The post-Caledonian thermo-tectonic evolution of Fennoscandia

Abstract

<p>Here we present apatite fission-track analysis (AFTA) data and thermal history interpretations in 332 samples from outcrops and boreholes at elevations between +2 and -6 km relative to sea level across Fennoscandia. The data define episodes of burial and exhumation which involved deposition and removal of kilometre-scale thicknesses of sediment as well as denudation of the underlying basement rocks that resulted in the formation of peneplains of different age and characteristics.  Many of these episodes correlate with similar episodes over a much wider region, and this argues for regional tectonic control, related to plate-tectonic processes.</p><p>Post-Caledonian development of Fennoscandia involved five dominant episodes of exhumation, beginning in late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene times.  These episodes affected not only the present-day Atlantic margin but also the continental interior which is considered by many to represent a stable cratonic region because of the low relief and limited remnants of sedimentary cover. Pronounced offsets in the magnitude of the pre-Cenozoic episodes over short distances occur close to the Atlantic margin, and around the Oslo Rift, attesting to the tectonic origin of these episodes.  In contrast, the Middle Triassic and mid-Cretaceous episodes display little variation over vast regions in the interior. Yet even here, our results show that the vertical movements involved deposition and removal of substantial sedimentary covers. </p><p>The late Carboniferous, Middle Triassic and Middle Jurassic episodes can be linked with the break-up of Pangaea.  The mid-Cretaceous episode correlates with a global plate reorganization.  The early Miocene episode appears to be earlier than analogous episodes in Greenland, and it is not yet clear how these episodes fit into the pattern of plate-tectonic forces.  The youngest tectono-thermal episode to affect Fennoscandia began in the early Pliocene and is only revealed by AFTA data from a few deep boreholes. But this episode had a major impact in shaping the present-day topography on both sides of the Atlantic and may have been driven by dynamic support from the Iceland Plume.</p><p>A key aspect of the paleo-thermal episodes identified in this study is that they involve both deposition and removal of kilometre-scale thicknesses of sediment (i.e. subsidence and uplift), rather than progressive emergence and monotonic cooling of the continents as assumed in many studies.  Dynamic topography and far-field transmission of stress thus appear to be likely candidates for driving the ups and downs of both marginal and interior regions. </p>