Multi-Cyclic and Isotopically Diverse Silicic Magma Generation in an Arc Volcano: Gorely Eruptive Center, Kamchatka, Russia

• Main Authors: Seligman, A., Bindeman, I., Jicha, B., Ellis, B., Ponomareva, V., Leonov, V.
• Language: English
• Published: 2017
• Subjects: Daly; Kamchatka Peninsula; Kamchatka
• Online Access: http://doc.rero.ch/record/302396/files/egu034.pdf

The Kamchatka Peninsula is home to some of the most frequent and prolific subduction-related volcanic activity in the world, with the largest number of caldera-forming eruptions per length of the volcanic arc. Among those, Gorely volcano has a topographically prominent Late Pleistocene caldera (13 km × 12 km, estimated to have produced >100 km3 of magma), which is now almost completely filled by a central cone. We report new 40Ar/39Ar ages and geochemical and isotopic data for newly recognized Mid-Pleistocene ignimbrite units of large but unknown volume sourced from the Gorely eruptive center, most of which were deposited in marginal glacial conditions. These ignimbrites have crystallinities of 9-24% and most are quartz-, amphibole-, and zircon-undersaturated. Additionally, we studied 32 eruptive units, including stratigraphically constrained Holocene tephra, and pre- and post-caldera lava sequences, to understand the petrogenetic and temporal evolution of this long-lived, multi-cyclic, arc volcano. Material erupted prior to the formation of the modern Gorely edifice, including the voluminous ignimbrites and eruptions of the ‘pra-Gorely' stage, consist primarily of dacite and andesite, whereas sequences of the modern Gorely edifice are represented by basalt to basaltic andesite. MELTS and EC-AFC modeling shows that it is possible to obtain silicic compositions near those of the evolved ignimbrite compositions through 60-75% fractional crystallization at 1 kbar and nickel-nickel oxide (NNO) oxygen fugacity. However, our newly compiled major and trace element data for Gorely yield two separate bimodal peaks in a SiO2-frequency diagram, showing a prominent Daly Gap, with a deficiency in andesite. Trace element concentrations define two separate trends, one for more silicic and another for more mafic sequences. Additionally, δ18Omelt values reconstructed from coexisting plagioclase and clinopyroxene phenocrysts range from a low value of 4·85‰ to a normal value of 6·22‰. The low δ18O values range throughout the ...