Title: Physical conditions of magmatic-hydrothermal fracturing in deep crust: Records of subvolcanic deep low frequency earthquakes?

Abstract:

Recent geophysical observations have revealed that subvolcanic deep low frequency earthquakes (DLFEs) in the lower crust are coupled with volcanic earthquakes in the upper crust, suggesting magmatic/hydrothermal fluid flow triggering the earthquakes. However, the actual physico-chemical processes of DLFEs is largely unknown. Here I show the occurrences of magmatic dikes and hydrothermal mineral veins in a exceptionally-well exposed high temperature metamorphic terrane, Sør Rondane Mountains, East Antarctica, whose P-T conditions corresponds to the source regions of DLFEs. The fluid-rock reaction zones are subjected to reactive-transport, thermodynamic and structural analyses, to reveal spatio-temporal scales fluid-assisted crustal fracturing and discuss their relation to the observed seismic activities.

The depths (20–30 km), temperature (~700°C), duration of high-pressure fluids (hours to months), the extensional-shear mode of fracturing, and magnitudes (-1.5 to 2) observed in these dikes/veins are largely comparable to the depth, characteristic duration, focal mechanisms and magnitudes of the subvolcanic DLFEs. The geological observations strongly support non-double couple mechanisms for crustal fracturing in these regions, and suggest a large seismic anisotropy during the activation of these fractures.