Eocene Granitoids of the Okhotsk Granodiorite Complex (South Sakhalin)
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As a result of U–Pb dating by LA-ICP-MS, the age of zircons from granitoids was determined to be 42.1–44.3 Ma for the rocks of first phase and 42.4–42.7 Ma for rhyolites from dikes of the second phase. On the basis of the geochemical studies of rocks, it was found for the first time that granodiorites of the Okhotsk massif (first phase) refer to A2-type granitoids. The most likely explanation of petrogenesis for A2-type granitoids of the Okhotsk complex is the gradual cessation of subduction as a result of deceleration of the Pacific Plate and the transition of the Ozerskii terrane to transform northward motion along the Merei suture zone with a certain role of syn-shear extension. Thus, the data obtained on the age and geochemistry of the Okhotsk complex granitoids suggest the possible time of geodynamic regime change in this area as about 43 Ma ago.
This work was supported by a joint grant of the Russian Foundation for Basic Research and the Taiwan Ministry of Science and Technology (project no. 15-55-52035) and also by project no. 15-I-2-004-o of the Far East program of basic research of the Far East Branch, Russian Academy of Sciences.
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