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Origin of the Lithosphere-Asthenosphere Structure in the Upper Mantle

UTIG Seminars

Origin of the Lithosphere-Asthenosphere Structure in the Upper Mantle

Shun-ichiro Karato

Yale University
When: Friday, March 22, 2013, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
Where: Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Luc Lavier, UTIG

Click for a Live Broadcast.

The lithosphere-asthenosphere structure is one of the most fundamental structure of the upper mantle. Such a mechanical layering is a key to the operation of plate tectonics and the survival and erosion of the lithosphere. A popular model to explain this layering is to assume that the asthenosphere is a layer where a significant amount of melt is present. However, the partial melt model has serious difficulties with being consistent with the petrological, geothermal and geodynamic model of the mantle. These models predict a small melt fraction in most of the asthenosphere that cannot explain the observed large velocity reduction at the lithosphere-asthenosphere boundary (LAB). Sub-solidus models need to be invoked to explain geophysical observations on LAB. Challenges for sub-solidus model are to explain large and sharp velocity reduction at (oceanic) LAB. I will present a new version of sub-solidus model of the LAB that explain a majority of geophysical observations. This model also explains the enigmatic mid-lithosphere discontinuity observed at ~100 km in the old continental upper mantle.