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A radiogenic isotopic (He-Sr-Nd-Pb-Os) study of lavas from the Pitcairn hotspot: Implications for the origin of EM-1 (enriched mantle 1)

Garapić, G. and Jackson, M. G. and Hauri, E. H. and Hart, S. R. and Farley, K. A. and Blusztajn, J. S. and Woodhead, J. D. (2015) A radiogenic isotopic (He-Sr-Nd-Pb-Os) study of lavas from the Pitcairn hotspot: Implications for the origin of EM-1 (enriched mantle 1). Lithos, 228-229 . pp. 1-11. ISSN 0024-4937.

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We present new He-Sr-Nd-Pb-Os isotopic compositions and major and trace-element concentrations for ten subaerially-erupted lavas and one seamount lava associated with the Pitcairn hotspot. The most geochemically-enriched lavas at the Pitcairn hotspot have signatures that are consistent with recycled sediments derived from upper continental crust. Pitcairn lavas have elevated Ti, which also supports the presence of a mafic protolith in the Pitcairn mantle. A subset of Pitcairn seamount samples, including the seamount sample presented here, are tholeiitic. Tholeiitic lavas are uncommon at ocean hotspots located far from mid-ocean ridges. Like tholeiites that erupted in Hawaii, the presence of tholeiites in the Pitcairn magmatic suite can be explained by melting a silica-saturated recycled mafic component in the Pitcairn mantle source. We also present the highest ^3He/^4He ratio (12.6 Ra, ratio to atmosphere) from the Pitcairn hotspot. This sample anchors the high ^(206)Pb/^(204)Pb portion of the Pitcairn array and provides evidence for a plume component in the Pitcairn mantle. In contrast, Pitcairn lavas that have the lowest ^(206)Pb/^(204)Pb are the most geochemically enriched, and have the highest ^(87)Sr/^(86)Sr and lowest ^(143)Nd/^(144)Nd in the Pitcairn suite; these EM-1 end-member lavas have MORB-like ^3He/^4He (~ 8 Ra, ratio to atmosphere). Recycled oceanic crust and sediment suggested to be in the Pitcairn EM-1 mantle are expected to have low ^3He/^4He (< 0.1 Ra). Therefore, the higher, MORB-like ^3He/^4He in Pitcairn EM-1 lavas is paradoxical, but might be explained by diffusive exchange of helium, but not the heavy radiogenic isotopes, with the ambient mantle over billion-year timescales.

Item Type:Article
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URLURL TypeDescription
Hauri, E. H.0000-0002-7449-4774
Farley, K. A.0000-0002-7846-7546
Blusztajn, J. S.0000-0002-5475-1948
Additional Information:© 2015 Elsevier B.V. Received 16 January 2015; Accepted 15 April 2015; Available online 25 April 2015. We acknowledge the seagoing efforts of Peter Stoffers, the chief scientist during the 1989 cruise of the FS Sonne, and H. Craig, the chief scientist of the Helious Expedition that visited Pitcairn Island in 1989. The authors acknowledge the constructive comments from Al Hofmann on a prior version of this manuscript. MGJ acknowledges support from NSF grants OCE-1153894, EAR-1348082, EAR-1347377 and EAR- 1145202.
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Subject Keywords:Pitcairn; EM-1; sediment recycling; crustal recycling; tholeiite; FOZO 3He/4He
Record Number:CaltechAUTHORS:20150717-090957442
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Official Citation:G. Garapić, M.G. Jackson, E.H. Hauri, S.R. Hart, K.A. Farley, J.S. Blusztajn, J.D. Woodhead, A radiogenic isotopic (He-Sr-Nd-Pb-Os) study of lavas from the Pitcairn hotspot: Implications for the origin of EM-1 (enriched mantle 1), Lithos, Volumes 228–229, July 2015, Pages 1-11, ISSN 0024-4937, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58915
Deposited By: Tony Diaz
Deposited On:22 Jul 2015 15:47
Last Modified:03 Oct 2019 08:41

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