Sinistral En Echelon Folding of the Sambagawa Schists and Its Tectonic Implication

The folds of the Sambagawa schists, which were produced during the last phase (Hijikawa—Oboke phase = Dh phase) of their folding history, are developed as a series of sinistral en echelon upright folds with half wavelength of less than 20 Km (Hara et al.,1977,1992). The Dh phase folds in Shikoku are accompanied with two culminations, Oboke culmination and Nakashichiban culmination, placed near the MTL. Their movement picture during the formation process of such the Dh phase folds has been analyzed on the basis of orientation pattern of parasitic folds and quartz microtextures. It has been clarified that the Dh phase folds were produced by left—lateral shear under N —S compression, being accompanied by the southward tectonic emplacement of two rigid bodies which gave rise to the Oboke and Nakshichiban culminations. These bodies can be assumed to be granitic and/or high—temperature metamorphic rocks tectonically derived from the Kurosegawa—Koryoke continent, as judged from the seismic refraction data in the Oboke district after Ichikawa (1968).