The weak slab interface controls long-term subduction dynamics. A weak hydrous layer at the slab interface promotes mechanical decoupling between the forearc mantle and the subducting slab and converts a hot forearc mantle to a cold mantle. Often referred to as a cold nose, the cold forearc mantle, plays a key role in the transition from subduction infancy to mature subduction. This study was the first to numerically demonstrate the self-consistent formation of a weak hydrous layer with permeability anisotropy based on the Southwest Japan subduction zone case, where transition-related geological features were present. Our models showed that mechanical decoupling by spontaneous downdip growth of the weak hydrous layer created a cold nose by converting a hot forearc mantle to a cold mantle. The emergence of a cold nose explained the migration of the forearc-to-arc volcanic front, expressed as the formation of mid-Miocene forearc high-magnesium andesite and Quaternary arc adakite. Furthermore, the weak hydrous layer providing a pathway for free-water transport toward the mantle wedge tip elucidates slab/mantle-derived geochemical components in deep groundwater as well as large S-wave delay times and non-volcanic seismic tremors in the forearc.

弱板片界面控制着长期的俯冲动力学。板片界面处的弱含水层促进了弧前地幔和俯冲板片之间的机械解耦，并将热的弧前地幔转变为冷地幔。冷前弧地幔通常被称为冷鼻，在俯冲婴儿期到俯冲成熟期的过渡中起着关键作用。这项研究首次以日本西南部俯冲带为例，数值论证了具有渗透率各向异性的弱含水层的自洽形成，该俯冲带存在与转变相关的地质特征。我们的模型表明，弱含水层自发下倾生长的机械解耦通过将热的弧前地幔转变为冷地幔而产生了冷鼻。冷鼻的出现解释了弧前火山锋向弧前的迁移，表现为中新世中期弧前高镁安山岩和第四纪弧埃达克岩的形成。此外，弱含水层为自由水向地幔楔尖输送提供了通道，阐明了深层地下水中板片/地幔衍生的地球化学成分以及弧前的大横波延迟时间和非火山地震颤动。