Partial Melting under Shallow-Crustal Conditions: A Study of the Pleistocene Caldera Eruption of Mendeleev Volcano, Southern Kuril Island Arc.

This article focuses on the petrological investigation of the 40,000-year-old Mendeleev caldera-forming eruption on Kunashir Island in the southern Kuril Island Arc, one of the world’s most active volcanic zones. The study reveals that the eruption involved a low-potassium dacitic magma generated primarily by partial melting of amphibole-bearing upper-crustal rocks at pressures of 107–314 MPa (approximately 4.2–12.3 km depth) and temperatures of 830–890°C, rather than by fractional crystallization of mafic magmas. Mineralogical evidence, including amphibole relics and melt inclusion compositions, supports a two-stage magmatic evolution involving amphibole breakdown followed by crystallization of plagioclase and quartz during magma ascent to shallower depths (3.0–4.5 km). The findings suggest that partial melting of amphibole-bearing substrates is a key mechanism for producing silicic magmas in young island arcs and that the magmatic plumbing system beneath Mendeleev volcano extends through much of the upper crust, consistent with regional geophysical data.