Evolution of Late Cenozoic Magmatism in the NE Honshu Arc and Its Relation to the Crust-Mantle Structures

Geological and petrological studies of late Cenozoic volcanic rocks from the NE Honshu arc of Japan have revealed secular variations in magmatism. These variations are closely related with tectonic evolution of the arc. Three prominent stages of volcanic activity are recognized: namely continental margin, back-arc basin, and island-arc stages. Volcanic products in each stage have unique across-arc chemical variations. This may be related to changes in the thermal structure of the wedge mantle during the back-arc basin opening and island-arc stages. The island-arc stage can be further subdivided into four substages: the submarine volcanism (13.5-8Ma), late Miocene caldera-forming (8-5Ma), Pliocene caldera-forming (5-1.7Ma), and Quaternary stratovolcano-forming (1.7-0Ma) substages. Change in mode of eruption reflects the intracrustal stress regime controlled mainly by plate motion. Recent advances in seismic tomography enable visualization of the crust-mantle structures beneath the NE Honshu arc. Combined with geology and petrology, the seismic images have become valuable tools for revealing the crust-mantle thermal structures of the arc. The thermal structure of the present mantle wedge inferred from geological and petrological data correlates well with the mantle seismic structures. Intra-crustal thermal structures would have been affected by intensive magma intrusions to form large magma storages beneath the late Miocene to Pliocene calderas. The remnants of these thermal disturbances are still detectable by seismology. The crust-mantle thermal structures of the NE Honshu arc appear to have developed in relation to the development of the igneous arc.