Fifty years after plate tectonic theory was developed, the defining mechanism of the plate is still widely debated. The relatively short, simple history of young ocean lithosphere makes it an ideal place to determine the property that defines a plate, yet the remoteness and harshness of the seafloor have made precise imaging challenging. We use S-to-P receiver functions to image discontinuities beneath newly formed lithosphere at the Juan de Fuca and Gorda Ridges. We image a strong negative discontinuity at the base of the plate increasing from 20 to 45 km depth beneath the 0- to 10-million-year-old seafloor and a positive discontinuity at the onset of melting at 90 to 130 km depth. Comparison with geodynamic models and experimental constraints indicates that the observed discontinuities cannot easily be reconciled with subsolidus mechanisms. Instead, partial melt may be required, which would decrease mantle viscosity and define the young oceanic plate.
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机译：板块构造理论发展了五十年，板块的定义机制仍被广泛争论。年轻的海洋岩石圈的历史相对较短，简单，因此是确定板块性质的理想场所，但是海底的偏远和粗糙性使精确成像具有挑战性。我们使用S-to-P接收器函数对Juan de Fuca和Gorda Ridges新形成的岩石圈下的不连续面进行成像。我们在0到1000万年的海底之下，从板底部的20到45 km深度增加到一个强的负不连续性，而在90到130 km深度融化开始时，一个正的不连续性。与地球动力学模型和实验约束条件的比较表明，所观察到的不连续性不易与亚固相机制协调一致。取而代之的是，可能需要部分融化，这将降低地幔粘度并限定年轻的洋洋板。
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