Episodes of post-Caledonian burial and exhumation in Greenland and Fennoscandia

Abstract

The forces that drive uplift of the continental lithosphere outside collision zones are a topic of considerable dispute. Here we review our studies of the post-Caledonian development of Greenland, Fennoscandia and adjacent regions based on apatite fission-track analysis (AFTA) and stratigraphic landscape analysis (SLA). AFTA defines episodes of cooling (exhumation) while SLA provides a relative denudation chronology. Integrating these results with the geological record can produce a coherent history of both positive and negative vertical crustal movements. Our studies reveal a history involving multiple regional episodes of burial and exhumation, leading to a) formation of peneplains graded to sea level, b) formation of distinct unconformities in sedimentary successions, and c) deposition of thick siliciclastic wedges in basins adjacent to the uplifting landmasses. Exhumation episodes which began in late Carboniferous, Middle Triassic and Middle Jurassic affected the entire study area (with some time variations). These episodes correlate with rifting episodes during the break-up of Pangea, attributed to accumulation of mantle heat beneath the supercontinent. Mid-Cretaceous exhumation affected wide parts of the study area and coincided with the inversion of the Sorgenfrei-Tornquist Zone in southern Scandinavia. This may be linked with changes in the relative motion between the European and African plates in the earliest Late Cretaceous. Maastrichtian exhumation affected wide areas around Greenland, probably reflecting doming above the rising Iceland Plume upon its arrival in the upper mantle, prior to the mid-Paleocene impact at the base of the lithosphere. The mid-Paleocene impact of the plume under Greenland contributed to the onset of sea-floor spreading west of Greenland. This represents the onset of the Eurekan Orogeny which affected wide areas around northern Greenland. End-Eocene exhumation interrupted the Eocene regime of subsidence following earliest Eocene break-up in the North-East Atlantic, coincided with a minimum rate of sea-floor spreading in the North-East Atlantic, possibly related to changes in the motion of Africa relative to Europe. Early Miocene exhumation affected only Fennoscandia and is attributed to intraplate stress transmitted across the Eurasian plate. Late Miocene uplift initiated the formation of Greenland's coastal mountains but did not affect Fennoscandia. This episode correlates with changes in the absolute motion of the North American Plate. Pliocene uplift – amplified by the isostatic response to erosion – raised all margins in the region with maximum elevations reached in coastal areas close to Iceland. This suggests support from the Iceland Plume due to outward-flowing asthenosphere extending beneath the conjugate margins of the North-East Atlantic. We use these observations to argue that these episodes reflect both lithospheric and sub-lithospheric forces, related either to changes in the motion of the plates caused by far-field stress induced by events outside the study area, or driven by movements within the mantle directly within the study area. Geodynamic modelling is required to obtain further insights into the properties of the Earth that allow recurrent episodes of uplift and subsidence of the continents.