Structural control on Late Miocene to Quaternary volcanism in the NE Honshu arc, Japan

Volcanological and structural field data are used to define the tectonic control on the N-S volcanic arc of NE Honshu (Japan) since Late Miocene. During Late Miocene-Pliocene, bimodal products were mainly erupted from along-arc and NE-SW aligned and elongated calderas. The deformation pattern mostly consisted of N-S dextral faults and subordinate NE-SW extensional structures, produced by NE-SW compression. This pattern, due to the indentation of the Kuril sliver, is similar to that of oblique convergence settings. Magma rose and extruded along NE-SW areas of localized extension created by the dextral faults. These extensional areas were uncoupled with regard to those, ~E-W trending, inferred to have focused the rise of melts from the subducting slab in the mantle. During Quaternary, a larger amount of andesite was mainly erupted from along-arc and ~E-W aligned and elongated stratovolcanoes. The deformation pattern mostly consisted of N-S thrust faults and subordinate ~E-W extensional structures, produced by ~E-W compression, resulting from orthogonal convergence due to the variation in the absolute motion of the Pacific Plate. The ~E-W extensional structures are the shallowest expression of ~E-W trending hot mantle fingers, suggesting mantle-crust coupling for the rise of magma. Such a coupling ensures: (a) higher extrusion and (b) mixing between a deeper mafic and a shallower felsic magma, generating the andesites. The significantly larger volumes (per Ma per 200 km of length of the arc) of magma erupted during Quaternary show that pure convergence conditions do not necessarily hinder the rise and extrusion of magma.