The Rödberget ultramafic-mafic Complex in the Handol area in Jämtland, central Swedish Caledonides, consists of various ultramafic rocks, metacumulate rocks, metagabbros, mafic dykes, plagiogranites and a melange. It is interpreted as a fragmented ophiolite. The overlying Bunnran Fonnation is a metasedimentary-meta-igneous unit usually consisting of finely Jaminated cal-careous psammitic and pelitic rocks with probable tuffitic components, intruded by and interlayered with mafic intrusive and extrusive rocks. Combined geological and geochemical evidence indicates a close spatia and tempora! genetic relationship between the Rödberget ultramafic-mafic Complex and the Bunnran Fonnation. It is suggested that they originated in a basin where oceanic crust was fonned during deposition of material derived from continental and volcanic source regions, an environment comparable to the Andaman Sea in the Indian Ocean. As a general model, such basins with their high frequency of fracture zones/transform faults could be the original settings of the solitary and detrital ultramafic rocks also in correlateable units in the central Scandinavian Caledonides.
Stefan Bergman, Department of Mineralogy and Petrology, Uppsala University, PO Box 555, S-751 22 Uppsala, Sweden.