Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

Liam A. Bullock; Ralf  Gertisser; Brian O’Driscoll

doi:10.2451/2017PM680

Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

Liam A. Bullock^* (Corresponding Author), Ralf Gertisser, Brian O’Driscoll

^*Corresponding author for this work

Geology and Geophysics

Research output: Contribution to journal › Article › peer-review

9 Citations (Scopus)

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Abstract

Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterisedby spatial, textural and geochemical variations, formed by different processes.Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate inshape, and show variable radial interiors. Spherulites occur individually or indeformation bands, and some are surrounded by clear haloes and brown rims.Spherulites typically contain cristobalite (α, β) and orthoclase, and rhyoliticglass, and grew over an average period of 5 days, with modification at lowertemperatures. Heterogeneity relates to formation processes of spherulite‘types’ at different stages of cooling and emplacement. Distinct populationsconcentrate within deformation structures, with variations in shape andinternal structure. Crystal Size Distribution (CSD) plots show differing sizepopulations and growth periods. Spherulites which formed at high temperaturesshow elongation, where deformation triggered further spherulite nucleationand growth. Spherulites formed at mid-glass transition temperatures arespherical, and spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation, and modification are therefore pivotal in thedevelopment spherulite heterogeneity in obsidian lavas.

Original language	English
Pages (from-to)	37-54
Number of pages	18
Journal	Periodico di Mineralogia
Volume	86
Early online date	Feb 2017
DOIs	https://doi.org/10.2451/2017PM680
Publication status	Published - 2017

Keywords

Spherulites
obsidian
Aeolian Islands
Glass Transition
Lipari
Vulcano

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Spherulite formation in obsidian lavas in the Aeolian Islands
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Cite this

@article{a643317eb841418da1019719261dfdcc,

title = "Spherulite formation in obsidian lavas in the Aeolian Islands, Italy",

abstract = "Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterisedby spatial, textural and geochemical variations, formed by different processes.Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate inshape, and show variable radial interiors. Spherulites occur individually or indeformation bands, and some are surrounded by clear haloes and brown rims.Spherulites typically contain cristobalite (α, β) and orthoclase, and rhyoliticglass, and grew over an average period of 5 days, with modification at lowertemperatures. Heterogeneity relates to formation processes of spherulite{\textquoteleft}types{\textquoteright} at different stages of cooling and emplacement. Distinct populationsconcentrate within deformation structures, with variations in shape andinternal structure. Crystal Size Distribution (CSD) plots show differing sizepopulations and growth periods. Spherulites which formed at high temperaturesshow elongation, where deformation triggered further spherulite nucleationand growth. Spherulites formed at mid-glass transition temperatures arespherical, and spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation, and modification are therefore pivotal in thedevelopment spherulite heterogeneity in obsidian lavas.",

keywords = "Spherulites, obsidian, Aeolian Islands, Glass Transition, Lipari, Vulcano",

author = "Bullock, {Liam A.} and Ralf Gertisser and Brian O{\textquoteright}Driscoll",

note = "The authors wish to gratefully acknowledge Andy Tindle (The Open University) for assistance with EMP analyses, and Richard Darton and David Evans (Keele University) for assistance with XRD and Prof Alun Vaughan and Nicola Freebody (University of Southampton) with Raman analyses. LAB is grateful to Sophie Blanchard for support with MATLAB. The authors acknowledge support from Keele University, and grants from the Mineralogical Society (UK and Ireland) and Volcanic and Magmatic Studies Group. The authors thank Silvio Mollo and Francesca Forni for their detailed and helpful comments.",

year = "2017",

doi = "10.2451/2017PM680",

language = "English",

volume = "86",

pages = "37--54",

journal = "Periodico di Mineralogia",

issn = "2239-1002",

publisher = "Bardi Editore",

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T1 - Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

AU - Bullock, Liam A.

AU - Gertisser, Ralf

AU - O’Driscoll, Brian

N1 - The authors wish to gratefully acknowledge Andy Tindle (The Open University) for assistance with EMP analyses, and Richard Darton and David Evans (Keele University) for assistance with XRD and Prof Alun Vaughan and Nicola Freebody (University of Southampton) with Raman analyses. LAB is grateful to Sophie Blanchard for support with MATLAB. The authors acknowledge support from Keele University, and grants from the Mineralogical Society (UK and Ireland) and Volcanic and Magmatic Studies Group. The authors thank Silvio Mollo and Francesca Forni for their detailed and helpful comments.

PY - 2017

Y1 - 2017

N2 - Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterisedby spatial, textural and geochemical variations, formed by different processes.Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate inshape, and show variable radial interiors. Spherulites occur individually or indeformation bands, and some are surrounded by clear haloes and brown rims.Spherulites typically contain cristobalite (α, β) and orthoclase, and rhyoliticglass, and grew over an average period of 5 days, with modification at lowertemperatures. Heterogeneity relates to formation processes of spherulite‘types’ at different stages of cooling and emplacement. Distinct populationsconcentrate within deformation structures, with variations in shape andinternal structure. Crystal Size Distribution (CSD) plots show differing sizepopulations and growth periods. Spherulites which formed at high temperaturesshow elongation, where deformation triggered further spherulite nucleationand growth. Spherulites formed at mid-glass transition temperatures arespherical, and spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation, and modification are therefore pivotal in thedevelopment spherulite heterogeneity in obsidian lavas.

AB - Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterisedby spatial, textural and geochemical variations, formed by different processes.Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate inshape, and show variable radial interiors. Spherulites occur individually or indeformation bands, and some are surrounded by clear haloes and brown rims.Spherulites typically contain cristobalite (α, β) and orthoclase, and rhyoliticglass, and grew over an average period of 5 days, with modification at lowertemperatures. Heterogeneity relates to formation processes of spherulite‘types’ at different stages of cooling and emplacement. Distinct populationsconcentrate within deformation structures, with variations in shape andinternal structure. Crystal Size Distribution (CSD) plots show differing sizepopulations and growth periods. Spherulites which formed at high temperaturesshow elongation, where deformation triggered further spherulite nucleationand growth. Spherulites formed at mid-glass transition temperatures arespherical, and spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation, and modification are therefore pivotal in thedevelopment spherulite heterogeneity in obsidian lavas.

KW - Spherulites

KW - obsidian

KW - Aeolian Islands

KW - Glass Transition

KW - Lipari

KW - Vulcano

U2 - 10.2451/2017PM680

DO - 10.2451/2017PM680

M3 - Article

VL - 86

SP - 37

EP - 54

JO - Periodico di Mineralogia

JF - Periodico di Mineralogia

SN - 2239-1002

ER -

Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

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