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Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

Spherulite formation in obsidian lavas in the Aeolian Islands, Italy
Spherulite formation in obsidian lavas in the Aeolian Islands, Italy
Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterised by spatial, textural and geochemical variations, formed by different processes across flow extrusion and emplacement. Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate in shape, and show variable radial interiors. Spherulites occur individually or in deformation bands, and some are surrounded by clear haloes and brown rims. Spherulites typically contain cristobalite (α, β) and orthoclase, titanomagnetite and rhyolitic glass, and grew over an average period of 5 days. Heterogeneity relates to formation processes of spherulite ‘types’ at different stages of cooling and emplacement. Distinct populations concentrate within deformation structures or in areas of low shear, with variations in shape and internal structure. CSD plots show differing size populations and growth periods. Spherulites which formed at high temperatures show high degree of elongation, where deformation may have triggered formation. Spherulites formed at mid-glass transition temperatures are spherical, and all spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation and post-emplacement modification are therefore pivotal in the development spherulite heterogeneity in obsidian lavas. Key words: Spherulites; Obsidian; Aeolian Islands; Glass Transition; Lipari; Vulcano
2239-1002
37-54
Bullock, Liam
c6ffb9b0-0a54-4ab2-9edb-f97280e6ce2d
Gertisser, Ralf
8b4ea978-2461-4a65-87c8-352c62e52c70
O'Driscoll, Brian
463f2f0c-856a-416a-8a8d-ac451edaac91
Bullock, Liam
c6ffb9b0-0a54-4ab2-9edb-f97280e6ce2d
Gertisser, Ralf
8b4ea978-2461-4a65-87c8-352c62e52c70
O'Driscoll, Brian
463f2f0c-856a-416a-8a8d-ac451edaac91

Bullock, Liam, Gertisser, Ralf and O'Driscoll, Brian (2017) Spherulite formation in obsidian lavas in the Aeolian Islands, Italy. Periodico di Mineralogia, 86, 37-54. (doi:10.2451/2017PM680).

Record type: Article

Abstract

Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterised by spatial, textural and geochemical variations, formed by different processes across flow extrusion and emplacement. Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate in shape, and show variable radial interiors. Spherulites occur individually or in deformation bands, and some are surrounded by clear haloes and brown rims. Spherulites typically contain cristobalite (α, β) and orthoclase, titanomagnetite and rhyolitic glass, and grew over an average period of 5 days. Heterogeneity relates to formation processes of spherulite ‘types’ at different stages of cooling and emplacement. Distinct populations concentrate within deformation structures or in areas of low shear, with variations in shape and internal structure. CSD plots show differing size populations and growth periods. Spherulites which formed at high temperatures show high degree of elongation, where deformation may have triggered formation. Spherulites formed at mid-glass transition temperatures are spherical, and all spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation and post-emplacement modification are therefore pivotal in the development spherulite heterogeneity in obsidian lavas. Key words: Spherulites; Obsidian; Aeolian Islands; Glass Transition; Lipari; Vulcano

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More information

Accepted/In Press date: January 2017
e-pub ahead of print date: February 2017

Identifiers

Local EPrints ID: 421648
URI: https://eprints.soton.ac.uk/id/eprint/421648
ISSN: 2239-1002
PURE UUID: 8b9f223c-0229-49d2-8c4c-550c142dfbfc

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Date deposited: 19 Jun 2018 16:30
Last modified: 13 Mar 2019 18:24

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