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

这项紧急拨款提案旨在利用现场勘测机会，支持英国牵头的IODP钻探北大西洋地下室的提案。去年10月，史蒂夫·琼斯(都柏林三一学院)和布拉姆利·默顿(NOCS)向爱尔兰科学基金会和爱尔兰海洋研究所投标，获得了45万欧元的船期。凯尔特人探险家已经在2008年4月中旬至5月中旬期间向琼斯和默顿提供了服务。为了支持这次探险，寻求资金来移动和安装一台便携式多波束交换器(Reson 8160)，并从NMFD租用几艘挖泥船。成本不高，约为装船时间的2.5%。科学目标是绘制并采样冰岛西南部雷卡内斯山脉西侧裸露的V形山脊的走向。这项紧急拨款提案是为了支持一项由英国牵头的IODP主要提案(646-FULL)，该提案涉及火山热点活动波动的原因及其对地球环境包括气候的影响等基本问题。地幔深部上涌、局部温度和成分异常或浅地幔流动是否会引起热点波动？所涉及的时间尺度和费率是多少？在涉及地幔流动的地方，当它离开热点时，它的命运是什么？为了解决这些问题，我们建议对热点与大洋中扩张海脊相互作用的常见时间超前特征进行采样。这些现象对于冰岛-雷克雅内斯海脊来说尤其明显，在那里，一系列历时的V型海脊(VSR‘s)保存了过去35 Ma北大西洋海底热点活动变化的记录。与冰岛热点的这些波动有关的是北大西洋组分水(NACW)流量的变化，它驱动着“全球海洋传送带”，其返流表现为缓和欧洲西北部气候的北大西洋漂移。冰岛VSR作为热点波动过程的指标的重要性在最近的大型火成岩省IODP研讨会(Colrain，2007)中得到了认可。在北大西洋雷卡伊内斯山脊的侧翼钻取历时VSR样本是获取这一地质记录的唯一途径。我们建议沿着最年轻的VSR之一的横断面取样熔岩，该横断面暴露在雷克雅内斯山脊的西侧。这些熔岩的地球化学特征将有助于深入了解VSR的成因，从而揭示热点波动的原因和过程。正在讨论的问题的性质和我们的方法是在过去4年里从四个单独的国际赞助的讲习班上了解到的。在最近的一次，2007年在南安普敦举行的英国-IODP研讨会‘Rift2Ridge’07‘中，我们确定了这一提议与Wright等人的另一项IODP提议之间的重要联系(正在准备中)。其目的是研究冰岛上VSR的启动与NACW溢流强度波动之间的相关性。

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.