Time constraints on the Early Palaeozoic docking of the Precordillera, central Argentina

Abstract

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Ordovician back arc foreland and Ocloyic thrust belt development on the western Gondwana margin as a response to Precordillera terrane accretion

“…This subsurface data has been later confirmed from surface geology and shows large-scale, top-to-the-west shear zones in various separate basement outcrops [e.g., Vujovich, 1994;Martino and Astini, 1995;Ramos et al, 1996Ramos et al, , 1998Casquet et al, 2001;Baldo et al, 2001] that represent various parts of the Precordillera terrane basement and that have been included in the Cuyania composite terrane [cf. Ramos, 1995].…”

“…Their thermobarometric analyses indicate that the Loma de Las Chacras metasediments were migmatized at high pressure, and illustrate the difference with migmatites and gneisses developed toward the east (into the craton) that showed signs of a Barrovian type (medium temperature-medium pressure) metamorphism [Dalquist and Baldo, 1996;Baldo et al, 2001;González et al, 2002]. This more external region to the east (e.g., Sierra de Chepes, Sierras de San Luis) has also yielded Ordovician metamorphic ages averaging 470 Ma [Pankhurst et al, 1998;González et al, 2002;Whitmeyer and Simpson, (Figure 12), immediately west of Loma de Las Chacras [Ramos et al, 1998;. The previously described Early Ordovician, high-level low-grade metamorphism within the internal part of the Famatina thrust-fold belt is consistent with the ages of associated metamorphism and deformation elsewhere and, Figure 12.…”

“…Pankhurst et al, 2000]), shortly after the beginning of flexural subsidence and the initiation of black shale deposition in the Precordillera [Thomas and Astini, 2003, and references therein]. Within the Grenville basement, which characterizes the Precordillera terrane basement, the Ocloyic event has also been confirmed from cooling ages of circa 464 Ma [Ramos et al, 1998] that overprint Grenville metamorphism in the Sierra de Pie de Palo. More recent U-Pb zircon ages of circa 460 Ma obtained by Casquet et al [2001] from high-strain zones developed within the Sierra de Pie de Palo (Figure 12), clearly indicate involvement of the eastern margin of the Precordillera terrane in the Ocloyic tectonothermal event.…”

Sr, C and O isotope geochemistry and stratigraphy of Precambrian and lower Paleozoic carbonate sequences from the Western Sierras Pampeanas of Argentina: tectonic implications

“…The position of the Caucete Group at the base of the Sierra de Pie de Palo pile of metamorphic nappes is probably the consequence of protracted thrusting of the inner part of the Famatinian mobile belt westward along the low-angle Pirquitas thrust (Fig. 1) (Ramos et al, 1998;Casquet et al, 2001). The fact that rocks with an Sr isotope signature similar to those of the Caucete Group also crop out in the Filo del Grafito can be explained as resulting from a younger (prob ably Andean) westward directed steep thrust located between the Filo del Grafito and the Sierra de Pie de Palo (Fig.…”

Edades de metamorfismo en las unidades con bajo grado de la region central del Famatina: la impronta del ciclo orogenico ocloyico (Ordovicico).Metamorphic ages of low-grade units in the central region of Famatina: The signature of the Ocloyic Orogeny (Ordovician).

“…Algunas edades obtenidas para fajas de cizalle localizadas (Fig. 7), sobre todo en el sector gondwánico del orógeno (Sims et al, 1998;González et al, 2004), pero también en la placa inferior (Ramos et al, 1998;Baldo et al, 1999;Casquet et al, 2001), indican que la deformación oclóyica con cinemática dominantemente inversa y vergencia oeste podría haberse extendido hasta el Silúrico. Cabe señalar que recientemente Thomas y Astini (2007) describen deformación con vergencia oeste afectando la cubierta sedimentaria en la Precordillera septentrional, también acotada al Ordovícico Superior.…”