GEOLOGICAL, GEOCHEMICAL AND GEOCHRONOLOGICAL EVIDENCE FOR A NEW PALAEOPROTEROZOIC TERRANE IN SOUTHEASTERN SWEDEN

The geological and geochronological relationships between a rhyolite, belonging to the Transscandinavian Igneous Belt (TIB), and an intrusiv e suite (the Backaby intrusion), southeast Sweden, have been investiga ted by means of bedrock mapping, geochemistry and radiometric age dete rminations (U-Pb on zircons). Field relations suggest that the rhyolit e rests unconformably on the Backaby intrusion, which previously has b een correlated with similar to 1.9 Ga granitoids within the Svecofenni an Domain. The rhyolite yielded an age of 1800 +/- 8 Ma and a tonalite belonging to the Backaby intrusion basement yielded an age of 1834 +/ - 3 Ma. The age of the rhyolite is slightly older (10-15 Ma) than adja cent granitoids belonging to the Transscandinavian Igneous Belt, and i s considered as the earliest magmatic expression of TIB in the area. T he age and the geochemical trends for the Backaby intrusion is signifi cantly different from that of the surrounding TIB granitoids and indic ate a rock forming event at about 1830-1840 Ma in southeastern Sweden represented by the Oskarshamn-Jonkoping Belt. This event is significan tly younger than the older Svecofennian rocks within the Svecofennian Domain proper, indicating a hitherto unidentified geological terrane i n southeastern Sweden.