TY - JOUR

T1 - The role of polybaric crystallization in genesis of andesitic magmas

T2 - Phase equilibria simulations of the Bezymianny volcanic subseries

AU - Almeev, Renat R.

AU - Ariskin, Alexei A.

AU - Kimura, Jun Ichi

AU - Barmina, Galina S.

N1 - Funding Information: We thank two anonymous reviewers for constructive suggestions, and Francois Holtz for his helpful comments. The editorial work of Candace O'Connor, Malcolm Rutherford and Pavel Izbekov is greatly appreciated. This work was supported by a DFG grant ( HO 1337/21 ).

PY - 2013/8/1

Y1 - 2013/8/1

N2 - Using the updated COMAGMAT model, the crystallization sequences of a Bezymianny Volcano basaltic andesite (Kamchatka, Russia) are simulated in a wide range of thermodynamic conditions (P-T-fO2) as a function of H2O concentration. Comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1.5-2wt.% H2O stored under 490-520MPa pressure in the magma plumbing system beneath Bezymianny Volcano. The initial magma originates as a result of the polybaric evolution of mantle-derived high-Mg basaltic magmas of the adjacent Kliuchevskoi Volcano. The subsequent evolution of derivative hydrous and alumina-rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of ~12MPa per 1% of crystallization. In the course of polybaric crystallization, compositions of pyroxene-bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent. However, hornblende-bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene-bearing andesite formation. They require high water contents and high pressures of crystallization. In this case, liquid composition should deviate from the chemical trend defined by the whole rock compositions.

AB - Using the updated COMAGMAT model, the crystallization sequences of a Bezymianny Volcano basaltic andesite (Kamchatka, Russia) are simulated in a wide range of thermodynamic conditions (P-T-fO2) as a function of H2O concentration. Comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1.5-2wt.% H2O stored under 490-520MPa pressure in the magma plumbing system beneath Bezymianny Volcano. The initial magma originates as a result of the polybaric evolution of mantle-derived high-Mg basaltic magmas of the adjacent Kliuchevskoi Volcano. The subsequent evolution of derivative hydrous and alumina-rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of ~12MPa per 1% of crystallization. In the course of polybaric crystallization, compositions of pyroxene-bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent. However, hornblende-bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene-bearing andesite formation. They require high water contents and high pressures of crystallization. In this case, liquid composition should deviate from the chemical trend defined by the whole rock compositions.

KW - Bezymianny Volcano

KW - COMAGMAT

KW - Phase equilibria simulations

KW - Polybaric crystallization

UR - http://www.scopus.com/inward/record.url?scp=84885072374&partnerID=8YFLogxK

U2 - 10.1016/j.jvolgeores.2013.01.004

DO - 10.1016/j.jvolgeores.2013.01.004

M3 - Article

AN - SCOPUS:84885072374

VL - 263

SP - 182

EP - 192

JO - Journal of Volcanology and Geothermal Research

JF - Journal of Volcanology and Geothermal Research

SN - 0377-0273

ER -