Neoproterozoic to Early Palaeozoic events in the Sierra de San Luis: implications for the Famatinian geodynamics in the Eastern Sierras Pampeanas (Argentina)

Abstract

The application of the sensitive high-resolution ion microprobe (SHRIMP) U/Pb dating technique to zircon and monazites of different rock types of the Sierra de San Luis provides an important insight into the provenance and timing of deposition of the sedimentary precursors as well as the metamorphic and igneous history of the various basement domains. Additional constraints on the Famatinian metamorphic episode are provided by Pb/Pb stepwise leaching experiments on one staurolite and two garnet separates. The results indicate that the sedimentary precursors of the Conlara Metamorphic Complex have a maximum age of c . 590 Ma, whereas the Pringles Metamorphic Complex metasediments appear to be sourced from the Pampean orogen in the Early Cambrian. Folded xenoliths within the c . 496 Ma El Peñón pluton suggest that the host Conlara Metamorphic Complex underwent a Pampean compression. From a 208 Pb/ 232 Th monazite age of 478 Ma for a migmatite from the Nogolí Metamorphic Complex, the structural evolution of this basement complex appears to be entirely post-Pampean. Onset of the Famatinian high-grade metamorphism, between c . 500 Ma and c . 450 Ma, follows a period of crustal extension on the western outboard of Gondwana and might not be related directly to a Mid-Ordovician accretion of the Cuyania Terrane.

International Lateinamerika-Kolloquium 2009

“…490 Ma). A younger age for the last unit is also consistent with the regional trend from pre-to post-Pampean units in the southern area of the Central Andean segment Steenken et al, 2006;, which essentially show a progressive decrease of Mesoproterozoic grains and increasing of the Neoproterozoic ages. Disregarding the Cambrian (Pampean) input, similarities between Negro Peinado Formation and the older Ancasti Formation (located further east of the study region) and between Achavil Formation and the younger La Cébila Formation are sticking.…”

“…For this second profile, 2D inversion shows some of the principal features in the region, as the Salar de Atacama as a very conductive zone close to the surface, the Atacama Block under it and the precordillera as resistive bodies, the conductive zone related with the volcanic arc, and a large conductor under the Puna. The geodynamic evolution of the southwestern margin of Gondwana, based on the geochemical and isotopic provenance studies of the (meta-) sediments, has been the focus of investigation for the last ten years in the Eastern Sierras Pampeanas and the Cordillera Oriental (Central and Northwestern Argentina, López de Luchi et al 2003;Bock et al 2000;Brogioni 2001;Aceñolaza et al 2002;Thomas et al 2002;Thomas and Astini 2003;Steenken et al 2004Steenken et al , 2006Zimmermann 2005;Escayola et al 2007;.…”

Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin

“…2; 460-435 Ma stage). Differences between intermediate-pressure metamorphism in La Aguadita Formation and low-pressure metamorphism associated to extension described for the other Ordovician units croping out to the east and north (Steenken et al, 2006;Delpino et al, 2007;Fernández et al, 2008;Verdecchia, 2009) could be attributed to their diachronic development. The characteristics of the tectono-metamorphic event that affected La Aguadita Formation indicate a compressive regime that is compatible with the termination of the subduction and with the beginning of the terrane collision and lithosphere cooling and thickening (cf.…”

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).

“…7), constituida por los complejos metamórficos Nogolí, Pringles y por las filitas de la Formación San Luis. En el Complejo Metamórfico Nogolí, edades de entre 458±2 Ma y 478±4 (González et al, 2004;Steenken et al, 2006) esta secuencia, que no presenta evidencias de haber sido afectada por episodios preoclóyicos. Para el Complejo Metamórfico Pringles, Sims et al (1998) obtuvieron edades U-Pb de 452±12 Ma y 459±5 Ma, mientras que Steenken et al (2006) obtuvieron una edad algo más antigua (edad U-Pb de ca.…”

“…En el Complejo Metamórfico Nogolí, edades de entre 458±2 Ma y 478±4 (González et al, 2004;Steenken et al, 2006) esta secuencia, que no presenta evidencias de haber sido afectada por episodios preoclóyicos. Para el Complejo Metamórfico Pringles, Sims et al (1998) obtuvieron edades U-Pb de 452±12 Ma y 459±5 Ma, mientras que Steenken et al (2006) obtuvieron una edad algo más antigua (edad U-Pb de ca. 498±10 Ma) a partir de la que sugieren que el episodio de metamorfismo por el que fue afectado este complejo habría comenzado en el Cámbrico Superior y se habría extendido por alrededor de 46 Ma.…”