『Abstract
The Cordillera Real of the Bolivian Andes is a large, tectonically
active mountain range that dominates sediment influx into the
Amazon Basin, but rates of exhumation in the orogen are poorly
known. We present 20 new apatite fission track ages from two valleys
in the Cordillera Real to constrain patterns of mountain range
exhumation over 106-107 yr. We interpret
these and previously published data from a third valley using
a 2-D thermal model that accounts for topographic and advective
influences on measured cooling ages. Exhumation rates in the Cordillera
Real are 〜0.2-0.6 mm/yr, comparable to rates in parts of Denali,
the Washington Cascades, the Olympic Mountains, and the European
Alps and an order of magnitude slower than rates in Taiwan, Nanga
Parbat, the Greater Himalaya of Nepal, and the Southern Alps of
New Zealand. Three- to fourfold cooling age variations in the
Cordillera Real imply at least twofold exhumation rate variations
within and between valleys over distances of only tens of kilometers.
Topography in the cross-valley dimension affects exhumation rate
estimates by 20%-30% in the downstream portions of two sample
transects. Along-valley topographic effects are less significant
in this setting, affecting exhumation rate estimates by <15%.
The most significant along-valley topographic effects are associated
with long-wavelength mountain shape, including both retreat of
the closure temperature isotherm near the mountain crest and compression
of low-temperature isotherms farther down the mountain flank.
Locally varying phenomena (e.g., subregional structural history
or transient patterns of local channel incision) must exert important
controls on long-term erosion patterns in order to produce observed
short-wavelength exhumation rate variations. Comparison of exhumation
rate estimates with modern erosion rates suggests that long-term
and short-term average erosion rates likely vary by less than
twofold.』
Introduction
Study area
Apatite fission track sampling and results
Previous interpretations of fission track data in the Cordillera
Real
A thermal modeling-based exploration of fission track age interpretation
Exhumation rate estimates in the Cordillera Real
Discussion
Conclusions
Acknowledgments
References cited