ILP - French National report for 1998, from Michel Campillo & Olivier Bellier

In this current report we present the major contributions to French teams to International Lithosphere Projects. It results from a meeting of the French ILP representative of which the concern was "Past and Present of France in ILP".

This report benefit to contributions from W. Sassi (Vice-chairman of the Project III-2, Institut Francais des Pétrols), A. Vauchez (Chairman of the past Project III-5, Univ. Montpellier), H. Zeyen (Coordinator of EUROPROBE, Univ. Paris-Sud "OrsayTerre") and Uli Achauer (Chairman of the Project III-6, EOST Strasbourg, Lab. of seismology).

ILP project II-2

French team ("OrsayTerre", Univ. Parsi-Sud and IRD, ex-ORSTOM) participated to task group II-2 "World Map of Major Active Fault, Western Hemisphere" of the International Lithosphere Program. This has as main goal, the map of Western hemisphere including North, Central and South America. "OrsayTerre" and IRD provided mapping data mainly from South America (Chile, Bolivia...).

ILP project II-5

French team (M. Sébrier and O. Bellier, "OrsayTerre", Univ. Paris-Sud) actively participates to task group II-5 "Earthquake Recurrence through Time" of the International Lithosphere Program. This has as main goal, the promotion of research devoted to a better understanding of how large earthquakes recur with time. "OrsayTerre" has to provide paleoseismological data from SE Asia and France; paleoseismological data which play a critical role in this project because they provide the opportunity to obtain informations on large earthquakes occurring over several seismic cycles. These data will be include in the world-wide paleoseismic database; the compilation of such a database representing an important tool for the global modelling of the earthquake recurrence.

ILP project III.3

French teams contributing to the Origin of Sedimentary Basin Task Force, a Theme III.3 led By Prof. S. Cloetingh (Free Un. of Amsterdam, The Netherlands), William Sassi (I.F.P., Rueil Malmaison, France) and Prof. F. Horvath (Eotvos Un., Budapest, Hungary): This dynamic task force, driven by its energetic leader Prof. S. Cloetingh, is being active since 1990. This task force represent now a sizeable group of around 60 regular members. They constitute a network aiming at deciphering the basin records through a combination of extensive data analysis (from the Natural Laboratories) and modelling applications (using and developing research mathematical models that stems from the thin-section, reservoir rocks, basin and up to the Lithosphere dimension in scale), for a better understanding of the Lithosphere dynamic processes and Basin formation and evolution processes. The task force is composed now by a stable number researchers coming from both academic laboratories and from industry private Petroleum companies. The French contribution have been sources from several university groups: Univ. Grenoble, Univ. Rennes, Univ. Paris-Sud "OrsayTerre", Univ. Jussieu Paris VI and IFP. Field workshops are organised each year to an area offering a key natural laboratory. The next meeting in France is scheduled for the year 2001 and will be located in the French Western Alps.

ILP project III-5

As a continuation of ILP project III-5 "Dynamics of the subcontinental mantle: from seismic anisotropy to mountain building", french groups involved in the task force have developed research activities on several targets:

• Data acquisition: In order to evaluate seismic anisotropy of the upper mantle, portable seismic experiments have been done in the eastern Pyrenees (Univ. Toulouse, Montpellier and Bilbao), in Germany (Eifel area, Univ. Strasbourg and Karlsruhe), in the Massif Central (Univ. Strasbourg and Montpellier) and in SE Brazil (Univ. Montpellier and São Paulo). The later two are to be continued in 1999.
• Theoretical development: Computation of seismic properties of rocks containing preferentially-oriented magma-filled cracks and multi-scale modelling of seismic properties evolution associated with lithospheric deformation (Univ. Montpellier); Evidence for an anisotropic layer at the 670 km discontinuity (IPG Paris and Moscow)
• Petrophysics studies: Extensive study of the seismic properties of the South African cratonic lithosphere using kimberlite mantle xenoliths from the Kapvaal (Univ. Montpellier and Washington).

ILP project III-6

The project ILP project III-6 is one of the 5 new projects set-up in 1998. The project is concerned with a multidisciplinary approach of research related to "Hot spots, mantle plumes and the geodynamics of continental rifting and breakup". The project, concentrating on studying the effects of above targets from the surface down to the lithosphere-asthenosphere boundary, i.e. their interaction with the lithosphere should be understood as the natural complement to SEDI's work on the deep mantle.

Currently 4 French labs are involved in the project. While the work of the EOST Strasbourg (U. Achauer, chairman of ILP-II/6 and M. Granet) is focusing on imaging hots spots by seismic tomography (projects Eifel plume and Track), researchers at the ENS Paris (L. Fleitout) and Univ. Paris-Sud, OrsayTerre (H. Zeyen) do numerical studies on the geodynamic evolution constrained by geoid and temperature data. Finally, researchers at the IPG Paris (E. Stutzmann and J. P. Montagner) look for the deep mantle sources and the images of hot spots from surface wave modelling.

Contact: Olivier Bellier
CNRS Orsayterre "tectonique et bassins sed.", Bat. 509, Universite Paris-Sud, Centre Orsay, 91 405 ORSAY Cedex