Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere
Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere
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DOI：
10.1073/pnas.1608269113
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发表时间：
2016-09-20
影响因子：
11.1
通讯作者：
Warren, Jessica M.
中科院分区：
文献类型：
--
作者：
Hansen, Lars N.;Qi, Chao;Warren, Jessica M.
板块构造是地球结构的一个关键特征，其行为和动力学是众多大规模过程的基本驱动因素。一般来说，板块构造的运作紧密依赖于岩石圈板块与对流的内部耦合的方式。当前的争论集中在从刚性岩石圈到流动的软流圈的转变是与温度升高有关，还是与成分变化有关，比如在特定深度以下存在少量熔体或含水量增加。因此，刚性岩石圈与流动的软流圈耦合的方式目前尚不清楚。在此，我们展示了对含熔体和不含熔体的橄榄石集合体进行的基于实验室的扭转实验的结果，得出了一个描述橄榄石颗粒晶体取向的改进数据库。我们将这个数据库与大洋上地幔的流动模型相结合，以预测大洋盆地下方地震各向异性的结构。我们的模型与地震观测结果相符，支持岩石圈底部受热控制的观点。该模型还支持这样一种观点，即速度和各向异性的不连续性（通常被认为是岩石圈底部）实际上是岩石圈内的特征，反映的是在大洋中脊形成的成分边界，而非流变边界。
Tectonic plates are a key feature of Earth's structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.