资源环境科技发展态势分析平台

Geophysical observations including surface heat flow data indicate the subducting slab becomes fully coupled to the overlying mantle wedge at ∼70-80 km depth. This maximum depth of decoupling (MDD) separates cool, stagnant forearc mantle from warmer, convecting mantle capable of generating arc magmas. Thermodynamic calculations demonstrate that talc is stable in H₂O-undersaturated parts of the mantle wedge where its stability is controlled by the pressure-dependent, fluid-absent reaction: talc + forsterite = antigorite + enstatite, which occurs at pressures ∼2-2.5 GPa (∼70-80 km depth) and temperatures < 650 °C. At shallower depths, H₂O-undersaturated portions of the basal mantle wedge contain talc, which experimental studies show dramatically weakens rocks. At greater depths, talc is restricted to silica-rich portions of the mantle wedge. The common MDD in subduction zones may reflect the downdip transition from a talc-present decoupled shear zone to a talc-absent fully coupled interface along the base of the mantle wedge.