Provenance, volcanic record, and tectonic setting of the Paleozoic Ventania Fold Belt and the Claromecó Foreland Basin: Implications on sedimentation and volcanism along the southwestern Gondwana margin

Luciano  Alessandretti

The intermediate to acid Choiyoi Magmatic Province is the most conspicuous feature along the Late Paleozic continental margin of southwestern Gondwana, and is generally regarded as the possible source for the widespread ash fall deposits interlayered with sedimentary sequences in the adjacent Gondwana basins. The Choiyoi magmatism is geologically constrained between the early Permian San Rafael orogenic phase and the Triassic extensional Huarpica phase in the region of Argentine Frontal Cordillera, Precordillera and San Rafael Block. In order to better assess the Choiyoi magmatism in Argentine Frontal Cordillera, we obtained 6 new LA-ICPMS UePb ages between 278.8 ± 3.4 Ma and 252.5 ± 1.9 Ma from plutonic rocks of the Colangüil Batholith and an associated volcanic rock. The global analysis of age data compiled from Chilean and Argentine Late Paleozoic to Triassic outcrops allows us to identify three stages of magmatism: (1) pre-Choiyoi orogenic magmatism, (2) Choiyoi magmatism (286e247 Ma), and (3) post-Choiyoi magmatism related to extensional tectonics. In the Choiyoi stage is there an eastward shift and expansion of the magmatism to the southeast, covering an extensive region that defines the Choiyoi magmatic province. On the basis of comparison with the ages from volcanogenic levels identified in the coeval Gondwana basins, we propose: (a) The pre-Choiyoi volcanism from the Paganzo basin (320 e296 Ma) probably has a local source in addition to the Frontal Cordillera region. (b) The pre-Choiyoi and Choiyoi events identified in the Parana basin (304e275 Ma) are likely to have their source in the Chilean Precordillera. (c) The early stage of the Choiyoi magmatism found in the Sauce Grande basin (284 e281 Ma) may have come from the adjacent Las Matras to Chadileuvú blocks. (d) The pre-Choiyoi and Choiyoi events in the Karoo basins (302e253 Ma) include the longest Choiyoi interval, and as a whole bear the best resemblance to the age records along the Chilean and Argentine Frontal Cordillera.

The U–Pb and Lu–Hf isotopic analyses of the different sedimentary sequences of the Ventania System, an old Paleozoic orogenic belt exposed in the southern region of the Río de la Plata Craton in the province of Buenos Aires, Argentina, provide new evidence for the understanding of the tectonic evolution of the western sector of the Gondwanides mountain belt. These ranges formed as result of the late Paleozoic collision of the Patagonia terrane against the continental margin of Gondwana. The provenance analysis together with the sedimentary paleocurrents confirm a dominant source from the Tandilia System, a Paleoproterozoic mountain belt formed during the amalgamation of the Río de la Plata Craton at about 1800–2200 Ma, and incorporated to Western Gondwana during the Brasiliano Orogeny at 550–530 Ma. The local dominant source at the base of the early Paleozoic changed to more distant supplies toward the top of the sequences, when an increasing participation of detritus from first, Cambrian (560–520 Ma) zircons from the Pampean Orogen, and later on Ordovician (480–460 Ma) zircons from the Famatinian Orogen is recorded. The detrital zircon patterns and the maximum age of the units shed light on some previous discrepancies in the early Paleozoic stratigraphy. The Balcarce Formation, an early Paleozoic sedimentary cover of the Tandilia metamorphic and igneous basement, shows striking differences when compared with the new data from the Ventania System. The two data-sets reveal different sources for the two regions. The late Paleozoic foreland basin deposits mark an abrupt change of 180° in the paleocurrent directions, in the petrographic composition of the sediments, and in the provenance of detrital zircons. These data indicate a southern provenance with the first evidence of Carboniferous and Permian magmatic zircons. The oldest Archean zircons together with the finding of clasts with archeocyathids support the provenance from Patagonia, which was derived from Eastern Gondwana. The U–Pb ages of the ash-fall tuffs in the Tunas Formation confirm the Early Permian age of the Eurydesma Fauna in the Ventania System. The U–Pb data together with the Lu–Hf isotopic data enhance the comprehension of the tectonic evolution of the Ventania System as part of the larger Gondwanides Belt that amalgamated to Western Gondwana during Late Permian times with some independent pieces derived from Eastern Gondwana.

The Las Lozas volcanic sequence, which crops out at northwestern border of the Famatina belt-southeastern Puna, NW Argentina, is constituted mainly by rhyolites and a lesser volume of basalts and trachytes, and volcanoclastic deposits. These rocks, previously considered of Early Paleozoic age, are now assigned to the Lower Pennsylvanian (320 Ma U-Pb age). They represent a bimodal volcanic succession that plot in the subalkaline/tholeiitic (rhyolites), alkaline basalts (basalts) and alkaline (trachytes) fields on the total alkali-silica diagram. The basalts display features comparable to transitional MORB and within-plate tholeiites, with contributions from a mantle source affected by crustal contamination. The acid members also show geochemical affinities to within-plate magmas, and their composition suggest a derivation from continental crustal material with mantle source interaction or a juvenile essentially mantle derived crust. The 320 Ma age from the Las Lozas volcanic successi...

Journal of South American Earth Sciences 47 (2013) 12e31 Contents lists available at SciVerse ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames Provenance, volcanic record, and tectonic setting of the Paleozoic Ventania Fold Belt and the Claromecó Foreland Basin: Implications on sedimentation and volcanism along the southwestern Gondwana margin Luciano Alessandretti a, *, Ruy Paulo Philipp a, Farid Chemale Jr. b, Matheus Philipe Brückmann a, Gustavo Zvirtes a, Vinícius Matté a, Victor A. Ramos c a Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Porto Alegre 91509-900, RS, Brazil Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, 70910-900, DF, Brazil c Instituto de Estudios Andinos, CONICET, FCEyN, Universidad de Buenos Aires, Argentina b a r t i c l e i n f o a b s t r a c t Article history: Received 16 August 2012 Accepted 22 May 2013 This study focuses on the provenance, volcanic record, and tectonic setting of the Paleozoic Ventania System, a geologic province which comprises the Cambro-Devonian Ventania Fold Belt and the adjoining Permo-Carboniferous Claromecó Foreland Basin, located inboard the deformation front. The Ventania Fold Belt is formed of the Curamalal and Ventana groups, which are composed mainly of mature quartzites that were unconformably deposited on igneous and metamorphic basement. The Pillahuincó Group is exposed as part of the Claromecó Basin and it has lithological and structural features totally distinct from the lowermost groups. This group is composed of immature arkoses and subarkoses with intercalated tuff horizons, unconformably overlaying the quartzites and associated with glacial-marine deposits of the lower Late Carboniferous to Early Permian section. The petrography, as well as major and trace elements (including rare earth elements) support that the Ventania quartzites were derived from cratonic sources and deposited in a passive margin environment. For the Pillahuincó Group, we suggest a transition between rocks derived from and deposited in a passive margin environment to those with geochemical and petrographical signatures indicative of an active continental margin provenance. LA-MC-ICP-MS analysis performed on euhedral and prismatic zircon grains of the tuffs revealed an age of 284 15 Ma. The geochemical ﬁngerprints and geochronological data of the tuffs found in the Claromecó Basin support the presence of an active and widespread Lower Permian pyroclastic activity in southwestern Gondwana, which is interpreted as part of the Choiyoi Volcanic Province in Argentina and Chile. Ó 2013 Elsevier Ltd. All rights reserved. Keywords: Geochemistry Provenance Tectonic setting Ventania fold belt Claromecó Foreland Basin 1. Introduction Regions exhibiting the interactions between two or more continental blocks in a convergent tectonic setting are keystones to understand the tectonomagmatic activity, sedimentary inﬁll, and metamorphic/deformational evolution both during and after collisional processes. In the context of their geotectonic settings, foreland systems are associated with convergent plate margins with orogenic fold-thrust belts formed along the edge of the overriding continent. It is generally accepted that the accommodation space in this type of basin is due to ﬂexural subsidence * Corresponding author. Tel: þ55 51 3308 7296. E-mail address: luciano.geoufrgs@gmail.com (L. Alessandretti). 0895-9811/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2013.05.006 driven by tectonic load of the thrust sheets and sediment load of the foreland region (DeCelles and Giles, 1996). The relationships between the Ventania Fold Belt, Claromecó Foreland Basin, and Somun Cura (or Northern Patagonian) Massif provide some insight into the geologic evolution of the southwest portion of the Gondwana supercontinent (Fig. 1). The Ventania System (Ventania Fold Belt-Claromecó Basin) is located in centraleast Argentina between the latitudes of 37 and 39 S and longitudes of 61 and 63 W. This system constitutes a mountain chain with a general N30 -45 W direction and approximately 180 km long by 60 km wide (Figs. 2 and 3). The Ventania System has a thick sedimentary sequence of Paleozoic age with interbedded tuff layers in the upper section of the basin ﬁll and small exposures of the Neoproterozoic-Cambrian basement, which consist of mylonitic granites and rhyolites as well as a scarce occurrence of gneisses. L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 13 Fig. 1. The Ventania System and its relationships with adjacent cratons and Paleozoic terranes in southern South America (modiﬁed from Ramos et al., 2010). This region was a key for the reconstruction of Gondwana since the pioneering work of Keidel (1916) who observed common characteristics between Paleozoic sequences in Argentina and South Africa. Du Toit (1927, 1937) conﬁrmed the similarities between the Ventania Fold Belt and Cape Fold Belt and considered them as a single belt called the “Samfrau Geosyncline”. The Ventania System is formed by the basal units of the Curamalal and Ventana groups and represents a stable platformal sequence of the old passive margin of Western Gondwana (Ramos and Kostadinoff, 2005; Ramos, 2008) and the Neopaleozoic Claromecó Basin, adjacent to the Ventania Fold Belt, which is ﬁlled with sediments from the Pillahuincó Group. A synorogenic molasse foreland sequence composed of arkoses and subarkoses with volcanic clasts from the Tunas Formation occurs in the upper Pillahuincó Group. The objectives of this contribution are to use various petrographical, geochemical and isotopic approaches to accomplish the following: (i) Constrain the provenance and tectonic settings of the Curamalal, Ventana and Pillahuincó groups through both petrography and major, trace, and rare-earth element geochemical data. 14 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Fig. 2. The different units of the Ventania fold and thrust belt associated with the Claromecó foredeep, formed by crustal loading in Early to Middle Permian. Note the location of the thrust deformation front and the axis of the >10 km foredeep (based on Ramos and Kostadinoff, 2005). Fig. 3. Generalized geological map of the Ventania Fold Belt-Claromecó Basin and adjacent areas with sample locations (modiﬁed from Harrington, 1947). L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 (ii) Apply whole-rock geochemistry analysis of the tuffs to constrain the possible tectonic setting and magmatic afﬁnity of the volcanic source. (iii) Chronocorrelate the tuff horizons of the Tunas Formation to ash fall deposits in the Karoo and Paraná Basins using geochemical and geochronological ﬁngerprints. 2. Geological setting The southern region of South America (Fig. 1) formed part of the Gondwana supercontinent during most of the Paleozoic and Early 15 Mesozoic (Valencio et al., 1983). Throughout most of the Paleozoic, this sector of Gondwana was an active convergent setting between the Gondwanic cratonic block and the oceanic lithosphere of Panthalassa (Coira et al., 1982). Such region underwent a geodynamic context involving successive amalgamation of allochthonous terranes that collided against Gondwana during the Paleozoic orogenies. According to Ramos et al. (1986) and Milani and Ramos (1998), the orogenic phases can be divided into three major tectono-sedimentary cycles: the Pampean (Neoproterozoic to Early Cambrian), the Famatinian (Ordovician to Devonian) and the Gondwanic (Carboniferous to Triassic). The Pampean cycle encompasses the ﬁnal assembly of Gondwana, which comprises a Fig. 4. Simpliﬁed stratigraphic column in the Ventania System. Based on Harrington (1947), Limarino et al. (1999) and Rapela et al. (2003) with the location of the analyzed samples. 16 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 complex framework of cratonic fragments. The Famatinian Cycle comprises two pulses of compressive deformation associated with magmatic and sedimentary events of the Ocloyic and Chanic orogenies, respectively related to the amalgamation of the allocthonous Cuyania and Chilenia terranes to the paleocontinent (Ramos, 2004). The Gondwanic Cycle comprises the Sanrafaelic Orogeny, which involved normal subduction and deformation along the Paciﬁc margin and the docking of the Patagonia terrane (Fig. 1). Most of the modern reconstructions of Gondwana accept that between the Cambrian and the Late Devonian its southwest margin consisted of a continuous siliciclastic passive margin that extended from the Ventania Fold Belt to the Cape Fold Belt in South Africa (Ramos, 1986; Milani, 2007). The foreland Karoo Basin in southern Africa is located adjacent to the thrust front of the Cape Fold Belt, and shares similar paleoclimatic, paleogeographic, paleotectonic, and lithological characteristics to the Claromecó Basin (LópezGamundi and Rossello, 1998). The built up of the Gondwana southwestern margin involved the amalgamation of different terranes during and after the Permian (Fig. 1). The Patagonian region has always been considered as an exotic fragment to the Gondwana paleocontinent, with a different geologic history when compared to the rest of the South American Platform deﬁned by Almeida (1970). Some authors fostered the autochthonous origin for the Patagonia terrane (Forsythe, 1982; Caminos et al., 1988), while others interpreted Patagonia as an accreted terrane (Ramos, 1984, 1986). Based on recent data, Ramos (2008) proposed that Patagonia is an allochtonous block that was amalgamated to Gondwana during the Early Permian. Winter and de la, 1984, 1986) proposed a similar evolution to the Cape System. The sedimentary inﬁll of Ventania, the development of the Claromecó foredeep, and the ductile deformation along the northern and southern boundaries of Patagonia require an important episode of deformation. Such episode is best explained by the collision of the allochthonous Patagonia against the old continental margin of Gondwana (Ramos, 2008). The stratigraphic record of the southwestern Gondwanan basins has strong evidence that support a wide explosive volcanic event that occurred over a wide area and temporal scale during the late Paleozoic and peaked during the Permian (Fig. 14) (Llambías et al., 2003). Occurrence of tuff layers with similar geochemical and geochronological afﬁnities have been reported far from the plate margin in several Paleozoic Gondwana basins (e.g. Karoo, Paraná, San Rafael). Based on geochronological data, Ramos and Ramos (1979) subdivided the magmatic history along the southwestern portion of Gondwana into two different episodes: (i) Carboniferous e Early Permian and (ii) Late Permian-Triassic. Both episodes are part of the Permo-Triassic Choiyoi Magmatic Province (Kay et al., 1989), which is a large silicic volcano-plutonic province composed of a complex succession of lava ﬂows, pyroclastic and sedimentary rocks, ignimbrites, sub-volcanic bodies and domes outcropping into central western Argentina and central Chile (Kleiman and Japas, 2009; Llambías et al., 2003; Strazzere et al., 2006). 3. Geology of the Ventania Fold Belt-Claromecó Basin The Paleozoic Ventania Fold Belt is a curved fold and thrust belt (Ramos, 1984) elongated in the NW direction (Figs. 2 and 3). A molasse sequence exposed east of the thrust front, and composed of arkoses and subarkoses of the Pillahuincó Group, unconformably overlying the quartzites of the Ventania Belt and is associated with glacial-marine deposits in the lower section (Fig. 4) (Keidel, 1916). The areas surrounding the Ventania System are composed of a plain underlain by Tertiary and Quaternary sedimentary rocks (Fig. 3) (Harrington, 1947). Different interpretations of the structural style and evolution of the Ventania System have been proposed. The ﬁrst Fig. 5. Petrographic features of the Curamalal and Ventana Groups. (A) Blastopsamitic texture characterized by the presence of 50e70% of medium sand-size quartz porphyroclasts. (B) Very ﬁne-grained equigranular interlobate granoblastic texture in quartz. (C) Schistose structure as characterized by the quartz clasts stretching. (D) Fine- to medium-grained polygonal equigranular granoblastic arrangement in quartz. L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 17 Fig. 6. QmFLt (A) and QtFL (B and C) provenance diagrams from Dickinson (1985) for the Curamalal, Ventana, and Pillahuincó Groups. attempt was done by Schiller (1930), who recognized the ﬁrst thrusts in the Ventania Fold Belt. At the end of the following decade and subsequent years, Harrington (1947, 1970) suggested that the structures preserved in the Paleozoic sequences of the Ventania System represent a typical example of pure folding associated with only minor faults. Cobbold et al. (1991) proposed a different interpretation by suggesting that the strain was generated by a transpressive regime. The Ventania Fold Belt is characterized by isoclinal folds with highly strained quartzites and a common northeast vergence (Andreis and Japas, 1991). Later on several authors recognized the occurrence of thrusts (Tomezzoli and Cristallini, 1998), criteria that have general consensus at present. This deformational event ended in Middle to Late Permian and was preserved in anchizonal to greenschist metamorphic facies (Von Gosen et al., 1991). 3.1. Sedimentary sequence of the Ventania System According to Harrington (1947, 1970), the Paleozoic Ventania System is composed of three groups named Curamalal, Ventana, and Pillahuincó from the base to the top (Figs. 3 and 4). The two foremost groups are composed primarily of mature quartzites unconformably deposited onto the igneous-metamorphic basement. The paleocurrent patterns in these mature sequences indicate a common provenance from the northeast (Fig. 4) (López-Gamundi and Rossello, 1998). Biostratigraphic control of these two groups is scarce and bracketed between the Middle-Late Cambrian and Devonian based on a well dated basement (Rapela et al., 2003) and overlying unconformity (Andreis et al., 1991). The total thickness of the Curamalal Group (Harrington, 1947) is between 1100 and 1150 m, bracketed between the Middle-Late Cambrian and the Ordovician (Uriz et al., 2010). It consists predominantly of mature quartzites deposited in a shallow marine environment (Fig. 4). Harrington (1947) divided the group into four formations (from the base to the top): La Lola, Mascota, Trocadero, and Hinojo. The Ventana Group (Harrington, 1947) is 1400 m thick, bracketed between the Silurian and lower to Middle Devonian (Cingolani et al., 2002; Uriz et al., 2010), and consists primarily of mature quartzites dominated by shallow marine sedimentary rocks (Fig. 4). According to the stratigraphic division proposed by Harrington (1947), this group is divided into following four formations (from the base to the top): Bravard, Napostá, Providencia, and Lolén. Andreis et al. (1989) attributed the group to the lower Devonian based on a brachiopod level found near the base of the Lolén Formation. The Pillahuincó Group, which has compositional features completely distinct from those of the Curamalal and Ventana groups, represents the top of the sedimentary pile and reaches a maximum thickness of approximately 2800 m (López-Gamundí et al., 1995). Harrington (1947) subdivided this group into the following four formations from the base to the top: Sauce Grande, 18 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Fig. 7. (A) Exposure of tuffs intercalated with sandstones and mudstones from the Tunas Formation in the location of Abra del Despeñadero. (B) Hand specimen showing the homogeneous appearance of the tuffs. (C) and (D) Photomicrographs of both in plane and cross-polarized light showing the scarce, very ﬁne-grained vitroclasts imbedded in a smectitic-rich matrix. Piedra Azul, Bonete and Tunas. These formations have glaciomarine sedimentary deposits (Sauce Grande Formation) followed by a transgression in an open platformal marine environment (Fig. 4) (López-Gamundí et al., 1998). Different source areas for the Tunas Formation have already been inferred as evidenced by both the dominant paleocurrents from the SW and detritic modes characterized by moderate to low percentages of quartz and abundant metamorphic/volcanic lithic fragments. Andreis et al. (1987) described the Sauce Grande Formation as being composed of diamictites (74%), sandstones (24%) and pelites (2%). Sedimentological studies interpret most of the diamictites as having a marine origin, most likely rain-out tills, with variable participation from gravity ﬂows (Harrington, 1980). The fossil record is limited to poorly preserved bivalves (Harrington, 1980). The Piedra Azul Formation outcrops into transitional contact with the Sauce Grande Formation, reaches a thickness of approximately 300 m, and consists of pelites and scarce ﬁne-grained sandstones (Harrington, 1947). According to Andreis and Japas (1991), the Piedra Azul Formation was deposited in a marine environment after the disintegration of the Gondwana Ice Sheet (GIS). The sedimentation in this transgressive context, favored the deposition of ﬁne-grained sediments. The Bonete Formation rests conformably on the post-glacial deposits of the Piedra Azul Formation and has abundant Glossopteris ﬂora and Eurysdesma fauna fossils (Fig. 4). Such fauna provides an excellent fossil guide for the Early Permian of Gondwana and can also be found in the Karoo and Paraná Basins. The Tunas Formation is a synorogenic clastic wedge (LópezGamundí et al., 1995; López-Gamundi, 2006; Ramos, 1984, 2008) located east of the thrust front. This formation consists of immature sandstones with subordinate shales with signiﬁcantly smaller portions of ash-fall tuffs in the upper half of the sequence. The Tunas Formation has signiﬁcant compositional, structural and textural changes relative to the previous formations (Figs. 4, 6 and 7, Fig. 8e and f). The compositional and textural immaturity is represented by the presence of quartz, plagioclase and K-feldspar crystaloclasts with subordinate muscovite and calcite grains as well as metamorphic and volcanic clasts suggesting that this formation had different source-areas. Sediment transport patterns in the Tunas Formation have been previously studied by means of paleocurrent and sedimentary petrography (Iñiguez et al., 1988). The authors indicated a dominant sediment transport from the Ventania Fold Belt located to the southwest. 4. Methods and material For the provenance studies with petrography and whole-rock geochemistry, we selected seventeen fresh representative surface samples from the primary depositional units of the Ventania System. All the selected samples (quartzites and sandstones) correspond to the very ﬁne to medium sand size interval (0.0625e 0.5 mm) (See Table 1). Of this set, ﬁve samples were from the Curamalal Group (VE-03, VE-04, VE-06, VE-09 and VE-10), ﬁve from the Ventana Group (VE-01, VE-05, VE-11, VE-12 and VE-13) and seven from the Pillahuincó Group (VE-14, VE-16, VE-17, VE-18, VE22, VE-23 and VE-24) (Table 1). The detrital modes of the Curamalal, Ventana, and Pillahuincó groups (Table 2) were determined using the GazzieDickinson pointcounting method to better determine the mineralogic/lithologic composition of the source areas independent of the grain size. Each sample had 300 points per section submitted at spacing of 0.5 mm. The samples were crushed, milled, and split into fractions for whole rock geochemistry, which were carried out at the Acme Analytical Laboratories (Canada). In addition to the traditional GazzieDickinson method, we performed geochemical analyses due L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 19 Fig. 8. Petrographic features of the Pillahuincó Group sandstones. (A) Fine grained subarkose from the Sauce Grande Formation with psamitic texture characterized by the presence of 70e75% quartz clasts. Carbonate clasts of unknown origin are observed (red arrow), as also reported by Von Gosen et al. (1991) (Fig. 8a). (B) The previous thin-section showing the abundant quartz, subordinate content of feldspar, and minor amounts of lithic fragments (quartzites and vein quartz, green and yellow arrows respectively). (C) Fine-grained arkose from the Bonete Formation showing the growth of epidote (blue arrow), proving the low grade metamorphism that affected these rocks. Lithics in the Bonete Formation are mainly ﬁne-grained metamorphic (quartz-mica shists, orange arrow) and sedimentary grains (D) The previous thin-section showing the abundant quartz, and minor amounts of feldspars and lithic fragments. (E) and (F) Lithic arkose from the Tunas Formation showing the decrease in quartz compared with the Sauce Grande-Piedra Azul-Bonete succession. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) to the fact that the rocks from the Curamal and Ventana groups were affected by greenschist facies metamorphism (Von Gosen et al., 1991). Innumerous previous works have demonstrated that the employment of major, trace, and REE are a robust tool to discriminate provenance areas and tectonic setting of sedimentary and metasedimentary rocks (Naipauer et al., 2010; Kutterolf et al., 2008; Osae et al., 2006; Toulkeridis et al., 1999). For the isotopic analyses, one tuff sample (VE-19) was crushed, milled, sieved, and washed to remove any very ﬁne materials (clay and silt sizes). The sieved samples were then treated with a hand magnet and isodynamic Frantz magnetic separator (w1.5 A) to concentrate the non-magnetic fractions. Zircon grains were concentrated and isolated using standard heavy liquid techniques and were hand-picked under a binocular microscope, mounted onto double-sided tape and cast in epoxy rounds. Grain cross sections were exposed via polishing for SEM imaging and dating. All of these analyses were performed at the Isotope Geology Laboratory of the University of Brasília. The UePb analytical methods and data treatment can be found elsewhere (Chemale et al., 2011). The depositional age of the tuffs was constrained by UePb dating of the volcanic zircon grains (sample VE-19) using LA-ICPMS. The tectonomagmatic afﬁnity of the tuffs was accessed via petrography and whole-rock geochemical analyses. The spatial location and stratigraphic position of the samples are presented in Figs. 3 and 4, while the geochemical data are in Tables 3 and 4, respectively. Isotopic data are presented in Table 5. 5. Petrography 5.1. Curamalal and Ventana groups The Curamalal (VE-03, VE-04, VE-09, and VE-10) and Ventana groups (VE-01, VE-11, VE-12, VE-13, and VE-14) are essentially composed of medium-grained mature quartzites. The primary 20 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Fig. 9. (A) Representation in pie diagrams for the average composition of the Upper Continental Crust, Curamalal, Ventana and Pillahuincó Groups. Note the strong similarity between the average compositions of the Curamalal and Ventana Groups and the Upper Continental Crust and the Pillahuincó Group. (B) Data from the Curamalal, Ventana and Pillahuincó Groups from the ternary Na2OeCaOeK2O plot based on Toulkeridis et al. (1999). OIA ¼ oceanic island arc, CIA ¼ continental island arc, ACM ¼ active continental margin, PM ¼ passive continental margin. (C) SceTheZr/10 diagram from Bhatia and Crook (1986) and Bahlburg (1998). A: oceanic island arc; B: continental island arc; C: active continental margin; D: passive/rifted margins; (1) recent deep-sea turbidites derived from and deposited on the continental arc margin; (2) recent deep-sea turbidites derived from and deposited on the passive margin (data from Bahlburg, 1998). L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 21 Fig. 10. Data from the Curamalal, Ventana and Pillahuincó Groups in the binary SiO2 K2O/Na2O plot of Roser and Korsch (1986). sedimentary structures for these groups were greatly transformed by microfracturing in the ridge clasts, pressure solution processes and recrystallization (Fig. 5). For Von Gosen et al. (1991), there is a direct correlation between the sizes of subgrains and recrystallization grains, and also the amount of strain. They divided the quartzites into two distinct groups (also adopted in this work), with the following features: (i) less deformed quartz clasts exhibiting larger subgrains (or they are free from subgrains) with only a few, but larger, recrystallization grains. They show weak ondulatory extinction. Subgrains formation seems to stabilize the interior of the older clasts (Fig. 5a). The matrix that developed from the metamorphic recrystallization of quartz surrounding the clasts constitutes a very ﬁne-grained equigranular interlobate granoblastic texture (Fig. 5b). Recrystallization grains mostly grow in the matrices and from there start to consume clast rims (Fig. 5b). These grain boundary migrations are accompanied by increasing subgrain formation (polygonization) which concentrate at the rims of clastic grains (Fig. 5b). Sericite and quartz “beards” occur deformed around quartz clasts (Fig. 5b). Blastopsamitic texture is characterized by the presence of 40e50% medium-grained quartz clasts (Fig. 5a). These quartz clasts are subangular to subrounded and are slightly deformed and stretched; and (ii) higher shear strains, at clast boundaries to adjacent shear planes, lead to higher subgrain densities with small-scale subgrains and also smaller dynamically recrystallized grains (Fig. 5c and d). The quartzites have a schistose structure as characterized by the quartz clasts stretching (Fig. 5c). The blastopsamitic texture is given by the presence of 85e90% of medium-grained quartz clasts which evolve into a very ﬁnegrained quartz-rich matrix with restricted occurrence of muscovite (Fig. 5c). The quartz grains are moderately sorted with subangular to subrounded shapes and generally little deformed. Matrix content is low (<5%) and fully recrystallized, which generates a ﬁne- to medium-grained polygonal equigranular granoblastic arrangement (Fig. 5d). Although the rocks of the Curamalal and Ventana groups underwent low grade metamorphism, thin-sectioned point counting of the quartzites was used for quantitative compositional analysis. All analyzed samples of the Curamalal Group fall into the cratonic provenance ﬁeld of Dickinson (1985) (Fig. 6a). For the Ventana Group, samples of the Lolén Formation (VE-01 and VE-13) fall into the recycled orogenic ﬁeld, while samples from the lowermost formations (Bravard, Napostá, and Providencia) fall into the cratonic provenance ﬁeld of Dickinson (1985). Their petrographic characteristics are given in Tables 1 and 2. 5.2. Pillahuincó Group The petrographic characteristics are presented below and in Fig. 8 and Tables 1 and 2. 5.2.1. Sauce Grande Formation The Sauce Grande Formation consists of diamictites, conglomerates, quartzites, sandstones and mudstones. The analyzed sample (VE-14) was taken from a ﬁne-grained sandstone lens interbedded with a succession of diamictites (Fig. 8a and b). The blastopsamitic texture is characterized by the presence of 70e75% ﬁne-grained quartz clasts. The quartz grains are moderately sorted with subangular to subrounded shapes. Carbonate clasts of unknown origin were reported by Keidel (1916) (Fig. 8a). The sample can be compositionally described as a subarkose using Folks’s (1980) terminology. The detrital mode of this sample has yielded a composition of Q ¼ 80.4%, F ¼ 12.8%, L ¼ 12.9% (Fig. 6). When plotted using Dickinson (1985) ternary discriminatory diagrams, both this sample and those studied by Andreis and Cladera (1992) and LópezGamundí et al. (1995) fall into the cratonic provenance ﬁeld. 5.2.2. Piedra Azul Formation The studied sample (VE-17) is a ﬁne-grained subarkose based on Folk’s terminology (1980). The sample is well sorted with massive structure. The clasts are matrix-supported with a low degree of compactation and low roundness. The percentage of matrix is elevated, between 20 and 25%, and is composed of muscovite and quartz. A composition of Q ¼ 73.7%, F ¼ 19.3%, L ¼ 7.1% (Fig. 6) was obtained for this sample, which indicates a transitional continental provenance according to Dickinson (1985). Fig. 6. 5.2.3. Bonete Formation Sample VE-18 is a ﬁne-grained arkose according to Folk’s terminology (1980) (Fig. 8c and d). The dominant clasts are quartz with a subordinated portion of plagioclase and muscovite in the arkosean patterns. The clasts are generally matrix-supported with a low degree of compaction, angular shape, low roundness and moderate sorting. The percentage of the matrix is elevated, between 10 and 20%, and it is composed of chlorite, muscovite and quartz. The sandstones are poorly sorted with massive structure with a signiﬁcant lithoclast content consisting of ﬁne- to coarsegrained quartz and plagioclase with predominantly angular shapes and low roundness. The lithoclastic ﬁne-grained quartzites, metaquartz-arenites, metapelites and limestones are supported by 22 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Fig. 11. (A) ZrTiO2 Nb/Y diagram of Winchester and Floyd (1977) for tuffs from the Tunas Formation and main Karoo, Paraná and Central Andes of northern Chile. (B) Samples from the Tunas Formation in a Jensen (1976) diagram and (C) Irvine and Baragar (1971) discriminant diagram. (D) and (E) Th/Ta Ta/Yb and Th/Ta Yb diagrams (after Pearce et al., 1984) for tuff rocks. All samples have clearly active continental margin afﬁnities. Tuffs from the Tunas Formation in (F) Rb versus Y þ Nb and (G) Ta versus Yb discriminant diagrams from Pearce et al. (1984). VAG e volcanic arc granite; ORG e oceanic ridge granite; WPG e within-plate granite; syn-COLG e syn-collisional granite. L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 23 Fig. 12. (A) Normalized plot for rare earth elements in Chondrite for tuff samples from the Tunas Formation. Chondrite normalization values are from Boynton (1984). (B) Primitive mantle normalized rare earth element plot for tuff samples from the Tunas Formation. Primitive mantle normalization values are from Sun and McDonough (1989). a ﬁne matrix with a low degree of compaction. The detrital mode of this sample revealed a composition of Q ¼ 71.9%, F ¼ 21.2%, and L ¼ 6.8%, which indicates a transitional continental provenance (Fig. 6). 5.2.4. Tunas Formation 5.2.4.1. Sandstones. Both ﬁeld aspects and microscopic features of the Tunas Formation sandstones are entirely distinctive from those of the other older formations (Fig. 8e and f). Like in many other molasses, the Tunas sediments are mostly arkoses and lithic arkoses. The framework grains of the sandstones are composed of monocrystalline quartz (Qm), polycrystalline quartz (Qp), K-feldspar, plagioclase, mica, and rock fragments. Based on their mineralogical content, the analyzed samples (VE-16, VE-23 and VE-24) were classiﬁed as lithic arkoses according to Folk’s terminology (1980). The arenites are arkosic and subarkosic sandstones with massive structure and ﬁne to medium-grains that generally contain a signiﬁcant lithoclast percentage. The degree of selection is low with lithoclasts varying from ﬁne to coarse-grained quartz and plagioclase. The matrix is composed of quartz and muscovite. The quartz and plagioclase clasts have angular forms, low sphericity and a low degree of selection. The clasts are generally supported by the matrix and the degree of deformation strain is low. Lithoclasts of ﬁne-grained quartzites, quartz-mylonites, pelites and limestones were identiﬁed. The lithoclasts have elongate shape with angular boundaries, low sphericity and millimetric dimensions. The ternary QFL diagram from Dickinson (1985) plots the samples exclusively in the recycled orogeny ﬁeld. In the QmFLt diagram, samples VE-23 and VE-24 fall within the magmatic arc provenance ﬁeld, while sample VE-16 plots in the mixed provenance ﬁeld (Fig. 6). The relatively low amounts of quartz in the Tunas sediments (Table 2) indicate the compositional immaturity typical of molasse deposits as noticed by Andreis and Cladera (1992). 24 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 5.2.4.2. Tuffs. Two types of tuffaceous sediments were identiﬁed in the upper portion of the Tunas Formation (Fig. 7a) by Iñiguez et al. (1988) based on their grain size: (i) sand-sized tuffs and ignimbrites with vitroclasts and fragments of vitric tuffs immersed in a smectitic matrix and (ii) ﬁner-grained tuffs consisting of scarce ﬁnegrained vitroclasts sands dispersed in a smectitic “groundmass” (Fig. 7b and c). The tuffs studied here are of the second type, which are classiﬁed by Iñíguez et al. (1988) and others as volcanic ash deposited in a subaqueous environment. These tuffs are commonly off-white in color, very ﬁne grained (<2 mm) and massive to thinly crossbedded with a unit thickness range between 20 and 40 cm in the studied area (Fig. 7). Thin section petrography reveals that the studied tuffs are matrix-supported and consist of scarce amounts of ﬁne-grained crystaloclasts of quartz and plagioclase embedded in a smectitic matrix. 6. Geochemistry Fig. 13. UePb in situ zircon age for sample VE-19 obtained by LA-MC-ICPMS. Major oxides were analyzed by fusion ICP, while minor, trace, and REE were analyzed by fusion ICP-MS at the Acme Analytical Laboratories (Canada). One of the objectives of this contribution is to characterize the provenance area of the studied samples using Fig. 14. Stratigraphic correlation between the Claromecó, Karoo and Paraná Basins showing the occurrence of tuffaceous intervals and their contemporaneity with peak magmatic activity in the Choiyoi Magmatic Province and Northern Patagonia region. Fildani et al., 2007; Guerra-Sommer et al., 2008a; Guerra-Sommer et al., 2008b; Outa Mori et al., 2012; Pankhurst et al., 2006; Ramos, 1988; Rocha-Campos et al., 2007; Santos et al., 2006; Wagner Simas et al., 2012. L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 25 Table 1 Geographical, lithological, mineralogical and structural information for the analyzed samples. Sample Structure and texture Mineral assemblage Lithology Formation Latitude Longitude VE-01 Qz þ Mus þ KF þ Pl þ L þ Acs Quartzite Lolén 37 580 18.700 61 540 19.800 Qz Qz Qz Qz Qz Qz Qz Quartzite Quartzite Quartzite Quartzite Quartzite Quartzite Quartzite La Lola La Lola Trocadero Bravard Mascota La Lola Napostá 37 560 43.700 37 560 43.700 37 560 22.100 37 450 36.900 38 040 06.500 38 050 15.600 38 040 22.700 62 100 41.700 62 100 41.700 62 090 37.800 62 080 35.400 62 270 38.700 62 110 45.300 62 000 35.600 Qz þ Mus þ KF þ Pl þ L þ Acs Qz þ Mus þ KF þ Pl þ L þ Acs Qz þ Mus þ KF þ Pl þ L þ Acs Quartzite Schist Sandstone 61 580 50.400 61 580 43.800 61 450 58.600 Qz þ Pl þ KF þ Mus þ L þ Acs Qz þ Pl þ KF þ L þ Acs Sandstone Sandstone 38 030 30.900 38 070 39.300 61 420 18.300 61 430 37.800 VE-18 VE-19 VE-20 VE-21 VE-22 VE-23 VE-24 Medium grained arkosean sandstone, laminated Very ﬁne grained, scarce vitroclasts imbedded in a smectitic matrix Very ﬁne grained, scarce vitroclasts imbedded in a smectitic matrix Very ﬁne grained, scarce vitroclasts imbedded in a smectitic matrix Medium grained, tabular beds with croos-bedded stratiﬁcation Medium grained, tabular beds with croos-bedded stratiﬁcation Medium grained, tabular beds with croos-bedded stratiﬁcation Qz þ Pl þ KF þ Smt þ Qz þ Pl Smt þ Qz þ Pl Smt þ Qz þ Pl Qz þ Pl þ KF þ Qz þ Pl þ KF þ Qz þ Pl þ KF þ Sandstone Tuff Tuff Tuff Sandstone Sandstone Sandstone Providencia Lolén Sauce Grande Tunas Piedra Azul Bonete Tunas Tunas Tunas Tunas Tunas Tunas 36 040 27.400 36 040 26.600 38 070 37.600 VE-16 VE-17 Fine to medium grained, shistosity foliation, lepidoblastic, granoblastic Quartzite lens in a matrix supported polimitic metaconglomerate Quartzite lens in a matrix supported polimitic metaconglomerate Fine grained, shistosity foliation, lepidoblastic, granoblastic Fine grained, shistosity foliation, lepidoblastic, granoblastic Fine grained, shistosity foliation, lepidoblastic, granoblastic Medium grained, shistosity foliation Medium grained, tabular beds often with cross bedded stratiﬁcation Medium grained, shistosy foliation, lepidoblastic, tabular beds Fine grained, shistosity foliation, lepidoblastic Microconglomeratic quartzite lens in metaconglomerate, croos bedded Cross bedded stratiﬁcation, ripple marks Very ﬁne-grained, cross bedded stratiﬁcation 38 090 20.700 38 120 40.600 38 120 39.200 38 120 39.200 38 120 39.200 38 150 39.300 38 150 39.300 61 420 29.000 61 290 04.700 61 290 03.900 61 290 03.900 61 290 03.900 61 210 31.400 61 210 31.400 VE-03 VE-04 VE-05 VE-06 VE-09 VE-10 VE-11 VE-12 VE-13 VE-14 geochemical data. Ten (10) metasedimentary samples from the Ventania Fold Belt (Curamalal and Ventana groups) and seven (7) sedimentary samples from the Claromecó Basin (also referred as the Pillahuincó Group) were analyzed for major, minor, trace and RE elements. Mobile elements such as Si, Na, K, Ca, Mg and Fe are more vulnerable to remobilization during weathering, erosion, transport, deposition, diagenetic processes and metamorphism. Even considering the complexity of working with the geochemistry of sedimentary and metasedimentary rocks, discriminant diagrams using major oxides to differentiate source areas were successfully created. Analytical data for the major, minor, trace and REE of the analyzed samples are given in Tables 3 and 4. The chemical composition of clastic sedimentary rocks is a function with complex variable interactions that primarily depends on the nature of the source area(s), type of active weathering on these rocks and subsequent diagenetic processes (McLennan et al., 1993). Taylor and McLennan (1985), Bhatia and Crook (1986) and McLennan et al. (2003) considered the trace elements to be relatively immobile. Elements þ þ þ þ þ þ þ Mus Mus Mus Mus Mus Mus Mus þ þ þ þ þ þ þ KF KF KF KF KF KF KF þ þ þ þ þ þ þ Pl Pl Pl Pl Pl Pl Pl þ þ þ þ þ þ þ L L L L L L L þ þ þ þ þ þ þ Acs Acs Acs Acs Acs Acs Acs Mus þ L þ Acs Mus þ L þ Acs Mus þ L þ Acs Mus þ L þ Acs such as Al, Ti, Zr, Hf, Nb, Sc, Cr, Ni, V, Co, Th and rare-earth elements can be observed as indicators of sedimentary provenance. McLennan et al. (1993) showed that geochemical approaches are more appropriate than petrographic techniques when working with metasedimentary rocks because the metasedimentary rocks have substantial pseudo-matrices. This research chose a geochemical approach due to the fact that the Curamalal and Ventana groups are composed essentially of mature quartzitic rocks, with substantial amounts of pseudo-matrix generated by the high degree of recrystallization. The Pillahuincó Group was approached by geochemical and petrographical studies because there is no evidence of strong hydrothermal and/or metamorphic events. 6.1. Metasedimentary and sedimentary units 6.1.1. Major element geochemistry The metasedimentary and sedimentary rocks of the Ventania System possess a variable SiO2 content (70.6e98.6%) that is higher Table 2 Detrital modes from the analyzed samples of the Curamalal, Ventana, and Pillahuincó groups. Qm ¼ monocrystalline quartz; Qp ¼ polycrystalline quartz; K ¼ K-feldspar; P ¼ plagioclase; Ls ¼ sedimentary lithic fragments; Lm ¼ metamorphic lithic fragments; M ¼ matrix; F ¼ K þ P; L ¼ Ls þ Lm; Lt ¼ Qp þ Ls þ Lm. Sample/Formation VE-03/La Lola VE-04/La Lola VE-05/Trocadero VE-06/Bravard VE-07/Napostá VE-09/Mascota VE-10/La Lola VE-01/Lolén VE-11/Napostá VE-12/Providencia VE-13/Lolén VE-24/Tunas VE-23/Tunas VE-16/Tunas VE-18/Bonete VE-17/Piedra Azul VE-14/Sauce Grande Qm 90.3 89.9 76.5 87.5 92.1 90.1 86.4 80.8 92.4 90.6 81.3 40.6 42.6 48.5 71.9 73.7 80.4 Qp 2.6 1.8 17.3 3.2 2.7 0.7 1.1 3.1 3.4 4.1 1.3 2.0 0.9 3.4 2.4 2.5 3.9 K 5.1 6.2 4.7 3.9 3 6.3 5.2 4.5 3.0 4.2 7.3 9.8 10.4 12.3 9.1 8.1 4.5 P 2.1 1.3 1.3 0.3 0.8 1.7 3.4 3.2 0.5 0.9 2.6 20.6 23.4 19.8 12.1 11.2 8.3 Ls 0 0.2 0 0 0.4 0.9 1.6 5.2 0.3 0.2 4.5 9.2 8.5 6.4 1.2 2.1 0.9 Lm 0.5 0.6 0.2 1.1 0.9 0.3 2.4 3.3 0.5 0.1 3.6 17.8 14.3 9.7 3.2 2.5 2.1 QFL (%) QmFLt (%) Q F L Qm F Lt 92.9 91.7 93.8 94.7 94.8 90.8 87.5 83.9 95.8 94.7 82.6 42.6 43.5 51.9 74.3 76.2 84.3 7.2 7.5 6 4.2 3.8 8 8.6 7.7 3.5 5.1 9.9 30.4 33.8 32.1 21.2 19.3 12.8 0.5 0.8 0.2 1.1 1.3 1.2 4 8.5 0.8 0.3 8.1 27 22.8 16.1 4.4 4.6 3 90.3 89.9 76.5 87.5 92.1 90.1 86.4 80.8 92.4 90.6 81.3 40.6 42.6 48.5 71.9 73.7 80.4 7.2 7.5 6 4.2 3.8 8 8.6 7.7 3.5 5.1 9.9 30.4 33.8 32.1 21.2 19.3 12.8 0.5 2.6 17.5 4.3 1.3 1.9 4.1 8.5 4.2 4.4 8.1 29 23.7 19.5 6.8 7.1 6.9 26 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Table 3 Major oxides (SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O and K2O) and minor oxides (MnO, TiO2 and P2O5) of the Curamalal, Ventana, and Pillahuincó samples. Units (N sample) SiO2 (%) La Lola VE-03 VE-04 VE-10 94.55 92.97 90.02 Mascota VE-09 Al2O3 (%) Fe2O3t (%) MnO (%) MgO (%) CaO (%) Na2O (%) K2O (%) TiO2 (%) P2O5 (%) LOI (%) Total 2.17 3.66 3.20 0.37 0.30 2.56 b.d.l. b.d.l. 0.02 0.07 0.05 0.06 b.d.l. b.d.l. b.d.l. 0.03 0.05 0.02 0.70 1.11 1.16 0.06 0.05 0.27 0.02 0.03 0.02 1 0.9 1.3 100.01 100.02 99.97 92.51 3.55 0.23 b.d.l. 0.16 b.d.l. 0.02 1.08 0.21 0.03 1.1 100 Napostá VE-11 98.61 1.11 0.10 b.d.l. 0.02 0.02 b.d.l. 0.28 0.03 b.d.l. 0.17 100.5 Providencia VE-12 96.07 0.75 0.81 0.04 0.02 0.02 b.d.l. 0.11 0.12 b.d.l. 0.39 98.72 Lolén VE-01 VE-13 86.86 85.18 5.20 5.87 1.79 2.66 0.02 0.01 0.30 0.21 0.03 0.04 0.12 0.07 1.66 1.48 0.17 0.22 0.02 0.03 1.28 1.54 98.69 98.81 Sauce Grande VE-14 87.53 4.98 1.59 0.02 0.56 0.41 1.19 1.40 0.34 0.07 0.9 99.93 Piedra Azul VE-17 72.81 11.93 2.68 0.02 0.57 0.79 3.86 1.14 0.65 0.18 2.12 98.84 Bonete VE-18 70.63 13.00 3.64 0.05 1.13 1.94 3.35 1.68 0.53 0.08 1.85 99.71 Tunas VE-16 VE-19a VE-20a VE-21a VE-22 VE-23 VE-24 72.71 67.16 66.94 73.46 66.64 71.88 74.55 12.31 19.29 20.65 14.31 12.89 12.72 11.02 3.47 3.24 1.82 3.60 4.81 3.22 2.80 0.07 0.04 0.05 0.07 0.10 0.04 0.02 0.47 1.81 1.67 1.67 1.21 0.50 0.83 3.65 0.40 1.19 1.30 3.42 1.90 0.48 2.75 0.75 1.19 0.86 3.60 3.54 2.96 1.15 6.82 6.12 4.17 0.64 1.45 2.06 0.41 0.47 0.29 0.44 0.64 0.41 0.25 0.07 b.d.l. 0.07 0.08 0.11 0.10 0.08 1.48 4.17 4.06 4.14 2.36 2.1 2.3 99.99 99.98 99.6 100.8 98.72 99.93 99.6 b.d.l.: below detection limit (0.01%). Major and minor elements were measured by ICP (inductively coupled plasma) at ACME Labs, Canada. a Tuff. than average for the Upper Continental Crust, 66%, according to Taylor and McLennan (1985) (Fig. 9a and Table 3). The Curamalal Group (VE-03, VE-04, VE-09, and VE-10) shows a high SiO2 content that varies between 90 and 94.5% (i.e., quartzrich following the criteria of Crook (1974)). The Al2O3 (2.1e3.6%), Fe2O3 (0.3e2.5%), CaO (below the detection limit for all of the analyzed samples, <0.01 ppm), Na2O (0.02e0.05%), K2O (0.7e1.1%) and TiO2 (0.05e0.2%) contents are all minor in the Upper Continental Crust (Fig. 9a). The major oxide content of the Ventana Group (VE-01, VE-11, VE-12, VE-13, and VE-14) is characterized by high quantities of SiO2 (85.1e98.6%), Al2O3 (0.7e5.8%), CaO (0.02e0.04), Na2O (0.07e 0.12%), and K2O (0.1e1.6%). Both the Curamalal and Ventana groups have values for all of the major elements (except for SiO2) below the average of the Upper Continental Crust (Fig. 9a). The increased Al, Fe, K, and Na content in the analyzed samples from the Lolén Formation (VE-01 and VE-13) most likely represented a higher muscovite and albite content relative to the Bravard (VE-06) and Napostá (VE-11) samples. The depletion of Na2O in the Curamalal and Ventana groups can be attributed to the small quantities of Na-rich plagioclase present as shown by the petrographical data. The analyzed rocks from the Pillahuincó Group presented homogeneous SiO2 values (approximately 75% with one sample showing 87.5%). The Al2O3 (5.0e13.0%), Fe2O3 (1.6e4.8), CaO (0.4e 3.6%), Na2O (1.1e3.8%) K2O (1.4e2.0%) and TiO2 (0.3e0.6%) contents were higher than for the Curamalal and Ventana Group rocks (Fig. 9a). The elevated CaO content with respect to the other groups is most likely caused by the carbonate lithoclasts observed in these rocks and plagioclase detrital grains (Fig. 8f). Provenance analyses can be obtained using the SiO2 x K2O/Na2O binary diagram of Roser and Korsch (1986). Here, the Curamalal and Ventana groups samples plot in the passive margin ﬁeld. The K2O/ Na2O ratios from the Pillahuincó Group approach 0.5 and reﬂect nearly equal plagioclase and feldspar content in the active continental margin ﬁeld (Fig. 10). Sample VE-22 from the Tunas Formation plotted in the magmatic arc ﬁeld. Provenance analyses can also be obtained using the CaOeNa2Oe K2O triangle diagram proposed by Bhatia (1983) and modiﬁed by Toulkeridis et al. (1999). The rocks analyzed in the Curamalal and Ventana groups plotted in the passive margin ﬁeld. Samples from the Pillahuincó Group showed a random distribution, varying from the active continental margin, ocean island arc, to the continental island arc ﬁelds (Fig. 9b). This random pattern probably occurs due to the greater mobility of the major elements during weathering and diagenetic processes. 6.1.2. Trace element geochemistry The sedimentary provenance studies are more robust when using immobile element ratios because these ratios are not vulnerable to post and pre-depositional processes (McLennan et al., 1993). According to Taylor and McLennan (1985), the Th/Sc ratio is a good indicator for differentiating maﬁc vs. felsic sources. Sediments derived from maﬁc and ultramaﬁc sources in the Upper Continental Crust have ratios below 0.6. Felsic sources lead to detritus with a ratio equal to or greater than 0.79 (McLennan et al., 1990). The Zr/Sc ratio is a robust marker of zircon enrichment due to high Zr concentration in zircon, whereas Sc preserves the provenance signature. The use of Zr/Sc and Th/Sc ratios is important for quantifying the degree of sedimentary recycling because the Zr concentration is Table 4 Trace elements of the Curamalal, Ventana, and Pillahuincó samples. Units Mascota Napostá Providencia Lolén Sauce Grande Piedra Azul Bonete Tunas VE-03 VE-04 VE-10 VE-09 VE-11 VE-12 VE-01 VE-13 VE-14 VE-17 VE-18 VE-16 VE-19a VE-20a VE-21a VE-22 VE-23 VE-24 b.d.l. b.d.l. b.d.l. 89.10 4.16 5.84 74.35 b.d.l. b.d.l. b.d.l. 4.36 7.92 2.67 b.d.l. b.d.l. 21.98 1.19 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.50 6.34 14.06 1.50 5.45 1.15 0.23 1.02 0.19 1.13 0.21 0.63 0.09 0.55 0.08 1.88 0.10 1.19 0.10 6.24 0.10 1.49 0.50 b.d.l. b.d.l. b.d.l. 150.63 14.37 11.89 93.25 b.d.l. b.d.l. b.d.l. 3.96 5.95 3.37 b.d.l. b.d.l. 33.89 6.24 0.10 b.d.l. b.d.l. b.d.l. b.d.l. 0.89 10.21 19.82 2.47 9.81 1.63 0.23 1.65 0.30 1.93 0.40 1.20 0.20 1.41 0.21 2.68 0.59 0.59 0.00 1.68 b.d.l. 8.23 1.39 1.97 0.99 11.84 156.93 20.83 18.85 281.10 b.d.l. 2.66 b.d.l. 3.55 12.83 3.65 b.d.l. b.d.l. 44.81 12.53 b.d.l. b.d.l. 0.00 0.99 b.d.l. 1.09 17.47 40.96 4.17 14.61 2.97 0.55 2.88 0.51 3.28 0.64 1.85 0.30 2.08 0.31 6.61 0.79 1.18 0.00 30.00 b.d.l. 7.80 3.26 0.99 0.99 b.d.l. 134.50 19.48 11.27 180.59 b.d.l. b.d.l. b.d.l. 3.56 5.93 3.66 b.d.l. b.d.l. 67.05 8.60 b.d.l. b.d.l. 0.00 0.99 b.d.l. 3.56 23.83 53.70 5.48 19.98 3.10 0.44 2.38 0.35 2.10 0.40 1.18 0.17 1.20 0.17 4.75 0.79 2.47 0.00 3.46 b.d.l. 11.67 0.79 b.d.l. b.d.l. b.d.l. 58.90 5.99 2.99 32.94 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 1.00 b.d.l. b.d.l. 9.98 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 3.99 8.49 0.98 3.89 0.90 0.13 0.70 0.10 0.70 0.10 0.40 0.06 0.40 0.05 0.90 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 2.00 0.30 b.d.l. b.d.l. 7.97 73.71 7.97 6.97 109.57 b.d.l. 1.00 b.d.l. b.d.l. b.d.l. 1.00 1.00 b.d.l. 4.98 1.99 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 8.37 18.33 2.09 8.37 1.79 0.20 1.29 0.20 1.20 0.20 0.70 0.12 0.80 0.11 2.69 0.20 b.d.l. b.d.l. 9.96 b.d.l. 3.39 0.60 2.96 b.d.l. 18.75 204.32 11.84 8.88 66.13 b.d.l. 1.97 b.d.l. b.d.l. b.d.l. 4.94 0.99 b.d.l. 56.26 2.96 b.d.l. b.d.l. b.d.l. 0.99 b.d.l. 2.57 17.37 29.91 3.90 15.00 2.86 0.56 2.07 0.30 1.58 0.30 0.89 0.14 0.89 0.14 1.78 0.30 b.d.l. 0.20 9.87 b.d.l. 4.94 0.89 3.94 0.98 37.41 173.26 19.69 18.70 95.49 b.d.l. 2.95 b.d.l. b.d.l. b.d.l. 6.89 1.97 b.d.l. 73.83 4.92 b.d.l. b.d.l. b.d.l. 0.98 0.59 3.54 12.70 24.51 2.87 10.73 2.56 0.52 3.15 0.59 3.74 0.69 1.97 0.30 1.97 0.32 2.46 0.49 b.d.l. 0.20 10.83 b.d.l. 6.60 1.87 3.96 0.00 23.78 421.17 60.45 16.45 354.87 b.d.l. 2.58 b.d.l. 5.95 20.81 4.76 b.d.l. 1.09 41.42 5.75 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.79 9.41 21.11 2.69 11.10 2.61 0.51 2.53 0.45 2.75 0.58 1.75 0.26 1.81 0.27 9.02 0.50 2.18 b.d.l. 10.21 b.d.l. 5.75 1.09 9.79 1.96 65.56 201.58 155.59 30.34 370.87 29.36 2.94 b.d.l. b.d.l. 39.14 11.74 1.96 10.76 47.95 12.72 b.d.l. 0.78 b.d.l. 2.94 b.d.l. 2.35 33.37 69.97 8.50 33.27 7.14 1.37 5.87 0.98 5.58 1.08 3.23 0.52 3.52 0.57 10.08 1.08 b.d.l. 0.20 13.70 b.d.l. 13.90 4.40 8.83 1.96 69.68 435.76 209.05 23.55 220.83 29.44 6.87 b.d.l. b.d.l. 49.07 14.72 1.96 b.d.l. 60.85 9.81 b.d.l. b.d.l. b.d.l. 2.94 b.d.l. 2.45 34.74 65.76 7.90 30.62 5.99 1.25 4.71 0.79 4.32 0.79 2.45 0.40 2.55 0.41 6.08 0.88 b.d.l. 0.20 14.72 b.d.l. 10.31 3.04 7.88 1.97 63.05 186.20 314.28 23.64 155.66 b.d.l. 3.94 b.d.l. 9.85 39.41 11.82 1.97 15.76 55.17 8.87 b.d.l. b.d.l. b.d.l. 2.96 0.69 2.56 34.38 58.62 7.61 29.16 5.71 1.13 4.53 0.79 4.04 0.79 2.17 0.34 2.36 0.36 4.24 0.89 b.d.l. 0.20 38.42 0.69 9.26 1.87 8.35 3.13 62.62 1429.91 53.23 25.05 220.23 b.d.l. 6.26 b.d.l. 31.31 73.06 22.96 b.d.l. b.d.l. 264.06 20.87 b.d.l. b.d.l. b.d.l. 5.22 b.d.l. 17.74 32.04 83.60 7.48 27.97 5.53 0.83 4.38 0.73 4.28 0.83 2.71 0.47 3.34 0.53 6.68 1.67 b.d.l. 1.36 18.79 1.15 19.31 3.13 4.19 4.19 49.19 1945.78 202.01 27.21 184.22 b.d.l. 2.09 b.d.l. 20.93 62.80 23.03 b.d.l. 7.33 243.88 33.49 b.d.l. b.d.l. b.d.l. 5.23 0.63 6.70 86.04 120.37 14.86 47.52 7.43 1.16 4.92 0.84 4.50 0.94 2.83 0.52 3.66 0.64 6.18 3.35 b.d.l. 1.15 20.93 0.84 43.96 4.08 8.28 3.10 55.87 1052.14 203.81 23.79 162.42 b.d.l. 7.24 b.d.l. 20.69 72.42 17.59 1.03 5.17 166.56 14.48 b.d.l. b.d.l. b.d.l. 4.14 b.d.l. 9.83 26.79 65.38 7.12 27.52 5.69 0.96 4.45 0.72 4.35 0.83 2.48 0.39 2.79 0.44 4.76 1.14 b.d.l. 0.83 21.73 0.62 16.97 2.38 8.78 1.95 92.73 100.54 314.30 20.50 183.51 29.28 10.74 b.d.l. 19.52 97.61 14.64 1.95 5.86 21.47 13.67 b.d.l. b.d.l. b.d.l. 3.90 b.d.l. 1.17 31.04 61.59 7.13 27.53 5.27 1.21 4.20 0.68 3.81 0.68 2.15 0.33 2.25 0.36 4.78 0.98 b.d.l. b.d.l. 68.33 b.d.l. 8.69 1.95 6.85 2.94 44.05 326.00 138.72 23.10 125.90 b.d.l. 5.97 b.d.l. 8.81 43.08 13.90 b.d.l. 4.80 69.21 9.40 0.10 b.d.l. b.d.l. 1.96 b.d.l. 2.64 31.91 52.18 7.63 29.27 5.14 1.22 4.78 0.73 4.21 0.81 2.30 0.33 2.25 0.34 3.43 0.59 3.52 0.00 3.92 b.d.l. 7.73 2.55 4.88 0.98 38.10 3152.48 286.92 12.31 120.84 b.d.l. 4.30 b.d.l. 6.74 32.24 10.26 b.d.l. 2.05 74.64 6.25 0.29 b.d.l. b.d.l. 1.95 b.d.l. 1.56 16.90 41.42 4.19 15.73 2.81 0.83 2.57 0.40 2.19 0.43 1.25 0.20 1.32 0.21 3.13 0.49 3.52 b.d.l. 6.74 b.d.l. 6.74 3.03 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Sc Be V Ba Sr Y Zr Cr Co Ni Cu Zn Ga Ge As Rb Nb Mo Ag In Sn Sb Cs La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Tl Pb Bi Th U La Lola b.d.l.: below detection limit. Trace elements were measured by fusion ICP-MS (inductively coupled plasma mass spectrometry) at ACME Labs, Canada. a Tuff. 27 28 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 Table 5 UePb zircon data from the Claromecó Basin’s tuff. Data were obtained by LA-MC-ICP-MS. Spot VE-19 069-E1 072-E2 073-E5 074-E6 075-E9 076-E11 077-E14 078-E16 079-E21 f206 0.0005 0.0007 0.0002 0.0004 0.0013 0.0008 0.0010 0.0082 0.0010 Pb Th U Isotopic ratios ppm ppm ppm 232 207 9 23 21 11 21 7 16 6 23 125 620 329 135 532 75 383 77 95 162 332 390 206 307 137 288 107 261 0.78 1.88 0.85 0.66 1.75 0.55 1.34 0.73 0.37 0.332 0.366 0.336 0.341 0.372 0.338 0.336 0.333 0.658 Th/238U Pb/235U 6.47 5.01 4.70 5.75 7.04 8.01 5.57 12.83 4.77 Ages 206 Pb/238U 0.0463 0.0491 0.046 0.046 0.049 0.046 0.046 0.045 0.082 5.37 4.16 4.29 4.89 4.45 6.58 4.52 5.60 4.10 directly related to the zircon content of the sediments and indicates the degree of recycling. The Th/Sc ratios in the Curamalal Group range between 3.95 and 11.8 with two samples from the La Lola Formation (VE-03 and VE04) with Sc content below 1 ppm. The Th/Sc ratios of the samples from the La Lola (VE-10) and Mascota (VE-09) formations are 11.8 and 3.95, respectively; these values are both above 0.79, which indicates a felsic source similar to the Upper Continental Crust. For the Ventana Group, samples VE-01 and VE-13 (Lolén Formation) show a fairly constant Th/Sc ratio of approximately 1.66, which is above the average for the Upper Continental Crust. The studied samples from the Naposta (VE-11) and Providencia (VE-12) formations showed values below the detection limit of 1 ppm. The Th/Sc ratios of the Sauce Grande and Piedra Azul formations are quite similar, 1.42 and 1.45, respectively. The ratios for the Bonete and Tunas Formations vary between 0.98 and 1.38. All of these values are above the Upper Continental Crust average and are indicative of felsic source areas. The Zr/Sc ratios for all of the samples from the Pillahuincó Group were low and varied between 0.01 and 0.05, which indicates a low degree of sedimentary recycling. No sample had a ratio below 0.6, which indicates that the source areas are not constituted by maﬁc/ultramaﬁc rocks. The low Sc content was also indicative that no maﬁc/ultramaﬁc rocks were involved in the source areas. In the SceTheZr/10 diagram from Bhatia and Crook (1986), the Curamalal and Ventana groups are assigned to a passive margin environment. A change between the Pillahuincó Group rocks derived from and deposited at a passive margin setting and those with a continental arc (of an active continental margin) provenance was observed (Fig. 9c). 6.2. Tuffs from the Tunas Formation Tuff horizons are ideal stratigraphic markers because, as the products of fallen volcanic ashes, they are widely distributed over large areas in a short period of geologic time. The geochemical and geochronological correlations between tuffs in the Tunas Formation of the Claromecó Basin and similar chronocorrelated units in the Paraná and Karoo Basins (Tankard et al., 2009) provide a good understanding of the volcanic activity and sedimentation along the southwestern margin of the Gondwana supercontinent during the Permian (Fig. 14). Whole-rock major, minor, trace and rare-earth element data were evaluated to characterize the tuffs from the Tunas Formation. Geochemical data (Zr/TiO2 and Nb/Y) for tuff samples from the Tunas Formation (VE-19, VE-20, and VE-21) plotted on the discrimination diagram of Winchester and Floyd (1977) suggest that the source magmas had rhyodacitc/dacitic to trachyandesitic composition (Fig. 11a). This conclusion is supported by the Rho 207 Pb/206Pb 0.83 0.83 0.91 0.85 0.63 0.82 0.81 0.44 0.86 0.0521 0.0540 0.0526 0.0530 0.0544 0.0530 0.0528 0.0527 0.0576 3.62 2.79 1.92 3.02 5.45 4.58 3.26 11.55 2.43 206 Pb/238U 292 309 292 294 313 292 291 290 513 16 13 13 14 14 19 13 16 21 207 Pb/235U 292 317 295 298 322 296 295 292 514 19 16 14 17 23 24 16 38 24 207 Pb/206Pb 290 373 314 329 388 329 320 316 517 10 10 6 10 21 15 10 36 13 Disc. Best estimated % Age 1 17 7 11 19 11 9 8 1 292 309 292 294 313 292 291 290 513 31 25 25 28 27 38 26 32 41 occurrence of quartz, plagioclase and pyroxene as fragmented phenocrysts in the tuffs, as proven by X-ray diffraction analysis carried out by Alessandretti (2012). When plotted on the Na2O þ K2O SiO2 (TAS) discrimination diagram by Le Bas et al. (1986), the tuffs demonstrated a dacitic to rhyolitic composition with a SiO2 content ranging from 66 wt.% to 74 wt.% (Fig. 11c). They are high K and follow a calc-alkaline trend (Fig. 11b). Based mainly on the tectonic discrimination diagram (Rb vs. Y þ Nb) of Pearce et al. (1984) (Fig. 11g), LREE enrichment in REE patterns (Fig. 12a), and the depletion of Nb, P, Ti, and Sr in rock/ primordial mantle patterns (Fig. 12b), we concluded that the tuffs of the Tunas Formation were derived from a normal calc-alkaline continental arc setting (Fig. 11d and e). The REE patterns for tuffs also show negative Eu anomalies (Fig. 12a), characteristic of calk-alkaline magmas (Pearce, 1996) in which Eu was retained by the source feldspar during partial melting or was removed by fractional crystallization of the plagioclase. 7. UePb dating The tuffs of the Tunas Formation crop out as laterally continuous decimetric white layers (10e50 cm), with tabular geometries and foliated structures (Fig. 7). One sample (VE-19) was analyzed by UePb zircon geochronology using LA-MC-ICP-MS (Laser Ablation Micropobe, Multi-Collector, Inductively Coupled Plasma, Mass Spectrometer) at the Isotope Geology Laboratory of the University of Brasilia, Brazil. The sample was collected at 38 12ʹ40.6ʺ S and 6129ʹ04.7ʺ W and corresponds to a vitric tuff interbedded with sandstones and pelites from the top of the Tunas Formation (Fig. 7a). The U content of the analyzed crystals is 107e390 ppm and the Th/U ratios (based on the GJ-1 reference zircon) are between 0.73 and 1.88. Of a total of nine (9) dated zircon crystals, three (3) had ages between 283 16 and 287 19 Ma, three (3) were between 290 12 and 292 16 Ma, two (2) between 309 13 and 313 14 Ma and, one (1) was 513 21 Ma (see Table 5). The error in the obtained age was uncommonly large due to the small size of the dated zircons and the small amount of 206 Pb and 207Pb. The three younger zircon grains revealed a mean 206 Pb/238U age of ca. 284 15 Ma (3 points with 95% of conﬁdence, MSWD ¼ 0.025) that was interpreted as the best estimate for the crystallization and depositional age of the volcanic ash rock (Fig. 13). The older zircon grains are interpreted as an inherited component. 8. Discussion Geochemical and petrographical data from the Curamalal and Ventana groups indicated that these rocks were deposited at a L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 passive margin setting with cratonic provenance (Fig. 6, Fig. 9b and c). On the top of the Ventana Group is observed a change in provenance pattern, marked by the recycled orogenic provenance of rocks of the Lolén Formation (Fig. 6a and b). Both major and trace elements revealed satisfactory results when employed in tectonic and provenance discriminant diagrams, clearly attributing the Curamalal and Ventana groups to the passive margin ﬁeld. The paleocurrent and compositional results suggest areas located to the northeast as the main source (the Tandilia Massif, Fig. 1). This agrees with previous studies that focused on petrographical (Andreis and Japas, 1991; Andreis and Cladera, 1992; LópezGamundí et al., 1995), sedimentological, stratigraphical (Harrington, 1947, 1970; Buggisch, 1987; Zavala et al., 1993) and structural (Von Gosen et al., 1991; Cobbold et al., 1991) approaches. Recent UePb and LueHf isotopic data for the Providencia and Lolén formations were obtained by Uriz et al. (2010), suggesting that the sedimentary input was derived from Gondwanan sources and from terranes accreted during the Pampean and Famatinian orogenies. Only a small number of Archean and Paleoproterozoic zircons grains were dated, meaning that the Río de la Plata/Kaapvaal cratons were not a signiﬁcant source for sedimentary input to the basins during Silurian-Devonian interval. According to the youngest zircon grains dated, the maximum depositional ages for the Providencia and Lolén formations are 476 and 387 Ma, respectively. Based on LueHf isotopes from zircon grains they also report an important recycling process with Mesoproterozoic crust, while more than 30% of analyzed zircon grains crystallized in a juvenile magmatic source. The diagrams for the Pillahuincó Group employing major elements (CaO, Na2O, and K2O) as their provenance discriminants exhibit a random pattern (Fig. 9b), making the application of these elements restricted for the provenance studies. When using immobile elements (Zr, Th, Sc) as discriminants a transition from rocks derived from and deposited at a passive margin is observed (Sauce Grande and Piedra Azul formations) to those derived from a magmatic arc setting (Bonete and Tunas formations), which may record the passage from passive to active margin. Both major and trace elements data for the Bonete and Tunas formations show very strong and consistent signatures from at least magmatic sources most likely related to continental arc volcanism (Fig. 9c). The data obtained for the Pillahuincó Group is also concordant with previous research that demonstrated a change in the direction of transport from NE to SW in the base, to SW to the NE in the upper section. (Andreis and Cladera, 1992; López-Gamundí and Rossello, 1998). When the average chemical composition of the Curamalal, Ventana and Pillahuincó groups is compared with each other and the average composition of the Upper Continental Crust, a clear compositional similarity between the ﬁrst two groups is revealed. On the other hand, the Pillahuincó Group has an average composition very similar to the Upper Continental Crust, supporting the origin of the detrital rocks of this group from different source areas (Fig. 9a). In an attempt to prove the reliability of the geochemical data used in this study of provenance, seventeen (17) representative samples of the Ventania System were subjected to the Gazzie Dickinson point-count method. Our detrital modes from the Sauce Grande-Piedra Azul-Bonete succession indicate a transitional continental to cratonic provenance, as do the results obtained by Andreis and Cladera (1992) and López-Gamundí et al. (1995) (Fig. 6a and b). The potential provenance terrane for this sequence is the Sierras de Tandilia, a cratonic complex located in the northeast (Fig. 1). The sandstone detrital modes of the Tunas Formation showed an important change in the transport direction of the basin with a clear afﬁnity to the magmatic arc ﬁeld, which was conﬁrmed by the polarity change in the paleocurrent patterns, 29 low quartz content and abundance of lithic fragments. Both the geochemical and petrographical data of this study converged into a common conclusion and proving that, in some cases, geochemical approaches can be employed with petrographical studies. Magmatic activity in SW Gondwana was distributed on large areal and temporal scale during the Permo-Carboniferous interval (Llambías, 1999). Two main magmatic episodes are recognized: (i) one during the Cisuralian and Guadalupian epochs from 299 to 260 Ma that is accepted as subduction related and (ii) one during the Late Permian to Lower Triassic from 251 to 245 Ma. Both episodes are part of the Choiyoi Magmatic Province which is to the top dominated by acid rocks (Kay et al., 1989). The ﬁrst episode occurred in the northern Patagonia region and along the Panthalassa margin from northern Chile to the south and consists of granitoids, cogenetic rhyolitic ignimbrites and coeval ash-fall tuffs. Evidence of explosive acidic volcanism in the south of the Paleozoic Gondwana basins has been reported during Permian times (Fig. 14) (Bangert et al., 1999; Stolhofen et al., 2000; Guerra-Sommer et al., 2005; Rocha-Campos et al., 2006, 2008; López-Gamundi, 2006, among others). These rocks have calk-alkaline afﬁnities that evolved to peraluminous, peralkaline magmas in the younger rocks (LópezGamundi, 2006). Geochemical data for the tuffs from the Tunas Formation point to pyroclastic volcanic activity derived from a calk-alkaline continental-arc setting. The analyzed samples were plotted in the geotectonic discrimination diagram of Pearce et al. (1984) in the VAG to WPG ﬁelds (Fig. 11f and g), which may be related to the observed change in the geotectonic setting of the Choiyoi Magmatic Province from the volcanic arc to within the plate extensional ﬁelds (Kay et al., 1989). The tuffs have been deposited under subaqueous conditions (Iñiguez et al., 1988; Alessandretti, 2012) as evidenced by the smectite interpreted as the result of altered volcanic material. López-Gamundi (2006) based on the age constrains and the similarities between the volcanic rocks along the plate margin and the tuffaceous horizons preserved in the Claromecó, Paraná, and Karoo basins proposed a genetic linkage between the two episodes. This link between geochemical and geochronological data for tuffaceous horizons and the knowledge of the stratigraphic record of the Gondwana basins offers a robust tool for understanding the widespread volcanism and sedimentation that occurred during the Permian along the southwest of Gondwana. The new UePb LA-MCICP-MS zircon age of 284 15 Ma (Fig. 13) obtained from tuff layers of the Tunas Formation is signiﬁcant to constrain the range of the volcanogenic material present in the Claromecó, Paraná, and Karoo basins. The present age overlaps that obtained by Tohver et al. (2012) for tuffs from the Tunas Formation, 282.4 2.8 Ma (UePb zircon SHRIMP age). The source of the ash-fall rocks in the Claromecó Basin, as well as in the Karoo and Paraná basins was suggested to be Choiyoi Magmatic Province along the Andean Cordillera and its equivalent in Patagonia. 9. Conclusions Based on the petrographical and geochemical data presented here, the Curamalal and Ventana groups consist of rocks derived from cratonic areas (Fig. 6c) and deposited in a passive margin environment (Fig. 9a, c, and Fig. 10). At the top of the Ventana Group, the rocks of the Lolén Formation present a recycled orogenic provenance, which mark sedimentary changes in the basin. The Pillahuincó Group shows a transition from rocks derived from and deposited in a passive margin setting (Sauce Grande and Piedra Azul formations) to rocks derived from magmatic arc sources (Bonete and Tunas formations). These data corroborate previous investigations showing a polarity change in the transport direction for the upper portion of the basin and therefore a change in the 30 L. Alessandretti et al. / Journal of South American Earth Sciences 47 (2013) 12e31 source-area(s) (Andreis and Japas, 1991; López Gamundí et al., 1995; López Gamundí and Rossello, 1998; Ramos, 2008). Geochemical analysis revealed that the volcanoes responsible for the tuffs of the Tunas Formation were located in a calc-alkaline continental-arc setting and had a rhyodacitic to dacitic composition. The geochronological age of 284 15 Ma obtained through zircon UePb ages (LA-ICPMS) of tuffs from the Tunas Formation was interpreted as the depositional age of the stratigraphic unit. A possible source for the tuffs of the Tunas Formation is the Somun Cura Massif in northern Patagonia, where the Permian granitoids and coeval volcanic rocks related to the Choiyoi Magmatic Province were largely preserved. This assertion is grounded in both the geochemical and geochronological data from rock outcrops in the two regions. Another possible source region are the rocks also associated to the Choiyoi Magmatic Province that crop out with a NeS trend on the border of Argentina and Chile between the latitudes 23 S and 42 S. The lower section of this volcanic sequence was related to a calc-alkaline arc (Kleiman and Japas, 2009). The combined geochemical ﬁngerprints of the tuffs found in the Tunas Formation and geochronological data strongly indicate that the source area for the tuffaceous horizons is the Choiyoi Magmatic Province. The geographical proximity of the units provides further evidence (Fig. 1). All of the information presented herein about the tuffs is consistent with the presence of an intense explosive acidic volcanism in the southern margin of Gondwana that was responsible for expelling huge amounts of volcanic ash and is now preserved in the chronocorrelated layers of Paraná, Karoo, and Claromecó basins. Acknowledgments This study was supported by research grants awarded by the “Fundação Coordenação de Aperfeiçoamento De Pessoal de Nível Superior” (CAPES, Brazil). We would like to thank Carlos Cingolani (Universidad Nacional de La Plata), Umberto Giuseppe Cordani (Universidade de São Paulo), Felipe Guadagnin (Universidade Federal do Espírito Santo), and an anonimous reviewer for thoughtful and constructive reviews. We thank also Márcia Correa Machado and Maximiliano Naipauer for helping with the analytical procedures. 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Provenance, volcanic record, and tectonic setting of the Paleozoic Ventania Fold Belt and the Claromecó Foreland Basin: Implications on sedimentation and volcanism along the southwestern Gondwana margin

Provenance, volcanic record, and tectonic setting of the Paleozoic Ventania Fold Belt and the Claromecó Foreland Basin: Implications on sedimentation and volcanism along the southwestern Gondwana margin

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