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Originally published as: Drobe, M., López de Luchi, M., Steenken, A., Wemmer, K., Naumann, R., Frei, R., Siegesmund, S. (2010): Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm-Nd, Pb-Pb and SHRIMP data. - Inteernational Journal of Earth Sciences, 100, 2-3, 631-657 DOI: 10.1007/s00531-010-0593-3 Int J Earth Sci (Geol Rundsch) (2011) 100:631–657 DOI 10.1007/s00531-010-0593-3 ORIGINAL PAPER Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm–Nd, Pb–Pb and SHRIMP data Malte Drobe • Mo´nica Lo´pez de Luchi • Andre´ Steenken • Klaus Wemmer • Rudolf Naumann • Robert Frei • Siegfried Siegesmund Received: 15 October 2009 / Accepted: 12 August 2010 / Published online: 13 October 2010 Ó The Author(s) 2010. This article is published with open access at Springerlink.com Abstract Whole-rock geochemical analyses using major Chepes (*1.82 Ga) and the Sierra Norte (*1.79 Ga) are and trace elements in combination with the Sm–Nd and significantly older than the data from the Sierras de Co´r- Pb–Pb isotope systems, together with SHRIMP age dating doba (1.67 Ga). The Pb data are homogeneous for the on metasedimentary rocks from the Sierras de Chepes, the different units. Only the 208Pb/204Pb ratios of some sam- Sierras de Co´rdoba, the Sierra Norte and the San Luis ples from the Sierras de Co´rdoba are higher. A late Formation in the Sierra de San Luis, have been carried out Pampean detrital zircon peak around 520 Ma from the to unravel the provenance and the geodynamic history of Sierras de Chepes is in accordance with the new data from the Eastern Sierras Pampeanas, Central Argentina. The the San Luis Formation. This is similar to the literature geochemical and the Sm–Nd data point to a slightly data from the Famatina Belt located to the northwest of stronger mafic and less-fractionated material in the prov- the Sierras de Chepes and also fits the detrital zircon peaks enance area of the Sierras de Co´rdoba when compared to in the Meso´n group. These maximum depositional ages the other units. The TDM model ages from the Sierras de were also reported from some locations in the Puncovis- cana Formation but are absent in the Sierras de Co´rdoba. An improved model for the development of the Eastern Electronic supplementary material The online version of this Sierras Pampeanas in the area between the Sierras de article (doi:10.1007/s00531-010-0593-3) contains supplementary Co´rdoba and the Puncoviscana Formation is provided. material, which is available to authorized users. This gives new insights into the late Pampean develop- M. Drobe (&) Á K. Wemmer Á S. Siegesmund ment of the Sierra de San Luis and the complex devel- Geoscience Centre of the Georg-August-Universita¨t, opment of the Eastern Sierras Pampeanas. This new model Goldschmidtstr. 3, 37077 Go¨ttingen, Germany explains the younger detrital ages in the Puncoviscana e-mail: [email protected] Formation compared with the older ages of the Sierras de M. L. de Luchi Co´rdoba. Another model of the Sierra de San Luis Instituto de Geocronologı´a y Geologı´a Isoto´pica, explains the younger depositional ages of the Pringles INGEIS, Pabello´n INGEIS, Ciudad Universitaria, Metamorphic Complex and the San Luis Formation when C1428EHA Buenos Aires, Argentina compared to the Nogolı´ Metamorphic Complex and the A. Steenken Conlara Metamorphic Complex. Additionally, the rather Institut fu¨r Geographie und Geologie, Universita¨t Greifswald, fast change of the high-grade metamorphic conditions in Friedrich-Ludwig-Jahn-Str. 17A, 17487 Greifswald, Germany the Pringles Metamorphic Complex and the low-grade metamorphic conditions in the San Luis Formation is R. Naumann GFZ Potsdam, Telegraphenberg 327 B, 14473 Potsdam, explained by extension, the ascent of (ultra) mafic material Germany and later folding and erosion. R. Frei Keywords Eastern Sierras Pampeanas Á Provenance Á Institute of Geography and Geology, University of Copenhagen, Nordic Center for Earth Evolution (NordCEE), Tectonic setting Á Gondwana margin Á Geodynamic Rˇ ster Voldgade 10, 1350 Copenhagen K, Denmark evolution 123 632 Int J Earth Sci (Geol Rundsch) (2011) 100:631–657 Introduction The aim of this study is to present new insights into the Neoproterozoic to Cambrian geodynamic history of the Metasedimentary rocks, which are a dominant component margin of Gondwana by the study of metasedimentary of the Neoproterozoic–early Palaeozoic metamorphic units (Fig. 1) of the Eastern Sierras Pampeanas, i.e. the complexes along the margin of Gondwana, may provide Sierras de Co´rdoba, Sierra Norte and the Sierras de Chepes. important information about their crustal evolution. Studies The data are compared and integrated with our previous about the provenance of (meta-) sediments have been results on the Sierra de San Luis, the southernmost mor- performed by: (1) the statistical analysis of lithoclasts in photectonic units of the Eastern Sierras Pampeanas and the thin sections (e.g. Dickinson and Suczek 1979; von Eyn- Puncoviscana Formation of the Cordillera Oriental. A atten et al. 2003; Zimmermann and Bahlburg 2003), (2) combination of major and trace elements, Nd and Pb iso- major and trace elements in minerals and whole-rock tope systematics as well as SHRIMP U–Pb zircon data are samples (e.g. Floyd and Leveridge 1987; McLennan et al. used in order to discriminate the provenance and the tec- 1990, 1993; Zimmermann and Bahlburg 2003) and (3) tonic setting of the different units. Previously suggested isotopic whole-rock systems like Pb–Pb or Sm–Nd and tectonic models for the Cambrian evolution of the margin single grain studies such as U–Pb dating of detrital zircons of Gondwana will be scrutinised by the combination of (e.g. Rapela et al. 1998; Sims et al. 1998; Bock et al. 2000; data presented here and already published results (e.g. Lucassen et al. 2001, 2002; Steenken et al. 2004, 2006). Rapela et al. 1998, 2007; Sims et al. 1998;Lo´pez de Luchi Different geological settings like passive or active et al. 1999, 2003; Bock et al. 2000; Brogioni 2001; margin, as well as autochthony or allochthoneity of the Steenken et al. 2004, 2006; Zimmermann 2005; Escayola involved units, were discussed for the Neoproterozoic to et al. 2007; Adams et al. 2008; Drobe et al. 2009; Sieg- early Palaeozoic evolution of the metasedimentary units of esmund et al. 2009). the Eastern Sierras Pampeanas and the Cordillera Oriental, (e.g. Ramos 1988; Bahlburg 1990; Astini et al. 1995; Pankhurst and Rapela 1998; Rapela et al. 1998, 2007; Bock Geological setting et al. 2000; Lucassen et al. 2000; Zimmermann and Bahl- burg 2003;Lo´pez de Luchi et al. 2003; Schwartz and The Eastern Sierras Pampeanas (Fig. 1) are composed of Gromet 2004; Steenken et al. 2004, 2006; Zimmermann uplifted basement blocks, triggered by Miocene to recent 2005; Rapela et al. 2007; Schwartz et al. 2008; Adams flat-slab subduction of the Nazca plate in the area of et al. 2008; Casquet et al. 2008; Drobe et al. 2009). 27–33° 300S (Ramos et al. 2002). The eastern sector of this The Eastern Sierras Pampeanas constitute a polyphase- morphostructural unit is mainly affected by the Pampean deformed morphotectonic unit, which was affected by three orogeny, which is characterised by late Neoproterozoic main events, the early Cambrian (580–510 Ma) Pampean, sedimentation and Ediacaran to Cambrian deformation, the late Cambrian–Ordovician (500–440 Ma) Famatinian magmatism and metamorphism (Rapela et al. 2007; Sieg- and the Devonian (420–350 Ma) Achalian orogenic cycles esmund et al. 2009). The western sector is dominated by (Toselli and Acen˜olaza 1978; Acen˜olaza and Toselli 1981; the Famatinian orogeny, which is characterised by upper Omarini 1983; Ramos et al. 1986; Acen˜olaza et al. 1988, Cambrian to early Ordovician marine sedimentation and 1990; Sims et al. 1998; Rapela et al. 1998, 2007; Stuart- Ordovician and Devonian magmatism (Sims et al. 1998; Smith et al. 1999; Bock et al. 2000; Siegesmund et al. Rapela 2000; Steenken et al. 2006). In the northern area 2004, 2009; Steenken et al. 2004, 2007; Zimmermann between 22 and 27°S, the Pampean belt in the Cordillera 2005; Drobe et al. 2009). These orogenies are related to the Oriental is dominated by the Puncoviscana Formation in accretion of different terranes integrated into the proto- which very low-grade rocks are associated with medium- Andean margin of Gondwana. The Cordillera Oriental grade rocks (Fig. 1). comprises a series of deformation belts. The Late Neo- The Sierras de Chepes, Malanza´n and Los Llanos (from proterozoic to Early Cambrian turbiditic sandstones of the now on only called Sierras de Chepes) are primarily Puncoviscana Formation (Turner 1960) were tightly folded composed of granitoid rocks (Fig. 2). The most important and affected by low-grade metamorphism in early Cam- granitoid unit is the 490 ± 5 Ma (U–Pb zircon age) Chepes brian time (Acen˜olaza et al. 2000). The low- to high-grade Granodiorite (Pankhurst et al. 1998). The metasedimentary metasedimentary successions of the Eastern Sierras rocks in the Sierras de Chepes occur as discontinuous Pampeanas were considered as an extension of the very outcrops, which are supposed to represent roof pendants of low- to low-grade metamorphic conditions in the Punco- the country rock (Pankhurst et al. 1998). These greenschist- viscana Formation (e.g. Schwartz and Gromet 2004; to amphibolite-grade rocks are largely metapelites with Steenken et al. 2004; Zimmermann 2005; Drobe et al. intercalations of silt and sandstone beds. Although most of 2009). the outcrops are smaller than 1 m, some can reach tens of 123 Int J Earth Sci (Geol Rundsch) (2011) 100:631–657 633 Fig.

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