Devitrification of natural rhyolitic obsidian glasses: petrographic and microstructural study (SEM+EDS) of recent (Lipari island) and ancient (Sarrabus, SE Sardinia) samples

Gimeno, D.

doi:10.1016/s0022-3093(03)00294-1

Cited by 17 publications

(5 citation statements)

References 15 publications

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“…Several studies exist on the devitrification textures found in the RR, which occur throughout in the form of spherulites, axiolites and lithophysae (Cole & Butler, 1892;Gimeno, 2003;Clay et al, 2012). Growth of these anhydrous crystalline aggregates, comprising alkali feldspars and cristobalite (Castro et al, 2008;Von Aulock et al, 2014) is controlled by H 2 O diffusion through the melt and can occur throughout cooling, both above and below the glass transition interval (620-750°C) (Castro et al, 2008;Clay et al, 2012;Watkins et al, 2009).…”

Section: Rocche Rosse Flow Descriptionmentioning

confidence: 99%

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: Rocche Rosse Flow Descriptionmentioning

confidence: 99%

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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“…The observed textures demonstrate a bimodal distribution: spherulites are either isolated individually in the glass or form dense trails and bands. Spherulite texture in the Rocche Rosse obsidian has previously been described in several studies (e.g., Cole and Butler 1892;Dellino and La Volpe 1995;Gimeno 2003), and it is not intended to duplicate that work here. However, for the most part the observations below have not previously been documented.…”

Section: Sample Petrographymentioning

confidence: 99%

Textural characterization, major and volatile element quantification and Ar–Ar systematics of spherulites in the Rocche Rosse obsidian flow, Lipari, Aeolian Islands: a temperature continuum growth model

Clay

O’Driscoll

Gertisser

et al. 2012

Contrib Mineral Petrol

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“…Gimeno 37 showed that SEM can be useful for analyzing the devitrification process by revealing the growth of the crystal components, and discovered that phenocrysts, microphenocrysts and all kinds of previous crystalline materials act as nucleation sites for spherulites. Moreover, the most viscous lava like felsic ones show poor development of spherulites, unlike the less viscous magma rocks that present advanced stages of spherulites.…”

Section: Resultsmentioning

confidence: 99%

Physico-Chemical Characterization of Macusanite and Inclusions: A Volcanic Glass from Peruvian Andes

Azevedo¹,

Santos²,

Pereira³

et al. 2021

Mat. Res.

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Macusanite is a volcanic glass extracted from the volcanic field Macusani -Peru, formed by the fast cooling of magma. This study shows physical and chemical characterization of Macusanite samples to better understand its molecular structure, elemental composition as well as to investigate the presence of natural inclusions. The characterization of the natural glass can give valuable geological information about the magma composition, the eruption intensity and age of volcanism activity. Moreover, the use of different characterization techniques can help in mineral prospecting. Macusanite was characterized by X-Ray Diffraction/Fluorescence (XRD/XRF), Optical Microscopy, Scanning Electron Microscopy (SEM) and micro-Raman spectroscopy. The latter suggests the presence of andalusite mineral incorporated in the glass structure, while the Energy-Dispersive X-ray Spectroscopy (EDS) analysis indicates the presence of some rich calcium inclusion. Moreover, XRD shows the glass characteristic amorphous band and that the sample is in the glassy stage.

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Devitrification of natural rhyolitic obsidian glasses: petrographic and microstructural study (SEM+EDS) of recent (Lipari island) and ancient (Sarrabus, SE Sardinia) samples

Cited by 17 publications

References 15 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

Textural characterization, major and volatile element quantification and Ar–Ar systematics of spherulites in the Rocche Rosse obsidian flow, Lipari, Aeolian Islands: a temperature continuum growth model

Physico-Chemical Characterization of Macusanite and Inclusions: A Volcanic Glass from Peruvian Andes

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