A new hypothesis for bimodal volcanism in the Kermadec Arc

Yasuhiro Hirai , Yoshihiko Tamura

Bimodal volcanism of basaltic and rhyolitic magmas in the Kermadec Arc has been attributed to the fractional crystallization of basaltic sources. However, new evidence from the Kibblewhite Volcano reveals two distinct differentiation pathways originating from mantle-derived basaltic and andesitic primary magmas. Here we employ geothermobarometric estimations, mass-balance calculations, and thermodynamic modeling to demonstrate that rhyolitic magmas in the Kibblewhite Volcano are derived from andesitic primary magmas through ~70% fractional crystallization. The andesite differentiation model provides a more efficient pathway for rhyolite generation than the basalt differentiation model, supported by rare earth element compositions and differentiation modelling. We propose a new hypothesis that bimodal volcanism in the Kermadec Arc arises from parallel differentiation of basaltic and andesitic primary magmas, a process facilitated by the thin crust in this arc and varied mantle melting conditions. This study challenges conventional basalt-centric paradigms of silicic magma genesis and highlights the importance of mantle-derived andesitic magmas in shaping oceanic arc volcanism.