Age and provenance of early Precambrian metasedimentary rocks in the Lapland±Kola Belt, Russia: evidence from Pb and Nd isotopic data D. Bridgwater, 1  D. J. Scott, 2 * V. V. Balagansky, 3 M. J. Timmerman, 4 M. Marker, 5 S. A. Bushmin, 6 N. L. Alexeyev 6 and J. S. Daly 4 1 Geological Museum, O È ster Voldgade 5±7, DK-1350 Copenhagen K, Denmark; 2 GEOTOP, Universite  du QueÂbec Montre Âal, Canada; 3 Geological Institute, Kola Science Centre, Russian Academy of Sciences, Fersman St. 14, Apatity, 184200 Russia; 4 Department of Geology, University College Dublin, Bel®eld, Dublin 4, Ireland; 5 Geological Survey of Norway, Leiv Eriksson vei 39, P.O.Box 3006, N-7002 Trondheim, Norway; 6 Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Makarov Emb. 2, St Petersburg, 199034 Russia Introduction An improved understanding of the evolution of complex Palaeoprotero- zoic collisional orogens requires an understanding of the timing and tec- tonic setting of primary deposition of their constituent metasedimentary rocks. The tectonic forces that shaped these ancient mountain belts have commonly obscured the primary sedi- mentary textures and original spatial relationships of the rocks, making evaluation of these features dicult or impossible. In order to overcome these diculties, U±Pb age informa- tion recorded in detrital zircons in such metasedimentary rocks can yield considerable information about both the source of the zircons and timing of deposition. By combining this infor- mation with whole-rock Nd-isotopic composition, additional information can be derived regarding the nature of the source of the detritus (Stevenson and Patchett, 1990). The present contribution reports 207 Pb/ 206 Pb determinations on single zircon grains and whole-rock Sm±Nd isotopic data in an attempt to evaluate the age and origin of metasedimentary units from the Lapland±Kola belt, northwestern Russia. The current work is part of ongoing isotopic studies of the Palaeoproterozoic oro- gens that ring the northern margin the Archaean North Atlantic ± Karelian cratons (Torngat Orogen in Labra- dor, the Nagssugtoqidian Orogen in Greenland, the Laxfordian in Scot- land and the Lapland±Kola belt of the northern Baltic Shield), and that are interpreted as fragments of a once continuous orogenic system com- parable in dimensions to modern collisional orogens such as the Alpine±Himalayan chain. Geological framework Umba granulite terrane The paragneisses of the Umba granu- lite terrane (UGT) crop out in a thrust-bound unit interpreted as the southeastern extension of the Lapland granulite terrane (LGT) along the northern White Sea coast (Fig. 1). The western part of this high-grade terrane consists of semipelitic to psammitic paragneisses, while the eastern part consists of a little- deformed enderbite±quartz monzo- nite±granite suite that intrudes the paragneisses and locally develops rapakivi granite textures. The LGT paragneisses comprise quartzofelds- pathic and aluminous gneisses; their sedimentary origin has been suggested by rare relict sedimentary textures (Merilinen, 1976), bulk composition (Merilinen, 1976; Kozlov et al., 1990), rare earth element patterns, as well as oxygen (Bibikova et al., 1993) and carbon (Korja et al., 1996) isotopic compositions. The Umba paragneisses and associated intrusions are strongly reminiscent of the metasedimentary rocks of the LGT. While the sedimen- tary origin of the Umba paragneisses has not been demonstrated to the same degree as those of the LGT, they do show the alternation of alu- minous and siliceous layers character- istic of the LGT paragneisses; this, together with geochemical data (Koz- lov et al., 1990), imply a sedimentary protolith. The disposition of these rocks has been interpreted to be the ABSTRACT 207 Pb/ 206 Pb ages are presented for detrital zircons (Laser Ablation Microprobe ICP-MS) and whole-rock Nd isotopic determinations (TIMS) from samples of Neoarchean and Palaeo- proterozoic metasedimentary rocks from the Umba granulite terrane and the Keivy domain of the Central Kola composite terrane, Kola Peninsula, north-western Russia. Three are sam- ples 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. Terra Nova, 13, 32±37, 2001 *Correspondence and present address: Canada-Nunavut Geoscience Oce, PO Box 2319, Iqaluit, Nunavut, X0A 0H0 Canada. Tel.: +1/867 9793539; fax: +1/ 867 9790708; e-mail: djscott@NRCan. gc.ca  Deceased 27 June 1998. 32 Ó 2001 Blackwell Science Ltd