The Ljugaren granite massif, Dalarna, central Sweden

Abstract

Abstract The circular, 13 km wide, c. 1700 Ma old Ljugaren granite massif intrudes and deforms 1890 to 1850 Ma old gneissose rocks and 1790 to 1740 Ma old late-orogenic granite sheets of the Svecofennian Orogenic Province. It is satellitic to the 1840 to 1680 Ma old Transscandinavian Granite-Porphyry Belt, and is partly overlain unconformably by Ordovician-Silurian sediments which are preserved around the Siljan Ring meteorite impact structure. Aeromagnetic and structural geological studies show that regional country-rock structure swings into concordance with the massif's margins 1–3 km from the contact. Gravity measurements indicate that the intrusion is shaped like an asymmetric funnel. Internally, the Ljugaren granite shows a weak, inwardly dipping, planar magmatic fabric concordant to its margins. Evidence to date indicates that the massif was emplaced into ductile crust as a magmatic diapir after the culmination of the Svecofennian orogeny c. 1700 Ma ago.