Conductivity-elevated by brucite amorphization and implication for electrical anomalies in shallow subduction zones

Pervasive high-conductivity anomalies in shallow cold subduction zones (40–70 km depths, corresponding to 1–2 GPa) remain unexplained by conventional mechanisms (e.g., dehydration fluids). Here we report a dramatic enhancement in brucite’s electrical conductivity at 1.2–2.0 GPa and 300–400 °C: conductivity rises sharply by 2–3 orders of magnitude over just 100 °C, ultimately reaching peak values of ~10−2 S/m, through integrated multi-anvil press experiments and in situ impedance spectroscopy analysis. Comprehensive post-experiment characterization of quenched samples confirms brucite preservation with no detectable dehydration byproducts (e.g., periclase). High-resolution transmission electron microscopy identifies high temperature-triggered distinct amorphous regions along grain boundaries above 300 °C, indicating conductivity enhancement arises from amorphization-facilitated proton transport in brucite. This result implies that high-conductivity anomalies in most shallow cold subduction zones likely originate from the amorphization of hydrous minerals (e.g., brucite), shedding light on the global water cycle and Earth’s deep electrical structure.