Strain Localization Along Aphrodite Terra's Chasmata System, Venus: The Role of Frictional Melting and Fault-Melt Interaction

We analyze large-scale shear zones that are exposed along the equatorial chasmata of Eastern Aphrodite Terra to understand the role of strain localization in the deformation of the Venusian crust. These shear zones dip at low angles opposite to the slopes, forming terraces that expose portions of the shear planes. Patchy areas associated with the shear zones form rugged hilly terrains surrounded by radar-smooth plains of presumably low-viscosity material. The hanging wall and footwall of the shear zones and the associated rugged terrain, and smooth surfaces show distinct differences in radar emissivity suggesting lithological contrasts. We propose here that the fault planes are coated with melt films extruding alongside fault breccia. While frictional melting should be enhanced on Venus due to higher ambient temperatures and the presence of water-free mafic rocks, their volumes are likely too small to be detected in synthetic aperture radar data. We suggest that these faults act as conduits transporting magma from shallow subsurface reservoirs to the surface. Melt veneers reduce friction along the fault planes, allowing normal faulting at shallow dips. The trough asymmetries suggest that the faults were initiated as thrust faults and were later reactivated as normal faults, indicating negative inversion tectonics and a change in the geodynamic state from a convergent to an extensional regime. The delicate features associated with the shear zones suggest that fault activation is geologically young. This is supported by small landslide deposits that were likely triggered by seismic activity of the faults.