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The Neoarchaean Belingwe greenstone belt of the Zimbabwe craton consists of a well-preserved succession of rocks of low metamorphic grade and low strain. We present new age constraints for the Ngezi Group of the belt and discuss them in the light of greenstone belt evolution. We propose crustal destabilization of the Zimbabwe proto-craton as a result of a global flare of mantle-derived magmatism at ~ 2.75 Ga. This gave rise to extension of a Mesoarchaean granitoid-greenstone terrain, rapid subsidence and, initially, deposition of a transgressive cover succession (Manjeri Formation). High degrees of stretching of proto-cratonic and mantle lithosphere provided accommodation space for the emplacement of several kilometres of submarine volcanic rocks on deeply submerged granitoid-greenstone basement, herein referred to as proto-cratonic flood basalts. Once extension and magmatism had ceased, chemical and clastic sedimentary rocks of the Cheshire Formation were deposited prior to 2.71 Ga as a result of, and subjected to, compressional deformation, and much earlier than previously assumed. [ABSTRACT FROM AUTHOR]

Temporal changes in Earth’s tectonic style play a crucial role in understanding the planet’s evolution. Modern-style tectonics is characterized by the formation of basaltic crust at divergent plate boundaries and its subsequent recycling at subduction zones, accompanied by wedge mantle formation and arc magmatism. It is commonly believed that the secular cooling of the mantle modified the tectonic style from stagnant lid or heat pipe on an early hotter Earth to horizontal tectonics during Meso-Neoarchean. However, various field, petrographic, and geochemical studies suggest that the onset of plate tectonics ranges from Hadean to Neoproterozoic. In this study, we re-evaluate the primary magma temperature (mantle potential temperature, Tp) of the upper ambient mantle, spanning from Eoarchean to Neoproterozoic. We used basalts from several Archean and Proterozoic greenstone belts worldwide, along with Proterozoic ophiolites, to (re)calculate the Tp using the FRACTIONATE-PT method. We observed a Tp range of 1444–1639°C during the Archean and 1414–1611°C during the Proterozoic. These findings indicate a strong correlation with previously estimated Tp values obtained from PRIMELT3 method. This further highlights strong internal consistency among different methods and supports models of a hot ambient mantle during the Archean and Proterozoic. We further reviewed numerical models regarding the effect of mantle temperature on the viability of early Earth plate tectonics. Such model results, composition of Archean continental crust, recent crustal growth models, and field evidence are consistent with the operation of plate tectonics on an early hotter Earth. The transition from a hotter mantle to a colder one from Eo-Neoarchean resulted in thinner oceanic lithosphere and a less depleted lithospheric mantle. Subduction of this thinner oceanic lithosphere led to modern-style tectonics. The intensity and style of plate tectonics on the early Earth differed from modern tectonics, which emerged during the Neoarchean. [ABSTRACT FROM AUTHOR]

The Neoarchean Qingyuan greenstone belt (QGB) is located at the northeastern margin of the North China Craton (NCC) and has experienced amphibolite- to granulite-facies metamorphism. The supracrustal rock assemblage is composed of biotite-hornblende (Bt-Hb) monzonitic gneiss, garnet-biotite-hornblende (Grt-Bt-Hb) monzonitic gneiss, Grt-Bt-Hb plagioclase gneiss, amphibolite and orthopyroxene-biotite-hornblende (Opx-Bt-Hb) plagioclase gneiss. This study involves thorough field and petrographic observations, whole-rock geochemistry and LA-ICP-MS zircon U‒Pb ages of these rocks to constrain the Neoarchean geodynamic setting of the QGB. Zircon U‒Pb dating indicates that these metavolcanic rocks formed during 2.57‒2.52 Ga and experienced subsequent regional metamorphism at 2.52‒2.47 Ga. Lithological and geochemical characteristics show that the QGB protoliths were tholeiitic to calc-alkaline basalts, andesites, dacites and rhyolites. The andesite-dacite-rhyolite assemblage exhibits high SiO2 and Mg# values, low Yb and Y contents, strongly fractionated chondrite-normalized REE patterns and depletion in Nb, Ta, Ti and P, resembling Phanerozoic adakites. These geochemical characteristics suggest an origin from the partial melting of a subducted slab interacting with mantle wedge material. The tholeiitic to calc-alkaline basalts exhibit slightly LREE-enriched chondrite-normalized REE patterns and negative Nb and Ti anomalies, like island arc basalts. These basalts might have originated by partial melting of a mantle source affected by metasomatism from subduction-derived fluids and melts. The lithological associations and geochemical characteristics imply that the Qingyuan greenstone belt developed in a continental margin arc setting. [ABSTRACT FROM AUTHOR]

Serpentinization is an important geochemical process producing natural hydrogen (H 2), and mafic and ultramafic serpentinized rocks, typically occurring in ophiolites and peridotite massifs, are major targets for H 2 exploration. Understanding the volumes of H 2 stored in these rocks is a key step towards establishing the potential of sepentinized systems to host H 2 sources and reservoirs. Nonetheless, published data on the concentration of H 2 directly extracted from serpentinized rocks are extremely scarce. This work provides a first dataset of H 2 extracted by planetary ball mill from 58 rock samples from different ophiolites in Greece, peridotites of the Tekirova ophiolite in Turkey, and chromitites and surrounding talc schist from an Archean-Paleoproterozoic greenstone belt in Brazil. The highest H 2 concentrations, from 0.1 mL/kg (considered as a threshold above which artificial H 2 by milling is negligible) to 16.2 mL/kg, were found in serpentinized harzburgites or dunites, and in chromitites hosted within serpentinized peridotites. The H 2 content of other mafic rocks that are not in contact or influenced by a serpentinized system, mostly basalts, is below 0.1 mL/kg. Serpentinized peridotites represent the logical source rocks of H 2 (i.e., hydrogen in peridotites is generally autochtonous) and chromitites, lacking significant olivine and serpentinized minerals, may host H 2 derived by the surrounding serpentinized rocks (hydrogen in chromitites is mostly allochtonous). The H 2 dataset of this work can be used as a reference for further studies on the capacity of ophiolitic rocks to produce and host natural hydrogen. • First dataset on H 2 concentration in mL/kg in different ophiolitic rocks. • Serpentinized harzburgites/dunites and chromitites host the highest H 2 concentrations. • Hypothesis of autochtonous hydrogen in peridotites, allochtonous hydrogen in chromitites. [ABSTRACT FROM AUTHOR]

The Palaeo- to Neoarchaean Bundelkhand Craton (BkC) in central India has received attention due to its felsic crust evolution. There are two linear patches of relict greenstone belts in the BkC, and the central greenstone belt has been the focus of extensive research for the past two decades. In contrast, the southern greenstone belt has received inadequate attention. At the southern BkC, the E-W Madawara Greenstone Belt is represented by patches of remnant mantle serpentinites and metasedimentary rocks that are tectonically juxtaposed with Archaean basement TTG gneisses and Proterozoic Bijawar Group of rocks. This study highlights key findings from fields, geological maps, petrography, and a large number of whole rock chemical analyses of serpentinites and spinel chemistry to unravel the tectonic evolution story. We identified two serpentinites with contrasting petrological and geochemical properties: spinel peridotite (SP) and talc-tremolite schist (TTS). SP is primarily dunite to harzburgite with relatively high MgO (33 wt%), enriched Yb, and shows strong re-fertilization. TTS, on the other hand, is lherzolitic and less refractory (MgO = 25 wt%). Chemically, these two serpentinites were mantle wedge and subducted peridotites, respectively. The unaltered cores of the chromium spinels represent a fore-arc setting. These findings, in conjunction with prior research, paint a compelling picture of a Neoarchaean (~2.5 Ga) subduction system once present in the southern Bundelkhand Craton. The serpentinites represent relict ophiolites – from a northerly dipping trench. It also explains a Mesoarchaean rift basin system between the two cratonic nuclei of southern Bundelkhand, which amalgamated during the Kenorland Supercontinent formation. [ABSTRACT FROM AUTHOR]

New mapping of the Barberton Greenstone Belt in South Africa shows that the central part is a pseudo-stratigraphy made of shallow-water and deep-water siliciclastic and volcanic slide blocks, with individual blocks ranging in size from tens of meters to >10 km in length. The outcrop pattern and scale are remarkably similar to those of large-scale Miocene to recent submarine landslides in New Zealand along the active Hikurangi subduction zone that are periodically triggered by earthquakes on the subduction megathrust, providing evidence for megathrust earthquakes in the Paleoarchean. [ABSTRACT FROM AUTHOR]

The late Archean Western Dharwar Craton supergroup has volcanic and sedimentary rocks deposited during 2900–2600 Ma underlain by the Sargur Group basement of 3.36–3.2 Ga granitic gneiss and older supracrustal rocks. The western part of the craton, known as the western province (Dharwar Foreland), comprises four major schist belts (Western Ghats-Bababudhan-Shimoga-Chitradurga). A regional gravity and magnetic (Total Field) survey was done in the Shimoga region. The geophysical data of the study area reveal the subsurface extension and behaviour of the exposed rocks of the area. The Euler deconvolution was used to define the depth of the anomaly sources. Euler depth solution for the spherical body (structural index 2), window size = 10, and depth tolerance = 5% depicts the depth of the various sources. The Euler depth solutions cluster over the hook-shaped schist rock of the Medur group (at the northern part of the area) reveals that the body's depth varies from 1 to 4 km in the central part, and at the northern flank, it goes up to 7 km. The solution also brought out the depth of the anomalous body near Hithala, within 4 km. The 2D forward depth modelling of the anomalous zone brings out the involvement of the tectonic forces in the generation of this anomalous body. The more precise depth from the model has been estimated between 2 and 3 km. The model clearly shows the relationship between schist rocks and the basement. However, the high-gravity anomaly has been modelled as the manganese bearing horizon, which has come to optimum depth because of folding and faulting in the region, thus providing a favourable zone for manganese deposition. [ABSTRACT FROM AUTHOR]

The Laird Lake property, southwest Red Lake greenstone belt, straddles the contact between the Balmer (2.99–2.96 Ga) and the Confederation (2.74–2.73 Ga) assemblages. The property is 10 km along strike from the Madsen and Starrat–Olsen Au mines that are hosted near the contact. The Balmer assemblage consists of fine-grained, aphyric, locally pillowed mafic volcanic rocks, ultramafic intrusive and volcanic rocks with flow breccia textures hosting local spinifex-bearing clasts, and banded-iron formations. In contrast, the Confederation assemblage comprises porphyritic mafic volcanic rocks intercalated with intermediate to felsic volcanic rocks that include crystal lapilli tuffs, crystal tuffs, and tuffs. The Balmer assemblage is composed of tholeiitic mafic volcanic rocks with minor Al-undepleted komatiites, whereas the Confederation assemblage is calc–alkalic. Neodymium isotopes, in conjunction with trace element geochemistry, suggests that parts of the Balmer assemblage were weakly contaminated by an older intermediate basement. Both arc and back-arc volcanism occurs in the Confederation assemblage, with the arc rocks showing a stronger crustal component than the back-arc rocks. A maximum U–Pb age of 2741 ± 19 Ma for a crystal tuff and an age of 2737.68 ± 0.79 Ma for a diorite are consistent with a Confederation assemblage affinity for the intermediate calc–alkaline rocks south of the Au-bearing horizon. The Balmer assemblage represents an oceanic plateau formed by plume magmatism on the margins of the North Caribou Terrane, whereas the Confederation assemblage at Laird Lake formed in an oceanic arc setting where both arc and back-arc volcanism occurred simultaneously. [ABSTRACT FROM AUTHOR]

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe2O3) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets. [ABSTRACT FROM AUTHOR]

There are numerous Neoarchean metasedimentary rock packages in the Slave craton, and they serve as important archives of tectonic processes. Little is documented on the Neoarchean sedimentary packages of the Winter Lake greenstone belt of the central Slave craton, however, and their interpretation can aid in the understanding of the final stages of Slave craton amalgamation. This project investigates the depositional environments and tectonic settings of the Itchen Formation and Sherpa Formation of the Winter Lake greenstone belt. Our study provides constraints for reconstructing the Neoarchean evolution of the central Slave craton through bedrock mapping and facies analysis. The Itchen Formation consists of submature mudstone, siltstone, and sandstone, with preserved graded bedding, planar bedding, and flame structures. Unconformably overlying the Itchen Formation is the Sherpa Formation, which is dominated by polymictic conglomerates and coarse-grained sandstones with preserved cross-bedding, imbricated clasts, and scour surfaces. The Itchen Formation is interpreted to have been deposited in a convergent basin (i.e., retro-arc foreland basin), where two facies associations outline turbidite and suspension sedimentation consistent with submarine fan deposition on a continental slope and a basin floor environment. By contrast, the Sherpa Formation has three facies associations representing dominantly alluvial–fluvial environments in terrestrial–marine–lacustrine settings deposited in pull-apart basins resulting from transtensional forces associated with the Beniah fault zone. [ABSTRACT FROM AUTHOR]

Zircon is not a common accessory mineral of banded iron formation (BIF), but it occurs in all BIF samples from the Kostomuksha Greenstone Belt (KGB) in the Karelian Craton of the Fennoscandian Shield. The Kostomuksha BIF is of Algoma type and is part of three variably old rock associations: BIF-1 is part of a sedimentary sequence in Mesoarchean (2.87–2.84 Ga) basaltic komatiites with dacites, BIF-2 is located in Meso-Neoarchean (2.8–2.79 Ga) felsic volcanics, and BIF-3 is part of a Neoarchean (2.76–2.74 Ga) greywacke unit with felsic volcanics. Analysis of zircon has revealed grains with cores and several generations of rims. The U-Th-Pb systems of zircon indicate that its isotopic age varies considerably from 2.98 to 1.89 Ga, forming up to 4 age clusters in each sample. Most samples contain single inherited grains. The bulk of zircon in BIF is younger than the host rocks and is interpreted as metamorphic. Most of metamorphic zircons display an oscillatory zoning, and their Th/U ratio varies from 0.01 to 4.7, i.e. their origin is hard to interpret reliably, based on the above characteristics. Paleoproterozoic (1.89–1.85 Ga) zircons from BIF-1 and 3, occurring as rims and individual grains, are related to local tectono-thermal processes simultaneous with the formation of the Svecofennian orogen and were described for the central Karelian Craton for the first time. Thus, both inherited and metamorphic zircons have been revealed in Meso-Neoarchean BIF metamorphosed repeatedly in the Neoarchean-Paleoproterozoic under up to amphibolite-facies conditions. All metamorphic generations of zircons from BIF are correlated with the tectono-thermal events in the Karelian Craton, including the effect of the Svecofennian orogeny. [ABSTRACT FROM AUTHOR]

Three variably old groups of banded iron formation (BIF) are known in the Kostomuksha Greenstone Belt (KGB) of the Karelian Craton. This paper deals with the earliest of them, Mesoarchean (2.87–2.81 Ga) BIF-1. BIF-1 occurs among the komatiite–basalt unit of the KGB. BIF-1 consists mainly of quartz and magnetite, with varying amounts of amphibole, biotite, and garnet; the variations of SiO2 (48.3–58.6 wt %) and (21.34–33.82 wt %) suggest that the rocks are BIF. BIF-1 of the KGB, as well as most Archean BIFs, contain high concentration, display a contrasting positive Eu anomaly, lack of Ce anomaly, and the depletion of LREE relative to HREE. However, they differ from other BIFs in the higher Al2O3, TiO2, MgO, K2O, Cr, Ni, Zr, Ba, Cu and Zn concentrations. BIF-1 was formed in a marine basin at an anoxic atmosphere due to hydrothermal fluids, the proportion of which varies from 20 to 80%, and a terrigenous component derived mainly from basalts, komatiites, and dacites of host rocks. Mesoarchean BIF-1 of the KGB was accumulated in a small rift structures within an oceanic volcanic plateau, the formation of which is associated with the influence of a mantle plume on the oceanic lithosphere. [ABSTRACT FROM AUTHOR]

Volcaniclastic deposits are cynosures for reconstructing volcanic archives and evaluating the tectonic imprints of the study area. This paper presents an elaborate geological field litholog, petrography and geochemistry of ~1.2 km thick sequence of the quartz-feldspar porphyry (QFP) and rhyolites in the Kadiri–Hindupur section of the Kadiri Greenstone belt from Eastern Dharwar Craton (EDC). The QFP exhibits primary stratification; the thickness of the beds varies from very thin to thick (3–8 cm) and shows large-scale tabular cross-bedding in the lower half of the section. The bedding surfaces of QFPs are marked by current crescent-shaped marks (long axis: 5–25 cm, short axis: 2–8 cm), speculated as possible remnants of volcanic bombs and pyroclastic debris during the explosive volcanism. Petrographically, these QFPs are characterised by spectacular blue opalescent quartz grains with embayed grain boundaries, anhedral feldspar with sieved texture, fractured plagioclase and polycrystalline groundmass suggesting a volcaniclastic origin. They are also endowed with significant post-depositional textures such as domino-listric faulting and sigma-shaped porphyroblasts. Geochemically, QFPs are unaltered with trachyte-trachy dacite compositions showing high-potash, calc-alkaline nature displaying shoschonitic affinity. The primitive mantle normalised trace and rare earth elements are marked by an enriched LREE-LILE pattern coupled by negative zircon–hafnium, niobium–tantalum and titanium anomalies affirming their common genetic link to a prominent island arc–back-arc system where explosive volcanism produced the felsic crystal tuffs that were deposited and preserved as volcaniclastic QFP. The associated blocks and bombs produced the current crescent-shaped marks preserved on the bedding surfaces of QFPs. Research highlights: Research Highlights Quartz-feldspar porphyry (~1.2 km thick) occurs in the Kadiri Greenstone Belt, Eastern Dharwar Craton. Blue opalescent quartz and deformed plagioclase porphyry indicate volcaniclastic origin. Enigmatic current crescent-shaped marks represent remnants of volcanic bombs and pyroclastic debris. The primitive mantle normalised REE diagram is characterised by LREE-LILE enrichment. They represent Neoarchean pyroclastic volcanism and sedimentation in an island arc–back-arc setup. [ABSTRACT FROM AUTHOR]

The biological nitrogen (N) cycle on early Earth is enigmatic because of limited data from Archean (meta-)sediments and the potential alteration of primary biotic signatures. Here we further investigate unusual 15N enrichments reported in 2.7 Ga meta-sediments from the Abitibi greenstone belt, Canada, purportedly related to a 15N-enriched Archean atmosphere. Given that sediments from this region are contemporaneous with large-scale volcanogenic massive sulfide deposits, we utilize Cu and Zn contents to trace the effects of hydrothermal circulation on N isotope fractionation. We show that high δ15Nbulk values as high as +23‰ are associated with Cu-Zn mineralization, whereas unmineralized organic-rich shales exhibit much lower δ15Nbulk and δ15Nkerogen values. Moreover, we find a large offset between δ15Nbulk and δ15Nkerogen of as much as 17‰ and relate this to the addition of organic-bound N during the late-stage emplacement of organic-rich veins. We conclude that the previously reported high δ15N values are most parsimoniously explained by biotic and abiotic mechanisms rather than a 15N-enriched atmosphere. Crucially, both mechanisms require the presence of NH4 + in hydrothermal fluids, supporting the hypothesis that hydrothermal discharge was an important nutrient source for Neoarchean marine life. [ABSTRACT FROM AUTHOR]

The results of studies of carbonaceous matter (CM) and the S isotopic composition of associated sulfides in metapelites of the Neoarchean banded iron formation of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandinavian Shield) are presented. The petrographic observations show that the CM occurs inside and between silicates, in sulfides, or at the grain boundaries between the sulfide crystals and biotite or amphibole. The results of scanning electron and atomic force microscopy showed the presence of several CM types distinct in structure and C content. The analysis of Raman spectra of CM revealed the presence both of well-ordered graphite and weakly structured kerogene in samples. The isotopic composition of the total organic carbon is typical of biogenic processes. The δ13Corg values from –27.9 to –30.6‰ are consistent with the fixation of carbon by photo- or chemoautotrophs. The S isotopic composition of associated sulfides is characterized by a positive Δ33S anomaly (up to +0.94‰) and negative δ34S values (from –2.06 to –4.1‰). The positive Δ33S values indicate a genetic link with photochemical elemental sulfur (S8) from the atmosphere, whereas the negative δ34S values reflect the fractionation of isotopes during bacterial-related processes. Based on these observations, we suggest that the primary CM mostly has a biogenic origin. [ABSTRACT FROM AUTHOR]

Reactivation of pre-existing fractures is attributed to fluid pressure conditions and orientation of fractures with respect to the tectonic stress field. In most cases, multiple fluid pressure events reactivate fracture networks. However, it is difficult to perceive and quantify the number of such fluid pressure events directly from a heterogeneous vein data distribution. In the present study, we undertake a statistical approach, well known and extensively used for fuzzy clustering of planar data to approximate the minimum number of fluid pressure events which formed/reactivated fractures. We have also combined the deterministic method for quantifying the minimum number of such fluid pressure events with the traditional method of scaling 3D Mohr circles to determine the absolute fluid pressure magnitudes. The method has been applied to published data of the Gadag-Chitradurga greenstone belt, a prominent Archean greenstone belt of the western Dharwar Craton, south India, to understand the mechanism behind shallow crustal emplacement of auriferous quartz veins within a transtensional tectonic regime. Further, we provide field evidence of fracture reactivation and estimate their reactivation potential, which play a significant role in the spatial variation of fluid pressure along the greenstone belt. Identifying data clusters using Bingham statistics for Pf determination. [ABSTRACT FROM AUTHOR]

Petrochronology of monazite in volcanic rocks of the Hutti deposit in the Eastern Dharwar Craton (India) has been studied to understand the magmatic and hydrothermal events that have affected the area. The volcanic rocks occurring in the Hutti greenstone belt are bimodal in nature and contain both felsic and metabasalt. The felsic volcanic rocks in the area preserve accessory minerals like monazite, allanite, and apatite, whereas the same is absent in metabasalts. Petrographic observation of felsic volcanic rock shows corona growth of allanite and apatite (in addition to huttonite) clustering around monazite grains. This corona texture, termed allanite cluster, occurs parallel to the shear planes (C‐plane) of the felsic volcanic rock and characterizes late‐stage hydrothermal activity in the area. Texturally, monazite in the felsic volcanic rock occurs included within arsenopyrite (<1 μm), and in association with apatite, allanite, and occasionally with huttonite/thorite (~10–40 μm), in which monazite grains preserve geochemical heterogeneity in both intra‐ and inter‐grains. The U–Th–PbTotal dating of monazite associated with the allanite cluster shows two age peaks (both from intra‐ and inter‐grains) at 2658 ± 17 Ma (older) and 2534 ± 38 Ma (younger), in which the older age represents the magmatic/crystallization age of the studied felsic volcanic rock overprinted by a later hydrothermal event in the study area. Based on monazite geochemistry‐geochronology, the present study deduces two texturally constrained events related to the primary crystallization of monazite (~2.65 Ga) and subsequent alteration of the same during a later hydrothermal event (ca. 2.53 Ga) that has affected the felsic volcanic rock in the Hutti gold deposit. [ABSTRACT FROM AUTHOR]

The greenstone belts of the Crixás-Goiás Domain are economically important due to significant epigenetic gold deposits and the potential for under-researched syngenetic deposits. The gold occurrences associated with the volcanogenic massive sulfide (VMS) deposits in the region are documented only in the volcanoclastic rocks of the Digo-Digo Formation, Serra de Santa Rita greenstone belt. The objective of this work is to discuss the efficiency of the induced polarization methods in the time and frequency domains for differentiating and identifying potentially mineralized zones in the exhalites associated with the VMS-type gold of the Digo-Digo Formation. Data were acquired using a multielectrode resistivity meter with the dipole–dipole array and 10 m spacing between electrodes, as well as different current injection times (250, 1000, and 2000 ms). After the electrical data processing and inversion, the sections were integrated into ternary red-green-blue and cyan-magenta-yellow models to highlight areas of high chargeability, low resistivity, and high metal factor (frequency domain) and, thus, map the higher potential zones to host polarizable metallic minerals. The geological–geophysical model elaborated from the correlation of electrical and surface geological data allowed us to identify four anomalous areas related to potential mineralized zones. The geological data confirm that two targets are associated with the geological contacts between metamafic and intermediate metavolcanic units and the exhalative horizon. One of the targets coincides with a sulfide-rich exhalative horizon (VMS), while the last target occurs in the occurrence area of metaultramafic rocks, where gold mineralization occurrences have not been previously described, being a promising target for future investigations. [ABSTRACT FROM AUTHOR]

Singhbhum Craton (SC), one of the oldest continental crusts, has a nucleus of Singhbhum Granite Complex with volcano-sedimentary belts in peripheral parts. Deciphering the inter-relationship between volcano-sedimentary packages and surrounding granitoids offers considerable challenges. The present study area lies in the northwestern parts of SC. Lithounits of volcano-sedimentary packages drapes around the Paleoarchean Bonai Granite Complex (BGC). An attempt has been made to understand the basin development over BGC based on the mutual relationship between lithopackages of Iron Ore Group (IOG) and their structural disposition. It is proposed that two distinct basins, Koira and Gurundia, developed over BGC during Mesoarchean. While the Eastern Koira basin witnessed continuous development accompanied by subsidence wherein lithopackages of Bonai–Kendujhar Iron-ore Belt were deposited, Western Gurundia Basin is marked by a hiatus after the deposition of Gurundia quartzite and mafic volcanics in a shoreline to shallow marine environment. Darjing Group of rocks deposited as platformal package over Gurundia, Koira groups and BGC. Litho packages of Koira, Gurundia and Darjing groups exhibit structural unity as they co-deformed during Iron ore orogeny. The first deformation phase has led to a series of NE–SW to ENE–WSW trending low plunging overturned folds with southeasterly vergence. The second deformation, near coaxial with the first, has led to low northerly plunging open folds with steep northwesterly dipping axial planes. BGC occupies the core of a major second-generation fold with volcano-sedimentary sequence draping around it. It is proposed to put them under Iron Ore Super Group (IOSG), where IOGs (Koira and Gurundia groups) represent the lower part and Darjing Group as the upper part. Research Highlights: IOSG consists of IOGs (Koira and Gurundia groups) and Darjing Group as per present observation. Volcano sedimentary litho packages of IOG were deposited in two distinct basins (Koira and Gurundia basins) developed over BGC in a continental shelf-slope facies. Darjing Group deposited all over Gurundia and Koira groups and BGC after a hiatus which is marked by polymictic basal conglomerate. All the litho members of IOSG were co-deformed during Iron-Ore Orogeny (during the formation of Ur) and exhibit two distinct phases of folding as observed from field and this is reported for the first time with an attempt to bring Darjing group within Iron Ore Supergroup (IOSG). [ABSTRACT FROM AUTHOR]

Vast clay deposits of Chitradurga and Sandur greenstone belts of the Dharwar Craton, southern peninsular India, hosting pockets of high‐grade manganese (Mn) ore, provide remarkable clues related to the ore‐forming processes and palaeo‐environmental conditions. In this study these Fe–Mn‐rich clays were investigated through mineralogical and geochemical characteristics to comprehend their palaeo‐weathering and genetic constraints and their role in the supergene accumulation of Mn ore. Their mineralogy is characterized by predominant kaolinite, muscovite, birnessite, haematite, goethite, halloysite along with quartz and traces of ilmenite. Chemical indices of alteration and weathering indicate intense weathering conditions under high palaeo‐precipitation rates in a humid, tropical climate under shallow burial conditions and K‐metasomatism. The presence of authigenic kaolinite and absence of illite reflect on diagenesis up to mesodiagenetic stage. Positive to negative Ce anomalies (Ce/Ce* = 0.67–5.93) of these clays suggest varying oxic‐anoxic conditions during their genesis, whereas conspicuous negative Eu anomalies (Eu/Eu* = 0.61–0.99) are attributed to precursor sediment signatures and hydrothermal imprints of the Mn ore. These kaolinite‐rich clays are suggested to have been formed by in situ chemical alteration, whereas kaolinitization of the Fe–Mn‐rich arenaceous and argillaceous sediments was derived from predominant tonalite and felsic provenance in a shallow marine passive margin setting. Based on the morphologies of birnessite, haematite and goethite in the investigated clays, we propose that these clays have played a key role in the oxidation and deposition of Mn (II) from the migrating aqueous solutions and acted as organo‐polymerization templates for the proliferation of ancient microbial life on the planet Earth. [ABSTRACT FROM AUTHOR]

Geophysical inversions give non-uniqueness solutions and unless constrained by appropriate initial values and geological constraints can give unrealistic results. One of the critical constraints can be the physical property values of different lithologies. We have compiled a density and magnetic susceptibility database consisting of thousands of measurements collated from different organisations and/or projects across the Abitibi greenstone belt. Statistical tools (histograms, quantile-quantile probability plots and boxplots) are applied to characterise systematically major and minor lithologies. We observed that the magnetic susceptibility frequently has a bimodal distribution, while density is typically unimodal. Our results are summarized in a table that includes the representative mean (or median) and a range of acceptable values. These values can be used to better understand the regional geology, but in this paper, we used the tabulated properties in a geophysical/petrophysical inversion of gravity data from the Chicobi area in the Abitibi subprovince to show the level of improvements that the petrophysical constraints can add to an unconstrained model. When our density database is used to seed the initial guess in a gravity inversion, an anomalous zone becomes apparent that was less evident on an unconstrained inversion. [ABSTRACT FROM AUTHOR]

The north‐dipping Hout River Shear Zone (HRSZ), which marks the boundary between the high‐grade Limpopo Complex in its hanging wall and the low‐grade granite‐greenstone terrane of the Kaapvaal Craton in South Africa in its footwall, is a deep‐crustal shear zone that controlled emplacement of hot Limpopo Complex granulites over and against low‐grade granite‐greenstones during exhumation at ~2.72–2.62 Ga. This major shear zone controlled migration of large volumes of hydrous fluids released during devolatilization of underthrusted greenstones that infiltrated into hot overlying granulites, establishing a retrograde anthophyllite‐in isograd and associated zone of retrograde rehydrated granulite that bounds the Limpopo Complex in the south. Here, we report new petrological data based on mineral equilibrium modelling of amphibolites from the Rhenosterkoppies Greenstone Belt (RGB) located in the immediate footwall of the HRSZ and discuss evidence that these rocks also interacted with high‐temperature fluids that infiltrated along the HRSZ. This study provides an important perspective of the interaction of hot granulites with underthrusted relatively cold greenschist‐facies rocks along the steeply north‐dipping section of the HRSZ, and shows that evidence for such interaction is restricted to a relatively narrow zone in the footwall of the HRSZ termed a hot‐iron‐zone. The peak mineral assemblage of a garnet‐free amphibolite from the RGB (magnesio‐hornblende + plagioclase + quartz + clinopyroxene + titanite + ilmenite) yielded the peak P–T condition of 7–8 kbar and 640–680°C with H2O content of 3.5–3.8 mol%. Clinopyroxene is replaced by actinolite + quartz and epidote + quartz symplectites by a post‐peak hydration event at <5 kbar and <590°C caused by elevated H2O content in the rock (>4.0 mol%), possibly related to fluid infiltration along the HRSZ. Mineral equilibria in a garnet‐bearing amphibolite records a prograde path from 5 to 7 kbar and 540–630°C to the peak conditions at 7.6–8.7 kbar and 620–650°C. A clockwise P–T path suggesting rapid compression and decompression has been inferred for the amphibolites from the RGB, possibly because of pressure increase related to overthrusting of the high‐grade terrane (Southern Marginal Zone of the Limpopo Complex) onto the low‐grade granite‐greenstone terrane, followed by rapid exhumation. The quantity of H2O associated with the amphibolite‐facies metamorphism in the RGB was elevated from the peak stage (M(H2O) = 3.5–3.8 mol%) to the retrograde stage (M(H2O) = 4.0–4.5 mol%) of metamorphism in the RGB, possibly suggesting fluid infiltration not only from internal sources but also from external sources. The results of this study indicate that a H2O‐bearing fluid, which infiltrated along the HRSZ, affected both the footwall and the hanging wall sections of the shear zone, although the effect on the footwall section was limited. [ABSTRACT FROM AUTHOR]

We report abundant small calcareous mounds associated with fossilized kerogenous microbial mats in tidal-facies sandstones of the predominantly siliciclastic Moodies Group (ca. 3.22 Ga) of the Barberton Greenstone Belt (BGB), South Africa and Eswatini. Most of the bulbous, internally microlaminated mounds are several centimeters in diameter and formed at the sediment-water interface contemporaneously with sedimentation. They originally consisted of Fe-Mg-Mn carbonate, which is now largely silicified; subtle internal compositional laminations are composed of organic matter and sericite. Their presence for >6 km along strike, their restriction to the inferred photic zone, and the internal structure suggest that mineral precipitation was induced by photosynthetic microorganisms. Similar calcareous mounds in this unit also occur within and on top of fluid-escape conduits, suggesting that carbonate precipitation may either have occurred abiogenically or involved chemotrophic metabolism(s) utilizing the oxidation of organic matter, methane, or hydrogen, the latter possibly generated by serpentinization of underlying ultramafic rocks. Alternatively or additionally, carbonate may have precipitated abiotically where heated subsurface fluids, sourced by the intrusion of a major Moodies-age sill, reached the tidal flats. In summary, precipitation mechanisms may have been variable; the calcareous mounds may represent "hybrid carbonates" that may have originated from the small-scale overlap of bioinduced and abiotic processes in space and time. Significantly, the widespread occurrence of these stromatolite-like structures in a fully siliciclastic, high-energy tidal setting broadens search criteria in the search for life on Mars while their possible hybrid origin challenges our ability to unambiguously identify a biogenic component. [ABSTRACT FROM AUTHOR]

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment. [ABSTRACT FROM AUTHOR]

A high‐resolution seismic reflection transect was acquired over a hard‐rock geological setting along an existing roadway in the Larder Lake area of the Superior Craton of Canada for the Metal Earth project in 2017. This profile, as well as other Metal earth transects, primarily aims to enhance the knowledge and to better understand the subsurface geology of the Abitibi Greenstone Belt within the Canadian Shield. The complex geological settings of the study area as well as the tribulations caused by the survey geometry have made the imaging and velocity field estimation more challenging. A recently introduced 2.5D multifocusing stacking method is one potential solution for processing crooked‐line seismic data with a poor signal‐to‐noise ratio. The 2.5D multifocusing approach offers more realistic modelling of the zero‐offset wavefield by explicitly accounting for the midpoint dispersion and cross‐dip effects. The main practical problem of the 2.5D multifocusing implementation is the simultaneous determination of the optimal wavefield parameters for each image point and time location. We address this optimization problem using a multidimensional constrained differential evolution global optimization algorithm, as this improves the efficiency and accuracy of the estimation. We have also designed an efficient processing sequence for multifocusing seismic imaging. The performance of the 2.5D multifocusing procedure has been examined on a synthetic model, generated using the same real acquisition geometry. Numerical tests demonstrate that the 2.5D multifocusing technique can produce a more focused stack with the primary reflections appearing at their poststack correct locations, and the procedure can also provide reliable estimates of interface dips. Due to the importance and difficulty of imaging the data, several conventional and advanced processing strategies have been attempted on the transect, specifically: 2D phase‐shift time migration of a dip moveout corrected stack; 2D prestack Kirchhoff time migration; swath 3D poststack migration; and our 2.5D multifocusing imaging algorithm. We found that applying the 2.5D multifocusing stacking algorithm followed by a poststack time migration approach improved the resolution of the image significantly compared to all the conventional and advanced methods and identified new reflections. The 2.5D multifocusing method also focused the steeply dipping reflections more coherently, which resolved ambiguities in geological architecture by understanding the location and continuity of structures. The method also accurately extracts 3D structural information and results in an improved signal‐to‐noise ratio. [ABSTRACT FROM AUTHOR]

Established 2D seismic data processing methods such as Kirchhoff pre‐stack time migration and Kirchhoff pre‐stack depth migration function relatively well for regular acquisition geometries and well‐constrained velocity models. Recently developed focusing pre‐stack depth migration methods have the potential to enhance image quality in the case of sparse and non‐regular source–receiver distribution. We have tested the performance of the coherency migration method as one of these focusing migration approaches in comparison to standard dip‐moveout and Kirchhoff pre‐stack time migration techniques by applying them to the Swayze East seismic profile acquired in the Abitibi greenstone belt of Canada. This seismic profile represents a crooked‐line survey that intersects several metal‐bearing deformation zones, providing good target geometries to examine various pre‐stack migration methods. Analysis of the seismic data indicates reflectivity associated with shallowly dipping reflections appears relatively well preserved over the entire 0–6 km offset range for the frequency range between 20 to 90 Hz. Although most reflections are visible already in either the dip‐moveout or the Kirchhoff pre‐stack time migration results, the coherency migration method delivers the most improved image showing all reflective structures inferred for this area. The comparisons suggest the coherency migration method can be considered as superior in terms of resulting seismic image quality compared with conventional approaches for this type of crooked‐line seismic survey in such a complex geological setting. [ABSTRACT FROM AUTHOR]

This study investigates the structural control of the numerous gold occurrences in the southern part of the Barberton Greenstone Belt in the Malolotja and Steynsdorp areas. The gold-bearing event distribution is studied using field structural geology associated with a petrological and microstructural analysis. Three major tectonic events have been identified in quartz veins and direct country rocks. The first event (De) created a regional schistosity (Se), probably associated with an early thrusting event. The second event (Df) is related to a large-scale folding, which formed the anticline at Steynsdorp and synform at Malolotja. It resulted from a main E–W direction of shortening and is responsible for the folding of the Se schistosity. It formed a N–S-striking axial planar cleavage (Sf), observed and associated with the emplacement of the main gold-bearing veins. The mineralised system exhibits a complex vein network, in which shallow dipping veins have developed coevally with steep west- and east-dipping veins. A third deformation event (Dl) produced by NE–SW shortening is related to the late barren hydrothermal quartz vein formation. Mineralogically, the veins are filled with abundant quartz, and scarce tourmaline and feldspars. Alteration halos composed of neoformed tourmaline and plagioclase within a talc and white mica matrix developed specifically during the late Dl event. A model of regional deformation giving rise to large-scale folds and quartz vein formation formed in response to E–W and NE–SW directions of shortening globally is proposed and discussed in this paper. [ABSTRACT FROM AUTHOR]

The first data on the multi-isotopic S composition of sulfides of the Neoarchean banded iron formations (BIFs) of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandian Shield) formed 2760–2740 Ma ago are presented in this paper. Pyrite associated with fine-grained magnetite has negative δ34S (to –7.8‰) and positive Δ33S (to +0.7‰) values. Pyrrhotite from stringer-disseminated ores associated with schists exhibits negative values of both δ34S (to –6‰) and Δ33S (to –0.46‰). Our data provide grounds to suggest that the BIF sulfides sourced photolitic elementary sulfur from the atmosphere, sulfate from seawater, and sulfur from magma. The S isotope ratios of sulfides reflect the interaction between abiotic (atmospheric, hydrothermal) and biotic (microbial dissimilation reduction) processes during the formation of iron deposits of the Kostomuksha greenstone belt of Karelia. [ABSTRACT FROM AUTHOR]

The ca. 3.5 Ga Bon Accord Ni deposit was located in the Barberton Greenstone Belt of the Kaapvaal Craton, South Africa, and contained a unique assemblage of Ni-rich minerals including trevorite (NiFe2O4). It was initially interpreted as a metamorphosed extraterrestrial body, recently ruled out by Cr isotope data, and subsequently as a fragment of the Archean Earth's core. More recent suggestions have highlighted similarities between Bon Accord and Archean magmatic sulfide mineralization. We present a geochemical (rare earth element [REE], halogen, and highly siderophile element [HSE] abundance) and isotopic (noble gases, Zn, Cr, and Re-Os) study to elucidate the origin of this enigmatic body. Bon Accord is enriched in the REE relative to primitive mantle (PM), with a pattern resembling that of Aldepleted komatiites. The bulk material has >10 PM Os and Ir, >100 - PM Ru, Pt, Pd, and Re, and radiogenic 187Os/188Os. Trevorite, silicates, and two bulk-rock samples are consistent with chondritic to sub-chondritic initial 187Os/188Os at the time of formation. The new REE data implicate a komatiite precursor in the formation of Bon Accord, and the HSE data bear striking similarities to those of Ni-enriched Archean magmatic sulfide deposits. Enrichment in the heavier Zn isotopes supports desulfurization of a sulfide (isotopically light) deposit during serpentinization to produce the trevorite-dominated body. We conservatively estimate this process could have mobilized as much as -9.2 x 104 tonnes of H2S, offering an intriguing possibility for sourcing of the sulfur that fixes the historically important gold mineralization in the Barberton Greenstone Belt. [ABSTRACT FROM AUTHOR]

The nitrogen isotopic composition of organic matter is controlled by metabolic activity and redox speciation and has therefore largely been used to uncover the early evolution of life and ocean oxygenation. Specifically, positive δ15N values found in well‐preserved sedimentary rocks are often interpreted as reflecting the stability of a nitrate pool sustained by water column partial oxygenation. This study adds much‐needed data to the sparse Paleoarchean record, providing carbon and nitrogen concentrations and isotopic compositions for more than fifty samples from the 3.4 Ga Buck Reef Chert sedimentary deposit (BRC, Barberton Greenstone Belt). In the overall anoxic and ferruginous conditions of the BRC depositional environment, these samples yield positive δ15N values up to +6.1‰. We argue that without a stable pool of nitrates, these values are best explained by non‐quantitative oxidation of ammonium via the Feammox pathway, a metabolic co‐cycling between iron and nitrogen through the oxidation of ammonium in the presence of iron oxides. Our data contribute to the understanding of how the nitrogen cycle operated under reducing, anoxic, and ferruginous conditions, which are relevant to most of the Archean. Most importantly, they invite to carefully consider the meaning of positive δ15N signatures in Archean sediments. [ABSTRACT FROM AUTHOR]

Petrographic, whole‐rock geochemical and geochronological analysis of polymictic conglomerate, associated siltstone and greywacke in the Neoarchean Gadag Greenstone Belt in the Western Dharwar Craton, India, provides new insights into sedimentary provenance and tectonic setting. The polymictic conglomerate contains granitic, gneissic, felsic and mafic volcanic, quartzite and banded ferruginous chert clasts within a quartzo‐feldspathic matrix. Framework grains in the siltstone and greywacke are quartz, feldspar with rock fragments, embedded in a chlorite‐dominant matrix. The chemical index of alteration values (~70) and A‐CN‐K plot for the rocks suggest a low‐to‐moderate degree of weathering. Rare earth element (REE) patterns show moderate fractionation (LaN/YbN ~ 12.31) with a weak negative europium anomaly (0.82). Enrichment in transition elements (Ni, Cr, Co, Sc) and depletion in high‐field‐strength elements, as well as relatively low La/Co (0.62), moderate to high Th/Yb (3.06), La/Th (5.16), La/Yb (17.5), and La/Sc (~2.37) ratios, suggest a mixed felsic‐mafic provenance. U–Pb dating of detrital zircon from the conglomerate and greywacke revealed major age peaks at ca. (3.2, 2.9, 2.8, 2.6, 2.5 Ga) and a maximum age of deposition of 2,508 ± 26 Ma, 2,493 ± 20 Ma, respectively. The above data suggest low to moderately weathered proximal sources for both conglomerate and greywacke, indicating that these two rock types were not deposited simultaneously, but rather separately. The association of these conglomerates and greywacke with continental arc‐related volcanics indicates the closing of an arc at the time of sedimentation. Complex provenance consisting of recycled and magmatic arc during basin closure confirm the notion of modern style plate tectonics operating during Neoarchaean. [ABSTRACT FROM AUTHOR]

A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, Canada, images a 50-km-long north-dipping conductor (<20 Ω·m) at 20-25 km depth and subvertical conductors spatially correlated with crustal-scale shear zones and large orogenic gold deposits. The conductors are interpreted to be the conductivity signature of the deep crustal source of the auriferous fluids and pathways of the orogenic gold system. The geophysical results, supported by existing geochemical and fluid inclusion studies, suggest that the Au- and CO2-rich fluids responsible for gold mineralization were released by devolatilization of supracrustal rocks underthrust to mid- to lower-crustal levels during subduction. This MT study links shallow gold mineralization to a deep crustal source region, demonstrating the connection between a crustal suture zone and the formation of orogenic gold deposits in an Archean greenstone belt. [ABSTRACT FROM AUTHOR]

The mafic volcanic rocks from the eastern felsic volcanic terrane (EFVT) of the Neoarchean Sandur greenstone belt of Western Dharwar Craton (WDC) are studied to evaluate their geochemical characteristics and tectonic implications. Characterised as subalkaline, tholeiitic basalts, they display moderate SiO2 (49.82–53.74 wt.%), Al2O3 (9.08–15.91 wt.%), TiO2 (0.25–0.66 wt.%) and total alkalies (Na2O+K2O= 0.60–3.97 wt.%) with Mg# ranging from 37–55 at low Cr (7–33 ppm), Ni (8–24 ppm) and V (252–612 ppm). Their rare earth and trace element patterns are coherent exhibiting moderate fractionation (La/Yb=0.16–1.09), slight negative Eu anomalies indicating limited plagioclase fractionation (Eu/Eu*= 0.69–0.96), negative Nb, Ta, Ti and Zr-Hf anomalies revealing their arc signatures. The Nb-Th and Zr-Y relationships of these basalts suggest their derivation from the partial melting of depleted mantle in an intra-oceanic arc setting. Trace element modelling of these basalts indicates their genesis by ∼15% partial melting of depleted MORB-mantle and depletion of the source is attributed to previous melting events. These basalts are geochemically similar with the depleted arc and forearc basalts of the Phanerozoic Tonga and Izu-Bonin-Mariana arcs emphasising the operation of analogous tectonic processes during the Archean era. [ABSTRACT FROM AUTHOR]

The metamorphosed ultramafic-mafic bodies of the Kudada area are located close to the Singhbhum Shear Zone (SSZ) in eastern India, where the major rock types are talc-magnesite schist and serpentinite with accessory chromite and magnetite veins. The ultramafic bodies and associated metavolcanic rocks are part of the northern extension of the Early Archean Gorumahisani greenstone belt and belong to the Iron Ore Group (IOG) supracrustal sequence. This study reveals intense compositional variability in accessory chromites of serpentinite with core composition of chromites are characterized by the variable Cr# [Cr/(Cr+Al)] = 0.53–0.82 and Mg# [Mg/(Mg+Fe2+)] = 0.01–0.17. Compositional variability on the scale of a single chromite grain occurs in the form of multi-stage zoning. To identify the patterns of compositional zoning, chromites of serpentinite are subdivided into four types depending on their grain size, reflectivity of different rims, intensity of fracture, and porosity, and supported by in-situ mineral chemistry. The type-I chromites are less fractured and non-porous variety showing the outermost chrome magnetite rim envelops the inner ferritchromit rim. Porosity is mainly developed in the type-II grains where the inner ferritchromit is formed surrounding the pore spaces. The type-III chromites are small clustered grains having ferritchromit core and chrome magnetite rim while the type-IV grains are completely altered to chrome magnetite. Textural relations and mineral chemistry indicate that metamorphism and activities of H2O and CO2-rich hydrothermal fluids during tectonic evolution of the Singhbhum Shear Zone (SSZ) might have caused these zoning patterns and compositional variabilities in accessory chromites of the Kudada area. Cation exchange between chromite and silicate minerals along with intra-grain cation diffusion within different Cr-spinel zones further intensified these processes. [ABSTRACT FROM AUTHOR]

This study presents multiple sulphur isotope (32S, 33S, 34S, 36S) data on pyrites from silicified volcano‐sedimentary rocks of the Paleoarchean Onverwacht Group of the Barberton greenstone belt, South Africa. These rocks include seafloor cherts and felsic conglomerates that were deposited in shallow marine environments preserving a record of atmospheric and biogeochemical conditions on the early Earth. A strong variation in mass independent sulphur isotope fractionation (MIF‐S) anomalies is found in the cherts, with Δ33S ranging between −0.26‰ and 3.42‰. We explore possible depositional and preservational factors that could explain some of this variation seen in MIF‐S. Evidence for microbial activity is recorded by the c. 3.45 Ga Hooggenoeg Formation Chert (HC4) preserving a contribution of microbial sulphate reduction (−Δ33S and –δ34S), and a c. 3.33 Ga Kromberg Formation Chert (KC5) recording a possible contribution of microbial elemental sulphur disproportionation (+Δ33S and –δ34S). Pyrites from a rhyo‐dacitic conglomerate of the Noisy Formation do not plot along a previously proposed global Felsic Volcanic Array, and this excludes short‐lived pulses of intense felsic volcanic gas emissions as the dominant control on Archean MIF‐S. Rather, we suggest that the MIF‐S signals measured reflect dilution during marine deposition, early diagenetic modification, and mixing with volcanic/hydrothermal S sources. Given the expanded stratigraphic interval (3.47–3.22 Ga) now sampled from across the Barberton Supergroup, we conclude that large MIF‐S exceeding >4‰ is atypical of Paleoarchean near‐surface environments on the Kaapvaal Craton. [ABSTRACT FROM AUTHOR]

The carbonates of the Dodguni area of the Chitradurga greenstone belt, Dharwar Craton, India were studied to understand the Archean diagenetic and palaeo‐depositional conditions using carbon and oxygen isotopes along with whole‐rock geochemistry. These carbonates show significant variation in δ13C and δ18O (−1.73‰ Vienna Peedee Belemnite [VPDB] to −0.45‰ VPDB and δ18O vary from −13.51‰ VPDB to −8.46‰ VPDB, respectively). The rare earth element (REE) + Y (rare earth elements and yttrium) of the studied carbonate rocks exhibit flat and uniform patterns (PrSN/YbSN = 0.4–1), slight positive La, Eu and Gd anomalies (CeSN/CeSN* = 0.8–0.9; EuSN/EuSN* = 0.7–1.4 and GdSN/GdSN* = 2–2.3, respectively) with slight positive Ce anomalies (PrSN/PrSN* = 0.84–0.86) and superchondritic Y/Ho ratios (Y/Ho = 29–45; chondritic Y/Ho = 28). Their negative δ13C (−1.75‰ to −0.45‰) values are attributed to the influence of higher bio‐productivity during their deposition and oxidation of organic carbon. The geochemical and isotopic systematics suggest that the Dodguni limestones are not affected by the diagenetic and metamorphic processes and record the REE geochemistry of the ancient seawater in which they were precipitated. The comprehensive geochemical including the isotopic studies of the Archean carbonate rocks of the Dharwar Craton, indicate their deposition in shallow marine conditions, precipitation in high temperatures with significant hydrothermal input under the influence of high bio‐productivity, thereby providing valuable constraints on the palaeoceanography and geochemical evolution of the Archean sea. [ABSTRACT FROM AUTHOR]

Mass movements naturally occurring along slopes, especially after heavy rains, cause heavy losses of materials and life and affect highways, pipelines, and bridges, among other structures. Among the most common mass movements, landslides and subsequent mass flows especially stand out. Remote sensing and geoprocessing techniques are useful tools for geological and geotechnical analysis, here applied to characterization of mass movements from the analysis of the influence of slopes, lineaments or fractures, and geological-geotechnical at the junction of the Curral homocline and the Moeda syncline, Quadrilátero Ferrífero, Southeast Brazil. The area consists of Archean granitic-gneissic basement and the greenstone belt sequence of the Rio das Velhas Supergroup with Proterozoic metasedimentary rocks of the Minas Supergroup covering these two older successions. Based on satellite images, a preliminary map of lineaments was created, and fractures were grouped according to their direction before being rasterized. Each lineament group was associated with a previously known geological and/or structural feature. Geological units mapped in the area were numerically classified according to their mass movement susceptibility and related geotechnical units. Using a Shuttle Radar Topography Mission (SRTM) image, a terrain slope raster was generated. The objective was to obtain a raster indicating low and high probabilities of mass movements. Four sets of lineaments were identified: the first set associated with the northeast strike stratification of the rocks of the Moeda Formation; the second set related to eastward-trending warp axis lineations; the third set related to the southeast trend of stretch lineaments or mafic dykes directions; and the fourth set evidently associated with the watershed pattern of the Curral Range crest, perpendicular to the strike of the rocks in the area. Simulations with different combinations of parameters produced eight scenarios were generated were constructed to classify the area as to its susceptibility to rupture through changes in slope, lithotype, and lineament density; the first four (1 to 4) were classified by using the slope percentage raster without interval reclassification, so its values in the cartographic algebra were not grouped. The last for (5 to 8), consider the slope percentage classified. This methodology successfully combines mathematical models for predicting mass movements and determining areas in the urban landscape most susceptible to these phenomena. As such, it comprises a useful tool for government planning of preventative actions for areas of high risk. [ABSTRACT FROM AUTHOR]

This paper presents a complex interpretation of structural–petrological studies and new geochemical and isotope–geochronological data on the Paleoarchean metamorphic and metaintrusive rocks of Mts. Rymill and Bloomfield in the northern part of the granite-greenstone Ruker terrane (Prince Charles Mountains, East Antarctica). The detailed sequence of changing Archean tectonomagmatic processes in the northern block of the Ruker area has been revealed and the main stages of tectonic deformations and metamorphism of Precambrian geodynamic evolution are shown, which is a key for the understanding of the geological evolution of the Archean metamorphic complexes of East Antarctica and ancient Earth's regions. The northern part of the Ruker Terrane is composed of the Meso-Neoarchean granite–gneiss domes, which are tectonically framed by fragments of greenstone belt of the metavolcanosedimentary Meso-Neoarchean Menzies Series. The detached blocks or packages of sheets of metavolcanosedimentary sequences are a section of weakly metamorphosed intermediate–felsic sandstones, quartzites, and micaceous schists. An assemblage of rocks spans a significant period from 3.2 to 2.5 Ga. The composition of the Mesoarchean granite–gneiss domes of the Mawson Series (3.2–3.1 Ga) corresponds to those of ancient granitoids, is similar to tonalite–trondhjemite–granodiorite (TTG) complexes, and is comparable with similar associations of ancient cratons of Australia, Canada, and Fennoscandia. The rocks of the Mawson Series are polymetamorphic and a significant part of their recrystallization is related to the Mesoarchean stage of metamorphism, whose end is comparable with the formation of the Meso-Neoarchean blocks of the granite–gneiss association of the TTG dome of ~2.8 Ga identified by the author. The age of the striking tectonothermal event of ~2.7 Ga is determined by overgrowths of zircons from the TTG gneisses. The Mawson Orthogneiss and TTG gneisses are compared with intraplate A‑granitoids and are ascribed to low-Ti high-K Archean granitoids. The geochemistry of the rocks indicates that primary melts of the Meso-Archean Mawson Orthogneiss formed in crust at shallower depths (P < 8–10 kbar) in comparison with Meso-Archean TTG gneisses, whose formation is possibly caused by the increasing thickness of the crust followed by its extension and thinning at a boundary of ~2.5 Ga. [ABSTRACT FROM AUTHOR]

Our ability to understand the geological evolution of Archean cratons is fundamentally dependent on stratigraphic reconstructions across greenstone belts. Here, we integrate published stratigraphic, geochemical and geochronological data to produce a revised stratigraphic model for the Agnew-Wiluna Greenstone Belt of the Yilgarn Craton. The Agnew-Wiluna Greenstone Belt records ca 130 m.y. of magmatism that occurred between ca 2820 and 2690 Ma and can be divided into three cycles. Cycle 1 is marked by ca 2820–2740 Ma mafic–ultramafic volcanic rock successions. Cycle 2 is associated with ca 2740–2720 Ma felsic volcanic rocks, associated fragmental deposits and contemporaneous mafic–ultramafic intrusions. Cycle 3 consists of ca 2720–2690 Ma mafic–ultramafic volcanic rock successions and co-magmatic intrusions. Exhumation and reworking of these continental rift basin successions after ca 2690 Ma resulted in two younger, additional, depositional cycles in the Agnew-Wiluna Greenstone Belt. Cycle 4 is associated with intermediate to felsic volcanoclastic rocks and epiclastic rocks erupted/deposited between ca 2690 and 2665 Ma. Cycle 5 is associated with the deposition of polymict conglomerates and sandstones in localised depocentres between ca 2665 and 2655 Ma. The stratigraphic scheme identified at the scale of the Agnew-Wiluna Greenstone Belt is the local expression of craton-wide tectono-thermal events. Our revised stratigraphic model for the Agnew-Wiluna Greenstone Belt and proposed correlations at the craton scale support a para-autochthonous model whereby crust from a proto-Yilgarn continental mass was extended/thinned, favouring the activation of translithospheric pathways associated with the ca 2720–2690 Ma Kalgoorlie Large Igneous Province. Inversion of this intra-cratonic rift basin after ca 2680 Ma led to the protracted activation of shear zones and multiple shifts in sedimentary depocentres. The widespread occurrence of previously unidentified fragments of ca 2820–2720 Ma substrate within the Kalgoorlie-Kurnalpi Rift has significant implications for craton-scale stratigraphic reconstructions and challenges existing terrane and domain boundaries. We propose a revised, coherent and testable stratigraphic model for the Agnew-Wiluna Greenstone Belt of the Kalgoorlie Terrane. We compare our revised stratigraphic model for the Agnew-Wiluna Greenstone Belt with that of the Murchison and Southern Cross domains of the Youanmi Terrane in order to build a new space–time–integrated stratigraphic cross-section across the western half of the Yilgarn Craton. We demonstrate for the first time the existence of a magmatic continuum (i.e. no significant magmatic hiatus) between ca 2820 and 2690 Ma, providing the missing link between the geological record of the Youanmi Terrane and that of the Eastern Goldfields Superterrane. [ABSTRACT FROM AUTHOR]

The preliminary field, petrographic and whole-rock geochemical data of the amphibolites from the southwestern part of the Gadag greenstone belt is presented in this study. The studied amphibolites in the southwestern part of the Gadag greenstone belt occur as isolated bands and occasionally exhibit distinct banding. The NE trending amphibolites are composed chiefly of hornblende+quartz±plagioclase. The analysed samples show tholeiitic basalt affinity, characterised by flat REE patterns and display no Nb–Ta or Zr–Hf anomalies on the multi-element spidergrams. The elemental ratios indicate that the studied rock samples are relatively immobile and devoid of crustal contamination. Petrogenetic studies indicate that their source of studied amphibolites was derived from the partial melting of the amphibole+spinel bearing peridotite within the spinel stability field. Trace elemental modelling suggests that the chemical composition can be reproduced by ~10–11% partial melting of the source with 38% olivine, 35% clinopyroxene, 25% amphibole, 1% plagioclase, and 1% spinel. The studied amphibolites show a strong affinity towards the MORB-type plate tectonic setting. [ABSTRACT FROM AUTHOR]

Rhenium-Os isotope and highly siderophile element (HSE, including Re, Os, Ir, Ru, Pt, and Pd) abundance systematics of Archean komatiites can be used to estimate the stirring rates of the mantle for the HSE and the timing of homogenization of late accreted materials within the mantle. In this study, we report Re-Os isotope and HSE abundance data for ~2.9 Ga komatiites and basalts from the Sumozero-Kenozero greenstone belt in the SE Fennoscandian Shield. The lavas are characterized by excellent preservation of the primary textural, chemical, and Re-Os isotope characteristics. The Re-Os isotopic data for spinifex-textured and cumulate komatiite and massive basalt samples from the lowermost sequences define a precise 10-point isochron (MSWD = 2.6) with an age of 2904 ± 18 Ma and an initial 187Os/188Os = 0.10758 ± 18 (γ187Os(2904) = +0.45 ± 0.17). This is the first direct age determination for the Sumozero-Kenozero lower komatiite-basalt sequences. Our modeling indicates that the mantle source of the komatiites and basalts evolved with a time-integrated 187Re/188Os = 0.418 ± 6. This ratio is well within the uncertainty of the bulk chondritic average 187Re/188Os = 0.410 ± 51 (2SD), also consistent with the chondritic evolution of the majority of komatiite mantle sources observed globally. The mantle source of the Sumozero-Kenozero komatiites has been calculated to contain the total HSE abundances of 58 ± 7% of those in the estimates for modern Bulk Silicate Earth (BSE). This estimate is in the middle of the range for other late Archean and Proterozoic komatiite systems. Using the estimated HSE abundances in the sources of komatiite systems as a function of their ages and ISOPLOT regression analysis, we calculated the average time in the past by which late accreted materials have been completely homogenized within the mantle to be 2.48 ± 0.23 Ga. These data require that the residence times of the late accreted planetesimals within the mantle, before complete homogenization, were on average 1.92 ± 0.23 Ga. This estimate represents a constraint on the average mixing rates of the mantle in terms of the HSE abundances in the Hadean and the Archean. [ABSTRACT FROM AUTHOR]

This work is based on the unprecedented Tectonic-Geochronological Map of Bahia (TGMBA): metallogenic implications. In the TGMBA, sixteen tectonic domains were identified, and the main mineral occurrences and deposits in each were recorded. Of the Palaeo-Mesoarchean blocks, the Gavião (GB), Serrinha (SB) and Uauá (UB) blocks were highlighted. The southern GB was formed by plate tectonics, in two stages, at ca. 3403–3378 and 3259–3240 Ma. These rocks served as basement for the Umburanas Greenstone Belt, which comprises felsic metavolcanic rocks (3147 Ma) interspersed with ocean floor mafic metavolcanics and could have been the source of the recently found orogenic gold. This crust could also have formed the basal section of the Brumado metavolcanic-sedimentary sequence, which hosts one of the most important magnesite mines in the world. The northern part of the GB hosts TTGs with ages of ca. 3642–3520 Ma, the oldest known rocks in the whole São Francisco Craton. This region served as a passive margin for the Jacobina-Umburanas Sea, where quartzites and conglomerates (3305 Ma) with detrital gold were deposited and, in the deeper portions of this sea, Mesoarchean ocean floor or Island-arc basalts (3200 Ma) with pillow-lava structures were formed. On the platform of this basin, Mn deposits were formed in association with pelites and sandstones [ABSTRACT FROM AUTHOR]

Archean Serpentinised dunite is important not only for understanding the evolution of the ultramafic deposit of magnesium, but also serves as a possible sink material for the carbon dioxide sequestration. Future anti-pollution measures may include sequestering of waste CO2 as magnesite (MgCO3) by processing ultramafic rocks to obtain reactable Mg. For the first time, the Raman spectroscopic investigation of dunite is presented from the Karya, Sargur supracrustals (3Ga) Greenstone Belt. The Raman spectra of the sample reveal abundant presence of serpentine. Polymorphs of serpentine: lizardite, antigorite and chrysotile exhibit typical intense band at 685–692 cm−1 in the Raman spectrum. The Raman peaks in this study also indicates the presence of chromite and magnesite. The lunar dunite 72415, one of the oldest lunar samples of the Mg-suite, contains chromite symplectites indicative of crystallization at 40–50 km rather than at a shallow depth of <1 km, also having a olivine content of about 85%. The present study showed the dunite has about 85% olivine, which is almost identical to the Martian dunite, meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ∼ 85% vol. The present study on the Karya dunite of Sargur supracrustals (3 Ga) greenstone belt, Western Dharwar Craton Karnataka, indicates a possibility of using this as a terrestrial analogue material for improving the Martian surface mineralogy and occurrence of hydrous minerals and life support system in Mars. [ABSTRACT FROM AUTHOR]

The nature of the early Archean ocean floor remains a topic of important debate. There are relatively few well-preserved occurrences worldwide where such terrains may be studied in detail because of structural dismemberment, metamorphic overprinting and pervasive early stage hydrothermal alteration to recent weathering. The 3.41-Ga dominantly mafic formations of the Nondweni Greenstone Belt (NGB) covering 270 km2 in the south-eastern Kaapvaal Craton comprise submarine volcanics that exhibit a wide range of textural features, including pillows, chill zones and brecciated flow tops, and various spinifex textures, including the rare platy pyroxene type, cumulate layers, and tuffs. Channelized subaqueous lava lakes that underwent fractionation are capped by thick spinifex-textured units and pillows. Early stage seafloor alteration is regionally variable, ranging from intense to minimal, with preservation of original mineralogy in many areas. Mafic volcanic rocks of the NGB contrast with those of the Barberton Greenstone Belt both in the style of volcanism and in the associated compositional range of komatiitic basalt to basalt with a complete absence of high-Mg komatiites. Olivine-phyric rocks, or derivatives thereof, are largely absent and pyroxene is the main controlling phase with orthopyroxene in the most primitive komatiitic basalts and clinopyroxene in the evolved lava lake sequences. The abundance of orthopyroxene typifies the long-standing silica-enriched character of the Kaapvaal Craton. Three exceptionally well-preserved and well-exposed sequences were studied utilizing hand-drilled samples and deep coring providing unprecedented stratigraphic and textural detail and field controls for more than 400 samples. A unifying feature of the mafic volcanics of the NGB is the range of compositions and ratios of incompatible elements most clearly illustrated by a series of high- and low-Ti compositional lineages reflecting differing sources or degrees of mantle partial melting. Sharp boundaries between high- and low-Ti flow successions indicate sudden changes in the melting regimes or the interaction of flow sequences from different volcanic centres. Th/Nb ranges from 0.1 to 0.2 and reveals crustal contamination of primitive lavas. The primary magma that gave rise to the most primitive komatiitic basalts with 19.5% MgO was derived from partial melting of a mantle plume source in the garnet stability field. Trace element modeling shows that the sequences studied in detail have been modified by fractionation and crustal contamination with the most likely contaminant being the Ancient Gneiss Complex (3.43–3.66 Ga), which is extensively exposed in Eswatini and probably underlies the Paleoarchean terrains in the southern Kaapvaal Craton. The geotectonic setting was likely that of a submerged felsic crustal platform as enclaves within an oceanic plateau. [ABSTRACT FROM AUTHOR]

Orogenic gold deposits are comprised of complex quartz vein arrays that form as a result of fluid flow along transcrustal fault zones in active orogenic belts. Mineral precipitation in these deposits occurs under variable pressure conditions, but a mechanism explaining how the pressure regimes evolve through time has not previously been proposed. Here we show that extensional quartz veins at the Garrcon deposit in the Abitibi greenstone belt of Canada preserve petrographic characteristics suggesting that the three recognized paragenetic stages formed within different pressure regimes. The first stage involved the growth of interlocking quartz grains competing for space in fractures held open by hydrothermal fluids at supralithostatic pressures. Subsequent fluid flow at fluctuating pressure conditions caused recrystallization of the vein quartz and the precipitation of sulfide minerals through wall-rock sulfidation, with some of the sulfide minerals containing microscopic gold. These pressure fluctuations between supralithostatic to near-hydrostatic conditions resulted in the post-entrapment modification of the fluid inclusion inventory of the quartz. Late fluid flow occurred at near-hydrostatic conditions and resulted in the formation of fluid inclusions that have not been affected by post-entrapment modification as pressure conditions never returned to supralithostatic conditions. This late fluid flow is interpreted to have formed the texturally late, coarse native gold that occurs along quartz grain boundaries and in open spaces. The systematic evolution of the pressure regimes in orogenic gold deposits such as Garrcon can be explained by relative movement of fault-fracture meshes across the base of the upper crustal brittle-ductile transition zone. We conclude that early vein quartz in orogenic deposits is precipitated at near-lithostatic conditions whereas the paragenetically late gold is introduced at distinctly lower pressure. [ABSTRACT FROM AUTHOR]

In Cameroon, most of the iron formation occurrences reported are found within the Nyong and Ntem Complexes. The Anyouzok iron deposit is located in the Nyong Complex greenstone belts, which represent the NW margin of this Congo craton. The main lithological units comprise the iron formations (IFs) unit, consisting of banded IFs (BIFs) and sheared BIFs (SBIFs), and the associated metavolcanic rocks unit consisting of mafic granulite, garnet amphibolite, and biotite gneiss. Within the Anyouzok area, BIFs are rare, while SBIFs are ubiquitous. This study reports the petrography, mineralogy, and whole rock geochemistry of IFs and interbedded metavolcanic rocks of the Anyouzok iron deposit. The abundance of cavities, higher Fe contents (49.60–55.20 wt%), and strong Eu anomalies (Eu/Eu* = 2.14–3.17) within the SBIFs compared to the BIFs suggest that SBIFs were upgraded through post-depositional hydrothermal alteration activities. REE signatures indicate the contribution of both seawater and hydrothermal fluids during BIFs precipitation. Mafic granulite and garnet amphibolite protoliths were derived from the partial melting of a metasomatized spinel lherzolite depleted mantle source. The overall compositional variations of the Anyouzok IFs and interbedded metavolcanic rocks endorse an Algoma-type formation deposited in the back-arc basin under suboxic to anoxic conditions. [ABSTRACT FROM AUTHOR]

The paper summarizes major and trace-element compositions and Sm–Nd isotope data on metabasites (amphibolites) and gabbroids of the Onot granite–greenstone block in the Sharyzhalgai basement uplift, southwestern Siberian craton. The Onot block consists of tectonically combined nappes of the Paleoarchean tonalite–trondhjemite–granodiorite (TTG) complex and the metasedimentary-volcanic complex of the greenstone belt (GB). The Mezoarchean (∼2.88 Ga) metabasalts of the greenstone belt and Paleoproterozoic (∼1.86 Ga) gabbronorites and vein gabbros were formed at rifting and postcollisional extension, respectively. The Archean metabasites of the greenstone belt and enclaves in the TTG complex compositionally correspond to low-Ti tholeiitic basalts and basaltic andesites. The basaltic rocks are characterized by flat REE patterns [(La/Sm)n = 0.9–1.9], depletion in Nb relative to Th and La (Nb/Nb* = 0.4–1.1), and a wide range of mostly positive εNd(T) values (from +5.2 to –1.0). The enrichment of the basaltic andesite in incompatible elements, its Eu minimum, and negative εNd(T) values resulted from contamination by Paleoarchean TTG gneisses, that form the basement of GB. The Paleoproterozoic gabbronorites have high Mg# and extremely low concentrations of Ti and incompatible elements. The rocks are characterized by low (Nb/Y)PМ (0.8–1.0), negative εNd(T) values (from 0 to –1.4), and weak enrichment in Th and LREE relative to Nb. The vein gabbros have low (La/Sm)n, positive εNd(T) values of +2.8 and +0.3, and a negative Nb anomaly (Nb/Nb* = 0.3–0.4). The trace element-composition of the amphibolites, gabbronorites, and gabbros and the results of geochemical modeling indicate that the parental melts were derived mainly from weakly depleted mantle sources. The Nd isotope composition of the Paleoproterozoic gabbroids resulted from the evolution of the heterogeneous Archean lithospheric mantle. Variations in the isotope and trace-element composition of the amphibolites reflect the initially depleted nature of the Mezoarchean mantle and its metasomatic alteration by fluids/melts, which occurred before its melting at ∼2.88 Ga. The geochemical and Nd isotopic characteristics of gabbronorites and gabbros indicate that the lithospheric mantle had become progressively more heterogeneous by the Paleoproterozoic due to preceding Archean processes. The variable depletion of both the Archean and the Paleoproterozoic mafic rocks in Nb relative to Th and La may be explained by mantle metasomatism and does not reflect the geodynamic settings of the mafic magmatism. [ABSTRACT FROM AUTHOR]

In orogenic gold systems, the source of the fluids and the processes leading to mobilization, transport, and deposition of gold remain debated. Most studies focus on endowed rather than on gold-poor orogenic systems to unravel the "key" parameters of gold mineralizing processes. Here, we present stable isotope (O, H) data from the Moly-Desgagné–Guercheville fault system (gold-free to low gold endowment) in the Chibougamau area, Abitibi greenstone belt, Canada. The gold-free Moly-Desgagné showing and nearby poorly endowed Hazeur showing and Monster Lake deposit share similar features typical of orogenic systems. The stable isotope compositions of tourmaline and quartz from the Moly-Desgagné–Guercheville fault system also display similar characteristics, such as (1) temperature of vein formation of 345 ± 86 °C (1σ); (2) fluid mixing between an upper crustal reservoir (low T – high δD – low δ18O) and a metamorphic water reservoir (high T – low δD – high δ18O); and (3) positive δDfluid values consistent with multiple boiling-condensation cycles related to fault-valve processes. These characteristics are similar to those from the gold-endowed Val-d'Or vein field. The difference in gold endowment between the Moly-Desgagné–Guercheville and Val-d'Or vein fields may be related to the nature of the fault system (i.e., terrane-bounding or "intragreenstone belt") and the volume and (or) composition (i.e., gold, its ligands, CO2) of the fluid source rocks. [ABSTRACT FROM AUTHOR]

[Display omitted] • The NW–NWW-trending ductile shear zones in the western Shandong granite-greenstone belt show consistent sinistral strike-slip kinematics. • 40Ar–39Ar and zircon U–Pb La-ICP-MS dating results show that the deformation age is ∼ 2.58–2.47 Ga. • The ductile shear zones were shearing deformation caused by the SE-ward plate convergence during the late Neoarchean. The granite-greenstone belt is the main component of Archean crust, and is critical for resolving the disputes on the tectonic evolution and dominant regime of the early Earth. The North China Craton (NCC) is one of the oldest cratons in the world, and is composed of several continental micro-blocks. The greenstone belts, welding the micro-blocks, were generally considered to be continental or arc-continental collision belts during the amalgamation of the micro-blocks in the late Neoarchean. Thus, the structural pattern of these greenstone belts can provide essential clues for the crustal deformation style during early Precambrian orogeny. The western Shandong granite-greenstone belt (WSGB) located in the eastern NCC was considered as the collision belt of the Jiaoliao and Qianhuai Blocks. There exists a series of ductile shear zones with strike-slip kinematics, including Qixingtai, Nanliu, Yanlingguan, Xintai, Dongling–Huacun, Mengshan, Fengyang–Liangqiu, Qingyi and Baiyan. This paper conducts detailed geometric, kinematic and deformation geochronology studies, and reveal that the mylonitic foliation of the ductile shear zones in the WSGB strikes NW280–350° with angles of 60–80°. The mineral stretching lineation gently plunges to NE or SW at 2–25°. Kinematic indicators show sinistral strike-slip shearing sense. The deformation temperature can be divided into two ranges: 550–600 ℃ and 400–500 ℃, implying that the ductile shear zones in the WSGB was ought to experience early-stage high-temperature and late-stage low-temperature deformation. The deformation age is ∼ 2.58–2.47 Ga constrained by zircon LA-ICP-MS U–Pb and 40Ar–39Ar dating, and this age range includes early-stage high-temperature deformation. Structural restoration through balanced profiles and stereographic projection shows that the initial orientation of NW–NWW-trending ductile shear zones was dipping to the SW, and still were featured by strike-slip kinematics. Syn-kinematic arc-affinity magmatism and sedimentation demonstrate that the NW–NWW-trending ductile shear zones in the WSGB were caused by SE-ward plate convergence, which also led to the NW–SE-trending movement of different blocks along the strike of ductile shear zones. The WSGB represents an active continental margin in the southwestern Jiaoliao Block with intense arc-affinity magmatism and back-arc sedimentation, post-collision crustal-derived granites, traspressive shearing deformation, also indicating that the NCC was dominated by modern-style plate tectonism in the late Neoarchean. [ABSTRACT FROM AUTHOR]