科研之友
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摘要
We present a one-dimensional shear zone model with a power-law flow law and a temperature dependent viscosity. The analytical solution for the velocity profile across the shear zone depends only on the single dimensionless parameter beta. beta depends on the activation energy of the applied flow law, the temperature at the base of the shear zone and the temperature difference across it. The solution can describe three types of shear deformation: (1) homogeneous simple shear for beta %26lt;%26lt; 1, (2) thrust-sheet emplacement on top of a thin ductile shear zone for beta %26gt;%26gt; 1 and (3) heterogeneous simple shear potentially generating fold nappes for beta similar to 5-10. We perform a systematic parameter search and determine the parameters that provide the best fit between a sheared model line and a reference line representing the first-order geometry of the frontal part of the Morcles nappe. We also apply a more elaborated pressure-driven model to test whether published flow laws for calcite and realistic pressure gradients provide realistic velocities and strain rates for the Morcles nappe. The value of %26lt;%26lt; applicable to the Morcles nappe is estimated with three independent methods: (1) applying reported values for temperatures and activation energy to the analytical formula for beta, (2) fitting the first-order geometry of the Morcles fold nappe and (3) comparing results of a velocity-driven (i.e. kinematic boundary condition) and pressure-driven (i.e. pressure source term and free surface) shear zone model. All three methods yield consistent estimates for beta between 3 and 15. Our results show that previously published kinematic models, which explain the tectonic evolution of the Morcles fold nappe within a crustal shear zone, are physically feasible. The results further suggest that viscous heterogeneous simple shear played a dominant role during the formation of the Morcles fold nappe.
- 出版日期2013-1-11
