The Novo Progresso Formation, Tapajós Gold Province, Amazonian Craton: zircon U-Pb and Lu-Hf constraints on the maximum depositional age, reconnaissance provenance study, and tectonic implications

*Corresponding author Evandro Klein E-mail address: evandro.klein@cprm.gov.br


Introduction
The sedimentary Novo Progresso Formation crops out in the southeastern portion of the Tapajós Gold Province, which evolved between about 2.05 and 1.76 Ga, central Amazonian Craton (Figs. 1 and 2).Santos (2003) and Ferreira et al. (2004) attributed an Orosirian age for this formation and related it to the development of a cratonic association (1.87 to 1.80 Ga) of the Iriri-Xingu Domain (east of the Tapajós Gold Province, Fig. 2), which includes the A-type granitoids of the Maloquinha Intrusive Suite and the still poorly understood Iriri Group (volcanic and pyroclastic rocks), both with ages ranging from 1.89 to 1.88 Ga.On the other hand, Vasquez et al. (2008), based on the spatial association of the Novo Progresso Formation with the volcanic and pyroclastic rocks of the Vila Riozinho Formation (Fig. 2), suggested a temporal relationship with this orogenic formation, which formed from 2001 to 1995 Ma (Lamarão et al. 2002) in the Tapajós Gold Province.Therefore, in addition to the controversial timing of sedimentation, the provenance of the sediments, and the tectonic setting of deposition remain unconstrained.In order to address these issues, we make use of field and petrographic data, whole-rock Nd isotopes, along with the first U-Pb and Lu-Hf analysis of detrital zircon applied to the Novo Progresso sedimentary formation.As a result, we discuss the maximum depositional age, and present a reconnaissance investigation on the potential sources (provenance) for the zircon crystals contained in a lithic arenite of this formation.

Geology of the Tapajós Gold Province
The study area is located in the central portion of the Amazonian Craton, at the boundary zone between the Tapajós Domain (or Tapajós Gold Province -TGP, as used here) and the Iriri-Xingu Domain (Figs. 1 and 2).The TGP comprises a volcano-plutonic belt with subordinate metamorphic and sedimentary rocks (see the most recent compilation of the geology in the map of Vasquez et al. 2017b).The geological evolution of this domain spans from ca. 2050 Ma to ~1760 Ma.The metasedimentary Castelo dos Sonhos Formation was included in the TGP area by Klein et al. (2017).This formation is composed of auriferous   Klein et al. 2017).The Cuiú-Cuiú Complex (2033 to 2005 Ma) is composed of amphibolite-facies orthogneisses and unmetamorphosed and undeformed coeval granitoids, which are partially associated with the greenschist facies metavolcano-sedimentary sequence of the Jacareacanga Group (~2010 Ma) (Santos et al. 2004;Vasquez et al. 2008).This association formed in a subduction-related setting (Tassinari and Macambira 2004;Santos et al. 2004;Vasquez et al. 2002Vasquez et al. , 2008)).Undeformed and unmetamorphosed calcalkaline felsic to intermediate volcanic and pyroclastic rocks occur in spatial and temporal association with the plutonic rocks and include the Comandante Arara (2020 to 2012 Ma) and Vila Riozinho (2002( -1998 Ma) Ma) formations (Lamarão et al. 2005;Vasquez et al. 2017a).Batholiths of high-K, calcalkaline granites of the Creporizão Suite intruded the Cuiú-Cuiú Complex between 1997 ± 5 and 1968 ± 7 Ma, and show geochemical characteristics of magmatic arc to post-collision rocks (Vasquez et al. 2002;Santos et al. 2004).The intrusion of the poorly-understood calc-alkaline tonalite to granite of the Tropas Suite occurred between 1907 and 1892 Ma (Santos et al. 2001(Santos et al. , 2004)), slightly preceding the intrusion of voluminous batholiths and stocks of the Parauari Intrusive Suite of 1883-1879 Ma (Vasquez et al. 2008 and references therein).This suite comprises granodiorite and subordinate tonalite and other minor granitoid varieties that show high-K calc-alkaline signature (Vasquez et al. 2002(Vasquez et al. , 2008)).Both continental arc (Santos et al. 2004;Juliani et al. 2015) and post-orogenic extensional (Vasquez et al. 2002(Vasquez et al. , 2008) ) settings have been invoked for the origin of this suite, which could be also related to the onset of the intracontinental rift system known as Uatumã Silicic Large Igneous Province (Uatumã SLIP - Klein et al. 2012).This rift was also filled by the alkaline granites of the Maloquinha Intrusive Suite and coeval alkaline volcanic and pyroclastic rocks of the Iriri Group (1895-1864 Ma; Lamarão et al. 2002;Santos et al. 2004;Vasquez et al. 2008), and by sedimentary rocks of the Novo Progresso Formation, as we will demonstrate below.This was followed by the establishment of Statherian sedimentary basins, such as the siliciclastic Crepori basin of up to 1780 Ma-old and the associated alkaline intracratonic magmatism (Fig. 2).The Iriri-Xingu Domain (Figs. 1 and 2) is broadly contained in the Uatumã-SLIP, in addition to calc-alkaline granitoids, felsic to intermediate volcanic rocks, and undifferentiated A-and I-type granitoids, with ages and petrographic characteristics similar to those found in the Creporizão, Parauari, Maloquinha and Vila Riozinho units of the TGP (Vasquez et al. 2008;Semblano et al. 2016).These magmatic rocks are covered by continental sedimentary rocks (Vasquez et al. 2008).

Summary of the geology and petrography of the Novo Progresso Formation
The Novo Progresso Formation crops out mostly as narrow NNW-SSE-trending low hills, which are parallel to the main regional structures, and five cropping areas have been recognized in southeastern TGP (Fig. 2).The formation is surrounded by granites of the Maloquinha, Parauari and Creporizão intrusive suites, felsic metavolcanic and pyroclastic rocks of the Vila Riozinho Formation and Iriri Group, and by metasedimentary rocks of the Castelo dos Sonhos Formation (Fig. 2).Contacts with these units are probably faulted and erosive.The rocks show sedimentary structures (stratification and lamination) that strike predominantly to N15-55°W/3-45°NE, which is grossly parallel to the regional structures, and locally to N50-70°E/75-84°NE (fault-related?).Crossstratification occurs locally at N25°E/24°SE.This regional structural set differs from that of the Crepori sedimentary basin, which is grossly oriented to the E-W direction (Fig. 2), and associated to a younger Statherian (<1780 Ma) extensional event (e.g., Klein et al., 2017;Vasquez et al., 2017a).Therefore, a minimum depositional age of 1780 Ma is inferred for the Novo Progresso Formation.
In previous works, the Novo Progresso Formation has been described as composed of lower polymictic conglomerate with rounded to angular pebbles of granite, volcanic and volcanoclastic rocks, set in an arkosic matrix, and upper lithic sandstones and massive to layered, fine-to medium-grained arkose with intercalation of laminated argillite and siltstone (Ferreira et al. 2004;Vasquez et al. 2008).During field work we have found one conglomerate outcrop, that grossly fits with to the described above, only outside the outcropping areas of the Novo Progresso Formation.Furthermore, our petrographic work has not identified arkosic rocks among the sandstones (see below).

Analytical procedures
Location of the samples analyzed in this study is listed in Table 1.In situ zircon U-Pb and Lu-Hf LA-ICP-MS analyses were undertaken at the Laboratório de Estudos Geocronológicos, Geodinâmicos e Ambientais of the Universidade de Brasília (UnB), Brasília, Brazil.The analyses followed procedures described in detail in Bühn et al. (2009) and Matteini et al. (2010) for the U-Pb and Lu-Hf techniques, respectively.Concentrates of zircon were obtained by crushing the rock and then sieving and panning.Zircon crystals with sizes between 0.177 mm (80#) and 0.074 mm (200#) were hand-picked under a binocular microscope, mounted in epoxy resin, and polished with diamond paste.The analyses were performed with a Thermo Finnigan Neptune multicollector inductively coupled plasma mass spectrometer with an attached New Wave 213μm Nd-YAG solid state laser.For the U-Pb analysis, the acquisition followed a standard -sample bracketing technique with four sample analyses between a blank and a GJ-1 zircon standard.The accuracy was controlled using the zircon standard 91500.Ablation time and spot diameters were, respectively, 40 s and 30 mm for the U-Pb analyses, and 50 s and 40 mm for the Lu-Hf analyses.Raw data were reduced using an in-house program and corrections were done for background, instrumental massbias drift and common Pb, as described in Bühn et al. (2009).The ages were calculated using ISOPLOT 3.0 (Ludwig 2003) with 1s uncertainties, and data presentation follows Gehrels (2012).Analyses were preceded by backscattered electron (BSE) imagery also done at UnB using a Scanning Electron Microscope FEI Quanta 450.
The Lu-Hf isotopic data were collected during ablation time of 50 s and using a spot size diameter of 40 mm.The signals of the interference-free 171 Yb, 173 Yb and 175 Lu isotopes were monitored in order to correct for isobaric interferences of the 176 Yb and 176 Lu on the 176 Hf signal.The contribution of 176 Yb and 176 Lu were calculated using the isotopic abundance of Lu and Hf proposed by Chu et al. (2002).The contemporaneous measurements of 171 Yb, 173 Yb permit to correct the mass-bias of Yb using the 173 Yb/ 171 Yb normalization factor of 1.132685 (Chu et al. 2002).The Hf isotope ratios are normalized to 179 Hf/ 177 Hf value of 0.7325 (Patchett 1983).To calculate eHf(t) values, we have adopted the 176 Lu decay constant of 1.867x10 -11 /year (Söderlund et al. 2004), the chondritic values of 176 Hf/ 177 Hf = 0.0336 and 176 Lu/ 177 Hf = 0.282785 (Bouvier et al. 2008), and the model depleted mantle with present day 176 Hf/ 177 Hf = 0.28325 and 176 Lu/ 177 Hf = 0.0388 (Griffin et al. 2000; updated by Andersen et al. 2009).
Whole-rock Sm-Nd analyses were also undertaken at the UnB laboratory and the analytical procedures are described in Gioia and Pimentel (2000).Fifty mg of wholerock powders were mixed with a 149 Sm/ 150 Nd spike and dissolved in Savillex vessels.The Sm-Nd separation used cation exchange Teflon columns with Ln-Spec resin, then Sm and Nd were deposited in Re filaments and the isotopic ratios were determined on a Thermo Finnigan Triton thermal ionization mass spectrometer.The Nd data were normalized to a 146 Nd/ 144 Nd ratio of 0.7219 and uncertainties in the Sm/ Nd and 143 Nd/ 144 Nd ratios were about 0.4% (1s) and 0.005% (1s), respectively, based on repeated analysis of the BHVO-1 and BCR-1 standards.The crustal residence ages were calculated using the values of DePaolo (1988) for the depleted mantle (TDM).

U-Pb results
U-Pb isotopic results were obtained for one lithic arenite (CE7), sampled in the type area of the Novo Progresso Formation (43 crystals).Only the isotopic results of 37 grains with less than 10% discordance, analytical errors below 5%, and low common Pb concentrations (f206 below 3%) are presented in Table 2 and were used for age and provenance interpretation.

Lu-Hf results
Lu-Hf isotopic results were obtained in 23 zircon crystals of the dated sandstone sample (CE7), and the analyses were performed on the same zircon domains that have previously been analyzed by the U-Pb technique.The selected zircons cover the detrital age populations and the analytical data are presented in Table 3.There is no clear correlation between crystallization and depleted mantle model ages (TDM) (Fig. 7).Most of the model ages are in the range of 2.13 to 2.79 Ga, a few zircons show TDM between 2.95 and 3.12 Ga, and one zircon 3.95 Ga.The eHf(t) values are highly variable, from +8.1 to -14.5 (one outlier at -44.9), and there is some difference between individual age populations.The two groups of Orosirian zircons (1.8 and 1.9 Ga) display almost the whole variation in the eHf(t) values.The Rhyacian zircons show only slightly negative values, and the Archean zircons have highly positive to slightly negative values (Fig. 7).The highly positive value (zircon NZ04 in Table 3) indicates a 2.50 Ga-old event of crustal growth, whilst the model-age of 3.95 Ga (zircon Z15 specific potential sources.One lithic arenite (CE7) shows the older (Mesoarchean) Nd model age, which might have been imparted by lithic fragments coming from Archean sources.However, considering that the high 147 Sm/ 144 Nd ratio could have been caused by mafic contributions to the sediments, the model age may have been overestimated.A young (juvenile?)component is present in the microcrystalline (cherty) laminated quartz-rich layers that present a Sm-Nd model age of 1.81 Ga, which is very close to the depositional age (see below).The most likely potential sources with this age are the late-Orosirian sequences of the Rondonia-Juruena Province occurring to the south of the study region (Figs. 2 and 8B), which is in line with the detrital zircon data (significant age peak at 1.84 Ga).Older Paleoproterozoic (Siderian) and Archean sources were likely positioned to the east of Tapajós (e.g., Bacajá, Carajás, Rio Maria domains, basement of the Iriri-Xingu domain, and their counterparts in the Guyana Shield) (Fig. 8B).

Depositional age and tectonic setting
The Novo Progresso Formation was deposited in a NNW-SSE-trending graben, predominantly in alluvial and lake settings.The age of the youngest concordant detrital zircon (1836 ± 7 Ma) and the significant youngest peak (1846 Ma) set the maximum depositional age of the Novo Progresso Formation at about 1840 Ma (Fig. 8A), indicating that this unit is not associated with the ca.2000 Ma-old orogenic volcanic rocks of the Vila Riozinho Formation.Therefore, deposition occurred at the end of most of the anorogenic magmatic activity in the TGP, slightly after the onset of the intracontinental rift system (Uatumã SLIP), and before the development of the structurally discordant, grossly E-W-trending, Statherian continental basin (Crepori Basin, ~1780 Ma).Considering this timing relationship, the predominantly proximal sediment sources, and the lithological constitution of the formation, we interpret Novo Progresso as a basin associated with the evolution of the Uatumã SLIP (Fig. 9).

Figure 1 -
Figure 1 -Simplified geological map of the Amazonian Craton (modified from Fraga et al. 2017), with indications of the tectonic domains discussed in the text, and location of the study area.
metaconglomerates and metasandstones deposited by fan and fluvial systems between 2011 and 2050 Ma (Queiroz et al. 2015;

Figure 2 -
Figure 2 -Location (inset) and simplified map of tectonic associations of the Tapajós and Iriri-Xingu domains of the Amazonian Craton (modified from Vasquez et al. 2017).

Figure 3 .
Figure 3. (A) Schematic W-E cross-section of the Novo Progresso Formation, and (B) interpreted sedimentary section, with the approximate location of samples used for isotopic analyses (black stars; sample numbers as in Table4).

Figure 4 -
Figure 4 -Outcrop images of rock units of the Novo Progresso Formation.(A) Massive sandstone.(B) Sandstone with moderately dipping sedimentary bedding (S 0 ) and internal stratification.(C) Detail of sandstone with plane-parallel and cross stratification.(D) Channeled stratification in sandstone.(E) Laminated siltstones.(F) Package of brown siltstones with intercalation of light grey, fine grained quartz-rich (cherty) layers (detail in the inset).

Figure 5 -
Figure 5 -Photomicrographs of sandstones.(A) Lithic arenite with rounded and subrounded quartz grains, quartz overgrowths (arrows), and lithic (L) fragments.(B) Lithic arenite with mono and polycrystalline quartz grains and broken and sericitized feldspar (F) crystals set in a sericitized matrix.(C) Quartz arenite with little matrix irregular to subrounded quartz grains and rare lithic fragments (L).

Figure 6 -
Figure 6 -(A) Backscattered electrons images of some detrital zircon images from sample CE7 (lithic arenite) of the Novo Progresso Formation.(B).Probability density plot of detrital zircon 207Pb/206Pb ages.The main age peaks are indicated.

Figure 8 -
Figure 8 -(A) Probability density plot of detrital zircon ages for the Novo Progresso Formation displayed on the fields of ages of the magmatic events from tectonic domains of the central-southeastern portion of the Amazonian Craton.The upper thick bar shows the range of ages of detrital zircons from sedimentary basins within the same tectonic domains.Data compiled from Vasquez et al. (2008), Klein et al. (2012), Klein et al. (2014),Corrêa and Macambira (2014),Tavares (2015), and primary references in these works.(B) Simplified map of the Amazonian Craton with internal domains (modified fromFraga et al. 2017).Same legend as in Figure1.The arrows show the potential source areas for the sediments of the Novo Progresso Formation.

Figure 9 -
Figure 9 -Schematic (not to scale) W-E crustal sections of the SE Amazonian Craton depicting the proposed scenario for the geological evolution of the Novo Progresso Formation.Geological units are described in Figure 2 and the source areas (tectonic domains) are those presented in Figures 1 and 8. (A) Formation of Rhyacian orogenic belts.(B) Development of Rhyacian foreland systems over an Archean -Paleoproterozoic block.(C) Orogenic phase in the Tapajós Gold Province.(D) Extensional phase with intrusion of early granitoids followed by rifting and development of the Uatumã Silicic Large Igneous Province and deposition of the Novo Progresso Formation (adapted from Klein et al. 2107).The Castelo dos Sonhos Formation was interpreted (Klein et al. 2017) as part of the foreland system, which remained in margin of the Tapajós domain after the Uatumã rifting.

Table 1 -
Location of the samples analyzed in this study

Table 2 -
U-Pb isotopic results for sample CE7 (lithic arenite) of the Novo Progresso Formation