Composition, age and tectonic meaning of granite boulders in the devonian conglomerates of the north-west part of Spitzbergen

Abstract

Identifying complexes of the early Proterozoic age in the composition of crystal foundation is a key task in studying pre-Cambrian formations of the whole of Spitzbergen and its northwestern part in particular. The territory of that region is formed by three deeply metamorphosed complexes that underwent the processes of migmatization and granitization in mid-Rifey and were broken through by granitoids of mid-Rifey and mid-Paleozoic. In their turn, the outbursts of the foundation are overlayed by terrigene rocks of the Devonian graben of Spitzbergen, conglomerates forming a large share among them. In the course of petrographic and chemical studies of such compositions, as well as isotopic characteristics of zircons from the boulders of basal conglomerates of Red Bay (D1) series, the suite of Wolfberget at Cape Conglomeratodden the presence was identified of reddish (meat-red) granites of isotopic age of 1631±19 Mil years, which is comparable to late Karelian processes manifested actively across the archipelago. It is also proven that transformations of these rocks within the range of 380±42 Mil years are well associated with mid-paleozoic events, considerable restructuring of the foundation associated with them. The age range we defined is another proof of manifestation of early pre-Cambrian (late Karelian) processes in the northwestern Spitzbergen.