Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, Texas 77005, USA.
Nature. 2010 Feb 18;463(7283):930-3. doi: 10.1038/nature08824.
Except for the first 50-100 million years or so of the Earth's history, when most of the mantle may have been subjected to melting, the differentiation of Earth's silicate mantle has been controlled by solid-state convection. As the mantle upwells and decompresses across its solidus, it partially melts. These low-density melts rise to the surface and form the continental and oceanic crusts, driving the differentiation of the silicate part of the Earth. Because many trace elements, such as heat-producing U, Th and K, as well as the noble gases, preferentially partition into melts (here referred to as incompatible elements), melt extraction concentrates these elements into the crust (or atmosphere in the case of noble gases), where nearly half of the Earth's budget of these elements now resides. In contrast, the upper mantle, as sampled by mid-ocean ridge basalts, is highly depleted in incompatible elements, suggesting a complementary relationship with the crust. Mass balance arguments require that the other half of these incompatible elements be hidden in the Earth's interior. Hypotheses abound for the origin of this hidden reservoir. The most widely held view has been that this hidden reservoir represents primordial material never processed by melting or degassing. Here, we suggest that a necessary by-product of whole-mantle convection during the Earth's first billion years is deep and hot melting, resulting in the generation of dense liquids that crystallized and sank into the lower mantle. These sunken lithologies would have 'primordial' chemical signatures despite a non-primordial origin.
除了地球历史的最初 5 亿到 10 亿年左右，当时大部分地幔可能经历过熔融，地球硅酸盐地幔的分化一直受到固态对流的控制。随着地幔上升并穿过固相线减压，它部分熔融。这些低密度的熔体上升到表面，形成大陆和海洋地壳，驱动着地球硅酸盐部分的分化。由于许多微量元素，如产热的 U、Th 和 K 以及惰性气体，优先分配到熔体中（这里称为不相容元素），熔体的提取将这些元素浓缩到地壳中（或在惰性气体的情况下到大气中），这些元素现在几乎占据了地球预算的一半。相比之下，从中洋脊玄武岩中采样的上地幔严重缺乏不相容元素，这表明与地壳之间存在互补关系。质量平衡论证要求这些不相容元素的另一半隐藏在地壳内部。对于这个隐藏储层的起源有很多假设。最广泛的观点是，这个隐藏的储层代表了从未经过熔融或脱气处理的原始物质。在这里，我们认为，地球最初 10 亿年期间整个地幔对流的一个必要副产品是深部和高温熔融，导致形成密集的液体，这些液体结晶并沉入下地幔。尽管起源非原始，但这些下沉的岩石具有“原始”的化学特征。
