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Precipitation, focussed erosion and crustal flexural
accommodation in the Eastern Altiplano (Bolivia)
G.
Zeilinger (1), M. Strecker (1), B. Bookhagen (2), S. Tawakholi (3), E.
Baldellon (4)
(1) Institute of Geosciences, University of Potsdam, Karl-Liebknecht-Str.
24/25, D-14476 Golm/Potsdam (zeilinger@geo.uni-potsdam.de)
(2) School of Earth Sciences, Stanford University,
397 Panama Mall, Stanford, CA 94305-2210
(3) APEMIN II, Av. del Minero 54, Oruro - Bolivia
(4) Sergeotechmin, Calle Federico Zuazo No. 1673, La Paz, Bolivia
The Rio Consata and the Rio La Paz drain the Bolivian Altiplano and cut
across the Eastern Cordillera, immediately adjacent to the highest peak of
the Cordillera Real (e.g., the 6.368 m-high Illampú). Both rivers are
important in routing sediments from the orogen interior to the Andean
foreland.
Previous studies of the Rio La Paz (~ 175 km SSE of Rio Consata) have shown
that deep incision in the Cordillera Oriental and the removal of sediments
from the catchment on the Altiplano have had an important effect on the
general pattern of rock uplift and the evolution of drainages beyond the
watershed on the Altiplano.
Overall, the Rio Consata has removed approx. 1320 km³ of rock from the
Altiplano catchment area (~ 2600 km²) and has cut down into the Eastern
Cordillera more than 2500 m. The timing of initiation of the sediment
removal from the Rio Consata catchment is yet not known. However, based on
field relationships and correlation of volcanic ash layers the onset of
sediment removal most likely coincides with the Rio La Paz, which began
downcutting approx. 2.7 m.y. ago. Sediments related to glacial overprint in
the past are efficiently removed in the headwaters of the catchment, whereas
they are stored beyond the watershed. Farther downstream, the presence of
braided alluvial channels and gravel sheets indicate sediment bypassing.
However, fluvial incision has resulted in partial exposure of bedrock on the
channel floor where the river cuts through the Cordillera. Two locations
correspond to enhanced surface erosion: the area of the drainage on the
Altiplano and the sector in the Eastern Cordillera affected by bedrock
incision. Interestingly, the rainfall pattern along the Eastern Cordillera
mimics the patterns of topographic relief and is curved in the region of the
Rio Consata valley. Here, based on high-resolution Tropical Rainfall
Measurement Mission (TRMM) rainfall data, we observe an influx of higher
rainfall along the trend of the valley towards the Altiplano.
Morphometric data and precipitation pattern suggest a significant link
between precipitation, topographic evolution and erosion processes. Flexural
modelling indicates that crustal flexural uplift is fundamentally influenced
by erosional removal of material. Flexural uplift in turn helps intercept
westward moisture transport, thus suggesting a positive feedback mechanism
between tectonics and climate, which ultimately influences the overall
morphology of the Eastern Cordillera.