Metamorphism-facilitated faulting in deforming orthopyroxene: Implications for global intermediate-depth seismicity

• DOI: 10.1073/pnas.2112386119
• Publication Date: 2022-03-07T20:06:41Z
• Authors: Feng Shi; Yanbin Wang; Jianguo Wen; Tony Yu; Lupei Zhu; Taizi Huang; Kelin Wang
• Keywords: Physical Sciences; 01 natural sciences; 0105 earth and related environmental sciences

Significance The exothermic metamorphic reaction in orthopyroxene (Opx), a major component of oceanic lithospheric mantle, is shown to trigger brittle failure in laboratory deformation experiments under conditions where garnet exsolution takes place. The reaction product is an extremely fine-grained material, forming narrow reaction zones that are mechanically weak, thereby facilitating macroscopic faulting. Oceanic subduction zones are characterized by two separate bands of seismicity, known as the double seismic zone. The upper band of seismicity, located in the oceanic crust, is well explained by dehydration-induced mechanical instability. Our newly discovered metamorphism-induced mechanical instability provides an alternative physical mechanism for earthquakes in the lower band of seismicity (located in the oceanic lithospheric mantle), with no requirement of hydration/dehydration processes.