U-Pb dating and provenance of detrital zircons from the Upper Precambrian deposits of North Timan

Abstract

Timan comprises the southwest edge of the Pechora Plate. The plate basement is composed of variably metamorphosed sedimentary, mainly terrigenous, and igneous rocks of the Late Precambrian age that are generally overlain by Ordovician-Cenozoic platform cover. Poor exposition and discontinuous dis� tribution of the Upper Precambrian outcrops of dominantly fossilfree sedimentary rocks cause considerable disagreements in stratigraphic correlation. This applies equally to North Timan, which represents an uplifted block of basement, in which sedimentary-metamorphic rocks form the Barminskaya Group (~5000 m thick), previously dated as Early Riphean to Vendian. Earlier Rb-Sr and Sm-Nd isotope dating of schist and crosscutting gabbro-dolerite and dolerite establish ed the timing of greenschist facies metamorphism at 700 Ma. Thus, Late Riphean age of the Barminskaya Group has been suggested. Results of local U-Pb dating of detrital zircon from silty sandstones of the Malochernoretskaya Formation, which constitutes the middle part of the outcropping section of the Barminskaya Group, confirm this conclusion. Age data for 95 zircon grains cover the range of 1035-2883 Ma with age peaks at 1150, 1350, 1550, 1780, and 1885 Ma. The mini� mum age of zircons, considered as the lower age constraint on sediment deposition, provides grounds to date the Barminskaya Group as Late Riphean and indicates eroded rock complexes of the Fennoscandian Shield as the possible provenance areas.