Post-Eocene extensional tectonics in Southern New Caledonia (SW Pacific):: Insights from onshore fault analysis and offshore seismic data

Ductile to brittle extensional deformation following thrusting of the peridotites nappe during the Upper Eocene has been shown to play a major role in the Tertiary tectonic evolution of the northern part of the main island of New Caledonia and its eastern and western margins. In this study, we provide new tectonic data from southern New Caledonia that allow to better constrain the tectonic evolution of the southern part of the main island. We present a kinematic analysis of faults and striations obtained mainly from exposures of sedimentary rocks in the region of Noumea with complements from measurements made farther north at Nepoui within post-obduction Middle-Miocene deposits. We also present additional results of an interpretation of seismic lines from the lagoon south of the Noumea Peninsula which provide constraints on the current tectonic regime of southern New Caledonia. Extensional faults in the Noumea region have been studied within terranes of various ages including pre- and syn-obduction deposits and ophiolites. Hence, we demonstrate that important extensional events have affected the southern part of the New Caledonia block after the obduction of the peridotite nappe. The direction of maximum extension is variable at the scale of the region. Both high angle and low angle normal faults are present and block rotation is observed at some localities. This suggests that detachments accommodating significant displacements are cutting through the sedimentary pile. The average final strain pattern of the region can be regarded as the results of a multidirectional flattening, a hypothesis consistent with vertical uplift associated with regional extension. These results are in good agreement with conclusions of earlier workers showing late extensional evolution of the ophiolites along