Abstract
Takamatsu crater has been identified and named by Kono et al., (1994), based on the presence of a concentric gravity low in the southern part of the Takamatsu plain, northeast Shikoku, Japan. The crater is 1-2 km deep and ca. 4 km across buried under Miocene volcanic formation and alluvium deposit. Both impact and volcanic origins have been proposed for the crater, but not dissolved yet. We searched for the evidence of the impact origin of the Takamatsu crater, such as shock metamorphic features of minerals, variable and extraordinary high contents of SiO2, FeO, NiO, and low Na2O content of fresh glass in the Miocene deposit. The glass fragments in the pyroclastic flow deposit in the southern part of the Takamatsu crater contain abundant xenocrysts of quartz and feldspar and lack idiomorphic phenocrysts. The glass show heterogeneous appearence with variable red tints and vesicularity, somewhat similar to suevite of Ries crater. The glass of Takamatsu crater, however, showed uniform and rhyolitic chemical composition common for calc-alkalic volcanics of the Miocene Setouchi volcanic suite. Further, the chemical composition of the glass is almost identical to those of welded tuff blocks and the bulk matrix of the pyroclastic flow deposit, indicating that the glass fragments are of volcanic origin. K-Ar age of the glass and associated rhyolite concentrates around 14 Ma, which coincides with the Setouchi volcanic activity. Although present analyses pointed to the cauldron origin for the Takamatsu crater, further analyses, escpecially on the deep drill core, are requisit for conclusive discussions.
Keywords: Takamatsu crater, glass, pyroclastic flow, cauldron, suevite.