Amphibolites of the metamorphic basement of Wrangel island: age, nature of the protolite and conditions of metamorphism

Abstract

New data on petrography, geochemistry and geochronology of metamorphic rocks sampled from Neoproterozoic basement of Wrangel Island are presented. Oceanic affinity for mafic rocks underwent greenschist to amphibolite facies conditions (350600C) has been established by geochemical data. Protolith of this rock belongs to products of the evolution of magmatic melts parental for MORB. Protoliths age is 61713 and 69812 Ma was determined by U-Pb isotope dating of Zircons from these rocks (SHRIMP II and La-ICP MS). There are two main stage of metamorphism could be established: Neoproterozoi Early Paleozoi (amphibolite and greenschist facies conditions) and Middle Cretaceous (greenschist facies condition only), Last stage of metamorphism related to Chukcha deformation events accompanied by formation of folded nappes structure and consequent extension. An comparison of studied rocks with samples dredged at Chukcha Borderland evidenced for certain similarity existing between these rock assemblages judging by their petrography and chemistry.