Wasser im ozeanischem Mantel am schnell spreizenden ostpazifischen Rücken; Infrarot-Spektroskopie an nominell wasserfreiem Orthopyroxen

以名义无水矿物（NAM’s）形式存在于地幔中的水对地幔动力学有重大影响。正硅石是一种非常重要的水容器。在最上层的地幔中可能含有几百百万分之百的水，在更深的部分甚至含有更多的水，因为它的储存能力是加压的。以往关于地幔正辉石中水的研究仅限于来自次大陆地幔的橄榄岩捕虏体。来自海底地幔的第一批样品最近在一个自己的、由英国天然气集团资助的项目中进行了研究。这些第一批数据揭示了缓慢扩张的大西洋中脊中橄榄岩的水含量对比，从ODP-Leg 153的正辉石含水饱和度水平到ODP-Leg 209的含量始终低一个数量级。这一对比意味着熔体枯竭后不同的地幔停留时间和/或不同的隆升/挖掘速率。这一初步研究不仅使我们对地幔含水量有了更好的认识，而且对扩展中心下的动力学过程也有了新的认识。为了建立一个更一般的模型并检验初步的假设，研究快速扩张脊的橄榄岩是绝对必要的。建议的项目旨在通过调查来自Hess Deep， ODP-Leg 147的橄榄岩正辉石（水，主要、少量和微量元素含量，平衡条件）来弥补基本的知识差距。

Water that is present in the Earth's mantle in nominally anhydrous minerals (NAM's) has a significant influence on mantle dynamics. Orthopyroxene is a very important container for water. It may incorporate several hundred wt.-ppm H2O in the uppermost mantle and even higher amounts in deeper parts, because its storage capacity is pressure-enhanced. Any previous studies on water in mantle orthopyroxene were restricted to peridotite xenoliths from the sub-continental mantle. The first samples from the sub-oceanic mantle were recently studied in the course of an own, DFG-financed project. These first data reveal contrasting water contents in peridotite from the slow spreading Mid-Atlantic Ridge, from levels equal to water saturation in orthopyroxene at ODP-Leg 153 to contents that consistently are one order of magnitude lower at ODP-Leg 209. This contrast implies different mantle residence times after melt depletion and/or different uplift/exhumation rates. This preliminary investigation not only provides us with a better knowledge of the water contents in the mantle but also puts constraints concerning dynamic processes below spreading centers. To develop a more general model and to test the preliminary hypotheses, it is absolutely necessary to study peridotite from a fastspreading ridge. The project suggested is aimed at closing a fundamental gap of knowledge by investigating peridotitic orthopyroxene (water, major, minor and trace element contents, equilibrium conditions) from the Hess Deep, ODP-Leg 147.