Geological, Structural and Mineralogical Approach to Investigate the Evolution of Low- and very Low-Grade Metamorphic Units from the Intra-Pontide Suture Zone, Central Pontides, Turkey

A multidisciplinary approach combining multiscale geological-structural analyses (from field to microscale) and clay mineral transformations (clay mineralogy, illite and chlorite “crystallinity” and b cell dimension (b0) of K-white mica) was adopted to unravel the tectono-metamorphic evolution of low- and very low-grade tectono-metamorphic units from the Intra-Pontide suture zone in northern Turkey. The mineralogical study allowed to better evaluate the structural stacking outlined during the geological mapping, leading to distinguish three tectono-metamorphic units, two in epizone (Daday and Emirköy units) and one in anchizone (Çifter Unit) metamorphic conditions. The mesostructural and microstructural analyses suggest a polyphase tectonic-metamorphic evolution. The different macroscopic features observed between the two units characterized by the same epizone metamorphism, can be justified by the evidence that these metamorphic conditions were acquired during the last stages of exhumation in the Daday Unit, while they constrained the metamorphic-peak conditions in the Emirköy Unit. Contemporary analyses and comparison between structural and mineralogical data have thus proven to be a powerful tool to investigate the low-grade and very low-grade metamorphic environments, allowing at the same time to solve the apparent contradictions deriving from the mineralogical study and to significantly improve the detail of the geological mapping in the field.