Paleoproterozoic basement of Içana Domain, Rio Negro Province, northwestern Amazonian Craton: Geology, geochemistry and geochronology (U-Pb and Sm-Nd)

Journal of South American Earth Sciences 86 (2018) 384–409

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Paleoproterozoic basement of Içana Domain, Rio Negro Province, northwestern Amazonian Craton: Geology, geochemistry and geochronology (U-Pb and Sm-Nd)

T

Renata da Silva Verasa,∗, Rielva S.Campelo Nascimentoa, Marcelo Esteves Almeidaa,b, Jean-Louis Paquettec, Marcia Caroline R. Carneiroa a Universidade Federal do Amazonas (UFAM)/Postgraduation Program, Av. General Rodrigo Otávio, nº 6.200, Campus Universitário Senador Arthur Virgílio Filho, Setor Norte, Coroado I, CEP: 69077-000, Manaus, AM, Brazil b CPRM - Serviço Geológico do Brasil, Av. André Araújo, nº 2160, Aleixo, CEP 69060-000, Manaus, AM, Brazil c LMV-Laboratoire Magmas et Volcans – Université Clermont Auvergne, CNRS, IRD, OPGC – Campus des Cézeaux, 63000, Clermont-Ferrand, France

A R T I C LE I N FO

A B S T R A C T

Keywords: Amazonian craton Içana domain basement U–Pb zircon Sm–Nd isotopes Paleoproterozoic

The oldest rocks of the Rio Negro Province in the Amazonian Craton, have a complex evolutionary history and little known about them. In this paper are presented field, microtextural data, amphibole and plagioclase mineral chemistry, zircon U–Pb ages, and Sm–Nd isotope composition from Içana Domain basement rocks which belong to the Rio Negro Province. The studied area of the province is located in the extreme northwestern portion of Brazil (Amazonas State). The integration of the data obtained in this study allowed to propose the tectonometamorphic evolution of Içana Domain in the Rio Negro Province. The basement rocks comprise orthogneiss and metagranite of the Cauaburi Complex and homogeneous/heterogeneous diatexite of the Taiuaçu–Cauera diatexite. The Cauaburi Complex rocks exhibit a predominantly porphyroclastic texture and has a mafic mineralogy constituted by biotite, amphibole, sphene, epidote, and allanite. On the other hand, Taiuaçu–Cauera diatexite varies from inequigranular to porphyroclastic, being constituted by biotite, muscovite, allanite, and epidote. Basement rocks of the Içana Domain record three tectonic–metamorphic events, which were associated to regional events. The M1/D1 event was marked by the syn-tectonic emplacement of the Cauaburi Complex protolith rocks (1813 ± 19 Ma), and also by crystallization (1821 ± 14 Ma) and migmatization (1788 ± 11 Ma) of the Taiuaçu-Cauera diatexites in an orogenic event. The M2/D2 event reached high temperatures, similar to the M1/D1 event and was related to emplacement of S–type granites in the Içana Domain basement during the Içana Orogeny (ca. 1520 Ma). Furthermore, the lower temperature of the M3/D3 event was related to intracontinental reworking of the K'Mudku event (ca. 1200 Ma). The Cauaburi Complex basement rocks shows epsilon Nd(t) values range from +1.53 to +0.13, which allow the identification of a crustal contribution to the magma source (likely Orosirian sialic crust). Geochemistry data indicate that these rocks have been generated from partial melting of amphibolitic rocks, and also with an important crustal component related to magmatic arc settings. All igneous (1967 ± 25 Ma) and metamorphic (1911 ± 15 Ma) zircons grains within the Cauaburi Complex basement rocks are compatible with those found in Tapajós-Parima/Ventuari–Tapajós Province, reinforcing the crustal contribution hypothesis. Geochemistry and mineralogical data indicate that Taiuaçu-Cauera diatexite was likely formed by the partial melting of the metagraywacke. Two age populations (1993 ± 33 and 1842 ± 9 Ma) from detrital zircon of the homogeneous diatexite, suggest that the sediments were derived from different rocks of the Tapajós-Parima/Ventuari–Tapajós Province. The age of the Taiuaçu-Cauera diatexite is probably between 1842 ± 9 Ma (youngest detrital zircon) and 1788 ± 11 Ma (anatectic zircon). The youngest detrital zircon (1842 ± 9 Ma) and anatectic zircons (1788 ± 11 Ma), indicates that the protolith of TaiuaçuCauera diatexite is not a part of the Tunuí basin (Tunuí Group).

∗

Corresponding author. E-mail addresses: [email protected] (R.d.S. Veras), [email protected] (R.S.C. Nascimento), [email protected] (M.E. Almeida), [email protected] (J.-L. Paquette), [email protected] (M.C.R. Carneiro). https://doi.org/10.1016/j.jsames.2018.07.003 Received 8 February 2017; Received in revised form 12 July 2018; Accepted 12 July 2018 0895-9811/ © 2018 Elsevier Ltd. All rights reserved.

Journal of South American Earth Sciences 86 (2018) 384–409

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Fig. 1. Amazonian Craton division model in the geochronological provinces proposed by (A) Tassinari and Macambira (1999, 2004). (B) Santos et al. (2000, 2006). (C) Geological clipping of Rio Negro Province in the Brazilian territory (Amazon state), modified after CPRM (2006). Tectonic domains division according to Almeida et al. (2013). Addition of the Cauaburi Complex: São Jorge Facies (Carneiro et al., 2017), Cumati Facies (Almeida et al., 2013; Carneiro et al., 2017) and the Santa Izabel do Rio Negro Facies, which crops out in the Içana Domain (Veras et al., 2015), and Taiuaçu–Cauera diatexite (this work). 385

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Table 1 U–Pb ages available for the Uaupés, Imeri and Içana Domains. Sample

Imeri Domain 8697–8679 6580–6085 8699 MS-63 J-199 CJR-19 PR-3092 AH-1419 AF-1 PR-3141 Uaupés Domain PR-3215 J-263 AH-1213A J-98 UA-39 AH-1231 PRA-4 Içana Domain HB-667 JH-18

Rock

Crystallization (age) Ma

methods

Ref.

migmatite tonalite augen-gneiss laterite orthogneiss sienogranite sienogranite monzogranite granite with sphene monzogranite

1859 1835 1823 1810 1796 1593 1578 1530 1518 1501

1 2 1 3 5 4 4 4 3 5

orthogneiss orthogneiss orthogneiss monzogranite quartz-diorite monzogranite biotite granite

1756 1732 1736 1752 1703 1510 1552

monzogranite two-mica granite

± ± ± ± ± ± ±

9 3.7 06 27 21 25 9.5

A B A B B C C B A B

± ± ± ± ± ± ±

9.5 17 19 21 7 26 34

C C B B B B D

4 4 5 5 2 5 6

1778 ± 5.9 1521 ± 32

B D

5 7

± 17

Metamorphism Age (Ma)

methods

Ref.

1279

E

6

Methods: A. TIMS; B. U-Pb SHIRIMP; C. MC-ICP-MS; D. single zircon Pb-evaporation; E. K-Ar. Ref. - References: 1.Gaudette and Olszewski (1985); 2. Tassinari et al. (1996); 3. Santos et al. (2000); 4. Ibañez-Mejia et al. (2011); 5. Cordani et al. (2016); 6. Priem et al. (1982); 7. Almeida et al. (1997).

1. Introduction

2003). Additionally, Veras et al. (2015) identified metagranite from the Cauaburi Complex in the region of the Tunuí Mission area (Fig. 1C). The intrusive rocks in the basement of the Rio Negro Province are A–, I–, and S–type granites. The A–type granites are found in the Imeri and Uaupés domains and have a Pb–Pb zircon evaporation age ranging between 1756 ± 12 and 1746 ± 6 Ma (CPRM, 2006: Fig. 1C). The I– and S–type granites are the youngest with U–Pb zircon ages ranging between 1521 ± 32 and 1518 ± 25 Ma (Almeida et al., 1997; Santos et al., 2000). I–type granites are the most abundant and are found indiscriminately throughout the Rio Negro Province (Fig. 1C). On the contrary, S–type granites are less abundant in this province and initially were also mapped in the Içana Domain and in the eastern portion of the Imeri Domain (Fig. 1C). Previous studies have related the evolution of the Rio Negro Province to a collisional environment (i.e. magmatic arc) and subsequent intracrustal reworking (Tassinari et al., 1996; Santos et al., 2003; Almeida et al., 2013; Cordani et al., 2016). According to Almeida et al. (2013), the Rio Negro Province was formed by three distinct orogenic events. The first event (Cauaburi arc) was responsible for the generation of calc-alkaline igneous protoliths of the Cauaburi Complex, aged between 1810 and 1789 Ma. The second event (Querari Arc) aged from 1740 to 1703 Ma, generated calc-alkaline protoliths of the Uaupés Domain basement (Querari Complex) and sediment deposition of the Tunuí Group. Furthermore, the Cauaburi and Querari arcs were amalgamated during the Içana Orogeny, aged between 1483 and 1536 Ma, and generating the I–and S–type granites of the Rio Negro Province and closure of the Tunuí basin. Another model of evolution for the Rio Negro Province has been proposed by Cordani et al. (2016), which was based on the new U–Pb geochronological data and also from Rb–Sr, Sm–Nd, and U–Pb data. Cordani et al. (2016) proposed that the Rio Negro Province was structured by two orogenic cycles that were related to the magmatic arc setting. The first orogenic pulse (1800–1740 Ma) was associated with stacking of the magmatic arc against the cratonic area formed by the Ventuari–Tapajós continent. The second orogenic pulse (1580–1520 Ma) was related to the stacking of a new magmatic arc against an already-cratonized area of the first pulse. Table 1 shows the previously obtained geochronological results in the Rio Negro Province, mainly from northwestern Brazil near the

The Amazonian Craton is the largest geological unit of South America. It is located in the northern part of Brazil and extends to Bolivia, Colombia, Venezuela, French Guiana, Guyana, and Suriname (Fig. 1). The most widespread tectonic evolution proposals for the Amazonian Craton are based on mobilistic models and were elaborated from K–Ar, Rb–Sr, Sm–Nd, and U–Pb isotopic studies (Cordani et al., 1979; Teixeira et al., 1989; Tassinari et al., 1996; Tassinari and Macambira, 1999, 2004; Santos et al., 2000, 2006). Among these models, the ones proposed by Tassinari and Macambira (1999, 2004: Fig. 1A) and Santos et al. (2000, 2006: Fig. 1B) are the most widespread models in present literature. In the model proposed by Tassinari and Macambira (1999), the Amazonian Craton was divided into six provinces and included four mobile belts accreted to an older nucleus. On the contrary, in the model proposed by Santos et al. (2000, 2006), the Amazonian Craton was subdivided into seven geochronological provinces along with the K'Mudku Belt. The K'Mudku Belt was formed due to the intracontinental reflexes of Sunsás collisions in the western margin of the Amazonian Craton during the Mesoproterozoic, which has affected the Rio Negro, Transamazonic, and Tapajós–Parima Province rocks. The Rio Negro Province is located in the extreme northwestern portion of the Amazonian Craton (Fig. 1C) and is dominated by banded or foliated granitic rocks along with the local remnants of metasedimentary sequences and I- and S-type intrusive granites (Santos et al., 2000). This province was originally divided into tectonostratigraphic Alto Rio Negro and Imeri domains (Santos, 2003; CPRM, 2006). However, based on integration of field, geochemical, and geochronological data of basement rocks, Almeida et al. (2013) subdivided the Rio Negro Province into three tectonic domains (Fig. 1C). Thus, the basement of the Imeri Domain is made up of calc-alkaline orthogneiss and metagranite of the Cauaburi Complex aged between 1810 ± 6 and 1789 ± 6 Ma. Similarly, calc-alkaline orthoderived rocks with crystallization ages ranging between 1740 ± 2 and 1703 ± 7 Ma (Querari Complex), represent the basement of the Uaupés Domain. However, the basement of the Içana Domain is comprised of metasedimentary sequences of the Tunuí Group, which a minimum sedimentation age of 1720 ± 11 Ma was obtained from younger clastic zircon (Santos, 386

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Fig. 2. Geological map of Içana Domain in Tunuí Mission and surrounding areas, show the distribution of orthoderived rocks from Cauaburi Complex, paraderived rocks from Taiuaçu-Cauera, and granitoids from Rio Içana Intrusive Suite.

(hornblende) granodiorite gneiss, monzogranite, rare tonalite, enclaves of quartz diorite, and mylonite, which were probably formed under greenschist facies conditions (Almeida et al., 2002, 2007). According to Brito et al. (2000), the Santa Izabel do Rio Negro Facies rocks are chemically similar to medium– to high-K calc–alkaline granites. The high CaO and MgO contents in these rocks are comparable to that in the Australian I–type granites and granites of pre-to post-collisional settings (Brito et al., 2000). The Cumati and São Jorge Facies have been included in the Cauaburi Complex (Almeida et al., 2013; Carneiro et al., 2017) based on their geochemical/geochronological (Cumati Facies) and structural/ metamorphic (São Jorge Facies) characteristics. The Cumati Facies (previously known as the Cumati Complex; CPRM, 2006) consist of fine-grained banded tonalitic and granodioritic orthogneiss, with calcalkaline affinity and aged 1784 ± 7 Ma (Almeida et al., 2013, Fig. 1C). The São Jorge Facies ranges from fine to medium-grained monzogranitic leucogneiss, with millimeter-sized gneissic banding. Although alkaline, their structural/metamorphic characteristics are comparable to the other facies of the Cauaburi Complex (Carneiro et al., 2017). More recently, Carneiro et al. (2017) proposed three tectono-metamorphic events (D1, D2/M2, and D3 events) for the Imeri Domain, based on the Cauaburi Complex basement rocks. According to the authors, the D1 event was related to the Cauaburi Orogeny (1789–1810 Ma; Almeida et al., 2013) and caused S1 foliation in the rocks during the syn-tectonic emplacement of the basement rocks. The D2/M2 event was associated with the Içana Orogeny (1520–1480 Ma; Almeida et al.,

Colombian and Venezuelan borders. However, there is not enough data on the rock distribution, i.e., basement, granites, and metasedimentary sequence, in the Rio Negro Province, which makes it difficult to propose an evolutionary model. The previously proposed models lack robust field data because these studies were conducted on the basis of isotopic data, which involved sampling on the regional scale (Tassinari et al., 1999; Santos et al., 2000; Cordani et al., 2016). To overcome the above mentioned problems, the proposed study aims to contribute towards the knowledge of tectono-metamorphic evolution in the Rio Negro Province by studying rocks from Içana Domain basement in the region of Tunuí Mission (Fig. 2 using field, petrographic, geochemical, and geochronological data.

2. Basement rocks in the Rio Negro Province: a regional overview 2.1. Cauaburi Complex Based on the compositional and deformational characteristics, the Cauaburi Complex has been subdivided into Tarsira and Santa Izabel do Rio Negro Facies (Almeida et al., 2002). It has been determined that the Tarsira Facies occurs mainly in the Imeri Domain. This facies is composed of augen biotite gneiss and ovoid (meta)granitoid, with predominantly monzogranitic composition (Melo and Villas Boas, 1993; Almeida et al., 2002, 2013). The Santa Izabel do Rio Negro Facies crops out in the middle Negro River, near Santa Izabel do Rio Negro (Almeida et al., 2002, 2007; Carneiro et al., 2017), and it is formed by biotite 387

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Fig. 3. Macroscopic aspects of Cauaburi Complex rocks. The location of samples is provided in Fig. 2. Photos B - 08; C and D - 21; E − 02. (A) Classification modal schemes, according to Le Maitre (2002) and Streckeisen (1976). (B) Biotite metagranite with prominent lath-shaped feldspar megacrystals. (C) Biotite metagranite with preferential orientation of lath-shaped feldspar crystals free of deformation. (D) Dextral shear zones generated by the magmatic flow (Blumenfeld and Bouchez, 1988). (E) Biotite gneiss with preferential orientation of mafic minerals.

psamo–pelite deformed under low metamorphic conditions and mainly comprises quartzite (sericite quartzite, sericite-andaluzite quartzite, and ferruginous quartzite), metapelite, graphite pelite, phyllite, schist, and itabirite (CPRM, 2006). In the Brazilian territory, it constitutes of Tunuí and Caparro mountains, which trending NNE–SSW and N–S, respectively (Fig. 2). In addition to low-grade metamorphic rocks, the CPRM (2006) also described paragneiss at high metamorphic degree, locally migmatized, with NE–SW trending, and folded with a dome-andbasin interference pattern. The paragneiss is informally known by the authors as Taiuaçu–Cauera Paragneiss. The Tunuí Group rocks has the sedimentation interval established between 1720 ± 11 and 1520 ± 32 Ma. The maximum age of sedimentation is 1720 ± 11 Ma and was obtained from youngest detrital zircon in quartzite of the Serrinha Unit (Santos, 2003). The minimum age is tentatively inferred based on Tunuí Group xenoliths in the Içana S-type granite (1520 ± 32 Ma; Almeida et al., 1997).

2013) and it was responsible for S2 foliation under P and T conditions at around 718 °C and 5.84 kbar (amphibolite facies), as well as emplacement of I- and S-type granites, i.e., Uaupés and Içana intrusive suites (Santos et al., 2000; Almeida et al., 1997). The D3 event was associated with the K'Mudku Event (1300–1110 Ma; Santos et al., 2000) and generated S3 foliation under greenschist facies conditions. 2.2. Querari Complex The geological data available on the basement of the western part of the Rio Negro Province is not sufficient. According to Almeida et al. (2013), the Querari Complex basement is made up of gneiss and metagranite, with composition varying from monzogranitic to dioritic (Fig. 1C) and has a medium-to high-K calc-alkaline affinity. These rocks present trending NE–SW (locally E–W), defining the regional foliation, which are associated with mega sinistral shear zones. The basement of the Querari Complex has yielded ages ranging between 1703 ± 7 (Tassinari et al., 1996) and 1740 ± 2 Ma (Almeida et al., 2013).

3. Field geology of basement rocks at Tunuí Mission and surrounding areas

2.3. Tunuí Group The Tunuí Mission is located in the northwestern part of the State of Amazonas near the Brazil -Colombia borders. The field work conducted

The Tunuí Group represents a metasedimentary sequence of 388

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Fig. 4. Macroscopic aspects of Taiuaçu-Cauera diatexites at the margin of Matiri Creek (29 - see map; Fig. 2). (A) Overview of the heterogeneous diatexite outcrop. (B) Heterogeneous diatexite with discontinuous compositional banding relicts. (C) Heterogeneous diatexite with nebulite relict structure. (D) S1 foliation with crenulation marking the development of S2 foliation. (E) Deflection of the S1 foliation (NNE-SSW) to the NW (S2) due to E-W trending shear zone.

Fig. 5. Macroscopic aspects of Taiuaçu-Cauera diatexite outcrop at the margin of Içana River (44 – see map; Fig. 2). (A) Homogeneous diatexite with porphyroclastic texture. (B) Homogeneous diatexite with igneous texture. (C) Homogeneous diatexite with fold ghosts.

389

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Table 2 Modal composition of Cauaburi Complex and Taiuaçu-Cauera diatexite in the Içana Domain. Sample

Qz Kfs Pl Bt Ms Ed Spn Ep* Aln Ap Zrn Opq Chl Ep Ser ΣM Q A P

Cauaburi Complex

Taiuaçu-Cauera diatexite

02

08A

10

12

14A

18

19

20A

20B

21A

21B

21C

44

29A

29B

29C

28.1 34.1 28.5 6.0 – tr 0.8 0.9 0.4 tr 0.2 0.4 tr tr 0.6 9.0 31.0 37.6 31.4

21.3 27.5 35.4 11.0 – 2.4 0.1 1.1 0.3 0.1 0.3 0.2 tr tr 0.3 15.5 25.3 32.7 42.0

25.2 30.5 28.9 11.7 – 0.2 0.6 2.1 tr tr tr 0.7 tr tr 0.1 15.3 29.8 36.1 34.2

27.4 15.3 34.1 21.4 – – 0.4 0.1 0.1 0.4 0.1 0.1 0.1 tr 0.5 22.6 32.2 19.9 44.4

40.0 25.4 22.1 9.3 – – 2.1 tr tr tr 0.1 0.8 tr tr 0.3 11.9 45.7 29.0 25.3

21.2 22.6 30.3 17.3 – 3.5 2.3 2.0 tr tr 0.1 0.6 tr tr 0.1 25.8 28.6 30.5 40.9

30.2 32.3 28.1 8.3 – – 0.3 0.6 tr tr tr tr tr tr 0.2 9.2 33.3 44.5 31.0

31.7 40.3 25.9 1.6 – – tr tr tr tr tr 0.5 tr tr tr 2.1 32.8 41.2 26.5

29.3 36.8 26.4 6.3 – – 0.3 tr tr tr tr 0.9 tr tr tr 7.5 31.6 39.8 28.5

22.0 39.4 32.8 5.1 – – 0.2 tr 0.1 0.1 Tr 0.3 tr tr tr 5.8 23.4 41.8 34.8

31.1 38.2 24.2 5.3 – – 0.3 0.2 0.1 0.1 0.1 0.5 tr tr tr 6.6 33.3 40.9 25.9

34.7 22.7 32.5 9.6 – – 0.2 0.1 tr tr tr 0.2 tr tr tr 10.1 38.6 25.3 36.2

31.3 33.1 29.5 4.3 0.6 – – 0.1 0.1 tr tr 0.5 – tr 0.5 5.5 33.3 32.3 31.4

32.5 27.0 25.1 13.7 1.5 – – 0.1 0.1 tr tr 0.8 – tr tr 14.5 38.4 31.9 29.7

24.8 37.51 30.3 4.0 1.3 – – tr 0.1 tr tr 0.2 – tr 1.8 6.1 26.8 40.5 32.7

25.2 32.9 36.6 2.4 0.9 – – 0.1 tr tr 0.1 tr – tr 1.8 4.4 26.6 34.7 38.6

Abbreviation of minerals by Whitney and Evans (2010). Other abbreviations: tr = trace minerals. Ep* igneous epidote.

The homogeneous diatexite exhibits a light gray color, varies from fine to medium matrix, and feldspar porphyroclasts measuring up to 1.5 cm on the largest axis (Fig. 5A and B). This foliation is usually folded with open folds as ghost structures (Fig. 5C) and an axial plane according to N70ºE, which coincides with the orientation observed in the shear zone (S3) where granites of the Içana Intrusive Suite are reworked.

in this area was concentrated along the main rivers. In the study area, the basement is comprised of Paleoproterozoic rocks (Cauaburi Complex and Taiuaçu–Cauera diatexites), covered by metasedimentary rocks of the Tunuí Group and intruded by younger S–type granites (Fig. 2). The rocks of the Cauaburi Complex crop out in the central and northern portions of the study area (Fig. 2). They range from metagranite to orthogneiss with monzogranitic composition (Fig. 3A). These rocks have a porphyroclastic texture, with tabular or ovoid K-feldspar and plagioclase megacrystals, measuring between 0.5 and 0.3 cm in size, varying from tabular or square forms, or in (less frequently) a subrounded shape (Fig. 3B and C). These porphyroclasts are oriented according to N25ºE/65ºNW and are immersed in a medium-grained matrix with mafic minerals oriented along N43ºW/70ºSW. Biotite-rich mafic enclaves measure more than 15 cm and are commonly oriented according to N35ºE. Igneous textures are apparently preserved in the rocks with higher concentrations of porphyroclasts, (Fig. 3B and C). This is due to the inhibition of metamorphic foliation development by the large amounts of porphyroclasts, which confers itself an igneous aspect. These rocks present microtextures such as intense recrystallization of the matrix that was a consequence of high-temperature metamorphic event. In the northern portion of the study area, at Jurupari Chute, in Peuá Creek (Fig. 2), megacrystals comprise approximately 80% of the rock (Fig. 3C and D). The centimeter-sized dextral shear zones (Fig. 3D) are generated where the concentration of megacrystals is higher as resulted from magma flow. A Predominantly square shape of the porphyroclasts, and lack of evidence macroscopic deformation in the solid state, indicate magmatic foliation (S0), which coincides with the S1 foliation of Taiuaçu-Cauera diatexite. However, in rocks with less porphyroclasts, it is possible to observe a metamorphic foliation marked by the orientation of deformed porphyroclasts and mafic minerals (Fig. 3E), which are oriented according to N43ºW/70ºSW; this correlates with S2 regional foliation (Carneiro et al., 2017). The Taiuaçu-Cauera diatexite varies from heterogeneous to homogeneous, with monozogranitic composition (Fig. 3A), and occurs in the southern portion of the area (Figs. 2 and 4A). The heterogeneous diatexite exhibits a weakly penetrative S1 foliation according to N08ºE/ 80ºNW (Fig. 4B and C), is crenulated, and generates asymmetric folds with a subvertical axial plane (S2) according to S80ºE/71ºSW (Fig. 4D). Shear zones with an E-W direction and sinistral kinematics deflect the foliation S1 to NW-SE (Fig. 4E).

4. Petrography and mineral chemistry Amphibole, biotite, and plagioclase chemical compositions were obtained using a CAMECA SX-50 electron microprobe with four WDS spectrometers and a Kevex EDS at the Electron Microprobe Laboratory of the University of Brasília. The accelerating voltage and beam current were set to 15 kV and 20 nA, respectively. The mineral chemistry data obtained for amphibole, biotite, and plagioclase are important for making both pressure and temperature estimates. 4.1. Cauaburi complex Orthogneiss is composed of quartz, microcline, plagioclase, biotite, and amphibole as essential minerals, and sphene, epidote (primary and secondary), allanite, zircon, apatite, and opaque minerals as accessories (Table 2). Microcline porphyroclasts are tabular or lath-shaped and are up-to 4 cm long. Their orientation results from magmatic flow (Fig. 6A). They present extinction, subgrain texture, deformation twinning (Fig. 6B), and mantle-and-core structure. Matrix crystals are on average 0.2 mm long and have a granoblastic texture (Fig. 6C). The composition of plagioclase porphyroclasts varies according to the presence of mafic minerals in rocks. In rocks with amphibole, plagioclase is andesine (porphyroclasts and matrix: Table 3), but in rocks without amphibole the plagioclase is oligoclase (porphyroclasts and matrix) and albite (rim crystals of the matrix: Table 4). Its main textures are undulose extinction, curved twinning, kink bands (Fig. 6D), and subgrain textures. Matrix crystals commonly occur with undulose extinction, except when they present a granoblastic texture. Quartz displays undulose extinction. In mylonitized parts, the contacts are lobate, which indicates recrystallization of the grain migration boundary (Fig. 6E). Subgrain textures, deformation bands, and sometimes chessboard patterns, are also developed in it. Biotite is an annite–siderophyllite (Tables 3 and 4) shaped dominant 390

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Fig. 6. Microtextural aspects of Cauaburi Complex rocks. (A) Feldspar and plagioclase porphyroclast with corroded rim, aligned due to the magmatic flow (MA21C). (B) Microcline porphyroclast with deformation twinning exhibiting undulose extinction (MA20A). (C) Recrystallized quartz-feldspar matrix with granoblastic texture (MA21A). (D) Plagioclase porphyroclast with discontinuous and deformation twinning (MA21C). (E) Quartz with deformation lamellae (MA12). (F) Relicts of edenite-type amphibole associated with biotite (MA18). (G). Anhedral sphene associated with biotite, opaque and allanite (MA21A).(H) Metamorphic euhedral sphene developed over foliation (MA02).

did not allow for the preservation of a gneissic structure (Fig. 7B). However, in other aspects, such as modal composition and the individual textures of minerals, there are no differences between these rocks. The essential minerals are quartz, plagioclase, microcline, biotite, muscovite, whereas the opaque, apatite, allanite, and zircon are the accessory minerals (Table 2). Quartz occurs in the form of rounded inclusions (Fig. 7C), or interstitial grains with lobed contacts with the plagioclase and/or microcline. It also occurs in the form of larger grains, presents undulose extinction and developed subgrains and deformation lamellae. Sometimes occurs in the form of irregular grains embayed (Fig. 7D). Plagioclase is andesine that measures up-to 1.5 mm in length. It

mafic mineral. It commonly occurs with corroded edges (Fig. 6F), and its main inclusions are apatite and epidote, with or without an allanite core. Amphibole is an accessory mineral of an edenite type (Table 3) and occurs as anhedral crystals (Fig. 6F). Sphene occurs as biotite inclusions (Fig. 6G) and porphyroblasts over the matrix material (Fig. 6H). Epidote is represented by primary zoned crystals with allanite core. In rocks with amphibole, allanite is rare (or even absent). 4.2. Taiuaçu-Cauera diatexite The heterogeneous diatexite presents remnants of banded structure (Fig. 7A), but in homogeneous diatexites, the advanced state of melting 391

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Table 3 Representative analyses of amphibole, biotite and plagioclase of porphyritic (amphibole) biotite metagranite of Cauaburi Complex. Sample MA10

Amphibole

Biotite

Plagioclase matrix

Analysis SiO2 TiO2 Al2O3 FeO CaO MnO MgO Na2O K2O (OH) Total Si Al Al iv Al vi Ti Mg Mn Fe Fe2+ Fe3+ Ca Na K Fe# Mg# Na Ab Or

1 43.29 0.31 8.75 18.30 11.60 0.54 10.06 1.24 0.81 4.97 99.98 6.65 – 1.35 0.24 0.04 2.30 0.07 – 1.66 0.69 1.91 0.37 0.16 0.51 – – – –

2 (c) 43.29 0.53 9.40 18.80 11.59 0.56 10,00 1.30 1.01 3.24 99.81 6.55 – 1.45 0.23 0.06 2.26 0.07 – 1.64 0.74 1.89 0.38 0.20 0.51 – – – –

2 (r) 42.80 0.51 9.70 19.10 11.63 0.50 9.65 1.38 1.09 3.50 99.94 6.51 – 1.49 0.25 0.06 2.19 0.07 – 1.72 0.71 1.90 0.40 0.21 0.53 – – – –

3 (c) 42.36 0.53 11.09 20.53 11.43 0.50 8.87 1.38 1.29 1.74 99.90 6.35 – 1.65 0.30 0.06 1.98 0.06 – 1.67 0.90 1.84 0.41 0.25 0.57 – – – –

3 (r) 43.50 0.70 9.26 18.90 11.49 0.55 9.89 1.30 1.00 3.13 99.80 6.58 – 1.42 0.23 0.08 2.23 0.07 – 1.67 0.72 1.86 0.38 0.19 0.52 – – – –

1 36.10 1.52 15.79 19.44 0.00 0.40 11.19 0.08 9.41 5.77 99.93 5.54 – 2.47 0.39 0.18 2.56 0.05 2.49 – – 0.00 0.02 1.84 0.49 0.51 – – –

2 (c) 35.64 1.70 16.00 19.40 0.01 0.41 11.34 0.06 9.38 5.82 100.00 5.48 – 2.52 0.38 0.20 2.60 0.05 2.49 – – 0.00 0.02 1.84 0.49 0.51 – – –

2(r) 36.67 1.58 15.98 19.28 0.04 0.34 11.30 0.13 9.22 5.22 100.01 5.56 – 2.45 0.41 0.18 2.55 0.04 2.44 – – 0.01 0.04 1.78 0.49 0.51 – – –

3 36.73 1.81 15.82 19.51 0.02 0.42 11.33 0.12 9.30 4.65 100.03 5.54 – 2.46 0.36 0.21 2.55 0.05 2.46 – – 0.00 0.03 1.79 0.49 0.51 – – –

4 (c) 36.40 1.53 15.72 19.64 0.04 0.32 11.43 0.07 9.41 5.15 100.03 5.54 – 2.46 0.36 0.18 2.59 0.04 2.50 – – 0.01 0.02 1.83 0.49 0.51 – – –

4 (r) 35.80 1.71 15.61 20.27 0.08 0.35 11.02 0.15 9.25 5.50 100.02 5.51 – 2.50 0.34 0.2 2.53 0.05 2.61 – – 0.01 0.05 1.81 0.51 0.49 – – –

5 36.79 1.602 15.90 18.43 0.03 0.33 12.02 0.07 9.53 5.04 100.06 5.55 – 2.45 0.37 0.18 2.70 0.04 2.32 – – 0.01 0.02 1.83 0.46 0.54 – – –

6 36.26 1.33 15.07 19.94 0.03 0.39 11.58 0.07 9.36 5.67 100.07 5.57 – 2.43 0.30 0.15 2.65 0.05 2.56 – – 0.00 0.02 1.84 0.49 0.51 – – –

1(c) 58.29 0.00 26.12 0.03 7.041 – – 8.12 0.06 – 100.11 2.19 1.16 – – 0.00 – – – – 0.86 0.30 0.59 0.03 – – 33.40 66.27 0.33

porphyroclast 1(r) 60.11 0.00 25.48 0.05 6.33 – – 9.06 0.09 – 101.11 2.24 1.12 – – 0.00 – – – – 0.85 0.25 0.65 0.00 – – 27.72 71.79 0.49

5 58.27 0.00 25.83 0.07 7.50 – – 7.84 0.11 – 99.69 2.20 1.15 – – 0.00 – – – – 0.86 0.30 0.57 0.01 – – 34.37 65.01 0.62

7 58.36 0.00 26.08 0.03 7.61 – – 7.95 0.90 – 100.18 2.19 1.15 – – 0.00 – – – – 0.86 0.31 0.58 0.00 – – 34.43 65.11 0.46

(c) = core; (r) = rim; Fe# = Fe/(Fe + Mg) and Mg# = Mg/(Mg + Fe), in the case of amphibole use Fe2+ + Fe3+ as Fe. Amphibole: calculated based on 23 oxygen atoms and the Fe2+ and Fe3+ values were obtained from the normalization of 13 cations according to the method of Schumacher (in Leake et al., 1997); Biotite: calculated based on 22 oxygen atoms (Deer et al., 1966); Plagioclase: calculated based on 32 oxygen atoms (Deer et al., 1966).

The pressure conditions of the M2 event were obtained using the Alin-hornblende barometer (Anderson and Smith, 1995), and the temperature conditions were calculated using edenite–tremolite and pargasite–hornblende reactions, according to Holland and Blundy (1994). The thermometer's use was restricted to granitic igneous rocks and amphibolite grade metamorphic rocks, where T varied from 400 °C to 900 °C. Pressure and temperature limits were obtained from amphibole and plagioclase compositions (Table 6). Temperatures obtained using the andesine-edenite geothermometer range between 746 °C and 780 °C, which indicates a metamorphic peak; this temperature interval is compatible with microtextures of Içana Domain basement rocks. The microcline with granoblastic texture (Figs. 6C and 7F), lobate grain boundaries between quartz and feldspar (Fig. 7C), chessboard subgrain in quartz (Fig. 6E), and sphene porphyroblast (Fig. 6H; Cauaburi Complex rocks) indicate recrystallization temperatures between 630 °C and 700 °C (Vidal et al., 1980; Yund and Tullis, 1991; Stipp et al., 2002; Kruhl, 1996; Corfu, 1996; Pidgeon et al., 1996). If the values obtained from the border of edenite crystals are used (Table 6), it is estimated that pressures associated with this metamorphic event would be ranging between 4.5 and 4.86 kbar. The M3 event is marked by quartz with undulose extinction and deformation lamellae that indicates temperatures between 300 °C and 400 °C (Passchier and Trouw, 2005).

presents inclusions of quartz with a myrmekite texture that is in contact with microcline (Fig. 7E) showing deformation twinning and undulose extinction. Plagioclase from matrix is also andesine (An34: Table 5), is rarely albite (An8 is only in homogeneous diatexites: Table 5), and is commonly developed with a polygonal texture. Microcline occurs with an irregular shape measuring up to 4.0 mm in size, and presents undulose extinction. The smaller grains of the matrix have a cuspate-like contact with plagioclase, and portions of the matrix contain aggregate of microcline with a granoblastic texture (Fig. 7F). Muscovite occurs as recurved grains with undulose extinction. The biotite is an annite–siderophyllite type (XFe 0.48–0.521 and Ti 0.26–0.31 pfu: Table 5) and has corroded edges and undulose extinction. Muscovite and biotite occur dispersed in homogeneous diatexite, but in heterogeneous diatexite they together define the foliation of the rock. Epidote occurs as euhedral primary crystals, often bordering allanite crystals, and as anhedral crystals resulting from the alteration of plagioclase. Zircon occurs as prismatic and tabular crystals and usually has oscillatory zoning. 5. Pressure–temperature conditions of metamorphism Microtextural analysis identifies the superposition of tectonometamorphic events: high temperature (M2) event reworked by a second low-temperature event (M3). Magmatic flow foliations of the Cauaburi Complex coincide with the relict S1 foliation of heterogeneous diatexite. This points out that the emplacement of the Cauaburi granite and migmatization of Taiuaçu–Cauera were concomitant with the first deformational event, which implies a syn-tectonic emplacement for the Cauaburi Complex rocks.

6. Multielement geochemistry A set of 13 rocks were analyzed for major and trace elements (Table 7): 9 monzogranitic metagranite and orthogneiss from the Cauaburi Complex and 4 rocks from Taiuaçu–Cauera diatexite. The samples were crushed and milled to form a very fine powder (∼200 mesh) in an iron carbide cup. Whole-rock powders were analyzed for 392

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Table 4 Representative analyses for biotite and plagioclase of porphyroclastic metagranite of Cauaburi Complex. Sample MA21A

Biotite

Plagioclase porphyroclast

Analysis SiO2 TiO2 Al2O3 FeO MgO CaO MnO Na2O K2O (OH) Total Si Al Aliv Alvi Ti Fe Fe3 Mn Mg Ca Na K Fe# Mg# An Ab Or

1 (c) 35.73 2.53 16.09 19.48 9.52 0.00 0.68 0.06 9.50 6.06 100.0 5.53 – 2.47 0.47 0.30 2.52 – 0.09 2.20 0.00 0.02 1.88 0.53 0.47 – – –

1 (r) 35.44 2.68 15.83 20.03 9.60 0.00 0.71 0.03 9.28 6.05 100.00 5.51 – 2.49 0.41 0.31 2.61 – 0.09 2.23 0.00 0.01 1.84 0.54 0.46 – – –

2 (c) 35.73 2.53 16.09 19.48 9.52 0.00 0.68 0.06 9.50 6.06 100.03 5.53 – 2.47 0.47 0.30 2.52 – 0.09 2.20 0.00 0.02 1.88 0.53 0.47 – – –

2 (r) 35.44 2.68 15.83 20.03 9.60 0.00 0.71 0.03 9.28 6.05 99.95 5.51 – 2.49 0.41 0.31 2.61 – 0.09 2.23 0.00 0.01 1.84 0.54 0.46 – – –

3 (c) 36.12 2.47 16.12 19.95 9.53 0.00 0.55 0.07 0.09 9.28 99.90 5.55 – 2.45 0.47 0.29 2.57 – 0.07 2.19 0.00 0.02 1.82 0.54 0.46 – – –

3 (r) 35.10 2.64 16.21 19.81 9.46 0.04 0.45 0.09 9.28 6.63 100.00 5.49 – 2.51 0.47 0.31 2.59 – 0.06 2.21 0.01 0.03 1.85 0.54 0.46 – – –

1(c) 60.24 0.00 24.54 0.06 – 5.74 – 9.12 0.10 – 99.89 2.26 1.09 – – 0.00 – 0.86 – – 0.23 0.66 0.01 – – 25.66 73.82 0.52

1(r) 59.32 0.03 24.92 0.12 – 6.13 – 8.85 0.20 – 99.72 2.23 1.11 – – 0.00 – 0.86 – – 0.25 0.65 0.01 – – 27.36 71.56 1.08

matrix 2(c) 60.4 0.00 24.70 0.00 – 5.72 – 9.26 0.16 – 100.33 2.26 1.09 – – 0.00 – 0.85 – – 0.23 0.67 0.01 – – 25.25 73.89 0.86

6(c) 60.08 0.00 24.06 0.03 – 5.31 – 9.40 0.16 – 99.16 2.27 1.07 – – 0.00 – 0.86 – – 0.22 0.69 0.01 – – 23.58 75.59 0.83

6(r) 60.65 0.00 23.48 0.06 – 4.68 – 9.83 0.13 – 98.88 2.29 1.05 – – 0.00 – 0.86 – – 0.19 0.72 0.01 – – 20.70 78.62 0.67

2(r) 66.20 0.00 19.58 0.01 0.26 – 13.01 0.10 – 99.16 2.47 0.86 – – 0.00 – 0.85 – – 0.01 0.94 0.01 – – 1.09 98.41 0.50

3(c) 60.40 0.00 24.70 0.00 – 5.72 – 9.26 0.16 – 100.33 2.26 1.09 – – 0.00 – 0.85 – – 0.23 0.67 0.01 – – 25.25 73.89 0.86

4(c) 63.48 0.00 22.49 0.01 – 3.35 – 10.81 0.15 – 100.35 2.36 0.99 – – 0.00 – 0.85 – – 0.13 0.78 0.01 – – 14.50 84.75 0.75

5(c) 59.03 0.00 24.61 0.05 – 6.14 – 8.66 0.12 – 98.62 2.24 1.10 – – 0.00 – 0.87 – – 0.25 0.64 0.01 – – 27.95 71.40 0.66

5(r) 66.38 0.00 20.02 0.03 – 0.46 – 12.31 0.08 – 99.35 2.47 0.88 – – 0.00 – 0.85 – – 0.02 0.89 0.00 – – 2.03 97.56 0.41

c) = core; (r) = rim; Fe# = Fe/(Fe + Mg) and Mg# = Mg/(Mg + Fe). Calculated based on oxygen atoms: Biotite: 22 (Deer et al., 1966); Plagioclase: 32 (Deer et al., 1966).

and/or possible fractionation of associated mineral phases. The rare earth element (REE) distribution pattern is characterized by variably enrichment in light rare earth element (LREE) related to high rare earth element (HREE) ((La/Yb)n: 5.21–29.30; Fig. 10A), and higher LREE fractionation ((La/Sm)n: 3.52–8.91) in comparison to HREE ((Gd/Yb)n:1.07–1.94). This character may be attributed to the presence of some mineral phases, such as sphene and allanite, or due to the fractionation of some mineral phases, rich in HREE, such as amphibole and zircon (Hanson, 1978; Romick et al., 1992; Hoskin et al., 2000). The Eu anomaly is negative (Eu/Eu* = 0.48–0.76), except for the MA19 sample, which yields positive anomaly of 1.06. The multielement diagram, shows negative anomalies of Sr, P, and Ti, and positive anomalies of Th, La, and Nd (Fig. 10B). Furthermore, the chondrite-normalized rare earth element (REE) and multi-element patterns diagram of the Cauaburi Complex basement rocks are correlated to the basement rocks (Santa Izabel do Rio Negro Facies) from the Imeri Domain (Fig. 10A and B). The Taiuaçu–Cauera diatexite has a REE distribution in a regular pattern with enrichment of LREE in relation to HREE ((La/Yb)n: 7.12–14.8), and higher LREE fractionation ((La/Sm)n: 3.57–3.77) in comparison to HREE ((Gd/Yb)n: 1.32–2.47; Fig. 11A), and shows a negative Eu anomaly (Eu/Eu*: 0.57–0.69). Similar to Cauaburi Complex rocks, the patterns obtained in the multi-element diagram display negative anomalies of Sr, P, and Ti and positive anomalies of Nd (Fig. 11B). Assuming that Cauaburi Complex rocks evolved by a fractional crystallization process (Fig. 12A), the negative Sr and Eu anomalies and compatible behavior of both CaO and Al2O3 relative to SiO2, indicate plagioclase fractionation. Negative anomalies of P and Ti indicate fractional crystallization of apatite and Fe-Ti oxides. Despite small compositional variation in the Taiuaçu-Cauera diatexite samples, the fractional crystallization curve (Fig. 12A) suggests that there may have

major, minor, and certain trace elements (Cu, Ni, Pb, Sr, Zn, and Zr) using inductively coupled plasma emission spectrometry (ICP-ES). The remaining trace elements were determined using inductively coupled plasma mass spectrometry (ICP-MS). All analyses were conducted at the ACME Mineral Laboratories, Canada (further information relating to the procedure of the analytical package can be found at www.acmelab. com). The orthogneiss and metagranite of the Cauaburi Complex are Sirich (SiO2: 61.5–69.2%), Mg-poor (MgO: 0.31–1.66%, with higher values related to amphibole-rich rocks), and K-rich (K2O: 3.5–7.8%, the sample MA21A shows the highest K2O concentration, which reflects the high percentage of K-feldspar porphyroclasts in this rock; Table 1, Fig. 3C and D), and results in geochemistry patterns slightly different of the other rocks from this unit. The Taiuaçu–Cauera diatexite are slightly more evolved rocks, compared to the Cauaburi Complex (SiO2: 68.2–69.9%, K2O: 4.52–6.12%, Al2O3: 14.82–16.05%, MgO: 0.66–0.72%). In comparison to average greywackes sampled worldwide (Wedepohl, 1995), the diatexite studied are depleted in MgO. In broad terms, the rocks that composed the Içana Domain basement are characterized by a metaluminous to slightly peraluminous character, and display a narrow range of A/CNK ratio (0.81-1.00 in Cauaburi Complex and 1.00-1.08 in Taiuaçu-Cauera diatexite; Fig. 8A and B). Both Cauaburi gneiss and Taiuaçu–Cauera diatexite present calc-alkaline affinity (Fig. 8C and D). Using the SiO2 as a differentiation index, major and trace elements show the one trend for Cauaburi Complex rocks. A compatible pattern is observed for TiO2, CaO, MgO, P2O5, Fe2O3t, Al2O3, Sr, Zr, and Ga, whereas an incompatible pattern is observed for K2O and Rb (Fig. 9), which suggests either a cogenetic or a similar evolutionary (i.e., fractional crystallization) for these rocks. However, owing to the small number of samples of Taiuaçu–Cauera diatexite and the limited SiO2 variation therein, it was not possible to consider evolutionary processes

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Fig. 7. Microtextural aspects of Taiuaçu-Cauera diatexite. (A) Biotite defining the foliation relicts in the heterogenous diatexite (MA29B). (B) Homogeneous diatexite (MA29C). (C) Rounded quartz inclusions in K-feldspar (MA29C). (D) Quartz with lobate contacts, indicated by the red arrow (MA29C). (E) Mirmekite texture formed in plagioclase at the boundary with K-feldspar (MA44). (F) Recrystallized matrix microcline with granoblastic texture (MA29C). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

7. Analytical methods and U-Pb and Sm-Nd results

been an active process involved in the magmatic evolution of these rocks. The experimental diagrams of the Patiño Douce (1999: Fig. 12B and C) were used to investigate possible sources for the Cauaburi Complex and Taiuaçu–Cauera diatexite. These images were obtained during the melting experiments using metamorphic rocks (metagraywacke, mafic metapelite, and felsic metapelite) and reactions between basaltic magmas and metamorphic rocks. In these circumstances, the rocks of the Cauaburi Complex point to a source of composition similar to magmas generated by the partial melting of amphibolite. The source of the Taiuaçu–Cauera diatexite is attributed to metagraywacke, which is consistent with its mineralogical composition. In a geotectonic context, the Içana Domain basement rocks have a similarity to magmatic arc rocks and calc-alkaline granites from a continental collisional setting (Fig. 12D). This idea is in accordance with multi-element diagrams (negative anomalies of Sr, P, and Ti and positive anomalies of Nd; Fig. 10B e 11B), typical characteristic of rocks formed in a subduction environment.

7.1. Zircon U-Pb dating Selected samples were crushed and milled in iron jaw crusher. Zircons were separated via standard density and magnetic techniques, and then mounted in epoxy resin under the binocular magnifying glass and polished to expose grain interiors. Morphology and internal structure of the zircons were studied in detail using cathodoluminescence (CL) imaging, and CL images were taken as a guide for selecting sites for U–Pb dating spots. U–Pb isotopic analyses of zircons were performed by LA-ICP-MS at the Laboratoire des Magmas et Volcans of the Blaise Pascal University (Clermont-Ferrand), France, employing a mass spectrometer Agilent 7500cs ICP-MS (quadrupole) coupled to a Resonetics M-50E laser. The maximum amplitude of the spots was 26 μm. Further details on analytical procedures LA-ICP-MS U–Pb are provided in the study proposed by Hurai et al. (2010) and Paquette et al. (2014, 2015). Results were plotted using Isoplot/Exv.4 (Ludwig, 2008). 7.2. Sm-Nd isotopes Whole-rock Nd isotopic ratios were determined at the Isotope 394

Analysis SiO2 TiO2 Al2O3 MgO CaO MnO FeO Na2O K2 O (OH) F Cl Total Si Al Aliv Alvi Ti Mg Mn Fe Fe3 Na K Ca Fe# Mg# An Ab Or

Sample

1(c) 36.67 2.61 16.51 10.81 0.00 0.39 19.29 0.09 9.58 3.64 0.36 0.031 100.03 5.51 – 2.49 0.43 0.30 2.42 0.05 2.42 – 0.03 1.84 – 0.50 0.50 – – –

1(r) 37.36 2.48 16.86 11.05 0.02 0.30 18.53 0.12 9.61 3.40 0.28 0.022 100.01 5.57 – 2.44 0.53 0.28 2.45 0.04 2.31 – 0.03 1.83 – 0.49 0.52 – – –

4(c) 36.66 2.79 16.95 11.22 0.00 0.38 18.65 0.11 9.73 3.18 0.41 0.028 100.10 5.46 – 2.54 0.43 0.31 2.49 0.05 2.32 – 0.03 1.85 – 0.48 0.52 – – –

4(r) 36.82 2.31 16.45 11.09 0.00 0.24 18.59 0.14 9.43 4.69 0.40 0.015 100.16 5.55 – 2.45 0.48 0.26 2.49 0.03 2.34 – 0.04 1.81 – 0.49 0.52 – – –

1(c) 35.43 2.09 16.46 10.40 0.06 0.33 19.98 0.03 9.08 5.92 0.29 0.023 100.08 5.47 – 2.53 0.47 0.24 2.40 0.04 2.58 – 0.01 1.79 – 0.52 0.48 – – –

1(r) 36.06 1.97 16.23 10.71 0.12 0.35 19.62 0.11 9.28 5.37 0.08 0.043 99.94 5.55 – 2.45 0.49 0.23 2.46 0.05 2.53 – 0.03 1.82 – 0.51 0.49 – – –

2(c) 46.12 1.25 30.84 1.18 0.03 0.00 4.64 0.23 9.81 4.37 0.03 0.000 98.53 6.31 – 1.69 3.28 0.13 0.24 0.00 0.53 – 0.06 1.71 0.00 – – – – –

2(r) 46.15 0.93 31.46 1.18 0.00 0.01 4.92 0.21 9.59 4.40 0.00 0.003 98.92 6.29 – 1.72 3.34 0.01 0.24 0.00 0.56 – 0.06 1.67 0.00 – – – – –

MA-29B

MA-29A

MA-29A

Heterogeneous

Homogeneous

Heterogeneous MA-29C

Muscovite

Biotite

Table 5 Representative analyses for biotite, muscovite and plagioclase of Taiuaçu-Cauera diatexite.

4(c) 44.03 0.42 31.86 0.91 0.01 0.01 4.58 0.17 9.80 4.27 0.00 0.010 96.15 6.18 – 1.82 3.46 0.04 0.19 0.00 0.54 – 0.05 1.76 0.00 – – – – –

MA-29B 4(r) 45.14 0.74 30.97 1.33 0.02 0.07 4.75 0.30 10.02 4.33 0.00 0.022 97.94 6.24 – 1.76 3.29 0.08 0.27 0.01 0.55 – 0.08 1.77 0.00 – – – – –

Homogeneous

2(c) 46.19 0.93 29.97 1.38 0.00 0.02 5.15 0.24 10.22 4.35 0.00 0.031 98.59 6.35 – 1.65 3.21 0.10 0.28 0.00 0.59 – 0.06 1.79 0.00 – – – – –

MA-29C 2(r) 46.45 0.97 29.15 1.73 0.04 0.07 5.23 0.21 9.89 4.35 0.00 0.011 98.34 6.40 – 1.60 3.13 0.10 0.36 0.01 0.60 – 0.06 1.74 0.01 – – – – –

1 59.56 0.00 25.62 – 7.42 – 0.03 7.70 0.16 – – – 100.53 2.22 1.127 – – 0.00 – – – 0.85 0.56 0.01 0.30 – – 34.45 64.66 0.90

MA-29A 2(c) 59.12 0.00 25.91 – 7.41 – 0.04 7.64 0.24 – – – 100.39 2.21 1.142 – – 0.00 – – – 0.85 0.55 0.01 0.30 – – 34.43 64.23 1.40

Heterogeneous

Plagioclase

1(c) 57.41 0.00 26.55 – 8.07 – 0.01 7.61 0.08 – – – 99.72 2.17 1.180 – – 0.00 – – – 0.86 0.56 0.00 0.33 – – 36.80 62.78 0.42

MA-29B 1(r) 58.61 0.00 25.99 – 7.05 – 0.03 8.11 0.13 – – – 100.06 2.20 1.150 – – 0.00 – – – 0.86 0.59 0.01 0.28 – – 32.23 67.07 0.70

Homogeneous

1 64.23 0.00 23.79 – 1.83 – 0.00 9.60 1.46 – – – 100.96 2.37 1.03 – – 0.00 – – – 0.84 0.69 0.07 0.07 – – 8.72 83.00 8.28

MA-29C 3(r) 60.68 0.00 25.40 6.96 – 0.00 7.94 0.13 – – – 101.21 2.25 1.11 – – 0.00 – – – 0.85 0.57 0.01 0.28 – – 32.40 66.90 0.70

3(c) 60.49 0.00 25.36 6.99 – 0.00 8.09 0.18 – – – 101.16 2.25 1.11 – – 0.00 – – – 0.85 0.58 0.01 0.28 – – 31.99 67.04 0.97

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Table 6 Representative amphibole-plagioclase pairs for (amphibole) biotite metagranite. P and T estimates according to Anderson and Smith (1995), Holland and Blundy (1994), respectively. The complete data set for plagioclase and amphibole is available in Table 3. Sample MA10 (amphibole) biotite metagranite Analysis

Andesine matrix 1 (c)

Edenite

Andesine matrix 5 (c)

Edenite

1 (r) – 33.40 66.27 0.33

FeOt/(FeOt + MgO) Anorthite Albite Orthoclase T ( ± 40 °C) P ( ± 0.6 kbar)

0.51 – – – 746 4.56

– 34.37 65.01 0.62

Andesine matrix 7 (c)

2 (r)

2 (c)

0.51 – – – 762 4.98

0.53 – – – 778 5.34

– 34.43 65.11 0.46

Mg-Hg

Edenite

3 (c)

3 (r)

0.57 – – – 780.7 6.34

0.52 – – – 757.6 4.86

Number of cations recalculated for plagioclase and amphibole based on 13 and 8 oxygen, respectively. Mg-Hs = magnesio-hastingsite; (c) = core; (r) = rim. Table 7 Major and trace element analyses of selected samples of Içana Domain basement. Sample

SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 LOI Total Ba Rb Th Nb Ta Sr Zr Hf Y U V Zn W Ga La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Cauaburi Complex

Taiuaçu-Cauera

18

10

08A

12

19

02

14A

21C

21A

29B

61.50 0.80 15.68 4.94 4.45 0.08 1.46 5.62 3.08 3.80 0.95 0.81 98.72 802 119.7 25.8 18.6 1.5 480.1 639.7 17.7 52.1 5 102 46 1 18.4 206.9 303.7 32.75 125.10 14.61 2.520 10.61 1.40 7.82 1.42 4.13 0.70 4.76 0.72

61.90 1.13 15.10 5.00 4.50 0.09 1.66 5.29 3.06 3.72 0.63 0.62 98.22 852 124.9 10.2 18.3 1.2 420.6 553.1 15.2 46 5.2 98 57 1.7 17.5 72.9 124.4 15.94 66.70 10.80 2.17 9.35 1.31 7.57 1.39 3.94 0.59 3.88 0.56

63.10 0.92 18.23 2.82 2.54 0.05 0.99 4.36 3.71 3.56 0.27 1.81 99.82 579 109.9 29.6 31.7 2.8 432 483.7 15.2 29.8 12.8 62 21 2.3 16.9 44.2 136.2 11.01 41.20 7.32 1.73 6.23 1.04 6.31 1.17 3.67 0.64 4.72 0.65

64.60 0.64 15.95 4.48 4.03 0.07 1.38 3.70 2.93 4.08 0.38 0.79 99.00 583 165.8 37.5 20.4 1.7 291.9 413.9 12.9 81.6 13.6 77 49 1.9 18.4 58.7 120.8 14.15 56.90 10.48 1.85 10.66 1.83 12.23 2.56 7.92 1.21 7.59 1.05

64.60 0.79 17.3 2.67 2.40 0.04 0.88 4.65 3.45 3.80 0.42 1.02 99.62 944 104.4 21.2 13.8 0.9 589.2 799.8 23.5 28.8 7 55 29 1.5 15.5 144.2 246.4 30.41 103.80 11.74 3.28 6.2 0.86 4.26 0.76 2.61 0.43 3.38 0.60

65.80 0.80 14.03 4.48 4.03 0.08 1.47 3.82 2.60 4.78 0.42 0.81 99.09 703 177.8 30.3 26 2.1 307.7 411.7 12.8 58.3 7.8 79 51 < 0.5 15.5 66.50 147.1 17.15 69.70 11.40 1.88 9.89 1.47 8.99 1.77 5.47 0.89 5.90 0.86

66.40 0.66 14.76 4.39 3.95 0.07 1.53 3.06 3.10 4.25 0.32 0.89 99.43 503 192.5 38 19.6 1.3 259.1 330 10.3 33.6 5.2 73 42 1.1 18.1 56.70 113.6 12.69 51.90 8.00 1.59 6.74 0.98 5.98 1.09 3.26 0.54 3.71 0.57

66.80 0.48 16.68 2.45 2.20 0.05 0.75 3.53 3.56 4.64 0.29 0.70 99.93 605 168.7 35.8 24.9 2.2 351.5 479.5 14.6 45.9 10.2 38 33 < 0.5 16 152.30 166.6 31.22 103.40 12.58 2.16 8.56 1.25 7.08 1.21 3.81 0.55 4.46 0.72

69.20 0.41 15.22 1.75 1.57 0.04 0.31 1.64 2.57 7.38 0.09 0.74 99.35 742 226.7 86.5 21.9 2.9 230.4 501.8 16.3 56.2 16.2 31 20 1.5 13.8 168.90 331.1 39.76 141.40 20.05 2.68 12.89 1.95 10.28 1.69 5.39 0.75 6.07 0.86

68.20 0.52 15.50 2.92 2.63 0.07 0.70 2.92 2.92 5.12 0.25 0.61 99.73 718 168.8 28.7 16.1 1.4 176.7 323.2 10.6 53.5 5.4 33 36 1.1 14.2 81.20 181.8 20.77 75.70 14.17 2.96 11.32 1.74 8.64 1.28 3.54 0.49 3.70 0.53

29A

44 68.20 0.48 16.05 2.51 2.26 0.05 0.66 2.46 2.95 5.16 0.11 1.13 99.76 768 168.4 20.1 21.4 1.9 187.4 377.6 12.4 40.3 4.5 31 32 1.7 14.1 65.60 148.5 16.88 62.80 11.23 1.98 9.71 1.66 9.45 1.74 5.45 0.73 5.10 0.76

29C 68.30 0.56 15.10 3.18 2.86 0.07 0.72 3.06 2.83 4.52 0.24 0.62 99.20 610 153 40.9 18.1 1.3 186.8 547.4 17.1 61.2 9.6 40 39 0.9 15.4 68.40 153.9 17.81 69.10 12.06 2.14 10.56 1.81 10.25 1.89 5.82 0.82 6.48 1.01

69.90 0.41 14.82 2.35 2.11 0.05 0.69 2.22 2.53 6.12 0.22 0.75 100.06 739 186.4 27.8 14.9 1.5 169.4 291.3 9.3 23.8 3.1 28 28 1.3 12.9 430 102.1 11.11 40.40 7.170 1.51 5.80 0.98 5.35 0.79 2.32 0.30 2.33 0.33

146 Nd/144Nd = 0.7219. Model ages were calculated using the values proposed by De Paolo (1981) for a depleted mantle (TDM). The εNd(t) values were obtained using zircon ages or estimated ages based on regional geology.

Geology Laboratory of the Federal University of Rio Grande of Sul, according to procedures described by Gioia and Pimentel (2000). Ratio measurements were determined using a thermal ionization multi-collector mass spectrometer, Finnigan TRITON, in static mode. Uncertainties for Sm/Nd and 143Nd/144Nd ratios are estimated to be lower than ± 0.5% (2σ) and ± 0.005% (2σ), respectively. Measured values were adjusted to the JNDI international standard and BHVO-1 reference material. The 143Nd/144Nd ratio was normalized relative to

7.3. U-Pb zircon LA-ICP-MS Samples were carefully chosen to characterize zircon in different 396

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Fig. 8. (A) Alumina saturation diagram (Shand Index; Shand, 1927), according to Maniar and Piccoli (1989). (B) Ternary diagram showing fields of saturation in alumina (Shand, 1947). (C) Barker and Arth (1976) ternary diagram. (D) Wright (1969) alkalinity diagram.

with very close ages– Table 8). The zircon is bipyramidal shaped euhedral crystal with a length of ca. 400 μm (1:3 ratio) with no inclusions or cracks and low luminescence in the CL image. Fine-scale oscillatory zoning is well preserved in the rim (Fig. 13A), indicating a magmatic origin (Pidgeon, 1992; Vavra et al., 1999; Hoskin and Black, 2000). The Th/U ratios in the core and rim are 0.55 and 0.07, respectively (Table 8: spot 09 e 10, Fig. 16A). (b) 1911 ± 15 Ma (MSWD = 0.66; n = 6): This age is a weighted average 207Pb/206Pb of the zircon population, which is characterized by euhedral–subhedral and bipyramidal forms and lengths of 250–300 μm (1:2 ratio). Most zircons contain inclusions, cracks, and local metamictization. The rims analyzed have oscillatory zoning that is clearly magmatic, and Th/U ratios vary between 0.39 and 0.58 (average 0.49, Table 8: Fig. 13B and C; spot 18 and 21). Zircon cores have low luminescence in CL images and weak oscillatory zoning (Fig. 13C, D, 13F; spot 22, 36, 57), and Th/U ratios vary between 0.22 and 0.29 (Table 8). Among the analyzed cores, there was only one which was unzoned, slightly rounded, highly luminescent in CL images (Fig. 13E; spot 55) and with a Th/U ratio of 0.57. CL images were used to establish the nature of this group of zircons: low luminescent rims and cores suggest an igneous origin (Fig. 13C, D, 13F), whereas the core with high luminescence indicates a metamorphic origin (Fig. 13E). The results of all analyses conducted on this group fall on the Discordia line (Fig. 16A). (c) 1813 ± 19 Ma (MSWD = 2.5; n = 13): This age is the weighted average of 207Pb/206Pb obtained in zircons with euhedral (slightly rounded) and bipyramidal forms, lengths of 320–400 μm (1:2 to 1:3 ratios), exhibiting local metamictic areas and small brighter inclusions in CL images (Fig. 13G to R). These crystals have euhedral cores with low to moderate luminescence and a Th/U ratio varying between 0.20 and 1.13 (average 0.53; spot 11, 29, 32, 41, 68, 20, 25, 47, 51). The rims are isometric with fine-scale oscillatory zoning (clearly magmatic), have a low luminescence, and a Th/U ratio varying between 0.29 and 0.72 (average 0.50; spot 59, 65, 67, 06). The thirteen analyses yielded 207 Pb/206Pb age of 1813 ± 19 Ma. (Fig. 16A).

varieties of rocks composing the basement. Sample MA21A was collected in Peuá Creek and represents porphyroclastic biotite metagranite of the Cauaburi Complex with sphene, epidote (primary and secondary), and allanite as accessory minerals. In this rock, the alignment of porphyroclasts defines the magmatic flow (Fig. 3C, D and 6A). Samples MA29 and MA44 were collected at the Içana River. These samples represent heterogeneous diatexite with a nebulite relict structure (MA29 sample: Figs. 4C and 7A) and homogeneous diatexite with ghost folds (MA44 sample: Figs. 5C and 7B), both from Taiuaçu–Cauera diatexite. A geological map showing the location of all samples is provided in Fig. 2. Using a combination of CL images and U–Pb ages, it was possible to identify three zircon populations for the Cauaburi Complex (MA21A sample) and heterogeneous diatexite Taiuaçu–Cauera (MA29 sample), and one population for homogenous diatexite Taiuaçu–Cauera (MA44 sample). The following text presents the textural and isotopic characteristics of the zircons analyzed. The Th/U ratio is used to discriminate between igneous and metamorphic origins: usually, a Th/U ratio > 0.1 indicates the magmatic origin and Th/U < 0.1 indicates the metamorphic origin (Hoskin and Black, 2000; Rubatto et al., 2001; Rubatto, 2002), although there are numerous examples where this rule does not hold valid (Pidgeon, 1992; Vavra et al., 1999; Zeck and Whitehouse, 1999; Kelly and Harley, 2005; Wan et al., 2011; Lopez-Sanchez et al., 2015). Since using Th/U ratio for discriminating the nature of zircon is not consensual, in this study CL images were mainly used to discriminate the nature of zircons. CL images combined with U–Pb isotope compositions of zircons enables elucidation of the evolutionary history of these high-grade metamorphic rocks.

7.3.1. Porphyroclastic metagranite of the Cauaburi Complex (MA21A sample) (a) 1967 ± 25 Ma (n = 2): This age is a weighted averaged 207 Pb/206Pb and comprises the analysis of only one crystal (core–rim 397

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Fig. 9. Harker plots for selected major and trace elements from Cauaburi Complex and Taiuaçu-Cauera diatexite rocks, Içana Domain.

Fig. 10. Cauaburi Complex shown for comparison are data from the orthoderived rocks of the Cauaburi Complex in the Imeri Domain, Santa Izabel do Rio Negro Facies (Carneiro et al., 2017). (A) Chondrite-normalized REE patterns (Boynton, 1984). (B) Multielement diagram normalized to chondrite (Thompson, 1982).

398

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Fig. 11. Trace element and multielement distribution patterns of Taiuaçu-Cauera diatexite. (A) Chondrite-normalized REE patterns (Boynton, 1984). (B) Multielement diagram normalized to chondrite (Thompson, 1982).

Fig. 12. (A) Rb/Sr vs. Sr diagram proposed by Allègre et al. (1977) to indicate magmatic differentiation. (B) and (C) Source rock (metapelite, metagraywacke, and amphibolite) discrimination diagrams by Patiño Douce (1999). (D) Tectonic setting (Nbn/Zrn) vs. Zr (ppm) discrimination diagrams (Thiéblemont and Tégyey, 1994).

discordant ages (207Pb/206Pb ages of 2020 ± 42 Ma: spot 89; 2005 ± 59 Ma: spot 86; 1954 ± 43 Ma: spot 87) have the lowest Th/U ratios and the highest U content (Table 8), which could be related to metamorphic recrystallization. (b) 1842 ± 9 Ma (MSWD = 1.05; n = 20): This age is the weighted average 207Pb/206Pb obtained in crystals with external morphology varying from a prismatic form with a length of ca. 240 μm (1:3 ratio) to a stubby form with a length of ca. 200 μm (1:2 ratio) or to rounded and ovoid forms (Fig. 14B and D to 14U). Based on the CL images, zircon cores were grouped into two types. Type 1 cores (n = 9) are slightly rounded, structureless, highly luminescent in CL images (Fig. 14D, I, 14J, 14K, 14M, 14O, 14Q, 14T, 14U; spot 08, 26, 30, 32, 37, 50, 59, 75, 77), and have Th/U ratios varying between 0.00 and 0.57 (average 0.24). Although type 1 cores have a mean Th/U ratio > 0.2, this does not rule out their metamorphic origin. According to Hoskin and Black (2000), high-grade metamorphic rock zircons may have Th/U ratios of > 0.2. Type 2 cores have oscillatory zoning (clearly igneous), low to moderate

7.3.2. Heterogeneous diatexite with nebulite relict structure (MA29 sample) (a) 1993 ± 33 Ma (n = 5): This age is the weighted average 207 Pb/206Pb obtained from the cores of individual crystals and from the core and rim of the same crystal. The morphology and internal structure of the isometric overgrowth has resulted in euhedral and bipyramidal forms with lengths between 200 and 250 μm (1:3 ratio) (Fig. 14A and C). The core has a rounded form, is structureless and has moderate to high luminescence (Fig. 14B and C; spot 86, 89). One zircon has a xenocrystal core with an angular form, low luminescence, and oscillatory zoning (Fig. 14A; spot 11). The angular shape of the xenocrystal has been described as relating to metasedimentary rocks resulting from grain breakage (Vavra et al., 1999). The Th/U ratio in the core varies between 0.00 and 0.41 (average 0.11), with the highest Th/U ratio obtained in the zoned xenocrystal. The only rim analyzed has a magmatic zoning, low luminescence, and a Th/U ratio of 0.30 (Fig. 14A; spot 10). This group of zircons has 207Pb/206Pb age of 1993 ± 33 Ma (Fig. 16B). Most 399

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Table 8 U-Pb LA-ICP-MS data on zircon from the Cauaburi Complex and Taiuaçu Cauera diatexite. Spot

Isotopic ratios Pb ppm

Th ppm

U ppm

Th/U

207

Pb

2σ error

235

Pb

2σ error

Rho

238

U

Sample MA21A - Porphyroclastic metagranite of the Cauaburi Complex Population 1 09040111b core 876 2163 3954 0.55 5.51736 10040111b rim 388 85 1193 0.07 3.72369 Population 2 18040111b rim 278 449 1154 0.39 4.53326 21040111b rim 134 255 440 0.58 4.88595 22040111b core 483 253 1152 0.22 4.74767 36040111b core 115 229 793 0.29 4.71008 55040111b core 207 413 726 0.57 3.88657 57040111b core 148 112 392 0.29 4.98170 Population 3 11040111b core 1036 1603 2865 0.56 4.09647 29040111b core 287 183 892 0.20 4.93489 32040111b core 132 190 386 0.49 4.45677 41040111b core 90 232 272 0.85 3.94167 59040111b rim 76 167 231 0.72 4.26725 65040111b rim 399 451 1572 0.29 4.10733 67040111b rim 941 2222 3605 0.62 3.78870 68040111b core 65 98 205 0.48 4.42464 06040111b rim 229 328 904 0.36 3.84826 20040111b core 318 565 1100 0.51 3.96343 25040111b core 106 191 232 0.82 4.08378 47040111b core 99 304 268 1.13 4.22740 51040111b core 84 169 229 0.73 4.27848 Sample MA29 - Heterogeneous diatexite with nebulite relict structure of the Population 1 10040111c rim 95 84 277 0.30 5.53218 11040111c core 134 146 353 0.41 6.00056 86040111c core 124 5 1460 0.00 5.09173 87040111c core 183 0 1574 0.00 3.78941 89040111c core 172 29 728 0.04 4.45831 Population 2 08040111c core 28 42 73 0.57 4.95504 12040111c core 46 57 137 0.41 4.80847

Age (Ma) 206

207

206

U

Pb

2σ error

Pb

206

Pb

238

U

2σ error

Conc. (%)

0.14338 0.09666

0.33086 0.22407

0.00856 0.00580

0.99 0.99

1970 1964

36 36

1848 1307

26 42

94 67

0.11850 0.12944 0.12316 0.12248 0.10244 0.12930

0.27860 0.30369 0.29300 0.29019 0.24479 0.30889

0.00716 0.00780 0.00750 0.00734 0.00610 0.00766

0.98 0.97 0.99 0.97 0.95 0.96

1926 1906 1919 1922 1882 1910

37 39 37 38 40 39

1210 1478 1905 784 1402 1770

29 34 42 19 31 38

63 78 99 41 74 93

0.10664 0.27302 0.12710 0.32330 0.11614 0.29342 0.10292 0.26202 0.11156 0.28465 0.10714 0.27326 0.09792 0.25237 0.11634 0.28902 0.10134 0.24717 0.10262 0.25294 0.11246 0.26513 0.11114 0.27024 0.11172 0.27579 Taiuaçu Cauera diatexite

0.00706 0.00820 0.00744 0.00660 0.00706 0.00672 0.00620 0.00710 0.00642 0.00648 0.00682 0.00678 0.00688

0.99 0.98 0.97 0.96 0.95 0.94 0.95 0.93 0.99 0.99 0.93 0.95 0.96

1780 1811 1802 1784 1778 1783 1780 1816 1847 1858 1827 1855 1840

38 38 39 39 41 41 40 41 38 37 42 40 40

1834 1781 1743 1507 1612 1357 1433 1634 1330 1437 1922 1560 1700

42 40 39 34 35 30 31 35 32 33 43 35 37

103 98 97 84 91 76 80 90 72 77 105 84 92

0.14028 0.1503 0.12836 0.0989 0.11438

0.33102 0.35191 0.29947 0.22933 0.25996

0.00834 0.00884 0.00696 0.00536 0.00606

0.99 0.99 0.92 0.90 0.91

1974 2010 2005 1954 2020

37 36 40 43 42

1817 1933 542 730 1393

40 42 12 16 29

92 96 27 37 69

0.13074 0.12242

0.31825 0.31185

0.0081 0.00784

0.96 0.99

1847 1829

39 38

1848 1736

41 38

100 95

Notes: Isotopic ratios errors in %; Aln Pb in ratios are radiogenic component, Aln corrected for 204Pb. discordance, as 100 - 100{t[206Pb/238U]/t[207Pb/206Pb]}; 4f206 = (common 206Pb)/(total measured 206Pb) based on measured 204Pb. Uncertainties are 2σ.

classified into three types: Type 1 rims have isometric overgrowths and oscillatory zoning (clearly magmatic), low to moderate luminescence (Fig. 14D, I, 14S, 14T; spot 09, 27, 68, 76), and Th/U ratios varying between 0.00 and 0.55 (average 0.38); Type 2 rims have non-isometric overgrowth, are ovoid with oscillatory zoning, display moderate to high luminescence (Fig. 14F, P; spot 19, 56), have Th/U ratios varying between 0.00 and 0.04 (average 0.02), and border type 2 cores; type 3 rims are characterized by nebulous overgrowth, are not zoned, display high luminescence (Fig. 14L, 14U; spot 36, 78), and have Th/U ratios varying between 0.18 and 0.23 (average 0.20). The thirteen analyses yielded 207Pb/206Pb age of 1798 ± 7 (Fig. 16B) and one is concordant with 207Pb/206Pb age of 1795 ± 39 Ma (core, spot 52; Fig. 14F; Table 9).

luminescence (Fig. 14E and H, 14L, 14N, 14P, 14R, 14S; spot 12, 18, 21, 25, 35, 48, 55, 61, 69), and Th/U ratios varying between 0.08 and 0.80 (average 0.48). Although most type 2 cores have a high Th/U ratio, one core has a Th/U < 0.1 (spot 61: Table 9; Fig. 14R); however, the presence of oscillatory zoning in this core indicates the igneous origin of a type 2 core. There are two rims within this age interval that present with textural and Th/U ratio differences: one rim has oscillatory zoning, moderate luminescence, and a Th/U ratio of 0.70 (Fig. 14G; spot 20), thereby indicating a igneous origin; and the other has a structureless rim, moderate luminescence, and a Th/U ratio of 0.22 (Fig. 14B; spot 82), thereby indicating a metamorphic origin. Among all the 20 analyses, three were concordant with 207Pb/206Pb ages of 1839 ± 37 Ma (type 2 core, spot 18; Fig. 14F), 1838 ± 39 (type 1 core, spot 26; Fig. 14I). The results of other analyses plot close to Concordia, or fall on or near to a discordia line, thereby yielding an upper intercept age of 1847 ± 16 Ma (Fig. 16B). Some type 1 and 2 cores are bordered with rims of a younger overgrowth (ca. 1798 ± 14 Ma). (c) 1798 ± 11 Ma (MSWD = 0.12; n = 13): This age is the weighted average 207Pb/206Pb obtained in core zircons and in the rim of zircons with type 1 and 2 inherited cores (previously described in this paper). The core analyses within this age group were obtained in zircons with a prismatic form, lengths between 200 and 250 μm, and exhibiting magmatic oscillatory zoning (Fig. 15A and E; spot 38, 40, 46, 52, 66). Th/U ratios vary between 0.01 and 0.73 (average 0.35). CL images enable the rims of the this group to be

7.3.3. Homogeneous diatexite (MA44 sample) The homogeneous diatexite presents with a single group of 22 zircons with external morphologies varying from a prismatic bipyramidal form with a length of ca. 240 μm (1:3 ratio) to an irregular form with a length of ca. 200 μm (1:2 ratio). All crystals have slightly rounded faces (Fig. 17A to 17T), most of these are fractured, and there are local metamitic areas (Fig. 17C, F, 17G, 17I) in almost all crystals (Fig. 17L, M, 17O). The cores have irregular and rounded forms, exhibit weak oscillatory zoning, with predominantly low luminescence, except for those that are metamitic (Fig. 17A, I; spots 05, 29). Th/U ratios in the core vary between 0.10 and 0.70 (average 0.44; spot 05, 06, 10, 29, 42, 46, 57, 58, 65; Table 10). The rims show isometric oscillatory zoning 400

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Fig. 13. Cathodoluminescence images by analyzed zircon crystals showing different ages and morphologies from porphyroclastic metagranite of Cauaburi Complex (MA21A sample).

with a thickness reaching 15 μm. The Th/U ratio in the rim varies between 0.07 and 0.78 (average 0.37; 07, 09, 18, 22, 26, 27, 28, 38, 40, 45, 47, 48, 49, 50, 51, 55, 56, 61, 66; Table 10) with lower values in thicker rims. The weighted average of 207Pb/206Pb ages obtained in the core and rim are 1821 ± 14 and 1788 ± 11 Ma, respectively (Fig. 16C).

by prismatic bipyramidal forms and growth zoning, indicating an igneous origin. This age is also obtained in the rim and core of inherited zircons in heterogeneous diatexite (MA29 sample). The fractured and angular shape of the core suggests a metasedimentary provenance, which is perhaps metagreywacke, although the welldeveloped growth zoning suggests an igneous origin for it. The age of the group is similar to rocks from the plutonic suites of the Tapajós–Parima Province (neighboring the Rio Negro Province: Santos et al., 2000), such as the orthogneisses/metagranites of the Rio Urubu Suite (Gaudette et al., 1996), charnockite of the Serra da Prata Suite (Fraga et al., 2009), and calc-alkaline granitoid of the Pedra Pintada and Martins Pereira (Santos et al., 2003; Almeida et al., 2007). The inherited zircons in this group perfectly agree with the Nd model ages (see Topic 7.5. for Sm-Nd whole rock).

7.4. Zircon genesis and significance of U-Pb ages 7.4.1. Ages of inherited zircon crystals (a) 1.93–2.0 Ga: This interval age is observed in the rim and core of a euhedral zircon of porphyroclastic metagranite in the Cauaburi Complex (MA21A sample). The morphology of this zircon is marked 401

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Fig. 14. Cathodoluminescence images by analyzed zircon crystals showing different ages and morphologies from heterogeneous diatexite with nebulite relict structure (MA29 sample).

Valério, 2006) and Mucajaí orthogneiss (metamorphic zircon: Santos et al., 2009): both of these units are located in the Tapajós–Parima Province. The inherited ages found in the Cauaburi Complex and Taiuaçu–Cauera diatexite (MA29 sample) are representative of an older crust that contributed to magma generation

(b) ca. 1.84 Ga: This age was obtained in heterogeneous diatexite zircons, with morphologies consistent to that of igneous (growth zoning) and metamorphic zircons (rims with poorly defined internal zoning). Possible sources of these zircons are granites of the Mapuera and Água Branca suites (igneous zircons: Almeida, 2006; 402

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Table 9 U-Pb LA-ICP-MS data on zircon from the Taiuaçu Cauera diatexite.

Spot

Pb Ppm

Isotopic ratios

Age (Ma)

Th

U

ppm

Th/U

ppm

Sample MA29 - Heterogeneous diatexite with nebulite relict structure of the Population 2 continuation 18040111c core 108 210 261 0.80 20040111c rim 65 119 169 0.70 21040111c core 46 63 126 0.50 25040111c core 47 70 134 0.52 26040111c core 153 16 495 0.03 30040111c core 235 3 893 0.00 32040111c core 52 37 191 0.19 35040111c core 157 361 494 0.73 37040111c core 46 40 185 0.21 48040111c core 34 47 103 0.46 50040111c core 68 134 217 0.62 55040111c core 41 49 117 0.42 59040111c core 57 9 197 0.04 61040111c core 256 83 1094 0.08 69040111c core 354 592 1430 0.41 75040111c core 60 39 198 0.20 77040111c core 70 76 223 0.34 82040111c 69 50 227 0.22 Population 3 09040111c rim 48 73 150 0.49 19040111c rim 78 0 357 0.00 27040111c rim 48 79 143 0.55 36040111c rim 199 178 766 0.23 38040111c core 50 61 145 0.42 40040111c core 150 6 533 0.01 46040111c core 146 76 476 0.16 52040111c core 69 144 196 0.73 56040111c rim 282 54 1372 0.04 66040111c core 30 45 101 0.45 68040111c rim 77 109 233 0.47 76040111c rim 157 0 633 0.00 78040111c rim 67 52 288 0.18

207

Pb

2σ error

235

206

238

U

Pb

2σ error

Rho

207

Pb

2σ error

206

U

Pb

206

Pb

238

U

2σ error

Conc. (%)

Taiuaçu Cauera diatexite 4.98388 4.13137 5.25327 4.89448 5.09048 4.26248 3.96434 4.19216 4.60595 4.75897 4.33025 4.42643 4.25159 3.89107 4.63452 4.49447 4.73343 4.97731

0.12478 0.10744 0.13504 0.12322 0.13026 0.11468 0.10542 0.10458 0.11664 0.11972 0.10698 0.10972 0.111 0.09422 0.11496 0.11202 0.11614 0.12258

0.32138 0.26924 0.33363 0.31541 0.32853 0.26993 0.25496 0.2718 0.30209 0.30034 0.28175 0.2879 0.27641 0.24716 0.30108 0.2881 0.30074 0.31717

0.00802 0.00674 0.00832 0.00782 0.00814 0.00672 0.00632 0.00666 0.0074 0.00726 0.00678 0.0069 0.00664 0.00586 0.0071 0.00676 0.00702 0.00738

0.99 0.96 0.97 0.98 0.97 0.93 0.93 0.98 0.97 0.96 0.97 0.97 0.92 0.98 0.95 0.94 0.95 0.94

1839 1820 1867 1840 1838 1872 1844 1829 1808 1878 1823 1824 1824 1866 1826 1850 1866 1861

37 39 39 38 39 42 41 38 39 39 38 39 42 38 39 40 39 40

1868 1816 1785 1750 1778 1523 1515 1551 1390 1699 1572 1781 1670 1350 1384 1657 1678 1665

40 39 39 38 38 34 33 34 35 36 33 37 35 29 30 34 34 34

102 100 96 95 97 81 82 85 77 90 86 98 92 72 76 90 90 89

4.59075 4.42035 4.64877 3.52401 4.56185 4.14699 4.73747 4.73964 3.17021 4.26773 4.26887 3.81968 4.46293

0.1172 0.1149 0.11796 0.08706 0.11386 0.10758 0.11816 0.11734 0.07856 0.10634 0.10538 0.10066 0.1122

0.30512 0.29094 0.30482 0.23211 0.29971 0.27382 0.31281 0.31321 0.2094 0.28102 0.28296 0.25083 0.29446

0.0077 0.00728 0.00754 0.00566 0.00732 0.0067 0.00756 0.00752 0.005 0.00666 0.00668 0.00594 0.0069

0.99 0.96 0.97 0.99 0.98 0.94 0.97 0.97 0.96 0.95 0.96 0.90 0.93

1785 1802 1809 1801 1805 1796 1796 1795 1796 1801 1789 1806 1798

38 39 38 37 38 41 39 39 39 40 39 43 41

1680 1328 1704 1445 1789 1640 1715 1706 1207 1550 1700 1483 1317

37 31 37 31 38 35 36 36 26 33 35 31 28

94 74 94 80 99 91 95 95 67 86 95 82 73

Fig. 15. Cathodoluminescence images by analyzed zircon crystals, showing different ages and morphologies from heterogeneous diatexite with nebulite relict structure (MA29 sample).

Complex (MA21 sample) yield a weighted average of 207Pb/206Pb age of 1813 ± 19 Ma. These crystals have a low to moderate luminescence, oscillatory zoning in the CL images, and Th/U ratios varying between 0.2 and 1.13, presenting clear characteristics of magmatic zircons

at ca. 1.82 Ga.

7.4.2. Crystallization ages of igneous protoliths and migmatization 1.80–1.82 Ga: Approximately 12 zircons from the Cauaburi 403

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Fig. 16. ICP-MS-LA U-Pb Concordia Diagrams: (A) Porphyroclastic metagranite of Cauaburi Complex - MA21A sample. (B) Heterogeneous diatexite with nebulite relict structure - MA29 sample. (C) Homogeneous diatexite - MA 44 sample.

7.5. Sm-Nd whole-rock

(Vavra et al., 1999; Hoskin, 2000; Corfu et al., 2003). In this study, this age was interpreted as representing crystallization of the Cauaburi Complex igneous protoliths. Ages obtained within this interval of error in clearly igneous zircons of homogeneous diatexite (MA44 sample) yield a concordant 207Pb/206Pb age of 1821 ± 19 Ma. Slightly lower ages obtained in igneous zircon rims of homogeneous diatexites have a weighted average 207Pb/206Pb age of 1788 ± 19 Ma. In the heterogeneous diatexites (MA29 sample), types 1, 2, and 3 rims have a weighted averaged 207Pb/206Pb age of 1798 ± 11 Ma. Type 1 rims exhibit magmatic zoning, low luminescence in CL images, and high Th/U ratios, thereby indicating their magmatic origin; Type 2 rims have magmatic zoning and low Th/U ratios of < 0.1, thereby reflecting their growth during partial melting, and subsequent interpretation as an anatectic zircon (Zeck and Whitehouse, 1999; Rubatto et al., 2001; Liu et al., 2015); Type 3 rims appear cloudy, structureless, highly luminescent, and have Th/U ratio of > 0.18. The shapes, internal textures, and unusual Th/U ratios > 0.1 of type 3 rims are consistent with that of the metamorphic zircons reported in high-grade environments (Vavra et al., 1999; Hokada and Harley, 2004; Kelly and Harley, 2005). The two distinct ages obtained in the core (207Pb/206Pb of 1821 ± 19 Ma) and rims (207Pb/206Pb of 1788 ± 19 Ma) of homogeneous diatexite (MA44 sample) can be interpreted as the beginning of partial melting and the crystallization end age of melts for Taiuaçu–Cauera diatexites.

To estimate the relative amount of continental crust accreted or recycled during each geological time interval, the initial Nd ratios were used together with geochronological, petrogenetic, and structural criteria of magmatic rocks as indicators of source materials. New Sm-Nd isotopic data (Santa Izabel do Rio Negro Facies, MA21A and MA02 samples; this paper) and previous data (Tarsira Facies; VR2A, VR6, VR15, VR2B, and VR13 samples; Rodrigues, 2016) were compiled and/ or modified using different Nd models for the depleted mantle (Table 11). They were also employed to recognize similar sources for the regional orthoderived basement of the Rio Negro Province. The Sm–Nd isotopic results obtained in this study agree with some previous data (Sato and Tassinari, 1997; Santos, 2003) and coincide with the Nd evolution field for the Rio Negro Province (Fig. 18). The data show positive εNd (1.78Ga) (+1.53 to +0.13) and 1.94–2.08 Ga Nd TDM model ages (Table 11), pointing to a mantle-derived (juvenile) origin for the granitic magmas (protoliths) that have local crustal source contributions possibly belonging to an Orosirian sialic crust.

8. Discussion and conclusions Orthogneiss and metagranite of the Cauaburi Complex and Taiuaçu–Cauera diatexite have a monzogranitic composition, but they differ in texture and mafic mineralogy. The Cauaburi Complex rocks exhibit predominantly porphyroclastic textures and mafic mineralogy of biotite, amphibole, sphene, epidote, and allanite. However, those of 404

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Fig. 17. Cathodoluminescence images by analyzed zircon crystals showing different ages and morphologies from homogeneous diatexite (MA44 sample).

magmatic flow foliation (S0 = N25ºE/65ºNW) of porphyroclastic metagranite, which is concordant with the relicts foliation (S1 = N08ºE/ 80ºNW) in solid state Taiuaçu-Cauera diatexite. The agreement between S1 and S0 foliation indicates that the emplacement of Cauaburi Complex protolith rocks and migmatization of the Taiaçu–Cauera diatexites occurred concomitantly in the same syn-tectonic event. S2

Taiuaçu–Cauera diatexite are inequigranular to porphyroclastic, with biotite, muscovite, allanite, and epidote. Three tectonic-metamorphic events can be recognized in the Içana Domain basement rocks. These events, D1/M1, D2/M2, and D3/M3, were responsible for S1, S2, and S3 foliation development, respectively. S1 foliation has trending NE-SW, and in the Cauaburi Complex, is given by 405

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Table 10 U-Pb LA-ICP-MS data on zircon from the Taiuaçu Cauera diatexite. Spot

Isotopic ratios Pb Ppm

Th

U

ppm

Sample MA44 - Homogeneous diatexite 05030111b core 99 281 06030111b core 89 133 07030111b rim 75 108 09030111b rim 69 163 10030111b core 50 201 18030111b rim 104 69 22030111b rim 36 95 26030111b rim 38 92 27030111b rim 90 63 28030111b rim 147 61 29030111b core 58 150 38030111b rim 104 133 40030111b rim 172 292 42030111b core 181 412 45030111b rim 121 95 46030111b core 18 101 47030111b rim 108 77 48030111b rim 234 408 49030111b rim 169 54 50030111b rim 107 202 51030111b rim 135 240 55030111b rim 94 160 56030111b rim 214 650 57030111b core 104 137 58030111b core 346 254 61030111b rim 308 239 65030111b core 76 165 66030111b rim 83 41

Th/U

207

235

ppm

Pb

Age (Ma)

2σ error

Pb

2σ error

Rho

238

U

of the Taiuaçu Cauera diatexite 401 0.70 2.98530 259 0.51 4.57583 239 0.45 4.37713 254 0.64 2.89929 651 0.31 3.40769 367 0.19 4.45737 146 0.65 3.62067 114 0.80 4.25766 411 0.15 2.93980 908 0.07 2.89977 269 0.56 3.26736 491 0.27 3.23690 1562 0.19 4.33887 727 0.57 3.94302 522 0.18 3.57756 480 0.21 3.30739 378 0.20 4.46144 745 0.55 3.98234 645 0.08 4.18492 335 0.60 4.31148 624 0.39 2.97660 326 0.49 4.04121 833 0.78 3.55862 477 0.29 4.86734 2599 0.10 4.06312 1346 0.18 3.29933 249 0.67 4.06421 344 0.12 3.93538

206

Pb

2σ error

206

U

0.05242 0.07452 0.07226 0.05576 0.05924 0.07294 0.06424 0.07592 0.05802 0.05008 0.05916 0.05864 0.07312 0.06942 0.06180 0.07142 0.07944 0.07014 0.07178 0.07810 0.05660 0.07586 0.06288 0.08764 0.07194 0.06074 0.07660 0.07348

207

Pb

0.19418 0.29819 0.29118 0.19008 0.22301 0.29120 0.24008 0.28362 0.19702 0.19025 0.21258 0.21835 0.29059 0.25612 0.23990 0.21864 0.28830 0.26891 0.28188 0.28103 0.19733 0.26851 0.23815 0.31708 0.26420 0.21972 0.26315 0.26059

0.00300 0.00454 0.00446 0.00298 0.00344 0.00446 0.00374 0.00442 0.00312 0.00294 0.00332 0.00342 0.00450 0.00400 0.00374 0.00356 0.00452 0.00420 0.00438 0.00442 0.00312 0.00426 0.00372 0.00498 0.00414 0.00346 0.00418 0.00412

0.88 0.93 0.93 0.82 0.89 0.94 0.88 0.87 0.80 0.89 0.86 0.86 0.92 0.89 0.90 0.75 0.88 0.89 0.91 0.87 0.83 0.85 0.88 0.87 0.89 0.86 0.84 0.85

1824 1820 1783 1810 1813 1816 1789 1781 1770 1808 1823 1758 1771 1826 1768 1794 1836 1756 1760 1820 1789 1785 1772 1821 1824 1781 1832 1791

40 38 38 42 39 38 40 40 43 39 40 40 39 39 39 46 40 39 39 40 42 41 40 40 39 41 41 41

206

Pb

238

U

1144 1682 1647 1122 1298 1648 1387 1610 1159 1123 1243 1273 1645 1470 1386 1275 1633 1535 1601 1597 1161 1533 1377 1776 1511 1280 1506 1493

2σ error

Conc. (%)

18 24 22 18 6 21 19 22 18 14 16 16 10 18 19 4 22 22 21 22 16 20 18 18 12 18 21 20

63 92 92 62 72 91 78 90 66 62 68 72 93 80 78 71 89 87 91 88 65 86 78 98 83 72 82 83

Table 11 Nd isotopic data of basement rocks from the Cauaburi Complex. Sample

Rock

T crist (Ma)

Santa Izabel do Rio Negro Facies (MA-sample) 21A bt ph meta grt 1809 02 meta gnd 1809, ea Tarsira Facies (VR-sample) 2A lcgn 1795, ea 6 bt gn 1795, ea 15 bt gn 1795, ea 2B bt gn 1795, ea 13 bt gn 1795, ea

Ref

Sm ppm

Nd ppm

f (Sm

147

Nd

Nd)

144

Sm

Sm

143

Nd

144

Nd

ԐNd (0)

ԐNd(t)

TDM

Ref

Nd

1 1

21.73 3.66

152.24 22.42

0.14 0.16

−0.56 −0.45

0.0863 0.1086

0.511425 0.511614

−23.66 −19.98

+1.53 +0.13

1.94 2.08

1 1

3 3 3 3 3

13.77 10.82 13.14 10.86 18.75

97.77 60.72 77.60 57.65 153.97

0.14 0.18 0.17 0.19 0.12

−0.57 −0.45 −0.48 −0.42 −0.63

0.0852 0.1077 0.1024 0.1138 0.0736

0.511396 0.511607 0.511542 0.511674 0.511156

−24.23 −20.11 −21.38 −18.81 −28.91

+1.46 +0.39 +0.34 +0.29 −0.56

1.96 2.07 2.06 2.09 2.06

2 2 2 2 2

Nd TDM ages are calculated using the model of De Paolo (1981) for Nd evolution of the depleted mantle. Obs: ea. estimated age; Ref. References: 1. This paper; 2. modified from Rodrigues (2016); 3. Santos (2003). Abbreviations: lc. leuco; ph. porphyritic; gn. gneiss; grt. granite; gnd. granodiorite; bt. biotite.

Imeri Domain basement subducted under the Tapajós–Parima continent. In addition, Cordani et al. (2016) proposed an orogenic pulse between 1800 and 1740 Ma, with the stacking of a magmatic arc against the cratonic area formed by the Ventuari–Tapajós continent. We consider that the origin of the Içana Domain basement (Cauaburi Complex and Taiuaçu–Cauera diatexite) is related to a collisional environment. Assuming this tectonic context, the Cauaburi rocks were formed by the partial melting of amphibolitic rocks with a crustal contribution (perhaps the lower crust), and this represents the nature of the granitic magma that evolved in a fractional crystallization process. The ages of all the igneous and metamorphic inherited zircons found in the Içana Domain basement are compatible with the ages of those found in the Tapajós–Parima/Ventuari–Tapajós Province, which is in agreement with the crustal contribution hypothesis. Geochemistry and mineralogical data suggest that the Taiuaçu–Cauera diatexite could

foliation occurs at an axial plane of S1 foliation. It has trending NW-SE with an average orientation of N43ºW/70ºSW, and is characterized by the orientation of mafic minerals in both porphyroclastic metagranite of the Cauaburi Complex and in Taiuaçu–Cauera diatexite. Finally, these rocks underwent a third deformation event associated with shear zones and trending NE-SW. The M1/D1 event was marked by the syn-tectonic emplacement of Cauaburi Complex protolith rocks (1813 ± 19 Ma) and crystallization (1821 ± 19 Ma) and migmatization (1798 ± 11 Ma) of the Taiuaçu–Cauera diatexite. The suitable environment for the D1/M1 event is a magmatic arc setting. Orogenic events have been reported in this sector of the Amazonian Craton (Almeida et al., 2013; Cordani et al., 2016). For example, according to Almeida et al. (2013), an orogenic event designated Cauaburi Orogeny occurred between 1810 Ma and 1789 Ma, which represents an accretionary system, where the 406

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Fig. 18. εNd vs. time diagram for the basement rocks of the study area. Nd evolution field for previous data obtained for the Rio Negro Province (older basement: 1.81–1.77 Ga) is also plotted for comparison. For details, see text and Table 11. Data for the Rio Negro Province were compiled from Sato and Tassinari (1997), Cordani et al. (2016), Rodrigues (2016).

This research had financial support from the CNPq (CT-Amazônia), Process No. 5754490/2008-0.

have been formed by the partial melting of metagraywacke. Analyses conducted on the detrital zircon from this diatexite reveal two age populations: 1993 ± 33 and 1842 ± 9 Ma, which suggests that the sediments were derived from a provenance comprising different rocks from the Tapajós–Parima/Ventuari–Tapajós Province. The Içana Domain basement rocks underwent metamorphism under amphibolite to granulite-facies conditions, reaching temperatures between 740 °C and 780 °C and pressures between 4.5 and 6 kbar, with the generation of metamorphic sphene. Almeida et al. (2013) described an orogenic event at 1483 and 1536 Ma, which is known as the Içana Orogeny. Although zircons of that age were not identified in the Içana Domain basement rocks, we attribute the M2/D2 event to this orogeny because this age is recorded in the S-type granites of the Intrusive Suite Rio Içana (Almeida et al., 1997), which occurs in the Içana Domain. A reworking of Içana Domain basement rocks using low-temperature shear zones shows marked recrystallizations of the mineral assembly under greenschist facies conditions (300 °C−350 °C). From this viewpoint we associated the D3/M3 event with the K'Mudku Event intracontinental reworking (1100–1300 Ma; Santos et al., 2000). It has been reported that diatexites (Taiuaçu–Cauera Paragneiss) were included in the Tunuí Group CPRM (2006). In this research, we prove that Içana Domain basement is represented by orthoderived rocks of the Cauaburi Complex (Santa Izabel do Rio Negro Facies) and heterogeneous/homogenous diatexite of the Taiuaçu–Cauera diatexite. Our analytical results show that age of the Taiuaçu-Cauera is comprised between 1842 ± 9 Ma (detrital zircon grain) and 1788 ± 19 Ma (anatectic zircon). Therefore, Taiuaçu–Cauera diatexites cannot be part of the Tunuí Group, and represents a sequence older than that of the Tunuí Group.

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Acknowledgements The authors thank the Brazilian Army/5th Jungle Infantry Battalion for all logistical support during the fieldwork; the Geological Brazilian Survey - Manaus for the structure offered for field and laboratory work; the Electron Microprobe Laboratory of the University of Brasília for mineral chemistry analyses; the Isotope Geology Laboratory of the Federal University of Rio Grande do Sul for Sm-Nd isotopic analyses. 407

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