Geochemical Features and Geodynamic Settings of the Formation of Cretaceous Terrigenous Rocks of the West Sakhalin Terrane

The geochemical composition of Cretaceous terrigenous rocks of the West Sakhalin terrane is analyzed and their paleogeodynamic interpretation is suggested. It is revealed that the rocks are characterized by the low maturity of clastic material. They contain fragments of both volcanomictic and sialic material and in composition correspond to graywackes, being petrogenic or “first cycle” rocks. The geochemical data were generalized and interpreted on the basis of their comparison with compositions of the present-day and ancient rocks formed in known geodynamic settings. The obtained results indicate that terrigenous rocks of the terrane were formed in a pull-apart basin at an active continental margin. The source area, which supplied clastic material in this sedimentation basin during the Berriasian–Danian, included a sialic land made up of granite-metamorphic and sedimentary rocks and the mature (deeply dissected) ensialic Moneron–Samarga island arc, which was accreted to the continental margin at the moment of basin initiation. Sediments were accumulated in general along the continent–ocean boundary against the background of large-scale sinistral transform strike-slip movements of the Izanagi Plate relative to the Eurasian continent.