HR: 08:15h
AN: T31F-02    [Abstracts]
TI: VOLATILE MANTLE UPWELLINGS, SUBDUCTION AND EMERGENCE OF PLATE TECTONICS
AU: * Regenauer-Lieb, K
EM: klaus.regenauer-lieb@csiro.au
AF: Geology & Geodynamics, Johannes Gutenberg-University, Mainz, 55099 Germany
AU: * Regenauer-Lieb, K
EM: klaus.regenauer-lieb@csiro.au
AF: Computational Geosciences, CSIRO Exploration & Mining, Kensington, WA 6151 Australia
AU: van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Department of Gelogical Sciences, Northwestern University, Evanston, IL 60208-2150 United States
AU: Yuen, D A
EM: davey@krissy.geo.umn.edu
AF: Department of Geology and Geophysics and Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455-0219 United States
AU: Wang, S M
EM: shuom@msi.umn.edu
AF: Department of Geology and Geophysics and Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455-0219 United States
AB: We propose a scenario below where the Earth has episodically degassed over its history with the release of hydrogen and associated siderophile elements into the lithosphere of the Earth. Tomographic images of deep upper-mantle low-velocity anomalies now give some first clues as to how and where this may happen. Surprisingly, low-velocity anomalies are found to as deep as 400 km and deeper beneath early Paleozoic suture zones such as the Tornquist-Tesseire Zone in Eurasia (Nolet and Zielhuis, 1994) and the Appalachians in North America (Van der Lee and Nolet, 1997). Such suture zones have no reason to be hot and the low velocities are more likely explained by increased volatile content associated with metasomatism of the deep upper mantle. Computations on the residence time of water in olivine suggest that this metasomatized upper mantle could presently be diffusing and/or welling upwards, in which case it would hydrate the shallow lithosphere from below. The vertical extent and lateral bending of the low-velocity anomaly beneath the Appalachians is suggestive of such an upwelling. We have used a 3-D visualization package (AMIRA) to delineate this feature which has important implications for the near-future evolution of the Atlantic North-America plate margin. We are presenting the hypothesis where plate tectonics is lubricated by wet upper mantle plumes and sheets. These sheets are attracted and advected by the strong guidance of the top layer, the lithosphere, in much the same way as the hot spots are rooted on the D$^{II}$-layer and held fixed by the lower mantle. In the Archean the young Earth is expected to have been hotter and richer in volatiles. While sheet like upwellings might be linked to the presence of some style of subduction (A), circular plume-like upwellings are a robust feature of plume tectonics (B). The early Earth must thus have gone through a convective fluid mechanical (A) and a plate tectonic solid mechanical mode (B). Self-organization of plate tectonics is suggested to have emerged out of both modes A and B in transition.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8125 Evolution of the Earth
DE: 8149 Planetary tectonics (5475)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting