Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands

S. Turner, T. Kokfelt, K. Hoernle, T. S. Johansen, F. Hauff, C. Lundstrom, P. van den Bogaard, A. Klügel

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Volcanic sequences on ocean islands record the temporal evolution of underlying magmatic systems and provide insights into how silicic crust is produced away from convergent margins. Assimilation has often been suspected to contribute, but the detection of such a process and its evolving maturity during migration across a mantle plume is less well documented. Here we present new major and trace element and Sr-Nd-Pb-U-Th-Ra-Pa isotope data that facilitate comparison of basanite to phonolite evolution on Tenerife (Canary Islands) with that shown by published data from La Palma. On both islands, (230Th/238U) ratios decrease with differentiation from parental magmas with 230Th excess toward different, silicic contaminants in secular equilibrium. On La Palma, this is inferred to reflect assimilation of small amounts of mafic wall rock. On Tenerife, both (230Th/238U) and (231Pa/235U) ratios decrease toward 1 with increasing differentiation, and this is accompanied by a subtle increase in Pb isotope ratios. At the same time, (226Ra/230Th) ratios change from >1 to <1 (a hitherto unreported magnitude). The Tenerife assimilant is thus constrained to be a partial melt of syenite formed in equilibrium with residual feldspar. The differences reflect a primarily deeper, more mafic magma system beneath La Palma during its late shield-building stage, whereas recent magmatic evolution at Tenerife occurs primarily at lower temperatures in small, shallower magma systems formed during its post-basaltic shield stage. Differentiation takes millennia or less.

LanguageEnglish
Pages147-150
Number of pages4
JournalGeology
Volume45
Issue number2
DOIs
Publication statusPublished - Feb 2017

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cannibalism
shield
magma
isotope
phonolite
basanite
convergent margin
syenite
mantle plume
wall rock
temporal evolution
mafic rock
feldspar
trace element
melt
crust
pollutant
ocean
assimilation

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Turner, S., Kokfelt, T., Hoernle, K., Johansen, T. S., Hauff, F., Lundstrom, C., ... Klügel, A. (2017). Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands. Geology, 45(2), 147-150. https://doi.org/10.1130/G38566.1
Turner, S. ; Kokfelt, T. ; Hoernle, K. ; Johansen, T. S. ; Hauff, F. ; Lundstrom, C. ; van den Bogaard, P. ; Klügel, A. / Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands. In: Geology. 2017 ; Vol. 45, No. 2. pp. 147-150.
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Turner, S, Kokfelt, T, Hoernle, K, Johansen, TS, Hauff, F, Lundstrom, C, van den Bogaard, P & Klügel, A 2017, 'Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands', Geology, vol. 45, no. 2, pp. 147-150. https://doi.org/10.1130/G38566.1

Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands. / Turner, S.; Kokfelt, T.; Hoernle, K.; Johansen, T. S.; Hauff, F.; Lundstrom, C.; van den Bogaard, P.; Klügel, A.

In: Geology, Vol. 45, No. 2, 02.2017, p. 147-150.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands

AU - Turner, S.

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AU - van den Bogaard, P.

AU - Klügel, A.

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AB - Volcanic sequences on ocean islands record the temporal evolution of underlying magmatic systems and provide insights into how silicic crust is produced away from convergent margins. Assimilation has often been suspected to contribute, but the detection of such a process and its evolving maturity during migration across a mantle plume is less well documented. Here we present new major and trace element and Sr-Nd-Pb-U-Th-Ra-Pa isotope data that facilitate comparison of basanite to phonolite evolution on Tenerife (Canary Islands) with that shown by published data from La Palma. On both islands, (230Th/238U) ratios decrease with differentiation from parental magmas with 230Th excess toward different, silicic contaminants in secular equilibrium. On La Palma, this is inferred to reflect assimilation of small amounts of mafic wall rock. On Tenerife, both (230Th/238U) and (231Pa/235U) ratios decrease toward 1 with increasing differentiation, and this is accompanied by a subtle increase in Pb isotope ratios. At the same time, (226Ra/230Th) ratios change from >1 to <1 (a hitherto unreported magnitude). The Tenerife assimilant is thus constrained to be a partial melt of syenite formed in equilibrium with residual feldspar. The differences reflect a primarily deeper, more mafic magma system beneath La Palma during its late shield-building stage, whereas recent magmatic evolution at Tenerife occurs primarily at lower temperatures in small, shallower magma systems formed during its post-basaltic shield stage. Differentiation takes millennia or less.

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Turner S, Kokfelt T, Hoernle K, Johansen TS, Hauff F, Lundstrom C et al. Contrasting magmatic cannibalism forms evolved phonolitic magmas in the Canary Islands. Geology. 2017 Feb;45(2):147-150. https://doi.org/10.1130/G38566.1