照来コールドロンのK-Ar年代

抄録

K-Ar ages of volcanic rocks from the Teragi cauldron were determined. The earliest volcanic products were the Lower Tuff (about 100 km³), which erupted 3.1 Ma, and was succeeded by the Teragi cauldron subsidence (17km×14km). The Yudani conglomerate and overlying Haruki mud deposited in the northeast part of the cauldron, and andesitic volcanism (Terada volcanics) began 2.8 Ma in the southwest part. The upper and lower parts of the Haruki mud were intruded or intercalated by andesitic sheet or lava of 2.6 and 2.3 Ma, which show an approximate period of deposition of the mud. The latest volcanic activity was 2.2 Ma, which was characterized by rhyolitic volcanism forming domes and pyroclastic flows mainly around the northeastern cauldron rim. The period of volcanic activity related to the Teragi cauldron was about 0.9 Ma (3.1 to 2.2 Ma).