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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Gondwana Research 19 (2011) 275–290 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Provenance of Ordovician clastic sequences of the San Rafael Block (Central Argentina), with emphasis on the Ponón Trehué Formation P. Abre a,⁎, C. Cingolani b, U. Zimmermann a,d, B. Cairncross a, F. Chemale Jr. c a Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa b Centro de Investigaciones Geológicas, CONICET-Universidad Nacional de La Plata, Calle 1 no. 644, B1900TAC La Plata, Argentina c Núcleo de Geociencias, Universidade Federal do Sergipe, Brazil d Present address: Department of Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway article info abstract Article history: The Ordovician Ponón Trehué Formation is the only early Palaeozoic sedimentary sequence known to record Received 23 May 2009 a primary contact with the Grenvillian-age basement of the Argentinean Cuyania terrane, in its southwards Received in revised form 26 April 2010 extension named the San Rafael block. Petrographic and geochemical data indicate contributions from a Accepted 23 May 2010 dominantly upper continental crustal component and a subordinated depleted component. Nd isotopes Available online 4 June 2010 indicate εNd of −4.6, ƒSm/Nd −0.36 and TDM 1.47 Ga in average. Pb-isotope ratios display average values for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 19.15, 15.69 and 38.94 respectively. U–Pb detrital zircon ages Keywords: Cuyania terrane from the Ponón Trehué Formation cluster around values of 1.2 Ga, indicating a main derivation from a local Provenance basement source (Cerro La Ventana Formation). The Upper Ordovician Pavón Formation records a younger Geochemistry episode of clastic sedimentation within the San Rafael block, and it shows a more complex detrital zircon age Isotope geochemistry population (peaks at 1.1 and 1.4 Ga as well as Palaeoproterozoic and Neoproterozoic detrital grains). Detrital zircon dating Detailed comparison between the two Ordovician clastic units indicates a shift with time in provenance from Ordovician Ponón Trehué and Pavón localized basement to more regional sources. Middle to early Upper Ordovician age is inferred for accretion Formations of the Cuyania terrane to the proto-Andean margin of Gondwana. © 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction The evolution of the Cuyania terrane concept could be summarized as follows: The term ‘Precordillera’ was first used for a physiographic The Cuyania terrane (Fig. 1) in central Argentina is characterized province within the deformed Andean foreland of western Argentina. by a Mesoproterozoic (Grenvillian-age) basement with depleted Pb Mainly Palaeozoic sedimentary rocks are exposed in a Cenozoic thin- isotopic signatures and Mesoproterozoic Nd model ages resembling skinned fold-thrust belt (Fig. 1) generated by flat slab subduction of the basement rocks of the same age from Laurentia (Ramos, 2004; Sato Nazca Plate (28° to 33° SL). This geological province is characterized by et al., 2004 and references therein). Several authors have proposed the extent of its fossil-rich Cambrian–Middle Ordovician carbonate para-autochthonous (Aceñolaza et al., 2002; Finney et al., 2005) platform, unique in South America and was called the Precordillera s.st. versus allochthonous (e. g. Ramos et al., 1986; Dalla Salda et al., 1992; The Precordillera terrane concept was coined later on (Ramos et al., Cingolani et al., 1992; Dalziel et al., 1994; Astini et al., 1995; Thomas 1986; Ramos, 1988) to name an early Palaeozoic Laurentian derived and Astini, 1996; Keller, 1999) geotectonic models for the early exotic block, with a Grenvillian-age basement (registered in xenoliths Palaeozoic evolution of the Cuyania terrane. No consensus has been in Tertiary volcanic rocks), that was accreted to the pre-Andean reached since all the stratigraphical, palaeontological, palaeomag- Gondwana margin (Pampia terrane). Strong evidence that the netic, and isotopic data available thought to support the palaeogeo- Grenvillian-age basement and the early Palaeozoic carbonate and graphic proximity of this terrane to Laurentia (e.g. Benedetto, 1993; siliciclastic cover extended further to the East and South of the original Lehnert and Keller, 1993; Buggisch et al., 1993; Ramos et al., 1998; proposed terrane, lead Ramos et al. (1998) to introduce the concept of a Thomas et al., 2001; Rapalini and Cingolani, 2004), can also be greater Cuyania composite terrane. This terrane incorporates the early interpreted as indicating a Gondwanan signature (Aceñolaza et al., Palaeozoic Precordillera s.st. as well as its southern extension into the 2002; Finney, 2007). San Rafael and Las Matras blocks, along with adjacent parts of the Western Pampeanas Ranges (e.g. Pie de Palo Range) that comprise a Grenvillian-age basement (Ramos, 2004). However, some authors ⁎ Corresponding author. Tel.: +27 727195504; fax: +54 221 4215677. ‘ E-mail addresses: [email protected] (P. Abre), as Finney, (2007) described the Cuyania terrane as the greater [email protected] (C. Cingolani), [email protected] (F. Chemale). Precordillera’ or ‘Precordillera terrane’. Whether minor ranges from 1342-937X/$ – see front matter © 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2010.05.013 Author's personal copy 276 P. Abre et al. / Gondwana Research 19 (2011) 275–290 Fig. 1. Satellite image based map showing Cuyania terrane boundaries as dashed lines and blocks boundaries as continuum lines (based on Ramos et al., 2000; Astini and Dávila, 2004; Porcher et al., 2004). All the entities forming the Cuyania terrane develop a Grenvillian-age basement characterized by Nd, Sr and Pb depleted isotopic signatures (Ramos, 2004; Sato et al., 2004). Righter inlet: location of neighbouring terranes. the Western Pampeanas Ranges form as well part of this crustal block is (Ramos et al., 1996; Fig. 1). Despite the disagreement regarding the still under debate (e.g. Umango Range; Porcher et al., 2004). geotectonic evolution of the Cuyania terrane, provenance analyses of The western boundary of the Cuyania terrane coincides with the its early Palaeozoic sedimentary record using modern techniques are western boundaries of the Precordillera s.st., and the San Rafael scarce (e.g. Loske, 1994; Cingolani et al., 2003; Naipauer, 2007; and the Las Matras blocks, being delimited by the Chilenia terrane Gleason et al., 2007; Naipauer et al., 2010). Author's personal copy P. Abre et al. / Gondwana Research 19 (2011) 275–290 277 Two Ordovician units are found within the San Rafael block, two members, which comprise Conodont Biozones (Heredia, 2006). named the Ponón Trehué (Darriwilian to Sandbian) and Pavón The lower member (Peletay) is composed of conglomerates and (Sandbian) Formations. The main purpose of this paper is to examine conglomeratic arkoses, limestones, quartz–arenites and black shales. newly obtained data from the Ponón Trehué Formation using The upper member (Los Leones) is composed of mudstones, petrography, whole-rock geochemistry and isotope geochemistry siltstones, arenites and conglomeratic arenites. Blocks of limestones, (Sm–Nd and Pb–Pb systematics). U–Pb detrital zircon laser ablation granitoids, gneisses and amphibolites are common in the upper part dating from the Ponón Trehué and Pavón Formations is also of the younger member (Bordonaro et al., 1996). The limestone presented. Comparison of the provenance indicators of the Ponón blocks bearing invertebrate fossils resemble the Lower/Middle Trehué Formation, which is the only unit that directly contacts the Ordovician La Silla and San Juan Formations of the Precordilleran Cerro La Ventana Formation (basement of the San Rafael block), with platform (Heredia, 2006), while the crystalline clast and block the Pavón Formation, reveals important information of the sources for compositions resemble Cerro La Ventana Formation basement, the clastic deposition during the proposed Ordovician accretion of the indicating substantial reworking of local lithologies. The continental Cuyania terrane. sedimentary Carboniferous arkosic sandstones overlie the Ponón Trehué Formation through either an unconformity or a fault contact 2. Geological setting of the Ponón Trehué Formation (Fig. 3). The Ponón Trehué Formation is exposed in three areas (Fig. 3). The The Darriwilian to Sandbian Ponón Trehué Formation is a fossil- outcrops located to the south of the Ponón Trehué Creek (Fig. 3, areas rich, carbonate-siliciclastic sequence unconformably overlying 2 and 3) were synchronously named as Ponón Trehué Formation Mesoproterozoic