Lithostratigraphic and structural data from Hardangervidda, southern Norway supporting extended interaction between Avalonia and Baltica

Abstract

Abstract Lithostratigraphic and structural data from the Early Paleozoic Hardangervidda Group in southern Norway indicate that SW Baltica was affected several hundred kilometres NE of the inferred collision zone with Avalonia (Thor Suture). The first sign of plate interaction was the deposition of a 50–60 m-thick quartz arenite (Holberg Formation) of Floian/Dapingian age in an otherwise mud- and carbonate-dominated shelf. An overlying 5–6 m-thick marble unit of Dapingian–Darriwilian age (‘Orthoceratite Limestone’) marks a change into greenish-grey, calcareous phyllite, locally with beds of impure marble and poorly sorted metasandstone (Solnut Formation). A series of décollement folds (D2 structures) with axes orientated NW–SE (cross-folds) which superimposed a thin-skinned fold thrust with a NE–SW trend (D1 structures) are interpreted as having developed during the progressive underthrusting of Baltica underneath Avalonia. Support for this model is seen in detrital zircon populations: with the Holberg and underlying formations having a Baltican signature, in contrast to the overlying Solnut Formation with a peri-Gondwana signature, including a distinct Late Neoproterozoic zircon population. It is further speculated that the c. 471–458 Ma Garborg eclogite and surrounding paragneisses in the Stavanger area are related to the suture zone between Baltica and Avalonia rather than being related to the Iapetus Ocean and Laurentia, as generally thought.