Search

Abstract The Mamão gold deposit is located in the eastern portion of the Amazonian Craton, Northern Brazil, and hosted in Archean metamafic rocks of the Andorinhas greenstone belt. Troy Resources Ltd. mined the deposit between 2008 and 2015, producing about 350 koz via underground operation. The deposit exhibits structural and mineralogical characteristics that allow its classification as an orogenic gold deposit. Reflectance spectroscopy is a non-destructive, fast, and low-cost technique that was applied in drill cores at the Mamão deposit to map and refine stages of hydrothermal alteration. The hydrothermal alteration is marked by a distal or chlorite zone; an intermediate or carbonate zone; a proximal or potassic zone, and a gold-rich quartz vein-hosted orebody. The reflectance spectroscopy has confirmed the diversified mineralogical compositions (tourmaline, amphibole, mica, epidote, carbonate, and chlorite) observed along the hydrothermal zones, having been confirmed by a petrographic study. The study has also demonstrated that chlorite abundance decreases from the edge to the center of the altered profile, proving a fast and reliable result to the mapping of the hydrothermal halos in Archean greenstone belts, which is an important tool for the vectoring of gold mineralization, acting as an excellent mineral prospecting tool.

Juína is the second-largest diamond-producing municipality in Brazil and is globally known for its outstanding sublithospheric diamond occurrences in both placer and kimberlite-hosted deposits. However, the scarcity of petrological data for Juína kimberlite pipes hampers understanding the nature and mantle source of these primary diamond sources in this region. Here, we present a textural and mineralogical study of ten kimberlite pipes from the Juína area. Based on petrographic features and mineral compositions, we interpret the studied Juína pipes as archetypal kimberlites with pyroclastic emplacement styles filled with resedimented volcaniclastic kimberlite and Kimberley-type pyroclastic kimberlite variants. The composition and texture of the magmatic phases, particularly spinel and phlogopite, suggest crystallisation from kimberlite sensu stricto magmas. The presence of high-Na eclogitic garnets and the absence of high-Cr low-Ca G10 garnets within the mantle xenocryst suite suggest the likelihood of eclogitic diamonds among Juína's lithospheric diamond populations. The Zr and Y contents, Ti/Eu and Zr/Hf ratios in the peridotite garnets, and Zr contents, Ca/Al, LaN/YbN (primitive-mantle normalised), Ti/Eu, and Zr/Hf ratios in the clinopyroxenes suggest a solid connection to kimberlite melt-related mantle metasomatism. Thermobarometry calculations indicate a relatively narrow stability window (825–936 ºC and 32–36 kbar) for lithospheric diamonds in the Juína region. Our findings have important implications for regional diamond exploration programs, shedding light on the primary sources of Juína's diamonds and contributing to understanding the deep geological processes in the underlying lithospheric mantle beneath the Amazonian craton. [ABSTRACT FROM AUTHOR]

On the southern edge of the Amazonian Craton, the Mirassol d'Oeste and Guia formations constitute the cap carbonate of the Araras Group. Petrography, X-ray diffraction, and quantification of terrigenous material allowed the identification of detrital grains (e.g., mica, quartz, and feldspar) in different proportions and diagenetic features. The sequential leaching of carbonates along a section of the upper portion of the Guia Formation yielded 87Sr/86Sr ratios increasing from 0.7070 to 0.7077, which is considered the primary Sr isotopic signature of seawater. The increasing continental influx of dissolved Sr from freshwater accounts for the increase in 87Sr/86Sr along the section. Such abrupt change toward more radiogenic values is also observed in carbonate layers soon after the Marinoan glaciation, elsewhere in the world. The same samples provided Nd-TDM model ages (1.84-2.54 Ga) comparable with those of the continental crust of the Paleoproterozoic provinces of the Amazonian Craton, which forms the basement of the Araras Group. The εNd(635Ma) values between -4.7 and -11.1, probably indicate the presence of Nd from the suspended material transported by continental waters to the ocean where the carbonates precipitated. The random variations of Nd-TDM ages and εNd(635Ma) values suggest important and rapid variations in the continental contribution to the post-Marinoan oceans. [ABSTRACT FROM AUTHOR]

The Araguaia Orogen, located in Central Brazil, represents an Ediacaran-Cambrian collisional orogen associated with the final assembly of West Gondwana. Two contrasting tectonic models have been proposed for the evolution of this orogen, involving different histories for the Amazonian palaeocontinent drift: (i) subduction of a large ocean and final collision of the Amazonian palaeocontinent with Gondwana between ~ 560 and 500 Ma and (ii) intracontinental orogeny after early amalgamation of the Amazonian palaeocontinent at ca. 620 Ma. Detailed tectono-metamorphic studies in this key locality for the evolution of Gondwana are also still scarce. Hence, in this study we present a detailed metamorphic investigation of two metapelite samples (schists) and one garnet amphibolite aiming to unravel the pressure-temperature-time (P-T-t) paths for the higher grade rocks exposed in this orogen. Pressure-temperature estimates based on thermodynamic modelling using isochemical phase diagrams in the MnNCKFMASHTO system for the schists constrained a single and continuous prograde metamorphic path (burial and heating) from ~ 4–6 kbar and ~ 450–500°C to ~ 7–8 kbar and ~ 580–650°C. The near-peak metamorphic conditions of the garnet amphibolite were estimated from classic geothermobarometry at 7.5 ± 0.8 kbar and 552 ± 40°C. Lutetium-hafnium garnet dating constrained an average age for the prograde metamorphism at around 537–533 Ma. These results show that the Araguaia Orogen records one single metamorphic event during the late Ediacaran-early Cambrian, and likely represents part of a collisional system developed between the Amazonian Craton and Parnaíba Block after the closure of the Clymene Ocean. [ABSTRACT FROM AUTHOR]

Abstract On the southern edge of the Amazonian Craton, the Mirassol d’Oeste and Guia formations constitute the cap carbonate of the Araras Group. Petrography, X-ray diffraction, and quantification of terrigenous material allowed the identification of detrital grains (e.g., mica, quartz, and feldspar) in different proportions and diagenetic features. The sequential leaching of carbonates along a section of the upper portion of the Guia Formation yielded 87Sr/86Sr ratios increasing from 0.7070 to 0.7077, which is considered the primary Sr isotopic signature of seawater. The increasing continental influx of dissolved Sr from freshwater accounts for the increase in 87Sr/86Sr along the section. Such abrupt change toward more radiogenic values is also observed in carbonate layers soon after the Marinoan glaciation, elsewhere in the world. The same samples provided Nd-TDM model ages (1.84–2.54 Ga) comparable with those of the continental crust of the Paleoproterozoic provinces of the Amazonian Craton, which forms the basement of the Araras Group. The ԐNd(635Ma) values between -4.7 and -11.1, probably indicate the presence of Nd from the suspended material transported by continental waters to the ocean where the carbonates precipitated. The random variations of Nd-TDM ages and ԐNd values suggest important and rapid variations in the continental contribution to the post-Marinoan oceans.

The Bacajá domain, southeastern Amazonian craton, comprises Mesoarchaean and Siderian terrains reworked during the Transamazonian cycle. Combined analyses of zircon LA-ICP-MS U-Pb and Lu-Hf with whole-rock Sm-Nd from the northeast portion of this domain made it possible to propose an evolutionary sequence between ca. 2.60 and 2.06 Ga. Gneisses with an igneous protolith age of 2630±15 Ma show negative signatures (εHf(t) = -0.3 to -1.7 and εNd(t) = -3.08 to -2.98) and a Mesoarchaean formation (Hf-TDMC and Nd-TDM model ages range from 3.0 to 3.2 Ga). Rhyacian granite genesis lasted about 40 million years (2.10-2.06 Ga) and was divided into two magmatic periods. The first is represented by deformed granitoids with zircons yielding crystallization ages between 2.10 and 2.09 Ga and model ages (Hf-Nd) at about 2.5 Ga. The second event is represented by granitoids with preserved magmatic texture, crystallization ages of 2.06 Ga, and Siderian model ages (Hf-Nd) of around 2.3 Ga. The overall Hf isotopic analyses of this Rhyacian granite genesis exhibit a spread of εHf(t) values between 1.8 and -2.9, which show a probably underestimated mantle-derived contribution in this period. [ABSTRACT FROM AUTHOR]

This paper presents zircon U-Pb, REE and Hf data for Paleoproterozoic felsic volcanic rocks from the Colíder Group with outcrops in the southwestern Amazonian Craton. It is estimated that these rocks cover an area of 85,000 km2 with a volume of 2.7 × 106 km3. The Colíder volcanics are comprised of basalts, andesites and a variety of felsic rocks. The felsic rocks are characterized by rhyolite, andesite and dacite lavas with frequent intercalated pyroclastic and epiclastic deposits. Effusive and pyroclastic rocks are intruded in places by hypabyssal porphyritic rocks. The U-Pb ages obtained for the northeastern domain (1782–1776 Ma) are younger than the ages obtained for the southern domain (1800–1787 Ma). The NE volcanic facies show Hf TDM ages between 2.3 and 2.5 Ga (εHf from +1 to −3) and greater fractionation (Ce/Yb – 0.03–0.06) than the younger facies that has TDM from 2.4 to 2.7 Ga (εHf from −3 to −6) with Ce/Yb values of 0.025–0.030. The Hf isotope compositions, REE contents and U-Pb analyses suggest geographic (north-south) variations in composition, crystallization ages, and TDM age zonation during the generation of the Colíder large igneous province. [ABSTRACT FROM AUTHOR]

The understanding of the crustal transition between orogenic zones and cratonic portions in distal regions of foreland basins has received increasing attention, but the analysis is often hampered by the sedimentary cover. Despite the peculiar location of the Acre Basin, specifically between the Amazonian Craton and the sub‐Andean zone, local basement studies are still scarce due to lacking seismic data and exploratory wells. Therefore, this work aims to map basement depths, estimate crustal compositions and identify the main depocenters, structures and limits of Acre Basin using an integrated analysis to understand better the region lithospheric evolution, its relationship with the Amazonian Craton and its positioning within the Andean orogeny. For that, we used well, 2D seismic reflection, airborne and ground gravity and magnetic data as well as the EMG2008. Tilt Depth estimates indicate basement depths between 500 and 7800 m and larger sedimentary thicknesses in the northern portion. Additionally, we modelled groups of potential sources between 0.1 and 22 km and Moho depths between 26 and 37 km. Compositionally, the upper crust consists dominantly of meta‐sedimentary and low‐grade metamorphic rocks and granites, indicating that the sub‐Andean and Acre Basins share a similar basement. Thus, there are indications that the basement of the Acre Basin is essentially formed by the Sunsás province in the Amazonian Craton. However, local differences in basement depth, magnetic susceptibility and exploratory potential led to the subdivision into Divisor and Xapuri sub‐basins, north and south of the Fitzcarrald Arch, respectively. Finally, it was possible to establish the limits of the Andean orogeny influence in the Acre Basin and delimit the area of the Western Amazon Foredeep installed during the Neogene. [ABSTRACT FROM AUTHOR]

Abstract The Bacajá domain, southeastern Amazonian craton, comprises Mesoarchaean and Siderian terrains reworked during the Transamazonian cycle. Combined analyses of zircon LA-ICP-MS U-Pb and Lu-Hf with whole-rock Sm-Nd from the northeast portion of this domain made it possible to propose an evolutionary sequence between ca. 2.60 and 2.06 Ga. Gneisses with an igneous protolith age of 2630±15 Ma show negative signatures (ɛHft = -0.3 to -1.7 and ɛNdt = -3.08 to -2.98) and a Mesoarchaean formation (Hf-TDMC and Nd-TDM model ages range from 3.0 to 3.2 Ga). Rhyacian granite genesis lasted about 40 million years (2.10–2.06 Ga) and was divided into two magmatic periods. The first is represented by deformed granitoids with zircons yielding crystallization ages between 2.10 and 2.09 Ga and model ages (Hf-Nd) at about 2.5 Ga. The second event is represented by granitoids with preserved magmatic texture, crystallization ages of 2.06 Ga, and Siderian model ages (Hf-Nd) of around 2.3 Ga. The overall Hf isotopic analyses of this Rhyacian granite genesis exhibit a spread of ɛHft values between 1.8 and -2.9, which show a probably underestimated mantle-derived contribution in this period.

The Carajás (3.0-2.5 Ga) and Xingu-Iricoumé (1.99-1.86 Ga) blocks comprise the Central Amazonia Province (CAP) that is in contact with the Maroni-Itacaiúnas Province (MIP) within the Amazonian craton. The CAP is the oldest portion (Nd-TDM) of the craton and corresponds to an Archean nucleus bordered by younger Paleo-Mesoproterozoic mobile belts, including the MIP. Because the location and tectonic boundaries between these provinces are insufficiently known, we carried out a geological survey along the Middle Xingu River, cutting the WNW-ESE regional trend, to further understand cratonic evolution of the MIP and its southeastern boundary in this key area. Geochronologic results (Pb-evaporation and U-Pb SHRIMP in zircon and monazite), supported by petrographic and field observations, allowed identification of the following lithotypes and their ages: migmatitic gneisses (2859--2080 Ma), tonalitic gneisses (2554 ± 3 Ma, 2480 ± 9 Ma), enderbites (2114 ± 3 Ma), charnockites (2094 ± 4 Ma, 2084 ± 2 Ma), granodiorites (2079 ± 3 Ma), leucogranitic vein (2075 ± 2 Ma), and pelitic paragneisses (2062 ± 8 Ma). These ages are related to the reworking of Archean crust during Rhyacian magmatic arc amalgamation (2.22--2.13 Ga) and collision in the Transamazonian cycle (ca. 2.1 Ga). [ABSTRACT FROM AUTHOR]

[Display omitted] • First integrated geochemical and geochronological data for the Buem structural unit. • Passive and active margin units in the Dahomeyide belt akin to Borborema Province. • Three provenances: Amazonian Craton, Benino-Nigerian Shield, ± West African Craton. • West African and Amazonian Cratons coexisted during Rodinia and Gondwana. We present new field, petrological and geochemical data, combined with U-Pb zircon ages and Lu-Hf isotope compositions for the sandstones of the Neoproterozoic Buem structural unit (BSU) of the Dahomeyide belt, and whole-rock geochemical data of BSU shale to investigate their provenance and depositional setting. The BSU contains siliciclastic sequences and fragments of oceanic lithosphere (pillow lavas, gabbro, and peridotite) that have archived the entire evolution of the Ediacaran West Gondwana Orogen (WGO), from early accretion to final amalgamation of the West African Craton (WAC) with the Benino-Nigerian Shield. Three broad groups of samples exist within the BSU in Ghana: those with dominantly older age fractions of 2300 – 1800 Ma, represented by samples from the base of the BSU; those with prominent 1700 – 1100 Ma zircons, occupying the middle part of the BSU; and those with significant 1000 – 970 Ma age fractions, forming the uppermost part of the BSU. Results from this study, together with published data on the BSU, and adjacent Togo structural unit and Voltaian Supergroup, reveal two main sedimentary sequences in the Dahomeyide belt, i.e., passive margin and foreland basin sequences with three potential provenances: Amazonian Craton, Benino-Nigerian Shield, ± WAC. This interpretation resembles that for the sedimentary rocks of the Borborema Province, NE Brazil, which implies similar evolution along the WGO. Thus, a long, >2500 km passive margin basin developed at 1000 – 700 Ma, which was subsequently inverted during the Braziliano/Pan-African plate convergence and collision, and the concomitant formation of the foreland basin during the assembly of the supercontinent Gondwana. Because a greater portion of the detritus in the BSU is probably from the Amazonian Craton, we propose that the WAC and the Amazonian Craton adjoined each other from the Paleoproterozoic onward within the supercontinents Rodinia and Gondwana, until the opening of the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

To the south of the Carajás Province, Amazonian Craton, 2.85–1.88 Ga old rock units underlie the Santana do Araguaia Domain (SAD), bounded by the Iriri-Xingu and Rio Maria domains and the Tocantins Province. The SAD differs from the Rio Maria Domain, as indicated by the scarcity of TTGs and the dominance of both high-K to weakly sodic granites, sodic granodiorites, and monzodiorite/quartz monzodiorite with high-Ba + Sr contents. Therefore, the SAD is a particular case to assess tectonic settings in the Archean, continental crust generation and the timing/nature of the Meso-Neoarchean transition from TTG-type to calc-alkaline high-K and sodic granitoid magmatism to the south of the Rio Maria Domain. The magmatic evolution of the SAD started at 2.85 and extended up to ∼1.88 Ga with a significant contribution from the pre-existing crust, differing from that of the Rio Maria Domain (3.0–2.86 Ga). The Santana do Araguaia Complex (SAC) comprises deformed to non-deformed rocks divided into (i) tonalite (TTG with high Al 2 O 3 and medium La/Yb ratio), (ii) sodic granodiorite group (K 2 O/Na 2 O < 1) with Ba- and Sr-rich varieties, which can be divided into type 1 displaying high Sr/Y and La/Yb ratios, and type 2 with low Sr/Y and low to intermediate La/Yb, both resembling the sanukitoids low-Ti, (iii) hybrid granite group (high-K calc-alkaline), composed of two sub-types of high-Ba + Sr monzogranites, one of high Sr/Y that shares many features with the CA2-type of Archean calc-alkaline granites and HSG, and a second type, with low Sr/Y ratio and akin chemistry with the CA1 and normal granite (NG). Group (iv) is of biotite or low Ba–Sr granites classified as syenogranites CA1/NG strongly fractionated calc-alkaline rocks. Group (v) consists of rocks with high Ba–Sr but with moderate Mg# (mean = 44.8), low contents of transition elements, and moderate K 2 O/Na 2 O ratios (mean = 0.72); the group is divided into monzodiorite with high Sr/Y, La/Yb ratios, and low Y, and quartz monzodiorite with low Sr/Y, moderate La/Yb ratio and Y values, both with sanukitoids high-Ti characteristics. The rocks that constitute the studied complex show arc-like geochemical signatures, suggesting emplacement during the end of phase B (collisional) and the start of phase c (thermal relaxation/colappse) of stage 2 in the two-stage tectonic-magmatic model (subduction/collision-post-collision). In the Carajás Province the first stage of the model is marked by the genesis of TTG (3.0–2.94 Ga) –juvenile magmatism of the Rio Maria Domain, and the second stage, collisional phase, between 2.89 and 2.85 Ga with sanukitoid rocks, hybrid and biotite granites as well as significant occurrences of high Ba + Sr rocks and post-collisional granitic suites (∼2.74 Ga). However, the elemental whole-rock geochemistry and geochronology datasets show that the Santana do Araguaia Complex (SAC) is marked by high-K and Ba + Sr rocks such as abundant sanukitoid suites, hybrid and biotite granites, but with very scarce TTGs. The ages between 2.85 and 2.81 Ga obtained from SAC suggest the final phase "a" and beginning of phase "b" of the second evolutionary stage, collisional phase, and slab-breakoff/post-collisional, probably the terminal tectonic-thermal episode of Archean accretion and differentiation in the Amazonian Craton. The SAC rocks' contrasting Sr/Y and La/Y ratios cannot be explained exclusively by variation in the melting pressure (melts of mafic crust at >50 km) in a thickened continental crust. Multiple crustal petrogenetic processes or heterogeneous sources can produce the heterogeneous geochemical signatures that characterize the rocks of the complex. The admitted sources of these Archean granitoid magmas include basaltic andesite, sanukitoids, and metagreywackes, subordinate TTGs, at low to moderate pressures melting as they suggest low values of (Dy/Yb)n below 1.9 and relatively high-Sr contents. The mesostructure data indicate that the studied rocks were affected by high-temperature deformation (>600 °C) with partial melting. • Low and high-Ti TTG, sanukitoids, hybrid granitoids, and fractionated Bt granites comprise the Santana do Araguaia Complex. • TTGs show high Al 2 O 3 and Sr with a medium La/Yb ratio of intermediate pressure (∼1.0–1.5 GPa). • Sanukitoids are dominantly granodioritic with subordinate monzodiorites and quartz monzodiorites resembling sanukitoids of Rio Maria, Ourilândia do Norte in Amazonian craton, and Karelia domain, Baltic shield, Finland. • Hybrid granites, composed of high-Ba + Sr monzogranites are of CA2-type and HSG, and a second type, with low Sr/Y, displays chemistry akin to CA1 and normal granite (NG). • Hybrid granites show U–Pb crystallization ages of 2815 ± 10 Ma affected by a 1976 Ma thermal event. [ABSTRACT FROM AUTHOR]

We examine some aspects of the tectonic evolution of Precambrian cratonic roots beneath South America based on lithospheric distribution of shear-wave velocities. We derive our model by inverting 26,984 fundamental mode Rayleigh wave group velocity dispersion curves, at periods of 9–180 s. We first regionalize our measurements and then invert the result for a 3D S-wave velocity model extending to 200 km depth. Fast velocities beneath the Amazonian and São Francisco cratons, and beneath buried cratonic units in the Parnaíba and Paraná basins, are long wavelength features consistent with previous tomography studies. For the Amazonian craton at 150 km depth, we find an increase of velocities with province age, except for the Maroni-Itacaiúnas province, where we hypothesize that K'Mudku intraplate tectono-thermal events at the middle-late Mesoproterozoic and emplacement of a large igneous province following the breakup of Pangea could have altered at least partially its lithosphere. Our results are consistent with a São Francisco paleocontinent whose borders extend beyond the surface limits of the present São Francisco craton into the neighboring Araçuaí and Brasília belts. Based on slow shear-wave velocities in the upper mantle beneath the Borborema province, consistent with lithospheric thinning, we argue that a possible cratonic root of the São Francisco Paleocontinent beneath this province has likely been eroded away. This analysis is further corroborated by tectonic events that led to the alteration of the Borborema mantle, including hydration in the Paleoproterozoic, rifting in the early-middle Tonian, reworking during Neoproterozoic Brasiliano events, and lithospheric stretching during the breakup of Pangea. Finally, we also image a fast shear-wave velocity structure in the region of the Río de la Plata craton, consistent with magnetotelluric studies. • A new 3-D shear-wave velocity model of South America extending up to 200 km depth. • Age-velocity correlation is disrupted in a province of the Amazonian craton. • The root of an old paleocontinent might have been eroded under Borborema province. • The velocity beneath the Río de la Plata craton agrees with electrical studies. [ABSTRACT FROM AUTHOR]

• 27 new U-Pb SHRIMP and LA-ICPMS zircon ages for the northern Amazonian Craton. • Early Orosirian belts are the main tectonic features of the central Guiana Shield. • Cauarane-Coereoni belt, 2025–2000 Ma, collisional phase of the Akawai Orogeny. • Orocaima Igneous Belt, 1.99–1.96 Ga post-collisional high-crustal level magmatism. • Rio Urubu Belt, 1.96–1.92 Ga deeply emplaced granitoids and deformation. The Cauarane-Coeroeni Belt (CCB), the Orocaima Igneous Belt (OIB) and the Rio Urubu Belt (RUB) are the main tectonic features of the central part of the Guiana Shield. The CCB is a sinuous NW-SE/NE-SW/NW-SE trending high-grade supracrustal belt, bordered to the north by the OIB, formed by volcanics and high-crustal level granitoids, and to the south by the RUB, made up of deeply emplaced granitoids and gneisses. We present 27 new U-Pb SHRIMP and LA-ICP-MS zircon ages for these belts. The geochronological data obtained for 10 granitoid samples of the OIB indicate that magma pulses of different typologies were coeval along the belt and confirm its continental scale extension. Crystallization ages obtained for the high-K calc-alkaline granitoids vary from 1990 ± 5 Ma to 1957 ± 17 Ma and those of reduced A-type granites vary from 1980 ± 14 Ma to 1974 ± 8 Ma. Only four samples of granitoids and gneisses of the RUB were analysed. Crystallization ages of 1964 ± 7 Ma and 1956 ± 8 Ma were calculated respectively for a granodiorite and for an orthogneiss and are in agreement with the 1.96–1.92 Ga age period regionally considered for the evolution of the RUB. However, an age of 1973 ± 7 Ma was calculated for a foliated S-type granite, indicating that slightly older granitoid rocks are also present within the RUB. In addition, an age of 1935 ± 10 Ma was calculated for the high-grade metamorphism along the belt. A microgranitic dyke that crosscuts the foliation of a gneiss of the RUB was dated at 1884 ± 7 Ma, and probably represents one of the feeder dykes for the large 1.89–1.87 Ga Uatumã magmatic event. Twelve samples of the CCB were analysed. The data for the detrital nuclei of the zircon crystals of the paragneisses and schists suggest an overall similar inheritance pattern along the length of the CCB, recording the contribution of Archean to early Orosirian sources, with a major participation of Rhyacian domains. The oldest detrital zircon crystals yielded an age of 3.65 Ga, but the age of most of the Archean zircon grains fall in the 3.50–2.50 Ga range and they were probably derived from the Imataca and Amapá blocks. Results in the 2.50–2.30 Ga age interval were obtained for detrital zircon grains of many samples, indicating the contribution of Siderian source-areas, possibly the Bacajá Domain, located outside the shield. Those terranes formed within the shield during the Rhyacian phase of the Transamazonian Cycle were probably the source of the 2.30–2.05 Ga detrital zircon grains. In addition, zircon grains with ages between 2.05 Ga and 2.03 Ga were possibly derived from the Trairão-Anauá terranes. The U-Pb SHRIMP zircon dating allowed to better constrain the metamorphic events along the CCB. The syn-kinematic M1 high-grade metamorphic phase could not be directly dated, and we suggest it occurred between 2025 Ma and 2000 Ma. The imprint of the thermal M2 metamorphic event is recorded by the presence of rims and cores of zircon crystals with very low Th/U ratios (<0.1), showing secondary texture. Upper intercept ages of 1983 ± 9 Ma, 1978 ± 9 Ma and 1967 ± 27 Ma were obtained for M2. Zircon grains with secondary textures and very low Th/U ratios (<0.1) from a sample collected in the vicinities of the RUB yielded an upper intercept age of 1955 ± 14 Ma, tentatively interpreted as reflecting M3. The ages obtained for the M2 and M3 metamorphic phases coincide, respectively with those measured for the rocks of the OIB and for the high-grade metamorphism in the RUB. We envisage that the M2 and M3 metamorphic overprints in the paraderived rocks of the CCB reflect important fluid input and thermal perturbation respectively during the emplacement of the OIB granitoids to the north, and the assemblage of granitoid bodies of slightly different ages, deformation and high-grade metamorphism within the RUB, south of the CCB. The early Orosirian terranes of the central part of the Guiana Shield were formed during Akawai Orogeny. The 2.04–2.03 Ga Trairão-Anauá terranes and the CCB supracrustal rocks represent the pre-collisional and collisional stages of the orogeny, the OIB records post-collisional, late-orogenic magmatism. The RUB is probably reflecting a post-collisional setting associated with transpressive deformation. The Akawai Orogeny is interpreted as the late stage of the Transamazonian Cycle, after the main Rhyacian orogeny of the cycle, and was responsible for the final amalgamation of this part of the Columbia paleocontinent. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3.34 Ga igneous zircons reveal the crystallisation age of the layered complex. • 3.0-3.3 Ga metamorphic zircons show typical coupled dissolution-precipitation textures. • Paleoarchean crust has been reworked in the Amazonian craton since the Mesoarchean. • Bacuri chromites are the best preserved and oldest orthomagmatic deposit known. The age and tectonic history of the chromite-mineralised Bacuri Complex, a layered mafic–ultramafic intrusion emplaced into Archean terranes of the Guyana Shield in the Amazonian Craton, are here investigated. The stratigraphy of the Bacuri Complex consists of an Ultramafic Zone composed of interlayered metaperidotites and chromitites and two mafic zones composed of metamafic rocks (amphibolites). In this study we present whole-rock lithogeochemical data integrated with zircon U-Pb isotopic and trace-element data from amphibolites from the Mafic Zone. The investigated amphibolites consist of hornblende + plagioclase ± diopside ± biotite with whole-rock compositions like noritic rocks of Archean layered intrusions. These samples are representative of amphibolites with variable proportions of hornblende and plagioclase, interpreted as resulting from amphibolite facies metamorphism of interlayered norite and leuconorite. We suggest that progressive fractionation of a primitive parental magma led to the formation of plagioclase and orthopyroxene cumulates in the mafic zones. We found that zircons from three metanorite samples comprise euhedral crystals with oscillatory zoning (interpreted to preserve a magmatic crystallisation age), as well as variably recrystallised metamorphic zircons. Their U-Pb 207Pb/206Pb ages span over 682 million years, from 3628 Ma to 2942 Ma. Trace element data suggest that magmatic zircons precipitated from late-stage magmatic fluids at ∼ 3.34 Ga (3343 ± 3.5 Ma weighted average age, n = 48, MSWD = 1.3), which defines the Bacuri Complex as one the oldest and best-preserved layered intrusions known. We show that fluid-mediated coupled dissolution-precipitation recrystallisation during metamorphism altered the composition and ages of magmatic zircons. We could not accurately define the number and age of metamorphic events in the 2942–3379 Ma age interval of metamorphic or 'disturbed' zircon domains. Our results indicate that continental crust was already established in the Amazonian craton in the Paleoarchean and possibly in the Eoarchean and that it has been reworked since at least the Mesoarchean. [ABSTRACT FROM AUTHOR]

The Alto Guaporé Belt represents a key component in the investigation of the geological history and reconstruction of the SW Amazonian Craton. Airborne geophysical, isotopic and geochronological data integrated with field data have provided new insight into the tectonic framework of this terrane. More than 90,000-line kilometers of airborne geophysical data, including magnetic and gamma-spectrometry data, acquired over of 43,018 square kilometers in the southeastern part of Rondônia and northwestern limit of Mato Grosso states between 2005 and 2006. Aeromagnetic data allowed the generation of geophysical maps, including the total magnetic intensity, the first order derivative, and the analytic signal amplitude, which enabled the identification of terrane limits, structural pattern and geometry of magnetic bodies. Integration of these products resulted in qualitative models of magnetic and structural domains highlighting and characterizing the three deformation events. The pseudo-gravity map enhanced the deep structures, it shows clear discrimination of deep sources between the Alto Guaporé Belt and the Jauru Terrane. This relation is not easily understood when a conventional analysis of magnetic data is performed. The airborne gamma-ray spectrometry data showed areas of concentration and dispersion of radioelements, improving the geologic mapping for the definition of geologic contacts, intrusive bodies and the overlap of areas with sedimentary covers and regolith material. The geological, geochronological U-Pb and isotopic Sm-Nd data helped constrain the geodynamic evolution for this portion of the Amazonian Craton. The geodynamic history and geologic architecture are important parameters for the definition of mineral systems and mineral exploration targeting models at regional and local scales.

The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial εNd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages. [ABSTRACT FROM AUTHOR]

This paper presents a literature review of the geology of the Alto Rio Negro region, located in northwestern Brazil. Firstly, we summarize the Amazonian Craton tectonic models and how the study area fits in these different tectonic models. The aim is to organize the literature data and better guide the consultation for new studies. The first geological reports about the Alto Rio Negro are from the Mid-19th century, when the British naturalist Alfred Russel Wallace travels to this country and, since then, long periods of scientific production absence occur. However, after the RADAMBRASIL Project in the 1970s, there was a significant research advance. Recent publications reveal a complex tectonic evolution, with three events that mark periods of generation and reworking of the Proterozoic basement. Two Paleoproterozoic magmatic arc systems generated the geological basement. The Calymmian collision of these terrains produced a large volume of crustal granites, in addition to pre-, and post-tectonic granites. A crustal reworking period (1.4-1.1 Ga) reactivated the basement structures and, possibly, generated the Ectasian carbonatitic intrusions. There are many difficulties to access this region, so the literature data are of great value and provide a background for new studies. The lack of more detailed geological maps covering the Alto Rio Negro region is the main obstacle. Still, it offers a fertile research field for geologists interested in contributing to diverse research fields of Geology focusing on the Amazonian Craton.

[Display omitted] • The 1110 Ma Rio Perdido pole passed a baked contact test and meets six out of the seven pole's reliability criteria. • The Rio Apa Terrane (RAT) was likely linked to the southwestern Amazonian Craton at 1110 Ma. • The RAT and the Paraguá Terrane (PT) had a joint geological evolution during the Paleo- and Mesoproterozoic. The Rio Apa Terrane (RAT) is situated at the south end of the Amazonian Craton (AC) separated from it by the aulacogen Tucavaca belt. It encompasses basement rocks that evolved mainly during the Paleoproterozoic. Its relationship to the AC during Proterozoic is yet undefined, although geologic, geochronologic and isotopic evidence suggest it was close to the Ventuari-Tapajós and Rio Negro-Juruena Provinces at Paleoproterozoic and linked to southwestern AC at ca. 1320 Ma. Aiming to elucidate the paleogeographic relation of the RAT to the AC during the Proterozoic, we performed a paleomagnetic study of the 1110 Ma Rio Perdido mafic dike swarm that crosscut the RAT. These dikes strike preferentially WNW-ESE and are mostly undeformed and unmetamorphosed. Magnetic experiments (hysteresis curves, isothermal remanent magnetization (IRM) curves, thermomagnetic curves and first order reverse curves-FORCs) revealed pseudo-single domain (PSD) Ti-poor titanomagnetite as the main magnetic carrier in these dikes. Alternating field (AF) and thermal demagnetization were efficient in isolating southwestern and northeastern directions with low inclinations, whose mean direction (Dec = 51.8°, Inc = −0.8°, N = 14, α 95 = 13.8°, k = 9.3) yielded the paleomagnetic pole (RP) at 34.8°S/197.3° (A95 = 10.9°). This pole passed a baked contact test and meets 6 out of 7 pole reliability criteria (R = 6). The Rio Perdido pole implies that RAT could be linked to the southwestern AC at 1110 Ma but rotated counterclockwise ∼ 110° related to its present position. The AC linked to RAT probably belonged to the 1100 Ma Umkondia megacontinent which later collided with Laurentia during the formation of Rodinia at ca. 1000–900 Ma. Also, paleomagnetic data suggest that the RAT and the southwestern AC (Paraguá Terrane) were linked to Ventuari-Tapajós and Rio Negro-Juruena provinces at ca. 1780 Ma and had a joint geological evolution during the Paleo- and Mesoproterozoic. Finally, during the amalgamation of West Gondwana, the RAT rotated clockwise to its present position. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chromitite and metanorite host xenocrysts (>3.4 Ga) and magmatic zircon (∼3.34 Ga) • Coupled dissolution-precipitation processes led to > 800 Myr span of U-Pb ages. • Hallmark chromite-zircon intergrowths are related to magmatic-metamorphic processes. • Paleoarchean events of crust formation indicated by Hf-TDMC model ages. The chromite deposits of the Paleoarchean Bacuri Mafic-Ultramafic Complex in the Guyana Shield-Amazonian craton, Brazil, were recently identified as the oldest economic orthomagmatic mineralization deposits on Earth and provide an exceptional glimpse into early Earth processes. Despite its economic and geological significance, the knowledge about the Bacuri Complex is still limited. In this study, we report zircon U-Pb and Lu-Hf isotopic data for chromitite and metanorite from the chromite-mineralized layered sequence and present hallmark textural and microstructural evidence for the precipitation of zircon from late-stage, evolved mafic melt. The investigated samples consist of metamorphosed chromitite from the > 25 m-thick Main Chromitite Layer (3 samples) and metanorite of the Lower Mafic Zone (3 samples). We found that the mode of zircon is higher in metanorite than in chromitite samples, and zircon grains exhibit a range of morphologies, textures, grain sizes, and mineral inclusions, reflecting three zircon types investigated: (i) > 3400 Ma inherited zircon xenocrysts, (ii) magmatic zircon precipitated at c. 3340 Ma from late-stage, evolved melt, in pockets of the cumulate pile, and (iii) micrometric zircon neoblasts or very thin overgrowth rims formed from the break-down of Zr-bearing minerals during metamorphic events. Additionally, we show that xenocrystic and magmatic zircon types were modified by coupled dissolution-precipitation processes at varied degrees in the magmatic system and during younger tectonic and metamorphic events, resulting in a > 800 Myr span in near concordant spot ages. We hypothesize that xenocrystic zircon grains were entrained from the magmatic pathways or wall rocks of the mafic–ultramafic melts and suggest that crustal contamination was a major triggering factor in the genesis of the massive chromitite layers of the Bacuri Complex. This conclusion is supported by the positive and near chondritic εHf(3343 Ma) values (+2.2 – 0.0) obtained on magmatic zircon domains. The elevated Sc/Yb ratio (0.61 – 1.24) in magmatic zircon indicates an extensive fractionation of the interstitial melts in the Bacuri cumulate pile. In addition, the 0.82 U/Yb ratio indicates a plume-related origin for the mafic–ultramafic melts. We suggest these plume-related melts have mixed with crustal materials during continental rifting in within-plate settings, forming the Bacuri chromite deposits at ∼ 3340 Ma. Significantly, the U-Pb concordant ages on inherited cores (3563 ± 47 Ma to 3407 ± 38 Ma) overlap with the Hf-TDMC model ages of magmatic zircon domains, suggesting that they represent actual events of crust formation in the Paleoarchean of the Guyana Shield. [ABSTRACT FROM AUTHOR]

The Querari Complex corresponds to the basement rocks from Uaupés Domain and represents one of the least studied units in the northwest of the Rio Negro Province, Amazonian Craton. In this paper, we present new field geology, petrographic, and geochemical data of deformed granites from the Querari Complex. Based on our results, we suggest the differentiation of the Querari Complex into two magmatic facies. The Panã-Panã Facies comprise mainly porphyritic syeno to monzogranites with biotite as the main mafic mineral, and titanite, epidote, and allanite as accessory phases. The rocks of the Panã-Panã Facies have calc-alkaline and metaluminous affinities. The Matapi Facies have a syenogranite composition, coarse to porphyritic texture with magmatic muscovite and biotite, normative corundum higher than 1% (1.85-2.06), and mostly a peraluminous character. Both facies are generally enriched in silica and have a small spectrum of variation. (67.5 to 70.1 wt.% Panã-Panã Facies - 71.1 to 73 wt.% Matapi Facies), but they differ by the high Al2O3, Fe2O3, MgO, CaO, Sr, and Ba contents in the Matapi Facies. Geological and geochemical compositions suggest that the magmatic precursors of these rocks of Matapi Facies may be derived from partial melting of metasedimentary sources, whereas the Panã-Panã Facies are probably derived from a meta-ignea source of intermediate composition, such as tonalitic gneisses. The rocks of the Querari Complex would have been generated in the collisional tectonic settings during the Paleoproterozoic (between 1778 and 1740 Ma). During this 1.78-1.74 Ga tectono-magmatic event (D1), the magmatic fabric (S0) and the parallel S1 foliation have been developed, with NE-SE orientation. A subsequent tectonic event (D2) was responsible for the folding S1 foliation, creating the S2 axial planar foliation with an approximate orientation E-W. This D2 event is thought to represent a Calymmian (1.52 - 1.48 Ga) tectono-metamorphic event, associated with widespread I- and S-type granite emplacement in the Rio Negro Province. The deformation textures, as well as the mineral paragenesis for the Panã-Panã and Matapi facies, reveal temperature conditions at upper amphibolite facies, up to 700ºC. Finally, the D3 tectono-metamorphic event comprises the reactivation of many NE-SW ductile shear zones with sinistral kinematic, creating a mylonitic foliation (S3) in the rocks of the Querari Complex. This D3 tectono-metamorphic event is probably linked to the intracratonic K´Mudku tectono-metamorphic event (between 1317 and 1198 Ma) of the Amazonian Greenvillian-Sunsás continental collision.

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Guaviare Complex is a new unit defined in the Colombian Amazonian Craton, which is part of the Precambrian basement located in southeastern Colombia. It is divided into three units according to their textural and compositional characteristics, termed Termales Gneiss, Unilla Amphibolite, and La Rompida Quartzite. Termales Gneiss rocks are petrographically classified as gneisses and quartz-feldspar granofels, with the local formation of blastomylonite-like dynamic rocks. The Unilla Amphibolite consists of only amphibolites, and La Rompida Quartzite consists of muscovite quartzites, quartz-feldspar granofels, and quartz-muscovite schists. The protoliths of Termales Gneiss and Unilla Amphibolite were formed in the Mesoproterozoic at 1.3 Ga due to bimodal magmatism (felsic and mafic) derived from mantle material, with some crust contamination that was probably related to the formation of extensional arcs associated with trans-arc basins in the NW section of the Amazon Craton. La Rompida Quartzite rocks originated from sediments derived from granite rocks and from other, older areas of the craton. These rocks have a maximum age of 1.28 Ga. The low-to-medium grade metamorphism that affected these units occurred from 1.28 to 0.6 Ga, most likely concurrently with the Putumayo orogeny of approximately 1.0 Ga, although it may have been an independent event.

Abstract Quartz and cassiterite crystals of granite, greisens, and quartz veins from Mocambo Granite, Carajás Province, were studied by scanning electron microscopy — cathodoluminescence and electron microprobe. Five types of quartz were identified: Qz1, magmatic and Qz2, Qz3, Qz4, and Qz5 hydrothermal. Qz1, anhedric to subhedric, luminescent and fractured at different intensities, predominating in less evolved rocks. Qz2, with low luminescence, is younger than Qz1; it occurs as irregular patches, filling fractures or forming veins that cut Qz1. Qz3, non-luminescent, resulting from continuous alteration, dissolution, and recrystallization processes; fills fractures that cut Qz1 and Qz2. Qz4 occurs in the most evolved and hydrothermalized rocks and in greisens bodies mineralized in cassiterite; is euhedral to subhedral, exhibits well-defined zoning, and has been interpreted as later than the previous one. Qz5 has poor luminescence; occurs in mineralized veins with wolframite and, secondarily, cassiterite. Qz1 shows Ti enrichment, while Qz4 associated with cassiterite is enriched with Al. Well-formed cassiterite crystals exhibit concentric zoning and low Fe, Ti, W, Nb and Mn contents. Qz5-associated cassiterite crystals form inclusions in the wolframite, suggesting that cassiterite and wolframite precipitated from hydrothermal processes at different times.

Copyright of Geologia USP: Série Científica is the property of Geologia USP and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geologia USP: Série Científica is the property of Geologia USP and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Numerous rivers, interrupted by large waterfalls and extensive rapids, drain the geologically ancient Guiana Shield Highlands. We describe a new armoured catfish genus and two new species endemic to the upper Ireng and Kuribrong rivers, respective tributaries of the Amazon and Essequibo basins in western Guiana. Corymbophanes ameliae sp. nov. is distinguished by having vermiculations on the abdomen, bands on the caudal fin, the anal fin i,5 and narrow caudal peduncle. Yaluwak primus gen. & sp. nov. is distinguished by having evertible cheek odontodes, a plated snout, a tall caudal peduncle and absence of adipose fin and iris operculum. We present a new molecular phylogenetic analysis inclusive of these and several related genera that suggests that the Corymbophanes clade (Araichthys , Corymbophanes , Cryptancistrus , Guianancistrus , Hopliancistrus and Yaluwak) originated in the Guiana Shield with secondary dispersal to the Brazilian Shield. Within the Guiana Shield, relationships among Corymbophanes and Yaluwak are consistent with geodispersal between drainages via headwater capture, although an uplift-mediated relictual distribution cannot be ruled out. ND2 haplotype structure among C. ameliae populations suggests that ichthyofaunal diversity on the Guiana Shield escarpment is shaped not only by inter-, but also intrafluvial barriers to gene flow. [ABSTRACT FROM AUTHOR]

In recent years, there has been a significant increase in the paleomagnetic data of the Amazonian Craton, with important geodynamic and paleogeographic implications for the Paleo-Mesoproterozoic Columbia supercontinent (a.k.a., Nuna, Hudsoland). Despite recent increase of paleomagnetic data for several other cratons in Columbia, its longevity and the geodynamic processes that resulted in its formation are not well known. A paleomagnetic study was performed on rocks from the ∼1535 Ma AMG (Anorthosite-Mangerite-Rapakivi Granite) Mucajaí Complex located in the Roraima State (Brazil), in the northern portion of the Amazonian Craton, the Guiana Shield. Thermal and AF treatments revealed northwestern/southeastern directions with upward/downward inclinations for samples from twelve sites. This characteristic remanent magnetization is mainly carried by Ti-poor magnetite and in a lesser amount by hematite. Site mean directions were combined with previous results obtained for three other sites from the Mucajaí Complex, producing the dual polarity mean direction: Dm = 132.2°; Im = 35.4° (N = 15; α 95 = 12.7°; k = 10.0) and a paleomagnetic pole located at 0.1°E, 38.2°S (A 95 = 12.6°; K = 10.2). The Mucajaí pole favours the SAMBA (South AMerica-BAltica) link in a configuration formed by Amazonia and Baltica in Columbia. Also, there is geological and paleomagnetic evidence that the juxtaposition of Baltica and Laurentia at 1.76–1.26 Ga forms the core of Columbia. The present paleomagnetic data predict a long life 1.78–1.43 Ga SAMBA connection forming part of the core of the supercontinent. Image 1 • Paleomagnetic study of AMG Mucajaí Complex rocks (1535 Ma) from Amazonian Craton. • The Mucajaí pole favours the SAMBA link in a Columbia Supercontinent. • Mucajaí data predict a long-lived SAMBA link forming part of the core of Columbia. [ABSTRACT FROM AUTHOR]

Kimberlite magmatism provides insights into periodic tectonothermal processes linked to the evolution of supercontinents. Paleozoic and Mesozoic kimberlites overlapping with the Pangea cycle are exposed in the Amazonian Craton (Pimenta Bueno field) and the Neoproterozoic Brasília Belt. Phlogopite in mantle xenoliths in kimberlites from the Amazonian Craton are characterized by low Cr 2 O 3 (< 1 wt%) and an enrichment in TiO 2 (> 2 wt%), akin to secondary phlogopite formed by kimberlite magma infiltration in the mantle. Low Ti-Cr (< 1 wt%) and high #Mg (91–92) grains are linked to extensive metasomatism of garnet peridotites resulting in clinopyroxene-phlogopite rocks. In situ phlogopite Rb-Sr isochron ages of 250–220 Ma constrain the emplacement of pipes in the Amazonian Craton with no age difference between distinct phlogopite compositions (higher and lower TiO 2 phlogopite) and microstructures (porphyroclasts, neoblasts, reaction rims). Mantle xenoliths in kimberlite pipes from the Brasília Belt present high TiO 2 (> 2 wt%) akin to secondary phlogopite formed by magma infiltration, and low Ti-Cr (1 wt%), and high #Mg (> 92) phlogopite akin to primary grains in equilibrium with garnet. In situ phlogopite Rb-Sr isochron ages from all Brasília Belt phlogopite types span 90–80 Ma, constraining the emplacement of diamondiferous and barren pipes, with no relic of older metasomatic events. The kimberlites from the Pimenta Bueno field (Amazonian Craton) are coeval with the beginning of the extension within Pangea that culminated with the Central Atlantic rifting. In fact, the Permian-Triassic kimberlites occur close to intracratonic basins that are crosscut by ca. 200 Ma dykes and sills of the Central Atlantic Magmatic Province. In situ phlogopite Rb-Sr isochron ages spanning 90–80 Ma in the pipes from central and southeastern Brazil (Brasília Belt) may be associated with propagation of far-field stresses linked to opening of the South Atlantic Ocean during the Pangea break-up. • New in situ Rb–Sr ages of phlogopite represent the emplacement of kimberlites. • There is no age difference between distinct phlogopite composition and microstructure. • Permian-Triassic pipes are timely associated with the early extension within Pangea. • The emplacement of diamondiferous and barren kimberlites was coeval after Pangea breakup. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Amazon Craton preserves most complete Paleoproterozoic magmatic events. • The Colíder Group is characterized by an effusive/subvolcanic phase, an explosive phase, and epiclastic rocks. • Subaerial volcanism in a probable eroded volcanic caldera system. The eastern side of Alta Floresta Mineral Province (AFMP) (União do Norte region) comprises an effusive/subvolcanic phase, explosive phase, and epiclastic rocks. The effusive/subvolcanic phase comprises massive porphyritic rhyolite with different degrees of crystallinity, porphyritic rhyolite with flow structure, and microcrystalline rhyolite. The explosive phase is characterized by welded lapilli tuff, lapilli tuff with flow structure, stratified lapilli tuff, and tuff with accretionary lapilli. Sandstones and siltstones characterize epiclastic rocks. There are porphyritic rhyolite dikes that cut the volcanic sequence. The rocks of the Colíder Group are rhyolites (>70 % SiO 2) with calcic-alkaline to alkaline-calcic affinity. A rhyolitic rock is predominantly ferroan and metaluminous, while a pyroclastic rock is predominantly magnesian to ferroan and meta- to peraluminous in composition. The rocks have a high LREE content, and slight fractionation of HREE suggests they have hybrid geochemical characteristics of high potassium calc-alkaline, shoshonitic, and suggestive affinities of A-type magmas, probably produced in a post-collisional orogenic environment. These rocks have a relatively high level of Ba and Rb and a negative anomaly for Sr, P, Nb, Ta, and Ti, suggesting an intra-plate mantle source with contributions from a metasomatized mantle edge. The rocks do not have adakitic characteristics nor fertility for Cu-Au (Sr/Y < 1.9 and La N /Yb N < 38.0) as in other regions of the AFMP. The welded lapilli tuff rocks show U-Pb age of 1838 ± 17 Ma and 1817 ± 2 Ma and are the older explosive phases. The effusive/subvolcanic phase has U-Pb ages of 1800 ± 3 Ma and 1792 ± 3 Ma obtained in the massive porphyritic rhyolite. The age interval of approximately 46 Ma (1838–1792 Ma) suggests the presence of two or more volcanic cycles or distinct volcanic events. Based on the interpretation of volcanic and epiclastic deposits and remote sensing products, the paleoenvironmental reconstruction includes subaerial with effusive/subvolcanic and explosive stages in a probable eroded volcanic caldera system with epiclastic rocks from a fluvial depositional system. This volcanic scenario provides more information about the Colíder–Teles Pires volcano-plutonic event, uniquely mapped in AFMP, and offers new insights into the tectonic frame of the Amazonian craton. [ABSTRACT FROM AUTHOR]

The Rondônia Tin Province, situated in the southwestern part of the Amazonian Craton in Brazil, is renowned for hosting the country's largest cassiterite deposits and substantial mineral reserves of Sn, Nb, Ta, and W, primarily found in A-type rapakivi granites. Despite its significance, this area lacks comprehensive regional studies. Over time, the province has undergone a series of post-tectonic to anorogenic magmatic events, resulting in the formation of several intrusive suites: Serra da Providência (1.60–1.53 Ga), Santo Antônio (1.40 Ga), Teotônio (1.39 Ga), Alto Candeias (1.35–1.34 Ga), São Lourenço-Caripunas (1.31 Ga), Santa Clara (1.08–1.07 Ga), and Rondônia (1.00–0.97 Ga). These suites typically exhibit high-K calc-alkaline to alkaline affinity, often leaning towards shoshonitic compositions. They are primarily ferroan, varying from metaluminous to peraluminous, and weakly peralkaline. Notably, they display enrichments in large ion lithophile elements and light rare earth elements (LREE), along with depletion of heavy rare earth elements, marked by a strong negative Eu anomaly. Based on Rb–Ba–Sr content, the older suites—Serra da Providência, Santo Antônio, Teotônio, and Alto Candeias—show normal granite signatures. In contrast, the younger tin-bearing rocks—Santa Clara, São Lourenço-Caripunas, and Rondônia—demonstrate highly evolved geochemical characteristics. Tectonic discrimination diagrams position the older suites within the post-collisional field, while the younger, mineralized suites exhibit intraplate characteristics. This study integrates compiled geochemical, geochronological, and isotope data from various studies to comprehensively delineate the regional tectono-magmatic framework evolution of the Rondônia Tin Province. Notably, it suggests a potential equivalence between the Santo Antônio and Teotônio suites, highlighting their geochemical similarities, overlapping ages, and geographical proximity. The analysis uncovers that tin mineralization in this province arose from at least two distinct tectonic events linked to intrusions of alkaline granites displaying intraplate affinity. These granites crystallized post the cessation of compressive forces from the Rondonian-San Ignacio (ca. 1.3 Ga) and Sunsás (ca. 1.0 Ga) orogenies. The São Lourenço-Caripunas Suite marks the initial mineralizing event, while the mineralized Santa Clara and Rondônia suites align with a subsequent tectonic cycle. Hydrothermal activities in greisen deposits within the Rondônia Tin Province intricately link to younger evolved suites characterized by heightened Sr ratios, implying unique potential for ore formation during anorogenic stages. Tectonic events significantly drive tin mineralization, recurring during anorogenic episodes at the conclusion of each orogenic cycle. These mineralizations reflect the phases of anorogenic magmatism, notably in the closing stages of the Rondonian-San Ignacio (∼1.3 Ga) and Sunsás (∼1.0 Ga) orogenies. This study offers crucial insights into the geological evolution and tin mineralization processes within the Rondônia Tin Province, contributing to the global understanding of similar geological settings and guiding effective exploration strategies for the region. The dataset provides a robust foundation for future research and underscores the province's potential for further discoveries. • A review of the magmatic, tectonic and metallogenetic evolution of the Rondônia Tin Province. • Identifying a transition in the Rondônia Intrusive Suite from A2 to A1-type granites. • Potential of Santo Antônio and Teotônio suites represent a unified intrusive suite. • Dual Mineralization Events linked to the Rondonian San-Ignacio and the Sunsás orogenies. • Rb concentration serving as a pivotal exploration indicator of greisen deposits. [ABSTRACT FROM AUTHOR]

The study of granite rocks is important in order to understand chemical evolution of the continental crust. Their isotopic composition provides information on their magmatic sources, whether being mantle, crust or a mixture of both. In the SW border of the Amazonian Craton, suites of rapakivi granites related with tin-polymetallic mineralization emplaced within heterogeneous Proterozoic crust. Zircons from twelve rocks from three granite intrusions, Massangana, São Carlos and Caritianas, representative of the Younger Granites of Rondônia have been studied by using laser ablation inductively coupled plasma source mass spectrometry (LA-ICP-MS) in order to obtain U-Pb ages and Hf isotopic compositions. The samples from Massangana massif, show greater range in age (between 1026 – 993 Ma) and initial 176Hf/177Hf = 0.2817-0.2823. The ԐHf values are both negative and positive (-6.2 to +3.4) in some samples, and only negative in others (-14.1 to -1.6) which reflects the heterogeneity of crust that they intruded. The TDM age varying between 2.40 to 1.61 Ga also indicates that different sources were involved in the formation of these rocks. The samples from São Carlos massif show U-Pb ages between 996 to 974 ± 10 Ma and initial ԐHf between -15 and +11, corresponding to a TDM age range between 2.65 and 1.08 Ga. The samples from Caritianas massif with U-Pb ages of 1001 and 999 Ma, show more initial ԐHf positive values (13 zircon grains) than negative (6 zircon grains), different from the other massifs. The range of initial ԐHf of the Caritianas massif is -1.5 to +8.2, and residence crustal ages between 1.76 and 1.25 Ga. The great variation in the ԐHf values indicates heterogeneity of sources; the Massangana and São Carlos massifs represent mainly crustal melts with a subordinate mantle contribution. The Caritianas massif, which shows more positive values of the ԐHf parameter, seems to have had more mantle contribution than the other massifs studied here. The characterization of the sources of the rapakivi rocks may play an important role in the genesis of cassiterite ore and could represent an important tool for mineral exploration.

Abstract The Iriri-Xingu domain, located in the central part of the Amazonian craton, consists of extensive occurrences of Paleoproterozoic volcanic rocks and granites with published ages of ca. 1990 to 1840 Ma, which show a strong crustal contribution for their magmas. Exposures of basement rocks are small and rare. Samples from two areas were dated in this work by U-Pb SHRIMP in zircon. In the northern Maribel area, a high-grade pelitic paragneiss presented an age of 2160 ± 8 Ma and the leucosome of a migmatitic orthogneiss, probably a diatexite, crystallized at 2149 ± 20 Ma. These Rhyacian ages suggest that it is part of the Bacajá domain, related to the Trans-Amazonian cycle. The Morro Grande area occurs in the central part of Iriri-Xingu domain, where a high-grade muscovite gneiss with a protolith of 2120-2180 Ma is dated at 1982 ± 7 Ma, and the leucosome of a migmatitic orthogneiss is crystallized at 1979 ± 8 Ma. These are the first records of high-grade metamorphism at ca. 1980 Ma in the Central Brazil shield and may be related to the generation of this Orosirian felsic magmatism, which is widespread throughout the nearby Ventuari-Tapajós province.

The southeastern Guyana Shield, northeast Amazonian Craton, in the north of Brazil, is part of a widespread orogenic belt developed during the Transamazonian orogenic cycle (2.26–1.95 Ga) that includes a large Archean continental landmass strongly reworked during the Transamazonian orogeny, named Amapá Block. It consists mainly of a high-grade metamorphic granulitic-migmatitic-gneiss complex, of Meso- to Neoarchean age and Rhyacian granitoids and supracrustal sequences. For the first time, coupled U-Pb and Lu-Hf isotope data were obtained on zircon by LA-ICP-MS from five tectono-stratigraphic units of the Archean basement and one Paleoproterozoic intrusive rock, in order to investigate the main episodes of crustal growth and reworking. Whole-rock Sm-Nd isotope data were compared to the zircon Lu-Hf data. Three main magmatic episodes were defined by U-Pb zircon dating, two in the Mesoarchean (∼3.19 Ga and 2.85 Ga) and one in the Neoarchean (∼2.69–2.65 Ga). Subchondritic ɛ Hf (t) values obtained for almost all investigated units indicate that crustal reworking processes were predominant during the formation of rocks that today make up the Amapá Block. Hf- T DM C model ages, ranging from 2.99 Ga to 3.97 Ga, indicate that at least two important periods of mantle extraction and continental crust formation occurred during the Archean in southeastern Guyana Shield, an older one in the Eoarchean (∼4.0 Ga) and a younger one in the Mesoarchean (∼3.0–3.1 Ga). The latter is recognized as an important period of crustal accretion worldwide. The recognition of an Eoarchean episode to the southeastern most part of the Guyana Shield is unprecedented and was not recorded by whole-rock Sm-Nd data, which were restricted to the Meso–Paleoarchean (2.83 Ga to 3.51 Ga). This finding reveals that continental crust generation in the Amazonian Craton began at least 500 Ma earlier than previously suggested by the Sm-Nd systematics. Image 1 • Two Mesoarchean and one Neoarchean magmatic episodes in the Amapá Block. • Crustal growth occurred in the Eoarchean (∼4.0 Ga) and Mesoarchean (∼3.0-3.1 Ga). • Crust generation in Amazonian Craton began 500 Ma earlier than previously thought. [ABSTRACT FROM AUTHOR]

The Iriri-Xingu domain, located in the central part of the Amazonian craton, consists of extensive occurrences of Paleoproterozoic volcanic rocks and granites with published ages of ca. 1990 to 1840 Ma, which show a strong crustal contribution for their magmas. Exposures of basement rocks are small and rare. Samples from two areas were dated in this work by U-Pb SHRIMP in zircon. In the northern Maribel area, a high-grade pelitic paragneiss presented an age of 2160 ± 8 Ma and the leucosome of a migmatitic orthogneiss, probably a diatexite, crystallized at 2149 ± 20 Ma. These Rhyacian ages suggest that it is part of the Bacajá domain, related to the Trans-Amazonian cycle. The Morro Grande area occurs in the central part of Iriri-Xingu domain, where a high-grade muscovite gneiss with a protolith of 2120-2180 Ma is dated at 1982 ± 7 Ma, and the leucosome of a migmatitic orthogneiss is crystallized at 1979 ± 8 Ma. These are the first records of high-grade metamorphism at ca. 1980 Ma in the Central Brazil shield and may be related to the generation of this Orosirian felsic magmatism, which is widespread throughout the nearby Ventuari-Tapajós province. [ABSTRACT FROM AUTHOR]

The study of Paleoproterozoic rocks is crucial for understanding Earth's tectonic evolution during the time when most of the modern crust and ore deposits were formed. The rocks of the Brazilian Amazonian Craton record some of the most-complete and best-preserved Paleoproterozoic magmatic and volcanic episodes on Earth. Following previous investigations, we present new lithofaciological and stratigraphic records of the felsic rocks of the Tapajós Mineral Province (TMP) (~2–1.88 Ga) and the São Felix do Xingú region (SFX) (~1.88 Ga) which, combined with new petrological and geochronological data, help providing a more complete understanding of the tectonic, magmatic and volcanological evolution of the Amazonian Craton. This magmatism/volcanism is thought to be formed in a late-/post-orogenic to extentional regime confirmed by the new geochemical data presented here. The transition from late-convergent to extensional tectonic setting could register the beginning of the taphrogenesis that marked the Amazonian Craton throughout the Mesoproterozoic. The volcanological approach of this contribution can serve as a strategy for the modelling of the evolution of Precambrian volcano-sedimentary basins around the world. The large amount of rocks analyzed are divided into primary and secondary volcaniclastic products depending on if they resulted from a direct volcanic activity (pyroclastic) or processes that reworked pyroclastic fragments. Furthermore, the deposits are subdivided into massive and stratified, depending on their primary mechanisms of transport and emplacement. By confirming the results from previous studies, our study permits to depict a more precise paleo-environmental picture of the processes that occurred in the Amazonian Craton during the Late-Paleoproterozoic. In particular, the presence of large regional-scale fissural systems and caldera collapses produced large silicic explosive volcanic eruptions, also accompanied by the emission of large volume effusive products. Although studies on the Amazonian Craton are still scarce and controversial, the present study provides new evidence that this volcanism may have formed one of the largest Silicic Large Igneous Provinces (SLIP) on earth. Our data also confirm that at least two major Paleoproterozoic periods of formation of volcanic rocks exist in the Amazonian craton. This point is of great relevance for any future interpretation of the geological evolution of this craton. Unlabelled Image • The modern lithofaciological approach is used here to describe the volcanic rocks of the Precambrian Amazonian Craton. • The U-Pb geochronological data presented here yield three new ages of ca. 2.0 Ga and one new age of ca. 1,88 Ga. • The ancient volcanism described is formed by extensive lava flows, high-grade ignimbrites and other fragmental products. [ABSTRACT FROM AUTHOR]

The Nova Monte Verde metamorphic core complex is an arched structure located in the southern portion of the Rio Negro-Juruena geochronological Province and is part of a belt of metamorphic rocks containing gneiss and migmatite domes exhumed during Statherian extension of rifted Ventuari-Tapajós crust. This metamorphic core is bordered, both to the north and south, by felsic volcanic and plutonic rocks intensely foliated near the metamorphic core and becoming progressively undeformed as one moves away from the metamorphic core. U-Pb analyses of zircon and monazite from migmatites exposed in the core of the complex, coupled with a detailed structural analysis, enlighten the timing and duration of migmatite crystallization, indicating that crystallization, extensional deformation and exhumation of the core-complex were coeval. Analysis of a high melt fraction from migmatites outcroping near Bacaeri Farm suggest that the Nova Monte Verde metamorphic core complex records a history of neosome formation spanning at least 37 Ma, as indicated by 206Pb/238U ages (1800-1763Ma) for new zircon growth attributed to migmatization. Monazite from two samples yielded U-Pb ages of 1798 ± 29 Ma for the aluminous metatexite and 1754 ± 11 Ma for sillimanite-biotite metatexite. The former is interpreted as the metamorphic peak and main generation of leucosomes, and the latter as the second phase of partial melting or as an alternative, the timing of cooling and exhumation of metamorphic core complex. Crystallization of the Nova Monte Verde migmatites was therefore coeval in part with upper crustal extension and ductile flow of the mid-crust, suggesting that crustal anatexis was widespread over much of the mid-crust during Statherian time (∼1800-1760Ma). Therefore, the tectonic history of the Nova Monte Verde core complex involved regional extension and exhumation of high-grade metamorphic rocks by transtensional tectonics. The following results are at least more compatible with, if not suggestive of, a continental rift setting than the traditionally accepted continental arc setting. • Migmatites and the Statherian felsic magmatism is related to thermal perturbations in the upper mantle and mafic underplating. • Nova Monte Verde complex is a dome not related to subduction, and was exhumed during Statherian extension of rifted crust. • The crystallization, extensional deformation and exhumation of the Nova Monte Verde core-complex were coeval. • Migmatites of metamorphic core complex records a history of neosome formation spanning at least 37 Ma. [ABSTRACT FROM AUTHOR]

Abstract The Colider Group ignimbrites and rhyolites, located between Guarantã do Norte and Serra do Cachimbo, Brazil derives from a felsic magmatism with a wide spatial distribution at the Alta Floresta Gold Province (AFGP). The geological mapping and petrographic studies allow distinguishing three volcanic successions of the Colider Group at the study area, named Lower (LS), Intermediate (IS) and Upper (US). The LS characterizes by its abundance in pyroclastic density current deposits, such as ignimbrites and surge deposits, with subordinated effusive rocks. The US consists of effusive rhyolites and trachytes and, subordinately, rheomorphic ignimbrites. The magmas that generated the volcanic rocks of the LS is of a subsolvus character. The US rocks present, dominantly, a mineralogy indicating a hypersolvus character. This characteristic can be indicating a variation of the fluid pressure conditions within the magma chambers that generated this magmatism. Regarding the chemical composition of the volcanic rocks from the two successions, we can point out that both have a metaluminous to slightly peraluminous character and affinity with A2-type magmas. The zircon U-Pb LA-ICPMS isotopic data of a LS rhyolite indicate a crystallization age of 1810 ± 9 Ma, interpreted as the Lower Succession age. One of the hypotheses that may be suggested to the generation of the volcanic successions is that the petrographic, lithochemical, and geochronological contrasts indicate the occurrence of two distinct magmatic events, one of ∼1.80 Ga and another of ∼1.76 Ga. The second hypothesis is that both successions belong to the same magmatic event, which occurred from 1.81 Ga to 1.76 Ga. Highlights • Felsic volcanism of the Colíder Group in the Alta Floresta Gold Province. • Study of volcanic terranes of the Colíder Group in the light of volcanic succession principles. • Three overlapping volcanic and volcanogenic events or a wide volcanism in a complex terrane?. • Review of the geological and geotectonic evolution of the Alta Floresta Gold Province in the light of its granitogenesis. [ABSTRACT FROM AUTHOR]

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present new and compiled U–Pb zircon ages and Hf zircon and Nd constraints for rocks of the Bolivian Precambrian Shield southwestern fringe of the Amazonian Craton. The database and updated geologic information provide new insights into the Orosirian-Early Stenian evolution. This shield can be subdivided into the San Diablo and Paraguá domains considering their particular geologic histories and lithostratigraphic units: i) the southern San Diablo Domain consists mainly of amphibolite facies gneissic rocks with documented ages as old as 1940 Ma, intruded by the Correreca, Santo Corazón, Tauca, and Santa Terezita plutons with documented ages between 1874 and 1849 Ma; ii) the Paraguá Domain comprises the Lomas Maneches Granulite Complex (1820 Ma), the Chiquitania meta igneous-sedimentary complex (1750-1690 Ma), and the roughly coeval San Ignacio Schist Group (1690 Ma). Locally, the country rocks are crosscut by the Yarituses Suite (1683-1610 Ma), which is contemporary with the Lomas Maneches Granitoid Suite (1690-1660 Ma). The Pensamiento Granitoid Complex (1440-1270 Ma), constituted by syn-to late-kinematic and late-to post-kinematic granites, collectively known as San Ignacio Granitoids, is widespread in the studied region. Six zircon U–Pb datings and 76 compiled data determine that the continental crust experienced a long-lived tectonic-magmatic history, distinguished by three accretionary events: 1941–1849 Ma, 1690-1610 Ma, and 1430-1340 Ma. These events have relationships with the Proterozoic growth of Amazonia enclosing the distal Rio Apa Terrane. Later, the southern portion of the Bolivian Precambrian Shield experienced crustal shortening, magmatism, and overprints due to the Sunsás/Greenville (1200-1000 Ma) orogeny that marks the Amazonia-eastern Laurentia collage in Rodinia times. From a petrogenetic perspective, the country rocks of the San Diablo Domain yield documented Sm–Nd T DM ages and ε NdT values of ca. 1.69 to 2.29 Ga and −5.7 to +1.8 respectively, suggestive of the derivation of short-lived protoliths. The Correreca intrusion (1874–1862 Ma) gives published zircon Hf model ages of 2.68 Ga and 2.29 Ga and coupled ε HfT values of −4.6 to +2.8. The bulk isotopic signature for the San Diablo rocks is consistent with magma genesis in a moderately juvenile-like accretionary arc, where the calc-alkaline types show a subduction-related signature. In contrast, the country rocks in the adjoining Paraguá Domain show published Sm–Nd T DM model ages of ca. 1.55 to 2.48 Ga and ε NdT values of −4.9 to +5.2, pointing to distinct protoliths in the magma genesis. The Yarituses Suite includes the following granites: La Cruz (1673 ± 21 Ma), Refugio (1673 ± 25 Ma; 1641 ± 4 Ma), San Pablo (1609 ± 17 Ma), San Miguel (1681 ± 13 Ma), and Rosario (1678 ± 21 Ma). These granites yield variable Sm–Nd T DM model ages of ca. 1.67 to 2.48 Ga and ε NdT of +4.1 to −3. 8 (Ta ble 1), suggesti ng the derivation of distinct crustal components. The new and compiled data demonstrate first time that the Lomas Maneches and Yarituses suites, in conjunction with the Chiquitania complex and the newly dated Ambaybo rhyolite (1691 ± 8 Ma) of the San Ignacio Schist Group, belong to a distinct tectonic-magmatic episode akin to an active continental margin. The Pensamiento Granitoid Complex (1440-1270 Ma) shows documented Sm–Nd T DM model ages between ca. 1.55 and 2.42 Ga and predominantly crustal-like isotopic signatures as low as −4.6 typical of a continental arc setting. On a broader scale, the San Ignacio Granitoids are products of the Alto Guaporé orogeny, previously established in the Brazilian counterpart, characterized by an accretionary phase (ca. 1440 Ma) and a collisional one (ca. 1330 Ma) against the active margin of proto-Amazonia at the Ectasian. The regional structural framework of those plutons in the Bolivian counterpart suggests that the San Ramón and Coronación granodiorites (1429-1423 Ma) are pre-to syn-kinematic to the collisional phase. In contrast, the La Junta (1380 ± 17 Ma) and San Martin (1409 ± 17 Ma) granites are syn-to-late kinematic. The Diamantina granite (1357 ± 19 Ma) is coeval with the Alto Guaporé collisional phase, while the San Andrés granite (1289-1275 Ma) is a post-kinematic pluton. The ε NdT of the Pensamiento Granitoid Complex varies from +5.2 to −4.6. The onset of the Sunsás orogeny, characterized by an allochthonous collisional-type belt (1.2–1.0 Ga) ends the polycyclic evolution of the Bolivian Precambrian Shield, leading to tectonic stability of the Amazonian Craton. • The Precambrian Shield of Bolivia comprises two different domains: The San Diablo and Paraguá, each with different structural and tectonic settings. • The oldest rock in the San Diablo Domain has 1941 Ma and is metamorphosed into amphibolite metamorphic facies. The Paraguá Domain comprises the Lomas Maneches Granulite Complex of 1818 Ma and contains high-grade metamorphic rocks with granulite facies. A new unit called Yarituses Suite crops out in the Paraguá domain, comprising granites from 1683 to 1610 Ma. The San Ignacio granites from 1450 to 1275 Ma crop out in both domains, e.g., San Diablo and Paraguá. [ABSTRACT FROM AUTHOR]

Abstract 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 Paleoproterozoic times. This work presents new LA-MC-ICPMS U-Pb zircon data and geochemical analyses carried out on metavolcanic rocks of the VNGB. This information was supplemented by petrography, stratigraphic and structural data acquired through geologic mapping and boreholes descriptions. In the Vila Nova region, the VNGB units rest on the Archean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB consists of metabasalts and andesitic metabasalts, covered by an upper metasedimentary domain with subordinate metavolcanic and exhalative chemical rocks. The metavolcanic rocks include metabasalts, meta-andesites, amphibolites and amphibole schists, deformed and elongated according to the regional NW-SE structure. U-Pb zircon data yielded an age of 2154 ± 6 Ma for a meta-andesite of the lower portion of VNGB. One orogenic metamorphism followed by three deformational events were recognized. The D 1 and D 2 events formed the schistosity (S 1), preserved as intrafolial folds (F 2) and the crenulation cleavage (S 2) associated with the development of the oblique shear zones. Two distinct assemblages: 1) garnet, hornblende and biotite, and 2) hornblende, plagioclase and diopside define two distinct metamorphic peaks: M 1 and M 2 with temperatures of 450 and 650 °C, and lithostatic pressure between 4 and 6 kbar. The metabasites comprise geochemical compositions of Fe- and Mg-tholeiites with komatiitic affinity. The first group is enriched in LREE and HFSE. The second group shows MORB-like REE patterns in association with negative Nb, Ti and P anomalies. The observed features indicate that the metavolcanic rocks of the VNGB represent the evolution of back-arc basins and island arcs associated with the Trans-Amazonian Orogeny. These rocks characterize the Rhyacian evolution of the Maroni-Itacaiunas Province in the eastern portion of the Guyana Shield. Graphical abstract Image 1 Highlights • La-ICP-MS U-Pb zircon geochronology data on meta-andesite established a Rhyacian age (2,154 ± 6 Ma) for the magmatism. • The protoliths are tholeiitic basalts and andesites with geochemistry associated with an island arc-back-arc system. • E-MORB, N-MORB and plume type sources were involved in the formation of the volcanic rocks. • The volcanic rocks were affected by metamorphic events under greenschist-amphibolite and hb-px hornfels facies conditions. [ABSTRACT FROM AUTHOR]

Abstract Structural data collected in the Carajás Province region led to a new interpretation of the southeastern Amazonian Craton geotectonic evolution. The purpose of this article is to present a new evolutionary proposal for the region. A detailed analysis of the several extensional-compressional cycles that overprinted each other from the Archean to the Neoproterozoic-Cambrian is presented. At about 2.87–2.83 Ga, collisional processes led to the formation of a stable crustal substrate that supported the installation of an extensional basin at 2.76–2.70 Ga and the deposition of the Itacaiúnas Supergroup shallow marine volcanosedimentary sequences, together with contemporary bimodal plutonism. Paleoproterozoic arc magmatism in the Bacajá Domain was followed by collision with the Carajás Province between 2.09 and 2.06 Ga, resulting in expressive tectonic thickening and low to high grade regional metamorphism, and in the deposition of the Águas Claras Formation. A second Paleoproterozoic orogenic event affected the Carajás Province, which resulted in oblique tectonism and regional counterclockwise rotation of previous associations, followed by late to post-orogenic sedimentation and 1.88 Ga anorogenic alkaline A-type magmatism. The eastern Carajás Province margin was extensionally reactivated during the Neoproterozoic, in a rifting event, followed by tectonic inversion during the Ediacaran/Cambrian. Highlights • Carajás Province tectonic evolution is related to several Precambrian extensional-compressional cycles. • The province was extensively reworked in the Rhyacian (Transamazonian Orogenic Cycle) and in the Orosirian (Sereno Event). • The three main Archean-Paleoproterozoic depositional ages are late to post-tectonic to the major orogenic events. [ABSTRACT FROM AUTHOR]

Abstract U-Pb and Lu-Hf isotopic studies were performed in igneous zircon crystals from orthogneisses, metagranodiorites and a gabbro of the Tumucumaque Complex, in Vila Nova region, south of Amapá state, Brazil. The complex is located in the southeastern region of the Guyana Shield, northeastern portion of the Amazonian Craton. The Tumucumaque Complex is represented by tonalitic to granodioritic gneisses and amphibolites, with subordinate metagranites and intrusive gabbros, metamorphosed in conditions of middle to Upper Amphibolite facies. The complex represent the basement of the metavolcano-sedimentary associations of the Vila Nova and Serra do Navio regions, and occur as NW-SE elongated domes. The contact of infra- and supracrustal rocks is defined by N45°-55°W-trending high-angle ductile shear zones. In this contribution we provide U-Pb zircon ages by LA-MC-ICPMS which attest for the presence of a broad area of Archean rocks in the Guyana Shield. In addition, we present stratigraphic relationships and structural data between the Tumucumaque Complex and the Rhyacian Vila Nova Greenstone Belt. The orthogneisses yielded zircon igneous ages of 2.851 ± 37 Ma and 2.852 ± 32 Ma and the metagranodiorites of 2.822 ± 33 Ma and 2.812 ± 17 Ma. Intrusive gabbro present age of 2.671 ± 46 Ma. The Lu-Hf data suggest an enriched mantle source and reworking of Paleo-archean crustal rocks. The results obtained suggest a magmatic orogenic episode during the Meso-archean (2.85–2.81 Ga) and a later Neo-archean (2.67 Ga) event, probably anorogenic. Highlights • The geochronological results suggest a broad Archean area in the study area. • Were identified two magmatic episodes, an Meso-archean and a Neo-archean. • The Lu-Hf data suggest an enriched mantle source and reworking of Paleo-archean crustal rocks. [ABSTRACT FROM AUTHOR]

The oldest rocks of the Rio Negro Province in the Amazonian Craton, have a complex evolutionary history and little known about them. In this paper are presented field, microtextural data, amphibole and plagioclase mineral chemistry, zircon U–Pb ages, and Sm–Nd isotope composition from Içana Domain basement rocks which belong to the Rio Negro Province. The studied area of the province is located in the extreme northwestern portion of Brazil (Amazonas State). The integration of the data obtained in this study allowed to propose the tectono-metamorphic evolution of Içana Domain in the Rio Negro Province. The basement rocks comprise orthogneiss and metagranite of the Cauaburi Complex and homogeneous/heterogeneous diatexite of the Taiuaçu–Cauera diatexite. The Cauaburi Complex rocks exhibit a predominantly porphyroclastic texture and has a mafic mineralogy constituted by biotite, amphibole, sphene, epidote, and allanite. On the other hand, Taiuaçu–Cauera diatexite varies from inequigranular to porphyroclastic, being constituted by biotite, muscovite, allanite, and epidote. Basement rocks of the Içana Domain record three tectonic–metamorphic events, which were associated to regional events. The M 1 /D 1 event was marked by the syn-tectonic emplacement of the Cauaburi Complex protolith rocks (1813 ± 19 Ma), and also by crystallization (1821 ± 14 Ma) and migmatization (1788 ± 11 Ma) of the Taiuaçu-Cauera diatexites in an orogenic event. The M 2 /D 2 event reached high temperatures, similar to the M 1 /D 1 event and was related to emplacement of S–type granites in the Içana Domain basement during the Içana Orogeny (ca. 1520 Ma). Furthermore, the lower temperature of the M 3 /D 3 event was related to intracontinental reworking of the K'Mudku event (ca. 1200 Ma). The Cauaburi Complex basement rocks shows epsilon Nd (t) values range from +1.53 to +0.13, which allow the identification of a crustal contribution to the magma source (likely Orosirian sialic crust). Geochemistry data indicate that these rocks have been generated from partial melting of amphibolitic rocks, and also with an important crustal component related to magmatic arc settings. All igneous (1967 ± 25 Ma) and metamorphic (1911 ± 15 Ma) zircons grains within the Cauaburi Complex basement rocks are compatible with those found in Tapajós-Parima/Ventuari–Tapajós Province, reinforcing the crustal contribution hypothesis. Geochemistry and mineralogical data indicate that Taiuaçu-Cauera diatexite was likely formed by the partial melting of the metagraywacke. Two age populations (1993 ± 33 and 1842 ± 9 Ma) from detrital zircon of the homogeneous diatexite, suggest that the sediments were derived from different rocks of the Tapajós-Parima/Ventuari–Tapajós Province. The age of the Taiuaçu-Cauera diatexite is probably between 1842 ± 9 Ma (youngest detrital zircon) and 1788 ± 11 Ma (anatectic zircon). The youngest detrital zircon (1842 ± 9 Ma) and anatectic zircons (1788 ± 11 Ma), indicates that the protolith of Taiuaçu-Cauera diatexite is not a part of the Tunuí basin (Tunuí Group). [ABSTRACT FROM AUTHOR]

The Apiaú Alkaline Complex (AAC) represents a rift-related intracontinental magmatism and occurs as intrusions within the Precambrian basement of the central-southern portion of the Guyana Shield, Amazonian Craton. The complex extends for over 200 km and comprises monzonites, syenites, nepheline syenites, nepheline-bearing syenites, trachytes and phonolites. It differs from other alkaline rocks of the craton both in age and tectonic setting. Here we report new petrologic, geochemical, and zircon and baddeleyite U-Pb geochronological information on the nepheline-bearing syenites and phonolites to discuss the petrogenetic and tectonic evolution of the AAC. Our new bulk rock major and trace elements analyses show that the complex is predominantly miaskitic, with potassic and sodic affinity, strong enrichment in light REE and negative Eu, Ba, Sr, P, and Ti anomalies. The phonolites and syenites geochemistry suggests similar fractionation processes from closely related parental melts for their genesis. Zircon and baddeleyite U-Pb crystallization ages of 111 ± 1 Ma and 116 ± 3, respectively, indicate a relationship between the alkaline magmatism and the opening of the Equatorial Atlantic Ocean. The spatial disposition of the alkaline rocks following major faults of the Amazonian Craton denotes a structurally controlled emplacement history by reactivation of ancient weakness zones. Crystallization ages are coincident with the Tacutu basin filling, evidencing a relative tectonic stability period and suggesting that the progressive subsidence contributed to the reactivation of the main structures in the region. The presence of inherited zircon from the orthoderived granitic basement (U-Pb ages of 1931 ± 4 Ma and 1958 ± 7 Ma) in a nepheline-bearing syenite, addition to petrography features and geochemical behaviour indicate that the alkaline magma was contaminated with Precambrian crustal rocks. [ABSTRACT FROM AUTHOR]

The granitic rocks of the Erepecuru-Trombetas Domain, southeastern Guyana Shield, are part of two extensive volcano-plutonic associations that marked the central portion of the Amazonian Craton during the Orosirian. The older episode (2.0–1.97 Ga) encompasses the Igarapé Paboca volcanic Formation and Caxipacoré Suite and the younger episode (1.90–1.87 Ga) comprises the Água Branca and Mapuera plutonic suites and the pyroclastic/effusive rocks of the Iricoumé Group. LA-ICP-MS U-Pb zircon dating of granitoids provided ages of 1991 ± 5.9 and 1989 ± 7 Ma for the Caxipacoré Suite, 1887.5 ± 4.8 Ma for the Água Branca Suite and 1881 ± 8.1 Ma for the Mapuera Suite, which reinforce the occurrence of two Orosirian magmatic episodes in the southeastern Guyana Shield. The geochemical characteristics of the Caxipacoré granitoids suggest that they formed in an orogenic tectonic setting, related to a subduction environment, while the geochemical signatures of the Água Branca and Mapuera granitoids betray the evolution from a convergent context to an extensional intracontinental environment. Nd-T DM (2.19–2.22 Ga) and Sr-T UR (1.95–1.96 Ga) model ages and slightly positive ε Nd (+0.26 to +0.66) for the Caxipacoré granitoids point to an origin from melting of mantle-derived magmas with participation of Rhyacian sialic crust. The Água Branca and Mapuera granitoids display Nd-T DM (1.95–2.30 Ga) and Sr-T UR (1.84–2.02 Ga) model ages and positive to negative ε Nd (+2.92 to −1.96) that indicate parental magmas derived from melting of dominantly Rhyacian crustal sources with minor mantle contribution. In addition, the Nd signature and the lack of Archean inherited zircon in the plutonic rocks do not favor the existence of an Archean basement in this part of the southern Guyana Shield. This assumption together with similarities with the adjacent Uatumã-Anauá Orosirian Domain, westward, led to suggest that the Erepecuru-Trombetas Domain should not be longer interpreted as belonging to the Central Amazon Province, as defined in the current geotectonic models of the Amazonian Craton. [ABSTRACT FROM AUTHOR]

The basic rocks of the Salto do Céu Suite outcrop as sills and flows in the southwestern Amazon Craton, Rondonian-San Ignacio Province, with an age of about 1.44 Ga. Sills are 2 to 30 m thick being hosted by pelites of the Aguapei Group. The flows are up to 5 m thick and cover this unit. Typical textures of magma mingling are observed near the contact with granites of Rio Branco Suite. The Rio Branco Intrusive Suite is composed of basic and acid rocks, as well as hybrid rocks that indicate mixing processes between basic and acids magmas. U-Pb (TIMS zircon) results indicate ages around 1.4 Ga for both terms. The Salto do Céu Suite rocks have tholeiites affinity classified as subalkaline and iron-rich tholeiitic basalts, with mg# values between 0.30 and 0.51. They can be separated into two groups, based on LaN; one is richer in ETR with LaN greater than 100, while the other one has LaN less than 100. Rocks of the Salto do Céu Suite and Rio Branco Suite are interpreted as a bimodal suites showing magma mingling features such as those developed in continental intraplate settings, extensional regime associated to the Columbia/Nuna breakup. [ABSTRACT FROM AUTHOR]

Zircons of rare metal specialized granites from five large Brazilian tin provinces were compared morphologically and chemically through backscattered electron images and X-ray dispersive spectroscopy (SEM-EDS) in terms of Hf, Zr/Hf and Hf + Y + Th + U contents. Zircon crystals from the mineralized, evolved hydrothermalized rocks are fine-grained, anhedral, corroded and show little or no obvious zoning. They exhibit high Hf and Hf + Y + Th + U contents and low Zr/Hf values (generally <15) compared to those from less evolved unmineralized granites. Electron microprobe and LA-ICP-MS analyses of zircons from tin-mineralized and barren granites identified similar geochemical trends to those obtained by semiquantitative SEM-EDS. The Geochemical signature of zircon can be used as a prospective guide for specialized granites and zircon SEM-EDS analyses are a reliable tool in preliminary prospecting for this type of mineralization. [ABSTRACT FROM AUTHOR]