Petrology of glassy rocks of the Takamatsu crater, Kagawa Prefecture, Japan
Ryoko Yamada and Hiroaki Sato
Department of Earth and Planetary Sciences, Kobe University
Kobe, 657-8501, Japan
We searched for the evidence of the impact origin of the Takamatsu crater, northeast Shikoku Japan, such as shock metamorphism of minerals, and extraordinary chemical compositions, i.e., variable and high SiO2, FeO, and NiO contents and low Na2O content of the glass. The fresh glass fragments of the Takamatsu crater, however, showed uniform calc-alkalic composition (SiO2=75wt.%) in major and trace element, although the glass contains only xenocrysts and carries no idiomorphic phenocrysts. The chemical composition of the glass is almost identical to those of welded tuff blocks and the bulk matrix of the pyroclastic flow deposit, suggesting that the glass fragments are of volcanic origin.
