房総半島, 黄和田層下部の火山灰の研究

概要

論文の詳細を見る
Modal proportions of heavy minerals and chemical compositions of orthopyroxene and cummingtonite were measured from 100 tuff layers in the lower sequence of the Kiwada Formation along the Yoro River. The sequence is divided into three zones on the basis of the modal proportion of hornblende. The upper zone, rich in hornblende, includes a biotite-rich tuff, Kd24,and several cummingtonite-bearing tuffs. Tuffs in the middle zone are composed mostly of pyroxenes in heavy fractions. The lower zone is rich in hornblende and is characterized by presence of cummingtonite-rich tuffs, Kd38 and YK14. Chemical composition of orthopyroxene varies widely in the sequence. Although simple correlation by its composition may not be available, peak position of X_<Mg> in orthopyroxene can be used as a correlation factor referring to modal proportion and lithology. The results of this study demonstrate the potential of the methods for tuff discrimination in distal areas, especially for tuffs in the Boso Peninsula.
国立科学博物館の論文
1998-12-22