The internal deformation of the Peridotite Nappe of New Caledonia: a structural study of serpentine-bearing faults and shear zones in the Koniambo Massif

Benoît Quesnel (1) , Pierre Gautier (1) , Michel Cathelineau (2) , Philippe Boulvais (1) , Clément Couteau (3) , Maxime Drouillet (3)

1 GR - Géosciences Rennes
2 GeoRessources
3 Service Geologique de la Nouvelle-Calédonie

We present a structural analysis of serpentine-bearing faults and shear zones in the Koniambo Massif, one of the klippes of the Peridotite Nappe of New Caledonia. Three structural levels are recognized. The upper level is characterized by a dense network of fractures. Antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics. As a result, the upper level keeps the record of at least two deformation events, the first associated with the growth of antigorite (WNW-ESE extension), the second with the growth of polygonal serpentine (NW-SE compression). The lower level coincides with the ‘serpentine sole’ of the nappe, which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites. The sole records pervasive tangential shear with top-to-SW kinematics and represents a décollement at the base of the nappe. The intermediate level is characterized by the presence of several meters-thick conjugate shear zones accommodating NE-SW shortening. Like the sole, these shear zones involve polygonal serpentine and magnesite as the main syn-kinematic mineral phases. The shear zones likely root into the basal décollement, either along its roof or, occasionally, around its base. Compared to top-to-SW shearing along the sole, the two deformation events recorded in the upper level are older.

Domaines: Sciences de la Terre

Benoît Quesnel, Pierre Gautier, Michel Cathelineau, Philippe Boulvais, Clément Couteau, et al.. The internal deformation of the Peridotite Nappe of New Caledonia: a structural study of serpentine-bearing faults and shear zones in the Koniambo Massif. Journal of Structural Geology, 2016, 85, pp.51-67. ⟨10.1016/j.jsg.2016.02.006⟩. ⟨insu-01278589⟩