Origin of Silicic Magmas at Kibblewhite Volcano: Implications for Bimodal Volcanism in the Kermadec Arc

This study investigates the origin of silicic magmas at the Kibblewhite Volcano in the Kermadec arc. Two alternative differentiation pathways are evaluated: fractional crystallization of primary basaltic magmas producing low‐Mg andesites, and fractional crystallization of primary andesitic magmas represented by magnesian andesites. Major‐ and trace‐element geochemistry, rare earth element (REE) systematics, geothermobarometric constraints, and thermodynamic modeling demonstrate that the low‐Mg andesites represent already evolved melts and cannot generate the observed dacitic to rhyolitic magmas through further crystallization. In contrast, magnesian andesites show close agreement with the silicic magmas in both major‐element and REE compositions, indicating that they provide a viable parental magma for the silicic magmas at Kibblewhite Volcano. These results indicate that two distinct differentiation pathways coexist beneath the Kibblewhite Volcano, in which basaltic and andesitic primary magmas evolve independently to produce low‐Mg andesites and dacitic to rhyolitic magmas, respectively. When considered in a broader context, parallel differentiation of basaltic and andesitic primary magmas may also contribute to the bimodal SiO 2 distributions characteristic of the Kermadec Arc; however, this arc‐scale application should be regarded as a working hypothesis requiring further evaluation at other volcanic centers.