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| Titel |
Tectonically controlled denudation rates in the central Bolivian Andes |
| VerfasserIn |
Gerold Zeilinger, Florian Kober, Kristina Hippe, Odin Marc |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089156
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| Publikation (Nr.) |
 EGU/EGU2014-3348.pdf |
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| Zusammenfassung |
| A new dataset of 10Be (and 26Al) catchment wide denudation rates from the Central Andean
Rio Grande catchment exposes a strong zoning. The denudation rates - which integrate over
millennial timescales - reveal 3-5 times faster denudation in the Subandean Zone
(SAZ)(mean 0.8 mm/yr) than in the Eastern Cordillera (EC) and in the Interandean Zone
(IAZ). The Rio Grande main reach drops approx. 5000 m when flowing from W-E through
the EC, IAZ and SAZ physiographic provinces to the Chaco Plain at the E side of the Central
Andes.
Local relief, mean slopes and channel steepness indices are largely similar across these
physiographic regions. In addition, climatic parameters like precipitation do not show a
significant gradient. The orientation of major structural trends and the predominant
orientation of fluvial channels reveal in the EC and IAZ only little to uniform preferred
orientation of drainages, suggesting a balance between structural control and drainage
occupation. In contrast, the distinct pattern of drainages oblique to the structural grain in the
SA controls the E-W alignment of tributaries and suggests a tectonic control on drainage
orientation.
Based on above mentioned results and observations, we infer that seismic and tectonic
activity in the Subandean belt generates and rejuvenates its topography. This is supported
by a higher cumulative surface uplift in the thrust fault setting of the Subandes
compared to the other regions. We conclude that the overall denudation rate signature of
the Central Eastern Andes is dominated primarily by tectonic, and secondary, by
climate and geological boundary conditions causing a complex pattern of geomorphic
processes and responses. The absence of a distinct tectonic topographic signature in the
Subandes might be caused by (1) landscape processes that evolve on scales that are not
characteristic for a single geomorphic parameter and (2) partially by nonlinear
responses.
Results from the outlet of the Rio Grande catchment at Abapó, located at the transition to
the Chaco Plain, indicate that the current high denudation rates of the SAZ can be overprinted
by headwater signals. Consequently, it requires caution when postulating tectonic
and/or climatic forcing as the cause when such bypassing events affect the catchment
area.
The above mentioned study is part of an integrated attempt for a better understanding of
the processes of natural and current denudation and their spatial distribution as a basis for an
assessment of erosion rates in the Rio Grande catchment and the planning of protective
measures. |
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