Accretion of the lower oceanic crust at fast-spreading ridges: a rock drill and near-bottom seafloor survey in support of IODP drilling in Hess Deep.

洋中脊海底扩张形成的海洋岩石圈是地球上运行的基本地质过程之一。最重要但也最棘手的问题之一，是了解山脊下的岩浆储层如何产生下地壳，尤其是在快速扩张的情况下。来自快速扩张下地壳的辉长岩通常难以接近；只有在赫斯深裂谷（东太平洋）有一大块已知是暴露的。我们建议使用遥控车辆调查这一独特的部分，以满足高排名的IODP提案#551的现场调查要求。此外，我们计划利用英国地质调查局的“BRIDGE”海底岩石钻机进行自己的采样计划，在辉长岩剖面的样带中获得大量短（1米）定向岩心。限制从地幔到地壳和地壳到海洋的热量和质量通量，以及检验大洋中脊岩浆库功能的相互矛盾的模型，只能通过直接观察和抽样来检验。全定向岩心是解决许多突出问题的必要条件，BRIDGE钻井的这些能力仍然是独一无二的。这项调查不仅将增加IODP提案，而且将以其自身的权利回答IODP运营无法解决的许多关键问题。

Generation of ocean lithosphere by seafloor spreading at mid-ocean ridges is one of the fundamental geological processes operating on Earth. One of the most important yet most intractable problems is to understand how the magma reservoir beneath ridges generates the lower crust, especially at fast spreading rates. Gabbroic rocks from fast-spread lower crust are normally inaccessible; only in the Hess Deep rift valley (E Pacific) is a substantial section known to be exposed. We propose to survey this unique section using a remotely-operated vehicle in order to satisfy site survey requirements for the highly-ranked IODP proposal #551. In addition we plan to conduct our own sampling programme using the British Geological Survey's 'BRIDGE' seabed rock drill to obtain large numbers of short (1 m) orientated cores in transects through the gabbro section. Constraining heat and mass flux from the Earth's mantle to crust and crust to ocean, and testing conflicting models for the functioning of mid-ocean ridge magma chambers, can only be tested by direct observation and sampling. Fully oriented cores are imperative to address many of the outstanding questions and these capabilities of the BRIDGE drill remain unique. This survey will not only augment the IODP proposal but will in its own right also answer many critical questions that IODP operations cannot tackle.