J10      Characterization of the Lithosphere-Asthenosphere Boundary
GA 1.09
        Lead Convener (IAGA): Alan G Jones, Geological Survey of Canada, 
1 Observatory Crescent, Ottawa Ontario  K1A 0Y3 CANADA;  fax: 1 613 992
8836; e-mail: jones@cg.nrcan.gc.ca
Co-conveners: IASPEI [R Kind (Germany)], IAVCEI [S O'Reilly (Australia)]
 
 
 
The lithosphere-asthenosphere boundary (LAB) beneath the continents is a
fundamental physico-chemical boundary in the upper mantle at typically
100 - 200 km.  It has been observed as a rheological boundary, a low
P- and S-wave velocity layer, a change in seismic anisotropy, a
region of increased electrical conductivity, a thermal boundary layer,
a phase change, and a geochemical boundary. Are these phenomena reflecting a
fundamental cause? Or are some of them fortuitously spatially
coincident?
 
The recent extensive tomographic studies provide information on the
seismic characteristics of the LAB region, but they need integrating
with other geophysical data and with tectonic and geochemical information.
Mantle fragments in volcanic rocks of different ages can be used to
track thermal and depth changes in the LAB and thus help to further the
understanding of processes and mechanism of lithospheric evolution and
large-scale tectonic events.
 
This symposium seeks to draw together these disparate datasets and find a
common ground for their interpretation, and to understand the nature of the
LAB in different tectonic settings and the significance of these
differences in understanding how the Earth works.