Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces

Abstract

The origin of the Norwegian mountains (the Scandes) is a key controversy in modern geoscience. Are they remnants from the Caledonian Orogeny, modified shoulders of late Mesozoic rifts, or are they evidence of Neogene uplifts? Our synthesis of geological data, landscape analysis and new thermochronological data from Norway south of c. 60°N, combined with previously published data from southern Sweden, reveals a four-stage history: (1) Middle Triassic and Middle Jurassic exhumation produced a weathered basement surface with a hilly relief; (2) after late Mesozoic rifting, Upper Jurassic–Oligocene sediments accumulated across most of the area; (3) early Miocene uplift and erosion to the base level of the adjacent ocean led to formation of a peneplain that extended across sedimentary basins and Caledonian rocks; the subhorizontal Hardangervidda plateau represents this peneplain; (4) early Pliocene uplift raised Hardangervidda to its present elevation of c. 1200 m above sea-level and led to re-exposure of the tilted, Mesozoic surface at lower elevations. The Southern Scandes are thus, like other elevated passive continental margins around the world, the product of post-breakup uplift. Identification of the mechanisms driving these uplifts awaits geodynamic modelling constrained by observations such as those presented in this study. Supplementary material: Table S1: AFTA data, sample details and associated thermal history interpretations; southernmost Norway. S2: analytical details and thermal history reconstructions for all apatite fission-track analysis (AFTA) samples as well as analytical data for one vitrinite reflectance sample, together with background information on the AFTA technique, are available at https://doi.org/10.6084/m9.figshare.c.4085996