Frictional Properties and Healing Behavior of Tectonic Mélanges: Implications for the Evolution of Subduction Fault Zones

Here, we report data from velocity-step experiments using rocks collected from ancient subduction fault zones, the Lower Mugi and Makimine mélanges of the Cretaceous Shimanto belt. The two mélanges preserve paleotemperature records corresponding to the updip and downdip limits of the seismogenic zone and deformation recording a lower versus higher degree of pressure solution. The compostions of the mélanges analyzed with X-ray diffraction (XRD) are also included in the datasets. Our data show that the Lower Mugi mélange sample exhibits velocity-weakening to velocity-neutral behavior under low normal stress, and the Makimine mélange sample shows velocity-strengthening behavior under high normal stress. This is consistent with the slip behavior observed at the depths they have been subducted to along the plate interface. We also perform a series of slide-hold-slide experiments under different hydrothermal conditions using the Lower Mugi mélange sample to evaluate the role of pressure solution in fault healing and its dependency on temperature. The results show that healing rates increase in tests operated at higher temperatures, which suggests the importance of pressure solution healing along plate interfaces.