The alteration mineralogy, major and trace element chemistry, and Sr-Nd-Pb-Hf
isotopic compositions of post-shield lavas from Mauna Kea, Kohala, and Hualalai on the
island of Hawaii in the Pacific Ocean are used to constrain the origin and distribution of
heterogeneities in the Hawaiian mantle plume. Ocean island basalts contain a variety of
secondary minerals that must be removed by acid-leaching to achieve high-precision Pb
isotopic compositions, a powerful geochemical tracer of variation in plume source
composition. Post-shield lavas range from transitional/alkalic basalt to trachyte and are
enriched in incompatible trace elements (e.g. LaN/YbN=6.0-16.2) relative to shield stage
tholeiites. Post-shield lavas are characterized by a limited range of Sr-Nd-Hf isotopic
compositions(⁸⁷Sr/⁸⁶Sr=0.70343-0.70365; ¹⁴³Nd/¹⁴⁴Nd = 0.51292-0.51301;¹⁷⁶Hf/¹⁷⁷Hf=
0.28311-0.28314) and have Pb isotopic compositions(²⁰⁶Pb/²⁰⁴Pb = 17.89-18.44;
²⁰⁷Pb/²⁰⁴ 15.44-15.49;²⁰⁸Pb/²⁰⁴Pb= 37.68-38.01) that belong to their respective Kea or
Loa side of the Pb-Pb boundary. Mauna Kea lavas show a systematic shift to less
radiogenic Pb isotopic compositions from the shield to post-shield stage and trend to low
⁸⁷Sr/⁸⁶Sr towards compositions characteristic of rejuvenated stage lavas. Hualalai post
shield lavas lie distinctly above the Hf-Nd Hawaiian array (ƐHf = +12 to +13; ƐNd = +5.5 to
+6.5) and have some of the least radiogenic Pb isotopic compositions (e.g.²⁰⁶/²⁰⁴pb=
17.89-18.01) of recent Hawaiian volcanoes. In contrast, comparison of Kohala with the
adjacent Mahukona shows that lavas from these volcanoes become more radiogenic in Pb
during the late stages of volcanism. The Sr-Nd-Pb-Hf isotope systematics of the post
shield lavas cannot be explained by mixing between the Kea and Koolau end-members or
by assimilation of Pacific lithosphere and are consistent with the presence of ancient recycled lower oceanic crust and sediments in their source. More than one depleted
component is sampled by the post-shield lavas and these components are long-lived
features of the Hawaiian plume that are present in both the Kea and Loa source regions.
The geochemistry of the post-shield lavas provide evidence for a bilaterally zoned plume,
where the compositional boundary between the Kea and Loa sources is complex and
vertical components of heterogeneity are also significant.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/2864 |
| Date | 11 1900 |
| Creators | Hanano, Diane |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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