RAPID: A Nonmagnetic Sinker Bar for Magnetic Logging on IODP Expedition 330

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Intellectual Merit: IODP Expedition 330 to the Louisville Seamounts starts 12 December 2010 from Auckland, New Zealand. A primary objective of drilling at the Louisville volcanic chain is to document the possible motion of the Louisville hotspot between 80 and 50 Ma. High quality paleomagnetic data are required to document this motion and to compare with the 15° shift observed for the Hawaiian hotspot over this time interval. These data, together with detailed radiometric ages, will provide the basis for calibrating and testing various geodynamic models.The most robust paleolatitude information will be derived from detailed demagnetization studies of the aziumuthally-unoriented core samples. In addition, we will deploy the Göttingen Borehole Magnetometer (GBM) to make 3-componentmagnetic borehole measurements. The main benefit of the GBM is that fiber-optic gryos should allow fully oriented component magnetic anomalies to be determined and magnetization declination to be estimated, facilitating identification of individual flows and a more robust estimate of hotspot and Pacific plate motions. Tests reveal that the sinker bar and centralizer to be used with the GBM both generate substantial magnetic anomalies (up to 10,000 nT at a distance of 1m). These large signals, and importantly the likely changes in these signals on different deployments, compromise the benefits of the magnetic logging.We therefore propose fabrication of a nonmagnetic sinker bar that will allow determination of accurate component magnetic anomalies (and remanent declinations) on Expedition 330 and subsequent expeditions. The large magnetic signature of the existing sinker bar and centralizer were documented in August; the short time before Expedition 330 begins requires rapid requires rapid fabrication of this tool.Broader Impacts: High quality paleomagnetic and age data are required to document the motion of the Louisville hotspot, a primary goal of Expedition 330. The proposed GBM magnetic logging has the potential to provide fully oriented vector magnetic anomalies in the borehole, significantly enhancing the constraints on the past motion of the Louisville hotspot and Pacific plate motion. A number of Expedition participants will be involved in interpretation of the borehole magnetometer results and integrating these results with data from the recovered core material.