210Pb-226Ra disequilibria in young gas-laden magmas

Mark Reagan, Simon Turner, Heather Handley, Michael Turner, Christoph Beier, John Caulfield, David Peate

Research output: Contribution to journalArticleResearchpeer-review

Abstract

We present new 238U-230 Th-226 Ra-210 Pb and supporting data for young lavas from southwest Pacific island arcs, Eyjafjallajökull, Iceland, and Terceira, Azores. The arc lavas have significant 238U and 226Ra excesses, whereas those from the ocean islands have moderate 230Th and 226Ra excesses, reflecting mantle melting in the presence of a water-rich fluid in the former and mantle melting by decompression in the latter. Differentiation to erupted compositions in both settings appears to have taken no longer than a few millennia. Variations in the (210Pb/226Ra)0 values in all settings largely result from degassing processes rather than mineral-melt partitioning. Like most other ocean island basalts, the Terceira basalt has a 210Pb deficit, which we attribute to ∼8.5 years of steady 222Rn loss to a CO2-rich volatile phase while it traversed the crust. Lavas erupted from water-laden magma systems, including those investigated here, commonly have near equilibrium (210Pb/226Ra)0 values. Maintaining these equilibrium values requires minimal persistent loss or accumulation of 222Rn in a gas phase. We infer that degassing during decompression of water-saturated magmas either causes these magmas to crystallize and stall in reservoirs where they reside under conditions of near stasis, or to quickly rise towards the surface and erupt.

LanguageEnglish
Article number45186
Pages1-12
Number of pages12
JournalScientific Reports
Volume7
DOIs
Publication statusPublished - 24 Mar 2017

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disequilibrium
decompression
degassing
melting
gas
mantle
ocean island basalt
water
island arc
partitioning
basalt
magma
melt
crust
fluid
ocean
mineral
young
loss

Bibliographical note

Copyright the Author(s) 2017. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Cite this

Reagan, M., Turner, S., Handley, H., Turner, M., Beier, C., Caulfield, J., & Peate, D. (2017). 210Pb-226Ra disequilibria in young gas-laden magmas. Scientific Reports, 7, 1-12. [45186]. https://doi.org/10.1038/srep45186
Reagan, Mark ; Turner, Simon ; Handley, Heather ; Turner, Michael ; Beier, Christoph ; Caulfield, John ; Peate, David. / 210Pb-226Ra disequilibria in young gas-laden magmas. In: Scientific Reports. 2017 ; Vol. 7. pp. 1-12.
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Reagan, M, Turner, S, Handley, H, Turner, M, Beier, C, Caulfield, J & Peate, D 2017, '210Pb-226Ra disequilibria in young gas-laden magmas', Scientific Reports, vol. 7, 45186, pp. 1-12. https://doi.org/10.1038/srep45186

210Pb-226Ra disequilibria in young gas-laden magmas. / Reagan, Mark; Turner, Simon; Handley, Heather; Turner, Michael; Beier, Christoph; Caulfield, John; Peate, David.

In: Scientific Reports, Vol. 7, 45186, 24.03.2017, p. 1-12.

Research output: Contribution to journalArticleResearchpeer-review

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AU - Reagan, Mark

AU - Turner, Simon

AU - Handley, Heather

AU - Turner, Michael

AU - Beier, Christoph

AU - Caulfield, John

AU - Peate, David

N1 - Copyright the Author(s) 2017. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2017/3/24

Y1 - 2017/3/24

N2 - We present new 238U-230 Th-226 Ra-210 Pb and supporting data for young lavas from southwest Pacific island arcs, Eyjafjallajökull, Iceland, and Terceira, Azores. The arc lavas have significant 238U and 226Ra excesses, whereas those from the ocean islands have moderate 230Th and 226Ra excesses, reflecting mantle melting in the presence of a water-rich fluid in the former and mantle melting by decompression in the latter. Differentiation to erupted compositions in both settings appears to have taken no longer than a few millennia. Variations in the (210Pb/226Ra)0 values in all settings largely result from degassing processes rather than mineral-melt partitioning. Like most other ocean island basalts, the Terceira basalt has a 210Pb deficit, which we attribute to ∼8.5 years of steady 222Rn loss to a CO2-rich volatile phase while it traversed the crust. Lavas erupted from water-laden magma systems, including those investigated here, commonly have near equilibrium (210Pb/226Ra)0 values. Maintaining these equilibrium values requires minimal persistent loss or accumulation of 222Rn in a gas phase. We infer that degassing during decompression of water-saturated magmas either causes these magmas to crystallize and stall in reservoirs where they reside under conditions of near stasis, or to quickly rise towards the surface and erupt.

AB - We present new 238U-230 Th-226 Ra-210 Pb and supporting data for young lavas from southwest Pacific island arcs, Eyjafjallajökull, Iceland, and Terceira, Azores. The arc lavas have significant 238U and 226Ra excesses, whereas those from the ocean islands have moderate 230Th and 226Ra excesses, reflecting mantle melting in the presence of a water-rich fluid in the former and mantle melting by decompression in the latter. Differentiation to erupted compositions in both settings appears to have taken no longer than a few millennia. Variations in the (210Pb/226Ra)0 values in all settings largely result from degassing processes rather than mineral-melt partitioning. Like most other ocean island basalts, the Terceira basalt has a 210Pb deficit, which we attribute to ∼8.5 years of steady 222Rn loss to a CO2-rich volatile phase while it traversed the crust. Lavas erupted from water-laden magma systems, including those investigated here, commonly have near equilibrium (210Pb/226Ra)0 values. Maintaining these equilibrium values requires minimal persistent loss or accumulation of 222Rn in a gas phase. We infer that degassing during decompression of water-saturated magmas either causes these magmas to crystallize and stall in reservoirs where they reside under conditions of near stasis, or to quickly rise towards the surface and erupt.

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