Abstract
New data on the Fennoscandian Shield and the Baltic area suggest a need for reinterpretation of the stratigraphy of Estonian Precambrian rock complexes. The rocks of the Tallinn Zone formed in the framework of the Fennian orogeny at the margin of the Bergslagen microcontinent 1.90-1.88 Ga ago. The precise age of the Alutaguse Zone is not known. It may have formed either during the 1.93-1.91 Ga Lapland-Savo orogeny or as a rifted eastern part of the Tallinn Zone in the Fennian orogeny. The granulites of western and southern Estonia belong to the volcanic arcs inside the 1.84-1.80 Ga Svecobaltic orogenic belt and show peak metamorphic conditions of 1.78 Ga. Small shoshonitic plutons formed 1.83-1.63 Ga, the small granitic plutons of the Wiborg Rapakivi Subprovince 1.67-1.62 Ga, and the Riga pluton 1.59-1.54 Ga ago.
Highlights
New achievements in the Precambrian geology in general and especially in the geology of the Fennoscandian– Baltic region enable development of a new insight into the history of the formation of the basement rocks
Only a few new results have been obtained on the Estonian–Latvian territory, whereas a considerable amount of new geological-geochemical and geophysical material on the Precambrian basement structure and rocks in the surrounding areas in Fennoscandia and in the southern Baltic Sea region has been accumulated through various research programmes such as, for example, Europrobe-Eurobridge (Bogdanova et al 2006, 2008; Korja et al 2006; Lahtinen et al 2008)
According to the up-to-date stratigraphic chart of the Precambrian issued by IUGS 2004 (Gradstein et al 2004), the folded basement rocks of Estonia formed during the Orosirian Period of the Palaeoproterozoic
Summary
New achievements in the Precambrian geology in general and especially in the geology of the Fennoscandian– Baltic region enable development of a new insight into the history of the formation of the basement rocks. Inside the Svecofennian Domain it is expressed as a series of orogenic belts retreating from north to south (Bogdanova et al 2006; Korja et al 2006) According to these views, the structurally different blocks of the Estonian orogenic basement are located in the internal part of the mosaic of 1.93–1.80 Ga amalgamated Palaeoproterozoic orogenic belts and microcontinents (Fig. 1). To the southwest of the Lapland–Savo Orogenic Belt and the Keitele microcontinent, 1.90–1.88 Ga dated latitudinally extending Fennian orogenic suites form the Tampere, Häme, and Uusimaa volcanic-sedimentary belts of island arc origin in southern Finland (Korja et al.2006) As it was revealed by the interpretation of geophysical anomalies, and lithological and isotope age studies, the Tallinn Zone of northern Estonia belongs to this assemblage of accreted island arc belts (Puura et al 1983, 2004; Koistinen 1996).
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