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Journal of Petrology Advance Access originally published online on June 18, 2008
Journal of Petrology 2008 49(7):1365-1396; doi:10.1093/petrology/egn029
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Multiple Pulses of the Mantle Plume: Evidence from Tertiary Icelandic Lavas

Hiroshi Kitagawa, Katsura Kobayashi, Akio Makishima and Eizo Nakamura*

The Pheasant Memorial Laboratory for Geochemistry & Cosmochemistry, Institute for Study of the Earth's Interior, Okayama University, Misasa, 682-0193, Japan

RECEIVED MARCH 17, 2007; ACCEPTED MAY 26, 2008


  Abstract

We present major and trace element concentrations and Sr–Nd–Hf–Pb isotope data for the c. 13–2 Ma Tertiary lavas from eastern Iceland. Our new geochemical results, together with published geological, geochronological, geochemical and geophysical data, are used to evaluate temporal changes in mantle sources contributing to the Tertiary Icelandic magmatism and the relative roles of these sources in magma productivity. The trace element and radiogenic isotopic compositions clearly distinguish three distinct end-member components in the Tertiary magmatism. Temporal variations in lava geochemistry can be attributed to changes in the relative contributions of these three end-member components to the erupted magmas and correlated with temporal variations in magma productivity. The extrusion of lavas with geochemically and isotopically enriched compositions was particularly pronounced at ~13–12 and 8–7 Ma, coincident in time with higher magma productivity. However, the geochemical characteristics of the lavas are different during these two periods: the 13–12 Ma lavas have more radiogenic 176Hf/ 177Hf and less radiogenic 206Pb/ 204Pb than those erupted from 8 to 7 Ma. The eruption of relatively depleted lavas, at around 10 Ma and younger than 6·5 Ma, is coincident with lower magma productivity. The correlation between the composition and productivity of the Tertiary lavas from eastern Iceland is probably due to periodic changes in the involvement of the enriched end-member component, followed by a gradation to periods dominated by the signature of the depleted end-member component and lower magma productivity, at an approximate frequency of 5 Myr.

KEY WORDS: mantle plume; magma productivity; mantle source; temporal variation; trace element and isotope geochemistry

*Corresponding author. Telephone: +81-858-43-3745. Fax: +81-858-43-3745. E-mail: eizonak{at}misasa.okayama-u.ac.jp


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