On the origin and evolution of the 1.86–1.76 Ga Mid-Baltic Belt in the western East European Craton

• A Mid-Lithuanian Domain (MLD) was distinguished by Bogdanova et al. (2015) as part of the large Mid-BalticBelt (MBB) in the western East European Craton. Zircon U-Pb dating by SIMS, Sr- and Nd-isotope systematics and a detailed geochemical study have allowed to subdivide the MLD into two parts: NW and SE. The NW magmatic rocks have been emplaced at 1.86 to 1.83 Ga from either an enriched mantle source or from a mantle magma with presence of older crustal material. The SE MLD magmatic rocks originated from a slightly depleted mantle source at 1.87 to 1.82 Ga. At 1.79 Ga, they were intruded by gabbronorites which at 1.76 Ga were crosscut by thin veinlets of microgabbronorite. The SE MLD magmatic series with their oceanic island arc affinity correlate well with the contemporaneous Fröderyd metavolcanics of the Vetlanda-Oskarshamn belt in Sweden, while the NW MLD rocks are similar to the TIB-0 Askersund granitoids in the southern Bergslagen area. The younger (1.81–1.79 Ga) intrusives in both areas are time-equivalents of the TIB-1 magmatism on the Swedish side. Thus, the MLD as well as its counterparts on the Swedish side of the Baltic Sea may belong to the same Mid-Baltic Belt, representing an active, south-facing continental margin established at ca. 1.86 Ga. The shape and outline of the belt was affected by the Fennoscandia-Sarmatia collision at ca. 1.82–1.80 Ga, as well as by later magmatism.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

East European Craton

U-Pb geochronology

Sr and Nd isotopes

Geochemistry

Proterozoic reconstructions

Fennoscandia

The changing Earth

Den föränderliga jorden

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