OCEANIC RIDGE-ARC COLLISION AS A TRIGGER FOR ACTIVE MARGIN CONTINENTAL GROWTH: EVIDENCES FOR THE SAKHALIN REGION AND SEA OF OKHOTSK, EASTERN RUSSIA

We present here a new model on the Late Cretaceous-Tertiary tectonic evolution of Sakhalin and the NW Pacific region. This model is based on field observations on the geological structure of Sakhalin and a review of geophysical and geological data on the Sea of Okhotsk region. A structural and kinematic analysis complemented by detailed and regional cross sections across Central Sakhalin and northern Sakhalin provides new insights into the tectonic evolution of the NW Pacific region. In this model, it is suggested that the Sea of Okhotsk, north of the Kuril Basin, is formed by continental crust, younging to the south from latest Cretaceous ages to Cenozoic ages. This crust is interpreted as the result of the growth of NW Pacific Magmatic Arcs and the southeasterward expansion of the Sea of Okhotsk following a 40° counter-clockwise rotation of the Sikhote Alin Magmatic Arc and Sakhalin during the Late Cretaceous and Early to Mid Paleogene. The eastern flank of Sakhalin is considered as a dextral transform boundary between the eastern edge of Eurasia and the south-easterly growing Sea of Okhotsk crust. During the Neogene, narrow transtensional basins were created and parts of SE Sakhalin and Central Hokkaido were progressively isolated from the proto-Kuril accretion wedge. Since the Pliocene, convergence between the Eurasian Plate and the North American Plate, to which the Sea of Okhotsk belongs, induced uplift of Sakhalin Mountains and the growth of giant N-S trending detachment anticlines currently exploited and explored for hydrocarbons in the north Sakhalin Basin.