Proterozoic geologic evolution of the SW part of the Amazonian Craton in Mato Grosso state, Brazil

Precambrian Research 111 (2001) 91 – 128 www.elsevier.com/locate/precamres

Proterozoic geologic evolution of the SW part of the Amazonian Craton in Mato Grosso state, Brazil Mauro C. Geraldes a, W. Randall Van Schmus b,*, Kent C. Condie c, Stephanie Bell c, Wilson Teixeira a, Marly Babinski a a Instituto de Geocieˆncias, Uni6ersidade de Sa˜o Paulo, Sao Paulo, SP 05422 -970, Brazil Department of Geology, Uni6ersity of Kansas, 120 Lindley Hall, Lawrence, KS 66045, USA c Department of Earth and En6ironmental Sciences, New Mexico Institute of Technology, Socorro, NM 87801, USA b

Received 1 February 2000; accepted 1 December 2000

Abstract This paper presents new geochronologic, isotopic, and geochemical data bearing on the evolution of Proterozoic crust in SW Mato Grosso state, Brazil, which is at the southern end of the : 1.6– 1.8 Ga Rio Negro– Juruena orogenic belt of the Amazonian Craton (Amazonia). Our data define three major crustal events: (i) the Alto Jauru terrane occurs in the eastern part of the region and is comprised of island arc-related rocks with U/Pb ages from 1.79 to 1.74 Ga. These rocks have mNd(t) values range from + 2.8 to + 2.0 with crustal residence ages (TDM) from 1.93 to 1.78 Ga, indicating a mainly juvenile signature at 1.8 Ga; (ii) the Cachoeirinha suite occurs in the central part of the region and consists of calc-alkaline plutons emplaced into Alto Jauru terrane host rocks. These plutons have U/Pb ages from 1.56 to 1.54 Ga and mNd(t) values ranging from +1.0 to −0.8, with crustal residence ages (TDM) from 1.88 to 1.75 Ga. We interpret this orogen as the roots of a continental margin arc built upon basement comprised of the Alto Jauru terrane; (iii) the Santa Helena batholith occurs in the western part of the region and is a large, elongate body of calc-alkaline rocks ranging from granodiorite to highly evolved granite. These units yield U/Pb ages from 1.45 Ma to 1.42 Ga, with mNd(t) values ranging from + 4.1 to + 2.6 and crustal residence ages (TDM) from 1.70 to 1.50 Ga. The Rio Alegre domain occurs west of the Santa Helena batholith and includes juvenile 1.52 to 1.47 Ga volcanic and mafic plutonic rocks. Regional geologic relationships suggest that these rocks are part of the crust into which the Santa Helena batholith was emplaced. We interpret this batholith as the magmatic core of a juvenile arc accreted to the edge of the Alto Jauru terrane, with incorporation of some older crust (Alto Jauru terrane) in the east and derivation from mainly juvenile crust (Rio Alegre domain) in the west. The Rio Branco suite occurs to the east of exposed Alto Jauru terrane rocks as large hills protruding through younger Aquapeı´ Group sedimentary rocks. It consists of gabbro and granophyric rocks with U/Pb ages of 1.47 Ga (gabbro) and 1.43 Ga (granophyre) and inherited older Nd, suggesting hinterland derivation from Alto Jauru terrane basement during development of the Santa Helena batholith. Several undeformed 1.5–1.4 Ga granitic plutons occur within the Alto Jauru terrane; these are also regarded as inboard manifestations of subduction related magmatism associated with accretion of the Rio

* Corresponding author. Tel.: + 1-785-8644974; fax: + 1-785-8645276. E-mail address: [email protected] (W.R. Van Schmus). 0301-9268/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 1 - 9 2 6 8 ( 0 1 ) 0 0 1 5 8 - 9

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Alegre domain and formation of the Santa Helena batholith. The siliciclastic Aguapeı´ Group was deposited sometime between 1.0 and 1.4 Ga; it overlies Jauru terrane basement, rocks of the Santa. Helena batholith, and the Rio Alegre domain. In the east, it is flat-lying and undeformed, but in the west it is deformed and metamorphosed in the NNW trending Aguapeı´ thrust belt. Farther west the Aguapeı´ Group is horizontal, undeformed, and overlies the Paleoproterozoic Paragua block in Bolivia, where it has been correlated with the Sunsa´ s Group. The Aguapeı´ thrust belt has K/Ar cooling ages of about 930 Ma and is apparently a foreland fold and thrust belt formed by reactivation of an older rift basin during the 1.0 Ga Sunsa´ s orogeny, which occurs west of the Paragua block in Bolivia. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Brazil; Amazon craton; Mesoproterozoic; Paleoproterozoic; Geochronology

1. Introduction The Amazonian Craton (Amazonia) is an important component in many supercontinent reconstructions. In Rodinia reconstructions, for example, it has been proposed that Amazonia collided with Laurentia– Baltica during the 1.1– 1.0 Ga Grenvillian orogeny (Dalziel, 1991; Hoffman, 1991; Dalziel, 1992). In SW Amazonia, recently improved access has enabled studies leading to the identification of new tectonostratigraphic units and acquisition of U/Pb and Sm/Nd geochronologic data. These studies include the work of Bettencourt et al. (1996) who concluded that paleomagnetic and geochonologic data support the juxtaposition of Amazonia with Laurentia – Baltica : 1000 Ma, and that of Sadowski and Bettencourt (1996) who suggested that Amazonia was joined to Laurentia– Baltica at 1.6 Ga. Other recent advances in mapping SW Amazonia and newly acquired geochronological and geological data (Tassinari et al., 1996; Pinho et al., 1997; Sato and Tassinari, 1997; Geraldes et al., 1998, 1999a,b, 2000; Payolla et al., 1998; Sato, 1998; Van Schmus et al., 1998, 1999; Bettencourt et al., 1999; Rizzotto, 1999; Darbyshire, 2000; Geraldes, 2000; Leite and Saes, 2000; Tassinari et al., 2000) provide the basis for better understanding of its origin, evolution, and potential correlation with other Proterozoic terranes. The Amazonian Craton (Fig. 1) consists of older Archean cores bordered by the 2.1 Ga Maroni – Itacaiunas mobile belt, which is largely composed of mylonitized granulites and supracrustal sequences. Santos et al. (1999) recently divided the Maroni –Itacaiunas mobile belt (as used here) into the Baixo Rio Uac¸ a belt (Brazil and French

Guyana) and the Parima–Tapajo´ s belt (Surinam, Guyana, Venezuela, northern Brazil). New Sm/ Nd data (Tassinari et al., 1996) suggest that there is a major accretionary belt, the 2.0–1.8 Ga Ventuari–Tapajo´ s province, that trends NW–SE, along the SW margin of the Archean–Paleoproterozoic core. To the west of the Ventuari– Tapajo´ s province is the 1.8–1.6 Ga Rio Negro–Juruena province. The basement of this belt is dominated by granitic, granodioritic, and tonalitic gneisses and migmatites. At present, two main magmatic events have been defined in this province. The first is defined by ages of 1.79–1.72 Ga for older gneissic and supracrustal rocks (Carneiro et al., 1992; Bettencourt et al., 1996, 1999; Tassinari et al., 1996, 2000; Pinho et al., 1997). The second event occurred 1.57–1.52 Ga and consists of rapakivi granites to the NW in Rondoˆ nia (Serra da Provideˆ ncia suite: Bettencourt et al., 1999) and newly defined calc-alkaline granitoids to the SE in Mato Grosso (Cachoerinha suite: Geraldes, 2000; this work). The Rondoˆ nia–San Ignacio province of SW Amazonia (Litherland et al., 1989) is parallel to and outboard of the Rio Negro–Juruena province and is exposed in Brazil and Bolivia. Rondoˆ niaSan Ignacio events have traditionally been regarded as extending from 1.5 to 1.3 Ga, with a wide geographic distribution (Litherland et al., 1989; Sadowski and Bettencourt, 1996). Our results demonstrate that most early Mesoproterozoic events in SW Mato Grosso occurred between 1.5 and 1.4 Ga; these include the newly recognized 1.52–1.47 Ga juvenile rocks in the Rio Alegre domain and the 1.45–1.42 Ga Santa Helena batholith. Rondoˆ nia –San Ignacio province events are still not well defined to the NW in Rondonia

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or to the west in Bolivia and may include events younger than 1.4 Ga (Bettencourt et al., 1999). New Sm/Nd data (Darbyshire, 2000) indicate that much of the Rondoˆ nia –San Ignacio province basement in Bolivia is late Paleoproterozoic and may consist of westward outliers of the Rio Negro–Juruena province. Both the Rio Negro– Juruena province and Rondoˆ nia – San Ignacio province were intruded by a variety of late Meso-

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proterozoic (1.3– 1.0 Ga) granitic plutons (Bettencourt et al., 1999; Geraldes, 2000). Low grade to undeformed supracrustal sequences (e.g. Aguapeı´ Group) locally overlie basement of the Rio Negro–Juruena and Rondoˆ nia –San Ignacio provinces. The : 1 Ga Sunsa´ s province occurs west of the Rondoˆ nia – San Ignacio province in Bolivia (Litherland et al., 1989) and includes the Nova Brasilaˆ ndia terrane

Fig. 1. Geologic sketch map of Amazon Craton. (1) Archean core; (2) Maroni-Itacaiunas province; (3) Ventuari – Tapajo´ s province; (4) Rio Negro – Juruena province; (5) Rondoˆ nia–San Ignacio province; (6) Sunsa´ s, Aguapeı´ and Nova Brasilaˆ ndia belts; (7) Brasiliano– Pan African belt (620 –580 Ma); (8) Phanerozoic sedimentary rocks; (9) province limits; and (10) national borders. The outline of Mato Grosso State is shown in the map. Modified after Teixeira et al. (1989).

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Table 1 Summary of major geologic formations and events (based on results from this work) Age (Ma)

Name

Rock types

:950

Young granites Sunsas deformation

Unknown 1380–1420 1420–1450

Aguapeı´ group Alvorada granite, etc. Rio Alegre tonalite Santa Helena batholith

1420–1450 :1500

Rio Branco suite Rio Alegre domain

:1550

Cachoerinha suite

1750–1800

Alto Jauru terrane, Jauru belt, Araputanga belt, Cabac¸ al belt

Undeformed granites, young dikes. Thrust faults, folds, low to medium grade metamorphism Sandstones, conglomerates Undeformed granite (Alto Jauru terrane) Deformed tonalite (Rio Alegre domain) Strongly foliated granites with less deformed late-stage granitic and pegmatitic dikes Gabbro, granophyre, hybrid mixtures Mafic to intermediate volcanics, plutons; variably deformed and metamorphosed. Metasedimentary rocks (chert, iron-fm.) Variably deformed tonalite to granite (commonly well foliated) Metabasalts, metatonalites, metasedimentary rocks (greenstone belt sequences); granitic to tonalitic gneisses

in Rondoˆ nia (Rizzotto et al., 1998; Rizzotto, 1999). Deformation in the Aguapeı´ thrust belt in SW Mato Grosso (Saes et al., 1992) is apparently coeval with that in the Sunsa´ s province, and some authors have shown the Aguapeı´ thrust belt as a branch of the Sunsa´ s province (Fig. 1). This paper presents a summary of the 1.8– 1.0 Ga evolution of SW Amazonia in Mato Grosso based on new geochronologic and geochemical data obtained by the authors and data recently available in the literature; Table 1 summarizes the major units described in this report. The bulk of the new analytical data consist of U/Pb ages using zircons (University of Kansas), Sm/Nd crustal residence (TDM) ages (University of Kansas), whole-rock major and trace element analyses (New Mexico Tech), and initial Pb isotope compositions of plutonic rocks using Pb extracted from K-feldspars (University of Sa˜ o Paulo). Brief sample descriptions are presented in Appendix A, analytical methods are presented in Appendix B, and analytical data are presented in Appendix C and Appendix D. Results are summarized below in Sections 2–7, followed by general discussion of their regional and global significance (Section 8). To conserve space, we only included here a few representative concordia plots for U/Pb samples, although regression details for all samples are included in Appendices A and B.

2. Alto Jauru terrane Proterozoic basement in SW Mato Grosso consists of igneous and metamorphic rocks that were interpreted by Tassinari et al. (1996) as SE extensions of the Rio Negro–Juruena province. Precambrian basement in the eastern part of the region (Fig. 2) includes several domains of distinctly different rock types, including several volcano-sedimentary belts, felsic orthogneisses, and intrusive granitoids. Volcanic rocks were designated initially by Saes et al. (1984) as the Quatro Meninas volcanic complex and later as the Alto Jauru greenstone belt by Monteiro et al. (1986). In this paper, we will refer to the region as the Alto Jauru terrane, to recognize its probable tectonicstratigraphic origins. Three smaller belts of supracrustal rocks were recognized within the overall terrane; from east to west they are the Cabac¸ al, Araputanga and Jauru volcanic belts, and they are separated by orthogneisses that may represent basement to the supracrustal rocks, subsequently deformed intrusive complexes, or both. Carneiro (1985) and Carneiro et al. (1992) described Paleoproterozoic and Mesoproterozoic rocks in the region of Sao Jose´ dos Quatro Marcos (SE Alto Jauru terrane), suggesting at least two rock suites: gray orthogneisses (Rb/Sr age of 19719 70 Ma) and pink gneisses and granites

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exhibiting ages ranging from 1.74 Ga to 1.40 Ga (Rb/Sr whole-rock isochrons). Tassinari et al. (1996) reported a Pb/Pb isochron age of 17179 20 Ma for orthogneiss in the Jauru River area. Chemical results of plutonic rocks (tonalites and granodiorites) from the Alto Jauru terrane reported by Toledo (1997) and Pinho (1996) indicated a tonalite–trodhjemite affinity, whereas results reported by Geraldes et al. (1998) indicated a calc-alkaline tonalite-granodiorite trend. As we show below, however, many of the granitiod rocks included in these prior studies are of different ages, making interpretations of their geochemical data suspect. Pinho et al. (1997) reported

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chemical results for volcanic rocks from the Jauru volcanic belt in the western Alto Jauru terrane that indicate a possible ocean-floor (MORB?) origin. In contrast to the ultramafic to mafic rocks observed in the western part of the Alto Jauru terrane (Jauru belt), the intermediate to felsic volcanic units in the Cabac¸ al belt (Pinho, 1996) have a predominantly calc-alkaline magmatic affinity. This allowed Pinho et al. (1997) to suggest that the Jauru volcanic belt (western Alto Jauru terrane) formed in an oceanic ridge setting, while the Cabac¸ al volcanic belt (eastern Alto Jauru terrane) was formed in an arc-related setting. Younger granitoids of different compositions

Fig. 2. Regional geologic map of SW Mato Grosso showing the major geologic units, structures, and key sample localities. Modified from Anexo I of Ruiz (1992). Cachoerinha suite rocks in the Alto Jauru terrane are not shown separately because current mapping has not resolved them from basement gneisses in most of the area.

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Table 2 Summary of U/Pb ages and Sm/Nd results for the Alto Jauru terranea U/Pb age (Ma)

mNd(0)

mNd(t)

Cabac¸ al greenstone belt 97-130 Cabac¸ al gabbro 97-131 Metasediment, Cabac¸ al mine 97-133 Granitic gneiss near Santa Fe 97-149 Alianca gneiss, Cachoerinha area

Not determined 1758 9 27 1790 9 24 1740 9 27

−11.9 −17.7 −18.1 −18.1

– 2.8 2.2 2.4

Cachoeirinha suite 97-132 Granite, S.J. de Quatro Marcos area 97-134 Tonalite, S. 3. de Quatro Marcos area 97-138 Gneissic granite, Cachoerinha area 97-145 Santa Cruz granite, Cachoerinha area 97-150 Gneissic tonalite, Cachoeirinha area

1564 9 15 1536 9 05 1536 9 04 1556 9 03 1546 9 09

−19.6??0.9 −14.1??0.5 −22.2??0.5 −20.2??0.9 −14.7??1.0

1.78 1.88 1.75 1.79 1.83

Other intrusi6e granitoids 97-129 Alvorada Granite (type locality) 97-136 Agua Clara type granodiorite 97-139 Granite, undeformed, Cachoerinha area

1389 9 03 1480 9 08 Not determined

−20.3 −17.2??1.7 −20.2

−1.3 1.78

Field number

a

Description (Ma)

TDM (Ga)

1.77 1.87 1.93 1.87

1.77 1.74

See Appendices A, B, C and D for details.

have been distinguished from basement rocks by Saes et al. (1984), Leite (1989), and Ruiz (1992).

2.1. Cabac¸ al 6olcanic belt Monteiro et al. (1986) described the following sequence for the Cabac¸ al volcanic belt: The lowest unit comprises massive amygdaloidal and variolitic lavas and volcanic breccias. These are locally overlain by intermediate metavolcanic rocks (andesitic lavas and tuffs interlayered with felsic lavas, tuffs and metapelites). The next youngest unit includes dacite– rhyodacite lavas, tuffs, and epiclastic rocks that contain the main gold- and silver-bearing units of the Cabac¸ al mine (Pinho, 1996; Toledo, 1997). The felsic metatuffs are overlain by metasedimentary units, which locally include quartz–sericite– chlorite schists. Epiclastic debris is common, together with metacherts and, locally, garnetiferous magnetite-bearing banded iron formation. The latter two were interpreted by Pinho et al. (1997) as chemical sediments. At present relatively few U/Pb ages exist from older rocks of the Alto Jauru terrane, and all of them come from the Cabac¸ al volcanic belt (Table 2). A banded silicic volcaniclastic metasediment (97-131) from the Cabac¸ al gold mine yielded zir-

cons with a U/Pb age of 17589 7 Ma (Fig. 3) that we interpret as the crystallization age for the zircons; it is probably close to the depositional age of the metasedimentary sequence. Pinho (1996) reported SHRIMP U/Pb data for individual zircons from a metavolcanic unit in the area and obtained an age grouping at 17699 29 Ma and a second grouping at 17249 30 Ma. These results are consistent with volcanism and deposition about 1750 Ma. The TDM for 97–131 is 1.87 Ga with mNd(t) of 2.4 (Table 2), indicating that the source for this rock was largely juvenile at 1750 Ma. Plutonic rocks of tonalitic to granitic composition were also described in the region of the Cabac¸ al belt, and they were considered coeval with the volcanic rocks. Carneiro et al., (1992) described the petrography and Sr isotopes in a unit named ‘Pink Gneiss’, reporting a Rb/Sr isochron, which yielded an imprecise age of 17349226 Ma and an initial 87Sr/86Sr ratio of 0.7019. U/Pb dating of three zircon fractions from this rock yielded an age of 17909 24 Ma (Table 2); Sm/Nd whole-rock analysis yielded TDM = 1.93 Ga and mNd(t)= 2.2. Ruiz (1992) mapped the area around the town of Cachoerinha (Fig. 2) and described several orthogneisses, which are in-

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

truded by undeformed granite. Most of the gneisses are Mesoproterozoic and are discussed below (Section 2.2). Only one of the units mapped by Ruiz, the Alianc¸ a Gneiss (97-149), yielded a Paleoproterozoic U/Pb zircon age (17409 27 Ma); Sm/Nd whole-rock analysis yielded TDM = 1.87 Ga and mNd(t)=2.4. Thus, it appears that the older crust in the eastern part of the Alto Jauru terrane formed about 1.74– 1.79 Ga from juvenile or very young sources; no comparable ages have been obtained from the western part of the terrane yet, although work continues.

2.2. Cachoeirinha plutonic suite The existence of the Cachoeirinha plutonic suite is a new discovery and was revealed by our U/Pb dating program (Table 2). This suite represents an important rock generation event about 1565– 1535 Ma in the region. Prior to our study, these rocks were thought to be generally coeval with the units of the adjacent Cabac¸ al, Araputanga, and Juaru volcanic belts (e.g., : 1.7 – 1.8 Ga).

97

Host rocks to the Cachoeirinha suite are represented locally by units of the Alto Jauru terrane; supracrustal rocks coeval with the Cachoeirinha plutonic suite have not yet been found. Rocks of the Cachoeirinha suite were initially described by Figueiredo et al. (1974) and Barros et al. (1982) as part of the Xingu Complex (presumed at that time to be Archean basement). Subsequent work by Ruiz (1992) in the Cachoeirinha region placed these units in the Paleoproterozoic, but he did not differentiate them from older basement. Tonalites now known to be part of the Cachoeirinha suite were also observed in the Sa˜ o Jose´ dos Quatro Marcos region (Carneiro et al., 1992), and undated tonalites, granodiorites and granites which we now ascribed to Cachoeirinha suite occur in the Jauru region (western part of the Alto Jauru terrane), where they intrude gneissic basement. The Cachoeirinha suite comprises a group of coeval, but not necessarily comagmatic, plutons, each with a distinct composition and structural history. Rocks in the Cachoeirinha suite range from granite to tonalite in composition (Table 3), with single plutons having limited ranges in com-

Fig. 3. Plot of zircon data for sample 97-131, a tuffaceous metasediment from the Cabac¸ al mine in the Cabac¸ al volcanic belt. Regression does not include most discordant analysis (box). Uncertainties at 2|.

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Table 3 Representative chemical analysis of granitic and related rocks from southwestern Mato Grossoa Santa Helena batholith

Cachoeirinha suite

Central zone 115

Marginal zone

116c

116f

105

169

108

132

134

138

145

147

77.31 0.14 11.47 1.57 0.11 0.46 3.20 5.02 0.02 0.01 0.30

74.92 0.27 12.29 1.90 0.27 0.84 3.02 5.45 0.04 0.04 0.33

76.44 0.14 12.04 1.13 0.07 0.60 2.87 5.96 0.02 0.02 0.27

68.11 0.53 14.71 4.27 1.08 3.05 3.58 3.60 0.06 0.12 0.55

75.83 0.16 13.52 1.47 0.27 0.16 3.5 4.86 0.03 0.02 0.15

73.88 0.12 13.53 1.12 0.28 1.23 3.49 4.74 0.03 0.04 0.26

69.79 0.35 15.05 3.03 0.88 2.93 4.11 2.50 0.05 0.10 0.66

70.31 0.33 15.31 2.96 0.84 2.95 4.18 2.59 0.05 0.10 0.30

73.27 0.22 14.04 2.05 0.4 1.3 3.48 5.14 0.03 0.09 0.10

68.26 0.52 15.73 3.94 1.02 2.62 4.61 2.79 0.05 0.21 0.20

68.87 0.53 13.42 6.01 1.04 1.37 3.50 4.07 0.18 0.13 0.46

Total

99.61

99.37

99.56

99.66

99.97

98.72

99.45

99.92

100.12

99.95

99.58

Rb Ba Sr Pb Th U Cr Ni Y Zr Nb Ga Ta Hf La Ce Nd Sm Eu Tb Yb Lu

184 284 22 26 12 8.0 5.0 2.0 86 200 21 18 1.68 6.9 63.1 91.1 56.8 13.2 0.62 2.36 8.82 1.33

270 247 43 34 21 8.0 7.0 3.0 81 205 20 17 1.60 2.4 47.7 77.0 27.2 6.11 0.11 1.32 7.17 1.14

296 21 11 35 34 16 6.0 3.0 84 172 20 18 1.60 8.2 54.6 82.6 39.9 8.43 0.38 1.65 10.6 1.65

85 1206 268 11 4.0 1.6 11 7.0 36 276 7.0 16 0.56 7.7 48.9 90.6 38 6.87 1.10 0.96 2.78 0.41

101 937 83 11 5.2 2.7 0 0 13 76 7.0 16 0.56 2.7 10.7 32.4 9.43 2.07 0.45 0.28 1.62 0.29

168 660 138 22 6.0 7.0 8.0 3.0 10 95 6.0 16 0.48 5.8 44.4 63.2 28.1 4.95 1.18 0.64 1.99 0.26

63 1252 423 17 16 3.0 12 6.0 16 168 7.0 19 0.56 4.8 61.9 115 39.7 6.5 0.86 0.63 2.26 0.38

71 1206 421 28 19.2 3.65 0 0 17 180 7.9 15 0.53 4.8 55.7 101 35.0 5.31 0.91 0.44 1.69 0.29

74 2376 282 32 16.3 2.1 0 0 14 187 2.6 14 0.22 4.7 104 200 75.0 10.2 1.95 0.53 0.89 0.16

46 2134 552 19 5.8 1.1 0 0 19 236 3.7 16 0.30 5.8 50.9 95.6 41.7 6.67 2.12 0.53 1.33 0.22

106 1183 301 18 6.4 1.6 0 0 35 139 7.8 16 0.62 3.9 35.8 68.6 36.3 7.66 1.77 0.95 3.43 0.54

A/CNK ZNCY [La/Yb]n

0.99 398.1 4.34

0.99 383 4.03

0.98 358.6 3.12

1.2 128.4 4.0

1.03 174.2 13.52

1.02 306 16.6

1.02 305.9 19.97

1.03 403.6 70.82

1.02 354.3 23.19

1.06 250.4 6.33

0.965 409.6 10.66

a A/CNK= Al2O3/CaO+Na2O+K2O (mole ratio); ZNCY = Zr+Nb+Ce+Y (ppm); [La/Yb]n=chondrite-normalized ratio; major elements as oxides in weight percent; trace elements in ppm.

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SiO2 TiO2 Al2O3 Fe2O3T MgO CaO Na2O K2O MnO P2O5 LOI

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Fig. 4. Plot of zircon data for sample 97-150, a representative member of the Cachoerinha suite. Regression forced through the origin because of clustering of analyses near concordia. Uncertainties at 2|.

position. Most granitoids from the Cachoeirinha suite are medium to fine grained. Plagioclase ranges from 25 to 40%, K-feldspar from 10 to 35%, quartz from 20 to 30%, and biotite from 5 to 15%. Hornblende is common in some of the granodiorites and tonalites of this suite, and accessory phases include, sphene, zircon, iron oxides, and apatite. Plagioclase is usually partially sericitized (15 – 35%) and K-feldspars are altered chiefly around grain boundaries. Both hornblende and biotite are partially altered to chlorite. U/Pb ages for the Cachoerinha suite cluster tightly around 1550 Ma (Table 2), as exemplified by a the Sa˜ o Domingos gneiss (97-145), which yielded a U/Pb zircon age of 15569 03 Ma (Fig. 4); Sm/Nd analysis yielded mNd(t) = + 0.9 and TDM = 1.79 Ga. Granitic rocks of the Cachoeirinha suite are apparently widespread; a granite from the Cachoeirinha region (97-138) yielded a U/Pb age of 153694 Ma with mNd(t) = + 0.5 and TDM = 1.75 Ga; a granite in the Sa˜ o Jose´ dos Quatro Marcos region (97-132) yielded a U/Pb age of 15649 15 Ma with mNd(t) = + 0.9 and

TDM = 1.78 Ga; a tonalite (97-134) in the Sa˜ o Jose´ dos Quatro Marcos region yielded a U/Pb age of 153695 Ma with mNd(t)= + 0.5 and TDM = 1.88 Ga; and a tonalite in the Cachoeirinha region (97-150) yielded a U/Pb age of 15469 9 Ma with mNd(t)= + 1.0 and TDM = 1.83 Ga (Table 1). The Cachoeirinha plutonic suite is still considered part of the Rio Negro–Juruena province, but the Sm/ Nd data clearly show that it represents early Mesoproterozoic melting of late Paleoproterozoic Alto Jauru terrane juvenile crust.

2.3. Geochemical results for the Cachoerinha suite From the large suite of granitoid samples collected from SW Mato Grosso, we selected two populations for detailed geochemical studies: the Cachoeirinha suite (: 1550 Ma) from the eastern part of the Alto Jauru terrane and the 1450-Ma Santa Helena batholith in the west (Section 3). In the Cachoeirinha suite, SiO2 ranges from about 68–73% and, if our sampling is representative, it does not contain highly evolved (high-K, Rb)

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Fig. 5. A/CNK vs. ZNCY plot for granitoids from the Cachoerinha suite.

phases like those in the Santa Helena batholith (Table 3; Section 3). Cachoeirinha granitoids plot near the peraluminous – metaluminous boundary on an A/CNK versus ZNCY diagram, and show mixed I- and A-type affinities, with four out of the five samples analyzed falling in the I-type field (Fig. 5). On primitive-mantle normalized plots all samples show an overall enrichment in incompatible elements (Fig. 6; Table 3). In addition, the samples show negative Ta/Nb and positive Pb anomalies, a feature characteristic of subduction related magmas. Both granitoid suites show negative P and Ti anomalies, but the size of these anomalies is much

greater in the Santa Helena samples (Section 3) than in the Cachoeirinha suite; the Cachoeirinha suite does not show significant negative Sr anomalies. The variations in K, Rb, and Ba distributions may reflect later remobilization of these elements. REE data for the Cachoeirinha suite (not shown) have steep LREE patterns and relatively flat HREE patterns with moderately negative to absent Eu anomalies. Both major and trace elements in the Cachoeirinha granitoids show distributions characteristic of fractional crystallization. We have modeled fractional crystallization using mass balance relations and Raleigh fractionation for the trace elements Rb, Sr, and Ba using the methods described in Rollinson (1993). An increasing Rb/Sr ratio with decreasing Sr content can be explained by removal of plagioclase, K-feldspar, and biotite in the approximate proportions that they occur in the rocks (shown below with Santa Helena batholith data, Section 3). The relative depletions in Sr, P, and Ti shown on the primitive-mantle normalized graphs (Fig. 6), as well as the slightly negative Eu anomalies, probably reflect fractional crystallization of feldspars, apatite, and ilmenite or sphene. Mass balance calculations for the Cachoeirinha granitoid suites confirm that the major element patterns on silica variation diagrams also can be explained by fractional crystallization (Bell, 2000).

Fig. 6. Variation diagram showing concentrations of selected trace elements in Cachoerinha suite samples normalized to concentrations in primitive mantle.

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2.4. Post-Cachoerinha plutonic rocks in the Alto Jauru terrane Mapping in the Alto Jauru terrane has revealed numerous less deformed to undeformed plutonic units emplaced into the older gneissic and supracrustal complexes. These include the Alvorada granite in the type area on Alvorada farm (Monteiro et al., 1986; Toledo, 1997), several plutons correlated with the Alvorada granite by Carneiro et al., (1992), the Agua Clara granodiorite (Saes et al., 1984; Monteiro et al., 1986; Matos et al., 1996) which is described as the largest batholith in Jauru region (600 km2), and other unnamed plutons. Some of these have been shown by our data to be part of the Cahoeirinha suite (e.g. 97-132). The others are distinctly younger than the Cahoeirinha suite. Alvorada granite (97-129) from the type area yielded a U/Pb age of 138993 Ma, while Sm/Nd analysis yielded mNd(t) = − 1.3 and TDM =1.77 Ga (Table 1). Agua Clara type granodiorite from the Cachoerinha area (Table 2) yielded a U/Pb age of 148098 Ma with mNd(t) = + 1.7 and TDM = 1.78 Ga. A few other younger plutons were also studied (e.g., 97-139, Table 2), but the zircon data were not co-linear, possibly due to inheritance. These will have to be studied further. Nonetheless, there appears to be a significant pulse of 1.4–1.5 Ga magmatism within the Alto Jauru terrane that is younger than and unrelated to the Cachoeirinha event.

3. Santa Helena batholith

3.1. General characteristics of the Santa Helena batholith Proterozoic basement rocks of the Santa Helena batholith were initially recognized by Saes et al. (1984). These granites were later studied by Menezes et al. (1993) and Lopes et al. (1992), who renamed them Santa Helena granite– gneiss; using geochemical data, they classified the suite as intraplate A-type granites. In this paper. we will use the Santa Helena batholith designation of Saes et al. (1984). The Santa Helena batholith is bounded

101

to the west by both the Rio Alegre domain and the Aguapeı´ thrust belt (Fig. 2). Limits to the east include several domains of distinctly different rock types, including units of the Alto Jauru terrane and the Cachoeirinha plutonic suite. A group of orthogneisses in the northeast previously referred to as the Alto Guapore´ suite by some workers was also thought to be host rocks of the batholith (older basement). Our data, as presented below, now show that they are, in fact, deformed marginal phases of the batholith. The northern and southern limits of the batholith are buried beneath Phanerozoic sedimentary cover. The Santa Helena batholith is a large elongate body extending for a minimum of 35 km in an east– west direction and over 75 km in a northernly direction (Fig. 2). Although there are many textural variants of the batholith, most phases are variably deformed. The Santa Helena granites are generally characterized by a NNW trending foliation with steeply plunging lineations (Menezes et al., 1993). Lineations are best developed by the micas and hornblende, but in some samples feldspars also show the fabric and the rocks are, in effect, augen gneisses. The central zone of the Santa Helena batholith is characterized by coarsegrained facies (e.g., 97-115), which is highly deformed and intruded by medium-grained granitoid dikes that are much less deformed. The marginal zone of the Santa Helena batholith shows variable degrees of deformation; locally the rocks are mylonitized. Rocks of the Santa Helena batholith are chiefly granites, with only one sample falling in the modal granodiorite field. K-feldspar is abundant in the granites, averaging 40–50%, with quartz and plagioclase averaging 20–25%. Biotite ranges from about 5 to 10% and trace minerals include apatite, zircon, and iron oxides. Allanite was found in one sample. Quartz and feldspars are medium-grained to very coarse-grained with subhedral to anhedral shapes. Feldspars, and especially plagioclase, are variably altered to sericite and clays, and in the most intensely altered rocks quartz is recrystallized into many anhedral patches. Perthitic textures are common in the K-feldspars. Biotite shows incipient chloritization in most samples, but alteration is locally intense

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Table 4 Summary of U/Pb and Sm/Nd results for rock units of the Santa Helena batholitha Field number

Description

U/Pb age (Ma)

mNd(0)

mNd(t)

TDM (Ga)

97-102 97-105 97-106 97-108 97-115 97-120E 97-120W 97-120P 97-135 97-168 97-169

Granodioritic augen gneiss Granitic augen gneiss Granodioritic gneiss Granodioritic augen gneiss Santa Helena granite Cardoso gneissic granite Cardoso magnetite-granite Pegmatite vein in 97-120E Santa Elina granite Ellus farm granite Ellus mine granite

1449 904 1424 907 1423 9 13 1456 934 1433 910 1422 9 04 1423 9 15 1419 9 09 1444 9 13 1430 9 20 1444 9 15

−15.5 −12.8 −8.6 −11.8 −8.9 −13.4 −11.7 −4.9 −10.2 −11.1 −10.8

+2.9 +2.8 +4.0 +3.4 +3.1 +3.9 +3.6 +3.1 +2.7 +3.7 +3.6

1.56 1.57 1.49 1.54 1.62 1.48 1.52 1.63 1.55 1.52 1.51

a

See Appendices A, B, C and D for details.

in some rocks of the marginal zone. The marginal zone of the Santa Helena batholith also contains less K-feldspar (averaging about 30– 40%) and more biotite (averaging 15%) than the central zone.

3.2. Geochronology of the Santa Helena batholith Table 4 presents U/Pb and Sm/Nd results from 11 samples distributed throughout the batholith (Fig. 2); Figs. 7 and 8 show representative plots for the U/Pb data. The U/Pb ages cluster over a relatively narrow range of 1.42– 1.45 Ga, indicating that the diverse phases of the batholith were emplaced as part of a major magmatic episode. Field and isotopic data are insufficient at present to define by themselves a precise evolutionary sequence or the total duration of the magmatism. The Sm/Nd results are also relatively uniform, with mNd(t) ranging from 92.6 to 9 4.0 and TDM ranging from 1.48 to 1.63 Ga (Table 4). The strongly positive mNd(t) values indicate that the magmas for the Santa Helena batholith were derived largely from juvenile or nearly juvenile sources. This is supported by the corresponding model ages, which are mostly less than 1.6 Ga and include values comparable to the crystallization ages. Clearly, only a small part of the magma, if any, could have come from melting crust like that in the Alto Jauru terrane, which borders the Santa Helena batholith immediately to the east.

3.3. Geochemistry of the Santa Helena batholith Both major and trace element data support the existence of two zones in the Santa Helena batholith. The central zone is characterized by high SiO2 (75–77%; Table 3) and the outer zone shows a broad range in SiO2 (66–77%). Considered collectively, the Santa Helena granite suite shows a well-developed fractionation trend on silica variation diagrams. The most evolved samples (high SiO2 and K2O; low A12O3, TiO2, etc.) are found in the central zone, suggesting fractionation in the batholith from the margins inward. With exception of one sample (97-169), which is highly sericitized, granitoids from the Santa Helena batholith plot near the peraluminous–metaluminous boundary on an A/CNK versus ZNCY diagram and show mixed I- and A-type affinities with the latter dominating (Fig. 5). A similar pattern occurs on other A-type discriminant diagrams such as those involving the Ga/Al ratio (Whalen et al., 1987). On primitive mantle normalized plots, all samples show an overall enrichment in incompatible elements (Fig. 9; Table 3). In addition, samples show negative Ta/Nb and positive Pb anomalies, a feature characteristic of subduction-related magmas. The central zone of Santa Helena batholith is relatively enriched in Rb, Th, U, REE and most HFSE (not Zr and Hf, however) and depleted in Sr, Ba, and Ti compared to the marginal zone. The Santa Helena granites show negative P and

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

Ti anomalies, but the size of these anomalies is much greater in the Santa Helena suite than in the Cachoeirinha suite (above). Unlike the Cachoeirinha suite, the Santa Helena batholith suite has significant negative Sr anomalies. The variation in K, Rb, and Ba distributions may reflect some later remobilization of these elements. The Santa Helena REE patterns (not shown) are slightly enriched in LREE and have variable slopes to the HREE; the negative Eu anomalies in the Santa Helena batholith are much larger than those in the Cachoeirinha suite. Both major and trace elements in the Santa Helena granites show distributions characteristic of fractional crystallization. We have modeled fractional crystallization using mass balance relations and Raleigh fractionation for the trace elements Rb, Sr, and Ba using the methods described in Rollinson (1993). A rapidly increasing Rb/Sr ratio with decreasing Sr content can be explained by removal of plagioclase, K-feldspar, and biotite in the approximate proportions that they occur in the rocks (Fig. 10). The highest degree of fractional crystallization is shown by the samples from the central zone of the Santa Helena

103

batholith, consistent with cooling from the margins of the batholith inwards. On a Ba/Sr plot (Fig. 11), a sharp change in slope occurs at about 150 ppm Sr in the Santa Helena suite. This can be explained by the onset of K-feldspar and biotite crystallization at this point, which decreases the Ba content of the magma. Hence, the fractional crystallization for the Santa Helena batholith can be divided into two stages: pre- and syn-crystallization of K-feldspar and biotite (labeled as FXL 1 and 2 in Figs. 10 and 11). Because K-feldspar does not appreciably fractionate Rb or Sr, these two stages are continuous on the Rb/Sr – Sr diagram. The relative depletions in Sr, P, and Ti shown on the primitive mantle normalized graphs (Fig. 9), as well as the negative Eu anomalies, probably reflect fractional crystallization of feldspars, apatite, and ilmenite or sphene. The changes in slope of the REE patterns in the Santa Helena granitoids are probably caused by minor phase fractionation (zircon, allanite, sphene, etc.). Mass balance calculations for the Santa Helena granites confirm that the major element patterns on silica variation diagrams also can be explained by fractional crystallization (Bell et al., 1999; Bell, 2000).

Fig. 7. Plot of zircon data for sample 97-120E, a representative member of central granites in the Santa Helena batholith.

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Fig. 8. Plot of zircon data for sample 97-102, a representative member of marginal phases in the Santa Helena batholith. Regression forced through the origin because of clustering of analyses near concordia. Uncertainties at 2|.

3.4. Pb isotopes from the Santa Helena batholith and Cachoerinha suite Pb initial isotopic compositions were determined from K-Feldspars of 1.45 Ga rocks of the Santa Helena batholith (granites and augen gneisses), 1.55 Ga rocks of Cachoeirinha suite, : 1.8 Ga rocks of the Alto Jauru terrane, and : 950 Ma plutons, which intrude Santa Helena batholith (Table 5). The results are plotted on a 207 Pb/204Pb vs. 206Pb/204Pb evolutionary diagram (Fig. 12) along with Stacey and Kramers (1975) second-stage evolution curves with v values of 9.85 and 9.50. These v values were chosen to explain the distribution of the Pb compositions as discussed below. Pb isotopic compositions from the 1.8 Ga Alto Jauru terrane, including the 1.55 Ga Cachoeirinha suite, plot at : 1.45 Ga on a Stacey and Kramers (1975) second-stage evolution curve having a v value of 9.85. We suggest that Pb in the Alto Jauru terrane evolved along this growth curve from 1.8 to 1.45 Ga, at which time regional

deformation and metamorphism caused the Pb to be rehomogenized and that the Pb compositions in the K-feldspar have been unchanged since then due to absence of U in the feldspar and absence of a significant, younger metamorphic event. This is consistent with the fact that K/Ar ages for hornblendes in the Sa˜ o Jose´ dos Quatro Marcos area (Fig. 2) cluster around 1500 Ma (Carneiro et al., 1992). Pb compositions for K-feldspars from young, undeformed granites fall on the same evolution curve at : 950 Ma and probably represent average crustal Pb for the Alto Jauru terrane at the time those granite magmas formed. Data from Santa Helena rocks show a more complex behavior and present a large range in isotopic compositions (Fig. 12). These rocks have crystallization ages of : 1.45 Ga, but they are strongly deformed (augen gneisses) with a probable age of deformation about 0.95 Ga, during formation of the Aguapeı´ thrust belt. Thus, the linear array presented by the data (solid line with arrow) probably represents growth of radiogenic Pb from 1.45 to 0.95 Ga in granites that were

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

105

Fig. 9. Variation diagram showing concentrations of selected trace elements in the Santa Helena batholith samples normalized to concentrations in primitive mantle.

originally derived at 1.45 Ga from a crustal source with a v value of approximately 9.50 (shaded box). These granites had a large range of v values and their Pb evolved along third-stage curves until 0.95 Ga. At 0.95 Ga, the Pb was rehomogenized within each rock, with no subsequent growth of radiogenic Pb in the K-feldspars since that time and producing the array shown. This array does not intersect the v = 9.85 growth curve at 1.45 and 0.95 Ga as would be required if the Santa Helena batholith had a source with a v value (9.85) similar to that of the Alto Jauru terrane. We have shown a second-stage growth curve for v = 9.50 that does intersect the Santa Helena array at approximately 1.45 and 0.95 Ga, and we conclude that the source for the Santa Helena magmas probably had a U/Pb ratio slightly lower than that for the Alto Jauru terrane.

formed and metamorphosed 1000–950 Ma during the Sunsa´ s orogeny (Litherland et al., 1989; Sadowski and Bettencourt, 1996). Between the Sunsa´ s and Aguapeı´ belts sedimentary rocks of the Aguapeı´ Group are relatively flat-lying and undeformed and, together with underlying basement, comprise the Paragua block. Basement rocks in the Aguapeı´ thrust belt were initially described by Barros et al. (1982) and correlated with the Rincon del Tigre complex in Bolivia by Litherland et al. (1989). Menezes et al. (1993) coined the term Pontes e Lacerda volcanosedimentary Sequence for these rocks. Pinho

4. Rio Alegre domain Precambrian basement continues west of the Santa Helena basement several hundred kilometers into Bolivia (Fig. 1) as the Guapore´ craton. The eastern part of this craton includes the Aguapeı´ thrust belt, where deformed sedimentary rocks of the Aguapeı´ Group overlie basement of mafic to ultramafic volcanic and plutonic rocks with associated iron-rich sedimentary rocks and chert. The western part of the Guapore´ craton is occupied by the Sunsa´ s fold belt, which was de-

Fig. 10. Plot of Rb/Sr versus Sr for samples of the Santa Helena batholith and five samples from the Cachoerinha suite (data from Table 3 and Bell et al., 1999; Bell, 2000).

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Fig. 11. Ba/Sr plot for samples of the Santa Helena batholith and five samples from the Cachoerinha suite (data from Table 3 and Bell et al., 1999; Bell, 2000).

(1992) correlated the mafic metavolcanic rocks of the Rio Alegre valley with the Alto Jauru terrane, but as shown below this correlation is not valid. Matos (1992) presented a detailed geologic map of these units showing them to be restricted to the Rio Alegre valley; he renamed it as the Rio Alegre volcanosedimentary sequence. We will follow a broader definition and refer to basement rocks between the Santa Helena batholith and the Paragua block as the Rio Alegre domian (Fig. 2); this domain may include parts of two or more terranes, represent a single terrane, or only be a portion of a larger terrane that continues westward in the basement of the Paragua block. Rocks of this domain crop out in a large (50× 200 km2) NNW trending area (Fig. 2). The volcanic units observed in the Rio Alegre domain range from basalt to intermediate tuffs, and the associated sedimentary rocks are iron-rich sedimentary units and quartzites. Matos (1992) and Menezes et al. (1993) proposed different subdivisions of the supracrustal rocks, but each recognized three formations comprised of (a) basal mafic volcanic rocks (now amphibolites) and chemical sediments, (b) mostly volcanic rocks, and (c) siliciclastic and pelitic rocks with minor volcanic rocks. Plutons in the Rio Alegre domain range from tonalite and granodiorite to granite. Contact relationships are rarely exposed, but the

relationship of plutonic rocks to the supracrustal sequence suggests that the plutonic rocks are intrusive bodies rather than underlying basement. Table 6 presents U/Pb ages and Sm/Nd data for several units in the Rio Alegre domain. Outcrops of intermediate to felsic volcanic rocks are rare, and we only have U/Pb ages for two samples, both of which may represent the same general part of the section. The dacitic pyroclastic rocks (97-122 and 97-124) yielded zircons which give ages of 15179 27 and 15139 9 Ma, respectively, with a composite regression age of 15129 9 Ma (Fig. 13). Sm/Nd analyses yield mNd(t)= + 4.3 and TDM = 1.54 Ga for 97-122 and mNd(t)= + 4.7 and TDM = 1.48 Ga for 97-124. The Sm/Nd data clearly indicate that the volcanic rocks are juvenile. Two tonalites (97-113 and 97-140) yield U/ Pb ages of 14659 4 Ma (Fig. 14) and 14819 7 Ma, respectively, with mNd(t)= + 3.8 and TDM = 1.53 Ga for 97-113 and mNd(t)= + 4.1 and TDM = 1.50 Ga for 97-140. The Sm/Nd data suggest that these plutonic rocks may be part of a juvenile terrane represented by the volcanic rocks (97-122 and 97-124). Two other units in the Rio Alegre domain yield juvenile (at 1.5 Ga) signatures; these are the Rio Aguapeı´ tonalitic gneiss (97-121; no precise U/Pb age yet) and the Carrapato granite (97-123; no precise age yet). The tonalite is probably part of the Rio Alegre terrane, but the granite is probably a younger intrusive body derived from that terrane. Rocks in the western part of Rio Alegre domain may represent part of a different, though approximately coeval, block or terrane. Regional studies carried out along the Aguapeı´ River by Pinho (1990) identified tonalitic rocks associated with amphibolitic rocks and intrusive monzosyenite rocks. The monzosyenitic intrusions locally have gradational contacts with foliated tonalite, suggesting localized melting. The Rio Alegre granodiorite (97-142) appears distinctly younger at 14129 5 Ma, but also has a distinctly older Sm/ Nd crustal residence age (TDM = 1.58 Ga). The Santa Barbara amphibolite in the north (97–137) at 1494910 Ma is the same age as the Rio Alegre domain juvenile rocks, but Sm/Nd data show indications of older material (mNd(t)= + 2.5 and TDM = 1.68 Ga). Recent Sm/Nd analyses on base-

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

ment rocks to the west in Bolivia yield late Paleoproterozoic TDM ages (Darbyshire, 2000). Thus, these rocks from the western part of the Rio Alegre domain may contain some older crustal contributions from terranes to the west. Important geochemical and petrologic studies were carried out by Menezes et al. (1993), Matos (1992), and Matos and Schorscher (1997a,b) in the Rio Alegre volcanosedimentary sequence. Their geochemical data suggest an oceanic affinity for these rocks; the geochemical data on the intrusive rocks suggest an evolution resulting from differentiation of tholeiitic magmas. The domain was later metamorphosed at greensehist facies and cut by pyroxenites and amphibolites. The Rio

107

Alegre domain rocks may be interpreted as originating in a  1.50 Ga oceanic island arc. Metamorphism under greenschist to lower amphibolite facies (biotite to garnet–kyanite zone) and deformation, including mylonitization (NW foliation) were associated with subsequent accretion of the terrane to the proto-Amazonian craton during the Mesoproterozoic.

5. Rio Branco intrusive suite Rocks of the Rio Branco intrusive suite were initially described by Oliva (1979), as the Sierra Rio Branco Complex. Barros et al. (1982) carried

Table 5 Isotopic composition of Pb from K-feldspars in Mato Grossoa Sample

Sample description

Normalized Pb isotopic ratios 206

Pb/204Pb

207

Santa Helena batholith rocks (1.45 Ga) 97-102 Gneissic granite 97-105 Gneissic granite 97-106 Gneissic granodiorite 97-168 Gneissic granite 97-169 Gneissic granite 97-108 Gneissic granite 97-115 Gneissic granite 97-116c Gneissic granite (coarse gr.) 97-116f Gneissic granite (fine gr.) 97-120 Gneissic granite 97-141 Gneissic granite

17.092 16.960 17.404 17.121 17.134 20.044 18.363 19.155 19.263 18.177 18.752

15.545 15.423 15.512 15.467 15.409 15.789 15.643 15.725 15.772 15.592 15.670

36.012 35.875 35.905 36.192 36.258 36.814 36.627 37.561 37.707 36.828 37.163

Cachoerinha suite (1.55 Ga) 97-132 Granite, S.J.Q.M. 97-138 Granite, Cachoerinha 97-145 Granitic gneiss, Sta. Cruz 97-148 Granitic gneiss, Q. Meninas 97-150 Tonalite, Cachoerinha

16.214 16.137 16.148 16.232 16.221

15.406 15.408 15.407 15.450 15.426

35.750 35.763 35.795 35.918 35.860

Alto Jauru terrane basement (1.75 Ga) 97-133 Granitic gneiss 97-149 Granitic gneiss

16.408 16.164

15.484 15.406

35.924 35.771

Younger plutonic units ( : 0.95 Ga) 97-101 Granite (undeformed) 97-103 Aplite dike in 97-102 97-107 Granite (undeformed) 97-118B Granite (undeformed)

17.206 17.323 16.980 17.231

15.563 15.542 15.511 15.538

36.555 36.514 36.374 36.523

a

See Appendix B for analytical details.

Pb/204Pb

208

Pb/204Pb

108

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Fig. 12. 207PbI Pb vs. 206Pb/204Pb for Pb extracted from K-feldspars for rock units in the region of the Santa Helena batholith (Table 5). Data fall into three groups: (a) samples from the Cachoerinha suite – Alto Jauru basement represent : 1450 Ma crustal Pb with a second stage v value of 9.85; (b) samples from young ( :950 Ma) plutons represent : 950 Ma crustal Pb with a second-stage v value of 9.85; and (c) samples from the Santa Helena batholith that represent evolution of rocks with variable third-stage v values which were formed :1450 Ma from a source with second-stage v value of 9.50 and were deformed and metamorphosed about 950 Ma. Solid line with arrow denotes third-stage Pb at 950 Ma; dashed line indicates third-stage Pb at present. See text for further discussion.

out a detailed study during the RADAMBRASIL Project, defining the Rio Branco Group. These rocks occur in a large area (1200 km2) east of the Alto Jauru terrane; its eastern and southern limits are represented by the Brasiliano (:600 Ma) Paraguai–Araguaia belt. The northern limit is covered by Cretaceous sedimentary rocks, and the western limit is covered by Aguapeı´ group sedimentary rocks. Leite et al. (1986) mapped the Rio Branco region and referred to these rocks as the Rio Branco Intrusive Suite, which they regarded as a differentiated, layered complex. The Rio Branco rocks were reevaluated by Geraldes (2000), who considered them as part of a bimodal igneous suite. The felsic part of the Rio Branco suite includes red to pink rocks of syenitic to granitic composition; members of the mafic part include gabbro, tholeiitic diabase dykes, and porphyritic basalt. Hybrid composition rocks occur in the zone be-

tween the felsic and mafic portions, with centimeter-size alkali-feldspar crystals bordered by plagioclase (rapakivi texture) in a plagioclasebearing groundmass. Trace element abundances of Rb, Y, and Nb (Geraldes, 2000) indicate a within-plate affinity for both the mafic and felsic rocks, according to tectonic discrimination diagrams. Analyses of zircons from one of the granites (RE-10; Table 7) yield an upper intercept on concordia of 14279 10 Ma, which is interpreted as the crystallization age of the felsic magma. Analyses of zircons from a porphyritic gabbro sample (RB-04) yielded an age of 147198 Ma. The approximately 40 million year difference in these two ages suggests either that the zircons from the gabbro may have a small inherited component (if the two suites are co-magmatic) or that the felsic phase represents distinctly younger phase of magma genesis. Crustal formation ages

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

(TDM) for the mafic and felsic rocks are indistinguishable, with most being between 1.75 and 1.85 Ga. These crustal formation ages are typical for those of the nearby Alto Jauru terrane (Table 1) and indicate that the Rio Branco intusive suite was probably derived from melting of : 1.8 Ga subcontinental mantle (mafic rocks) with contributions from coeval continental crust (felsic rocks). This source could have been either eastward continuation of the Alto Jauru terrane or a slightly older Paleproterozoic belt adjacent to the Alto Jauru terrane. 6. Aguapeı´ Group The Aguapeı´ Group occurs in the SW part of the SW Amazonian Craton in Brazil and comprises sedimentary rocks deposited in a cratonic environment. This unit partially covers basement ascribed to the Rio Negro– Juruena province and the Rondoˆ nia– San Ignacio province. The sedimentary sequence was first described as the Aguapeı´ Unit by Figueiredo et al. (1974). Souza and Hildred (1980), Saes et al. (1992), and Menezes et al. (1993) proposed group status. Saes et al. (1992) interpreted this group as the result of deposition in a developing continental rift and correlated it with units described in the Sunsa´ s Group by Litherland et al. (1989) in Bolivia. Litherland et al. (1989) also suggested this correlation, indicating the link between Sunsa´ s and Aguapeı´ basins and the contemporaneity of the respective deformed belts.

109

According to Saes et al. (1992) and Saes (1999), the Aguapeı´ Group includes three formations: a lower conglomerate and sandstone unit, an middle pelitic unit, and an upper sandstone unit. The units of the Aguapeı´ Group (in Brazil) and the Sunsa´ s Group (in Bolivia) record a complete cratonic depositional sequence with (1) a transgressive phase with tidal-dominated deposition of sandstone and conglomerate; (2) a marine progradation allowing psamitic deposition in an oceanic, current-dominated environment; and (3) an upper unit recording a marine regression with deposition of sandstones in a fluvial system. In the vicinity of the Aguapeı´ thrust belt the thicknesses of the sedimentary units are greater, suggesting that part of the Sunsa´ s–Aguapeı´ basin developed in a depression originated by crustal extension inboard of the western margin of the Amazonian protocraton.

7. Aguapeı´ thrust belt The Aguapeı´ thrust belt is a : 25 km wide, NNW trending fold and thrust belt that lies between the Santa Helena batholith on the east and the Paragua block on the west. The deformation involved sedimentary rocks of the late Mesoproterozoic Aguapeı´ Group and underlying Rio Alegre domain basement rocks; the deformation increases in intensity toward the center of the belt. Bulk K/Ar muscovite ages reported by Geraldes et al. (1997) vary from 964 to 843 Ma with most

Table 6 Summary of U/Pb ages and Sm/Nd data for rocks of the Rio Alegre domaina Field number

Description

U/Pb age (Ma)

mNd(0)

mNd(t)

TDM (Ga)

97-113 97-121 97-122 97-123 97-124 97-137 97-140 97-141 97-142

Lavrinha tonalite Rio Aguapeı´ tonalite gneiss Metadacite Carrapato microgranite Metadacite Santa Barbara amphibolitic gneiss Pau-a-Pique tonalite Maraboa granite Rio Alegre granodiorite

1465 904 Not determined 1517 9 27 Not determined 1513 909 1494 910 1481 907 1449 9 07 1412 9 05

−13.1 −4.7 −2.8 −11.2 −2.5 −11.3 −4.9 −7.1 −5.1

3.8

1.53 1.52 1.54 1.49 1.48 1.68 1.50 1.70 1.58

a

See Appendices A, B, C and D for details.

4.3 4.7 2.5 4.1 2.6 3.6

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Fig. 13. Plot of zircon data for samples 97-122 and 97-124, dacitic metavolcanic rocks from the Rio Alegre domain, west of the Sta. Helena batholith. A composite regression was used because of the similarities in the zircon data from these two regionally close samples. Uncertainties at 2|.

in the range 918– 964 Ma (Table 8), indicating that the deformation was coeval with and probably related to formation of the 1000– 950 Ma Sunsa´ s tectonic belt to the west of the Paragua block in Bolivia (Litherland et al., 1989). A tectonic model of the Aguapeı´ deformation was constructed by Geraldes et al. (1997) based on the observation of planar structures such as bedding, metamorphic foliation, cleavage, shear zones and quartz-veins, linear structures (stretching lineation, fold axes and intersection lineation), and open folds. The deformation is characterized by a sub-horizontal mylonitic foliation concentrated in a detachment zone of high shear strain between the basement and the Aguapeı´ quartzites. These structures are derived from NE– SW compression under ductile to ductile– brittle conditions. During this event, the volcanic and sedimentary rocks of the basement were thrust from NE to SW over sedimentary rocks of the Aguapeı´ Group, giving rise to open folding and secondary faults and fractures, which are well observed in the vicinity of the town of Pontes e

Lacerda. As a result, axial planes of the folds generally dip to the NE, with local overturning of the western flanks.

8. Discussion and conclusions The Paleoproterozoic orogenic belts reported in SW Mato Grosso State (SW Amazonian craton) represent SE extensions of the Rio Negro–Juruena province, formally defined by Tassinari (1981) and better constrained by Tassinari et al. (1996). In Mato Grosso, the units of the Rio Negro–Juruena province were formed in two distinct events: formation of the Alto Jauru juvenile terrane : 1750 Ma and the Cachoeirinha magmatic event : 1550 Ma. These were followed by major magmatic events between 1500 and 1400 Ma, which produced the Santa Helena batholith, plutons intruded into the Alto Jauru terrane (including the Rio Branco suite), and units of the Rio Alegre domain to the west of the Santa Helena batholith. Tectonism in the region con-

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

cluded with :1 Ga deformation, magmatism, and metamorphism associated with the Sunsa´ s orogeny, which may represent Grenvillian collision of Amazonia with Laurentia or Baltica during the assembly of Rodinia.

8.1. Alto Juaru terrane The Alto Jauru terrane includes the Cabac¸ al, Araputanga, and Jauru metavolcanic belts (felsic metatuffs, mafic volcanic rocks and dacite-rhyodacite lavas), and metasedimentary rocks (epiclastic rocks, metacherts, quartz– sericite – clorite schists, and garnetiferous magnetite bands) separated by granitic to tonalitic gneiss domains that may (or may not) be basement to the volcanic sequences. Volcanic rocks, plutons, and gneisses in the Cabac¸ al volcanic belt yielded U/Pb ages from 1795910 to 17479 13 Ma. TDM ages range from 1926 to 1868 Ma, indicating that this belt probably represents juvenile material accreted to the SW Amazonian Craton about 1.80– 1.75 Ga (Fig. 15a). At present there are no reliable U/Pb

111

ages from the Araputanga or Jauru volcanic belts or their associated gneisses, so it is unclear at this time whether the western part of the Alto Jauru terrane also formed 1.80–1.75 Ga. Metamorphism and deformation described in rocks of the Alto Jauru terrane are quite complex, probably due to superimposed events. As described in the next section, plutonic and volcanic rocks of the Alto Jauru terrane were intruded by a calc-alkaline suite dated at 1.57–1.52 Ga, which resulted in migmatization and deformation of the Alto Jauru basement. The subsequent development of the Santa Helena batholith (1.48–1.42 Ga) and the Sunsa´ s/Aguapeı´ events (1.2– 0.95 Ga) probably also overprinted the original structures locally. Carneiro et al. (1992) reported numerous 1500–1450 Ma K/Ar ages on amphiboles from the Sa˜ o Jose´ dos Quatro Marcos area in the southern part of the Cabac¸ al volcanic belt. This suggests that thermal and deformation events younger than 1400 Ma were relatively unimportant in the eastern part of the Alto Jauru terrane.

Fig. 14. Plot of zircon data for sample 97-113, a tonalite from the Rio Alegre domain west of the Sta Helena batholith. Uncertainties at 2|.

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Table 7 Summary of U/Pb and Sin/Nd data for rocks of the Rio Branco suitea Field number

Description

RB-01 RB-02 RB-03 RB-04 RB-05 RB-06 RB-07 RB-08 RB-09 RB-10 RB-11 RB-12

Gabbro Gabbro Gabbro Porphyritic gabbro Monzosyenite Monzosyenite Monzosyenite Granophyre Granophyre Granophyre Granophyre Granophyre

a

U/Pb age (Ma)

1471 908

1427 9 10

mNd(0) −9.8 −10.4 −10.0 −25.1 −9.4 −14.1 −13.1 −14.3 −14.9 −14.8 −13.4 −15.2

mNd(t)

−2.3

−0.2

TDM (Ga) 1.75 1.80 1.73 1.86 1.79 1.81 1.82 1.84 1.85 1.82 1.84 1.89

See Appendices A, B, C and D for details.

8.2. Cachoerinha magmatic e6ent The Cachoerinha suite is represented by several tonalite to granite plutons intruded into the Alto Juaru terrane. So far most dated examples occur in the eastern part of the terrane (Cachoerinha –Sa˜ o Jose´ dos Quatro Marcos areas; Fig. 2) and yielded U/Pb ages ranging from 15679 06 to 1536911 Ma with Sm/Nd model ages (TDM) from 1.88 to 1.77 Ga, indicating that their magmas were probably derived mainly from the surrounding Alto Jauru terrane. Geochemical data are most consistent with a calc-alkaline magmatic arc origin for rocks of the Cachoerinha suite that we studied, and we believe that the Cachoerinha suite probably represents plutons from a continental margin magmatic arc (Fig. 15b). Coeval volcanic rocks or possible accretionary terranes associated with this event have not yet been recognized. If the arc was an Andean-type arc, such rocks may not have survived uplift and erosion. Alternatively, such rocks may be present in the western part of the Alto Jauru terrane, but not yet recognized or correctly dated. The nearest coeval rocks occur to the northwest in the state of Rondoˆ nia as the Serra de Provideˆ ncia rapakivi suite (Bettencourt et al., 1999). The Serra de Provideˆ ncia rapakivi suite (1570–1530 Ma) is virtually coeval with the Cachoerinha calc-alkaline suite in Mato Grosso,

but the two suites have very different compositions and petrologic features. A, ha¨ ll et al. (2000) recently reported data and interpretations from the Baltic shield that may bear on this problem. In the Baltic shield some of the classic rapakivi suites have ages similar to those under consideration here: the A, land suite at 1.58–1.56 Ga and the Salmi suite at 1.55–1.53 Ga. A, ha¨ ll et al. (2000) reported the presence of coeval accretionary crust to the west in the Gothian orogen of southern Sweden: stage 2 crust at 1.62– 1.58 Ga and stage 3 crust at 1.56–1.55 Ga. These authors concluded that the rapakivi suites to the east are inboard manifestations of coeval accretionary process in the west. In the case of the Cachoerinha suite and the Serra de Provideˆ ncia rapakivi suite in SW Amazonia, we suggest that within the Rio Negro– Juruena province that the Cachoerinha suite occurs in the outboard (marginal) portion of the province and that the Serra de Provideˆ ncia rapakivi suite occurs in a more inboard portion of the province. This is permissible, given the fact that major portions of the Rio Negro–Juruena province are covered by younger rocks and that the structural trends are not fully mapped. If this supposition is correct, further study in the western basement of Rondoˆ nia may reveal calcalkaline plutons coeval with the Serra de Provideˆ ncia rapakivi suite.

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8.3. Santa Helena batholith and domains to the west

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characterized, and only future work will allow full definition of the tectonic meaning of these rocks. However, in view of recent verification that basement in the Paragua block to the west is Paleoproterozoic (Darbyshire, 2000), we suggest here that there may be a suture within the Rio Alegre domain and that the proposed suture represents closure of a middle Mesoproterozoic ocean about 1400 Ma by accretion of the Paragua block to the growing Amazonian craton (Fig. 15c). There is insufficient information from regions to the northwest (e.g., Rondoˆ nia, Bolivia) to determine if the Santa Helena batholith and associated rocks represent a major arc along the SW margin of Amazonia or whether it represents more localized terrane accretion.

West of the Alto Jauru terrane the region is dominated by the Santa Helena batholith and approximately coeval basement rocks in the Rio Alegre domain. The latter rocks are mafic to intermediate in composition, have relatively primitive compositions, and (at 1.51– 1.46 Ga) are slightly older than the Santa Helena rocks. Many of these units also have juvenile Nd signatures (TDM :1.5 Ga), suggesting that much of this domain represents juvenile material accreted to the western margin of the Alto Jauru terrane. Rocks of the Santa Helena batholith range from normal I-type granites to more fractionated granites with A-type affinities. We suggest that the Santa Helena batholith formed during east-directed subduction subsequent to accretion of units in the Rio Alegre domain, and that most of the batholith was derived from the recently accreted Rio Alegre crust. Santa Helena samples have Sm/ Nd crustal residence ages that range from juvenile at 1.5 Ga to slightly older (but not older than 1.7 Ga), consistent with eastward continuation of Rio Alegre domain basement as the main source of the magma, but allowing for some admixture of Alto Jauru terrane crust. The presence of 1.4–1.5 Ga polycyclic rocks with older Sm/Nd crustal residence ages (1.6– 1.7 Ga) in the western part of the Rio Alegre domain may indicate that they are part of a terrane different from that represented by the juvenile rocks of the Rio Alegre domain. Their petrologic and geochronological aspects are not yet well

8.4. Rio Branco suite and eastern plutons Within the Alto Jauru terrane there are numerous 1.4–1.5 Ga granitic plutons, the younger of which are commonly undeformed. Farther east, the :1.43 Ga Rio Branco mafic –felsic suite apparently intrudes Alto Jauru basement, although contacts with the older rocks are not exposed. We interpret these rocks as inboard manifestations of the terrane accretion and magmatism associated with the Santa Helena–Rio Alegre complex, suggesting that the supposed 1.5–1.4 Ga subduction regime was able to produce granites and gabbros from the Paleoproterozoic lithosphere to the east. The 1.45–1.50 Ga K/Ar ages from amphibolites in the Sa˜ o Jose´ dos Quatro Marcos area (Carneiro et al., 1992) show that the magmatism was accompanied by significant thermal metamor-

Table 8 K/Ar ages of sericite samples from the Pontes e Lacerda regiona Deposit

Potassium (%)

Radiogenic

Mineiros Incra Pau-a-Pique Ellus Pombinha Ernesto Japones

6.69 7.18 8.42 7.18 7.93 8.42 6.30

313.7 288.5 393.2 334.8 368.8 395.1 311.5

a

40

Ar (ppm)

Data obtained as bulk K/Ar ages at CPGeo/IG/USP (Geraldes et al., 1997).

Atmospheric argon (%)

Age (Ma)

1.60 0.75 1.26 0.85 1.62 0.61 0.34

948 9 17 843 9 17 936 9 10 934 9 10 918 9 10 924 9 10 964 9 40

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Fig. 15. Summary of Proterozoic tectonic history for SW Mato Grosso: (A), formation of Alto Jauru greenstone belt (AJGB) as an accretionary complex; (B), formation of the Cachoerinha suite in a continental margin magmatic arc developed within the AJGB; (C), formation of the Santa Helena batholith as a magmatic arc in a newly accreted 1.5 Ga terrane complex; (D) deformation and magmatism associated with :1 Ga continental collision to the west.

phism. Since many of the younger granites are undeformed (e.g., Alvorada granite, 97-129; 138993 Ma), we suggest that major deformation in the eastern part of the Alto Jauru terrane may have effectively ceased by 1400 Ma.

8.5. Sunsa´ s/Aguapeı´ deformation The final tectono-thermal events in the region occurred about 950 Ma and are represented by formation of the Aguapeı´ fold and thrust belt (Fig. 15d), intrusion of several isolated granitic plutons (e.g., Sa˜ o Domingos granite, 97-118, Appendix C), and thermal metamorphism as shown by K/Ar ages in the Aguapeı´ thrust belt (Table 8). Many of the rocks in the Santa Helena batholith are strongly deformed, being represented today by augen gneisses. In some cases, the strongly foliated Santa Helena rocks are cut by pre-1.4 Ga plutons or dikes, which are much less deformed or

undeformed, indicating that much of the augen gneiss structure developed between 1.45 and 1.40 Ga. However, significant Sunsa´ s-age deformation east of the Aguapeı´ thrust belt cannot be ruled out and full understanding of the deformational history will have to await further field and geochronologic studies.

8.6. Global correlations? The age pattern of 1450 Ma rocks intruded into or adjacent to 1.7–1.8 Ga continental crust is similar to relationships along the eastern and southern margin of Laurentia prior to 1400 Ma and would be compatible with tectonic models, which propose proximity between Laurentia and Amazonia about 1800–1400 Ma (Sadowski and Bettencourt, 1996). However, we believe that there are many geometric problems in trying to make such an association at this time. Instead, we

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

will briefly summarize the points that deserve consideration as evaluation of Proterozoic continental reconstructions evolves. (1) The Alto Jauru terrane represents a significant :1.75 Ga juvenile accretionary province, coeval with many other orogenic belts or provinces around the world, especially the Yavapai –Central Plains orogen (Inner Accretionary Belt) in Laurentia (Van Schmus et al., 1993). (2) We have not found in this part of Amazonia any evidence of ‘Mazatzal’ or ‘Labradorian’ orogenesis (1700–1630 Ma) that is common in Laurentia (Van Schmus et al., 1993; Rivers, 1997). (3) Magmatism and orogenesis between 1600 and 1500 Ma is relatively uncommon globally, but it is present in Mato Grosso as the 1.55 Ga Cachoerinha suite (this work) and in Rondoˆ nia as the coeval Serra de Provideˆ ncia rapakivi suite (Bettencourt et al., 1999). Similar age rocks are found in the Baltic shield (A, ha¨ ll et al., 2000) and include both calc-alkaline accretionary terranes and rapakivi within-plate suites. We suggest that Amazonia and Baltica were connected during the late Paleoproterozoic such that their paired accretionary-rapakivi suites represent parts of a major, laterally continuous continental margin at 1.6–1.5 Ga (Fig. 16). The relationship of Baltica–Amazonia to Laurentia at this time is not certain, but known relationships would be compatible with the proposed Amazonia –Baltica continental margin being a lateral extension of the : 1600 Ma continental margin of Laurentia (heavy line, Fig. 16; Van Schmus et al., 1996). (4) Although :1450 Ma ‘anorogenic’ plutons are common within the Paleoproterozoic marginal belts of Laurentia (Van Schmus et al., 1993; Rivers, 1997), orogenic belts of that age are relatively uncommon. A significant example is the Pinware terrane of Labrador (Tucker and Gower, 1994), although in contrast to the Santa Helena batholith– Rio Alegre domain, it is underlain by older crust (Dickin, 2000). Van Schmus et al. (1993, 1996) reported juvenile 1.50–1.45 Ga crust in the midcontinent region of the US, and Dickin (2000) reported evidence for a : 1450 juvenile terrane (Quebecia) within

115

the Grenville province. Thus, the Santa Helena batholith–Rio Allegre domain could represent 1.5–1.4 Ga continental margin accretionary processes that were laterally continuous with those in Laurentia if the hypothetical lateral correlation mentioned above (3) is valid. (5) There is ample evidence of : 1000 Ma orogenesis in SW Amazonian Craton. The deformation and metamorphism in the study area are probably inboard manifestations (folding, thrusting, deformational metamorphism) of the more intense orogenesis occurring to the west in Bolivia during the Sunsa´ s orogeny (Litherland et al., 1989).

Fig. 16. Possible early to middle-Neoproterozoic (Rodinian) configuration of Laurentia, Baltica, and Amazonia (modified from Fig. 10 of Dalziel, 1997). Amazonia has been rotated slightly counter-clockwise relative to Baltica to facilitate proposed lateral correlation of their 1.55 Ga orogenic and rapakivi suites. Amazonia-Baltica probably occupied a very different position relative to Laurentia at 1.6 – 1.5 Ga. One option is to rotate Amazonia – Baltica counterclockwise and make the 1.6 Ga continental margins laterally continuous. 1: :1.55 Ga rapakivi granite suites in Baltica and Amazonia (Rhon6nia). 2: :1.55 Ga orogenic suites in Baltica and Amazonia. 3: 1.75 Ga orogenic suites in Baltica and Amazonia. Solid line in Laurentia denotes southeastern limit (present day geography) of crust older than 1.6 Ga (1.6 Ga continental margin; Van Schmus et al., 1996).

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Acknowledgements This paper was improved by discussion with J.S. Bettencourt, Valdecir Janasi, and C.C.G. Tassinari. This work was sponsored by FAPESP Grant 96-04819-7 to Geraldes, FAPESP Grant

96-1207-1 to Teixeira and NSF grants EAR9705759 to Van Schmus and EAR 97-05758 to Condie. Reviews by Charles Gower and Drew Coleman substantially improved the manuscript. This paper is a contribution to IGCP-426: Granite Systems and Proterozoic Lithospheric Processes.

Appendix A. Sample numbers, rock types, and sample localities

Sample

Rock unit, region

S. latitude

W. longitude

Rio Alegre domain 97-113 Tonalite, Lavrinha mine, Rio Alegre domain 97-121 Tonalitic gneiss, Rio Aguapeı´, Rio Alegre domain 97-122 Metadacite, Rio Alegre domain 97-123 Carrapato granite, Rio Alegre domain 97-124 Metadacite, Rio Alegre domain 97-137 Granulite, Santa Barbara, Rio Alegre domain 97-140 Pau-a-Pique tonalite, Rio Alegre domain 97-141 Maraboa Granite, Rio Alegre domain (?) 97-142 Granodiorite, Rio Alegre domain

15°21.17% 15°52.31% 15°45.81% 15°44.19% 15°40.67% l5°38.21% 15°40.27% 15°24.64% l5°47.24%

59°15.43% 59°12.47% 59°11.20% 59°11.88% 59°11.99% 59°20.55% 59°09.05% 59°14.65% 59°14.79%

Santa Helena batholith 97-102 Granitic orthogneiss, Fazenda Guape´ 97-105 Gneissic granodiorite, Guape´ farm 97-106 Gneissic granite, Guape´ farm 97-108 Gneissic granite, near Jauru 97-115 Gneissic granite, roadcut, Hwy 97-116c Gneissic granite, Serrana quarry 97-116f Finer grained granite, Serrana quarry 97-120E Gneissic granite, west of Cardoso 97-120P Pegmatitic vein in 97-120E 97-120W Gneissic magnetite granite, west of Cardoso 97-135 Gneissic granite, Santa Elina 97-168 Gneissic granite, Ellis farm 97-169 Gneissic granite, Ellis mine

15°06.70% 15°04.96% 15°04.96% 15°09.12% 15°25.30% 15°28.30% 15°28.30% 15°47.09% l5°47.09% 15°47.09% 14°35.02% 15°53.01% 15°55.95%

58°01.53% 58°59.05% 58°59.05% 58°55.34% 59°07.60% 59°07.60% 59°07.60% 59°03.44% 59°03.44% 59°03.44% 59°41.49% 59°05.43% 59°05.72%

Alto Jauru terrane 97-129 Alvorada Granite, Alvorada farm 97-130 Gabbro, Cabac¸ al area 97-131 Tuffaceous metased, Cabac¸ al mine 97-132 Granite, north of S. J. dos Quatro Marcos 97-133 Granitic gneiss, Santa Fe 97-134 Tonalite, north of S.J. dos Quatro Marcos 97-136 Granodiorite, NW of Cachoeirinha 97-138 Granite, 2 km east of Cachoeirinha

15°29.99% 15°21.21% 15°19.97% 15°34.28% 15°29.47% 15°35.98% 15°17.72% 15°17.97%

58°14.83% 58°1l.90% 58°12.45% 58°10.58% 58°09.48% 58°07.83% 58°22.17% 58°19.71%

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97-139 97-145 97-147 97-149 97-150

Granite, Alvorada type, 2 km east of Cachoeirinha Santa Cruz gneiss, Cachoeirinha-Sta. Cruz road Sa˜ o Domingos gneiss, Cachoeirinha Gneiss, Alianc¸ a, 4 km east of Cachoeirinha Tonalite, 2 km east of Cachoeirinha

117

15°17.97% 15°11.25% 15°18.06% 15°18.00% 15°17.97%

58°19.71% 58°19.80% 58°20.49% 58°18.50% 58°19.71%

Rio Branco suite RB01-04 Gabbro, Salto do Ce´ u RB05-07 Monzosyenite, Salto do Ce´ u RB08-12 Granophyric granite, Salto do Ce´ u

15°08.22% 15°08.22% 15°08.22%

58°07.05% 58°07.05% 58°07.05%

Young intrusions 97-101 Granite, Sarare 97-103 Aplite in 97-102, Guape´ farm 97-107 Guape´ granite, Guape´ farm 97-118a Sa˜ o Domingos granite 97-118b Sa˜ o Domingos granite

14°43.48% 15°06.70% 15°06.42% 15°14.46% 15°12.92%

59°22.57% 59°01.53% 59°02.93% 58°59.92% 59°04.06%

Appendix B. Analytical methods B.1. Major and trace element analytical methods A total of 17 granitoid xenoliths were selected for chemical analysis by X-ray fluorescence (XRF) and ICP-MS. Samples were coarsely crushed with a steel jaw crusher and then pulverized to a coarse sand using porcelain plates. An aliquot of the coarse sand to be used for ICP-MS was hand ground with a ceramic mortar and pestle, and another aliquot for XRF was ground to a fine powder in a steel swing mill. Major elements and trace elements including Ba, Nb, Ni, Pb, Rb, Sr, V, Y, and Zr were analyzed by XRF at New Mexico Tech. Fused disks were prepared using the methods described by Hallett and Kyle (1993). Analyses were made with an automated Philips PW2400 XRF spectrometer and Philips PC software following the procedures described in Hallett and Kyle (1993). Precision and detection limits for both XRF and INAA are also discussed in this reference. Trace elements including Sc, Cr, Co, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th, and U were analyzed by ICP-MS at Activation Laboratories Ltd., Ancaster, Ontario using an ELAN 6000 ICP-MS. Analytical methods are similar to those of Fan and Kerrich (1997). Samples were dissolved by HF-HNO3 and the preci-

sion is generally between 2% and 5% RSD. Representative analyses are summarized in Table 3 of the paper. A complete data set can be obtained from K.C. Condie at New Mexico Tech. B.2. Geochronologic data Sm/Nd and U/Pb data summarized in Tables 2, 4, 6 and 7 plus Appendix C and Appendix D were obtained at the Isotope Geochemistry Laboratory (IGL), Department of Geology and Kansas University Center for Research, University of Kansas, Lawrence, KS. Feldspar Pb data summarized in Table 5 were obtained at Centro Pesquisa de Geocronologia (CPGeO), Institute de Geociencias (IG), Universidade de Sa˜ o Paulo (USP), Sa˜ o Paulo, Brazil. U/Pb analyses: Zircon fractions used for isotope dilution analyses were air-abraded (Krogh, 1982) and individual grains carefully selected by hand prior to dissolution. Zircons were dissolved and Pb and U were separated using procedures modified after Krogh (1973) and Parrish (1987). All samples were total-spiked with a mixed 205Pb/ 235 U tracer solution. The U/Pb isotopic analyses were done in single-collector ion-counting mode using a newly fitted ion-counting Daly system on our VG-Sector mass spectrometer. Most analyses included ion exchange purification of Pb and U, with both loaded on the same Re filament using

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phosphoric acid-silica gel and measured as Pb+ and UO+ 2 . In some single crystal analyses the entire dissolved sample was loaded with phosphoric acid and silica gel on a Re filament and measured in the mass spectrometer without ion exchange column purification. Pb compositions were corrected for mass discrimination as determined by analysis of NBS SRM-982 (equal-atom) Pb and monitored by analysis of NBS SRM-983 (radiogenic) Pb. Uranium fractionation was monitored by analyses of NBS SRM U-500. Uncertainties in Pb/U ratios due to uncertainties in fractionation and mass spectrometry for typical analyses are 90.5%; in some instances weak signals caused uncertainties to range up to 9 2%. Radiogenic 208Pb, 207Pb, and 206Pb were corrected for modern blank Pb and for nonradiogenic original Pb corresponding to Stacey and Kramers (1975) model Pb for the approximate age of the sample. Uncertainties in radiogenic Pb ratios are typically less than 9 0.1% at the 2| level unless the samples had a low 206 Pb/204Pb ratio, in which case uncertainties in the common Pb correction could cause greater uncertainties. Decay constants used were 0.155125×l0 − 9/year for 238U and 0.98485× l0 − 9/year for 235U. Blanks ranged from :10 to B2 pg total Pb; in most cases they do not contribute significantly to uncertainties in the ages of samples, although some of the single-crystal analyses may show the effects of blank Pb as larger uncertainties in the calculated ages. Zircon data were regressed using the Microsoft Excel version of ISOPLOT (Ludwig, 1999). Model 1 regressions were accepted if probabilities of fit were better than 20%; Model 2 regressions were used if probabilities of fit were less than 20%. Uncertainties in concordia intercept ages are given at the 2| level (recalculated from the ISOPLOT results). Sm/Nd analyses: Rock powders for Sm/Nd analysis were dissolved and REE were extracted using the general methods of Patchett and Ruiz (1987). Isotopic compositions for Nd were measured with a VG Sector multi-collector mass spectrometer. Sm was loaded with H3P04 on a single Ta filament and typically analyzed as Sm+ in

static-multicollector mode or single-collector mode. Nd was loaded with phosphoric acid on a single Re filament having a thin layer of AGW-50 resin beads and analyzed as Nd+ using dynamicmulticollector mode. External precision based on repeated analyses of our internal standard is 9 40 ppm (2|) or better; all analyses are adjusted for instrumental bias determined by measurements of our internal standard for periodic adjustment of collector positions; on this basis our analyses of La Jolla Nd average 0.5118609 0.000010. Eight recent analyses of BCR-l yielded Nd=29449 0.70 ppm, Sm=6.7790.21 ppm, 147Sm/144Nd = 0.13939 0.00071, and 143Nd/144Nd = 0.512641 90.000007, yielding mNd(0)= 0.079 0.12 (all at 1|). Sm/Nd ratios are correct to within 9 0.5%, based on analytical uncertainties; mNd(t) values were calculated using the U/Pb ages defined from zircons where available or estimated ages based on the regional geology and current results from nearby samples. Crustal residence ages (TDM) were calculated following the model of DePaolo (1981). Feldspar Pb analyses: Whole rock samples were crushed and sieve to − 60+ 100 mesh. KFeldspars were purified with heavy liquids (density= 2.59 g/cc) and the Frantz isodynamic separator. Final purification was done under binocular microscope. About 40 mg of K-feldspar were leached sequentially with HNO3 and HCl (L1), a mixture of 5% HF and 7N HNO3 (L2 – L4), and the last leach (L5) was performed with concentrated HF and HNO3, as suggested by Housh and Bowring (1991). The solutions were purified by ion exchange technique using HBr– HCl media. Samples were loaded onto Re filaments with silica gel and H3PO4, and the isotopic ratios were measured on a five-collector VG-354 thermal ionization mass spectrometer at the University of Sa˜ o Paulo. Isotopic ratios were corrected for fractionation of 0.12% per mass unit based on repeated analyses of NBS 981 Common Pb. Analytical uncertainties on Pb/Pb ratios are about 0.05–0.10%; blanks ranged from 20 to 30 pg. Our preliminary results show that the least radiogenic Pb isotopic ratios were obtained from the third and fourth leaches. Toward the end of this study, we analyzed only the fourth leaches.

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119

Appendix C. Data for zircons from Mato Grosso

Radiogenic ratiosc

Observed Sample fractiona

Size U Pb (mg) (ppm)b (ppm)b

206 204

Pb/ Pb

207 235

Pb*/ U

206 238

Pb*/ U

Calculated agesd

207

206

207

206

238

235

Pb*/ Pb*

Pb*/ U

Pb*/ U

207 206

Pb*/ Pb*

Region west of Santa Helena batholith 97 -113: La6rinha Tonalite NM(−3) [4] 0.015 46 12 590 3.1748 0.25090 0.09177 14439 00 14519 00 14639 04 M(−2) [4] 0.017 45 12 482 3.1550 0.24885 0.09195 14339 00 14469 00 14669 00 M(3) [7] 0.016 159 33 3855 2.5081 0.20070 0.09063 11799 00 12749 00 14399 03 M(3) [3] 0.009 129 31 3002 3.0484 0.23874 0.09261 13809 00 14209 00 14809 12 UI =14659 4 Ma, LI= 156 928 Ma (2|); MSWD = 0.4; P= 0.53 (Model 1; 3 points) 97 -121 Rio Aguapeı´ Tonalitic gneiss NM(−1) [1] 0.008 178 45 1161 2.8926 0.23863 0.08791 13809 13 13809 12 13819 04 NM(−1) [1] 0.013 148 39 574 2.9187 0.23337 0.08915 13739 07 13879 08 14089 03 M(0) [1] 0.003 212 61 317 2.9651 0.24223 0.08878 13989 10 13999 10 13999 05 M(1) [1] 0.006 152 42 347 2.8335 0.23536 0.08732 13639 10 13659 12 13689 09 Indeterminate; : 1400 Ma? 97 -122 Metadacite M(0) [1] 0.008 2180 514 2839 2.9950 0.23303 0.09321 13509 14 14069 14 14929 02 M(3) [1] 0.004 2280 552 2170 2.9105 0.22531 0.09369 13109 10 13859 11 15029 04 M(4) [1] 0.005 1272 366 1405 3.2549 0.25052 0.09423 14419 13 14709 13 15139 04 M(5) [1] 0.002 2450 594 1344 2.8917 0.22422 0.09354 13039 08 13809 10 14999 03 UI =15179 27 Ma, LI=184 9233 Ma (2|); MSWD = 33; PB0.01 (Model 2) 97 -123 Carrapato Granite NM(−1) [1] 0.007 1371 261 1779 2.2334 0.18009 0.090 10689 06 11929 06 14249 03 NM(−1) [1] 0.003 1204 242 728 2.3241 0.18459 0.091 10929 07 12209 07 14539 02 NM(−1) [1] 0.003 1355 144 503 1.9118 0.16015 0.087 9589 06 10859 07 13519 06 NM(1) [1] 0.003 460 76 452 1.7309 0.15312 0.082 9189 11 10209 12 12459 03 NM(−1) [1] 0.005 254 66 1017 3.8549 0.23256 0.120 13489 12 16049 15 19609 03 Indeterminate 97 -124 Metadacite M(5) 0.005 832 248 645 4.7314 0.28232 0.12155 16039 18 17739 23 19799 03 M(5) 0.002 522 169 744 3.3990 0.26241 0.09395 15019 13 15049 12 15079 05 M(5) 0.003 420 124 750 3.2698 0.25240 0.09396 14519 12 14749 12 15079 04 M(5) 0.009 552 165 1619 3.2089 0.24682 0.09429 14229 08 14599 07 15149 02 M(5) 0.007 1201 304 933 2.2363 0.18672 0.08686 11049 05 11939 06 13589 03 UI = 15139 9 Ma, LI =0 9 0 Ma (2|); MSWD = 8.2; PB0.01 (forced; Model 1; n= 3, omits discordant point) UI = 151299 Ma, LI = 131 9125 Ma (2|); MSWD = 24; PB0.01 (Model 2; 122 and 124 combined) 97 -137 Santa Barbara Granulite M(4)F [1] 0.005 792 141 1124 2.2332 0.17302 0.93609 10299 06 11929 07 15009 02 M(4)E [1] 0.003 333 90 422 3.1077 0.24196 0.09315 13979 15 14359 16 14919 03 M(4)C [1] 0.005 471 123 263 3.1058 0.24089 0.09351 13919 08 14349 09 14989 02 M(4) D [1] 0.003 95 31 139 3.2661 0.25484 0.09296 14639 45 14739 46 14879 09 M(4) A [1] 0.004 175 49 266 2.8924 0.23656 0.08868 13699 20 13809 20 13979 05 UI =14909 7 Ma, LI=-39 965 Ma (2|); MSWD = 8.9; PB0.01 (Model 2; n= 4) UI =149799 Ma, LI =0 90 Ma (2|); MSWD = 9.2; PB0.01 (forced; Model 1; n= 3, omits discordant point)

120

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

97 -140 Pau-a-Pigue Tonalite M(0) [1] 0.007 633 160 892 2.7974 0.22621 0.08969 13159 00 13559 00 M(1) [1] 0.003 710 183 685 2.8586 0.22890 0.09057 13299 00 13719 00 M(2) [1] 0.003 1111 258 1219 2.6564 0.21679 0.08887 12659 00 13169 00 M(−1) 0.002 313 88 294 2.9913 0.23862 0.09092 13809 00 14059 00 M(−1) 0.002 385 126 121 2.5291 0.21525 0.08522 12579 00 12809 00 UI = 1481947 Ma, LI= 591 9 205 Ma (2|); MSWD = 6.5; PB0.01 (Model 2) 97 -141 Maraboa Granite M(2) [1] 0.005 295 106 122 2.7553 0.22284 0.08960 12979 00 13429 00 M(3)[3] 0.006 297 72 215 2.2306 0.18563 0.08715 10989 00 11919 00 M(2) [1] 0.006 1432 295 144 1.5902 0.14017 0.08228 8469 00 9669 00 UI = 14499 7 Ma, LI=361 914 Ma (2|); MSWD = 0.004; P= 0.95 (Model 1) M(3) [3] 0.003 835 152 263 1.5754 0.14366 0.07954 8659 00 9619 00 M(5)[1] 0.006 1949 272 541 1.2809 0.12361 0.07516 7519 00 8379 00 UI =14509 72 Ma, LI=484 944 Ma (2|); MSWD = 0.0; P= 1.0 (2 points) 97 -142 Rio Alegre Granodiorite NM(−1) [2] 0.011 295 79 666 2.9946 0.24318 0.08931 14039 10 14069 12 M(−1) [2] 0.004 115 41 140 3.0257 0.24576 0.08929 14179 18 14149 18 M(−1) [l] 0.015 41 12 294 2.9756 0.24252 0.08999 14009 15 14019 17 M(0) [1] 0.010 40 11 263 3.0055 0.24353 0.08995 14059 22 14099 22 M(0) [1] 0.004 96 29 169 2.7701 0.22700 0.08851 13199 26 13479 26 NM(1)[1] 0.011 18 6 153 2.9707 0.24330 0.08856 14039 32 14009 40 M(1) [1] 0.016 40 9 422 2.8111 0.22228 0.08943 13259 28 13599 28 UI = 141295 Ma, LI= 377 9 l70 Ma(2|); MSWD = 1.6; P= 0.17 (Model 1; n= 6) Santa Helena batholith 97 -102: Augen Gneiss M(−1) [1] 0.006 1188 298 5057 3.0756 0.24557 0.09088 14169 00 14279 00 M(0) [1] 0.008 901 219 6829 2.9766 0.23780 0.09079 13759 00 14029 00 M(1) [1] 0.005 1974 495 2370 3.0096 0.24066 0.09070 13909 00 14109 00 NM(−1) 0.010 1820 384 3291 2.5263 0.20514 0.08932 12039 00 12809 00 NM(−1) 0.002 172 74 67 2.5368 0.20876 0.08813 12229 00 12839 00 UI =14499 4 Ma, LI= 260 951 Ma (2|); MSWD = 9.6; PB0.01 (Model 2) 97 -105: Grandiorite Gneiss M(0) [1] 0.007 1865 432 3550 2.8723 0.23288 0.08945 13509 00 13759 00 M(0) [1] 0.007 2119 470 4797 2.7773 0.22492 0.08955 13089 00 13499 00 M(0) [1] 0.004 1591 378 2384 2.9686 0.23951 0.08990 13849 00 14009 00 M(0) [1] 0.003 1338 355 1939 3.0295 0.24486 0.09988 13129 00 14159 00 M(0) [1] 0.003 4520 933 3814 2.5466 0.20827 0.08868 12209 00 12869 00 UI =14249 7, Ma, LI= 211 994 Ma (2|); MSWD = 31; PB0.01 (Model 2) 97 -106: Augen Gneiss. M(0) [1] 0.004 198 57 240 2.9864 0.24193 0.08953 13989 00 14049 00 M(0) [1] 0.004 84 72 41 3.2121 0.25815 0.09024 14809 00 14609 00 M(0) [1] 0.004 305 74 1061 3.0152 0.24304 0.08998 14039 00 14129 00 UI =1423913 Ma, LI=0 90 Ma (2|); MSWD = 7.5; PB0.01 (Model 1; forced) 97 -108: Augen Gneiss M(−1) [6] 0.045 293 63 5167 2.6111 0.21176 0.08943 12389 00 13039 00 M(1) [10] 0.008 214 46 6008 2.5329 0.20465 0.08977 12009 00 12829 00 M(1) [2] 0.030 42 10 6170 2.7974 0.22445 0.09040 13059 00 13559 00 M(−3) 0.005 334 86 412 2.7421 0.22002 0.09039 12829 00 13409 00 M(−3) 0.008 540 124 1235 2.6234 0.21201 0.08974 12409 00 13079 00 UI = 14569 34 Ma, LI= 278 9207 Ma (2|); MSWD = 40; PB0.01 (Model 2)

14199 02 14389 05 14019 02 14459 05 13209 19

14179 08 13649 04 12529 05 11869 15 10739 06

14119 09 14109 06 14049 10 14159 05 13949 07 13959 31 14139 06

14439 01 14429 01 14409 0l 14119 01 13859 18

14149 01 14169 01 14239 0l 14209 02 13979 02

14169 04 14319 18 14259 03

14139 02 14209 02 14349 02 14349 04 14209 03

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

97 -115: Santa Helena Granite-Gneiss M(0) [4] 0.008 43 9 1860 2.5884 0.20962 0.20962 12279 00 M(l) [1] 0.002 894 152 538 2.0096 0.16448 0.08861 9829 00 M(3) [1] 0.017 170 30 1344 2.0381 0.16734 0.08833 9979 00 M(3) [1] 0.009 39 9 465 2.5647 0.20739 0.08969 12159 00 UI =1433910 Ma, LI= 130 9 42 Ma (2|); MSWD = 40; PB0.01 (Model 2)

121

12979 00 11199 00 11289 00 12919 00

97 -120E: Augen Gneiss west of Cardoso NM(−l) [1] 0.010 345 95 4640 2.9933 0.24113 0.09003 13939 00 14069 00 M(−l) [1] 0.015 5505 1374 4105 3.0146 0.24321 0.08990 14039 00 14119 00 M(−1) [1] 0.006 554 144 646 2.9157 0.23506 0.08996 13619 00 13869 00 M(−1) [1] 0.002 1301 333 787 2.9595 0.23888 0.08985 13809 00 13979 00 M(−1) [1] 0.003 326 80 263 2.9215 0.23522 0.09008 13629 00 13889 00 M(−1) [1] 0.016 728 189 822 3.0504 0.24614 0.08989 14199 00 14209 00 UI = 142294 Ma, LI=0 9 0 Ma (2|); MSWD = 4.4; PB0.01 (Model 1; forced) 97 -120P Pegmatitic Vein hosted in 97 -120E (Augen-Gneiss west of Cardoso) NM(−1) 0.008 163 39 497 2.7700 0.22548 0.08910 13119 00 13479 00 NM(−1) 0.004 296 64 555 2.5467 0.20584 0.08973 12069 00 12859 00 NM(−1) 0.006 42 12 217 2.9976 0.24258 0.08897 14009 00 14019 00 NM(−1) 0.002 1093 240 4227 2.6447 0.21401 0.08971 12509 00 13189 00 NM(−1) 0.002 248 66 440 3.0183 0.24319 0.09002 14039 00 14129 00 NM(−1) 0.003 85 28 139 2.9344 0.23774 0.08952 13759 00 13919 00 UI =141999 Ma, LI= 31 9144 Ma (2|); MSWD = 18; PB0.01 (Model 2) 97 -120W Magnetite-Granite west of Cardoso NM(−1) 0.009 108 37 161 2.9946 0.24250 0.08956 14009 00 14069 00 NM(−1) 0.013 732 169 3179 2.7541 0.22174 0.09008 12919 00 13439 00 NM(−1) 0.003 690 160 2207 2.8041 0.22642 0.08982 13169 00 13579 00 NM(−1) 0.005 646 134 1540 2.3825 0.19469 0.08875 11479 00 12379 00 UI =1425920 Ma, LI=123 9191 Ma (2|); MSWD = 22; PB0.01 (Model 2) 97 -135: Santa Elina Granite M(0) [1] 0.005 1657 389 1310 2.8145 0.22643 0.09015 13159 00 13599 00 M(1) [1] 0.007 2584 591 2529 2.7710 0.22366 0.08986 13019 00 13489 00 M(2) [1] 0.011 1312 317 2272 2.9744 0.23853 0.09044 13799 00 14019 00 M(1) [1] 0.001 720 293 89 2.8456 0.22861 0.09028 13279 00 13689 00 UI =14449 13 Ma, LI= 243 9 159 Ma (2|); MSWD = 4.5; P= 0.01 (Model 2) 97 -168 Ellus Farm Granite NM(2) [1] 0.005 388 90 388 2.4538 0.19853 0.08964 11679 00 12599 00 M(1) [1] 0.001 1019 277 323 2.8948 0.23331 0.08999 13519 00 13819 00 M(2) [1] 0.003 351 81 297 2.3980 0.19271 0.09025 11369 00 12429 00 M(2) 0.002 301 86 112 2.2289 0.18152 0.08906 10759 00 11909 00 M(2) 0.005 292 77 168 2.3132 0.18775 0.08936 11099 00 12169 00 UI =14309 20ma, LI= 789 113 Ma (2|); MSWD = 5.1; PB0.01 (Model 2) 97 -169 Ellus Mine Granite NM(1) [3] 0.002 787 205 228 2.5589 0.20635 0.08994 12099 00 12899 00 M(1) [4] 0.013 659 165 159 2.1174 0.17404 0.08824 10349 00 11559 00 M(2) [4] 0.015 212 44 119 1.5468 0.13337 0.08412 8069 00 9499 00 NM(1) 0.003 184 50 132 2.2305 0.18371 0.08806 10879 00 11919 00 NM(1) 0.003 141 41 226 2.9061 0.23391 0.09011 13559 00 13839 00 NM(1) 0.003 84 25 143 2.7118 0.21959 0.08957 12809 00 13319 00 UI = 1444915 Ma, LI=242 955 Ma (2|); MSWD = 3.3; P=0.01 (Model 2) Alto Jauru terrane 97 -129 Al6orada Granite NM(3) [1] 0.003 866 240 431 2.9391 0.24140 0.08830 13949 09 13939 10 M(3) [1] 0.005 2860 403 1355 1.5260 0.13619 0.08126 8239 04 9419 05 M(4) [1] 0.004 2219 267 1111 1.2788 0.11257 0.08239 6889 03 8369 05 NM(3) 0.002 1356 261 624 2.1657 0.17781 0.08834 10559 07 11709 09

14169 03 13969 05 13909 02 14199 04

14269 05 14239 02 14259 02 14229 02 14279 02 14239 02

14069 04 14209 03 14039 10 14199 13 14269 05 14159 08

14169 10 14279 02 14229 02 13999 08

14299 02 14239 0l 14359 02 14319 12

14189 03 14259 05 14319 09 14049 08 14129 05

14249 13 13889 08 12959 21 13849 15 14289 10 14169 11

13899 03 12289 02 12559 02 13909 04

122

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

NM(3) 0.002 594 148 194 2.2464 0.18657 0.08733 11039 13 11969 16 13689 11 Data not co-linear; age of 13899 3 Ma based on nearly concordant analysis. Reference line through 1390 Ma shown.

97 -131 Tuff (Felsite at Cabac¸ al mine) M(0) [1] 0.001 1313 439 2209 4.4467 0.30064 0.10727 1695908 17219 09 17549 01 M(1) [1] 0.005 725 212 3437 3.9062 0.26613 0.10645 15219 08 16159 08 1740901 M(3) [1] 0.006 855 246 4369 3.8539 0.26215 0.10662 15019 08 16049 08 17439 01 M(4) [1] 0.008 883 244 3082 3.6288 0.24846 0.10593 14319 08 15569 09 1731903 M(2) [1] 0.005 887 222 3496 3.3004 0.22966 0.10423 13339 08 14819 09 17019 02 UI = 1758 9 7 Ma, LI= 181 9 60 Ma (2|); MSWD =13; P B0.01 (Model 2) 97 -132 Al6orada type Granite NM(S) 0.002 1348 323 3873 3.2470 0.24843 0.09479 14309 11 14699 12 15249 03 NM(5) [1] 0.001 1327 239 602 1.9246 0.16038 0.08703 9599 10 10909 10 13619 03 M(6) [1] 0.002 1553 318 1516 2.3875 0.19195 0.09021 11329 08 12399 09 14309 03 UI = 1564915 Ma, LI=412 939 Ma (2|); MSWD = 13; PB0.01 (Model 2) 97 -133 Granitic Gneiss near Santa Fe NM(0) [1] 0.002 512 154 480 3.8176 0.25919 0.10683 14869 18 15979 20 17469 07 NM(0) [3] 0.003 845 225 890 3.4258 0.23538 0.10556 13639 08 15109 10 17249 03 NM(1) [4] 0.006 439 107 641 2.9912 0.20946 0.10358 12269 06 14059 07 16899 02 M(1) [1] 0.007 1601 407 1516 3.3293 0.22864 0.10561 13279 07 14889 07 17259 02 UI = 1790924 Ma, LI= 319 9 84 Ma (2|); MSWD = 20; PB0.01 (Model 2) 97 -134 Tonalite Gneiss NM(−1) [1] 0.007 1013 256 3749 3.0960 0.23424 0.09586 13579 07 14329 07 15459 12 M(1) [1] 0.006 802 184 2667 2.8077 0.21244 0.09586 12429 07 13589 07 15459 01 M(−1) [1] 0.009 977 276 3601 3.4426 0.26153 0.09547 14989 08 15149 08 15379 01 M(0) [1] 0.002 688 148 1595 2.6171 0.19701 0.09634 11599 06 13059 07 15559 01 UI = 153695 Ma, LI= -81 9 43 Ma (2|); MSWD = 21; PB0.01 (Model 2) 97 -136 Agua Clara type Granodiorite NM(0) [1] 0.007 632 139 1099 2.7362 0.21153 0.09382 12379 06 13389 07 15059 02 M(1) [1] 0.007 479 83 3144 2.2987 0.17573 0.09487 10449 06 12129 07 15269 03 NM (0) 0.004 799 192 674 2.9578 0.23040 0.09311 13379 11 13969 12 14909 05 M(0) [1] 0.004 395 85 1824 2.8456 0.21321 0.09680 12469 07 13689 08 15639 03 NM(0) 0.004 62 22 106 3.0691 0.24203 0.09197 13979 54 14259 57 14679 19 UI = 148098 Ma, LI= -187 9 58 Ma (2|); MSWD = 4.0; P= 0.05 (3 points; Model 2) 97 -138 Cachocirinha Granite NM(0) [2] 0.008 161 51 411 3.5017 0.26627 0.09538 15229 13 15289 13 15369 04 M(1) [2] 0.004 1156 284 1316 2.9069 0.22360 0.09429 13019 07 13849 07 15149 03 M(2) [2] 0.004 2103 430 1191 2.2729 0.18209 0.09053 10789 12 12049 12 14379 13 M(0) [2] 0.011 668 150 702 2.0180 0.17121 0.08549 10199 08 11219 06 13279 03 UI =15449 39 Ma, LI=323 9124 Ma (2|); MSWD = 31; PB0.01 (Model 2) 1536904 Ma from nearly concordant fraction is probably better estimate of age. 97 -145 Santa Cruz Gneiss M(−1) [1] 0.004 1262 329 322 2.8386 0.21308 0.09662 12459 12 13669 15 15609 10 M(1) [1] 0.013 262 74 956 3.4414 0.25935 0.09624 14879 13 15149 13 15529 02 M(2) [1] 0.004 807 180 855 2.7433 0.20886 0.09526 12239 12 13409 14 15339 03 UI = 155693 Ma, LI= 129 9 27 Ma (2|); MSWD = 0.0; P= 1.0 (2 points; Model 1). For all three data, UI=1555 9 112 Ma (unforced); UI= 15479 27 Ma (forced through zero). 97 -149 Alianca Gneiss NM(−1) [4] 0.006 557 164 544 3.6937 0.25592 0.10468 14699 26 15709 29 17099 08 M(−1) [4] 0.009 469 151 807 4.1712 0.28546 0.10598 16199 18 16689 20 17319 09 M(1) [4] 0.008 740 249 439 4.0793 0.28429 0.10407 16139 08 16509 10 16989 05 M(0) [3] 0.003 2134 540 767 2.9358 0.22340 0.09531 13009 10 13919 11 15349 05 NM(−1) [1] 0.001 268 81 337 3.8127 0.27129 0.10193 15479 27 15959 28 16609 09

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

NM(−1) [1] 0.001 298 83 NM(−1) [1] 0.001 339 94 NM(−1) [1] 0.001 244 87 UI =1740 9 27 Ma LI =750 9115

123

510 3.6876 0.26100 0.10247 1495923 15699 25 16699 04 466 3.5543 0.25639 0.10023 1471924 15369 29 16289 15 234 4.2807 0.29590 0.10492 16719 33 16909 33 17139 05 Ma (2|); MSWD =5.3; P= 0.02 (Model 2)

97 -150 Cachoeirinha Tonalite M(−1) [1] 0.004 223 76 195 3.5135 0.26563 0.09593 15199 18 15309 21 M(0) [1] 0.002 244 73 262 3.4620 0.26130 0.09609 14979 26 15199 25 M(1)[1] 0.001 1312 380 618 3.3797 0.25396 0.09652 14599 12 15009 12 M(0) [1] 0.002 592 168 1247 3.4871 0.26402 0.09579 15109 12 15249 12 UI =15469 9 Ma (2|, forced through zero); MSWD= 14; PB0.01 (Model 1).

15469 12 15509 06 15589 04 15449 02

Rio Branco suite RB-04 Coarse-grained Gabbro M(5) [2] 0.005 440 92 886 2.5436 0.20065 0.09194 11799 13 M(5) 0.004 788 207 998 2.2049 0.18731 0.08538 11079 06 M(5) [1] 0.002 517 108 569 1.7567 0.15468 0.08237 9279 06 M(5) 0.002 193 59 494 3.2470 0.25552 0.09216 14679 18 M(5) [1] 0.003 497 137 616 2.4889 0.20427 0.08837 11989 07 UI =147198 Ma, LI= 469 9 16 Ma; MSWD = 0.005; P= 0.94 (Model 1)

12859 16 11839 06 10309 07 14689 23 12699 08

14669 08 13249 02 12549 04 14719 18 13919 03

RB-10 Granophyre NM(0) [1] 0.002 133 38 520 M(1) [1] 0.003 299 78 1525 M(2) [1] 0.002 280 77 686 M(0) [1] 0.002 293 90 1004 UI =1427910 Ma, LI= 216 9 350 Ma;

14139 17 13939 10 14009 11 15509 12

14249 05 14219 03 14239 03 15979 03

97 -118a Sao Domingos Granite M(5) [1] 0.011 649 134 1140 1.9594 0.20308 0.06998 11929 06 M(5) [1] 0.005 754 188 411 2.1892 0.22673 0.07003 13179 08 M(5) [1] 0.005 75 18 418 2.2239 0.23301 0.07008 13359 17 M(5) [1] 0.006 311 72 282 1.8716 0.19517 0.06955 11499 09 M(5) [1] 0.005 783 126 301 1.3293 0.13830 0.06971 8359 06 M(5) [1] 0.004 550 85 400 1.3931 0.14455 0.00699 8709 08 M(5) [1] 0.005 523 71 327 1.1541 0.12118 0.06907 7379 06 NM(5) [1] 0.003 1804 294 198 1.2199 0.12849 0.06886 7799 05 UI =9369 26 Ma, LI= 194 9126 Ma (2|); MSWD = 9.9; PB0.01 (Model 2)

11029 05 11779 07 11899 15 10719 08 8599 06 8869 08 7799 07 8109 06

9289 02 9299 05 9319 04 9159 04 9209 06 9259 04 9019 07 8959 05

97 -118b Sao Domingos Granite NM(0)[1] 0.003 1153 167 NM(0) [1] 0.005 1069 193 M(0) [1] 0.005 1423 236 M(1) [1] 0.009 869 138 NM(0) [1] 0.003 782 96 NM(0) [1] 0.005 769 127 UI =9309 12 Ma, LI=−21 9 82

8759 14 8949 06 8899 07 7309 05 7889 07 8599 06

9709 12 9349 04 9339 05 9279 06 9449 03 9229 04

3.0208 0.24357 0.08995 14059 16 2.9440 0.23779 0.08979 13759 09 2.9688 0.23951 0.08990 13849 11 3.6034 0.26520 0.09855 15169 12 MSWD = 0.31; P= 0.58 (Model 1)

Miscellaneous samples

584 1.3669 0.13881 0.07142 8749 12 242 1.4123 0.14596 0.07018 8789 05 336 1.3991 0.14462 0.07016 8719 07 148 1.0555 0.10919 0.06994 6689 04 649 1.1742 0.12076 0.07053 7359 07 266 1.3306 0.13827 0.06979 8359 05 Ma (2|); MSWD = 22; PB0.01 (Model 2)

(a) NM= nonmagnetic, M= magnetic, numbers in parentheses indicate side tilt used on Franz separator at 1.5 A power; [1]=number of grains analyzed (where recorded).(b) Total U and Pb concentrations, corrected for analytical blank. (c) Pb corrected for blank and non-radiogenic Pb (see text); *denotes radiogenic Pb. (d) Ages given in Ma using decay constants recommended by Steiger and Ja¨ ger (1977); uncertainties in ages are 2|.

124

Appendix D. Sm/Nd data

Sample

Location

Age (Ma)

Nd (ppm)

Sm (ppm)

147

143

Nd/144Nd

Tonalite Tonalite Dacite Granite Dacite Granulite Tonalite Granite Granodiorite

1465 ind. 1517 ind. 1513 1494 1481 1449 1412

11.97 29.33 9.29 40.45 4.68 25.12 9.11 139.35 40.42

2.11 7.26 2.46 7.63 1.23 5.19 2.22 33.39 10.01

0.10658 0.14968 0.16007 0.11409 0.15967 0.12501 0.14737 0.14485 0.14976

0.511965 0.512397 0.512497 0.512063 0.512512 0.512061 0.512385 0.512274 0.512375

−13.1 −4.7 −2.8 −11.2 −2.5 −11.3 −4.9 −7.1 −5.1

Granite Orthogneiss Orthogneiss Orthogneiss Young granite Orthogneiss Gneissic Gr. Gneissic Gr. Gneissic Gr. Gneissic Gr. Gneissic Gr. Gneissic Gr.

nd 1449 1424 1423 950 1456 1433 1422 1425 1444 1430 1444

13.82 37.14 37.86 47.1 16.81 16.08 47.54 18.47 50.2 16.99 58.23 10.05

2.73 5.97 6.96 9.93 2.34 3.04 10.45 3.11 9.41 3.45 11.21 1.998

0.11961 0.09719 0.11110 0.12751 0.08447 0.11445 0.13289 0.10194 0.11337 0.12289 0.11636 0.11946

0.512131 0.511841 0.511981 0.512194 0.511894 0.512036 0.512183 0.511950 0.512039 0.512114 0.512068 0.512084

−9.9 −15.5 −12.8 −8.7 −14.5 −11.8 −8.9 −13.4 −11.7 −10.2 −11.1 −10.8

Granite Gabbro Felsite tuff Granite Granitic Gn. Tonalite Granodiorite Granitic Gn. Granite Granitic Gn. Gneiss Alia. Granite

1389 nd 1758 1564 1790 1536 1480 1536 ind. 1556 ind. 1740

64.21 23.07 22.04 38.65 34.4 25.88 21.61 67.67 35.82 38.91 23.7 15.74

9.55 4.85 3.9 5.96 6.2 5.24 3.48 9.01 5.23 5.89 5.97 2.75

0.08993 0.12716 0.10720 0.09336 0.10889 0.12247 0.09751 0.08050 0.08834 0.09165 0.12673 0.10557

0.511595 0.512029 0.511740 0.511632 0.511711 0.511913 0.511758 0.511501 0.511602 0.511605 0.511869 0.511712

−20.3 −11.9 −17.7 −19.6 −18.1 −14.1 −17.2 −22.2 −20.2 −20.2 −15.0 −18.1

oNd(t)

TDM (Ga)

3.8

4.7 2.5 4.1 2.6 3.6

1.53 1.52 1.54 1.49 1.48 1.68 1.50 1.70 1.58

2.9 2.8 4.0 −0.2 3.4 3.1 3.9 3.6 2.7 3.7 3.5

1.47 1.56 1.57 1.49 1.36 1.54 1.62 1.48 1.52 1.55 1.52 1.51

4.3

−1.3 2.6 0.9 2.2 0.5 1.7 0.5 0.9 2.4

1.77 1.77 1.85 1.78 1.93 1.88 1.68 1.75 1.74 1.79 2.05 1.87

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

Rio Alegre domain 97-113 Lavrinha 97-121 Rio Aguapeı´ 97-122 Rio Alegre 97-123 Carrapato 97-124 Rio Alegre 97-137 Sta. Barbara 97-140 Pau a Pique 97-141 Maraboa 97-142 Rio Alegre Santa Helena batholith 97-101 Sarare river 97-102 Faz. Guape 97-105 Faz. Guape 97-106 Faz. Guape 97-107 Faz. Guape 97-108 Jauru 97-115 Pont. e Lacer. 97-120E Cardoso 97-120W Cardoso 97-135 Santa Elina 97-168 Ellus farm 97-169 Ellus mine Alto Jauru terrane 97-129 Alvorada Farm 97-130 Cabac¸ al 97-131 Cabac¸ al Mine 97-132 S.J.Q.M. area 97-133 S.J.Q.M. area 97-134 S.J.Q.M. area 97-136 Cachoeirinha 97-138 Cachocirinha 97-139 Cachoeirinha 97-145 Cachoeirinha 97-147 Jauru belt 97-149 Cachocirinha

Sm/144Nd

oNd (0)

Rock type

Cachocirinha suite Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Salto do Ceu Santo do Ceu Salto do Ceu Salto do Ceu

Tonalite

1546

28.41

5.53

0.11774

0.511884

−14.7

1.0

1.83

Gabbro Gabbro Gabbro Por. Gabbro Monzosyenite Monzosyenite Monzosyenite Granophyre Granophyre Granophyre Granophyre Granophyre

1470 1470 1470 1471 1470 1430 1430 1430 1430 1427 1430 1430

25.02 25.17 21.35 89.82 20.62 64.33 58.69 81.12 74.28 69.55 58.09 92.76

5.59 5.62 4.72 11.29 4.73 12.69 12.04 16.08 14.49 13.40 11.91 18.17

0.13511 0.13497 0.13380 0.07603 0.13867 0.11930 0.12410 0.11987 0.11793 0.11650 0.12392 0.11853

0.512137 0.512104 0.512132 0.511351 0.512158 0.511914 0.511972 0.511903 0.511877 0.511878 0.511956 0.511858

−9.8 −10.4 −10.0 −25.1 −9.4 −14.1 −13.1 −14.3 −14.9 −14.8 −13.4 −15.2

1.9 1.2 1.9 −2.3 1.6 0.0 0.2 −0.3 −0.5 −0.2 −0.1 −1.0

1.75 1.80 1.73 1.86 1.79 1.81 1.82 1.84 1.85 1.82 1.84 1.89

Notes: 143Nd/144Nd normalized to 146Nd/144Nd = 0.72190. mNd(0) calculated relative to CHUR(0)=0.512638. Model ages (TDM) were calculated according to the single-stage depleted mantle model of DePaolo (1981). Primary ages used for mNd(t) are based on U/Pb ages where known or estimated (italics) based on regional geology.

M.C. Geraldes et al. / Precambrian Research 111 (2001) 91–128

97-150 Rio Branco RB-01 RB-02 RB-03 RB-04 RB-OS RB-06 RB-07 RB-08 RB-09 RB-10 RB-11 RB-12

125

126

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