Discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts using thermogravimetric analysis

Giachetti, Thomas; Gonnermann, H. M.; Gardner, James E.; Shea, Thomas; Gouldstone, Andrew

doi:10.1016/j.gca.2014.10.017

Cited by 51 publications

(44 citation statements)

References 98 publications

(159 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The amount of volatile loss in the temperature range associated with magmatic water (~550-1000°C, Roulia et al, 2006;Giachetti et al, 2015) shows a very weak correlation with TVC. Bulk volatile results are therefore assumed to predominantly reflect the amount of meteoric (or secondary water) in RR samples i.e., hydration post-emplacement.…”

Section: Water Content Variabilitymentioning

confidence: 96%

“…Magmatic glasses typically contain both primary (magmatic) and secondary (meteoric) water (Newman et al, 1986;Tuffen et al, 2010;Denton et al, 2012), the latter recording hydration by external water, which diffused into the glass post eruption, plus water adsorbed during sample preparation (Giachetti et al, 2015). It has been assumed previously that, at the low water concentrations characteristic of obsidian (b 1 wt.%), water dissolves in the glass predominantly as hydroxyl groups OH − , as a result of equilibrium speciation (Dixon et al, 1995;Zhang, 1999).…”

Section: Volatile Content Measurementsmentioning

confidence: 99%

“…Furthermore, the derivative of the TGA curve (dTG curve, shown in supplementary material) gives the rate of weight loss with time, from which we measure the peak degassing temperature, which gives information on the speciation of volatiles (Denton et al, 2012;Tuffen et al, 2012b). dTG peaks depend on many factors, including grainsize, heating rate, spatial distribution of water within grains, and volatile concentration (Tuffen et al, 2012b;Giachetti et al, 2015).…”

Section: Volatile Content Measurementsmentioning

confidence: 99%

“…Analysis of degassing rate with temperature indicates that several volatile phases contribute to the bulk TVC value ( Table 2). The patterns of volatile release on heating provide insights into the relative contributions of primary and secondary water in the glasses (Roulia et al, 2006;Denton et al, 2012;Tuffen et al, 2012b;Giachetti et al, 2015). In most samples the predominant dTG peak and mass loss is in the 250-550°C temperature range, which is thought to correspond to strongly bound molecular water present in pore spaces, usually ascribed to meteoric water (Roulia et al, 2006).…”

Section: Water Content Variabilitymentioning

confidence: 99%

“…In most samples the predominant dTG peak and mass loss is in the 250-550°C temperature range, which is thought to correspond to strongly bound molecular water present in pore spaces, usually ascribed to meteoric water (Roulia et al, 2006). It can also represent adsorbed meteoric water in samples containing b1 wt.% TVC (Giachetti et al, 2015). Contributions from weakly-bound H 2 O m (b250°C) and halogens (N 1000°C) are much less significant.…”

Section: Water Content Variabilitymentioning

confidence: 99%

See 4 more Smart Citations

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Shields

Mader

Caricchi

et al. 2016

Journal of Volcanology and Geothermal Research

View full text Add to dashboard Cite

Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2 km long, 100 m thick,~800 year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian (b15% vesicles), 'pumiceous' lava (N 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and low aspect ratio, 'frothy' obsidian with 30-60% vesicles. Textural heterogeneity is observed on all scales (m to μm) and occurs as the result of strongly localised strain. Magnetic fabric, described by oblate and prolate susceptibility ellipsoids, records high and variable degrees of shearing throughout the flow. Total water contents are derived using both thermogravimetry and infrared spectroscopy to quantify primary (magmatic) and secondary (meteoric) water. Glass water contents are between 0.08-0.25 wt.%. Water analysis also reveals an increase in water content from glassy obsidian bands towards 'frothy' bands of 0.06-0.08 wt.%, reflecting preferential vesiculation of higher water bands and an extreme sensitivity of obsidian degassing to water content. We present an outgassing model that reconciles textural, volatile and magnetic data to indicate that obsidian is generated from multiple shear-induced outgassing cycles, whereby vesicular magma outgasses and densifies through bubble collapse and fracture healing to form obsidian, which then re-vesiculates to produce 'dry' vesicular magma. Repetition of this cycle throughout magma ascent results in the low water contents of the Rocche Rosse lavas and the final stage in the degassing cycle determines final lava porosity. Heterogeneities in lava rheology (vesicularity, water content, microlite content, viscosity) play a vital role in the structural evolution of an obsidian flow and overprint flow-scale morphology. Post-emplacement hydration also depends heavily on local strain, whereby connectivity of vesicles as a result of shear deformation governs sample rehydration by meteoric water, a process previously correlated to lava vesicularity alone.

show abstract

Section: Water Content Variabilitymentioning

confidence: 96%

Section: Volatile Content Measurementsmentioning

confidence: 99%

Section: Volatile Content Measurementsmentioning

confidence: 99%

Section: Water Content Variabilitymentioning

confidence: 99%

Section: Water Content Variabilitymentioning

confidence: 99%

See 3 more Smart Citations

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Shields

Mader

Caricchi

et al. 2016

Journal of Volcanology and Geothermal Research

View full text Add to dashboard Cite

show abstract

Permeability Evolution in Variably Glassy Basaltic Andesites Measured Under Magmatic Conditions

Kushnir

Martel

Champallier

et al. 2017

Geophysical Research Letters

View full text Add to dashboard Cite

Heat from inflowing magma may act to seal permeable networks that assist passive outgassing at volcanic conduit margins and in overlying domes, reducing the efficiency of overpressure dissipation. Here we present a study of the evolution of permeability—measured under magmatic conditions—with increasing temperature in glassy and glass‐poor basaltic andesites from Merapi volcano (Indonesia). Whereas the permeability of glass‐poor rocks decreases little up to a temperature of 1,010°C, glassy specimens experience a pronounced decrease in permeability above the glass transition once the viscosity of the crystal suspension is low enough to relax under external stresses. Changes in temperature alone are thus not enough to significantly modify the permeability of the glass‐poor rocks that commonly form Merapi's dome. However, the presence of glass‐rich domains in a dome may lead to local sealing of the volcanic plumbing between eruptions, exacerbating localized overpressure development that could contribute to explosivity.

show abstract

Permeability During Magma Expansion and Compaction

et al. 2017

Self Cite

View full text Add to dashboard Cite

Plinian lapilli from the 1060 Common Era Glass Mountain rhyolitic eruption of Medicine Lake Volcano, California, were collected and analyzed for vesicularity and permeability. A subset of the samples were deformed at a temperature of 975°, under shear and normal stress, and postdeformation porosities and permeabilities were measured. Almost all undeformed samples fall within a narrow range of vesicularity (0.7–0.9), encompassing permeabilities between approximately 10−15 m2 and 10−10 m2. A percolation threshold of approximately 0.7 is required to fit the data by a power law, whereas a percolation threshold of approximately 0.5 is estimated by fitting connected and total vesicularity using percolation modeling. The Glass Mountain samples completely overlap with a range of explosively erupted silicic samples, and it remains unclear whether the erupting magmas became permeable at porosities of approximately 0.7 or at lower values. Sample deformation resulted in compaction and vesicle connectivity either increased or decreased. At small strains permeability of some samples increased, but at higher strains permeability decreased. Samples remain permeable down to vesicularities of less than 0.2, consistent with a potential hysteresis in permeability‐porosity between expansion (vesiculation) and compaction (outgassing). We attribute this to retention of vesicle interconnectivity, albeit at reduced vesicle size, as well as bubble coalescence during shear deformation. We provide an equation that approximates the change in permeability during compaction. Based on a comparison with data from effusively erupted silicic samples, we propose that this equation can be used to model the change in permeability during compaction of effusively erupting magmas.

show abstract

Discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts using thermogravimetric analysis

Cited by 51 publications

References 98 publications

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Permeability Evolution in Variably Glassy Basaltic Andesites Measured Under Magmatic Conditions

Permeability During Magma Expansion and Compaction

Contact Info

Product

Resources

About