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Muscovite 40Ar/39Ar geochronology on ten samples from complex-type, rare-metal (e.g., Li, Cs, Ta, Rb, Be, Nb, Sn and W) pegmatites from the Bikita and Mweza pegmatite fields in Zimbabwe yield ages that range from ca. 2622 – 1940 Ma. One pegmatite from the Bikita field yield a relict age of ca. 2622 Ma which is similar to the ca. 2.62 Ga emplacement age of the Main Bikita Pegmatite previously determined by laser ablation analyses of Ta–Nb–Sn oxides. Younger muscovite 40Ar/39Ar ages of ca. 2580 – 2539 Ma in the Bikita field may reflect post-pegmatite emplacement tectono-thermal events under fluid-mediated conditions. Data from the Mweza pegmatite district yield dates of ca. 2027 – 1940 Ma which reflect a Palaeoproterozoic overprint. Palaeoproterozoic 40Ar/39Ar ages are spatially restricted to near the Northern Marginal Zone – Zimbabwe Craton boundary and are absent towards the interior of the craton in the Bikita pegmatite field. • Muscovite 40Ar/39Ar geochronology on rare-metal pegmatites from the Bikita & Mweza districts, Zimbabwe. • Re-set muscovite argon ages related to deformation and metamorphic episodes. • Multiple post-pegmatite emplacement tectono-thermal events along the southern margin of the Zimbabwe Craton. • Palaeoproterozic overprint of Neoarchaean muscovite ages under fluid-mediated conditions. • Muscovite argon geochronology complements other mineral chronometers in elucidating regional tectonic events. [ABSTRACT FROM AUTHOR]

The stone named “Hypatia” found in the Libyan Desert Glass area of southwest Egypt is carbon-dominated and rich in microdiamonds. Previous noble gas and nitrogen isotope studies suggest an extraterrestrial origin. We report on a reconnaissance study of the carbonaceous matrix of this stone and the phases enclosed in it. This focused on areas not affected by numerous transecting fractures mostly filled with secondary minerals. The work employed scanning electron microscopy (SEM) with energy-dispersive (EDS) and wavelength-dispersive (WDS) electron microprobe (EMPA) analysis, Proton Induced X-ray Emission (PIXE) spectrometry and micro-Raman spectroscopy. We found that carbonaceous matrices of two types occur irregularly intermingled on the 50–500 μm scale: Matrix-1, consisting of almost pure carbonaceous matter, and Matrix-2, containing Fe, Ni, P and S at abundances analyzable by microprobe. Matrix-2 contains the following phases as inclusions: (i) (Fe,Ni) sulphide occurring in cloud-like concentrations of sub-μm grains, in domains of the matrix that are enriched in Fe and S. These domains have (Fe + Ni)/S (atomic) = 1.51 ± 0.24 and Ni/Fe = 0.086 ± 0.061 (both 1SD); (ii) grains up to ∼5 μm in size of moissanite (SiC); (iii) Ni-phosphide compound grains up to 60 μm across that appear cryptocrystalline or amorphous and have (Ni + Fe)/P (atomic) = 5.6. ± 1.7 and Ni/Fe = 74 ± 29 (both 1SD), where both these ratios are much higher than any known Ni-phosphide minerals; (iv) rare grains (observed only once) of graphite, metallic Al, Fe and Ag, and a phase consisting of Ag, P and I. In Matrix-2, Raman spectroscopy shows a prominent narrow diamond band at 1340 cm −1 . In Matrix-1 the D and G bands of disordered carbon are dominant, but a minor diamond band is ubiquitous, accounting for the uniform hardness of the material. The D and G bands have average full width at half maximum (FWHM) values of 295 ± 19 and 115 ± 19 cm −1 , respectively, and the D/G intensity ratio is 0.75 ± 0.09 (both 1SD). These values are similar to those of the most primitive solar system carbonaceous matter. The diamond phase is considered to be a product of shock. The (Fe, Ni) sulphide phase is probably pyrrhotite and a shock origin is likewise proposed for it. Moissanite is frequently associated with the Ni-phosphide phase, and a presolar origin for both is suggested. The lack of recrystallization of the Ni-phosphide phase suggests that the Hypatia stone did not experience long-lasting thermal metamorphism, in accord with the Raman D-G band characteristics. A lack of silicate matter sets the stone apart from interplanetary dust particles and known cometary material. This, along with the dual intermingled matrices internal to it, could indicate a high degree of heterogeneity in the early solar nebula. [ABSTRACT FROM AUTHOR]

Following the publication (Granger DE et al., Nature 2015;522:85-88) of an 26Al/10Be burial isochron age of 3.67±0.16 Ma for the sediments encasing hominin fossil StW573 ('Little Foot'), we consider data on chert samples presented in that publication to explore alternative age interpretations. 10Be and 26Al concentrations determined on individual chert fragments within the sediments were calculated back in time, and data from one of these fragments point to a maximum age of 2.8 Ma for the sediment package and therefore also for the fossil. An alternative hypothesis is explored, which involves re-deposition and mixing of sediment that had previously collected over time in an upper chamber, which has since been eroded. We show that it is possible for such a scenario to yield ultimately an isochron indicating an apparent age much older than the depositional age of the sediments around the fossil. A possible scenario for deposition of StW573 in Member 2 would involve the formation of an opening between the Silberberg Grotto and an upper chamber. Not only could such an opening have acted as a death trap, but it could also have disturbed the sedimentological balance in the cave, allowing unconsolidated sediment to be washed into the Silberberg Grotto. This two-staged burial model would thus allow a younger age for the fossil, consistent with the sedimentology of the deposit. This alternative age is also not in contradiction to available faunal and palaeomagnetic data. [ABSTRACT FROM AUTHOR]

An extraterrestrial origin for a carbonaceous, diamond-bearing and silicate-free stone named "Hypatia", found in 1996 in southwest Egypt, was determined in 2013 and confirmed in 2015 on the basis of argon, helium, neon, xenon and nitrogen isotope characteristics. Petrography and Raman spectroscopy has indicated that the parent body was primitive, i. e. not thermally processed in the solar nebula. Here we report the results of in situ chemical analyses of this object using proton induced X-ray emission (PIXE) spectroscopy. The stone has a bimodal matrix. Type 1 is essentially devoid of elements heavier than oxygen, whereas matrix 2 shows a unique, consistent element abundance pattern from aluminum to zinc, up to a sum of 4.5 wt%. Fe is dominant and Si markedly depleted, with a CI-chondrite normalized Si/Fe ratio of c. 0.1. Element abundance ratios to Fe show several correlations, with one group (Al, Si, K, Ca, Ti and Cu) being negatively correlated to another one (P, S and Ni). Since the parent body was primitive, magmatic differentiation cannot be invoked to account for any part of this dataset. Considering published Raman spectroscopic data and interstellar dust models, we hypothesize that Hypatia's parent body consisted of interstellar dust. However, Hypatia's matrix 2 chemistry does not fit predictions for the average interstellar dust composition based on absorption spectroscopic studies of element depletions in gas along stellar lines of sight. Instead, it shows similarities to the nucleosynthesis yields of specific supernova Ia models, whereby the element abundance correlations and the strong depletion of Si may be understood as resulting from nuclear photodisintegration. It has been known for decades that the chemistry of interstellar space is made up of many components, each bearing the signature of the nucleosynthesis processes giving rise to them. Now it appears from the case of Hypatia that an individual component was preserved in dust, and delivered to a region of the solar nebula where mixing did not obliterate it prior to the coagulation of larger bodies. • The parent body of the carbonaceous, extraterrestrial stone "Hypatia" was primitive. • We report proton microprobe analyses of elements Al to Zn in the object. • A consistent element abundance pattern includes Si/Fe and Mn/Fe 0.1 × the solar value. • Relative even-Z element abundances are similar to some modeled supernova Ia yields. • The results imply that matter forming the solar nebula included heterogeneous dust. [ABSTRACT FROM AUTHOR]

We have carried out a geochronological study in the high grade metamorphic Southern Marginal Zone of the Limpopo Complex, South Africa, aimed at providing time constraints on episodes of fluid activity. This work chiefly comprises 40 Ar/ 39 Ar dating, with accompanying petrography, of amphibole and mica, and further incudes zircon U–Pb geochronology on a post peak metamorphic trondhjemite intrusion. The so-called Zone of Rehydration within 30 km N of the Hout River Shear Zone (where the Southern Marginal Zone is thrust over the Kaapvaal Craton) was studied in particular, but sampling also included areas of patchy metasomatism in the Granulite Zone further north, where no post-peak metamorphic rehydration on a regional scale occurred. Amphibole in a mafic granulite and an older generation of zircons in the Petronella trondhjemite yielded dates in the 2700–2730 Ma range, corresponding to the published age of peak granulite metamorphism in the Southern Marginal Zone. A cluster of 40 Ar/ 39 Ar dates on amphiboles from the Zone of Rehydration indicate an age between 2660 and 2670 Ma for this event, in accord with results from previous work on the Hout River Shear Zone. The main population of U–Pb zircon dates from the trondhjemite, dating its intrusion, also falls in this age range, as does the published age of the Matok pluton. These data suggest that rehydration at 2660–2670 Ma was a discrete episode. A further 40 Ar/ 39 Ar age cluster, defined by dates on both amphiboles and micas, is seen at 2010–2040 Ma, which is the age of a major tectonometamorphic event in the Central Zone of the Limpopo Complex, and previously reported from the Southern Marginal Zone as Rb–Sr biotite dates. Events we found in the 2010–2040 Ma bracket are strike-slip shearing (dated by fabric forming amphibole), as well as localized potassic metasomatism (dated by both amphiboles and micas). The latter was not confined to the Zone of Rehydration, and appears in one case to be associated with gold mineralization. A number of 40 Ar/ 39 Ar dates intermediate between 2600 and 2000 Ma were obtained, but these are diverse and can be accounted for by mixing, incomplete resetting and/or excess 40 Ar. They do not indicate events in this intermediate age bracket. [ABSTRACT FROM AUTHOR]

Abstract: We have studied a small, very unusual stone, here named “Hypatia”, found in the area of southwest Egypt where an extreme surface heating event produced the Libyan Desert Glass 28.5 million years ago. It is angular, black, shiny, extremely hard and intensely fractured. We report on exploratory work including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy with EDS analysis, deuteron nuclear reaction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respectively. The major cations of silicates add up to less than 5%. The stone consists chiefly of apparently amorphous, but very hard carbonaceous matter, in which patches of sub- diamonds occur. values (ca. 0‰) exclude an origin from shocked terrestrial coal or any variety of terrestrial diamond. They are also higher than the values for carbonaceous chondrites but fall within the wide range for interplanetary dust particles and comet 81P/Wild2 dust. In step heating, 40Ar/36Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheric Ar. Isotope data of Ne, Kr and Xe reveal the exotic noble gas components G and P3 that are normally hosted in presolar SiC and nanodiamonds, while the most common trapped noble gas component of chondritic meteorites, Q, appears to be absent. An origin remote from the asteroid belt can account for these features. We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage. [Copyright &y& Elsevier]

Abstract: The Cradle of Humankind cave sites in South Africa preserve fossil evidence of four early hominin taxa: Australopithecus africanus, Australopithecus sediba, Paranthropus robustus and early Homo. In order to integrate this record into a pan-African scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern African hominins. In the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites. Here we report new uranium–lead (U–Pb) radiometric ages obtained from sheets of calcium carbonate flowstone inter-bedded between clastic cave sediments at the site of Swartkrans, providing bracketing ages for the fossiliferous deposits. The fossil bearing units of Swartkrans, specifically the Hanging Remnant and Lower Bank of Member 1, are underlain by flowstone layers dated to 2.25±0.05Ma and 2.25±0.08Ma and capped by layers of 1.8±0.01Ma and 1.7±0.07Ma. The age bracket of the Member 1 deposits is therefore between 2.31 and 1.64Ma. However, by combining the U–Pb with biostratigraphic data we suggest that this can be narrowed down to between 1.9 and 1.8Ma. These data can be compared with other recently dated sites and a radiometrically dated U–Pb age sequence formed: Sterkfontein Member 4, Swartkrans Member 1, Malapa, and Cooper''s D. From this new U–Pb dataset, a pattern of contemporary flowstone development emerges, with different caves recording the same flowstone-forming event. Specifically overlapping flowstone formation takes place at Swartkrans and Sterkfontein at ~2.29Ma and ~1.77Ma, and at Sterkfontein and Malapa at ∼2.02Ma. This suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation, both internal to specific deposits and regionally between sites. [Copyright &y& Elsevier]

Abstract: Sterkfontein Caves is the single richest early hominin site in the world with deposits yielding one or more species of Australopithecus and possible early Homo, as well as an extensive faunal collection. The inability to date the southern African cave sites accurately or precisely has hindered attempts to integrate the hominin fossil evidence into pan-African scenarios about human evolutionary history, and especially hominin biogeography. We have used U-Pb and U-Th techniques to date sheets of calcium carbonate flowstone inter-bedded between the fossiliferous sediments. For the first time, absolute age ranges can be assigned to the fossil-bearing deposits: Member 2 is between 2.8 ± 0.28 and 2.6 ± 0.30 Ma and Member 4 between 2.65 ± 0.30 and 2.01 ± 0.05 Ma. The age of 2.01 ± 0.05 Ma for the top of Member 4 constrains the last appearance of Australopithecus africanus to 2 Ma. In the Silberberg Grotto we have reproduced the U-Pb age of ∼2.2 Ma of for the flowstones associated with StW573. We believe that these deposits, including the fossil and the flowstones, accumulated rapidly around 2.2 Ma. The stratigraphy of the site is complex as sediments are exposed both in the underground chambers and at surface. We present a new interpretation of the stratigraphy based on surface mapping, boreholes logs and U-Pb ages. Every effort was made to retain the Member system, however, only Members 2 and 4 are recognized in the boreholes. We propose that the deposits formally known as Member 3 are in fact the distal equivalents of Member 4. The sediments of Members 2 and 4 consisted of cone-like deposits and probably never filled up the cave. The U-Th ages show that there are substantial deposits younger than 400 ka in the underground cave, underlying the older deposits, highlighting again that these cave fills are not simple layer-cakes. [Copyright &y& Elsevier]

The abundances of the elements H, C, N, Ne, primordial Ar, Cl, Br, Kr, I and Xe, in the atmo-hydrosphere, continental crust and MORB-source mantle (termed the outer Earth reservoirs (OER)) are examined and compared with solar matter and an average of carbonaceous chondrites (CC). The aim is to assess the likelihood of various possible sources for these volatile elements now on Earth, and discuss and possibly quantify processes whereby volatiles were lost, in order to narrow down scenarios for the earliest terrestrial environment.Al-normalized abundance patterns show a depletion relative to solar matter which varies from 2×10−11 for Ne to 4×10−3 for the halogens. The overall relative pattern is broadly similar to an average abundance pattern of CC, with two to three orders of magnitude depletion relative to this. For H, C, N and the halogens this similarity, against the background of the huge diversity compared to solar matter, makes CC-type material a much more likely source than a gravitationally captured solar atmosphere. A small admixture of solar matter (Alsolar/Altotal≈10−7) acquired in accretion can account for the solar Ne isotope signatures in the deep mantle. The abundance pattern of C, N, Ne, primordial Ar, Br and Kr relative to such a “solar spiked” CC-type source shows depletions dependent of the masses of the molecules (C as CO, N as N2, Br as Br2), which can be modeled assuming a hydrodynamic escape mechanism with H2 fluxes varying from 1 to 3×1013 molecules cm−2 s−1. Relative to this depletion pattern, H (as H2O) and Cl (as HCl) are overabundant by about an order of magnitude. Delivery by comets over Earth history is a highly unlikely explanation for the H overabundance, as measured cometary D/H ratios are ∼2×, and C/H ratios ∼4× higher than those of the OER. The overabundance of both H and Cl can be understood and quantitatively modeled if it is assumed that a liquid water ocean existed in which major portions (on average, between 50 and 70%) of H2O and HCl resided during hydrodynamic escape, so that their volume proportion in the atmosphere (and therefore their loss) was reduced. [Copyright &y& Elsevier]

The eastern escarpment in South Africa has a combination of geology and climate that is unique in the entire Great Escarpment. Yet, no studies have been undertaken before to quantify the landscape changes at this locality. In this study, we assess the denudation history of the eastern escarpment using cosmogenic beryllium-10 (10Be) on quartz from rock outcrops and river sediments, and carry out uranium‑thorium‑helium ((U,Th)-He) and argon‑argon (40Ar/39Ar) dating of Fe-oxides and Mn-oxides, respectively, in the soils. The erosion rates obtained on the eastern escarpment vary from 1.8 m/Ma to 24 m/Ma and are similar in range to values from the entire Great Escarpment. We found that the catchment-averaged erosion rates of the gentle catchments above the eastern escarpment are lower, whereas those from steep catchments draining the escarpment edge are higher. We also determined that the catchment-average erosion rates of the eastern escarpment are similar to those of the western escarpment in Namibia, lower than those of the Drakensberg Escarpment and lower than those of the Lowveld adjacent to it. The 40Ar/39Ar dating of cryptomelane-bearing Mn nodules yield Palaeoproterozoic ages unrelated to the pedogenic processes, and might indicate that these nodules are not pedogenic, but inherited from weathered bedrock. The (U,Th)-He ages of goethite concretions range from 0.85 Ma to 1.05 Ma and they date the last period of intensive chemical weathering on the eastern escarpment, which coincides with the Mid-Pleistocene Transition from humid to more arid conditions on the southern African subcontinent. Given the low erosion rates above the escarpment, an area that experiences intensive chemical weathering, and the high erosion rates down the escarpment we conclude that at the eastern escarpment, pediplanation is a more important driver of denudation than peneplanation. [Display omitted] • Intensive chemical weathering dates to Mid-Pleistocene Transition • Eastern Great Escarpment has low erosion rates despite humid climate. • Denudation largely driven by interplay of climate and pediplanation • Erosion rates of eastern section similar to entire Great Escarpment [ABSTRACT FROM AUTHOR]

The Ordovician-Silurian siliciclastic units of the Table Mountain Group (TMG; Cape Supergroup) of the Cape Fold Belt (CFB) are classically considered to signify a period of long-lived sedimentation along the southern margin of southern Africa. Despite its vast, prominent outcrop, meaningful interpretations regarding the provenance of the TMG, based on a representative number of U Pb detrital zircon age fractions, remains lacking. Within southern Gondwana, the TMG succession is considered broadly time-correlative to the Sierra del Volcan and Balcarce formations of the Sierras Tandilia and lowermost successions of the Ventana Group of the Sierras Australes in Argentina and the Port Stephens Formation of the West Falkland Group (WFG) in the Falkland/Malvinas Islands and Natal Group (South Africa). U Pb detrital zircon ages have previously been reported for the Balcarce Formation and Ventana and West Falkland groups. However, their age fractions have not necessarily been compared to the broadly time –equivalent units of the TMG. In addition to the overall scarcity of detrital zircon age data on the TMG, the validity of using conventional, qualitative probability density diagrams to display and interpret such data sets have come into question, with some authors arguing for a quantitative approach for comparing detrital zircon age data sets. A total of 1521 concordant U Pb detrital zircon ages and some 330 Lu Hf isotope analysis for the Peninsula- and Skurweberg formations (TMG) are therefore contributed, from samples obtained throughout the CFB, along with detrital zircon age fractions for the Balcarce, Providencia and Port Stephens formations. A qualitative as well as quantitative approach to compare the U Pb detrital zircon age fractions measured for these units were adapted. Noticeable similarities among detrital zircon age fractions of the Peninsula- and Skurweberg formations throughout the western to south-eastern reaches of the CFB could be confirmed by quantitative pairwise comparisons. These point towards very little change in sediment source during the deposition of the lower to upper formations of the TMG during the Ordovician-Silurian. Pairwise comparisons of the TMG zircon age fractions to those of the Balcarce-, Providencia and Port Stephens formations revealed that they all have major late Neoproterozoic to Cambrian and a late Mesoproterozoic to early Neoproterozoic age fractions in common, with some minor contributions from Ordovician-Silurian sources. Due to the overlap in prevalent detrital zircon age fractions as well as Hf-isotope signature of these units, it is difficult to assign a specific provenance area for them with a fair amount of confidence, even if dominant palaeocurrent directions are considered. A quantitative pairwise comparison among data sets of the same or time-equivalent formation did not necessarily allow for age fractions from different source areas to be sufficiently distinguished from each other. In contrast to the classically inferred Namaqua-Natal Metamorphic Complex (NNMC) as source major proto-source for the TMG, it is argued that the sediment sources were located much further to the north such as the Damara and Mozambique belts, given that parts of the NNMC were likely denudated and covered by the sediments such as those of the Nama and Vanrhynsdorp Groups during the Ordovician-Silurian. Older sedimentary successions such as the Nama Group, were likely recycled during the deposition of the TMG: a scenario which also provides a feasible explanation for the noticeable lack of Archean ages among the detrital zircon age fractions. The ages of the youngest detrital zircon fraction conforms to the maximum age of deposition as proposed in literature, although the newly reported ages does not allow for more stringent cross-basin correlations. Regions within Patagonia, considered to have been in relatively close proximity to the relevant depositories, and possibly the Famatinian Belt (Argentina), are considered the source of the youngest Ordovician-Silurian detrital zircons. • New U Pb detrital zircon age data for the Peninsula and Skurweberg formations. • Quantitative assessment of similarities among U Pb age fractions. • Possible proto source terrains form throughout southern Gondwana. • Recycling of older sedimentary units a likely source of detritus. • A reassessment of Ordovician-Silurian cross-basin correlations. [ABSTRACT FROM AUTHOR]

• Ar-Ar hornblende data confirm a crustal gradient largely over Sverdrupfjella and Kirwanveggan at ca. 530 Ma of ca. 12 km to surface. • Sr/Nd and published SHRIMP data identify CDML type rocks as provenance to the Urfjell Group. • The uplift data imply the Kuunga Orogeny is limited to Kirwanveggan and Sverdrupfjella and doesn't extend to Heimefrontfjella. • Combined interpretation of lithologies and geophysics facilitate a revision of WDML tectonic units. • A closer source to the Urfjell Group is provided by a revised Kuunga Nappe Complex extent. Biotite 40Ar/39Ar ages from Mesoproterozoic gneisses from Kirwanveggan and Sverdrupfjella vary between 868–497 Ma and 547–326 Ma respectively. Hornblende ages from Kirwanveggan and Sverdrupfjella gneisses vary between 1067–480 Ma and 550–450 Ma respectively. The similar ages for hornblende and biotite from Sverdrupfjella are consistent with rapid uplift in a single event. The differences in ages between biotite and hornblende from Kirwanveggan imply differential heating southwards through Kirwanveggan and suggest heating over northern Kirwanveggan at ~500 Ma with central to southern Kirwanveggan preserving older Mesoproterozoic 40Ar/39Ar ages in hornblende. The heating is inferred to result from burial in the footwall of a nappe. Biotite ages throughout Sverdrupfjella and Kirwanveggan are similar to ages of deposition of Urfjell Group clastic sediments, with the Urfjell Group defining the southern limit of uplift and deposition at ~530 Ma. Radiogenic Nd/Sr isotope characteristics of the Urfjell Group are similar to basement gneisses from nearby Kirwanveggan and eastern Sverdrupfjella, Gjelsvikfjella and central Dronning Maud Land (CDML) but dissimilar to western Sverdrupfjella. In contrast detrital zircon patterns of the Urfjell Group suggest derivation from a source similar to distant CDML, ca. 500 km away. Tectonic analysis of Dronning Maud Land (DML), using available and new Sr/Nd radiogenic isotope and 40Ar/39Ar data, SHRIMP U/Pb zircon data, P-T-t estimates and structural analysis allow an interpretation that eastern Sverdrupfjella, Gjelsvikfjella and CDML comprise a nappe complex, emplaced toward S-SE over western Sverdrupfjella at ca. 500–480 Ma. The timing of the nappe complex emplacement is constrained by 510–490 Ma syn-D3 granitic intrusions and rapid uplift reflected by the 40Ar/39Ar data in Sverdrupfjella. Earlier top-to-the-NW D1-D2 folds and thrust faults preserved in the nappe complex predate the D3 nappe implacement. The emplacement of the nappe complex would position the Urfjell Group source much closer to its basin depository without intervening topography. The reach of the Kuunga Orogeny in DML is limited to central Kirwanveggan, with its southern limit being the Urfjell Group basin at ca. 530 Ma. Planar fabrics defined by hornblende and biotite, with older ages up to ~1100 Ma in southern Kirwanveggan, impliy dominantly Mesoproterozoic deformation in that area. with partial resetting of 40Ar/39Ar ages in northern Kirwanveggan. In contrast, D3 deformation in Sverdrupfjella is Cambrian in age. Integration of geochronological and geochemical data with published aeromagnetic and aerogravity data from WDML support the structural differences observed between Kirwanveggan and Sverdrupfjella and support a depth/heating gradient at ~530 Ma between N. Sverdrupfjella and S. Kirwanveggan. The absence of significant Neoproterozoic deformation in Kirwanveggan and the relatively undeformed nature of the ~530 Ma Urfjell Group rocks and Permian cover rocks, extending from southern Kirwanveggan to Vestfjella, indicate the Kuunga Orogeny is limited to Sverdrupfjella and possibly N. Kirwanveggan but is not continuous to Heimefrontfjella along the margin of the Grunehogna Craton. [ABSTRACT FROM AUTHOR]

The Sand River area is in the northeastern part of the Central Zone (CZ) of the Limpopo Belt, and represents a key terrane to reveal early Precambrian tectonic processes in southern Africa. Based on petrology, U–Pb zircon ages, and major and trace element data of high-pressure (HP) mafic granulites from the Sand River area, the tectonic evolution of the Central Zone of the Limpopo Belt is re-evaluated here that allows revision of previous interpretations. The protoliths of the HP mafic granulites and amphibolites are sub-alkaline tholeiitic basalts similar to those formed at a mid-ocean ridge and intruded at 2.8 Ga. Based on the distinct mineral assemblages, three metamorphic stages (M1–M3) are recognized in the studied samples: (1) a peak HP granulite facies stage M1 (~1.17–1.32 GPa/~825–870°C), (2) a post-peak near-isothermal decompression stage M2 (~0.70–0.73 GPa/~835–880°C), and (3) a later, independent metamorphic stage M3 (~0.53–0.69 GPa/~793–801°C). M1 and M2 define together a clockwise P–T path. It reveals important information related to the Neoarchean collisional orogeny, and its later overprinted by an independent orogeny with subsequent exhumation and cooling. U–Pb zircon dating of two mafic granulites samples yielded protolith formation of the mafic granulites is prior to ~2.72 Ga, and the two metamorphic age peaks of ~2.72 (M1) and ~2.0 Ga (M3), which present the peak and post-peak cooling stages, respectively. The metamorphic evolution of HP mafic granulites in the Sand River area as reconstructed in this study suggests the Neoarchean collision of the Kaapvaal and Zimbabwe cratons and a discrete Paleoproterozoic orogenic overprint followed by post-orogenic exhumation and cooling. [ABSTRACT FROM AUTHOR]

Arising from: B. J. Wood & A. N. Halliday 437, 1345–1348 (2005); Wood & Halliday replyTimescale and the physics of planetary core formation are essential constraints for models of Earth's accretion and early differentiation. Wood and Halliday use the apparent mismatch in core-formation dates determined from tungsten (W) and lead (Pb) chrono-meters to argue for a two-stage core formation, involving an early phase of metal segregation followed by a protracted episode of sulphide melt addition. However, we show here that crust–;mantle Pb isotope systematics do not require diachronous core formation. Our observations indicate that very early (≤ 35 Myr) core formation and planet accretion remain the most plausible scenario. [ABSTRACT FROM AUTHOR]

The source rocks of the Main Karoo Basin, South Africa are believed to have undergone thermal over-maturation close to the Jurassic-aged Karoo Large Igneous Province (KLIP) dolerite intrusions. Yet, the cause and timing of this source rock exhaustion event likely to have extensively destroyed their shale gas potential remain controversial. Based on drill core samples from the central Main Karoo Basin, we investigated the clay mineralogy of the 2:1:1 and 2:1 phyllosilicate groups, and have carried out 40 Ar/ 39 Ar radiometric dating of illite. The X-ray diffractograms (XRD) and mineral chemistry reveal that chlorite and illite phases of samples close to the dolerite intrusions are characterized by higher crystallinity with a chemical composition indicative of formation in a metamorphic environment. In contrast, chlorite and illite distal to any dolerite intrusion show lower crystal growth rates with chemical compositions suggesting formation in a diagenetic environment. 40 Ar/ 39 Ar radiometric dating indicates that illite in samples distal to the dolerite intrusions formed between 292 and 245 Ma with some ages clustering around 281 Ma. The oldest ages are consistent with a detrital fraction probably recycled from the erosion of the ash bed at the top of the underlying Dwyka Group. However, ages around 281 Ma can be linked with estimated depositional age of the Ecca Group at ∼280 Ma, while the youngest ages may reflect late diagenesis to regional metamorphism. Illite fractions from samples close to dolerite shows formation age between 204 and 170 Ma, consistent with the time of the KLIP dolerite sills and dykes intrusions at ∼180 Ma. This illustrates that the ages of these illites were partially or totally re-set due to recrystallization in a late thermal anomaly induced by the intrusion of dolerites. The correlation between the timing of the youngest mineral transformation processes and the KLIP represents strong evidence suggesting that source rocks of the Ecca Group experienced a thermal overprinting event ∼180 Ma ago. This late thermal anomaly is consistent with previous data illustrating thermal over-maturation and metamorphic devolatilization of Ecca Group shales situated close to the dolerite intrusions. [ABSTRACT FROM AUTHOR]

Dehnert, A., Preusser, F., Kramers, J. D., Akçar, N., Kubik, P. W., Reber, R. & Schlüchter, C. 2010: A multi-dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss Alps. Boreas, Vol. 39, pp. 620–632. 10.1111/j.1502-3885.2010.00146.x. ISSN 0300-9483. The number and the timing of Quaternary glaciations of the Alps are poorly constrained and, in particular, the age of the Most Extensive Glaciation (MEG) in Switzerland remains controversial. This ice advance has previously been tentatively correlated with the Riss Glaciation of the classical alpine stratigraphy and with Marine Isotope Stage (MIS) 6 (186–127 ka). An alternative interpretation, based on pollen analysis and stratigraphic correlations, places the MEG further back in the Quaternary, with an age equivalent to MIS 12 (474–427 ka), or even older. To re-evaluate this issue in the Swiss glaciation history, a multi-dating approach was applied to proglacial deltaic ‘Höhenschotter’ deposits in locations outside the ice extent of the Last Glacial Maximum. Results of U/Th and luminescence dating suggest a correlation of the investigated deposits with MIS 6 and hence with the Riss Glaciation. Cosmogenic burial dating suffered from large measurement uncertainties and unusually high 26Al/10Be ratios and did not provide robust age estimates. [ABSTRACT FROM AUTHOR]

The Palala Shear Zone (PSZ) is a c. 13 km wide part of a vertical, crustal-scale lineament that forms the southern boundary of the polymetamorphic high grade Central Zone of the Limpopo Belt in Southern Africa. We have studied a set of strongly sheared samples of Palala granite, taken at the southern edge of the shear zone at the Palala River transect, in order to determine the deformation patterns and evolution history of the PSZ as well as the age and petrogenesis of the granite. We studied the characteristics of macro- and microscopic deformations, analyzed the finite strain and quartz electron backscatter diffraction (EBSD) fabrics, and estimated the rheological parameters of these mylonitic gneisses. We also carried out zircon U–Pb dating and geochemical analysis. The former yielded a weighted mean 207Pb/206Pb age of 2053.5 ± 9.9 Ma which is within error identical to the age of the Bushveld Igneous Complex (BIC). The Palala granite is an alkaline A-type ferroan granite very similar in major- and trace element chemistry to the voluminous and well-studied Nebo Granite, considered to be a final differentiation product of the BIC magma. The deformed samples have uniform subhorizontal lineation and exhibit steady-state microstructures. The quartz CPO's in a non-coaxial deformation regime are promoted by pervasive dynamic recrystallization with a dominant prismatic slip and rhomb slip system. The main high-grade dextral shearing along the PSZ in the study area is associated with this high-medium temperature deformation at 500–600 °C. The strain measurement indicates that the strain types of all these SL-type and L = S-type tectonites were a flattening strain within a steady-state simple shear-dominant ductile deformation. Rheological parameter estimations suggest differential stress within the range of 15.67–17.50 MPa with the paleo-strain rate in a relatively high range of 3.97 × 10−12 to 1.06 × 10−13 S−1. Together with published research, these data impose a constraint on the initiating of the transpression stage of a Paleoproterozoic intracontinental orogenic event of the Limpopo Belt. The main ductile deformation was the product of an NNW-SSE directed shortening that produced flattening strain and horizontal lineations along dextral sense shear zones, and resulted from NNW-SSE compression of the area between the Zimbabwe and Kaapvaal cratons. This high-level ductile deformation and mylonitization occurred after the emplacement of the Palala Granite at 2.05 Ga, and is thought to have taken place at medium crustal levels under upper greenschist to low amphibolite facies conditions. A late low-temperature deformation phase might be related to low-temperature basal slip which is identified by our EBSD analysis. • The deformed Palala Granite with a formation age of 2053.5 ± 9.9 Ma is an alkaline, ferroan A-type granite. • It belongs to the Lebowa suite of granites as an ultimate fractionation of the Bushveld Igneous Complex magma. • All SL-type and L=S-type tectonites were flattening indicating a steady-state simple shear-dominant ductile deformation. • A dextral shearing apparently resulting from the NNW-SSE transpressive collision of the Zimbabwe and Kaapvaal cratons. [ABSTRACT FROM AUTHOR]

Cosmogenic nuclide (CN) applications offer methods to quantify rates of landscape change and of dating geomorphological deposits and surfaces. Over the past two decades, CNs have been used to determine denudation rates, constrain uplift rates and determine burial ages of sediments in different geomorphological settings across the Southern African landscape. Here, we first give an overview of the landscape evolution of Southern Africa and how CN-based studies have contributed to this subject. Then we give a compilation of CN denudation data from Southern Africa, which show that average erosion rates have decreased by an order of magnitude since the late Cenozoic. Finally, we present the state of CN infrastructure and capabilities in South Africa as well as envisaged future developments. An Accelerator Mass Spectrometer (AMS) has become operational for carbon-14, beryllium-10 and aluminium-26 measurements at the National Research Foundation (NRF) iThemba Laboratory for Accelerator Based Sciences (LABS) in Gauteng since 2017. The measurements' accuracy and precision compare well with other AMS laboratories internationally. Local sample preparation laboratories are currently available with limited capabilities and are mostly still under development. [ABSTRACT FROM AUTHOR]

The Choma-Kalomo Block in south-eastern Zambia was hitherto considered as solely Mesoproterozoic in age based on granitoids which were previously dated at 1.37 and 1.18 Ga respectively. The Choma-Kalomo Block was therefore thought to constitute an exotic terrane with respect to the neighbouring Palaeoproterozoic Magondi Belt and Archaean Zimbabwe Craton. This study of the Choma-Kalomo Block presents new U-Pb SIMS age data for zircons collected from previously undated metasedimentary rocks, revealing an abundant Palaeoproterozoic component (2040–1861 Ma). Palaeoproterozoic (2040 ± 5 Ma) xenocrystic zircons in a Mesoproterozoic (1370 ± 3 Ma) leuconorite point to reworking of older crustal material, and suggest that the Choma-Kalomo Block is not a juvenile Mesoproterozoic terrane. Our U-Pb age data on columbite-tantalite fragments from tin-bearing pegmatites in both the Choma-Kalomo Block and the Dete-Kamativi Inlier (which is part of the Magondi Belt) indicates that Sn-(Ta-Nb-W-Li-Be) mineralisation within the two terranes occurred c. 1030 to 920 Ma. New 40 Ar- 39 Ar dating, confirms previous data, and indicates that a thermal event affected the region between 1020 and 980 Ma. The similarities between the Choma-Kalomo Block and the Dete-Kamativi Inlier imply that these two terranes have a common history, at least as far back as the Palaeoproterozoic, but were certainly juxtaposed by the late Mesoproterozoic era. A large difference in lithospheric thickness between the Choma-Kalomo Block and the adjacent Zimbabwe Craton could explain the different rheological behaviour of the Choma-Kalomo and Dete-Kamativi areas, with the former being strongly deformed during the Neoproterozoic (Pan-African) orogeny. Our data indicate that the Choma-Kalomo Block is not an exotic terrane, rather it may represent a reworked portion of the Zimbabwe Craton, however what is unclear is whether the subcontinental lithosphere has been thinned, or the Choma-Kalomo Block represents a terrane with an originally thinner lithosphere. [ABSTRACT FROM AUTHOR]

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of 222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/-70 ka, whilst a minimum age scenario yields an average age of 200 +70/-61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology. [ABSTRACT FROM AUTHOR]

An unusual sediment-hosted manganese deposit is described from the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. MnO contents up to 15 wt.% were observed in marine clastic and chemical sedimentary rocks. Mn enrichment is interpreted to have resulted from the hydrothermal alteration of manganiferous shale and BIF parent rocks, the primary MnO contents of which are as high as 8.5 wt.%. A detailed mineralogical and petrographic study shows that these parent rocks are characterized by manganoan siderite, ferroan rhodochrosite and other Mn–Fe-rich mineral phases, such as kutnohorite and Fe–Mn-chlorite. Their hypogene alteration gave rise to a diversification of mineral assemblages where ferroan tephroite, calcian rhodochrosite, rhodochrosite, pyrochroite, pyrophanite, cronstedtite, manganoan Fe-rich chlorite and manganoan phlogopite partially or totally replaced the previous mineral assemblage. Thermodynamic modeling performed on chlorite phases associated with the described mineral assemblages illustrates a decrease of average crystallization temperatures from ca. 310 °C during early metamorphic stages to ca. 250 °C during a hydrothermal stage. Mineral transformation processes were thus related to retrograde metamorphism and/or hydrothermal alteration post-dating metamorphism and gave rise to progressive Mn enrichment from unaltered parent to altered rocks. The timing of hypogene alteration was constrained by 40 Ar/ 39 Ar dating to between about 1500 and 1100 Ma ago, reflecting tectonic processes associated with the Namaqua-Natal orogeny along the southern Kaapvaal Craton margin. Manganiferous shale and BIF of the Mozaan Group may represent the oldest known examples of primary sedimentary Mn deposition, related to oxidation of dissolved Mn(II) by free oxygen in a shallow marine environment. Oxygenic photosynthesis would have acted as a first-order control during Mn precipitation. This hypothesis opens a new perspective for better constraining secular evolution of sediment-hosted mineral deposits linked to oxygen levels in the atmosphere-hydrosphere system during the Archean Eon. [ABSTRACT FROM AUTHOR]

This is a follow-up study of a work by Kramers et al. (2013) on a very unusual diamond-rich rock fragment found in the area of south west Egypt in the south-western side of the Libyan Desert Glass strewn field. This pebble, called Hypatia, is composed of almost pure carbon. Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) results reveal that Hypatia is mainly made of defect-rich diamond containing lonsdaleite and multiple deformation bands. These characteristics are compatible with an impact origin on Earth and/or in space. We also analyzed concentrations and isotopic compositions of all five noble gases and nitrogen in several ∼mg sized Hypatia samples. These data confirm the conclusion by Kramers et al. (2013) that Hypatia is extra-terrestrial. The sample is relatively rich in trapped noble gases with an isotopic composition being close to the Q component found in many types of meteorites. 40 Ar/ 36 Ar ratios in individual steps are as low as 0.4 ± 0.3 . Cosmic-ray produced “cosmogenic” 21 Ne is present in concentrations corresponding to a nominal cosmic-ray exposure (CRE) age of roughly 0.1 Myr if produced in a typical meter-sized meteoroid. Such an atypically low nominal CRE age suggests high shielding in a considerably larger body. In addition to the Xe–Q composition, an excess of radiogenic 129 Xe (from the decay of short-lived radioactive 129 I) is observed ( Xe 129 / Xe 132 = 1.18 + / − 0.03 ). Two isotopically distinct N components are present, an isotopically heavy component ( δ N 15 ∼ + 20 ‰ ) released at low temperatures and a major isotopically light component ( δ N 15 ∼ − 110 ‰ ) at higher temperatures. This disequilibrium in N suggests that the diamonds in Hypatia were formed in space rather than upon impact on Earth ( δ N atm 15 = 0 ‰ ). All our data are broadly consistent with concentrations and isotopic compositions of noble gases in at least three different types of carbon-rich meteoritic materials: carbon-rich veins in ureilites, graphite in acapulcoites/lodranites and graphite nodules in iron meteorites. However, Hypatia does not seem to be directly related to any of these materials, but may have sampled a similar cosmochemical reservoir. Our study does not confirm the presence of exotic noble gases (e.g. G component) that led Kramers et al. (2013) to propose that Hypatia is a remnant of a comet nucleus that impacted the Earth. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydrothermal formation of illite, chamosite and berthierine in the FA Formation. [•] Differentiation of clay alterations in the main sedimentary units of FA Formation. [•] FA clay minerals as a hygrometer, rather than exclusively a thermometer. [•] Hydrothermal clays synchronous with intense leaching of U ca. 2040–2010Ma ago. [•] U mobilization controlled by oxidized and high temperature hydrothermal fluids. [Copyright &y& Elsevier]

We describe the geological, geochronological, geomorphological, and faunal context of the Malapa site and the fossils of Australopithecus sediba. The hominins occur with a macrofauna assemblage that existed in Africa between 2.36 and 1.50 million years ago (Ma). The fossils are encased in water-laid, clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system, immediately above a flowstone layer with a U-Pb date of 2.026 ± 0.021 Ma. The flowstone has a reversed paleomagnetic signature and the overlying hominin-bearing sediments are of normal polarity, indicating deposition during the 1.95- to 1.78-Ma Olduvai Subchron. The two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers. [ABSTRACT FROM AUTHOR]

Abstract: An in situ fossil latrine is reported from Gladysvale Cave, South Africa. The latrine area is c. 1.5 m in observable horizontal length and varies in height with a maximum of 20 cm, indicating that deposition may have occurred over a considerable period of time. The size of individual coprolites in the latrine varies, with larger specimens >30 mm in diameter, but the majority generally smaller (c. 15–20 mm). The overall size and morphology of the coprolites and latrine are consistent with modern Parahyaena brunnea, which inhabit the caves today. Dated to between 195 and 257 ka, the latrine indicates that troglodytic latrine-making behaviour in P. brunnea may be traced to at least the Late Middle Pleistocene of southern Africa. [Copyright &y& Elsevier]

Abstract: Australopithecus robustus is one of the best represented hominin taxa in Africa, with hundreds of specimens recovered from six fossil localities in the Bloubank Valley area of Gauteng Province, South Africa. However, precise geochronological ages are presently lacking for these fossil cave infills. In this paper, we provide a detailed geological background to a series of hominin fossils retrieved from the newly investigated deposit of Cooper''s D (located partway between Sterkfontein and Kromdraai in the Bloubank Valley), including uranium-lead (U-Pb) ages for speleothem material associated with A. robustus. U-Pb dating of a basal speleothem underlying the entire deposit results in a maximum age of 1.526 (±0.088) Ma for Cooper''s D. A second U-Pb date of ca. 1.4Ma is produced from a flowstone layer above this basal speleothem; since this upper flowstone is not a capping flowstone, and fossiliferous sediments are preserved above this layer, some of the hominins might be slightly younger than the calculated age. As a result, we can broadly constrain the age of the hominins from Cooper''s D to between 1.5 and approximately 1.4Ma. Extinct fauna recorded in this comparatively young deposit raise the possibility that the Bloubank Valley region of South Africa represented a more stable environmental refugium for taxa relative to tectonically more active East Africa. The sediments of the deposit likely infilled rapidly during periods when arid conditions prevailed in the paleoenvironment, although it is unclear whether sediment deposition and bone deposition were necessarily contemporaneous occurrences. We reconstruct the paleoenvironment of Cooper''s D as predominantly grassland, with nearby woodlands and a permanent water source. The hominin teeth recovered from Cooper''s D are all from juveniles and can be confidently assigned to A. robustus. In addition, two juvenile mandibular fragments and an adult thoracic vertebra are tentatively attributed to A. robustus. [Copyright &y& Elsevier]

Abstract: New evidence from uplifted marine isotope stage (MIS) 5e carbonate deposits in the Gulf of Corinth demonstrate two rapid, sub-orbitally forced, sea-level oscillations in the early part of MIS 5e. Microbial bioherms with inter-grown marine coralline algae are interpreted as early highstand deposits. Presence of thin vadose flowstone (speleothem) coating inter-bioherm surfaces mark a short-lived regression of >10 m, followed by sea-level recovery and re-establishment of the highstand, marked by coralline algae coating inter-bioherm cavity surfaces. These marine algae are then coated by a younger vadose flowstone, thick enough to provide an uncontaminated U/Th date of 134.8±2.0 ka. The dated flowstone is itself encrusted by marine fauna and the entire sequence overlain by highstand marine sediments and marine aragonite cements dated to 114–118 ka, part of the sustained MIS 5e highstand. The age of the younger flowstone demonstrates that the early highstand occurred before 134.8±2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than ∼136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (±4) m below present sea-level, 6–18 (±4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of >10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr. The flowstone dated at 134.8±2.0 ka is interpreted to record the early part of the ‘Aladdin''s Cave'' regressive event from Papua New Guinea, although in Greece only the first 16 m of the event is recorded. The new data presented here support a recently published Red Sea TII sea-level curve: they also highlight minor discrepancies in the absolute dating of these early MIS 5e sea-level events worldwide. [Copyright &y& Elsevier]

The chronology of the crustal evolution of the granulite facies fault-bounded Epembe Unit south of the anorthositic Kunene Intrusive Complex (KIC) in NW Namibia is presented. U–Pb zircon ages by ion microprobe (SHRIMP II) from a heterogeneous set of granulite facies rocks from the Epembe Unit reveal Mesoproterozoic ages between 1520 and 1510 Ma for prograde zircon growth. Cathodoluminescence (CL) imaging clearly shows metamorphic growth of zircon grains and zircon rims around igneous cores. Zircon core analyses obtained by SHRIMP yield ages between 1635 and 1810 Ma. These ages are comparable to those of the Epupa basement and indicate derivation of the inherited zircon cores from Palaeoproterozoic protoliths. Pb–Pb stepwise leaching (PbSL) TIMS ages on peak-metamorphic garnet and retrograde sapphirine reflect granulite facies conditions at ca. 1490 to 1447 Ma.Our combined age data from the granulite facies Epembe Unit reveal a complete early Mesoproterozoic orogenic cycle between ca. 1640 and 1450 Ma. The cycle begins with erosion of the Palaeoproterozoic Epupa basement and involves sedimentation, burial down to the crust–mantle boundary leading to high-grade metamorphism and rapid exhumation. An orogenic cycle of this age matches in time with events dated in the Pinwarian (Grenville Province, Canada), in the Amazonian craton (Brazil) and in the Gothian (Baltic Shield, Sweden) but has not been reported in southwestern Africa before. [Copyright &y& Elsevier]

New high-precision isotope ratios of dissolved Mo in seawater from different ocean basins and depths show a homogeneous isotope composition (‘mean ocean water 98Mo/95Mo’ (MOMO)), as expected from its long ocean residence time (800 kyr). This composition appears to have been constant for the past 60 Myr at a 1–3 Myr time resolution as indicated from thick sections of Fe–Mn crusts from the Atlantic and Pacific. These records yield a constant offset from MOMO (average of −3.1 and −2.9‰). They are similar to our new data on recent oxic Mo sinks: pelagic sediments and six Fe–Mn crust surface layers range from −2.7 to −2.9‰ and −2.7 to −3.1‰, respectively. Recent suboxic Mo sinks from open ocean basins display heavier and more variable isotope ratios (−0.7 to −1.6‰ relative to MOMO). Crustal Mo sources were characterized by measuring two granites (and a mild acid leach of one granite), seven volcanic rocks and two clastic sediments. All show a narrow range of compositions (−2.0 to −2.3‰). These data indicate that isotope fractionation by chemical weathering and magmatic processes is insignificant on a global scale. They therefore represent good estimates of the composition of dissolved Mo input to the oceans and that of the average continental crust. Thus, the Mo input into the oceans appears to be distributed into lighter oxic sinks and heavier reducing sinks. This is consistent with steady-state conditions in the modern ocean. The constant isotope offset between oxic sediments and seawater suggests that the relative amounts of oxic and reducing Mo removal fluxes have not varied by more than 10% over the last 60 Myr. An equilibrium fractionation process is proposed assuming that Mo isotope fractionation occurs between (dominant) MoO42− and (minor) Mo(OH)6 species in solution, of which the latter is preferentially scavenged. [Copyright &y& Elsevier]

The temporal evolution of atmospheric lead deposition and its possible sources were assessed in eastern Canada and in western Scotland, using blanket peat bogs as geochemical archives. Short cores were taken from two remote sites located close to the sea. Significant lead enrichments in the upper layers at both sites reflect the increasing emission of lead into the atmosphere due to anthropogenic activities during the last century. At the Scottish site, a region under aeolian influence from Europe, anthropogenic derived lead could be recognized by the distinctive unradiogenic composition (206Pb/207Pb ratios down to ∼1.115), being clearly different from the pre-industrial values (206Pb/207Pb ∼1.166). In contrast, the lead pollution in eastern Canada (influenced by North American sources) is identified by a more radiogenic lead isotope composition (206Pb/207Pb ratios up to ∼1.199) compared to pre-industrial values (206Pb/207Pb ∼1.161). Emission inventories and isotope characteristics suggest that industrial (coal burning, mining) and traffic (leaded gasoline) outputs are the most likely sources during the first and the second half of the 20th century, respectively, in both, western Scotland and eastern Canada alike. The Scottish record is in line with previous studies of past atmospheric lead deposition. However, the Canadian deposit suggests that the wind derived, pre-industrial lead, is less radiogenic as previously implied using sediment archives. These results are thus the first to report pre-industrial lead isotope ratios and concentrations of atmospheric derived aerosols in North America. [Copyright &y& Elsevier]

Presents a combined procedure for separating Lu, Hf, Sm, Nd and rare earth elements (REE) from a single rock digest. Dissolution of sample via sodium peroxide sintering; Separation of the high field strength elements from REE and other matrix elements; Influence of garnet on the overall budget and pattern of the REE in rocks.

The degree of early Archaean terrestrial differentiation into mantle and crust is long debated. A number of studies rely on bulk rock Hf and Nd isotope data to gain further insight. Here we present Hf-Nd data from two igneous basements suites of Barberton Mountain Land, namely a tonalite-trondhjemite-granodiorite (TTG) and granodiorite-granite-monzogranite (GGM) suite to further decipher crust formation and its timing in the Archaean. TTG show high initial ε(Hf) and ε(Nd) if corrected using their respective U/Pb zircon ages that can be interpreted in two ways: (i) early differentiation of bulk silicate Earth or (ii) overcorrection of these data caused by decoupling of zircon from the 'zircon-free' bulk rock due to metamorphic overprint. Indeed, regional metamorphism affected the early TTG ca. 250 Ma after their emplacement and disturbed their bulk rock Hf and Nd systematics. Correction of bulk rock Hf and Nd data to the age of metamorphism yields values between +0.9 and − 6.2 and from −1.3 to −4.3, respectively, thus indicating open-system behaviour. Lu-Hf and Sm-Nd mineral isochron ages of two TTG plutons are significantly younger than their corresponding U/Pb zircon age, but agree within uncertainty perfectly with external age constraints for the age of the metamorphic overprint. The same accounts for the 40Ar-39Ar systematics of the investigated plutons. Amphibole samples consist of a mixture of heterochemical generations that yield ages that are both older and younger than the metamorphic overprint at 3.2 Ga. The metamorphic minerals in each plutons provide a highly divergent age information from the coexisting zircon. Hence, the positive ε(Nd) and ε(Hf)-values that resulted from age-correction to the respective U/Pb zircon age are most probably over-corrected. Finally, if all data is age-corrected to the metamorphic overprint all samples agree with models for the Nd-Hf isotopic evolution in the mantle that do not require a large-scale early differentiation of Earth into enriched and depleted reservoirs. Mantle extraction ages (T DM) of TTG are interpreted as minimum ages for the generation of felsic Archaean crust whereas T DM of GGM are interpreted as maximum ages for the last major crust growth episode in the Barberton Mountain Land. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1st documentation of primary copper-gold mineralization in the Amani area. • Mineralization associated with the ~550 to 600 Ma Kuunga orogeny. • Ore-forming fluids contain H 2 O-NaCl ± CO 2 ± CH 4 compositions. • Mineralization occurred at 1.7–6.9 kbar and 330–400 °C. The Amani area in southwestern Tanzania contains several prospects where primary Cu-Au mineralization occurs at surface, the most noteworthy of these being the Amani Hills and Mpanga Hill prospects. At the Amani Hills prospect, structurally-controlled gold mineralization is hosted in quartz-muscovite schists of the Amani Group and minor high-grade gneisses belonging to the Kabelege Group. Here, quartz-carbonate veins contain pyrite-pyrrhotite-chalcopyrite, with free-milling gold occurring predominantly in quartz and along sulphide grain boundaries. These veins are associated with sericite-epidote-albite alteration of the wallrocks. At the Mpanga Hill prospect, Cu ± Au mineralization is hosted within impure micaceous marbles of the Rafiki Group. At this prospect, both the sulphidised carbonate host rocks and quartz-carbonate veins contain chalcopyrite, bornite and pyrite assemblages, with accessory phases of Au ± Pb ± Zn ± Ag ± Bi ± Se. Fluid inclusion microthermometry indicate that auriferous veins at both prospects record a bimodal occurrence of early low-temperature and low-salinity (≤23.2 wt% NaCl eq.) fluids that are overprinted by later, high temperature and hypersaline fluids (32.8 – 54 wt% NaCl eq.). These ore-forming fluids contain H 2 O-NaCl ± CO 2 ± CH 4 compositions and were trapped at near-lithostatic to supralithostatic conditions of 330 – 400 °C and 1.7 – 6.9 kbar. These hydrothermal fluids were likely variably sourced and were focussed along kilometre-scale brittle-ductile reverse shear zones in the Amani area, where fluid-rock interactions led to Cu-Au mineralization. 40Ar/39Ar dating of muscovite constrained the timing of copper – gold mineralization in the Amani area to between c. 550 – 600 Ma. Mineralization is therefore related to the Pan-African aged Kuunga orogeny, which resulted from the collision between the Tanzania Craton and Bangweulu Block during the assembly of supercontinent Gondwana. The new findings presented in this study highlight the exploration potential of copper – gold mineralization along large-scale Proterozoic shear zones in the underexplored and overlooked Upangwa terrane of southwestern Tanzania. [ABSTRACT FROM AUTHOR]

Rising Star Cave in the Cradle of Humankind, South Africa, contains one of the richest hominin-bearing deposits in the world, and is the type locality for the Homo naledi fossils. This paper provides a stratigraphic and geochronological framework, within which published and future fossil finds from Rising Star Cave can be placed. Detailed mapping of flowstone horizons combined with new age constraints based on both U-Th disequilibrium and 234U/238U dates and one new OSL date help define seven periods of flowstone formation that punctuate episodes of clastic sedimentation and erosion. Clastic sediments entered the cave through an opening in the roof of the Postbox Chamber from about 600 ka onward, until the opening was choked by coarse breccia blocks, probably sometime after 180 ka. Depositional and erosional events changed the internal morphology of the cave chambers over time, and thereby changed the access route into the Dinaledi Chamber where the bulk of the H. naledi fossils were found. Periods of pervasive flowstone formation at all levels of the cave occurred at >600 ka, ~500–400 ka, ~225–190 ka and ~110-90 ka. Additional periods of localised flowstone growth restricted to individual chambers (or parts thereof) occurred at ~300 ka, ~160 ka, ~70 ka, ~50 ka, ~30 ka, and ~10 ka. Flowstone horizons bracket sedimentary units that include a variety of sediment types that changed with time. The oldest flowstones overlie lithified mud clast breccias (LMCB), which were partly eroded before they were covered by externally derived laminated orange sands (LOS) and 500–400 ka flowstones. These flowstones and sands were removed between 290 ka and 225 ka, with sediment transported to deeper parts of the cave via erosion channels characterised by massive orange sands (MOS). In this period of time, the access route into the Dinaledi Chamber may have further changed due to the collapse of the Dragon's Back block. Deposition of laminated orange-red mud (LORM) from suspension occurred between 225 and 190 ka and temporally overlaps with widespread flowstone formation around ~225 ka and ~200 ka. The LORM deposits were largely removed from the upper chambers by ~110 ka, before the youngest group of flowstones formed in the cave; some of which are still growing today. The U-Th ages from Rising Star Cave, combined with other dating constraints reveal age clusters of flowstone formation, which coincided with warmer interglacial or interstadial periods. The patterns recognised in Rising Star Cave overlap with periods of flowstone formation recognised in nearby caves in the Cradle of Humankind, thereby confirming a regional climatic control on flowstone growth in caves during the past 500 ky. The new ages further constrain the minimum age of H. naledi to ~241 ka. Thus, H. naledi entered the cave between 241 ka and 335 ka, during a glacial period, at which time clastic sediments inside the cave were undergoing erosion. H. naledi would probably have entered the cave through an access point in the roof of the Postbox Chamber and made its way along a SW trending fracture towards the Dragon's Back and Dinaledi Chambers. [ABSTRACT FROM AUTHOR]

Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the ‘Cambrian explosion’. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water. [ABSTRACT FROM AUTHOR]

Replying to: S.-Y. Jiang et al. 459, 10.1038/nature08048 (2009)Jiang et al. present a new SHRIMP U–Pb zircon age of 532.3 ± 0.7 million years (Myr) ago for an ash bed in the lowermost black shale sequence of the Niutitang Formation, China, and claim that the data presented in our recent paper do not firmly support the idea that the biological and environmental changes at the Precambrian/Cambrian transition can be explained by a single global hydrogen sulphide (H2S) release event. Their new age seems to be supported by another recent SHRIMP investigation which indeed suggests that the Chinese metal-enriched sulphide layer does not represent the Precambrian/Cambrian boundary and shows that the redox history of both basins (Oman and South China) was much more complex. [ABSTRACT FROM AUTHOR]