Microstructural development in ductile deformed metapelitic-metapsamitic rocks: A case study from the greenschist to granulite facies megashear zone of the Pringles Metamorphic Complex, Argentina

The Pringles Metamorphic Complex, located in the central sector of the Sierra de San Luis, Argentina, is characterized by a several kilometers wide ductile shear zone developed over a geothermal gradient variable between greenschist and granulite facies. The main component of the geothermal gradient comes from the intrusion of mafic-ultramafic bodies in a sequence of metapelitic-metapsamitic rocks. The relative compositional monotony of the original country-rocks and the systematic variation of thermal conditions along profiles normal to the NNE general trend of the structures, make this area a suitable natural laboratory to study ductile deformation. The present work combines field surveys and detailed petrographic-microstructural studies with phase relation analyses, geochemistry of rocks and minerals, and geothermobarometry. The construction of a suitable pseudosection together with geothermobarometric studies, allowed us to draw a reliable thermal curve for the mylonitization event along a representative cross-section. This study aims to give the field geologists the basic tools for a quick identification of deformation microstructures in polymineral aggregates, and correlation with temperatures during the development of mylonitic shear zones in metapelitic-metapsamitic rocks.