HR: 1340h
AN: T23D-1656    [Abstracts]
TI: Rapid Late Miocene Exhumation in the Central Alps, Constrained by (U-Th)/He and Fission Track Thermochronology
AU: Aramowicz, A
EM: Aleksander.Aramowicz@unil.ch
AF: University of Lausanne, Institute of Mineralogy and Geochemistry, Anthropole, Lausanne, 1015, Switzerland
AU: * Cosca, M
EM: Michael.Cosca@unil.ch
AF: University of Lausanne, Institute of Mineralogy and Geochemistry, Anthropole, Lausanne, 1015, Switzerland
AU: Stockli, D
EM: stockli@ku.edu
AF: University of Kansas, Department of Geology, 120 Lindley Hall, Lawrence, KS 66045-7613, United States
AU: Farley, K
EM: farley@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, Caltech, MS 170-25, Pasadena, CA 91125, United States
AU: Seward, D
EM: diane.seward@erdw.ethz.ch
AF: Geological Institute, ETH Zurich, Leonhardstrasse 19, Zurich, 8092, Switzerland
AB: Zircon and apatite (U-Th)/He thermochronological data together with apatite fission track analyses are used to explore uplift and exhumation of the western part of the Aar massif in the central Swiss Alps. A total of 27 samples were collected from the surface and underground, from the world's deepest tunnel (Loetschberg NEAT), with an overall elevation difference of almost 2500 m. Zircon (U-Th)/He ages range from 5.5 to 7.6 Ma, apatite fission track ages range from 5.7 to 6.5 Ma and apatite (U-Th)/He ages range from 3 to 5.5 Ma. All zircon age-elevation profiles from three traverses, show distinct brakes in slope that mark a drastic, 10-fold acceleration of exhumation at 6 ± 0.5 Ma ago (from 0.3 km/Ma to 3 km/Ma). The trend of fast exhumation appears to be maintained in the apatite fission track data while apatite (U-Th)/He ages suggest a return to moderate, apparent exhumation rates of 0.5 km/Ma. We propose that the accelerated exhumation may be linked to the Messinian desiccation of the Mediterranean. During that event, Mediterranean sea level dropped locally by as much as 3 km which accelerated erosion in the Alps. Consequently, the erosion in the Alps must have increased. If wedge mechanics are considered, the increased erosional flux reduced the active width of the orogen and, during latest convergence, deformation focused in the internal parts of the Alps, i.e. Aar massif. This interpretation implies a strong and prompt feedback between external forcing and tectonic response of the orogen. The slower exhumation rate apparent from the apatite (U-Th)/He data may reflect a decline in deformation. Alternatively, due to its low closure temperature, this system is prone to resetting by heat advected through hydrothermal circulation. This scenario needs further investigation but abundant hot-water (ca. 50 °C) discharge in the sampled tunnel is not uncommon.
DE: 8100 TECTONOPHYSICS
DE: 8108 Continental tectonics: compressional
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting