Klyuchevskoy Volcano, Kamchatka, Russia: The Role of High-Flux Recharged, Tapped, and Fractionated Magma Chamber(s) in the Genesis of High-Al2O3 from High-MgO Basalt

• Published in: Journal of Petrology
• Main Authors: KERSTING, ANNIE B., ARCULUS, RICHARD J.
• Format: Text
• Language: English
• Published: Oxford University Press 1994
• Subjects: Articles; Kamchatka
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/35/1/1; https://doi.org/10.1093/petrology/35.1.1

Mineral Chemistry, and major and trace element variations of the basalts from Klyuchevskoy, the world's most active island are volcano, are most consistently explained by the persistence of a non-steady state, erupting, recharging, and fractionating magma chamber in which fractionation of a parental high-MgO basalt melt produces high-Al 2 O 3 basalt. Although fractional crystallization is the dominant controlling mechanism, periodic recharge with a more primitive high-MgO basalt is also an important process contributing to the chemical evolution of the magmas. Hybrid basalts are the mixed product of high-Al 2 O 3 basalt recharged with high-MgO basalt. The lavas range in composition from high-MgO, low-Al 2 O 3 (∼ 12 wt. % MgO, 14 wt. % Al 2 O 3 ) to high-Al 2 O 3 , low-MgO (∼ 18 wt. % Al 2 O 3 , 4 wt. % MgO). The high-MgO lavas are characterized by phenocrysts of olivine (cores FO 90–80 and rims FO 85–75 ) with chromite inclusions [Cr/(Cr + Al)≥0.7], clinopyroxene (Wo 46–42 En 48–42 Fs 15–7 ), and the rare occurrence of orthopyroxene (En 72–70 ). All the phenocrysts are normally zoned and set in a groundmass of plagioclase, pigeonite, clinopyroxene, magnetite, � orthopyroxene. The high-Al 2 O 3 basalts contain plagioclase (An 85–55 ), olivine (Fo 80–65 ), clinopyroxene (Wo 45–30 En 50–38 Fs 23–11 ), � orthopyroxene (En 72–70 ) phenocrysts, that preserve both normal and reverse zoning in a groundmass of plagioclase, pigeonite, olivine, clinopyroxene, magnetite, � orthopyroxene. Hybrid basalts have characteristics of both high-MgO basalts and high-Al 2 O 3 basalts and preserve complicated normal-to-reverse, reverse-to-normal, and normally zoned phenocrysts. No hydrous minerals are present in any of the lavas. The varied basaltic magmas erupted from Klyuchevskoy are derived from a magma chamber(s) located near the base of the Kamchatka crust (pressures ∼ 0.5–0.9 GPa) and characterized by relatively high crystallization temperatures, some in excess of ∼1150�C. Under these conditions, the fractionation of a parental ...