続成過程における粘土鉱物の生成, 変化とその性質

抄録

Illite/smectite mixed-layer minerals occur widely in diagenetic process of argillalaceous and acid pyroclastic sediments. The relative proportion of constituent layers and ordering in the mixed-layer structure are regarded as reflecting formation temperature (Fig. 1). Chemical changes from random to regular interstratification are remarkable in tetrahedral Al and octahedral Al/(Al+Mg+Fe) ratio (Fig. 2).
Chlorite/saponite mixed-layer minerals are found in MgFe bearing sediments such as basic-intermediate pyroclastics. The proportion of chlorite layers in the interstratification is discontinuous and is concentrated on ranges of less than 10, 50, 75 and morethan 90%. Randomly interlayering of chlorite/saponite occurs as replacement products of volcanic glass. An increase in chlorite layers with increasing burial depth is observed in the Miocene pyroclastic rocks of Yamagata-Yoshino (Fig. 3). Whereas corrensite type minerals occurring as cementing materials of andesitic sandstone are found over the thick strata regardless of burial depth. Chemical changes of chlorite/saponite mixed-layer with increasing burial depth are characterized by an increase of tetrahedral Al and octahedral Fe (Fig. 4).