Edited by
R.D. van der Hilst, M.I.T., Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA 02139, USA
W.F. McDonough, Harvard University, Department of Earth & Planetary Sciences, 20 Oxford Street, Cambridge, MA 02138, USA
Description
The ensemble of manuscripts presented in this special volume captures the stimulating cross-disciplinary dialogue from the International
Symposium on Deep Structure, Composition, and Evolution of Continents, Harvard University, Cambridge, Massachusetts, 15-17 October 1997.
It will provide an update on recent research developments and serve as a starting point for research of the many outstanding issues.
After its formation at mid-oceanic spreading centers, oceanic lithosphere cools, thickens, and subsides, until it subducts into the
deep mantle beneath convergent margins. As a result of this continuous recycling process oceanic lithosphere is typically less than 200
million years old (the global average is about 80 Myr).
A comprehensive, multi-disciplinary study of continents involves a wide
range of length scales: tiny rock samples and diamond inclusions may yield isotope and trace element signatures diagnostic for the formation
age and evolution of (parts of) cratons, while geophysical techniques (e.g., seismic and electromagnetic imaging) constrain variations
of elastic and conductive properties over length scales ranging from several to many thousand kilometers. Integrating and reconciling
this information is far from trivial and, as several papers in this volume document, the relationships between, for instance, formation
age and tectonic behavior on the one hand and the seismic signature, heat flow, and petrology on the other may not be uniform but may
vary both within as well as between cratons. These observations complicate attempts to determine the variations of one particular observable
(e.g., heat flow, lithosphere thickness) as a function of another (e.g., crustal age) on the basis of global data compilations and tectonic
regionalizations.
Important conclusions of the work presented here are that (1) continental deformation, for instance shortening,
is not restricted to the crust but also involves the lithospheric mantle; (2) the high wavespeed part of continental lithospheric mantle
is probably thinner than inferred previously from vertically travelling body waves or form global surface-wave models; and (3) the seismic
signature of ancient continents is more complex than expected from a uniform relationship with crustal age.
Included in series
Developments in Geotectonics
Audience:
For geophysicists, tomographers, geologists, geomagnetists, oceanographers, seismologists and solid earth scientists.
