房総半島の凝灰岩中の重鉱物の量比と化学組成の予察的研究

概要

論文の詳細を見る
Modal proportions of heavy minerals in a tuff are different in fractions divided by grain size. Heavy minerals such as zircon and magnetite are strongly enriched in the fine-grained fractions. The proportion changes within a tuff layer even if it consists of the same mineral assemblage. Both chemical compositions and modal proportions of minerals in most of the tuffs depend more or less on grain size, due to the complex mixing of different volcanic fragments at eruption or at depositional stage. Only in a few tuffs, mineral composition and proportion are homogeneous within a layer and are not significantly affected by grain size. There are many characteristic tuffs such as cummingtonite tuff and Fe-rich orthopyroxene-bearing tuff in the Tertiary-Quaternary sequence from the Boso Peninsula. Although simple correlation by mineral proportion may not be available, chemical compositions of minerals can be used as a correlation factor if they are specific. Otherwise it is better to correlate tuffs referring to modal proportion, mineral composition and lithology.
国立科学博物館の論文
1997-12-22