Abstract:
Mesozoic island-arc and oceanic volcanic-sedimentary complexes were sampled at eight localities at the Taigonos Peninsula on the northern coast of the Sea of Okhotsk. Out of more than 250 samples, most proved to be completely remagnetized at the final stage of deformation by the end of Early Cretaceous; this pervasive remagnetization is probably related to onset of volcanic activity in the Okhotsk-Chukotka belt. Geological data and overall agreement of these remagnetization directions with the Eurasian and North American reference values imply that the Taigonos Peninsula did not move with respect to the continental margin since the Early Cretaceous. A pre-remagnetization remanence was isolated only from Middle-Upper Jurassic cherts, where mean direction of a prefolding component (D = 296°, I = 54°, a95 = 4.5° after tilt correction) was determined by combining four component directions and 20 remagnetization circles. These results imply the original position of the cherts at about 35°N and their later northward transport over more than 3000 km. Geological data indicate docking of the studied chert units during the second half of the Early Cretaceous. Kinematic analysis shows that the only permissible scenario includes chert accumulation and subsequent motion on the Izanagi Plate and docking to the continental margin at about 115 Ma. It means that this plate was being subducted under the active margin of Siberia during the Early Cretaceous, and thus the convergent boundary of the Izanagi and Farallon Plates in the central North Pacific was located much to the east from its earlier proposed position.