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Frictional melt homogenisation during fault slip: Geochemical, textural and rheological fingerprints

DOI: 10.1016/j.gca.2019.04.010 DOI Help

Authors: Paul A. Wallace (University of Liverpool) , Sarah Henton De Angelis (University of Liverpool) , Adrian J. Hornby (University of Liverpool; Ludwig-Maximilians-Universität (LMU)) , Jackie E. Kendrick (University of Liverpool) , Stephen Clesham (University of Liverpool) , Felix W. Von Aulock (University of Liverpool) , Amy Hughes (University of Liverpool) , James E. P. Utley (University of Liverpool) , Takehiro Hirose (Kochi Institute for Core Sample Research (KCC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)) , Donald B. Dingwell (Ludwig-Maximilians-Universität (LMU)) , Yan Lavallee (University of Liverpool)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Geochimica Et Cosmochimica Acta

State: Published (Approved)
Published: April 2019
Diamond Proposal Number(s): 9220

Abstract: Volcanic environments often represent structurally active settings where strain localisation can promote faulting, frictional deformation, and subsequent melting along fault planes. Such frictional melting is thermodynamically a disequilibrium process initiated by selective melting of individual mineral phases and softening of volcanic glass at its glass transition as a response to rapid frictional heating. The formation of a thin melt layer on a fault plane surface can drastically accelerate or terminate slip during fault motion. A comprehensive understanding of the physical and chemical properties of the frictional melt is required for a full assessment of slip mechanism, as frictional rheology depends on the contributions from selectively melted mineral and glass phases as well as the physical effects of restite fragments suspended in the frictional melt. Here, we experimentally investigate the impact of host-rock mineralogy on the compositional and textural evolution of a frictional melt during slip. High-velocity rotary shear (HVR) experiments were performed under controlled, volcanically relevant, coseismic conditions (1 m s−1 slip rate and 1 MPa normal stress) using three intermediate dome lavas with contrasting mineral assemblages, sampled from volcanic systems where fault friction is evident: (1) an amphibole-bearing andesite (Soufrière Hills Volcano, Montserrat); (2) an amphibole-poor dacite (Santiaguito dome complex, Guatemala); and (3) an amphibole-free andesite (Volcán de Colima, Mexico). For each sample, five HVR experiments were terminated at different stages of frictional melt evolution, namely: (1) at the onset of melting and (2) formation of a steady-state melt layer; and (3) after 5 m, (4) 10 m, and (5) 15 m of slip at steady-state conditions. Progressive mixing and homogenisation of selective, single-phase melts within the frictional melt layer through double-diffusion convection demonstrates the dependence of melt composition on slip behaviour. Amphiboles melted preferentially, leading to lower shear stress (∼1 MPa) and pronounced shear weakening during the frictional melting of amphibole-bearing lavas. The results highlight the implications of mineral assemblage on volcanic conduit flow processes, which may influence the explosivity of eruptions, and run-out distances of rapid granular flows.

Journal Keywords: Amphibole; Chemical homogenisation; Faulting; Frictional melt; Viscosity; Volcano

Subject Areas: Earth Science, Chemistry

Instruments: I18-Microfocus Spectroscopy