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| Titel |
Extracting quantitative information on denudation and relief history from thermochronological age-elevation profiles: an example from the French Western Alps |
| VerfasserIn |
P. A. van der Beek, P. G. Valla, F. Herman, J. Braun, C. Persano, E. Labrin, K. J. Dobson, F. Stuart |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022206
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| Zusammenfassung |
| Constraining landscape evolution from thermochronological data remains challenging
because topography impacts the underlying isotherms and thus disturbs the
thermochronometric record. 2D numerical modeling is needed to avoid this pitfall and may
allow quantitative estimates on both denudation and relief histories from low temperature
thermochronology.
We test this hypothesis in the Ecrins-Pelvoux massif, French Western Alps, a region that
has experienced modest tectonic activity but intense glaciation during the last few Myr and
that is thus suitable to test the ability of thermochronology to provide independent
constraints on denudation rates and relief development. We present new zircon
and apatite fission-track and (U-Th)/He data collected along a roughly north-south
elevation profile up the north-western flank of La Meije peak (between 1310 and
3215 m elevation). Age-elevation relationships can be interpreted to first order as
reflecting a history of continuously increasing regional denudation rates through
time from ~0.16 km/Myr between 27 and 13 Myr ago (recorded by ZFT data) to
~0.55 km/Myr between 13 and 8 Myr ago (recorded by AFT data). Rapid final
cooling to surface temperatures between ~6 and 4 Myr ago is suggested by partially
overlapping AFT and AHe ages. However, the above interpretation is qualitative,
one-dimensional and neglects the possible effects of surface topography and its evolution on
thermochronometers.
We thus use a 3D thermal-kinematic model (Pecube) that enables predictions of thermal
histories and thermochronological ages from input exhumation and relief histories; we
combine this model with an inversion method based on the neighbourhood algorithm (NA) to
extract quantitative information on both exhumation rates and relief change from
our thermochonological dataset. Our numerical results with all the combined data
suggest that exhumation of the Ecrins-Pelvoux massif was episodic and can be
divided into at least 3 stages of exhumation during the last 30 Myr: two phases
of slow exhumation (0.2 to 0.5 km/Myr) before ~8 Myr and after ~5 Myr ago,
punctuated by a short phase of rapid exhumation (1.5 to 2.5 km/Myr) between 8
and 5 Myr ago. This rapid exhumation event has recently also been documented
around the same period in other external alpine massifs like the Mont Blanc or the
Aar.
Concerning landscape evolution, our results suggest that relief carving was significant
during the last ~8 Myr; however, our data cannot resolve whether this topographic change
occurred between 8 and 5 Myr ago or later, and thus are unable to relate relief production
directly to Quaternary glaciations. |
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