Fig. 4: Arc-wide compilation of δ18O values in mafic minerals and equilibrium melts.
From: Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis
a Map of Java and Bali showing Moho depths estimated from Bouguer gravity anomalies (after ref. 40). The Moho lies at ca. 18-20 km beneath Bali compared to ca. 25-30 km beneath Central to East Java. b Box-and-whisker plots of pyroxene and olivine δ18O values from volcanoes along the Java-Bali segment of the Sunda arc, showing grain averaged SIMS clinopyroxene data for Merapi, Kelut, Batur, and Agung (dark grey), pyroxene LF data for Salak36, Gede30, and Ijen37, and olivine LF data for Gede30, Ijen37, and Batur (ref. 14 and this study). The number of analyses per volcano are given in parentheses. c Box-and-whisker plots of equilibrium melt δ18O values calculated for the mineral data shown in panel b by employing the silica-dependent fractionation formulations of ref. 24. The clinopyroxene data suggest a parental melt δ18O value of 5.7 ‰ (±0.2 1sd) for the Sunda arc. For most Javanese volcanoes, magmas are stored in the arc crust where they evolve while assimilating crustal materials, resulting in variably elevated δ18O values in clinopyroxene. Data plotting was performed using the “ggplot2” package available via CRAN (Comprehensive R Archive Network; https://cran.r-project.org/). Abbreviations: cpx, clinopyroxene; ol, olivine; px, pyroxene.
