Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano
Abstract Strike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4–6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long tr...
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Cambridge University Press (CUP)
1989
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Online Access: | http://dx.doi.org/10.1017/s0016756800006956 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800006956 |
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crcambridgeupr:10.1017/s0016756800006956 2024-09-15T18:14:21+00:00 Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano Gautneb, Håvard Gudmundsson, Agust Oskarsson, Niels 1989 http://dx.doi.org/10.1017/s0016756800006956 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800006956 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Geological Magazine volume 126, issue 6, page 659-673 ISSN 0016-7568 1469-5081 journal-article 1989 crcambridgeupr https://doi.org/10.1017/s0016756800006956 2024-07-24T04:01:31Z Abstract Strike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4–6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long traverses perpendicular to the average strike of sheets, the percentage of sheets ranges from about 6 to 11. Of 140 chemically analysed sheets most are quartz-tholeiites; a few are intermediate or acid. The sheets are chemically more evolved than the host rock and were generated by a shallow crustal magma chamber at a mature stage of the central volcano, whereas the host rock was generated earlier before the chamber was established. Trace element results suggest that the sheet magmas evolved by low-pressure fractional crystallization as well as by mixing of primitive magmas and crustal melts. A model is proposed where most of the sheets are generated by a growing shallow magma chamber. As the chamber grows its shape changes, and so does the local stress field associated with it. Because the sheets follow the stress trajectories of the local stress field, the potential pathways of the sheets change with the growth of the chamber, which may explain the common occurrence of cross-cutting sheets. From the evolved chemistry of the sheets, as well as from the pattern of the stress trajectories, it is concluded that the bulk of the sheets were injected from the upper part of the shallow magma chamber. Article in Journal/Newspaper Iceland Cambridge University Press Geological Magazine 126 6 659 673 |
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Open Polar |
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Cambridge University Press |
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English |
description |
Abstract Strike, dip, and thickness were measured for 504 sheets (inclined sheets and dykes) in the 4–6 Ma old Hafnarfjall central volcano in southwest Iceland. The average dip of sheets is 65°, 80% are less than 1.2 m thick, and the thickness tends to decrease with decreasing dip. In 0.5 km long traverses perpendicular to the average strike of sheets, the percentage of sheets ranges from about 6 to 11. Of 140 chemically analysed sheets most are quartz-tholeiites; a few are intermediate or acid. The sheets are chemically more evolved than the host rock and were generated by a shallow crustal magma chamber at a mature stage of the central volcano, whereas the host rock was generated earlier before the chamber was established. Trace element results suggest that the sheet magmas evolved by low-pressure fractional crystallization as well as by mixing of primitive magmas and crustal melts. A model is proposed where most of the sheets are generated by a growing shallow magma chamber. As the chamber grows its shape changes, and so does the local stress field associated with it. Because the sheets follow the stress trajectories of the local stress field, the potential pathways of the sheets change with the growth of the chamber, which may explain the common occurrence of cross-cutting sheets. From the evolved chemistry of the sheets, as well as from the pattern of the stress trajectories, it is concluded that the bulk of the sheets were injected from the upper part of the shallow magma chamber. |
format |
Article in Journal/Newspaper |
author |
Gautneb, Håvard Gudmundsson, Agust Oskarsson, Niels |
spellingShingle |
Gautneb, Håvard Gudmundsson, Agust Oskarsson, Niels Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
author_facet |
Gautneb, Håvard Gudmundsson, Agust Oskarsson, Niels |
author_sort |
Gautneb, Håvard |
title |
Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
title_short |
Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
title_full |
Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
title_fullStr |
Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
title_full_unstemmed |
Structure, petrochemistry and evolution of a sheet swarm in an Icelandic central volcano |
title_sort |
structure, petrochemistry and evolution of a sheet swarm in an icelandic central volcano |
publisher |
Cambridge University Press (CUP) |
publishDate |
1989 |
url |
http://dx.doi.org/10.1017/s0016756800006956 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800006956 |
genre |
Iceland |
genre_facet |
Iceland |
op_source |
Geological Magazine volume 126, issue 6, page 659-673 ISSN 0016-7568 1469-5081 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0016756800006956 |
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Geological Magazine |
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126 |
container_issue |
6 |
container_start_page |
659 |
op_container_end_page |
673 |
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1810452109900906496 |