CONSTRAINING THE EXHUMATION HISTORY OF THE NORWEGIAN PASSIVE MARGIN THROUGH LOW-TEMPERATURE THERMOCHRONOLOGICAL DATA FROM THE SOGNEFJORD-HARDANGERFJORD REGIONS, SW-NORWAY

The Sognefjord is one of the world’s deepest fjord with very steep and high cliffs, and therefore an ideal target for low-temperature thermochronological studies. Previous data are scarce, and we are therefore carrying out a low-temperature thermochronological studies along vertical sample transects to reconstruct its thermal history. To the south another major fjord, the Hardengerfjord, represents similar opportunities. In contrast to the Sognefjord, the Hardangerfjord area is dominated by a major tectonic structure, the Hardangerfjord Shear Zone (HSZ), which is a crustal-scale structure that formed during Devonian extension shortly following the Caledonian orogeny. The HSZ might be part of an even larger zone of crustal deformation stretching across the North Sea into the Highland Boundary Fault in Scotland. The Hardangerfjord itself follows the trend of the Devonian shear zone and acted as one of the largest sediment pathways in the area. The amount of inland erosion and the corresponding depositional patterns are strongly affected by onshore uplift tectonics.

This project aims to constrain the amount and timing of post-Caledonian uplift along this part of the margin by a combination of fission track, (U-Th)/He and K/Ar dating. In particular, the apparent absence of Mesozoic brittle reactivation of the HSZ is targeted by sampling of detailed profiles parallel and across the HSZ. Furthermore, vertical profiles on steep flanks of the Hardangerfjord and especially of the Sognefjord are analysed in order to obtain more precise uplift and erosion rates. Combining detailed thermochronological studies of these two major, geomorphic features provides us with new insights into the evolution of the northern North Sea rift margin and the Norwegian passive continental margin. This study will further improve our understanding of onshore tectonic processes and their effect on offshore sedimentation cycles in the North Sea. In addition, it will add to the ongoing dispute about the geomorphic evolution of the present-day high topography of western Norway: the classic Neogene domal uplift model versus the Isostasy-Climate-Erosion (ICE) hypothesis.