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Abstract: A suite of picrites and basalts from the Muli area, in the northwestern part of the Emeishan continental flood basalt province, provides new and valuable information on the geochemistry of the Emeishan Large Igneous Province (LIP) and its source. The Muli picrites can be classified as type-1 or type-2. The former shows ocean–island basalt-like trace element characteristics, with γOs (260Ma) values and εNd (260Ma) values ranging from +7.5 to +11.5 and from +6.0 to +7.8, respectively. This is the first time that picrites with highly radiogenic Os and high Os contents (up to 3.3ppb) have been recognized in the Emeishan LIP. These characteristics probably reflect a relatively enriched component in the Emeishan LIP source. The type-2 picrites are characterized by non-radiogenic γOs (260Ma) values ranging from −4.2 to −0.3, and they may be further subdivided into type-2A and type-2B picrites. Type-2A picrites contain moderate amounts of the light rare earth elements (LREEs), have low CeN/YbN values (1.1–2.0), and a relatively high initial εNd (+5.0 to +6.6). In terms of Os and Nd isotopes, the Muli type-2A picrites are similar to the Song Da komatiites of Vietnam and the Gorgona Island picrites, revealing the existence of a depleted mantle component in the Emeishan LIP source. In contrast with the type-2A picrites, type-2B lavas exhibit a negative Nb anomaly and relatively lower initial εNd and γOs values (Nb/La>1.8; εNd (260Ma)=−5.5 to +6.4; γOs (260Ma)=−4.2 to −1.9), suggesting that the type-2B lavas have a depleted mantle source, similar to type-2A, but that the type-2B lavas are also influenced by various degrees of mixing of depleted plume-derived melt, sub-continental lithospheric mantle, and/or continental crust. Given that the basalts in the Muli area show similar geochemical features to those of the type-2B picrites, their origins are inferred to be similar. [Copyright &y& Elsevier]

Abstract: The volatile content of komatiite is a key to constrain the thermal and chemical evolution of the deep Earth. We report the volatile contents with major and trace element compositions of ~80 melt inclusions in chromian spinels (Cr-spinels) from beach sands on Gorgona Island, Colombia. Gorgona Island is a ~90Ma volcanic island, where picrites and the youngest komatiites known on the Earth are present. Melt inclusions are classified into three types on the basis of their host Cr-spinel compositions: low Ti (P type), high Ti with high Cr# (K1 type) and high Ti with low Cr# (K2 type). Chemical variations of melt inclusions in the Cr-spinels cover all of the island''s lava types. P-type inclusions mainly occur in the picrites, K1-type in high-TiO2 komatiites (some enriched basalts: E-basalts) and K2-type in low-TiO2 komatiites. The H2O and CO2 contents of melt inclusions within Cr-spinels from the beach sand are highly variable (H2O: 0.03–0.9wt.%; CO2: 40–4000ppm). Evaluation of volatile content is not entirely successful because of compositional alterations of the original melt by degassing, seawater/brine assimilation and post-entrapment modification of certain elements and volatiles. However, the occurrence of many melt inclusions with low H2O/K2O ratios indicates that H2O/K2O of Gorgona komatiite is not much different from that of modern mid-oceanic ridge basalt (MORB) or oceanic island basalt. Trend of CO2/Nb and Zr/Y ratios, accounted for by two-component mixing between the least degassed primary komatiite and low-CO2/Nb evolved basalt, allow us to estimate a primary CO2/Nb ratio of 4000±2200 or a CO2 content of 0.16±0.09wt.%. The determined CO2/Nb ratio is unusually high, compared to that of MORB (530). Although the presence of CO2 in the Gorgona komatiite does not affect the magma generation temperature, CO2 degassing may have contributed to the eruption of high-density magmas. High CO2/Nb and the relatively anhydrous nature of Gorgona komatiite provide possible resolution to one aspect of the hydrous komatiite debate. [Copyright &y& Elsevier]