Accumulation of 'anti-continent' at the base of the mantle and its recycling in mantle plumes
Accumulation of 'anti-continent' at the base of the mantle and its recycling in mantle plumes
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DOI：
10.1016/j.gca.2013.11.019
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发表时间：
2014-10
影响因子：
5
通讯作者：
Y. Tatsumi;Toshihiro Suzuki;Haruka Ozawa;K. Hirose;T. Hanyu;Y. Ohishi
中科院分区：
文献类型：
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作者：
Y. Tatsumi;Toshihiro Suzuki;Haruka Ozawa;K. Hirose;T. Hanyu;Y. Ohishi
大陆地壳是固体地球中轻元素的独特储存库;它具有中间成分，据信主要是沿着火山弧形成的，火山弧是陆地安山岩岩浆活动的主要场所。然而，幔源弧岩浆一般是镁铁质或玄武质的。一个简单的机制，以克服这一明显的困境，并产生安山岩熔体在这样的设置是通过部分重熔的初始镁铁质弧地壳的热量提供的底侵玄武岩浆。与这种大陆地壳形成方式相反的是产生了难熔的熔融残渣，这里称之为“反大陆”。这种反大陆可能是由于密度反转而从弧壳中分离出来，并下降到上地幔中。高压实验表明，与俯冲洋壳相反，下沉的反大陆总是比周围的地幔更致密，这表明它穿过上地幔-下地幔边界，没有停滞，并在地幔底部积累形成200-400 km厚的物质，称为D″层。地球化学模拟提供了进一步的证据，证明这种积累的反大陆有助于形成一个深层次的热点源。因此，通过互补的过程，地球在地幔的顶部和底部分别创造了浮力大陆和致密的反大陆，并在地幔柱中回收了部分反大陆。
The continental crust is a unique reservoir of light elements in the solid Earth; it possesses an intermediate composition and is believed to have been created principally along volcanic arcs, which are major sites of terrestrial andesitic magmatism. Mantle-derived arc magmas are, however, generally mafic or basaltic. A simple mechanism to overcome this apparent dilemma and generate andesitic melts in such a setting is through the partial remelting of an initial mafic arc crust by heat supplied from underplating basaltic magmas. An antithesis to the formation of continental crust in this way should be the production of refractory melting residue, here referred to as ‘anti-continent’. This anti-continent is likely to detach from arc crust as a result of a density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking anti-continent is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that it penetrates through the upper-lower mantle boundary, without stagnation, and accumulates at the base of the mantle to form a 200–400 km thick mass known as the D″ layer. Geochemical modeling provides further evidence that this accumulating anti-continent contributes to a deep-seated hotspot source. Therefore, through complementary processes, Earth creates buoyant continents and dense anti-continents at the top and the base of the mantle, respectively, and has recycled portions of anti-continent in mantle plumes.