島根県出雲大社、稲佐海岸に漂着した姶良カルデラ由来軽石を含む多量の軽石

その他

Many pumice clasts（190 specimens）were found in modern beach sands on the lnasa Coast Taisha district．The pumice clasts are mainly rounded to subrounded，with a maximum diameter of 9 cm，and mean of 3-4 cm．Petrographic and X-ray microprobe analysis of volcanic glasses and constituent minerals was carried out，along with XRF whole rock major and trace element analyses of individual clasts．The major constituent minerals of the pumices are plagioclase，quartz，hypersthene，magnetite，ilmenite，and apatite．Both the chemistry of the volcanic glasses and minerals and the whole rock compositions are close to those of pumices from Aira Caldera in southern Kyushu．The Taisha pumices were recently derived from Aira Caldera，and transported northward by the Tsushima ocean current．This suggests that drifted pumice can potentially be preserved within marine beds．Pumice-bearing beds can play important roles as key marker beds．However，if they are to be so used，detailed assessment must be made of their geological characteristics and origin．