Inversion of thermochronological age-elevation profiles to extract independent estimates of denudation and relief history - I: Theory and conceptual model


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Inversion of thermochronological age-elevation profiles to extract independent estimates of denudation and relief history - I: Theory and conceptual model
Earth and Planetary Science Letters
Valla P.G., Herman F., Van der Beek P.A., Braun J.
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We determine to what extent low-temperature thermochronology data, in
particular from age-elevation profiles, provide independent and
quantitative estimates on denudation rates and relief development.
Thermochronological age-elevation profiles have been widely used to
infer exhumation histories. However, their interpretation has remained
inherently one-dimensional, neglecting potential effects of lateral
offsets between samples. Furthermore, the potential effects of transient
topography on crustal isotherms and consequently on thermochronological
data have not yet been addressed in detail. We investigate this problem
with the aim of deriving independent estimates of both denudation rates
and relief history from low-temperature thermochronometers, measuring
the relative uncertainties on these parameters and finally constraining
the timing of potential variations in denudation rate and/or relief
development. We adopt a non-linear inversion method combining the
three-dimensional thermal-kinematic model Pecube, which predicts thermal
histories and thermochronological ages from an input denudation and
relief history, with an inversion scheme based on the Neighbourhood
Algorithm. We use synthetic data predicted from imposed denudation and
relief histories and quantitatively assess the resolution of
thermochronological data collected along an age-elevation profile. Our
results show that apatite fission-track (AFT) ages alone do not provide
sufficient quantitative information to independently constrain
denudation and relief histories. Multiple thermochronometers (apatite
(U-Th)/He (AHe) ages and/or track-length measurements combined with AFT
ages) are generally successful in constraining denudation rates and
timing of rate changes, the optimum combination of thermochronometers
varying with the input scenario (relief change or varying denudation
rates). However, relief changes can only be quantified and precisely
constrained from thermochronological age-elevation profiles if the rate
of relief growth is at least 2-3 times higher than the background
denudation rate. This limited resolution is due to the depth of the
closure isotherm (between similar to 70 and 110 degrees C) for the AFT
and AHe systems, which only partly record topographic change. New
thermochronometers (such as (4)He/(3)He or OSL) that are sensitive to
lower temperatures may be the key for resolving this issue. (C) 2010
Elsevier B.V. All rights reserved.
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07/10/2012 19:46
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20/08/2019 15:58
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