UPPER CRETACEOUS PALEOMAGNETIC DATA FROM SHIKOTAN ISLAND, KURIL ARC -IMPLICATIONS FOR PLATE KINEMATICS

Maastrichtian tuffaceous sandstones and siltstones were sampled from f our sites in the northern part of Shikotan Island in the Lesser Kuril Islands. A characteristic component (ChRM) isolated from most samples passes the reversal and fold tests and is most probably a primary rema nence. The ChRM mean direction (D = 3340, I = 56-degrees, k = 36, alph a95 = 3.2-degrees) is 14-degrees +/- 3.5-degrees steeper than the Paci fic reference direction and 13 +/- 4-degrees more gentle than the Eura sian reference direction. We assume that the Lesser Kuril Islands toge ther with their southwestern extension into the Nemuro Peninsula, Hokk aido were originally an island arc situated at about 36-degrees-N in t he central-west Pacific. Soon afterwards, probably by the end of the L ate Cretaceous, the Nemuro-Shikotan island arc became inactive and sta rted moving with the Pacific plate. In the Miocene, about 15 m.y. ago, the Nemuro-Shikotan island arc collided with the Eurasian plate, over rode the subduction zone, and occupied its present-day position on the Pacific side of the Kuril island arc. Although this scenario fits the available paleomagnetic data and kinematics of the Pacific plate itse lf, it disagrees somewhat with the kinematic models for the North Paci fic as a whole. In particular, by the end of the Late Cretaceous, the northern margin of the Pacific plate together with the extinct Nemuro- Shikotan island arc should have been in an area close to the transform or ridge-type Kula-Pacific boundary. The available paleomagnetic data from Northeast Asia, however, indicate that active islands arcs exist ed in mid-northern latitudes of the modern Pacific Ocean in the Cretac eous.