Absence of density crossover between basalt and peridotite in the cold slabs passing through 660 km discontinuity
Absence of density crossover between basalt and peridotite in the cold slabs passing through 660 km discontinuity
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DOI：
10.1029/2004gl021306
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发表时间：
2004-12
影响因子：
5.2
通讯作者：
K. Litasov;E. Ohtani;A. Suzuki;T. Kawazoe;K. Funakoshi
中科院分区：
文献类型：
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作者：
K. Litasov;E. Ohtani;A. Suzuki;T. Kawazoe;K. Funakoshi
660公里不连续面附近的俯冲板片与周围地幔之间的相互作用是地球深部动力学的关键问题之一。明显的相变发生在板块的两个主要部分：玄武岩地壳和下面的橄榄岩。橄榄岩中的尖晶石后转变发生在 660 公里处，而玄武岩中的石榴石后转变被认为发生在 720-800 公里处，从而产生了密度交叉。在本文中，我们通过原位 X 射线衍射研究确定了大洋中脊玄武岩（洋壳的代表）中的石榴石后相界。相界可表示为 P(GPa) = 0.0041 T(K) + 17.92。目前的结果表明，冷板片的玄武岩成分在比周围地幔更低的压力下转变为钙钛矿组合体，并为洋壳侵入下地幔而没有与板片橄榄岩体重力分离提供了直接证据。
Interaction between subducting slabs and surrounding mantle near 660 km discontinuity is one of the key issues in the dynamic of deep Earth. Distinguishing phase transformations occur in the both major parts of the slab: basaltic crust and underlying peridotite. Post‐spinel transformation in peridotite takes place at 660 km, whereas post‐garnet transformation in basalt is considered to occur at 720–800 km creating density crossover. In this paper we determined the post‐garnet phase boundary in Mid‐Ocean Ridge basalt (representative for oceanic crust) by in situ x‐ray diffraction studies. The phase boundary can be expressed as P(GPa) = 0.0041 T(K) + 17.92. The present results imply that the basaltic component of the cold slab transformed to perovskite assembly at lower pressure than the surrounding mantle and provide direct evidence for penetration of the oceanic crust into the lower mantle without gravitational separation from the peridotite body of the slab.