Silicic volcanism at Ljósufjöll, Iceland: insights into evolution and eruptive history from Ar-Ar dating

S. Flude; R. Burgess; D.W. McGarvie

doi:10.1016/j.jvolgeores.2007.08.019

Silicic volcanism at Ljósufjöll, Iceland: insights into evolution and eruptive history from Ar-Ar dating

S. Flude^*, R. Burgess, D.W. McGarvie

^*Corresponding author for this work

Civil And Environmental Engineering

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

38 Citations (Scopus)

Abstract

Ljósufjöll volcano is the largest outcrop of silicic volcanic material in the volcanic Snaefellsnes flank (non-rifting) zone of Iceland. The silicic eruptives range from trachytes to alkaline and peralkaline (comenditic) rhyolites and show evidence for eruption in both subaerial and subglacial environments. Thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation. The trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar-rich trachytic mush, with continued fractionation of the interstitial melt producing low Ba and Sr rhyolite magma. Ar-Ar dating of feldspars and matrix (glass or holocrystalline groundmass) has been carried out on twelve of the units. Many units have a complex Ar-isotopic system, with many samples showing evidence for inherited ⁴⁰Ar in the form of feldspar xenocrysts. The deduced eruption ages span an age range from < 129ka to > 650ka. The eruptive history of Ljósufjöll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried. A syenite xenolith was dated at 1.1Ma, indicating that silicic, alkaline magmatism has been occurring at Ljósufjöll for over one million years. Eruptions of silicic material at Ljósufjöll appear to be more common during times of rapid climate change and fluctuating ice volume.

Original language	English
Pages (from-to)	154-175
Number of pages	22
Journal	Journal of Volcanology and Geothermal Research
Volume	169
Issue number	3-4
Early online date	18 Sept 2007
DOIs	https://doi.org/10.1016/j.jvolgeores.2007.08.019
Publication status	Published - 10 Feb 2008

Funding

S. Flude was supported by NERC studentship number NER/S/A/2001/06307. D. McGarvie would like to thank the Science Staff Tutor Research Fund of The Open University for fieldwork support. Dave Emley at Keele University carried out the XRF analyses. Dave Plant is thanked for assistance with the probe work. Dave Blagburn and Bev Clementson are thanked for keeping the Ar–Ar lab and MS1 running smoothly. Ben Hill is thanked for assistance in the field. Bob Thompson, Sarah Sherlock, Mike Henderson, Dan Morgan and Gareth Davies are thanked for constructive comments and discussion, as are two anonymous reviewers.

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 13 Climate Action

Keywords

Ar-Ar dating
Iceland
rhyolite
Snaefellsnes
trachyte

Access to Document

10.1016/j.jvolgeores.2007.08.019

Cite this

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title = "Silicic volcanism at Lj{\'o}sufj{\"o}ll, Iceland: insights into evolution and eruptive history from Ar-Ar dating",

abstract = "Lj{\'o}sufj{\"o}ll volcano is the largest outcrop of silicic volcanic material in the volcanic Snaefellsnes flank (non-rifting) zone of Iceland. The silicic eruptives range from trachytes to alkaline and peralkaline (comenditic) rhyolites and show evidence for eruption in both subaerial and subglacial environments. Thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation. The trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar-rich trachytic mush, with continued fractionation of the interstitial melt producing low Ba and Sr rhyolite magma. Ar-Ar dating of feldspars and matrix (glass or holocrystalline groundmass) has been carried out on twelve of the units. Many units have a complex Ar-isotopic system, with many samples showing evidence for inherited 40Ar in the form of feldspar xenocrysts. The deduced eruption ages span an age range from < 129ka to > 650ka. The eruptive history of Lj{\'o}sufj{\"o}ll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried. A syenite xenolith was dated at 1.1Ma, indicating that silicic, alkaline magmatism has been occurring at Lj{\'o}sufj{\"o}ll for over one million years. Eruptions of silicic material at Lj{\'o}sufj{\"o}ll appear to be more common during times of rapid climate change and fluctuating ice volume.",

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N2 - Ljósufjöll volcano is the largest outcrop of silicic volcanic material in the volcanic Snaefellsnes flank (non-rifting) zone of Iceland. The silicic eruptives range from trachytes to alkaline and peralkaline (comenditic) rhyolites and show evidence for eruption in both subaerial and subglacial environments. Thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation. The trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar-rich trachytic mush, with continued fractionation of the interstitial melt producing low Ba and Sr rhyolite magma. Ar-Ar dating of feldspars and matrix (glass or holocrystalline groundmass) has been carried out on twelve of the units. Many units have a complex Ar-isotopic system, with many samples showing evidence for inherited 40Ar in the form of feldspar xenocrysts. The deduced eruption ages span an age range from < 129ka to > 650ka. The eruptive history of Ljósufjöll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried. A syenite xenolith was dated at 1.1Ma, indicating that silicic, alkaline magmatism has been occurring at Ljósufjöll for over one million years. Eruptions of silicic material at Ljósufjöll appear to be more common during times of rapid climate change and fluctuating ice volume.

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KW - Ar-Ar dating

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KW - trachyte

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ER -

Silicic volcanism at Ljósufjöll, Iceland: insights into evolution and eruptive history from Ar-Ar dating

Abstract

Funding

UN SDGs

Keywords

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