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Age and geochemistry of granitoids in the Precambrian basement of Öland, SE Sweden – implications for the extension of the Transscandinavian Igneous Belt in the Baltic Sea region

List of Authors: Salin E., Sundblad K., O´Brien H., Lahaye Y., Woodard J.
Publication year: 2018
Title of series: Abstract volume
Number of pages: 2


The Precambrian crust in the Baltic
Sea region is mostly covered by Phanerozoic sedimentary rocks but can be
studied in drill cores. Two granitoids from the crystalline basement below
Öland were collected from the archives of the Geological Survey of Sweden and
analyzed for geochemistry and dated with the U-Pb method on zircons. The Böda
Hamn granitoid (northern Öland) has a monzodioritic composition and an age of
1799.8±3 Ma while the Valsnäs granitoid (central Öland) has a quartz monzonitic
composition and an age of 1784.9±5.7 Ma. These geochemical-isotopic
characteristics are compatible with those of generation 1 of the
Transscandinavian Igneous Belt (TIB) in the Fennoscandian Shield, ≥30 km west
of Öland.

A more detailed review of the TIB-1
generation shows that two
sub-generations (1a and 1b) can
be distinguished on each respective side of the Oskarshamn-Jönköping Belt
(OJB). Sub-generation 1a (north of OJB) has an age span of 1794-1808 Ma while sub-generation
1b (south of OJB) has an age span of 1769-1793 Ma. According to this subdivision, the Böda Hamn monzodiorite belongs to sub-generation 1a, which also can be followed to southernmost Gotland
(Sundblad et al. 2003) and the Valsnäs quartz monzonite belongs to sub-generation 1b, which can be followed to
the Latvian/Lithuanian border, where a marginally younger granitoid was
reported from off shore drill core E-7 (Salin et al. 2016). Taken
together, these data suggest that the Transscandinavian Igneous Belt can
be traced across the Baltic Sea from the exposed parts within the Fennoscandian
Shield to the Latvian/Lithuanian border.

Salin, E.,
Sundblad, K., Woodard, J. and Lahaye, Y. 2016
: The Precambrian crust in the
Baltic Sea region. Bulletin of the Geological Society of Finland, 32nd Nordic
Geological Winter Meeting, Helsinki. Abstract volume, p. 162.

Sundblad, K., Claesson, S.
& Gyllencreutz, R. 2003
: The Precambrian of
Gotland – a key to the understanding of the geologic environment for granitoids
in the Baltic Sea region. Granitic systems – State of the art and future
avenues. An international symposium in honor of professor Ilmari Haapala.
Abstract volume, Helsinki, 102­–106.

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