HR: 1330h
AN: V12B-0588    [PDF]
TI: Modeling the Effects of the 670 km Boundary on the Dispersion of Plume Heads Within the Upper Mantle.
AU: * Harris, A
EM: aharris@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882
AU: Kincaid, C
EM: kincaid@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882
AB: The large, leading head of a mantle plume has been suggested as the source for large igneous provinces (LIPs). We present results from a finite element numerical model, which looks at the growth and rise of mantle plumes from the core mantle boundary. We look specifically at how the nature of the 670 km interface (e.g. chemical versus phase boundary) modulates the passage of plume heads and their eventual dispersion beneath the lithosphere. Models begin with initial thermal boundary layers at the base (D$\prime\prime$)) and the surface (lithosphere) of the domain and, in some cases, at the 670 km interface. We track three distinct chemical fields including the upper and lower mantle and a recycled slab component residing within the D$\prime\prime$) layer. Primary variables include the compositional values for the slab component and both the upper and lower mantle components. For the phase boundary, we vary the clapeyron slope and density difference associated with the phase change. The results show that when the 670 km discontinuity marks only a compositional change between upper and lower mantle, plumes either stagnate below this interface or trigger a complete mantle overturn, depending on the magnitude of the density contrast. With the addition of a phase boundary, there exists an intermediate regime represented by stable layering with short-lived pulses of plume penetration through the 670 and melting beneath the lithosphere. Within this regime, the 670 km interface acts as an effective filter by modulating the relative proportions of recycled slab and entrained lower mantle components, which ultimately rise through to the melting region beneath the lithosphere.
DE: 3210 Modeling
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting