FEC Recovery for Co-Chief Scientists Duties for Prof Damon A.H. Teagle and Petrologist Dr Michelle Harris; IODP Expedition 335 Superfast 4

大洋中脊在海洋中形成一系列山脉，环绕地球，就像棒球上的接缝一样。这些海脊是板块构造扩张形成新洋壳的建设性板块边界。这是地球释放内部热量的主要过程，地球表面的60%是在过去的1.8亿年中形成的。由于岩浆在约1200摄氏度的温度下喷发并侵入海洋地壳，因此渗入地壳的海水变得剧烈加热，通常导致被称为黑烟的海底间歇泉喷出>350摄氏度的富含硫化物的流体。岩浆和热液“热水”循环之间有着非常密切的关系，由于洋脊位于水深超过2000米的地方，因此，对洋脊形成的许多过程仍然知之甚少。使用潜水器的科学家只能观察最近喷发的熔岩。地球物理学家可以使用地震速度（波穿过岩石的速度）测量海洋地壳，但他们的结果必须根据实际岩石进行校准才能理解。对海洋地壳的次表层取样需要进行深钻，自1960年代以来，回收基底岩芯一直是科学海洋钻探的一个主要目标。保存在陆地上的古代海洋岩石，被称为蛇绿岩，表明海洋地壳由三个基本层组成：喷发的熔岩，通常具有枕形形状，过度垂直的侵入体被称为席状岩脉，过度，粗粒辉长岩是结晶的岩浆房。到目前为止，只有两个科学钻孔已经完全穿透熔岩进入堤坝; ODP孔504 B和1256 D。2005年，IODP Expeditions 309-312号考察队返回到1256 D孔，并将该孔加深至>1500米，完全穿过熔岩、岩脉，进入岩脉-辉长岩过渡带。东太平洋的1256 D孔被钻到以非常快的扩张速度（>200毫米/年）形成的地壳中，因为辉长岩被正确地预测为在那里最浅。虽然只有约20%的全球海脊轴以快速扩张速度（>80毫米/年）扩张，但目前60%的海洋盆地和约30%的地球表面是通过快速扩张形成的。以快速扩张速度形成的地壳应该是相对均匀的，因此可以合理地推断出在一个单一位置钻探可以描述地壳的重要部分。这个洞现在的深度，我们将能够采样辉长岩的第一次在完整的海洋地壳。这些岩石构成了古代岩浆房形成的海洋基底的三分之二。然而，这种岩浆房的体积和几何形状知之甚少。同样鲜为人知的是，海水通过地壳向下蒸发对冷却下地壳和带走结晶过程中产生的热量的影响。其他基本参数，如地震层3和层2/3边界的地质意义，以及下大洋地壳对海底磁异常的贡献仍然知之甚少。IODP Expedition 335从1256 D孔恢复的岩心和地球物理数据将为了解大洋地壳的火成岩结构提供独特的资源。通过与船上（和巡航后）化学分析相联系的仔细描述，我们将能够计算岩浆房的大小，流体-岩石相互作用的物理条件，并校准远程区域地震和磁性地球物理测量。这将大大提高人们对洋壳是如何构成和年龄远离洋脊的认识，并检验长期存在的相互竞争的岩浆吸积和热液冷却模型。

The mid-ocean ridges form a chain of mountains in the oceans that circuit the Earth like seams on a baseball. These ridges are the constructive plate boundaries where new ocean crust is formed by plate tectonic spreading. This is the major process by which the Earth releases its internal heat, and ~60% of the Earth's surface was formed in the past 180 million years. Because magma is erupted onto and intruded into the ocean crust at ~1200 deg C, seawater that percolates into the crust becomes vigorously heated, commonly resulting in submarine geysers known as black smokers that disgorge >350 deg C, sulfide-rich fluids. There is a very close relationship between magma and hydrothermal "hot water" circulation.Because the ocean ridges are beneath >2000 m of water many of the processes related to their formation remain poorly understood. Scientists using submersibles can observe only the most recently erupted lavas. Geophysicists can make measurements of the ocean crust using seismic velocities (the speed that waves travel through rocks), but their results must be calibrated against actual rocks to be understood. Sampling the sub-surface of the ocean crust requires deep drilling and the recovery of basement rock cores has been a major goal of scientific ocean drilling since the 1960s. Ancient oceanic rocks preserved on land, known as ophiolites, suggest that the ocean crust is made of three basic layers: erupted lavas, commonly with pillowed shapes, that overly vertical intrusions known as sheeted dikes, which overly, coarse-grained gabbroic rocks that are crystallized magma chambers. To date only two scientific drill holes have penetrated the completely through lavas into the dikes; ODP Holes 504B and 1256D. IODP Expeditions 309-312 returned to Hole 1256D in 2005 and deepened that hole to >1500 m, completely through the lavas, dikes, and into the dike-gabbro transition.Hole 1256D in the eastern Pacific Ocean, was drilled into crust that formed at a very fast spreading rate (>200 mm/yr), because gabbros were correctly predicted to be at their shallowest there. Although only ~20% of the global ridge axis is spreading at fast spreading rates (>80 mm/yr full rate), 60% of the current ocean basins and ~30% of the Earth's surface was formed by fast spreading. Crust formed at fast spreading rates should be relatively uniform, therefore drilling at a single location can be reasonably extrapolated to describe a significant portion of the Earth's crust. This hole is now at a depth where we will be able to sample gabbros for the first time in intact ocean crust. These rocks make up two thirds of the oceanic basement formed in ancient magma chambers. However, the volume and geometry of such magma chambers are poorly known. Also poorly known is the influence of seawater percolating down through the crust on cooling the lower crust and removing heat generated during crystallization. Other fundamental parameters such as the geological meaning of Seismic Layer 3 and the Layer 2/3 boundary, as well as the contribution of the lower oceanic crust to seafloor magnetic anomalies remain poorly understood.The cores and geophysical data recovered on IODP Expedition 335 from Hole 1256D will provide a unique resource for understanding the igneous construction of the ocean crust. By making careful descriptions linked with shipboard (and post-cruise) chemical analyses we will be able to calculate the size of magma chambers, the physical conditions of fluid-rock interactions, and calibrate remote regional seismic and magnetic geophysical measurements. This will lead a significantly improved knowledge of how the oceanic crust is constructed and ages away from the ocean ridges, and test long-standing, competing models magmatic accretion and hydrothermal cooling.