Provenance Study on Neoproterozoic Rocks of Nw Argentina: Puncoviscana Formation – First Results

U N I V E R S I D A D D E C O N C E P C I Ó N DEPARTAMENTO DE CIENCIAS DE LA TIERRA 10° CONGRESO GEOLÓGICO CHILENO 2003

PROVENANCE STUDY ON NEOPROTEROZOIC ROCKS OF NW ARGENTINA: PUNCOVISCANA FORMATION – FIRST RESULTS

ZIMMERMANN, U.1

1Dep.of Geol., RAU University, Auckland Park 2092, South Africa [email protected]

INTRODUCTION Since more than 20 years the western border of Gondwana is object of controversies related to the basic question if crustal growth is related to terrane accretion or to “recycling” of the same crustal rocks during the Vendian and Lower Paleozoic. Different hypotheses were developed regarding the evolution of that margin. One of the key element to understand the crustal evolution, is the Vendian to Lower Cambrian so-called PVF. Turner (1960) described rock successions in northwestern Argentina (Fig. 1) of Pre-Ordovician age comprising greywackes and sand- and siltstones, but dominated by pelites as the PVF. Afterwards, it was established that mostly all Vendian to Lower Cambrian very-low to low grade metasedimentary rocks in the region are classified, such as Suncho, Negro Peinado or La Cébila Formation (e.g. comp. in Aceñolaza et al., 1988), are equivalents of the PVF. Widely distributed medium- to high-grade metasedimentary rocks (Fig. 1), those rocks were interpreted as exhumed deeper crustal levels of the PVF (Willner, 1990). Other authors deny this opinion and interpret the different metamorphic rocks related to different events, consequently of different ages (Mon and Hongn, 1990). Based on only punctual petrographic work, the depositional area was defined as a passive margin based on petrography and mainly major element geochemistry (Jezek, 1990, Willner et al., 1985, Rossi Toselli et al., 1997), or on preliminary trace element data (Do Campo and Ribeiro Guevara, 2002). Only few publications interpret the entire formation as a product of an evolution from passive margin to back-arc deposits (Omarini et al., 1999) or as foreland deposits (Kraemer et al., 1995; Keppie and Bahlburg, 1999). This contribution likes to review new and published petrographic and geochemical data based on a modern approach in provenance studies, including the modelling and quantification of alteration, rock composition and tectonic setting (e.g. McLennan et al., 1990, 1993; Bahlburg and Floyd, 1999). Finally, a working hypothesis is established to give a productive input in the current discussion.

PROBLEMS The difficult situation of understanding the metasedimentary deposits of the Puncoviscana Foramtion and equivalents is based on mainly four problem complexes:

1. A complete lithostratigraphic column is lacking: The PVF is composed of mainly shales, siltstones, rare coarse-grained sandstones, greywackes, conglomerates and few carbonates. However, it is not clear if these lithofacies are repetitive or not.

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2. The depositional and diagenetic age of the formation is controversial: Intrusive ages of mainly felsic plutonites and subordinated mafic magmatites are determined with different dating techniques, pre-dates the PVF to Lower Cambrian to Uppermost Vendian 500-530 Ma (comp. in Rapela et al., 1992, 1998; Pankhurst and Rapela, 1998). K/Ar data on whole rock samples of the sedimentary successions (Adams et al., 1990) coincide with trace fossil interpretations in some outcrops (e.g. Durand and Aceñolaza, 1990) and point to a similar depositional age. However, Do Campo et al. (1999) argue, their K-Ar age dating on authigenic single grains (K/Ar on mica) reflect an older age for deposition (630 Ma) and diagenesis (580 Ma).

3. Relation between medium- to high-grade and low grade metasedimentary rocks: The Sierras Pampeanas s.l. contains a high amount of medium- to high grade metamorphic rocks, associated are gneisses and migmatites. Willner (1990) shows arguments to interpret those rocks as deeper crustal levels of the PVF, where Mon and Hongn (1991) find reasons to state a different tectonic evolution. However, an unresolved problem, are the occurrences of low-grade (PVF and equivalents) metasedimentary rocks in the higher grade terrains.

4. Unresolved geodynamic and paleotectonic setting of the Puncoviscana basin: The rocks of the PVF were interpreted based on petrological and mainly major element data (e.g. Willner et al., 1985; Rossi Toselli, 1997) and trace element data for the region in the Puna (Bock et al., 2000; Do Campo and Ribeiro Guevara, 2002; Fig. 1 nr. 1) as passive margin deposits, probably related to a rifting process. Subsequentely the units were folded during the Pampean Orogeny. Kraemer et al. (1995) and Keppie and Bahlburg (1999) interpret the same deposits as a foreland basin infill, evolved syntectonically during the collision of Pampia with the western border of Gondwana, represented by the (Sierra) Córdoba magmatic arc (Rapela et al., 1998). However, the petrological, geochemical and isotopegeochemical data-set is too sparse to model a provenance for the whole formation. For quantitative petrography in a sense of the point-counting method of Gazzi-Dickinson a scarcity of representative distribution of suitable rocks has to be stated.

SAMPLING LOCALITIES AND DESCRIPTION Samples were taken from several localities in the southern region (Fig. 1) and combined with published geochemical data of outcrops in the central part and northern part (Willner et al., 1985, 1990, Bock et al., 2000) as well with data from Precambrian formations of the Famatina Range (Rossi et al., 1997, Zimmermann et al., in press.)

Area 1: Puna and Cordillera Oriental: Campo Volcán (S25°39’ W67°47’2; Fig. 1; 7 samples; VOL): quartz-rich and plagioclase-poor red pelites, siltstones. The rocks are preliminarily described as Volcán Formation (Zimmermann and van Staden, 2002). - Northern Puna and Cordillera Oriental (16 samples): Purmamarca, El Muñano, Rio Taique and Quebrada del Toro (Fig. 1): sandstones, pelites, greywackes, litharenites (Jezek, 1990; Do Campo et al., 1999; Bock et al., 2000). Willner et al. (1985) presented mostly major element analyses, Bock et al. (2000) mainly trace elements geochemistry. Newer data from Do Campo and Ribeiro Guevera (2002) could not incorporated, because data sets were not available during the writing of the manuscript.

Area 2: Sierra Ambato: Siján (35 samples, ((±S28°15’ W66°08’; Fig. 1)): pelites, siltstones are overlain by conglomerates and greywackes, and are named preliminarily Rincón Formation (Zimmermann and van Staden, 2002). The red pelites were compared with those of Volcán (see above) and it could be shown that they show similarities, in mineralogy, deformation and geo- chemistry (Zimmermann and van Staden, 2002). - Concepción (S28°38’ W66°03’; 7 samples; Fig. 1): bluish feldspathic metaarenites, -greywackes (matrix: 15-20%), Qt70-80 F15-25 L5-10. The rocks are named El Quemadito Formation (van Staden and Zimmermann, 2002).

Area 3: Sierra Famatina: Negro Peinado and La Aguadita Formation (19 samples) were sampled in the same locations to those of Rossi et al. (1997). The relation ship between the two formations is not clear. Dark fine-grained rocks (pelite to siltstones), dominated by sub-rounded quartz (60%) with scarce feldspar (10%) and metamorphic lithoclasts (< 2%) (Rossi et al., 1997). The new data are combined with the most representative samples from Rossi et al. (1997). Area 4: Cachi (Valles Calchaquies): Cuesta de Obispo, Sierra de Amblayo, Cachi, El Escoipe, Quebrada Don Bartolo (Fig. 1) and are composed mostly of quartz and high amounts of plagioclase (P/F 0.68-0.98), as well as sedimentary lithoclasts (Jezek, 1990).

Area 5: Tucumán: Sierra San Javier, Rio Choromoro, Rio Gonzalo and Sierra de Nogalito close to the city of Tucumán (Fig. 1). The petrographic composititon is similar to Area 4 (Jezek, 1990). For both outcrops mainly major element geochemistry and few trace elements were carried through (Willner et al., 1985).

The metasedimentary rocks in all introduced outcrops are typically polyphase deformed to recognize them as pre-Ordovician deposits. Other outcrops which will not be discussed in the following chapters, but which were sampled are San Antonio de los Cobres, Rio Taique, Quebrada Randolfo, La Pedreda, El Corralito (Puna and Cordillera Oriental), around Siján and Pomán, La Cébila (Sierra Ambato), Suncho (Fig. 1, n°. 6), Molinos, Seclantes (Valles Calchaquies) and Choromoro (Tucumán).

PETROGRAPHY The framework mineral composition was quantified using the point-counting method of Gazzi and Dickinson as described by Ingersoll et al. (1984). Representative datasets for the PVF are difficult to arise because of the scarcity of applicable sandstones. In most of the outcrops the rocks are strongly altered what render more difficult the distinction (f.e. feldspars). The data presented by Jezek (1990) vary for quartz between 50-89 %, for feldspar between 4-38%) and lithoclasts between 8-49%. The rocks comprise a very high amount of plagioclase (P) in relation to alkali feldspar (AFS; P/AFS 0,68-1,0!). The partly absence of AFS and extremely low abundance of volcanic lithoclasts are a combination which is difficult to classify and interpret. It differs in general from anlyses by XRD of the rocks in the Puna, Siján and point-counting of rocks from Concepción, as shown above (e.g. Zimmermann and van Staden, 2002). The results could lead to model a depositional area similar to a rifted or passive margin. The immaturity of the coarse grained rocks, which points to a short transportation, would be an expected characteristic for a rift environment. However, thick packages of sandy to silty turbidites associated with different shales indicate more likely a shelf position. However, a typical rift sedimentation succession (Einsele, 1992: 437ff) cannot be observed. In contrary, conglomerates are rare and with small thicknesses, an exception is the outcrop at Suncho (Fig. 1, n°. 6). Basic volcanic activity is stated during the deposition of the PVF (comp. in Coira et al., 1990). However, only relicts of rhyolitic and dacitic volcanism are preserved in conglomerates of the Suncho Formation (Durand, 1990, van Staden and Zimmermann, subm.). In other coarse grained rocks no trace of volcanic activity is stated (e.g. van Staden and Zimmermann, subm.).

GEOCHEMISTRY In contrast to petrography geochemical analysis could be applied to fine and coarse grained clastic sediments for provenance purposes. Certain elements (like REEs, Th, and Sc) in terrigeneous sediments that are less easily mobilized provide information about the composition of the source (e.g. McLennan et al., 1990). Geochemistry can also give insights in identification of constituents that might be important to tectonic interpretations. REE are employed as reliable provenance indicators because they tend to be transferred unfractionated into sediment and therefore reflect the average REE composition of the source (McLennan, 1989). If geochemical techniques are applied to mineralogically altered samples, like in this case, they can aid to quantify the occurrence and/or the extent of some secondary processes (e.g. Fedo et al., 1995). Major elements – composition and alteration

Moderate SiO2-contents between 58 and 82% characterize the sedimentary rocks. Three samples from the La Aguadita Formation (LA2) are different from all samples as they show lower silica and elevated Fe2O3 and MgO abundances. Both samples are very fine grained and interpreted here as basic to intermediate ashes interlayered in siliciclastic rocks of the same outcrop, and should be seen separately in the whole discussion. The chemical index of alteration (CIA; Nesbitt and Young, 1984) ranges from about 70 to 80 (Fig. 2). Chemical weathering strongly affects the major-element geochemistry and mineralogy of siliciclastic sediments (e.g. Nesbitt and Young, 1982). High CIA values, as here observed, reflect the removal of labile cations (e.g. Ca2+, Na+, K+) relative to stable constituents (e.g. Ti4+) during weathering. In Fig. 2 the CIA is combined with the A-CN-K diagram, mole percent Al2O3 plotted versus CaO* + Na2O versus K2O where CaO* includes only calcium associated with silicate minerals (Nesbitt and Young, 1984). Typical unweathered igneous rocks, representing upper continental crust, fall in a field around 50% Al2O3, average shale is plotted for reference. The estimated weathering trend of a homogeneous source, based on the removal of alkali and earth alkali elements during weathering, (stippled arrow in Fig. 20, the interpreted weathering path (black arrow), the trend of metasomatic K addition (after Fedo et al., 1995) towards the K-apex (Fig. 2). The samples of all localities show a homogeneous and pronounced deviation from the expected trend, interpreted as a K-addition during K-metasomatism of kaolinite in weathered residues to illite, and as a substitution of K for Ca and Na in feldspar. The strong mobilization of alkali elements is reflected in all attempts to use major-elements for provenance aspects after Bhatia (1983) and Roser and Korsch (1986, 1988). The samples of each formation plot with a broad spread in provenances. Consequently, the use of major-elements characterizing provenance or tectonic setting of the PVF should be done carefully. It is suggested, according to results of Bahlburg (1998) and Zimmermann and Bahlburg (in press), that mobility of major-elements distorts provenance information for Lower Paleozoic sedimentary rocks, to interpret major-element geochemistry only as a measurement of alteration.

TRACE ELEMENTS The whole sample suite has homogeneously a rhyodacitic to dacitic compositions based on Zr/Ti and Nb/Y ratios (according to Winchester and Floyd, 1977). Exception is one of the two ashes, which has characteristics of trachyandesitic rocks. None of the sedimentary samples shows an enrichment in Cr, V, Ni or Sc that would be an indicator for a mafic (ophiolitic) precursor (Floyd and Leveridge, 1987). REE spider diagrams for all the formations (Fig. 3) show relatively uniform patterns comparable to PAAS (Post-archaen Average Australian Shale composite, Nance and Taylor, 1976). Comparing these values to the PAAS, the Negro Peinado Formation is enriched in all REE, Volcán and Siján Formations show similar pattern, the samples of the northern Puna and Cordillera Oriental are slightly depleted in REE. The other formations show depleted LREE and enriched HREE concentrations. LaN/YbN (the subscript “N” indicates chondrite normalized values) ratios are generally close or slightly depleted related to average Upper continental crust (UCC, after McLennan, 2001) value of 9.2. Depleted in REE are the ashes of La Aguadita Formation (LA2), and point to pattern similar as basalts. Eu/Eu* ratios are constant between 0.45 and 0.71 for all, but of LA2, which show values of about 0.9-1.0.

A good tracer for provenance is the ratio Th/Sc, as Th is highly incompatible and enriched in felsic rocks, and Sc traces a mafic component (e.g. Taylor and McLennan, 1985). Most all siliciclastic samples plot above the UCC of 0.79 (McLennan, 2001) and show a narrow scatter. Samples from Concepción, Sierra Famatina and the northern Puna and Cordillera Oriental show values close to 1,0 for Th/Sc (Fig. 4). The values for the samples from Siján and Volcán are higher (1.22 and 1.52). However, mainly all samples show only a slight trend towards a recycling component: Zr/Sc ratios vary between 8.73 for the non-volcanic samples of La Aguadita Formation to 27.87 for the Volcán Formation. There is no geographical trend to observe. Elevated Zr/Sc ratios do not coincide with grain sizes, except in the Negro Peinado Formation.

Interpretation of the trace element geochemistry Most of the trace element ratios pointing to UCC with few exceptions, underlining the scarcity of a mafic or ultramafic component. However, the volcanic samples of the La Aguadita Formation (LA2) show trace element composition related to a volcanic arc environment. For all other samples the trace element ratios like Th/Sc, Zr/Sc, Th/U, REE patterns, normalized ratios of LaN/YbN, LaN/SmN and GdN/YbN as well as Eu/Eu* values point to UCC. However, the formations show a spread, especially in Zr/Sc values (Fig. 4), which could reflect a variable recycling or different fractionated source areas. Source areas like medium- to high-grade metamorphic rocks including para- and orthogneisses of mainly felsic to intermediate composition combined with the influence of igneous rocks are likely. According to GdN/TbN and Eu/Eu* values no Archean component can be detected (McLennan, 1989).

TECTONIC SETTING Trace element ratios such as La/Th, La/Sc, and Ti/Zr have been used to discriminate sandstones of different tectonic settings (Bhatia and Crook, 1986; Floyd and Leveridge, 1987; McLennan et al., 1990, 1993). Such an approach has to be used with caution because it has been shown that specific tectonic settings do not necessarily produce sedimentary rocks with unique geochemical signatures (McLennan, et al., 1990; Bahlburg, 1998), however the use for coarse- and fine- grained rocks could be shown (e.g. McLennan et al., 1990; Zimmermann and Bahlburg, in press). In Fig. 5 most of the samples plot in the fields continental island arc and active continental margin. However, the volcanic samples of La Aguadita Formation points to an oceanic island arc reflecting a strong mafic influence. The interpretation leads to an arc-related or active continental margin setting, which cannot be confirmed by other trace element compositions. Nearly all samples of all formations have normalized to average upper continental crust (after McLennan, 2001), depleted Pb, enriched Nb and Ta (Fig. 6) and enriched Ti concentrations. After Hofmann (1988, 1997), arc derived rocks show exactly contrary characteristics. The three volcanic rocks of LA2 accomplish an arc related signature. 4 samples of the Siján Formation show negative Nb and Ta anomalies, but they are high in silica (77-81%) and diluted in all trace elements including REE. The sum of the latter is ≤300 ppm, whereas other samples of the same formation range between 400-500 ppm. A difference of about 30%, comparable with the difference in silica composition, can be stated, and interpreted as a dilution effect. The restricted recycling component, suggested by the low Zr/Sc ratios (Fig. 4) and low Zr concentrations, shifts the samples away from the upper crust composition (from the Zr/10 apex in Fig. 5). As Hf and Zr are usually concentrated in heavy minerals, especially in zircon, this effect can be interpreted as a result of restricted recycling. The UCC nature of the PVF was shown in Figs. 3 and 4, and is obvious in the selected element ratios of Fig. 6. Combining Eu/Eu* values, as an indicator for provenance, with the mentioned trace element ratios, a trailing edge setting shows mainly comparable values in the characteristics after McLennan et al. (1990, 1993), with Th/Sc ≥ 1, Th/U > 3.8, Eu/Eu* 0.6–0.7, and LaN/YbN between 4.4 and 13.6. It is possible to interpret the metasedimentary rocks of the PVF as first or second cycle deposits, which were not well mixed. However, a significant amount of sedimentary lithoclasts could be observed, which points a to cannibalistic reworking or an older sedimentary source in the region. Nd-isotopes of Tremadocian deposits in the Puna showed older Nd-model ages (2.1-2.2 Ga; Zimmermann and Bahlburg, in press), than rocks from the Puncoviscana Foamtion (1.5-1.8 Ga; Bock et al., 2000).

CONCLUSIONS Different outcrops of very-low to low-grade metamorphic rocks of the PVF were sampled to model the provenance of and leads to following preliminary conclusions:

Representative data for the whole PVF from sandstones using the quantifying petrographic method after Gazzi-Dickinson are not possible to carry through, because (i) of the low abundance of coarse grained sandstones and (ii) the unmaturity of the rocks. The few petrographic data points to a mixed provenance, related to a collisional (?) orogen, and Jezek (1990) interpret the signature as a “fold-thrusted foreland deposits”, according to the here presented model. Major element geochemistry shows a high chemical index of alteration (CIA) between 70 and 82 related to a substantial K-metasomatism. The pronounced mobility of alkali and earth-alkali elements yield provenance discrimination diagrams based on major elements not useful.

Trace element geochemistry could define the rocks of all formations as mostly upper continental crust related with only a slight recycling component, and no significant geochemical trend in N-S or E-W directions. Three samples of the La Aguadita Formation are interpreted as probable retro- arc volcanics or rift basalts in an arc related tectonic setting. This does not coincide with data of the siliciclastic rocks. Trace element geochemistry combined with petrography suggests a depositional area not far away from the sources, supported by the immaturity of the rocks, the low recycling component and the notable spread in the compositions of the mainly fine-grained rocks, which points to not well mixed detrital material. This is expressed in a shifting of the samples away from a rifted margin or an active continental margin to a more arc-like composition. This signature is not supported by geochemical characteristics like low Ti, Nb, Ta and high Pb anomalies, Th/Sc or Zr/Sc ratios. In contrary, mostly all samples show enriched values in Nb and Ta, UCC values of Th/Sc. The siliciclastic rocks of the different formations were not deposited in a volcanic arc. The mafic ashes of the La Aguadita Formation could be transported sub-areal from an adjacent volcanic arc, probably the Sierra Córdoba. However, as no further data on the ashes are available, this is a first hypothesis to combine the data at this point. The upper crustal composition combined with their low recycled component and the immature mineralogy denies a passive margin setting and suggests depositional areas like continental rifts or foreland basins. A strong argument against a rift interpretation is the absence of a typical rift sedimentation sequence. The rocks are characterized mainly by monotonous turbiditic sequences of different, but mainly fine, grain-sizes, more typical for deeper shelf regions. The introduced foreland basin model would favor the collision of Pampia and Western Gondwana during the Uppermost Neoproterozoic and the syntectonic evolution of the Puncoviscana basin. This is a contribution to the IGCP 436 Pacific Gondwana margin.

Acknowledgments: The author thanks RAU for financial support and especially Mr. R. Lucero (Mina Rodohuasi in Catamarca) for logistic support, Fernando Hongn and Heinrich Bahlburg for inspiring discussions.

REFERENCES Aceñolaza, F.G., Miller, H and Toselli, A.J. 1988. The Puncoviscana Formation (Late Precambrian-Early Cambrian). Sedimentology, tectonometamorphic history and age of the oldest rocks of NW Argentina. In: The southern Central Andes: contributions to structure and evolution of an active continental margin. Bahlburg, H. Breitkreuz, C. and Giese, P. (Eds), Lect. Notes Earth Sci.. Vol. 17. p. 25-38. Adams, C., Miller, H. and Toselli, A.J. 1990. Nuevas edades de metamorfismo por el método K-Ar de la foramación Puncoviscana y equivalents, NW de Argentina. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p. 209-219. Bahlburg, H. 1990. The Ordovician basin in the Puna of NW Argentina and N Chile: geodynamic evolution from back-arc to foreland basin. Geotektonische Forschungen. Vol. 75. p. 1-107. Bahlburg, H. 1998. The geochemistry and provenance of Ordovician turbidites in the Argentine Puna. In: The Proto-Andean Margin of Gondwana. Pankhurst R.J. and Rapela C.W. (Eds.). Geological Society, London Spec. Publ. Vol. 142. p. 127-142. Bahlburg, H. and Floyd, P.A. 1999. Advanced techniques in provenance analysis of sedimentary rocks. Sed. Geol. Vol. 124. p. 1-220. Bhatia, M. R. 1983. Plate tectonics and geochemical composition of sandstones. J. Geol. Vol. 91. p. 611-627. Bhatia, M. R. and Crook, K.A.W. 1986. Trace element characteristics of graywackes and tectonic setting discrimination of sedimentary basins. Contribution to Mineralogy and Petrology. Vol. 92. p. 181-193. Bhatia, M.R. and Crook, K.A.W. 1986. Trace elements characteristics of greywackes and tectonic setting discrimination of sedimentary basins. Contribution to Mineralogy and Petrology. Vol. 92. p. 181-193. Bock, B., Bahlburg, H., Wörner, G. and Zimmermann, U. 2000. Tracing crustal evolution in the southern Central Andes from Late Precambrian to Permian with geochemical and Nd and Pb isotope data. Journal of Geology. Vol. 108. p. 515-535. Coira, B., Manca, N. & Chayle, W. 1990. Registros Volcanicos en la Formación Puncoviscana. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p 53-60 Dickinson, W.R. 1985. Interpreting provenance relations from detrital modes of sandstones. In Provenance of Arenites. Zuffa, G.G. (Ed.). p. 3-33. Do Campo, M., Nieto, F., Omarini, R. and Ostera, H. 1999. Neoproterozoic K-Ar ages for the metamorphism of the Puncoviscana Formation, northwestern Argentina. III ISAGI. Villa Carlos Páz. Argentina. Abstract volume. p. 37-42. Do Campo, M. and Ribeiro Guevara, S.R. 2002. Geoquimica de las sequencias clásticas de la Formación Puncoviscana (Neoproterozoico, NO Argentina), proveniencia y marco tectónico. XV Congreso Geológico Argentino. Calafate. Argentina. Durand, F.R. 1990. Los conglomerados del Ciclo Pampeanos en el Noroeste Argentino. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p. 61-70. Durand, F.R. and Aceñolaza, F.G. 1990. Caracteres biofaunísticos, paleoecológicos y paleogeográficos de la Formación Puncoviscana (Precámbrico Superior-Cámbrico Inferior) del Noroeste Argentino. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p. 71-112. Einsele, G. (1992): Sedimentary Basins. Springer. 628 pp. Heidelberg. Fedo, C.M., Nesbitt, H.W. and Young, G.M. 1995. Unravelling the effects of potassium metasomatism in sedimentary rocks and paleosoils, with implications for paleoweathering conditions and provenance. Geology. Vol. 23. p. 921-924. Floyd, P.A. and Leveridge, B.E. 1987. Tectonic environment of the Devonian Gramscatho basin, south Cornwall: Framework mode and geochemical evidence from turbidite sandstones. J. Geol. Soc. London. Vol. 144. p. 531-542. Grissom, G.C., DeBari, S.M. and Snee, L.W. 1998. Geology of the Sierra de Fiambalá, northwest Argentina: Implications for Early Palaeozoic Andean tectonics. In: The Proto-andean Margin of Gondwana. Pankhurst R.J. y Rapela C.W. (Eds.). Geological Society, London, Spec. Publ. Vol. 142. p. 297-323. Hofmann, A. 1988. Chemical differentiation of the Earth: The relationship between mantle, continental crust and oceanic crust. Earth Planet. Sci. Lett.. Vol. 90. p. 297-314. Hofmann, A. 1997. Mantle geochemistry: the message from oceanic volcanism. Nature. Vol. 385. p. 219-229. Ingersoll, R.V, Bullard, T.F., Ford, R.L., Grimm, J.P., Pickle, J.D. and Sares, S.W. 1984. The effect of grain size on detrital modes: a test of the Gazzi-Dickinson point-counting method. J. Sed. Petrol. Vol. 54. p. 103-116. Jezek, P. 1990. Analisis sedimentológico de la Formación Puncoviscana entre Tucumán y Salta. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p 9-35 Keppie, J.D. and Bahlburg, H. 1999. Puncoviscana Formation of northwestern and central Argentina: Passive margin or foreland basin deposits?. In Laurentia-Gondwana connections before Pangaea. Ramos, V.A. and Keppie, J.D. (Eds), Geol. Soc. Am. Spec. Pap. Vol. 336. p. 139-144. Kraemer, Escayola, M.P. and Martino, R.D. 1995. Hipótesis sobre la evolución tectónica neoproterozoica de las Sierras Pampeanas de Córdoba (30°40’-32°40’), Argentina. Revista de la Asociación Geológica Argentina. Vol. 50. p. 47-59. Lucassen, F., Becchio, R., Wilke, H.G., Franz, G., Thirlwall, M.F., Viramonte, J. and Wemmer, K. 2000. Proterozoic-Paleozoic development of the basement of the Central Andes (18-26°S) – A mobile belt of the South American Craton. Journal of South American Earth Sciences. Vol. 13. p. 697-715. McLennan, S.M. 1989. Rare earth elements in sedimentary rocks: Influence of provenance and sedimentary process. In: Geochemistry and Mineralogy of Rare Earth Elements. Lipin, B.R. and McKay, G.A. (Eds), Mineralogical Society of America, Rev. Mineral. Vol. 21. p. 169-200. Mclennan, S.M., 2001. Relationships between the trace element composition of sedimentary rocks and upper continental crust, G- cubed. Vol. 2. 2000gc000109. McLennan, S.M., Taylor, S.R., McCulloch, M.T. and Maynard, J.B. 1990. Geochemical and Nd-Sr isotopic composition of deep- sea turbidites: Crustal evolution and plate tectonic associations. Geochim. Cosmochim. Acta. Vol. 54. p. 2015-2050. McLennan, S. M., Hemming, S., McDaniel, D.K. and Hanson, G.N. 1993. Geochemical approaches to sedimentation, provenance and tectonics. In Processes controlling the composition of clastic sediments. Johnsson M.J. and Basu, A. (Eds.). Geological Society of America, Spec. Publ. Vol. 284. p. 21-40. Mon, R. and Hongn, F. 1991. The structure of the Precambrian and Lower Paleozoic Basement of the Central Andes between 22° and 32° Lat.. Geologische. Rundschau, Vol. 80, p. 745-758. Nance, W.B. and Taylor, S.R. 1976. Rare earth element patterns and crustal evolution - I. Australian post-archean sedimentary rocks. Geoquim. et Cosmoquim. Acta. Vol. 40. p. 1539-1551. Nesbitt, H.W. and Young, Y.M. 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature. Vol. 299. p. 715-717. Nesbitt, H.W. and Young, Y.M. 1984. Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations. Geochim. Cosmochim. Acta. Vol. 48. p. 1523-1534. Omarini, R.H., Sureda, R.J., Götze, H.J., Seilacher, A. and Pflüger, F. 1999. Puncovisca folded belt in northwestern Argentina: testimony of Late Proterozoic Rodininia fragmentation and pre-Gondwana collisional episodes. Int. J. Earth Scs. Vol. 88. p.76-97. Pankhurst, R., Rapela, C., Saavedra, J., Baldo, E., Dahlquist, J., Pascua, I. and Fanning, C. 1998. The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid Ordovician continental arc on the Gondwana margin. In: The Proto-Andean Margin of Gondwana. Pankhurst, R.J. and Rapela, C.W. (Eds.). Geological Society, London Spec. Publ. Vol. 142. p. 181-217. Rapela, C.W., Coira, B., Toselli, A. and Saavedra, J. 1992. El magmatismo del Paleozoico en el Sudoeste de Gondwana. In Paleozoico Inferior de Ibero-América. Gutiérrez Marco, J.G., Saavedra, J. and Rabano, I. (Eds.). Univ. de Extremadura. p. 21-68. Rapela, C.W., Pankhurst, R.J., Casquet, C., Baldo, E., Saavedra, J., Galindo, C. and Fanning, C.M. 1998. The Pampean Orogeny of the southern proto-Andes: Cambrian continental collision in the Sierras de Cordoba. In: The Proto-Andean Margin of Gondwana. Pankhurst, R.J. and Rapela, C.W. (Eds.). Geological Society, London Spec. Publ. Vol. 142. p. 181-217. Roser, B.P. and Korsch, R.J. 1986. Determination of tectonic setting of sandstone-mudstone suites using SiO2 and K2O/Na2O ratio. J. Geol. Vol. 94. p. 635-650. Roser, B.P. and Korsch, R.J. 1988. Provenance signatures of sandstone-mudstone suites determined using discrimination function analysis of mayor-element data; Chem. Geol. Vol. 67. p. 119-139. Roser, B.P., Cooper, R.A., Nathan, S. and Tulloch, A.J. 1996. Reconnaissance sandstone geochemistry, provenance, and tectonic setting of the lower Paleozoic terranes of the West Coast and Nelson, New Zealand. New Zeal. J. Geol. Geophys. Vol. 39. p. 1-16. Rossi, J.N., Durand, F.R., Toselli, A.J. and Sardi, F.G. 1997. Aspectos estratigráficos y geoquímicos comparativos del basamento metamórfico de bajo grado del Sistema de Famatina, Argentina. Rev. de la Asociación Geológica Argentina. Vol. 52. p. 469-480. Taylor, S.R. and McLennan, S.M. 1985. The Continental Crust: its Composition and Evolution. Blackwell. 312 pp. Oxford. Turner, J.C.M. 1960. Estratigrafía de la Sierra de Santa Victoria y adyacencias, Boletín de la Academia Nacional de Ciencias, Córdoba. Vol. 41. p. 163-196. Van Staden, A. and Zimmermann, U. 2002. Very-low to low-grade sedimentary rocks from Concepción (Sierra de Ambato, Cata- marca Province): An equivalent of the Puncoviscana Formation? XV Congr. Geol. Arg.. Calafate. Argentina. Vol. 2. p. 787-793. Van Staden, A. and Zimmermann, U. (subm.) Tillites or ordinary conglomerates? Provenance studies on diamictites of the Neoproterozoic Puncoviscana in NW Argentina. XI Congreso Geológico Chileno. Concepción. Chile. 2003 Willner, A. 1990. División tectonometamórfica del basamento del Noroeste Argentino. In: El Ciclo Pampeano en el Noroeste Argentino. Aceñolaza, F.G., Miller, H. and Toselli, A.T. (Eds.). Serie: Correlación Geológico. Vol. 4. p. 113-159. Willner, A., Miller, H. and Jezek, P. 1985. Geochemical features of an Upper Precambrian-Lower Cambria greywacke/pelite sequence (Puncoviscana trough) from the basement of the NW-Argentine Andes. N. Jahr. Geol. Pal.. Vol. 56. p. 498-512. Winchester, J.A. & Floyd, P.A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology. Vol. 20. p. 325-343 Zimmermann, U. and van Staden, A. 2002. Neoproterozoic to Pre-Ordovician very-low to low-grade metasedimentary rocks from Sijan (Sierra de Ambato) and Campo Volcán (Puna) in northwestrn Argentina. XV Congreso Geológico Argentino. El calafate. Argentina. Vol. 2. p. 229-234. Zimmermann, U. and Bahlburg, H. (in press). Provenance analysis and paleotectonic setting of the clastic Ordovician deposits in the southern Puna, NW Argentina. Sedimentology. Zimmermann,, U., Esteban, S. and Bahlbrug, H. (in press) Depositional history of the Ordovician Famatina Basin (Western Gondwana; NW argentina). 9th international Symposium on the Ordovician System. San Juan. Argentina.

Figure 1: Outcrop locations of the Puncoviscana Formation and equivalents, as well as medium- to high grade metamorphic rocks of Pre-Ordovicican age. Outcrops: 1=Puna; 2=Sierra Ambato; 3=Sierra Famatina; 4=Valles Calchaquies; 5=Tucumán; 6=Suncho (Sierra de la Ovejería) (after Grissom et al., 1998).

Qt F L P/F Lv/L PVF (Jezek, 1990) 64.8 (55-89) 11.3 (4-38) 23.9 (8-50) 0.68-1 (P/K) 0 PVF-this work 70-80 15-25 5-10 0.2 0 passive margin Guinea 73.1 26.1 0.7 0.44 South Korea 47.7 49.8 2.5 0.34 Puna-Tremadoc 89 7 4 0.36 0.06 continental collision Ganges 45 32.3 22.6 0.45 0.01 continental arc Middle America 10.1 74.6 15.3 0.78 0.99 Java 54.8 35.4 9.8 0.47 Peru-Chile 33.3 49 17.7 0.79 1 back-arc South China 19.2 37.8 43 0.8 1 Puna-Tremadoc 33 42 25 0.4 0.3 Puna-Arenig 49 17 34 0.81 0.98 Puna-Llanvirn 78 12 9 0.22 0 Puna-Llandeilo 67 8 25 0.72 0.62 fore-arc Marianes 0 5.9 94.1 1 1 Japan 3.8 18.3 77.9 0.9 0.99 Qt=quartz total; f=feldspar; l=lithoclasts; p=plagioclase; k=alkalifeldspar; lv=volcanic lithoclasts Table 1: Petrographic data of the Puncoviscana Formation from Jezek (1990), Zimmermann and van Staden (2002), data for comparison from compilation in Bahlburg (1998) and Zimmermann and Bahlburg (in press).

Figure 2: Cia and A-CN-K diagram (after Fedo et al., 1005) combined. Ka0= kaolinite; ill=illite; plag=plagioclase; ksp=alkalifeldspar; LAII= mafic ashes from La Aguadita Formation.

Figure 3: Average REE-patterns of the rocks from the different outcrops. LA1= siliciclastics from the La Aguadita Fm.; LA2= mafic ashes from La Aguadita Fm.; PAAS (post-Archean average Australian shale after Nance and Taylor, 1976; chondrite normalization after Taylor and McLennan, 1985).

Figure 4: Th/Sc//Zr/Sc relation (after McLennan et al., 1993). LA2= mafic ashes from La Aguadita Fm.

Figure 5: Provenance plots after Bhatia & Crook (1986). LA1= siliciclastics from the La Aguadita Fm.; LA2= mafic ashes from La Aguadita Fm.

Figure 6: Ta-Nb-Th/Sc-Zr/Sc concentrations and values normalized to UCC (McLennan, 2001) and silica concentrations. LA1= siliciclastics from the La Aguadita Fm.; LA2= mafic ashes from La Aguadita Fm.