ASYMMETRIC DEFORMATION IN THE BACKARC REGION OF THE KURIL ARC, NORTHWEST PACIFIC: NEW INSIGHTS FROM ANALOGUE MODELING

Abstract

The Eocene to middle/late Miocene tectonic evolution of the Kuril arc and backarc region has been simulated with analogue experiments. The experiments simulate asymmetric deformation in the overriding plate due to anticlockwise rollback of the subducting Pacific plate. The results show the formation of a N-S to NE-SW-oriented dextral shear zone near the far edge of the retreating boundary analogous to the Sakhalin-Hokkaido dextral shear zone. Contemporaneously, normal faults and grabens form, striking parallel to the retreating boundary near the far edge but striking more oblique near the hinge point and away from the retreating boundary. This is similar to extensional structures observed in the Kuril Basin and the Sea of Okhotsk. Furthermore, the model shows that the amount of extension progressively decreases away from the retreating boundary. This appears to have also happened in the Kuril-Okhotsk region, as evidenced by crustal thickness variation in the region. Finally, the model results show that extension is increasingly accommodated by the region close to the retreating boundary with progressive deformation. This can account for the Eocene-early Miocene extension in the Sea of Okhotsk followed by Miocene spreading in the Kuril Basin.