Fig. 2: The composition evolution of carbonated alkalic OIB magmas.
From: Deep evolution of carbonated magmas controls ocean island basalt chemistry
a SiO2-MgO relations. b SiO2-SiO2/FeOT relations; and (c) FeOT-MgO relations. In each subplot, grey symbols with grey trendlines represent the compositions of primary magmas derived from partial melting of carbon-free peridotite52,53 at 3 GPa and 1430-1630 °C and carbonated peridotite1 at 3 GPa and 1350-1600 °C. The red solid diamond (CP-2) represents the primary melt (picritic melt) formed by the partial melting of carbonated peridotite with 1.0 wt% CO2 (ref. 1) at 1450 °C and was selected as the starting composition in our high-pressure (HP) crystallization experiments. The red diamonds as guided by the red line represent HP-derived melts at various crystallization fractions (shown as percentage numbers next to the data points) of the carbonated picritic melt (CP-2). Both the CP-2M composition (blue solid triangle), representing a typical HP-derived melt, and the CP-2 composition, representing a primary magma without experiencing crystallization, were used as the starting compositions for melt-orthopyroxene reaction experiments. The blue empty triangle and the orange empty triangle represent the compositions after melt-orthopyroxene reactions at shallow lithosphere conditions (see text) from CP-2M (as guided by the blue line) and CP-2, respectively. The compositions of alkalic OIB lavas (cyan) are the same as those plotted in Figs. 1b, c. Arrows indicate the evolving directions of HP crystallization of clinopyroxene and garnet (Cpx and Grt, red), orthopyroxene (Opx) assimilation (yellow), and olivine (Ol) fractionation (green).
