Rodingite‐Derived Melt as a Recipe for Ultra‐Calcic Magmas

Abstract Rodingite is a high‐CaO rock formed by Ca‐rich fluid metasomatism on mafic protoliths. It typically occurs within serpentinite and represents an often‐overlooked constituent of the altered oceanic lithosphere that may be subducted into the mantle. However, the fate of rodingite in the mantle and its role in magma genesis remain poorly constrained. Here we present experimental results on the partial melting of rodingite and subsequent melt–peridotite reaction at 1–3 GPa, 1050–1400°C. Rodingite‐derived melts are characterized by low SiO 2 (43.5–45.2 wt%), high CaO (>∼30 wt%) and high CaO/Al 2 O 3 ratios (up to 4.3). Reaction of these melts with mantle peridotite produces mafic melts with elevated SiO 2 contents (45.7–49.1 wt%) and high CaO/Al 2 O 3 ratios (1.1–2.2). These reacted melts closely resemble silica‐saturated, ultra‐calcic mafic magmas in arcs, back‐arcs, mid‐ocean ridges and ocean islands, suggesting that rodingite‐derived melts contribute a distinctive Ca‐rich chemical signature to mantle sources tapped by diverse tectonic settings.