Post-collisional Ediacaran volcanism in oriental Ramada Plateau, southern Brazil

Accepted Manuscript Post-collisional Ediacaran volcanism in oriental Ramada Plateau, southern Brazil Vinícius Matté, Carlos Augusto Sommer, Evandro Fernandes de Lima, Ruy Paulo Philipp, Miguel Angelo Stipp Basei PII:

S0895-9811(16)30130-4

DOI:

10.1016/j.jsames.2016.07.015

Reference:

SAMES 1598

To appear in:

Journal of South American Earth Sciences

Received Date: 15 February 2016 Revised Date:

19 July 2016

Accepted Date: 20 July 2016

Please cite this article as: Matté, V., Sommer, C.A., de Lima, E.F., Philipp, R.P., Basei, M.A.S., Postcollisional Ediacaran volcanism in oriental Ramada Plateau, southern Brazil, Journal of South American Earth Sciences (2016), doi: 10.1016/j.jsames.2016.07.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Post-collisional Ediacaran volcanism in oriental Ramada Plateau, southern Brazil. Vinícius Mattéa*, Carlos Augusto Sommerb, Evandro Fernandes de Limab, Ruy Paulo Philippb, Miguel Angelo Stipp Baseic a

Programa de Pós-Graduação em Geociências, UFRGS, Brazil Instituto de Geociências, UFRGS, Brazil c Centro de Pesquisas em Geocronologia (CPGEO), Instituto de Geociências, USP, Brazil

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b

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* Corresponding author. E-mail address: [email protected] (V. Matté).

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Abstract Ediacaran volcanic sequences in southernmost Brazil are related to intense post-collisional magmatism of the Brasiliano Orogeny. A portion of this volcanism occurs in the oriental Ramada Plateau located in the center part of the Rio Grande Sul State and is correlated with Hilário and Acampamento Velho formations. The first one is represented dominantly by lava flows and dikes of shoshonitic andesitic composition, besides of volcanogenic sedimentary deposits. The acid rocks of the Acampamento Velho Formation are expressive in the area, comprising high-silica ignimbrites, usually densely welded. Dikes and domes are common too and rhyolitic lava flows occur at the top and intercalated to ignimbrites in the middle of the sequence. The acid rock association has a sodic alkaline affinity. In this unit we mapped a subvolcanic sill of trachyte showing evindence for magma mixing with the rhyolitic magma. It has sodic alkaline affinity, and FeOt/FeO+MgO ratios and agpaitic index lower than those recorded in the rhyolites/ignimbrites. The Acampamento Velho Formation includes in this area, subordinately, basalts as àà flows and dikes intercalated with acid rocks. They have sodic alkaline nature and characteristics of intraplate basic rocks. New zircon U-Pb dating indicates crystallization age of 560 ± 2 Ma in a densely welded ignimbrite, 560 ± 14 Ma for a mafic trachyte and 562 ± 2 Ma for a subvolcanic rhyolite. The sodic alkaline rocks in this region evolved by fractional crystallization processes and magma mixing with major crustal contribution at approximately 560 Ma. The chemical characteristics are similar to those of A-type granites associated with Neoproterozoic post-collision magmatism in the Sul-rio-grandense Shield. Keywords: Volcanic rocks; Post-collisional; Ediacaran; Petrology; Geochronology 1. Introduction The Sul-rio-grandense Shield, which is located in the southern portion of

Mantiqueira Province (Fig. 1A), evolved largely during the Brasiliano Orogeny, between ~900 and 500 Ma, leading to consolidation of the Gondwana supercontinent. The oldest rocks in the shield (2.55-2.0 Ga) are those of the Paleoproterozoic Taquarembó Terrane and are characterized by fragments of the Rio de La Plata Craton (Hartmann et al., 2000, 2007; Soliani Jr. et al., 2000). This unit was reworked during the Neoproterozoic, when the region became an important

ACCEPTED MANUSCRIPT zone of tectonic accretion, the Dom Feliciano Belt (Soliani Jr., 1986; Fragoso-Cesar,

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1991; Hartmann et al., 2007). This is represented by: i) São Gabriel Terrane (880680 Ma), with a juvenile signature and petrotectonic associations of magmatic arcs, ophiolites, and passive margin and retroarc environments; ii) Tijucas Terrane (800620 Ma), with metavolcanic and metasedimentary rocks resulting from deposition in

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extended continental crust and continental magmatic arc, with continental Paleoproterozoic crustal reworking (2.2-1.9 Ga, e.g., Encantadas Gneiss).The main

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collision was followed by a post-collisional period, which involved the generation of voluminous granitic magmatism as the Pelotas Batholith and other granitic intrusions between 650 and 550 Ma, mainly along strike-slip faults and shear zones (Soliani Jr., 1986; Chemale Jr., 2000; Bittencourt & Nardi, 2000; Philipp & Machado, 2002; Hartmann et al., 2007; Philipp et al., 2007). Simultaneously (630-535 Ma), lithospheric delamination prompted the development of a depositional locus in which

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the Camaquã Basin formed (e.g. Fragoso-Cesar, 1984; Chemale Jr. et al., 1995;

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Paim et al., 2000). This basin was characterized by the generation of sub-basins, whose tectonic mechanisms remain controversial, but that likely indicate retroarc, strike-slip, and transtensive rift environments (e.g., Chemale Jr., 2000; Fragoso-

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Cesar et al., 2000, 2003; Paim et al., 2000, 2014; Sommer et al., 2006; Janikian et al., 2008, 2012).

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Within the Ramada sub-basin (Paim et al., 2000), the Ramada Plateau preserves a volcanic sequence, showing only brittle deformation and no metamorphism, with prevalent acid pyroclastic rocks known as the Acampamento Velho Formation (sensu Ribeiro & Fantinel, 1978) of Ediacaran age (574-549 Ma; Janikian et al., 2012; Sommer et al., 2005). These rocks developed by fractional crystallization processes of basic to acid compositions with a sodic alkaline nature and an important contribution from crustal assimilation (Wildner et al., 2002; Sommer et al., 2005; Matté et al., 2012). In this paper, we describe and analyze the facies of volcanic and subvolcanic rocks in the eastern portion of the Ramada Plateau, using petrographic, lithochemical, and geochronological data, in order to establish their stratigraphy and relationships with the post-collisional Ediacaran magmatism in the Sul-rio-grandense Shield.

2. Geological setting

ACCEPTED MANUSCRIPT The Camaquã Basin records an evolution of sedimentary siliciclastic

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environments from shallow marine, through coastal, lacustrine, and alluvial to continental desert environments, with intercalated volcanic episodes (Paim et al., 2000, 2014), deposited between about 630 Ma (Ediacaran) and 535 Ma (Cambrian). Outcrops occur discontinuously in the Sul-rio-grandense Shield for about 150 km in

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the E-W direction, between the towns of Encruzilhada do Sul and São Gabriel, and about 120 km in the N-S direction, between Sao Sepé and Bagé (Fig. 1B). The

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basement of the basin is heterogeneous, ranging from a Paleoproterozoic granulitic complex (Taquarembó Terrane) to Neoproterozoic units (São Gabriel and Tijucas Terranes) represented by igneous and metamorphic associations (Paim et al., 2000; Lima et al., 2007).

The Camaquã Basin rocks consist, from base to top, of the following units: - Maricá Group, predominantly coastal and marine deposits with ages between 630

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and 601 Ma (Borba, 2006; Almeida et al., 2012);

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- Bom Jardim Group, intercalated alluvial and basic-intermediate volcanic rocks (Hilário Formation) with ages between 593 and 580 Ma (Almeida et al., 2012; Janikian et al., 2012);

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- Santa Bárbara Group, alluvial, fluvial, and lacustrine deposits (Borba & Mizusaki, 2003) with ages between 567 and 547 Ma (Oliveira et al., 2014; Bicca et al., 2013)

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contemporaneous with the Acampamento Velho Formation, which includes effusive and pyroclastic acid rocks and subordinate effusive and subvolcanic basic to intermediate rocks (Lima et al., 2007) with ages that range from 574 to 549 Ma (Janikian et al., 2012; Sommer et al., 2005); - Guaritas Group, alluvial, fluvial, and eolian deposits (Almeida et al., 2009) with basic volcanic rocks at the base (Rodeio Velho Member sensu Ribeiro et al., 1966) generated between 547 and 535 Ma (Almeida et al., 2012). Ediacaran volcanism plays an important role in Camaquã Basin evolution, especially in the filling phases, in which volcanic episodes were dominant, often at the base of the groups listed above. The magmatic features reveal tholeiitic and calcalkaline high-K to shoshonitic and finally sodic alkaline evolution, and the crustal contribution is represented by peraluminous granitoids (Sommer et al., 2006). The Acampamento Velho volcanism comprises mainly effusive and pyroclastic acid rocks associated with basic lavas and dikes. Several authors, such as Wildner et al. (2002), Sommer et al. (1999, 2005), and Almeida et al. (2002), have investigated the stratigraphic organization of this formation. The best exposures (Fig. 1B) are

ACCEPTED MANUSCRIPT located on the Ramada Plateau and in Cerro Tupanci (both in Vila Nova do Sul) and

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on the Taquarembó Plateau (Dom Pedrito) and the Santa Barbara ridge, which includes Perau, Bugio, and Espinilho Hills (Caçapava do Sul). Subvolcanic rocks with similar features occur over the Pelotas Batholith, in its southwest domain (Chato and Partido Hills), central domain (Asperezas Rhyolite and Piratini dikes warm), and

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northeast domain (Ana Dias Rhyolite), the latter having an age of 582 ± 2 Ma

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(Oliveira et al., 2015). 3. Geology of the oriental Ramada Plateau

The oriental Ramada Plateau (Fig. 2) is a geomorphological feature located about 20 km south of the town of Vila Nova do Sul in the west-central part of the Rio Grande do Sul state (Fig. 1). It has an average elevation of 400 m and occupies an

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area of 20 km (E-W) by 12 km (N-S) limited roughly by the geographic meridians of 53°40'W and 53°50'W and the parallels of 30°28'S an d 30°35'S. It comprises

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effusive, pyroclastic, and subvolcanic rocks essentially of the Acampamento Velho Formation, which overlaps and cuts sedimentary and volcanic rocks of the Maricá

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and Bom Jardim groups. The Bossoroca Complex forms the basement and is composed dominantly of greenschist to amphibolite facies metavolcanic rocks that

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date to 753 ± 13 Ma (Machado et al., 1990). Rocks of the Maricá Group crop out at the base of the oriental Ramada

Plateau, especially in its northern and eastern parts, intruded by numerous subvolcanic acid bodies. The group was subdivided into three units by Pelosi & Fragoso-Cesar (2003).The basal unit is the Passo da Promessa Formation, which is characterized by siltstones, sandstones, and fluvial conglomerates of arkosic to subarkosic composition. The São Rafael Formation, the intermediate unit, represents marine sedimentation and consists predominantly of greenish shales, siltstones, and lithic arkose sandstones with volcanic rock fragments. The Arroio América Formation, at the top, represents fluvial sedimentation and consists of sandstones and conglomerates including volcanic rock fragments. Some studies have indicated the existence of syndepositional volcanogenic layers (Santos et al., 1978; Bitencourt et al., 1997; Wildner et al., 2002; Borba et al., 2004a, 2004b), whose clasts have a maximum age of 630 ± 34 Ma (Borba et al., 2007) and a minimum age of 601 ± 13 Ma (Almeida et al., 2012).

ACCEPTED MANUSCRIPT The Hilário Formation (593 ± 6 to 580 ± 3.6 Ma; Remus et al., 1999; Janikian

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et al., 2008), of the Bom Jardim Group (Ribeiro et al., 1966), is the first volcanic episode with an expressive record in the Camaquã Basin. It occurs with a thickness of approximately 10 m in the northern and eastern portions of the study area, at the base of the plateau, where there is an abrupt change in lithology between

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Acampamento Velho Formation volcanics and Maricá Group sedimentary rocks. This magmatism is characterized by shoshonitic-affinity volcanic and subvolcanic rocks,

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showing variation from basic to acid and intermediate compositions (trachyandesites to basaltic trachyandesites). A volcaniclastic portion occurs intercalated within effusive facies and consists of volcanogenic conglomerates characterized by a predominance of subrounded to subangular andesite fragments within a sandy groundmass.

The Ramada Intrusive Suite consists mainly of syenogranites with subordinate

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monzogranites, monzodiorites, and diorites called in this area the Ramada Granite

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and "dioritic rock" (Bitencourt et al., 1997) units, respectively, which date to 558 ± 2 Ma and 563 ± 3 Ma (Matté et al., in prep.). These rocks are included within the Saibro Intrusive Suite (Nardi & Bonin, 1991), which is associated with sodic alkaline

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magmatism linked to the Acampamento Velho Formation volcanic rocks (Naime, 1987; Gastal & Lafon, 1998).

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The Acampamento Velho Formation follows the shoshonitic magmatism of the

Hilário Formation and the sedimentary rocks of the Maricá Group. Geochronological data provide ages 574 ± 7 and 549 ± 5 Ma for the volcanic rocks of this unit in this region (Sommer et al., 2005; Janikian et al., 2008; Almeida et al., 2012). This unit is characterized predominantly by ignimbrites, rheoignimbrites (Sommer et al., 2011, 2013) and rhyolites and subordinately by basalts and acid to basic subvolcanic bodies.

4. Facies analysis and petrography The volcanism in the oriental Ramada Plateau is represented by the wide variety of Hilário and Acampamento Velho formation rocks. Lapilli tuffs (LT) produced by pyroclastic density currents and here referred to genetically as ignimbrites, prevail in the latter formation. Based on the stratigraphic facies of the sequences studied, and following the nomenclature proposed by Branney & Kokelaar (2002) to the

ACCEPTED MANUSCRIPT the area, as shown in figure 3.

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characterization of the ignimbrite lithofacies, we propose a stratigraphic column for

Sedimentary rocks of the Maricá Group range from shales to conglomerates and show low-grade metamorphic effects caused by thermal contact of intrusions.

northeastern portion of the study area.

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They occur in the areas of gentle relief surrounding the plateau, mainly in the

The contact between the Maricá and Bom Jardim groups was not observed,

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but Paim et al. (2000) suggested that regional angular unconformities occur between these units. The sedimentary portion of the Bom Jardim Group occurs mainly in the southern part of the studied area (São José Farm region), where it is represented by massive layers of breccias and conglomerates (VSd1) described by Janikian et al. (2005) as having been generated in fluvial systems with large contributions of acid volcanic rocks. These rocks also crop out in a small area south of the Ramada

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Granite, where they are locally metamorphosed by basic to intermediate subvolcanic

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intrusions (Hilário Formation).

The subvolcanic bodies (SvAd) related to the Hilário Formation occur in this area essentially as meter-thick dikes of gabbro, diorite, monzodiorite, monzogabbro,

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quartz diorite, and monzonite. They have inequigranular fine- to medium-grained texture and a predominance of albite (probably due to albitization of an originally

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more calcic plagioclase, cf. Nemec, 1966) and oligoclase (An4-18). The rocks commonly have euhedral zoned phenocrysts of these plagioclases up to 5 mm in length and sometimes show glomeroporphyritic texture. Quartz, orthoclase, hornblende, and augite also occur. Hornblende occurs as euhedral crystals , reaching up to 0.5 mm. Augite (Wo39-42, En35-46, Fs11-19) occurs as phenocrysts up to

0.4 mm. Apatite (up to 0.3 mm) and hematite (Hem96-98) occur as accessory phases. Chlorite and calcite are alteration minerals. The volcanic portion is represented dominantly by porphyritic andesites (Ad; Fig. 4A) and subordinately by basalts, both composing the base of the plateau, especially in the north-central portion of the studied area (Fig. 2). The flows are often not very thick (5 to 10 m), which is common in the upper portions, and include vesicles up to 3 cm,sometimes with a shape elongated toward the direction of flow, filled with opaque minerals, quartz, chlorite, calcite, and epidote. Auto-brecciated portions occur and are suggestive of an àà flow upper crust. They are aphanitic to porphyritic rocks with fine to very fine phaneritic groundmass and plagioclase phenocrysts up to 1 cm (Figs. 4A and 5A) with sieve texture locally. Microlites smaller than 0.1 to 0.5 mm in some places are oriented and

ACCEPTED MANUSCRIPT define a hyalopilitic texture. Hornblende (up to 3 mm) and augite (average of 0.5

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mm), occur as euhedral crystals (Fig. 5B) and may be partially altered. Apatite is the main accessory mineral, while chlorite and calcite occur as alteration of mafic minerals.

Superimposed with respect to the Hilário Formation andesites, the

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Acampamento Velho Formation is a sequence of dominantly subaerial pyroclastic acid flow. These rocks, due to their resistance to weathering, form a

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geomorphological topographic high. In this study, we estimated an approximate thickness of this unit of 100 m, but Paim et al. (2000) indicated a package with a thickness of 500 m. Detailed structural studies are required to better quantify the real thickness due to the brittle tectonics that generated large faults in the area. These volcanic rocks, in particular the acid rocks, are in the majority completely devitrified and characterized by granophyric texture sometimes accompanied by spherulites

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and axiolites. Poorly sorted pyroclastic rocks occupy much of this unit and are

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classified granulometrically as lapilli tuff.

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4.1. Acampamento Velho Formation

i-Lithic-rich ignimbrites (lLT)

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Comprises densely welded ignimbrites with pinkish-brown color, including remarkable occurrences of accessory lithics (approximately 10%) of plutonic and metamorphic rocks as granite, diorite, gabbro (Fig. 4B), monzonite, schist besides volcanic and sedimentary rocks (up to 15 cm) of the Bom Jardim and Maricá groups. Pumice (20%), quartz and sanidine crystaloclasts (10%), and a glass shard groundmass (60%) represent the juvenile material. ii-Ignimbrites with eutaxitic texture (eLT) This middle facies, with textural characteristics of lLT and rheoLT, consists of densely welded ignimbrites (Figs. 4C and 6A) with remarkable fiamme, defining its eutaxitic texture, as well as smaller amounts of lithic clasts (less than 10%). iii-Rheomorphic ignimbrites with mafic magma mixing features (rheoLT) These consist of tabular layers of extremely welded brownish-pink to dark-gray ignimbrites with parataxitic and eutaxitic textures (Fig. 4D) and pumice grains ranging from lens to stretched-ribbon shaped fragments with length/thickness ratios greater than 100. They include lithics (less than 5%) along with rotation features in crystaloclasts and flow folds that allow them to be classified as rheomorphic

ACCEPTED MANUSCRIPT ignimbrites ("lava-like" ignimbrites). The rocks contain quartz and sanidine

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crystaloclasts up to 3 mm and rarely zircon crystals up to 0.1 mm. The groundmass is fine-grained and is composed of shards, which are also very stretched. Features of mechanical mixing process (magma mingling) with mafic magma occur, as indicated by lenses and disseminated portions that are enriched in mafic minerals, probably

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riebeckite (Fig. 6B).

iv-Massive rhyolites with mafic magma mixing features (mRi1)

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These are dark-gray porphyritic rhyolites with quartz and sanidine (Or89-96) phenocrysts (1 to 2 mm, representing 15% of the rock) within a fine-grained equigranular to aphanitic groundmass (85%). Riebeckite microliths, showing mixing features with the felsic portion of the rock (similar to described in the previous facies), are widespread in the groundmass (Fig. 4F) or occur in lenses or enclaves. The rocks are typically massive, but foliation and flow folds occur locally. Coronitic texture

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occurs where microliths surround lithoclasts. Augite (euhedral and up to 0.2 mm) is a

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subordinate mineral, and chlorite and calcite occur as late crystallization phases. Ilmenite (Hem3-5), zircon (up to 0.4 mm), apatite, and titanite occur as accessory minerals.

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v-Subvolcanic trachytes (SvTq) These rocks vary from quartz latite, latite, and trachyte (Fig. 4E) and as

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recommended by Le Maitre et al. (2002) are generally named trachytic rocks. They occur in the central area as a 6×2 km sill, intrusive over an important NE-SW sinistral strike-slip fault zone. They have fine- to medium-grained equigranular or porphyritic textures (Figs. 6C and 6D) consisting predominantly of oligoclase and andesine (An26-37; 35%), orthoclase (40%), quartz (10%), augite (Wo34-38, En25-38, Fs24-36) and

ferrosilite (Wo3-6, En12-21, Fs74-81; 10%), and edenite. In porphyritic portions, plagioclase phenocrysts (up to 5 mm) are euhedral and zoned. Pyroxene (up to 5 mm) and orthoclase (up to 1.5 cm) phenocrysts, the latter sometimes as an outer border around plagioclase (anti-rapakivi texture), also occur. Apatite (up to 0.3 mm) and Ti-hematite (Hem52-59) represent the accessory phases, amounting to approximately 5%. vi-Volcanogenic sedimentary rocks (VSd2) These have isolated occurrences, mainly in the central part of the ignimbritic unit, and consist mainly of sedimentary breccias, conglomerates, sandstones, and siltstones, which are massive to locally stratified (Fig. 4G) and composed

ACCEPTED MANUSCRIPT predominantly of angular to subangular granitic and rhyolitic clasts with subordinate

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andesitic clasts. vii-Basalts (Bas1 and Bas2)

The effusive basaltic facies occurs in two positions, in the upper portion of the sequence (Fig. 3), both with very similar features. The basalts have àà flow

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morphology with meter thicknesses, sometimes show lava/sediment interaction features (mainly Bas1, with the VSd2 facies), and may contain many vesicles (up to 1

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cm; Fig. 4H) at their tops. In the central portion of the area, the facies occurs as dikes up to 30 m thick. They have very fine-grained groundmass (40%), labradorite (An5766)

phenocrysts (20%) up to1 mm, hematite (Hem99-100; 20%), and chlorite (15%) as a

mafic alteration (Figs. 5C and 5D). Remnants of altered diopside (Wo40-48, En27-39, Fs13-22) are visible (5%), and apatite and rare zircon crystals represent the accessory minerals.

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viii-Rhyolitic lithic-rich ignimbrites (lrioLT)

remarkable

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This facies includes slightly to moderately welded ignimbrites with the occurrence

of

angular

to

subangular

cognate

rhyolitic

lithics

(approximately 20%) of about 2 cm (Fig 4I). Pumice (25%), quartz and sanidine

material.

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crystaloclasts (15%), and glass-shard groundmass (40%) represent the juvenile

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ix-Moderately welded ignimbrites (//bpLT) These are moderately welded ignimbrites with fiamme and incipient eutaxitic

texture. They include cognate basalt, rhyolite, and ignimbrite lithics (Fig. 6E) and accessories clasts of sedimentary and metamorphic rocks that range up to 5 mm and make up 10% of the rock. Pumice (25%), quartz and sanidine crystaloclasts (15%), and glass-shard groundmass (50%) represent the juvenile material. x-Massive ignimbrites with incipient welding (mLT) This facies consists of whitish-gray to pinkish-red low to moderately welded

ignimbrites. Rounded white to light-green pumice clasts, approximately 0.5 to 1 cm but ranging up to 3 cm (Fig. 4J), are immersed in a tuffaceous groundmass (Fig. 6F) that makes up 50% of the rock. In some pumices, it is possible to see the shape of the tubular vesicles. Rare cognate rhyolitic lithics, up to 2 cm, also occur. Quartz and sanidine crystaloclasts of up to 2 mm (10%) and tuffaceous groundmass (40%) complete the rock. xi-Massive (mRi2), auto-brecciated (bRi) and foliated (fRi) rhyolites

ACCEPTED MANUSCRIPT The massive facies is represented by dome-shaped bodies or decameter-thick

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dikes, mainly in the northeastern portion of the study area (Fig. 2). Pink rhyolites have a massive aspect, although autobreccias, consisting of angular fragments ranging up to 10 cm in a “jigsaw-fit” texture (Figs. 4K and 6G) and flow foliation (Fig. 4L) occur locally, and are porphyritic with a fine-grained equigranular groundmass.

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They include euhedral plagioclase phenocrysts (0.3 mm), zoned sanidine (up to 3 mm; Fig. 6H), quartz (up to 1 mm), and strongly weathered riebeckite (up to 5 mm).

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Zircon crystals ranging up to 2 mm, apatite and ilmenite (Hem0) are the accessory phase. The foliated rhyolites are from lava flows and domes, and possess pronounced millimeter-thick flow foliation defined by layers of varying degrees of crystallinity and locally include gentle to isoclinal flow folds.

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5. Radiometric dating

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5.1 Materials and methods

Three samples were collected in the oriental Ramada Plateau from outcrops located a few meters from a secondary road (Fig. 2). These include a porphyritic,

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foliated rhyolite (VM 136: 30°28'46"S-53°40'01"W), a rheomorphic ignimbrite (VM 9A: 30°31'05"S-53°47'30"W), and a

subvolcanic

trachyte

(VM 9C:30°31' 04''S-

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53°47'33''W).

Approximately 10 kg of each sample was crushed, pulverized, and sieved for

zircon separation. The zircon grains were concentrated using conventional magnetic and heavy liquid separation techniques. Then, about 60 grains from each sample were handpicked and mounted in epoxy resin. Each mount was polished using diamond pastes of different grain sizes to expose the internal features of the zircon crystals. For zircon dating, the grains were imaged using backscattered electrons and cathodoluminescence to determine their internal structures and crystallization phases. Only zircon grains without imperfections, fractures, and mineral inclusions were selected for isotopic analysis. All U-Pb isotopic analyses were performed at the Geochronological Research Center of the Geosciences Institute, University of São Paulo (USP), using a NEPTUNE inductively coupled plasma-mass spectrometer (ICP-MS) and an excimer laser ablation (LA) system. Table 1 provides the cup and ICP-MS configuration as well as the laser

parameters used during the analyses. U-Pb analysis was used to measure the materials in the following order: two blanks, two NIST standard glasses, three

ACCEPTED MANUSCRIPT external standards, 13 unknown samples, two external standards, and two blanks. 204

Each experiment consisted of 40 cycles of 1 s/cycle. The was corrected using

Hg, where

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Hg/

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202

Hg interference for

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Hg ¼ 4.2. The

207

Pb/

204

Pb

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to normalize both the NIST and external standards, whereas the

Pb ratio was used

238

U/206Pb ratio was

used to normalize the external standard. The standard GJ (602±4.4 Ma; Elhlou et al.,

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2006) was used for the zircon analyses. Zircon typically contains low concentrations of common Pb. Thus, the reliability of the measured

207

Pb/206Pb and

238

U/206Pb ratios

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depends critically on accurately assessing the common Pb component. The residual common Pb was corrected based on the measured

204

Pb concentration using the

known terrestrial composition (Stacey & Kramers, 1975). The uncertainty introduced by laser-induced fractionation of elements and mass instrumental discrimination was corrected using a reference zircon standard (GJ-1; (Jackson et al., 2004). The isotope ratios and inter-element fractionation of

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data collected using the ICP-MS instrument were evaluated by interspersing the GJ-1

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zircon standard in each set of 13 zircon samples (spots). The GJ-1 standard comprises the requirements for the methods used in the laboratory, and the ratios 238

U/206Pb*,

207

Pb*/206Pb*, and

232

Th/238U were homogeneous throughout application

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of the bracket technique. External errors were calculated using error propagation for the individual measurements of the standard GJ-1 and the individual zircon sample

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measurements (spots). The ages were calculated using Isoplot version 4 and were based mainly on

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U/206Pb and

207

Pb/206Pb (Ludwig, 2008). Chemale et al. (2012)

detailed the analytical methods and data treatment.

5.2 Results

The zircon grains from the rhyolite sample (VM 136) are prismatic subhedral crystals with size ranging from 130 to 250 µm and average length-to-width ratio of 2:1 and pinacoidal and pyramidal terminations, and showed oscillatory zoning in some crystals (Fig. 7). Fifteen zircon grains were analyzed, and the isotopic data and calculated ages are presented in table 2. They are shown in a concordia diagram based on the

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U/206Pb and

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Pb/206Pb ratios in figure 7. The crystallization age for

sample VM 136 is 561.7 ± 1.8 Ma (95% confidence level, MSWD = 0.76), which corresponds to the Ediacaran period. The zircon grains from the ignimbrite sample (VM 9A) are prismatic euhedral crystals with size ranging from 150 to 450 µm and average length-to-width ratio of 2:1 and pinacoidal and pyramidal terminations, and showed oscillatory zoning (Fig. 7).

ACCEPTED MANUSCRIPT Twenty zircon grains were analyzed and the isotopic data and calculated ages are 238

U/206Pb and

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presented in table 3. They are also shown in concordia diagram based on the 207

Pb/206Pb ratios figure 7. The crystallization age of sample VM 9A is

560 ± 2.2 Ma (95% confidence level, MSWD = 0.107), which corresponds to the Ediacaran period.

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The zircon grains from the trachyte sample (VM 9C) are prismatic euhedral crystals with size ranging from 70 to 250 µm and average length-to-width ratio of 4:1

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and pinacoidal and pyramidal terminations, showed oscillatory zoning in some crystals (Fig. 7). Four zircon grains were analyzed and the isotopic data and calculated ages are presented in table 4. They are also shown in concordia diagram based on the

238

U/206Pb and

207

Pb/206Pb ratios figure 7. The crystallization age for

sample VM 9C is 560 ± 14 Ma (95% confidence level, MSWD = 0.65), which

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corresponds to the Ediacaran period.

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6. Geochemistry

6.1 Analytical procedures

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Whole-rock chemical analyses of 29 representative volcanic and subvolcanic samples (Tab. 5) were performed at ACME Laboratories Ltd. (Vancouver, Canada).

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Particular attention was given to choosing samples with lower contents of vesicles and a minimum amount of lithics. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for major elements, and inductively coupled plasma emission mass spectrometry (ICP-MS) was used for trace and rare earth elements (REEs).The analytical protocol at the ACME laboratory included analysis of standard STD SO-18 and BLK and three sample duplicates. The data were organized and analyzed statistically in the Microsoft Excel 2013 Petrograph 2beta (Petrelli et al., 2005) and the Geochemical Data Toolkit 2.3 (GCDkit; Janousek et al., 2006) programs to generate graphs and facilitate interpretation of results.

6.2 Major, trace, and rare earth element data The volcanic and subvolcanic rocks belong to a silicic alkaline magmatism, which is subdivided into (i) potassic alkaline (shoshonitic) rocks, represented by the Hilário Formation andesitic rocks, and (ii) sodic alkaline rocks, comprising the

ACCEPTED MANUSCRIPT Acampamento Velho Formation, and consisting predominantly of rhyolites and

Shoshonitic magmatism - Hilário Formation

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ignimbrites and subordinately of trachytes and basalts.

Hilário Formation andesitic lava flow and dikes have SiO2 contents ranging

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from 52.97 to 55.5 wt.% and alkalis (Na2O + K2O) from 6.27 to 7.71 wt.%, suggesting that they are alkaline rocks. This alkaline nature is also demonstrated by the TAS (Le

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Bas et al., 1986), R1-R2 (De la Roche et al., 1980), and Zr/TiO2 vs. SiO2 (Winchester & Floyd, 1977) diagrams illustrated in figure 8A, B, and C, where the andesites are positioned close to the line that separates alkaline and subalkaline rocks. They have K2O>(Na2O-2), which allows them to be characterized as potassic alkaline (trachybasalts and shoshonites according Le Maitre, 2002). Additionally, the sliding normalization diagram (Liégeois et al., 1998), which

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uses Zr-Ce-Sm-Y-Yb vs. Rb-Th-U-Ta averages normalized by the Yenchichi-Telabit

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series (NYTS) also attests to the shoshonitic character (Fig. 8D). The molar ratio (Na2O + K2O)/Al2O3 (agpaitic index) is between 0.59 and 0.69, indicating a mildly metaluminous character, as is also suggested by the Shand

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diagram (Maniar & Piccoli, 1989) shown in figure 8E. The rocks have high concentrations of Al2O3 (14.36 to 15.06 wt.%) and MgO

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(3.3 to 5.27 wt.%), allied with low FeOt (8.7 to 9.49 wt.%) and Zr (149.8 to 378.6 ppm; Tab. 5 and figs. 9 and 10), which is typical of shoshonitic affinity rocks. In the Harker diagrams, silica is the differentiation index that best expresses

the variation of the other elements (despite the small amount of shoshonitic rock samples, figures 9 and 10). Negative correlation of TiO2, CaO, MgO, Fe2O3, MnO

with silica is observed, suggesting magma differentiation processes especially with pyroxene, magnetite and plagioclase fractionation. Dispersions of the Al2O3, Na2O, K2O, Rb, Sr, and Ba contents probably suggest crystals accumulation process. An enrichment of LILE (Rb, Ba, and K) is observed when normalized to NMORB (Sun & McDonough, 1989; Fig. 11A), with Sr and LREE contents close to 1 and a flattened pattern, typical for shoshonite magmatism. Nb is depleted relative to LREE and K, which is considered as typical of magmas produced from sources modified by a previous subduction-related metasomatism (e.g. Kelemen et al., 1993). Their low Nb/La and Ba/La ratios are comparable to those reported for orogenic andesites by Davies & Hawkesworth (1994).

ACCEPTED MANUSCRIPT Chondrite normalized REE (Nakamura, 1974) patterns (Fig. 11B) show a slight

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enrichment between LREE and HREE (ΣREE = 214 to 297 ppm) with LaN/YbN ratio between 10.72 and 19.57. The CeN values are between 104 and 147 ppm, YbN between 7 and 17 ppm and there is a small Eu anomaly (Eu/Eu* = 0.77 to 0.88). Such features are also indicative of shoshonitic or high-potassium calc-alkaline

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magmas (Jakes & White, 1972; Nardi, 1989; Nardi & Lima, 2000).

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Sodic alkaline magmatism - Acampamento Velho Formation: basic rocks Basaltic lava flows

These rocks have SiO2 contents ranging from 47.29 to 49.13 wt.% and alkali (Na2O + K2O) contents of 4.62 to 5.32 wt.%. K2O amounts less than (Na2O-2) and K2O/Na2O values between 0.16 and 0.24 allow them to be characterized as sodic alkaline (e. g. Nardi, 2015). They are basalts and hawaiites, and their alkaline to sub-

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alkaline nature is confirmed in the TAS (Le Bas et al., 1986), R1-R2 (De la Roche et

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al., 1980), and Zr/TiO2 vs. SiO2 (Winchester & Floyd, 1977) classification diagrams, illustrated in figure 8A-C, as well as the sliding normalization diagram (Liégeois et al., 1998) shown in figure 8D.

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The agpaitic index is between 0.41 and 0.47, indicating strong metaluminous character, also shown by the Shand diagram (Maniar & Piccoli, 1989) illustrated in

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figure 8E.

An evolutionary trend of the basic, intermediate and acid compositions is

observed in the Harker diagrams (Figs. 9 and 10). The strong negative correlation between most of the major elements and silica suggest magmatic differentiation processes, involving the fractionation of pyroxene, magnetite and plagioclase of the basic and intermediate types. The rhyolitic and ignimbritic rocks represent the most differentiated magmatic liquids. In general, most elements negatively correlate with silica, except for Na2O and K2O, suggesting magma differentiation processes such as fractional crystallization, especially with pyroxene, plagioclase and K-feldspar fractionation. The basic rocks have low Ba (159 to 241 ppm), Nb (4.9 to 7 ppm), Y (22 to 32.5 ppm), and Zr (130 to 184 ppm) contents (Tab. 5 and fig. 10). Trace elements show a positive correlation with silica, with exception of Sr, in the trend observed between basic and trachytic rocks, suggesting a strong plagioclase fractionation. Ba, Sr and Zr show compatible behavior with the magmatic differentiation process in the

ACCEPTED MANUSCRIPT evolution of the rhyolitic liquids suggesting, plagioclase, K-feldspar and zircon

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fractionation. The data are consistent with the character of the alkaline series. There is a strong enrichment of trace elements compared to Sun & McDonough (1989) NMORB and a remarkable Nb anomaly (Fig. 11A). Normalized by Nakamura (1974) chondrite, there is a smooth LREE enrichment relative to HREE,

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no Eu anomaly, and LaN/YbN ratio close to 3 (Fig. 11B).

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Sodic alkaline magmatism - Acampamento Velho Formation: intermediate do acid rocks

These rocks can be separated into two associations, subvolcanic trachytes and rhyolites (dikes and lava flows)/ignimbrites, with K2O/Na2O values between 0.9 and 1.6 and considerably higher Zr concentrations in the trachytes (Fig. 10), both typical sodic alkaline association characteristics (Pearce et al., 1984; Whalen et al.,

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1987; Nardi, 2015). It is important to note that this value may be slightly modified,

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because the loss of alkalis during crystallization of peralkaline magmas, postmagmatic alteration processes (Leat et al., 1986), devitrification (Lipman, 1965) or

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hydrothermalism can promote variation.

Subvolcanic trachytes

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The trachytes have transitional character between intermediate and acid, with silica contents between 61.7 and 65.86 wt.%. They are trachytes (100*Q/(Q + an + ab + or) = 11%, according to Le Maitre et al., 2002) in the TAS diagram (Fig. 8A) as well as the Zr/TiO2 vs. SiO2 diagram (Winchester & Floyd, 1977; Fig. 8C). The agpaitic index is between 0.76 to 0.87, showing metaluminous character, as also evidenced by the Shand diagram (Maniar & Piccoli, 1989; Fig. 8E). The rocks have FeOt/(FeOt + MgO) ratios between 0.85 and 0.89 (Figs. 13A and 13B) and elevated Ba (1143 to 1789 ppm) and Zr (882.3 to 1128.8 ppm) contents, as seen in figure 10, that are typical of peralkaline rocks (Leat et al., 1986). The La/Nb ratio is high, around 5.92 to 7.9, which may indicate a greater crustal contamination (Nardi & Bitencourt, 2009). In the FeOt vs. Al2O3 diagram (MacDonald, 1974), the trachytic rocks plot in the pantalleritic trachyte field (Fig 8G). When normalized by ORG (Pearce et al., 1984), these rocks show Ba, Ce, and Zr positive anomalies and Nb and Ta negative anomalies (Fig. 11C). Compared to Nakamura (1974) chondrite, they show moderate LREE enrichment relative to HREE, with a smooth Eu negative anomaly (Fig. 11D).

Rhyolitic (dikes and lava flows)/ignimbritic rocks

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The rhyolites and rhyolitic composition ignimbrites have SiO2 values between 72.03 and 76.01 wt.%. The alkali content (Na2O + K2O) is between 7.64 and 9.2 wt.%. The agpaitic index shows values between 0.8 and 1.03, and in the Shand

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diagram (Maniar & Piccoli, 1989), the ratios of alumina and alkali are concentrated near the 1 (Fig. 8E), indicating a metaluminous to peralkaline tendency for these

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rocks. In the R1-R2 diagram (De la Roche et al., 1980), they plot in the alkali rhyolite field (Fig. 8B), which is a similar behavior as shown in the Zr/TiO2 vs. SiO2 diagram (Winchester & Floyd, 1977), because they show a comenditic/pantelleritic tendency (Fig. 8C). In the FeOt vs. Al2O3 diagram (MacDonald, 1974), the rocks plot in the comendite field (Fig. 8G). The FeOt/(MgO + FeOt) ratios vary from 0.9 to 0.99 (Figs. 13A and 13B) and are typical of the alkaline rhyolite series (Ewart, 1979). The high Zr

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content (352 to 914 ppm) supports the peralkaline affinity (Leat et al., 1986; Sommer

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et al., 2005), a character also shown by the Sr vs. Rb diagram (Hedge, 1966) in which the rhyolitic rocks plot in the peralkaline rocks field (Fig. 8F). Normalized by ORG (Pearce et al., 1984), the acid rocks show enrichment in most incompatible

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elements (Fig. 11C). There is a strong Ba negative anomaly accompanied by less significant Nb and Ta negative anomalies and Ce and Rb positive anomalies. The

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acid rocks have moderate to high REE values (ΣREE = 331 to 843 ppm). The fractionation between LREE and HREE is high, with LaN/YbN ratios ranging from 8.69 to 19.55. The LREE fractionation is greater than that of HREE with LaN/SmN ratios

(3.78 to 5.07) higher thanTbN/LuN ratios (1.3 to 2.15). Normalized by Nakamura (1974) chondrite, a strong Eu negative anomaly is observed (Fig. 11D).

7. Tectonic setting and discussion

The Hilário Formation andesitic rocks crop out as flows and dikes at the base of the oriental Ramada Plateau volcanic sequence. They are shoshonitic and moderately metaluminous, similar to the rocks described by Sommer et al. (2005) in the Ramada Plateau and by Lima & Nardi (1998), Nardi & Lima (2000) and Lopes et al. (2014) in the Lavras do Sul Shoshonitic Association. The low Nb content relative to LREE can be associated, according to Kelemen et al. (1993), with magmas generated from metasomatized subduction-related sources during post-collisional episodes. Several authors ascribe a significant role to

ACCEPTED MANUSCRIPT lower crust as the source or a significant contaminant to shoshonitic magmas. In

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order to evaluate the petrogenetic involvement, the shoshonitic rocks were compared to the lower crust averages (from Wedepohl, 1995). The rocks show enriched patterns mainly for Ba, Sr and LREE, while Y and Yb are depleted relative to lower crustal values. It suggests probably that lower crust is not compositionally suitable as

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a source for shoshonitic magmas or even as a contaminant capable of explaining the increase of LILE or HFS element contents. Another important question is the high Sr

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contents, because plagioclase is frequently an abundant residual phase during crustal melting. In this case and if low-melt fractions are envolved, high Sr magmas are not expected.

In Pearce & Norry (1979) and Pearce (1980) diagrams, which use incompatible elements for consideration of tectonic setting, these rocks occupy a position corresponding to within-plate basalts (Figs. 12A and 12B).

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Geochronological data in Lavras do Sul Shoshonitic Association provided an

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Ar40-Ar39 (plagioclase in andesite) age of 590 ± 6 Ma at the base of the volcanic sequence and 586 ± 8 Ma and 588 ± 7 Ma at the top. Granitic rocks of this association show U-Pb zircon ages of 592 ± 5 Ma (Remus et al., 1997) and 594 ± 4

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Ma (Remus et al., 1999), while younger monzonites of the same association were dated by Liz et al. (2009) at 587 ± 4 Ma.

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Available isotopic data on shoshonitic rocks of the Lavras do Sul Shoshonitic Association indicate Sr87/Sr86 initial ratio about 0.7048 and ƐNd values close to -0.2,

which are suggestive of EM1 type lithospheric mantle sources (Gastal & Lafon, 1998; Nardi & Lima, 2000). Acampamento Velho Formation basic rocks in this area occur as flows in the

middle and top portions of the volcanic sequence and as meter to decameter thick dikes that intrude the ignimbritic rocks. They have characteristics similar to those reported for the low Ti-P basalts in the Ramada Plateau (Sommer et al., 2005). In the diagrams of Pearce & Norry (1979) and Pearce (1982), they occupy a position corresponding to within-plate basalt (Figs. 12A and 12B), which is characteristic of continental extension or post-collisional settings, according to Leat et al. (1986). Rocks with similar characteristics were also studied in Neoproterozoic post-collisional volcanic associations in the Santa Barbara Ridge (Almeida et al., 2002), the Taquarembó Plateau (Wildner et al., 1999, 2002), and the Campo Alegre Basin (Waichel et al., 2000). Almeida et al. (2012) obtained a U-Pb zircon (LA-ICP-MS) age

ACCEPTED MANUSCRIPT Velho Formation in the Santa Barbara Ridge.

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of 553 ± 5 Ma for an andesitic basalt supposedly from the base of the Acampamento

The trachytic rocks occur as a NE-SW-elongated hypabissal mafic body, intrusive into ignimbritic rocks, and in some places display petrographic evidence of magma mingling processes with more felsic rocks, as indicated mainly by lenses that

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are enriched in mafic minerals (Fig. 6B) in rhyolites and ignimbrites. Their position over a fault or shear zone was probably important as a facilitator of mixing between

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these two magmas. The geochronological data support the hypothesis of contemporaneity (560 ± 2 Ma for the ignimbrites and 560 ± 14 Ma for the trachytes). The rocks have FeOt/(FeOt + MgO) ratios between 0.85 and 0.89 and they are ferroan and oxidized rocks (Figs. 13A and 13B; Frost et al., 1991; Frost et al., 2001; Dall'Agnol & Oliveira, 2007), generated in an oxidized environment, probably because the intrusion was established at a shear zone. The low agpaitic index (0.56

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to 0.65) and the high La/Nb ratio (5.92 to 7.9) also suggest that crystallization of the

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A-type magmas may have taken place throughout a shear setting in which occurred contamination of peraluminous and HFSE-depleted basic magmas (cf. Dall’Agnol & Oliveira, 2007; Nardi & Bittencourt, 2009).

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These petrographic and geochemical characteristics are similar to those of subvolcanic dioritic rocks described by Matté et al. (2012) in the southern portion of

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the Ramada Plateau, although the trachytic rocks represent more evolved liquids (Fig. 13). In that region, U-Pb zircon data indicate an age of 550 ± 2 Ma for the subvolcanic diorite (Matté et al., 2011). The rhyolitic (and ignimbritic) rocks have SiO2 values greater than 72 wt.% and

therefore belong to the so-called "high-silica rhyolitic systems" described by Mahood & Hildreth (1983) and Metz & Mahood (1991). Their parental magma probably had peralkaline character, indicated by the presence of alkaline minerals such as riebeckite, but these rocks display low agpaitic index (0.66 to 0.78) due to loss of alkaline elements by weathering and devitrification processes. According to Leat et al. (1986), loss of these elements may occur in post-magmatic alteration processes, and this may be one of the factors responsible for the metaluminous features of these rocks. Their FeOt/(FeOt + MgO) ratios, ranging from 0.9 to 0.99, suggest that the rocks are ferroan and generated in a reduced environment (Figs. 13A and 13B). Consistent with the low agpaitic index and high La/Nb ratio (3.34 to 7.33; Dall'Agnol & Oliveira, 2007; Nardi & Bittencourt, 2009), it is inferred that these rocks evolved in an extensional setting with a possible strike-slip component.

ACCEPTED MANUSCRIPT Acid rocks with a similar pattern occur in the Taquarembó Plateau (Sommer et

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al., 1999), the Ramada Plateau (Sommer et al., 2005), and the Tupanci region (Leitzke et al., 2015). In the tectonic settings diagram of Pearce et al. (1984), these rocks plot in the post-collisional field (Fig. 13C). In the granites classification diagram proposed by Whalen et al. (1987), the vast majority of the samples occupy the

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granite "A" type field, which are alkaline and anorogenic (Fig. 13D). In the diagram Al2O3 vs. FeOt/FeOt+MgO (Frost et al., 1991; Frost et al., 2001; Dall'Agnol & Oliveira,

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2007), they also occupy a position corresponding to "A-type" granites (Fig. 13B). Depletion of Ba and Nb accompanied by enrichment in Ce and Rb is characteristic of mantle sources with enrichment in incompatible elements during crustal melting processes. Leitzke et al. (2015) described high-silica rhyolites with the same characteristics in the Tupanci region. Shellnut et al. (2009) showed that the Th/Ta ratio may be used as an indicator of crust-mantle interaction. Rocks originated by

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mantle melting have ratios close to 2, and those caused by crustal melting have

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ratios ≥ 6.9. The acid rocks of the region show Th/Ta ratios predominantly greater than 6.9, indicating strong crustal contribution. As pointed out by Nardi & Bitencourt (2009), it is common for A-type granitoids to be associated with syenitic rocks (or

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trachytic rocks) and to show K2O/Na2O ratios close to 1. Volcanic and subvolcanic acid rocks of the oriental Ramada Plateau have

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sodic alkaline characteristics consistent with A-type granites, according to the criteria reviewed by Barbarin (1999), and these have affinity with the Ramada Intrusive Suite, included in the Saibro Intrusive Suite that elsewhere in the Sul-rio-grandense Shield has volcanic equivalents and sodic alkaline nature (Nardi & Bonin, 1991; Sommer et al., 2005). Isotopic data obtained from basic-intermediate rocks of this stratigraphic unit (Gastal & Lafon, 1998; Wildner et al., 1999; Chemale et al., 1999) yielded Sr87/Sr86 initial ratio variyng from 0.7048 to 0.709, whilst the ƐNd values vary around -3. The origin of this magmatism is considered by many authors as resulting from mantle sources, probably of EM1 type (Wildner et al, 1999; Nardi & Bonin 1991; Sommer et al., 2005, 2006). 8. Conclusions

Volcanic rocks of the oriental Ramada Plateau represent a part of the postcollisional magmatism associated with the Neoproterozoic Brasiliano Orogeny in

ACCEPTED MANUSCRIPT southern Brazil, which generated voluminous alkaline volcanism with associated

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sedimentation, initially in a strike-slip basin (Bom Jardim Group) and then in a transtensive rift (Santa Barbara Group). Ages obtained in this region support the proposed stratigraphy and demonstrate the contemporaneity between the rhyolitic and trachytic magmas (560 ± 2 Ma and 560 ± 14 Ma, respectively), as well as with

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rhyolitic subvolcanic bodies in the northeastern portion of the area (562 ± 2 Ma). Future work should attempt to explain the role of mixing between rhyolitic and

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trachytic magmas in the explosive events that occurred in the area. The geochronological data presented here, allied with data from the literature allow to conclude that the Acampamento Velho Formation magmatism had an activity period between 574 ± 7 Ma (Janikian et al., 2008) and 549 ± 5 Ma (Sommer et al., 2005).

In southernmost Brazil the Neoproterozic post-collisional period had a

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evolution from high-K subalkaline to shoshonitic and eventually to mildly sodic

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alkaline magmatism (Nardi & Bonin, 1991; Bitencourt & Nardi, 1993, 2000; Gastal & Lafon, 1998, 2001; Nardi & Lima, 2000; Waichel et al., 2000; Wildner et al., 2002; Sommer et al., 2005, 2006; Nardi & Bitencourt, 2009). The post-collisional period in

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this region is marked by the activity of important transcurrent and extensional faults and shear zones, which allowed the mantle melts to ascend and differentiate by

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fractional crystallization and crustal contamination (Bitencourt & Nardi, 1993, 2000; Nardi & Bitencourt, 2009). This is similar to sequences referred elsewhere as in Snowdonia and Parys Mountain associations in the British Caledonides (Leat et al., 1986), Devine Canyon Tuff - USA (Greene, 1973), Miocene post-collisional volcanism of the Eastern Rif in Morocco (El Bakkali et al., 1998), and for the evolution of the Alpine Belt since the end of the Variscan orogeny in Europe (Bonin, 2004). The evolution of post-collisional magmatism in southern Brazil is interpreted by several authors as resulting mainly from melting of a heterogeneous mantle source, eventually with the addition of an asthenospheric component and crustal contamination (Wildner et al., 2002, Sommer et al., 2006). Crustal melts can be significant within the major post-collision shear belts where peraluminous acid rocks occur (Bitencourt & Nardi, 1993, Nardi & Bitencourt, 2009). Isotope features typical of EM1 sources associated to Nb negative anomalies are the evidence for the subduction-related metasomatic character of post-collisional magmatism mantle

ACCEPTED MANUSCRIPT sources in southern Brazil (Nardi & Lima, 2000; Wildner et al., 2002, Sommer et al.,

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2006). Acknowledgments

V. Matté would like to thank CNPq (PhD research grant (141977/2011-6) for

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the financial support for the fieldwork and analyses. D. S. Oliveira, L. M. M. Rossetti and B. M. Friedrich are thanked for helping with the collecting of the samples. This

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work had partial financial support to C.A. Sommer from the National Research Council (CNPq) 400724/2014-6, 441766/2014-5, 302213/2012-0, 303584/2009-2, 473683/2007, 5470641/2008-8, 470203/2007-2, 471402/2012-5, 303038/2009-8 and 470505/2010-9, from the Rio Grande do Sul State Research Foundation (FAPERGS) 1180/12-8, and PRONEX 10/0045-6. We also thank the laboratory support from the IGEO/UFRGS and CPGEO/USP. We would like to acknowledge the editor Reinhardt

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A. Fuck, and JSAES reviewers Jaime E. Scandolara as well as two anonymous

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References

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reviewers, for their valuable comments and constructive reviews.

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Almeida, D.P.M., Chemale Jr., F., Machado, A., 2012. Late to post-orogenic Brasiliano-Pan-African volcano-sedimentary basins in the Dom Feliciano Belt, southernmost Brazil. In: Ismail Al-Juboury, Ali (Ed.), Petrology e New Perspectives and Applications, vol. 2012. InTech e Open Access Publisher, Rijeka, 73-130. Almeida, D.P.M., Zerfass, H., Basei, M. A., Petry, K., Gomes, C. H., 2002. The Acampamento Velho Formation, a Lower Cambrian Bimodal Volcanic Package: Geochemical and Stratigraphic Studies from the Cerro do Bugio, Perau and Serra de Santa Bárbara (Caçapava do Sul, Rio Grande do Sul, RS - Brazil). Gondwana Research 5(3), 721-733. Almeida, R.P., Janikian, L., Fragoso-Cesar, A.R.S., Marconato, A., 2009. Evolution of a rift basin dominated by subaerial deposits: the Guaritas Rift, Early Cambrian, Southern Brazil. Sedimentary Geology 217, 30-51. Barbarin, B., 1999. A review of the relationships between granitoid types, their origins and their geodynamic environments. Lithos 46, 605-626. Bicca, M.M., Chemale Jr., F., Jelinek, A.R., Oliveira, C.H.E., Guadagnin, F., Armstrong, R., 2013. Tectonic evolution and provenance of the Santa Bárbara Group, Camaquã Mines region, Rio Grande do Sul, Brazil. Journal of South American Earth Sciences 48, 173-192. Bitencourt, M.F., Nardi, L.V.S., 1993. Late to Post-collisional Brasiliano granitic magmatism in southernmost Brazil. Anais da Academia Brasileira de Ciências 65, 316.

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Bitencourt, M.F., Nardi, L.V.S., 2000. Tectonic setting and sources of magmatism related to the southern Brazilian Shear Belt. Revista Brasileira de Geociências 30, 184-187.

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Bitencourt, M.F., Philipp, R.P., Lisbôa, N.A., Azevedo, G.C., Holz, M., 1997. Projeto Vila Nova - Mapa Geológico 1:50000. Instituto de Geociências, Universidade Federal do Rio Grande do Sul.

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Bonin, B., 2004. Do coeval mafic and felsic magmas in post-collisional to within-plate regimes necessarily imply two contrasting, mantle and crustal, sources? A review. Lithos 78, 1-24. Borba, A.W., 2006. Evolução geológica da “Bacia do Camaquã” (Neoproterozóico e Paleozóico Inferior do Escudo Sul-Riograndense, RS, Brasil: uma visão com base na integração de ferramentas de estratigrafia, petrografia e geologia isotópica. Tese de Doutorado, Porto Alegre, UFRGS/IG, 110p.

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Borba, A.W., Maraschin, A.J., Mizusaki, A.M.P., 2004a. Stratigraphic analysis and depositional evolution of the Neoproterozoic Maricá Formation (southern Brazil): constraints from field data and sandstone petrography. Gondwana Research 7(3), 871-886.

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Borba, A.W., Maraschin, A.J., Mizusaki, A.M.P., 2007. Evolução tectonoestratigráfica e paleoclimática da Formação Maricá (Escudo Sul-rio-grandense, Brasil): um exercício de geologia histórica e análise integrada de uma bacia sedimentar neoproterozóica. Pesquisas em Geociências 34, 57-74.

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Borba, A.W., Mizusaki, A.M.P., 2003. Santa Bárbara formation (Caçapava do Sul, southern Brazil): depositional sequences and evolution of an Early Paleozoic postcollisional basin. Journal of South American Earth Sciences 16, 365-380. Borba, A.W., Mizusaki, A.M.P., Silva, D.R.A., Noronha, F.L., 2004b. Petrographic and Sr-isotopic constraints on the provenance of the Neoproterozoic Maricá Formation (southern Brazil). In: International association of sedimentologists - IAS Meeting 2004, Abstracts…, Coimbra, Portugal, CD-ROM. Branney, M.J., Kokelaar, B.P., 2002. Pyroclastic density currents and the sedimentation of ignimbrites. Geological Society London Memoir 27, 143p. Chemale Jr., F., 2000. Evolução geológica do escudo Sul-Rio-Grandense. In: De Ros, L.F., Holz, M. (Eds.), Geologia do Rio Grande do Sul. CIGO/UFRGS, Porto Alegre, 13-52. Chemale Jr., F., Dussin, I.A., Alkmim, F., Martins, M.S., Queiroga, G., Armstrong, R., Santos, N.M., 2012. Unravelling a Proterozoic basin history through detrital zircon geochronology: the case of the Espinhaço Supergroup, Minas Gerais, Brazil. Gondwana Research 22, 200-206. Chemale Jr., F., Hartmann, L.A., Silva, L.C., 1995. Stratigraphy and Tectonism of Precambrian to Early Paleozoic Units. XVIII Acta Geologica Leopoldensia 42, 5-117.

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Dall’Agnol, R., Oliveira, D.C., 2007. Oxidized, magnetite-series, rapakivi-type granites of Carajás, Brazil: implications for classification and petrogenesis of A-type granites. Lithos 93, 215-233. Davies, J., Hawkesworth, C.J., 1994. Early calcalkaline magmatism in the MogollonDatil Volcanic Field, New Mexico, USA. Journal of the Geological Society 151, 825843.

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De la Roche, H., Leterrier, J., Grandclaude, P., Marchal, M., 1980. A classification of volcanic and plutonic rocks using R1R2-diagram and major element analyses - its relationships with current nomenclature. Chemical Geology 29, 183-210. El Bakkali, S., Gourgaud, A., Bourdier, J.L., Bellon, H., Gundogdu, N. 1998. Postcollision neogene volcanism of the Eastern Rif (Morocco): magmatic evolution through time. Lithos 45, 523-543. Elhlou, S., Belousova, E., Griffin,W.L., Pearson, N.J., O'reilly, S.Y., 2006. Trace Element and Isotopic Composition of GJ-red Zircon Standard by Laser Ablation. Goldschmidt Conference Abstracts, A-5.

TE

D

Ewart, A., 1979. A review of the mineralogy and chemistry of Tertiary-Recent dacitic, latitic, rhyolitic and related salic volcanic rocks. In: Baker, F. (Ed.). Trondhjemites, dacites and related rocks. The Hague: Elsevier, 113-121.

EP

Fragoso-Cesar, A.R.S., 1991. Tectônica de Placas no Ciclo Brasiliano: As orogenias dos Cinturões Dom Feliciano e Ribeira no Rio Grande do Sul. Tese de Doutoramento. Instituto de Geociências, Universidade de São Paulo, 367p.

AC C

Fragoso-Cesar, A.R.S., Almeida, R.P., Fambrini, G.L., Pelosi, A.P.M.R., Janikian, L., 2003. A Bacia Camaquã: um sistema intracontinental anorogênico de rifts do Neoproterozóico III - Eopaleozóico no Rio Grande do Sul. In: Encontro sobre a estratigrafia do Rio Grande do Sul: escudo e bacias, 1, Anais..., Porto Alegre, RS 139-144. Fragoso-Cesar, A.R.S., Fambrini, G.L., Paes de Almeida, R., Pelosi, A.P.M.R., Janikian, L., Riccomini, C., Machado, R., Nogueira, A.C.R., Saes, G.S., 2000. The Camaquã extensional basin: Neoproterozoic to early Cambrian sequences in southernmost Brazil. Revista Brasileira de Geociências 30, 438-441. Fragoso-Cesar, A.R.S., Lavina, E.L., Paim, P.S.G., Faccini, U.F., 1984. A Antefossa Molássica do Cinturão Dom Feliciano no Escudo do Rio Grande do Sul. Congresso Brasileiro de Geologia, 33, Rio de Janeiro, RJ, Brasil, SBG 7, 3272-3283. Frost, B.R., 1991. Introduction to oxygen fugacity and its petrologic importance. In: Lindsley, D.H. (Ed.), Oxide minerals: petrologic and magnetic significance. Reviews in Mineralogy, vol. 25. Mineralogical Society of America, 489-509. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J, Frost, C.D., 2001. A geochemical classification for granitic rocks. Journal of Petrology 42, 2033-2048. Gastal, M.C.P., Lafon, J.M., 1998. Gênese e evolução dos granitóides metaluminosos de afinidade alcalina da porção oeste do escudo sul-rio-grandense:

ACCEPTED MANUSCRIPT

RI PT

geoquímica e isótopos de Rb-Sr e Pb-Pb. Revista Brasileira de Geociências 28, 1128. Gastal, M.C.P., Lafon, J.M., 2001. Novas idades 207Pb/206Pb e geoquímica isotópica Nd-Sr para granitóides shoshoníticos e alcalinos das regiões de Lavras do Sul e Taquarembó, RS. VIII Congresso Brasileiro de Geoquímica, 21-26.

SC

Greene, R.C., 1973. Petrology of the welded tuff of Devine Canyon, Southeastern Oregon. USGS professional paper 797, 26p.

M AN U

Hartmann, L.A., Chemale Jr., F., Philipp, R.P., 2007. Evolução geotectônica do Rio Grande do Sul no Pré-Cambriano. In: Ianuzzi, R., Frantz, J.C. (Eds.), 50anos de Geologia, vol. 1. Editora Comunicação e Identidade, Porto Alegre, 97-123. Hartmann, L.A., Leite, J.A.D., Silva, L.C., Remus, M.V.D., McNaughton, N.J., Groves, D.I., Fletcher, I.R., Santos, J.O.S., Vasconcellos, M.A.Z., 2000. Advances in SHRIMP geochronology and their impact on understanding the tectonic and metallogenic evolution of southern Brazil. Australian Journal of Earth Sciences 47, 829-844.

D

Hedge, C.E., 1966. Variations in radiogenic strontium found in volcanic rocks. Journal of Geophysical Research 71(24), 6119-6126.

EP

TE

Jackson, S., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004. The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology. Chemical Geology 211, 47-69. Jakes, P., White, A.J.R., 1972. Major and trace element in volcanic rocks of orogenic areas. Geological Society of America Bulletin 87, 861-867.

AC C

Janikian, L., Almeida, R.P., Fragoso-Cesar, A.R.S., Corrêa, C.R.A., Pelosi, A.P.M.R., 2005. Evolução paleoambiental e sequências deposicionais do Grupo Bom Jardim e Formação Acampamento Velho (Supergrupo Camaquã) na porção norte da SubBacia Camaquã Ocidental. Revista Brasileira de Geociências 35, 245-256. Janikian, L., Almeida, R.P., Fragoso-Cesar, A.R.S., Martins, V.T.S., Dantas, E.L., Tohver,E., McReath, I., D’Agrella-Filho, M.S., 2012. Ages (U-Pb SHRIMP and LA ICPMS) and stratigraphic evolution of the Neoproterozoic volcano-sedimentary successions from the extensional Camaquã Basin, Southern Brazil. Gondwana Research 21, 466-482. Janikian, L., Almeida, R.P., Trindade, R.I.F., Fragoso-Cesar, A.R.S., D'Agrella-Filho, M.S., Dantas, E.L., Tohver, E., 2008. The continental record of Ediacaran volcanosedimentary successions in southern Brazil and its global implications. Terra Nova 20, 259-266. Janousek, V., Farrow, G., Erban, V., 2006. Interpretation of whole-rock geochemical data in igneous geochemistry: introducing Geochemical Data Toolkit (GCDkit). Journal of Petrology 47(6), 1255-1259. Kelemen, P.B., Shimizu, N., Dunn, T., 1993. Relative depletion of niobium in some arc magmas and the continental crust: partitioning of K, Nb, La and Ce during

ACCEPTED MANUSCRIPT

RI PT

melt/rock reaction in the upper mantle. Earth and Planetary Science Letters 120, 111-134. Le Bas, M.J., Le Maitre, R.W., Streckeisen, A., Zanettin, B., 1986. A chemical classification of volcanic rocks based on the total alkali-silica diagram. Journal of Petrology 27, 745-750.

SC

Le Maitre, R.W., 2002. Igneous rocks: a classification and glossary of terms. In: Recommendations of the International Union of Geological Sciences Subcommission on the Systematic of Igneous Rocks. Cambridge: Cambridge University Press, 252p.

M AN U

Leat, P.T., Jackson, S.E., Thorpe, R.S., Stillman, C.J., 1986. Geochemistry of bimodal basalt - subalkaline/peralkaline rhyolite provinces within the Southern British Caledonides. Journal of Geological Society 143, 259-273. Leitzke, F.P., Sommer, C.A., Lima, E.F., Matte, V., 2015. O vulcanismo alta-sílica da região do Tupanci, NW do Escudo Sul-Rio-Grandense: faciologia, petrografia e litoquímica. Pesquisas em Geociências 42, 5-24.

TE

D

Liégeois, J.P., Navez, J., Hertogen, J., Black R., 1998. Contrasting origin of postcollisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids. The use of sliding normalizantion. Lithos 45, 1-28.

EP

Lima, E.F., Nardi, L.V.S., 1998. The Lavras do Sul shoshonitic association: implications for the origin and evolution of Neoproterozoic shoshonitic magmatism in southernmost Brazil. Journal of South American Earth Sciences 11, 67-77.

AC C

Lima E.F., Sommer C.A., Nardi L.V.S., 2007. O vulcanismo neoproterozóicoordoviciano no Escudo Sul-riograndense: os ciclos vulcânicos da Bacia do Camaquã. In: Iannuzzi R., Frantz J.C. (Eds.), 50 anos de Geologia. Instituto de Geociências, vol. 1. Editora Comunicação e Identidade, Porto Alegre, 79-95. Lipman, P.W., 1965. Chemical comparison of glassy and crystalline volcanic rocks. US Bull 1201-D: 24p. Liz, J.D., Lima, E.F., Nardi L.V.S., Sommer, C.A., Saldanha D.L., Pierosan, R. 2009. Caracterização geológica e petrologia das rochas monzoníticas da Associação Shoshonítica de Lavras do Sul (RS). Revista Brasileira de Geociências 39 (2), 244255. Lopes, R.W., Fontana, E., Mexias, A.S., Gomes, M.E.B., Nardi, L.V.S., Renac, C., 2014. Caracterização petrográfica e geoquímica da sequência magmática da Mina do Seival, Formação Hilário (Bacia do Camaquã - Neoproterozoico), Rio Grande do Sul, Brasil Pesquisas em Geociências 41 (1), 51-64. Ludwig, K.R., 2008. User's Manual for Isoplot 3.6: a Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, Berkeley. MacDonald, R., 1974. Nomenclature and Petrochemistry of the peralkaline oversaturated extrusive rocks. Bulletin of Volcanologique 38, 498-516.

ACCEPTED MANUSCRIPT

RI PT

Machado, N., Koppe, J.C., Hartmann, L.A., 1990. A Late Proterozoic U-Pb age for the Bossoroca Belt, Rio Grande do Sul, Brazil. Journal of South American Earth Sciences 3 (2/3), 87-90. Mahood, G.A., Hildreth, W., 1983. Nested calderas and trapdoor uplift at Pantelleria, Strait of Sicily. Geology 2, 722-726.

SC

Maniar, P.D., Piccoli, P. M., 1989. Tectonic discrimination of granitoids. Geological Society of America Bulletin 101, 635-643.

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Matté, V., Sommer, C.A., Lima, E.F., Dantas, E.L., 2011. Relação das rochas dioríticas do Platô da Ramada (RS) com o vulcanismo alcalino da Formação Acampamento Velho (Neoproterozóico do Escudo Sul-Rio-Grandense). In: V Simpósio de vulcanismo e ambientes associados. Cidade de Goiás. Anais do V Simpósio de vulcanismo e ambientes associados.

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Matté, V., Sommer, C.A., Lima, E.F., Saldanha, D.L., Pinheiro-Sommer, J.A., Liz, J.D., 2012. Rochas dioríticas do Platô da Ramada, Rio Grande do Sul, e sua relação com o vulcanismo alcalino da Formação Acampamento Velho, Neoproterozoico do Escudo Sul-Rio-Grandense. Revista Brasileira de Geociências 42 (2), 343-362.

TE

Metz, J.M., Mahood, G.A., 1991. Development of the Long Valley, California, magma chamber record in precaldera rhyolite lavas of glass Mountain. Contributions to Mineralogy and Petrology 106(3), 379-397.

EP

Miyashiro, A., 1978. Nature of alkalic volcanic rock series. Contributions to Mineralogy and Petrology 66, 91-104.

AC C

Naime, R.H., 1987 Geologia, Geoquímica e Petrologia do Complexo Granítico Ramada e do Granito Cerro da Cria. Porto Alegre. Dissertação de Mestrado, UFRGS, 148p. Nakamura, N., 1974. Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary chondrites. Geochimica et Cosmochimica Acta 38, 757-775. Nardi, L.V.S., 1989. Geoquímica dos Elementos Terras Raras em Rochas Graníticas da Região Centro-Sul do Brasil. In: M. Formoso, L.V.S. Nardi, L.A. Hartmann (Eds.), Geoquímica dos Elementos Terras Raras no Brasil. Rio de Janeiro: DNPM/CPRM, 71-81. Nardi, L.V.S., 2015. Granitoides e séries magmáticas: o estudo contextualizado dos granitoides. Pesquisas em Geociências 43(1), 85-99. Nardi, L.V.S., Bitencourt, M.F.S., 2009. A-type granitic rocks in post-collisional settings in southernmost Brazil: their classification and relationship with tectonics and magmatic series. Canadian Mineralogist 47(6), 1493-1503. Nardi, L.V.S., Bonin, B., 1991. Post-orogenic and non-orogenic alkaline granite associations: the Saibro intrusive suite, southern Brazil - A case study. Chemical Geology 92, 197-212.

ACCEPTED MANUSCRIPT

RI PT

Nardi, L.V.S., Lima, E. F., 2000. O magmatismo shoshonítico e alcalino da Bacia do Camaquã-RS. In: Holz, M., de Ros, L. F. (Org.). Geologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS,119-131. Nemec, D., 1966. Plagioclase albitization in the lamprophyric and lamproid dykes at eastern border of the Bohemian massif. Beitrage zur Mineralogie und Petrographie 12, 340-353.

M AN U

SC

Oliveira, C.H.E., Chemale Jr., F., Jelinek, A.R., Bicca, M.M., Philipp, R.P., 2014. UPb and Lu-Hf isotopes applied to the evolution of the late to post-orogenic transtensional basins of the dom feliciano belt, Brazil. Precambrian Research 246, 240-255. Oliveira, D.S., Sommer, C.A, Philipp, R.P., Lima, E.F., Basei, M.G.S., 2015. Postcollisional subvolcanic rhyolites associated with the Neoproterozoic Pelotas Batholith, southern Brazil. Journal of South American Earth Sciences 63, 84-100.

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Paim, P.S.G., Chemale Jr., F., Lopes, R.C., 2000. A Bacia do Camaquã. In: Holz, M., DeRos, L.F. (Eds.), Geologia do Rio Grande do Sul. CIGO-UFRGS, Porto Alegre, 231-274.

TE

Paim, P.S.G., Chemale Jr., F., Wildner, W., 2014 Estágios evolutivos da Bacia do Camaquã (RS). Ciência e Natura 36, 183-193.

EP

Pearce, J.A., 1980. Geochemical evidence for the genesis and eruptive setting of lavas from the tethyan ophiolites. In: Proceedings of the International Ophiolite Simposium. Nicosia. Cyprus, 261-272.

AC C

Pearce, J.A., 1982. Trace elements characteristics of lavas from destructive plate boundaries. In: Thorpe, R.S. (Ed.), Andesites: Orogenic Andesites and Related Rocks. Wiley, New York, 525-546. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace elements discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25(4), 956-983. Pearce, J.A., Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y, and Nb. Variations in volcanic rocks: Contributions to Mineralogy and Petrology 69, 33-37. Pelosi, A.P.M.R., Fragoso-Cesar, A.R.S., 2003. Proposta litoestratigráfica e considerações paleoambientais sobre o Grupo Maricá (Neoproterozóico III), Bacia do Camaquã, Rio Grande do Sul. Revista Brasileira de Geociências 33(2), 137-148. Petrelli, M., Poli, G., Perugini, D., Peccerillo, A., 2005. Petrograph: a new software to visualize, model, and present geochemical data in igneous petrology, geochemistry, geophysics and geosystems. 6: Q07011, DOI 10.1029/2005GC000932. Philipp, R.P., Machado, R., 2002. Suítes graníticas do Batólito Pelotas no Rio Grande do Sul: petrografia, tectônica e aspectos petrogênicos. Revista Brasileira de Geociências 31(3), 257-266.

ACCEPTED MANUSCRIPT

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Philipp, R.P., Chemale Jr., F., Machado, R., 2007. A Geração dos granitoides Neoproterozoicos do Batólito Pelotas: evidências dos isótopos de Sr e Nd e implicações para o crescimento continental da porção sul do Brasil. In: Iannuzzi R., Frantz J.C. (Eds.), 50 anos de Geologia. Instituto de Geociências, vol. 1. Editora Comunicação e Identidade, Porto Alegre, 59-77.

SC

Porcher, C.A., Leites, S.R., Ramgrab, G.E., Camozzato, E., 1995. Passo do Salsinho, folha SH.22-Y-A-I-4, escala 1:50.000, estado do Rio Grande do Sul. Brasília, CPRM, Programa Levantamentos Geológicos do Brasil, 352p.

M AN U

Remus, M.D.V., Hartmann, L.A., McNaughton, N.J., Fletcher, I.R., 1999. Shrimp UPb zircon ages of volcanism from the São Gabriel Block, southern Brazil. In: Simpósio sobre vulcanismo e ambientes associados, 1. Boletim de Resumos, 83. Remus, M.V.D., McNaughton, N.J., Hartmann, L.A., Fletcher, I.R., 1997. Zircon SHRIMP dating and Nd isotope data of granitoids of the São Gabriel Block, southern Brazil: evidence of an Archaean/Paleoproterozoic basement. Extended Abstracts, International Symposium on Granites and Associated Mineralization, 2, Salvador, 217-272.

TE

D

Ribeiro, M., Bocchi, P.R., Figueiredo Filho, P.M., Tessari, R., 1966. Geologia da Quadrícula de Caçapava do Sul. Rio Grande do Sul. Boletim da Divisão de Fomento da Produção Mineral. Brasil, Rio de Janeiro, 127, 1-232.

EP

Ribeiro, M., Fantinel, L.M., 1978. Associações Petrotectônicas do Escudo SulRiograndense: I tabulação de distribuição das associações petrotectônicas do Escudo do Rio Grande do Sul. Iheringia 5, 19-54.

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Santos, E.L., Becker, J., Macedo, P.M., Gonzales Filho, F., Chabam, N., 1978. Divisão litoestratigráfica do Eo-Cambriano - Pré-Cambriano Superior do Escudo SulRiograndense. In: Congresso Brasileiro De Geologia, 30, 1978, Recife. Anais... Recife, 2, 670-684. Shellnutt, J.G., Wang, C.Y., Zhou, M.F., Yang, Y., 2009. Zircon Lu-Hf isotopic compositions of metaluminous and peralkaline A-type granitic plutons of the Emeishan large igneous province (SW China): constraints on the mantle source. Journal of Asian Earth Sciences 35, 45-55. Soliani Jr., E., 1986. Os dados geocronológicos do Escudo Sul-Rio-Grandense e suas implicações de ordem geotectônica. Tese de Doutorado. Instituto de Geociências, Universidade de São Paulo, 425p. Soliani Jr., E., Koester, E., Fernandes, L.A.D., 2000. Geologia isotópica do Escudo Sul-rio-grandense, parte II: os dados isotópicos e interpretações petrogenéticas. In: Holz, M.; De Ros, L.F. (Eds.) Geologia do Rio Grande do Sul. CIGO-UFRGS, 175230. Sommer, C.A., 2003. O vulcanismo neoproteozóico do Platô da Ramada, região de Vila Nova do Sul, RS. Porto Alegre. Tese de doutorado em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul. 194p.

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Sommer, C.A., Lima, E.F., Machado, A., Rosseti, L.M.R., Pierosan, R., 2013. Recognition and characterisation of high-grade ignimbrites from the neoproterozoic rhyolitic volcanism in southernmost Brazil. Journal of South American Earth Sciences 47, 152-165.

SC

Sommer, C.A., Lima, E.F., Nardi, L.V.S., 1999. Evolução do vulcanismo alcalino na porção sul do Platô do Taquarembó, Dom Pedrito - RS. Revista Brasileira de Geociências 29(2), 245-254.

M AN U

Sommer, C.A., Lima, E.F., Nardi, L.V.S., Figueiredo, A.M.G., Pierosan, R., 2005. Potassic and low- and high-Ti mildly alkaline volcanism in the Neoproterozoic Ramada Plateau, Southernmost Brazil. Journal of South American Earth Sciences 18(3), 237-254. Sommer, C.A., Lima, E. F., Nardi, L. V. S., Liz, J. D., Waichel, B. L., 2006. The evolution of Neoproterozoic magmatism in southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins. Anais da Academia Brasileira de Ciências 78, 573-589.

TE

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Sommer, C.A., Lima, E.F., Pierosan, R., Machado, A., 2011. Reoignimbritos e ignimbritos de alto grau do Vulcanismo Acampamento Velho, RS: origem e temperatura de formação. Revista Brasileira de Geociências 41, 420-435.

EP

Stacey, J.S., Kramer, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26, 207-221.

AC C

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.) Magmatism in Ocean Basins. Geological Society of London Special Publication, 42, 313-345. Szubert, C.C., Kirchner, C.A., Garcia, C.A., Andreotti, J.L.S., Shintaku, I., 1977. Projeto Cobre nos Corpos Básico-Ultrabásicos e Efusivas do Rio Grande do Sul. Porto Alegre, CPRM/DNPM. v. 2, 113p. Tera, F., Wasserburg, G.J., 1972. U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks. Earth and Planetary Science Letters 14, 281-304. Waichel, B., Lima, E.F., Nardi, L.V.S., Sommer, C.A., 2000. The alkaline postcollisional volcanism of Campo Alegre Basin in southern Brazil: petrogenetic aspects. Revista Brasileira de Geociências 30(3), 393-396. Wedepohl, K.H., 1995. The composition of the continental crust. Geochimica et Cosmochimica Acta 95, 1217-1232. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology 95, 407-419. Wildner, W., Nardi, L.V.S., Lima, E.F., 1999. Post-collisional alkaline magmatism on the Taquarembó Plateau: a well preserved Neoproterozoic-Cambrian plutono-

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volcanic association in southern Brazil. International Geology Review 41(12), 10821098. Wildner, W., Lima E.F., Nardi, L.V.S., Sommer, C.A., 2002. Volcanic cycles and setting in the Neoproterozoic III to Ordovician Camaquã Basin succession in southern Brazil: characteristics of post-collisional magmatism. Journal of Volcanology and Geothermal Research 118, 261-283.

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Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325-343. Figure Captions

Figure 1: A) Sul-rio-grandense Shield location and tectonic setting (modified from Hartmann et al., 2007); B) Oriental Ramada Plateau location and regional geological

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setting (modified from Lima et al., 2007; Paim et al., 2000; Wildner et al., 2002).

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Figure 2: Geological map of oriental Ramada Plateau as located geographically in figure 1B (modified from Szubert et al., 1977; Porcher et al., 1995; Bitencourt et al.,

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1997; Sommer, 2003).

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Figure 3: Schematic stratigraphic column of the oriental Ramada Plateau.

Figure 4: Macroscopic aspects of representative rocks of oriental Ramada Plateau. A) Porphyritic andesite - Ad (Hilário Formation); B) Ignimbrite with gabbroic rock accessory lithoclast - lLT; C) Densely welded ignimbrite with eutaxitic texture - eLT; D) Rheomorphic ignimbrite with vertical parataxitic texture - rheoLT; E) Mafic latite with plagioclase phenocrysts - SvTq; F) Massive rhyolite mixed with mafic magma mRi1; G) Volcanogenic conglomerate - VSd2; H) Vesicular basalt - Bas1; I) Rhyolite lithic-rich ignimbrite - lrioLT; J) Massive ignimbrite - mLT with incipient welding; K) Auto-brecciated rhyolite with jigsaw-fit texture - bRi; L) Foliated rhyolite - fRi.

Figure 5: Microscopic aspects of representative basic and intermediate rocks of oriental Ramada Plateau. A and B) Hilário Formation porphyritic andesite - Ad, with plagioclase and hornblende phenocrysts; C and D) Acampamento Velho Formation basalt - Bas1 with plagioclase phenocrysts and chlorite and opaque minerals in amygdales.

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rocks of oriental Ramada Plateau. A) Densely welded ignimbrite with eutaxitic texture - eLT; B) Rheomorphic ignimbrite with mafic magma mixing features - rheoLT; C) Augite phenocryst in latite - SvTq; D) Plagioclase and augite phenocrysts in latite SvTq; E) Moderately welded ignimbrite - //bpLT; F) Massive ignimbrite - mLT with

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incipient welding; G) Auto-brecciated rhyolite - bRi, in jigsaw-fit texture; H) Zoned

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sanidine phenocryst in massive rhyolite - mRi2.

Figure 7: Tera-Wasserburg diagram (Tera & Wasserburg, 1972) from dated samples and cathodoluminescence pictures of selected zircon grains. The individual analyses (black and white circles) and their numbers are indicated according with the data presented in tables 2, 3 and 4.

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Figure 8: A) TAS Diagram (Le Bas et al., 1986). Dashed line separates alkaline

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(above) and sub-alkaline (below) rocks (Miyashiro, 1978); B) R1 vs. R2 classification diagram (De la Roche et al., 1980); C) Zr/TiO2 vs. SiO2 classification diagram (Winchester & Floyd, 1977); D) Sliding normalization diagram (Liégeois et al.,

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1998).*NYTS: Normalization to the Yenchichi-Telabit series; E) Shand diagram with Al2O3/ CaO+Na2O+K2O vs. Al2O3/Na2O+K2O molar ratios (Maniar & Piccoli, 1989); F)

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Sr vs. Rb diagram (Hedge 1966); G) FeOt vs. Al2O3 diagram (MacDonald, 1974) for acid rocks. A line separates rhyolites (below) and trachytes (above) and B line separates comendites and pantellerites.

Figure 9: Binary diagrams displaying major elements variation (wt.%) relative to SiO2.

Symbols as in figure 8.

Figure 10: Binary diagrams displaying trace elements variation (wt.%) relative to SiO2. Symbols as in figure 8. Figure 11: A) Trace elements and REE diagram normalized to NMORB (Sun & McDonough, 1989) for basic and intermediate rocks; B) REE diagram normalized to chondrite (Nakamura, 1974) for basic and intermediate rocks; C) Trace elements and REE diagram normalized to ORG (Pearce et al., 1984) for acid rocks; D) REE diagram normalized to chondrite (Nakamura, 1974) for acid rocks. Symbols as in figure 8.

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Figure 12: Tectonic setting discriminant diagrams for basic and intermediate rocks: A) Zr vs. Zr/Y (Pearce & Norry, 1979); B) Zr vs. Ti (Pearce, 1980). Symbols as in figure 8.

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Figure 13: Tectonic setting and granitoid classification diagrams for Acampamento Velho Formation acid rocks: A) SiO2 vs. FeOt/FeOt+MgO (Frost et al., 2001); B)

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Al2O3 vs. FeOt/FeOt+MgO (Frost et al., 1991; Frost et al., 2001; Dall'Agnol & Oliveira, 2007); C) Y+Nb vs. Rb (Pearce et al., 1984); D) 10000*Ga/Al vs. Zr (Whalen et al., 1987). Symbols as in figure 8.

Table Captions

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Table 1: Instrument parameters used during the acquisition of U-Pb isotopic data. L-

TE

low mass to Faraday cup position, H-high mass to Faraday cup position, and IC - ion counting, continuous dynode system.

EP

Table 2: U-Pb zircon grains data from sample VM 136 (rhyolite) obtained by LA-ICPMS. The spot size has 30µm diameter for all zircons. The highly discordant results

AC C

are not shown.

Table 3: U-Pb zircon grains data from sample VM 9A (ignimbrite) obtained by LAICP-MS. The spot size has 30µm diameter for all zircons. The highly discordant results are not shown.

Table 4: U-Pb zircon grains data from sample VM 9C (trachyte) obtained by LA-ICPMS. The spot size has 30µm diameter for all zircons. The highly discordant results are not shown.

Table 5: Lithochemical results of representative samples of oriental Ramada Plateau for major elements (wt.%), trace and REE (ppm). * Loss on ignition.

202

Hg (Hg+Pb) 206 Pb 207 Pb 208 Pb 232 Th 238 U

M AN US

204

CR

Configurations Cup IC3 IC4 L4 IC6 L3 H2 H4 LA Energy Repetition rate Spot size Helium carrier gas ICP Ratio frequency power Cool gas flow rate Auxiliary gas flow rate Sample gas flow rate

IP T

ACCEPTED MANUSCRIPT

6 mJ 5 Hz 25-38 µm 0.35 + 0.5 L min-1

AC C

EP

TE

D

1100 W 15 L min-1 Ar 0.7 L min-1 Ar 0.6 L min-1 Ar

4.1

Isotopic ratios 207

Pb/

235

U

1σ

Age (Ma)

206

Pb/

238

U

1σ

Corr.

238

U/

206

Pb

207

1σ

Pb/

206

U

0.7175

0.0159

0.0886

0.0011

0.99

11.2886

0.1391

0.0587

1σ 0.0015

208

Pb/

206

U

0.1914

1σ

0.0105

M AN US

Zircon/spot

CR

IP T

ACCEPTED MANUSCRIPT

206

Pb/

238

U

Concordant 1σ

207

Pb/

206

U

1σ

(206Pb/238U) / (207Pb/206Pb)

547

0.007

557

0.054

98

0.716

0.0197

0.0894

0.0013

0.47

11.1878

0.1631

0.0581

0.0017

0.2419

0.0178

552

0.008

533

0.063

103

0.7271

0.0195

0.0894

0.0013

0.24

11.1858

0.1628

0.059

0.0017

0.0926

0.0041

552

0.008

567

0.066

97

23.1

0.7336

0.0192

0.0895

0.0011

1

11.1722

0.1386

0.0594

0.0015

0.1929

0.0143

553

0.007

583

0.053

94

11.1

0.7271

0.0179

0.0902

0.0012

0.86

11.0809

0.1491

0.0584

0.0016

0.1879

0.0053

557

0.007

546

0.057

101

8.1

0.7474

0.0171

0.0909

0.0012

0.99

11.006

0.142

0.0597

0.0015

0.1866

0.008

561

0.007

591

0.055

94

17.1

0.7478

0.0187

0.091

0.0011

0.99

10.9884

0.1373

0.0596

0.0013

0.2253

0.0178

561

0.007

589

0.048

95

24.1

0.7522

0.0197

0.091

0.0012

0.76

10.9944

0.1416

0.06

0.0014

0.2241

0.0038

561

0.007

603

0.05

93

14.1

0.7372

0.0212

0.0914

0.0012

0.18

10.935

0.1446

0.0585

0.0015

0.1883

0.0094

564

0.007

547

0.055

103

22.1

0.743

0.0196

0.0918

0.0012

0.57

10.8973

0.1412

0.0587

0.0014

0.1428

0.005

566

0.007

557

0.051

101

TE

D

5.1 12.1

0.7493

0.0206

0.092

0.0012

0.47

10.8642

0.757

0.0202

0.0921

0.0012

0.46

10.8539

0.145

0.059

0.0014

0.21

0.0038

568

0.007

569

0.052

99

0.1391

0.0596

0.0014

0.2069

0.0033

568

0.007

589

0.051

96

21.1

0.7585

0.0229

0.0923

0.0013

0.75

10.8318

0.1477

0.0596

0.0016

0.2052

0.0105

569

0.007

589

0.058

96

19.1

0.762

0.0206

0.0924

0.0012

0.47

10.8217

0.1408

18.1

0.7546

0.022

0.0927

0.0012

0.57

10.7905

0.144

0.0598

0.0014

0.1835

0.0027

570

0.007

597

0.051

95

0.0591

0.0016

0.1685

0.0185

571

0.007

569

0.057

100

AC C

EP

16.1 20.1

Zircon/spot

Isotopic ratios 207

235

206

238

206

18.1

Pb/ U 1σ 0.7236 0.0357

U/ Pb 1σ 11.2594 0.2348

17.1

0.7133

0.0332

0.0892

0.0017

0.18

11.2059

0.2189

25.1

0.7311

0.0216

0.0893

0.0013

0.62

11.2007

0.1625

6.1

0.7144

0.0514

0.0894

0.0019

0.39

11.1868

0.2394

207

206

Pb/ U 1σ 0.0591 0.0035

208

206

Pb/ U 1σ 0.1662 0.0087

Age (Ma) 206

Concordant

238

Pb/ U 1σ 549 0.011

207

206

Pb/ U 1σ 570 0.131

(206Pb/238U) / (207Pb/206Pb) 96

551

22.1

0.7376

0.0374

0.0894

0.0019

0.34

11.1893

0.2394

13.1

0.7252

0.0346

0.0896

0.0018

0.51

11.1576

0.2277

1.2

0.6964

0.0622

0.0901

0.0022

0.19

11.0956

0.2696

10.1

0.7306

0.0426

0.0901

0.0017

0.42

11.1045

0.2133

M AN US

Pb/ U 1σ Corr. 0.0888 0.0019 0.5

238

CR

IP T

ACCEPTED MANUSCRIPT

0.0588

0.0036

0.216

0.0102

556

0.01

561

0.141

99

2.1

0.7236

0.0312

0.0903

0.0015

0.67

11.0729

0.1787

0.0581

0.0026

0.2011

0.0084

557

0.009

534

0.096

104

23.1

0.7494

0.0221

0.0904

0.0013

0.34

11.0648

0.1601

0.0601

8.1

0.7268

0.0554

0.0907

0.002

0.65

11.0216

0.2445

24.1

0.7292

0.0254

0.0912

0.0014

0.19

10.969

0.1742

20.1

0.7503

0.0206

0.0912

0.0013

0.78

10.9629

0.151

3.1

0.767

0.0688

0.0918

0.0023

0.01

1.1

0.7465

0.0603

0.092

0.0021

0.11

9.1

0.7405

0.0254

0.0922

0.0013

0.45

11.1

0.7598

0.0418

0.0921

0.0017

4.1

0.7579

0.0223

0.0929

0.0013

15.1

0.7768

0.0409

0.0907

14.1

0.6882

0.0528

0.0904

0.0032

0.2241

0.0125

0.01

529

0.121

0.0594

0.002

0.2471

0.0117

551

0.008

581

0.072

94

0.058

0.0044

0.2273

0.0197

552

0.011

528

0.169

104

0.0599

0.0036

0.2082

0.0209

552

0.011

598

0.137

92

0.0587

0.0033

0.2374

0.0103

553

0.011

555

0.127

99

0.056

0.0053

0.2162

0.0273

556

0.013

454

0.202

122

D

0.058

0.002

0.2348

0.0065

558

0.008

609

0.074

91

0.0047

0.2052

0.0139

560

0.012

534

0.170

104

0.058

0.0023

0.2158

0.0094

562

0.009

530

0.088

106

0.0597

0.0019

0.1991

0.0049

563

0.007

591

0.067

95

TE

EP

104

0.0581

0.2723

0.0606

0.006

0.1716

0.0164

566

0.014

626

0.226

90

10.8643

0.2518

0.0588

0.0052

0.2091

0.0161

568

0.013

561

0.197

101

10.85

0.1585

0.0583

0.002

0.2345

0.0062

568

0.008

540

0.077

105

0.59

10.8612

0.2013

0.0598

0.0036

0.2292

0.0112

568

0.01

598

0.131

94

0.57

10.7676

0.1497

0.0592

0.0017

0.1686

0.0035

572

0.008

574

0.061

99

0.002

0.2

11.0269

0.2481

0.0621

0.0039

0.2441

0.0202

560

0.012

678

0.136

82

0.0026

0.04

11.0645

0.3151

0.0552

0.0051

0.2384

0.0167

558

0.015

421

0.207

132

AC C

10.8981

Isotopic ratios 207

Age (Ma)

235

206

238

2.1

Pb/ U 0.8198

1σ 0.144

3.1

0.7506

0.139

0.0905

0.004

4.1

0.9085

0.2702

0.0894

0.0072

0.4

6.1

0.8889

0.1934

0.0942

0.0053

0.43

Pb/ U 1σ Corr. 0.0891 0.0042 0.55 0.15

238

206

U/ Pb 1σ 11.226 0.5238

11.0508

207

206

Pb/ U 1σ 0.0667 0.0135

208

206

Pb/ U 0.495

1σ 0.054

M AN US

Zircon/spot

CR

IP T

ACCEPTED MANUSCRIPT

206

Concordant

238

Pb/ U 1σ 550 0.025

207

206

Pb/ U 1σ 830 0.434

0.484

0.0602

0.0127

0.4489

0.0503

558

0.023

609

11.1858

0.8974

0.0737

0.0251

0.6072

0.3474

552

0.043

10.6198

0.6018

0.0685

0.0193

0.4989

0.0915

580

0.032

(206Pb/238U) / (207Pb/206Pb) 66

0.386

91

1033

0.625

53

883

0.431

65

1.1029

0.13

0.0951

0.0038

0.36

10.5185

0.4159

0.0841

0.012

0.3092

0.0437

585

0.022

1296

0.312

45

1.2878

0.2022

0.0983

0.0053

0.65

10.1775

0.5523

0.0951

0.0188

0.4601

0.0544

604

0.031

1529

0.362

39

11.1

1.2381

0.2603

0.0922

0.0068

0.05

10.8493

0.8017

0.0974

0.022

0.5616

0.1198

568

0.04

1575

0.394

36

8.1

1.4014

0.289

0.1015

0.0074

0.26

9.8529

0.7223

0.1001

0.0258

0.4647

0.0804

623

0.044

1627

0.507

38

9.1

1.1993

0.2539

0.1037

0.0066

0.01

9.6443

0.6126

0.0839

0.0227

0.4693

0.1051

636

0.039

1290

0.449

49

AC C

EP

TE

D

5.1 10.1

ACCEPTED MANUSCRIPT Acampamento Velho Formation Basaltic lava flows

Subvolcanic trachytes

RI PT

Hilário Formation Andesitic lava flow and dike Sample

VM52A

VM103A

VM131

RM15A

RM27A

RM 317A

VM7A

VM9C

VM39A

VM41A

VM68A

VM70B

VM72A

SiO2

52.97

53.42

55.45

47.29

47.73

48.19

49.13

61.67

63.04

62.23

62.14

63.38

65.86

64.17

Al2O3

15.06

14.36

14.95

17.17

17.84

17.38

16.38

14.35

13.87

14.1

14.13

13.85

13.54

13.82

FeOt

9.49

9.07

8.71

13.86

11.18

12.16

11.62

7.88

7.62

7.35

7.26

7.32

6.36

7.02

MnO

0.14

0.12

0.11

0.24

0.28

0.265

0.24

0.16

0.18

0.18

0.16

0.16

0.13

0.17

MgO

3.63

5.27

3.27

4.02

4.5

4.16

4.33

1.33

1.12

0.9

1.2

1.1

1.06

0.89 1.72

5.4

6.02

4.23

8.68

8.5

8.5

10.67

2.91

2.81

3.81

2.68

4.09

3.86

4.13

4.35

3.67

3.94

4.01

K2O

2.46

5.03

2.89

0.76

0.98

0.97

0.59

4.11

Na2O + K2O (mNa2O+mK2O)/ mAl2O3 TiO2

6.27

7.71

6.98

4.62

5.11

5.32

4.26

8.05

0.59

0.69

0.66

0.42

0.44

0.47

0.41

0.76

1.78

0.92

1.75

1.73

1.81

1.97

1.76

1.14

P2O5

0.64

0.38

0.52

0.23

0.23

0.3

0.24

0.39

4.2

2.2

3.7

1.2

2.6

99.62

99.58

99.66

97.84

97.2

Ga

18.4

14.3

17.1

18

18

Rb

69.4

141.3

50.8

22

33

Sr

636.5

722

563.3

437

496

Y

37.7

18.9

41.4

24

22

Zr

330.2

149.8

378.6

140

130

Nb

19

8.4

17.3

6

7

Ba

1081

1421

983

241

178

59.9

45.8

61.1

12.5

12.3

117.5

90.3

127.8

29.3

29.1

Pr

13.4

10.41

14.21

-

53.7

42.3

52.5

16

9.47

7.83

10.01

5.02

Eu

2.62

1.98

2.36

Gd

8.81

6.59

9.13

1.89

4.02

4.03

3.82

4.52

4.32

4.43

4.7

4.8

4.58

8.53

8.24

8.4

8.72

8.83

8.4

0.83

0.79

0.8

0.84

0.87

0.81

0.94

0.91

0.97

0.9

0.77

0.79

0.33

0.32

0.34

0.31

0.26

0.23

2.46

1.1

1.7

1.1

2.7

1.9

1.5

0.9

2.4

99.75

99.56

99.56

99.58

99.58

99.59

99.63

99.64 19.8

19

16.9

17.9

20

20.1

19.9

18.5

19.9

33

14.9

48.8

51.4

48.4

52.4

58.1

63.6

56.4

450

498.1

190.2

115.6

91

141.6

111.8

112.6

68.9

32.5

29.6

46.6

52.3

48.6

49.8

51

54.6

53.2

176

184

887.2

1069

1128.8

976.4

973.3

882.3

1002.4

4.9

6.3

16.3

19.7

19.2

19.3

19

23.2

19

159

164

1789

1607

1406

1611

1507

1224

1143

12.4

13.4

128.8

147.4

147.4

142.1

142.4

137.4

145.3

31.2

31.9

263.2

278.5

283.5

271.2

268.9

269.3

279.1

4.31

28.3

31.38

31.58

30.08

29.91

29.61

30.36

-

4.09

16

17.9

17.5

108.2

124.5

120

113.4

115.7

111.8

117.1

4.62

4.7

4.74

15.48

17.68

17.47

16.42

17

17.33

16.64

1.9

1.6

1.76

1.73

4.07

4.33

4.26

4.21

3.94

3.28

3.46

-

-

5.82

5.32

12.31

13.85

13.81

12.96

13.2

13.75

14.12

0.9

0.58

1.02

0.92

1.81

1.89

1.85

1.8

1.8

1.92

1.97

-

-

5.68

5.12

9.35

9.75

9.47

9.54

9.77

11.01

10.73 2.04

TE

Nd Sm

2.32

3.97

100.7

D

La Ce

3.06

M AN U

LOI* Total

2.66

3.92

SC

CaO Na2O

VM112A

1.28

0.79

1.41

6.83

3.88

8.16

Ho

1.47

0.74

1.56

-

-

1.09

1.15

1.78

2.05

2

1.9

1.98

2.12

Er

4.02

1.89

4.28

-

-

3.22

3.04

4.93

6.06

5.76

5.28

5.47

5.94

5.75

Tm

0.56

0.26

0.64

-

-

0.46

0.49

0.78

0.88

0.82

0.82

0.85

0.9

0.85

Yb

3.69

1.56

5.77

Lu

0.54

0.23

La/Nb Hf Ta Th U

3.76

2.9

2.5

2.83

2.81

5.03

5.58

5.6

5.18

5.43

6.16

0.58

0.38

0.33

0.432

0.41

0.85

0.92

0.91

0.88

0.89

0.91

0.94

17.07

17.61

17.55

18.29

17.48

14.87

16.79

AC C

LaN/YbN

EP

Tb Dy

10.82

19.57

10.83

2.87

3.28

2.92

3.18

3.15

5.45

3.53

2.08

1.76

2.53

2.13

7.9

7.48

7.68

7.36

7.49

5.92

7.65

7.4

3.3

8.5

3.61

3.67

4

4.4

15.8

19.1

18.5

16.7

17.1

16.5

18.4

0.9

0.4

1.1

-

0.14

0.35

0.4

1.1

1

1

1

0.9

1.1

1

3.9

8.3

5.3

0.7

1

0.59

0.8

6.8

7.5

7.3

7

7

8.4

8.3

0.7

2.1

1

0.4

0.4

0.23

0.3

1.4

1.3

1.2

1.3

1.2

1.5

1.5

Continues below

ACCEPTED MANUSCRIPT Rhyolitic dikes

Rhyolitic lava flows

Ignimbrites

RI PT

Acampamento Velho Formation

Sample

VM5

VM63A

RM14A

RM25B

VM70A

VM79

VM90

VM95A

VM9A

VM53A

VM71A

VM84

VM 105

VM121B

SiO2

75.96

73.97

73.12

72.03

73.39

74.79

74.37

74.71

76.05

74.63

73.3

75.54

74.5

74.81

VM157 75.11

Al2O3

12.03

12.86

11.83

11.69

11.78

11.62

11.98

12.63

12.16

11.83

11.8

11.62

11.8

11.77

11.53 3.05

FeOt

2.95

2.91

3.38

3.23

3.63

2.87

3.55

3

2.08

3.22

3.54

2.8

3.2

3.49

MnO

0.02

0.11

0.08

0.09

0.07

0.06

0.07

0.02

0.02

0.05

0.08

0.04

0.1

0.06

0.07

MgO

0.03

0.34

0.25

0.21

0.12

0.04

0.06

0.05

0.06

0.22

0.11

0.06

0

0.1

0.05

0.02

0.27

0.46

0.9

0.8

0.5

0.5

0.05

0.04

0.39

0.87

0.55

0.5

0.45

0.26

3.26

3.49

3.88

3.87

3.73

3.66

3.95

4.55

3.56

3.55

3.63

3.17

3.9

3.36

3.67 4.77

4.67

4.15

5.32

5.21

4.92

4.77

4.59

4.13

7.93

7.64

9.2

9.08

8.65

8.43

8.54

8.68

4.76

5.05

4.94

5.09

4.7

4.67

8.32

8.6

8.57

8.26

8.58

8.03

0.87

0.8

1.03

1.03

0.97

0.96

0.96

0.95

8.44

0.91

0.96

0.96

0.92

0.97

0.9

0.97

0.22

0.25

0.27

0.25

0.25

0.2

0.22

0.13

P2O5

0.02

0.06

0.03

0.03

0.04

<0.01

0.02

0.03

0.21

0.23

0.25

0.2

0.2

0.19

0.18

0.02

0.05

0.04

<0.01

<0.01

0.02

LOI*

0.6

1.4

0.8

1.8

1.1

1.3

0.5

0.01

0.6

0.8

0.6

1.3

0.8

0.9

0.9

Total

99.84

99.86

98.62

97.51

99.82

99.85

99.83

1.2

99.88

99.8

99.82

99.82

99.85

99.8

99.84

99.87

M AN U

K2O Na2O + K2O (mNa2O+mK2O)/ mAl2O3 TiO2

SC

CaO Na2O

141.1

Ce

192.8

147

329

283

281

282.3

122.8

338.2

239.7

272.7

258.6

338

254.1

224.3

Pr

23.32

15.33

-

-

30.84

30.01

31.92

32.66

41.59

26.62

30.26

27.88

35.4

27.73

24.77

Nd

84.8

52.3

131

117

112.6

107.8

113.3

123.9

156.1

98.6

113.3

101.6

127.7

99.9

91.3

Sm

15.23

8.85

21

19

18.98

17.61

18.65

24.28

26.71

17.83

18.7

17.16

20.3

17.56

17.09

Eu

0.68

0.71

1

Gd

13.74

7.71

-

Ga

21.5

15.9

24

22

20.8

Rb

87.7

98.3

82

123

85.5

11.9

91

15

135

24.4

Y

66.1

39

55

42

66.4

Zr

592.2

236.5

914

352

Nb

29.2

17.8

35

Ba

179

646

127

La

97.5

79.6

173

145

145

1.19

2.44

6.69

-

Ho

2.57

1.42

-

Er

7.61

4.32

-

Tm

1.13

0.67

Yb

7.48

4.51

Lu

1.15

0.66

La/Nb Hf Ta Th U

21.2

20.7

20.1

20.4

21.4

21.9

93.1

85.3

88.5

81.5

83.5

90.7 5.5

6.5

15.8

8.7

9.9

38.1

18.1

11.7

9.7

9.3

62

87.1

91.6

68.5

63.7

57.6

61.5

60.4

61

705.3

578.7

646.4

350.2

643.2

584.9

692.2

558.9

652.1

532.8

516.5

25

30.2

25.2

27.4

41.2

28.8

31.1

28.4

25.9

26.4

25.4

26.6

137

99

32

56

37

89

127

100

67

42

55

23

139.9

147.7

149.1

211.2

120.7

131.2

166.1

127.5

108

302

0.93

0.83

0.56

0.66

0.33

1.09

0.66

0.8

0.55

0.6

0.57

0.53

-

15.92

14.57

15.21

20.7

24.51

15.29

15.94

15.16

15.8

15.32

14.79

2.4

2.34

2.23

2.36

2.99

3.57

2.36

2.32

2.24

2.3

2.32

2.29

-

12.55

12.19

12.74

16.24

17.52

12.93

12.91

11.99

12.7

12.5

12.59

-

2.6

2.38

2.56

3.4

3.22

2.67

2.62

2.3

2.4

2.48

2.54

-

7.38

6.5

6.92

9.22

8.69

7.38

7.53

6.5

7

7.04

7.31

-

-

1.11

0.99

1.02

1.39

1.31

1.17

1.09

0.96

1

1.09

1.08

5.9

7

7.24

6.72

6.82

8.25

8.18

7.25

7.06

6.54

6.9

7.11

6.91

1.05

1.08

1.15

1.05

1.06

1.23

1.2

1.16

1.2

1.05

1.1

1.07

1.05

13.81

13.35

13.88

14.44

12.05

17.21

11.1

13.32

13.37

16.12

11.95

10.42

AC C

LaN/YbN

22

93.4

TE

2.28 13.06

26.4

106.3

59.6

EP

Tb Dy

21.1

78.9

D

Sr

20.9

80.2

8.69

11.77

19.55

3.34

4.47

4.94

5.8

4.8

5.55

5.39

3.62

7.33

3.88

4.97

5.07

6.29

5.02

4.06

15.7

6.7

16.25

16.28

16.7

13.9

15.3

12.3

16.1

14.9

15.8

13.9

15.5

13.6

13.8

1.6

1.4

1.59

1.8

1.4

1.1

1.4

2

1.6

1.5

1.4

1.3

1.5

1.4

1.4

12.1

14.7

12.1

12.7

11.1

11.4

11.4

12.5

11.8

11.1

11.2

11.3

12.5

10.9

11.7

2.1

2.6

1.57

1.97

1.9

2

2.1

1.6

2.7

2.2

1.9

1.8

2

1.8

1.9

ACCEPTED MANUSCRIPT A

60°W

Santa Catarina

57°W

BRAZIL

RIO GRANDE DO SUL

30°S

A O tlan ce tic an

Porto Alegre

B

an

SC

on La go Mir im

0

100 Km

Passo do Marinheiro Shear Zone

São Sepé

Tupanci and Picados Hills

São Gabriel

30°S

M AN U

54°W

At la

Uruguay Phanerozoic Cover Camaquã Basin Pelotas Batholith Tijucas Terrane São Gabriel Terrane Taquarembó Terrane

nt ic

Pa

tos

O ce

La

go

on

RS

RI PT

Argentina 0°

Ramada Plateau

B

Caçapava Lineament

D

Vila Nova do Sul

30°30’S Ibaré Lineament

EP

4

TE

1

Taquarembó Plateau

Caçapava do Sul

Santa Bárbara Ridge

2

Zo ne

Santana da Boa Vista

3

uç

u

She ar

Dom Pedrito

AC C

Lavras do Sul

n Ca

Bagé

0

l rsa Do

g

de

50 Km Oriental Ramada Plateau

CAMAQUÃ BASIN (630-535 Ma) Guaritas Group Sedimentary rocks Guaritas Group Rodeio Velho Member Santa Bárbara Group Sedimentary rocks

TIJUCAS TERRANE (2.2 - 0.62 Ga) NEOPROTEROZOIC POST-COLLISIONAL MAGMATISM (650-550 Ma)

SÃO GABRIEL TERRANE (0.88 - 0.68 Ga)

A-type granitoids

Cambaí, Imbicuí and Cambaizinho Complexes

Santa Bárbara Group Acampamento Velho Formation

Shoshonitic affinity granitoids

Bossoroca (1) / Passo Feio (2) / Arroio Marmeleiro (3) / Palma(4) Complexes

Bom Jardim Group Hilário Formation and sedimentary rocks

Subalkaline granitoids

Maricá Group

TAQUAREMBÓ TERRANE (2.55 - 2.0 Ga) Santa Maria Chico Granulitic Complex

VM 136

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

VM 9C

CONVENTIONS Santa Bárbara Group

AC C

EP

TE

D

VM 9A

Serra dos Lanceiros Fm. ACAMPAMENTO VELHO FM.

CAMAQUÃ BASIN

Estância Santa Fé Fm.

Rhyolitic lava flows, domes and dikes ( Basaltic lava flows and dikes (

)

Ramada Intrusive Suite (Ramada Granite)

)

Ignimbrites. Locally rhyolitic lava flows

Subvolcanic trachytes

Bom Jardim Group Hilário Fm. (Basaltic to andesitic lava flows and dikes ( Volcanogenic sedimentary rocks

Maricá Group

BASEMENT Bossoroca Complex Lineaments Roads unpaved and tracks Rivers and streams Samples analyzed for U/Pb zircon geocronology

))

mE

mN

EP

Massive, auto-brecciated (Fig. 4k) and foliated (Fig. 4l) rhyolites

AC C Pyroclastic flows Effusive flows Pyroclstic flows

Acampamento Velho Formation

Samples analysed for U/Pb zircon geochronology

Facies abbreviation

Lithofacies description Effusive flows

Units

TE

D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

mRi2, bRi, fRi

Basalt

Bas2

Massive ignimbrite (Fig. 4j)

mLT

Welded ignimbrite with pumices flattened and aligned, defining a foliation subparallel to bedding

//bpLT

Ignimbrite rich in rhyolitic lithics (Fig. 4i)

lrioLT

Basalt (Fig. 4h)

Bas1

Volcanogenic sedimentary rocks (Fig. 4g)

VSd2

Rhyolite (Fig. 4f)

mRi1

Subvolcanic trachyte (Fig. 4e)

SvTq

Rheomorfic ignimbrite, poorly sorted, with constituents strongly flattening and elongated (Fig. 4d). Presence of rotational structures

rheoLT

Ignimbrite with eutaxitic texture (Fig. 4c)

eLT

VM 136

VM 9C VM 9A

10 m

Hilário Formation

Bom Jardim Group

Lithic-rich ignimbrite (Fig. 4b)

Andesite (Fig. 4a) Volcanogenic sedimentary rocks and intrusives

lLT 0m (estimated)

Ad VSd1; SvAd 2

64

256 mm

AC C

EP

TE

D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE

D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE

D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE

D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Tephrite Basaltic (ol < 10%) trachyBasanite andesite (ol > 10%) Trachybasalt Alkali basalt Basaltic Andesite Subalkali andesite Picrobasalt basalt

4.0

2.0

Alkaline

SC e tr it

as a lt

ite

Tholeiite

Al ka li b

Ba

Picritic rock

n sa

Tephrite

Subalkali rhyolite

Phono-tephrite

Basalt

Dacite

Hawaiite Latibasalt

Mugearite

Phonolite

Latite

Trachyphonolite

500

6.0

Nephelinite

ra ka

M AN U

Trachyandesite

An

2000

Trachydacite (if q > 20%)

Phonotephrite

8.0

Alkali rhyolite

1500

10.0

Trachyte

Andesite

Latiandesite

Quartz latite

Trachyte

Andesibasalt

Dacite Rhyodacite

Rhyolite

Quartz trachyte

Alkali rhyolit e

0

Subalkaline

35

40

45

50

55

60

65

70

-1000

75

C

Rhyolite/Dacite

Rhyodacite/Dacite

SiO2

Trachyte TrAn Phonolite

Sub-AB

40

Bas/Trach/Neph

AC C

AB

0.01

0.001

Mean (Rb-Th-U-Ta)NYTS*

70

50

4

TE

Com/Pant

Andesite

1000

D

80

60

0

2000

3000

R1 = 4Si - 11(Na + K) - 2(Fe + Ti)

SiO2

EP

0.1

Sommer et al., 2006: Shoshonitic rocks Sodic alkaline rocks

D

3 Shoshonitic Alkaline 2

1

0 0

1

1

2

3

4

5

Mean (Zr-Ce-Sm-Y-Yb)NYTS*

Zr/TiO2

7

1000.00

E

Andesite

Rhyolite

6

Trachyte

F

Dacite

100.00

A/NK

5

Metaluminous 10.00

4

Peralkaline rocks Alkaline basalt

Rb

(Na2O+K2O)

Tephriphonolite

1000

Foidite

R2 = 6Ca + 2Mg + Al

Phonolite

12.0

B

2500

A

14.0

Peraluminous 3

1.00 Subalkaline basalt

2 0.10 1 Peralkaline

0.01

0 0.8

0.6

1.0

1.2

1.6

1.4

1.8

0.1

2.0

1.0

10.0

100.0

1000.0

10000.0

Sr

A/CNK

G

19 Comenditic trachytes

17

Acampamento Velho Fm.

Comendites

15

Al2O3

0.0

3000

16.0

RI PT

ACCEPTED MANUSCRIPT

Pantalleritic trachytes

13 Pantellerites

11

A

9 7

Hilário Fm. Andesitic lava flow and dikes

B

5 0

Rhyolitic dikes Basaltic lava flows Subvolcanic trachytes Rhyolitic lava flows Ignimbrites

2

4

6

FeOt

8

10

RI PT

ACCEPTED MANUSCRIPT

SC

14

17

12

16

8

6

15

M AN U

Al2O3

FeOt

10

14

13

4

12

11

2 45

50

55

60

65

70

75

45

50

55

60

65

70

75

65

70

75

65

70

75

65

70

75

SiO2

D

SiO2

5

TE

0.25

4

3

MgO

0.15

EP

MnO

0.20

0.10

0.00 45

50

AC C

0.05

55

60

65

2

1

0 70

45

75

50

55

4.5

6

5

4

K2O

4.0

Na2O

60

SiO2

SiO2

3.5

3

2 3.0 1

2.5

0 45

50

55

60

65

70

75

45

50

55

SiO2

60

SiO2

10 0.6 8

0.5

0.4

CaO

P2O5

6

0.3

4 0.2 2 0.1

0.0

0 45

50

55

60

SiO2

65

70

75

45

50

55

60

SiO2

800

140

M AN US

700 120

CR

IP T

ACCEPTED MANUSCRIPT

600

100

500

80

Sr

Rb

400

60

300

40

200

20

100

0

0

50

55

60

SiO2 100

70

75

45

80 70

40

AC C

30

60

65

70

75

65

70

75

65

70

75

1000

800

600

Zr

Y

50

55

1200

EP

60

50

SiO2

TE

90

65

D

45

400

200

20

0

10

45

50

55

60

65

70

45

75

50

55

60

SiO2

SiO2

45

2000

40

1800 1600

35

1400

30

1200 25

Ba

Nb

1000 20 15

800 600

10

400

5

200

0

0 45

50

55

60

SiO2

65

70

75

45

50

55

60

SiO2

10

M AN US

CR

IP T

ACCEPTED MANUSCRIPT

4

A

10

3

B

Andesitic lava flow and dikes

10

3

10

10

10

2

1

10

0

-1

10

2

Subvolcanic trachytes 1

0

-1

10

-2

10

Dy Y

10

0

Yb Lu

C

EP

10

La Ce Pr Sr Nd Zr Sm Eu Ti

AC C

10

Nb K

TE

Cs Rb Ba Th U

10

1

Basaltic lava flows

D

10

2

La

10

10

10

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Rb

Ba

Th

Ta

Nb

Er

Tm

Yb

Lu

D

2

1

Rhyolitic dike 10

Ce

Ho

3

Rhyolitic lava flows and ignimbrites

K2 O

Dy

Hf

Zr

Sm

Y

0

Yb

Andesites of the Lavras do Sul Shoshonitic Association (Lima & Nardi, 1998; Lopes et al., 2014) Basalts of the Acampamento Velho Fm. (Almeida et al., 2002; Sommer et al., 2005)

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Subvolcanic dioritic rocks (Matté et al., 2012) Ramada Intrusive Suite (Ramada Granite) (Matté et al., in prep.) Rhyolites and ignimbrites of the Acampamento Velho Fm. (Sommer et al., 2005)

20

M AN US

CR

IP T

ACCEPTED MANUSCRIPT

B

A

10000

10

20000

Within−Plate Basalts

MORB

D

5000

Zr/Y

Ti

5

Within−Plate Basalts

20

50

100 Zr

200

500

2000 1000

TE

2 1 10

Island Arc Basalts

MORB

Island Arc Basalts

1000

10

20

50

100 Zr

200

Andesites of the Lavras do Sul Shoshonitic Association (Lima & Nardi, 1998; Lopes et al., 2014)

AC C

EP

Basalts of the Acampamento Velho Formation (Almeida et al., 2002; Sommer et al., 2005)

500

0.8

Ferroan

1.0

A

M AN US

1

CR

IP T

ACCEPTED MANUSCRIPT

B

Reduced A-type

FeOt/(FeOt+MgO) 0.8

Oxidized A-type

Calc-alkaline

60

65 SiO2

70

75

1000

10

80

12

14

16

18

20

Al2O3 5000

55

TE

50

D

0

0.6

0.2

FeOt/(FeOt+MgO) 0.4 0.6

Magnesian

C

D

1000

syn−COLG

Zr

EP

Rb

100

WPG

post−COLG

10

I&S

10

VAG

1

AC C 1

A

100

ORG

10

100

1000

1

3

10 10000*Ga/Al

Y+Nb Subvolcanic dioritic rocks (Matté et al., 2012) Ramada Intrusive Suite (Ramada Granite) (Matté et al., in prep.)

Rhyolites and ignimbrites of the Acampamento Velho Fm. (Sommer et al., 2005)

20

ACCEPTED MANUSCRIPT

AC C

EP

TE

D

M AN U

• •

RI PT

•

Ediacaran volcanic and subvolcanic rocks occur in southernmost Brazil. This volcanism is associated with the Hilário and Acampamento Velho Formations (Camaquã Basin). Basic to acid magmatism is related to shoshonitic and sodic alkaline series. They are associated to a post-collisional setting. U-Pb ages indicate a crystallization age of approximately 560 Ma

SC

• •