CHARACTERISING THE DEEP STRUCTURE OF AN EXHUMED DUCTILE SHEAR ZONE VIA EBSD: THE ULUDAĞ MASSIF, TURKEY

Geophysical models that explore the deep rheology of continental-scale fault zones often lack realistic physical parameters that define the actual behaviour expected for a specific fault. This study aims to bridge the gap between geophysical- and geological-derived seismic models of continental scale fault zones by providing lithology and deformation state specific elastic properties from an exhumed ductile shear zone in north-central Turkey. This will allow better understanding of how major faults act at depth, and the degree at which strain partitions in the lower crust.

The Uludağ Massif represents a mid-crustal section of the dextral strike-slip Eskişehir shear zone, which was active during the Oligocene and accommodated ~100km of displacement with a component of late oblique-normal slip. The exhumed Massif consists of high-grade metamorphic rocks belonging to the Uludağ Group, thought to be ‘post-Ordovician’ in protolith age, pierced by the Central and South Uludağ granites in the Oligocene. The elastic and hence seismic properties across the ductile Eskişehir shear zone can be estimated from the crystallographic preferred orientation (CPO) of individual and combined mineral phases measured via electron back scattered diffraction (EBSD) in the scanning electron microscope (SEM). Elastic properties determined from CPO are used to populate geological models with realistic values to investigate their impact on the seismic response. The study forms part of larger project on the North Anatolian Fault Zone (NAFZ), for which the Uludağ Massif provides a mid-crustal field analogue. The 3 component synthetic seismic response generated from the model can then be converted into receiver functions and allow comparison with real seismic data from dense network over the NAFZ to better understand the 3D dynamics of this major continental-scale fault zone.