HR: 17:45h
AN: U44A-06    [Abstracts]
TI: Can we derive a continental growth curve from global S seismic tomography?
AU: * Poupinet, G
EM: Georges.Poupinet@obs.ujf-grenoble.fr
AF: LGIT, CNRS and UJF, BP 53, Grenoble, 38041, France
AU: Shapiro, N
EM: nshapiro@ipgp.jussieu.fr
AF: IPG Paris, 4 Place Jussieu, Paris, 75007, France
AB: The origin of continents is a standard question in geology; the worldwide application of geochronology lead to propose several models for the rate of formation of continental surfaces: see Hurley and Rand (1969), Amstrong (1981), Allègre (1982), McLennan and Taylor (1982), McCulloch and Bennett(1994), Condie (1998) ... In a diagram plotting the percentage of continental surface as a function of surface rock age, each model is characterized by a different curve - see Rino et al (2004) for example. In seismology, the structure of the continental lithosphere has been mapped in detail on all continents during the last 20 years. Large scale studies suggest a close relationship between the average P and S vertical travel times across the lithosphere inside continents and the age of surface rocks. The vertical travel time is directly related to the velocity and to the thickness of the lithosphere. It is correlated to the geotherm which is also known to be nearly dependent on the age of the continents. Using such a vertical traveltime - age relationship, it is straightforward to build a seismological curve which would be the seismic equivalent of the crustal growth curve familiar to geochronologists. This curve relates the percentage of continental surface to the average S vertical travel time and indirectly to age. We present various attempts to build such a curve. Our basic input is the S-tomography model obtained from global surface wave measurements by Shapiro and Ritzwoller (2002). P-delays derived from ISC residuals could in principle be used but they are a local measurement. S-tomography models have the advantage that they are surface measurements. We finally compare our growth curve with standard crustal growth curves and find that it is an "intermediate" curve. The S-tomography derived growth curve does not exhibit fast growth episodes as in McCulloch and Bennett (1994) and Condie (1998). A regular rate of formation of continents seems the most probable hypothesis at a worldwide scale from the S-tomography data set. This may reflect the smoothing inherent in computing S-models. On the contrary, P-station delay histograms are compatible with a few faster growth episodes but unfortunately, their spatial coverage is not good enough to conclude if fast growth episodes have been the rule or not.
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
SC: Union [U]
MN: 2007 Joint Assembly