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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]

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]

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]

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]

A new model for Archaean granitoid magmatism is presented which reconciles the most important geochemical similarities and differences between tonalite–trondhjemite–granodiorite (TTG) and potassic granitoids. Trace element abundances reveal a strong arc magmatism signature in all studied granitoids from Barberton Mountain Land. Characteristic features include HFSE depletion as well as distinct enrichment peaks of fluid-sensitive trace elements such as Pb in N-MORB normalisation, clearly indicating that all studied granitoids are derived from refertilised mantle above subduction zones. We envisage hydrous basaltic (s.l.) melts as parental liquids, which underwent extensive fractional crystallisation. Distinctive residual cumulates evolved depending on initial water content. High-H2O melts crystallised garnet/amphibole together with pyroxenes and minor plagioclase, but no olivine. This fractionation path ultimately led to TTG-like melts. Less hydrous basaltic melts also crystallised garnet/amphibole, but the lower compatible element content indicates that olivine was also a liquidus phase. Pronounced negative Eu-anomalies of the granitic melts, correlating with Na, Ca and Al, indicate plagioclase to be of major importance. In the context of our model, the post-Archaean disappearance of TTG and concomitant preponderance of granites (s.l.), therefore, is explained with secular decrease of aqueous fluid transport into subduction zones and/or efficiency of deep fluid release from slabs. [ABSTRACT FROM AUTHOR]

The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (230Th/238U) and (234U/238U) activity ratios. Importantly, most subsamples had high initial (230Th/238U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which 230Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (230Th/238U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work. • Helium is retained in calcite speleothems even in surface samples. • Three methods for calculating (U,Th)–He ages with U/Th disequilibrium. • Method for calculating U/Th ages of speleothems with older detrital component. • Speleothems with high initial (230Th/238U) activity ratios up to 19.7 dated. • (U,Th)–He dating of Pliocene and Pleistocene speleothems improved. [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]

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]