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| Titel |
Topographic evolution of a continental indenter: The eastern Southern Alps |
| VerfasserIn |
Jörg Robl, Bianca Heberer, Günther Prasicek, Franz Neubauer, Stefan Hergarten |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145571
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| Publikation (Nr.) |
 EGU/EGU2017-9525.pdf |
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| Zusammenfassung |
| The topographic evolution of the eastern Southern Alps (ESA) is controlled by the Late
Oligocene - Early Miocene indentation of the Adriatic microplate into an overthickened
orogenic wedge emplaced on top of the European plate. Rivers follow topographic gradients
that evolve during continental collision and in turn incise into bedrock counteracting the
formation of topography. In principle, erosional surface processes tend to establish a
topographic steady state so that an interpretation of topographic metrics in terms of the
latest tectonic history should be straightforward. However, a series of complications
impede deciphering the topographic record of the ESA. The Pleistocene glaciations
locally excavated alpine valleys and perturbed fluvial drainages. The Late Miocene
desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to
significant base level changes in the far field of the ESA and the Eastern Alps (EA),
respectively. Among this multitude of mechanisms, the processes that dominate
the current topographic evolution of the ESA and the ESA-EA drainage divide
have not been identified and a number of questions regarding the interaction of
crustal deformation, erosion and climate in shaping the present-day topography
remain.
We demonstrate the expected topographic effects of each mechanism in a 1-dimensional
model and compare them with observed channel metrics. Modern uplift rates are largely
consistent with long-term exhumation in the ESA and with variations in the normalized
steepness index (ksn) indicating a stable uplift and erosion pattern since Miocene times. We
find that ksn increases with uplift rate and declines from the indenter tip in the northwest to
the foreland basin in the southeast. The number and magnitude of knickpoints and the
distortion in longitudinal channel profiles similarly decrease towards the east. Most
knickpoints probably evolved during Pleistocene glaciation cycles, but may represent the
incrementally reactivated, buried incision signal triggered by the Messinian desiccation of the
Mediterranean Sea. Changes in slope of χ-transformed channel profiles coincide
spatially with the Valsugana - Fella fault linking crustal stacking and uplift induced by
indenter tectonics with topographic evolution. Gradients in χ across the ESA-EA
drainage divide imply an ongoing, north-directed shift of the Danube-ESA watershed.
This implies that ESA streams spread to the domain of the EA by drainage divide
migration and river capture events. As already observed in the Adige catchment, the
Periadriatic fault system loses its significance for the morphological evolution of the
EA-ESA. The observed northward migration of the ESA-EA drainage divide is most
likely driven by a base level rise in the northern Molasse basin, which leads to a
growth of the ESA and Rhine catchments at the expense of the Danube drainage
area.
We conclude that the regional uplift pattern controls the geometry of ESA-EA channels,
while base level changes in the far field control the overall architecture of the orogen by
drainage divide migration (Robl et al., 2016).
Robl, J., B. Heberer, G. Prasicek, F. Neubauer, and S. Hergarten (2016), The topography
of a continental indenter: The interplay between crustal deformation, erosion and
base level changes in the eastern Southern Alps, J. Geophys. Res. Earth Surf., 121,
doi:10.1002/2016JF003884. |
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