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The Neoproterozoic Difunta Correa meta-sedimentary sequence (DCSS) of Western Sierras Pampeanas is a cover to a rejuvenated Grenvillian basement. The Western Sierras Pampeanas are allegedly part of the exotic Precordillera Terrane, which was accreted to the proto-Andean margin of Gondwana in lower Palaeozoic times. A para-amphibolite from this sedimentary sequence contains abundant zircons mostly consisting of detrital igneous cores with a metamorphic overgrowth. The latter formed at 439±34 Ma, i.e., during the Famatinian orogeny, although mantles are also found with mixed Grenvillian - Ordovician ages due to Pb-loss. Ages of igneous cores are ~ 625 Ma , 1050-1150 Ma and 1200-1500 Ma with a peak at c. 1.4 Ga. The ~ 625 Ma group zircon is of Gondwanan provenance and this age is an upper value for the age of the host amphibolite. An age between 580 Ma and 620 Ma is inferred for the DCSS. The provenance of zircons between 1.05 Ga and c. 1.2 Ga probably lies in the underlying Grenvillian basement. However zircons older than 1.2 Ga were derived from an unexposed area: palaeogeographical considerations suggest that this area could be either in Laurentia (trans-Laurentia belt) or in southern Amazonia (Rondonia- San Ignacio belt), both 1.3-1.5 Ga in age., Depto. de Mineralogía y Petrología, Fac. de Ciencias Geológicas, TRUE, pub

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, 4°Ar/39Ar and K-Ar) suggests that at least two tectonothermal events are present in the allochthonous: Grenville (ca. 1 Ga) 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, 111, 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 600ºC). The second is related to mylonitization (Mm 1) with T - 575ºC and P < 1 Okb. We suggest that this rock is polymetamorphic, M, metamorphism beirig probably related to the Grenville orogeny and Mmyl to the Famatinian orogeny., Depto. de Mineralogía y Petrología, Fac. de Ciencias Geológicas, TRUE, pub

The fluorite mineralization from the La Nueva Mine, has a Sm-Nd age of 130 ± 19 Ma, and thus must be related to the Lower Cretaceous late-Gondwanic extensional and magmatic event that affected the Sierras Pampeanas Basement of Argentina. Hydrothermal fluids involved in the formation of fluorite were probably derived by mixing of two fluids, an ascending high 87Sr/86Sr one, probably equilibrated with basement metamorphics, as suggested by the very negative ENd(130) values, and a second, "descending", with a low 87Sr/86Sr value., Depto. de Mineralogía y Petrología, Fac. de Ciencias Geológicas, TRUE, pub

Preliminary results on the regional metamorphism of the Sierra Chica (Sierras Pampeanas) are reported. The work is based on a detailed textural and mineral study of high-grade cordierite-garnet metapelitic migmatites of diatexitic type. Three events are recognized on the basis of garnet textural and chemical zoning: M7 probably represents an older metamorphism and took place under subsolidus conditions; M2 is synchronous to the main regional foliation (Sn+1). The peak of metamorphism was reached at this stage under granulite facies conditions (P1= 5.7 ± O.4kb, T= 820 ± 25°C). This event is assigned to the Pampean Orogeny; M3 represents a lower P-T event which is temptatively assigned to the uplift of the previously thickened continental crust. Registered P-T conditions for this retrograde event have been determined at 4±0.5kb and 775 ± 75°C respectively., Depto. de Mineralogía y Petrología, Fac. de Ciencias Geológicas, TRUE, pub