Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lapierre, H. Articles by Canard, E. Search for Related Content GeoRef GeoRef Citation

Potassic late orogenic Stephanian volcanism in the Southwest French Massif central (Decazeville, Figeac, Lacapelle-Marival basins): an example for mantle metasomatism along strike-slip faults?

Henriette Lapierre, Christophe Basile^1,*, Thomas Berly¹ and Emmanuel Canard¹

Laboratoire de Géodynamique des Chaînes Alpines, CNRS UMR 5025, Observatoire des Sciences de l’Univers de Grenoble, Université Joseph Fourier. Maison des Géosciences, 1381 rue de la Piscine, 38400 St Martin d’Hères, France.

Correspondence: ^* Corresponding author cbasile{at}ujf-grenoble.fr

In the southwestern part of the French Massif central (Decazeville basin, at the Sillon Houiller fault termination; Figeac and Lacapelle-Marival basins along the Argentat fault), Stephanian volcanism exhibits shoshonitic affinities. Their chondrite-normalized rare earth element (REE) patterns are enriched in light REE, but almost flat for heavy REE, with marked negative Eu anomalies. Primitive mantle-normalized element spectra show negative Nb, Ta, P, Sm, Ti, and positive Th, U, Pb anomalies, respectively. _Nd values are negative and homogeneous (–6 to –4). This volcanism shares the same geochemical patterns as the late-orogenic Stephanian-Permian magmatism from the southern part of the Variscan belt (Pyrénées, Alps, Sardinia). We explain these geochemical characteristics as resulting from the partial melting of a metasomatised mantle. We propose a new mechanism to explain this melting process: horizontal displacement along the main late-orogenic strike-slip faults might bring into contact a hydrated lower crust with the lithospheric mantle. Mantle metasomatism within the strike-slip fault zone may then induce partial melting.

Key Words: Late orogenic magmatism • Shoshonitic magma • Metasomatism • Sillon Houiller fault • Variscan