Lithium isotope geochemistry of the Hawaiian plume: Results from the Hawaii Scientific Drilling Project and Koolau Volcano

• Lui‐Heung Chan

  Department of Geology and Geophysics Louisiana State University Baton Rouge LA 70803 USA

• Frederick A. Frey

  Department of Earth, Atmospheric, and Planetary Sciences Massachusetts Institute of Technology Cambridge MA 02139 USA

Abstract

We determined lithium isotopic compositions of Mauna Loa and Mauna Kea basalts from the 3.1 km drill hole of the Hawaiian Scientific Drilling Project (HSDP); for comparison Li isotopic ratios were also determined for basalts from Koolau volcano. These two suites of samples define geochemical extremes in the range of Hawaiian shield lavas. The 400 Ka record of Mauna Kea in the HSDP core shows temporal fluctuations between low δ 7 Li (∼4‰ relative to the L‐SVEC standard) and high δ 7 Li (5–6‰), suggesting that the source components in the Hawaiian plume are heterogeneous in Li isotopic composition. Based on SiO 2 content and isotopic ratios of He, Li, Nd, Hf and Pb, three geochemical groups are identified in Mauna Kea lavas. Mauna Kea basalts between 1900 and 2500 mbsl have relatively low δ 7 Li of about 4‰. They are low SiO 2 lavas distinguished by the highest 3 He/ 4 He and 208 Pb/ 204 Pb, and low 176 Hf/ 177 Hf and 143 Nd/ 144 Nd. Like basalt from Loihi seamount, this Mauna Kea group is considered to originate from the core of the plume. Above 1900 mbsl, high δ 7 Li lavas with high SiO 2 contents appear in both the submarine and subaerial sections. They are marked by low 3 He/ 4 He and high 176 Hf/ 177 Hf. The 7 Li‐rich signature of some samples (δ 7 Li up to 5.7) is indicative of recycled oceanic crust in the plume. This magma group defines the Kea component. The low SiO 2 lavas in the subaerial section have low δ 7 Li (∼4‰), 3 He/ 4 He and 208 Pb/ 204 Pb. Their δ 7 Li values overlap the range of δ 7 Li in unaltered mid‐ocean ridge basalt (MORB) and are consistent with upper mantle material entrained by the plume or contamination of plume‐derived magmas by the Pacific lithosphere. The δ 7 Li of Koolau lavas mostly fall within the range of 4.5 ± 0.3‰. Exceptions are two samples that have δ 7 Li of 2–3‰. The lightest isotopic values may indicate subducted Li that was isotopically fractionated during slab dehydration. In contrast to other isotopic systems, most Koolau samples, however, resemble Mauna Kea samples in Li isotopic composition. Mauna Loa samples have δ 7 Li values of 3.5 to 4.9‰, within the range of the Koolau and Mauna Kea lavas. Based on these data, the Loa trend volcanoes and Kea trend volcanoes have largely overlapping Li isotopic compositions. In summary, the Hawaiian plume is not highly variable in Li isotopic composition; δ 7 Li is typically ∼4‰ with perturbations by subducted components to lower and higher ratios (2.5 to 5.7‰). The overlap of most Hawaiian basalt and MORB in their range of Li isotopic ratios suggests minor influence of recycled oceanic crust in the plume and perhaps similar Li isotopic ratios in the upper and lower mantle.

Journal

• Geochemistry, Geophysics, Geosystems

  Geochemistry, Geophysics, Geosystems 4 (3), 2003-03

  American Geophysical Union (AGU)

Keywords

• Geochemistry and Petrology
• Geophysics

Details

• CRID: 1360574094408072064
• NII Article ID: 30022964193
• DOI: 10.1029/2002gc000365
• ISSN: 15252027
• Web Site: https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F2002GC000365
• Web Site: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002GC000365
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