Two greenstone formations in the Jofjllet area, central Swedish Caledonides, have been analysed for major and trace elements in order to establish their petrology and tectonic environment of origin. The formations - the Ruffe Greenstone and the Brackfjllet Greenstone - are situated in the uppermost part of the Seve-Kli Nappe Complex. The enrichment in volatiles, depletion in SiO2, redistribution of CaO and alkali contents are certainly caused by post-eruptive alteration processes. The Ruffe Greenstone is a tholeiite of a transition type between ocean-floor and within-plate basalt, while the Brackfjllet Greenstone is an alkaline basalt showing a clear within-plate basalt affinity. The basalts are possibly formed during the later stages of rifting and ocean basin opening in a near-continental environment. The basalts can probably be correlated with the Stren greenstone in Norway.
Godkänd; 1981; 20100210 (andbra)