2D-thermo-mechanical modelling of spatial P-T variations in heterogeneous shear zones

We present a suite of two-dimensional thermo-mechanical
simulations of a compositionally heterogeneous shear zone
characterized by viscous matrix and inclusions. The experiments
have been performed using a visco-elasto-plastic 2D finite difference
code that reproduces the stress, strain, temperature and pressure
variations occurring within the shear zone at lithospheric scale. From
here, we extrapolated and discuss the results of a narrow (<10 km)
domain where strong inclusions with respect to a weaker matrix are
inserted. The experimental setting simulates the geological conditions
common to several (ultra-) high-pressure (U-HP) rocks worldwide.
Particularly, we shaped the model in order to roughly reproduce the
distribution of the (U)HP ultramafic rocks of the Adula-Cima Lunga
nappe system. Results indicate that significant overpressure (up to
0.3 GPa) within the strong inclusions and viscous shear heating (up
to 100°C) can be generated already with a short time of deformation
(ca. 1.2 Myr) in small rock units. These data suggest that, in specific
structural domains, pressure and temperature deviations may play a
not trivial role in the pressure-temperature-time paths recorded by
the rocks through the metamorphic reactions.