Metastable olivine within oceanic lithosphere in the uppermost lower mantle beneath the eastern United States
Metastable olivine within oceanic lithosphere in the uppermost lower mantle beneath the eastern United States
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DOI：
10.1130/g49879.1
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发表时间：
2022-04
期刊：
影响因子：
5.8
通讯作者：
F. Kong;Stephen S. Gao;Kelly H. Liu;Yinxia Fang;Hejun Zhu;R. Stern;Jiabiao Li
中科院分区：
文献类型：
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作者：
F. Kong;Stephen S. Gao;Kelly H. Liu;Yinxia Fang;Hejun Zhu;R. Stern;Jiabiao Li
大约三分之二的地球最外层是由海洋板块组成的，这些板块形成于扩张的山脊，并在俯冲带中循环回地球内部。随着温度和压力的增加，俯冲岩石圈板片发生了一系列物理和化学变化。特别是，橄榄石，在上地幔中最丰富的矿物，逐步转变为高压多晶型地幔过渡带附近，这是由410公里和660公里的不连续面。然而，橄榄石是否仍然存在于板片的核心，一旦他们穿透660公里的不连续性仍然存在争议。SKS和SKKS剪切波差分分裂时间的基础上，我们报告的新证据，揭示了亚稳橄榄石的存在下地幔最上部的古老的Farallon板块下美国东部。我们估计，低密度的橄榄石层在俯冲Farallon板可能会补偿高密度的板的其余部分与低温，导致中性浮力和防止进一步下沉的板到更深的部分的下地幔。
Approximately two-thirds of Earth’s outermost shell is composed of oceanic plates that form at spreading ridges and recycle back to Earth’s interior in subduction zones. A series of physical and chemical changes occur in the subducting lithospheric slab as the temperature and pressure increase with depth. In particular, olivine, the most abundant mineral in the upper mantle, progressively transforms to its high-pressure polymorphs near the mantle transition zone, which is bounded by the 410 km and 660 km discontinuities. However, whether olivine still exists in the core of slabs once they penetrate the 660 km discontinuity remains debated. Based on SKS and SKKS shear-wave differential splitting times, we report new evidence that reveals the presence of metastable olivine in the uppermost lower mantle within the ancient Farallon plate beneath the eastern United States. We estimate that the low-density olivine layer in the subducted Farallon slab may compensate the high density of the rest of the slab associated with the low temperature, leading to neutral buoyancy and preventing further sinking of the slab into the deeper part of the lower mantle.