Skip Navigation LinksEXCURSION NO 53

Milestones of the Early Precambrian history of northern Fennoscandia

Leaders: Dr. Victor Balagansky (chief organizer: balagan@geoksc.apatity.ru), Prof. Felix Mitrofanov, Dr. Tatiana Kaulina, Geological Institute of the Kola Science Centre, Russian Academy of Sciences, Apatity (Russia). Co-leaders from Institute of Geology of the Karelian Research Centre, Russian Academy of Sciences (Petrozavodsk) and Geological Institute of the Russian Academy of Sciences (Moscow) are presently contemplated to involve.

Purpose: The Early Precambrian rocks in the Kola region are representative for the Earth's crust of northern Fennoscandia and display records of more than a 1.2 Ga long evolutionary history from the beginning of the Mesoarchaean to the end of the Palaeoproterozoic. The overwhelming majority of key Early Precambrian complexes are easy to see during a single excursion. Of first priority is an ophiolite-like complex (2.88-2.86 Ga) and eclogites (2.88-2.72 Ga) recently discovered in the Belomorian Province. Participants will examine evidence suggesting the plate tectonics to operate in the Archaean. Trips to other objects provide an opportunity to follow the Archaean history in many details. This history starts with 2.90-2.85 Ga paragneisses developed under amphibolite-facies conditions in the Belomorian Province and granulite-facies conditions in the Kola Province. The following evolution is recorded in three generations of greenstone belts. The oldest generation is represented by the Kolmozero-Voron'ya belt in the Kola Province displaying spectacular komatiitic rocks, including varieties with superb lava breccias and spinifex texture, in the Ura Guba area and dated at 2.83 Ga, as well as metasediments, metaconglomerates and BIF. The Pecha Guba fragment of the 2.7-2.8 Ga Olenegorsk greenstone belt shows BIF and provides an opportunity to observe in which framework they occur and how they have been deformed. The youngest generation is represented by the Voche-Lambina greenstone belt volcanism and sedimentation in which has occurred between 2.76 Ga and 2.66 Ga. A unique feature of the Voche-Lambina belt is conglomerates spread throughout the structural section, with TTG rocks from clasts and a supposed depositional basement having 2.81 Ga magmatic zircons. TTG granitoids so characteristic of the Archaean are represented by distinctive varieties exposed everywhere and dated at 2.8-2.6 Ga. The Archaean-Proterozoic transition is marked by coronitic mafic intrusions (drusites) and dykes of potassium granites as well as by unconformity between an Archaean depositional basement and the basal metavolcanics of the Palaeoproterozoic Imandra-Varzuga belt. Participants will revise field observations suggesting the emplacement of the plutonic rocks and their following deformational and metamorphic reworking in extensional setting (incipient break-up of the Kenorland supercontinent). The Kola Region has been long regarded as an Archaean craton, but the recent investigations have shown that it contains an important component of juvenile Palaeoproterozoic crust. In the Umba area participants will become familiar with metasediments and 1.91-1.94 Ga granitoids that contain this juvenile component (tDMNd from 1.9 to 2.4 Ga). Formation of these rocks is linked with the opening and closure of a narrow, Red Sea type oceanic basin between c. 2.05 Ga and 1.91 Ga (final break-up of the supercontinent and then amalgamation of its fragments during the Lapland-Kola orogeny). In the core of the Lapland-Kola orogen late collisional leucosome has been dated at 1.90-1.91 Ga whereas in the orogen footwall (Belomorian Province) at 1.89 to 1.84 Ga. In the Umba area the orogenic core was uplifted immediately after collision and cooled (cooling rate 5-7 (C Ma-1) more rapidly than its footwall (cooling rate 2-4 (C Ma-1).

Excursion no. 53
START/END: Murmansk/
Murmansk, Russia
DURATION: 9 days
TIME: 15 - 24 August