Melt Flux from the Mantle Regulates the Crustal Processing and δ18O Variations of Kamaʻehuakanaloa Magmas.

This article focuses on the oxygen isotopic (δ¹⁸O) variations in basalts from Kamaʻehuakanaloa (formerly Lōʻihi Seamount), an active submarine Hawaiian pre-shield volcano, to understand mantle versus crustal influences on magma composition during its transition from alkalic to tholeiitic volcanism. Analyses of volcanic glass and olivine crystals reveal a north–south spatial division in δ¹⁸O and geochemical parameters, with northern Kamaʻehu lavas being more alkalic, enriched, and differentiated, showing higher δ¹⁸O values due to assimilation of low-temperature seawater-altered volcanic edifice. In contrast, southern lavas are predominantly tholeiitic with lower δ¹⁸O values attributed to assimilation of high-temperature hydrothermally altered crust. The study concludes that mantle melt flux controls crustal magmatic processing and δ¹⁸O variations, with average δ¹⁸O values of ~5.4‰ for glass and ~5.0‰ for olivine representing the best estimate of mantle-derived magma at Kamaʻehu, similar to the most depleted mid-ocean ridge basalts (MORB).