Ocean transformation faults, a key component of plate tectonics, represent first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in the lithosphere. However, the thermal structure along transformation faults and its effects on generating earthquakes are poorly understood. We report here the presence of a 10 to 15 km thick microseismicity band at depth in a 10 to 34 km depth range associated with a high temperature mantle (700 ° to 900 ° C) under the fragile lithosphere. along the Romanche. mega transformation fault in the equatorial Atlantic Ocean. The occurrence of the 2016 shallow magnitude 7.1 supershear rupture earthquake in 2016 and these deep micro-earthquakes indicate that although large earthquakes are occurring in the upper brittle lithosphere, a substantial amount of deformation is housed in the semi-small mylonitic mantle that resides at depths below the 600 ° C isotherm. We also observe a rapid deepening towards the west of this band of seismicity indicating a strong lateral heterogeneity.
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