Search

The paper presents results of the first geochronologic study (LA-ICP-MS zircon method) of metasedimentary rocks that host the banded iron formation (BIF) and the metarhyolites (halleflinta) of the Gimoly Group in the Kostimuksha greenstone belt,Karelian Craton. Felsic magmatism that produced the rhyolite sills and dikes was dated at 2759 ± 19–2743 ± 15 Ma. The clearly predominant group of zircons in the schists (metagraywacke) has an isotope age of 2753 ±19 Ma, and scarce zircon grains of these rocks vary in age from 3.1 to 2.8 Ga. Geochemically, zircons from metarhyolites fall into three types (1) Eu-depleted and Ce-enriched, (2) Eu- and Ce-enriched, and (3) LREE- and MREE-enriched. The zircons of geochemical types (1) and (2) are also predominant in the sediments. The morphology and structure of zircon crystals in the rhyolites and sediments are also identical. The rhyolites were thus a major source of zircons for the metagraywacke, which alternates with BIF, while the Mesoarchean rocks played a subordinate role. The BIF of the Gimoly Group in the Kostomuksha Greenstone Belt was formed simultaneously with felsic volcanism at 2760–2740 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • Garnet-hosted xenotime and gold are dated at ca. 1827 Ma • Early gold veins are metamorphosed to amphibolite facies (505–689 °C) • New ages for gold mineralization also post-date metamorphism by up to 80 Myr • Post-orogenic gold mineralization is coeval with biotite cooling ages (ca. 1746 Ma) • Exhumation of the Trans-Hudson orogen triggered gold mineralization Metamorphic devolatilization is thought to be the critical process that can liberate gold from amphibolite facies source rocks to form orogenic gold deposits. However, a growing number of studies demonstrate that orogenic gold deposits are the product of multiple hydrothermal stages over 10 s to 100 s of Myr rather than one metallogenic event. Herein we report new geochronology results for orogenic gold deposits hosted within the Paleoproterozoic Lynn Lake greenstone belt (Manitoba, Canada) to address the knowledge gap. Garnet-hosted xenotime crystals, which occur in a folded pyrite veinlet with gold, yield a weighted average 207Pb/206Pb date at 1827 ± 8 Ma. This new and more precise age demonstrates that the earliest auriferous fluids at the MacLellan gold deposit coincided with the rapid burial of ca. 1836 Ma sedimentary rocks before regional metamorphism. New garnet-biotite geothermometry results further demonstrate that the earliest auriferous veins were preserved despite being metamorphosed to amphibolite facies conditions (505–689 °C). The peak metamorphic mineral assemblage is overprinted by: (1) the main xenotime- and gold-bearing deformation fabric (S 2 ; 1790–1827 Ma); (2) an overprinting xenotime- and monazite-bearing S 3 fabric that is also associated with gold-rich arsenopyrite (1769–1790 Ma); and (3) chlorite-hosted xenotime and gold (1747 ± 12 Ma) that are coeval with the oldest U-Pb apatite dates (1691–1740 Ma) and a prominent mode of 40Ar/39Ar biotite dates at ca. 1746 Ma. We suggest that the post-orogenic gold events are incompatible with the standard devolatilization model because they post-date subduction and peak-metamorphism by up to 80 Myr. Instead, the new geochronological results suggest that gold deposition at the MacLellan deposit was linked to burial and the subsequent exhumation of chemically reactive trap rocks through favourable temperature windows that allowed gold transport as sulphide complexes. Exhumation and far-field tectonics are interpreted as the most likely drivers of post-orogenic auriferous fluids rather than regional metamorphism and active subduction. This revised mineral systems model provides an explanation for the high prospectivity of high- and low-temperature mineral assemblages and suggests that mineral exploration should focus on the earliest ore-forming structures that are reactivated during multiple stages of orogenesis. [ABSTRACT FROM AUTHOR]

• Geochronological data suggested deposition maximum age for the Algodão Formation of 1958 ± 18 Ma. • The youngest zircon was dated as 894 ± 38 Ma in the Serra da Garapa Formation. • Zircon ages in the Santo Onofre Group were similar to glacial units of the Macaúbas Group. The evolutionary history of the Paramirim Aulacogen is characterized by the superposition of rifts that developed from 1770 to 675 Ma. In the Northern Serra do Espinhaço Fold Thrust Belt, two units of this aulacogen were analyzed in the present study: the Algodão Formation (Espinhaço Supergroup) and the Santo Onofre Group (São Francisco Supergroup). In the study area, the Algodão Formation consists of alternating of quartzose to feldspathic metasandstones, sericitic metasandstones, oligomictic metaconglomerates, metasandstones and quartzites, laminated metapelites, metarhythmites and metasiltites, and quartzites. In turn, the Santo Onofre Group, the Serra da Garapa Formation was subdivided into two lithofacies associations. The first is composed predominantly by quartzites and hematite-rich, graphite-rich and/or manganese-rich metapelites and phyllites. The second lithofacies association comprises staurolite-garnet-quartz-biotite aluminous schist and quartzites. In the Boqueirão Formation predominates metasubarkoses and lithic metasandstones and metasiltites, besides oligomictic metamicroconglomerates. U-Pb geochronological studies (LA-ICPMS) were performed on detrital zircons from these units. Ages ranging were 2870 ± 17–1958 ± 18 Ma and 3177 ± 42–894 ± 38 Ma, respectively. The main primary sources were related to rocks from the basement of the Western Bahia orogeny, of siderian-orosirian age, as well as volcanites and plutonites, both mafic and felsic, with ages between ca. 1.7 and 0.8 Ga, related to the evolution of the precursor basins of the Araçuaí-West Congo Orogen. As secondary sources, results suggest Metavolcanosedimentary sequences and Greenstone Belts of Archean and Paleoproterozoic ages, as well as rocks from the Espinhaço Supergroup and Macaúbas Group. The lithofacies of Serra da Garapa formation, as well as the ages found in detrital zircons, suggest that this formation is chronocorrelate with Rio Peixe Bravo Formation of the Macaúbas Group. Together, these formations, and Matão and Duas Barras Formation represent the pre-glacial unit of the Santo Onofre-Macaúbas basin initiated in Tonian. Some characteristics suggest that the Boqueirão Formation may be correlated to some of the glacial units of this basin. This work suggests that the formations Fazendinha and Serra da Vereda are excluded from the Santo Onofre Group. [ABSTRACT FROM AUTHOR]

• New geotectonic model of crust formation and evolution from ∼2.35–2.15 Ga. • Three principal stratigraphic sequences can be distinguished in the study area. • Eight new age constraints including the oldest supracrustal Birimian age at 2.35 Ga. • Physical, geochemical and geochronological data reconstructs evolution of arc. This study reconstructs the evolution of one of the oldest Paleoproterozoic arcs, which formed shortly after a period of momentous change when the Earth transitioned out of the Archean. We present new stratigraphic, geochemical and geochronological data of the Toumodi Greenstone Belt (Ivory Coast, West Africa) integrated with local and regional data to better constrain its construction and evolution. The belt consists of four main stratigraphic events: [1] A ca. 2345 Ma tholeiitic sequence formed on the sea floor far from any landmass. This juvenile crust is the oldest Birimian supracrustal sequence known and represents either a dismembered oceanic plateau or ridge basalt; [2] Nascent arc formation (ca. 2220–2160 Ma) developed initially in a subaqueous environment and transitions into emergent volcanic centres. Near Toumodi, most deposits consist of volcaniclastic debris emplaced in subaerial to shallow-water environments, but also include minor pyroclastic vent-proximal deposits. Magmas for this event are mainly basaltic andesite to andesite and are enriched in LILE and have negative Nb, Ta and Ti signatures, all of which are consistent with water-fluxed melting typical of arc magmatism. Inherited zircons and mafic xenocrysts/xenoliths together reflect the older history and nature of underlying mid- to lower-crustal rocks, [3] An intra-arc rifting-event marked by a unconformity between events 2 and 4 the correlation with pillowed tholeiitic basalts; and [4] Construction of a mature arc (ca. 2150–2100 Ma) that consists of emergent dacitic volcanic centres and more distal volcaniclastic sediments, and overlain by post-magmatic sedimentation and red-bed formation (ca. 2100–2050 Ma). Magmas for this time period are dominantly dacitic and also display geochemical characteristics of arc magmatism, but also contain high-K, indicative of melting in a thickened volcanic arc. [ABSTRACT FROM AUTHOR]

The Red Lake greenstone belt is situated in northwestern Ontario within the Uchi Subprovince, Superior Province. Most gold deposits therein are associated with major deformation corridors; the east-west oriented 'Mine trend' hosts most of the large deposits and the northeast-southwest 'East Bay trend' hosts several small deposits and showings. Gold along the East Bay trend typically occurs in quartz replacement veins that were emplaced into pre-existing quartz-carbonate veins. Gold can occur as free gold or along vein margins associated with pyrite and pyrrhotite. Most primary fluid inclusions, preserved in relatively undeformed portions of veins, are carbonaceous with lesser quantities of aqueous inclusions. The average homogenization temperature of aqueous fluids is ~250 °C; however, the abundance of three-phase inclusions, variation in liquid-vapor ratios, and a wide range in homogenization temperatures indicate that immiscibility, effervescence, and fluid mixing are mechanisms associated with gold deposition. The age (~2550 Ma) of alteration minerals in the Abino area is considerably younger (by ~100 Myr) than alteration minerals in other deposits in the Red Lake district, indicating that the mineralizing fluid history was more protracted than previously thought. Along the East Bay trend, barren veins generally have lower δO values (0.0 to 8.5‰) relative to auriferous veins (9.6 and 13.1‰). Consequently, the oxygen isotopic composition of quartz could be used as a vector for gold mineralization. The genetic model for the East Bay trend involves several stages of vein formation. Auriferous veins formed near the upper boundary of the mesozonal regime (depth of ~5-6 km). [ABSTRACT FROM AUTHOR]

[Display omitted] • Granitoids of Chitradurga belt were emplaced at ∼ 3.2 Ga, ∼3.0 Ga and ∼ 2.6 Ga. • Two metamorphic events are documented at ∼ 3.0 Ga and ∼ 2.56 Ga. • Nd isotopes infer juvenile crustal addition at 3.2 Ga, reworking at 3.0 Ga and 2.6 Ga. • Role of convergent margin tectonics in the evolution of Chitradurga granitoids. The Chitradurga Greenstone Belt is one of the largest belts in the central part of the Western Dharwar Craton (WDC). We present new SHRIMP U-Pb zircon and titanite ages, whole-rock geochemical and Sm-Nd isotopic data for granitoids that developed at both its eastern and western margins, and for those that are intrusive into the belt. Western margin TTG samples yield emplacement ages ofca. 3.21 Ga and are of the high-Al TTG type characterized by weakly negative ɛNd t values. Eastern margin granite samples yield emplacement ages of ∼ 3.0 Ga and 2.56 Ga with negative ɛNd t values. The granites intrusive into the belt are of Neoarchean age (∼2.61 Ga) with more-evolved Nd isotopic signatures consistent with the involvement of older crustal material. Metamorphic events are documented at ca. 3.0 Ga and ca. 2.5 Ga. The ca. 3.0 Ga event is synchronous with the diapiric emplacement of trondhjemites and high-K granitic plutons in the WDC. The peak metamorphic event at ∼ 2.5 Ga is the major tectono-thermal event evident throughout the Dharwar Craton. Geochemical systematics imply the involvement of convergent margin tectonics in the evolution of studied granitoids. The role of horizontal tectonics in the crustal growth of WDC is evident from at least 3.2 Ga, whereas signatures for the reworking of the older crust are more prominent from ∼ 3.0 Ga. [ABSTRACT FROM AUTHOR]

The Maevatanana greenstone belt in north-central Madagascar contains widespread exposures of tonalite-trondhjemite-granodiorite (TTG) gneisses, and is important for its concentrations of various metal deposits (e.g., chromium, nickle, iron, gold). In this paper we report on the petrography, and major and trace element compositions of the TTG gneisses within the Berere Complex of the Maevatanana area, as well as LA-ICP-MS U-Pb ages and Lu-Hf isotopic compositions of zircons from the gneisses. The gneisses consist mainly of granitoid gneiss and biotite (± hornblende) plagiogneiss, and analysis of thin sections provides evidence of crushing, recrystallization, and metasomatism related to dynamic metamorphism. Samples have large variations in their major and trace element contents, with SiO2 = 55.87-68.06 wt%, Al2O3 = 13.9-17.8 wt%, and Na2O/K2O = 0.97-2.13. Geochemically, the granitoid gneisses and biotite plagiogneisses fall on a low-Al trondhjemite to granodiorite trend, while the biotite-hornblende plagiogneisses represent a high-Al tonalite TTG assemblage. Zircon U-Pb dating shows that the Berere Complex TTG gneisses formed at 2.5-2.4 Ga. Most ∊Hf(t) values of zircons from the biotite (± hornblende) plagiogneisses are positive, while most ∊Hf(t) values from the granitoid gneisses are negative, suggesting a degree of crustal contamination. Two-stage Hf model ages suggest that the age of the protolith of the TTG gneisses was ca. 3.4-2.6 Ga, representing a period of paleocontinent formation in the Mesoarchean. Geothermometries indicate the temperature of metamorphism of the TTG gneisses was 522-612°C. Based on these data, the protolith of the TTG gneisses is inferred to have formed during the development of a Mesoarchean paleocontinent that is now widely exposed as a TTG gneiss belt (mostly lower amphibolite facies) in the Maevatanana area, and which records a geological evolution related to the subduction of an ancient oceanic crust and the collision of microcontinents during the formation of the Rodinia supercontinent. The lithological similarity of Precambrian basement, the close ages of metamorphism within greenstone belts and the comparable distribution of metamorphic grade all show a pronounced Precambrian geology similarity between Madagascar and India, which can provide significative clues in understanding the possible Precambrian Supercontinent tectonics, and also important constraints on the correlation of the two continental fragments. [ABSTRACT FROM AUTHOR]

The eastern margin of the Zimbabwe Craton, along the Mozambique-Zimbabwe border, includes the oldest rocks of west-central Mozambique constituting a large terrain of granite-greenstone type dated between 3000 and 2500 Ma. These rocks consist mainly of gneisses and granitoid rocks of tonalitic-trondhjemitic-granodioritic composition belonging to the Mudzi Metamorphic Complex in the northern part and to the Mavonde Complex in the southern part. The latter is associated with a granite-greenstone terrain, which includes the eastern part of Mutare-Odzi-Manica greenstone belt. A volcano-sedimentary sequences cover, belonging to the apparently Mesoproterozoic and Paleoproterozoic Umkondo and Gairezi groups respectively was deposited along the eastern margin of the craton and is exposed in the territory of Mozambique. The Umkondo minimum age is marked by intrusive dolerite in Zimbabwe dated at 1100 Ma while for the Ghairezi it is still not well established. The Gairezi Group was subjected to progressive metamorphism of Pan-African age. At the margin of the Zimbabwe Craton, in its northern part, metasedimentary units occur representing a passive margin of Neoproterozoic age. They make up the Rushinga Group, which includes felsic metavolcanic rocks dated at ca .800 Ma. Granulites and medium- to high-grade paragneisses, and migmatites of the Chimoio, Macossa and Mungari Groups of Neoproterozoic metamorphic age, overly the ortho-metamorphic pre-existing rock of ca . 1100 Ma, which belongs to the Báruè Magmatic Arc. They characterize the N-S trend Mozambique Belt, which appears to the east of the craton tectonically juxtaposed on the Archean rocks. The maximum age of deposition of these rocks, indicated by U-Pb dating of detrital zircons, is ca . 700 Ma and their minimum age is limited by a few monzonitic Cambrian intrusions dated at ca. 500 Ma. The Neoproterozoic bimodal Guro Suite, dated at ca . 850 Ma and composed of felsic and mafic members characterizes the east-dipping outer rim of the craton margin in the north. The felsic member comprises the Serra Banguatere aplitic granite gneiss-migmatite and the mafic member consists of the Magasso metagabbro and mafic gneiss-migmatite. The geochemical signature and bimodality are all characteristics of anorogenic, A-type granites. The tectono-thermal effects of the Pan-African orogenic event, of approximately 500 Ma, are visible along the margin of the Zimbabwe Craton. Deformation and metamorphism are progressive from the craton towards the belt, from greenschist facies to granulite facies. The main suture in the study area shall be placed along the frontal thrusts of the Mungari and Macossa/Chimoio nappes of Neoproterozoic to Cambrian age. To the west of the suture the rejuvenated margin of the craton occurs, indicated by K-Ar dating. To the east, the Mozambique Belt occurs with its paragneisses of the Neoproterozoic overlaying the Mesoproterozoic granitoids of the Báruè magmatic arc. [ABSTRACT FROM AUTHOR]

The Plutonic Well Greenstone Belt (PWGB) is located in the Marymia Inlier between the Yilgarn and Pilbara cratons in Western Australia, and hosts a series of major Au deposits. The main episode of Au mineralisation in the PWGB was previously interpreted to have either accompanied, or shortly followed, peak metamorphism in the late Archean atca2650 Ma with a later, minor, event associated with the Capricorn Orogeny. Here we present new Pb isotope model ages for sulfides and Rb–Sr ages for mica, as well as a new207Pb–206Pb age for titanite for samples from the Plutonic Gold Mine (Plutonic) at the southern end of the PWGB. The majority of the sulfides record Proterozoic Pb isotope model ages (2300–2100 Ma), constraining a significant Au mineralising event at Plutonic that occurred >300 Myr later than previously thought. A Rb–Sr age of 2296 ± 99 Ma from muscovite in an Au-bearing sample records resetting or closure of the Rb–Sr system in muscovite at about the same time. A younger Rb–Sr age of 1779 ± 46 Ma from biotite from the same sample may record further cooling, or resetting during a late-stage episode of metasomatism in the PWGB. This could have been associated with the 1820–1770 Ma Capricorn Orogeny, or a late-stage hydrothermal event potentially constrained by a new207Pb–206Pb age of 1725 ± 26 Ma for titanite in a chlorite–carbonate vein. This titanite age correlates with a pre-existing age for a metasomatic event dated at 1719 ± 14 Ma by U–Pb ages of zircon overgrowths in a sample from the Marymia Deposit. Based on the Pb-isotope data presented here, Au mineralising events in the PWGB are inferred to have occurred atca2630, 2300–2100 Ma, during the Glenburgh and Capricorn orogenies, and 1730–1660 Ma. The 2300–2100 Ma event, which appears to have been significant based on the amount of sulfide of this age, correlates with the inferred age for rifting of the Marymia Inlier from the northern margin of the Yilgarn Craton. The texturally-later visible Au may have been deposited during the Glenburgh and Capricorn orogenies. [ABSTRACT FROM PUBLISHER]

Archean granitic domes and intervening volcano-sedimentary basins are commonly interpreted as the product of “sagduction”, a process involving the gravitational sinking of surficial greenstone cover sequences into narrow belts and the coeval exhumation of deeper granitic crust into broad domes. Alternatives to the sagduction model that can account for the regional dome and basin pattern include fold interferences and extensional metamorphic core complexes. In order to provide quantitative constraints on the pressure–temperature–time (P–T–t) evolution experienced by greenstone–granite pairs we investigate the Warrawoona greenstone belt and adjacent Mount Edgar granitoid dome the East Pilbara craton (Western Australia). We adopt a multidisciplinary approach that includes structural, metamorphic, geochronological and numerical investigation of the 3.5–3.2 Ga Mount Edgar high-grade metamorphic rocks. Garnet-bearing metasediments and metabasalts collected along the SW and SE rims of the Mount Edgar Dome show higher pressure but lower temperature of equilibration (9–11 kbar and 450–550 °C) than enclaves collected in the core of the dome (6–7 kbar and 650–750 °C). In situ oxygen isotope analysis and U–Pb dating of zircons from the enclave indicate a metasedimentary origin ( ) for the protoliths and a metamorphic age of . In addition, monazites included in garnet from the SW dome margin yield an age of . These monazites suggest the existence of an older metamorphic cycle and imply a polymetamorphic evolution of the unit. The P–T–t data support fast, gravity-driven tectonics, wherein sedimentary rocks were buried to lower crustal conditions, metamorphosed and exhumed back to the surface during a cycle lasting only a few million years. Forward thermo-mechanical modeling confirms the P–T–t evolutions deduced from thermobarometry and geochronology. Our model shows a large range of possible apparent geothermal gradients during sagduction, including low apparent geothermal gradients that are similar to those proposed for Archean and modern subduction. [ABSTRACT FROM AUTHOR]

The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous part of the Tocantins Province, a large Brasiliano/Pan-African orogen of the South American Platform formed during the Brasiliano orogeny. The terrane amalgamated to the province during the late stages of the orogeny as a crustal segment consisting of six Archean orthogneiss complexes and five low-grade metamorphic, in part Paleoproterozoic (Rhyacian) greenstone belts. The Uvá complex is the southernmost orthogneiss association of the Archean-Paleoproterozoic terrane of central Brazil. New U–Pb LA-ICP-MS data from zircon crystals show that the complex formed at least during two magmatic stages. The older consists of polydeformed tonalite and granodiorite batholitic and diorite stock protoliths with igneous age of 3040 Ma to 2930 Ma. The youngest comprises tonalite, monzogranite and granodiorite tabular bodies formed between 2876 and 2846 Ma. As compared to the orthogneisses of the northern portion of the terrane, both the oldest and youngest granitogenesis stages of the Uvá complex are, in average, about 150 Ma older. This suggests that the northern and southern orthogneisses formed during different times as independent crustal segments, but when and why they amalgamated is still under investigation. [ABSTRACT FROM AUTHOR]

Abstract: The ∼3Ga North Caribou greenstone belt comprises a package of volcanic and sedimentary rocks metamorphosed from greenschist to upper amphibolite grade, surrounded by ∼2.7–3.0Ga granitoids and gneisses and is host to the Musselwhite gold mine, a large orogenic gold deposit. New U–Pb (zircon, monazite), Ar–Ar (biotite) and Sm–Nd (garnet) ages for volcanic, sedimentary and intrusive rocks from the Musselwhite mine and surrounding plutons have been obtained. Felsic volcanic rocks yielded ages of 2972.4±1.6 and 2982.4±0.8Ma, broadly consistent with existing ages for volcanic rocks and plutonism. An age of 2857.3±1.4Ma for the Schade Lake gneiss is consistent with published plutonic and volcanic ages. A younger, and previously unrecognized, plutonic event is represented by three granites dated at 2723.1±0.8, 2727.7±1.0 and 2729.4±7.1Ma. An Sm–Nd age of 2690±9Ma for garnets associated with gold mineralization is bracketed by peraluminous granites with ages of 2668.8±1.1 and 2715.8±1.6Ma. Ar–Ar ages range from 2420±11.97 to 2658±13.46Ma, broadly synchronous with the youngest intrusive age, and are consistent with progressive resetting due to metamorphism. The new geochronological data for the NCGB show that volcanism in the Opapimiskan Lake area spanned 10 million years from 2982.4 to 2972.4Ma, allow for new stratigraphic interpretations of the belt and are broadly correlative with other greenstone belts in the North Caribou terrane. The new data for the NCGB and associated plutons are consistent with ∼3Ga plume-related activity forming a proto-craton that was the site of successive sedimentary basins over the next ∼150 million years. Subsequent plutonism is consistent with supra-subduction zone processes at the margins of this proto-continent by ∼2.87Ga and is best interpreted as the result of horizontal tectonic processes consistent with those operating in the Phanerozoic, with the plutons emplaced behind continental margin arcs on the edges of the craton. Sm–Nd ages of garnets that are coeval with mineralization suggest that the orogenic gold mineralization at the Musselwhite mine was broadly synchronous with the ∼2700Ma orogeny caused by the collision of the Oxford-Stull domain with the North Caribou terrane ∼75km northeast of the Musselwhite mine and furthermore argues that S-type granites may play a greater role in the formation of some orogenic gold deposits than has been previously recognized. [Copyright &y& Elsevier]

Abstract: Gold mineralization in the Mesoarchaean New Consort gold mine in the Barberton greenstone belt, South Africa, is situated in the immediate hanging wall of an exhumed, composite granitoid gneiss dome known as the Stentor Pluton. The granitoid-greenstone contact is characterized by a contact-parallel high-strain zone that separates the mid-crustal gneisses from the greenschist facies greenstone belt. In contrast to the lower greenschist facies deposits in the central parts of the greenstone belt, the mineralized shear zones at New Consort are hosted by distinctly higher grade metamorphic rocks, ranging from upper greenschist to upper amphibolite facies conditions. A distinct change of ore and alteration assemblages with increasing metamorphic grade points to a temporal and spatial relationship between gold mineralization and the juxtaposition of the Stentor gneiss dome against the overlying greenstone belt. Examination of the structural and petrologic evolution of the mineralized high-strain zone, combined with new U–Pb and Ar–Ar data and previously published ages, indicates a multistage tectono-metamorphic evolution. Early high-T, medium-P metamorphism (ca. 600–700°C and 5±1kbar) in the structurally deeper parts of the mine is interpreted to be related to an early period of orogen-parallel (NE–SW) extension and associated detachment shearing during the main (D2) accretionary event in the centre of the greenstone belt, between ca. 3260 and 3225Ma. Recent work has shown that these early high-T fabrics were reactivated at ca. 3105Ma during the subsequent D3 tectonism and associated emplacement of large potassic granite batholiths. The gold mineralization was coeval with NE–SW extensional exhumation and solid-state doming of the Stentor gneiss dome during the subsequent D4 deformation. This late-stage deformation and the gold mineralization postdate the emplacement of the D3-related potassic granites by more than 50 million years, as indicated by (1) a U–Pb age of 3046±27Ma for a retrograde titanite generation in a D2-related amphibolite (sample 113), and (2) a 3027±7.5Ma age for hydrothermal titanite from the so-called footwall lens mineralization, which temperature has been estimated at 590±40°C. This high-T event is also recorded by a “corrected” 3040±4Ma hornblende Ar–Ar age from the same sample, suggesting that cooling of the Stentor gneiss dome shortly followed the exhumation. A considerably younger Ar–Ar age (2966±4Ma) has been obtained for an amphibolite from the contact-parallel high-strain zone, pointing to non-uniform cooling following the mineralization. The gold mineralization was largely contemporaneous with the emplacement of NNW trending, syn-kinematic granitic pegmatites and strain localization along the pegmatite swarm at ca. 3030–3040Ma. The mineralization is also considerably younger than the gold mineralization in the greenschist facies gold deposits in the Barberton greenstone belt, which has previously been dated at ca. 3080Ma. In conjunction with previously published ages, the data indicate the Au mineralization in the Barberton greenstone belt to have occurred during, at least, two mineralization episodes at ca. 3080 and 3040Ma. The main phase of Au mineralization was introduced during the end of an either protracted or episodic structural and thermal evolution of the granitoid-greenstone terrain that may have lasted some 200Ma. [Copyright &y& Elsevier]

Abstract: The Serrinha magmatic suite (Mineiro belt) crops out in the southern edge of the São Francisco craton, comprising the Brito quartz-diorite, Brumado de Cima and Brumado de Baixo granodiorites, granophyres and felsic sub-volcanic and volcanic rocks, part of which intruded into the Nazareno greenstone belt. The suite rocks have petrographic features that are consistent with magma supercooling due to the low water content combined with volatile loss, leading to crystallization of quartz and alkaline feldspar at the rims of plagioclase phenocrysts (granophyric intergrowth). The investigated rocks are sub-alkaline, calc-alkaline and show low content in rare earth elements. The U–Pb zircon crystallization ages for the Brumado de Cima granodiorite [2227±22 (23) Ma] and a coeval granophyre [2211±22 (23) Ma], coupled with available single-zircon Pb evaporation ages for the Brito and Brumado de Baixo plutons, are significantly older than the “Minas orogeny” (ca. 2100–2050Ga) of Quadrilátero Ferrífero area, eastward from the Serrinha suite. Our data establish an early Rhyacian event tectonically linked with the evolution of the Mineiro belt. The bulk Nd isotopic signature [low negative to positive ε Nd( t ) values] of the Serrinha samples are consistent with the important role of Paleoproterozoic mantle components in the magma genesis. The integrated geologic, geochemical and isotopic information suggests that Paleoproterozoic evolution of the Mineiro belt initiated in a passive continental margin basin with deposition of the Minas Supergroup at ca. 2500Ma. This stage was succeeded by outboard rupture of the oceanic lithosphere with development and coalescence of progressively younger magmatic arcs during Rhyacian time. One of the earliest arcs formed the Serrinha suite. The tectonic collage of the Serrinha and Ritápolis (2190–2120Ma) arcs produced the NE–SW Lenheiro shear zone, resulting in mylonitization and recrystallization of both the granitoid intrusions and host rocks. As a matter of fact juxtaposition of distinct magmatic units in age and origin took place along the Lenheiros structure in this sector of the Mineiro belt. [Copyright &y& Elsevier]

Abstract: The Archean Bird River greenstone belt (BRGB) is located on the southwestern edge of the Superior Province between the 3.2Ga old Winnipeg River subprovince to the south and the metasedimentary belt of the English River subprovince (ERSP) to the north. This position between two major subprovinces makes the BRGB a primary target for investigating the geodynamic and kinematic evolution of a major structural boundary. New structural and geochronological data have allowed us to present an evolutionary framework for the southern boundary of the North Caribou superterrane. The BRGB underwent 3 main deformation phases. The D1 event took place ca. 2698Ma and displays a north-side-up shearing. The D2 event, occurring at ca. 2684Ma in a transpressive context, presents a complex structural pattern mixing vertical tectonics in the BRGB and strike-slip tectonics along the boundaries of the greenstone belt with other subprovinces. Between the BRGB and the ERSP, the 2832–2858Ma old Maskwa batholith acted as a rigid passive block during the collision and marks the boundary between pure dextral strike-slip tectonics along his northern boundary with the ERSP and vertical south-side-up motion in the BRGB. The BRGB can be considered as a pop-up structure with anastomosed shear zones displaying different horizontal offset according to the orientation of the shear zones. The southern boundary with the Winnipeg River subprovince is represented by a sinistral south-side-up shear zone. The same pattern is found at the regional scale where major shear zones acted as a conjugate set in the horizontal plane. At ca. 2640Ma, the D3 event occurred in a general dextral transpressive tectonic regime coeval with the emplacement of rare-elements pegmatitic plutons in a still hot (400–500°C) country rock. The geodynamical and mechanical significance of the partitioning between pure strike-slip tectonics in the English River subprovince and vertical motion in the BRGB can be explained by the rheological behaviour of a hot and weak lithosphere undergoing transpressive strain. The structural framework of the BRGB is the result of strong interactions between hot and weak domains, coeval with widespread plutonism, and a rigid older domain (Maskwa batholith) during the D2 transpressive event. [Copyright &y& Elsevier]

Abstract: U–Pb single zircon crystallization ages were determined using TIMS and sensitive high resolution ion microprobe (SHRIMP) on samples of granitoid rocks exposed in the Serrinha nucleus granite–greenstone terrane, in NE Brazil. Our data show that the granitoid plutons can be divided into three distinct groups. Group 1 consists of Mesoarchaean (3.2–2.9Ga) gneisses and N-S elongated TTG (Tonalite-Trondhjemite-Granodiorite) plutons with gneissic borders. Group 2 is represented by ca. 2.15Ga pretectonic calc-alkaline plutons that are less deformed than group 1. Group 3 is ca. 2.11–2.07Ga, late to post-tectonic plutons (shoshonite, syenite, K-rich granite and lamprophyre). Groups 2 and 3 are associated with the Transamazonian orogeny. Xenocryst ages of 3.6Ga, the oldest zircon yet recorded within the São Francisco craton, are found in the group 3 Euclides shoshonite within the Uauá complex and in the group 2 Quijingue trondhjemite, indicating the presence of Paleoarchaean sialic basement. Group 1 gneiss-migmatitic rocks (ca. 3200Ma) of the Uauá complex constitute the oldest known unit. Shortly afterwards, partial melting of mafic material produced a medium-K calc-alkaline melt, the younger Santa Luz complex (ca. 3100Ma) to the south. Subsequent TTG melts intruded in different phases now exposed as N-S elongated plutons such as Ambrósio (3162±26Ma), Araci (3072±2Ma), Requeijão (2989±11Ma) and others, which together form a major part of the Archaean nucleus. Some of these plutons have what appear to be intrusive, but are probably remobilized, contacts with the Transamazonian Itapicuru greenstone belt. The older gneissic rocks occur as enclaves within younger Archaean plutons. Thus, serial additions of juvenile material over a period of several hundred m.y. led to the formation of a stable micro-continent by 2.9Ga. Evidence for Neoarchaean activity is found in the inheritance pattern of only one sample, the group 2 Euclides pluton. Group 2 granitoid plutons were emplaced at 2.16–2.13Ga in a continental arc environment floored by Mesoarchaean crust. These plutons were subsequently deformed and intruded by late to post-tectonic group 3 alkaline plutons. This period of Transamazonian orogeny can be explained as a consequence of ocean closure followed by collision and slab break-off. The only subsequent magmatism was kimberlitic, probably emplaced during the Neoproterozoic Braziliano event, which sampled older zircon from the basement. [Copyright &y& Elsevier]

Abstract: The Nuvvuagittuq supracrustal belt (NSB) in northwestern Québec ranks as one of the oldest granitoid gneiss complexes thus far discovered. Emplacement ages for intrusive trondhjemitic dikes that transect amphibolites and quartz–magnetite schists at the Porpoise Cove outcrops of the NSB cluster at 3.75 Ga. As with all other pre-3.7 Ga terranes thus far documented, the NSB has been metamorphosed and multiply deformed. In a combined approach to explore the thermal history of the NSB, conventional garnet–biotite and plagioclase–hornblende geothermometry was coupled with zircon U–Th–Pb depth profiles, REE partitioning and Ti-in-zircon thermometry to show that Neoarchean metamorphism in the belt reached upper amphibolite facies conditions (~640 °C). This metamorphism resulted in some cases in thick zircon overgrowths on older cores and likely corresponds to the amalgamation of terranes in the Northeast Superior Province and the initiation of widespread igneous activity in the vicinity of the NSB. An earlier (resolvable) metamorphic episode from a zircon depth-profile, recorded at 3.62 Ga, probably corresponds to the intrusion of the granitoids which envelope the NSB. [Copyright &y& Elsevier]

Abstract: Archean terrains of the Quadrilátero Ferrífero comprise a greenstone belt association surrounded by granitoid–gneiss complexes, mainly composed of banded TTG gneisses whose igneous protoliths are older than 2900 Ma. This early continental crust was affected by three granitic magmatic episodes during the Neoarchean: ca. 2780 to 2760 Ma; 2720 to 2700 Ma; and 2600 Ma. Dating of felsic volcanic and volcaniclastic rocks defines a felsic magmatic event within the greenstone belt association around 2772 Ma, contemporaneous with emplacement of several of the granitic plutons and constrains a major magmatic and tectonic event in the Quadrilátero Ferrífero. Lead isotopic studies of lode–gold deposits indicate that the main mineralization episode occurred at about 2800 to 2700 Ma. Proterozoic evolution of the Quadrilátero Ferrífero comprises deposition of a continental-margin succession hosting thick, Lake Superior-type banded iron formations, at ca. 2500 to 2400 Ma, followed by deposition of syn-orogenic successions after 2120 Ma. The latter is related to the Transamazonian Orogeny. The western part of the Quadrilátero Ferrífero was also affected by the Brasiliano Orogeny (600 to 560 Ma). [Copyright &y& Elsevier]

Abstract: Widespread gold showings have been found in an Archean greenstone belt on Storø in Godthåbsfjord, West Greenland. The Storø Greenstone Belt (SGB) comprises metasedimentary and metavolcanic rocks with minor magnetite-rich bands. Gold mineralization is hosted by amphibolites, mica schists and garnetite rocks. Gold occurs in various mineral associations, but its presence in löllingite–arsenopyrite–pyrrhotite parageneses is prevalent. To a lesser extent, native gold occurs within seriticized plagioclase, in sheeted quartz veins, and as inclusions in garnet. Based on petrographic observations and comparison with similar ore mineral textures from other deposits we propose the following model for the deposition of the gold-bearing löllingite–arsenopyrite–pyrrhotite assemblage on Storø: In the first stage, arsenopyrite likely formed with gold in solid solution. In the second stage, gold-bearing arsenopyrite was replaced by löllingite and pyrrhotite. This took place during regional prograde metamorphism. Gold accumulated within löllingite as discrete grains. During subsequent retrograde metamorphic conditions, löllingite and pyrrhotite reacted and formed arsenopyrite, and gold was subsequently exsolved and preferably deposited as discrete grains or films along arsenopyrite–löllingite grain boundaries. During a later event a garnet overgrowth partly affected the gold-bearing löllingite–arsenopyrite–pyrrhotite assemblage. The isotopic composition of Pb released from these garnets by Pb stepwise leaching experiments (PbSL) and the bulk Pb isotopic compositions of arsenopyrite and pyrrhotite indicate a common source of Pb in the fluid from which first the sulfides and subsequently garnet were formed. Bulk Pb analyses and PbSL experiments of arsenopyrite and PbSL experiments of garnet yield ages of 2863±24 Ma (2σ; MSWD=0.2) for arsenopyrite and 2748±62 Ma (2σ; MSWD=220) for garnet. The 2863±24 Ma age is thus a minimum age for the mineralization. Rb–Sr isotopic analyses of cogenetic biotite from within strongly mineralized zones reveal Middle Proterozoic (ca. 1.65 Ga) mineral ages, well in accordance with a regional reheating event known to have affected the area, and are thus interpreted as cooling ages thereof. This regional reheating event has apparently not affected the Pb–Pb isotopic system of arsenopyrite, implying that the blocking temperature of the U–Pb system in arsenopyrite is likely to be above ∼300 °C. The Late Archean ages for arsenopyrite and garnet are consistent with the regional amphibolite facies metamorphism related to major terrane assemblies in the study area occurring at that time. The ore textures preserved today are interpreted as those formed under this regional metamorphic event. [Copyright &y& Elsevier]

Well-preserved Archean pillow lavas from the Ca. 3.35 Ga Euro Basalt of the Pilbara Craton, Western Australia, contain micron-sized tubular structures mineralized by titanite (CaTiSiO4) with residual organic carbon preserved along their margins. Direct U-Pb dating of titanite in the tubular structures demonstrates an Archean age. These tubular microstructures are identical to microbial ichnofossils in modern basalts, ophiolites, and greenstone belts, and are interpreted as a biogenic signature in these ancient rocks. Microbial colonization of basaltic glass thus appears to have been part of a deep subsurface biosphere established early in Earth's history. [ABSTRACT FROM AUTHOR]

Abstract: This article focuses on the discrepancy between the often advocated stratigraphic continuity of greenstone belts in the Pilbara Craton (Australia) on the one hand, and the observations of syndepositional deformation and other tectonic disturbance on the other hand. The Coppin Gap Greenstone Belt of the East Pilbara consists predominantly of mafic, intermediate and felsic rocks, with minor amounts of silicified sedimentary rocks of the early Archaean Warrawoona Group. Several well-defined zones subparallel to the bedding show intense brittle to ductile deformation, testifying to differential movements of the tectono-stratigraphic slices they delimit. These deformation zones were at least partly related to west-block-down normal faults and accommodated upper block to the west transport. However, new U–Pb zircon dates, geochemical analyses and detailed field observations show that the overall stratigraphic succession in the Coppin Gap Greenstone Belt has not been fundamentally disturbed. The normal faults occur in several irregularly superposed arrays of km-spaced faults, part of which were active during deposition. Normal faults also occur throughout the entire belt. Combined, the early deformation structures indicate east–west extension over a minimum period of 20Ma, from ∼3469Ma onwards. Likely, the extension took place over an even longer period of time, during much of the time of deposition of the Warrawoona Group, from ∼3490Ma onwards. Syndepositional extension of the Warrawoona Group was geometrically unrelated to the doming of granitoid batholiths. Surficial (i.e. uppermost crustal) gravitational collapse during or shortly after deposition may have caused the apparent contradictory co-existence of deformation zones and stratigraphic continuity. Although the deformation has not caused major disruptions of the stratigraphic succession, the precision of the U–Pb SHRIMP ages is insufficient to rule out excisions or duplications of stratigraphy on the order of a few million years. [Copyright &y& Elsevier]

New U–Pb zircon ages are reported for 17 volcanic, plutonic and sedimentary rocks from the Neoarchean Central Hearne supracrustal belt in the Western Churchill Province of the Canadian Shield. The Central Hearne supracrustal belt, historically referred to as the Rankin-Ennadai greenstone belt, is a major granite-greenstone terrain with a strike length of over 700 km. This study, focused on the central and eastern segments of the belt in the Kaminak Lake area, represents the first detailed chronological study of this extensive greenstone belt. The geochronological data indicate rapid formation of crust between 2711 and 2667 Ma. Rocks of the oldest assemblage (I) formed between 2711 and 2691 Ma and consist of mixed tholeiitic and calc-alkaline mafic and felsic, submarine to subaerial volcanic rocks. Minor plutonic rocks (Group 1) are associated with this interval. A younger assemblage (II) of volcanic rock with significant calc-alkaline plutonic rocks (Group 2) developed between 2686 and 2679 Ma. A period of deformation (D1) locally separates the two assemblages. Major regional, penetrative deformation and metamorphism developed during the latter stages of the plutonic event at ca. 2680 Ma. An extensive belt of metasedimentary rocks and associated iron formation was deposited after 2681 Ma, based on ages of detrital zircon. The youngest events include intrusion of 2666.4±1.1 Ma post-deformational granite (Group 3), 2659 Ma carbonatite [Can. J. Earth Sci. 29 (1992) 896], and deposition of post-2660 Ma conglomerates and arenites of possible “Timiskiming”-type. There is no indication of contributions from Mesoarchean crust either in inherited grains in igneous rocks, or as detrital grains in sedimentary rocks. Although the evolutionary sequence has parallels to greenstone belts such as the Abitibi belt, in terms of the rock types and relative timing of events, there are some differences. We envision development of the belt in an extensional, oceanic suprasubduction environment. [Copyright &y& Elsevier]

The Quadrilátero Ferrífero (QF) is an important, polydeformed mineral province, located in the southernmost portion of São Francisco Craton. The Rio das Velhas greenstone belt (RVGB) is an Archean meta-volcano-sedimentary succession from the QF, the Córrego do Sítio unit (CdS) being its most widely distributed sedimentary sequence. Detailed sedimentology study allied to x-ray diffraction-XRD and geochronological (LA-ICP-MS in detrital zircon) analyses provide evidence for a new interpretation of the CdS. The identified sedimentary structures of the CdS (e.g. flaser and lenticular bedding, sharp and erosional base, normal grading, mud drapes, quartz granules, syndepositional deformation, and ball & pillow) led the interpretation of these couplets as turbidity currents deposits corresponding to TA and TE facies of the classic Bouma Sequence. The CdS sequence was deposited on distal portions of an ancient submarine fan environment by turbidity current mechanisms, then it was partially reworked by tidal bottom currents. Geochronological data pointed out the main influence of the Rio das Velhas II magmatic event in the deposition of the eastern QF metasedimentary sequence, as evidenced by the maximum depositional age at 2818 ± 31 Ma. The surrounding metamorphic complexes terrains may have acted as source areas during the deposition of the sedimentary sequences, probably in a convergent to a collisional marginal tectonic setting (subduction stage). • Córrego do Sitio unit sedimentary sequences interpreted as turbiditity currents partially influenced by tidal bottom currents. • Eastern Rio das Velhas greenstone belt metagraywacke maximum depositional age at 2818 ± 31 Ma. • Sedimentary provenance from surrounding Archean metamorphic complexes. [ABSTRACT FROM AUTHOR]

This study addresses the Neoarchean to Paleoproterozoic thermal evolution from the Buhwa Greenstone Belt (BGB) along the contact zone between the Archean Zimbabwe Craton (ZC) and a granulite terrane of the Northern Marginal Zone (NMZ) of the Limpopo Complex. Available tectonic models suggest a thrusting of the hot NMZ over and onto the cold ZC, which possibly gave rise to local heating of the margin of the craton by a "hot-iron effect". Petrographic, pressure–temperature data, along with hornblende Ar–Ar ages for metabasites from the BGB were coupled with a discussion of the tectonics of this region. The metabasites typically occur interlayered with metasediments. Four types of metabasites occur, namely, calcic amphibole–epidote schist, amphibolite (garnet-bearing and garnet-free), calcic amphibole–clinopyroxene schist, and mafic granulite, indicating a varying metamorphic grade from epidote–amphibolite facies to granulite facies. The lower-grade calcic amphibole–epidote schists occur in the northwestern margin of the belt, whereas the higher-grade amphibolites and mafic granulites are present along the southeastern margin of the BGB adjacent to the granulite terrane. The increase in metamorphic grade towards the NMZ of the Limpopo Complex is supported by temperature estimates of <500 °C to >700 °C from northwest to south east. The results of our study are consistent with the pervailing tectonic model which considers the NMZ–ZC boundary as a major thrust-sense shear zone dipping southward, and the hot NMZ thrusted over the cold ZC. New hornblende Ar–Ar ages indicated two discrete thermal events recorded in the BGB rocks: 2525 ± 19 Ma from mafic granulite and 2020 ± 8 Ma to 1968 ± 10 Ma from amphibolites. The Neoarchean age probably corresponds to a cooling age after the peak metamorphism, indicating that the NMZ thrusting onto the ZC took place at >2525 Ma. The age of the thrusting of the NMZ is younger than that of the Southern Marginal Zone (SMZ) of the Limpopo Complex onto the Kaapvaal Craton (KC) (ca. 2.72–2.69 Ga). Therefore, the formation of the Limpopo Complex is not because of a simple collision of the KC and the ZC, but the SMZ-KC collision is more than 100 Myr earlier than the NMZ–ZC collision, suggesting multiple collision for the formation of the Limpopo Complex. In contrast, the younger Paleoproterozoic thermal event coincidental with the last high-grade metamorphic event within the Limpopo Complex might correspond to a thermal reactivation along the NMZ–ZC boundary possibly caused by the global ca. 2.0 Ga orogenic events. • Low-to high-grade metabasites in the Buhwa Greenstone Belt along the southern Zimbabwe Craton margin. • Increase of peak temperature from NW (<500 °C) to SE (>700 °C) within the belt. • 2525 Ma Ar/Ar age from mafic granulite indicates the timing of peak metamorphism and thrusting. • Paleoproterozoic (ca. 2.0 Ga) thermal overprint affected the southern margin of the Zimbabwe Craton. [ABSTRACT FROM AUTHOR]

• • Montagne d'Or is a bimodal mafic Au-rich VMS of Northern Paramaca Greenstone Belt. • • VMS related magmatism is from ≈2152 Ma to ≈2130 Ma with a late intrusion at ≈2117 Ma. • • A coeval activity of two submarine volcanic centers at a water depth ≈500 to 1000 m. • • The sequence is transposed by a principal deformational event younger than 2117 Ma. • • Paramaca Greenstone Belt hosts several other VMS systems like Montagne d'Or deposit. In French Guiana, the Montagne d'Or gold deposit (5 Moz at 1.5 g/t Au) is located in the northern branch of the Rhyacian Paramaca Greenstone Belt. The sulphide deposit is hosted by a south-facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative E-W striking and steeply south-dipping foliation. The volcanic sequence is composed of three members, (1) the Lower unit in the stratigraphic footwall, (2) a bimodal mafic-felsic formation hosting the orebody, and (3) the Upper sedimentary and volcanic rocks unit in the stratigraphic hanging-wall. The bimodal formation is dominated by calc-alkaline felsic volcanic rocks in the west, interbedded/interdigitated with tholeiitic mafic rocks in the east. Pillowed mafic flows and graded-bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment. The mineralization consists of thick and laterally extensive sulphide zones forming (1) stratiform sulphide disseminations, (2) structurally-transposed stringer stockworks, and (3) thin layers of deformed semi-massive sulphides. The gold-rich sulphide mineralization consists mainly of pyrite, pyrrhotite and chalcopyrite with minor sphalerite, magnetite, galena and arsenopyrite, hosted by chlorite-sericite-rich alteration zones mainly developed in the felsic tuff facies. U-Pb zircon geochronology shows that most of the Montagne d'Or volcanic and intrusive sequence has crystallized during a multi-cycle magmatic event, from ca. 2152 Ma to ca. 2130 Ma. A porphyry intrusion crosscutting the ore yields a U-Pb zircon age of 2117.6 ± 5.1 Ma, hence constraining a minimum age for the auriferous sulphide mineralization. This also indicates that the sulphide mineralization was coeval with arc magmatism, demonstrating the volcanogenic nature of the Montagne d'Or gold deposit. [ABSTRACT FROM AUTHOR]

The Serra das Pipocas Greenstone Belt is one of the rare Paleoproterozoic greenstone belts within the Borborema Province. It is on the west border of the Archean/Paleoproterozoic Nucleus (Cruzeta and Mombaça Complex) of the Ceará Central Domain, northern portion of the Borborema Province. The Serra das Pipocas Greenstone Belt has an elongated sigmoidal shape encompassing about 1000 km2 of the Ceará Central Domain. It consists of a metavolcanosedimentary sequence formed by metasedimentary psammitic-pelitic-marly rocks and interleaved metaultramafic and metamafic rocks, represented by chlorite-anthophyllite-actinolite/tremolite schists and amphibolites. Layers of metatuffs, metabasic, meta-acid sills (metadacites), metacherts, gondites and banded iron formations occur within the metamafic rocks. Actinolite, metagabbro, metadiorite bodies, metabasic dike, Neoproterozoic metagranodiorites and leucogranites crosscut the metavolcanosedimentary sequence. Close to the borders of metagranodioritic bodies (zircon U–Pb 2181 ± 4.4 Ma), the metavolcanosedimentary sequence is hydrothermally altered. The metaultramafic rock (chlorite-anthophyllite-actinolite/tremolite schist) contains high MgO (>18 wt%), low alkali (≤1 wt%) and TiO 2 (<0.8 wt%) and Al 2 O 3 /TiO 2 ratios between 9.94 and 27.26, with a mean value of 17.13. Values of (Gd/Yb) N vary between 1.00 and 1.88, which attest affiliation with komatiite protoliths, between the Munro and Barberton types. The amphibolites are usually fine-grained and depleted in ΣREE (33.14–45.02 ppm), with low (La/Yb) CH values (0.74–3.82). This reflects weak LREE enrichment in relation to HREE, and no Ce and Eu anomalies [(Eu/Eu*) n between 0.98 and 1.04]. Such patterns are similar to T-MORB (1.7–4.3). Additionally, some mafic-ultramafic metaplutonic rocks present chemical composition similar to their volcanic counterparts, and this may indicate cumulates or sills contemporary to this sequence. Zircon U–Pb dating using LA-ICP-MS of three distinct metadacite occurrences (western border: 2234 ± 13 Ma, eastern border: 2212 ± 13 Ma, and central portion: 2156 ± 45 Ma) and metagranodiorites (2181 ± 4.4 Ma) indicates that the sequence was formed during the Rhyacian/Orosirian and later affected by late Neoproterozoic. [ABSTRACT FROM AUTHOR]