Syn-tectonic, meteoric water-derived carbonation of the New Caledonia peridotite nappe

Benoît Quesnel (1) , Pierre Gautier (1) , Philippe Boulvais (1) , Michel Cathelineau (2) , Pierre Maurizot (3) , Dominique Cluzel (4) , Marc Ulrich (2, 5) , Stéphane Guillot (6) , Stephane Lesimple (7) , Clément Couteau (8)

1 Terre, Temps, Traçage
2 GeoRessources
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
4 PPME - Pôle Pluridisciplinaire de la Matière et de l'Environnement
5 ISTerre - Institut des Sciences de la Terre
6 Tectonique reliefs et bassins
7 Service Geologique de la Nouvelle-Calédonie
8 Service géologique

Exceptional outcrops recently exposed in the Koniambo massif allow the study of the serpentine sole of the peridotite nappe of New Caledonia (southwest Pacific Ocean). Many magnesite veins are observed, with characteristics indicating that they were emplaced during pervasive top-to-the-southwest shear deformation. The oxygen isotope composition of magnesite is homogeneous (27.4‰ < δ18O < 29.7‰), while its carbon isotope composition varies widely (−16.7‰ < δ13C < −8.5‰). These new data document an origin of magnesite from meteoric fluids. Laterization on top of the peridotite nappe and carbonation along the sole appear to represent complementary records of meteoric water infiltration. Based on the syn-kinematic character of magnesite veins, we propose that syn-laterization tectonic activity has enhanced water infiltration, favoring the exportation of leached elements like Mg, which has led to widespread carbonation along the serpentine sole. This calls for renewed examination of other magnesite-bearing ophiolites worldwide in order to establish whether active tectonics is commonly a major agent for carbonation.

Domaines: Sciences de la Terre

Benoît Quesnel, Pierre Gautier, Philippe Boulvais, Michel Cathelineau, Pierre Maurizot, et al.. Syn-tectonic, meteoric water-derived carbonation of the New Caledonia peridotite nappe. Geology, 2013, 41 (10), pp.1063-1066. ⟨10.1130/G34531.1⟩. ⟨insu-00866244⟩