Correlation of widespread tephra beds using the major-element chemistry of glass shards and glass inclusions in hornblende: Case study of the Sakate tephra, western Japan

Chisato Nakamura, Ken-ichi Yasue, Tsuneari Ishimaru, Koji Umeda, Akira Furusawa
2011 Chishitsugaku zasshi  
The Sakate tephra beds occur stratigraphically between late Pleistocene K-Ah and AT tephra beds in the Kinki and Hokuriku districts. The Sakate beds are characterized based on petrographic and mineralogical properties, such as the abundance of hornblende and the minor amount of cummingtonite. In this paper, two tephra beds (Kannabe -and OK--, considered to be Sakate-type tephra) are correlated based on their petrographic properties and the major-element chemical compositions of volcanic glass
more » ... ards. The Sambe-Ukinuno tephra is also considered to be the Sakate tephra, based on the similarity in petrographic properties and the compositions of glass shards. Accordingly, all three tephras are considered to be Sakate-type. However, it is difficult to correlate tephra beds if volcanic glass shards are absent. Therefore, we analyzed the chemical composition of glass inclusions in hornblende from the Sambe-Ukinuno, Kannabe -and OK--tephra beds. The chemical compositions of the inclusions are the same as or similar to those of the volcanic glass shards in the tephras studied here (i.e., Sambe-Ukinuno, Kannabe -and OK--). Therefore, the chemical composition of glass inclusions in hornblende is an effective index for correlating thinned and weathered tephra beds.
doi:10.5575/geosoc.117.495 fatcat:4xb2q5rl6vgbhbgkgcluwlxxle