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

洋中脊形成了地球上最大的岩浆系统。当上地幔因板块分离而上涌并部分融化时，海洋地壳就形成了。由此形成的熔体向上上升，形成下洋壳的岩浆库，并喷发形成洋中脊玄武岩。对洋中脊岩浆储层的性质仍然知之甚少。传统的模型认为它们是纯熔体，其中岩浆的演化受部分结晶控制。这种模式正日益受到挑战，现在出现了一种新的模式，即岩浆储层由晶体糊状物（熔体和晶体的混合物）组成。浆液储层的熔融运移和演化可能受多孔流动控制，这对洋中脊玄武岩的喷发动力学和地球化学特征具有重要意义。本项目将重建大西洋中脊岩浆储层的构造和演化。它将利用科学海洋钻探从U1309D孔（北纬30度）回收的岩心。之前在这个位置进行的钻探表明，在缓慢扩张的洋中脊下，这一段包含了极好的岩浆储层化石记录。该项目将把岩心观测与最先进的元素测绘和矿物主要元素和微量元素测量相结合，以解决以下三个挑战：1)岩浆储层的规模；2)储层内熔体组成及演化；3)储层热史。总之，这些不同的组件将能够测试水库结构和熔体运输的不同末端构件模型。结果是对中大西洋脊下岩浆储层的性质和演化进行了严格的评估，并对海洋玄武岩的岩浆演化产生了影响，这可能作为一般的基性火成岩系统的模板。

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.