Mesozoic-Cenozoic tectonic and magmatic evolution of the northeast Russian margin

This thesis addresses three fundamental questions that provide new insight into the relative roles of subduction-related magmatism, lateral terrane accretion, and crustal extension in the growth and stabilization of continental crust along the active margin of northeastern Russia: (1) What is the timing and nature of magmatism in the Okhotsk-Chukotka Volcanic Belt (OCVB)? (2) What are protoliths of the high-grade metamorphic rock and when and why did the metamorphism of the Sredinniy Range, Kamchatka, occur? (3) What is timing and mode of formation of the Sea of Okhotsk?; The Taigonos Peninsula exposes a calc-alkaline batholith that cross-cuts the accretionary wedge of the earlier Uda-Murgal arc, and records the inception of the OCVB. SHRIMP U/Pb zircon data show that granitoid emplacement in the “interior zone” of the belt occurred from 106.5 Ma to 97.0 Ma. The Arman and Maltan-Ola volcanic fields, located in the “exterior zone” of the OCVB, consist of Cretaceous volcanic rocks and intercalated, fossiliferous sediments rich in flora used to infer mid-Albian age for inception of volcanism. Here, new 40Ar/39Ar geochronologic data indicate magmatism occurred from ∼86 Ma to 74 Ma. These data revise the chronostratigraphy of the floral assemblages by 15 m.y.; SHRIMP U/Pb zircon data from the Sredinniy Range, Kamchatka, permit the following conclusions: (1) Detrital zircons range in age from ∼2050 to 58 Ma, indicating a Paleocene protolith age for the high-grade metasedimentary rocks; (2) Metamorphism occurred between ∼58 Ma and 48 Ma (Rb-Sr bioite and K-Ar biotite); (3) Achaivayam-Valaginskaya arc-continent collision is coincident with metamorphism; and (4) Similarity of zircon grain-ages from unmetamorphosed Paleocene marginal strata and metasedimentary rocks suggests that the Sredinniy Range protolith comprises strata native to the northeast Russian margin that were metamorphosed during Eocene arc-continent collision.; A new back-arc extension model is presented for the origin of the Sea of Okhotsk. Satellite gravity data, reflection seismic profiles, S-wave mantle velocity anomalies, and thermochronometry of the Magadan Batholith all indicate that Tertiary extensional faulting dominates the tectonic history and determines the character of the basement of the Sea of Okhotsk. The lack of Late Cretaceous contractile deformation within the OCVB supports this model.