Abstract
The Early Proterozoic metavolcanic complex in the Garpenberg enclave of central Sweden displays bimodal basaltic-rhyolitic volcanism reflecting alternating compressional and tensional tectonic regimes. The acid metavolcanics show a continuous calcalkaline differentiation trend geochemically unrelated to the associated interbedded metabasalts. A dacitic horizon indicates mixing of the two end-member magmas during a compressional stage. Bimodal volcanism is characteristic of the Early Proterozoic supracrustals (Leptite formation) throughout the central Swedish province of the Baltic shield. The paucity of ocean floor rocks and high-pressure metamorphism together with the lack of abundant andesites suggest that this province does not represent an island arc. Rather the combination of an ensialic edifice with alternating compressional and tensional tectonic regimes suggests Andinotype, subduction-coupled spreading-subsidence within the margin of a continental plate.
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