Characterising the deep structure and seismic signature of an exhumed ductile shear zone.

Understanding the behaviour of active continental scale fault zones at depth and how surface displacement is accommodated through the crust is important to improve understanding of large scale tectonics. Various studies on exhumed ductile shear zones have been carried out to investigate the processes that were active during deformation in the mid to lower-crust. This study adds to the growing knowledge by investigating processes recorded in the Uludağ Massif, NW Turkey. The Uludağ Massif and constituent faults provide an analogue for the mid-crust beneath the North Anatolian Fault (NAF) and forms part of a wider study incorporating geodesy and seismology. This study contributes to the wider project by providing a geological context to geodetic and seismological observations made using the DANA array over the NAF. In the first instance initial field observations are used to analyse the structural architecture of the shear zone to define the large scale structure and kinematics. Microstructures are observed and analysed to provide information on deformation kinematics, temperature, stress and strain rate for the exhumed shear zone. Techniques such as Electron Back Scatter Diffraction (EBSD) provide a data set from which crystal preferred orientation (CPO), CPO intensity and visco plastic self-consistency (VPSC) calibrations are used to consider how strain is distributed across shear zones. Concomitantly, Schmid factor analysis is used to ascertain active crystal slip systems in calcite across the shear zone related to strain localisation and effects such as strain hardening. Seismic properties are then calculated from the CPO to examine how different lithologies and structures within the Uludağ Massif affect the seismic properties using modelling techniques. Synthetic receiver functions are then created from these models and compared against the real seismic data and receiver functions from the DANA array on the NAF itself. Information on stress, shear strain, temperature and strain-rate build up a picture of localised deformation on strands including the Eskişehir and Bursa Faults over the shear zone on the scale of 100m – 10km. Thin section analysis and Schmid factor analysis show several weakening mechanisms are active along the Eskişehir Fault zone, whilst fault strengthening can be inferred within calcite deformation respectively. These observations have important implications for the contemporary seismogenic response if similar lithologies and structures comprise the current mid-crust beneath the NAF. However, the seismic properties of different lithologies and fabric orientations show little difference on the seismic response but the presence of a fault is obvious and could account for results of natural receiver function study via the DANA array.