Dipartimento di Geoscienze, Università di Padova, Padova, Italy.
Nature. 2020 Mar;579(7797):88-91. doi: 10.1038/s41586-020-2045-y. Epub 2020 Feb 26.
Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, to slab devolatilization at subduction zones, or to mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China and the young petit-spot volcanoes offshore of the Japan Trench cannot readily be associated with any of these mechanisms. In addition, the mantle beneath these types of volcanism is characterized by zones of anomalously low seismic velocity above and below the transition zone (a mantle level located at depths between 410 and 660 kilometres). A comprehensive interpretation of these phenomena is lacking. Here we show that most (or possibly all) of the intraplate and petit-spot volcanism and low-velocity zones around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous mantle transition zone. Numerical modelling indicates that 0.2 to 0.3 weight per cent of water dissolved in mantle minerals that are driven out from the transition zone in response to subduction and retreat of a tectonic plate is sufficient to reproduce the observations. This suggests that a critical amount of water may have accumulated in the transition zone around this subduction zone, as well as in others of the Tethyan tectonic belt that are characterized by intraplate or petit-spot volcanism and low-velocity zones in the underlying mantle.
地球上大多数的岩浆活动通常归因于大洋中脊的被动地幔上涌、俯冲带的板块脱水作用或地幔柱。然而，中国东北广泛存在的新生代板内火山活动和日本海沟近海的年轻小斑点火山活动却不能轻易与这些机制中的任何一种联系起来。此外，这些类型的火山活动下方的地幔，在转换带（位于 410 至 660 公里深处的地幔层）上下都有异常低速区的特征。对这些现象缺乏全面的解释。在这里，我们表明，大多数（或可能全部）的板内和小斑点火山活动以及日本俯冲带周围的低速区，可以用俯冲的太平洋板块与含水的地幔转换带在新生代的相互作用来解释。数值模拟表明，从俯冲和板块后退的转换带中带出的地幔矿物中溶解的 0.2 到 0.3 重量百分比的水足以重现这些观测结果。这表明，在这个俯冲带周围的转换带以及特提斯构造带中的其他俯冲带中，可能已经积累了大量的水，这些俯冲带的特征是板内或小斑点火山活动以及下方地幔中的低速区。
