Field and textural evidence of two migmatization events in the Sierras de Córdoba, Argentina

In the metamorphic basement of the central eastern Sierra de Comechingones (Sierras Pampeanas of Córdoba, Argentina), two types of migmatites are found: Tala Cruz metatexites and Cañada del Sauce diatexites. Rafts of deformed metatexites in the diatexites are interpreted as dismembered and partially assimilated remnants of the Tala Cruz metatexites. Two migmatization events are recognized: the M2 metamorphic peak produced high-grade paragenesis and the first anatexis generating the metatexites; 810–840 °C and 8.5–9 kbar were calculated for M2. The M4 decompression event produced the diatexites by a second melting of the metatexites; 725–780 °C and 5.5–6 kbar were estimated for M4. A dynamic contractional M3 event in high-ductility and high-temperature conditions was recognized between the two migmatization events. A correlation could be established between the second migmatization event (M4) and the event dated as Cambrian (520–530 Ma) in other areas in the Sierras de Córdoba, in which case the first migmatization event (M2) would have been older, perhaps as old as Neoproterozoic. The tectonic evolution of the Sierra de Comechingones would imply the occurrence of extension–shortening cycles, interpreted as “pull–push” cycles mirroring the subduction and collision of Pampia terrane against the western Gondwana margin. These cycles would have controlled the evolution of the Eastern Sierras Pampeanas, during the Neoproterozoic?–Early Palaeozoic times.