Mid-Cretaceous Hawaiian tholeiites preserved in Kamchatka

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 208 Pb*/ 206 Pb* 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 Pacifi c seafl oor) 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.