PALAEOPROTEROZOIC RIFTING AND FORMATION OF SULFIDE DEPOSITS ALONG THESOUTHWESTERN MARGIN OF THE SVECOFENNIAN DOMAIN, SOUTHERN SWEDEN

A mineralized Palaeoproterozoic volcanic sequence has been identified southwest of Vetlanda in southern Sweden. The sequence, which is defin ed as the Froderyd Group, is surrounded by 1.78 Ga granitoids and may be considered as the southernmost segment of Svecofennian crust in Swe den. The Froderyd Group has a bimodal geochemical character and is dom inated by pillow basalts and associated gabbros but rhyolites, thin in tercalations of marble and stratiform sulphide ores do also occur. The carbonate intercalations and the stratiform sulphide ores are interpr eted as submarine exhalites formed syngenetically with the volcanic ac tivity. The mafic rocks have a typical mid-ocean ridge basalt geochemi stry with fiat rare earth elements patterns. The lead isotopic composi tions of the mafic rocks and the associated stratiform sulphide ores s upport such a close affinity to juvenile sources with mantle character . In contrast, the rhyolites display more evolved geochemical signatur es and isotopic patterns and are interpreted to represent remelted pro ducts of slightly older sialic crust. A model for the formation of the Froderyd Group is presented, suggesting rifting along a continental m argin which may have occurred in the final stage of the Svecofennian c rust-forming period. (C) 1997 Elsevier Science B.V.