Geochemical and petrographic evidence for adze production at Pu'u Pāpa'i, East Moloka'i, Hawai'i

Abstract

An unusually long and flat adze found in the ocean off O'ahu Hawai'i has distinctive micro-texture, including apatite microphenocrysts, and unusual chemical composition with ~2.5wt.% P2O5. The 37-cm-long adze is among the largest in the Bishop Museum collection and has a relatively flat, un-tanged morphology reminiscent of ancient adzes from the Marquesas Islands. However, the petrologic characteristics of the adze match exactly those of a lava flow erupted from Pu'u Pāpa'i on the Hawaiian island of Moloka'i, including microtexture, whole-rock composition and the chemistry of included apatite crystals. These data indicate that the adze and the Pu'u Pāpa'i lava are indistinguishable, strongly suggesting the presence of a previously unrecognized adze quarry on East Moloka'i. New field investigations revealed working areas on Pu'u Pāpa'i, consisting of large flakes and cores showing evidence of percussion. Although our data strongly support the hypothesis that this unusual adze was fabricated on Moloka'i, they do not explain why the adze has a nearly unique morphology for Hawaiian adzes, nor its age. This study uses a novel approach to determining the adze source, utilizing distinctive petrography, major element composition and mineral chemistry to indicate a previously unknown adze source in the Hawaiian Islands.