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ESR and OSL-thermochronometry in the Western European Alps.
- Source :
- Ancient TL; Jun2023, Vol. 41 Issue 1, p202-202, 1p
- Publication Year :
- 2023
-
Abstract
- The western European Alps are characterised by deeply incised valleys, however the timing of their formation and the impact of Quaternary glaciation on rates of erosion remains disputed. This is mainly due to a lack of geochronological methods that cover the timespan of 10³-10<superscript>6</superscript> years. Electron spin resonance (ESR) thermochronometry using both the Al and Ti centres in quartz has high potential to fill this temporal gap because of its low closure temperature (<100 °C), potentially allowing changes in erosion rates to be related to glacial advance and retreat. We took surface rock samples for ESR and OSL-thermochronometry from two elevation transects in the Rhône valley, Switzerland near to the towns of Sion and Visp. Before applying the ESR thermochronometry method, a series of ESR protocol validation experiments were conducted using the Sion samples. A single aliquot regenerative additive measurement protocol was used that involves an annealing step at 400°C following the measurement of the natural signal. The suitability of this protocol was tested by using preheat plateau, dose recovery and recycling ratio tests, as well as through comparison with single aliquot additive dose response. To estimate the thermal kinetic parameters, both isochronal and isothermal decay experiments were performed. OSL-thermochronometry measurements were done following Bouscary and King (2022)[1]. The preheat plateau experiment showed that 170°C is the appropriate preheat temperature whilst sensitivity changes are not significant. ESR thermochronometric ages of seven samples from Sion range between 240 kyr and 650 kyr, while Ti centre ESR signals of samples from Visp are saturated. Although the lithology of the two sites is similar, the D0 values of samples from Visp are 2-3 times smaller than those measured at Sion. The frequency factors were >8 orders of magnitude smaller for the isochronal experiment relative to the isothermal experiment, with the latter experiment yielding the most plausible parameters. For most samples the Al-centre has higher thermal stability than the Ti-centre, although the thermal stability of the different samples investigated is highly variable (e.g., s ranges from 7.5*10<superscript>9</superscript> - 4.5*10<superscript>12</superscript> s<superscript>-1</superscript> and Et from 1.3-2 eV for the Ti-centre). Preliminary inversion of the Sion ESR data yield consistent cooling histories, with the exception of the valley bottom sample that suggests more rapid rock cooling. These data show that the low closure temperatures of the Al and Ti signals in quartz allow the Late Quaternary exhumation of the Alpine valleys to be resolved. In contrast, first luminescence measurements on the samples from Sion yielded saturated values (e.g., D0 values of the IR50 signals are between 130 and 200 Gy), demonstrating the additional potential of ESR-thermochronometry in these kinds of settings. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 07351348
- Volume :
- 41
- Issue :
- 1
- Database :
- Complementary Index
- Journal :
- Ancient TL
- Publication Type :
- Academic Journal
- Accession number :
- 172265828