Geochemistry and origin of the Rhyacian tholeiitic metabasalts and meta-andesites from the Vila Nova Greenstone Belt, Guyana Shield, Amapá, Brazil

Accepted Manuscript Geochemistry and origin of the Rhyacian tholeiitic metabasalts and meta-andesites from the Vila Nova Greenstone Belt, Guyana Shield, Amapá, Brazil Itiana Hoffmann, Ruy Paulo Philipp, Cristiano Borghetti PII:

S0895-9811(17)30352-8

DOI:

10.1016/j.jsames.2018.07.009

Reference:

SAMES 1972

To appear in:

Journal of South American Earth Sciences

Received Date: 22 August 2017 Revised Date:

31 July 2018

Accepted Date: 31 July 2018

Please cite this article as: Hoffmann, I., Philipp, R.P., Borghetti, C., Geochemistry and origin of the Rhyacian tholeiitic metabasalts and meta-andesites from the Vila Nova Greenstone Belt, Guyana Shield, Amapá, Brazil, Journal of South American Earth Sciences (2018), doi: 10.1016/j.jsames.2018.07.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

FeT+Ti

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High-Fe tholeiite basalt

G2

G3

G4

Ti (ppm)

G1

Komatiitic Basalt

MORB

5000 Island Arc Lavas

Calcalkaline

1000 10

Komatiite

Al

20

50 100 200 Zr (ppm)

500

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High-Mg tholeiite basalt

Within-Plate Lavas

Mg

data-point error ellipses are 68.3% conf.

CB - 13 A Meta-andesite

0.43

2250

4

3

G2 G3 G4+ LILE, Th,

Depleted upper mantle

H2O

2150

0.39

2050

2

0.37

M AN U

+ Nb, Ta

1

SC

0.41

P

238U/206Pb

G1

0.35

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Graphical Abstract

6.2

6.6

7.0

Concordia Age = 2154 ± 5.5 Ma ( 1σ, decay-const. errs included) MSWD (of concordance) = 0.022 Probability (of concordance) = 0.88 7.4

235U/207Pb

7.8

8.2

8.6

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Geochemistry and origin of the Rhyacian tholeiitic metabasalts and meta-andesites from

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the Vila Nova Greenstone Belt, Guyana Shield, Amapá, Brazil

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1

Programa de Pós-Graduação em Geociências, Instituto de Geociências, UFRGS, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, RS, Brasil, CEP: 91509-900, e-mail: [email protected] 2 Centro de Estudos em Petrologia e Geoquímica, Instituto de Geociências, UFRGS, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, RS, Brasil, CEP: 91509-900, e-mail: [email protected]

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Itiana Hoffmann1, Ruy Paulo Philipp2 & Cristiano Borghetti1

Abstract

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The origin and significance of the metavolcanic rocks of the Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of the Guyana Shield in

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Paleoproterozoic times. This work presents new LA-MC-ICPMS U-Pb zircon data and

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geochemical analyses carried out on metavolcanic rocks of the VNGB. This information was

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supplemented by petrography, stratigraphic and structural data acquired through geologic

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mapping and boreholes descriptions. In the Vila Nova region, the VNGB units rest on the

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Archean basement composed of orthogneisses of the Tumucumaque Complex. The lower

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portion of the VNGB consists of metabasalts and andesitic metabasalts, covered by an upper

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metasedimentary domain with subordinate metavolcanic and exhalative chemical rocks. The

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metavolcanic rocks include metabasalts, meta-andesites, amphibolites and amphibole schists,

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deformed and elongated according to the regional NW-SE structure. U-Pb zircon data yielded

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an age of 2,154±6 Ma for a meta-andesite of the lower portion of VNGB. One orogenic

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metamorphism followed by three deformational events were recognized. The D1 and D2

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events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation

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cleavage (S2) associated with the development of the oblique shear zones. Two distinct

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assemblages: 1) garnet, hornblende and biotite, and 2) hornblende, plagioclase and diopside

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define two distinct metamorphic peaks: M1 and M2 with temperatures of 450 and 650 °C, and

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lithostatic pressure between 4 and 6 kbar. The metabasites comprise geochemical

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compositions of Fe- and Mg-tholeiites with komatiitic affinity. The first group is enriched in

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LREE and HFSE. The second group shows MORB-like REE patterns in association with

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negative Nb, Ti and P anomalies. The observed features indicate that the metavolcanic rocks

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of the VNGB represent the evolution of back-arc basins and island arcs associated with the

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Trans-Amazonian Orogeny. These rocks characterize the Rhyacian evolution of the Maroni-

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Itacaiunas Province in the eastern portion of the Guyana Shield.

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Keywords: Amazonian Craton, Guyana Shield, Vila Nova Greenstone Belt, Paleoproterozoic, Geochemistry, U-Pb zircon.

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1. Introduction

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In Brazil, most of the area comprised by the Guyana Shield is inaccessible, covered by

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a thick mantle of weathering alteration and dense tropical forest. Consequently, the major

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continental cores of Archean and Paleoproterozoic ages in the Amazonian Craton present

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limited information regarding the evolution of their paleogeographies and tectonic

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environments.

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The Amazonian Craton is an extensive continental nucleus, comprising the Archean

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Central Amazonian Province (> 2.5 Ga), surrounded by mobile belts of Paleo- and

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Mesoproterozoic ages (Cordani and Neves 1982; Teixeira et al., 1989; Tassinari &

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Macambira, 1999, Santos et al., 2000, Tassinari et al., 2000; Tassinari and Macambira, 2004).

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These belts include granite-gneiss domes separated by elongated bodies of metavolcano-

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sedimentary associations of the greenstone-belt type, poorly investigated under the

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petrological aspect. The Vila Nova region is located in the northeast portion of the Amazonian

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Craton, in the Guyana Shield, and is part of the geological context of the Maroni-Itacaiúnas

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Province, a significant Paleoproterozoic mobile belt (2.2-1.9 Ga) bordering the Central

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Amazonian Province.

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Metavolcano-sedimentary sequences in the Guyana Shield constitute thick and

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discontinuous elongated bodies according to major NW structures, which are separated by

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large portions of basement rocks. These belts are exposed in Brazil (Vila Nova Complex),

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Guyana (Barama-Mazaruni Supergroup), Suriname (Marowijne Supergroup), French Guiana

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(Paramaca Series) and Venezuela (Pastora Supergroup) and present similarities in structural

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framework and lithological pattern, geochronology and metamorphism (Vanderhaegue, 1998;

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Mc Reath and Faraco, 2006; Voicu et al., 2001). The Paleoproterozoic greenstone sequences

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in Guyana Shield yield U-Pb and Pb-Pb zircon ages between 2,267 and 2,120 Ma, in

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agreement with evolution in the Rhyacian period and related to the Trans-Amazonian

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Orogeny. The supracrustal sequences also show many features associated with greenstone belts

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of Paleoproterozoic and Archean age, including the presence of mafic to ultramafic volcanic

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rocks, with subordinate occurrence of felsic rocks, interspersed with clastic and chemical

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sedimentary rocks, low to medium metamorphic grade, volcanic cyclicity and show potential

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mineral resources (Condie, 1981; Anhaeusser, 2014).

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In the literature, tectonic generation environments of greenstones belts have been

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interpreted as back-arc basins associated with island arcs, mid-ocean ridges, oceanic plateaus,

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intracontinental rifts, or some combination of these environments (De Wit and Ashwal, 1986;

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Heubeck and Lowe, 1994; Lowe and Byerly, 1999; Kusky and Polat, 1999; Zeh et al., 2009,

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2013). These environments are related to submarine volcanism and are very common in the

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Archaean and Paleoproterozoic eons, being responsible for a large number of deposits of

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precious metals like gold, silver, copper, lead, nickel, chromium and zinc (Grant, 1985;

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Sawkins, 2013). In Brazil, the occurrence of greenstone belts in the Amazonian and São

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Francisco cratons stands out, with emphasis on the mineralization of the greenstones of Rio

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das Velhas (Au, Fe, Mn) in Minas Gerais State, Rio Itapicuru (Au, Fe) in Bahia State, Crixás

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(Ni, Cr) in Goiás State (Jost et al., 2014) and associated with the Carajás Province (Au, Fe,

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Mn, Cu), in Pará State (Lobato et al., 2001; Noce et al., 2007).

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This study aims to discuss the origin of the Vila Nova Greenstone Belt (VNGB)

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metavolcanic rocks, based on the integration of stratigraphic and structural data relationships

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obtained in geologic mapping and description of boreholes, integrated with petrographic,

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geochemical and geochronological analyses. The metavolcano-sedimentary associations that

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occur in the regions of Cupixi and Vila Nova were reunited as Vila Nova Greenstone Belt by

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Borghetti et al. (2017, 2018b), based on the integration of field (geological mapping and

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structural geology) and geophysical data (magnetometry and gammaspectroscopy). The data

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integration allowed to investigate the magma series, to evaluate the differentiation processes,

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the magma sources and the tectonic discrimination of the units. The geological map (1:

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100.000 scale) presented in this paper was obtained from the integration of geophysical and

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field data, supported by petrographic and geochemical analyses. The integration of these data

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with others available in the literature constitutes the basis for the investigation of the

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processes responsible for the generation of the metabasalts and andesitic basalts of the VNGB

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in order to understand the evolution of ancient island arc/back-arc system and successive

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stages of metamorphism and deformational processes.

101 2. Geological Setting

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2.1 Geology of the Vila Nova region

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The Vila Nova region is located in the northeast portion of the Amazonian Craton,

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inserted in the context of the Maroni-Itacaiúnas Province, a Paleoproterozoic mobile belt

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related to the Trans-Amazonian Orogeny (2.25-2.05 Ga) (Figure 1). The Paleoproterozoic

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mobile belts that surround the Archean nucleus of the Central Amazon Province are extensive

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basins represented by discontinuous greenstone belts associated with magmatic arcs,

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interspersed with granite associations of the TTG type (Avelar et al., 2003; McReath and

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Faraco, 2006; Rosa-Costa et al., 2003, 2006).

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In the Vila Nova region, the basement rocks were initially included in the Maroni-

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Itacaiunas Province. Based on the contact relations, lithological types, geophysical and

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geochronological data, Rosa-Costa et al. (2003, 2006) identified within this province a vast

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segment of the Archean crust called Amapá Block (Figure 2). The Meso- and Neoarchean

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units of this block were intensely reworked in the Paleoproterozoic during the Trans-

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Amazonian Orogeny. The regional basement of the studied area is represented by the Tumucumaque

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Complex, by the Anauerapucu and Mungubas granites, and by the intrusive rocks of the

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Bacuri Complex (Spier and Ferreira Filho, 1999; Pimentel et al., 2002; Barbosa et al., 2013;

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Borghetti and Philipp, 2017; Borghetti et al., 2018b) (Figure 3). On these units rest the

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VNGB rocks, affected by low- to medium-grade orogenic metamorphism and intruded by

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Late Rhyacian granites.

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The Tumucumaque Complex is the oldest unit and is composed of tonalitic,

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granodioritic and dioritic gneisses of Archean age, with a subordinate occurrence of

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amphibolites (metagabbros) that are concordant with the regional gneissic banding (Rosa-

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Costa et al., 2006; Borghetti et al., 2014, 2018a). The orthogneisses are light to dark gray in

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color and show incipient banding marked by discontinuous layers of biotite and/or

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hornblende, generated under metamorphic conditions of mid to upper amphibolite facies

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(Borghetti and Philipp, 2017). The orthogneisses are cut by stocks of Archean gabbros, as

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well as by Paleoproterozoic granitoids with varying dimensions (Borghetti et al., 2018a). In

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the Tartarugalzinho greenstone belt region, the orthogneisses were dated at 3.48 Ga by the Pb-

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Pb zircon method (TIMS) (Avelar et al., 2003). In the Vila Nova region, Nd TDM model ages

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(whole-rock) between 3.03-2.85 Ga were obtained in amphibole schist (Rosa-Costa et al.,

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2006). Rosa-Costa et al. (2006) and Borghetti et al. (2014, 2018a) obtained Pb-Pb (TIMS) and

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U-Pb (LA-MC-ICPMS) crystallization zircon ages of the orthogneisses of Tumucumaque

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Complex in the range of 2.85 to 2.67 Ga.

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The Mafic-Ultramafic Bacuri Complex (BMUC) corresponds to a stratiform body,

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elongated in the E-W direction, consisting of the intercalation of metagabbros, amphibolites,

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metaperidotites, chromitites, serpentinites, and tremolitites (Spier and Ferreira Filho, 1999).

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These units show a record of intense ductile deformation and amphibolite facies

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metamorphism. The BMUC rocks occur in the southern part of the studied area, showing

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intrusive relationships with the basement orthogneisses and tectonic contact with the

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metasedimentary rocks of the Vila Nova Complex (Spier and Ferreira Filho, 1999). The metavolcano-sedimentary associations that occur in the Brazilian portion of the

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Guyana Shield, comprising the Vila Nova, Serra do Navio, Ipitinga, Tumucumaque,

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Tartarugalzinho and Lombarda greenstone belts, were included in the Vila Nova Complex

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(McReath and Faraco, 2006) (Figure 2). The VNGB is composed of basic to intermediate

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metavolcanic

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geochronological relationships of the metasedimentary units were investigated by Borghetti et

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al. (2014, 2018b), which presented U-Pb detrital zircon ages between 3.6 and 2.4 Ga,

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confirming the erosion of the Archean basement in the formation of the VNGB. The authors

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obtained the age of 2,170 ±9 Ma for one sample of meta-andesite of the Vila Nova region,

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establishing the Rhyacian period as the maximum deposition age of the VNGB basin. The

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ages obtained for the VNGB are compatible with the available ages for other greenstones that

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occur in the region as can be seen in table 1.

chemical-exhalative

rocks

and

metasedimentary

rocks.

The

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The units of the VNGB are cut by the Amapari and Porto Grande granites and by other

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undisturbed granite bodies of Late Rhyacian age. The first one is represented by syeno- and

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monzogranites with massive structure and medium to coarse inequigranular texture. The Porto

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Grande Granite varies from syenogranite to monzogranite, showing a magmatic flow foliation

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and equigranular to porphyritic texture (Barbosa et al., 2013). The intrusion of these granites

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causes thermal metamorphism in the metavolcano-sedimentary rocks. The U-Pb zircon ages

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obtained in the intrusive granites, such as the Igarapé Careta Suite (2.06 Ga) and the Amapari

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Granite (1.99 Ga), suggest that the orogenic metamorphism occurred in the interval between

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2.15 and 2.07 Ga.

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The Phanerozoic cover that occurs to the east of the studied area includes fluvial and

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estuarine deposits consisting of pelites, sandstones and ferruginous conglomeratic sandstones,

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and sandy-clayey sediments to friable sandy-conglomeratic sediments associated with a

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fluvial system.

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Figure 1. A) Map of the Amazonian Craton in South America and location of the Guyana and

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Central Brazil shields, B) Location of the study area in relation to the Geochronological

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Provinces of the Amazonian Craton proposed by Tassinari and Macambira (2004).

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Figure 2. Archean and Paleoproterozoic tectonic-geochronological domains of the eastern

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portion of the Guyana Shield, modified from Rosa-Costa et al. (2006). The geochronological

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provinces are in agreement with Tassinari and Macambira (2004). The area highlighted in the

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black rectangle corresponds to Vila Nova and Serra do Navio greenstone belts of the

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geological map of Figure 3. Greenstone belts: 1-Vila Nova, 2-Serra do Navio, 3-Ipitinga, 4-

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Tumucumaque, 5-Tartarugalzinho and 6-Lombarda. Shear Zones: SNSZ: Serra do Navio,

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CSZ: Cupixi, ISZ: Ipitinga.

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Figure 3. Geological map of Serra do Navio and Vila Nova regions. The black rectangle

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shows the location of figure 4. Modified from Rosa-Costa et al. (2006), Magalhães et al.

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(2007) and Barbosa et al. (2013). Shear Zones: SNSZ: Serra do Navio, CSZ: Cupixi, ISZ:

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Ipitinga. Locality: C: Cupixi, SN: Serra do Navio.

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Table 1. Summary of geochronological data of the greenstone belts of the Guyana Shield.

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*This work, 1Daoust (2011), 2Faraco (1997), 3Renner and Gibbs (1987), 4Milèsi 1995,

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Vanderhaeghe (1998), 6Day (1995), 7Velásquez (2011), 8Padoan (2014).

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2.2. The Vila Nova Greenstone Belt (VNGB) The VNGB occurs as a main elongated body along the E-W direction, with six

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subordinate belts in the N40-50oW direction, interconnected in their southern portion by the

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Vila Nova Shear Zone (VNSZ) (Figure 3). This medium-angle ductile shear zone with top-to-

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the-north oblique kinematics defines the contact of the greenstone belt with the basement

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rocks (Borghetti and Philipp, 2017).

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produced by Borghetti and Philipp (2017), supported by descriptions of drilling holes,

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petrography and geochemical data generated by this research, the VNGB metavolcano-

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sedimentary rocks were subdivided into two petrotectonic associations. (Figure 3). The basal

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domain presents the largest area of occurrence and is composed of mafic metavolcanic rocks,

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interspersed with subordinate lenses of mica schists. The upper domain occupies a restricted

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area, constituted by clastic metasedimentary rocks, with subordinate intercalations of mafic

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metavolcanic and chemical-exhalative rocks. The contact between both these domains is

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defined by the VNSZ and was partly inferred by the aerogeophysical data interpretation

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(Borghetti and Philipp, 2017).

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The basal domain is exposed as an elongated belt along the E-W direction for about

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30 km, from Vila Nova, extending eastward through the localities of Nova Canaã and Pelado

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(Figure 4A). Amphibole schists and amphibolites are the dominant metamafic rocks. The

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metaultramafites are represented by tremolite schists and hornblende-tremolite schists and

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occur subordinately as lenses of 2 to 20 meters in thickness. Mafic cornubianites have also

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been recognized as products of thermal metamorphism associated with the Late Rhyacian

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granites, which constitute elongate bodies concordant with the VNSZ.

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The upper domain is more restricted to the western portion of the area, occurring as

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three major elongated belts about 20 to 25 km long and 1 to 10 km wide (Figure 4A). These

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belts are dominantly composed of quartzites, ferruginous quartzites, and fuchsite-quartz

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schist, with two continuous lenses of metaconglomerates, with subordinate lenses of pelitic

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schists, calc-silicate schists and BIF's (banded iron formations) with hematite phyllites,

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hematite schists and ferruginous quartzite. Based on the borehole descriptions made available

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by the company Amapari Mineração Ltda., a schematic geological section representative of

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the compositional variation occurring in the Vila Nova region was assembled, which

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illustrates well the presence of F2 tight folds (Figure 4C). Structural surveys indicate that the VNGB units were affected by an event of orogenic

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metamorphism followed by three major deformation events (Borghetti et al., 2018a). These

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processes resulted in a regional foliation in the N50-60ºW direction. The main schistosity is

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represented by an S2 crenulation cleavage, which preserves partial remains of the S1 foliation

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in the form of F2 intrafolial tight folds of metric to decametric scales. The previous structures

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are affected by F3 folds, of gently plunging upright fold, with open to closed forms and axes

226

plunging between 10 and 25º in the N40-50ºW and S40-50ºE directions (Borghetti et al.

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2018a). The metasedimentary rocks present partial preservation of the primary structures,

228

such as compositional bedding, plane-parallel and trough cross-bedding.

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Figure 4. A) Geological map of the Vila Nova region and indication of the map of figure 4B.

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B) Geologic map of the area of the Pedra Pintada-Gaivotas (A-A’) geological cross-section

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and the main drilling holes sampled for chemical analyses. C) Schematic geological cross-

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section representing the main structures and the compositional variation observed from the

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description of the drilling holes. Localities: P: Pelado, VN: Vila Nova, NC: Nova Canaã.

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3. Material and Methods

Sampling was based on an integrated analyses of satellite images, aerogeophysical

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(magnetometry and gammaspectrometry) survey data and geologic mapping, which clearly

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defined the metasedimentary and metavolcanic domains. In addition to the sampling for

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petrography, geochemistry and geochronological analyses, structural and stratigraphic data

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were collected to validate satellite and aerogeophysical interpretation. To investigate the

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stratigraphy and to improve the geology, a total of 5.000 meters of drill core data were

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described.

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3.1 Whole-rock chemistry Thirty one samples were selected for geochemical analysis. The analyzed samples

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were collected in drilling holes located in the vicinity of Vila Nova, Nova Canaã and Pelado.

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They were collected from drilling holes along one transverse section of the VNGB and

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comprise metabasalts, meta-andesites, amphibole schists and amphibolites. Sample

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preparation was conducted at the facilities of Geoscience Institute of the Rio Grande do Sul

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Federal University. The samples were comminuted in jaw crusher steel, processed in an agate

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mill, sieved and homogenized. Quartered rock powders were conducted for whole-rock

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chemical analysis at ACME Analytical Laboratories LTDA, Canada. Major and trace elements

254

concentrations were determined using ICP-MS, while base metals, such as Ni, Cr, Co and Zn,

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were analyzed with X-Ray fluorescence after Aqua Regia digestion (LF200 and AQ200

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procedures, respectively, after metaborate/tetraborate fusion). Detections limits were 0,01 %

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wt. for major oxides and 0.01-0.1 ppm for trace elements. Geochemistry diagrams were

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plotted using the GCD Kit version 4.0 (Janousek et al., 2006).

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3.2 Geochronology

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One sample of meta-andesitic basalt (CB-13A) from the basal domain was selected to

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determine the U-Pb zircon age of the volcanism from VNGB. The LA-MC-ICPMS method

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was used for U-Pb zircon analysis at the Geochronological Research Center (CPGEO) of the

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Geosciences Institute of São Paulo University (USP). Sample preparation was carried out in

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the laboratories of the Rio Grande do Sul Federal University (UFRGS). Rock samples were

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crushed and milled using a mandible crusher and then pulverized. Zircon grains were

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concentrated by conventional magnetic and heavy liquid techniques. The final concentrate

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was obtained by handpicking. To avoid any bias, no visual morphological or color

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differentiation was made.

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of the grain thickness was exposed, to ensure that all internal oscillatory zoning was visible

272

for further imaging. Backscattered-electron (BSE) and cathodoluminescence (CL) imaging

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was performed to record internal structures and crystallization phases. Only zircon grains free

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of imperfections, fractures, and mineral inclusions were selected for isotopic analysis. CL

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images of zircon grains were obtained using a Quanta 250 FEG electron microscope equipped

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with Mono CL3+ cathodoluminescence spectroscope (Centaurus) at the CPGEO of USP.

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Isotopic data were obtained using a NEPTUNE inductively coupled plasma-mass

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spectrometer (ICP-MS) coupled with an Excimer laser ablation system (LA). The diameter of

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laser spots for the zircon U-Pb analyses was 35 µm. The routine of the U-Pb method consists

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of the analysis of 2 blanks, 2 NIST standards, 3 external (GJ1) standards, 13 unknown

281

samples, 2 external standards and 2 blanks. The

282

was corrected by

283

normalization was achieved by combining NIST and external standards. The

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normalization was achieved by external standards. The GJ1 standard (602 ± 4.4 Ma, Elholou

285

et al. 2006) was utilized for mass bias correction. The residual common Pb was corrected

286

according to the measured

287

(Stacey and Kramers, 1975). The uncertainty introduced by laser-induced fractionation of

288

elements and mass instrumental discrimination was corrected using the zircon reference

289

standard GJ-1 (Jackson et al. 2004). External errors were calculated using error propagation

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of the individual GJ-1 measurements and measurements of the individual zircon samples

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(spots). Age calculations were made using Isoplot version 4 and

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2008). Chemale et al. (2011) described in detail the analytical methods and data treatment

293

used here.

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Hg, adopting a

204

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Hg interference on

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Hg/202Hg ratio of 4.2. The

Pb measurements 207

Pb/206Pb ratio

206

Pb/238U ratio

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Pb concentration using the known terrestrial composition

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238

U/206Pb data (Ludwig,

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295

4. Results

296

4.1 Petrography of metamafic and metaultramafic rocks

297

Amphibolites Amphibolites are the commonest rocks among the metamafic rocks. They have a dark

299

gray color and a schistosity defined by the amphibole and biotite orientation, constituting the

300

medium-grained nematoblastic and lepidoblastic textures (Figure 5A). Polygonal granoblastic

301

texture is subordinate and occurs at the discontinuous plagioclase layers. The

302

blastoamygdaloidal texture is characterized by 2 to 4 mm round to elliptical shape portions

303

composed of fine mosaics of recrystallized quartz (Figure 5B). The mineral composition is

304

dominated by hornblende (60-65% of modal volume) and plagioclase (25-45%), with low

305

contents of biotite and diopside. Titanite, magnetite, epidote, quartz and chlorite are accessory

306

minerals. Diopside is rare and occurs at the edges of the hornblende, indicating progressive

307

metamorphism (Figure 5C). Titanite has granular and xenoblastic shape, with sizes smaller

308

than 0.1 mm. The magnetite crystals have octahedral shape and are subhedral to anhedral.

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The metabasalts and meta-andesites are rare and occur associated to the amphibolites.

310

They present blastoporphyritic texture characterized by 0.5 to 1 mm prismatic porphyroclasts

311

of plagioclase with normal zonation and polysynthetic and Carlsbad-Albite twinning. The

312

matrix is composed of green amphibole, epidote, chlorite, titanite and opaque minerals. The amphibolites show S1 schistosity well defined by the orientation of hornblende

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314

and biotite. The transposition of the S1 results in crenulation cleavage (S2) and closed to

315

intrafolial tight F2 folds (Figure 4C). The S2 cleavage domains are discrete and sinuous. The

316

schistosity is cut by irregular fractures filled by chlorite, sericite, and epidote, indicating a

317

low-temperature retrometamorphic event (Figure 5D).

318 319

Amphibole Schists

13

ACCEPTED MANUSCRIPT The hornblende-tremolite and biotite-hornblende schists have a dark green color and

321

coarse nematoblastic texture characterized by the orientation of amphibole. The lepidoblastic

322

texture is subordinate and defined by the biotite orientation.The main mineralogy is composed

323

of tremolite (30-55%), hornblende (40-60%) and biotite (4-10%), with clinochlore (0.5-3%),

324

chlorite (0.5-4%), titanite and opaque minerals (0.1-2%) as accessory phases. Amphiboles

325

constitute idioblastic acicular crystals with sizes between 2 and 5 mm. The crystals show

326

zoning, with a colorless tremolite core and a green-colored border composed of hornblende

327

(Figure 5E). Biotite occurs interstitially, with reddish brown color, lamellar form and sizes

328

from 1 to 1.5 mm.

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330

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329 Mafic Cornubianites

A small fraction of the analyzed metavolcanic rocks show the thermal effects

332

superimposed by intrusive granites. They range from hornblende hornfels to tremolite-

333

diopside-hornblende hornfels, with acicular texture defined by disoriented amphibole crystals

334

(Figure 5F). Decussate texture is marked by biotite. Polygonal granoblastic texture occurs

335

interstitially, consisting of aggregates of plagioclase crystals with sizes between 0.06 and 0.1

336

mm. The main mineralogy is composed of hornblende (40-50%), tremolite (15-20%),

337

plagioclase (15-20%) and diopside (15-20%), with epidote (2%), chlorite and opaque

338

minerals (1%) as accessory phases. Carbonate veins occur with millimetric thickness. In the

339

regions adjacent to the veins, an irregular formation of epidote and chlorite aggregates occurs

340

on the mafic minerals.

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341 342

Magnesium Schists

343

Tremolite schists and hornblende-tremolite schists have a very subordinate occurrence,

344

with usually less than 30 meters in thickness. They have gray to light green color, with

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schistosity defined by the amphibole orientation, characterizing the medium-grained

346

nematoblastic texture. The main mineralogy is composed of tremolite (70-75%) and

347

hornblende (15-20%), with clinochlore (3-5%) and magnetite (1-2%) as accessory minerals.

348

The S1 schistosity is determined by tremolite microlithons, constituting intrafolial isoclinal

349

microfolds observed within the domains of the S2 crenulation cleavage. The cleavage domains

350

are sinuous, with spacing between 0.5 and 1 mm. The schistosity is cut by quartz veins with

351

thicknesses between 1 and 5 mm. The veins have an irregular distribution, are deformed,

352

discontinuous and composed of quartz aggregates with fine granoblastic texture.

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353

Figure 5. Microscopic aspects of VNGB metabasites. A) Composite banding in amphibolite

355

evidenced by the alternation of hornblende layers and discontinuous layers of plagioclase and

356

biotite, B) Blastoamigdaloidal texture in metabasalt consisting of deformed elliptic quartz

357

aggregates, C) Diopside crystals growing on the edges of hornblende in amphibolite, D)

358

Amphibolite presenting hornblende disequilibrium and transformation to chlorite, indicating

359

greenschist facies retrometamorphism, E) Tremolite-hornblende schist with zoned

360

amphiboles, with hornblende core wrapped by tremolite border, F) Mafic cornubianite with

361

porphyroblasts of acicular hornblende.

362 4.2 Geochronology

364

Meta-andesite (CB-13A)

The CB-13A sample was collected from a road cut located next to the Vila Nova gold-

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366

digging site (UTM zone 22N, coordinates 413860 and 51672) at the top of the basal domain

367

of the VNGB (Figure 4A). The outcrops are much altered, however, we observed porphyritic

368

texture with euhedral phenocrysts of plagioclase and a flow structure, highlighted by the

369

weathering alteration.

370

These data suggest that the meta-andesite constitutes a lava flow with horizontal

371

disposition, an approximately 20-35 m-thick tabular body, surrounded by muscovite schists,

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muscovite-biotite schists and magnetite-garnet-muscovite schist. Sample CB-13A is from a

373

reddish, fine-grained meta-andesite showing prominent foliation and blastoporphyritic texture

374

with rare plagioclase porphyroclasts of 0.2 to 1.0 mm in size. It contains some garnet

375

porphyroblasts of 5 to 8 mm in size. The matrix has a fine lepidoblastic texture marked by

376

muscovite and biotite, subordinately with plagioclase, chlorite and epidote.

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Eighteen out of 139 igneous zircon crystals were selected for U-Pb analysis. Sample

378

CB-13A contains translucent to opaque zircon grains, ranging in color from brown to dark

379

brown. The igneous zircon crystals are euhedral to sub-euhedral, showing prismatic shapes

380

and almost always straight terminations and range in size from 70 to 380 µm. They are well

381

preserved and show oscillatory zoning. A few luminescent zircon grains with inherited nuclei

382

are visible under CL images, some of them with sector or faint oscillatory zoning (Figure 6).

383

Reabsorbed and metamict grains are also present (e.g., 6.1, 8.1). Concentric zoning resulting

384

from metamorphic recrystallization was not observed. Xenocryst cores with magmatic

385

overgrowths are also present. Eighteen analyses in cores are nearly collinear in the Concordia

386

diagram. The

387

yelds an upper intercept age of 2,154 ±5.5 Ma (MSWD = 0.022) (Figure 7). This age is

388

interpreted as the magmatic zircon crystallization age. Th/U ratios obtained from 17

389

concordant analyses range between 0.15 and 0.88, which is consistent with a magmatic origin

390

for these zircon grains (Belousova et al. 2002) (Table 2).

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Pb/206Pb ages range from 2,110 Ma to 2,199 Ma and regression of the data

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392

Figure 6. Cathodoluminescence images of selected zircon crystals from CB-13A meta-

393

andesite sample. The circle locates the spot of the analysis in the zircon grains and the

394

corresponding 207Pb/206Pb age.

395

Figure 7.- Concordia diagram for analyzed zircon crystals from CB-13A meta-andesite.

396

Table 2. Summary of U-Pb zircon data by LA-MC-ICPMS for CB-13A meta-andesite. The

397

data were collected with a routine spot size of 35 µm.

398

16 399

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4.3 Geochemistry The results of the geochemical analyses performed on 31 metabasite samples are

401

shown in Table 3. The selected samples show little evidence of weathering or hydrothermal

402

alteration and ignition (LOI) values generally vary between 0.5 and 1.8, with some samples

403

reaching 3.5%, after ignition at 1,000 °C. Based on major and trace elements- contents (LILE,

404

HFSE, and REE), their classification and evaluation, two main compositional groups

405

denominated G1-G2 and G3-G4 were defined.

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As in most of the Paleoproterozoic terranes, the polyphase metamorphism and the

407

thermal metamorphism that affected the VNGB rocks could have remobilized the mobile

408

elements of the metabasites and modified the composition of the protoliths. In order to

409

evaluate this possibility, igneous trend models formulated by Beswick and Soucie (1978)

410

based on the logarithmic molecular ratios of major elements in unaltered Phanerozoic igneous

411

rocks were used. Some samples display locally effects of post-magmatic alteration that could

412

produce element remobilization. These samples are identified by the presence of carbonate,

413

epidote and sericite. Meanwhile the remobilization processes were not sufficiently pervasive

414

in order to obliterate the composition of the igneous protolith. As can be observed in Figure

415

8, the VNGB metabasites have preserved igneous trends. Therefore, some samples that fall

416

out of the igneous trends identify K2O, Al2O3 and CaO gain (8A, 8B, 8C).

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418

Figure 8. Logarithmic molecular proportion ratios diagrams of Beswick and Soucie (1978)

419

for evaluation of metasomatic effects on VNGB metabasites. Fm = FeOT + MgO + MnO.

420

Table 3. Litogeochemistry data from VNGB metabasites.

421 422

The major elements show that most of the metabasites present a basic composition,

423

with rare intermediate rocks, with SiO2 contents ranging from 45.23% to 54.78%. Most part

424

of G1 group samples exhibit moderate concentrations of MgO (4.07-5.93%), and reach higher

17

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values of TiO2 (2.63-3.06%), Al2O3 (13.66-16.20%), FeOt (14.71-16.02%) and P2O5 (0.27-

426

0.43). The TiO2 > 2 wt.% and FeOt/MgO ratio > 1.75 allows classifying these samples as Fe-

427

Ti basalts (Melson et al., 1976; Sinton et al., 1983). The most magnesian samples from this

428

group show lower contents of Al2O3 (5.81-6.83%), FeOt (12.59-12.86%), TiO2 (1.04-1.32%)

429

and P2O5 (0.09-0.14%) and higher concentrations of MgO (17.20-17.34%), characterized by a

430

magnesium number (mg#) ratio [MgO/(MgO + FeOt)]) with values of 72-73, much higher

431

than the average values of the Fe-Ti basalts, of 33-43. The G2-G3-G4 subgroups have lower

432

contents of TiO2 (0.23-1.15%), FeOt (9.23-14.42%), P2O5 (0.01-0.26) and variable content of

433

MgO (6.67-16.43%). The mg# displays values of 54-64 in G2, 51-65 in G3 and of 56-76 in G4.

434

The binary diagrams using MgO as the variation index are shown in Figure 9. The

435

arrangement of the samples constitutes discontinuous to partial linear trends, which reflect a

436

complex chemical evolution of the magmatic liquids.

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All groups show relative dispersion for CaO and FeO oxides (Figures 9B, 9C). In G1

438

samples the oxides form a bimodal tendency. The Al2O3 shows positive correlation with

439

decreasing MgO values in the least magnesium samples. In G2-G3-G4, TiO2 forms linear

440

trends with incipient enrichment in the later phases of the differentiation.

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In the binary diagrams with compatible elements, the decrease of Ni is observed with

442

magmatic fractionation in all groups, attesting the compatible behavior of this element.

443

Similar pattern is observed for Co and Cr2O3 (not shown). V shows enrichment with decrease

444

of MgO. The incompatible elements Sr and Zr show a linear trend and more enriched pattern

445

in subgroups G1 and G2, when compared to G3 and G4.

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446

The composition of the VNGB metabasites in the TAS (Le Maitre et al., 1989)

447

diagram characterizes the protoliths as basalts (G1) and as basalt to andesitic basalts (G2-G3-

448

G4), subalkaline in nature (Figure 10A). In the AFM diagram proposed by Irvine and Baragar

449

(1971), the analyzed metabasites showed a dominant trend with Fe enrichment, characteristic

18

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of the tholeiitic series (Figure 10B). When arranged in the Jensen (1976) diagram, the G1

451

group metabasites are composed of high-Fe basalts and komatiites (Figure 10C). The G2 and

452

G3 samples plot in the field defined for high-Mg tholeiitic basalts. The G4 group samples plot

453

in the fields of the komatiites to high-Mg tholeiitic basalts. In the Winchester and Floyd

454

diagram (1977), which uses the Zr/TiO2vs Nb/Y ratio, most of the samples plot in the field of

455

basalts and subalkaline andesites, with two G1 samples falling in the field of alkaline basalts

456

(Figure 10D).

457

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Figure 9. Diagrams of variation between the major and minor elements (% by weight) and the

459

MgO content (% by weight) for the VNGB metabasites.

460

Figure 10. Representation of the VNGB metabasites in several classification diagrams. A)

461

TAS (Na2O+K2O)-SiO2) from Le Maitre (1989), B) Irvine and Baragar AFM (1971), C)

462

Jensen (1976) and D) Winchester and Floyd (1977).

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463

The MORB-normalized multi-element diagrams (Pearce, 1983) and chondrite-

465

normalized REE patterns (Boynton, 1984) allow the individualization of the sample set into

466

four distinct groups. The metabasites of the group G1 show higher total REE contents and an

467

enriched light REE pattern (Figure 11 B). The rocks of group G2 show lower REE contents,

468

with a moderately enriched LREE pattern (Figure 11 D). The samples of groups G3 and G4

469

show flat REE patterns and higher contents than those of chondrite (Figures 11 F, H). The

470

distribution of the VNGB metabasites in MORB-normalized multi-element diagrams also

471

identifies enrichment in LILE in all groups (Figure 11 A, C, E, G). However, groups G1 and

472

G2 have higher overall contents of minor elements than MORB, while subgroups G3 and G4

473

exhibit lower contents of HFS and heavy REE than those of MORB.

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474

The Fe-Ti basalts of G1 are enriched in Sr, Ba, Ti and Th and depleted in K and Rb

475

relative to MORB. Compared to the other analyzed groups, they have the highest contents of

476

HFSE elements, with moderate enrichment and a distinctive Nb-Ta positive anomaly. The

19

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477

high-Mg and high-Fe tholeiite basalt samples present Nb and Ta contents very close to

478

MORB values and strong Ce positive anomalies, and incipient negative anomalies of Ti, Y,

479

and Yb. The high-Mg tholeiitic basalts of the G2 group show K, Rb and Ba enrichment and Sr

481

concentrations close to the MORB pattern. The Nb, Ta and Ce contents show slight

482

enrichment, with incipient negative Nb anomaly and weak to strong positive Ce anomalies.

483

The remaining HFSE elements in general exhibit slight depletion, with weak negative Hf, P,

484

Ti and Yb anomalies and mild to moderate positive Sm and Zr anomalies.

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The high-Mg tholeiitic basalts and the G3 group komatiite basalts are enriched in LILE

486

(Sr, K, Rb and Ba), with strong positive Rb anomalies. The HFSE elements (Ta, Nb, Ce, P, Zr,

487

Hf, Sm, Ti, Y and Yb) are moderately depleted compared to MORB and show weak positive

488

Ce anomalies, and relatively homogeneous behavior for the other HFSE.

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485

The G4 group samples are characterized by compositions of komatiites to high-Mg

490

tholeiitic basalts. They present variable enrichment in LILE elements, generally with strong to

491

slight positive anomalies of Rb and Ba and slight to moderate negative anomalies of Sr. HFSE

492

elements are slightly depleted relative to the MORB, and have positive Ce anomalies and

493

negative Nb and P anomalies.

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The samples of group G1 show (La/Lu)n ratio between 3.13 to 7.19 in Fe-Ti basalts,

495

from 11.07 to 14.00 in komatiites and 11.07 in high-Fe tholeiitic basalt. The rocks of group G2

496

show a concentration of total REE higher than chondrite values, slightly heavy rare earth

497

elements (HREE) fractionation and (La/Lu)n ratio between 1.98 and 2.34. The G3 group

498

shows slightly enriched REE contents compared to chondrite values, and low (La/Lu)n ratio

499

with values ranging from 0.79 to 1.11. Group G4 shows slightly enriched concentrations

500

compared to the chondrite values, with (La/Lu)n ratio between 1.12 and 2.25. The G4 samples

501

show depletion in middle REE with positive Eu anomalies ranging from weak (komatiitic

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502

basalts to high-Mg tholeiitic basalts) to strong (komatiites to komatiitic basalts), and weak

503

negative anomalies for the samples of komatiitic basalts.

504 Figure 11. A), C), E) and G) Multi-element diagrams standardized by MORB (Pearce, 1983)

506

and B, D, F and G) chondrite-normalized REE (Boynton, 1984) for the VNGB metabasite

507

groups.

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509

5. Discussion

510

5.1 Magmatic Evolution

SC

508

Despite the limited number of samples the compositional differences observed among

512

the samples of groups G1, G2, G3 and G4 based on the analysis of the diagrams of major and

513

trace elements suggest that the magmatic evolution has been controlled by mixing processes

514

such as assimilation combined with fractional crystallization from liquids of different

515

compositions. In G1, the strong enrichment in Fe and Ti with the advancement of

516

crystallization is characteristic of magmas generated under reducing conditions. In these

517

environments, the low ƒO2 inhibits the early crystallization of oxides such as magnetite and

518

chromite/ilmenite, leading to the enrichment of Fe and Ti. In more oxidizing environments,

519

the addition of water favors the early crystallization of oxides, such as chromite and

520

magnetite, and Mg-rich silicates, as olivine and orthopyroxene. Consequently, samples G3 e

521

G4 show slight or no enrichment in FeOt and TiO2.

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Besides the differences in the contents and patterns identified in the binary variation

523

diagrams, the decrease of Ni, as other compatible elements, Cr and Co (not shown) with the

524

magmatic fractionation observed in all groups suggests that the crystallization of olivine

525

played a fundamental role in the evolutionary process of these magmas. Though less

526

pronounced, other considerations can be made. In general, the slight enrichment in Sr

527

combined with the decrease of MgO suggest the late fractionation of plagioclase. The

21

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528

compositional differences between the groups are also indicated by the behavior and different

529

levels of zirconium and nickel. In evolutionary terms, the magnesium number (mg#) with relatively low values (33-

531

43) attests the Fe-Ti basalts of G1 as derived from a mantle more enriched in Fe. The G2 (54-

532

64), G3 (51-65) and G4 (56-76) samples show mg# values of moderately or slightly

533

fractionated magmas. The metabasites of group G4 with Ni > 250 ppm and magnesium

534

number from 69 to 76 may represent more primitive liquids.

536

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535

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5.2 Tectonic environments

The discussion of the tectonic environments of formation of the volcanic rocks is

538

based on field association and, mainly, on the geochemistry of the magmatism. It is important

539

to note that the rocks studied are of Paleoproterozoic age and present a small modification in

540

their geochemical compositions associated to the effects of metamorphism and weathering

541

alteration. In this aspect, major, trace and RE elements have been used to establish the

542

tectonic environments in comparison with the main associations of Phanerozoic volcanic

543

rocks (Shervais 1982; Pearce 1982; Pearce, 2008).

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Shervais (1982) suggests that the Ti/V ratios are intrinsic to the magma-forming

545

tectonic environments, since the V compatibility is controlled by the ƒO2, as well as the

546

partial melting degree and consequent fractional crystallization. The Ti presents incompatible

547

behavior regardless of the oxy-reducing conditions and the partition coefficient of V is

548

affected by the increase of ƒO2 in oxidizing environments, such as island arcs and continental

549

margin. The magmas generated by conditions between 20 and 30% partial melt have a Ti/V

550

ratio between 10 and 20. In tectonic environments with reducing conditions, such as the mid-

551

ocean ridges, magmas generated with a similar degree of melt have Ti/V ratios between 20

552

and 50, while ratios higher than 50 are characteristic of alkaline rocks. In back-arc basins, the

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Ti/V ratio shows values between 10 and 50. This wide variation can occur due to the

554

interaction between the mantle (depleted or enriched) and the input of fluids due to the

555

dehydration of the oceanic lithosphere during the subduction process (Shervais, 1982). In the

556

diagram in Figure 12A, the samples of the G2 (18-30), G3 (14-15) and G4 (10-19) groups

557

show similar composition to the basalts of island arcs, while the samples of group G1 are

558

similar to basalts generated in back-arc and/or mid-ocean ridge basins. The VNGB

559

metabasites show features of a poorly developed subduction environment, such as in island

560

arc and back-arc basins. However, the extraction of magma in a ridge from a previously

561

metasomatized mantle (with inherited subduction components) should also be considered.

562

Similar behavior is observed in the Pearce (1980) diagram, based on Ti vs. Zr (Figure 12B).

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553

Pearce and Stern (2006) indicate that the main characteristics of basalts generated in

564

retro-arc basins is HFSE-depletion (Zr, Ta, Nb, P, Ti and Zr) and LILE-enrichment (Sr, K, Rb

565

and Th). According to the authors, these characteristics are related to the addition of aqueous

566

fluids derived from the dehydration of the oceanic plate during subduction. In the MORB-

567

normalized multi-element diagrams, the metabasites of the G3 and G4 groups show LILE

568

enrichment (Sr, K, Rb, Ba) and moderate depletion in HFSE, with negative anomalies of Nb,

569

Ta and P, which corroborate this interpretation. It should be noted that in the samples of the

570

studied metavolcanic rocks, the transformations imposed by the regional metamorphism and

571

by the ductile shear zones could also account for the LILE-enrichment.

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563

The selective enrichment of LREE and depletion of MREE, as observed in the G4

573

samples, could be both understood in terms of subduction processes. While the selective

574

depletion of middle REEs is attributed by some authors (Adam and Green, 1994; Sisson,

575

1994) to amphibole fractionation processes, a feature common to volcanic island arc

576

associations, the enrichment of light REEs could have resulted from the interaction of the

577

subducting rocks with a hydrous melt (Hermann et al., 2006a; Zhang et al., 2011a).

23

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578

The G1 and G2 samples also show moderate enrichment of LILE elements (Sr, Rb, Ba

579

and K), however, they show a higher content of HFSE (Zr, P and Ti) and Nb-Ta, suggesting

580

interaction with a more enriched source. Most of the metabasites of the G1 subgroup are characterized by high levels of TiO2

582

(>2%) and FeOt (>12%), similar to the basalts generated in propagation expansion centers.

583

These basalts were named by Sinton et al. (1983) as Fe-Ti type basalts. These expansion

584

centers originate at the extremities of the extension plate boundaries that progressively spread

585

through the rigid lithosphere, occurring within continents (Courtillot, 1982), oceans (Hey et

586

al., 1989), magmatic arcs and retro-arc basins (Parson and Wright, 1996). The low mg# values

587

associated with Fe-Ti basalts suggest they are generated from a high degree of parent magma

588

fractionation. Based on geochemical composition, such as high contents of MgO, FeO, Ni, Cr

589

and Co, the G1 samples plotted on the komatiitic fields in the Jensen diagram (1976) and can

590

be reported as cumulate rocks. The high enrichment in light REEs, characteristic of low

591

melting conditions, favors the interpretation that these rocks have a residual origin.

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592

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Figure 12. Representation of the VNGB metabasites in tectonic diagrams for mafic rocks. A)

594

V vs. Ti (Shervais, 1982), B) Ti vs. Zr (Pearce, 1980).

596 597

5.3 Mantle Sources and Contamination

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593

Contamination seems to be an important petrological process to evaluate considering

598

Archean and Paleoproterozoic lavas, since the high heat flow has the potencial to assimilate

599

more crustal material than its modern analogues (Sparks, 1986), and especially the most

600

primitive lavas in contrast with more evolved basalts (Huppert et al., 1985). Otherwise the

601

depletion of HFSE, as well as Nb and Ti is the most distinctive geochemical fingerprint of

602

subduction magmatism (Pearce and Peate, 1995). Some of the hypotheses link negative HFSE

603

anomalies to the presence of Ti-rich minerals or amphibole that retain these elements during

24

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melt generation and/or transport (Kelemen et al., 1990; Stalder et al., 1998; Tiepolo et al.,

605

2000) in the mantle above the downgoing slab, or due to the higher mobility of LILE

606

elements in presence of fluid released by desvolatization of slab rocks (Kelemen et al ., 2013).

607

Meanwhile, it is difficult to assess the individual effect of contamination and metassomatism

608

of mantle wedge on the LILE and REE concentrations once that these processes may overlap

609

when considering only whole-rock geochemistry.

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The variation of the Ti/Yb ratio is sensitive to the depth of the partial melting that gave

611

rise to the basic magmas, whereas the Nb/Yb ratio can be used to characterize the mantle

612

fertility (Pearce, 2008). The TiO2/Yb vs Nb/Yb diagram proposed by Pearce (2008) shows

613

different mantle reservoirs for the VNGB metabasite groups. The high values of Nb and TiO2

614

(normalized by Yb) attributed to Fe-Ti basalts and to G1 cumulates identify deeper sources,

615

originating from the asthenospheric mantle, in a likely interaction of plume and mid-ocean

616

ridge (Figure 13A). The Ce/Yb ratio, ranging from 10.38 to 20.28 for the Fe-Ti metabasalts

617

of G1, can be attributed to low degrees of melting at high depths and/or the presence of garnet

618

as a residual phase. These characteristics suggest a model of genesis associated with mantle

619

plume. The lower concentrations of Nb and TiO2 (normalized by Yb) identified in G2, G3 and

620

G4 suggest shallow melt generation in the normal to slightly enriched mantle region at

621

subduction zones (Figure 13A). The lower Ce/Yb ratios in part of the G2 group (6.34-9.03),

622

and in the G3 (2.98-4.03) and G4 (3.91-6.39) groups, may have originated from a high degree

623

of melting and/or the presence of spinel as a residual phase.

M AN U

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EP

AC C

624

SC

610

In the Th/Yb vs. Nb/Yb diagram (Pearce, 2008), the ratio variations are sensitive to the

625

composition of the source of basic magmas and the effects of crustal contamination or related

626

to the subduction components, independent of fractional crystallization and/or partial melting.

627

Thus, the basaltic magmas derived from the depleted mantle, asthenospheric plume and

628

lithospheric mantle enriched by a low-degree asthenosphere melt, are positioned within or

25

ACCEPTED MANUSCRIPT

very close to the diagonal field defined by constant Th/Nb ratios (Figure 13B). Since Th is a

630

mobile element in the hydrated mantle, the mantle sources metasomatized by processes

631

related to subduction or crustal contamination are enriched in Th relative to Nb, resulting in

632

Th/Yb ratios higher than Nb/Yb. In general, the G2, G3 and G4 samples are close to but

633

slightly above the field defined for MORB-OIB rocks, and common to volcanic arc

634

associations. The enrichment of LILE, with the depletion of HFSE and the negative anomalies

635

of Nb and P, observed in the MORB-normalized multi-element diagrams, suggests that the

636

increase of Th is related to subduction. The G1 group metabasites identify crustal components,

637

but are associated with higher Nb values, and require a more enriched source.

SC

RI PT

629

M AN U

638 639

Figure 13. A) TiO2/Yb vs. Nb/Yb (Pearce, 2008) and B) Th/Yb vs. Nb/Yb (Pearce, 2008)

640

diagrams for the metabasites of VNGB. N-MORB: normal meso-oceanic basalts; E-MORB:

641

enriched meso-oceanic basalt and OIB: basalts of oceanic islands.

642

Comparing the Nb/Yb and Th/Yb ratios of the VNGB metabasites from East Scotia

644

Ridge basalts and South Sandwich Island Arc basalts (data from Fretzdorff et al., 2002), the

645

G1 samples show a trend towards vertex A, represented by the Bouvet Island, a plume

646

influenced environment (Figure 14). The G2 samples show a parallel trend to vertex B, which

647

can be understood as subducted slab-released components from sediments. The G3 and G4

648

metabasites plot very close to the delimited field for samples of South Sandwich Island Arc

649

(vertex C). This trend is suggested to be generated from sub-arc mantle modified by

650

subduction-related components from the downgoing slab. Thus, the East Scotia Ridge basalts

651

could represent a modern analogue to explain the geochemical variations observed in the

652

metabasites of VNGB.

AC C

EP

TE D

643

653

The coexistence of Fe-Ti basalts (G1) with basalts and andesitic basalts (G2, G3 and

654

G4), with characteristics of spreading centers with subduction components, points to a model

26

ACCEPTED MANUSCRIPT

655

of island arcs associated with propagation from a mid-ocean ridge in a back-arc basin (Figure

656

15).

657 Figure 14. Variation of Th/Yb vs. Nb/Yb for the East Scotia Ridge lavas (data from Fretzdorff

659

et al., 2002) compared with the metavolcanic rocks of VNGB.

660

Figure 15. Block diagram illustrating the probable tectonic environment of the formation of

661

the metabasites of VNGB and the sources of the mantle heterogeneity in back-arc basins. 1)

662

Interaction of the subduction components with the depleted upper mantle, 2) Interaction of the

663

upper mantle with asthenospheric source, 3) Interaction of the hydrous melt with the depleted

664

upper mantle and 4) Propagating rift structures and origin of Fe-Ti basalts.

SC

RI PT

658

665

5.4 Comparison with Archean and Paleoproterozoic Greenstone Belts

M AN U

666

The origin of a depleted upper mantle and an enriched lower mantle is attributed to the

668

first half of Earth’s history and resulted from extraction of magmas that led to the formation

669

of the continental crust. The generation of the magmas that gave origin to the continental crust

670

led to the depletion of incompatible elements in the upper mantle, whereas the lower mantle

671

did not experience such process. A faster increase in rates of continental growth is associated

672

with modern plate-tectonic processes, although in Paleoproterozoic times, it might have

673

operated in a different way.

EP

TE D

667

For a comparative approach, we selected geochemical data available at GEOROCK

675

database from metavolcanic rocks from Archean to Paleoproterozoic ages. The transition

676

between Archean and Paleoproterozoic, or A-P boundary, have been reported by several

677

works as a period of change in thermal conditions, consolidation of a crust and compositional

678

changes in early basic magmatism (Sun & Nesbit, 1978; Sun & McDonough 1989; Hall &

679

Hughes, 1993).

AC C

674

680

The selected metavolcanic rocks compound greenstone belts of Onverwacht Group

681

(3.5-3.2 Ga), in Barberton, Kaapvaal Craton, the Superior Province Craton (2.86-2.7) and

27

ACCEPTED MANUSCRIPT

682

Barama-Mazaruni Group (2.25-2.12 Ga), in the Amazonian Craton. A great majority of the

683

volcanic suites are tholeiitic to komatiitic in nature (e.g. Superior Province and Kaapvaal

684

cratons) but andesite to rhyolite with calc-alkaline affinity (Barama-Mazaruni Group) are also

685

present. Archean rocks (>3 Ga) are dominantly characterized by low Al2O3/TiO2 (8-12), in

687

contrast with Paleoproterozoic rocks that show higher Al2O3/TiO2 (18-22) (Hall & Hughes.,

688

1993). In Barama-Mazaruni Greenstone Belt (BMGB) samples, low Al2O3/TiO2 (4-6) is

689

coupled with higher Gd/Ybn contents. Most of VNGB samples are characterized by higher

690

Al2O3/TiO2 ratios (16-22), as expected for Paleoproterozoic volcanic rocks (Figure 16).

691

Generally, higher contents in CaO are associated to Al2O3 depletion. Meanwhile, in G1

692

samples the low Al2O3/TiO2 ratio (4-6) seems to be an effect of the higher TiO2 contents.

693

Most of the SPGB samples show Al2O3/TiO2 ratios expected for Paleoproterozoic volcanic

694

rocks, but also include low Al2O3/TiO2 ratio samples (7-24). Most of VNGB, as well as

695

Superior Province Greenstone Belt (SPGB) show the lowest (Gd/Yb)n ratios, near chondritic

696

values (Figure 16). Higher (Gd/Yb)n associated to G1 samples identifies a deeper source.

SC

M AN U

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697

RI PT

686

Figure 16. A) (Gd/Yb)n vs CaO/Al2O3 and B) (Gd/Yb)n vs Al2O3/TiO2 diagrams. Black

699

rectangle represents Chondritic (Gd/Yb)n, CaO/ Al2O3 and Al2O3/TiO2 ratios taken from

700

Mason (1979). Data sources for Barama-Mazaruni Greenstone Belt (BMGB) from Renner

701

and Gibbs (1987); for Superior Province Greenstone Belt (SPGB) from Kerrich (1999) and

702

for Barberton Greenstone Belt (BGB) from Jahn (1982).

704

AC C

703

EP

698

Based on petrological data of peridotites in the upper mantle, the “primitive mantle”

705

(PM) is conceived as the chemical composition of mantle after core segregation but before the

706

extraction of continental crust (Sun and McDonough, 1989). In the primitive mantle-

707

normalized spider diagram (Figure 17), VNGB and BMGB samples display variable LILE-

708

enrichment (e.g. Cs, Ba, K and Sr). K, Pb and Sr positive anomalies can be understood in

28

ACCEPTED MANUSCRIPT

terms of contamination and post-magmatic processes, while the negative anomalies observed

710

in some HFSE elements (Ti, Zr, Th and Nb) coupled with REE patterns should reflect the

711

composition of mantle source. When compared to BMGB, in the Guyana Shield, the VNGB

712

samples show quite similar and variable LILE content, but higher P, Nd, Zr, Sm and depletion

713

in HREE contents. SPGB samples show a more rectilinear pattern, enriched 10 times those of

714

Primitive Mantle.

RI PT

709

Despite the few data available, BMGB samples are more REE-enriched compared

716

with VNGB samples (Figure 17). Probably, the BMGB samples are characterized by higher

717

degrees of melting than VNGB. BGB samples show LREE-enrichment, in contrast with

718

almost all Archaean komatiites that are strongly LREE depleted. SPGB samples (2.86-2.7 Ga)

719

are more depleted in LREE and LILE contents in comparison with VNGB and BMGB rocks

720

(2.26-2.15 Ga), a feature that corroborates other studies concerning mantle´s thermal

721

evolution.

M AN U

SC

715

TE D

722

Figure 17. A) Primitive mantle normalized spiderdiagram and B) REE distribution patterns

724

for VNGB metavolcanics. Normalization values are taken from Sun & McDonough (1989).

725

Data sources for Barama-Mazaruni Greenstone Belt (BMGB) from Renner and Gibbs (1987);

726

for Superior Province Greenstone Belt (SPGB) from Kerrich (1999) and for Barberton

727

Greenstone Belt (BGB) from Jahn (1982).

729 730

AC C

728

EP

723

5.5 Metamorphism and Deformation The successive stages of deformation and metamorphism are commonly preserved in

731

metamorphic rocks. The recognition and correct interpretation of the relations between the

732

foliations and the porphyroblasts are essential for the understanding of the evolution of the

733

metamorphic conditions.

734

Two major metamorphic events were recognized, an orogenic metamorphism and a

735

contact metamorphism. In the orogenic metamorphism event, the S1, S2 foliations and a fine

29

ACCEPTED MANUSCRIPT

and discontinuous S3 schistosity were recognized. The S1 is preserved as F2 intrafolial folds,

737

transposed by the S2 crenulation cleavage, both generated under upper greenschist to medium

738

amphibolite facies and intermediate pressure conditions. The S3 foliation is defined by a

739

cleavage, locally a fine schistosity. The cleavage is filled by fine quartz and carbonate veins,

740

associated with a retrometamorphic event under lower greenschist facies conditions.

RI PT

736

The contact metamorphism is associated to the emplacement of Late Rhyacian to

742

Orosirian granites and is identified by the overprinting of textures with no mineral orientation,

743

characterized by a massive structure and acicular and fine decussate textures (<0.1 mm). The

744

identified assemblages indicate conditions between Ab-ep hornfels to pyroxene hornfels

745

facies. The main microstructures and metamorphic events are summarized in Table 4.

M AN U

SC

741

The metabasites of the VNGB were affected by orogenic metamorphism that

747

transformed the volcanic rocks into amphibolites, amphibole schists and magnesium schists.

748

The mineral associations indicate that the transformations occurred under conditions between

749

the upper greenschist and medium amphibolite facies, and under intermediate pressure

750

conditions. The structural relationships indicate that the metamorphism occurred associated

751

with three deformation events related to compressive tectonics. The relationships between the

752

foliations and metamorphic and stretching lineations indicate oblique collisional kinematics,

753

generating medium-angle shear zones in the areas of maximum deformation. These zones are

754

responsible for the contacts between the metavolcano-sedimentary rocks of the VNGB and

755

the orthogneisses of the Tumucumaque Complex, which represent the Archean basement. The

756

internal relationships between the VNGB rocks were also affected mainly by the VNSZ,

757

which puts in contact a lower domain composed mainly of metavolcanic rocks and an upper

758

domain composed mainly of metasedimentary rocks. The final evolution of the Cupixi and

759

Serra do Navio shear zones is characterized by transcurrent movements associated probably to

AC C

EP

TE D

746

30

ACCEPTED MANUSCRIPT

760

escape tectonics. The final movement of these zones generates the space for the ascent and

761

positioning of the Late Rhyacian to Orosirian granitic magmatism.

762 Table 4. Relationship between the main microstructures and metamorphic events observed in

764

the VNGB units. Legend: OM= orogenic metamorphism, CM= contact metamorphism; S1=

765

schistosity, S2= crenulation cleavage, S3= fracture cleavage. Minerals: Hb= hornblende, Pl=

766

plagioclase, Grt= garnet, Di= diopside, Chl= chlorite, Ser= sericite, Ep= epidote, Trem=

767

tremolite, Bt= biotite, Qz= quartz.

RI PT

763

769

SC

768 6. Conclusions

The VNGB metavolcanic rocks have preserved petrographic features, such as

771

phenocrysts and flow structure, and geochemical features compatible with basalts and

772

andesitic basalts of tholeiitic to komatiitic nature. These rocks were affected by a polycyclic

773

orogenic metamorphism of Paleoproterozoic age, and later to a contact metamorphism

774

associated with the emplacement of the post-collision granites. The available ages indicate

775

that the volcanism occurred between 2.17 and 2.15 Ga, while the intrusive granites

776

responsible for the contact metamorphism were positioned between 2.06 and 1.99 Ga.

777

Therefore, the orogenic metamorphism affected these units between 2.15 and 2.07 Ga. The

778

deformational phases (D1 and D2) associated to this metamorphic event is responsible for the

779

structuring of the VNGB units and for the generation of the Vila Nova, Ipitinga and Serra do

780

Navio shear zones.

TE D

EP

AC C

781

M AN U

770

The geochemical signatures of the VNGB metabasites correspond to island-arc basalts

782

(G2, G3 and G4 groups) and back-arc basalts (G1 group). The composition of the minor

783

elements indicates that the formation of the metabasites involved the interaction between

784

enriched MORB (G1, G2) and normal MORB (G3, G4) type sources with subduction

785

components.

31

ACCEPTED MANUSCRIPT The geochemical data and the observed field features indicate that the metavolcanic

787

rocks of the VNGB represent probably the evolution of back-arc basins and island arcs

788

associated with the Trans-Amazonian Orogeny. This metavolcano-sedimentary sequence

789

characterizes the Rhyacian evolution of the Maroni-Itacaiunas Province in the eastern portion

790

of the Guyana Shield and represents the closure of an ancient ocean that separated the two

791

Archean nuclei that constitute the Amapá Terrane.

792 Acknowledgments

SC

793

RI PT

786

We thank the National Research Council (CNPq) for the research scholarships and

795

grants to Ruy Paulo Philipp; the Amapari Mining Company for field logistics and making

796

geologic and drill core data available. We thank the editor Dr. Reinhardt Fuck, Dr. Cristina de

797

Campos and one anonymous reviewer for their critical suggestions.

M AN U

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References Adam, J., Green, T.H., 1994. The effects of pressure and temperature on the partitioning of Ti, Sr and REE between amphibole, clinopyroxene and basanitic melts. Chemical Geology, 117, 219-233. Anhaeusser, C.R., 2014. Archaean greenstone belts and associated granitic rocks – A review. Journal of African Earth Sciences, 100, 684–732. Avelar, V.D., Lafon, J.M., Delor, C., Guerrot, C., Lahondère, D., 2003. Archean crustal remnants in the easternmost part of the Guyana Shield: Pb–Pb and Sm–Nd geochronological evidence for Mesoarchean versus Neoarchean signatures. Géologie de la France, 2, 3-4. Barbosa, J.P.O., Costa Neto, M.C., Rosa-Costa, L.T., Anjos, G.C., Chaves, C.L., 2013. Mapa Geológico da Folha Macapá (NA.22-Y-D) 1:250.000, Levantamentos Geológicos do Brasil. CPRM. Belousova, E.,Griffin, W.L., O'Reilly, S.Y., Fisher, N.L., 2002. Igneous zircon: trace element composition as an indicator of source rock type. Contributions to Mineralogy and Petrology, 143, 602-622. Beswick, A.E.,Soucie, G., 1978. A correction procedure for metasomatism in an Archean greenstone belt. Precambrian Research, 6, 235-248. Borghetti, C., Philipp, R.P., Basei, M.A.S., Mandetta, P., 2014. New ages from Vila Nova and Tumucumaque Complex in the Cupixi region, Porto Grande, Amapá, Brazil. In: 9th South American Symposium on Isotope Geology, Boletim de Resumos Expandidos, São Paulo.

AC C

799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820

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Borghetti, C., Philipp, R.P., 2017. Geologia e geofísica do greenstone belt Vila Nova, porção NE do Cráton Amazônico, Amapá, Brasil. Geologia USP, Série científica, São Paulo, 17, 109-127. Borghetti, C., Philipp, R.P., Mandetta, P., Hoffmann, I.B. 2018a. Geochronology of the Archean Tumucumaque Complex, Amapá Terrane, Amazonian Craton, Brazil. Journal of South American Earth Sciences, in press. Borghetti, C., Philipp, R.P., Hoffmann, I.B., Basei, M.A.S.; Mandetta, P. 2018b. Geology and U-Pb zircon geochronology and Lu-Hf isotopes of the Vila Nova greenstone belt, Amapá, Brazil: arc-related associations of the Rhyacian orogeny in the northern Amazonian Craton, Brazil. Precambrian Research, submitted. Boynton, W.V., 1984. Geochemistry of the rare earth elements: Meteorite studies. In: Henderson P., Rare earth element geochemistry. Amsterdam, Elsevier, 63-114. Chemale, F., Philipp, R.P., Dussin, I.A., Formoso, M.L.L., Kawashita, K., Berttotti, A.L., 2011. Lu–Hf and U–Pb age determination of Capivarita Anorthosite in the Dom Feliciano Belt, Brazil. Precambrian Research, 186,117-126. Condie, K.C. 1981. Archean Greenstone Belts. Developments in Precambrian Geology, Elsevier, Amsterdam, The Netherlands, 3, 434. Cordani, U.G.,Neves, B.B., 1982. The geologic evolution of South America during the Archean and Early Proterozoic. Brazilian Journal of Geology, 12, 78-88. Courtillot, V., 1982. Propagating rifts and continental breakup. Tectonics, 1, 239-250. Day, W.C., Tosdal, R.M., Acosta, E.L., Aruspon, J.C., Carvajal, L., Cedeno, E., Lowry, G., Martinez, L.F., Noriega, J.A., Nunez, F.J., Rojas, J., Prieto, F., 1995. Geology of the Lo Increible mining district and U-Pb age of the early Proterozoic Yuruari Formation of the Pastora Supergroup, Guayana Shield, Venezuela. U.S. Geological Survey Open-File-Report 2124, E1-E13. Delor, C., Lahondère, D., Egal, E., Lafon, Cocherie, A., Guerrot, C., Rossi, P., Truffet, C., Theveniaut, H., Phillips, P., Avelar, V.G., 2003a. Transamazonian crustal growth and reworking as revealed by the 1:500000 scale geological map of French Guyana. Géologie de la France, 2-3-4, 5-57. DeWit, M.J. and Ashwal, L.D., 1986. Workshop on Tectonic Evolution of Greenstone Belts. Lunar Planetary Institute Technical Report. Lunar and Planetary Institute, Houston. 86-10, 227. Elholou, S., Belousova, E., Griffin, W.L., Pearson, N.J., O’Reilly, S.Y., 2006. Trace element and isotopic composition of GJ-red zircon standard by laser ablation. Geochimica et Cosmochimica Acta, 70, A158. Fretzdorff, S., Livermore, R.A., Devey, C.W., Leat, P.T., Stoffers, P., 2002. Petrogenesis of the back-arc east Scotia Ridge, South Atlantic Ocean. Journal of Petrology, 43, 14351467. Gibbs, A.K., Olszewski, W.J., 1982. Zircon U-Pb ages of Guyana greenstone-gneiss terrane. Precambrian Research, 17, 199-214. Grant, F.S., 1985. Aeromagnetics, geology and ore environments, II. Magnetite and ore environments. Geoexploration, 23, 335-362. Gruau, G., Martin, H., Leveque, B., Capdevila, R.,Marot, A., 1985. Rb-Sr and Sm-Nd geochronology of lower Proterozoic granite-greenstone terrains in French Guyana, South America. Precambrian Research, 30, 63-80. Hall, R. P., Hughes, D. J., 1993. Early Precambrian crustal development: changing styles of mafic magmatism. Journal of the Geological Society, 150, 625-635. Hermann J., Spandler C., Hack A., Korsakov A.V., 2006 Aqueous fluids and hydrous melts in high-pressure and ultra-high pressure rocks: implications for element transfer in subduction zones. Lithos, 92, 399-417.

AC C

821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870

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Heubeck, C., Lowe, D.R., 1994. Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa. Precambrian Research, 68,257-290. Hey, R.N., Sinton, J.M., Duennebier, F.K., 1989. Propagating rifts and spreading centers. The Geology of North America. The Eastern Pacific Ocean and Hawaii, 161-176. Huppert, H.E., Stephen, R., Sparks, J., 1985. Cooling and contamination of mafic and ultramafic magmas during ascent through continental crust. Earth and Planetary Science Letters, 74, 371-386. Irvine, T.N., Baragar, W.R.A., 1971. A Guide to the Chemical Classification of the Common Volcanic Rocks. Canadian Journal of Earth Sciences. 8, 523-548. Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004. The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology. Chemical Geology, 211, 47-69. Jahn, B. M., Gruau, G., Glikson, A. Y., 1982. Komatiites of the Onverwacht Group, S. Africa: REE geochemistry, Sm/Nd age and mantle evolution. Contributions to Mineralogy and Petrology, 80, 25-40. Janoušek, V., Farrow, C.M., Erban, V., 2006. Interpretation of whole-rock geochemical data in igneous geochemistry: Introducing Geochemical Data Toolkit (GCDkit). Journal of Petrology, 47, 1255-1259. Jensen, L.S., 1976. A New Cation Plot for Classifying Subalkalic Volcanic Rocks. Publications of the Ontario Division of Mines, 66, 22. Jost, H., Carvalho, M.J., Rodrigues, V.G., Martins, R., 2014. Metalogênese dos greenstone belts de Goiás. Metalogênese das províncias tectônicas brasileiras, Belo Horizonte, CPRM, 141-168. Kelemen, P.B., Johnson, K.T.M., Kinzler, R.J., Irving, A.J., 1990. High-field-strength element depletions in arc basalts due to mantle–magma interaction. Nature, 345, 521524. Kelemen, P.B., Hanghøj, K., Greene, A.R., 2013. One view of the geochemistry of subduction-related magmatic arcs, with an emphasis on primitive andesite and lower crust. Treatise on geochemistry, 2, 749-806. Kerrich, R., Polat, A., Wyman, D., Hollings, P., 1999. Trace element systematics of Mg-, to Fe-tholeiitic basalt suites of the Superior Province: implications for Archean mantle reservoirs and greenstone belt genesis. Lithos, 46, 163-187. Kusky, T.M., Polat, A., 1999. Growth of granite–greenstone terranes at convergent margins, and stabilization of Archean cratons. Tectonophysics, 305,43-73. Lafrance, J., Bardoux, M., Stevenson, R., Machado, N., Sauvage, J.F., Fournier, D.,1997. Geochemical characteristics of magmatic rocks of the St-Élie area, Northern greenstone belt, French Guyana: a Paleoproterozoic oceanic arc and collision zone within the Guyana Shield. GSA Annual Meeting, Denver, Abstracts with Programs 29, 158. Le Maitre, R.W., Streckeisen, A., Zanettin, B., LeBas, M.J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lameyre, J., Sabine, P.A., Schmid, R., Sorensen, H., Woolley, A.R., 1989. Igneous Rocks: A classification of igneous rocks and glossary of terms: recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, 193. Lobato, L., Ribeiro-Rodrigues, L., Zucchetti, M., Noce, C., Baltazar, O., Da Silva, L., Pinto, C., 2001. Brazil's premier gold province. Part I: The tectonic, magmatic, and structural setting of the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero. Mineralium Deposita, 36, 228-248. Lowe, D.R., Byerly, G.R., 1999. Geologic evolution of the Barberton greenstone belt, South African Geological Society of America, 329, 1-36.

AC C

871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920

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Ludwig, K.R., 2008. Isoplot/Ex version 3.7. A geochronological toolkit for Microsoft Excel. Berkeley Geochronological Centre, Special Publication. Magalhães, L.A., Souza Filho, C.R., Silva, A.M., 2007. Caracterização geológica- geofísica da porção central do Amapá com base em processamento e interpretação de dados aerogeofísicos. Revista Brasileira de Geociências. 37, 464-477. Mason, B., 1979. Cosmochemistry. In: Data of geochemistry, chapter B (ed. M. Fleischer), Washington: U.S Printing Office, B1-B124. McReath, I.,Faraco, M.T.L., 1997. Sm-Nd and Rb-Sr systems in part of the Vila Nova metamorphic suite, northern Brazil. In: South American Symposium on Isotope Geology, 1, 194-196. McReath, I., Faraco, M.T.L., 2006. Paleoproterozoic greenstone-granite belts in northern Brazil and the former Guyana Shield-West African Craton province. Geologia USP. Série Científica, 5, 49-63. Melson, W.G., Vallier, T.L., Wright, T.L., Byerly, G.,Nelen, J., 1976. Chemical Diversity of Abyssal Volcanic Glass Erupted Along Pacific, Atlantic, and Indian Ocean Sea-Floor Spreading Centers. The geophysics of the Pacific ocean basin and its margin, 351-367. Noce, C.M., Pedrosa-Soares, A.C., Silva, L.C., Alkmim., F.F., 2007. O embasamento Arqueano e Paleoproterozóico do Orógeno Araçuaí. Revista Geonomos, 15, 17-23. Norcross, C., Davis, D.W., Spooner, E.T., Rust, A., 2000. U-Pb and Pb-Pb age constraints on Paleoproterozoic magmatism, deformation and gold mineralization in the Omai area, Guyana Shield. Precambrian Research, 102, 69-86. Padoan, M., Rossetti, P., Rubatto, D., 2014. The choco 10 gold deposit (El Callao, Bolivar State, Venezuela): Petrography, geochemistry and U–Pb geochronology. Precambrian Research, 252, 22-38. Parson, L.M., Wright, I.C., 1996. The Lau-Havre-Taupo back-arc basin: A southwardpropagating, multi-stage evolution from rifting to spreading. Tectonophysics, 263, 122. Pearce, J.A., 1982. Trace element characteristics of lavas from destructive plate boundaries. Orogenic Andesites and Related Rocks, 8, 525-548. Pearce, J.A., 1983. Role of the sub-continental lithosphere in magma genesis at active continental margins. In: Hawkesworth, C.J. and Norry, M.J., Eds., Continental Basalts and Mantle Xenoliths, 230-249. Pearce, J.A., Peate, D.W., 1995. Tectonic implications of the composition of volcanic arc magmas. Annual Review of Earth and Planetary Sciences, 23, 251-285. Pearce, J.A., Stern, J.R., 2006. The Origin of Back-arc Basin Magmas: Trace Element and Isotopic Perspectives. In: Christie, D.M., Fisher, C.R., Lee, S.-M., Givens, S. (Eds.), Back-arc spreading systems: geological, biological, chemical, and physical interactions: AGU Monograph, American Geophysical Union. Geophysical Monograph, Washington DC, 63-86. Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos, 100, 14-48. Pimentel, M.M., Spier, C.A., Ferreira Filho, C.F., 2002. Estudo Sm-Nd do Complexo MáficoUltramáfico Bacuri. Amapá: Idade da Intrusão, Metamorfismo e Natureza do Magma Original. Revista Brasileira Geociências 32, 371-376. Priem, H.N.A., De Roever, E.W.F., Bosma, W., 1980. A note on the age of the Paramaka metavolcanics in northeastern Suriname. Geologie en Mijnbouw, 59, 171-173. Renner, R., Gibbs, A. K., 1987. Geochemistry and petrology of metavolcanic rocks of the early Proterozoic Mazaruni greenstone belt, northern Guyana. Geological Society, London, Special Publications, 33, 289-309.

AC C

921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969

ACCEPTED MANUSCRIPT

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Rosa-Costa, L.D., Ricci, P.S.F., Lafon, J.M., Vasquez, M.L., Carvalho, J.M.A., Klein, E.L., Macambira, E.M.B., 2003. Geology and geochronology of Archean and Paleoproterozoic domains of the southeastern Amapá and northwestern Pará, Brazil– southeastern Guyana Shield. Géologie de la France, 2, 4. Rosa-Costa, L.T., Lafon, J.M., Delor, C., 2006. Zircon geochronology and Sm–Nd isotopic study: further constraints for the Archean and Paleoproterozoic geodynamical evolution of the southeastern Guyana Shield, north of Amazonian Craton, Brazil. Gondwana Research, 10, 277-300. Santos, J.O.S., Hartmann, L.A., Gaudette, H.E., Groves, D.I., Mcnaughton, N.J., Fletcher, I.R., 2000. A new understanding of the provinces of the Amazon Craton based on integration of field mapping and U-Pb and Sm-Nd geochronology. Gondwana Research, 3, 453-488. Sawkins, F.J., 2013. Metal deposits in relation to plate tectonics (Vol. 17). Springer Science Business Media. Shervais, J.W., 1982. Ti-V plots and the petrogenesis of modern and ophiolitic lavas. Earth and Planetary Science Letters, 59, 101-118. Sinton, J.M., Wilson, D.S., Christie, D.M., Hey, R.N., Delaney, J.R., 1983. Petrologic consequences of rift propagation on oceanic spreading ridges. Earth and Planetary Science Letters, 62, 193-207. Sisson, T. W., 1994. Hornblende-melt partitioning measured by ion microprobe. Chemical Geology, 117, 331-344. Sparks, R.S.J., 1986.The role of crustal contamination in magma evolution through geological time. Earth and Planetary Science Letters, 78, 211-223. Spier, C.A., Ferreira Filho, C.F., 1999.Geologia, Estratigrafia e Depósitos Minerais do Projeto Vila Nova, Escudo das Guyanas, Amapá, Brasil. Revista Brasileira de Geociências, 29,173-178. Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters, 26, 207-221. Stalder, R., Foley, S.F., Brey, G.P., Horn, I., 1998. Mineral aqueous fluid partitioning of trace elements at 900- 1200 degrees ºC and 3.0-5.7 GPa: New experimental data for garnet, clinopyroxene, and rutile, and implications for mantle metasomatism. Geochimica et Cosmochimica Acta, 62, 1781-1801. Sun, S. S., Nesbitt, R. W., (1978). Petrogenesis of Archaean ultrabasic and basic volcanics: evidence from rare earth elements. Contributions to Mineralogy and Petrology, 65, 301-325. Sun, S. S., McDonough, W. S., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society, London, Special Publications, 42, 313-345. Tassinari, C.C.G., Bettencourt, J.S., Geraldes, M.C.,Macambira, M.J.B.,Lafon, J.M. 2000. The Amazonian Craton. In: Cordani, U.G.; Milani, E.J.; Filho, A.T.; Campos, D.A. (eds.) Tectonic Evolution of South America. Rio de Janeiro, 31º International Geological Congress, SBG, 41-95. Tassinari, C.C., Macambira, M.J.B., 1999. Geochronological provinces of the Amazonian Craton. Episodes - Newsmagazine of the International Union of Geological Sciences, 22, 174-182. Tassinari, C.C.G., Macambira, M.J.B., 2004. A evolução Tectônica do Cráton Amazônico, in: Geologia Do Continente Sul-Americano: Evolução Da Obra de Fernando Flávio Marques de Almeida, 471-485.

AC C

970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017

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Teixeira, W.,Tassinari, C.C.G., Cordani, U.G.,Kawashita, K., 1989. A review of the geochronology of the Amazonian Craton: tectonic implications. Precambrian Research, 42, 213-227. Tiepolo, M., Vannucci, R., Oberti, R., Foley, S., Bottazzi, P., Zanetti, A., 2000. Nb and Ta incorporation and fractionation in titanian pargasite and kaersutite: Crystal-chemical constraints and implications for natural systems. Earth and Planetary Science Letters, 176, 185–201 Vanderhaeghe, O., Ledru, P., Thiéblemont, D., Egal, E., Cocherie, A., Tegyey, M., Milési, J.P., 1998. Contrasting mechanism of crustal growth: Geodynamic evolution of the Paleoproterozoic granite–greenstone belts of French Guyana. Precambrian Research, 92, 165-193. Voicu, G., 1997. Metallogeny of the Omai gold deposit.The Geology, Geochemistry, Geophysics, and Mineral Deposits of the Guyana and West African Shields. Short Course Notes, Northwest Mining Conventions, USA, 42. Voicu, G., Bardoux, M., Stevenson, R., 2001. Lithostratigraphy, geochronology and gold metallogeny in the Northern Guyana Shield, South America: A review. Ore Geology Review 18, 211-236. Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical geology, 20, 325-343. Zeh, A., Gerdes, A., Barton J.M., J.M., 2009. Archean accretion and crustal evolution of the Kalahari Craton: the zircon age and Hf isotope record of granitic rocks from Barberton/Swaziland to the Francistown Arc. Journal of Petrology, 50, 933-966. Zeh, A., Gerdes, A.,Heubeck, C., 2013. U-Pb and Hf isotope data of detrital zircons from the Barberton Greenstone Belt: constraints on provenance and Archaean crustal evolution. Journal of the Geological Society, 170, 215-223. Zhang Z.M., Dong X., Liou J.G., Liu F., Wang W., Yui F., 2011a. Metasomatism of garnet peridotite from Jiangzhuang, southern Sulu UHP belt: constraints on the interactions between crust and mantle rocks during subduction of continental lithosphere. Journal of Metamorphic Geology, 29, 917-937.

AC C

1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047

ACCEPTED MANUSCRIPT

Legend Paraguay-Araguaia Belt (900-500 Ma)

ACCEPTED MANUSCRIPT Rondoniana-San Ignacio (1.5-1.3 Ga)

Greenstone Belt (2.26 - 2.12 Ga)

Rio Negro-Juruena (1.8-1.5 Ga)

Geochronological Provinces

Maroni-Itacaiúnas (2.2-1.9 Ga) Central Amazonian (>2.5 Ga)

Ventuari-Tapajós (1.9-1.8 Ga)

Sunsás (1.2-1.0 Ga)

AC C

EP

TE D

M AN U

SC

RI PT

Legend (1)

Stratigraphic Column

Reworked Archean Domain A- Amapá Terrane

Maroni-Itacaiúnas Province Paleoproterozoic Domain Metavolcano-sedimentary sequence Calk-alkaline TTG suite

Paleoprot.

Phanerozoic cover

B- Paru Terrane Paleoproterozoic charnockite suite

ACCEPTED MANUSCRIPT

Granitic rocks

Archean basement

Metavolcano-sedimentary Central Amazonian Province sequence Archean orthogneiss, Archean basement metagranite and gabbro

AC C

EP

TE D

M AN U

SC

RI PT

Legend (2)

Legend Phanerozoic cover Paleoproterozoic Porto Grande Granite Amapari Granite Igarapé Careta Suite Undifferentiated granitoid

Vila Nova Complex Upper Domain Quartzite, metaconglomerate, ACCEPTED Banded iron formation Lower Domain Amphibole schist, tremolite schist, mafic schist Bacuri Complex Amphibolite, metaperidotite chromitite, serpentinite, metagabbro

Archean Mungubas Granite MANUSCRIPT

Anauerapucu Granite Guianense Complex Tumucumaque Complex

AC C

EP

TE D

M AN U

SC

RI PT

Legend (3)

Legend Paleoproterozoic Granitoid

Metaconglomerate

Bacuri Complex Metagabro, amphibolite, metaperidotite, chromitite, serpentinite, tremolitite

Geochronology

ACCEPTED MANUSCRIPT (CB-13A sample)

Quartzite Vila Nova Basal Domain Complex Amphibolite, amphibole Archean Tumucumaque Complex Upper Domain schist, mafic schist Banded iron Tonalitic to granodioritic gneiss Tremolite schist formation

Locality Shear Zone Foliation Lineation

AC C

EP

TE D

M AN U

SC

RI PT

Legend (4)

ACCEPTED MANUSCRIPT

Marowijne Ipitinga

Country

Magma Series Igneous Age Method Tholeiitic to CalcSuriname 1.950 ±150 Ma Rb-Sr alkaline1 Tholeiitic2

Brazil

2.264 ±34 Ma 2.140 Ma 2.267 ±66 Ma

Serra do Navio Barama-Mazaruni

Guiana

Paramacá

French Guiana

Priem (1982)

Sm-Nd Mc Reath & Faraco (1997) Pb-Pb

Rosa-Costa (2006)

Sm-Nd Mc Reath & Faraco (2006)

Tholeiitic* 2.171 ±47 Ma U-Pb Borguetti (2017) Tholeiitic to Calc2.171 ±140 Ma Sm-Nd Voicu (1997) alkaline3 2.120 ±2 Ma U-Pb Norcross (2000) 2.250 ±106 Ma U-Pb Gibbs & Olszwesky (1982) Tholeiitic to Calc2.210 ±90 Ma Sm-Nd Gruau (1985) alkaline4 Delor (2003a) 2.137 ±6 Ma Pb-Pb

Calc-alkaline (restricted tholeiitic)6,7,8

U-Pb U-Pb

Vanderhaeghe (1998) Lafrance (1997)

2.131 ±10 Ma

U-Pb

Day (1995)

2.143 ±6 Ma 2.145 ±5 Ma

U-Pb U-Pb

Padoan (2014) Padoan (2014)

AC C

EP

TE

D

Venezuela

2.148 ±4 Ma

M AN US C

2.174 ±7 Ma

Pastora

Reference

RI PT

Greenstone Belt

ACCEPTED MANUSCRIPT 206

Pb/

238

207

Spot Th/U

Pb/

235

U

206

1σ

Pb/

238

U

238

1σ

rho

U/

206

Pb

207

1σ

Pb/

206

Pb

208

1σ

Pb/

206

Pb

1σ

U Age (Ga)

207

Error Ga

Pb/

235

U Age (Ga)

207

Error Ga

Pb/

206

Pb Age (Ga)

Error Ga

Conc. % 206

207

Pb/238U

Pb/206Pb 100

4.1 0.795 7.7082 0.1908 0.4019 0.0079 0.79 2.4885 0.0488 0.1363 0.0010 0.3008 0.2535 2.178 0.036 2.198 0.022 2.177 0.012

100

6.1 0.492 7.0951 0.1673 0.3881 0.0072 0.78 2.5769 0.0476 0.1314 0.0009 0.2981 0.2512 2.114 0.033 2.123 0.021 2.114 0.012

100

7.1 0.836 7.4635 0.1671 0.4012 0.0068 0.76 2.4926 0.0425 0.1343 0.0009 0.4337 0.3655 2.175 0.031 2.169 0.020 2.152 0.012

101

RI PT

3.1 0.487 7.4255 0.1699 0.3996 0.0073 0.80 2.5022 0.0458 0.1348 0.0010 0.2856 0.2407 2.167 0.034 2.164 0.020 2.158 0.012

8.1 0.734 7.2306 0.1615 0.3942 0.0067 0.76 2.5369 0.0432 0.1334 0.0010 0.4056 0.3418 2.142 0.031 2.140 0.020 2.139 0.012

100 100

12.1 0.411 7.8017 0.1789 0.4088 0.0071 0.75 2.4463 0.0422 0.1381 0.0010 0.2909 0.2451 2.209 0.032 2.208 0.020 2.199 0.012

100

13.1 0.886 7.6574 0.1726 0.4035 0.0070 0.77 2.4783 0.0428 0.1363 0.0010 0.2894 0.2440 2.185 0.032 2.192 0.020 2.177 0.012

100

16.1 0.481 7.1434 0.1877 0.3910 0.0085 0.83 2.5575 0.0555 0.1317 0.0015 0.7931 1.1297 2.128 0.039 2.129 0.023 2.117 0.020

100

17.1 1.145 6.9714 0.1885 0.3853 0.0087 0.84 2.5952 0.0587 0.1311 0.0014 0.9701 1.3816 2.101 0.040 2.108 0.024 2.110 0.019

100

18.1 0.775 7.1378 0.2324 0.3931 0.0106 0.83 2.5438 0.0686 0.1336 0.0015 0.7869 1.1221 2.137 0.049 2.129 0.029 2.142 0.019

100

19.1 0.277 7.3070 0.1933 0.3968 0.0086 0.82 2.5201 0.0549 0.1323 0.0015 0.5516 0.7857 2.154 0.040 2.150 0.023 2.125 0.019

101

21.1 0.278 7.2021 0.1901 0.3941 0.0087 0.84 2.5375 0.0562 0.1321 0.0015 0.4979 0.7092 2.142 0.040 2.137 0.023 2.123 0.019

101

22.1 0.765 7.2130 0.1920 0.3946 0.0087 0.83 2.5341 0.0559 0.1335 0.0015 0.9250 1.3174 2.144 0.040 2.138 0.023 2.142 0.019

100

M AN U

SC

10.1 0.694 7.4291 0.1685 0.3987 0.0070 0.78 2.5081 0.0443 0.1346 0.0010 0.3667 0.3092 2.163 0.032 2.164 0.020 2.155 0.012

100

25.1 0.869 7.2889 0.2382 0.3932 0.0109 0.85 2.5434 0.0704 0.1334 0.0016 0.6947 0.9906 2.138 0.050 2.147 0.029 2.140 0.020

100

26.1 0.192 7.1669 0.1881 0.3909 0.0085 0.83 2.5583 0.0555 0.1317 0.0014 0.3332 0.4745 2.127 0.039 2.132 0.023 2.118 0.019

100

AC C

EP

TE

D

24.1 0.157 7.6633 0.2522 0.3986 0.0108 0.82 2.5087 0.0679 0.1355 0.0016 0.3681 0.5246 2.163 0.050 2.192 0.029 2.166 0.021

ACCEPTED MANUSCRIPT Group/ Subgroup Sample

G1

PIA-12 ANT-57 ANT-59 CB-31 CB-08 VNG-56

G2 VNG-57 VNG-32 VNG-33 VNG-45 (CX66)

G3

VNG-57 VNG-38 VNG-44 (CX48)

VNG-20

VNG-28 VNG-28 VNG-57 (CX32) (CX33) (CX68-A)

SiO2

45.23

48.46

48.47

49.69 48.99

49.23

48.02

46.53

51.97

49.92

46.63

54.51

53.99

51.74

54.78

50.55

49.63

Al2O3

16.2

13.66

15.07

13.82 14.58

5.81

6.83

13.5

12.68

14.04

14.83

13.91

14.16

13.67

13.3

13.48

13.41

Fe2O3

15.65

16.02

14.71

15.7

15.14

12.59

12.86

9.23

10.89

14.8

12.79

9.77

10.14

11.26

12.58

13.59

13.68

MgO

5.65

4.07

5.75

4.65

5.93

17.34

17.2

9.91

8.38

5.29

7.83

8.94

7.35

8.99

6.67

7.84

12.83

CaO

8.45

11.62

7.5

9.88

8.13

8.51

7.92

16.01

12.64

9.4

7.66

6.49

9.23

8.43

7.56

8.78

4.4

0.87

0.05

0.12

0.12

0.15

2.77

2.85

0.78

0.25

0.86

4.35

2.58

1.4

0.28

0.74

1.1

1.43

2.7

0.64

3.23

1.71

3.04

0.32

0.38

0.15

0.61

2.7

0.63

1.15

1.2

3.48

2.19

2.13

2.35

TiO2

2.68

3.06

2.84

2.92

2.63

1.04

1.32

0.63

0.71

1.41

1.15

0.57

0.65

0.79

0.77

0.9

0.61

P2O5

0.27

0.39

0.43

0.38

0.34

0.09

0.14

0.2

0.26

0.34

0.12

0.07

0.08

0.04

0.05

0.05

0.04

RI PT

K2O Na2O

MnO

0.2

0.22

0.18

0.17

0.18

0.18

0.18

0.33

0.32

0.19

0.28

0.17

0.18

0.16

0.22

0.25

0.17

Sum

99.76

99.76

99.81

99.77 99.76

99.81

99.83

99.74

99.84

99.8

99.78

99.87

99.81

99.85

99.85

99.84

99.83

1.8

1.5

1.5

0.7

0.6

1.7

1.9

2.3

1.0

0.8

3.5

1.7

1.4

1.0

1.0

1.2

1.2

0.01

0.012

0.025

0.01

0.01

0.143

0.117

0.122

0.156

0.012

0.039

0.031

0.022

0.005

0.004

0.002

0.05

281

72

68

62

150

491

348

247

49

154

53.4

38.6

40.1

45.9

45.3

80.9

82.4

44.2

51.0

50.7

Hf

4.9

4.2

3.9

4.3

3.0

2.5

2.6

2.2

2.1

1.6

Nb

8.8

13.6

10.5

14.5

13.3

14.0

16.0

3.2

4.1

2.9

Rb

18.8

1.6

2.3

0.5

3.6

98.8

134.6

31

28

Sc

38

35

26

Sr

244.9

453.5

301.9

Ta

0.7

0.9

0.7

0.7

Th

3.6

3.5

2.7

3.3

14

15

64.5

86.7

0.8

0.8

1.3

3.4

4.1

5.5

409.0 530.5

V

482

406

318

400

360

136

173

Y

31.1

30.9

23.0

31.8

28.7

12.5

13.7

Zr

157.1

170.5

127.3

175.2 159.8

92.0

106.4

Cu

50.8

41.0

75.0

81.4

83.3

73.9

29.4 541.2

31.7

47.0

39.8

58.9

507.2

27.7

19.8

21.7

21.7

22.3

Ce

29.6

57.8

40.7

49.2

47.3

43.1

Pr

3.98

7.21

5.31

6.3

6.00

5.21

136

29

58

56

169

48.4

44.9

45.6

49.0

58.0 1.7

1.7

1.5

2.0

1.4

1.5

1.4

4.5

5.4

1.5

1.7

1.9

1.1

47.5

11.1

43.7

45.9

57.5

26.4

5.8

19.9

133.9

95.8

24

33

29

35

30

30

49

44

48

39

929.4

209.1

262.1

132.3

73.4

163.9

155.5

263.0

204.1

222.8

0.2

0.2

0.3

0.3

0.2

0.4

<0.1

<0.1

<0.1

<0.1

1.7

3.5

1.9

0.6

1.4

1.4

<0.2

0.2

0.2

0.3

178

205

283

229

187

213

313

315

349

234

13.9

16.1

17.2

21.0

18.0

20.3

16.9

15.6

17.0

13.9

90.8

93.9

68.5

78.4

69.6

77.8

42.9

39.8

45.2

43.4

25.2

23.3

165.0

375.9

22.0

203.1

152.5

37.9

29.5

16.4

72.7

95.3

56.1

45.1

15.6

27.9

18.2

63.4

24.4

184.9 22.0

36.4

30.4

28.8

6.1

6.1

8.6

2.9

2.6

2.8

2.5

49.2

50.1

78.7

52.9

13.0

15.3

18.7

8.1

6.6

7.0

6.8

6.2

6.55

9.68

6.51

1.94

2.02

2.42

1.06

1.00

1.04

0.91

D

44.8 13.3

188

39.2

3.0

TE

Ni La

349

45.3

M AN U

Ba Co

SC

LOI Cr2O3

Nd

19.4

30.6

24.8

31.0

26.1

20.5

25.3

29.9

39.7

25.9

8.7

8.8

10.8

5.8

4.9

5.1

5.4

Sm

5.18

7.28

5.51

6.94

6.04

3.84

4.66

5.06

6.94

4.46

2.5

2.31

2.51

1.89

1.48

1.64

1.57

1.77

2.78

2.17

2.47

2.16

1.02

1.26

1.7

2.1

1.61

1.00

0.71

0.87

0.72

0.67

0.82

0.53

5.91

7.2

5.3

6.61

6.56

3.29

3.61

3.83

4.83

4.25

3.25

3.05

3.52

2.61

2.33

2.56

2.16

Tb

1.08

1.1

0.9

1.06

0.95

0.44

0.53

0.48

0.72

0.59

0.56

0.48

0.57

0.48

0.4

0.46

0.37

Dy

6.87

6.66

5.14

5.74

5.78

2.28

3.38

2.92

3.85

3.46

3.43

3.18

4.06

3.22

2.84

2.82

2.59

Ho

1.37

1.22

0.97

1.13

1.14

0.41

0.53

0.54

0.59

0.7

0.76

0.69

0.81

0.65

0.56

0.67

0.51

Er

3.58

3.39

2.58

3.11

3.22

1.35

1.32

1.44

1.76

2.11

2.31

2.02

2.55

2.03

1.86

1.85

1.67

Tm

0.49

0.46

0.33

0.44

0.45

0.16

0.2

0.2

0.26

0.29

0.32

0.33

0.34

0.31

0.29

0.29

0.24

Yb

2.85

2.85

2.07

2.9

2.53

1.01

1.21

1.23

1.58

1.92

2.05

1.92

2.07

2.03

1.8

1.78

1.74

Lu

0.44

0.4

0.34

0.45

0.36

0.14

0.15

0.2

0.27

0.27

0.32

0.27

0.36

0.31

0.28

0.31

0.27

AC C

EP

Eu Gd

ACCEPTED MANUSCRIPT G3

G4

VNG-57 (CX68-B)

51.84

49.96

53.82

50.68

44.14

49.02

48.94

52.31

53.59

50.41

47.46

50.38

50.84

51.27

14.3

12.03

9.31

12.5

12.01

9.56

10.27

13.16

6.56

12.92

6.04

6.47

7.45

13.61

11.18

12.54

11.63

10.82

13.65

11.00

12.31

12.85

10.17

9.81

14.42

10.53

11.61

9.99

10.06

10.47

10.61

11.54

15.66

14.56

12.76

8.58

16.49

9.07

11.8

12.82

16.46

9.39

6.31

10.11

10.59

7.21

9.15

12.12

10.83

7.62

10.04

12.63

16.82

15.44

10.23

10.44

1.77

0.13

0.25

2.27

0.57

0.47

0.97

0.16

0.51

0.54

0.3

0.66

0.21

0.55

1.52

2.52

1.66

0.79

0.98

0.6

1.43

3.69

0.27

2.63

0.68

0.28

0.52

2.41

0.65

0.55

0.42

0.53

0.52

0.4

0.62

0.61

0.23

0.42

0.6

0.29

0.33

0.41

0.07

0.04

0.04

0.04

0.05

0.03

0.05

0.04

0.02

0.04

0.01

0.03

0.04

0.04

0.16

0.18

0.24

0.26

0.24

0.22

0.23

0.18

0.19

0.3

0.33

0.34

0.27

0.28

99.89

99.78

99.89

99.87

99.89

99.88

99.87

99.81

99.9

99.84

99.89

99.87

99.91

99.87

2.0

1.2

1.1

3.1

2.7

1.7

1.3

0.5

1.7

0.9

1.1

2.2

1.6

1.4

0.022

0.088

0.145

0.114

0.195

0.141

0.131

0.033

0.118

0.122

0.228

0.329

0.246

0.08

VNG-57 VNG-26 CB-19 VNG-12 VGN-14 VNG-51 VNG-55 (CX67)

277

10

182

16

94

159

50

15

136

17

60.9

62.3

61.3

80.3

63.3

68.4

54.7

55.9

68.3

74.9

0.8

0.8

0.8

1.0

0.9

0.6

1.1

1.3

0.2

0.4

1.2

1.2

1.2

1.2

1.4

1.4

0.9

1.4

0.8

0.3

1.5

2.4

44.7

1.5

5.0

90.3

15.6

15.8

33.4

2.4

36

13

33

91.8

92.6

47.9

0.6

0.4

0.7

0.9

0.4

M AN U

55 43.1

SC

VNG-15 VNG-16 VNG-18 VNG-35 VNG-42

RI PT

VNG-36

22.3

7.7

1.1

26.6

6.8

0.8

16.6

38

31

34

36

26

33

39

20

48

30

21

24

37

495.9

85.7

88.6

23.6

134.0

112.8

524.9

40.4

315.6

28.6

78.3

18.7

128.2

0.1

<0.1

<0.1

0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

0.1

<0.1

<0.1

<0.1

<0.2

0.3

0.2

0.4

0.3

0.4

0.4

0.3

<0.2

0.3

<0.2

<0.2

<0.2

0.2

269

220

180

211

209

156

201

228

112

237

181

112

130

205

14.2

13.5

6.3

8.7

9.4

7.9

10.9

14.1

6.2

13.3

11.3

5.5

6.9

11.3

35.8

39.1

24.9

35.2

32.0

23.5

38.1

40.5

12.6

28.6

36.2

18.7

16.9

25.0

30.2

275.4

81.2

30.0

97.6

53.6

23.6

138.7

39.6

19.7

51.7

67.4

9.0

197.5

47.2

109

98.7

214.3

275.5

295.2

101.2

56.3

62.1

79.8

232.8

855.6

256.2

77.9

2.0

2.8

2.6

2.6

3.1

2.7

2.5

3.5

1.8

4.0

2.5

2.3

3.3

2.7

4.9

6.7

4.1

5.5

6.2

5.0

5.3

7.2

3.6

7.1

6.2

4.2

6.2

5.3

0.8

0.9

0.6

0.79

0.88

0.7

0.77

0.93

0.41

1.07

0.98

0.54

0.8

0.67

2.9

3.3

4.0

0.83

1.13

1.15

0.54

0.35

0.27

0.45

0.47

2.02

1.87

1.07

1.48

1.6

0.39

0.36

0.18

0.25

0.25

2.47

2.41

1.27

1.78

1.91

0.61

0.61

0.25

0.35

1.74

1.64

0.81

1.03

0.25

0.27

0.12

0.17

0.19

1.64

1.66

0.84

1.08

0.97

0.26

0.26

0.12

0.19

0.17

TE

4.6 1.38

3.3

3.6

4.6

2.0

3.9

5.2

2.8

3.7

2.8

0.96

1.19

1.54

0.6

1.32

1.81

0.72

0.98

0.9

0.4

0.32

0.58

0.43

0.43

0.5

0.5

0.58

0.4

1.38

1.78

2.16

0.93

1.48

2.17

0.98

1.11

1.46

0.22

0.3

0.38

0.16

0.3

0.36

0.18

0.2

0.26

1.62

1.94

2.71

1.17

2.19

2.1

1.12

1.53

1.93

0.41

0.34

0.38

0.62

0.26

0.57

0.39

0.27

0.29

0.39

1.34

0.93

1.18

1.93

0.84

1.29

1.14

0.88

0.97

1.39

0.14

0.2

0.27

0.13

0.22

0.16

0.11

0.14

0.2

0.92

1.03

1.84

0.88

1.67

1.05

0.8

1.02

1.33

0.14

0.18

0.27

0.16

0.27

0.16

0.13

0.16

0.25

AC C

EP

3.7 1.46

D

44 79.9

ACCEPTED MANUSCRIPT Mineral Paragenesis/Tectonic event

Rock

Temporal Relation

Metamorphic Facies Upper Amphibolite

Amphibolites

Hbl + Pl + Grt (Di)

MO

syntectonic

Amphibolites

Chl + Ser + Ep

MO

tardi-tectonic

Greenschist Amphibolite

Microstructural/textural features Intrafolial folds and crenulation cleavage Retrograde metamorphism on fractures

S1, S2 S3

Amphibole schists Amphibole schists Amphibole schists

Bt + Tr

MO

syntectonic

Hbl + Chl + Clc

MO

syntectonic

Hbl + Tr

MO

syntectonic

Amphibolite

Mineralogical orientation

S1,S2

Mafic-Hornfels

Di + Hbl

MC

post-tectonic

Px-Hornfels

Decussate texture

-

Mafic-Hornfels

Hbl + Pl

MC

post-tectonic

Hb-Hornfels

Decussate texture

-

Metaultramafites

Tr

MO

syntectonic

Amphibolite

Intrafolial folds and crenulation cleavage

S1, S2

S1,S2

Upper Greenschist Mineralogical orientation

S1,S2

AC C

EP

TE

D

M AN U

SC

RI PT

Mineralogical orientation

ED

M AN

CE ED

PT

SC

M AN U

R

AC C

EP TE D

SC

M AN U

RI PT

D

M AN

D

M AN

ED

M AN

D

M A

D

M A

AC C

EP TE D

SC

M AN U

RI PT

AC C EP TE D

SC

M AN U

RI PT

TE D

S

M AN U

PT ED

SC

M AN U

CE ED

PT

SC

M AN U

RI

TE D

M AN U

ED

M AN U

PT ED

SC

M AN U

AC C

EP

TE D

SC

M AN U

R

ACCEPTED MANUSCRIPT Highlights -La-ICP-MS U-Pb zircon geochronology data on meta-andesite established a Rhyacian age (2,154 ±6 Ma) for the magmatism. -The volcanic rocks were affected by two metamorphic events: 1) regional metamorphism under conditions of greenschist-amphibolite facies and 2) contact

RI PT

metamorphism under hb-px hornfels facies. -The protoliths are metabasalts and meta-andesites of tholeiitic nature with geochemical affinities compatible with an island arc-back-arc system.

- A variable mixing of distinct sources (E-MORB, N-MORB and plume) is required to

AC C

EP

TE D

M AN U

SC

explain the range of composition of the studied metavolcanic rocks.