Transpressive deformation in the southwestern part of the Sierra de San Luis (Sierras Pampeanas, Argentina)

In the southwestern part of the Sierra de San Luis, clastic sediments of the Phyllite Group are assigned to the Late Precambrian–Early Cambrian interval and contain acid meta-mamatic dykes. Deposits of the Micaschist Group are interpreted as deeper crustal equivalents. Lower Ordovician intrusions of the Bemberg and Las Verbenas Tonalites, as well as the Lower Devonian La Escalerilla Granite pluton, led to a thermal overprint in the Phyllite Group. A first deformation, pegmatitic injections, and amphibolite facies metamorphism in the Micaschist Group are of Famatinian (Ordovician) age. Post-Famatinian (Devonian) ∼WNW–ESE compression affected all units under greenschist facies metamorphism, which locally reached amphibolite facies conditions, and is the second event in the Micaschist Group. Mostly sinistral, ductile shear zones within the granite, Las Verbenas Tonalite, and parts of the Phyllite Group were formed together with folds in the meta-clastic successions and an eastern mylonite zone along which the Micaschist Group was obliquely thrust northwestwards over the granite. They are related to the sinuous bending of the granite under sinistral transpression which probably was an important mechanism in this part of the sierra. Possible implications with respect to the collision of the Precordillera (Cuyania) Terrane are briefly discussed.