The volumetric change of eruptive magma since 2.0 Ma along the volcanic front in the Tohoku District is estimated. K-Ar ages, fission track ages, stratigraphic relations and other age data are taken from compilaions in the published literature and the volume of volcanic products is calculated for each volcano. Three stages are recognized with distinct types of volcanism, volumetric changes of eruptive magma and locations of eruptive centers. Stage 1 (2.0 to 1.0 Ma): This stage is characterized by felsic volcanism associated with large calderas. The location of eruptive centers before 1.0 Ma have a NE to ENE trend. Stage 2 (1.0 to 0.6 Ma): Felsic volcanism terminated at around 1.0 Ma, and stratovolcanoes became the dominant form of volcanism. Stage 3 (0.6 Ma onwards): The rate of magma eruption increased dramatically after 0.6 Ma, Felsic volcanism resumed and volcanism associated with the stratovolcanoes continued. The arrangement of eruptive centers have a SN trend. The volcanism along the volcanic front after 2.0 Ma was synchronous with the initiation of crustal shortening and the development of a narrow uplifted zone associated with faulting in the Ou Backbone Range. The change of the regional stress regime from neutral to compression at around 1.0 Ma caused a dominance of volcanism associated with stratovolcanoes. The increase of eruptive magma rate since 0.6 Ma is controlled by the local extensional stress regime in the Ou Backbone Range, caused by dislocation tectonics and gravity tectonics.
