in the deep lower mantle. Here we explore a simple physical mechanism that can explain this correlation. First, long-time subduction around the rim of the Pacific would drive flow in D" toward the center of the 'rim of fire' and the center of the African superplume. This continuous supply of D" would promote the concentration of plumes into the superplume regions. This is relatively independent of migration of the subduction zones as the Pacific closes in pace with the opening of the Atlantic and Indian oceans. Second, longterm outward conduction of heat from the plume pipes would heat the mantle between the pipes (it would heat outward ~100 km in 100 m.y.; ~200 km in 400 m.y.). This heating of the 'background' mantle to plume-rim temperatures would change the geotherm of the superswell region compared to the mantle beneath 'normal' suboceanic asthenosphere. The result would be that a larger fraction of ambient mantle would be heated enough for its lowest-solidus plums to begin to partially melt, and to become buoyant enough for this non-plume mantle to rise into and become part of the overlying layer of hot plume-fed asthenosphere – i.e. only in superplume regions is non-plume material hot and buoyant enough to upwell in significant amounts into the asthenosphere. We predict that Dupal material differs in its mean age from the age of the D'' source of other plume-fed asthenosphere, and also differs in that it has been (on-average) cooler and less-melted than ‘average' plume-fed asthenosphere. This leads to its distinctive isotopic differences. Global asthenosphere flow then preferentially transports Dupal material towards the southern ocean spreading centers (Yamamoto et al., 2007). The patchiness of superswell volcanism reflects the pulsing of higher-speed upwelling and melting within the background large-scale upwelling of superplume material.
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8410 Geochemical modeling (1009, 3610)
SC: Union [U]
MN: 2007 Fall Meeting