Paleomagnetism of late Cenozoic volcanic rocks (Enrei Formation) in Nagano Prefecture, central Japan

Abstract

Remanent magnetizations in andesite samples collected from 26 sites of the upper Cenozoic Enrei Formation in Nagano Prefecture, central Honshu, allow us to discuss the age of the formation and rotational motion in the study area. Stable magnetic components revealed by stepwise alternating-field and thermal demagnetization give a directional dataset that passes the reversal test. This reliable dataset delineates a sequence of reversed-normal-reversed magnetic polarity changes that is assigned to the younger part of the Matuyama Chron on the geomagnetic polarity time scale. The normal polarity is correlated either to the Jaramillo Subchronozone or to the Cobb Mountain Subchronozone. This magnetostratigraphic correlation suggests that most of the Enrei volcanic sequence belongs to the Lower Pleistocene. A paleomagnetic pole that is indistinguishable from the geographic north pole indicates no significant rotational motion and latitudinal movement in the study area.