Geology, geochemistry, and PbÁ/Pb zircon geochronology of
Transcrição
Geology, geochemistry, and PbÁ/Pb zircon geochronology of
Precambrian Research 119 (2002) 189 /223 www.elsevier.com/locate/precamres Geology, geochemistry, and Pb Pb zircon geochronology of the Paleoproterozoic magmatism of Vila Riozinho, Tapajós Gold Province, Amazonian craton, Brazil / Claudio N. Lamarão a, Roberto Dall’Agnol a,, Jean-Michel Lafon b, Evandro F. Lima c a Group of Research on Granite Petrology, Centro de Geociências, Universidade Federal do Pará, Caixa Postal 1611, 66075-900 Belem, PA, Brazil b Isotope Geology Laboratory, Centro de Geociências, Universidade Federal do Pará, Caixa Postal 1611, 66075-900 Belem, PA, Brazil c Centro de Estudos em Petrologia e Geoquı́mica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Caixa Postal 15001, 91501-900, Porto Alegre, RS, Brazil Received 20 April 2001; received in revised form 15 October 2001; accepted 27 March 2002 Abstract Pb /Pb zircon geochronologic data define two different periods of intense igneous activity in the Vila Riozinho region, Tapajós Gold Province (TGP), south-central Amazonian craton. At /2.00 /1.97 Ga, the Vila Riozinho volcanic sequence (20009/4 Ma, 19989/3 Ma) and the older São Jorge granite (19819/2 Ma, 19839/8 Ma) were formed. At /1.89 /1.87 Ga, the younger São Jorge (18919/3 Ma), Jardim do Ouro (18809/3 Ma), and Maloquinha (18809/9 Ma) granites and the Moraes Almeida volcanic sequence (18909/6 Ma, 18819/4 Ma, 18759/4 Ma) were emplaced. Similar age intervals are registered throughout the TGP that is thus a little younger than the Paleoproterozoic terranes of the Maroni-Itacaiúnas Province in the Guiana Shield. Geochemical and geochronologic data demonstrate that the São Jorge pluton is composed of two different granitoids, the older and younger São Jorge granites. These, as well as the Jardim do Ouro granite, are I-type and magnetite series. The São Jorge granites are high-K calc-alkaline and show significant geochemical variation, the Jardim do Ouro granite is more iron-rich and less oxidized. The Vila Riozinho Formation is calc-alkaline to shoshonitic and geochemically similar to the São Jorge granites. The Maloquinha granite and the Moraes Almeida Formation differ from the other studied rocks in petrographic and geochemical characteristics, have aluminous A-type affinities, and were probably derived by low-temperature crustal melting. The volcanic sequences of the studied area, formerly included into the Iriri Group of the Uatumã Supergroup, are divided into the Vila Riozinho and Moraes Almeida sequences. The presence of these two sequences in the same tectonic domain demonstrates the heterogeneity of the Uatumã Supergroup. The TGP registers accretionary processes related to the formation of the Atlantica supercontinent at /2.00 Ga. This was followed (at /1.88 Ga) by an intracontinental taphrogenic event that lasted throughout the Mesoproterozoic. The tectonic setting of the TGP was thus transitional between a subduction-related magmatic arc and a stable continental block undergoing extension. Corresponding author. Tel.: /55-91-211-1477; fax: /55-91-211-1609 E-mail address: [email protected] (R. Dall’Agnol). 0301-9268/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 1 - 9 2 6 8 ( 0 2 ) 0 0 1 2 3 - 7 190 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 # 2002 Elsevier Science B.V. All rights reserved. Keywords: Paleoproterozoic; High-K calc-alkaline; Shoshonitic; A-type; Granitoids; Amazonian craton 1. Introduction The Tapajós Gold Province (TGP; Faraco et al., 1997) in the Central Brazil Shield, southern Amazonian craton was included in the Central Amazonian Province in early tectonic models (Teixeira et al., 1989). Recently, Tassinari and Macambira (1999) and Santos et al. (2000) identified a Paleoproterozoic magmatic arc in the southwestern part of the TGP and coined it VentuariTapajós (or Tapajós-Parima) Province, assuming that it extends to the northwestern parts of the Guiana Shield (cf. Fig. 1). According to these models, the northeastern part of the TGP belongs to the Central Amazonian Province. However, the exact location of the border between the VentuariTapajós or (Tapajós-Parima) and Central Amazonian provinces is poorly defined. In the last 45 years, /600 tonnes of gold have been produced from the TGP. The deposits are related to widespread plutonic and volcanic rocks the relationships and geochemical signatures of which are not clearly understood. Intermediate to felsic volcanic sequences exposed in the TGP have been included into the Uatumã Supergroup, a major volcanic unit that covers large domains of the Central Amazonian Province and also extends to the neighboring provinces. Increasing evidence suggests that this is an oversimplified picture, however (Dall’Agnol et al., 1999a; Reis et al., 2000; Santos et al., 2000). The aim of this paper is to present new geologic, geochemical and geochronologic data on the volcanic sequences and granitoid plutons of the Vila Riozinho region in the TGP. This area, situated on the border of the Ventuari-Tapajós and Central Amazonian tectonic provinces, is a key area to test the proposed tectonic models. It also displays diversified examples of the igneous rocks exposed in the Tapajós province, including large domains of the Uatumã volcanic sequences. Finally, this is a suitable area to examine the evolution of magmatic series in a Paleoproterozoic orogenic to post-orogenic domain and their overall significance for gold mineralization. 2. Geology of the TGP Geologic knowledge of the TGP has improved substantially in recent years. The Brazilian Geological Survey (CPRM) accomplished geologic mapping on a 1:250 000 scale of a large part of the province and presented a reinterpretation of its stratigraphy, tectonic setting, and metallogenesis (Klein and Vasquez, 2000; Coutinho et al., 2000; Ferreira et al., 2000). Private companies have developed gold prospecting projects in the province (Jacobi, 1999), and new more precise geochronologic data have also been obtained (Lamarão et al., 1999; Klein and Vasquez, 2000; Santos et al., 2000; Vasquez et al., 2000, Table 1). The southwestern and western parts of the TGP are included in the Paleoproterozoic VentuariTapajós Province that has been interpreted as a magmatic arc related to subduction (Tassinari and Macambira, 1999; Santos et al., 2000). The eastern and northeastern parts of the TGP are situated in the Archean Central Amazonian Province (Fig. 1a). However, tectonic structures that could delineate the contact of these two provinces have not been identified and geologic structures are broadly similar accross the border of the provinces. The TGP is primarily composed of late Paleoproterozoic plutonic and volcanic rocks. Klein and Vasquez (2000) distinguished an orogenic domain Fig. 1. (a) Sketch map of the Amazonian craton (modified from Tassinari and Macambira, 1999) and (b) geological map of the TGP (simplified from Klein et al., 2001). Inset in (a) shows the two exposed parts of the Amazonian craton */Guiana Shield in the north and Central Brazil Shield in the south. Black dots in (b) refer to villages: J, Jacareacanga; JO, Jardim do Ouro; MA, Moraes Almeida; VR, Vila Riozinho. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 1 191 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 192 Table 1 Geochronologic data of the Paleoproterozoic granitoids and volcanic sequences of the TGP and other regions of the Amazonian craton Geologic unit Rock type Age Method Reference Tapajós region Cuiú /Cuiú complex Jacareacanga suite Tonalite Metaturbidite 20119/23 Ma /2.1 Ga U /Pb U /Pb DtZr Santos et al. (2000) Santos et al. (2000) Creporizão Creporizão Creporizão Creporizão Granite Granite Granite Granite 19579/6 Ma 19689/16 Ma 19979/3 Ma 19849/1 Ma U /Pb Pb /Pb Zr Pb /Pb Zr Pb /Pb Zr Santos et al. (2000) Klein and Vasquez (2000) Klein and Vasquez (2000) Klein and Vasquez (2000) Parauari suite Cumaru Parauari suite Rosa de Maio Tropas Tropas Penedo Granite Monzogranite Granite Monzogranite Granodiorite Granodiorite Granite 18939/2 Ma 18839/8 Ma 18839/2 Ma 18799/11 Ma 18989/2 Ma 2010 Ma 18839/4 Ma Pb /Pb Zr Pb /Pb Zr Pb /Pb Zr U /Pb U /Pb U /Pb IZr U /Pb Klein and Vasquez (2000) Santos et al. (2000)a Klein and Vasquez (2000) Santos et al. (2000) Santos et al. (2000) Santos et al. (2000) Santos et al. (2000)a Maloquinha Maloquinha Caroçal Caroçal Santa Rita Maloquinha Maloquinha Syenogranite Granite Granite Granite Monzogranite Granite Granite 18829/4 Ma 18729/4 Ma /1.87 Ga 26569/6 Ma 24599/11 Ma 18709/4 Ma 26809/18 Ma Pb /Pb Zr U /Pb Shrimp Zr Pb /Pb IZr U /Pb IZr Shrimp Zr Shrimp IZr Klein and Vasquez (2000) Santos et al. (2000) Ferreira et al. (2000)a Ferreira et al. (2000)a Santos et al. (2000) Santos et al. (2000)a Santos et al. (2000)a Iriri Volcanic Group Iriri Volcanic Group Iriri Volcanic Group Rhyolite Rhyodacite Rhyolite 18889/2 Ma 18889/2 Ma 18889/6 Ma Pb /Pb Zr Pb /Pb Zr Pb /Pb Zr Dall’Agnol et al. (1999b) Klein and Vasquez (2000) Moura et al. (1999) Cachoeira Seca suite Crepori suite Ingarana suite Troctolite Diabase Gabbro 10469/50 /10729/18 Ma 16119/42 Ma 18879/3 Ma K/Ar K/Ar Pb /Pb Zr Klein and Vasquez (2000)a Klein and Vasquez (2000)a Klein and Vasquez (2000) Roraima region Pedra Pintada granite suite Água Branca granite suite Água Branca granite suite Surumu Group Surumu Group (calc-alkaline granitoids and volcanic sequences) Monzogranite 19589/11 Ma Shrimp Zr Monzogranite 19609/21 Ma Pb /Pb Zr Monzogranite 19389/37 Ma Pb /Pb Zr Shrimp Zr Andesite 19779/8 Ma Andesite 19849/7 Ma Shrimp Zr Reis et al. (2000)a Almeida et al. (1997) Almeida et al. (1997) Reis et al. (2000)a Reis et al. (2000)a Pitinga region Madeira granite Madeira granite Madeira granite Iricoumé Group Iricoumé Group (A-type granites and volcanic sequences) Granite 18349/6 Ma hb-bt granite 18249/2 Ma bt syenogranite 18229/2 Ma Rhyodacite 19629/42 Ma Rhyolite 18889/3 Ma U /Pb Zr Pb /Pb Zr Pb /Pb Zr U /Pb Zr Pb /Pb Zr Costi Costi Costi Costi Costi Carajás region Serra dos Carajás granite Cigano granite Pojuca granite Musa granite Velho Guilherme granite Redenção granite (A-type granites and volcanic sequences) Granite 18809/2 Ma Granite 18839/2 Ma Granite 18749/2 Ma Granite 18839/5 Ma Granite 18749/34 Ma Granite 18709/68 Ma U /Pb Zr U /Pb Zr U /Pb Zr U /Pb Zr Pb /Pb wr Pb /Pb wr Machado et al. (1991) Machado et al. (1991) Machado et al. (1991) Machado et al. (1991) Teixeira et al. (1998)a Barbosa et al. (1995) suite suite suite suite suite suite suite suite et et et et et al. al. al. al. al. (2000)a (2000) (2000) (2000)a (2000) C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 193 Table 1 (Continued ) Geologic unit Rock type Age Method Reference Antonio Vicente granite Jamon granite Uatumã Supergroup Granite Granite Andesite, rhyolite 18679/4 Ma 18859/32 Ma 18759/79 Ma Pb /Pb Zr Pb /Pb Zr Pb /Pb wr Teixeira et al. (1998) Dall’Agnol et al. (1999c) Teixeira et al. (1998) Mato grosso region Matupá Moriru (calc-alkaline granite and volcanic sequence) Granite 18729/12 Ma Ignimbrite 17789/5 Ma Pb /Pb Zr U /Pb Zr Moura (1998) Pinho et al. (2001) Zr, zircon; IZr, inherited zircon; wr, whole-rock; DtZr, detrital zircon; hb, hornblende; bt, biotite. a Original age reference can be found in this paper. in the southwest, containing the oldest sequences and affected by compressive or transpressive tectonics, and a post-tectonic (mainly extensional) domain in the northeast where younger sequences are dominant (Fig. 1b). The major tectonic lineaments follow a general NW-SE trend and most of the granitic plutons are elongated in this direction (Fig. 1b). A geological map of the TGP and the stratigraphic sequence adopted by the CPRM (Klein et al., 2001) are presented in Fig. 1b. The oldest granitoids and gneisses in this region belong to the Cuiú/Cuiú complex; the Conceição tonalite yielded a U /Pb zircon age of 20119/23 Ma (Santos et al., 2000, Table 1). The supracrustal sequences of the Jacareacanga Group are considered broadly coeval with the Cuiú /Cuiú complex and both units are related to early stages of magmatic arc development (Ferreira et al., 2000; Klein and Vasquez, 2000; Klein et al., 2001). Detrital zircon ages of /2100 and /2875 Ma have been obtained for the Jacareacanga Group (Santos et al., 2000, Table 1). In stratigraphy, these units are followed by the 1960/2000 Ma syn- to late-orogenic calc-alkaline granitoids of the Creporizão suite (Table 1, Lamarão et al., 1999; Klein and Vasquez, 2000; Vasquez et al., 2000). The /1880 Ma Parauari suite corresponds to a younger generation of post-orogenic, calc-alkaline granitoids and is mainly exposed in the northeastern part of the region (Fig. 1b). Many /1880 Ma aluminous, A-type granite plutons (e.g. Caroçal and Maloquinha suite granites) are also found in the province (Table 1). Intermediate to felsic volcanic sequences are widespread and have been included in the /1880 Ma Iriri Group of the Uatumã Supergroup (Faraco et al., 1997; Klein and Vasquez, 2000, and references therein) or, more locally, in the Bom Jardim Formation (andesitic flows and related dikes; Klein et al., 2001, Fig. 1b). The Iriri volcanic rocks show, however, geochemical and petrologic differences and at least two different ages (Dall’Agnol et al., 1999b; Lamarão et al., 1999; Moura et al., 1999; Vasquez et al., 2000) that are discussed in Section 6. 1880 Ma or younger intermediate and mafic intrusions have been recognized in the TGP (Table 1, Fig. 1b); lamprophyric rocks have also been identified (Klein and Vasquez, 2000). Whole-rock K/Ar dating indicates a minimum age of 15369/31 Ma for these rocks. Proterozoic and Phanerozoic sedimentary rocks complete the stratigraphy of the province. In the TGP, mineralization has been related to two different periods: (1) at /1.96 Ga hosted by the Cuiú/Cuiú complex, the Jacareacanga Group and the Creporizão suite; and (2) at /1.88 Ga hosted by the Parauari suite (sometimes also by the Maloquinha suite, Iriri volcanic rocks, and Ingarana mafic rocks) (Coutinho et al., 2000; Klein et al., 2001). Coutinho et al. (2000) and Klein et al. (2001) argued that most of the Tapajós 194 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 2. Geological map of the Vila Riozinho region showing the distribution of the studied granitic rocks and volcanic sequences. A, amphibole; B, biotite; MZG, monzogranite; LMZG, leucomonzogranite; SG, syenogranite; QM, quartz monzonite; MD, monzodiorite; QMD, quartz monzodiorite. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 195 Fig. 3. Q/A/P and Q/(A/P)/M diagram (Streckeisen, 1976) showing the modal compositions of the (a) older São Jorge granite, younger São Jorge granite, and Jardim do Ouro granite and (b) Maloquinha granite. Lines 1, 2, and 3 denote, respectively, the tonalitic-trondhjemitic calc-alkaline, granodioritic calc-alkaline, and shoshonitic series trends (cf. Lameyre and Bowden, 1982). 196 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 gold deposits can be classified as mesozonal to epizonal orogenic (Groves et al., 1998) lode-gold deposits hosted by granitoids. Other authors emphasized presence of epithermal gold deposits hosted by gabbros and volcanic rocks (Dreher et al., 1998; Jacobi, 1999; Juliani et al., 2000; Nunes et al., 2000). except in the drill cores of the gold mineralized area where it is locally brecciated or foliated indicating a brittle /ductile deformation. The São Jorge granites include frequent, 5/10 cm long, oval-shaped mafic enclaves. They also display local rapakivi texture characterized by sparse crystals of K-feldspar mantled by plagioclase. 3.3. Moraes Almeida volcanic sequence 3. Geology of the Vila Riozinho region The Vila Riozinho region in the easternmost part of the TGP (Fig. 2) is covered by dense rain forest and thus field relationships between different units are hard to decipher. There are gold deposits associated with the São Jorge and Jardim do Ouro granites. In the study area, the following geologic units have been identified (Fig. 2): 3.1. Vila Riozinho volcanic sequence This sequence is well exposed along the Jamanxim and Riozinho das Arraias rivers and is a low relief region. It is composed of intermediate to felsic flows, formerly included in the Iriri Group of the Uatumã Supergroup. However, geochemical and geochronologic data presented below demonstrate that this sequence is not coeval nor cogenetic with the felsic volcanic sequence exposed in the Moraes Almeida area. Around Moraes Almeida, this sequence is formed dominantly of reddish brown, strongly welded and oxidized ignimbrites, rich in crystals fragments and mm- to cm-sized lithic fragments. To the northwest of Moraes Almeida, rhyolitic flows are exposed and to the north there is a local occurrence of trachytic rocks. Contact relationships between rhyolites and ignimbrites are not visible in the field, but geomorphologic, petrographic, geochemical, and geochronologic data (see below) suggest that they are related to the same volcanic event. The granites exposed around this volcanic sequence are leucogranites of the Maloquinha suite. The circular shape of the volcanic domain and the occurrence of a large volume of pyroclastic rocks indicate that the volcanic sequence is probably related to a caldera (Cas and Wright, 1987; Lowell, 1991). The southern contact between the volcanic sequence and the Maloquinha granite is marked by a /50-m thick granite porphyry dike. 3.2. São Jorge granite pluton 3.4. Maloquinha granitic suite South of Vila Riozinho, around the São Jorge gold deposit, a granitoid pluton dominantly composed of amphibole /biotite monzogranite (Fig. 3) is exposed. In the past, this pluton was interpreted to comprise one granitoid series. However, petrographic, geochemical, and geochronologic data discussed below indicate that the pluton is heterogeneous and composed of an older granitoid series that makes up most of the pluton (older São Jorge granite; Fig. 2) and a younger granite (younger São Jorge granite; Fig. 2). Granite porphyries have also been identified. The older São Jorge granite and associated granite porphyries are massive, displaying only local, non-penetrative foliation. The same is true for the younger São Jorge granite, A pluton of this suite around the volcanic sequence of Moraes Almeida was studied (Fig. 2). This pluton is irregularly shaped and well exposed along the roads and consists of isotropic leucogranite that crops out in relatively high relief areas. 3.5. Jardim do Ouro pluton This pluton is situated around the Jardim do Ouro village and is crossed by the Jamanxim River. Only a small part of the pluton in the northwestern section of the mapped area was studied. It is composed of an isotropic or weakly Table 2 Petrographic and mineralogic characteristics of the granitoids from the Vila Riozinho region Accessory minerals Secondary minerals Mean magnetic susceptibilitya Oxygen fugacitya Amphiboleb /20% Zircon Epidote 20.9890 /10 3 Slv Near Mg-hastingsite 0.80 / 0.75 Tschermakite 0.79 / 0.71 Mg-hornblende 0.79 / 0.74 8.2262 /10 3 Slv 5.1634 /10 3 Slv NNO and Mg-hornblende 0.81 / 0.64 Rare Titanite Amph-bt quartz monzonite/monzogranite bt leucomonzogranite/ syenogranite Granite porphyry Mg/ Biotiteb Mg/ (Mg/Fe) (Mg/ in amphb Fe) in btb Mg-bio- 0.59 / tite 0.53 Plagioclaseb Andesine 7 /12% Apatite Carbonate B/5% Magnetite Chlorite /10% Ilmenite Sericite Buffers Mg-hornblende 0.68 / 0.59 Fe-biotite Zircon, titanite, apatite Chlorite, car- 7.9652 /10 3 bonate, seri- Slv cite 2.6596 /10 3 Slv Near NNO and HITMQ buffers Mg-hornblende 0.81 / actinolite 0.71 Mg-bio- 0.62 / tite 0.57 (Andesine) oligoclase Lower than in Fe-hornblende the São Jorge granites Fe-biotite (Andesine) oligoclase Younger São Jorge granite Amph-bt monzogranite 8 /12% bt leucomonzogranite B/2% Magnetite, ilmenite Jardim do Ouro granite 7 /8% Zircon, titanite, apatite, magnetite Chlorite, seri- 4.7988 /10 3 cite, epidote Slv Maloquinha granite 1 /4% Magnetite, fluorite Chlorite Granite porphyry /10% Zircon, titanite, apatite, magnetite Chlorite, sericite, epidote 2.1534 /10 3 Slv HITMQ 0.63 / 0.60 0.45 (Andesine) oligoclase Oligoclase albite Oligoclase Rare Near NNO buffer 0.40 / 0.33 Absent Lower than in Fe-hornblende the São Jorge granites 0.32 / 0.29 Fe-biotite 0.43 / 0.40 Oligoclase, albite andesine oligoclase 197 bt, biotite; amph, amphibole. a Data from Figueiredo (1999). b Based on data obtained by electron microprobe at the Geosciences Institute of the Federal University of the Rio Grande do Sul */UFRGS. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Older São Jorge granite bt-amph monzodiorite/ quartz monzodiorite Mafic minerals 198 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 4. Classification diagrams (Leake, 1997) for amphiboles of the granitoids and volcanic sequences of Vila Riozinho, TGP. Abbreviations as in Fig. 2. foliated amphibole /biotite monzogranite that is coeval with the younger São Jorge granite and Maloquinha granite suite. 3.6. Granite porphyries and dikes Several granite porphyries have been identified in the mapped area. Those found in the São Jorge pluton are similar in mineralogy to the older São Jorge granite. Other granite porphyries cut the rhyolites and Maloquinha granite. The gold deposits may be related to these porphyry systems (Jacobi, 1999). Dacitic and andesitic dikes cut the Jardim do Ouro pluton, the older São Jorge granite and the rhyolites of the Vila Riozinho sequence. This suggests recurrence of volcanic episodes during the evolution of the province. 4. Petrography and mineral chemistry 4.1. Granitoid plutons Petrographic and mineralogical characteristics of the studied granitoids are summarized in Table 2. The older São Jorge is composed of biotite / amphibole monzodiorite and quartz monzodiorite to amphibole/biotite monzogranite and leucomonzo- or syenogranite (Fig. 3a). The latter two are light gray or pink gray and dominant in the pluton. Monzodiorite, quartz monzodiorite, and amphibole/biotite monzogranite display mediumor coarse-, even-grained granular hypidiomorphic textures. Leucomonzogranite and syenogranite are medium- to fine-grained. The younger São Jorge and Jardim do Ouro granites are more homogeneous and composed dominantly of amphibole/biotite monzogranite (Fig. 3a). In the mineralized area, the primary minerals of the younger São Jorge granite are, generally, intensively altered. Quartz-rich leucomonzogranite and microgranite are subordinate phases. Granite porphyries are monzogranitic and have quartz, plagioclase, alkali feldspar, amphibole, and biotite phenocrysts in a felsitic, finegrained groundmass. The Maloquinha suite is composed of reddish, medium- and even-grained leucosyenogranite with subordinate leucomonzogranite (Fig. 3b). Except for occasional amphibole pseudomorphs in quartz C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 199 boles and biotite of the São Jorge granites and associated granite porphyry 59 (Figs. 4 and 5, Table 2) are similar to the amphiboles and biotite of calc-alkaline or ‘subalkaline’ series granitoids */ they were formed in relatively oxidizing conditions. The Jardim do Ouro granite and granite porphyry 18a were formed in less oxidizing conditions and do not have a typical ‘calc-alkaline’ character. Plagioclases of the amphibole /biotite monzogranite facies of the São Jorge and Jardim do Ouro granites are quite similar (Table 2), displaying a conspicuous normal, oscillatory zoning. In the hydrothermally altered parts of the younger São Jorge granite, plagioclase is altered. Plagioclase of the Maloquinha granite is sodic oligoclase to albite approaching in composition that of the leucomonzogranites of the São Jorge pluton. 4.2. Volcanic sequences Fig. 5. (a) Total Al versus Mg (Nachit et al., 1985) and (b) MgO versus Al2O3 (Abdel-Rahman, 1994) diagram of biotite from the studied granitoids. BLMZG, biotite leucomonzogranite of the older São Jorge granite, other symbols as in Fig. 4. monzonite and quartz syenite, the leucogranites have chloritized biotite as the main mafic phase. Magnetite and fluorite are common accessory minerals. The São Jorge, Jardim do Ouro, and Maloquinha granites show relatively high magnetic susceptibility (Table 2), and are classified as magnetite series granites (Figueiredo, 1999; Ishihara, 1981). The Jardim do Ouro granite crystallized at a somewhat lower oxygen fugacity than the other granites (Figueiredo, 1999). The amphi- In the TAS diagram (Fig. 6), the Vila Riozinho sequence samples plot mostly in the fields of basaltic andesite, basaltic trachyandesite, trachyte, and rhyolite along the boundary between alkaline and subalkaline fields. The rhyolites and ignimbrites of Moraes Almeida are enriched in silica compared to the rhyolites of Vila Riozinho sequence. The fields of the São Jorge and Maloquinha granites correspond to those of the Vila Riozinho and Moraes Almeida volcanic rocks, respectively. Basaltic andesite and basaltic trachyandesite have phenocrysts of zoned plagioclase and clinopyroxene, late amphibole and biotite, and grains of opaque minerals and zircon in a microgranular or pilotaxitic groundmass. The mafic phases are often completely replaced by chlorite, epidote, actinolite, secondary titanite, and opaque minerals. Trachyte is flow-foliated and has phenocrysts of saussuritized plagioclase and subordinate alkali feldspar, biotite, and pseudomorphosed amphibole, in a quartz-poor, felsitic groundmass. Rhyolites have phenocrysts of sericitized plagioclase, alkali feldspar, and subordinate quartz in a felsitic, sometimes granophyric groundmass. Biotite and pseudomorphosed amphibole are the main mafic phases. 200 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 6. TAS diagram (Le Maitre et al., 1989) for the Vila Riozinho and Moraes Almeida volcanic sequences showing the fields of the studied granitoids for comparison. Dashed line separates alkaline and subalkaline fields (Irvine and Baragar, 1971). The ignimbrites surrounding the Moraes Almeida village (Fig. 2) are reddish brown, densely welded crystal-rich lapilli tuffs. Quartz, alkali feldspar, and subordinate plagioclase crystal fragments, as well as cm-sized lithic fragments, lie in a fine-grained felsic matrix with abundant welded, stretched, and recrystallized shards. The rock is strongly oxidized and scarce biotite and amphibole crystals are entirely pseudomorphosed by iron oxides. To the west of Moraes Almeida (Fig. 2), the dominant rock is a porphyritic, locally ignimbritic light brown rhyolite that has phenocrysts of quartz, alkali feldspar, and rare plagioclase in a felsitic groundmass. A gray porphyritic trachyte is found north of Moraes Almeida and has phenocrysts of plagioclase, quartz, augite, Fe /hornblende, and rare alkali feldspar in a fine-grained felsitic, sometimes granophyric, matrix. 5. Geochemistry 5.1. Analytical procedures Chemical analyzes were done at the LakefieldGeosol laboratories in Belo Horizonte, Brazil. SiO2, TiO2, Al2O3, total Fe2O3, MnO, MgO, CaO, K2O, Na2O, P2O5, Rb, Sr, Ba, Zr, Y, Nb, Ga, and V were analyzed by X-ray fluorescence combined with atomic absorption spectrometry. Rare earth elements (REE) were analyzed by inductively coupled plasma atomic emission spectrometry. FeO was analyzed by wet chemistry at the Geosciences Center of the Federal University of Pará. Additional information about analytic methods can be obtained from the authors by request. Table 3 Chemical composition of the granitoids and volcanic rocks of the Vila Riozinho region Older São Jorge granite Facies BAQMD to GP ABQM to ABQS ABMZG 103 27a BLMZ/SG-south BLMZ/SG-center 68a 85 Younger São Jorge granite Maloquinha granite ABMZG BLMZG ABQS BLMZ/SG 70 54a 22a GP JOG ABMZG BAMD Sample SiO2 (wt.%) TiO2 58 102 54.5 0.81 32 28 73a 74 35a 59 9/10 7/3 21 06a 18a 03a 58.40 64.50 66.80 67.80 68.90 71.60 72.50 73.20 74.20 75.10 68.60 67.50 68.20 73.90 70.30 74.80 76.10 76.60 67.40 0.79 0.43 0.50 0.39 0.37 0.26 0.27 0.24 0.19 0.19 0.41 0.40 0.39 0.08 0.26 0.21 0.07 0.11 0.48 71.10 0.28 18.4 15.90 17.80 16.00 16.20 15.30 14.70 14.70 14.30 14.10 13.50 15.20 15.80 16.10 14.00 14.80 13.50 13.00 12.50 15.80 14.60 Fe2O3 4.7 3.00 1.87 1.80 1.86 1.71 1.37 1.23 1.03 0.94 1.00 1.59 2.70 2.50 0.49 0.84 1.14 0.77 1.18 1.54 1.29 FeO 2.34 3.42 1.20 0.90 0.94 0.98 0.39 0.42 0.33 0.14 0.12 1.18 0.99 1.20 0.20 1.40 0.32 0.21 0.20 1.40 1.00 MnO 0.10 0.11 0.07 0.07 0.06 0.07 0.05 0.06 0.05 0.05 0.04 0.05 0.04 0.04 0.03 0.08 0.04 0.05 0.02 0.06 MgO 3.10 4.30 0.88 0.62 0.81 0.83 0.46 0.33 0.28 0.09 0.11 1.10 1.20 1.30 0.12 0.21 0.14 0.09 0.09 0.33 0.57 CaO 6.90 5.20 2.80 1.80 2.30 2.00 1.40 0.99 0.91 0.54 0.65 2.30 2.40 2.40 0.61 1.10 0.40 0.50 0.33 1.60 1.70 0.03 Na2O 4.00 3.40 4.70 4.50 4.40 4.00 4.00 4.30 4.40 4.10 4.10 4.20 4.40 4.20 4.60 4.40 4.20 4.40 3.60 4.40 3.90 K 2O 2.50 3.30 4.40 5.20 4.20 4.30 4.90 4.80 5.10 5.00 5.00 4.50 4.00 4.50 4.60 5.60 5.30 4.60 4.90 5.10 4.90 P2O5 0.37 0.27 0.18 0.12 0.14 0.11 0.08 0.06 0.05 0.02 0.02 0.14 0.14 0.13 0.01 0.04 0.03 B/ 0.01 B/ 0.01 0.12 0.05 LOI 1.51 1.34 0.64 0.50 0.61 0.80 0.39 0.51 0.21 0.45 0.38 0.71 0.57 0.62 0.32 0.47 0.53 0.74 0.61 0.72 0.55 Total 99.23 99.43 99.47 98.81 99.71 99.37 99.60 100.10 99.82 100.21 99.98 100.14 101.58 98.96 99.50 100.61 100.53 100.14 98.95 99.97 100.7 Trace elements (ppm) Ba 1319 1881 2230 1278 1312 1236 1053 959 675 409 423 1364 1730 1958 477 834 446 82 73 1667 Rb 54 112 135 234 155 163 150 212 158 217 190 145 100 101 182 246 251 492 387 140 236 Sr 1101 711 859 360 622 563 390 333 212 123 129 636 1215 1350 255 148 49 21 19 247 187 Zr 191 274 368 358 246 240 197 264 208 188 198 265 199 196 97 358 241 142 206 470 194 4 9 15 12 7 11 5 17 13 12 21 11 6 4 4 16 14 25 26 13 14 19 25 25 55 35 40 25 39 27 46 29 30 11 11 10 60 54 94 139 55 38 24 24 25 25 24 25 20 24 22 20 20 21 27 27 24 24 22 24 24 26 22 165 159 48 44 40 44 12 12 10 B/10 B/10 57 49 54 B/10 B/ 10 B/ 10 B/ 10 B/ 10 B/10 Nb Y Ga V 765 20 La 18.45 22.32 24.69 58.46 28.13 42.54 25.54 25.84 20.38 31.86 12.36 34.91 26.78 29.50 13.64 66.74 77.98 20.56 114.60 39.98 30.39 Ce 37.06 46.68 51.36 122.20 49.89 71.37 49.70 49.75 43.26 63.45 24.87 57.55 53.70 53.25 20.88 116.40 120.50 54.90 186.60 71.90 61.60 Nd 16.18 19.07 19.19 42.40 20.18 25.94 16.75 17.70 15.71 22.01 9.02 21.51 18.34 15.93 5.63 33.46 50.58 26.68 52.36 24.97 23.61 Sm 3.33 3.55 3.23 7.27 3.46 4.58 2.96 3.07 2.87 3.97 1.71 3.65 3.22 2.77 0.92 6.45 9.95 8.39 11.23 4.28 5.08 Eu 0.96 0.79 0.79 1.20 0.67 0.81 0.52 0.49 0.42 0.49 0.24 0.65 0.77 0.70 0.17 0.62 0.66 0.30 0.35 0.72 0.72 Gd 2.38 2.51 2.18 4.97 2.57 3.19 1.98 2.16 2.06 2.62 1.22 2.43 1.64 1.50 0.49 3.63 5.17 6.80 7.29 2.87 3.83 Dy 1.47 1.57 1.30 3.21 1.62 1.92 1.46 1.28 1.38 1.65 0.94 1.31 0.82 0.62 0.21 2.18 2.87 7.14 4.44 1.69 2.61 Ho 0.22 0.29 0.26 0.64 0.29 0.39 0.26 0.20 0.25 0.26 0.20 0.21 0.10 0.10 0.04 0.41 0.55 1.52 0.82 0.30 0.48 Er 0.72 0.74 0.73 1.66 0.75 0.95 0.80 0.55 0.70 0.73 0.58 0.55 0.20 0.16 0.11 0.89 1.23 4.44 1.83 0.75 1.32 Yb 0.43 0.50 0.57 1.35 0.53 0.69 0.66 0.46 0.59 0.54 0.49 0.35 0.20 0.16 0.10 0.70 0.91 4.89 1.26 0.45 1.06 Lu 0.06 0.07 0.13 0.20 0.08 0.11 0.10 0.09 0.11 0.08 0.08 0.05 0.03 0.03 0.02 0.10 0.13 0.69 0.17 0.06 0.16 Rb/Sr 0.05 0.16 0.16 0.65 0.25 0.29 0.38 0.64 0.75 1.76 1.47 0.23 0.08 0.07 0.71 1.66 5.12 23.43 20.37 0.57 1.26 Ba/Rb 24.43 16.79 16.52 5.46 8.46 7.58 7.02 4.52 4.27 1.88 2.23 9.41 17.30 19.39 2.62 3.39 1.78 0.17 0.19 11.91 3.24 Rb/Zr (La/Yb)n 0.28 0.41 0.37 0.65 0.63 0.68 0.76 0.80 0.76 1.15 0.96 0.55 0.50 0.52 1.88 0.69 1.04 3.46 1.88 0.30 1.22 28.89 30.01 29.44 29.27 35.82 41.37 26.00 37.75 23.32 39.97 17.06 67.71 92.22 122.16 96.88 64.26 57.90 2.84 61.39 60.24 19.32 Eu/Eu 0.99 0.77 0.86 0.58 0.65 0.62 0.63 0.55 0.50 0.43 0.48 0.53 0.92 0.95 0.68 0.36 0.25 0.12 0.11 0.60 0.48 A/CNKa 0.84 0.85 1.01 0.98 1.01 1.03 1.02 1.04 0.99 1.07 1.01 0.95 0.99 1.00 1.03 0.97 1.01 0.99 1.06 1.01 0.99 FeOtot/MgOb 0.68 0.59 0.77 0.80 0.76 0.75 0.78 0.82 0.82 0.92 0.89 0.70 0.74 0.73 0.84 0.91 0.91 0.90 0.93 0.89 0.79 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Al2O3 Table 3 (Continued ) 201 Facies BA BTR Sample 90b MV-154 SiO2 (wt.%) Moraes Almeida volcanic sequence Trachyte 36c 202 Vila Riozinho volcanic sequence 106a Rhyolite 107 92a 62a 98 93a 101 115 TRACH Rhyolite 48 52 Ignimbrite 12c 39a 51 15a 111 46 14 38 17 54.40 54.70 61.20 64.70 68.20 68.40 69.40 69.70 71.10 71.80 67.60 72.00 74.80 75.20 75.80 72.70 73.60 75.20 75.40 75.90 0.89 1.00 1.60 0.41 0.54 0.36 0.44 0.37 0.33 0.37 0.35 0.54 0.37 0.24 0.18 0.24 0.17 0.14 0.11 0.15 0.15 76.10 0.15 Al2O3 14.60 16.10 15.90 18.80 16.50 15.60 15.70 16.30 16.00 15.60 14.70 16.00 13.80 13.00 12.60 12.80 13.70 13.80 13.00 12.60 12.70 12.80 Fe2O3 2.54 3.43 4.50 1.93 2.63 1.56 1.80 1.66 1.66 1.38 1.78 1.11 1.10 0.87 1.06 0.89 0.91 1.88 1.28 1.58 1.38 1.48 FeO 5.72 4.83 4.86 1.05 1.41 0.49 0.72 0.58 0.31 0.11 0.11 1.70 0.99 0.39 0.22 0.28 0.80 0.11 0.11 0.11 0.11 0.11 MnO 0.16 0.13 0.14 0.10 0.14 0.05 0.05 0.06 0.08 0.02 0.05 0.08 0.10 0.06 0.05 0.07 0.03 0.04 0.03 0.03 0.03 0.04 MgO 5.80 5.50 3.60 0.95 1.20 0.59 0.57 0.37 0.44 0.52 0.25 0.61 0.40 0.24 0.25 0.25 0.28 0.24 0.21 0.18 0.22 0.14 CaO 7.80 7.30 6.40 1.60 2.90 0.86 2.30 1.20 0.90 0.68 1.20 2.00 0.70 0.54 0.40 0.45 0.89 0.91 0.31 0.79 0.80 0.70 Na2O 2.90 3.20 3.10 6.20 4.10 5.30 4.40 4.30 4.80 5.60 4.20 5.10 2.70 3.80 3.70 3.80 3.70 3.60 4.00 3.40 3.70 3.60 K 2O 2.10 2.50 3.10 5.80 4.40 5.50 4.30 4.80 5.00 2.90 4.80 5.10 6.50 5.40 5.00 5.30 5.40 5.60 4.80 4.90 4.90 4.80 P2O5 0.29 0.32 1.20 0.16 0.19 0.08 0.09 0.09 0.08 0.07 0.05 0.13 0.09 0.02 0.02 0.02 0.04 0.04 0.02 0.03 0.01 0.02 LOI 1.81 1.02 0.80 1.55 0.97 0.49 0.68 0.79 0.76 1.28 0.64 0.07 1.05 0.73 0.47 0.62 0.92 0.65 0.53 0.96 0.51 0.52 Total 99.41 99.73 99.90 99.75 99.68 99.08 99.45 99.92 100.06 99.63 99.93 100.04 99.80 100.09 99.15 100.52 99.54 100.61 99.60 100.13 100.41 100.46 Trace elements (ppm) Ba 912 1260 1154 2864 1338 1481 1352 2275 1592 1349 1410 2641 471 267 56 241 500 667 214 439 327 354 Rb 41 67 151 140 120 176 176 161 163 120 195 143 358 262 298 282 220 252 309 248 285 240 Sr 723 688 496 431 633 388 433 462 333 508 275 293 42 36 20 39 82 122 56 88 82 69 Zr 173 192 281 610 286 420 297 408 421 370 292 636 322 317 236 301 231 298 187 231 234 198 Nb Y Ga 6 5 12 10 10 20 6 12 12 15 15 16 18 17 21 18 11 14 20 14 16 11 23 19 32 20 27 28 38 29 35 21 41 39 52 56 61 49 42 204 167 53 103 58 23 23 28 20 26 18 22 21 19 17 21 22 23 19 20 22 20 22 21 19 24 21 V 206 195 198 61 67 14 32 24 22 23 17 B/ 10 10 B/ 10 B/ 10 B/ 10 B/ 10 B/ 10 B/ 10 B/ 10 B/ 10 B/ 10 Th B/5 B/5 B/5 B/5 B/5 12 B/5 B/5 9 11 B/5 B/ 5 16 25 24 18 22 21 35 25 20 21 La 17.95 17.27 43.16 22.26 48.48 23.36 34.94 32.46 27.05 42.71 34.69 61.85 142.10 Ce 39.31 35.85 87.26 40.59 93.68 51.98 71.55 64.53 53.22 83.85 70.37 114.70 215.20 Nd 16.50 16.53 36.09 13.42 33.36 19.83 24.48 22.19 16.91 35.59 25.16 38.54 86.19 Sm 3.44 3.52 6.36 2.41 6.05 3.62 4.20 4.28 3.27 7.51 5.88 8.06 18.76 Eu 0.81 0.92 1.52 0.45 1.10 0.72 0.88 0.79 0.49 2.05 0.23 0.71 1.06 Gd 2.58 2.77 4.02 1.43 3.50 2.64 2.74 2.72 2.20 6.01 4.35 5.89 15.40 Dy 1.59 2.00 2.07 0.76 1.83 1.92 1.54 1.72 1.40 4.75 2.93 3.72 9.75 Ho 0.31 0.42 0.40 0.12 0.33 0.37 0.30 0.31 0.24 0.93 0.54 0.75 1.84 Er 0.78 1.01 0.92 0.27 0.82 0.99 0.74 0.85 0.65 2.54 1.36 1.98 4.29 Yb 0.50 0.71 0.51 0.18 0.66 0.75 0.54 0.77 0.47 2.36 1.20 1.55 3.12 Lu 0.07 0.11 0.07 0.03 0.09 0.10 0.09 0.11 0.08 0.33 0.17 0.23 0.41 Rb/Sr 0.06 0.10 0.30 0.32 0.19 0.45 0.41 0.35 0.49 0.24 0.71 0.49 8.52 7.28 14.90 7.23 2.68 2.07 5.52 2.82 3.48 3.48 Ba/Rb 22.24 18.81 7.64 20.46 11.15 8.41 7.68 14.13 9.77 11.24 7.23 18.47 1.32 1.02 0.19 0.85 2.27 2.65 0.69 1.77 1.15 1.48 0.23 0.39 1.11 0.83 1.26 0.94 0.95 0.85 1.65 1.07 1.22 1.21 Rb/Zr (La/Yb)n Eu/Eu A/CNKa FeOtot/MgO b 0.24 0.35 0.54 24.28 16.42 56.79 0.42 0.42 0.59 0.39 83.47 49.96 20.97 43.84 0.32 0.67 0.22 28.60 39.01 12.23 19.51 26.86 0.14 30.73 0.80 0.87 0.86 0.69 0.67 0.69 0.75 0.66 0.53 0.91 0.69 0.76 0.79 0.97 0.98 0.96 0.98 1.13 1.07 1.15 1.03 0.91 1.08 0.99 1.03 1.00 1.01 0.30 1.01 1.05 0.19 1.02 0.99 1.03 0.58 0.59 0.71 0.75 0.76 0.76 0.80 0.85 0.80 0.72 0.87 0.82 0.83 0.83 0.82 0.81 0.85 0.88 0.86 0.89 0.86 0.91 A, amphibole; B, biotite; QMD, quartz monzodiorite; MD, monzodiorite; MZG, monzogranite; SG, syenogranite; QM, quartz monzonite; LMG, leucomonzogranite; QS, quartz syenite; GP, Granite Porphyry; JOG, Jardim do Ouro Granite; BA, basaltic andesite; BTR, basaltic trachyandesite; TRACH, trachyte. a Molecular Al2O3/(CaO/Na2O/K2O). b FeOtot denotes total Fe as FeO. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 54.80 TiO2 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 5.2. Results Representative analyses of the studied granitoids and volcanic rocks are presented in Table 3. The older São Jorge granite and the Vila Riozinho volcanic sequence consist of a compositionally wide series of rocks with SiO2 between 54.5 and 75.1 wt.%. The other studied granitoids and the Moraes Almeida volcanic sequence have a more limited SiO2 range (67.5 /76.6 wt.%). The São Jorge and Jardim do Ouro granites and the Vila Riozinho volcanic sequence are transitional between metaluminous and slightly peraluminous (Fig. 7a) and show FeOtot/(FeOtot/MgO) between 0.6 and 0.9 (Fig. 7b). The younger São Jorge granite is a little more enriched in Mg that the older São Jorge granite. The Maloquinha granite and the Moraes Almeida volcanic sequence are both dominantly peraluminous (Fig. 7a) and have FeOtot/(FeOtot/MgO) higher than 0.8 (Fig. 7b). In the Rb versus (Y/Nb) plot (Fig. 7c), the São Jorge and Jardim do Ouro granites and the Vila Riozinho sequence samples plot dominantly in the volcanic arc field (VAG). The Maloquinha granite and the Moraes Almeida volcanic sequence samples plot mostly in the within plate granite (WPG) field. Most of the analyzed samples fall in the postcollisional field of Pearce (1996) which could reflect transition from calc-alkaline to alkaline series in orogenic to post-orogenic tectonic settings (Bonin, 1990; Barbarin, 1999) or increase in arc maturity (Brown et al., 1984). In the (K2O/Na2O)/CaO versus Zr/Nb/ Ce/Y diagram (Fig. 7d), the São Jorge and Jardim do Ouro granites are like normal and fractionated S- and I-type granites. Their oxidized character, metaluminous to marginally peraluminous nature, and VAG character (Fig. 7c) point to strong I-type granite affinity. Samples from the Vila Riozinho sequence straddle the I- and A-type granite boundary. This reflects the higher zirconium contents (Table 3) and more alkaline character of these volcanic rocks compared to the older São Jorge granite. The Maloquinha granite and the Moraes Almeida volcanic sequence samples are transitional between fractionated I-type granite and A-type granite (Fig. 7d). Nevertheless, their 203 high FeOtot/(FeOtot/MgO), WPG affinity (Fig. 7c) and mildly metaluminous to peraluminous character (Fig. 7a) suggest that they are geochemically similar to evolved aluminous, A-type granites (King et al., 1997; Dall’Agnol et al., 1999a; Rajesh, 2000). The Maloquinha granite and the Moraes Almeida volcanic sequence have higher Rb/Zr and Rb/Sr ratios than the other studied rocks (Fig. 7e and f). The Rb/Zr ratio increases from the Vila Riozinho sequence to the younger São Jorge granite, the older São Jorge granite is intermediate between the two. This indicates that these rocks are not comagmatic. A similar conclusion is suggested by the geochronologic data discussed below. The granite porphyry associated with the older São Jorge granite is similar to the São Jorge granites with similar SiO2 contents (Fig. 7). The granite porphyry associated with the Maloquinha granite and the Moraes Almeida ignimbrites has a common geochemical affinity with the trachyte (sample 48) of the Moraes Almeida volcanic sequence. In the log[CaO/(Na2O/K2O)] versus SiO2 plot (Fig. 8a), the São Jorge and Jardim do Ouro granites and the Vila Riozinho sequence samples indicate calc-alkaline affinity and transitional character between normal and mature arc series. In the K2O versus SiO2 diagram (Fig. 8b) most of the granitoid samples plot in the high-K field. The Vila Riozinho volcanic sequence has a transitional high-K to shoshonitic character. In the TAS diagram (Fig. 6) the Vila Riozinho sequence is, on average, slightly more alkaline than the São Jorge granites (Table 3, Fig. 7e and f). The calcalkaline character of the São Jorge granites is also indicated by their relatively oxidized nature (Figs. 4 and 5; cf. Figueiredo, 1999). The Jardim do Ouro granite constitutes a more iron-rich amphibole and biotite (Figs. 4 and 5) and was probably crystallized from a less oxidized magma (Figueiredo, 1999). The REE contents of the studied rocks are relatively low (Fig. 9), except in a few samples of the Maloquinha granite and Moraes Almeida ignimbrites. The REE patterns of the São Jorge granites (Fig. 9a) and associated granite porphyries are enriched in the LREE and the younger São 204 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 7 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Jorge granite shows lower contents of the HREE than the older São Jorge granite. Negative Eu anomalies (Fig. 9a) are very small in the younger São Jorge granite, in the older São Jorge granite moderate. The Vila Riozinho volcanic sequence REE pattern (Fig. 9c) is broadly similar to that of the older São Jorge granite. The Maloquinha granite and Moraes Almeida volcanic rocks (Fig. 9b and d) are enriched in total REE compared to the São Jorge granites and the Vila Riozinho volcanic sequence. Overall, the REE patterns are similar but the Maloquinha granite shows higher HREE contents than the Moraes Almeida volcanic rocks (Table 3). Negative Eu anomalies are remarkable in both the Maloquinha granite and the Moraes Almeida rhyolites and ignimbrites (Fig. 9b and d). The REE signature of the Moraes Almeida trachyte (sample 48) differs from the Vila Riozinho trachytes by higher content of the HREE (Fig. 9d). The Jardim do Ouro granite and granite porphyry 18a have REE patterns similar to those of the low-silica samples of the Maloquinha granite (Fig. 9b; Table 3). Primordial mantle-normalized trace element patterns of the studied rocks with more than 60 wt.% of SiO2 (Fig. 10) corroborate the geochemical similarities of the São Jorge granites, Vila Riozinho volcanic sequence, and the calc-alkaline granitoids of normal arcs (cf. Brown et al., 1984). All are depleted in Nb, P, and Ti and do not show significant Sr and Ba depletion as observed for alkali-calcic granitoids of more mature arcs (Brown et al., 1984). The Vila Riozinho samples display a discrete positive Ba anomaly and the younger São Jorge granite (Fig. 10c) differs from the older São Jorge granite (Fig. 10a) by small positive Ba and Sr anomalies and depletion in Yb. The Maloquinha and Jardim do Ouro granites and Moraes Almeida volcanic sequence (Fig. 10d and e) are similar and show strong depletion in Ba, Nb, 205 Sr, P, and Ti. The patterns of the granite porphyry (18a) and trachyte of the Moraes Almeida sequence display less pronounced negative anomalies of Sr, P, and Ti, small positive Ba anomaly, and enrichment in Zr. These patterns are broadly similar to those of mature continental arc granitoids (Fig. 10f). 6. Geochronology 6.1. Analytical procedures Zircon crystals from volcanic and granitic rocks of the São Jorge region were dated by the single grain Pb evaporation method (cf. Kober, 1986, 1987) at the geochronological laboratory of Universidade Federal do Pará, Belém, Pará, Brazil. Isotope analyses were performed on a Finnigan MAT262 mass spectrometer in dynamic mode using the ion counting detector. When the Pb signal exceeded the ion counting saturation threshold, the isotopic measurements were done in static mode on Faraday cups. 207Pb/206Pb ratios were corrected by a mass discrimination factor of 0.129/ 0.03% determined by repeated analyses of the NBS-982 Pb standard. In the Amazonian craton and specifically in the Tapajós Province, 207 Pb/204Pb ratios may be slightly higher than the Stacey and Kramers (1975) model. However, the calculation of common Pb corrections using the mean Pb values of sulphides associated with primary gold deposits from the Tapajós Province (Coutinho et al., 2000) provided ages similar to those obtained when common Pb corrections were done using the Stacey and Kramers (1975) model. Analyses with 206Pb/204Pb ratios lower than 2500 were rejected, thus minimizing the effects of common Pb correction. The age of each sample was obtained using the mean of 207Pb/206Pb ratios Fig. 7. Geochemical diagrams for the granitic rocks and volcanic sequences of Vila Riozinho region. (a) Molecular Al2O3/(CaO/ Na2O/K2O) versus SiO2; (b) FeOtot/(FeOtot/MgO) versus SiO2 (FeOtot denotes total iron as FeO); (c) Rb versus Y/Nb, fields from Pearce et al. (1984): syn-COLG */syn-collision granites, WPG */within plate granites, VAG */volcanic arc granites, ORG */ocean ridge granites; (d) (K2O/Na2O)/CaO versus Zr/Nb/Ce/Y; average composition of A-type (A), M-type (M), S-type (S), and I-type (I) granites and fields for fractionated felsic granites (FG) and unfractionated M, I, and S type granites (OGT) according Whalen et al. (1987); (e) Ba/Rb versus Rb/Zr; (f) Rb/Sr versus Rb/Zr. 206 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 8 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 207 Fig. 9. Chondrite-normalized (Evensen et al., 1978) patterns of selected REE for (a) the São Jorge granites and associated granite porphyry; (b) Maloquinha and Jardim do Ouro granites and granite porphyry; (c) Vila Riozinho volcanic sequence; and (d) Moraes Almeida volcanic sequence. of at least four crystals at the highest step of temperature. When different heating steps of the same grain gave similar ages, all of them were included in the age calculation. Grains that yielded lower ages (probably because of Pb loss after crystallization) were discarded. Weighted mean and errors on the ages were calculated following Gaudette et al. (1998). The ages are presented in Table 4 at the 2s level. The Pb evaporation method provides a Pb/206Pb age, which is a minimum age as Pb/ U ratios are not determined. However, the assumption that they represent a ‘concordant’ crystallization age of zircons from magmatic rocks is probably valid in the case when repeated measurements of 207Pb/206Pb do not vary between different crystals or at different heating step in one grain (Kröner et al., 1999; Costi et al., 2000, and 207 Fig. 8. (a) log [CaO/(Na2O/K2O)] versus SiO2 plot (Brown et al., 1984) and (b) K2O versus SiO2 plot for the São Jorge and Jardim do Ouro granites, granite porphyry, and the Vila Riozinho volcanic sequence. In (b), the field of Vila Riozinho volcanic sequence is shown for comparison. Low-K, medium-K, and high-K calc-alkaline fields and shoshonite fields in (b) from Peccerilo and Taylor (1976), modified by Rickwood (1989). Symbols as in Figs. 6 and 7. 208 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Fig. 10. Primordial mantle-normalized spidergrams (Wood, 1979) for the (a) older São Jorge granite and associated granite porphyry; (b) volcanic sequence of Vila Riozinho; (c) younger São Jorge granite; (d) Maloquinha granite, Jardim do Ouro granite, and granite porphyry; (e) volcanic sequence of Moraes Almeida; and (f) primitive, normal, and mature arc granitoids (Brown et al., 1984). Table 4 Zircon single-crystal evaporation Pb isotopic data from the granites and volcanic rocks of the TGP Zircon Vila Riozinho volcanic sequence (sample 62a */trachyte) 62a/3 Temperaturea Number of (8C) ratios 206 Pb/204Pb 208 Pb/206Pb 2s 207 Pbb/206Pb 2s 18 868 25 000 0.22716 0.28489 364 71 1766 1977 18 3 62a/5 1450 F 1480 F 1520 38 134 72 23 810 43 478 28 571 0.31348 0.40531 0.43786 91 0.12294 125 0.12305 110 0.12232 62a/6 1480 1480 F 18 70 15 625 31 250 0.15653 0.15637 80 71 62a/7 1450 16 6623 0.25633 125 62a/8 1450 F 1480 F 75 108 23 810 111 111 0.24879 0.26016 62a/9 1450 F 1480 F 167 137 12 195 33 333 0.21612 0.19347 136 87 62a/10 1450 F 1500 F 49 152 20 833 34 483 0.26782 0.261490 109 0.12200 33 0.12276 33 1986 26 1997 5 4 1997 62a/14 1500 1500 F 88 55 18 519 45 455 0.30966 0.31038 75 109 27 30 3 3 34 2000 19 2001 53 1991 5 3 8 2000 0.20303 0.20333 56 71 2851 2853 5 6 0.12148 59 1978 44 0.12276 40 0.12252 0.12395 0.12494 0.17322 0.17353 73 1997 36 1993 34 15 2014 2028 2589 2592 4 9 11 5 1994 5 5 2 : 4 1998 3 1450 1500 1550 54 88 50 52 632 250 000 200 000 0.22479 0.23548 0.25652 150 0.12256 97 0.12263 85 0.12287 23 1994 40 1995 43 1999 3 6 6 1995 3 107/2 1500 84 166 667 0.22771 262 0.12253 26 1994 4 1994 4 107/3 1450 1500 1550 80 88 86 21 739 21 277 200 000 0.26976 0.30348 0.29800 69 70 77 0.12198 0.12208 0.12209 22 19 28 1986 1987 1987 3 3 4 107/4 1450 1500 84 84 4854 40 000 0.27940 0.31178 76 109 0.12226 0.12198 18 16 1990 1986 3 2 107/5 1450 1500 1550 34 86 42 100 000 66 667 76 923 0.11436 0.18156 0.26939 103 0.12338 310 0.12333 88 0.12297 48 2006 17 2005 28 2000 7 2 4 2004 4 107/6 1450 1500 82 88 6211 5102 0.08648 0.15006 78 0.12194 308 0.12288 17 1985 22 1999 2 3 1999 3 107/8 1450 1550 88 90 12 500 142 857 0.27741 0.29889 22 19 3 3 Mean (526 ratios; USD / 2.7) : 91 69 0.12224 0.12213 1989 1988 2000 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 18 90 Mean (579 ratios; USD / 1.6) 106 19 Age (Ma) 2s Crystal 1450 1500 Vila Riozinho volcanic sequence (sample 107 */trachyte) 107/1 0.10796 0.12141 Age (Ma) 2s step 4 209 210 Table 4 (Continued ) Zircon Older São Jorge granite (sample 27 */hornblende /biotite monzogranite) 27/1 Temperaturea Number of (8C) ratios 206 Pb/204Pb 208 Pb/206Pb 2s 207 Pbb/206Pb 2s Age (Ma) 2s step Age (Ma) 2s Crystal 76 5556 0.38319 67 0.12158 36 1980 5 1980 5 1450 1500 99 96 6098 12 048 0.30364 0.34729 53 0.12167 158 0.12204 15 1981 46 1987 2 7 1982 3 27/5 1450 1550 12 67 11 905 8197 0.32340 0.40542 304 0.12179 106 0.12158 186 1983 74 1980 27 11 1980 10 27/6 1450 1550 34 90 20 000 24 390 0.34918 0.36009 139 0.12162 84 0.12148 110 1980 24 1978 16 3 1978 3 1981 2 Mean (474 ratios; USD / 0.9) Older São Jorge granite (sample 35 */biotite leucomonzogranite) 35/1 : 1500 1550 84 18 4219 2695 0.32102 0.43022 73 0.12114 222 0.12137 26 1973 57 1977 4 8 1974 3 35/2 1450 1500 1550 34 18 16 3817 5525 4348 0.24192 0.29916 0.30033 754 0.12054 153 0.12115 175 0.12108 32 1965 95 1974 59 1973 5 14 9 1973 7 35/3 1450 1550 86 84 8130 8197 0.32950 0.37180 124 306 30 82 4 12 35/4 1450 1500 84 68 8475 13 514 0.52811 0.57281 120 0.12102 532 0.12150 24 1972 32 1979 4 5 1974 7 35/5 1450 1500 47 88 7042 22 727 0.22892 0.26499 132 0.12094 45 0.12247 64 1970 16 1993 9 2 1993 2 1983 8 0.11975 0.11912 1953 1943 Mean (376 ratios; USD / 5.0) Younger São Jorge granite (sample F09 */hornblende /biotite monzogranite) F09/1 1475 1500 1550 17 78 27 47 619 25 641 18 519 0.20933 0.21075 0.21480 125 0.11536 37 0.11544 73 0.11576 30 1886 13 1887 63 1892 5 2 10 1887 2 F09/2 1500 1550 8 82 3704 17 544 0.22023 0.20681 137 0.11527 138 0.11530 47 1885 28 1885 7 4 1885 4 F09/3 1425 1475 1550 36 88 80 13 514 9346 17 544 0.13981 0.26128 0.22682 156 126 56 41 25 23 6 4 3 F09/4 1500 85 12 987 0.18099 32 0.11610 29 1897 5 1897 5 F09/5 1425 1475 86 17 35 714 33 333 0.20538 0.21770 35 0.11536 641 0.11706 24 1886 38 1912 4 6 1893 24 F09/6 1500 95 32 258 0.19728 50 0.11589 54 1894 8 1894 8 F09/7 1450 77 5102 0.21933 39 0.11547 29 1888 5 1888 5 F09/8 1450 30 43 478 0.22055 89 0.11587 21 1894 3 1894 3 0.11588 0.12031 0.12032 1894 1961 1961 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 1500 27/4 Table 4 (Continued ) Zircon F09/10 Temperaturea Number of (8C) ratios 1550 81 206 Pb/204Pb 33 333 208 Pb/206Pb 2s 0.23068 207 Pbb/206Pb 2s 44 0.11592 Age (Ma) 2s step 16 1894 3 1894 3 1891 3 Mean (615 ratios; USD / 3.2) Moraes Almeida volcanic sequence (sample 39a */rhyolite) 39a/1 Age (Ma) 2s Crystal 25 2755 0.37874 145 0.11452 61 1873 10 1873 10 1450 1500 36 52 2519 3077 0.27689 0.41960 187 0.11664 138 0.11558 61 1906 39 1889 9 6 1894 15 39a/6 1500 88 3636 0.34135 311 0.11563 24 1890 4 1890 4 39a/7 1450 1500 18 52 14 706 83 333 0.40385 0.39994 752 0.11435 210 0.11567 206 1870 36 1891 33 6 1891 6 1890 6 1865 1874 1877 1879 7 4 3 5 1876 3 Mean (253 ratios; USD / 2.5) Moraes Almeida volcanic sequence (sample 48 */trachyte) 48/1 1450 1500 1533 1550 34 90 82 82 4831 7874 15 873 8547 0.2762 0.29191 0.30457 0.32278 98 72 73 92 0.11404 0.11458 0.11480 0.11491 45 28 22 34 48/3 1500 86 11 905 0.29172 67 0.11493 19 1879 3 1879 3 48/5 1450 1500 84 70 71 429 62 500 0.16951 0.16781 47 0.11522 52 0.11543 34 1884 23 1887 5 4 1886 3 48/6 1450 1500 52 84 4167 17 241 0.27616 0.26711 88 0.11554 73 0.11553 49 1889 24 1888 8 4 1888 3 1881 4 Mean (630 ratios; USD / 2.7) Moraes Almeida volcanic sequence (sample 15 */ignimbrite) 15/1 1450 1550 84 68 7092 7407 0.17298 0.17343 46 0.11467 111 0.11418 17 1875 19 1867 3 3 1872 8 15/2 1450 1500 32 54 8547 8197 0.18970 0.19640 113 0.11531 102 0.11498 36 1885 29 1880 6 5 1882 5 15/3 1500 52 58 824 0.20383 108 0.11479 47 1877 7 1877 7 15/4 1450 F 1500 F 76 89 12 987 37 037 0.16161 0.20417 59 0.11447 34 0.11498 27 1872 23 1880 4 4 1876 8 15/5 1500 F 94 38 462 0.23107 76 0.11468 24 1875 4 1875 4 1875 4 Mean (549 ratios; USD / 2.8) Jardim de Ouro granite (sample 03 */hornblende /biotite monzogranite) 03a/1 84 4695 0.28539 158 1450 1500 18 88 55 556 111 111 0.11505 0.11842 133 0.11476 59 0.11503 0.12141 113 1876 20 1881 23 1977 18 3 1880 3 3 03a/3 1500 88 31 250 0.16258 120 0.11482 44 1877 7 1877 7 211 1500 03a/2 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 1550 39a/5 212 Zircon Temperaturea Number of (8C) ratios 206 Pb/204Pb 208 Pb/206Pb 2s 207 Pbb/206Pb 2s 03a/4 1450 F 1500 35 52 40 000 15 625 0.12184 0.14995 63 0.11497 74 0.11476 55 1880 25 1876 9 4 1877 4 03a/5 1450 1500 84 88 11 765 21 277 0.11258 0.16585 39 0.11265 38 0.11524 16 1843 23 1884 3 4 1884 4 1880 3 Age (Ma) 2s step Mean (369 ratios; USD / 1.4) Age (Ma) 2s Crystal Maloquinha granite (sample 06a */biotite leucomonzogranite) 06a/1 1500 88 7463 0.22017 55 0.11555 21 1889 3 1889 3 06a/5 1550 82 2985 0.22842 60 0.11426 32 1869 5 1869 5 06a/6 1500 86 5102 0.17092 72 0.11471 21 1876 3 1876 3 06a/7 1450 82 4292 0.34699 98 0.11486 50 1878 8 1878 8 1880 9 Mean (338 ratios; USD /0.9) Note: Analyses excluded from age calculation in italic font. a F denotes analysis in static mode using Faraday cups. b Corrected for common Pb. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Table 4 (Continued ) C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 references therein). This assumption is reinforced by the fact that TIMS and SHRIMP U/Pb zircon data published from the same region (Santos et al., 2000) are consistent with our Pb evaporation results (cf. Table 1). 6.2. Results 6.2.1. Vila Riozinho volcanic sequence Two samples of trachytes were dated from Vila Riozinho (Fig. 2). Sample 62a shows two different zircon populations, clear and brown. In total, eight grains were dated. Two brown zircon grains gave ages of 28529/4 Ma and 25919/3 Ma. Six grains of the clear population gave Paleoproterozoic ages; one of these was excluded from age calculation. The remaining crystals yielded an age of 20119/12 Ma with a large scatter as indicated by the unified standard deviation (USD) of 8.8. Grain 9 (Table 4) is responsible for the scatter as it gave a 30 Ma older age. This may reflect a small inherited Pb component. The four remaining grains have 207Pb/206Pb indicating an age of 19989/3 (USD /1.6) that we assume as the crystallization age of the 62a trachyte. Archean ages of 2.59 and 2.85 Ga obtained for the brown zircon grains (6 and 14) indicate an inherited component with a minimum age of 2.85 Ga. Zircons recovered from sample 107 are clear. Pb isotopic determination of seven grains gave an age of 19939/4 (USD /4.3) and elimination of the three youngest grains yielded an age of 20009/4 Ma (USD /2.7). This is interpreted as the crystallization age of the trachyte. The ages of 19989/3 Ma and 20009/4 Ma of the two trachytes are quite similar and are interpreted as the crystallization age of the Vila Riozinho volcanic sequence. 6.2.2. Older São Jorge granite Two samples of the Older São Jorge granite were dated, sample 27 from the dominant hornblende /biotite monzogranite facies and sample 35 from the more evolved biotite leucomonzogranite facies (Fig. 2). Zircons from sample 27 were clear, light pink, and well-formed. Four grains were dated and these yielded similar ages at each step of heating. Their mean age is 19819/2 213 Ma (USD /0.9), which is interpreted as the crystallization age of the granite. Zircons from sample 35 were also clear and wellformed. Five grains were analyzed and they all had low 206Pb/204Pb ratios. Grain 35/3 (Table 4) provided a /20/30 Ma lower age than the four other ones and was discarded. The remaining grains yielded an age of 19839/8 Ma (USD /5). Grain 35/5 gave a slightly older age (19939/2 Ma) at the highest temperature (1500 8C) */this is responsible for the high value of USD. If 35/5 is excluded, an age of 19749/2 Ma (USD /1.1) is obtained. The older age of 19939/2 Ma may be related to the presence of a small amount of inherited Pb. The slightly lower age of 19749/2 Ma is in good agreement with the fact that it corresponds to a more evolved facies than the 19819/2 Ma old hornblende /biotite monzogranite. However, as no definitive criteria allow to exclude the highest heating step of grain 35/5, the age of 19839/8 Ma is used for the biotite leucomonzogranite. The older São Jorge granite was thus emplaced slightly after the Vila Riozinho volcanic sequence. 6.2.3. Younger São Jorge granite The dated sample F09 is from a drill core in the mineralized part of the younger São Jorge granite (Fig. 2) and represents a hornblende /biotite monzogranite without evidence of significant hydrothermal alteration. Zircon crystals were euhedral, zoned, clear, and light pink. Nine grains yielded good reproducibility except for one grain (F09/5) that was slightly older at the highest temperature step (Table 4). All nine crystals yielded an age of 18919/3 (USD /3.2). The older 19129/6 Ma age from grain F09/5 may indicate small amount of inherited Pb. Exclusion of this from the age calculation would not modify the result much (18909/3 and USD /2.3). Therefore, we consider 18919/3 Ma as the crystallization age of the younger São Jorge granite. This is /90 Ma younger than the two samples from the older São Jorge granite. 6.2.4. Moraes Almeida volcanic sequence Three volcanic samples were dated from the Moraes Almeida sequence. A rhyolite (39a) with 214 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 euhedral to sub-euhedral prismatic, elongated, and clear zircons was collected along the Transgarimpeira road (Fig. 2). Four grains were analyzed and provided low 206Pb/204Pb ratios. The mean 207 Pb/206Pb age for the four grains is 18909/6 Ma (USD /2.5) and is interpreted as the crystallization age of the rhyolite. Four grains were also analyzed from a trachyte (48) north of Moraes Almeida (Fig. 2). These yielded an age of 18819/4 Ma (USD /2.7) that is considered as the age of crystallization. The third analyzed sample (15) is an ignimbrite near Moraes Almeida (Fig. 2). Zircons were elongate, clear, and euhedral. Five grains gave similar ages at all steps of heating with a mean age of 18759/4 Ma (USD /2.8). This is interpreted as the age of crystallization of the ignimbrite. 6.2.5. Maloquinha granite The Maloquinha granite sample 06a was collected along the road between Jardim de Ouro and Moraes Almeida villages (Fig. 2). Zircons were subhedral clear and dominantly prismatic with a lot of inclusions and fractures. Four grains were analyzed, all of them had low 206Pb/204Pb ( B/7500; Table 4). The mean of Pb isotopic ratios corresponds to an age of 18809/9 Ma (USD /0.9), which is considered as the emplacement age of the granite. 6.2.6. Jardim do Ouro granite For the Jardim de Ouro granite, sample 03a from the Jardim do Ouro village was dated (Fig. 2). Zircons were dominantly clear, prismatic and zoned. Five grains were selected for dating and four gave reproducible results with an age of 18809/3 Ma (USD /1.4). This is considered as the crystallization age of the granite. Grain 03a/1 gave a significantly older age of 19779/3 Ma and was excluded of the age calculation. This age is within the range of ages obtained for the Vila Riozinho volcanic rocks and Older São Jorge granite (2.0 /1.98 Ga) and could represent inheritance. 7. Discussion 7.1. Magmatic series and granitoid typology The São Jorge and Jardim do Ouro granites display the geochemical characteristics of I-type granitoids. The classic I-type granitoids of the Lachlan Fold Belt, as envisaged by Chappell and White (1992) and Chappell et al. (2000), were produced by partial melting of an igneous crustal protolith of intermediate composition, and were not associated with subduction processes. The ICordilleran type granites, as defined by Pitcher (1983, 1987), correspond more strictly to the I-type granites generated in a subduction-related tectonic setting. Pitcher (1983, 1987) introduced the ICaledonian type as a variant of the I-Cordilleran type. Blevin and Chappell (1995) considered that the petrogenesis of the I-type granitoids of the Lachlan Fold Belt is not related to active subduction processes and that they are similar to the ICaledonian type granitoids in this respect. The I-type character of the Tapajós granitoids does not necessarily imply a subduction-related environment and the I-type classification adopted here is preliminary. The Maloquinha granite displays within plate or A-type affinities in some diagrams (Fig. 7c) but in others a more ambiguous character is evident (Fig. 7d). It probably corresponds to evolved leucogranites of the aluminousA type series (King et al., 1997; Dall’Agnol et al., 1999a; Rajesh, 2000). These magmas can result from low-degree melting of crustal quartz-feldspatic rocks and this is our preferred interpretation also. All of the studied granitoids contain magnetite, display relatively high magnetic susceptibility values, and were formed at relatively oxidizing conditions, near the NNO buffer (Figueiredo, 1999). Accordingly, they can be defined as magnetite series granitoids (Ishihara, 1981). The compositions of amphiboles and biotite also suggest that oxidizing conditions prevailed during the crystallization of the São Jorge and Jardim do Ouro granites. The Vila Riozinho and Moraes Almeida volcanic sequences are petrographically and geochemically similar to the São Jorge granites and the Maloquinha granite, respectively. C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Our mineralogical and geochemical data indicate that the São Jorge and Jardim do Ouro granites and the Vila Riozinho sequence have calc-alkaline affinities. They follow the classic calc-alkaline trend in the AFM and log[CaO/ (K2O/Na2O)] versus SiO2 diagrams (Fig. 8a) and their incompatible trace-element signatures are consistent with this. All these rocks are K2Orich and most of them plot in the high-K2O field in the K2O versus SiO2 diagram (cf. Peccerilo and Taylor, 1976; Rickwood, 1989). Some of them could be classified as shoshonites (Fig. 8b). In northeastern and southern Brazil, Brasiliano (Pan-African) granitoids are widespread and many calc-alkaline or shoshonitic batholiths have been identified (Nardi and Lima, 1985; Nardi, 1986; Sial, 1986; Sial and Ferreira, 1990; Lima and Nardi, 1998; Sial et al., 1999). Nevertheless, the distinction between high-K2O calc-alkaline and shoshonitic granitoids is also controversial. Mariano and Sial (1993) showed that, in northeast Brazil, shoshonitic rocks and the high-K2O calcalkaline granitoids partially overlap in several geochemical plots. The best chemical separation is found on a Ba versus Rb plot (Mariano and Sial, 1993, Fig. 6). The Ba and Rb contents of the São Jorge and Jardim do Ouro granites and the Vila Riozinho sequence (Table 3) overlap those of the high-K2O granites of northeast Brazil. The older São Jorge granite approaches the Itaporanga batholith, while the younger São Jorge granite is enriched in Ba and Sr compared to the former and is more similar to the Bodocó batholith. The REE patterns of the older São Jorge and younger São Jorge granites are similar to those of porphyritic quartz monzonite and granite, respectively, of the Serra da Lagoinha and Acari batholiths (Neves and Mariano, 1997). Despite the lower REE contents, the REE pattern of the Vila Riozinho sequence rocks does not differ significantly from that of the biotite diorites associated with the Serra da Lagoinha and Acari high-K calc-alkaline granitoids (Neves and Mariano, 1997). It is also similar to the REE patterns of the basalts and shoshonites of the Lavras do Sul shoshonitic association (Lima and Nardi, 1998). It is clear that the criteria for separation of highK2O and shoshonitic series are not unequivocal. 215 The absence of mafic compositions ( B/54 wt.% SiO2) in the studied rocks precludes evaluation of a possible rapid K2O increase with magmatic differentiation in low silica rocks (cf. Meen, 1987). However, the calc-alkaline granodioritic trend followed in the QAP diagram (Fig. 3) and geochemical analogy with the high-K calc-alkaline granitoids of northeast Brazil point to a dominant calc-alkaline rather than shoshonitic character for the São Jorge granites. The same is probably true for most of the Vila Riozinho volcanic sequence, but samples with exceptionally high K2O, Na2O and Zr (Table 3) may be shoshonitic. This suggests that the Vila Riozinho sequence is transitional between high-K2O and shoshonitic or that it does not comprise a consanquineous volcanic sequence. The post-tectonic setting of the TGP would certainly be typical of shoshonitic series (cf. Lima and Nardi, 1998). 7.2. Volcanic sequences of the Vila Riozinho region and the Uatumã volcanism The volcanic sequences of the Tapajós province have been included mostly in the Iriri Group or, more locally, in the Bom Jardim Formation (Faraco et al., 1997; Klein et al., 2001). Available geochronologic data (Santos et al., 2000; Vasquez et al., 2000, Table 1 and references therein) indicate an age of /1.88 Ga for these volcanic sequences. However, Lamarão et al. (1999) and Dall’Agnol et al. (1999b) emphasized the presence of volcanic sequences with different ages and geochemical affinities and stressed that the Uatumã Supergroup should be redefined. The data obtained by Lamarão et al. (1999) together with our new data reveal at least two volcanic sequences in the Vila Riozinho region. The /2.00 Ga Vila Riozinho volcanic sequence is composed of a high-K calc-alkaline to shoshonitic transitional series. The /1.88 Ga Moraes Almeida sequence is geochemically similar to the evolved leucogranites of the Maloquinha granite suite and has aluminous A-type affinity. The Vila Riozinho sequence is composed of basaltic andesite, trachyte, and rhyolite with similar geochemical signatures. The rhyolites are clearly distinct from the felsic volcanic rocks of the Moraes 216 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Almeida sequence and the chemical and chronologic differences justify the separation of these sequences. The two studied volcanic sequences should be considered as independent units and the names Vila Riozinho Formation and Moraes Almeida Formation are proposed for them. The latter can probably be included in the Iriri Group, but the former is older and related to another magmatic event. The identification of the two volcanic series has important implications for the understanding of the magmatic evolution of the Amazonian craton in late Paleoproterozoic and early Mesoproterozoic time. In fact, Dall’Agnol et al. (1987, 1994, 1999a) argued that the Uatumã volcanism that covers large regions of the Amazonian craton was unlikely to be composed of a single magmatic sequence that could be coeval with the associated widespread anorogenic granite magmatism. They stressed the distinct geochemical signatures of many of the calc-alkaline volcanic sequences that were included in the Uatumã Supergroup, and the typical A-type signature of the anorogenic granites. Conversely, Sidder and Mendoza (1991) considered the Uatumã-related volcanic sequences of the northern Guiana Shield late- to postorogenic rather than anorogenic. In this same region, Reis et al. (2000) demonstrated that the /1.96 Ga Surumu volcanic rocks, formerly correlated with the Uatumã Supergroup, have a calc-alkaline character and are geochemically similar to the /1.96 Ga Pedra Pintada granitoids (Table 1). Costi et al. (2000) reported ages of /1.82 Ga for the tin-mineralized A-type, anorogenic granites of Pitinga, whereas the felsic volcanic country rocks of the Iricoumé Group, also included in the Uatumã Supergroup, yielded ages of /1.96 and /1.88 Ga (Table 1). These data indicate that the anorogenic granites of the Central Amazonian Province are not necessarily coeval (or comagmatic) with the spatially associated intermediate to felsic volcanic rocks. Santos et al. (2000) also noted that the Uatumã Supergroup should be redefined and proposed that the Uatumã Supergroup should be reserved for the /1.88 /1.87 Ga volcanism of the Central Amazonian and Tapajós provinces. 7.3. Magmatic evolution of the Vila Riozinho region and its implication for the tectonic evolution of the TGP Geochronologic data obtained for the Vila Riozinho region are summarized in Fig. 11. The studied rocks were formed during two distinct time intervals, at 2.01 /1.97 Ga and 1.90 /1.87 Ga. These two periods of intense magmatic activity dominated the entire Tapajós Province (cf. Table 1). The oldest age, 20119/23 Ma, was obtained for the Conceição tonalite of the Cuiú /Cuiú complex (Table 1). Older inherited zircons have been identified in the Jacareacanga supracrustal sequence (Santos et al., 2000), the Vila Riozinho sequence (Lamarão et al., 1999), and granites of the Maloquinha suite (Santos et al., 2000). There is a gap of 70 m.y. and also a difference in the composition between the two magmatic events (Fig. 11). If an overall subduction-related tectonic setting is assumed for both events, the older event could be syn- to late-orogenic and the younger event post-orogenic. The geochemical characteristics of the studied rocks can be used to evaluate whether the Tapajós Province records a transition from an orogenic to a post-orogenic setting. Normally, an increase in alkalinity is expected in the rocks from primitive to more mature arcs (Brown et al., 1984) or from orogenic to post-orogenic settings (Bonin, 1990; Barbarin, 1999). A transition from low-K calcalkaline to high-K calc-alkaline and alkaline is normally encountered (Barbarin, 1999). Moreover, Brown et al. (1984) considered that the increase of arc maturity could be indicated by Rb/Zr and Nb behavior, as both display a positive correlation and increase parallel to the arc evolution. Low-K calc-alkaline series have not been identified in Vila Riozinho, but they could be represented by the Cuiú /Cuiú tonalites. The K-rich Vila Riozinho sequence and São Jorge granites, whose ages are between 2.00 and 1.88 Ga (Table 4; Fig. 11), do not show a trend of increasing arc maturity in a (Rb/Zr) versus Nb plot (Fig. 12). Conversely, these rocks show decreasing Nb and increasing Rb/Zr with decreasing age. However, the Moraes Almeida sequence and associated Maloquinha granites are more alkaline than the other studied rocks C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 217 Fig. 11. Summary of geochronologic data on the magmatic rocks of Vila Riozinho. Horizontal bars show the 2s error in the ages of the dated samples. and could represent mature arc rocks. Nevertheless, this cannot account for the strong geochemical contrasts between the approximately coeval younger São Jorge, Jardim do Ouro, and Maloquinha granites. High-K calc-alkaline magmas are generally associated with subduction (Brown et al., 1984; Barbarin, 1999). Roberts and Clemens (1993) and Clemens (1999) discussed experimental evidence for the origin of high-K, I-type granitoids and stated that they can be only derived from partial melting of hydrous mafic to intermediate crustal rocks of calc-alkaline or high-K calc-alkaline character. In their model, the thermal effects of underplated or intraplated basaltic magma into continental crust (Huppert and Sparks, 1988) would be responsible for fluid-absent partial melting of fertile metaluminous protoliths and generation of high-K magmas. Neves and Mariano (1997) adopted a similar model to explain the origin of the abundant high-K calc-alkaline granitoids of the Borborema Province in northeast Brazil. They proposed that these granitoids were emplaced in an intracontinental setting. The heat 218 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 source was a mantle plume impinging the base of the continental lithosphere and the K-rich calcalkaline granitoids were not subduction-related. This alternative model may be applicable for the TGP, at least to its northeastern part. The Vila Riozinho region is located near the boundary between the Central Amazonian and Tapajós-Parima provinces. Nd model ages (Sato and Tassinari, 1997; Santos et al., 2000) indicate that the Central Amazonian Province was formed during the Archean, the Tapajós tectonic province in the Paleoproterozoic. If the regional tectonic models are correct, the evolution of the southwestern and northeastern sectors of the TGP (Fig. 1) are distinct. Moreover, a subduction-related setting for at least part of the province is suggested by the presence of abundant gold deposits (Coutinho et al., 2000; Klein et al., 2001). These are generally classified as orogenic-type gold deposits (Groves et al., 1998) and associated with ‘calcalkaline’ sequences. Brito Neves (1999) discussed the tectonic evolution of South America from the supercontinent point of view and stressed the importance of two events at 2.159/0.05 Ga and 2.009/0.05 Ga. They can be distinguished on a continental scale and are attributed to the Transamazonian orogeny. The Paleoproterozoic evolution of the Northern Guiana (or Maroni-Itacaúnas) Province (Fig. 1) has been well documented in French Guiana and in the Amapá state of Brazil. According to Vanderhaeghe et al. (1998), the Paleoproterozoic terranes of French Guiana were assembled between 2.17 and 2.08 Ga. Similar ages have been obtained in Amapá (Lafon et al., 2000) where slightly younger granitoids (/2.05 Ga) are also found. For the TGP, available U/Pb and Pb /Pb zircon data suggest that its evolution could be related to the 2.00 Ga continental event, not to the 2.15 Ga event. However, the few available Nd model ages are only a little older than 2.0 Ga (Santos et al., 2000). Therefore, this hypothesis should be reevaluated when more geochronologic and isotopic information is available. In South America, the Paleoproterozoic supercontinent was rifted mostly during the Mesoproterozoic (Brito Neves, 1999). Extensional events led to the formation of dike swarms and sedimen- Fig. 12. Rb/Zr versus Nb diagram showing the composition of the magmatic rocks of Vila Riozinho. Increasing arc maturity trend from Brown et al. (1984). Symbols as in Figs. 6 and 7. tary and volcanic platform covers. The /1.88 Ga Uatumã Supergroup and widespread cratonic (or anorogenic) granite magmatism in different provinces of the Amazonian craton could represent the oldest magmatism related to these events. The /1.88 Ga event is well documented in several provinces, also by the anorogenic granites of the Carajás region (Table 1). It is concluded that this event was extensional and affected not only the new accreted terranes but also the older, stabilized Archean domains, such as Carajás (Dall’Agnol et al., 2000). A model for the evolution of the Vila Riozinho region (Fig. 13) involves a first stage of subduction-related magmatism at 2.01 /1.97 Ga (Fig. 13a) and two hypotheses for /1.90 /1.87 Ga: a second event of subduction (b1) would give origin to the magmas of the Jardim do Ouro, Maloquinha, and younger São Jorge granites and Moraes Almeida volcanic rocks, or a period of intracontinental magmatism related to a distensional event (b2) could have followed the /2.0 Ga subduction event. This distensional event would mark the beginning of the taphrogenesis that would continue throughout the Mesoproterozoic. The Vila Riozinho region would represent a transitional area between the orogenic and the intracontinental C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 219 Fig. 13. Schematic tectonic model for the Vila Riozinho and TGP. (a) At 2010 /1970 Ma oceanic crust subducts at the southwestern margin of the Central Amazonian Province. Melting of the subducted oceanic crust generates magmas and fluids that ascent to the overlying mantle wedge and lower crust. Different degrees of interaction with lower crust will result in the Vila Riozinho and older São Jorge magmas. Two hypotheses are envisaged to explain evolution at 1900 /1870 Ma: (b1) At a more advanced stage of subduction, a new series of magmas is generated. These magmas are related to a more mature arc and are emplaced at the border between the accreted Paleoproterozoic terranes and the Central Amazonian Province. (b2) After the Transamazonian event (a), the Amazonian craton experiences a major distensional event. Mantle plumes cause melting of the lithospheric mantle and the resulting mafic magmas are emplaced at the mantle-crust boundary. The lower crustal rocks melted yielding felsic magmas. These magmas ascend and form the Maloquinha granite and the Moraes Almeida volcanic sequence. The younger São Jorge and Jardim do Ouro granites could derive from mafic crustal sources or result from interaction between mantle and crustal sources. 220 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 domain. The younger high-K calc-alkaline granitoids could be associated with the late subductionrelated processes or, alternatively, represent intracontinental tectonic evolution (cf. Neves and Mariano, 1997). In this model, the felsic Maloquinha granites and the Moraes Almeida volcanic sequence correspond to melts derived by anatexis of the older crustal rocks. At this stage, we are more inclined for the second hypothesis (Fig. 13b2), but this question should be reevaluated when Nd and Pb isotopic data are available. 8. Concluding remarks The Pb /Pb zircon data for the volcanic and plutonic rocks of the Vila Riozinho region demonstrates two Paleoproterozoic periods of intense magmatic activity. At 2.00 /1.97 Ma, the Vila Riozinho volcanic formation and the older São Jorge granite were formed. During the second period, between /1.90 and 1.87 Ga, the Jardim do Ouro, younger São Jorge, and Maloquinha granites and the Moraes Almeida Formation were formed. The age intervals defined for the rocks of Vila Riozinho are largely coincident with ages throughout the TGP, demonstrating that they are relevant also on a regional scale. The studied terranes of the Tapajós region are a little younger than the Paleoproterozoic terranes of the Northern Guiana Province indicating that the tectonic processes in these provinces were not coeval. The older São Jorge, younger São Jorge, and Jardim do Ouro granites display the broad characteristics of I-type and magnetite series granites. The São Jorge granites are high-K and calc-alkaline. The Jardim do Ouro granite is more iron-rich and less oxidized than the São Jorge granites. The Vila Riozinho Formation displays a calc-alkaline to shoshonitic character and is geochemically similar to the São Jorge granites. The Maloquinha granite and the Moraes Almeida Formation are aluminous, A-type rocks, probably derived from low degrees of melting of crustal sources. The volcanic sequences of the studied area, formerly included in the Iriri Group of the Uatumã Supergroup, are divided in two sequences with different ages and geochemical signatures. The Vila Riozinho and Moraes Almeida sequences are considered as two independent formations and demonstrate that the huge continental Paleoproterozoic volcanic event of the Amazonian craton is more complex than previously thought. The evolution of the TGP records accretionary processes related, on a global scale, to the formation of the Atlantica supercontinent in the midPaleoproterozoic ( /2.00 Ga). This initial step was followed a (/1.88 Ga) by an intracontinental taphrogenetic event that extended to the Mesoproterozoic. The tectonic setting of the TGP is thus transitional, in time and space, between a subduction-related setting, involving the generation of a magmatic arc, and a stable continental block affected dominantly by extensional tectonics. Acknowledgements M.A.B.M. Figueiredo and R.M.K. Borges participated actively in field work and, together with L.H. Ronchi, H.T. Costi, A.A.S. Leite, E.S. Farias and C.E.M. Barros, contributed to the Tapajós research project. Rio Tinto Zinc Company gave support in the field, authorized sampling in the mineralized area and transmitted unpublished information about the São Jorge gold deposit area. M.L. Vasquez, E.L. Klein and M.T.L. Faraco, from CPRM-Belém, contributed to regional mapping, discussions about the Tapajós geology or furnished unpublished information. ADIMB stimulated the developing of this research. It received support from PADCT/FINEP/ FADESP (8/8/98/0400/01), CNPq (000400038/99 and 463196/00-7) and UFPA. This paper is a contribution to PRONEX/CNPq (Proj. 103/98 */ Proc. 66.2103/1998-0) and IGCP-426. References Abdel-Rahman, A.M., 1994. Nature of biotites from alkaline, calc-alkaline, and peraluminous magmas. J. Pet. 35 (2), 525 /541. Almeida, M.E., Fraga, L.M.B., Macambira, M.J.B., 1997. New geochronological data of calc-alkaline granitoids of Ror- C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 aima state, Brazil. In: S. Am. Symp. Isot. Geol. Ext. Abstr. Campos do Jordão, São Paulo, Brazil, pp. 34 /35. Barbarin, B., 1999. A review of the relationships between granitoid types, their origins and their geodynamic enviroments. Lithos 46, 605 /626. Barbosa, A.A., Lafon, J.-M., Neves, A.P., Vale, A.G., 1995. Geocronologia Rb-Sr e Pb /Pb do Granito Redenção, SE do Pará: Implicações para a evolução do magmatismo proterozóico da região de Redenção. Bol. Mus. Par. Emı́lio Goeldi, sér. Ciências da Terra 7, 147 /164 (in Portuguese). Blevin, P.L., Chappell, B.W., 1995. Chemistry, origin, and evolution of mineralized granites in the Lachlan Fold Belt, Australia: the metallogeny of I- and S-type granites. Econ. Geol. 90, 1604 /1619. Bonin, B., 1990. From orogenic to anorogenic settings: evolution of granitoid suites after a major orogenesis. Geol. J. 25, 261 /270. Brito Neves, B.B., 1999. América do Sul: quatro fusões, quatro fissões e o processo acrescionário andino. Rev. Brasil. Geoci. 29, 379 /392 (in Portuguese). Brown, G.C., Thorpe, R.S., Webb, P.C., 1984. The geochemical characteristics of granitoids in contrasting arcs and comments on magma sources. J. Geol. Soc. Lond. 141, 413 /426. Cas, R.A.F., Wright, J.V., 1987. Volcanic sucessions: modern and ancient. A geological approach to processes, products and sucessions. Allen & Unwin, London. Chappell, B.W., White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt. Trans. R. Soc. Edinburgh Earth Sci. 83, 1 /26. Chappell, B.W., White, A.J.R., Williams, I.S., Wyborn, D., Wyborn, L.A.I., 2000. Lachlan Fold Belt granites revisited: high-and low-temperature granites and their implications. Aust. J. Earth Sci. 47, 123 /138. Clemens, J.D., 1999. Origins of High-K Granitic Magmas: constraints from experimental petrology. In: Barbarin, B. (Ed.), The Origin of Granites and Related Rocks, 4th Hutton Symposium Abstr. Documents du BRGM 290, 49. Costi, H.T., Dall’Agnol, R., Moura, C.A.V., 2000. Geology and Pb /Pb geochronology of Paleoproterozoic volcanic and granitic rocks of Pitinga Province, Amazonian craton, northern Brazil. Int. Geol. Rev. 42, 832 /849. Coutinho, M.G.N., Santos, J.O.S., Fallick, A.E., Lafon, J.M., 2000. Orogenic gold deposits in Tapajós Mineral Province, Amazon, Brazil. In: 31st Int. Geol. Congress, Rio de Janeiro, Brazil, Abstr. Vol. Rio de Janeiro, Geol. Surv. Brazil [CD-ROM]. Dall’Agnol, R., Bettencourt, J.S., Jorge João, X.S., Medeiros, H., Costi, H.T., Macambira, M.J.B., 1987. Granitogenesis in the northern Brazilian region */a review. Rev. Brasil. Geoci. 17, 382 /403. Dall’Agnol, R., Lafon, J.-M., Macambira, M.J.B., 1994. Proterozoic anorogenic magmatism in the Central Amazonian Province, Amazonian Craton: geochronological, petrological and geochemical aspects. Miner. Pet. 50, 113 /138. Dall’Agnol, R., Costi, H.T., Leite, A.A.S., Magalhães, M.S., Teixeira, N.P., 1999a. Rapakivi granites from Brazil and adjacent areas. Precambrian Res. 95, 9 /39. 221 Dall’Agnol, R., Silva, C.M.G., Scheller, T., 1999b. Fayalitehedenbergite rhyolites of the Iriri Formation, Tapajós Gold Province, Amazonian Craton: implications for the Uatumã volcanism. In: Simpósio sobre Vulcanismo e ambientes Associados, 1. Gramado-RS. Boletim de resumos, pp. 31. Dall’Agnol, R., Rämö, O.T., Magalhães, M.S., Macambira, M.J.B., 1999c. Petrology of the anorogenic, oxidised Jamon and Musa granites, Amazonian Craton: implications for the genesis of Proterozoic A-type granites. Lithos 46, 431 / 462. Dall’Agnol, R., Lafon, J.M., Fraga, L.M., Scandolara, J.E., Barros, C.E.M., 2000. The Precambrian Evolution of the Amazonian Craton. In: 31st Int. Geol. Congress, Rio de Janeiro, Brazil, Abstr. Vol. Rio de Janeiro, Geol. Surv. Brazil [CD-ROM]. Dreher, A.M., Vlach, S.R.F., Martini, E.S.L., 1998. Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. Rev. Brasil. Geoci. 28, 397 /404. Evensen, N.M., Hamilton, P.J., O’Nions, R.K., 1978. Rareearth abundances in chondritic meteorites. Geochim. Cosmochim. Acta 42, 1199 /1212. Faraco, M.T.L., Carvalho, J.M.A., Klein, E.L., 1997. Carta metalogenética da Provı́ncia Aurı́fera do Tapajós. In: Costa, M.L.C., Angélica, R.S. (Eds.), Contribuição à Geologia da Amazônia (in Portuguese). SBG-NO, Belém, Brazil, pp. 423 /437. Ferreira, A.L., Almeida, M.E., Brito, M.F.L., Monteiro, M.A.S., 2000. Projeto especial Provı́ncia Mineral do Tapajós. Geologia e recursos minerais da folha Jacareacanga (SB.21-Y-B), Estado do Pará e Amazonas. Escala 1:250.000. Nota Explicativa. CPRM */Serviço Geológico do Brasil [CD-ROM] (in Portuguese). Figueiredo, M.A.B.M., 1999. Minerais Óxidos de Fe e Ti e Susceptibilidade Magnética em vulcânicas e granitóides Proterozóicos da Vila Riozinho, Provı́ncia Aurı́fera do Tapajós. M.Sc. Thesis, Univ. Fed. Pará, Belém, Brazil (in Portuguese). Gaudette, H.E., Lafon, J.M., Macambira, M.J.B., Moura, C.A.V., Scheller, T., 1998. Comparison of single filament Pb evaporation/ionization zircon ages with conventional U /Pb results: examples from the Precambrian of Brazil. J. South Am. Earth Sci. 11, 351 /363. Groves, D.I., Goldfard, R.J., Gebre-Mariam, M., Hegemann, S.G., Robert, F., 1998. Orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geol. Rev. 13, 7 /27. Huppert, H.E., Sparks, R.S.J., 1988. The generation of granitic magmas by intrusion of basalt into continental crust. J. Pet. 29, 599 /624. Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification of the common volcanic rocks. Can. J. Earth Sci. 8, 523 /546. Ishihara, S., 1981. The granitoid series and mineralization. Econ. Geol. 75, 458 /484. 222 C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 Jacobi, P., 1999. The discovery of epithermal Au /Cu /Mo Proterozoic deposits in the Tapajós province, Brazil. Rev. Brasil. Geoci. 29 (2), 277 /279. Juliani, C., Nunes, C.M.D., Bettencourt, J.S., Silva, R.M.C., Monteiro, L.V.S.M., Neumann, R., Alcover Neto, A., Rye, R.O., 2000. Early Proterozoic volcanic-hosted quartz-allunite epithermal deposit in the Tapajós Gold Province, Amazonian Craton, Brazil, Geol. Soc. Am. Abstr. Progr. 32 (7), A-49. King, P.L., White, A.J.R., Chappell, B.W., Allen, C.M., 1997. Characterization and origin of aluminous A-type granites from the Lachlan Fold Belt, southeastern Australia. J. Pet. 38, 371 /391. Klein, E.L., Vasquez, M.L., 2000. Projeto especial Provı́ncia Mineral do Tapajós. Geologia e recursos minerais da folha Vila Riozinho (SB.21-Z-A), Estado do Pará, escala 1:250.000. Nota Explicativa. CPRM */Serviço Geológico do Brasil [CD-ROM] (in Portuguese). Klein, E.L., Santos, R.A., Fuzikawa, K., Angélica, R.S., 2001. Hydrothermal fluid evolution and structural control of the Guarim mineralizations, Tapajós province, Amazonian Craton, Brazil. Miner. Deposita 36 (2), 149 /164. Kober, B., 1986. Whole grain evaporation for 207Pb/206Pb age investigations on single zircons using a double filament source. Contrib. Miner. Pet. 93, 482 /490. Kober, B., 1987. Single grain evaporation combined with Pb/ emitter bedding for 207Pb/206Pb investigations using thermal ion mass spectrometry, and implications for zirconology. Contrib. Miner. Pet. 96, 63 /71. Kröner, A., Jaeckel, P., Brandl, G., Nemchin, A.A., Pidgeon, R.T., 1999. Single zircon ages for granitoid gneisses in the central zone of the Limpopo Belt, southern Africa and geodynamic significance. Precambrian Res. 93, 299 /377. Lafon, J.M., Avelar, V.G., Rossi, P., Delor, C., Guerrot, C., Pidgeon, R.T., 2000. Geochronological evidence for reworked Neoarchean crust during Transamazonian Orogeny (2.1 Ga) in the southeastern Guiana Shield. In: 31st Int. Geol. Congress, Rio de Janeiro, Brazil, Abstr. Vol. Rio de Janeiro, Geol. Surv. Brazil [CD-ROM]. Lamarão, C.N., Dall’Agnol, R., Lafon, J.M., Lima, E.F., 1999. As associações vulcânicas e plutônicas de Vila Riozinho e Morais Almeida, Provı́ncia Aurı́fera do Tapajós, SW do estado do Pará. In: Simpósio sobre Vulcanismo e Ambientes Associados. 1, Gramado */RS, Boletim de resumos, pp. 93 (in Portuguese). Lameyre, J., Bowden, P., 1982. Plutonic rock types series discrimination of various granitoid series and related rocks. J. Volc. Geoth. Res. 14, 169 /186. Le Maitre, R.W., Batemman, P., Dudex, A., Keller, J., Lameyre, J., Le Bassabine, P.A., Schmid, R., Sorensen, H., Streckeisen, A., Woolley, A.R., Zannetin, B., 1989. A Classification of Igneous Rocks and Glossary of Terms. Blackwell, London. Leake, B.E., 1997. Nomenclature of amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names. Miner. Mag. 61, 295 /321. 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. J. South Am. Earth Sci. 11, 67 /77. Lowell G.R., The Butler Hill caldera: a mid-Proterozoic ignimbrite-granite complex. In: I. Haapala, K.C. Condie (Eds.), Precambrian Granitoid-Petrogenesis-Geochemistry and Metallogeny, Precambrian Res., 51, 1991, 245 /263. Machado, N., Lindenmayer, Z.G., Krogh, T.E., Lindenmayer, D., 1991. U /Pb geochronology of Archean magmatism and basement reactivation in the Carajás area, Amazon shield, Brazil. Precambrian Res. 49, 329 /354. Mariano, G., Sial, A.N., 1993. High K-calc-alkalic vs. shoshonitic granitic magmatism in northeast Brazil. An. Acad. Bras. Ci. 65, 119 /129. Meen, J.K., 1987. Formation of shoshonites from calc-alkaline basalt magmas: geochemical and experimental constraints from the type locality. Contrib. Miner. Pet. 97, 333 /351. Moura, C.A.V., Gorayeb, P.S.S., Matsuda, N.S., 1999. Geocronologia Pb /Pb em zircão do Riolito Vila Raiol, Formação Iriri-Sudoeste do Pará. In: 6th Simpósio de Geologia da Amazônia. SBG/NO, Manaus, Brazil, Boletim de resumos expandidos, pp. 475 /477 (in Portuguese). Moura, M.A., 1998. O Maciço Granı́tico Matupá e o depósito de ouro Serrinha (MT): Petrologia, Alteração Hidrotermal e Metalogenia. Doctorate Thesis, Univ. Brası́lia (DF), Brazil (in Portuguese). Nachit, H., Razafimahefa, N., Stussi, J.-M., Carron, J.-P., 1985. Composition chimique des biotites et typologie magmatique des granitoı̈des. C.R. Acad. Sci. Paris 301 (Série II), 813 /818. Nardi, L.V.S., 1986. As rochas granitóides da série shoshonı́tica. Rev. Brasil. Geoci. 16, 3 /10 (in Portuguese). Nardi, L.V.S., Lima, E.F., 1985. A Associação Shoshonı́tica de Lavras do Sul, RS. Rev. Brasil. Geoci. 15 (2), 139 /146 (in Portuguese). Neves, S.P., Mariano, G., 1997. High-K calc-alkalic plutons in northeast Brazil: Origin of the biotite diorite/quartz monzonite to granite association and implications for the evolution of the Borborema Province. Int. Geol. Rev. 39, 621 /638. Nunes, C.M.D., Juliani, C., Silva, R.H.C., Bettencourt, J.S., Jacobi, P., 2000. Paleoproterozoic quartz-alunite epithermal gold mineralization from Tapajós (Brazil). In: 31st Int. Geol. Congress, Rio de Janeiro, Brazil, Abstr. Vol. Rio de Janeiro, Geol. Surv. Brazil [CD-ROM]. Pearce, J.A., 1996. Source and settings of granitic rocks. Episodes 19 (4), 120 /125. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Pet. 25, 956 /983. Peccerilo, A., Taylor, S.R., 1976. Geochemistry of Eocene calcalkaline volcanic rocks from the Kastamonu area, northern Turkey. Contrib. Miner. Pet. 58, 63 /81. Pinho, M.A.S.B., VanSchmus, W.R., Chemale Jr., F., 2001. Nd isotopic compositions, U /Pb age and geochemistry of Paleoproterozoic magmatism of the southwestern Amazo- C.N. Lamarão et al. / Precambrian Research 119 (2002) 189 /223 nian craton-Mato Grosso-Brazil. In: Bettencourt, J.S., Teixeira, W., Pacca, I.I.G., Geraldes, M.C., Sparrenberger, I. (Eds.), Work-shop Geology of the SW Amazonian craton: State-of-the-Art, São Paulo, Ext. Abstr., pp. 83 /85. Pitcher, W.S., 1983. Granite type and tectonic environment. In: Hsu, K. (Ed.), Mountain Building Processes. Academic Press, London, pp. 19 /40. Pitcher, W.S., 1987. Granites and yet more granites forty years on. Geol. Rund. 76, 51 /79. Rajesh, H.M., 2000. Characterization and origin of a compositionally zoned aluminous A-type granite from South India. Geol. Mag. 137 (3), 291 /318. Reis, N.J., Faria, M.S.G., Fraga, L.M.B., Haddad, R.C., 2000. Orosirian calc-alkaline volcanism and the Orocaima event in the northern Amazonian craton, eastern Roraima state, Brazil. Rev. Brasil. Geoci. 30, 380 /383. Rickwood, P., 1989. Boundary lines within petrologic diagrams which use oxides of major and minor elements. Lithos 22, 247 /263. Roberts, M.P., Clemens, J.D., 1993. Origin of highpotassium, calc-alkaline, I-type granitoids. Geology 21, 825 /828. Santos, J.O.S., Hartmann, L.A., Gaudette, H.E., Groves, D.I., McNaughton, N.J., Fletcher, I.R., 2000. A new understanding of the provinces of the Amazon craton based on integration of field mapping and U /Pb and Sm-Nd geochronology. Gondwana Res. 3, 453 /488. Sato, K., Tassinari, C.C.G., 1997. Principais eventos de acreção continental no Cráton Amazônico baseados em idademodelo Sm-Nd, calculada em evoluções de estágio único e estágio duplo. In: Costa, M.L.C., Angélica, R.S. (Eds.), Contribuição à Geologia da Amazônia (in Portuguese). SBG-NO, Belém, Brazil, pp. 91 /142. Sial, A.N., 1986. Granite-types in northeast Brazil: current knowledge. Rev. Brasil. Geoci. 16, 54 /72. Sial, A.N., Ferreira, V.P., 1990. Granitoids in northeastern Brazil: oxygen and sulfur isotope compositions and depth of emplacement. J. South Am. Earth Sci. 3, 103 /112. Sial, A.N., Dall’Agnol, R., Ferreira, V.P., Nardi, L.V.S., Pimentel, M.M., Wiedemann, C.M., 1999. Precambrian granitic magmatism in Brazil. Episodes 22, 191 /198. 223 Sidder, G.B., Mendoza, S.V., 1991. Geology of the Venezuelan Guayana Shield and its relation to the entire Guayana Shield. U.S. Geol. Surv. Open-File Rep., 91 /141. Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotopic evolution by a two stage model. Earth Planet Sci. Lett. 26, 207 /221. Streckeisen, A.L., 1976. To each plutonic rock its proper name. Earth Sci. Rev. 12, 1 /33. Tassinari, C.C.G., Macambira, M.J.B., 1999. Geochronological provinces of the Amazonian craton. Episodes 22 (3), 174 / 182. Teixeira, N.P., Bettencourt, J.S., Moura, C.A.V., Dall’Agnol, R., 1998. Pb /Pb and Sm-Nd constraints of the Velho Guilherme Intrusive suite and volcanic rocks of the Uatumã Group, south-southeastern Pará, Brazil. In: Van Schmus, W.R., B.A. Brown, M.G. Mudrey Jr. (Eds.), Proterozoic Granite Systems of the Penokean Terrane in Wisconsin, USA. IGCP Project 426 International Field Conference, September 13 /19, 1998. Wisconsin Geol. Nat. Hist. Surv. Open File Rep. 1998-10, pp. 178 /180. Teixeira, W., Tassinari, C.C.G., Cordani, U.G., Kawashita, K., 1989. A review of the geochronology of the Amazonian craton: tectonic implications. Precambrian Res. 42, 213 / 227. Vanderhaeghe, O., Ledru, P., Thiéblemont, D., Egal, E., Cocherie, A., Tegyey, M., Milési, J.J., 1998. Contrasting mechanism of crustal growth geodynamic evolution of the Paleoproterozoic granite /greenstone belts of French Guiana. Precambrian Res. 42, 165 /193. Vasquez, M.L., Klein, E.L., Macambira, M.J.B., Santos, A., Bahia, R.B.C., Ricci, P.S., Quadros, M.L.E.S., 2000. Geochronology of granitoids, mafic intrusions and mineralizations of the Tapajós Gold Province-Amazonian Craton-Brazil. In: 31st Int. Geol. Congress, Rio de Janeiro, Brazil, Abstr. Vol. Rio de Janeiro, Geol. Surv. Brazil [CDROM]. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Miner. Pet. 95, 407 /419. Wood, D.A., 1979. A variably veined suboceanic upper mantle */genetic significance for mid-ocean ridge basalts from geochemical evidence. Geology 7, 499 /503.
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