Site Survey for IODP Proposal 646-Full:- Icelandic V-Shaped-Ridges

This Urgency Grant Proposal aims to take advantage of a site survey opportunity in support of a UK-led IODP proposal to drill the North Atlantic basement. A bid made last October to the Science Foundation, Ireland and the Irish Marine Institute by Steve Jones (Trinity Colege, Dublin) and Bramley Murton (NOCS) resulted in 450,0000 euros of ship-time being awarded. The Celtic Explorer has been made available to Jones and Murton between mid-April and mid-May 2008. To support this expedition, funds are sought to mobalise and set-up a portable multibeam exchosounder (Reson 8160), and to hire several dredges from NMFD. The costs are modest, at about 2.5% of the ship-time. The scientific objectives are to map and sample along the strike of a V-shaped ridge that is exposed on the western flank of the Rejkanes Ridge, southwest of Iceland. This Urgency Grant Proposal is in support of a major, UK-led, IODP proposal (646-Full) that addresses fundamental questions about the causes of fluctuations in the activity of volcanic hotspots and their effects on the Earth's environment including climate. Does deep upwelling in the mantle, localized temperature and compositional anomalies, or shallow-mantle flow cause hotspot fluctuations? What are the time scales and rates involved? Where mantle flow is involved, what is its fate as it flows away from a hotspot? To address these issues, we propose to sample time-transgressive features that are common where hotspots interact with mid-ocean spreading ridges. These phenomena are exceptionally clearly developed for the Iceland-Reykjanes Ridge couplet where a series of diachronous V-shaped ridges (VSR's) preserve a record of changing hotspot activity, over the last 35Ma, on the floor of the North Atlantic. Linked to these fluctuations in the Iceland hotspot are variations in the flux of North Atlantic Component Water (NACW) that drives the 'global ocean conveyor' and whose return flow is manifest as the North-Atlantic Drift that moderates the climate of northwestern Europe. The significance of the Iceland VSR's as indicators of the processes of hotspot fluctuations has been recognised in the recent Large Igneous Province IODP Workshop (Colrain, 2007). Sampling the diachronous VSR's by drilling on the flanks of the Reykajnes Ridge in the North Atlantic is the only way to access this geological record. We propose to sample lavas from a transect along one of the youngest VSR's, exposed on the western flank of Reykjanes Ridge. The geochemistry of these lavas will yield insights into the genesis of the VSR's, and hence the causes and processes of hotspot fluctuation. The nature of the questions being addressed and our methodology have been informed from four separate, internationally sponsored workshops over the past 4 years. During the most recent, an UK-IODP workshop 'Rift2Ridge '07', Southampton, 2007, we identified an important link between this proposal and another IODP proposal by Wright et al, (in prep.) that aims to investigate the correlation between the initiation of VSR's on Iceland and fluctuations of NACW overflow strength.