A Study of Svecofennian Supracrustal Rocks in Central Sweden: Lithological Association, Stratigraphy, and Petrology in the Northwestern Part of the Mälaren—Hjälmaren Basin

Abstract

Consideration is given to supracrustal Svecofennian rocks in the Orebro area and their migmatized continuation eastward. It is demonstrated that the strict subdivision of the Early Svecofennian Leptite Formation into a lower group of volcanics and an upper group of sediments docs not apply in the northwestern part of the Malaren—Hjälmaren basin. The lithological association implies intimate interbedding of units which have previously been considered typical of the two different subdivisions of the Leptite Formation. The cumulative strati-graphical thickness is between three and four kilometers, the rocks are leptites, metaargillites, metaarenites, rudites, and carbonate rock. The different units are arranged into a local stratigraphical succession. Petrographical data are given for the main supracrustal rock varieties and the origin of leptites is discussed.