Core-mantle boundary structures and processes
Core-mantle boundary structures and processes
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核幔边界结构和过程
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
E. Garnero
中科院分区：
文献类型：
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作者：
T. Lay;E. Garnero
地震学和地球动力学观测已经确定了在地幔底部存在一个主要的热化学边界层（TCBL）。这个边界层在调节通过核幔边界的热流方面起着关键作用，从而影响发电机产生的核流状态。它在地幔对流系统中也起着重要作用，可能是边界层不稳定性的来源，也可能是长期地球化学不均匀性的储存库。已经出现了两种TCBL端元概念模型，两者都与当前的观测限制相协调：在地幔最低的250公里处可能存在一个全球性的、稳定分层的、化学性质不同的层（全球TCBL模式），或者该区域可以是部分混合的边界层，化学异常，如海洋岩石圈板或榴辉岩海洋地壳成分和古代致密化学异常动态地集中在隆起之下的大团块（混合TCBL模型）。对于全球TCBL模型，横向变化的层内的部分熔融分数需要考虑到各种地震观测，并预计在这一层的上边界的大动态地形：有证据表明这两个属性的TCBL。混合TCBL模型需要额外的复杂性，如相变或结构组构转变，以考虑各种地震观测：一些矿物学候选人已被提出。突出的挑战，需要多学科的进步，是区分这些相互竞争的概念模型，因为它们不同的热历史，化学处理，和动力学行为的TCBL的影响。
Seismological and geodynamical observations have established the presence of a major thermo-chemical boundary layer (TCBL) in the lowermost mantle. This boundary layer plays a critical role in regulating heat flow through the core-mantle boundary, thereby influencing the dynamo-generating core flow regime. It also plays an important role in the mantle convection system, possibly serving as a source of boundary-layer instabilities and as a reservoir for long-lived geochemical heterogeneities. Two end-member conceptual models for the TCBL have emerged, both reconcilable with current observational constraints: a global, stably-stratified, chemically distinct layer may exist in the lowermost 250 km of the mantle (the global TCBL model), or this region may be a partially mixed boundary layer involving a composite of downwelling thermo-chemical anomalies such as oceanic lithospheric slabs or eclogitic oceanic crustal components and ancient dense chemical anomalies dynamically concentrated into large agglomerations beneath upwellings (the hybrid TCBL model). For the global TCBL model, laterally varying partial melt fractions within the layer are required to account for various seismological observations, and large dynamic topography on the upper boundary of this layer is expected: there is evidence for both of these attributes of the TCBL. The hybrid TCBL model requires additional complexity such as a phase transition or structural fabric transition to account for various seismological observations: some mineralogical candidates have been proposed. The outstanding challenge, requiring multi-disciplinary advances, is to discriminate between these competing conceptual models, as they differ in implications for thermal history, chemical processing, and dynamical behavior of the TCBL.