Fault-controlled hydration of the upper mantle during continental rifting
Fault-controlled hydration of the upper mantle during continental rifting
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DOI：
10.1038/ngeo2671
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发表时间：
2016-05-01
影响因子：
18.3
通讯作者：
Morgan, J. K.
中科院分区：
文献类型：
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作者：
Bayrakci, G.;Minshull, T. A.;Morgan, J. K.
水和碳从海洋转移到地幔的过程中，改变地幔橄榄岩，形成蛇纹岩，并支持不同的生态系统（1）。蛇纹石化地幔岩被发现于缓慢至超缓慢扩张的洋中脊（1）的海底之下，并被认为存在于世界上大约一半的裂谷边缘（2，3）。蛇纹岩也被推断存在于俯冲带的下行板块中（4），在那里它可能触发弧岩浆作用或使地球深部水合。水被认为是通过活动断层到达地幔的（3，4）。在这里，我们表明，在西班牙西部近海裂陷大陆边缘的蛇纹岩化可能开始时，整个地壳冷却，变得脆和变形集中沿着大的正断层。我们利用地震层析成像技术对地幔中蛇纹岩的三维分布进行成像，发现薄而脆的地壳下蛇纹岩的局部体积与沿沿着各断层的位移量有关。这意味着海水只有在断层活动时才到达地幔。我们估计的流体通量沿着断层，并发现它是推断大洋中脊热液系统。我们的结论是，地壳中的脆性过程可能最终控制全球海水流入地球。
Water and carbon are transferred from the ocean to the mantle in a process that alters mantle peridotite to create serpentinite and supports diverse ecosystems(1). Serpentinized mantle rocks are found beneath the sea floor at slow-to ultraslow-spreading mid-ocean ridges(1) and are thought to be present at about half the world's rifted margins(2,3). Serpentinite is also inferred to exist in the downgoing plate at subduction zones(4), where it may trigger arc magmatism or hydrate the deep Earth. Water is thought to reach the mantle via active faults(3,4). Here we show that serpentinization at the rifted continental margin offshore from western Spain was probably initiated when the whole crust cooled to become brittle and deformation was focused along large normal faults. We use seismic tomography to image the three-dimensional distribution of serpentinization in the mantle and find that the local volume of serpentinite beneath thinned, brittle crust is related to the amount of displacement along each fault. This implies that seawater reaches the mantle only when the faults are active. We estimate the fluid flux along the faults and find it is comparable to that inferred for mid-ocean ridge hydrothermal systems. We conclude that brittle processes in the crust may ultimately control the global flux of sea water into the Earth.