Open Session - SWISS GEOSCIENCE MEETINGs

16
Symposium 1: Structural Geology, Tectonics and Geodynamics
and temperature conditions.
The first three deformation types of tests already indicated that the mechanical behaviour of Carrara marble is dependent
on pre-existing deformation history. In comparison with undeformed marble, deformed Carrara marble undergoes plastic
strain at relatively lower shear stresses. Microstructures of deformed Carrara marble up to γ=2 are restored during strain
reversal. More strained marble demonstrates an evident foliation with shear sense indicators displaying a shear sense that
is in agreement with the reversed sense of shearing. Reversed strain of at least γ = 3 is required to overprint any pre-existing
foliation. Although developed fabric is very similar to that of single phase and equivalently deformed Carrara marble, CPO
development is less prominent, indicating a more complex microstructural interaction during plastic reactivation.
In addition, the first three types of deformation tests indicate that the prime cause of strain weakening in Carrara marble is
grain size refinement initiated by dynamic recrystallization. Development of CPO contributes about one third of the total
observed weakening.
REFERENCES
Delle Piane, C., & Burlini, L. 2008: Influence of strain history on the mechanical and micro-fabric evolution of calcite rocks:
insights from torsion experiments, Swiss J. Geosci, in press.
Figure 1. Sketch of type four deformation assembly, comprising a clockwise deformed top part, undeformed centre part and anticlockwise
deformed bottom part.
1.6
Neotectonics slip rate at the front of the Qilian Shan, NE Tibetan plateau
Champagnac Jean-Daniel*, Molnar Peter**, Yuan Daohuang*** & Ge Weiping ***
* Institut für Mineralogie, Universitat Hannover, Callinstrasse 1, D-30167 Hannover, champagnac@gmail.com
** Department of Geological Sciences and CIRES, University of Colorado, Boulder, USA,
*** Institute of Seismology, China Eearthquake Administration, Lanzhou, Gansu, China
We derive a slip rate for the frontal thrust at the north Qilian Shan (NE Tibet) mountain front by combining structural invstigations,
satellite imagery, topographic profiling, and 10Be exposure dating.
We used two terrace levels, and from each we took 6-7 samples in profiles dug to depths of two meters. These allowed us to
constrain inheritance (less than a couple of thousand years, for each) and to yield precise ages of abandonment of the terraces: