GEOCHEMICAL FLUXES AND WEATHERING ON HIGH STANDING ISLANDS

The sediment fluxes from high standing oceanic islands (HSIs) such as New Zealand are some of the highest known. Recent geochemical work has suggested that along with their extremely high physical weathering yields, many New Zealand watersheds also have very high chemical weathering yields. In New Zealand, the magnitude of both the physical and chemical yields are related to the lithology of the watershed. Most of the previous work on this topic has been undertaken on South Island in Southern Alps watersheds of schist and greywacke and on North Island in East Cape watersheds of semi-consolidated marine sediments and greywacke. We have recently sampled North Island watersheds in the Taranaki and Wanganui regions which have been subjected to volcanism since the Miocene. We have sampled watersheds that contain both volcanic and sedimentary rocks. A series of water and sediment samples was collected and analyzed for a wide range of geochemical parameters including major, minor and trace elements. This was done to quantify the weathering intensities in the watersheds and to begin establishing the relationship between physical and chemical weathering yields in these lithologies. Where possible, samples were collected from tributaries, off the main river stems, that drained different geologic materials in order to assess more accurately the elemental inputs from each rock type. Our initial results reveal geochemical differences within the rivers themselves as well as distinct chemical signatures when compared to previous work from other lithotypes.