Earthquake-induced dolomite decarbonation in the Dinar Fault Zone, western Türkiye

This work reports a multiscale study of the Dinar fault zone, focusing on a normal fault, hosted in Triassic dolostone, that is part of the fault system responsible for the 1995 Dinar earthquake (Mw = 6.2). Mirror surfaces are associated with the seismogenic fault zone, suggesting a relationship with the processes occurring during earthquakes. The investigation of mirror surfaces, from the outcrop to the micro- and nanoscale (i.e., high-resolution TEM imaging and electron diffraction) provided unambiguous evidence of dolomite thermal decomposition, occurring at similar to 550 degrees C, with formation of Mg-rich calcite nanograins and amorphous alumosilicatic material, possibly deriving from minor phyllosilicates in host dolostones. Our observations are in perfect agreement with high-velocity experiments on dolomite, which produces identical mineralogical assemblages and nanostructures. The Dinar case study represents a unique example, as it provides the first unequivocal evidence of dolomite decomposition associated to a mirror along the fault plane of a known seismogenic structure, likely formed during the coseismic slip compatible with the magnitude historical earthquakes in the region, including the 1995 Dinar earthquake.