Cleavage dating by K-Ar isotopic analysis in the Paleogene Shimanto Belt of eastern Kyushu, S. W. Japan

Abstract

An axial-planar cleavage associated with folded sedimentary rocks of the Paleogene Shimanto Belt of eastern Kyushu was sampled and a < 2μ clay fraction separated and dated by K-Ar isotopic analysis. Experimental results yield a K-Ar age of 48.4±1 Ma. The cleavage minerals sampled, being axial-planar to the folds, are assumed to be syn-tectonic, their crystallization age thus corresponding to the age of the folds themselves.