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| Titel |
Calibration of cosmogenic 3He and 10Be production rates in the High Tropics |
| VerfasserIn |
Pierre-Henri Blard, Léo Martin, Jérôme Lavé, Julien Charreau, Thomas Condom, Maarten Lupker, Régis Braucher, Didier Bourlès |
| 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 |
250100006
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| Publikation (Nr.) |
 EGU/EGU2014-15871.pdf |
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| Zusammenfassung |
| It is critical to refine both the accuracy and the precision of the in situ cosmogenic dating
tool, especially for establishing reliable glacial chronologies that can be compared
to other paleoclimatic records. Recent cross-calibrations of cosmogenic 3He in
pyroxene and 10Be in quartz [1, 2] showed that, both at low (1300 m) and high
elevation (4850 m), the 3He/10Be production ratio was probably ~40% higher than the
value of ~23 initially defined in the 90’s. This recent update is consistent with
the last independent determinations of the sea level high latitude production rates
of 10Be and 3He, that are about 4 and 125 at.g-1.yr-1, respectively [e.g. 3, 4].
However, major questions remain about these production rates at high elevation,
notably because existing calibration sites for both 3He and 10Be are scarce above
2000 m. It is thus crucial to produce new high precision calibration data at high
elevation.
Here we report cosmogenic 10Be data from boulders sampled on a glacial fan
located at 3800 m in the Central Altiplano (Bolivia), whose age is independently
constrained by stratigraphic correlations and radiocarbon dating at ca. 16 ka. These
data can be used to calibrate the production rate of 10Be at high elevation, in the
Tropics. After scaling to sea level and high latitude, these data yield a sea level high
latitude P10 ranging from 3.8 to 4.2 at.g-1.yr-1, depending on the used scaling
scheme.
These new calibration data are in good agreement with recent absolute and
cross-calibration of 3He in pyroxenes and 10Be in quartz, from dacitic moraines located at
4850 m in the Southern Altiplano (22°S, Tropical Andes) [2,5]. The so-obtained 3He/10Be
production ratio of 33.3±0.9 (1Ïă) combined with an absolute 3He production rate
locally calibrated in the Central Altiplano, at 3800 m, indeed yielded a sea level
high latitude P10 ranging from 3.7±0.2 to 4.1±0.2 at.g-1.yr-1, depending on the
scaling scheme [2,5]. These values are also consistent with the 10Be production
rate recently calibrated in Southern Peru, 1000 km north from the bolivian sites
[6].
These new refinements of the cosmogenic dating tool significantly improve both the
accuracy and the precision of paleoglaciers chronologies in the Tropical Andes. It is now
theoretically possible to reach precisions better than 5% (at 1Ïă) for dating glacial landforms
deposited during the last 20 ka.
[1] Amidon et al. (2009) Earth Planet. Sci. Lett. 280, 194-204.
[2] Blard et al., (2013) Earth Planet. Sci. Lett. 382, 140-149.
[3] Putnam et al. (2010) Quat. Geochron. 5, 392-409.
[4] Goehring et al. (2010) Quat. Geochron. 5, 410-418.
[5] Blard et al., (2013) Earth Planet. Sci. Lett. 377-378, 260-275.
[6] Kelly et al. (in press) Quat. Geochron. |
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