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, elastic sediments of th e Phyllite Group are assigned to the Late Precambrian-Early Cambrian interv al and contain acid meta-mamatic dykes. Deposits of the Micaschist Group ar e interpreted as deeper crustal equivalents. Lower Ordovician intrusions of the Bemberg and Las Verbenas Tonalites, as well as the Lower Devonian La E scalerilla Granite pluton, led to a thermal overprint in the Phyllite Group . A first deformation, pegmatitic injections, and amphibolite facies metamo rphism in the Micaschist Group are of Famatinian (Ordovician) age. Post-Fam atinian (Devonian) similar to WNW-ESE compression affected all units under greenschist facies metamorphism, which locally reached amphibolite facies c onditions, and is the second event in the Micaschist Group. Mostly sinistra l, 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 w as obliquely thrust northwestwards over the granite. They are related to th e sinuous bending of the granite under sinistral transpression which probab ly was an important mechanism in this part of the sierra. Possible implicat ions with respect: to the collision of the Precordillera (Cuyania) Terrane are briefly discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.