Geometry and deformation of the sole of a large obducted ophiolitic unit: insights from surface geology and airborne electromagnetics - Peridotite Nappe, New Caledonia

To clarify the serpentinite correlation and kinematics in New Caledonia, we focus on the northwestern boundary of the Massif du Sud and the Mont Do Massif, in the Boulouparis area. On the basis of airborne electromagnetics data, structural analysis, and field data, we propose a significantly different model to the one commonly proposed for Peridotite Nappe emplacement. The interpretation is that serpentinite slivers in basement actually correlate with the Peridotite Nappe instead of older basement terrane serpentinites. Therefore the basal Peridotite Nappe fault is not as planar and simple as previously thought. Some portions of the Peridotite Nappe are involved into major shear zones with the basement by duplexing or internal thrust within the peridotite. Most of the kinematic indicators, in the serpentinite slivers, and in the substrate, show a N-S shortening accommodated with lateral (both dextral and sinistral) senses of shear. Serpentinite plays a major role in this process by accommodating most of the deformation and by partitioning strain between the substrate and the nappe, i.e. between the lower and the upper plate. This model is consistent with the dextral oblique convergence model recently proposed by several authors for the emplacement of the subduction-obduction complex of New Caledonia.