中央日本のネオテクトニクスと伊豆小笠原弧

抄録

Central Japan has been tectonically situated at a triple juncture among Izu-Bonin, Northeast Japan, and Southwest Japan Arcs. Neotectonics of central Japan is geohistorically reexamined with the special reference to the results of ODP Leg126 transect of Izu-Bonin Arc. Three major points are claimed as follows:
(1) The tectonic belt along eastern margin of Japan Sea (EMJS) is characterized by severe compressional deformation including thrusts and folds have developed within the Miocene rifted trough, Uetsu sedimentary basin, by a tectonic reversal which occurred at the end of Miocene around 6 Ma. Since then, the belt have behaved as a newly formed plate boundary between Eurasia and North America Plates.
(2) During the period of 2.8-1.4 Ma, a bimodal volcanism occurred at the both flanks of the southern Hida Mountain Range. Area of such explosive acidic volcanism was bounded by a rift-like depression zone called “Omine Rift” was formed along the north-central segment of Itoigawa-Shizuoka Tectonic Line. This means that backarc rifting of Izu-Bonin arc forced the above colliding boundary between Northeast Japan and Southwest Japan to expand.
(3) As for plate tectonic frame-work in central Japan, two possibilities are pointed out based on contemporal changes throughout central Japan.
a) An eastward motion of Southwest Japan (EUR) has started at about 6 Ma, which immediately caused the jump of plate boundary from central Hakkaido to the EMJS following the tectonic reversal in the inner Northeast Japan arc.
b) Philippine Sea plate has changed the direction of its movement from North-northeast to West-southwest around 3.5 Ma, which activated the backarc rifting of Izu-Bonin arc.