Quadrupole inductively-coupled-plasma mass-spectrometers (Q-ICP-MS) are used to analyse enormous numbers of isotope ratios, most prominently 206Pb/238U for age determination. With the advent of reaction-cell equipped tandem Q-ICP-MS (Q-ICP-MS/MS), the scope for isotope ratio determination has grown, especially for beta-decay isotope systems (e.g., 87Rb/87Sr). Reaction of unwanted interfering species (e.g.204Hg on 204Pb) has also increased the feasibility of Pb-isotope ratio measurements by Q-ICP-MS. Unlike in sector-field MS isotope ratio analysis where mass bias is corrected via a known isotope ratio or with calibrated double or triple-spikes, Q-ICP-MS(/MS) analysts generally apply an 'external correction' with reference to interleaved calibration standard analyses. Despite this protocol, there remains inaccuracies in derived isotope ratios when compared to reference values which are inadequately explained. The aim of this study was to investigate the origin of the inaccuracy in Q-ICP-MS isotope analysis, which has so far received surprisingly little attention. We assessed whether improved detector dead time correction can achieve more accurate isotope results and explored fractionation effects arising from steering ion beams across complex Q-ICP-MS/MS paths. We investigated detector dead time as a function of Z in both single MS and mass-shifted MS/MS mode. We document how dead time varies over time as detectors and electronic components of the ICP-MS age. We show that session specific dead times yield substantially more accurate isotope ratios for mass shifted Sr isotope ratios than when applying a generic dead time. We also provide recommendations for how to incorporate session-specific dead time analyses into an isotope ratio run. Despite the much-improved quality of dead time and conventional mass bias corrected mass shifted Sr isotope ratios, small (up to 4 parts per thousand) inaccuracies remain. The inaccuracy is systematic and specific for each session. Therefore, it can be corrected with a small bias correction relative to a CRM analysed throughout the session. The origin of the Sr isotope ratio inaccuracy after dead time and conventional mass bias correction remains speculative. Our exploratory analysis suggests that voltages on lenses tuning and directing the ion beams through the MS/MS may be a source of an additional isotope fractionation process (bias) that cannot be fully corrected with conventional mass bias procedures.

Abstract The thermal state and volatile inventory of the Earth’s mantle changed through time as lithospheric architecture and crustal recycling also evolved. Here, we analyse a global geochemical database of continentally emplaced basalts to explore the reflection of these changes in normative mineralogy. The hypothetically crystallised basalt mineralogy is calculated from all 11 major oxides, affording a whole-rock secular petrological comparison. In the Phanerozoic, normative mineralogy distinguishes between oceanic and continental basalts. Because Precambrian oceanic crust is rarely preserved, the secular analysis was focused on continentally emplaced basalts. Results show that Archaean basalts were dominantly silica-oversaturated and closely resemble modern continental flood basalts. Their normative clinopyroxene-orthopyroxene relationships argue against a dominant hydrous flux-melting origin. Two lulls in Palaeoproterozoic basalt emplacement suggest reduced magma productivity. Alkali-rich, silica-undersaturated basalts were rare in the Archaean, emerged through the Proterozoic, and rose to prominence in the Phanerozoic, supporting a late onset of effective modern-style subduction.

Hawaiites are alkali-rich, sodic, silica-undersaturated lavas found as continental and oceanic intraplate volcanism, often associated with more evolved lavas of the alkaline series. Despite the long-known distinctive chemistry of hawaiites, there still is a lack of a petrological model that successfully explains low SiO2 chemistry, elevated alkalis and their often surprisingly depleted radiogenic isotope character.Building on the co-occurrence of hawaiite and pyroxenitic xenoliths in Hawaii and Cenozoic continental intraplate eruptive centres, we conducted systematic thermodynamic modelling of the reaction of tholeiitic basalt with peridotite at 12-20 kbar. The model outcome is that clinopyroxene-rich refractory pyroxenite readily forms by melt-rock interaction between basalt and mantle, regardless of how originally enriched either component was. The predicted net crystallisation of mainly clinopyroxene at depth simultaneously depletes silica but enriches alkalis in the concurrent melt, producing ubiquitous hawaiite and more alkaline compositions. Rapid exhumation of websterite xenoliths preserves subtle microtextures that independently imply mineral growth in the presence of melt.The model treats melt-solid reaction as assimilation-fractional-crystallisation, whereby the original peridotite solids are partly dissolved and replaced by new phases in response to reaction with tholeiite, which itself changes composition. The resulting reaction stoichiometries were used to calculate incongruent melting models that reproduce key rare earth element systematics of hawaiite and co-existing pyroxenite. The reactions are also consistent with the generally depleted Sr and Nd-isotope compositions. Mass balance calculations suggest that melt-solid interaction may be a significant process in generating intraplate lavas globally and that refractory pyroxenite may be an underestimated mantle component.

The oceanic crust grows in mid-ocean ridges where melt generation is followed by magmatic processing through vertically extended mush systems. The composition of global mid-ocean ridge basalts (MORBs) requires early crystallisation of clinopyroxene at depth, however, petrological observations in MORBs (scarce clinopyroxene phenocrysts) and gabbros (clinopyroxene occupying intercumulus space) suggest clinopyroxene crystallisation is late and restricted to relatively low pressure. These competing inferences constitute the long-standing 'pyroxene paradox'. Here, we report the discovery of rare (up to 4 vol.%) relict clinopyroxene 'cores' in intercumulus clinopyroxene from the Atlantis Bank slow spreading centre (southwest Indian Ridge ODP Hole 735B). We exploit slowly diffusing trace elements Cr, Zr and Ti to uncover relics that preserve evidence of an early, transported and largely resorbed, mafic pyroxene mush. Using dimensionality reduced semantic segmentation of elemental maps, we define the mode and outline of antecryst cores. The cores have rare earth element systematics that agree with crystallisation from MORB liquids, providing an empirical connection between deep melt crystallisation and erupted basalts. In contrast, clinopyroxene rims are notably enriched in incompatible elements because of late melt-rock reaction in the gabbroic mush. The rims have strong negative Eu anomalies, indicating crystallisation after development of plagioclase-dominated mush at low pressure. Thermodynamic modelling of clinopyroxene crystallisation from MORB parental melts at high pressure (8-10 kbar) reproduces the large spread in MORB Ca-Al-Mg systematics and generates a strong density contrast between the evolving liquid and cumulate pyroxenites. At the buoyancy peak, crystallinity remains low, liquid compositions approach observed MORB chemistries, and clinopyroxene compositions match antecryst cores. Our work supports the idea that polybaric mid-ocean ridge crystal mushes act as multi-stage magma filters, with cryptic clinopyroxene crystallisation as a driver of the early evolution of the oceanic crust.

In -situ chemical analysis on thin sections is a cornerstone of geochemical research. Despite massive advances in digital image analysis, the interpretation of such data within the optical petrological context of the thin section has largely remained an analogue task in geochemistry. In this contribution, we registered optical and microchemical images from large thin section areas. Chemical datasets from scanning electron microscopy energy dispersive spectrometry (SEM-EDX) and Synchrotron X-ray fluorescence microscopy (S-XFM) were exported from proprietary software. We then evaluated two dimensionality reduction techniques against false -colour images and phase maps to test whether previously unnoticed features became discoverable. Principal component analysis (PCA) and deep sparse autoencoder (DSA) neural networks were used to summarise the multi -channel SEM-EDX and S-XFM into one single red -green -blue (RGB) representation each. Applied to an oceanic gabbro, a cratonic peridotite, and a pelagic limestone, the PCA-based dimensionality reduction was found to produce crisp RGB maps of phases with less noise than false -colour three -element RGB maps. They were registered with optical images to form a simple multi -channel input for pixel -based classification into classes (i.e., semantic segmentation). This was fast and worked well for typical igneous and metamorphic rocks (1-3 h routine). In the chemically quite homogenous limestone, the combined optical and S-XFM PCA input was successfully classified into many phases that were unclassifiable on the conventional SEM-EDX phase map. From the segmented optical and S-XFM PCA map, we exported pixel locations of classified accessory phases back into the original proprietary S-XFM software. This allowed quantification of trace elements whose X-ray peaks were invisible in the original S-XFM quantification. The DSA-based approach yielded phase maps with greater noise, but the technique was very strong at detecting subtle features. In the gabbro sample, the DSA image identified cryptic relict cores in clinopyroxene more clearly than in the previously used Cr concentration map. A DSA training set can be obtained on a small ROI to generate a consistent large area DSA image from which more fragmental cores were observed. For a ROI on the gabbro thin section, the DSA representation map and the blended optical image were segmented and inspected with a loupe tool. This allowed us to generate interactive histograms and bin -scatter concentration plots of selected phases and to search for co -variations of element concentrations. This approach can be expanded to include data from any in situ geochemical acquisition tools and may help discover previously unseen features in complex elemental imagery.

The petrogenetic history of well characterised magmatic rocks may contain invaluable information of paleo-lithospheric thickness and structure that can inform on tectonic evolution. Petrographically distinctive rocks, such as lamprophyres, provide temporal and spatial constraints to build, assess, and verify tectonic models.An alkaline lamprophyre dyke that intrudes the rift-related sediments of the Eocene Tanjung Formation of the Senakin Peninsula in South Kalimantan, Indonesia has been investigated using petrology, whole rock geochemistry and Ar-Ar geochronology.The Senakin lamprophyre dyke is mostly geochemically homogenous but petrographically stratified with vesicle free monchiquite alkaline lamprophyre mineralogy at the base and an amygdale bearing kaersutite phenocryst free upper zone. The major and trace element chemistry is consistent with an intra-plate Ocean Island Basalt like affinity. Ar-40/Ar-39 dating of hornblende and groundmass aliquots indicates an emplacement age of 37.45 +/- 0.10 Ma (2 sigma), which is consistent with the Late Eocene age of the Tanjung Formation derived from microfossil analysis.The petrology and geochemistry of the Senakin lamprophyre dyke is consistent with magma genesis at > 2GPa beneath a thick lithosphere followed by fractional crystallisation at Moho depths equivalent to 0.5-0.8 GPa. This indicates a much thicker southeastern Kalimantan paleo-lithosphere. Lamprophyre magmatism was initiated by lithospheric extension associated with the opening of the Makassar Strait and also regional thermal upwelling. This extension continued to thin the lithosphere to its current thickness equivalent to 0.5 GPa.

Wildfires impact a large and increasing proportion of the Earth's surface. With documented soil surface temperatures of up to similar to 850 degrees C, wildfires may fundamentally alter the mineralogy and geochemistry of soils and regolith, more conventionally thought to be dominated by low temperature weathering processes. Here we use an experimental approach to test the effect of temperature on the formation of pyrogenic minerals, and on the distribution and mobility of major, trace and rare earth elements following post-fire chemical weathering. We focus on ferruginous nodules, common Fe-oxide cemented components of soils, which transform from nonmagnetic to maghemite-bearing, magnetic nodules under wildfire conditions. These transformations provide a valuable record of fire impacts and facilitate the study of thermal processes and element mobility. Our results show heating produces a typical pyrogenic mineral assemblage of hematite, maghemite, metakaolin and transition alumina. At 900 degrees C the high temperature Fe2O3 polymorph luogufengite forms, which has never been reported in natural fire-affected substrates and therefore places an upper boundary on palaeowildfire temperatures at the soil-fire interface. Chemical leaching, employed to simulate the impacts of post-fire weathering, demonstrates that formation and subsequent breakdown of these pyrogenic minerals results in increased mobility of several elements including Li, Si, Sc, Cr, Co, Cu, Zn, Rb, Cs, La, Pb and U. Further, we propose that incongruent dissolution of pyrogenic metakaolin may be responsible for the formation of fusic material, an aluminous cement commonly found in soils. We conclude by discussing the significance of these results for the release of potentially toxic metals following a fire, identify trace elements that have the greatest potential to be used as palaeowildfire geochemical proxies (decreased alkali metal concentrations, decreased U/Th ratios, and decreased La compared to other rare earth elements), and the potential impact of wildfire on global geochemical cycles.

Peralkaline-metaluminous felsic-intermediate rocks are differentiates of A-type magmatism. However, their origin, sometimes obscured by hydrothermal alteration, remains a longstanding puzzle. We present new whole-rock Nd-Hf isotope, zircon U-Pb, mineral chemistry, and whole-rock data of peralkaline aegirine +/- arfvedsonite granites and metaluminous aegirine-arfvedsonite quartz syenite from the Shira and Kila ring complexes in north-central Nigeria that were less affected by hydrothermal alteration. The granites are geochemically alkalic and more enriched in Zr, Hf, Rb, Y, and Nb than the quartz syenite. The Shira peralkaline aegirine-arfvedsonite granites were emplaced at 199.5 +/- 0.7 and 200.6 +/- 1.0 Ma, while the Kila metaluminous aegirine-arfvedsonite quartz syenite was emplaced at 232.3 +/- 0.98 Ma and aegirine granites at 202.3 +/- 1.3 Ma. The Kila aegirine-granites exhibit weakly to moderately negative epsilon Hf(t) (-4.19 to -2.54) and epsilon Nd(t) (-3.92 to -0.38) values, similar to the aegirine-arfvedsonite quartz syenite (epsilon Hf(t) = -4.46 to -0.78, epsilon Nd(t) = -4.15). This suggests fractionation of intermediate melts from the enriched subcontinental lithospheric mantle (SCLM), with prior melt extraction and enrichment, exhibiting crustal contamination. The Shira aegirine-arfvedsonite granites exhibit near-zero to widely positive epsilon Hf(t) values (+0.47 to +15.03) and mildly positive epsilon Nd(t) values (+0.28 to +0.42), reflecting intermediate melt fractionation from a complexly depleted SCLM source with multiple extraction episodes and localized enrichment. The magmas evolved polybarically, fractionating high-pressure and H2O-saturated phases, including Mg-rich olivine, calcic amphibole, calcic pyroxene, plagioclase, and Fe-Ti oxides, leading to the depletion of MgO, CaO, and TiO2. Magma evolution occurred under low pressure (similar to 1.6 kbar), high temperature (839-1065 degrees C), and reduced conditions. The transition to an extensional anorogenic regime induced lithospheric stresses, reactivating major shear zones and opening associated transcurrent faults, allowing the ascent of partially melted peralkaline-metaluminous magmas from the heterogenous SCLM, which crystallized at shallow (2.8 to 7.4 km) crustal depths.

The lower continental crust, representing up to 50% of the continental mass, is largely inaccessible, making its composition difficult to constrain. Previous composite models based on geophysical evidence and geochemical data of granulite terrains and xenoliths have proposed varying results, from a mafic, relatively refractory lower crust to an intermediate-felsic, more enriched composition. Here, we investigated the mineralogy and geochemistry of predominantly mafic granulite xenoliths from eastern Australia and the Kola Peninsula, Russia, using an in situ analytical approach that minimises host magma contamination. The resulting xenolith compositions are variably and often strongly depleted in most highly incompatible trace elements, including the heat-producing elements. These xenoliths represent an extremely refractory component of the lower continental crust, likely formed after high degrees of partial melting or crystallisation from a depleted source. A lower crust composed solely of this refractory endmember would be too exhausted in heat-producing elements to satisfy heat-flow constraints. However, a volumetrically significant component of the lower crust is this mafic and refractory material, combined with undifferentiated material and a felsic or metapelitic portion. Using geophysical constraints on proportions of refractory (55%), undepleted (38%) and enriched (7%) components, a new estimate for average lower continental crust that satisfies heat flow limits was calculated, including for elements such as Be, B, Cs, W and Tl, where previous estimates relied on very few data. Finally, we show that because much of the lower continental crust is so refractory and depleted in incompatible elements, it is unlikely to be a reservoir that can balance radiogenic isotope (unradiogenic Pb) and trace element ratios (e.g. Rb/Cs, Nb/Ta) for which bulk silicate Earth departs from chondritic ratios.

During active tectonic processes the lower continental crust plays a major role in the development and evolution of the overlying crustal column. The lower crust is heavily influenced by influx of mafic magma from the mantle and extraction of more felsic magma to the shallower crust. Evidence of such interactions are preserved in residues after melting that are rarely brought to the surface as suites of granulite-facies, lower-crustal xenoliths. Here we investigate the petrology, geochemistry and petrochronology of a set of granulite xenoliths from the Pleistocene Hill 32 volcanic cone that has intruded through the geologically complex Georgetown Inlier, north Queensland, which has experienced multiple magmatic-tectonic events since the Paleoproterozoic. Petrochronology constrains the temperature in the Pleistocene lower crust to above the closure temperature of U-Pb in apatite (350-550?) and rutile (-400-500?), which define an eruption age for Hill 32 at 1.6 +/- 0.1 Ma, and below the closure temperature of titanite (up to 800?), which gives an age of 219 +/- 4 Ma. The samples contain petrographic and petrochronological evidence of recrys-tallisation and melt extraction at > 900?, conditions able to reset U-Pb systematics in zircon. The zircons give U-Pb ages consistent with the timing of the Permo-Triassic New England orogeny, indicating zircon recrystallisation/regrowth coeval with major felsic magmatism in the upper crust at that time. U-Pb in zircon records minor preservation of earlier events. While, epsilon(Hf) indicates mixing between Proterozoic to Archean precursor crust with juvenile mantle-derived magma, which provided both heat and radiogenic Hf. The samples are interpreted to be the product of melt-precursor rock hybridisation followed by melt extraction in the lower crust that represents a critical and rarely observed component of crust formation processes. (c) , 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

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

Virtual Reality (VR) has gained attention for its potential in enhancing learning, particularly in domains like geology that require spatial understanding. This paper investigates the role of VR in geology instruction, with a focus on a VR module showcasing the Mars Perseverance Rover’s sample collection process. Through a presurvey-treatment-postsurvey design involving 147 students, we found that the VR experience significantly improved students’ familiarity with and interest in the Mars2020 mission. The VR module also enhanced their knowledge about the Mars2020 robots. Contrary to expectations, cognitive load did not significantly affect outcome measures. Furthermore, students found the experience both enjoyable and calming. This research contributes to the intersection of Human-Computer Interaction (HCI) and education by underscoring the potential of VR in pedagogical contexts, emphasizing the need for user-centric design in creating immersive educational experiences.

Lamprophyres are mantle-derived rocks characterized by enrichment of incompatible elements and volatiles; however, the origin of their enriched sources remains enigmatic. Here we present zinc isotopic data for contemporary Mesoproterozoic (~ 1.1 Ga) lamprophyres from three localities of the Eastern Dharwar Craton. The Mudigubba and Kadiri lamprophyres with island-arc basalt (IAB)-like trace element features, such as positive Pb and negative Nb–Ta, Zr–Hf and Ti anomalies, have mid-ocean ridge basalt (MORB)-like δ 66 Zn values ranging from + 0.22‰ to + 0.29‰. In contrast, the Udiripikonda lamprophyre shows higher-than-MORB δ 66 Zn values of + 0.39‰ to + 0.48‰ and elemental features of intra-plate magmas with a lack of pronounced Nb–Ta-negative anomalies. Based on the covariations between Zn isotopes and trace element ratios, we infer that the Mudigubba and Kadiri lamprophyres with MORB-like Zn isotopes and high Ba/La, K/Nb and low Nb/La, Ce/Pb ratios are inherited from sub-continental lithospheric mantle metasomatized by fluids derived from a subducted slab. On the contrary, the higher-than-MORB Zn isotopic compositions, with low Ba/La, K/Nb and high Nb/La, Ce/Pb, K/U and Ba/Th ratios for the Udiripikonda lamprophyre are inferred to derive from lithospheric mantle enriched by carbonatitic melts or subducted carbonate-bearing sediments within the mantle transition zone. Hence, our study suggests that contemporary lamprophyres can be derived from disparate enriched mantle sources.

Single and tandem quadrupole ICP-MS instruments are routinely used to determine isotope ratios, such as 206 Pb/ 238 U, 207 Pb/ 204 Pb, and 234 U/ 238 U, while tandem Q-ICP-MS have applications in in-situ 176 Lu/ 176 Hf and 87 Rb/ 87 Sr dating.However, there is limited consensus on an approach to mass bias correction, with most using standard-bracketing to correct for both elemental fractionation and mass bias.In tandem Q-ICP-MS 87 Sr/ 86 Sr analysis, several studies have proposed that the conventional IUPAC approach of using a known 88 Sr/ 86 Sr ratio for mass bias correction does not yield accurate 87 Sr/ 86 Sr and 84 Sr/ 86 Sr ratios, instead requiring an additional 'correction factor'.Incorrect detector deadtime has sometimes been implied[1] as one source of inaccurate IUPAC approach mass bias correction of isotope ratios.Here we present results of a wider investigation into deadtime effects on isotope ratios analysed by tandem Q-ICP-MS.All data were acquired on elemental solution ranging in z from Li to U, with a nominal deadtime of 0 ns on an Agilent 8900 both in no gas and mass shift mode.We confirm the previously proposed increase of deadtime with z (a few ns across the full mass range).However, in detail, this relationship cannot be used for accurate isotope ratio analyses, which require session specific deadtime determinations.This will be illustrated with Sr-isotope ratio analyses in no gas mode and mass shift mode.We find one consistent deadtime for all analyses modes, but this varies by 1-2 ns over the course of weeks.Accurate 87 Sr/ 86 Sr ratios were obtained in all modes with the IUPAC mass bias correction from the known 88 Sr/ 86 Sr ratio with no need for a further 'correction factor'.Accurate 84 Sr/ 86 Sr ratios were obtained in mass shift mode thanks to the removal of isobaric Kr interferences.Dead time linearity was demonstrated up to 4-6 10 6 cps in pulse count mode, overcoming issues of mixed pulse-count/analogue signals.Collectively, we anticipate that this method will yield more accurate isotope ratio data from Q-ICP-MS and will reduce apparent reverse discordance in U-Pb zircon and erroneous ages in the Rb-Sr dating.

The Devonian represents a period of transition for the accretionary orogens of the Australian Tasmanides where the largest and inboard Thomson Orogen became stabilised and orogenic processes became focused in the outboard and newly developing New England Orogen. The end of tectonic activity in the Thomson and the adjacent Delamerian and Lachlan orogens culminated with the development of sev-eral overlying intracratonic sedimentary basins. We examine the two largest cover basins, the Adavale and Darling, using stratigraphic logging, sandstone petrography, detrital zircon and rutile U-Pb geochronology to fingerprint sediment sources to test whether the basins were once connected and part of a much larger cover basin system. Sediment provenance in the Adavale Basin is characterised by (i) continuous input from a basement-derived Ordovician (-480 Ma) igneous zircon source, (ii) reworking of metasedimentary basement rocks with a 'Pacific-Gondwana' age signature (iii) reworking of detrital rutile from Cambro-Ordovician sedimentary rocks in the Thomson Orogen ultimately sourced from the Musgrave Block and (iv) an addition of syn-depositional volcanic zircon from contemporary volcanism between-380 and 360 Ma. Sediment provenance of the Darling Basin is dominated by reworking of (meta)sedimentary basement, evident from large proportions of rounded zircons exhibiting a 'Pacific -Gondwana' age signature and detrital rutile with Peterman Orogeny ages. A much less significant age population of syn-depositional volcanic detrital zircons suggests input from contemporary volcanic sources which were more distal and extra-basinal.The comparison of sandstone compositions and detrital age information indicate both basins record similar provenance signals in terms of reworking of their respective hinterlands and receiving contribu-tions from relatively distal syn-depositional volcanism. However, the comparison of sediment prove-nance proxies, suggests that the Adavale and Darling basins were not connected during the Devonian and that the basins are intracratonic or cover basins, recording the stabilisation of the Thomson and Lachlan orogens, respectively.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

In conjunction with major, trace and rare earth element data, this study presents the first whole-rock Lu???Hf isotope analyses of mafic-ultramafic rocks of the c. 3.3 Ga Kromberg type-section in the Barberton greenstone belt of South Africa. Three compositionally distinct volcanic rock types are identified namely Group 1 metabasalts, Group 2 metabasalts and komatiitic metabasalts. Group 1 metabasalts are Fe???Mg tholeiitic with compositions that plot close to the Primitive Mantle composition, have isochron intercept ??Hf(t) value of 0.01 ?? 0.4 and Eoarchean Hf model ages. Group 2 metabasalts have very high Al2O3/TiO2 ratios (c. 50), small negative Nb anomalies, LREE-depleted slightly concave up REE patterns, and negative ??Hf(t) values. The komatiitic basalts variably record small negative Nb anomalies in a primitive mantle normalized plot. Group 1 metabasalts and cumulate peridotites (wehrlites) yield a Lu???Hf isochron age of 3.340 ?? 0.190 Ga (95% confidence level). The highly variable major and trace element geochemistry of the rocks in the sequence implies highly dynamic and variable mantle melting environments. The Group 2 metabasalts have geochemical characteristics similar to that of boninites and are interpreted to have formed from a shallow, refractory mantle source. Group 2 metabasalts are argued to have formed in a proto-plate tectonic back-arc basin involving crustal contamination, whereas Group 1 metabasalts likely formed from within a deep mantle plume.

In Archean granite-greenstone terranes, domes represent multiple granitic magmatic emplacement events preserved as variably deformed granitic gneisses. Commonly, the oldest granitic components occur as slivers of deformed gneisses along the interface between domes and adjacent greenstone keels. The Callina Supersuite represent the first craton wide voluminous juvenile granitic magmatism in the Pilbara Craton between 3.49-3.45 Ga. However, rare pre-Callina orthogneiss complexes and detrital and inherited zircon attest to older Eoarchean to early Paleoarchean granitic crust. The extent of this early granitic crust is unclear. Thus, investigating rare pre-Callina granitic gneisses will yield valuable information on the initial formation of the Pilbara Craton. Here, we present an integrated geochemical and petrological study on 3.5-3.6 Ga granitic orthogneisses from the southern margin of the Muccan Granitic Dome [1]. We show that these gneisses have no resolvable 142 Nd anomalies and yield e Hf(t) of +1 to -3. The gneisses are petrologically and geochemically diverse, including epidote-bearing samples, and have been intensely deformed and migmatised during exhumation from >6 kbars at 3.4 Ga [1]. We propose that the pre-Callina gneisses formed from mafic precursor crust with chondritic to sub-chondritic ε Hf

Lamproites are rare mantle-derived peralkaline ultrapotassic rocks, and they are commonly geographically associated with the ultramafic lamprophyres and kimberlites. Their unique geochemistry and mineralogy make determining their mantle source and origin important because of the significance for inferring specific geo-dynamic processes. In this study, we further examine lamproite petrogenesis using new Mg and Zn isotopic data for the typical Gaussberg lamproites, Antarctica, the source of which were thought to be contributed by recycled crustal materials. Results show that these lamproites have lower delta Mg-26 (-0.44%o to-0.39%o) and higher delta 66Zn (0.36 parts per thousand to 0.39 parts per thousand ) values than terrestrial mantle (delta Mg-26 =-0.25 +/- 0.04%o, delta Zn-66 = 0.18 +/- 0.05 parts per thousand ). The post -magmatic alteration and crustal contamination as well as fractional crystallization and partial melting cannot account for these anomalous Mg and Zn isotopic values. By contrast, the involvement of sedimentary carbonates which are characterized by light delta 26Mg (average approximately-2.0%o) and heavy delta 66Zn (average -+0.91%o) values in their mantle source can explain these Mg and Zn isotopic anomalies. Quantitative modelling suggests that addition of 10-15% subducted dolomite into the source of Gaussberg lamproites can well reproduce their Mg and Zn isotopic values. The source component with light Mg and heavy Zn isotopic compositions can either be sub-continental lithospheric mantle metasomatized by carbonate melts or residue of subducted carbonate -bearing sediments after deep melting in the mantle transition zone. A lithospheric mantle contribution is indeed required to explain their strongly enriched radiogenic isotopic compositions. However, in terms of car-bonate component, their positive Zr-Hf anomalies (Hf/Hf* = 1.28-2.19), and extremely high K/U (-40, 000) and Ba/Th (-400) ratios lead us to favor the latter deep recycling model in which the recycled carbonate-bearing sediments subducted as K-hollandite and majorite underwent partial melting within the mantle transition zone.

The time-interval between 2.8 and 2.7 Ga is associated with the worldwide appearance of thick tholeiitekomatiite successions. However, their origin and affiliation, if any, is poorly understood. The Eastern Goldfields Superterrane of the Yilgarn Craton, Western Australia, is dominated by the 2.7 Ga Kalgoorlie and Kurnalpi terranes, both of which consist of well-preserved mafic-ultramafic volcano-stratigraphy. On a local scale, these supracrustal sequences permit reconstruction of volcano-sedimentary environments, which provides important constraints to the local conditions of magmatism and/or deposition. Regionally, these observations can be used to test correlations between greenstone belts, constrain basin architecture and the extent of volcanism. Studies of this nature provide important insights to global, Archean volcano-sedimentary processes.Here we present an integrated field, geochemical and U-Pb geochronological study from the well-preserved West Laverton Greenstone Belt in the Kurnalpi Terrane and compare it to the relatively well constrained Kalgoorlie Terrane. The sequence comprises three volcanic 'events' consisting dominantly of low-Th tholeiitic basalt and komatiite derived from depleted mantle sources. Magmatism commenced after 2854 +/- 4 Ma and ceased by 2717 +/- 4 Ma. Prominent banded iron formations separate volcanic cycles, indicating an overall quiescent subaqueous setting.The West Laverton Sequence is correlated with volcanic events in the neighbouring Kalgoorlie Terrane, where pre-existing basement with remarkably similar character is documented near Norseman, over 360 km away. Both terranes contain basal paragneiss (2.96-2.93 Ga) and epiclastic sediments (~2.93-2.85 Ga) that are overlain by three variably preserved and widespread tholeiite-dominated volcanic events, here defined as the 2.81-2.71 Ga 'Goldfields Tholeiitic Super Event'. These correlations support an autochthonous setting for the Kalgoorlie and Kurnalpi terranes with the eruption of volcanic tholeiites onto submerged continental crust. Voluminous tholeiitic volcanism at 2.8-2.7 Ga was a global event. The Zimbabwe and Slave cratons preserve remarkably similar basement overlain by thick basaltic units, that are compositionally similar to the 'Goldfields Tholeiitic Super Event'. This correlation indicates that a globally significant rifting event at 2.8-2.7 Ga affected much of the continental crust extant.