238U- and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean

Reagan, Mark K.; Turner, Simon; Legg, Matthew; Sims, Kenneth W.W.; Hards, V.

doi:10.1016/j.gca.2008.06.002

Cited by 25 publications

(9 citation statements)

References 50 publications

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“…5). Such excesses can result from crystal fractionation of K-feldspar and amphibole, but only in highly differentiated magmas such as phonolite8 (Fig. 5), not in magmas that crystallize olivine, augite, and plagioclase like the Serreta basalt19.…”

Section: Discussionmentioning

confidence: 99%

“…The phonolite whole rock from Tristan da Cunha8 and phonolite glass separates from Mount Erebus9 are shown separately because they demonstrably have had ( 226 Ra) lowered by crystal fractionation of K-rich feldspars or amphiboles. Data were excluded for samples with unusually high Pb concentrations and high ( 210 Pb/ 226 Ra) values that likely reflect the assimilation of young 210 Pb-enriched sublimates53647.…”

Section: Figurementioning

confidence: 99%

“…In terms of just how rapid some of these processes might be, many lavas exhibit disequilibria between 210 Pb (T 1/2 = 22.6 y), 210 Po (T 1/2 = 138 days), and 226 Ra (T 1/2 = 1,600 y), illustrating that magmatic differentiation processes can persist nearly to eruption6789.…”

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confidence: 99%

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

Reagan

Turner

Handley

et al. 2017

Sci Rep

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We present new 238U-230Th-226Ra-210Pb 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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Section: Discussionmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

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

Reagan

Turner

Handley

et al. 2017

Sci Rep

Self Cite

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“…For a magma chamber with longer residence time (e.g., 20,000 years), where decay removes all initial 226 Ra excess, ( 226 Ra/ 230 Th) of the differentiated melt (F < 0.4) is mainly a function of the bulk partition coefficients of Ra and Th. If the fractionated mineral phases include Na-rich plagioclase and amphibole, D Ra will be significantly greater than D Th (Blundy and Wood, 2003) such that fractional crystallization could result in lower 226 Ra/ 230 Th in the melt than in the crystals or whole rock (Reagan et al, 2007).…”

Section: Fractional Crystallization and Ageing In A Closed System (Fc)mentioning

confidence: 99%

The effect of assimilation, fractional crystallization, and ageing on U-series disequilibria in subduction zone lavas

Huang¹,

Gao²,

Lundstrom³

2008

Geochimica et Cosmochimica Acta

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“…Isotopic analyses of phonolitic pumice that erupted from a submarine vent in 2004 (O'Mongain et al, 2005) indicate that it was generated by rapid, extensive fractionation of a small parental magma body, unrelated to the 1961 tephri-phonolitic magma (Reagan et al, 2008). This further suggests that, rather than being dominated by one large chamber, magma is sourced rapidly from depth and siphons off into smaller, discrete magma pockets nearer the surface.…”

Section: Physiography Of Tristan and Timing Of Volcanic Eventsmentioning

confidence: 99%

An interdisciplinary approach to volcanic risk reduction under conditions of uncertainty: a case study of Tristan da Cunha

Hicks

Barclay

Simmons

et al. 2014

Nat. Hazards Earth Syst. Sci.

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Abstract. The uncertainty brought about by intermittent volcanic activity is fairly common at volcanoes worldwide. While better knowledge of any one volcano's behavioural characteristics has the potential to reduce this uncertainty, the subsequent reduction of risk from volcanic threats is only realised if that knowledge is pertinent to stakeholders and effectively communicated to inform good decision making. Success requires integration of methods, skills and expertise across disciplinary boundaries.This research project develops and trials a novel interdisciplinary approach to volcanic risk reduction on the remote volcanic island of Tristan da Cunha (South Atlantic). For the first time, volcanological techniques, probabilistic decision support and social scientific methods were integrated in a single study. New data were produced that (1) established no spatio-temporal pattern to recent volcanic activity; (2) quantified the high degree of scientific uncertainty around future eruptive scenarios; (3) analysed the physical vulnerability of the community as a consequence of their geographical isolation and exposure to volcanic hazards; (4) evaluated social and cultural influences on vulnerability and resilience; and (5) evaluated the effectiveness of a scenario planning approach, both as a method for integrating the different strands of the research and as a way of enabling on-island decision makers to take ownership of risk identification and management, and capacity building within their community.The paper provides empirical evidence of the value of an innovative interdisciplinary framework for reducing volcanic risk. It also provides evidence for the strength that comes from integrating social and physical sciences with the development of effective, tailored engagement and communication strategies in volcanic risk reduction.

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238U- and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean

Cited by 25 publications

References 50 publications

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

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

The effect of assimilation, fractional crystallization, and ageing on U-series disequilibria in subduction zone lavas

An interdisciplinary approach to volcanic risk reduction under conditions of uncertainty: a case study of Tristan da Cunha

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