Vertical motions of East Greenland: Impact of erosion, deposition, paleodrainage, and isostasy

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Medvedev, Sergei; Hartz, Ebbe; Faleide, Jan Inge; Podladchikov, Yuri
Holding Date 11 October 2008

We test potential mechanism of the uplift of passive margins on the example of the coastal mountain ranges in East Greenland. The area is characterized by a more than thousand kilometer long mountain chain, in which the high peaks (2.5 to 3.7 km elevation) reside above a relatively thin crust (30-40 km). These mountains contain Mesozoic marine sediments uplifted up to 1.2 km above sea level during mid- to late- Cenozoic tectonic quietness. The world’s biggest fjords cut this uplifted area. Scoresbysund alone is 400 km long and up to 50 km wide and cuts more than 4 km down from the peaks of the adjacent region. We test numerically the potential amount of regional uplift and subsidence caused by fjord incisions and associated deposition of sediments offshore. We ’restore’ paleolandscapes backwards in time; the fjords are filled back to the summit surface while similar weights of sediments are removed from the shelf. The model considers the isostatic response of the lithosphere due to loading and unloading of bedrock, sediments, water and ice. Our regional estimates show that an average of almost 1.2 km of rock was eroded in the region after the last major paleosurfaces formed (the summit surface), and deposited on the continental shelf outside the mouth of the fjords. Our regional calculations demonstrate that rocks in the central ’Fjord Mountains’ may be uplifted up to 1.1 km due to the erosional unloading and flexural isostatic effects. We illustrate the conservativeness of our estimation comparing results for different resolution of topography/bathymetry data and for different values of effective elastic thickness of the lithosphere. Collectively, the modeled effects represent the main part of the mechanisms responsible for Cenozoic uplift of East Greenland’s ’Fjord Mountains’, whereas the high and little incised mountains west of East Greenland fjords are older topographic features. We compare our model to published thermochronological data (on land) and seismic data (offshore), thereby attempting to differentiate Quaternary, Neogene, Paleogene and older mass transfers in Greenland and offshore. Mountain chains incised by glacial and/or fluvial erosion are often found along passive margins. Thus, our model may be widely applicable for reconstructions of on-land paleotopography and offshore stratigraphy and for studies of shallow crustal temperature, paleoclimate and paleodrainage.