Paleomagnetic evidence for the Miocene counter-clockwise rotation of Northeast Japan—rifting process of the Japan arc

Abstract

Paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of Cretaceous to Miocene age from Northeast Japan. The remanent magnetizations of welded tuffs with age between 32 Ma and 21 Ma old from 17 widely distributed sampling sites in Northeast Japan are fairly well grouped with a mean ofD = −41.2°, I = 56.5°, α95 = 7.2°. The remanent magnetization of welded tuffs of 14 Ma and 11 Ma from 4 sites shows a northerly direction (D = −11.7°, I = 60.5°, α95 = 15.3°). These data imply that Northeast Japan was apparently subjected to a counter-clockwise rotation through 47 ± 14° about a vertical axis on the representative point of Northeast Japan (141°E, 39°N) during the past 21 Ma. Comparing with the period of the clockwise rotation of Southwest Japan, the differential rotation between Northeast Japan and Southwest Japan is concluded to have occurred concurrently during the period between 21 Ma and 12 Ma. A rifting model of the Japan arc is proposed: Northeast Japan rotated counter-clockwise through 50° about a northern pivot at 146°E, 44°N, while Southwest Japan rotated clockwise through 54° about a southern pivot at 129°E, 34°N. The differential rotation about different rotation pivots gives rise to the opening of a diamond-shaped back arc basin, the Japan Sea.