男鹿半島戸賀火山,戸賀軽石層中のサニディン斑晶のレーザ融解^<40>Ar/^<39>Ar年代

概要

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Toga volcano is a tuff ring, located at Toga Bay of Oga Peninsula, NE Japan. The crater is 2.0km by 2.4km in dimension, filled with K-rich rhyolite pumice-bearing tephra (Toga Pumice). The crater rim deposit has been almost entirely lost and Late Pliocene shallow marine terrace deposits overlie the crater infillings. In order to determine the eruption age of Toga volcano, a laser-fusion ^<40>Ar/^<39>Ar dating was successfully applied to sanidine phenocrysts extracted from pumice lapilli of the Toga Pumice. Measurement was made 7 times by fusion of single, 2 or 4 grains, resulting in mutually consistent dates with a weighted average ^<40>Ar/^<39>Ar age of 0.42±0.01Ma. This result coincides with 0.42±0.04Ma, the fission-track age of zircon crystals from the same sample.
2010-08-31