Journal Article

Brittle Deformation of Damaged Mafic and Ultramafic Rocks and Their Implications on Plate Bending

Jayawickrama, Eranga, Katayama, Ikuo, Akamatsu, Yuya

2024

Overview

The effect of damage on the brittle deformation of mafic and ultramafic rocks has been investigated by performing triaxial deformation experiments on thermally cracked and intact rock samples. The investigation was performed by recording the axial and lateral strains during deformation while simultaneously capturing the ultrasonic velocity, and electrical resistivity. While the peak strength is presumably controlled by the stiff intrinsic fractures, the crack opening mode also showed critical effects on the attained peak strength. The pore pressure distribution showed an apparent control over the dynamic Young's modulus as the ratio between the dynamic and static modulus of thermally cracked rocks is significantly higher than that of intact rocks. The compliant nature and the higher inelastic volumetric strain of the thermally cracked samples further indicated a possible explanation to the steep dipping plates and the taller topographic heights at the trench outer rise systems of old subduction zones. Plain Language Summary The presence of fractures strongly influences the physical properties of rocks and not many experiments have been performed to understand the effect those fractures have on the deformation of mafic and ultramafic rocks. We find that, to address the deformation of the subduction zones, it is essential to perform experiments on such rocks under fully saturated conditions. As the incoming, relatively intact, oceanic plate sinks at the convergent boundaries, the plate bends significantly and creates a large number of faults. Therefore, the physical properties of the rock are subject to change and the way that rock deforms changes compared to an undamaged rock. However, so far, no research has been conducted to understand this change fully. Therefore, by performing experiments in the laboratory, we have attempted to understand how damage affects the physical properties and the deformation. By such experiments, we have identified that when fractures are present, the oceanic rocks show strong volume expansions before break by fracture and alter the physical properties. The results we have obtained here by gathering velocity, electrical resistivity, and strain, at the same time, can be related to the geophysical and topographic observations of the trench outer‐rise systems. Key Points The effect of damage on brittle deformation of mafic and ultramafic rocks has been addressed via experiments The ultrasonic velocity, electrical resistivity, and strain are measured simultaneously during deformation of rocks Presence of cracks strongly influence deformation and physical properties which are comparable to outer rise geophysical observations

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Brittleness / Damage / Deformation / Deformation effects / Electrical resistivity / Experiments / fracture / Fractures / mafic and ultramafic / Mechanical properties / Physical properties / Plates (tectonics) / Pore pressure / Pressure distribution / resistivity / Rock properties / Rocks / Sediment samples / Storage modulus / Subduction / Subduction (geology) / Subduction zones / Topography / Ultramafic materials / Ultramafic rocks / Velocity / Volumetric strain