Keywords

1 Introduction

The Neoproterozoic Brasiliano/Pan-African orogenic cycle in southwestern Gondwana was the consequence of convergence and collision between three main continental fragments: the Río de la Plata, Congo and Kalahari cratons (Fig. 7.1). Several minor crustal blocks were also incorporated during these collisional events, mostly being preserved as basement inliers within Neoproterozoic mobile belts (e.g., Oriolo et al. 2017). However, Neoproterozoic paleogeographic reconstructions focused on major cratons and paid little attention to these subordinated blocks (e.g., Alkmim et al. 2001; Tohver et al. 2006; Li et al. 2008; Saalmann et al. 2011; Rapalini et al. 2015), which in the eastern margin of South America in Uruguay and southern Brazil are mostly represented by the Nico Pérez Terrane and the Luís Alves and Curitiba microplates (Bossi and Campal 1992; Basei et al. 2009; Philipp et al. 2016a; 2018; Oriolo et al. 2016a) (Fig. 7.2).

Fig. 7.1
figure 1

Schematic reconstruction of south-western Gondwana showing the main Archean to Paleoproterozoic cratons and the Neoproterozoic orogenic belts. (Modified from Rapela et al. 2011 and Philipp et al. 2017a, b.)

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Fig. 7.2
figure 2

Main tectonic units of the Precambrian of southern Brazil and Uruguay. (Modified from Basei et al. 2010.) The location of detailed geological maps (Figs. 7.3, 7.4, 7.5, 7.6, 7.7 and 7.8) of areas with Archean-Paleoproterozoic and Mesoproterozoic outcrops is indicated

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Despite being traditionally considered as part of the Río de la Plata Craton (e.g., Mallmann et al. 2007; Bossi and Cingolani 2009), recent contributions have indicated the allochthony of the Nico Pérez Terrane and its African derivation (Oyhantçabal et al. 2011a; Rapela et al. 2011; Oriolo et al. 2016a; Philipp et al. 2016a). The Taquarembó Block and several basement inliers in the Dom Feliciano Belt in southernmost Brazil show similarities with the Nico Pérez Terrane in Uruguay, thus suggesting a more regional extension of the latter (Oyhantçabal et al. 2011a). A possible extension of the Nico Pérez Terrane even further to the north, including the suspected Paranapanema Craton (Mantovani and de Brito Neves 2005) and Luís Alves Microplate (Basei et al. 2009), is still unclear owing to the sedimentary cover of the Paraná Basin.

This contribution aims to present an updated review of the geology and tectonic evolution of the Nico Pérez Terrane in Uruguay and Rio Grande do Sul state in Brazil, also comparing it with adjacent basement blocks in order to determine the regional extension and tectonic evolution of this crustal terrane.

2 Geology of the Nico Pérez Terrane (Uruguay)

2.1 Introduction

The Nico Pérez Terrane is mostly exposed in central Uruguay and further north in the Isla Cristalina de Rivera (Fig. 7.3). The Sarandí del Yí Shear Zone constitutes the western margin of the Nico Pérez Terrane (Bossi and Campal 1992; Oriolo et al. 2015, 2016b), separating it from the Río de la Plata Craton. To the east, basement inliers of this terrane have been recognized within the Dom Feliciano Belt up to the Sierra Ballena Shear Zone (Bossi and Campal 1992; Oyhantçabal 2005; Oyhantçabal et al. 2009a, 2011b). Though the Nico Pérez Terrane was originally defined as a Paleoproterozoic block with Neoproterozoic magmatism and deformation (Bossi and Campal 1992), recent contributions have demonstrated a much more complex evolution extending up to the early Archean (Hartmann et al. 2001; Mallmann et al. 2007; Oyhantçabal et al. 2011a; Oriolo et al. 2016a).

Fig. 7.3
figure 3

Geological map of the Nico Pérez Terrane and adjacent blocks. (Modified from Oyhantçabal et al. 2011a, b, Spoturno et al. in press and Masquelín et al. 2017.)

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The Nico Pérez Terrane in Uruguay can be divided into two major blocks: Pavas and Cerro Chato, separated by the Sierra de Sosa Shear Zone (Fig. 7.3). Both blocks expose different crustal levels of Paleoproterozoic or older rocks. While the Pavas Block is characterized by amphibolite-facies metamorphism, the Cerro Chato Block displays granulite-facies metamorphism. In both blocks, granitic gneisses, mafic rocks and volcanosedimentary supracrustal sequences occur in the basement. The post-Paleoproterozoic cover in the Cerro Chato Block comprises only scarce Late Neoproterozoic metasediments, whereas in the Pavas Block both pre-Neoproterozoic and Neoproterozoic metasediments are widespread. A summary of available geochronological data from this terrane in Uruguay is presented in Table 7.1.

Table 7.1 Summary of available geochronological data of the Nico Pérez Terrane in Uruguay
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2.2 The Cerro Chato Block

This crustal block is bounded by the Sarandí del Yí and the Sierra de Sosa shear zones to the west and east, respectively (Oriolo et al. 2015, 2016b, c), and it comprises high-grade felsic and mafic orthogneisses with scattered relics of a supracrustal succession and an unmetamorphosed Late Paleoproterozoic granite intrusion.

2.2.1 The Valentines—Rivera Granulitic Complex

The Valentines-Rivera Granulitic Complex is one of the most important lithostratigraphic units of the Cerro Chato Block. It was originally defined as the Valentines Formation for the central region of Uruguay and was subsequently recognized further north in the Isla Cristalina de Rivera (Bossi and Umpierre 1969; Preciozzi et al. 1985; Ellis 1998; Oyhantçabal et al. 2011a). Felsic and subordinated mafic to intermediate granulitic orthogneisses are the main lithologies.

The felsic granulites present a mineral assemblage of mesoperthitic alkali feldspar, plagioclase and quartz with biotite, clinopyroxene and garnet as the main accessories. The texture is granoblastic to gneissic. Triple junctions, cusps and grain-boundary migration microstructures evidence fluid-assisted diffusional and dislocation creep of feldspars and pyroxene under high-T conditions. These high-T deformation features are partially overprinted by low-T deformation.

The mafic granulites, in turn, contain clinopyroxene, orthopyroxene, plagioclase and garnet, and show granoblastic texture with triple junctions at c. 120°. Retrograde metamorphic minerals are frequently present.

The available geochemical data (Oyhantçabal et al. 2012) indicate that granulitic orthogneisses have compositions ranging from gabbro to granite with calc-alkaline affinity and exhibit marked negative Nb, Ta and Ti anomalies. These features are compatible with a genesis of the protoliths in a continental magmatic arc setting.

U–Pb ages in zircon for this complex demonstrate multistage magmatism at 2.18–2.10 Ga, followed by high-grade metamorphism at 2.10–2.02 Ga (Santos et al. 2003; Oyhantçabal et al. 2012; Oriolo et al. 2016a). On the other hand, c. 1.8 Ga monazite ages (Th–U–Pb monazite; CHIME-EPMA method) reported by Oyhantçabal et al. (2012) record amphibolite-facies retrograde metamorphism and probably correspond to a different event from the one recorded by zircons. The slightly discordant U–Pb age in zircon obtained by Oriolo et al. (2016a) for a mafic granulite seems to confirm that felsic and mafic rocks are coeval. Archean zircon inheritance was reported for the Valentines and Isla Cristalina de Rivera areas (Santos et al. 2003; Oyhantçabal et al. 2012; Oriolo et al. 2016a).

2.2.2 Archean to Paleoproterozoic Supracrustal Rocks (Valentines and Vichadero Formations)

A high-grade platform metavolcanosedimentary sequence rich in BIFs crops out in two main areas in the Cerro Chato Block. The Vichadero Formation (Preciozzi et al. 1985; Ellis 1998; Oyhantçabal et al. 2011a, 2012) occurs in northern Uruguay in the Isla Cristalina de Rivera (Fig. 7.4), while the Valentines Formation (Bossi and Umpierre 1969) is located in the centre of the Nico Pérez Terrane.

Fig. 7.4
figure 4

Geological map of the Isla Cristalina de Rivera in northern Uruguay. (Modified from Oyhantçabal et al. 2012.)

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The Vichadero Formation (Ellis 1998) comprises BIFs, metaquartzites, forsterite marbles, mafic volcanic rocks and pyroxene granofelses. All lithologies were affected by high-grade metamorphism and occur as isolated and scattered kilometre-scale bodies hosted in the granulitic orthogneisses.

The Valentines Formation comprises lithologies similar to those of the Vichadero Formation including BIFs, leucocratic to mesocratic gneisses, pyroxene granofelses and rare forsterite marbles. The gneisses contain mesoperthitic alkali feldspar, plagioclase, pyroxene, amphibole and biotite, and they are finely interbedded with the BIF bands, thus suggesting a volcanic protolith. Retrograde metamorphism is recorded by secondary chlorite and epidote.

Both formations share the same lithological association and mineral parageneses. They are therefore considered to be part of the same platform succession of Neoarchean to Siderian age, the BIF deposits probably being of the Lake Superior type (Ellis 1998; Chap. 18).

2.2.3 The Late Paleoproterozoic Illescas Granite

The Illescas intrusion is a rapakivi-type granite (Campal and Schipilov 1995), which presents a high-K subalkaline signature based on scarce geochemical data (Gaucher and Blanco 2014). Subalkaline affinity and low Ga/Al ratios suggest that this intrusion belongs to the A2-type post-collisional granites of Eby (1992). Therefore an anorogenic (within-plate) setting for this granite can be ruled out and the correlation with the coeval calc-alkaline Campanero Unit is possible. The age of this intrusion is constrained at 1760 ± 32 Ma by Rb-Sr whole-rock data (Bossi and Campal 1992) and a comparable 207Pb/206Pb zircon age of c. 1.75 Ga (Campal and Schipilov 1995). Although ductile to brittle deformation is observed in the margins of the pluton, most of the intrusion preserves magmatic textures and mineralogy, and thus represents an important constraint for the tectonothermal evolution of the Cerro Chato Block.

2.3 The Pavas Block

The Pavas Block comprises the La China Complex and the Las Tetas sedimentary platform cover (Preciozzi et al. 1979, 1985; Hartmann et al. 2001). The contact between both units is tectonic, including low-angle thrusts as well as high-angle transcurrent shear zones. Hartmann et al. (2001) indicated that both complexes are separated by a thrust, which imbricates orthogneisses of the La China Complex over metasediments of the Las Tetas Complex. On the other hand, Oriolo et al. (2016c) recognized the María Albina Shear Zone as the main boundary separating the La China Complex to the west from the Las Tetas Complex to the east, although minor tectonic slices of metasediments and orthogneisses were also identified to the west and east, respectively.

2.3.1 The Gneissic-Migmatitic Basement (La China Complex)

The La China Complex is made up of orthogneisses, migmatites, amphibolites, actinolitites, talc-bearing schists and serpentinites (Preciozzi et al. 1979, 1985; Oyhantçabal and Vaz 1990; Hartmann et al. 2001). A metatonalite of this complex yields an age of 3404 ± 8 Ma (U–Pb SHRIMP) in zircon cores interpreted as the age of the magmatism, while slightly younger ages could represent partial resetting as a result of upper amphibolite-facies metamorphism documented in low Th/U zircon rims dated at 3.1 Ga (Hartmann et al. 2001). On the other hand, Gaucher et al. (2011) obtained a U–Pb LA-ICP-MS zircon age of 3096 ± 45 Ma in a migmatite cropping out in the surroundings of the metatonalite. This age seems to reflect partial melting during the upper amphibolite-facies event.

Although the La China Complex has only been recognized locally in the central Nico Pérez Terrane, the existence of Archean Sm–Nd and Lu–Hf model ages and zircon inheritance in Paleo- and Neoproterozoic magmatic units indicates the ubiquitous presence of Archean crust in the Nico Pérez Terrane (Santos et al. 2003; Mallmann et al. 2007; Oyhantçabal et al. 2011a; Oriolo et al. 2016a). Despite the lack of geochemical data for these rocks, a tonalite–trondhjemite–granodiorite (TTG) association affinity is assumed for the orthogneisses of this complex.

2.3.2 The Sedimentary Platform Cover (Las Tetas Complex)

The Las Tetas Complex comprises fuchsite-bearing quarzites, metaconglomerates, micaschists, marbles and BIFs (Oyhantçabal and Vaz 1990; Hartmann et al. 2001; Gaucher et al. 2014a, b, c).

The rocks of this complex show variable deformation, frequently very strong, and they are thrust stacked and crosscut by transcurrent shear zones. Mineral parageneses indicate variable metamorphic grade ranging from sillimanite-bearing quartzites in the north (Oyhantçabal and Vaz 1990) to staurolite-garnet micaschists in the south (Hartmann et al. 2001), and even anchimetamorphic rocks according to Gaucher et al. (2014a, b, c).

The depositional environment for this lithological association was a siliciclastic-carbonate platform in a stable shelf (Hartmann et al. 2001). According to Gaucher et al. (2014a, b, c), a shallowing up trend is observed in the facies association.

The maximum deposition age is constrained by the youngest detrital zircon yielding a concordant 207Pb/206Pb age of 2717 ± 24 Ma (U–Pb SHRIMP, Hartmann et al. 2001), which is further supported by similar detrital zircon ages of c. 2.8–2.7 Ga (Hartmann et al. 2001). The minimum age is poorly constrained by an Ar/Ar phlogopite age of 621.4 ± 1.0 Ma (Oriolo et al. 2016c). A Neoarchean or Siderian deposition age is the most plausible, taking into account the fact that Rhyacian protolith ages are widespread in the basement of the Nico Pérez Terrane, but detrital zircons of this age are not observed in this complex. On the other hand, Ar/Ar and K–Ar data between c. 630 and 580 Ma obtained in metasediments dates an Ediacaran metamorphic overprint and deformation event in the Las Tetas Complex (Oriolo et al. 2016c).

2.4 Basement Inliers of the Nico Pérez Terrane in the Dom Feliciano Belt

Several basement inliers occur within the schist belt of the Neoproterozoic Dom Feliciano Belt in Uruguay. They comprise gneissic basement as well as pre-Neoproterozoic supracrustal successions.

2.4.1 Late Paleoproterozoic Orthogneisses (Campanero Unit)

The Campanero Unit is one of the largest basement inliers and is located between the schist belt and the Sierra Ballena Shear Zone (Fig. 7.3). It comprises felsic orthogneisses, with scattered slivers of supracrustal rocks including amphibolites, micaschists, BIFs and migmatites (Sánchez-Bettucci 1998; Sánchez-Bettucci et al. 2003; Oyhantçabal 2005) that are interpreted as relicts of the Las Tetas Complex. Geochemical data indicate that felsic orthogneisses mostly display a high-K calc-alkaline, slightly peraluminous signature (Oyhantçabal 2005). A U–Pb conventional zircon age of 1735 ± 32 Ma was obtained from orthogneisses (Sánchez-Bettucci et al. 2004), later confirmed by an U–Pb SHRIMP zircon age of 1754 ± 7 Ma (Mallmann et al. 2007), and interpreted as the age of the gneiss protolith. High-T foliation and development of striped gneisses are typical microstructural features in these rocks. On the other hand, an Ar/Ar hornblende age of 564.0 ± 4.1 Ma reported for an amphibolite provides a minimum age for the high-T foliation and indicates cooling during the Ediacaran period (Oyhantçabal et al. 2009b).

2.4.2 Mesoproterozoic Metavolcanosedimentary Cover

Though scarce, two Mesoproterozoic low- to medium-grade metavolcanosedimentary sequences—the Parque UTE and Mina Verdún groups—were recognized in the schist belt of the southern Dom Feliciano Belt (Fig. 7.3). In the case of the Parque UTE Group, neither base nor top are exposed (Chiglino et al. 2008, 2010). On the other hand, the base of the Mina Verdún Group is not exposed, whereas the top is separated by a tectonic contact from the Verdún quartzites and is discordantly overlain by the Ediacaran Las Ventanas Formation (Poiré et al. 2003, 2005).

From base to top, the Parque UTE Group comprises mostly mafic and felsic metavolcanic rocks with intercalations of metapelites, dolomitic marbles, marble-metamarl-metapelite alternations and metatuffs (Chiglino et al. 2008, 2010). In the case of the Mina Verdún Group, metarhyolites are exposed at the base and overlain by metapelites, scarce metamarls and marbles, the latter corresponding mostly to limestones and minor dolostones only recognizable at the top (Poiré et al. 2003, 2005; Poiré and Gaucher 2009).

For the Parque UTE Group, Oyhantçabal et al. (2005) reported U–Pb ID-TIMS zircon ages of 1492 ± 4 Ma from a metagabbro at the base of the unit and of 1429 ± 21 Ma from a metavolcanoclastic rock at the top, whereas Gaucher et al. (2014a) reported a U–Pb SIMS zircon age of 1461.8 ± 3.9 Ma from a metatuff probably corresponding to the base. The age of the Mina Verdún Group is constrained by a U–Pb LA-ICP-MS zircon age of 1433 ± 6 Ma obtained from a basal metarhyolite (Gaucher et al. 2011).

Available geochronological data for the felsic volcanic rocks point to a similar time period. This fact, the very close geographic proximity and the lithological similarities demonstrate that both units most probably belong to one Mesoproterozoic stable platform cover above the Nico Pérez Terrane, subsequently incorporated into the Dom Feliciano Belt. Geochemical data for the metagabbros also support an anorogenic setting.

3 The Nico Pérez Terrane in Southernmost Brazil

3.1 Introduction

Several medium- to high-grade metamorphic complexes showing similarities with the Nico Pérez Terrane basement are recognizable in southern Brazil (Tables 7.2 and 7.3). These include the Santa Maria Chico Granulitic Complex in the Taquarembó Terrane, the Encantadas and Vigia complexes in the Tijucas Terrane and the Arroio dos Ratos Complex within the Neoproterozoic Pelotas Batholith (e.g., Hartmann et al. 2000; Leite et al. 2000; Santos et al. 2003; Philipp et al. 2008, 2016a; Oyhantçabal et al. 2011a; Camozzato et al. 2013a, b).

Table 7.2 Summary of available geochronological data in the Taquarembó Block of the Nico Pérez Terrane in Brazil
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Table 7.3 Summary of available geochronological data of Paleo- and Mesoproterozoic rocks related to the Nico Pérez Terrane cropping out as basement inliers and roof pendants in the Tijucas Block and the Pelotas Batholith of Brazil
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3.2 The Santa Maria Chico Granulitic Complex (Taquarembó Block)

The Santa Maria Chico Granulitic Complex constitutes the basement of the Taquarembó Terrane. To the northeast it is bounded by units of the São Gabriel Terrane and is partially covered by Ediacaran sedimentary and volcanic rocks of the Camaquã Basin and Carboniferous to Permian sedimentary rocks of the Paraná Basin. Neoproterozoic granite intrusions (c. 630–570 Ma) are also frequent in this complex (Fig. 7.5).

Fig. 7.5
figure 5

Geological map of the Santa Maria Chico granulitic Complex, Taquarembó Terrane. (Modified from Philipp et al. 2016a, 2017a, b.)

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The Santa Maria Chico Granulitic Complex comprises three main rock associations: (1) mafic to ultramafic granulites with associated metapyroxenites and meta-anorthosites; (2) sillimanite-garnet-biotite paragneisses, marbles, calc-silicate rocks, quartzo-feldspathic gneisses and BIFs; and (3) tonalitic to throndjemitic TTG orthogneisses (Hartmann 1998; Philipp et al. 2016a, 2017a) (Fig. 7.6 ). U–Pb SHRIMP and LA-MC-ICPMS detrital zircon ages between 2167 ± 15 and 2331 ± 31 Ma constrain the interval of the sedimentary deposition in the paragneisses (Table 7.2; Laux et al. 2012). In turn, U–Pb ages indicate two episodes of magmatism for the protoliths of the TTG gneisses. The older one have ages of`2380–2280 Ma (Girelli et al. 2016a, b) and the younger ones ages of 2240–2130 Ma (Girelli et al. 2016a, b; Philipp et al. 2017b).

Fig. 7.6
figure 6

Geological map of the Encantadas Complex in the Santana da Boa Vista region. (Modified from Philipp et al. 2016b, 2017a, b.) DCSZ Dorsal do Canguçu Shear Zone; SBSZ Santana da Boa Vista Shear Zone; PMSZ Passo do Marinheiro Shear Zone

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The mafic to ultramafic association presents two groups of U–Pb zircon ages. The older ages range from 2413 ± 13 Ma for a mafic granulite to 2349 ± 6 Ma for a metaleucogabbro (Laux et al. 2012; Girelli et al. 2016a, b). The younger group of ages includes 2244 ± 17 Ma (meta-anorthosite), 2186 ± 17 Ma (metapyroxenite), 2173 ± 20 Ma (metagabbro) and 2124 ± 8 Ma (mafic granulite) (Girelli et al. 2016a, b; Philipp et al. 2017b).

The main orogenic metamorphic event is indicated by U–Pb SHRIMP and LA-MC-ICPMS concordia zircon ages of 2078 ± 6, 2031 ± 40, 2022 ± 18, 2035 ± 9 and 2006 ± 3 Ma (Hartmann et al. 1999, 2008; Philipp et al. 2017b). Unmetamorphosed granites intruding the gneisses yielded U–Pb LA-MC-ICPMS zircon ages of 1840 ± 13 and 1766 ± 14 Ma (Table 7.2; Girelli et al. 2016a, b; Philipp et al. 2017b). These ages are similar to that of the unmetamorphosed Illescas Granite of Uruguay demonstrating the similar Paleoproterozoic evolution of Valentines (UY) and Taquarembó (BR) areas.

3.3 Pre-neoproterozoic Basement Inliers in the Tijucas Terrane

The Encantadas and Vigia complexes constitute two northeast–southwest elongated structural domes that occur as basement inliers in the central and southwestern portions of the Tijucas Terrane (Figs. 7.2, 7.6 and 7.7). The orthogneisses of these complexes occur tectonically interleaved with metavolcanosedimentary rocks of the Neoproterozoic Porongos Complex (Jost 1981; Saalmann et al. 2011; Camozzato et al. 2013a, b, 2017).

Fig. 7.7
figure 7

Geological map of Vigia Dome, southern portion of Tijucas Block. (Modified from Camozzato et al. 2013a, b.) DCSZ Dorsal do Canguçu Shear Zone

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3.3.1 The Encantadas Complex

The Encantadas Complex represents the deepest portion of the Santana da Boa Vista Dome (Fig. 7.6) and comprises gneisses of tonalitic to trondhjemitic and minor dioritic composition with associated metahornblendites (Philipp et al. 2008). The orthogneisses are intruded by porphyritic and equigranular metagranites. These metagranites show the same deformation phases founded in the tonalitic to trondhjemitic gneisses, indicating a common structural and metamorphic history. The magmatic protoliths of the Encantadas Complex show the features of a typical high-Al TTG association, like high-K calc-alkaline signature, high LREE/Nb ratios, and trace element patterns that are consistent with an active continental margin setting. The metagranites present high-K calc-alkaline composition, metaluminous to slightly peraluminous affinity, enrichment in LRRE and LIL elements, with strong negative anomalies of Nb, Ta, Ti and P.

Several U–Pb SHRIMP and LA-MC-ICPMS zircon ages of c. 2263–2234 Ma constrain the timing of intrusive magmatism to the Rhyacian period (Table 7.3; Hartmann et al. 2000, 2003; Saalmann et al. 2011). However, new U–Pb ages indicate that the complex is composed by two magmatic associations. The older belongs to the Siderian period with U–Pb LA-MC-ICPMS zircon ages of 2404 ± 23 Ma (granodioritic gneiss) and U–Pb SHRIMP zircon ages of 2352 ± 26 Ma (tonalitic gneiss) (Table 7.3; Camozzato et al. 2017; Lusa et al. 2017). The younger association is Rhyacian and comprises tonalitic to dioritic gneisses and equigranular metagranites intruding the orthogneisses and yielded LA-MC-ICPMS U–Pb zircon ages of 2211 ± 17 and 2210 ± 16 Ma (Lusa et al. 2017).

Upper amphibolite-facies metamorphism is dated by U–Pb SHRIMP Orosirian zircon ages of 2045 ± 10 and 2021 ± 11 Ma (Hartmann et al. 2000). A younger metamorphic overprint yielded U–Pb LA-MC-ICPMS zircon ages of 679 ± 49, 643 ± 3.2, 631 ± 6 and 626 ± 15 Ma (Camozzato et al. 2013a, b, 2017), indicating reworking during the Brasiliano orogeny.

3.3.2 The Vigia Complex

The Vigia Complex occurs in the southwestern portion of the Tijucas Terrane as a 25 km long and 10 km wide elongated body oriented north-northeast and surrounded by sedimentary rocks of the Camaquã Basin (Figs. 7.2 and 7.7). The Vigia Complex represents a north-northeast–south-southwest-trending dome, plunging towards both directions of strike. The core of the structure is occupied by tonalitic, trondhjemitic and granodioritic gneisses of the Vigia Complex, with the occasional occurrence of amphibolites and metahornblendites. In the eastern portion of the dome, the contact between the orthogneisses of the Vigia Complex and the metasedimentary and metaultramafic rocks of the Porongos Complex is defined by a low- to medium-angle ductile shear zone. U–Pb zircon data (LA-MC-ICPMS) of a syenogranitic gneiss and a quartz dioritic gneiss yielded crystallization ages of 2056 ± 38 Ma and 2008 ± 52 Ma, respectively (Camozzato et al. 2013a, b, 2017).

3.3.3 Seival Metagranite

The Seival Metagranite is a north-northeast–south-southwest-trending elongated body extending continuously up to the vicinity of the Seival Farm, site of its type locality. The metagranite is located in the southeastern portion of the Vigia Dome and intrudes into the orthogneisses of the Vigia Complex (Fig. 7.7). The Seival Metagranite consists of granodiorites and monzogranites of pinkish colour, and subordinate bodies of leucogranite. The composition of this metagranite plots in the volcanic arc and post-collisional fields of the Rb versus Y + Nb diagram (Camozzato et al. 2017). The fabric is near isotropic. However, on the southeastern edge of the body a mylonitic foliation is defined by the preferred orientation of K-feldspar porphyroclasts, stretched quartz grains and biotite laths.

U–Pb LA-MC-ICPMS in zircon yielded concordant ages of 1785 ± 42, 1768 ± 24, 1764 ± 29 and 1763 ± 28 Ma (Camozzato et al. 2013a, b, 2017) interpreted as the time of intrusion during the Statherian period (Table 7.3).

3.3.4 Tupi Silveira Amphibolite

The Tupi Silveira Amphibolite occurs in the southern portion of the Vigia dome, being constituted by two small bodies up to some tens of metres long (Fig. 7.7) (Camozzato et al. 2013a, b, 2017). The bodies are intrusive into the orthogneisses of the Vigia Complex.

The amphibolite displays a millimetre banding, defined by the intercalation of layers composed mainly of granoblastic plagioclase and layers rich in hornblende with nematoblastic texture. The metamorphic assemblage plagioclase + hornblende + garnet + diopside is indicative of regional metamorphism under conditions compatible with upper-amphibolite to granulite-facies and medium pressure.

A U–Pb zircon age (LA-MC-ICPMS) of 1567 ± 21 Ma was obtained by Camozzato et al. (2013a, b) interpreted to be the age of magma emplacement (Table 7.3). The time of the metamorphism is recorded by a U–Pb zircon age of 643 ± 3 Ma.

3.4 Pre-Neoproterozoic Basement Inliers, Roof Pendants and Septas in the Pelotas Batholith

3.4.1 The Arroio Dos Ratos Complex

The Arroio dos Ratos Complex was originally defined by Fernandes et al. (1990, 1992) as a sequence of orogenic intrusions of granodioritic to trondhjemitic composition including three generations named G1, G2 and G3. The complex is mostly exposed as roof pendants, septas and in situ wall rock fragments in Neoproterozoic intrusions in the Pelotas Batholith of the Dom Feliciano Belt (Fig. 7.8; Fernandes et al. 1990; Philipp and Campos 2004; Gregory et al. 2011; Martil et al. 2011). It is made up of tonalitic to granodioritic gneisses intruded by metatonalites, metadiorites and metagranodiorites (Philipp and Campos 2004; Gregory et al. 2011, 2015).

Fig. 7.8
figure 8

Simplified map of the Neoproterozoic Pelotas Batholith showing the Paleoproterozoic Várzea do Capivarita, Arroio dos Ratos and Encantadas complexes and the Mesoproterozoic Capivarita Meta-anorthosite. (Modified from Philipp et al. 2016a.)

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Geochemical data indicate that orthogneisses and metagranitoids mostly correspond to medium- to high-K calc-alkaline, metaluminous to slightly peraluminous intrusions (Philipp and Campos 2004; Martil et al. 2011; Gregory et al. 2015). The behaviour of major and trace elements and the pattern of moderate fractionation of the REE, with enrichment of LREE in relation to the HREE, indicate a mature continental arc setting for the magmatism of this association.

U–Pb SHRIMP and LA-MC-ICPMS zircon data (Table 7.3; Leite et al. 2000; Gregory et al. 2015) for this complex show Rhyacian-Orosirian magmatic ages for the protoliths. The first U–Pb TIMS zircon age yielded 2078 ± 13 Ma (Tommasi 1991). Afterwards, Leite et al. (2000) obtained a U–Pb SHRIMP in zircon age of 2067 ± 17 Ma. More recently, Gregory et al. (2015) dated this complex using LA-MC-ICPMS and obtained a concordia magmatic U–Pb zircon age of 2148 ± 33 Ma from a metatonalite of the G1 association; ages of 2150 ± 28 and 2136 ± 27 Ma for metatonalites of the G2 association; and ages of 2099 ± 10, 2081 ± 07 and 2077 ± 13 Ma for metatonalites to metagranodiorites of G3 association. Scarce inherited zircons dated at c. 2.7 Ga are reported in the G1 association (Gregory et al. 2015). Orosirian upper amphibolite to granulite-facies metamorphism (Lima et al. 1998) is dated by U–Pb SHRIMP at around 2.0 Ga (Leite et al. 2000).

The Neoproterozoic record includes granites that intrude into the complex, dated by Leite et al. (2000) at c. 780 Ma and U–Pb zircon metamorphic ages of 631 ± 13 Ma and 635 ± 6 Ma in the tonalitic and granodioritic gneisses (Leite et al. 2000; Gregory et al. 2015).

3.4.2 The Capivarita Meta-anorthosite

The Capivarita Meta-anorthosite crops out in two main bodies, oriented east–west and north–south, in the northeastern portion of the Rio Grande do Sul state. It mainly occurs as roof pendants in the Neoproterozoic Encruzilhada do Sul Suite granites of the Pelotas Batholith that are part of the Dom Feliciano Belt (Fernandes et al. 1990; Philipp et al. 2010) (Fig. 7.8).

The Capivarita Meta-anorthosite is bounded to the southeast by the Dorsal do Canguçu Shear Zone and to the west by the Passo do Marinheiro Shear Zone (Fig. 7.8), and it is covered to the north by the Phanerozoic sediments of the Paraná Basin (Philipp et al. 2010). The Capivarita Meta-anorthosite and the Paleoproterozoic basement rocks of this area are metamorphosed under medium-amphibolite to granulite-facies conditions. The Paleoproterozoic basement is represented by Al-rich, calc-silicate rocks and quartz-feldspar paragneisses of the Várzea Capivarita Complex, and by the Paleoproterozoic orthogneisses of the Arrroio dos Ratos Complex (Fernandes et al. 1990; Gregory et al. 2011; Martil et al. 2011; Philipp et al. 2013, 2016a, b).

Anorthosite is the dominant lithotype, but there are subordinate occurrences of metagabbros (amphibolites) and thin layers of Fe–Ti oxide-rich rocks. The Capivarita Meta-anorthosite is homogeneous, light grey, equigranular and medium- to coarse-grained, with a mafic content ranging from 2 to 5%. A discontinuous millimetre-thick layering is defined by the distribution of hornblende plus some titanite and Fe–Ti oxides (ilmenite and magnetite), grossular and rare diopside (Philipp et al. 2010; Chemale et al. 2011). Metagabbro layers and dykes are up to 5 m thick, tabular and concordant. The primary igneous layering is frequently preserved. The fabric of the hornblende is parallel to the regional tectonic grain and is connected with the main regional deformational phase observed in the Neoproterozoic Várzea Capivarita Complex (Philipp et al. 2013).

U–Pb LA-MC-ICPMS zircon and titanite data constrain the timing of the magmatism at 1573 ± 21 and 1530 ± 33 Ma, respectively, thus indicating a Calymmian age (Chemale et al. 2011). The metamorphic age is defined in the rims of zircon crystals and in metamorphic titanite, yielding ages of 652 ± 9 Ma for the collisional metamorphism and 606 ± 6 and 597 ± 6 Ma for the thermal metamorphism related to emplacement of Encruzilhada do Sul Granite (Chemale et al. 2011).

4 Discussion

4.1 Origin and Extension of the Nico Pérez Terrane

The Nico Pérez Terrane has been regarded as the eastern part of the Río de la Plata Craton (Bossi and Campal 1992; Mallmann et al. 2007; Chiglino et al. 2010; Frimmel et al. 2011; Gaucher et al. 2011; Chernicoff et al. 2015), although some recent contributions argued for an allochthonous origin of the Nico Pérez Terrane (Oyhantçabal et al. 2011a; Rapela et al. 2011; Oriolo et al. 2016a). Interestingly, Almeida et al. (1973) stated the following in their definition of the Río de la Plata Craton:

In Uruguay and Argentina, the Río de la Plata craton occurs, exhibiting Trans-Amazonian structures, which surely extend over the nearby continental shelf. The predominant trends are nearly east-west in disagreement with the NNE-NE trends of the Ribeira belt. This latter belt extends down to the Uruguay coastal region, close to the border of the cratonic area, indicating that the Río de la Plata craton also, in late Precambrian times, probably did not extend much further to the east.

After the redefinition of units by Fragoso Cesar (1980), the Neoproterozoic mobile belt that extends along eastern Rio Grande do Sul and Uruguay is considered to be the Dom Feliciano Belt and not the prolongation of the Ribeira Belt. The Dom Feliciano Belt clearly overprints the basement of the Nico Pérez Terrane (e.g., Oyhantçabal et al. 2011a, 2012; Oriolo et al. 2016a, c). Hence the assumption that the Nico Pérez Terrane was part of the Río de la Plata Craton can be ruled out, even if considering the original definition of the latter and an allochthonous origin related to the Congo Craton is well supported by recent geological, structural and isotopic data (Oyhantçabal et al. 2011a; Rapela et al. 2011; Oriolo et al. 2016a).

On the other hand, Oyhantçabal et al. (2011a, 2012) correlated the Valentines-Rivera Granulitic Complex of the Nico Pérez Terrane with the Santa María Chico Complex of the Taquarembó Terrane. The correlation is well established based on lithological association, age and isotopic constraints, metamorphic grade and geographic proximity. Leite et al. (2000), Saalmann et al. (2011) and Philipp et al. (2016a) in turn indicated that the Arroio dos Ratos and Encantadas complexes were part of the same block. Correlations are mostly based on Rhyacian-Orosirian multistage magmatism, the medium- to high-grade metamorphism recorded in all these complexes and the Neoproterozoic reworking (Tables 7.1, 7.2 and 7.3).

All pre-Neoproterozoic basement complexes of Uruguay located east of the Sarandí del Yí Shear Zone as well as those of Rio Grande do Sul state in southeastern Brazil represent reworked Archean crust. This fact was recognized using Sm–Nd data by Cordani and Sato (1999) in a revision of the South American Platform. Archean zircon inheritance was reported for gneisses of the Valentines-Rivera Granulitic Complex (Santos et al. 2003; Oriolo et al. 2016a), which are also dominated by Archean Sm–Nd and Lu–Hf model ages (Oyhantçabal et al. 2011a; Oriolo et al. 2016a). Archean zircons and Sm–Nd model ages were also obtained in the Santa Maria Chico Granulitic Complex (Mantovani et al. 1987; Hartmann 1998; Hartmann et al. 1999), whereas Saalmann et al. (2011) and Gregory et al. (2015) reported Neoarchean zircon inheritance in the Encantadas and Arroio dos Ratos complexes, respectively. Camozzato et al. (2017) present Lu–Hf data of the orthogneisses of Encantadas Complex, indicating ε Hf(t) between −7 and −15, with T DM ages between 3.2 and 3.6 Ga for the dioritic gneisses, and εHf(t) in the range −1.30 to −10 with T DM between 2.7 and 3.1 Ga for the syenogranitic gneiss.

The detrital zircon age patterns of the metavolcanosedimentary complexes in Rio Grande do Sul also record the ages observed in the Nico Pérez basement. LA-MC-ICPMS U–Pb ages in detrital zircons of the Porongos Complex (Dom Feliciano Belt) and in the Passo Feio Complex (São Gabriel Terrane) show a dominant Paleoproterozoic component and a subsidiary Archaean component up to 3.6 Ga (Hartmann et al. 2004; Gruber et al. 2011; Lopes et al. 2015; Pertille et al. 2015a, b), with subordinate occurrence of Proterozoic ages between 1.8 and 1.2 and between 1.0 and 0.6 Ga. This data confirm the presence of very old sources in the southern region of Brazil (Philipp et al. 2016a). A similar scenario is observed in Uruguay, as a compilation of detrital zircon age data from the metasedimentary cover shows these sediments were mainly derived from Paleoproterozoic sources, with subordinate contribution of Archean (up to 3.7 Ga), Meso- and Neoproterozoic sources (Gaucher et al. 2008; Blanco et al. 2009; Pecoits et al. 2016).

Reworking of Paleoproterozoic gneisses as a result of Neoproterozoic magmatism and metamorphism is also recorded in all units. Negative ε Nd and ε Hf values and T DM ages between 3 and 2 Ga for most of the granitic plutons in the Nico Pérez Terrane and in the Dom Feliciano Belt suggest a protracted recycling process of Paleoproterozoic to Late Archaean sources (e.g., Silva et al. 1999, 2000; Hartmann et al. 2000; Oyhantçabal et al. 2012; Basei et al. 2013; Camozzato et al. 2013a, b, 2017; Gregory et al. 2015; Oriolo et al. 2016a; Philipp et al. 2016a; Lara et al. 2016).

Further similarities are revealed by geochemical data. A medium-K calc-alkaline signature suggesting emplacement in a continental arc tectonic setting is a common feature of the roughly coeval Paleoproterozoic magmatism of the Valentines-Rivera (Ellis 1998; Oyhantçabal et al. 2012), Santa Maria Chico (Laux et al. 2012; Girelli et al. 2016a), Encantadas (Philipp et al. 2008), Arroio dos Ratos (Philipp and Campos 2004; Gregory et al. 2011, 2015) and Vigia complexes (Camozzato et al. 2017). Though poorly constrained, available data for high-grade metamorphism show similar conditions and timing in the Valentines-Rivera, Santa Maria Chico, Encantadas and Arroio dos Ratos complexes (Hartmann 1998; Lima et al. 1998; Massonne et al. 2001; Philipp et al. 2008, 2013, 2016a; Martil et al. 2011; Oyhantçabal et al. 2012; Basei et al. 2013).

Furthermore, the geochemistry of the early Mesoproterozoic magmatism shows characteristics that match a within-plate tectonic setting. The Capivarita Meta-anorthosite (1.57 Ga) and Tupi Silveira Amphibolite (1.55 Ga) in Rio Grande do Sul and bimodal magmatism including felsic volcanic rocks (c. 1.45 Ga) and metagabbros (c. 1.5 Ga) in the southern Dom Feliciano Belt in Uruguay support an extensional environment in an intraplate tectonic setting.

A tectonostratigraphic chart summarizing the observed Archean, Paleo- and Mesoproterozoic events and the proposed correlation between different areas is presented in Fig. 7.9. Despite the above-indicated common features of all outcrop areas considered here as belonging to the Nico Pérez Terrane, two contrasting subterranes are clearly defined when taking into account the degree of Neoproterozoic reworking. The Caçapava Shear Zone (Hartmann et al. 2016 and references therein) or Caçapava do Sul Lineament (Philipp et al. 2016a) of Rio Grande do Sul is, in its southern segment, the boundary between the Tijucas Terrane and the Taquarembó Terrane of the Nico Pérez Terrane, while its northern prolongation separates the São Gabriel Terrane from the Tijucas Terrane (Chemale 2000). An equivalent structure in Uruguay is the Sierra de Sosa Shear Zone, separating the Cerro Chato and the Pavas blocks of the Nico Pérez Terrane. Although the Phanerozoic cover hinders a final conclusion, it seems quite likely that the Sierra de Sosa Shear Zone represents the prolongation of the Caçapava do Sul Shear Zone. The Cerro Chato (UY)—Taquarembó (BR) subterrane is characterized by granulite-facies metamorphism and, even though Brasiliano granite intrusions and volcanosedimentary associations are common, the crustal architecture is not strongly overprinted by the north-northeast Brasiliano structural grain. The Pavas (UY)—Tijucas (BR) subterrane, on the other hand, displays a strong structural reworking, and basement inliers in the Dom Feliciano belt are normally parallel to the orogen structural grain. The basement shows mostly amphibolite-facies metamorphism and the pre-Ediacaran cover is widely extended. This different behaviour of both subterranes during the evolution of the Dom Feliciano Belt could be related to different degrees of crustal attenuation before the Brasiliano collision and the distance to the orogenic core.

Fig. 7.9
figure 9

Tectonostratigraphic chart of the Nico Pérez Terrane in Uruguay and southern Brazil. Rapakivi PO Post-orogenic rapakivi granites

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4.2 Tectonic Evolution

The Nico Pérez Terrane is dominated by Paleoproterozoic rocks. However, available geochronological and isotopic data reveals that in the Nico Pérez the main crustal growth occurred in the Archean and was subsequently reworked during the Paleo-, Meso- and Neoproterozoic (e.g., Oyhantçabal et al. 2011a; Girelli et al. 2016a; Oriolo et al. 2016a; Philipp et al. 2017b) (Fig. 7.9). Based on Hf isotopic data, Girelli et al. (2016a, 2016b), Oriolo et al. (2016a), Camozzato et al. (2017) and Philipp et al. (2017b) indicated Archean episodic crustal growth with Paleo- and Mesoarchean peaks of crust generation.

The Archean crust of the Nico Pérez Terrane underwent mostly crustal reworking during a major Rhyacian-Orosirian tectonometamorphic event (Tables 7.1, 7.2 and 7.3). The Valentines-Rivera Granulitic Complex records magmatism at c. 2.2–2.1 Ga succeeded by high-grade metamorphism and associated crustal anatexis at c. 2.1–2.0 Ga (Oyhantçabal et al. 2012; Santos et al. 2003; Oriolo et al. 2016a). Magmatism and metamorphism indicated for the Santa Maria Chico Granulitic Complex is coeval with that of the Valentines-Rivera Granulitic Complex (Hartmann et al. 1999, 2008; Laux et al. 2012; Girelli et al. 2016a, b; Philipp et al. 2017b), although Hartmann et al. (2008) and Camozzato et al. (2017) present U–Pb zircon data from the Siderian period. Even though this age seems to be older than those of the Valentines-Rivera Granulitic Complex, Siderian xenocrysts were also recognized in orthogneisses of the latter (Oriolo et al. 2016a). Rhyacian magmatism was reported for the Encantadas and Arroio dos Ratos complexes as well (Hartmann et al. 2000, 2003; Leite et al. 2000; Saalmann et al. 2011; Camozzato et al. 2013a, b; Gregory et al. 2015; Lusa et al. 2017), which in the latter is accompanied by Late Rhyacian to Early Orosirian metamorphism and magmatism, also recorded in the Vigia Complex (Hartmann et al. 2000, 2003; Camozzato et al. 2013a, b, 2017). Based on the existence of high-grade metamorphism and an arc geochemical fingerprint of orthogneisses, most tectonic models have favoured a magmatic arc setting for this major Paleoproterozoic event (e.g., Philipp et al. 2008, 2016a; Oyhantçabal et al. 2012; Gregory et al. 2015; Lusa et al. 2017), culminating in a collisional episode (Hartmann et al. 2000, 2003).

Subsequent Statherian magmatism is recorded during the intrusion of the Rapakivi-type Illescas granite and the protolith of the orthogneisses of the Campanero Unit (Bossi and Campal 1992; Campal and Schipilov 1995; Sánchez-Bettucci et al. 2004; Mallmann et al. 2007). Archean model ages of the latter also indicate the dominance of crustal reworking processes (Mallmann et al. 2007), whereas geochemical data point to a possible magmatic arc setting (Oyhantçabal 2005). Recently, Camozzato et al. (2013a, b) also presented Statherian U–Pb data for the magmatism of the Seival Metagranite in the Tijucas Terrane.

On the other hand, the Mesoproterozoic record of the Nico Pérez Terrane seems to be restricted to few passive margin metavolcanosedimentary units and mafic complexes with ages between c. 1.6 and 1.4 Ga (Table 7.1). The Capivarita Meta-anorthosite, which occurs as roof pendants in the Neoproterozoic granites of the Dom Feliciano Belt in southern Brazil, was correlated with the contemporaneous Mesoproterozoic units of Uruguay (Table 7.2; Chemale et al. 2011). Likewise, the age of the Tupi Silveira Amphibolite in the Tijucas Terrane is similar to that of the Capivarita Meta-anorthosite and an intraplate setting was suggested for this magmatism in southern Brazil (Camozzato et al. 2013a, b). In Uruguay, some authors suggested a major tectonometamorphic event related to the assembly of Rodinia for this magmatism (Campal and Schipilov 1999; Bossi and Cingolani 2009; Gaucher et al. 2011), whereas Oriolo et al. (2016a) argued for a more likely intraplate event. The latter hypothesis would also fit the tectonic setting inferred for this Calymmian event in southern Brazil, which implied local addition of relatively juvenile continental crust with some degree of crustal contamination (Chemale et al. 2011; Basei et al. 2013; Camozzato et al. 2013a, b, 2017).

Though elusive, the presence of a Cryogenian tectonomagmatic event seems to be well documented. U–Pb SHRIMP ages of 781 ± 5 and 777 ± 4 Ma were obtained for orthogneisses occurring as xenoliths within the Pelotas Batholith (Silva et al. 1999; Koester et al. 2016), whereas similar ages were reported in a metarhyolite and metadacites of the Porongos Complex. U–Pb SHRIMP and LA-MC-ICPMS zircon Cryogenian ages for metavolcanic rocks of the Porongos Complex were also presented by Chemale Jr. et al. (1997), Porcher et al. (1999), Saalmann et al. (2011) and Pertille et al. (2015b).

Metamorphic overprint at 875 ± 160, 702 ± 21 and 679 ± 49 Ma was indicated by U–Pb SHRIMP and LA-MC-ICPMS zircon data in rocks of the Encantadas Complex (Hartmann et al. 2003; Camozzato et al. 2017; Lusa et al. 2017). In Uruguay, no Cryogenian ages have been identified so far in the Nico Pérez Terrane basement. Nevertheless, Oriolo et al. (2016a) indicated that the Cerro Olivo Complex, which is located to the east of the Sierra Ballena Shear Zone and records Cryogenian magmatism (Hartmann et al. 2002; Oyhantçabal et al. 2009b; Basei et al. 2011; Lenz et al. 2011), might be linked to the evolution of the Nico Pérez Terrane.

Cryogenian magmatism has traditionally been assumed to be the result of an extensional event, mostly based on the coeval timing of Rodinia break-up (e.g., Oyhantçabal et al. 2009b; Basei et al. 2011; Rapela et al. 2011; Oriolo et al. 2016a, b, c). In contrast, Lenz et al. (2011, 2013), Koester et al. (2016) and Philipp et al. (2016a) indicated a magmatic arc setting resulting from the arc-like geochemical signature. Within this framework, the western margin of the Nico Pérez Terrane was probably the upper plate during subduction to the east in the Tonian and Cryogenian (Philipp et al. 2016a; Oriolo et al. 2017). Extensional tectonics and the disconnection of the Nico Pérez Terrane from the Congo Craton most probably took place during the Early Neoproterozoic (Cryogenian) and resulted in crustal attenuation (Goscombe and Gray 2007, 2008; Konopásek et al. 2014; Oriolo et al. 2016a,b, c).

During the Late Neoproterozoic, involvement of the Nico Pérez Terrane in convergent tectonics associated with the Pan-African/Brasiliano orogeny and the evolution of the Dom Feliciano Belt gave rise to widespread crustal reworking, probably facilitated by previous crustal attenuation (Oriolo et al. 2016a, 2017). High-K to shoshonitic calc-alkaline to alkaline magmatism is recorded at c. 630–580 Ma (Table 7.1; Hartmann et al. 2002; Philipp et al. 2002, 2003, 2005, 2007; Oyhantçabal et al. 2007, Oyhantçabal et al. 2009b, 2012; Gaucher et al. 2008, 2014b; Oriolo et al. 2016a; Lara et al. 2016). Contemporaneous metamorphism, extensive deformation along shear zones and cooling were also reported for basement units (Philipp et al. 2003, 2016b; Oyhantçabal et al. 2009b, 2011a, 2012; Oriolo et al. 2016a, c). In a similar way, Ediacaran overprint resulting from metamorphism and magmatism of the Dom Feliciano Belt is well documented in basement metamorphic complexes (e.g., Hartmann et al. 2000; Leite et al. 2000; Chemale et al. 2011; Basei et al. 2013; Camozzato et al. 2013a, b; Philipp et al. 2013, 2016b; Gregory et al. 2015). This major Late Neoproterozoic tectonometamorphic event resulted from the collision of the Río de la Plata and Congo cratons at c. 650–620 Ma, which also implied the accretion of the Nico Pérez Terrane to the Río de la Plata Craton margin along the Sarandí del Yí Shear Zone (Oriolo et al. 2015, 2016a, b, c; Philipp et al. 2016a, b).

As mentioned above, derivation of the Nico Pérez Terrane from the Congo Craton seems to be well supported based on the predominance of Archean model ages, widespread Paleoproterozoic crustal reworking at 2.2–2.0 and 1.8–1.7 Ga, and anorogenic magmatism at 1.5–1.4 Ga. Luft et al. (2011) reported 1.8–1.7 Ga ages for the gneisses of the Mudorib Complex in Namibia, and the 1.5–1.4 Ga event is also clearly present in the Congo Craton (e.g., Kibaran belt; Tack et al. 2010; or the Kunene Complex), further supporting the African signature of Nico Pérez.

5 Conclusions

  • The Nico Pérez Terrane of southernmost Brazil and Uruguay includes pre-Neoproterozoic basement evidencing an important component of Archean crustal growth. These basement rocks occur not only as basement blocks but also as basement inliers and roof pendants in the batholiths of the Dom Feliciano Belt. Though Sm–Nd and Lu–Hf Archean model ages predominate, zircon data indicate dominant Paleoproterozoic magmatic ages for the protoliths of the gneisses, which resulted from extensive Paleoproterozoic reworking associated with crustal anatexis. This terrane also contains relics of a Neoarchean to Siderian sedimentary cover including BIFs, quartzites and marbles.

  • Intraplate Mesoproterozoic magmatism is recorded in Uruguay and southernmost Brazil and includes meta-anorthosite complexes, metagabbros, amphibolites and felsic volcanic rocks. The latter are interbedded with sediments assumed to correspond to a Mesoproterozoic platform cover.

  • Two different subterranes are recognized separated by the north-northeast-trending Caçapava—Sierra de Sosa Shear Zone. The western subterrane includes the granulite-facies Valentines Rivera (UY) and Santa Maria Chico (BR) complexes and is less reworked by the Brasiliano Orogeny. The eastern subterrane was strongly reworked during the Brasiliano and comprises the Pavas Block of Uruguay and several basement inliers in the Dom Feliciano Belt of Uruguay and Brazil.

  • Neoproterozoic reworking recorded in cooling ages, extensive shear zones and granite intrusions evidence that, despite its Archean origin, the Nico Perez terrane was not endowed with a thick lithosphere during the Neoproterozoic, leading to its metacratonization during the Brasiliano.

  • A derivation of the Nico Pérez Terrane from the Congo Craton seems most likely owing to the similar tectonic evolution. Separation probably occurred during the Neoproterozoic and resulted in crustal attenuation that favoured subsequent metacratonization.