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.

DELPINO, S.; RUEDA, M.; URRAZA, I.; GRASEMANN, B.

Ductile Shear Zones: from Micro- to Meso-scales

Wiley Publisher

Lugar: Oxford; Año: 2016; p. 224 - 249

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 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 of 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 basic tools for a quick identification of deformation microstructures in polymineral aggregates, and correlate with temperatures during the development of mylonitic shear zones in metapelitic-metapsamitic rocks.