Search

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]

Due to the inherently fluid‐mobile nature of W, the 182W record of the early Earth may have been obscured by fluid‐induced mobilization of W. To investigate W mobilization in Archean greenstone sequences, we analyzed 182W isotope systematics and major and trace element concentrations in samples from the 3.53 Ga old Onverwacht Group of the Kaapvaal Craton (South Africa) and the >3.51 Ga old Badampahar Group of the Singhbhum Craton (India). Our results for mafic and ultramafic metavolcanic rocks show W/Th ratios significantly higher than primary magmatic values, which suggests fluid‐induced W enrichment. Samples least affected by secondary W enrichment (W/Th < 0.26) show no resolvable W isotope anomalies from modern mantle values in both cratons. Samples from the Kaapvaal Craton with elevated W/Th exhibit deficits in 182W as low as −8.1 ± 4.3 ppm compared to the modern mantle. Covariations of μ182W with W/Th, and Ce/Pb suggest that negative isotope signatures were introduced during secondary fluid‐mediated processes. The enrichment of W is most evident in altered ultramafic rocks comprising serpentine, resulting in additional covariations between MgO, LOI, and W/Th. The W isotope composition of serpentinized komatiites reflects the composition of younger intruding granitoids. We therefore infer the latter as a possible source of W‐rich fluids. The Badampahar Group samples exhibit little W isotope variability. A well‐resolved 182W deficit of −6.2 ± 2.9 ppm was determined in a single komatiite sample, which indicates an unknown fluid source, currently not represented in any other unit of the Singhbhum Craton. Plain Language Summary: The tungsten (W) isotope composition of ancient rocks can be used to trace processes that occurred during Earth's early evolution. However, interactions between rocks and fluids may alter the W concentration and therefore influence the interpretation of W isotope data. To identify the source of such fluids and the processes by which they affect the W isotope composition of rocks, we analyzed ancient rock samples from South Africa and India. The isotope composition of rocks with a low W concentration reflects that of the modern Earth. Therefore, they do not trace the processes that occurred during Earth's early evolution. Samples from South Africa with untypically high W concentrations show a different isotopic composition. The variation in the W isotope signature correlates with other chemical indices that are susceptible to modification by fluid‐related processes. This shows that the W within the rocks is derived from an external fluid source and not from their original magmatic source. Samples with the highest W enrichment have a similar isotope composition as spatially associated intrusive rocks. By inference, the latter likely represent the source of W‐rich fluids. The samples from India show similar enrichment in W, indicating similar fluid‐related processes and W sources at both localities. Key Points: The magmatic sources of metavolcanic rocks from the Onverwacht Group and the Badampahar Group do not exhibit W isotope anomaliesNegative W isotope signatures in the Onverwacht Group are likely derived from fluids sourced from younger intrusive granitoidsFelsic intrusive rocks are a major source of W‐rich fluids in Paleoarchean greenstone units [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]

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]

Understanding the dominant crustal accretion model in any Archean craton is the key to understanding the dominant geodynamic process responsible for early crust formation during the Hadean (> 4.0 Ga) and Archaean (4.0–2.5 Ga). The continental crust has been proposed to have formed through either horizontal/vertical accretion related to subduction or mantle plume tectonic processes. Here, the Moho depths and average crustal Vp/Vs ratios are modelled at 16 broadband stations in the Eastern Indian Shield (EIS) through HK stacking of radial P-receiver functions (PRFs). These modelled parameters are used to test both plume and subduction models, which might have played a key role in the crustal accretion of the EIS throughout the Archean. We observe a correlation between crustal age and composition within the ellipsoidal Paleoarchean cratonic domain in the Singhbhum-Odisha-Craton (SOC), which reveals an increase in age from the younger granitoid core of the SOC (with thinning of felsic crust) to the surrounding older greenstone belts (with thickening of felsic crust). A thinner mafic crust resulting from multiple magmatic events characterizes the neighbouring Meso-Proterozoic Chotanagpur Granitic Gneissic terrain (CGGT). The Common Conversion Point (CCP) image of radial PRFs reveals northward subduction of the Paleoarchean SOC below the Meso-Proterozoic CGGT. [ABSTRACT FROM AUTHOR]

The discovery and development of world-class Lithium–Caesium–Tantalum (LCT) spodumene-bearing pegmatites in Western Australia underpins growth of a significant new sector of its mining industry. Recently, several new spodumene discoveries have been delineated in the Yilgarn and Pilbara Cratons. Contrary to exploration narratives that new economic mineral discoveries will generally be made at increasingly greater depths, beneath barren cover rocks, or in remote geological environments, all new lithium discoveries have clear surface expressions in relatively 'mature' greenstone belts. The exploration implication is that the search space for pegmatite-hosted spodumene deposits in Western Australia remains immature. These recently discovered LCT pegmatites have geological features relevant to exploration including their age, amphibolite-facies metamorphic setting and syn-metamorphic timing, and 3D geometry, particularly their typically gentle dips, that match other such world-class pegmatites globally. Further spodumene discoveries within pegmatites at or near surface are likely in the Archean terranes of Western Australia based on these consistent exploration criteria and supportive capital market conditions. [ABSTRACT FROM AUTHOR]

• The study reveled the formation of the Neoarchean conglomeratic Ament Bay basin. • The basin is similar to the Timiskaming assemblage in sedimentation and setting. • The basin is dissimilar to the latter in crustal architecture and gold endowment. • The lack of gold in the basin is due to existence of underlying gneissic basement. • Timiskaming-like basins similar in geology may not contain similar gold endowment. The Neoarchean conglomeratic Timiskaming assemblage is considered to be one of the most gold-endowed rock associations in the Abitibi greenstone belt of the southern Superior craton. Identifying Timiskaming-like basins, therefore, may facilitate new discoveries of gold deposits in other Archean greenstone belts. This study focuses on the conglomeratic Ament Bay assemblage (ABA) in the Neoarchean Sturgeon Lake greenstone belt of the western Wabigoon terrane of the western Superior craton. Geologic mapping and petrographic analysis show that the ABA consists of a ≥1000 m thick conglomerate-arenite lithofacies and a conformably overlying ≥200 m thick greywacke-mudstone lithofacies, which are interpreted to indicate a sub-aerial fan delta that transitioned into subaqueous turbidites. The depositional age is constrained to be between 2697.5 ± 1.2 and 2693.2 ± 0.9 Ma by the statistically defined minimum age of the ABA detrital zircons and igneous zircons of an alkalic intrusion within the ABA, respectively. Detrital zircons from seven ABA samples are characterized by ca. 2930, 2780–2770, and 2750–2690 Ma age populations along with minor zircons of ca. 3300–3000 Ma, which are consistent with proximal sources mostly in the western Wabigoon terrane and secondarily in the adjacent Winnipeg River terrane. Petrography of conglomerate clasts and sandstone supports these provenances and reveals additional sources from proximal mafic volcanic rocks. The ABA is interpreted to result from uplift and erosion associated with the late-stage convergence between the western Wabigoon and Winnipeg River terranes and to be partially controlled by a regional fault zone and accompanied by broadly coeval alkalic magmatism. Overall, the ABA is similar to the typical Timiskaming assemblage in lithofacies, depositional environments, structural setting, and syn -depositional alkalic magmatism, but dissimilar to the latter in gold endowment. The apparent lack of gold in the ABA is likely due to assimilation of crustal components into the coeval alkalic melts and a shallow-penetrating fault zone, in contrast to the juvenile nature of alkalic magmatism and deep-penetrating fault zones associated with the Timiskaming assemblage. This study suggests that Timiskaming-like basins similar in geology are not necessarily equivalent to the typical Timiskaming assemblage in gold endowment. [ABSTRACT FROM AUTHOR]

The Sonakhan greenstone belt (SGB), located in the north‐eastern Bastar craton of the Indian shield, comprises mafic‐ultramafic and volcanic‐intrusive sequences in the lower stratigraphic units. We investigate the Platinum‐group element (PGE) relations of Boradih intrusion of the SGB to evaluate its tectono‐magmatic evolution. The chondrite‐normalized PGE patterns of boninitic cumulate rocks exhibit higher abundance of Palladium group PGEs (∑PPGE = 292–496 ppb) relative to the Iridium group PGEs (∑IPGE = 32–52 ppb) along with variable Au concentrations (51.34–718.05 ppb). The PGE concentrations are attributed to a boninitic parental melt, where the IPGEs in the source possibly partitioned into a monosulphide solid solution. The Cu (22–80 ppm), elevated Pt (22–238 ppb), and Pd (31–377 ppb) concentrations indicate Pt and Pd have partitioned into a semi‐metal rich melt during the later stages of crystallization. The geochemical characteristics of the basalts and ultramafic cumulates of the SGB indicate a supra‐subduction zone tectonic setting for its formation. Similar geochemical and litho‐tectonic correlations are also noticed between the SGB of Bastar craton and greenstone belts of the Eastern Dharwar craton of south India. The SGB (V/Yb =146 ± 25) and greenstone belts of Eastern Dharwar craton (V/Yb = 134 ± 52) record similar oxidation conditions of Phanerozoic subduction zones. Accordingly, we propose magmatic as well as tectonic correlations are possible for the Archean‐Palaeoproterozoic Bastar and Eastern Dharwar cratons. [ABSTRACT FROM AUTHOR]

Komatiitic magmatism is a characteristic feature of Archean cratons, diagnostic of the addition of juvenile crust, and a clue to the thermal evolution of early Earth lithosphere. The Slave craton in northwest Canada contains >20 greenstone belts but no identified komatiite. The reason for this dearth of komatiite, when compared to other Archean cratons, remains enigmatic. The Central Slave Cover Group (ca. 2.85 Ga) includes fuchsitic quartzite with relict detrital chromite grains in heavy-mineral laminations. Major and platinum group element systematics indicate that the chromites were derived from Al-undepleted komatiitic dunites. The chromites have low 187Os/188Os ratios relative to chondrite with a narrow range of rhenium depletion ages at 3.19 ± 0.12 Ga. While these ages overlap a documented crust formation event, they identify an unrecognized addition of juvenile crust that is not preserved in the bedrock exposures or the zircon isotopic data. The documentation of komatiitic magmatism via detrital chromites indicates a region of thin lithospheric mantle at ca. 3.2 Ga, either within or at the edge of the protocratonic nucleus. This study demonstrates the applicability of detrital chromites in provenance studies, augmenting the record supplied by detrital zircons. [ABSTRACT FROM AUTHOR]

• Analysis of four new volcano-sedimentary complexes (VSC) in the Pilbara increasing insight in Paleoarchean basin settings. • Multistorey architecture of the 3.5 Ma Coonterunah Subgroup, with a megaslide (new Bergamina Unit) as upper storey. • Recognition of the east-west Warrawoona Lineament as a D1 structure dividing two areas of basin superposition. • Comparison of VSC's of the Pilbara with the Buck Reef-VSC of the South African Barberton greenstone belt. • Introduction of a proxy for Paleoarchean basin depth by comparing VSC-architecture with Phanerozoic passive margins. Four new volcano-sedimentary complexes (VSC's), respectively c. 3510, 3460, 3430, and 3320 Ma old, are identified in the East Strelley, Coongan, and Kelly belts of the East Pilbara craton and compared with the extraordinarily complete c. 3450 Ma Buck Reef-VSC in the southern African Kaapvaal craton. The VSC's reveal an intricate relationship between volcanic deposition, sedimentation, development of syndepositional fault arrays, both extensional and contractional, and magmatism. The geometry and kinematics of these fault systems were analyzed after restoring the tilt of the stratigraphic sequences back to the depositional horizontal. The growth fault arrays are interpreted to have been generated by lack of lateral support of depositional basin margin prisms as known from present-day deltas and passive margins. This 'basin margin collapse' scenario for deformation and kinematics of the topmost section of the crust relies on topographic relief combined with vertical crustal oscillation. The relationship between supracrustal collapse and coeval deformation on deeper-seated detachments within the basement of the Pilbara remains as yet unsolved. The restoration corroborates the (semi-)circular basin architecture we proposed in 2017, which preceded, and is unrelated to, the present-day configuration of granitoid complexes and greenstone belts. The new findings also assess an early, syndepositional presence of the east–west Warrawoona Lineament as a major dividing line of as yet unknown structural character between two areas of basin superposition. For the Coonterunah Subgroup a multistorey architecture is established: the Table Top/Coucal-VSC with its near-water level chert top is overlain by regularly bedded Double Bar Basalt. The ensemble is truncated by the newly introduced tectono-stratigraphic Bergamina Unit, interpreted as a mega-avalanche emplaced somewhere between 3496 and 3466 Ma, possibly time-equivalent to the Duffer Fm. The crustal depths of the detachments below the (water-level) tops of all VSC's identified, in other words the thicknesses of the VSC's, are used as proxy for determining minimum basin centre depths ranging from 1000 to 3800 m. The greatest depth was reached in the North and South Coongan Basins, where voluminous bimodal volcanism of the Duffer Fm, maximum subsidence and deposition rates resulted in maximum basin margin instability. [ABSTRACT FROM AUTHOR]

Archean ultramafic–mafic magmatism associated with dynamic mantle melting processes represents an integral part of crustal evolution and continental growth. Archean mantle plumes and their high temperature derivatives in komatiitic magmas provide a cornerstone in understanding the thermal and chemical evolution of the early Earth and its mantle. In this study, we evaluate the geochemical characteristics of the temporally distinct Sargur Group and Dharwar Supergroup greenstone belts of Dharwar Craton in southern India. The komatiites associated with these greenstone belts are characterized by Al‐depleted and Al‐undepleted compositions. Their MgO, Ni, Co, and Cr concentrations reflect primitive, undifferentiated nature of precursor melts, whereas the HFSE and REE chemistry corroborates high‐degree (30–50%) partial melting of mantle with prominent role of majorite garnet and perovskite in the generation of komatiitic melts. The Al‐depleted komatiites were formed at a greater depth (~13 GPa) by equilibrium melting leaving a garnet‐bearing residue. The resultant komatiitic melt retained buoyancy under extreme pressure and high temperature conditions, segregated and accumulated in the ambient peridotite mantle source and subsequently escaped with progressive decrease in pressure in the ascending plume. The Al‐undepleted and relatively rare Al‐enriched komatiites were derived by fractional melting at intermediate to shallow depths after the discharge of a large proportion of melt ensued by the collapse and entrance of residual garnet into the melt phase. The Mesoarchean–Neoarchean Dharwar komatiites provide evidence for heterogeneous, hydrated Archean upper mantle trapped by ascending mantle plumes. The non‐plume, arc‐related signatures invoke contributions from (a) sub‐cratonic lithospheric mantle roots influenced by ancient subduction events and (b) hydrated Archean upper mantle. The Sargur Group and Dharwar Supergroup komatiites record a distinct temporal transition and geochemical heterogeneity in the Archean mantle beneath the Dharwar Craton and can be attributed to Archean upper mantle hydration by flat slab subduction of >3.3 Ga oceanic crust at shallow level with vestiges of primordial oceanic crust forming deep cratonic mantle roots beneath the Dharwar Craton. The temporal transition towards mantle hydration beneath Dharwar Craton during the Mesoarchean can be correlated with the onset of subduction‐driven plate tectonics and ocean–crust–mantle interactions. [ABSTRACT FROM AUTHOR]

• A new U-Pb ID-TIMS age 2256 ± 6 Ma is obtained for NE to ENE trending mafic dyke swarm. • Seven distinct Precambrian mafic dyke swarms are identified in the Singhbhum craton. • Two of them i.e. ~2.25 Ga and ~1.77 Ga have close match with the Dharwar craton. • This also implies that both swarms should be present in intervening Bastar craton. • 2.25–2.26 Ga and 1.77–1.79 Ga LIPs are analogous with different crustal blocks of the globe. Based on trend, cross-cutting relationships and U-Pb dating, Precambrian mafic dykes in the Singhbhum craton, earlier collectively identified as 'Newer Dolerite Swarm', have been separated into seven distinct swarms, which are thought to be the plumbing systems for Large Igneous Provinces (LIPs). These Singhbhum swarms range in age from ∼2.80 Ga to ∼1.76 Ga, and include the ∼2.80 Ga NE-SW trending Keshargaria swarm, ∼2.75–2.76 Ga NNE-SSW to NE-SW trending Ghatgaon swarm, the ∼2.26 Ga NE-SW to ENE-WSW trending Kaptipada swarm (based on a new U-Pb ID-TIMS age 2256 ± 6 Ma), the ∼1.77 Ga WNW-ESE trending Pipilia swarm, the early-Paleoproterozoic E-W to ENE-WSW trending Keonjhar swarm, the middle-Paleoproterozoic NW-SE to NNW-SSE trending Bhagamunda swarm, and the late-Paleoproterozoic N-S to NNE-SSW trending Barigaon swarm. Two of the Singhbhum swarms, the ∼2.26 Ga Kaptipada and ∼1.77 Ga Pipilia, are closely matched with the ∼2.26–2.25 Ga Ippaguda-Dhiburahalli and ∼1.79 Ga Pebbair swarms, respectively, of the eastern Dharwar craton. The correlations suggest that the Singhbhum and Dharwar cratons were close enough at these times to share two reconstructed LIPs, a 2.26–2.25 Ga Kaptipada– Ippaguda-Dhiburahalli LIP and a 1.79–1.77 Ga Pipilia-Pebbair LIP, and if so, both swarms must be present in the intervening Bastar craton (candidates are proposed). Also, the 2.76–2.75 Ga Ghatgaon swarm of the Singhbhum craton can be provisionally correlated with ∼2.7 Ga Keshkal swarm of the Bastar craton. The 2.26–2.25 Ga Kaptipada–Ippaguda-Dhiburahalli LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the Vestfold Hills of Antarctica (∼2.24 Ga dykes), the Kaapvaal craton (the ∼2.25–2.23 Ga Hekpoort lavas) and perhaps the Zimbabwe craton (2.26 Ga Chimbadzi troctolite intrusions). The 1.76–1.79 Ga Pipilia-Pebbair LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the North China, Australian Shield, Amazonian, Rio de Plata and Sarmatia cratons. The relevance of these matches for reconstructions will require future testing using paleomagnetic studies. While there are ∼2.7–2.8 Ga LIP-type greenstone belts in many crustal blocks, there are no precise matches with the 2.76–2.75 Ga Ghatgaon swarm of the Singhbhum craton. However, the 2.80 Ga Keshargaria swarm can be potentially linked with units in the Pilbara and Yilgarn cratons. [ABSTRACT FROM AUTHOR]

Highlights • Summary of internal lithological variations of coarse-crystalline mafic bodies from Archean greenstone belts in the Eastern Goldfields Superterrane (Australia) • Comparison of the world famous Golden Mile Dolerite (1700 t Au) to a number of other mineralised and unmineralised bodies. • Comparison of coarse-crystalline mafic bodies to ponded lavas from the literature. • Present an emplacement model for differentiated mafic sills. Abstract Coarsely crystalline mafic rocks, commonly referred to as dolerite and diabase, make up a substantial proportion of Archean greenstone belts and are hosts to major orogenic gold deposits, yet their internal architecture and contact relationships remain poorly documented and their emplacement origins are assumed rather than supported with evidence. We present results from drill core logging of several late Archean coarsely crystalline packages from the Eastern Goldfields Superterrane of the Yilgarn Craton, Western Australia, including the Golden Mile Dolerite. These large mafic bodies comprise mostly medium- to coarsely crystalline mafic rocks, but also include a variety of other products of differentiation. The bodies range from ∼75 to 460 m thick and extend for tens of kilometers, are primarily hosted in mudstones and basalt and appear to be concordant to stratigraphy. As such, this study excludes mafic dykes and extremely thick and internally complex bodies such as the Bushveld Complex. From base to top, the internal stratigraphy generally consists of a lower unit of aphyric basalt, dolerite/gabbro and peridotite ± pyroxenite, then a voluminous middle dolerite/gabbro, and an upper quartz dolerite/gabbro, and a topmost aphyric basalt. Granophyric veins and domains are common in the upper third of the mafic body. Contacts are gradational between all lithofacies, with the exception of granophric veins, which have sharp contacts. Within this overall stratigraphic framework there is variability in the relative thickness of lithofacies, number of lithofacies, as well as repetition of some lithofacies (several examples also include basalt in the interior). In well exposed examples, the key evidence for distinguishing intrusions from extrusions is provided by the top contact. However, the top contact from these examples is ambiguous. To overcome this gap, we review the character of well-studied thick ponded lavas from the literature. Most aspects of the internal character are not unique to intrusions, although the maximum groundmass grain size (excluding granophyric veins) of the Archean examples (>3 mm) is significantly coarser than that for any known ponded lavas (≪1 mm). The ability to distinguish intrusions from extrusions has important implications for reconstructing Archean greenstone stratigraphy and mineral exploration. [ABSTRACT FROM AUTHOR]

The ca. 2.54-2.51 Ga Dengfeng greenstone belt in the southern section of the Central orogenic belt of the North China craton consists of structurally juxtaposed slices of meta-ultramafic, metamafic, and felsic igneous rocks, metasedimentary rocks, including minor banded iron formation. The complex was metamorphosed to greenschist to amphibolite facies at ca. 2.5 Ga and intruded by ca. 2.50-2.42 Ga mafic and felsic plutons/dikes. Detailed field mapping and structural analyses show that the different lithostructural units, including a metamafic-dominant unit and a metasedimentary-dominant unit, are in tectonic contact, with complex thrust imbrication and multiple brittle and ductile deformation. The metasedimentary-dominant unit consists of coherent schist-metabasalt sequences, metaturbidites, and chaotic mélanges that are characterized by typical duplex structures and block-in-matrix fabrics, closely resembling the lithostratigraphy and structural patterns of Phanerozoic accretionary complexes. Together with distinctive and diagnostic geochemical signatures of metabasalts, sanukitoid-like metadiorite, and syntectonic adakitic sills/dikes, we interpret the Dengfeng greenstone belt as Neoarchean forearc and accretionary complexes consisting of dismembered forearc crustal sheets in the west and accreted oceanic plate stratigraphy in the east that were structurally imbricated at a convergent plate margin. The kinematic indicators and the spatial configurations of different tectonic units suggest a near-southwest-dipping intra-oceanic subduction zone beneath the arc in the Central orogenic belt, which later evolved into an arc-continent collision with the Eastern block. The accreted arc and accretionary prism are unconformably overlain by a clastic sedimentary wedge, the lower part of which has a maximum depositional age of ca. 2.45 Ga and is interpreted as a foreland basin sequence related to this collision. Documentation of the Neoarchean Dengfeng forearc and accretionary complexes demonstrates that ca. 2.5 Ga intra-oceanic subduction, oceanic plate stratigraphy accretion, and arc-continent collisional events occurred in the southern section of the Central orogenic belt of the North China craton. The accretion of the 2.54-2.51 Ga arc to the continental margin of the Eastern block marks an early episode of mountain building in the Central orogenic belt, which played an important role in the lateral growth of the North China craton. [ABSTRACT FROM AUTHOR]

Highlights • The migmatitic core of the Yalgoo Dome records map-scale vertical sheath folds. • Sheath folds reflect stretching during diapirism rather than fold interference. • Sheath folds are overprinted by structures indicative of horizontal shortening. • Structural evolution indicates a shift from vertical to horizontal tectonics. Abstract In Archean granite-greenstone terrains, both vertical and horizontal tectonic processes can generate the typical dome-and-keel structural geometries. One of the classic Archean domes interpreted to result from a horizontal tectonic regime is the Yalgoo Dome in the Yilgarn Craton of Western Australia. In this contribution, we reassess the structural evolution of the Yalgoo Dome by detailing the structures exposed in the migmatitic core. The core contains multi-scale domes-and-basins. These structures were previously interpreted as the result of superposed folding. Our structural mapping shows that the dome-and-basin patterns result from vertical sheath folds developed in a single, progressive deformation event (D 1). This first event most likely resulted from diapiric ascent of a buoyant partially molten tonalitic crust and was overprinted by two contractional episodes (D 2 –D 3) both reflecting bulk EW shortening. The structural evolution proposed here points towards a shift from an early history of vertical tectonics dominated by diapirism to a regional regime dominated by horizontal tectonics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • BIFs of the Qingyuan greenstone belts (QGB) display seawater-like REY patterns. • QGB BIFs deposited in anoxic environment with minor high-T hydrothermal input. • Ambient seawater receives Nd from a mixing of different dissolved components in river water. • The QGB BIFs can be used as archives of the Neoarchean seawater. Abstract Pure marine chemical sediments, such as banded iron formations (BIF), are excellent archives of ancient seawater and may also provide constraints on the coeval hydrosphere-atmosphere system. However, on the bases of interpreted depositional settings, it has long been argued that Algoma type BIF merely recorded the intrabasinal volcanic or hydrothermal conditions. Here we couple systematic major and trace elements data with samarium (Sm)-neodymium (Nd) isotopic analyses of ∼2.56 Ga old Algoma type BIFs and associated schists from different stratigraphic horizons of the Qingyuan greenstone belt (QGB) in the North China Craton (NCC) to characterize the source and depositional environment over a short period (∼30 Ma). Meanwhile, we also compare our results with data for other Archean to Paleoproterozoic Superior- and Algoma-type BIFs, especially those near-contemporaneous counterparts in the NCC, to further evaluate the reliability of QGB BIFs as proxies for the Neoarchean seawater. Low Al 2 O 3 (<1.0 wt%) and high field strength elements (HFSE; e.g., Zr, Hf, and Th) contents (<1 ppm) for most BIF samples indicate an essentially detritus-free depositional environment. Shale-normalized rare earth elements and yttrium (REE + Y) patterns of these chemically pure BIF samples display features characteristic of modern seawater, with positive La anomalies, superchondritic Y/Ho ratios, and HREE enrichment relative to LREE. The presence of distinctly positive Eu anomalies indicates a significant high-T hydrothermal input, while the slightly wide range of Eu/Sm ratios likely imply plausible contributions from low-T hydrothermal fluids or changing intensities of hydrothermal activity. Moreover, similar to other Neoarchean Algoma type BIFs in the NCC (e.g., the Anshan-Benxi and the eastern Hebei BIFs), the absence of negative Ce anomalies in combination with the narrow range of Pr/Yb SN ratios for all samples suggest that water columns from which these BIFs deposited were anoxic. The initial ε Nd values of the purest BIF samples (the most reliable archives for the Neoarchean QGB seawater) range between +0.8 and +3.6, lower than those of associated schists (+3.6 to +3.8) and coeval basalts (+2.8 to +4.3), indicating the existence of isotopically enriched or less depleted protocrustal landmasses (characterized by negative or obviously lower ε Nd values) which contributed materials to ambient seawater in the QGB basin. Significantly, the large similarity in depositional environment for all the Algoma type BIFs in the NCC, as well as the relatively consistent REY patterns for both Algoma and Superior types BIFs of Archean to Paleoproterozoic ages suggest that the QGB BIFs can be used reliably as Neoarchean seawater proxies. [ABSTRACT FROM AUTHOR]

Abstract Lamprophyres from the greenstone belts play a crucial role in deciphering tectonic and geodynamic processes operating during the Archean. This study presents a comprehensive mineralogical and geochemical study of three lamprophyre dykes with calc-alkaline to shoshonitic affinities from the Neoarchean Kadiri schist belt, eastern Dharwar craton, southern India. These rocks display porphyritic-panidiomorphic texture, typical of the lamprophyres with amphibole (magnesio-hornblende) as phenocrysts, biotite as microphenocrysts and feldspar, epidote, titanite and apatite confined to the groundmass. Alteration of biotite to chlorite is observed along with mild deformation in the amphibole phenocrysts. Based on mineralogy and major oxide geochemistry, these rocks are classified as the calc-alkaline lamprophyres. Higher Ba/Nb and low Nb/La points to their derivation from an enriched lithospheric mantle source and higher Th/Yb ratio along with negative TNT (Ti-Nb-Ta) and Zr-Hf anomalies on the primitive mantle (PM) normalized multi-element diagram indicates dehydrated fluids from the foundering slab could be the possible metasomatic agent. Fractionated HREE ratios (Gd N /Yb N >1.9) and higher Sm N /Yb N suggests that the source region lies in the garnet stability field. Higher than PM Rb/Sr along with positive correlation between K/La and Rb/La reveals presence of metasomatic phlogopite in the source region. Strong negative initial εNd along with radiogenic 87Sr/86Sr ratios further support an enriched mantle reservoir involved in their genesis. Non-modal batch melting (1–5%) of a mixed source (phlogopite-garnet peridotite) assuming 5% mixing of subducted sediment with ambient mantle wedge (depleted mantle) satisfies the multi-element concentration pattern shown by the Kadiri lamprophyres. The source enrichment can be linked to the accretion-related growth of Dharwar craton and its schist belts during Neoarchean. Our study shows that a majority of lamprophyres associated with the Archean greenstone belts display a shoshonitic character; this highlights the role of subduction-related processes in the growth and evolution of the greenstone belts Graphical abstract Unlabelled Image Highlights • Post-collisional calc-alkaline to shoshonitic lamprophyres from Kadiri greenstone belt, Dharwar craton. • Subduction-modified SCLM source with metasomatic phlogopite and garnet in the residue. • Neoarchean accretion related growth of Dharwar craton and its schist belts. [ABSTRACT FROM AUTHOR]

• Formation and evolution of a Neoarchean greenstone belt are demonstrated. • Three mafic-felsic magma-series are identified by bulk/zircon composition and Lu-Hf. • Geochemistry of some basalts and zircon is consistent with subduction zone setting. • Some volcanic rocks contain xenocrystic zircon indicating Mesoarchean inheritance. • Distinguishing rock types and zooming to greenstone belt subunits give new insights. Archean greenstone belts contain the oldest volcanic rocks on Earth and can provide critical insights into Earth's early evolution. This study chooses the Sturgeon Lake greenstone belt in the easternmost Western Wabigoon terrane (WWT) of the Superior craton to illustrate an option for better understanding the formation of Archean greenstone belts. Our dataset includes outcrop observations, bulk compositions of 77 mafic to felsic volcanic samples, and in-situ U-Pb, Lu-Hf, and trace elements of zircon from 14 intermediate to felsic volcanic samples. The results revealed that this greenstone belt had broadly continuous volcanism from ca. 2780 to 2725 Ma, followed by a tectonic quiescence prior to a ca. 2707–2703 Ma volcanism at the terrane boundary. The intermediate volcanic rocks are characterized by variable Th/Nb and highly depleted Hf (zircon ƐHf (i) = +3 to + 6), interpreted to be derived from mantle sources ranging from those of normal mid-ocean ridge basalts (N-MORB) to those of enriched MORB (E-MORB), which commonly assimilated various felsic crustal components. The mafic volcanic rocks are dominated by low La/Sm basalts with negligible Nb, Ta anomalies and limited range of Th/Nb, forming a mantle array on the Th/Yb-Nb/Yb plot and consistent with oceanic crust of N-MORB to enriched N-MORB affinities. Some basalts from the ca. 2738–2725 Ma assemblages, however, gave high La/Sm, negative Nb and Ta anomalies, and limited range of Th/Nb plotting above and parallel to the mantle array. These basalts might be associated with passive subcretion and rollback of oceanic crust of the stagnant-lids tectonics or subduction of oceanic lithosphere as in modern-style plate tectonics, both of which are supported by trace element compositions of zircon that indicate hydrous, oxidized, large-ion lithophile element-enriched, and medium- to high-pressure magmas. Identification of three magma-series would not be possible if the data were lumped together, which is commonly seen in terrane- or craton-scale studies that sometimes propose contrasting interpretations of rock origins and Archean geodynamic processes. This detailed approach of distinguishing rock types and zooming into the subunits of a greenstone belt offers a practical solution to more accurately characterize Archean volcanic rocks and to better understand the early Earth. [ABSTRACT FROM AUTHOR]

In this contribution, we present for the first-time field based evidence of a crustal scale shear zone from the southern margin of Geita Greenstone Belt. The Geita Shear Zone is a broad (∼800 m wide) ductile, high-strain, deformation zone that can be traced for at least 50 km along the southern margin of the Geita Greenstone Belt. It is near vertical, trends ∼E-W and separates the mafic volcanics of the Kiziba Formation, to the north, from the TTG gneisses that crop out south of the shear zone. The shear zone is hosted almost entirely by the TTG gneisses and is characterised by a well-developed mylonitic foliation near the greenstone margin that transitions into a gneissic foliation and eventually becomes a weakly developed foliation further south. It contains approximately equal amounts of dextral, sinistral, and asymmetric shear sense indicators suggesting that the shear zone accommodated mainly flattening strain while the mineral stretching lineation defined by quartz and feldspar ribbons and stretched biotite selvages plunges shallowly W. A series of younger, sub-vertical, NW trending brittle-ductile, strike-slip shear zones truncate and displace the Geita Shear Zone with dextral displacement in the order of 2–4 km. Deformed tonalite interpreted to predate the shear zone yielded U-Pb zircon ages of ∼2710 Ma while synshearing granodiorite samples have zircon ages between 2680 Ma and 2660 Ma. The ∼2630 Ma age of the undeformed Nyankumbu granite is interpreted to mark the minimum age of movement on the shear zone. The presence of 3000 Ma and 3200 Ma zircon xenocrysts in the tonalite and granodiorite opens the possibility that older basement rocks underlie the greenstone belts in the northern half of Tanzania Craton. Whether or not the greenstone belts were erupted on older basement, thrusted on top of older basement rocks or incorporated older basement fragments has profound implications for the tectonic framework and evolution of the Tanzania Craton. [ABSTRACT FROM AUTHOR]

The Sandstone Greenstone Belt is an exploration-immature, regolith-covered, approximately 1000 sq. km belt, in the Southern Cross Domain of the Yilgarn Craton. In order to estimate potential endowment, historical gold production and deposit resource estimates are required to be quantitatively analysed for calculation of natural and residual gold endowment. The total residual gold endowment within the oxide zone of the Sandstone Greenstone Belt is estimated, by application of a Zipf’s law statistical assessment, to be 2.3 Moz. This mineralisation is most likely contained in extensions of known deposits and several undiscovered deposits. The fresh rock of the Sandstone Greenstone Belt remains poorly explored. However, a conceptual endowment estimate can be made, based on a minerals system comparison between the exploration-immature Sandstone Greenstone Belt and the well-explored, geologically-similar Agnew Greenstone Belt, 100 km to the east. It is possible that natural endowment at Sandstone could total 21.3 Moz, with nine undiscovered deposits of >0.5 Moz. Application of such a minerals-system integrated endowment assessment represents an effective motivator to embark on a well-resourced gold exploration campaign in the Sandstone Greenstone Belt, a currently immature exploration search space. [ABSTRACT FROM AUTHOR]

Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18-1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids remain controversial. In this study, we present the estimates of the mantle potential temperature (Tp) for the WAC, which yields values of about 1500-1600 °C, pressure estimates of initial and final melting yield values of about 3.7-5.2 GPa and 1-1.3 GPa, respectively. Subsequently, 2D thermo-mechanical models have been constructed to explore the width of volcano-sedimentary basin on spatial-temporal evolution of diapirs that emplaced in the lower-middle crust during compression. The models show that the width of the volcano-sediment layer plays an important role in the formation mechanisms of greenstone-granitoid belts. The lower crust beneath sedimentary sequences is deformed into a buckle fold during the first compressional stage, through which relief uplifts slowly. Subsequently, the buckle fold is further deformed into several individual folds. Diapirs made of lower crust rocks ascend and emplace in the middle-upper crust resulting from instability. Benefitting from the mantle temperature, the pressure estimates and the numerical modelling results, a new geodynamic model was constructed. This model indicates that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting that are accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intrude into the upper crust through weakening zones between the diapirs. Our geodynamic model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts. [ABSTRACT FROM AUTHOR]

The Elu Link between the ∼2.7 Ga Hope Bay and Elu belts in the northeast Bathurst Block of the Slave craton comprises supracrustal and intrusive rocks variably deformed by three tectono-metamorphic events (D 1 –D 3 ). The geometry of D 1 structures formed during prograde metamorphism is uncertain, because of subsequent overprint. D 2 occurred in two stages predating (D 2a ) and postdating (D 2b ) peak metamorphism. D 1 and D 2a were thrusting events inferred from peak metamorphic pressures of ∼6.7 kbar (670 MPa) retained by a garnet orthogneiss. The latter is diagnostic of thrust tectonism in Archean granite-greenstone belts with no characteristic thrust faults. Unlike D 2a , D 2b was a vertical general flattening event prevailing during the formation of magmatic domes and interdomal folds that form the main strain patterns of the belts. This was followed by the formation of buckled F 3 folds associated with D 3 vertical constriction. The switch from thrust to vertical tectonics during peak metamorphism and subsequent deformation resulted in intense recrystallization that explains the poor preservation and scarcity of early-formed shears, including thrust zones. A tectonic process, combining D 1 +D 2a thrust stacking, sagduction, and vertical stretching during D 2b and D 3 , is suggested to explain crustal thickening in the Elu Link and terrains of similar ages. [ABSTRACT FROM AUTHOR]

Hafnium and oxygen isotopic compositions measured in-situ on U-Pb dated zircon from Archaean sedimentary successions belonging to the 2.9–2.8 Ga Belingwean/Bulawayan groups and previously undated Sebakwian Group are used to characterize the crustal evolution of the Zimbabwe Craton prior to 3.0 Ga. Microstructural and compositional criteria were used to minimize effects arising from Pb loss due to metamorphic overprinting and interaction with low-temperature fluids. 207 Pb/ 206 Pb age spectra (concordance >90%) reveal prominent peaks at 3.8, 3.6, 3.5, and 3.35 Ga, corresponding to documented geological events, both globally and within the Zimbabwe Craton. Zircon δ 18 O values from +4 to +10‰ point to both derivation from magmas in equilibrium with mantle oxygen and the incorporation of material that had previously interacted with water in near-surface environments. In ε Hf -time space, 3.8–3.6 Ga grains define an array consistent with reworking of a mafic reservoir ( 176 Lu/ 177 Hf ∼0.015) that separated from chondritic mantle at ∼3.9 Ga. Crustal domains formed after 3.6 Ga depict a more complex evolution, involving contribution from chondritic mantle sources and, to a lesser extent, reworking of pre-existing crust. Protracted remelting was not accompanied by significant mantle depletion prior to 3.35 Ga. This implies that early crust production in the Zimbabwe Craton did not cause complementary enriched and depleted reservoirs that were tapped by later magmas, possibly because the volume of crust extracted and stabilised was too small to influence (asthenospheric) mantle isotopic evolution. Growth of continental crust through pulsed emplacement of juvenile (chondritic mantle-derived) melts, into and onto the existing cratonic nucleus, however, involved formation of complementary depleted subcontinental lithospheric mantle since the early Archaean, indicative of strongly coupled evolutionary histories of both reservoirs, with limited evidence for recycling and lateral accretion of arc-related crustal blocks until 3.35 Ga. [ABSTRACT FROM AUTHOR]

Understanding the architecture of the West African craton at depth is essential to be able to reconstruct its evolution. Our study focuses on the crustal imaging of structures and geometries characterizing the crust of the Leo-Man shield with broadband and long period magnetotelluric data collected in southern Burkina Faso and covering a 220 km long profile. The resulting 3D resistivity crustal model highlights the distribution of the granite-greenstone assemblages with depth showing excellent correlation with mapped surficial lithologies. The whole crust of southern Burkina Faso is resistive, with lateral as opposed to vertical major resistivity contrasts, reflecting the location of major-scale shear zones characterizing this part of the Baoulé-Mossi domain. Ground gravity data acquired along the same line as the MT data were also modeled and show relatively good correspondence with the resistivity model. The new resistivity and gravity models compared with results from joint inversion of gravity and aeromagnetic data highlight significant changes between the greenstone belts and granitoid domains along the profile. The comparison of the geophysics with the geology enables us to define new depth constraints of the main tectonic features in the area. The observed large scale dipping shear zones favour the model of crustal building through major parallel thrust faults. [ABSTRACT FROM AUTHOR]

• New U–Pb and Lu-Hf data from the Daitari Greenstone Belt, Singhbhum Craton, India. • Detailed geochronological and tectonic evolution of the Daitari Greenstone Belt. • Zircon εHf (t) indicate a juvenile source for 3.5 Ga felsic volcanic rocks. • 3.5 Ga marks a significant period of growth of the continental crust. The Singhbhum Craton in India contains well-preserved Palaeoarchaean greenstone belts that rival their Australian and South African counterparts, but their stratigraphic make-up remains to be resolved. Here we provide new SHRIMP- and LA-ICP-MS-based U–Pb and Lu-Hf data on magmatic and detrital zircons from stratigraphically resolved samples of the Daitari Greenstone Belt (DGB) in the south of the Singhbhum Craton. A minimum age for the Kalisagar Formation, the lowermost mafic–ultramafic volcanic suite of the DGB, is provided by a felsic sill dated at 3505 ± 6 Ma. Felsic volcaniclastic rocks from the overlying Talpada Formation provided a weighted mean age of 3507 ± 5 Ma. Zircon εHf (t) indicate a juvenile source for 3.5 Ga felsic volcanic rocks. Erosion of the volcanic edifice of the Talpada Formation acted as a predominant source for the overlying turbidite sequence of the Sindurimundi Formation, having identical U-Pb detrital zircon ages of ∼ 3505 Ma. A maximum age of deposition of 3502 ± 2 Ma is proposed for the Sindurimundi Formation. Magmatic zircon ages obtained from different intrusive felsic rocks in the Daitari belt ranges from c. 3.37 to 3.35 Ga and support the notion of widespread felsic magmatism of the Singhbhum Suite in the southern part of the craton. Xenocrystic zircon crystals dated at c. 3.55 to 3.52 Ga may correspond to an earlier phase of magmatism. 3.5 Ga marks an important period in the Earth's history, when extensive felsic magmatism facilitated continental crustal growth as recorded in the Singhbhum, Kaapvaal and Pilbara cratons. [ABSTRACT FROM AUTHOR]

The low-grade Contendas-Mirante meta-volcano-sedimentary belt (CMB) was previously interpreted as an Archean greenstone belt with the uppermost formation deposited in the Paleoproterozoic. New zircon U-Pb LA-ICP-MS ages on sedimentary groups and granite sheets intrusive in the belt constrain the timing of basin development. Phyllites of the Lower Group and meta-arenites of the Upper Group yielded similar young zircon populations at ca. 2080 Ma, which are interpreted as the maximum deposition age for the entire sequence. The unique exception is the 3273–3338 Ma zircon-bearing quartzite that occurs in spatial association with the 3300 Ma rhyolite. A granite sheet intrusive into metagraywacke of the Lower Group constrains the minimum deposition age of 2045 ± 26 Ma for the CMB. Altogether four main age clusters of detrital zircon grains were recognized, namely 2075–2200 Ma, 2200–2440 Ma, 2500–2770 Ma, 3270–3380 Ma. These age intervals match the ages of igneous and metamorphic rocks in the different terranes that comprise the São Francisco craton. Maximum deposition age for both groups indicates that sedimentation occurred immediately prior the high-grade metamorphism in the adjacent Archean-Paleoproterozoic Jequié Block and Itabuna-Salvador-Curaçá Orogen. These observations, along with coarsening upwards in the sediments, indicate that the CMB represents a foreland basin developed along the eastern margin of the Gavião Block during plate convergence. Paleoarchean basement rocks were reactivated and emplaced into the CMB during basin inversion and is timely correlated with the granitic intrusion. Recognition of older supracrustal fragments is ambiguous, one main example is the 3273–3338 Ma zircon-bearing quartzite, which correlates with the northern Jacobina basin along the Contendas-Mirante lineament (e.g., Bahia gold belt) and may represent part of an Archean intracontinental rift sequence. [ABSTRACT FROM AUTHOR]

Archean granitic gneiss domes and greenstone belts are well-preserved in eastern North China Craton (NCC), one of the oldest Archean terrains in the world. The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei Province is located between an Archean granitic gneiss dome and a greenstone belt within an uplift in eastern NCC. Supracrustal rocks from the Neoarchean Shuangshanzi and Zhuzhangzi Groups, and some Archean granitic gneisses were involved in the shearing along the eastern margin. In the southern part, the narrow NE-trending shear zone dips NW with dip angles of 40–60° and, in the northern part, the shear zone dips NWN with dip angles of 70–85°. Microstructural and EBSD fabric analyses suggest that the shear zone was developed at upper greenschist facies to lower amphibolite facies conditions with deformation temperatures of 400–550 °C. LA-ICP-MS zircon U-Pb dating of mylonitized granitic rocks and undeformed quartz diorite cutting the shear zone suggest that the Shuangshanzi ductile shear zone was formed between 2550 Ma and 2452 Ma. Detailed kinematic studies of the shear zone show a clear sinistral shear sense with a slightly oblique-slip component in the northern part and a sinistral transtensional slip component in the southern part. It is therefore suggested that the shear zone was formed during the Anziling doming with respect to the down-slipping Neoarchean Shuangshanzi and Zhuzhangzi Groups. The difference in kinematics along the southern and the northern sections is interpreted to be caused by the doming with an uneven clockwise spiral rotation. The BIF-rich supracrustal rocks have higher density than their neighboring granitic gneisses, and therefore can easily sink to form synclines by sagduction processes. The sagduction is mainly triggered by gravitational inversion of high density supracrustal rocks with respect to relatively light granitic gneisses within the dome. As a result, the gneisses synchronously moved upward. A shear zone was thus developed in accommodation of the upward and downward movements. It is possible that such a tectonic model also applies to many Archean granite-greenstone terrains. [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]

This contribution presents a comprehensive synthesis on the origin of oldest (3600–3200 Ma) cratonic core in the Western Dharwar Craton (WDC), Southern India based our new field, geochronologic, elemental and Nd-Hf isotopes data on the Holenarsipur greenstone belt and adjacent granitoids combined with published record on the stratigraphically equivalent greenstone belts in the same region. Our study shows that the oldest cratonic core in the WDC formed through assembly of different tectonic units close to 3200 Ma. These tectonic units include microcontinental remnants with oceanic plateaus, oceanic island arcs and preserved oceanic crust similar to modern oceanic crustal section close to a spreading center. Isotopic age data for these greenstone sequences (detrital zircons -ca.3600–3230 Ma; volcanics 3384–3200 Ma) and adjoining granitoids (3430–3400 and 3350–3270 Ma with remnants of older 3600–3500 Ma gneisses) indicate that a large part of the old TTG-type granitoids in the WDC is either coeval to or slightly younger than associated greenstone units. The final stage of assembly of these tectonic elements into cratonic framework through horizontal motion of intervening oceanic crust and eventual slab breakoff is marked by the formation of ca. 3200 Ma trondhjemite magmas, emplacement of which into the lower crust caused partial convective overturn of the crust, thereby leading to the development of dome and keel patterns followed by metamorphism and cratonization of the WDC crust at 3100 Ma. Our study strongly suggests that the tectonic environments in which Archean cratons formed require some sort of horizontal motion but not necessarily modern plate tectonics. However, vertical addition of juvenile crust in hotspot environments associated with mantle plumes played a major role in building of early crustal nuclei. The model proposed for the formation of the cratonic core in the western Dharwar craton is compatible with observations made globally in most of the Paleoarchean cratons. [ABSTRACT FROM AUTHOR]

Two Archaean supracrustal complexes are documented in the Bundelkhand craton viz. 1) the Central Bundelkhand greenstone complex (formed the Babina and Mauranipur belts), and 2) the Southern Bundelkhand metasedimentary (paragneisses, schists) complex (formed the Girar belt). The Central Bundelkhand greenstone complex consists of (i) an early assemblage composed of basic-ultrabasic, felsic volcanics, banded iron formation (BIF), and (ii) a late assemblage which contains felsic volcanics. The U-Pb zircon ages of felsic volcanics from the early assemblage, formed in an arc-type subduction setting, are 2813 Ma (Mesoarchaean). The U-Pb zircon ages of felsic volcanics from the late assemblage, which also occur in subduction settings as an active continental marginal type, are 2542 Ma (Neoarchaean). The Girar belt, located in the southern part of the craton, consists generally of metasedimentary rocks namely quartzites and BIFs. Quartzites are represented by fuchsite- and hematite- bearing quartz arenite and lesser quartz pebble conglomerates that have been subjected to low-grade metamorphism. BIF is represented by thinly-bedded quartz-hematite (±magnetite) rocks. Some lenses of marble and chlorite schist are present at the contact between the two formations. BIF is fairly rich in Cr and Ni, poor in Zr, Hf, Ba, Th, Sr, Yb and Lu, and displays a distinct positive Euanomaly (Eu/Eu* = 1.14-2.46). Zircons from quartzites give two U-Pb ages: 3432±9.7 Ma and 3252±6.4 Ma. The Sm-Nd isotope study of quartzite from the Girar belt shows that the T is 3.29 Ga. This T correlates well with the U-Pb ages of zircon and indicates that the continental crust in the Girar area began to form in the Paleoarchaean (3.4-3.2 Ga). The Central Bundelkhand greenstone complex was thus formed in a subduction-accretion setting in Mesoarchaean (ca 2.8 Ga) and Neoarchaean (2.54 Ga) time, and the Southern Bundelkhand metasedimentary complex originated in a sedimentary basin on the old continental crust apparently at ca ~ 2.7 Ga. [ABSTRACT FROM AUTHOR]

The Jiapigou granite-greenstone belt of Southern Jilin Province is located at the northeastern margin of the North China Craton (NCC). The Neoarchean metavolcanic rocks of this region provide strong lines of evidence in petrology and geochemistry for Neoarchean crust–mantle geodynamic evolution and significant crustal growth events. The metavolcanic rock assemblage is dominated by amphibolite, hornblende/garnet biotite plagioclase gneiss, and minor felsic gneiss. Zircon LA–ICP–MS U–Pb isotopic analyses reveal that these supracrustal rocks may be formed by two episodes of magmatism. The first magmatic episode occurred at ∼2688 Ma and was recorded by minor felsic gneiss. The second episode occurred at ∼2588–2536 Ma and was marked by a major lithological assemblage of metavolcanic rocks in this area. All the supracrustal rocks experienced amphibolite facies metamorphism at ∼2510–2480 Ma. Except for the felsic gneiss, seventeen metavolcanic rock samples can be geochemically classified into three groups. Group #1 has tholeiitic basaltic chemical composition, and is characterized by slightly LREE-enriched chondrite-normalized REE pattern with low (La/Yb) N ratio and weakly negative Nb anomalies, similar to those of primitive arc tholeiite. Their magmatic precursor was most likely generated by partial melting of upper sub-arc mantle wedge slightly metasomatized by slab-derived fluids or melts in a subduction initiation environment. Group #2 with basaltic composition is akin to typical calc-alkaline basalt (CAB), showing fractionated chondrite-normalized REE patterns and evidently negative Nb, Ta and Ti anomalies. The magmatic precursor of the Group #2 was derived from partial melting of a sub-arc mantle wedge at relatively deeper levels, significantly metasomatized by slab-derived fluids or melts. Group #3 show chemical composition of andesite to dacite, and is distinguished by wide variations in SiO 2 , MgO and Mg# values, strongly fractionated chondrite-normalized REE patterns with higher (La/Yb) N ratios, low Yb and Y contents, and negative Nb, Ta, Ti and P anomalies, analogous to the Phanerozoic adakites. They might be derived from magma mixing between the mantle wedge melts metasomatized by slab-derived melts with perhaps an ancient crustal contribution. The felsic gneiss shows positive zircon ε Hf (t 2 ) values (+2.2 to +4.5), together with ∼2.7 Ga metamorphic volcanic rocks in the neighboring area, indicating a ∼2.7 Ga crustal growth episode. Most of the metavolcanic rocks display positive ε Hf (t 2 ) values of +0.4 to +7.4, the highest of which is close to the value of contemporaneous depleted mantle, suggesting a significant crustal growth event at ∼2.59–2.54 Ga. Combined with numerous ∼2.83–2.65 Ga inherited zircons and ∼2688 Ma felsic gneiss, the Jiapigou granite-greenstone belt evolved at an Andean-type active continental margin, recording the transition from primitive arc to mature arc. [ABSTRACT FROM AUTHOR]

The Murchison domain forms the northwest part of the Youanmi Terrane, a tectonic unit within the Neoarchean Yilgarn Craton in Western Australia. In the Cue-Weld Range area the Murchison domain has experienced a complex magmatic and deformation history that resulted in a transposed array of greenstone belts that host significant iron, gold, and base metal deposits. In this study, we interpret the upper 2 s (about 6 km) of a deep crustal seismic profile 10GA–YU1, near the town of Cue, and correlate rock units and structures in outcrop with corresponding reflections. We performed 3D constant velocity ray-tracing and calculate the corresponding travel times for the reflections for time domain pre-stack and post-stack seismic data. This allows us to link shallow reflections with mafic volcanic rocks of the Glen Group and basaltic rocks of the Polelle Group in outcrop. Based on our interpretation and published geological maps and data, we propose a model in which the local stratigraphy represents a refolded thrust system. To test our hypothesis, we applied 2D acoustic finite difference forward modeling. The corresponding synthetic data were processed in the same way as the acquired data. Comparisons between the acquired and the synthetic data show that the model is consistent with observations. We propose a new model for the subsurface of the Cue-Weld Range area and argue that some of the lithologies in the area are repeated structurally at different levels. Our approach highlights the benefit of imaging and modeling of deep seismic transects to resolve local structural complexity in Archean granite-greenstone terrains. [ABSTRACT FROM AUTHOR]

The Bagassi gold deposits are situated on the West African craton and hosted in Palaeoproterozoic rocks of the Houndé greenstone belt, southwest Burkina Faso. High-grade gold mineralisation is hosted in quartz–gold ± pyrite veins-lodes (V 1A ), in dilational zones and narrow shears in the Bagassi granitoid, and forms the majority of the resource–reserve portfolio in the Bagassi exploration permits, with gold grades of 18–21 g/t. Shear hosted gold-pyrite mineralisation in quartz veins in dilational jogs (V 1B ) occurs along narrow discontinuous shear zones that trend north-northwest in Birimian-aged metabasaltic units, and forms a secondary gold resource. Gold mineralisation is restricted to formation in the late Eburnean Orogeny and formed during a change from east-west to transcurrent compression and shearing. The Bagassi deposits demonstrate that granitoids emplaced prior to onset of the Eburnean Orogeny represent viable gold mineralisation in host rocks that are increasingly seen to be associated with significant gold resources. [ABSTRACT FROM AUTHOR]

The West African Craton hosts major resources of gold, iron ore, aluminium ore, diamonds, phosphates and manganese. This portfolio of ore deposits is linked to the formation of Archean–Paleoproterozoic greenstone belts, Jurassic rifting and extended periods of Mesozoic to Cenozoic weathering and erosion. We give a brief overview of the temporal and spatial distribution patterns of West African ore deposits with emphasis on the main commodity types. The oldest ore forming processes generated major resources in iron ore and gold in the Kénéma–Man and Reguibat Shields during the Neo-Archean. The majority of gold, porphyry copper, lead–zinc and sedimentary manganese deposits formed during the Paleoproterozoic, dominantly within the Baoulé-Mossi domain. At the same time diamond-bearing kimberlites developed in Ghana. Another distinct diamond event has been recognized in the Mesozoic of the Kénéma–Man shield. Isolated occurrences of IOCG's as well as copper–gold and gold formed in Pan-African/Variscan belts. During the Neoproterozoic, the majority of mineralization consists of sedimentary iron ore and phosphate deposits located within intracratonic basins. During the Phanerozoic aluminium ore, phosphates and mineral sands concentrated along the margins of the coastal and intracratonic basins. [ABSTRACT FROM AUTHOR]

The roots of the tectonically uplifted Archean continental crustal blocks containing various greenstone-granite terranes are the preserved crustal lithologies exposed in various Archean cratons of the world. The trace element geochemical signatures of some of the preserved lithologies of these magmatic belts reflect the primary melt compositions in the mantle which help in understanding the petrogenesis of the rocks and the involvement of subduction zone processes, if recognized, in the generation of these melts. The Dharwar craton (DC), one of the major cratons of the world located in the Indian subcontinent, is made up of different tectonic blocks amalgamated along various suture zones. Here we review the current understanding about the division of the DC, the polarity of subduction of the different blocks and the petrogenesis of the magmatic rocks of the greenstone belts, and present a synthesis based on the trace element characteristics of the primary basalts. Our study validates the heterogeneous nature of the Archean mantle during the Dharwar crustal evolution. Collation of geophysical, structural, lithological, geochemical and geochronological data imply that the Dharwar craton was accreted by the juxtaposition of at least three major cratonic blocks with noticeably distinct tectonic and magmatic histories. The continued preservation of siliciclastic sedimentary rocks in the greenstone belts of the western Dharwar craton combined with the dominant presence of the >3.0 Ga old gneissic crust, as compared to the central and eastern cratons, could be significant in constraining the involvement of continental crustal detritus in the generation of the magmatic rocks of the greenstone belts. In the central and eastern Dharwar cratons, granitoid crust older than 3.0 Ga was probably destroyed to different extents for the generation of magmatic rocks. The existence of such an older crust is implied by the available Nd model ages. The scattered records of bimodality in the greenstone belt rocks of the central and eastern Dharwar cratons attest for the presence of heterogeneous mantle during Neoarchean. Subduction processes had become predominant by Neoarchean as evidenced from the chemical composition of primary basalts of the greenstone belts of the Dharwar craton. In all likelihood, the polarity of subduction was directed westward with the WDC acting as the foreland and the amalgamation of distinct cratonic blocks were along suture zones represented scatteredly by and as greenstone belts. • Mantle heterogeneity and subduction-zone processes generated Dharwar primary basalts. • Dharwar craton is a collage of tectonic blocks amalgamated by subduction-accretion. • The polarity of subduction was directed westward. [ABSTRACT FROM AUTHOR]

The early Archaean East Pilbara Terrane of the Pilbara Craton represents the archetypical granite dome – greenstone keel terrain and preserves much of the primary geological features of dome-and-keel formation. Here we present the first detailed lithostratigraphic and structural transect from marginal gneisses of the Muccan Granitic Complex through 6 km of steeply dipping strata of the western Doolena Gap greenstone belt. Based on overprinting relationships, we identified five deformational events (D 1 –D 5 ) that can be correlated between four structural domains: (i) marginal orthogneisses of the polyphase Muccan Granitic Complex, (ii) a dominantly mylonitic shear zone (South Muccan Shear Zone) representing a granite dome – greenstone keel detachment zone, (iii) a Central Fold Belt of dominantly mafic greenschists, and (iv) a lower greenschist- to sub-greenschist facies southern Low-Strain Belt. The D 1 event in the Low-Strain Belt is recorded in syn-depositional normal faulting (f 1 ) during eruption of deep water low vesicular pillow basalts of the ca. 3.47 Ga Mount Ada Basalt, followed by a conformable transition towards shallow water stromatolites in the Duffer Formation. We interpret the D 1 event as the result of upper-crustal extension and subsequent uplift above the Muccan Granitic Complex. The D 2 event shows the most intense deformation with syn-anatectic tight folds within the Muccan Granitic Complex and tight to isoclinal transposed folds (F 2 ) and fluid-induced normal faults (f 2 ) within the Central Fold Belt. The D 2 event resulted in a regional EW composite S 1/2 foliation, and in the development of the mylonitic South Muccan Shear Zone along the dome-keel interface and within the Central Fold Belt, mineral lineations (L 2 ) in conjunction with increasing southward D 2 l -tectonite. This D 2 event is not observed in a ∼1 km-thick sandstone package (ascribed to the <3.43 Ga Strelley Pool Formation) in the Low-Strain Belt that was deposited over an angular unconformity indicating 45° SSW tilting of the underlying Mount Ada Basalt and Duffer Formation. This constrains the D 2 event to between 3.47 and 3.43 Ga. We propose that the D 1 and D 2 events record locally significant initiation of Muccan Granitic Complex doming and associated sagduction of greenstone keel rocks, suggesting that partial convective overturn initiated early in the evolution of the East Pilbara Terrane. [ABSTRACT FROM AUTHOR]

This paper shows the results of Short-Wavelength Infrared (SWIR) spectroscopy investigations of volcanic rocks sampled from low-grade metamorphic greenstone belts of the Archean Pilbara Craton in Western Australia. From the reflectance spectra a range of spectrally active minerals were identified, including chlorites, hornblende, actinolite, epidote and white micas. The rock samples were grouped into mineral assemblages based on their spectrally identified minerals and stratigraphic positions. The metamorphic amphibolite and greenschist facies could be identified from the SWIR spectroscopic data as well as three sub zones of the greenschist facies: 1) a zone containing Fe-chlorite; 2) a zone containing intermediate chlorite and epidote; and 3) a zone containing intermediate chlorite, actinolite and hornblende. Spectral parameters were calculated from the reflectance spectra to assess the metamorphic grade and zones. Plots of the depth parameters of the Fe-OH feature near 2250 nm versus the Mg-OH feature near 2390 nm differentiate the metamorphic amphibolite and greenschist facies and a transition zone between the two. The wavelength position parameter of the Mg-OH absorption feature near 2340 nm also serves to discriminate between the various metamorphic sub zones. The identification of the metamorphic grades of the volcanic sequences in greenstone belts with SWIR spectroscopy is useful for regional geological field studies, exploration for metamorphic mineral deposits hosted in the greenstone belts and the interpretation of hyperspectral remote sensing data sets covering similar types of terranes. [ABSTRACT FROM AUTHOR]

Archean greenstone belts host a significant proportion of the world's gold, typically in deposits that formed late during greenstone belt formation and cratonization. However, this is not always the case and, in the multiply reworked western Churchill Province (wCP), orogenic lode gold deposition post-dates greenstone belt formation by nearly one billion years. The spatial link between Proterozoic gold and Archean greenstone belts in the wCP is thus particularly striking although its significance is still not fully understood. The Meliadine gold district (2.8 Moz contained Au in reserves, plus an indicated and inferred resources of 5.8 Moz Au) represents an important example of this deposit style and is hosted within the Rankin Inlet greenstone belt (RIGB), which occupies a critical, but controversial position along the largely inferred boundary between the Hearne craton and the Chesterfield block. RIGB felsic volcanic rocks (ca. 2.66 Ga) are structurally intercalated, and broadly coeval, with mafic volcanic and volcaniclastic rocks (2.66–2.64 Ga), turbidite (≤2.66–2.64 Ga), argillite, auriferous banded iron formation successions and syn-volcanic granodioritic to tonalitic intrusions (2.67–2.64 Ga). Neoarchean basaltic to andesitic volcanic rocks possess calc-alkaline to primitive arc-like tholeiitic magmatic affinities along with lesser MORB-like basaltic compositions. Geochemically evolved lavas yield depleted 144 Nd/ 143 Nd ratios ( ɛ Nd 2.66 Ga = −1.1 to +1.6) that reflect variable interaction with an evolved and hitherto undocumented Meso- to Neoarchean basement underlying the RIGB, whereas transitional, arc-like primitive tholeiitic and MORB-like basaltic samples overlap with the Nd isotopic composition of depleted mantle at ca. 2.66 Ga ( ɛ Nd 2.66 Ga = +1.6 to +2.7). These Neoarchean volcano-sedimentary panels represent the main auriferous rock package within the Meliadine gold district and are intercalated with deformed Paleoproterozoic conglomerate (≤2.50 and ≤2.155 Ga). The latter are, in turn, unconformably overlain by a geochemically distinct pillowed-basalt sequence and a unique carbonate-siliciclastic package that presumably represent the remnants of Paleoproterozoic basins and are not known to host gold. The geological setting of gold deposits thus likely reflects this favourable Neoarchean lithostratigraphy in addition to metamorphism and fluid focusing along the reactivated faults during the collision of the Hearne and combined Chesterfield block-Rae craton at 1.90–1.85 Ga. [ABSTRACT FROM AUTHOR]

The Dengfeng granite-greenstone belt (DGGB), located in the southern segment of the Central Orogenic Belt (COB) of the North China Craton (NCC), consists of a volcano-sedimentary assemblage, intruded by tonalite, trondhjemite, granodiorite (TTG suite), diorite, granites and late mafic dikes. The volcano-sedimentary assemblage in the DGGB mainly consists of tectonically imbricated basaltic amphibolites, meta-gabbroic rocks with minor ultramafic rocks, and metagreywacke, marble and quartzite, consistent with characterisitics of typical Phanerozoic subduction-accretion complexes. The basaltic amphibolites yield a metamorphic zircon 207 Pb/ 206 Pb age of 2507 ± 26 Ma, interpreted to represent the peak age of amphibolite facies metamorphism that took place during subduction/accretion of the basaltic protolith. The basaltic amphibolites are characterized by a tholeiitic affinity, and flat LREE patterns with minor negative Nb and Zr anomalies. Based on mixed MORB- and arc-affinities, the basaltic amphibolites in the DGGB are interpreted to have formed in a fore-arc tectonic setting. One late potassic granite dike cutting across the fabrics of the volcano-sedimentary assemblage yields an intrusion age of 2492 ± 35 Ma, constraining the minimum deformation age for tectonic assembly of the package. The TTG gneisses and diorites intruded the western margin and the center of the subduction-accretion complex, respectively. One TTG sample and one diorite sample yield igneous zircon 207 Pb/ 206 Pb ages of 2514 ± 26 Ma and 2518 ± 36 Ma, respectively, constraining their intrusion ages. The TTG gneisses display high ratios of (La/Yb) cn and Sr/Y, and depletion in HFSE with negative Nb, Ta and Ti anomalies, consistent with those of typical Archean TTGs. The TTG gneisses are therefore considered to be generated from partial melting of a shallowly subducting oceanic slab and/or accreted arc amphibolites. The diorites have high concentrations of MgO (2.89–6.05 wt.%), Ni (148–178 ppm) and Cr (85.7–120.6 ppm), and highly fractionated REE patterns and are depleted in HFSEs with negative Nb, Ta, Zr, Hf and Ti anomalies. We suggest that the high-Mg diorites in the DGGB may have been derived from a hydrated mantle wedge which was previously metasomatized by subduction-derived melts and/or fluids. Collectively, a Neoarchean subduction-accretion-collision event is therefore proposed to have generated the DGGB. The volcano-sedimentary assemblage in the DGGB represents a fore-arc subduction-accretion complex, which is interpreted to be related to the suture zone of ca. 2.5 Ga arc-continent collision between a TTG-dominated arc terrane in the COB and the Eastern Block of the NCC. We further propose a long N-S striking Neoarchean suture zone occurring in the eastern margin of the COB mainly consists of the ca. 2.5 Ga subduction-accretion complex in the DGGB to the south, the ca. 2.5 Ga mélange belt in the Zanhuang Complex in the central, and the ca. 2.5 Ga ophiolitic mélange belt in the Zunhua-Dongwanzi structural belt to the north, which separate an arc terrane in the COB from the Eastern Block of the NCC. [ABSTRACT FROM AUTHOR]

In situ and laboratory 0.35 μm–2.5 μm spectra of rocks from a Paleoproterozoic granite-greenstone terrain along with its Neoproterozoic sedimentary cover and derived regolith materials were examined in western Burkina Faso. The reflectance spectra show the influence of typical arid to semi-arid weathering with the formation of desert varnish, iron films, and dust coatings. Fe and Mg–OH absorption features related to chlorite, amphibole, pyroxene, epidote, and biotite are observable in the mafic and intermediate meta-volcanic rocks as well as in the granodiorites and tonalites. Al–OH absorption caused by kaolinite, smectite, illite/muscovite are typical for meta-volcano-sedimentary schists, Tarkwaian-type detrital meta-sediments, sandstones of the Taoudeni basin, all of the weathered surfaces and regolith materials. Ferric and ferrous iron absorptions related to both primary rock-forming minerals and secondary weathering minerals (goethite, hematite) were observed in most of the sampled materials. The results show that although weathering alters the spectral signature of the fresh rock, indicative absorption features located in the short wave infrared region remain detectable. In addition, spectra of soils partially reflect the mineral composition of the weathered rock surfaces. The analysis of the hyperspectral data shows the potential of differentiating between the sampled surfaces. The library presents a primary database for the geological and regolith analysis of remote sensing data in West Africa. [ABSTRACT FROM AUTHOR]

As one of the major Neoarchean granite-greenstone belts in China, the Helong terrane is located at the northeastern margin (Southern Jilin Province) of the North China Craton (NCC). It is dominated by metamorphic supracrustal rock assemblage and granitoid gneiss. The former contains amphibolite, hornblende plagioclase gneiss, biotite plagioclase gneiss and banded iron formation (BIF), whereas the latter is dominated by the Tonalite–Trondhjemite–Granodiorite (TTG) gneisses. Zircon LA–ICP–MS U–Pb isotopic analyses indicate that the supracrustal rock assemblage was formed at 2683–2654 Ma and underwent regional metamorphism (lower amphibolite facies) at 2614–2553 Ma before the widespread emplacement of plutonic granitoids at 2551–2532 Ma. Both greenstone sequence and plutonic granitoid rocks experienced the subsequent regional metamorphism (greenschist to lower amphibolite facies) at 2508–2400 Ma. The supracrustal rocks can be divided into three groups based on their lithological and geochemical characteristics. Detailed petrogenetic and geochemical studies suggest that the Group #1 amphibolite samples were derived from partial melting of depleted upper mantle that had been metasomatized by slab-derived fluids; Group #2 amphibolite samples were derived by partial melting of a depleted mantle wedge that was strongly metasomatized by subduction-derived fluids or melts; and Group #3 hornblende/biotite plagioclase gneiss samples were derived from partial melting of juvenile basalt and minor amounts of older sediments in the lower crust level. The granitoid gneisses in the Helong granite-greenstone belt can be divided into relatively high magnesium group (HMG) and low magnesium group (LMG). The HMG samples were derived from parental magmas generated by partial melting of juvenile basalt and minor amounts of older sediments within the lower crust level, whereas magmatic precursors of the LMG samples were generated by partial melting of a metapelite-dominated source under lower temperature melting conditions. U–Pb dating of inherited or captured zircons, combined with zircon Lu–Hf isotope data, indicates a significant ∼2.9–2.7 Ga crustal growth episode, whereas the ∼2.55–2.53 Ga magmatism involved crustal recycling in the Helong terrane. Consequently, the Helong terrane preserves a record of Neoarchean tectonic environment of Andean-type active continental margin. [ABSTRACT FROM AUTHOR]

The Qingyuan high-grade granite–greenstone terrain is one of the first recognized granite–greenstone terrains in the Eastern North China Craton. Similar to other Archaean terrains, its tectonic environment is debated: was it an intra-continental rift or a modern analogy of arc? Occurrence and petrogenesis of major igneous series, the ultramafic–mafic and felsic volcanic rocks (> 2510 Ma) and the plutons of the quartz diorite (2570–2510 Ma), TTG (2570–2510 Ma) and quartz monzodiorite (2510–2490 Ma) series in Xinbin area are investigated. The mafic intrusives and volcanic rocks have high MgO content (5.4–7.5 wt.%) and Mg-number (48–61). They show slightly depleted to flat trace element patterns. The ultramafic rocks (serpentinite) could be genetically related to the mafic rocks. The meta-dacite–rhyolite is adakitic with enriched light and middle REEs and LILEs, but significantly depleted HFSEs. The quartz diorite has high Mg-number (60–64), moderately enriched light and middle REEs and LILEs. The TTG shows distinct light but moderate middle REE-enrichment, prominent Nb–Ta-depletion but Zr–Hf-enrichment (Zr/Sm > 100). The quartz monzodiorite has moderate light and middle REE-enrichment, significant Nb–Ta-depletion, and negative Eu-/Sr-anomalies. The TTG has more depleted Sr–Nd isotopes (εNd t = + 2–+ 6; 87 Sr/ 86 Sr t = ~ 0.700) than all the others (εNd t = 0–+ 2; 87 Sr/ 86 Sr t = 0.701–703). Their petrogenesis can be explained by an Archaean-style subduction defined as a mantle wedge–absent flat–‘hot’-subduction with significant vertical tectonism in the overriding slab: the ultramafic–mafic rocks were originated from primitive mantle; the meta-dacite–rhyolite was originated from the eclogite facies overriding crust; the quartz diorite was a mixture of melts from mantle and the overriding crust; the TTG was from the subducting slab under amphibolite to amphibole-bearing eclogite facies; and the quartz monzodiorite was from the subducting slab after the derivation of the TTG. The Qingyuan terrain represents remnants of the root of a Neoarchaean arc: its anticlockwise P–T-path recorded the initiation of the arc to its cession and exhumation/cratonization at ~ 2480 Ma. [ABSTRACT FROM AUTHOR]

The Neoarchean Kadiri greenstone belt (KGB) of eastern Dharwar Craton is dominated by metavolcanic rocks including basalts, andesites, dacites and rhyolites that have experienced lower amphibolite grade of metamorphism. The geochemical investigations of the basalts and basaltic andesites of KGB show 47–56 wt.% SiO 2 and Mg# ranging from 38 to 64. The rocks display sub-alkaline tholeiitic to transitional affinity. Based on REEs, the KGB basalts are classified as two types. Type I basalts show flat to slightly enriched LREE patterns while type II basalts have relatively enriched LREE patterns. Both types of basalts exhibit negative Nb, Zr, Hf and Ti anomalies along with distinct enrichment in Th and U. Type II basalts are characterized by a greater magnitude of negative Nb anomaly (Nb/Nb* = 0.1–0.32) compared to type I (Nb/Nb* = 0.41–0.82) basalts. Prominent island arc signatures are evident in both the types in terms of their LILE, LREE enrichments and relative HFSE depletion. Ba/Th vs. Nb/Th relationships reflect a frontal arc setting for type I basalts whereas type II basalts correspond to a rear arc setting. Th/Nb, La/Nb and Ce/Yb ratios show a gradual increase from type I to type II basalts reflecting melting of sediments from the subducted slab and their increased addition in type II basalts. The Zr/Hf (31–43), Zr/Sm (11–32) and Nb/Th (1–9) ratios suggest a depleted to enriched mantle source with variable influx of subduction-derived fluids and sediments. The flat to slightly enriched LREE patterns of type I basalts indicate a gradual progression from depleted MORB-type mantle melting in a fore-arc to slab-dehydration–mantle wedge metasomatism and fluid-fluxed melting in an arc regime within spinel peridotite compositional domain. Island arc signatures in type II basalts suggest their generation through melting of a subduction-modified MORB-type mantle within spinel to garnet peridotite stability field in a juvenile back-arc rift system that developed proximal to the intraoceanic arc. Variable input of subduction derived fluids and sediments in type I and type II basalts attests to across-arc geochemical variations. The subduction processes operating within arc–back arc system provided favourable pathways for the migration of gold-bearing fluids leading to economic mineralization in the northern (Hutti) and southern (Kolar) parts of this belt. [ABSTRACT FROM AUTHOR]

We report sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone belt of western Dharwar Craton which is associated with rhyolites, chlorite schists and pyroclastic rocks. The pyroclastic rocks of Yalavadahalli area of Shimoga greenstone belt host volcanogenic Pb–Cu–Zn mineralization. The sediment-infill volcanic breccia is clast-supported and comprises angular to sub-angular felsic volcanic clasts embedded in a dolomitic matrix that infilled the spaces in between the framework of volcanic clasts. The volcanic clasts are essentially composed of alkali feldspar and quartz with accessory biotite and opaques. These clasts have geochemical characteristics consistent with that of the associated potassic rhyolites from Daginkatte Formation. The rare earth elements (REE) and high field strength element (HFSE) compositions of the sediment-infill volcanic breccia and associated mafic and felsic volcanic rocks suggest an active continental margin setting for their generation. Origin, transport and deposition of these rhyolitic clasts and their aggregation with infiltrated carbonate sediments may be attributed to pyroclastic volcanism, short distance transportation of felsic volcanic clasts and their deposition in a shallow marine shelf in an active continental margin tectonic setting where the rhyolitic clasts were cemented by carbonate material. This unique rock type, marked by close association of pyroclastic volcanic rocks and shallow marine shelf sediments, suggest shorter distance between the ridge and shelf in the Neoarchean plate tectonic scenario. [ABSTRACT FROM AUTHOR]

Previous studies focused on banded iron formations (BIFs) from the eastern North China Craton (NCC), few were conducted on those of the western NCC. This paper concentrates on two BIFs, Sanheming and Gongyiming, from the Guyang Greenstone Belt (GB), western NCC. SIMS U-Pb analyses of zircons from the amphibolite interlayers of Sanheming and Gongyiming BIFs gave upper intercept ages of 2562 ± 14 Ma and 2569 ± 78 Ma, respectively, coupled with 2555 ± 56 Ma for the tonalite with BIF xenoliths, the formation age of the BIFs is inferred to be 2.56-2.57 Ga. Protolith reconstruction based on geochemistry and field occurrence of the amphibolites shows that they are originally basaltic. Trace elements reveal that the basalts of Sanheming and Gongyiming are T-MORB and N-MORB, respectively. Metabasites from other locations of the Guyang GB in previous studies display island arc geochemical characteristics. Plus the lithologic assemblage of komatiite, basaltic komatiite, boninite, tholeiite, high-Mg andesite and Nb-enriched basalt identified by previous work, the geodynamic setting of the BIFs from Guyang GB is deduced to be a mantle plume erupting into the subduction zone and they were deposited in arc-related basins. Relatively low contents of Al2O3, TiO2 and HFSE for the BIFs indicate negligible detritus involvement. PAAS-normalized REY profiles are characterized by LREE depletion and HREE enrichment, positive La, Gd, Y and Eu anomalies, weak negative Ce anomalies and Y/Ho weight ratios of 26-41, indicating a mixture of submarine high-temperature hydrothermal fluids and seawater. Chondrite-normalized REE patterns for the BIFs are similar to those of the komatiites occurring at the bottom of the GB. Collectively, it is speculated that submarine high-temperature hydrothermal fluids leached out the Fe and Si of oceanic volcanics during circulation, and they deposited due to the changed physiochemical conditions when the fluids mixed with the seawater. The hydrothermally altered amphibolites proximal to the Gongyiming upgraded iron ores are enriched in various elements added by the hydrothermal fluids. Plus the δ18O values of magnetites and quartzs, the genesis of the Gongyiming upgraded iron ores is proposed to be hydrothermal interaction with low-grade BIF. [ABSTRACT FROM AUTHOR]

We present data on the composition of metasedimentary rocks from the greenstone belt of the Onot terrane (Sharyzhalgay uplift) and results of U–Pb dating (SHRIMP II) and Lu–Hf isotope study of detrital zircon from garnet–staurolite schists. The metasedimentary rocks of the Onot greenstone belt are dominated by garnet- and staurolite-bearing schists alternating with amphibolites (metabasalts) in the upper part of the section. Compositionally the protoliths of garnet–staurolite schists correspond to sedimentary rocks, ranging from siltstone to pelitic mudstone. The trace-element characteristics of the garnet–staurolite schists indicate that the terrigenous material was derived from three different rock types, such as tonalite–trondhjemite plagiogneisses (elevated Gd/Yb ratios), mafic rocks (elevated Cr/Th ratios and reduced Th/Sc ratios), and felsic igneous rocks formed by crustal melting (the presence of a Eu minimum), which agrees with the set of potential source rocks from the Onot terrane. The age of predominant detrital zircon reflects the erosion of mainly Neoarchean igneous rocks; this fact, combined with the poor rounding of zircon and tectonically active sedimentation conditions accompanied by mafic volcanism, suggests that the probably depositional age is ca. 2.7 Ga. Older source rocks (2.80–3.35 Ga) contributed to the sediment deposition along with the Neoarchean ones. According to the Hf isotope composition of detrital zircon from the garnet–staurolite schists, the source provenances had different crustal prehistories. The source provenances include Paleoarchean and juvenile Neoarchean crust and rocks formed by the mixing of melts from ancient and juvenile crustal sources. [ABSTRACT FROM AUTHOR]

The structure of the Neoarchean Yilgarn Craton is dominated by craton-scale high-strain zones, mostly associated with highly-deformed elongate granitic bodies and transposed greenstone belts. These shear zones developed during widespread and prolonged magmatic activity that led to a nearly complete reworking of the felsic continental crust. The spatial, temporal and genetic relationships between such a voluminous and protracted event of crustal reworking and the development of the craton-scale shear zone network are unclear. Here, we combine new structural, geophysical and geochemical data to investigate the relationship between crustal-scale shear zones and large syntectonic plutons in the Yilgarn Craton of Western Australia. We propose that Archean granite-greenstone systems may have commonly evolved through the interaction of three fundamental geological processes: (I) emplacement of large scale syntectonic plutons; (II) activity of crustal-scale shear zones; (III) pervasive, largely syn-metamorphic polyphase deformation in greenstone belts adjacent to syntectonic plutons. We propose that the concept of “Archean regional deformation event” need to be reassessed: a regional event is probably pluton- (or batholith-) size, and the structural/metamorphic evolution of adjacent greenstone belts might have proceeded quite independently and potentially in a time-transgressive way, if those belts were not spatially related to the same syntectonic pluton. [ABSTRACT FROM AUTHOR]

The geodynamic setting of the Neoarchaean Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton is the subject of debate. Some authors propose plume models, while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences. Felsic volcanism in the Kalgoorlie Terrane, the westernmost terrane of the EGS, is considered to have a tonalite-trondhjemite-granodiorite/dacite (TTG/D) geochemical affinity. The Cosmos greenstone succession, which lies in the Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, contains several komatiite-hosted nickel sulphide deposits, the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite. Light rare earth elements (LREEs) and large ion-lithophile elements (LILEs) are strongly enriched relative to high field strength elements (HFSEs) across all volcanic units, and the rocks display strong positive Pb and negative Nb anomalies. These geochemical characteristics resemble closely those of modern high-K calc-alkaline to shoshonite continental arc successions. Contrasting REE, LILE and HFSE concentrations, coupled with assimilation-fractional crystallisation (AFC) modelling, shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co-genetic. Xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence. The geochemical characteristics of the Cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone. In contrast, two younger felsic porphyry intrusions, which cross-cut the volcanic succession, have a distinct TTG/D affinity. Therefore, these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high-Ca granitoid intrusions. The Cosmos volcanic succession represents the first extrusive high-K calc-alkaline to shoshonitic volcanic arc sequence described in the Kalgoorlie Terrane and, coupled with age dating of the stratigraphy, is indicative of formation in a long-lived volcanic arc setting active from 2736 Ma to later than 2724 Ma. The composition and geochemical affinity of the volcanic footwall succession to the Cosmos komatiite-hosted nickel-sulphide deposits contrasts with the majority of felsic volcanic rocks within the AWB and also the wider Kalgoorlie Terrane, suggesting that the overall architecture of this region is more complex than is currently thought. Our conclusions not only have consequences for recent models of the tectonic evolution of the EGS but also contribute to the debate on the operation of plate tectonics during the late Archaean in general. The arc affinity of the Cosmos volcanic succession, containing abundant high-K calc-alkaline andesite lavas, provides further support for the operation of plate tectonics in the Neoarchaean. [ABSTRACT FROM AUTHOR]

The Luxi area in the central part of Eastern North China Craton (NCC) is located in a relatively stable intraplate environment and preserves some of the large granite–greenstone belts in the North China Craton (NCC). The intensity and extent of multiple magmatic pluses associated with the destruction of the NCC during Mesozoic were comparatively less in this region. However, the nature and timing of the magmatic pulses in the Luxi area are critical to the evaluation of the differential destruction of the NCC's lithosphere as well as in understanding the origin and extent of the associated gold mineralization. In this study, we report new zircon U−Pb data on the basement rocks in the Luxi area which show that the protoliths of the TTG (tonalite–trondhjemite–granodiorite) gneisses, granitoids and amphibolites formed at 2572.2±8.8Ma, 2531±12Ma, and 2572±32Ma respectively. The Luxi area experienced two major crust accretions at 2.7−2.75Ga and ca. 2.5Ga. The Mesozoic Tongshi complex formed at 175.6±1.7−178.4±2.1Ma associated with fluid modification at the later stage of magma crystallization. The alteration age (162.2±3.2−165.4±2.8Ma) may represent the mineralization age of the Guilaizhuang gold deposit. The diorite porphyry of Tongjing complex was emplaced at 128.0±5.4Ma. The inherited zircon and Lu−Hf isotope data suggest extensive recycling of basement rocks in the Luxi area. The sequence of Mesozoic magmatic intrusions shows a clear variation from intermediate (alkaline) through intermediate (cal-alkaline), and felsic–mafic, and the main intrusive ages can be divided into distinct phases at 170–200Ma, 100–150Ma (with peak at 120–130Ma), and 80–90Ma respectively. The Tongshi complex formed during the compression–extension stage after the collision of the Yangtze Craton and North China Craton, whereas the Tongjing complex and other alkaline, felsic and mafic complexes in the Luxi area formed within the geodynamic setting of Pacific subduction. The early Cretaceous magmatism also simultaneously occurred in the Taihang Mountain area (far from the plate margin) in the central part of the North China Craton, with related gold mineralization. The Mesozoic gold mineralization in Jiaodong and Luxi in the eastern, and those in the central parts of the North China Craton appear to be linked to extensive crustal recycling in an extensional tectonic regime. [ABSTRACT FROM AUTHOR]

Highlights: [•] Granitoid magmatism changed in composition with evolution of Kadiri greenstone belt. [•] Initial sanukitoid magmatism was followed by transitional TTG, leucogranite and A-type granite. [•] A convergent setting characterized by repeated slab break-off and crustal reworking. [•] Finally post-subduction anorogenic granite magmatism. [•] Reworking of Mesoarchaean crust in eastern Dharwar craton identified. [Copyright &y& Elsevier]