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Geology; April 2004; v. 32; no. 4; p. 333-336; DOI: 10.1130/G20134.2
© 2004 Geological Society of America
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Restoration of lithosphere-scale wrenching from integrated structural and tomographic data (Hercynian belt of western France)

C. Gumiaux1, S. Judenherc2, J.-P. Brun3, D. Gapais3, M. Granet5 and G. Poupinet6

1 Géosciences Rennes UMR 6118 Centre National de la Recherche Scientifique, Campus de Beaulieu, 35042 Rennes cedex, France
2 Ecole et Observatoire des Sciences de la Terre, UMR 7516 Centre National de la Recherche Scientifique, 5 Rue René Descartes, 67084 Strasbourg cedex, France
3 Géosciences Rennes UMR 6118 Centre National de la Recherche Scientifique, Campus de Beaulieu, 35042 Rennes cedex, France
5 Ecole et Observatoire des Sciences de la Terre, UMR 7516 Centre National de la Recherche Scientifique, 5 Rue René Descartes, 67084 Strasbourg cedex, France
6 Laboratoire de Géophysique interne et de Tectonophysique, UMR 5559 Centre National de la Recherche Scientifique, 1381 Rue de la Piscine, 38041 Grenoble cedex, France

Tomographic images of the mantle below the Hercynian belt of Brittany display strong anomalies of P-wave traveltimes that likely represent variations in composition, and whose trends change above and below 130 km. A quantitative strain analysis of surface geological structures has shown that the crust in the area was affected by regional-scale distributed simple shear. The change of trends of tomographic anomalies below and above 130 km is largely removed by extending the simple shear model down to 130 km. From this, we infer lithospheric-scale wrenching, and therefore deep-seated horizontal decoupling, possibly at the lithosphere-asthenosphere boundary. Simple shear restoration further provides arguments for the occurrence of a steeply dipping slab. Geological data support its interpretation as a remnant of oceanic lithosphere subducted prior to the Hercynian collision. Beyond regional implications, the study underlines the interest of combining geology and tomography for the understanding of lithosphere deformation.

Key Words: Hercynian lithosphere • mantle deformation • seismic tomography • shear belt • central Brittany.




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M. Brown
Synergistic effects of melting and deformation: an example from the Variscan belt, western France
Geological Society, London, Special Publications, January 1, 2005; 243(1): 205 - 226.
[Abstract] [PDF]


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