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Relationship of potassium content in andesitic lavas and depth to the seismic zone

1973; American Geophysical Union; Volume: 78; Issue: 29 Linguagem: Inglês

10.1029/jb078i029p06887

2156-2202

Dianne R. Nielson, Richard E. Stoiber,

Geology and Paleoclimatology Research

These data along with the entire article are available on microfiche. Order from the American Geophysical Union, 1707 L Street, N.W., Washington, D.C. 20036. Document J73–003; $1.00. Payment must accompany order. The relationship of potassium content of basaltic andesite and andesitic lavas to silica content and depth, as defined by the depth from the volcano to the inclined seismic zone, has been investigated for the Honshū-Hokkaido, Izu-Bonins, Ryukyus, Kurile-Kamchatka, Aleutian, Central America, and Java volcanic arcs. Analyses of lavas with a silica content of 52–63% were used to test the hypothesis that the potassium content of a lava depends on its silica content and the depth of origin along an inclined seismic zone. Correlation coefficients for this multiple regression range from r = 0.83 to r = 0.23 and were found to be statistically significant at the 0.0005–0.025 level. A comparison of the percent K2O-percent SiO2-depth relationship for individual volcanic arcs reveals that the range of percent K2O in andesitic lavas is different in different arcs. Specifically, lavas from the Izu-Bonins and Honshū-Hokkaido are characterized by a lower potassium content than lavas from the Aleutians and Java. The low to moderate correlation coefficients obtained for the percent K2O-percent SiO2-depth relationship are not compelling evidence against the idea that some definite potassium content is set during melting along the seismic zone. However, if the potassium content is determined by the depth at which melting occurs, then some other factor or group of factors sufficiently alters the potassium content to render it of doubtful use as a quantitative indicator of the depth of origin of the lava.