Abstract
The landscape of the Karrat region, central West Greenland, contrasts between high elevation low relief topography, steep sided fjords and deep bathymetric troughs. The mechanisms controlling its formation are highly debated, with initial work suggesting it to be the result of episodic tectonic uplift throughout the late Cenozoic and alternative models implying it is the product of more recent isostatic uplift in response to differential glacial erosion. Here the results of a comprehensive low temperature thermochronological study (apatite fission track and apatite (UTh)/He) and landscape evolution model are presented that helps establish the source of the modern elevated landscape and the region's complex geomorphology. Joint modelling of the apatite fission track and apatite (UTh)/He data outlines two significant periods of cooling, in the Mesozoic and Cenozoic respectively. The first (150 Ma – 110 Ma) correlates to the onset of extension between West Greenland and eastern Canada, suggesting uplift of the region during active rifting, while the second period (50 Ma - 0 Ma) is coeval to the cessation of volcanism in the region and likely represents widespread erosion. These results suggest the basement escarpment likely remained at height during extrusive volcanism and was later uncovered following exhumation of the volcanic succession. Moreover, this latter phase of exhumation is outlined in the results of landscape evolution modelling, implying it likely encompassed localised differential erosion of the volcanic pile, producing a pre-glacial landscape that later aided ice stream onset and the advance of the Uummannaq Ice Stream. Glacial exhumation of the region was likely characterised by differential erosion, shaping the modern geomorphology through preferential ice stream development and isostatic rebound. These results highlight the complex interaction between rift tectonics and surface processes across the Karrat region and adds to a wider understanding of the post-rift evolution of passive continental margins.
Highlights
The elevated topography of glaciated Atlantic passive margins continues to stimulate considerable debate and discussion across the geological community (e.g., Rohrman et al, 1996; Hansen, 1996; Riis, 1996; Japsen and Chalmers, 2000; Japsen et al, 2005; Anell et al, 2009; Eidvin et al, 2014)
In addition to apatite low temperature thermochronology, the application of a landscape evolution model (LEM) within this study aims to determine if the underlying geology of the region acts as a primary control on the region's topographic evolution
Three samples produce anomalous ages linked to intrusive volcanism and are avoided, with Ka2 and Ka8 extracted from veins related to magmatism and Ka16 likely effected by adjacent dykes
Summary
The elevated topography of glaciated Atlantic passive margins continues to stimulate considerable debate and discussion across the geological community (e.g., Rohrman et al, 1996; Hansen, 1996; Riis, 1996; Japsen and Chalmers, 2000; Japsen et al, 2005; Anell et al, 2009; Eidvin et al, 2014). Medvedev et al (2013) and Jess et al (2018) proposed the basin's elevated topography may instead be the result of lengthy widespread exhumation, instigating significant positive feedback from the lithosphere and preserving much of the older topography under cold-based ice during glaciation (Strunk et al, 2017). This alternative interpretation of basin evolution appears to suit much of the data and geology in the Nuussuaq Basin better, though the cause of topography and the complex geomorphology across the surrounding basement margins remains unclear
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