The Phyllite and Micaschist Group with associated intrusions in the Sierra de San Luis (Sierras Pampeanas/Argentina) — structural and metamorphic relations

Structural analyses of the Phyllite and Micaschist Group with intercalated intrusions in the Sierra de San Luis (Sierras Pampeanas, western Argentina) reveal a multi-stage magmato-tectonic evolution during Early Paleozoic times. The Tamboreo Tonalite intruded the undeformed clastic sediments of both groups and led to the development of a contact aureole. The Paso del Rey Granite and associated pegmatite dikes are interpreted as pre-kinematic with respect to the first deformation of the micaschists. After a variable, pre- to syn-deformational metamorphism, ~ WNW-ESE compression with a regional greenschist facies metamorphism affected the Phyllite and Micaschist Group as well as the intrusions. The La Florida Granite and associated pegmatite dikes are interpreted to have intruded the micaschists after the first deformational event. The present contacts between the Phyllite and Micaschist Group either are metamorphic transitions or ductile reverse faults. The former suggest that both groups initially were part of one crustal profile. Steeply inclined reverse faults and fold structures do not record a single vergence. A preliminary interpretation suggests that deformations and regional metamorphism took place in the Upper Ordovician-Middle Devonian interval and can be related to the second stage of the Famatinian Cycle after initial emplacement of plutons. The low grade rocks of the Sierra de San Luis, and related micaschists, can be compared with different occurrences in the Sierras Pampeanas basement complex to the north and probably were part of one large “Puncoviscana Basin”.