Abstract
Geological investigations of a part of the crystalline basement in the Baltic Sea have been performed on a drill core collected from the depth of 1092–1093 m beneath the Phanerozoic sedimentary cover offshore the Latvian/Lithuanian border. The sample was analyzed for geochemistry and dated with the SIMS U–Pb zircon method. Inherited zircon cores from this migmatized granodioritic orthogneiss have an age of 1854 ± 15 Ma. Its chemical composition and age are correlated with the oldest generation of granitoids of the Transscandinavian Igneous Belt (TIB), which occur along the southwestern margin of the Svecofennian Domain in the Fennoscandian Shield and beneath the Phanerozoic sedimentary cover on southern Gotland and in northwestern Lithuania. It is suggested that the southwestern border of the Svecofennian Domain is located at a short distance to the SW of the investigated drill site. The majority of the zircon population shows that migmatization occurred at 1812 ± 5 Ma, with possible evidence of disturbance during the Sveconorwegian orogeny.
Highlights
The Precambrian basement in the Baltic Sea region is covered by km-thick successions of Phanerozoic sedimentary rocks, Quaternary sediments and overlying sea water
The plagioclase grains are sometimes replaced by clinozoisite, sericite and epidote
E6-1 migmatite was compared with the I-type Transscandinavian Igneous Belt (TIB) 0 Askersund granites and granodiorites of the Kuršiai batholith and the S-type late Svecofennian granites (Nuuksio granites) from the LSGM zone in southern Finland
Summary
The Precambrian basement in the Baltic Sea region is covered by km-thick successions of Phanerozoic sedimentary rocks, Quaternary sediments and overlying sea water. The relations between individual crustal segments in this region and the well-exposed adjacent Fennoscandian Shield have historically been restricted to geophysical (gravity, magnetic and seismic) data, which have recorded a significant decrease in the crustal thickness towards the south in the central parts of the Baltic Sea (BABEL Working Group 1993; Lund et al 2001). The southwestern border of the Svecofennian Domain is further traced in the eastern parts of the Baltic Sea. Using petrographic, geochemical and geochronological evidence from migmatite drilled from beneath the east-central Baltic Sea, correlations are made with known magmatic and metamorphic events recorded in southeastern Sweden Geochemical and geochronological evidence from migmatite drilled from beneath the east-central Baltic Sea, correlations are made with known magmatic and metamorphic events recorded in southeastern Sweden.
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