Geotectonism and Post-Miocene Volcanism in Northeast Japan

Abstract

The basic purpose of this paper is to reveal the Pliocene to Quaternary geotectonism of Northeast Japan using the Landsat images with geomorphological and geological data. The following conclusions are reached : a) Directions of tectonic lines which separated pre-Miocene basement into many blocks are NNW, NNE and NW. b) The tectonic lines of the Miocene predominate in NS, NNW and NW directions. c) Fractures of NW and NE directions have been formed since the Late Miocene and that of WNW one has been formed in the Pleistocene. d) Pleistocene and Holocene volcanoes distribute in the graben-like zones between two fractures of the Pliocene age, and the situations of the volcanoes correspond to the intersections of two fractures of NE and NW directions. e) Lateral movement of WNW or NW direction within the blocks of Backbone Range has been increased to form a westward curve of the Northeast Japan Arc. It seems that the movement began in Late Miocene and continued during Quaternary because many lineaments of WNW direction cut the Quaternary volcanoes. f) The Pliocene sediment along the Kitakami river increases its width of distribution southward, and many faults with NS directions dipping eastward exist in the Sendai Plain. These facts suggest the possibility of anti-clockwise rotational movement of the Kitakami Mountains. g) New grabens of NE directions distribute northward of the Kitakami Mountains and the Ishinomaki-Tyokaisan tectonic Zone with NW direction exists between the Kitakami Mountains and Abukuma Mountains. Based on these facts, it appears that the Kitakami Mountains has been remained as a rigid block and pressed the Backbone Range westward during the movement of the Plate with compressional stress from east to west.