続成・熱水変質作用におけるイライト/スメクタイト及び3入面体型緑泥石/スメクタイト混合層鉱物の生成と変化

Abstract

Conversion processes of illite/smectite and chlorite/smectite interstratified minerals during burial diagenesis and hydrothermal alteration are characterized from the standpoints of their structural and chemical changes. The decrease in expandability of illite/smectite takes place nearly continuously from 100 % to 0%, although the diagenetic and hydrothermal conversion processes are characterized by slightly different conversion trends. On the other hand, that of chlorite/smectite takes place discontinuously in both environments, with steps at about 100-80 %. 50-40%, and 15-0%. With such structural changes, illite/smectite gradually decreases the tetrahedral Si and octahedral Mg and increases the tetrahedral and octahedral Al and interlayer K. The chemical changes for chlorite/smectite take place apparently continuously from saponite to chlorite following that the tetrahedral Al and octahedral Fe increase and the tetrahedral Si and interlayer Ca decrease. In terms of chemical composition, a 1:1 regularly interstratified mineral, rectorate, has distinctive characteristics from those of common illite/smectite questioned here, as well as its distinctive structure. In chlorite/smectite, it is noticeable that there is a discordance between the discontinuous decrease in expandability and the continuous change in chemical composition during the aggrading conversion.