The Kataevo Island Arc System of the Paleoasian Ocean (Transbaikalia): Composition, Age, Paleomagnetism, and Formation Geodynamic Settings

––Based on new data on the geology, composition, U–Pb isotopic age, and paleomagnetism of the metavolcanic rocks of the Kataevo Formation, we consider the geodynamic conditions of their formation and alteration. The Kataevo Formation metavolcanic rocks belong to the K–Na-high-alumina andesite–andesibasalt–basalt volcanic series. Results for U–Pb analysis of magmatic zircon (SHRIMP II, 8 spots) from a metaandesibasalt sample of the stratotype section on Ungo River yielded and age of 852 ± 9 Ma. Isotope systems for Sm–Nd yield a positive εNd(852) = +9.29, which indicates a juvenile magmatic source, close to depleted mantle (DM), with a Neoproterozoic protolith TNd(DM) model age. The content of the less mobile HFSE and REE (ppm) is consistently low for Nb (8–15), Ti (7074–12,410), Ta (0.32–0.93), Eu (1.80–2.29), Се (50–79), Y (21–25), Yb (2.1–2.8), Rb (10–24) and elevated for Sr (1000–1500), Zr (170–270), La (25–41), and Ba (600–800). All studied parameters place the metavolcanic rocks close to the contemporary Kurile–Kamchatka type of developed island arcs. Paleomagnetic analysis of the section of metavolcanic rocks shows a complete remagnetization ca. 120 Ma. This is synchronous with manifestations of intraplate basaltoid magmatism in the studied region, the most typical example of which is the Lower Cretaceous Khilok Formation.