Abstract

We report geochemical data on a peculiar group of Albian–Cenomanian (120–93 Ma) basalts preserved in ophiolites on the Kamchatsky Mys peninsula (Kamchatka, Russia) that share trace element and isotopic compositions with enriched tholeiites from the Detroit and Meiji Seamounts in the Hawaiian-Emperor Seamount chain. Melt inclusions in chromium spinel from these rocks, representative of melt composition unaffected by post-magmatic alteration, exhibit Hawaiian-type [Th/Ba]n (0.25–0.77; i.e., distinctively low compared to the majority of oceanic island basalts and mid-oceanic ridge basalts). Low 208Pb*/206Pb* of ~0.93 in rocks and high [Nb/La]n = 1.1–4.6 in melt inclusions suggest the presence of a distinctive “Kea”–type component in their source. We propose that the ophiolitic basalts represent older (Early to middle Cretaceous) products of the Hawaiian hotspot (older than preserved on the northwest Pacific seafloor) that were accreted to the forearc of Kamchatka. The presence of similar compositional components in modern and Cretaceous Hawaiian hotspot lavas suggests a persistent yet heterogeneous composition of the mantle plume, which may have sampled ≥15% of the core-mantle boundary layer over the past ~100 m.y.

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