Abstract
The Estonian Precambrian crystalline basement that consists of Paleo- to Meso-Proterozoic metamorphic and igneous rocks is covered by a 100-780 m thick deposit of Paleozoic sedimentary rocks. Thus, the basement is unavailable for direct surficial observations and our present knowledge is based on information from cores of deep drillings and interpretation of potential - gravity and magnetic - fields. Accordingly, the basement of Estonia is subdivided into two major geological units – North Estonian amphibolite and South Estonian granulite complexes. Further division includes six structural - petrological zones such as Tallinn, Alutaguse, Johvi, West-Estonian, Tapa and South-Estonian zones. The present article provides an updated overview of the Estonian Precambrian basement, its rock types, geophysical fields, geochronology, metamorphism and metallogenesis.
Highlights
The Precambrian crystalline basement of Estonia is covered by a 100–780 m thick deposit of Paleozoic sedimentary rocks
Since there are no outcrops of the crystalline basement rocks, drill core material, geophysical and geochemical methods were used for geological reconstructions
In the 1990th, a number of articles dealing with general geology [Soesoo, 1991; Petersell and Levchenkov, 1994], geochronology [Petersell, 1991; Puura and Huhma, 1993], metamorphism [Höltta and Klein, 1991], post-orogenic rocks [Soesoo and Niin, 1992; Soesoo, 1993; Kirs and Petersell, 1994; Rämö et al, 1996; Puura and Floden, 1996, 1999, 2000], and partial melting and migmatization [Soesoo et al, 2004a, b, 2006] were published
Summary
The Precambrian crystalline basement of Estonia is covered by a 100–780 m thick deposit of Paleozoic sedimentary rocks. 30 km wide, NW-trending PPDZ separates the structural domains in northern and north-eastern Estonia from those in the west and the south of Estonia (Fig. 1) It comprises two principal sub-parallel shear zones dipping between 65° and 75° SSW [All et al, 2004], features strong deformation, and contain slivers of both granulite- and amphibolite-facies rocks. On the basis of previous geophysical and petrological studies, six geological zones are distinguished within these two units: Tallinn, Tapa, Alutaguse and Jõhvi zones (located north of the PPDZ), and the West-Estonian and South-Estonian zones (located south of the PPDZ; Fig. 1) [Puura et al, 1983; Koistinen, 1994; Soesoo et al, 2004а] These zones mostly differ in rock assemblages (with metasedimentary or metavolcanic/-igneous origin), metamorphic grade and petrophysical properties of rocks, reflected in their potential fields. In the South-Estonian and Jõhvi Zones, the granulite facies mineral assemblages are still preserved, while in the Tapa and West-Estonian Zones the rocks were mostly retrogressed under amphibolite facies conditions [Puura et al, 1983, 2004; Fig. 1]
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