Origins of Mount St. Helens cataclasites: Experimental insights
-
Lori A. Kennedy
,
James K. Russell
Abstract
The 2004-2006 eruption of Mount St. Helens produced a sequence of lava domes characterized by a 1-3 m thick outer carapace of highly brecciated and comminuted dacite fault rocks. This outer layer of fault rocks is proposed to be a physical manifestation of the “drumbeat” microseismicity, such that magma extrusion occurred via integration of rapid, co-seismic slip along small displacement (<5 mm) faults.
A suite of deformation experiments performed on samples of Mount St. Helens (MSH) dacite under confining pressures of 0, 25, 50, and 75 MPa, at room temperature, and an average displacement rate of ~10-4/s were run to reproduce fault textures found in nature. The MSH dacite starting material has low porosity (7-8%), and a microcrystalline groundmass with little glass. A subsidiary set of deformation experiments on dacite samples from the 2006 Augustine eruption was run under identical experimental conditions to evaluate the effect of increased porosity (φ ~ 20-24%) on failure mechanisms.
The MSH dacite samples show a progressive increase in peak strength with increasing confining pressure, are strong (peak stress at 75 MPa is 700 MPa) and failed by localized, brittle behavior, characterized by macroscopic fractures and rapid stress drops. In contrast, Augustine dacite deformed by distributed cataclastic flow and is much weaker (peak stress at 75 MPa is 220 MPa). We propose that the generation of low-porosity dacite was an important variable in promoting wholesale localized faulting and the attendant drumbeat microseismicity at Mount St. Helens. Microstructures of gouge developed experimentally at room temperature are remarkably similar to those developed at ~730 °C at MSH. Mode I microcracking, shear fracture of grains, and grain size comminution occurred in both natural and experimental fault rocks. Laser grain size particle analyses show peaks at 1.5 μm for experimental run products vs. peaks at 1.9 and 4 μm for natural MSH gouge. We conclude that because the MSH lava had solidified prior to faulting, temperature is secondary in importance in the formation of the gouge material. Based on the amount of fault displacement per microseismic event, the number of “drumbeats,” and the aggregate radial thickness (1-3 m) of the gouge, we calculate that the 3-6 m/day eruption rate allows for gouge-filled slip surfaces having thicknesses of 0.8-5 mm and strike lengths of 98-190 m per seismic event.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- 27Al NMR spectroscopy at multiple magnetic fields and ab initio quantum modeling for kaolinite
- The effect of oxygen fugacity on the olivine to wadsleyite transformation: Implications for remote sensing of mantle redox state at the 410 km seismic discontinuity
- Spectroscopic characteristics of synthetic olivine: An integrated multi-wavelength and multi-technique approach
- Effects of hydration on thermal expansion of forsterite, wadsleyite, and ringwoodite at ambient pressure
- Forsterite, hydrous and anhydrous wadsleyite and ringwoodite (Mg2SiO4): 29Si NMR results for chemical shift anisotropy, spin-lattice relaxation, and mechanism of hydration
- Structural transitions and electron transfer in coffinite, USiO4, at high pressure
- Fe-Mg partitioning between perovskite and ferropericlase in the lower mantle
- Primitive oxygen-isotope ratio recorded in magmatic zircon from the Mid-Atlantic Ridge
- Determination of the potential for extrinsic color development in natural colorless quartz
- X-ray diffraction and Raman spectroscopic study of clinopyroxenes with six-coordinated Si in the Na(Mg0.5Si0.5)Si2O6-NaAlSi2O6 system
- Phase behavior of protoenstatite at high pressure studied by atomistic simulations
- Metasomatic replacement of inherited metamorphic monazite in a biotite-garnet granite from the Nízke Tatry Mountains, Western Carpathians, Slovakia: Chemical dating and evidence for disequilibrium melting
- Shear viscosity and diffusion in liquid MgSiO3: Transport properties and implications for terrestrial planet magma oceans
- Polarized infrared spectroscopic study of diffusion of water molecules along structure channels in beryl
- The vibrational spectrum of lizardite-1T [Mg3Si2O5(OH)4] at the Γ point: A contribution from an ab initio periodic B3LYP calculation
- Origins of Mount St. Helens cataclasites: Experimental insights
- The crystal structure and hydrogen bonding of synthetic konyaite, Na2Mg(SO4)2·5H2O
- Joëlbruggerite, Pb3Zn3(Sb5+,Te6+)As2O13(OH,O), the Sb5+ analog of dugganite, from the Black Pine mine, Montana
- Cathodoluminescence characterization of tridymite and cristobalite: Effects of electron irradiation and sample temperature
- Sequential extraction and DXRD applicability to poorly crystalline Fe- and Al-phase characterization from an acid mine water passive remediation system
- Thermoelasticity of ε-FeSi to 8 GPa and 1273 K
- Demicheleite-(Cl), BiSCl, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy
- Biomineralization associated with microbial reduction of Fe3+ and oxidation of Fe2+ in solid minerals
- Evidence for residual elastic strain in deformed natural quartz
- Mineralogy of mine waste at the Vermont Asbestos Group mine, Belvidere Mountain, Vermont
- Structural parameters of chromite included in diamond and kimberlites from Siberia: A new tool for discriminating ultramafic source
- Structure determination of the 2.5 hydrate MgSO4 phase by simulated annealing
Articles in the same Issue
- 27Al NMR spectroscopy at multiple magnetic fields and ab initio quantum modeling for kaolinite
- The effect of oxygen fugacity on the olivine to wadsleyite transformation: Implications for remote sensing of mantle redox state at the 410 km seismic discontinuity
- Spectroscopic characteristics of synthetic olivine: An integrated multi-wavelength and multi-technique approach
- Effects of hydration on thermal expansion of forsterite, wadsleyite, and ringwoodite at ambient pressure
- Forsterite, hydrous and anhydrous wadsleyite and ringwoodite (Mg2SiO4): 29Si NMR results for chemical shift anisotropy, spin-lattice relaxation, and mechanism of hydration
- Structural transitions and electron transfer in coffinite, USiO4, at high pressure
- Fe-Mg partitioning between perovskite and ferropericlase in the lower mantle
- Primitive oxygen-isotope ratio recorded in magmatic zircon from the Mid-Atlantic Ridge
- Determination of the potential for extrinsic color development in natural colorless quartz
- X-ray diffraction and Raman spectroscopic study of clinopyroxenes with six-coordinated Si in the Na(Mg0.5Si0.5)Si2O6-NaAlSi2O6 system
- Phase behavior of protoenstatite at high pressure studied by atomistic simulations
- Metasomatic replacement of inherited metamorphic monazite in a biotite-garnet granite from the Nízke Tatry Mountains, Western Carpathians, Slovakia: Chemical dating and evidence for disequilibrium melting
- Shear viscosity and diffusion in liquid MgSiO3: Transport properties and implications for terrestrial planet magma oceans
- Polarized infrared spectroscopic study of diffusion of water molecules along structure channels in beryl
- The vibrational spectrum of lizardite-1T [Mg3Si2O5(OH)4] at the Γ point: A contribution from an ab initio periodic B3LYP calculation
- Origins of Mount St. Helens cataclasites: Experimental insights
- The crystal structure and hydrogen bonding of synthetic konyaite, Na2Mg(SO4)2·5H2O
- Joëlbruggerite, Pb3Zn3(Sb5+,Te6+)As2O13(OH,O), the Sb5+ analog of dugganite, from the Black Pine mine, Montana
- Cathodoluminescence characterization of tridymite and cristobalite: Effects of electron irradiation and sample temperature
- Sequential extraction and DXRD applicability to poorly crystalline Fe- and Al-phase characterization from an acid mine water passive remediation system
- Thermoelasticity of ε-FeSi to 8 GPa and 1273 K
- Demicheleite-(Cl), BiSCl, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy
- Biomineralization associated with microbial reduction of Fe3+ and oxidation of Fe2+ in solid minerals
- Evidence for residual elastic strain in deformed natural quartz
- Mineralogy of mine waste at the Vermont Asbestos Group mine, Belvidere Mountain, Vermont
- Structural parameters of chromite included in diamond and kimberlites from Siberia: A new tool for discriminating ultramafic source
- Structure determination of the 2.5 hydrate MgSO4 phase by simulated annealing
