Amphibolites of the Metamorphic Basement of Wrangel Island: Age, Nature of the Protolith, and Conditions of Metamorphism

Resumo

The paper presents newly acquired data on the petrography, geochemistry, and geochronology of metamorphic rocks sampled at the Neoproterozoic basement of Wrangel Island. Geochemical data on the mafic rocks metamorphosed at greenschist to amphibolite facies parameters (350–600°C) indicate their oceanic affinity. As follows from the geochemical data, the protolith of these rocks was made up of products of the evolution of magmatic melts parental for MORB. The U–Pb zircon age (SHRIMP II and LA-ICP MS) of the protoliths is 617 ± 13 and 698 ± 12 Ma. The rocks were affected by two episodes of metamorphism: one in the Neoproterozoic–Early Paleozoic (to the amphibolite and greenschist facies) and the other in the Middle Cretaceous (greenschist facies), with the latter episode related to the Chukchi deformation phase, which was accompanied by the development of the folded nappe structure and consequent extension. Comparison of the studied rocks with samples dredged at the Chukchi Borderland reveals certain petrographic and chemical similarities between these rock assemblages.