AGE AND PROVENANCE OF EARLY PRECAMBRIAN METASEDIMENTARY ROCKS IN THE LAPLAND-KOLA BELT, RUSSIA: EVIDENCE FROM PB AND ND ISOTOPIC DATA

Abstract

207Pb/206Pb ages are presented for detrital zircons (Laser Ablation Microprobe ICP-MS) and whole-rock Nd isotopic determinations (TIMS) from samples of Neoarchean and Palaeoproterozoic metasedimentary rocks from the Umba granulite terrane and the Keivy domain of the Central Kola composite terrane, Kola Peninsula, north-western Russia. Three are samples of rocks from the Umba granulite terrane that were deposited ≈ 2.20–1.90 Ga; they contain Archaean detritus, much of it older than 3.0 Gyr, as well as abundant 2.20–1.95-Gyr-old material. Deposition may have occurred on the margin of an Archaean craton with an exposed Palaeoproterozoic magmatic arc source, possibly during orogenesis. Two samples from the Keivy domain have remarkably similar, dominantly Archaean detrital zircon age spectra. One was deposited pre-2.4 Ga, whereas the other was probably deposited post-2.01 Ga. Both had similar sources, compatible with the proximal country rocks, and possible shallow-water (?) cratonic margin depositional settings.