The Sierra de Pie de Palo belongs to the Western Sierras Pampeanas. Although still poorly known in detail, the sierra consists of a relatively autochthonous sequence of shelf sediments metamorphosed to low grade (the Caucete Group) and an allochthonous complex of polymetamorphic medium-to-high grade igneous and sedimentary rocks thrust towards the west and northwest. Mylonitization is widespread. Radiometric dating by different methods (U-Pb, 40Ar/39Ar and K-Ar) suggests that at least two tectono-thermal events are present in the allochthonous: Grenville (ca. 1Ga) and Famatinian (480-312Ma).
Metamorphism has been studied in a Ca-rich pelite with a complex mineralogical composition (Qtz, Ms, Pg, Bt, Grt, Ky, Hbl, St, Rt, III, PI, Ep). This rock is a mylonite. Three metamorphic stages are recognized: the first two correspond to a prograde M, metamorphism under relatively high P/T conditions (peak at 13kb and about 6002C). The second is related to mylonitization (Mmy|) with T ~ 575eC and P <10kb. We suggest that this rock is polymetamorphic, M, metamorphism being probably related to the Grenville orogeny and Mmy| to the Famatinian orogeny
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