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The age and origin of high-grade metamorphic rocks of the Sredinnyi Range, Kamchatka have been the subject of a long and controversial debate. Based on geochronologic data and its association with a collage of accreted oceanic terranes, leading interpretations argue that the Sredinnyi Range metamorphic rocks represent an accreted Precambrian or Mesozoic microcontinent. In this contribution, we present new data that indicate that these metamorphic rocks were formed from the Cretaceous-Paleocene sedimentary margin of northeast Russia when it was overridden during Eocene obduction of the Olyutorsky arc, a far-travelled oceanic island arc. Our data include new mapping and structural observations along the northern and eastern flanks of the Sredinnyi Range, and SHRIMP zircon and monazite U-Th-Pb age data from 15 key samples. These new isotopic data demonstrate that paragneissic units were formed from sediments with depositional ages locally no older than Late Cretaceous to Paleocene. Furthermore, the statistical similarity of zircon U-Pb grain-ages from the Kamchatka Schist with very low-grade turbidite sandstones of the Ukelayat and Khozgon Groups indicate that metasediments of the Sredinnyi Range are upgraded stratigraphic equivalents of northeast Russian marginal strata. SHRIMP U-Pb ages of zircon overgrowths and metamorphic monazite extracted from migmatite and gneiss indicate that peak metamorphism occurred at 52 Ma, which is synchronous with the onset of the Olyutorsky arc-continent collision. Heating and cooling occurred rapidly, at rates approaching 80°C/m.y. Rapid heating is attributed to syn-collisional, subductionrelated magmatism. Thermochronology and structural observations indicate that exhumation was due to a combination of ductile and brittle thinning of the crust. We speculate that this thinning was caused by diapiric ascent of a low-density low-viscosity continental material beneath a dense structural lid of the obducted island arc.

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Morphological analysis and U/Pb LA ICP MS dating were carried out for detrital zircon (400 age determinations) from four core samples of Triassic rocks recovered by Well Severnaya (Graham Bell Island, Franz Josef Land Archipelago). It is shown that source areas were mainly composed of peraluminous gran ites. U/Pb LA ICP MS zircon data were used to decipher the provenance evolution in the northern Barents Sea region. The main source of clastic material in the North Barents sedimentary basin in the Middle-Late Triassic was the Uralian fold belt, with lesser contribution from the East European Craton (Baltica), Timanides, Taimyr, and rocks related to the Siberian plume. The clastic material was mainly transported from the south and southeast. From the beginning of the Middle to the terminal Late Triassic, influence of the Neoproterozoic sources systematically decreased, whereas contribution of Caledonian sources increased.