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Journal of the Geological Society; 2004; v. 161; issue.2; p. 277-289;
DOI: 10.1144/0016-764903-115
© 2004 Geological Society of London

Original Article

Magnetic fabric of granitoids from Southern Corsica and Northern Sardinia and implications for Late Hercynian tectonic setting

J. Gattacceca1, J.-B. Orsini2, J.-P. Bellot1, B. Henry3, P. Rochette1, P. Rossi4 & G. Cherchi5

1 1CEREGE, BP 80, 13545 Aix-en-Provence Cedex 4, France (e-mail: gattacceca@cerege.fr)
2 2Université J. Monnet, 42023 St-Etienne Cedex 2, France
3 3IPGP, 4 avenue de Neptune, 94107 St-Maur des Fossés Cedex, France
4 4BRGM, BP 6009, 45060 Orléans cedex 02, France
5 5Progemisa S.p.A., Cagliari, Italy

Anisotropy of magnetic susceptibility (AMS) data (180 sites) from Hercynian granitoids from Southern Corsica (France) and Northern Sardinia (Italy) provide a high-density net of structural information for this part of the European Hercynian belt. Two main groups of granitoids, defined according to petrography and relative chronology, provide contrasting AMS results. For both groups, shallowly dipping magnetic foliations and lineations suggest that these granitoids were emplaced as large-scale shallowly dipping sheets or open funnel-shaped structures at a high structural level. In non-leucocratic granitoids (305–300 Ma), foliation and lineation trajectory maps reveal antiforms and synforms with a N130 axial trace. Intersection of the foliation planes indicates a N120 low-plunging ‘fold’ axis, revealing a N120 maximum stretching direction. Slightly younger leucocratic granitoids (295–285 Ma), bounded by late Hercynian faults, display N50 lineations parallel to the elongated shapes of these intrusions. This structural pattern is undisturbed by the faults, and suggests an intrusion in decakilometre-scale tensional fractures indicating a N140 instantaneous stretching direction compatible with the stretching direction evidenced in non-leucocratic granitoids. A younger c. N20-oriented Permian dyke swarm confirms the permanence of this stretching direction over at least 35 Ma and indicates a coaxial strain regime. To integrate these new data within a broader context in the Hercynian belt, Corsica has to be back-rotated clockwise by 70° to its Permian position, which indicates a north to N30 stretching direction for the 305–285 Ma interval, compatible with the post-collisional strain and stress fields of the French Massif Central at about the same period.

Key Words: Corsica • Sardinia • Hercynian belt • magnetic susceptibility • granites