Cainozoic sedimentation in basins adjacent to a major continental transform boundary in southern New Zealand

Abstract

The Indo-Australian/Pacific plate boundary crosses the New Zealand continental block as the Alpine fault system, an oblique continental transform. Plate tectonic calculations for the SW Pacific imply the inception of this plate boundary in the latest Eocene. In western South Island, rapidly subsiding flysch basins were established at this time. Southeast of the Alpine Fault, basins developed along an active tectonic trend, the Moonlight Tectonic Zone. Early Oligocene infilling by thick submarine fan sequences was accompanied by regional subsidence, so that by late Oligocene, deep marine mudstone was dominant in basins and limestone on adjacent shelf areas. In contrast, early to mid Miocene time was characterized by contemporaneous uplift and subsidence, with tectonic activity on basin margins and development of new source areas adjacent to the Alpine Fault. Reverse faulting, folding and uplift developed at about 12 Ma and continues today. The sedimentary history is consistent with the development of the plate boundary from a zone of slow oblique extension, to a through-going continental transform, to a compressive transform system. Continental transform boundaries appear to be characterized by small, tectonically active basins, and by a complex tectonic history, particularly when close to the pole of relative rotation. Although difficult to recognise, they may be important in the geologic record.