Abstract

Despite significant efforts in studying komatiites, their primary melt compositions and volatile abundances remain largely unknown because of significant alteration. Late Cretaceous komatiites of Gorgona Island, Colombia, are unambiguous samples of high-Mg melts derived from depleted mantle peridotite and are much fresher than most of their Archean counterparts. This work presents major, trace, and volatile element data for homogenized melt inclusions in olivine (forsterite, Fo89.0–91.5) from the cumulate and upper sections of lava flows representing typical Gorgona Island komatiite (type G1). Major elements and lithophile trace elements of melt inclusions belong to a single fractionation series, which extends to the whole-rock komatiite compositions by addition of olivine. Melt inclusions are significantly enriched in volatile elements relative to elements of similar incompatibility (e.g., Cl/K 0.6–1.5; B/La 1.1–2.9; H2O/Ce 600–4000). The melt inclusions have a primary melt composition of ∼17 wt% MgO with a calculated anhydrous liquidus temperature of ∼1390 °C. However, given the presence of 0.2–1.0 wt% H2O, the initial crystallization temperature could be as low as 1330–1340 °C, but still higher than the temperature of common mid-ocean ridge magmas. The magmatic origin of volatiles in the komatiite melt has significant implications for composition and melting of the mantle source.

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