The hydration and alteration of perlite and rhyolite

Denton, Jo S.; Tuffen, Hugh; Gilbert, Jennifer; Odling, Nicholas

doi:10.1144/0016-76492008-007

Cited by 65 publications

(57 citation statements)

References 26 publications

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“…16, see also supplementary material). Glassy obsidian (type 1) and 'frothy' obsidian (type 2) have the lowest TVC and the highest peak degassing temperature, whereas pumiceous (type 3) and shear banded (type 4) samples have higher TVC and consistently low peak degassing temperatures (see also Denton et al, 2009). Although texture additionally influences the temperature of volatile loss, with vesicular samples degassing at lower temperatures due to shorter diffusive path lengths (Giachetti et al, 2015), we can nonetheless broadly group the major lava types into those that have experienced significant (types 3 and 4) and insignificant hydration (types 1 and 2).…”

Section: Water Content Variabilitymentioning

confidence: 93%

“…Thermal Gravimetric Analysis (TGA) Multi-species volatile contents and degassing patterns of 16 obsidian samples (representing a wide spatial distribution) were characterised by simultaneous differential scanning calorimetry-thermogravimetric analysis (DCS-TGA) using TA Instruments SDT Q600 and STA 449 devices, following the methods set out in (Denton et al, 2009) and (Applegarth et al, 2013). The DSC-TGA technique subjects the sample to a controlled heating programme (0-1250°C at 5°C/min), during which sample weight and differential heat flow are continually measured.…”

Section: Volatile Content Measurementsmentioning

confidence: 99%

“…A previous study by (Giachetti et al, 2015), however, found that experimental volcanic glass lost magmatic water in the temperature range 250-550°C, ordinarily associated with meteoric water. Nonetheless, these samples contain over 4 wt.% total water, and samples with higher volatile concentrations are known to degas at lower temperatures (Denton et al, 2009). For samples with water contents similar to those in this study, all measured peak degassing temperatures were over 550°C (Giachetti et al, 2015).…”

Section: Discrimination Between Magmatic and Meteoric Watermentioning

confidence: 99%

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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

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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.

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Section: Water Content Variabilitymentioning

confidence: 93%

Section: Volatile Content Measurementsmentioning

confidence: 99%

Section: Discrimination Between Magmatic and Meteoric Watermentioning

confidence: 99%

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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

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“…In the field, perlite is commonly distinguished by its vitreous, pearly luster, and concentric (conchoidal) fractures, with colors ranging from transparent light gray to glossy black. The geologic settings in which perlite occurs include the glassy parts of domes and lava flows of rhyolitic composition (Marshall, 1961); pyroclastic flows and ignimbrites (White and McPhie, 1997;McArthur et al, 1998); vitric tephra and the chill margins of dykes and sills (Davis and McPhie, 1996;Allen and McPhie, 2002;Orth and McPhie, 2003;Denton et al, 2009;Tuffen and Castro, 2009); and welded ash-flow tuffs (Koukouzas and Dunham, 1994;Tait et al, 2009;Denton et al, 2012). Perlite can transform (devitrify) into clays in response to low temperature metamorphism and/or hydrothermal activity (Marshall, 1961;Lofgren, 1970;Friedman and Long, 1984), but can also remain quite stable under surficial conditions for millions of years (Yamagishi and Dimroth, 1985;Davis and McPhie, 1996;McArthur et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Geology of the Selene perlite deposit in the northern Sierra Madre Occidental, northeastern Sonora, Mexico

Hinojosa-Prieto¹,

Vidal-Solano²,

Kibler³

et al. 2016

BSGM

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The Selene perlite ore deposit of northeastern Sonora, Mexico, lies at the southern edge of an extensive (85 × 35 km) assemblage of Early Oligocene-Miocene volcanic rocks. This fault-bounded and east-tilted volcanic assemblage is of variable composition and was erupted onto Cretaceous non-volcanic rocks. The volcanic ridge is located within the tectonically extended region of the northern Sierra Madre Occidental (SMO) silicic large igneous province. Geologic mapping reveals a faulted and uplifted bimodal volcanic sequence, dated as Late Oligocene, that contains more perlite outcrops than previously recognized and two new coplanar normal faults of Early Miocene age or younger that promoted the development of an adjacent, small half-graben filled by a volcaniclastic unit. The bimodal volcanic sequence comprises a basal Early Eocene rhyolitic lava and rhyolitic tuff overlain by a rhyolitic ignimbrite sheet, a middle flow-banded rhyolitic lava dome that hosts the Selene perlite flow, and the upper basalt on an erosional unconformity. The volcaniclastic unit rests in angular unconformity with the bimodal volcanic sequence, and was likely deposited in the Early Miocene. It comprises a lower fault breccia containing clasts of local eruptive products, a previously unidentified thin quartz arenite bed, and an upper, thick polymictic conglomerate containing clasts of perlite, rhyolite, andesite, and basalt. Potential sources for the bimodal (silicic and mafic) volcanic facies are distal and proximal-distal volcanic fissure vents, the locations of which were controlled by preexisting NW-SE and N-S normal faults and related fractures linked to the Mexican Basin and Range Extensional Province. This implies the bimodal volcanism to be synchronous with crustal extension, as recently shown for other areas of the SMO silicic large igneous province. Normal faulting in the area also influenced the formation, preservation, and exposure (uplift) of the Selene perlite flow. The structural discontinuities created a permeable uppermost crust that channeled meteoric water into the subsurface and promoted both the percolation and underground circulation of meteoric water and gases rising into the subsurface. The water-lava interactions led to the hydration of the flow-banded rhyolitic lava flow and the formation of huge amounts of perlite. The Selene perlite was partly preserved by the overlying basalt, but continued local normal faulting and subsequent erosion exposed the perlite ore at its current location.

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“…However, a controversy exists concerning the parameters of perlite formation (diffusion coefficient of water, activation energy of hydration) (Friedman et al 1966;Marshall 1961). The degree of perlitization also depends on the total volatile contents and temperature (Denton et al 2009). The alteration of perlitized obsidian was shown to result in the dissolution of glass and crystallization of secondary minerals (smectite, zeolite), as well as in a change in the colour from dark grey to green or dull brown (Noh and Boles 1989;Denton et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Obsidian balls (marekanite) from Cerro Tijerina, central Nicaragua: petrographic investigations

Mrázová¹,

Gadas²

2012

J. Geosci.

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The paper describes a find of volcanic glass in central Nicaragua. We investigated obsidian samples in perlite from a large profile of volcanic rocks (Cerro Tijerina) in the vicinity of the town of Matagalpa. The obsidian occurs in the form of up to 3-cm dark-coloured balls (spheres) randomly distributed in brittle grey perlite, which also has spherulitic texture. These balls, previously called marekanite, are characterised by an abundance of microphenocrysts (feldspar, biotite, amphibole, apatite and magnetite). Microprobe analysis of the homogenous glass of obsidian balls and perlite has confirmed their subalkaline, and particularly high-K calc-alkaline character (SiO 2 ≥ 70 %, Na 2 O + K 2 O < Al 2 O 3 ), which is typical of rhyolitic melts. A sharp contact was observed between the core and the surface layer (approx. 0.1-0.2 mm) of the obsidian balls, reflecting changes in the H 2 O content.

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The hydration and alteration of perlite and rhyolite

Cited by 65 publications

References 26 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

Geology of the Selene perlite deposit in the northern Sierra Madre Occidental, northeastern Sonora, Mexico

Obsidian balls (marekanite) from Cerro Tijerina, central Nicaragua: petrographic investigations

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