The origin of the early Proterozoic supracrustal rocks in the Garpenberg district, south central Sweden

Abstract

The early Proterozoic supracrustal sequence in the Garpenberg district, south central Sweden, consists mainly of quartz-feldspar gneissses (‘leptites’) and subordinate amphibolites, quartz gneisses, mica schists, skarns and marbles. Stratabound iron and sulfide deposits are intercalated within this sequence. Most of the quartz-feldspar gneisses and amphibolites are interpreted as acid and basic metavolcanic rocks. The quartz gneisses and mica schists represent the metamorphic equivalents of originally altered felsic volcanic and sedimentary rocks. The geologic development of the Garpenberg district was dominated by extensive acid volcanism of calc-alkaline affinity, which was interrupted by periods of intense hydrothermal activity, ore deposition and sedimentation. Most of the volcanic activity occurred was submarine in a shallow-water environment. Subsequently, the supra crustal sequence was affected by the Svecokarelian orogeny (1800–1750 Ma) and the rocks were metamorphosed in the amphibolite facies, folded and intruded by synorogenic granitoids.

Key Words:

• Leptite formation
• metavolcanics
• Garpenberg
• south central Sweden
• N6018 N 6019 E1613 E1610