Extreme enriched and heterogeneous                          
                        87
                                                 Sr/                         
                        86
                                                 Sr ratios recorded in magmatic plagioclase from the Samoan hotspot

M. A. Edwards; M. G. Jackson; A. R.C. Kylander-Clark; J. Harvey; G. A. Hagen-Peter; G. G.E. Seward; C. B. Till; J. V. Adams; J. M. Cottle; B. R. Hacker; F. J. Spera

doi:10.1016/j.epsl.2019.01.040

Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot

M. A. Edwards^*, M. G. Jackson, A. R.C. Kylander-Clark, J. Harvey, G. A. Hagen-Peter, G. G.E. Seward, C. B. Till, J. V. Adams, J. M. Cottle, B. R. Hacker, F. J. Spera

^*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

17 Citations (Scopus)

Abstract

We report the major-element, trace-element, and ⁸⁷ Sr/ ⁸⁶ Sr compositions of six plagioclase crystals from two Samoan lavas with extreme EM2 isotopic compositions (ALIA-115-18 with whole-rock ⁸⁷ Sr/ ⁸⁶ Sr of 0.718592, and ALIA-115-21 with whole-rock ⁸⁷ Sr/ ⁸⁶ Sr of 0.720469). We employed laser-ablation split-stream mass spectrometry (LASS) to simultaneously measure ⁸⁷ Sr/ ⁸⁶ Sr ratios, major-element concentrations, and trace-element concentrations in the same plagioclase crystal volume. We find that two plagioclase crystals have extreme ⁸⁷ Sr/ ⁸⁶ Sr heterogeneity in excess of 5000 ppm (where ppm of ⁸⁷ Sr/Sr variability86=10 ⁶ ⋅[Sr/8687Sr _max − ⁸⁷ Sr/ ⁸⁶ Sr _min ]/ ⁸⁷ Sr/ ⁸⁶ Sr _avg ). In two of the plagioclase crystals, we identify the highest ⁸⁷ Sr/ ⁸⁶ Sr ratios (0.7224) ever measured in any fresh, mantle-derived ocean island basalt (OIB) or OIB-hosted mineral phase. We find that in ⁸⁷ Sr/ ⁸⁶ Sr-versus-Sr concentration space, the six plagioclase crystals overlap in a “common component” region with higher ⁸⁷ Sr/ ⁸⁶ Sr than has been previously identified in whole-rock Samoan lavas or mineral separates. We use the occurrence of olivine mineral inclusions (Fo=74.5±0.8, 2 SD) in the high- ⁸⁷ Sr/ ⁸⁶ Sr zone of one plagioclase crystal to infer the bulk composition (Mg#=46.8±0.8, 2 SD) of the extreme EM2 magma from which the olivine and high- ⁸⁷ Sr/ ⁸⁶ Sr plagioclase crystallized. We argue that a relatively evolved EM2 endmember magma mixed with at least one lower- ⁸⁷ Sr/ ⁸⁶ Sr melt to generate the observed intra-crystal plagioclase isotopic heterogeneity. By inferring that subducted terrigenous sediment gives rise to EM2 signatures in Samoan lavas, we estimate that the quantity of sediment necessary to generate the most-elevated ⁸⁷ Sr/ ⁸⁶ Sr ratios observed in the Samoan plagioclase is ∼7% of the mantle source. We also estimate that sediment subduction into the mantle over geologic time has generated a sediment domain that constitutes 0.02% of the mass of the mantle, a much lower proportion than required in the EM2 mantle source. Even if subducted sediment is concentrated in large low-shear-velocity provinces (LLSVPs) at the base of the mantle (which constitute up to 7.7% of the mantle's mass), then only 0.25% of the LLSVPs are composed of sediment. This requires that the distribution of subducted sediment in the mantle is heterogeneous, and the high relative abundance of sediment in the Samoan EM2 mantle is an anomalous relic of ancient subduction that has survived convective attenuation.

Original language	English
Journal	Earth and Planetary Science Letters
Volume	511
Pages (from-to)	190-201
Number of pages	12
ISSN	0012-821X
DOIs	https://doi.org/10.1016/j.epsl.2019.01.040
Publication status	Published - Apr 2019

Keywords

isotope geochemistry
LA-ICP-MS
LASS
mantle geochemistry
mantle heterogeneity

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10.1016/j.epsl.2019.01.040

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Edwards, M. A., Jackson, M. G., Kylander-Clark, A. R. C., Harvey, J., Hagen-Peter, G. A., Seward, G. G. E., Till, C. B., Adams, J. V., Cottle, J. M., Hacker, B. R., & Spera, F. J. (2019). Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot. Earth and Planetary Science Letters, 511, 190-201. https://doi.org/10.1016/j.epsl.2019.01.040

Edwards, M. A. ; Jackson, M. G. ; Kylander-Clark, A. R.C. et al. / Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot. In: Earth and Planetary Science Letters. 2019 ; Vol. 511. pp. 190-201.

@article{6144db121d8b495b8e2566778cf3ec09,

title = "Extreme enriched and heterogeneous 87 Sr/ 86 Sr ratios recorded in magmatic plagioclase from the Samoan hotspot",

abstract = " We report the major-element, trace-element, and 87 Sr/ 86 Sr compositions of six plagioclase crystals from two Samoan lavas with extreme EM2 isotopic compositions (ALIA-115-18 with whole-rock 87 Sr/ 86 Sr of 0.718592, and ALIA-115-21 with whole-rock 87 Sr/ 86 Sr of 0.720469). We employed laser-ablation split-stream mass spectrometry (LASS) to simultaneously measure 87 Sr/ 86 Sr ratios, major-element concentrations, and trace-element concentrations in the same plagioclase crystal volume. We find that two plagioclase crystals have extreme 87 Sr/ 86 Sr heterogeneity in excess of 5000 ppm (where ppm of 87 Sr/Sr variability86=10 6 ⋅[Sr/8687Sr max − 87 Sr/ 86 Sr min ]/ 87 Sr/ 86 Sr avg ). In two of the plagioclase crystals, we identify the highest 87 Sr/ 86 Sr ratios (0.7224) ever measured in any fresh, mantle-derived ocean island basalt (OIB) or OIB-hosted mineral phase. We find that in 87 Sr/ 86 Sr-versus-Sr concentration space, the six plagioclase crystals overlap in a “common component” region with higher 87 Sr/ 86 Sr than has been previously identified in whole-rock Samoan lavas or mineral separates. We use the occurrence of olivine mineral inclusions (Fo=74.5±0.8, 2 SD) in the high- 87 Sr/ 86 Sr zone of one plagioclase crystal to infer the bulk composition (Mg#=46.8±0.8, 2 SD) of the extreme EM2 magma from which the olivine and high- 87 Sr/ 86 Sr plagioclase crystallized. We argue that a relatively evolved EM2 endmember magma mixed with at least one lower- 87 Sr/ 86 Sr melt to generate the observed intra-crystal plagioclase isotopic heterogeneity. By inferring that subducted terrigenous sediment gives rise to EM2 signatures in Samoan lavas, we estimate that the quantity of sediment necessary to generate the most-elevated 87 Sr/ 86 Sr ratios observed in the Samoan plagioclase is ∼7% of the mantle source. We also estimate that sediment subduction into the mantle over geologic time has generated a sediment domain that constitutes 0.02% of the mass of the mantle, a much lower proportion than required in the EM2 mantle source. Even if subducted sediment is concentrated in large low-shear-velocity provinces (LLSVPs) at the base of the mantle (which constitute up to 7.7% of the mantle's mass), then only 0.25% of the LLSVPs are composed of sediment. This requires that the distribution of subducted sediment in the mantle is heterogeneous, and the high relative abundance of sediment in the Samoan EM2 mantle is an anomalous relic of ancient subduction that has survived convective attenuation. ",

keywords = "isotope geochemistry, LA-ICP-MS, LASS, mantle geochemistry, mantle heterogeneity",

author = "Edwards, {M. A.} and Jackson, {M. G.} and Kylander-Clark, {A. R.C.} and J. Harvey and Hagen-Peter, {G. A.} and Seward, {G. G.E.} and Till, {C. B.} and Adams, {J. V.} and Cottle, {J. M.} and Hacker, {B. R.} and Spera, {F. J.}",

year = "2019",

month = apr,

doi = "10.1016/j.epsl.2019.01.040",

language = "English",

volume = "511",

pages = "190--201",

journal = "Earth and Planetary Science Letters",

issn = "0012-821X",

publisher = "Elsevier B.V.",

}

Edwards, MA, Jackson, MG, Kylander-Clark, ARC, Harvey, J, Hagen-Peter, GA, Seward, GGE, Till, CB, Adams, JV, Cottle, JM, Hacker, BR & Spera, FJ 2019, 'Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot', Earth and Planetary Science Letters, vol. 511, pp. 190-201. https://doi.org/10.1016/j.epsl.2019.01.040

Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot. / Edwards, M. A.; Jackson, M. G.; Kylander-Clark, A. R.C. et al.
In: Earth and Planetary Science Letters, Vol. 511, 04.2019, p. 190-201.

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

TY - JOUR

T1 - Extreme enriched and heterogeneous 87 Sr/ 86 Sr ratios recorded in magmatic plagioclase from the Samoan hotspot

AU - Edwards, M. A.

AU - Jackson, M. G.

AU - Kylander-Clark, A. R.C.

AU - Harvey, J.

AU - Hagen-Peter, G. A.

AU - Seward, G. G.E.

AU - Till, C. B.

AU - Adams, J. V.

AU - Cottle, J. M.

AU - Hacker, B. R.

AU - Spera, F. J.

PY - 2019/4

Y1 - 2019/4

N2 - We report the major-element, trace-element, and 87 Sr/ 86 Sr compositions of six plagioclase crystals from two Samoan lavas with extreme EM2 isotopic compositions (ALIA-115-18 with whole-rock 87 Sr/ 86 Sr of 0.718592, and ALIA-115-21 with whole-rock 87 Sr/ 86 Sr of 0.720469). We employed laser-ablation split-stream mass spectrometry (LASS) to simultaneously measure 87 Sr/ 86 Sr ratios, major-element concentrations, and trace-element concentrations in the same plagioclase crystal volume. We find that two plagioclase crystals have extreme 87 Sr/ 86 Sr heterogeneity in excess of 5000 ppm (where ppm of 87 Sr/Sr variability86=10 6 ⋅[Sr/8687Sr max − 87 Sr/ 86 Sr min ]/ 87 Sr/ 86 Sr avg ). In two of the plagioclase crystals, we identify the highest 87 Sr/ 86 Sr ratios (0.7224) ever measured in any fresh, mantle-derived ocean island basalt (OIB) or OIB-hosted mineral phase. We find that in 87 Sr/ 86 Sr-versus-Sr concentration space, the six plagioclase crystals overlap in a “common component” region with higher 87 Sr/ 86 Sr than has been previously identified in whole-rock Samoan lavas or mineral separates. We use the occurrence of olivine mineral inclusions (Fo=74.5±0.8, 2 SD) in the high- 87 Sr/ 86 Sr zone of one plagioclase crystal to infer the bulk composition (Mg#=46.8±0.8, 2 SD) of the extreme EM2 magma from which the olivine and high- 87 Sr/ 86 Sr plagioclase crystallized. We argue that a relatively evolved EM2 endmember magma mixed with at least one lower- 87 Sr/ 86 Sr melt to generate the observed intra-crystal plagioclase isotopic heterogeneity. By inferring that subducted terrigenous sediment gives rise to EM2 signatures in Samoan lavas, we estimate that the quantity of sediment necessary to generate the most-elevated 87 Sr/ 86 Sr ratios observed in the Samoan plagioclase is ∼7% of the mantle source. We also estimate that sediment subduction into the mantle over geologic time has generated a sediment domain that constitutes 0.02% of the mass of the mantle, a much lower proportion than required in the EM2 mantle source. Even if subducted sediment is concentrated in large low-shear-velocity provinces (LLSVPs) at the base of the mantle (which constitute up to 7.7% of the mantle's mass), then only 0.25% of the LLSVPs are composed of sediment. This requires that the distribution of subducted sediment in the mantle is heterogeneous, and the high relative abundance of sediment in the Samoan EM2 mantle is an anomalous relic of ancient subduction that has survived convective attenuation.

AB - We report the major-element, trace-element, and 87 Sr/ 86 Sr compositions of six plagioclase crystals from two Samoan lavas with extreme EM2 isotopic compositions (ALIA-115-18 with whole-rock 87 Sr/ 86 Sr of 0.718592, and ALIA-115-21 with whole-rock 87 Sr/ 86 Sr of 0.720469). We employed laser-ablation split-stream mass spectrometry (LASS) to simultaneously measure 87 Sr/ 86 Sr ratios, major-element concentrations, and trace-element concentrations in the same plagioclase crystal volume. We find that two plagioclase crystals have extreme 87 Sr/ 86 Sr heterogeneity in excess of 5000 ppm (where ppm of 87 Sr/Sr variability86=10 6 ⋅[Sr/8687Sr max − 87 Sr/ 86 Sr min ]/ 87 Sr/ 86 Sr avg ). In two of the plagioclase crystals, we identify the highest 87 Sr/ 86 Sr ratios (0.7224) ever measured in any fresh, mantle-derived ocean island basalt (OIB) or OIB-hosted mineral phase. We find that in 87 Sr/ 86 Sr-versus-Sr concentration space, the six plagioclase crystals overlap in a “common component” region with higher 87 Sr/ 86 Sr than has been previously identified in whole-rock Samoan lavas or mineral separates. We use the occurrence of olivine mineral inclusions (Fo=74.5±0.8, 2 SD) in the high- 87 Sr/ 86 Sr zone of one plagioclase crystal to infer the bulk composition (Mg#=46.8±0.8, 2 SD) of the extreme EM2 magma from which the olivine and high- 87 Sr/ 86 Sr plagioclase crystallized. We argue that a relatively evolved EM2 endmember magma mixed with at least one lower- 87 Sr/ 86 Sr melt to generate the observed intra-crystal plagioclase isotopic heterogeneity. By inferring that subducted terrigenous sediment gives rise to EM2 signatures in Samoan lavas, we estimate that the quantity of sediment necessary to generate the most-elevated 87 Sr/ 86 Sr ratios observed in the Samoan plagioclase is ∼7% of the mantle source. We also estimate that sediment subduction into the mantle over geologic time has generated a sediment domain that constitutes 0.02% of the mass of the mantle, a much lower proportion than required in the EM2 mantle source. Even if subducted sediment is concentrated in large low-shear-velocity provinces (LLSVPs) at the base of the mantle (which constitute up to 7.7% of the mantle's mass), then only 0.25% of the LLSVPs are composed of sediment. This requires that the distribution of subducted sediment in the mantle is heterogeneous, and the high relative abundance of sediment in the Samoan EM2 mantle is an anomalous relic of ancient subduction that has survived convective attenuation.

KW - isotope geochemistry

KW - LA-ICP-MS

KW - LASS

KW - mantle geochemistry

KW - mantle heterogeneity

UR - http://www.scopus.com/inward/record.url?scp=85061187863&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2019.01.040

DO - 10.1016/j.epsl.2019.01.040

M3 - Journal article

AN - SCOPUS:85061187863

SN - 0012-821X

VL - 511

SP - 190

EP - 201

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

ER -

Edwards MA, Jackson MG, Kylander-Clark ARC, Harvey J, Hagen-Peter GA, Seward GGE et al. Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot. Earth and Planetary Science Letters. 2019 Apr;511:190-201. doi: 10.1016/j.epsl.2019.01.040

Extreme enriched and heterogeneous ⁸⁷ Sr/ ⁸⁶ Sr ratios recorded in magmatic plagioclase from the Samoan hotspot

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Keywords

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