![Sample our Earth Sciences journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5930/TOC-Subject-Sample-2021-Earth-Sciences.jpg"})
Abstract
K-Ar analyses of 20 hornblendes from skarns and associated metabasites in the Hjulsjö area of the Bergslagen ore province, central Sweden, define an age of 1.83 ± 0.05 Ga. This age is interpreted in terms of the geological relationships as signalling a period of skarn-formation and metamorphism along with episodes of shearing and basic dike intrusion. Following the hypothesis that the skarn ores were formed by sea-floor hydrothermal metamorphism, this age should also be attributed to the deposition of the enclosing volcano-sedimentary leptite-hälleflinta sequence and the injection and extrusion of basic magma. Analyses of 13 biotites from the skarns and enclosing metavolcanic leptites produce K-Ar and Rb-Sr ages of 1.69 ± 0.05 Ga and 1.65 ± 0.04 Ga, respectively; these are related to an episode of mild crustal heating associated with nearby post-orogenic granite intrusions dated at 1.70 Ga.