HR: 14:40h
AN: V33D-05 INVITED    [Abstracts]
TI: Earth's deep water cycle
AU: * van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Northwestern University, Dept. of EPS; 1850 Campus Dr., Evanston, IL 60208, United States
AU: Regenauer-Lieb, K
EM: klaus.regenauer-lieb@csiro.au
AF: CSIRO, 26 Dick Perry ave., Kensington, WA 6151, Australia
AU: Jacobsen, S
EM: steven@earth.northwestern.edu
AF: Northwestern University, Dept. of EPS; 1850 Campus Dr., Evanston, IL 60208, United States
AU: Yuen, D
EM: daveyuen@gmail.com
AF: Univ. of Minnesota & Minnesota Supercomputer Inst., 310 Pillsbury Dr., Minneapolis, MN 55455-0219, United States
AB: Major minerals in the upper mantle and particularly in the transition zone can hold considerable quantities of hydrogen from water. Exactly how much there is and how this hydrogen affects the mineral's physical properties is actively being researched. Observed seismic waves show clear evidence for regions of anomalous seismic velocity, which may or may not be a result of spatial variations in hydrogen content. How much hydrogen is needed to explain the observations and how to discriminate the effects of hydrogen from those of heat is also a subject of ongoing research. We will discuss some of this recent and ongoing research on detecting water in the mantle and then focus on a seismic anomaly beneath the eastern margin of the US. This anomaly is a region of weakly reduced shear-wave velocity that stretches laterally in a direction parallel to the eastern margin and stretches vertically from the top of the lower mantle to lithospheric depths. In the lower mantle, this low S-velocity anomaly sits adjacent to and above an east-dipping high S-velocity region, which likely represents subducted lithosphere from the Farallon Plate. The least unlikely explanation for the low-velocity anomaly is that it is relatively hydrous, with up to 1 wt % of water above average. If this hydrous region is slightly buoyant, it could well up and hydrate the strong lithosphere at the currently passive margin between the North-American continent and Atlantic Ocean. If the lithosphere is sufficiently weakened by hydration it might give way to typical forces from ridge push and sediment loads to develop a new subduction zone. We will discuss implications of such a scenario for the evolution of plate tectonics.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8125 Evolution of the Earth (0325)
DE: 8180 Tomography (6982, 7270)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting