Geochemical characterization of rocks and glasses from dykes in selected sites in Kaua’i, Hawai’i : implications on the Loa and Kea trends

Abstract

Petrological and geochemical characterization (major element, trace element and Pb isotopes) is done on 11 rock and 13 glass samples from dykes in selected sites in the island of Kaua’i (4.0-5.1 Ma). Petrography of hand sample and thin section indicate dykes are composed of tholeiitic basalt and picritic basalt. Major element analyses show all dykes are tholeiitic with consistent enrichment in major elements consistent with the mineralogy, with significant overlap in glass and rock composition in each location. Tholeiitic sample signature suggests dyke magma may be from the shield-building stage of Kaua’i. C1 Chondrite-normalized REE plots indicate dykes are consistent with geochemical signature typical of tholeiitic ocean island basalts. Binary trace element plots represent complex melting processes within the Hawaiian mantle plume resulting from partial melting of a depleted peridotite lithology source. Primitive mantle-normalized extended trace element diagram show typical composition of mantle-plume derived ocean island basalt with primitive mantle source, with enrichment in LIL and HFS elements. Pb isotopes composition show relatively low ²⁰⁶Pb/²⁰⁴Pb for a given ²⁰⁸Pb/²⁰⁴Pb and indicate dyke samples plotted on the Loa trend field with significant overlap with Kea trend lavas, and straddles the Loa-Kea trend boundary line. Comparison with Kaua’i rejuvenated lavas indicate dykes have higher concentrations of radiogenic ²⁰⁶Pb/204Pb and ²⁰⁸Pb/²⁰⁴Pb, and there is significant overlap between dykes and shield stage Kaua’i lavas indicating that overall, Kaua’i shield stage lava sampled transitional to Loa trend magmatism.