Magma reservoir evolution at a slow-spreading mid-ocean ridge

大洋中脊形成了地球上最大的岩浆系统。洋壳是当上地幔因板块分离而向上涌出并部分熔融时形成的。由此形成的熔体向上上升，形成下部洋壳的岩浆储集层，并喷发形成大洋中脊玄武岩。大洋中脊岩浆储集层的性质仍然没有得到很好的约束。传统模型认为它们是纯熔体，其中岩浆的演化受分离结晶作用的控制。这一模式日益受到挑战，现在出现了一种新的模式，即岩浆库由晶体泥--熔体和晶体的混合物--组成。岩浆储集层中的熔体运移和演化可能受多孔渗流的控制，这对大洋中脊玄武岩的喷发动力学和地球化学特征具有重要的意义。它将利用将通过科学海洋钻探从U1309D(北纬30度)孔中回收的岩芯。此前在该地区进行的钻探表明，该区段包含了在一个缓慢扩张的大洋中脊之下的化石岩浆储集层的良好记录。该项目将把岩心观察与最先进的元素制图以及矿物主量元素和微量元素的测量相结合，以应对三个挑战：1)岩浆储集层的大小；2)这些储集层内的熔体组成和演化；3)储集层的热史。这些不同的成分结合在一起，将使对储集层结构和熔体运输的不同末端成员模型的测试成为可能。其结果是对中大西洋海脊下岩浆储集层的性质和演化进行了严格的评估，并对大洋玄武岩的岩浆演化进行了暗示，这通常可以作为镁铁质火成岩系统的模板。

Mid-ocean ridges form the largest magmatic system on Earth. Oceanic crust is formed when the upper mantle wells up and partially melts in response to plate separation. The melts thus formed rise upwards, forming the magma reservoirs of the lower oceanic crust, and erupt to form mid-ocean ridge basalts.The nature of magma reservoirs at mid-ocean ridges remains poorly constrained. Traditional models hold that they are bodies of pure melt in which magma evolution is controlled by fractional crystallisation. This model is increasingly challenged, and a new paradigm in which magma reservoirs are comprised of crystal mush - a mixture of melt and crystals - has now emerged. Melt transport and evolution in mush reservoirs may be controlled by porous flow, which has fundamental implications for the eruption dynamics and geochemical signatures of mid-ocean ridge basalts.This project will reconstruct the architecture and evolution of magma reservoirs at the Mid-Atlantic Ridge. It will capitalise on core that will be recovered from Hole U1309D (30 degrees N) by scientific ocean drilling. Previous drilling at this location has shown that this section contains an excellent record of fossilised magma reservoirs beneath a slow-spreading mid-ocean ridge.This project will integrate core observations with state-of-the-art element mapping and measurements of mineral major- and trace elements to address three challenges:1) The size of magma reservoirs;2) The melt composition and evolution within these reservoirs;3) The thermal histories of the reservoirs.Together, these different components will enable a test of the different end member models for reservoir architecture and melt transport. The outcome is a rigorous assessment of the nature and evolution of magma reservoirs beneath the Mid-Atlantic Ridge, with implications for magma evolution of oceanic basalts, which may serve as a template for mafic igneous systems generally.