Quake-induced redox change in the interior of planets

Abstract:

A quake releases elastic energy stored in the interior of planets. The most of the stored energy instantaneously convert into heat along a fault during a quake, which facilitates physico-chemical reactions and eventually changes in redox conditions in the planets. In order to explore a hypothesis that the redox reactions associated with a quake could provide a potential metabolic energy source for life on the planets, we have conducted high-velocity friction experiments that is capable of reproducing coseismic faulting and determined redox change within a fault by X-ray absorption near edge structure (XANES) analysis.

Friction experiments have been conducted on olivine and synthetic chondrite powders (with grain sizes of 100~180 μm) using a fluid pressure controlled, rotary shear apparatus at Kochi/JAMSTEC. Coseismic faulting was reproduced at slip velocity of 1.0 m/s with different displacements up to 18 m under normal stress and fluid pressure conditions of 30 and 25 MPa, respectively. After the experiments, the specimens were thin-sectioned to observe microstructures under FE-SEM and to determine the contribution of bivalent Fe to the total Fe (Fe²⁺/ΣFe) by the Fe L_III-edge μ-XRF-XANES analyses using the BL27SU at SPring-8.

Friction coefficient increased to 0.8-0.9 at the onset of rapid sliding, followed by slip weakening during which it decreased down to ~0.2 after the displacement of ~10 m. As increasing frictional work with displacement to ~34 MJ/m², the mean Fe²⁺/ΣFe values in the fault zone decreases from 0.68 to 0.59 and from 0.61 to 0.56 for olivine and chondrite samples, respectively. Such rapid oxidation reaction is likely attributed to the combination of the formation of very fine‐grained Fe minerals with fresh reactive surfaces and the transformation of liquid water into supercritical state by frictional heat. If we could observe quakes by seismometers on the planets, the proposed correlation between the frictional work (equivalent to quake magnitude) and the oxidation progress enables us to estimate the redox change associated with quakes in the planets.