Lower Miocene coarse conglomerate that crop out in the Népoui Peninsula does not represent the base of the marine transgression that followed obduction in New Caledonia. Instead, the conglomeratic alluvial fan that contains peridotite... more
Lower Miocene coarse conglomerate that crop out in the Népoui Peninsula does not represent the base of the marine transgression that followed obduction in New Caledonia. Instead, the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short-lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition. Considering the Miocene sea level evolution reported in literature, it is concluded that neither Lower Miocene subsidence nor erosion were driven by sea level variation. In contrast, south-eastward propagating slab tear initiated at the latitude of the HP-LT metamorphic complex of northern New Caledonia likely generated east to west tilt of New Caledonia, subsidence along the West Coast and hence fringing reef development together with moderate erosion of older regolith. Coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of post-obduction granitoids influenced by slab window suggests a genetic link. Therefore, it is concluded that short-lived Lower Miocene erosion was due to slab break-off and subsequent uplift that occurred at ~ 22 Ma. Early Miocene erosion profoundly dissected the Peridotite Nappe and in the northern half of New Caledonia, only leaved isolated klippes along the west coast. On the top of these klippes, a restricted water table did not allow ferricrete development to continue, thus accounting for paleomagnetic ages at ~25 Ma.
