Qin Yanfang, Singh Satish C, Grevemeyer Ingo, Marjanović Milena, Roger Buck W
Institut de Physique de Globe de Paris, 1 rue Jussieu, 75238, Paris, France.
Now at Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan.
Nat Commun. 2020 Aug 17;11(1):4122. doi: 10.1038/s41467-020-17946-3.
Crustal properties of young oceanic lithosphere have been examined extensively, but the nature of the mantle lithosphere underneath remains elusive. Using a novel wide-angle seismic imaging technique, here we show the presence of two sub-horizontal reflections at ∼11 and ∼14.5 km below the seafloor over the 0.51-2.67 Ma old Juan de Fuca Plate. We find that the observed reflectors originate from 300-600-m-thick layers, with an ∼7-8% drop in P-wave velocity. They could be explained either by the presence of partially molten sills or frozen gabbroic sills. If partially molten, the shallower sill would define the base of a thin lithosphere with the constant thickness (11 km), requiring the presence of a mantle thermal anomaly extending up to 2.67 Ma. In contrast, if these reflections were frozen melt sills, they would imply the presence of thick young oceanic lithosphere (20-25 km), and extremely heterogeneous upper mantle.
年轻海洋岩石圈的地壳属性已得到广泛研究，但其下方地幔岩石圈的性质仍然难以捉摸。利用一种全新的广角地震成像技术，我们在此展示了在0.51 - 2.67百万年老的胡安德富卡板块上海底以下约11公里和14.5公里处存在两个亚水平反射。我们发现观测到的反射层源自厚度为300 - 600米的地层，纵波速度下降约7 - 8%。它们可以通过部分熔融岩床或冻结辉长岩床的存在来解释。如果是部分熔融的，较浅的岩床将定义厚度恒定（11公里）的薄岩石圈底部，这需要存在一直延伸到2.67百万年的地幔热异常。相比之下，如果这些反射是冻结的熔浆岩床，它们将意味着存在厚的年轻海洋岩石圈（20 - 25公里）以及极其不均一的上地幔。
