New U–Pb SHRIMP-II zircon intrusion ages of the Cana Brava and Barro Alto layered complexes, central Brazil: Constraints on the genesis and evolution of the Tonian Goias Stratiform Complex

The Cana Brava, Niquelândia and Barro Alto complexes (Goiás, central Brazil) are three of the largest mafic-ultramafic layered complexes in the world and their origin has been a matter of debate for several decades. One hypothesis suggests that Niquelândia and Barro Alto were both formed by two distinct igneous events at 1.3 Ga and at 790 Ma and were later overlapped during tectonic exhumation at 650 Ma; according to this reconstruction Cana Brava belongs to the youngest intrusion at 790 Ma. A second hypothesis suggests that the three complexes formed during the same event. Here we provide new U-Pb SHRIMP-II zircon ages for the Cana Brava and Barro Alto complexes, constraining their intrusion age to the Neoproterozoic (between 770-800 Ma), coeval with Niquelândia. A review of new and literature ages indicate that these complexes formed during a single igneous event and were not modified by regional metamorphism. We propose that the complexes represent fragments of the part of a back-arc environment connected to the formation of the Goiás Magmatic Arc at about 790 Ma, later disrupted and accreted to the São Francisco craton. Here, we present new U-Pb SHRIMP-II data on zircons from the Barro Alto and Cana Brava complexes to finally constrain their age and model of formation (one- versus two-intrusions). We studied four samples (three gabbros and one diorite) from Cana Brava, being the least studied among the three complexes and with poor intrusion ages, and two samples (one gabbro from the lower units and one anorthosite from the upper units) from Barro Alto. We carefully reviewed the geochronology and stratigraphy of both complexes and compared them with those of Niquelândia. We comprehensively discuss the one-intrusion model that best fits our data and the possible former existence of the Tonian Goiás Stratiform Complex whose disruption might have originated the three mafic-ultramafic complexes. These in the E-W trending the the two-intrusion model: at 1.29 Ga for BAL-09 zircons (US), at 1.27 Ga for BAL-04 zircons (US) and at c.a. 800 GA for BAL-05 zircons (LS). The recalculated εHf(t) are indicative of mantle values for the US zircons and of crustal values for the LS (εHf(t) = 5.13 to 7.22 for BAL-09, 7.00 to 9.88 for BAL-04 and -7.84 to -12.76 for BAL-05). These results are consistent with Rb-Sr and Sm-Nd isotope systematics and indicate crustal contamination of the MZ of the LS in Niquelândia and Cana Brava, and none or poor contamination of the US (Rivalenti et al., 2008; Correia et al., 2012; Giovanardi et al., 2016). It is worth noticing that, the Neoproterozoic zircon grains from sample BAL-04 (Della Giustina et al., 2011) result in positive eHf(t) when recalculated to the age inferred by their model, however, they become mainly negative εHf(t) from 0.06 to -4.68, when recalculated to their measured U-Pb age The single Mesoproterozoic zircon grain the same shows a positive εHf(t) at 6.04 consistent with values the BAL-09 US leucogabbro


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4 Over the years, several names and stratigraphic subdivisions have been attributed to the three Goiás complexes (Girardi and Kurat, 1982;Girardi et al., 1986;Ferreira Filho et al., 1994;Correia and Girardi, 1998;Ferreira Filho et al., 2010;Giovanardi et al., 2015). A review of their literature names and subdivisions is reported in Table 1. Each stratigraphy begins with a basal gabbroic unit followed by one (or more) ultramafic unit and one (or more) mafic gabbroic unit. Above the latter, in Niquelândia and Barro Alto a gabbroic-anorthositic unit and a roof unit outcrop, which are alternatively considered as part of the complexes (one-intrusion model) or different intrusives (twointrusions model).
A first attempt to simplify the stratigraphy of the three complexes was recently made based on the two-intrusions model (Ferreira Filho et al., 2010), which suggests that the complexes are formed by Meso-and Neoproterozoic intrusive events which have crystallized the upper and the lower parts of the complexes. This attempt has unified the names of the lower units of the complexes and differentiated the upper units as different intrusive. Conversely, according to the one-intrusion model (which suggests that complexes were formed during a single Neoproterozoic event), the Niquelândia complex is divided in a Lower Sequence (LS hereafter) and an Upper Sequence (US hereafter) with several sub units (Correia et al., 2007(Correia et al., , 2012Rivalenti et al., 2008). In this work, we revisit the classification of Ferreira Filho et al. (2010) for the lower units and the model of Correia et al. (2007Correia et al. ( , 2012 and Rivalenti et al. (2008) for the upper units and propose a new unified terminology as discussed throughout the paper.

Field observations from Barro Alto
In contrast to Niquelândia and Cana Brava and according to Ferreira  (Rivalenti et al., 2008;Correia et al., 2012;Giovanardi et al., 2016). Magmatic amphibole has been recognized in the rocks of the central and upper stratigraphic sequence of the E-W trending part of Barro Alto, as well as xenoliths (Fig. 5).

New unified stratigraphy
According to our new stratigraphic evidence of Barro Alto, we assert the close similarity among the three complexes. Therefore, starting from the E, the LS of the Barro Alto, Niquelândia and Cana Thrust Zone, which also favoured a pervasive percolation of fluids in the lower units (Girardi et al., 1986;Correia and Girardi, 1998;Correia et al., 1999;Biondi, 2014). iii) Mafic Zone (MZ), formed by gabbros, gabbro-norites and norites. Amphibole abundance increases discontinuously along the stratigraphic succession, reaching its maximum at the top of this unit (named by Girardi et al., 1986, as  Palmeirópolis, Indaianopólis and Juscelândia) is magmatic in all the complexes and in both LS and US (Girardi and Kurat, 1982;Girardi et al., 1986;Correia and Girardi, 1998;Ferreira Filho et al., 2010 These sequences mainly consist of metasedimentary successions (i.e. metacherts, metapelites and calc-silicate rocks) with interbedded amphibolites, gneisses and intrusive and sub-volcanic granites (Brod and Jost 1991;Araújo et al. 1995;Araújo 1996;Fuck 1994, 1999;Moraes et al. 2003Moraes et al. , 2006Ferreira Filho et al. 2010). The metavolcanic rocks show geochemical affinities with E-MORB and N-MORB. This compositional variability might indicate a transitional setting from a continental rift to an aborted ocean basin (Araújo, 1996;Moraes et al. 2003Moraes et al. , 2006. Geochronological data on the metavolcanic rocks suggest that the magmatic event occurred during the Mesoproterozoic, between 1.26-1.30 Ga (Pimentel et al., 2000;Moraes et al., 2006;Ferreira Filho et al., 2010). The rocks show metamorphic recrystallization from amphibolite-facies near the contacts with the complexes, where local granulite-facies conditions have also been observed as in the Cafelandia amphibolite (Moraes and Fuck, 1994), to greenschist-facies to the W (Araújo 1996; Moraes et al. 2003Moraes et al. , 2006Ferreira Filho et al. 2010 and references therein).

Previous age data and intrusion models
Although the Barro Alto, Niquelândia and Cana Brava complexes have been the focus of several geochronological studies, a unique interpretation of the intrusion age is still a matter of debate. A review of intrusion age data currently available in the literature is reported in Table 2.
Recent studies have demonstrated that the MZ unit of Niquelândia and Cana Brava during their growth have incorporated rocks from the metavolcanic-metasedimentary sequence (Rivalenti et al., 2008;Correia et al., 2012;Giovanardi et al., 2016). This contamination calls into question the reliability of the whole-rock isochron method applied to date these rocks (contamination evidence are provided for the K-Ar, Ar-Ar, Rb-Sr and Sm-Nd isotopic systematics and for K content; Rivalenti et al., 2008;Correia et al., 2012;Giovanardi et al., 2016). In the frame of this evidence, the only reliable intrusion ages of the complexes are those provided by zircon. published comparable U-Pb SHRIMP-II data, but with slightly older concordia ages, of 792 ± 9 Ma and 778 ± 7 Ma. Both authors have interpreted these ages as intrusion ages.
The presence of inherited zircon cores that provide discordant older ages at 1553, 1493 and 1242 Ma has also been reported (Giovanardi et al., 2015). These ages are consistent with those reported for the formation of the Palmeirópolis Sequence or their inherited sources (Moraes et al., 2003), and thus these cores of zircon grains are interpreted as inherited (Giovanardi et al., 2015).

Similar Mesoproterozoic ages have been reported for zircon grains from the Barro Alto and
Niquelândia complexes (Ferreira Filho et al., 1994, 1998Pimentel et al., 2004Pimentel et al., , 2006Correia et al., 1999Correia et al., , 2007Correia et al., , 2012Della Giustina et al., 2011), together with younger Neoproterozoic ages. The occurrence of two different age clusters (i.e., the Mesoproterozoic and the Neoproterozoic ones) has been interpreted up until now with two different models that are explained in details in the two following sections.

Two-intrusions model
Danni and Leonardos (1981) and Danni et al. (1982) were the first to suggest that Niquelândia consisted of two different complexes with distinct ages, structural and metamorphic recrystallization history. According to them, the older complex represented by the LS was a protoophiolitic sequence, while the younger one represented by the US was a metamorphed ocean-floor basalt sequence. Pimentel et al. (2004) (Correia et al., 1999;Moraes et al. 2003Moraes et al. , 2006Pimentel et al., 2006;Ferreira Filho et al., 2010) According to the two-intrusion model, the US of the complexes was metamorphosed during the intrusion of the LS (c.a., 800 Ma) and both were successively recrystallized in granulite-and amphibolite-facies during a regional metamorphic event, which is responsible for the complexes foliation (Ferreira Filho et al., 1994, 2010Pimentel et al., 2004Pimentel et al., , 2006Della Giustina et al., 2011).

One-intrusion model
Based on field and petrological evidences, Rivalenti et al. (1982) and Girardi et al. (1986) suggested that the LS and the US of Niquelândia represent a single intrusion. They attributed the differences between the LS and the US to polybaric fractionation and were the first to recognize the enrichment of hydrous phases in the MZ, in the US and up to the complex roof and the occurrence of xenoliths from the host Indaianópolis metavolcanic-metasedimentary sequence. the Niquelândia US (sample Niq1552) of 780.8 ± 3.7 Ma. This age was interpreted as an intrusion age, although the data distribution suggests that the concordia age could have been affected by younger single-spot ages possibly related to the slow cooling of the complex, and thus they set the intrusion age slightly older at c.a. 790 Ma. In addition, Correia et al. (2012) revised the data of samples CF03 and CF04 and, based on the petrographic evidence provided by Pimentel et al. (2004), concluded that sample CF04 is an embedded xenolith of the metavolcanic-metasedimentary sequence. According to these authors, the Mesoproterozoic ages in Niquelândia US were obtained in inherited zircons (similarly to the interpretation of Mesoproterozoic ages in sample CF03 of Pimentel et al., 2004). They also were the first to report field evidence of late undeformed layers and domains with magmatic texture, which crosscut the over-imposed foliation interpreted as metamorphic in the literature. Correia et al. (2012) concluded that the LS and US of Niquelândia are

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parts of the same body that intruded via multiple-melt pulses under syn-magmatic hyper-to subsolidus shear conditions. According to this model, the high-T recrystallization observed in several parts of the complex has occurred during the slow-cooling process and is not due to later metamorphic events. The metasomatic process that affected the three complexes, giving rise to serpentinites, talc-carbonate rocks, rodingites (in Cana Brava, Dreher et al. 1989), is a much later event associated to local fracturing at low temperature (about 400°; Girardi et al. 1991;Biondi, 2014

Samples and analytical methods
Zircons were separated after crushing, milling, magnetic and heavy liquid separation and hand Gabbro CB1175 was collected at 13°28'0.01"S and 48°16'3.61"O; it shows a foliation parallel to the complex direction (i.e. NNE) due to the alignment of pyroxenes and plagioclase. Biotite is commonly associated to amphibole, which is the most abundant hydrous phase. Minor amounts of K-feldspar and quartz are also recognized. Spinel and zircon occur as accessory phases.
Sample CB1100, a non-foliated almost-anhydrous gabbro from the roof of the complex, was collected at 13°29'10.48"S and 48°18'38.12"O; amphibole is the only hydrous phase and it occurs in minor amount. Orthopyroxene is largely subordinated to clinopyroxene. Spinel is more abundant with respect to other samples. Sample CB1382, a hydrous foliated gabbro from the complex roof, was collected at 13°22'6.06"S and 48°15'32.05"O; Foliation results from alignment of pyroxenes, plagioclase and biotite. Biotite is the most abundant hydrous phase but amphibole also occurs.
Spinel, quartz and K-Feldspar occur in minor amounts. Zircon and apatite occur as accessory phases. Sample CB1030, a diorite pod near the complex roof, was collected at 13°22'9.49"S and 48°15'21.99"O. Orthopyroxene is more abundant than clinopyroxene. Biotite is the major hydrous phase, while amphibole is accessory. K-feldspar and quartz are more abundant than in gabbros.
Apatite, titanite and zircons occur as accessory phases.
Notwithstanding that Barro Alto is more studied than Cana Brava, its intrusion age is still debated.
Therefore, we decided to separate zircons from one gabbro from the MZ (BA06T) and from one Correction for common Pb was based on the measured 204 Pb, and the typical error component for the 206 Pb/ 238 U ratio is less than 2%; U abundance and U-Pb ratios were calibrated against the TEMORA standard and age calculations were performed with Isoplot© 4.1 (Ludwig, 2009). Data are reported in Table 3.

Cana Brava gabbros from the MZ of the Lower Sequence
Zircon grains from sample CB1175 are colourless and have anhedral to sub-euhedral habits. CL images show complex structures composed by irregular chaotic oscillatory zoning and domains often superimposed by other structures (Fig. 6). When occurring, linear zoning is partially erased. Often the core structures are truncated by one or more growth accretion of new domains or oscillatory zoning. In sample CB1100, the rim structures are brighter and sometimes reabsorb the previous growth structure with superimposed accretion (Fig. 8).
In all samples, zircon grains composed only by oscillatory zoning are recognizable (Figs. 7,8 and 9).
Twenty-one U-Pb SHRIMP-II analyses were obtained from 15 zircon grains of sample CB1175, 28 analyses from 17 zircon grains of sample CB1030, 7 analyses from 7 zircon grains of sample CB1100 and 5 analyses from 4 zircon grains of sample CB1382. In CL, zircon grains show two different zoning: a darker internal linear zoning and, in the zircon rims, a brighter zoning commonly organized in domains (Fig. 10). The brighter external domain zoning commonly envelops the internal zoning but follows the same growth direction.

Barro Alto anorthosite from the UGAZ of the Upper Sequence
Zircon grains from BA01T are colourless with rounded anhedral to subeuhedral habits. Small rounded inclusions have been identified in two crystals. CL images show different and complex structures (Fig. 11). Usually, zoning is partially to completely erased, and appears as a dark/grey homogeneous area. In the few zoned grains, the crystals have small cores with different internal structure and overgrowth zoning (Fig. 11). Extremely bright domains overgrow discordantly all the other structures (Fig. 11).
Nineteen analyses were performed on 16 zircon grains.  (Correia et al., 2007(Correia et al., , 2012Rivalenti et al., 2008). The fact that anorthosite ages are slightly older than gabbro ages is also in agreement with the idea that the anorthosite crystallized from a plagioclase-rich crystal mush separated during the initial segregation of the ultramafic cumulates (i.e., the UZ) (Rivalenti et al., 2008;Correia et al., 2012). We interpret few older ages in the MZ gabbro and in the UGAZ anorthosite as inherited zircon grains from the metavolcanic-metasedimentary sequence. The discordant nature of these ages is possibly ascribed to a rejuvenation effect of partial re-opening of the zircon system and/or Pb loss during residence in the magmatic chamber. This rejuvenation mechanism could have also affected four crystals in the anorthosite with discordant ages between 644-600 Ma. These ages are currently the youngest ever reported in the literature for the three complexes (e.g. Pimentel et al., 2004Pimentel et al., , 2006Correia et al., 2007Correia et al., , 2012Ferreira Filho et al., 2010;Della Giustina et al., 2011;Giovanardi et al., 2015).
However, their discordant nature and the absence of similar zircon data suggest that they could be the result of Pb loss during local tectonism (visible in the many faults and shear zones in the area),

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19 possibly related to the bending/exhumation of the complex. A similar age at 650 Ma was obtained from U-Pb dating of rutile from Niquelândia and interpreted as consistent with the tectonic event responsible for the exhumation of the complex (Ferreira Filho et al., 1994, 1998. Our new data from Barro Alto suggest that the mafic-ultramafic LS and the US units are coeval and genetically related to the same intrusion event between 800-770 Ma, similarly to what observed in Niquelândia (Correia et al., 2007(Correia et al., , 2012Rivalenti et al., 2008). Our data also support the interpretation of a common exhumation scenario of the complexes between 600 and 650 Ma.

Inconsistencies in Barro Alto US ages
Although our data of Barro Alto definitely confirm a Neoproterozoic intrusion age for the US and LS units, literature ages of the US around 1.30-1.27 Ga and of supposed 'metamorphic ages' around 800 Ma reveal a more complicated history (Table 2; Fig. 13), whereas the LS data are more consistent with the 800-770 Ma interval for the intrusion (Fig. 13).  Cana Brava, and none or poor contamination of the US (Rivalenti et al., 2008;Correia et al., 2012;Giovanardi et al., 2016). It is worth noticing that, the Neoproterozoic zircon grains from sample BAL-04 (Della Giustina et al., 2011) result in positive eHf(t) when recalculated to the age inferred by their model, however, they become mainly negative εHf(t) from 0.06 to -4.68, when recalculated to their measured U-Pb age (Fig. 14). The single Mesoproterozoic zircon grain from the same sample shows a positive εHf(t) at 6.04 consistent with values from the BAL-09 US leucogabbro (Fig. 14). Assuming the zircon ages as crystallization ages, Mesoproterozoic and Neoproterozoic zircon grains define two different εHf(t) groups, the first one with mantle values and the second one with more crustal values (Fig. 14). Similar εHf(t) positive mantle values have been found in zircon grains from the Cafelandia amphibolite (Della Giustina et al., 2011), commonly interpreted as part of the metavolcanic-metasedimentary sequence (Moraes and Fuck, 1994;Moraes et al., 2003Moraes et al., , 2006. This evidence suggests that, similarly to what observed in the LS and other complexes, the Mesoproterozoic zircon grains within the Barro Alto US are inherited from the metavolcanicmetasedimentary sequence. This scenario is also supported by the anomalous morphology and CL structure of the BAL-09 zircon grains compared to other zircon grains showed in this work and in literature for gabbroic rocks of the three complexes. In particular, they are described as fragments with 'stubby habit with rounded terminations, which render oval morphologies' and with CL images revealing 'texture indicating metamorphic recrystallization' (Della Giustina et al., 2011). These features are described in zircon grains from gabbroic rocks only in Mesoproterozoic cores from inherited zircons, which are commonly overgrowth by magmatic oscillatory CL zoning zircons with euhedral to sub-euhedral habits (see Figs. 9 and 10 and CL images in Pimentel et al., 2004;Correia et al., 2007Correia et al., , 2012Giovanardi et al., 2015).
The εHf(t) from 0.06 to -4.68 of sample BAL-04 are consistent with Rb-Sr and Sm-Nd bulk rock data and suggest that anorthosites fractionated early during the complexes intrusion from poorly/uncontaminated melts during the segregation of the UZ (Rivalenti et al., 2008;Correia et al., 2012).
Because zircon grains crystallize as a late phase during mafic intrusions, they can record, more The U-Pb zircon age distribution in both Cana Brava and Barro Alto complexes and the absence of ages younger than the intrusive event further support the hypothesis that the complexes deformation occurred during their growth in hyper-to sub-solidus shear conditions and that regional

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22 metamorphism does not overprint the Goiás complexes. Similar geochemical and structural evidences have been also discussed for Niquelândia (Correia et al., 2012).

The fact that US anorthosites commonly show slightly older ages than MZ gabbros in both Barro
Alto and Niquelândia complexes (Correia et al., 2012; this study) also suggests that these lithologies were formed from an anorthositic crystal mush probably separated during the segregation of the UZ at the beginning of the complexes crystallization. The least contaminated εHf(t) values for the Neoproterozoic zircon grains of the Barro Alto anorthosite with respect to the zircon grains of the gabbros are consistent with this scenario.
Based on structural evidences such as the occurrence of late undeformed magmatic layers crosscutting the super-imposed foliation and layers repetition in the stratigraphy, it has been proposed that the large mafic-ultramafic Goiás complexes has grown via multiple melt pulses (Correia et al., 2012;Giovanardi et al., 2016). This hypothesis seems confirmed by the U-Pb ages of Cana Brava, which show a direct correlation between the age and the stratigraphic position of the sample.

The Tonian Goiás Stratiform Complex and its geodynamic significance
Because of their petrographic, chemical and isotopic similarities, the three Goiás complexes, together with the associated metavolcanic metasedimentary sequences, were long considered related to each other (Danni et al., 1982;Ferreira Filho, 1998;Ferreira Filho et al., 1994, 2010Correia et al., 2007Correia et al., , 2012Della Giustina et al., 2011;Giovanardi et al., 2016). Ferreira Filho (1998) was the first to suggest that the three complexes are fragments of a larger body, based on the almost identical stratigraphy of the three complexes (see chapter 'geological setting'), the geochemical and petrological similarities of their lithologies and the identical 'metamorphic overprint'. However, this hypothesis was discarded after the re-introduction of the two-intrusions model (Pimentel et al., 2004). M A N U S C R I P T

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The idea of a single body was later reproposed based on geophysical and gravimetric data (Carminatti et al., 2006).  Pimentel et al., 2004Pimentel et al., , 2006Correia et al., 2007). Thus, it was concluded that the three complexes were not only formed by two distinct events, but were also According to structural evidence in the Niquelândia and Cana Brava complexes, the TGSC has grown by multiple melt pulses that during the crystallization formed a crystal mush deformed by the stress field conditions derived from an active tectonic setting (Correia et al., 2012;Giovanardi et al., 2016;this study). Given the stratigraphy of the Cana Brava MZ and the slightly older ages of the US compared to the LS, the age distribution supports the multiple pulses model and suggests that the time-span of the pulses was relatively slow compared to the crystallization and deformation processes. This timespan has allowed not only the crystallization of zircons, but also the closure of the U-Pb zircon system. Another evidence for this model is the full tectonic accommodation of the complex within continental crust, which differs from other layered complexes because it formed in active tectonic setting (e.g., the Val Sesia-Val Sessera mafic complex, Italy; Quick et al., 1992Quick et al., , 1994Sinigoi et al., 2010 and references therein) and, therefore, shows an extremely linear structure parallel to the deformation. The segregation model of the US of Niquelândia (Rivalenti et al., 2008), the increase in crustal contamination along the MZ of Niquelândia and Cana Brava and the increase of crustal delamination, as revealed by the highest abundance of xenoliths at the top of the MZ (Rivalenti et al., 2008;Correia et al., 2012;Giovanardi et al., 2016), all suggest that the heating of Several geodynamic scenarios for the intrusion of the three Goiás complexes have been proposed: oceanic ridge (Danni and Leonardos, 1981;Danni et al., 1982), continental rifting (Ferreira Filho et al., 1998;Pimentel et al., 2004Pimentel et al., , 2006Ferreira Filho et al., 2010;Della Giustina et al., 2011) or back-arc extension in continental crust near a subduction setting (Della Giustina et al., 2011).Among these hypotheses, the oceanic ridge scenario was discarded because it was quickly recognized that the Goiás complexes are not ophiolites (Rivalenti et al., 1982;Girardi et al., 1986) and that the metavolcanic metasedimentary sequence is representative of old continental crust (Araujo, 1996;Moraes et al., 2003Moraes et al., , 2006. The evidence of syn-magmatic deformation during the TGSC growth, the large volume of magma accomodated during the intrusion and the evidence of crustal delamination suggest an active tectonic setting for the TGSC intrusion. However, as discussed by Kröner and Cordani (2003) and  (Fig 1). Thus, we conclude that a back-arc extensional setting in continental crust, probably related to the subduction that originated the Goiás Magmatic Arc, is currently the best geodynamic scenario for the intrusion of the TGSC.

Concluding remarks
New U-Pb zircon data on rocks from the Cana Brava and Barro Alto complexes provide evidence for a coeval intrusion of the two igneous bodies during the Neoproterozoic, between 770-800 Ma and for a coeval history with Niquelândia.
The Niquelândia support the idea that these rocks formed by a plagioclase-rich crystal mush that was separated during the segregation of the ultramafic unit at the early stages of intrusion.
The age distribution of the Tonian Goiás Stratiform Complex supports a growth model via multiple pulses, forming a crystal mush under shear condition. The absence of significant age spikes younger than the complex intrusion, together with structural and field work evidence suggest that the high-T recrystallization that partially affected the Tonian Goiás Stratiform Complex occurred during the long cooling process and is not the consequence of metamorphic events. Few U-Pb zircon discordant ages between 600-640 Ma are comparable with a U-Pb rutile age at 650 Ma and are thus interpreted as exhumation ages of the Tonian Goiás Stratiform Complex. Mineralizing Processes, Reviews in Economic Geology 7, 1-35.     and probability density plot of 206 Pb/ 238 U ages.    of the below growth model sketch.

Table captions
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