The slab–mantle interface in subduction zones is one of the geological boundaries with the most significant chemical potential gradients, which leads to fluid-mediated metasomatic reactions and chemical transport. As subducting sediment and basaltic crust often contain silica in various forms, the Si-metasomatism of mantle rocks is thought to occur along the subduction zone interface. However, growing evidence from the geochemistry of altered rocks and thermodynamic modelling has revealed the presence of multi-component fluids at the slab interface. Here, we review the laboratory experiments, geochemical models, and natural observations that improve our understanding of mass transport and metasomatic reactions at the crust–mantle interface, focusing on the relative mobility of Mg and Si. Hydrothermal experiments using analogues for the boundary between mantle (olivine) and crust (quartz or plagioclase) under vapor-saturated pressures indicate that Si is preferentially transported from crust to mantle, whereas Mg is immobile. This result is consistent with the distribution of talc rocks in oceanic lithosphere. On the other hand, at the contact between ultramafic (e.g., serpentinite) and crustal (pelitic schist or basaltic rocks) rocks in high-pressure metamorphic terranes, a large volume of chlorite rocks form in the crustal rocks, and the volume of chlorite often exceeds talc in serpentinites. Geochemical modeling reveals that in the shallow part of a subduction zone, the dissolved Si content of fluids in equilibrium with pelitic schist (C_Si,crust) is significantly higher than the dissolved Mg content of fluids in equilibrium with mantle peridotite (C_Mg,mantle); however, C_Mg,mantle becomes dominant at depth, resulting in the Mg-metasomatism of crustal rocks to form chlorite rocks. This Mg-metasomatism is more widespread in warmer subduction zones (e.g., the Nankai and Cascadia subduction zones) than in colder subduction zones (e.g., in Northeast Japan). In addition, the infiltration of CO₂-bearing fluid can form talc (along with carbonates) in ultramafic rocks without Si-metasomatism. Variations in the relative mobility of Si and Mg at the subduction zone interface produce variations in the overall solid volume change of mantle (expansion or contraction), the types of sheet silicates (talc versus chlorite), and the fluid budget (dehydration or hydration) during metasomatic reactions, which affects the pore fluid pressure, frictional strength of the subduction megathrust, and the location of seismicity around the mantle wedge corner.

俯冲带的板片-地幔界面是化学势梯度最显着的地质边界之一，导致流体介导的交代反应和化学输运。由于俯冲沉积物和玄武岩地壳经常含有各种形式的二氧化硅，因此认为地幔岩石的硅交代作用沿着俯冲带界面发生。然而，来自蚀变岩石地球化学和热力学模型的越来越多的证据表明，板片界面处存在多组分流体。在这里，我们回顾了实验室实验、地球化学模型和自然观测，这些实验、地球化学模型和自然观测提高了我们对地壳-地幔界面的质量传递和交代反应的理解，重点关注镁和硅的相对迁移率。在蒸汽饱和压力下，使用类似物对地幔（橄榄石）和地壳（石英或斜长石）之间的边界进行的热液实验表明，Si 优先从地壳迁移到地幔，而 Mg 则不可移动。这一结果与大洋岩石圈中滑石岩的分布一致。另一方面，在高压变质地体中的超镁铁质（如蛇纹岩）与地壳（泥质片岩或玄武岩）岩石接触处，地壳岩石中形成大量的绿泥石岩，且绿泥石的体积常常超过蛇纹岩中的滑石粉。地球化学模拟表明，在俯冲带浅部，流体中溶解的 Si 含量与泥质片岩处于平衡状态（而 Mg 是不动的。这一结果与大洋岩石圈中滑石岩的分布一致。另一方面，在高压变质地体中的超镁铁质（如蛇纹岩）与地壳（泥质片岩或玄武岩）岩石接触处，地壳岩石中形成大量的绿泥石岩，且绿泥石的体积常常超过蛇纹岩中的滑石粉。地球化学模拟表明，在俯冲带浅部，流体中溶解的 Si 含量与泥质片岩处于平衡状态（而 Mg 是不动的。这一结果与大洋岩石圈中滑石岩的分布一致。另一方面，在高压变质地体中的超镁铁质（如蛇纹岩）与地壳（泥质片岩或玄武岩）岩石接触处，地壳岩石中形成大量的绿泥石岩，且绿泥石的体积常常超过蛇纹岩中的滑石粉。地球化学模拟表明，在俯冲带浅部，流体中溶解的 Si 含量与泥质片岩处于平衡状态（地壳岩石中形成大量的绿泥石岩，蛇纹岩中绿泥石的体积常超过滑石。地球化学模拟表明，在俯冲带浅部，流体中溶解的 Si 含量与泥质片岩处于平衡状态（地壳岩石中形成大量的绿泥石岩，蛇纹岩中绿泥石的体积常超过滑石。地球化学模拟表明，在俯冲带浅部，流体中溶解的 Si 含量与泥质片岩处于平衡状态（C _Si,地壳)显着高于地幔橄榄岩平衡流体中溶解的Mg含量( C _Mg,地幔); 然而，C _Mg，地幔在深处占主导地位，导致地壳岩石的镁交代作用形成绿泥石岩石。这种镁交代作用在较温暖的俯冲带（例如南海和卡斯卡迪亚俯冲带）中比在较冷的俯冲带（例如日本东北部）中更为普遍。此外，CO _2的渗透含流体可以在超镁铁质岩石中形成滑石（以及碳酸盐），而无需硅交代作用。俯冲带界面处硅和镁相对迁移率的变化会导致地幔整体固体体积变化（膨胀或收缩）、片状硅酸盐类型（滑石粉与绿泥石）以及流体收支（脱水或水合）的变化在交代反应期间，这会影响孔隙流体压力、俯冲巨型逆冲断层的摩擦强度以及地幔楔角周围地震活动的位置。