HR: 0800h
AN: V41E-1516    [Abstracts]
TI: Laboratory Experiments Concerning Upwellings From the Slab-Graveyard: Implications For Geochemical and Seismic Models
AU: * Harris, A C
EM: aharris@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, S Ferry Rd, Narragansett, RI 02882 United States
AU: Kincaid, C
EM: kincaid@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, S Ferry Rd, Narragansett, RI 02882 United States
AU: Hall, P
EM: hall@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138
AB: The ongoing plume debate appears to focus on upwellings characterized by large heads and smaller tails, that form from a deep or basal thermal boundary layer (BTBL), which are driven by temperature excesses in the range of 200° C. We use 3-D laboratory experiments to explore how upwellings might differ from this common plume description when BTBLs are influenced by subducted plates. An important aspect of the models is the representation of ridge chemical differentiation processes resulting in slabs with two distinct layers; a lighter, depleted upper mantle component (Harzburgite:H) and a heavier, iron-rich crustal component (Basalt/Eclogite:B/E). Laboratory experiments utilize a working fluid of glucose syrup with temperature dependent density and viscosity. Compositionally distinct mantle reservoirs are represented through isothermal density/viscosity contrasts controlled by water content. The ambient fluid (AF) is contained within a rectangular tank that is heated from below and cooled from above to produce background convection with a Rayleigh number of 10^-5-10^-6. Highly viscous, tabular slabs are produced by pouring compositionally distinct syrup from two slab reservoirs (B/E and H) into a mold which is chilled to -5° C. The viscous layered slab is emplaced at the fluid surface and subsequently sinks through, stalls and spreads within a BTBL roughly twice the slab thickness (1 cm). Results show that a wide variety in upwelling morphologies form when layered slabs reside within the BTBL and that plume heads/tails are largely dissimilar to those of the standard plume model. The manner in which the slab laminae vs. AF in the BTBL combine (or segregate) within upwellings depends on viscosity/density contrasts, how slabs collapse in the BTBL, and time. End-member regimes include: experiments dominated by a very light H-slab component with early, cold H-plumes and late, hot B/E-AF plumes and experiments where density differences between H, B/E and AF are small and mottled upwellings contain very thin <1mm B/E and H streaks. In an intermediate regime, larger scale thermal-chemical variability is seen through time and within individual upwellings. Detailed temperature data are used to estimate melting within distinct upwelling regimes and how distinct upwelling types might appear in seismic images.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005