INDIVIDUALIZATION OF A FORE-ARC BASIN DUR ING THE ACTIVE MARGIN EVOLUTION - HIKURANGI SUBDUCTION MARGIN, NEW-ZEALAND

Sedimentological studies from the Hikurangi forearc domain (New Zealan d) outlined a major unconformity at the Miocene-Pliocene boundary, aro und 6-4 My ago. This discontinuity marks the transition between two ma in periods in the evolution of the active margin during the Neogene. T he first one is Miocene (about 18-5 My)) and is characterized by a gen eral deepening in water depths, linked to a major subsidence of the wh ole margin. The second period is Pliocene-Pleistocene (about 4-0 My) a nd exhibits the formation of a real forearc basin. This basin is an el ongated narrow depression between the frontal are (landward) and the C oastal Ranges (seaward) corresponding to the highest ridge of the accr etionary wedge.