This file was created by the TYPO3 extension publications --- Timezone: CEST Creation date: 2026-05-13 Creation time: 23:46:38 --- Number of references 45 article Reinhardt2024 Microbial life on Earth was well established in the Paleoarchean, but insight into early ecosystem diversity and thus, the complexity of the early biological carbon cycle is limited. Here we investigated four carbonaceous chert samples from the lower platform facies of the ca. 3.42-billion-year-old Buck Reef Chert, Barberton greenstone belt. The analysis on multiple scales revealed exceptionally well-preserved carbonaceous matter, even on molecular level (aliphatic and aromatic hydrocarbons), resulting from rapid silicification. Geochemical evidence from stable carbon and multiple sulfur isotopes supports the presence of different microbial metabolisms in the Paleoarchean ecosystem. The local biological carbon cycle was dominated by photoautotrophs, but autotrophic sulfate reducers and methane- or acetate-producing microbes were also present. In areas of microbial methane or acetate release, methanotrophs or acetotrophs contributed to the overall biomass. These results highlight the metabolic diversity in the lower platform environment of the Buck Reef Chert, and underline that an advanced biological carbon cycle already existed in the early Archean. © 2024 The Authors Article 2024 10.1016/j.precamres.2024.107289 Precambrian Research 402 Elsevier B.V. Archean; carbon cycle; chert; geochemistry; greenstone belt; marine ecosystem; metabolism; paleoecology; species diversity https://www.scopus.com/inward/record.uri?eid=2-s2.0-85182576861&doi=10.1016%2fj.precamres.2024.107289&partnerID=40&md5=a98f04b076257aec9987de00a4345ece Cited by: 9; All Open Access, Green Open Access, Hybrid Gold Open Access M. Reinhardt V. Thiel J.-P. Duda A. Hofmann D. Bajnai W. Goetz A. Pack J. Reitner M. Schanofski J. Schönig M.J. Whitehouse H. Drake article Hofmann2024 Article 2024 10.1016/j.precamres.2024.107584 Precambrian Research 414 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85206607366&doi=10.1016%2fj.precamres.2024.107584&partnerID=40&md5=cd37089721556ddea30f3ce99d259349 Cited by: 1; All Open Access, Hybrid Gold Open Access A. Hofmann article Kitoga2024 Article 2024 10.1016/j.chemgeo.2024.122407 Chemical Geology 670 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85205665959&doi=10.1016%2fj.chemgeo.2024.122407&partnerID=40&md5=dc9dc460807a2a3b8daf470656a97084 Cited by: 0; All Open Access, Hybrid Gold Open Access L.S. Kitoga D. Zakharov J. Marin-Carbonne M. Boyet J.-F. Moyen T. Di Rocco A. Pack N. Olivier G. Stevens article WOS:000915946900001 The nitrogen isotopic composition of organic matter is controlled by metabolic activity and redox speciation and has therefore largely been used to uncover the early evolution of life and ocean oxygenation. Specifically, positive delta N-15 values found in well-preserved sedimentary rocks are often interpreted as reflecting the stability of a nitrate pool sustained by water column partial oxygenation. This study adds much-needed data to the sparse Paleoarchean record, providing carbon and nitrogen concentrations and isotopic compositions for more than fifty samples from the 3.4 Ga Buck Reef Chert sedimentary deposit (BRC, Barberton Greenstone Belt). In the overall anoxic and ferruginous conditions of the BRC depositional environment, these samples yield positive delta N-15 values up to +6.1% . We argue that without a stable pool of nitrates, these values are best explained by non-quantitative oxidation of ammonium via the Feammox pathway, a metabolic co-cycling between iron and nitrogen through the oxidation of ammonium in the presence of iron oxides. Our data contribute to the understanding of how the nitrogen cycle operated under reducing, anoxic, and ferruginous conditions, which are relevant to most of the Archean. Most importantly, they invite to carefully consider the meaning of positive delta N-15 signatures in Archean sediments. Article 2023 10.1111/gbi.12540 GEOBIOLOGY 21 WILEY

111 RIVER ST, HOBOKEN 07030-5774, NJ USA

277-289 Pellerin, A (Corresponding Author), Univ Bourgogne Franche Comte, CNRS, Lab Biogeosci, UMR 6282, Dijon, France. Pellerin, Alice; Thomazo, Christophe; Vennin, Emmanuelle, Univ Bourgogne Franche Comte, CNRS, Lab Biogeosci, UMR 6282, Dijon, France. Thomazo, Christophe, Inst Univ France IUF, Paris, France. Ader, Magali, Univ Paris Cite, CNRS, Inst Phys Globe Paris, Paris, France. Marin-Carbonne, Johanna; Alleon, Julien, Univ Lausanne, Inst Sci Terre, Lausanne, Switzerland. Alleon, Julien, Univ Lyon, Univ Lyon 1, ENS Lyon, CNRS,LGL TPE, Lyon, France. Hofmann, Axel, Univ Johannesburg, Dept Geol, Johannesburg, South Africa. 3 ammonium oxidation; biogeochemistry; Buck Reef Chert; Feammox; ferruginous ocean; nitrogen isotopes; Paleoarchean Alice Pellerin Christophe Thomazo Magali Ader Johanna Marin-Carbonne Julien Alleon Emmanuelle Vennin Axel Hofmann article Bassez20231 Article 2023 10.1007/s11084-023-09638-x Origins of Life and Evolution of Biospheres 53 1 – 41 1-2 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85168101645&doi=10.1007%2fs11084-023-09638-x&partnerID=40&md5=c98c48e68b6751c833b95745209ec3e8 Cited by: 0; All Open Access, Hybrid Gold Open Access Marie-Paule Bassez article Tusch2022 Article 2022 10.1073/pnas.2120241119 Proceedings of the National Academy of Sciences of the United States of America 119 18 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85129778446&doi=10.1073%2fpnas.2120241119&partnerID=40&md5=73f9a2d52aeb21cc4d8cf4d027711168 Cited by: 25; All Open Access, Hybrid Gold Open Access Jonas Tusch J. Elis Hoffmann Eric Hasenstab Mario Fischer-Gödde Chris S. Marien Allan H. Wilson Carsten Münker article Wagner2021 Article 2021 10.1016/j.chemgeo.2021.120121 Chemical Geology 576 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85106326432&doi=10.1016%2fj.chemgeo.2021.120121&partnerID=40&md5=6bd2be8bd0df0dbc7afe8b63c88ad5f5 Cited by: 19 Luise J. Wagner Ilka C. Kleinhanns Nadja Weber Michael G. Babechuk Axel Hofmann Ronny Schoenberg article Stoll2021 Article 2021 10.1016/j.precamres.2020.106041 Precambrian Research 354 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85098990181&doi=10.1016%2fj.precamres.2020.106041&partnerID=40&md5=fc3f25ac939ef717c0fa95df97e4922a Cited by: 8 Emily Stoll Nadja Drabon Donald R. Lowe article Boyet2021141 Komatiites and sedimentary rocks sampled during the International Continental Drilling Program (BARB1-2–3-4–5) in the Barberton greenstone belt, South Africa, were analyzed for 146Sm-142Nd systematics. Resolved negative μ142Nd values (down to −7.7 ± 2.8) were identified in komatiites from the 3.48 Ga Komati Formation and this signature correlates with low Hf/Sm ratios measured in these samples. The negative μ142Nd point to a source with subchondritic Sm/Nd ratio which formed during the Hadean. No analytically resolvable 142Nd anomalies were measured in crustal detritus-rich, Si-rich, Ca-Fe-rich sediments and cherts from the Buck Reef (3.42 Ga) and the Fig Tree Group (3.23–3.28 Ga). Our new measurements are incorporated into a larger set of 147Sm-143Nd and 176Lu-176Hf data to better understand the 142,143Nd-176Hf isotope signatures in the mantle source at the time of komatiite crystallization. Our calculations show that the 142,143Nd-176Hf isotope signatures and Hf/Sm ratios cannot be produced by recycling into the komatiite source of detrital sediments like those sampled in the Barberton area. Only cherts have the required trace element characteristics – low Hf/Sm, radiogenic ε176Hf –but the trace element concentrations in the cherts are so low that unrealistic amounts of chert would need to be added. We propose a four-stage model for the formation of these rocks. Negative μ142Nd and low Hf/Sm ratios developed during the crystallization of a deep magma ocean soon after Earth accretion. The material that ultimately became the source of komatiites was a residual liquid produced by 50% crystallization leaving a bridgmanite/ferropericlase/Ca-perovskite cumulate. The Lu-Hf and Sm-Nd isotope systems were decoupled at this stage. After extinction of 146Sm around 4 Ga, parent/daughter ratios fractionated during a melt extraction event. With this model we explain the positive ε176Hf and slightly negative ε143Nd in these samples. The 3.55 Ga Schapenburg komatiites in another part of the Barberton belt share similar chemical signatures, supporting our model of fractionation in a deep magma ocean early in Earth's history. © 2021 Elsevier Ltd Article 2021 English 00167037 10.1016/j.gca.2021.04.020 Geochimica et Cosmochimica Acta 304 Elsevier Ltd 141 – 159 Barberton Greenstone Belt; crystallization; detrital deposit; drilling; Hadean; isotopic ratio; komatiite; magma; mantle source; neodymium isotope; samarium https://www.scopus.com/inward/record.uri?eid=2-s2.0-85107680053&doi=10.1016%2fj.gca.2021.04.020&partnerID=40&md5=e8d494597a11915e86e8f18fb0c02a90 Cited by: 9; All Open Access, Bronze Open Access, Green Open Access M. Boyet M. Garçon N. Arndt R.W. Carlson Z. Konc article deOliveira2021297 Early Archean spherule layers, widely accepted to represent distal ejecta deposits from large-scale impact events onto the early Earth, have been described from several stratigraphic levels of the Barberton greenstone belt in South Africa. Recently, exploration drilling at the Fairview Gold Mine (25°43'53'S, 31°5'59'E) in the northern domain of the belt resulted in the discovery of a new set of spherule layer intersections. The Fairview spherule layers in drill cores BH5901, BH5907, BH5911, and BH5949 were intersected just a few meters apart, at about the same stratigraphic position within the transition from the Onverwacht Group to the Fig Tree Group. The Fairview spherule layers have petrographic and chemical similarities to at least three other well-known Barberton spherule layers (S2-S4), and multiple spherule layer bed intersections in drill cores BARB5 and CT3, all from about the same stratigraphic position. They are not uniform in composition, in particular with respect to abundances of highly siderophile elements. The highest concentrations of moderately (Cr, Co, Ni) and highly siderophile (Ir) elements are within the range of concentrations for chondrites and, thus, reinforce the impact hypothesis for the generation of the Fairview spherule layers. Iridium peak concentrations and Cr/Ir interelement ratios for spherule layer samples from drill cores BH5907, BH5911, and BH5949 suggest admixtures of 50%-60% chondritic material, whereas for the BH5901 spherule layer, only an admixture of 1% chondritic material is indicated. We discuss whether these four Fairview spherule layers represent the same impact event, and whether they can be correlated to any of the S2-S4, CT3, and BARB5 intersections. © 2021 The Geological Society of America. Article 2021 English 00721077 10.1130/2021.2550(12) Special Paper of the Geological Society of America 550 Geological Society of America 297 – 331 Barberton Greenstone Belt; Core drilling; Economic geology; Gold deposits; Gold mines; Infill drilling; Stratigraphy; Admixture; Archaean; Barberton; Chemical component; Drill core; Greenstone belts; Impact events; Impact spherules; Large-scale impacts; South Africa; Archean; chemical composition; chondrite; concentration (composition); drilling; iridium; mine; petrography; spherule; Drills https://www.scopus.com/inward/record.uri?eid=2-s2.0-85126281105&doi=10.1130%2f2021.2550%2812%29&partnerID=40&md5=91b76e9eb0eab1983c9df039c8ef67e7 Cited by: 0 Grace Juliana Gonçalves Oliveira Wolf Uwe Reimold Alvaro Penteado Crósta Natalia Hauser Christian Koeberl Dieter Mader Ralf-Thomas Schmitt Tanja Mohr-Westheide article Oliveira2020 The oldest known evidence of large impacts in Early Earth history are Archaean to Palaeoproterozoic impact spherule layers of the Barberton Greenstone Belt in South Africa and the Pilbara craton in Western Australia. Four drill core sections (BH5901, BH5907, BH5911 and BH5949) containing spherule layers were intersected in exploration drilling at Fairview Gold Mine in the northern Barberton Greenstone Belt. Here, we provide a first detailed mineralogical study of these new spherule layer intersections. The spherule layers are densely packed with sand-sized, spherical to ovoid, i.e., in part strongly deformed, “beads”. They generally have morphological and textural features similar to other 3.4–3.2 Ga old spherule layers of the Barberton Greenstone Belt. The Fairview spherule layers are stratigraphically positioned at the contact between the silicified volcanic tuff of the uppermost unit of the Onverwacht Group and the lowermost siliciclastic rocks of the Fig Tree Group, like the S2 and S4 layers in the southern, and S3 layer in the northern, domain of the greenstone belt. Micro-XRF scanning allowed (i) to distinguish spherule layers from their host rocks by their major element distribution, and (ii) to characterize secondary alteration and micro-deformation features in the SL and host rocks. Ni–Cr spinel, the only primary mineral in evidence in these sections, is not distributed uniformly along a spherule layer intersection, and occurrences can not be stratigraphically correlated between the four layer intersections either. Spinel crystals vary with respect to Ni, Cr, Fe and Zn contents and respective zonation patterns for these elements. Zinc abundances are likely related to post-depositional hydrothermal overprint. The results of this investigation comprising geological, petrographic, semiquantitative micro-X-ray fluorescence spectrometry, and quantitative electron microprobe analysis on spinel support a complex and heterogeneous genetic process that must have taken place during spherule formation in an impact vapor plume and in post-depositional times. The Fairview spherule layers are thought to possibly represent the product of a single impact event. They represent fallout into deep-water conditions, as they lack evidence for reworking or sorting by current or wave action. The heterogeneous Ni–Cr spinel concentrations are similar to what has been reported for spinel occurrences in the S3 layer, but considering the complex tectonic overprint on this lithostratigraphic sequence at the changeover from the Onverwacht to the Fig Tree Group it is not possible to conclude whether or not these spherule layers represent the same impact event. © 2019 Elsevier Ltd Article 2020 English 1464343X 10.1016/j.jafrearsci.2019.103718 Journal of African Earth Sciences 162 Elsevier Ltd Australia; Barberton Greenstone Belt; Pilbara Block; Western Australia; Ficus (angiosperm); Archean; host rock; lithostratigraphy; mineralogy; petrography; Proterozoic; siliciclastic deposit; spinel; tuff; X-ray fluorescence https://www.scopus.com/inward/record.uri?eid=2-s2.0-85076193591&doi=10.1016%2fj.jafrearsci.2019.103718&partnerID=40&md5=b2352f6036f944e61e52e791182b23b6 Cited by: 2 Grace Juliana Gonçalves de Oliveira Wolf Uwe Reimold Alvaro Penteado Crósta Natalia Hauser Tanja Mohr-Westheide Roald Tagle Douglas Galante Felix Kaufmann article Brüske2020 Article 2020 10.1016/j.precamres.2019.105583 Precambrian Research 338 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85077239124&doi=10.1016%2fj.precamres.2019.105583&partnerID=40&md5=2689ea016fb4f071739a6ca4c45b0919 Cited by: 27 A. Brüske A.N. Martin P. Rammensee S. Eroglu M. Lazarov G. Albut S. Schuth S. Aulbach R. Schoenberg N. Beukes A. Hofmann T. Nägler S. Weyer article Drabon20191 Article 2019 10.1016/j.precamres.2019.02.010 Precambrian Research 325 1 – 19 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85061905713&doi=10.1016%2fj.precamres.2019.02.010&partnerID=40&md5=ff0b77de89dcf3c980ce2340d18e6de3 Cited by: 30 Nadja Drabon Aleksandra Galić Paul R.D. Mason Donald R. Lowe article Ledevin2019 The Buck Reef is a 250–400 m thick sequence of banded black and white (B&W) cherts deposited ca. 3416 Ma ago in a shallow basin. We provide field, petrological and geochemical constraints on the chert-forming process and the origin of the banding. White layers consist of nearly pure microquartz, while black layers are mixed with detrital carbonaceous matter, quartz grains and carbonaceous microlaminae, interpreted as remnants of microbial mats. The circulation of Si-rich fluid is recorded by abundant chert veins and pervasive silicification. However, the high purity of the white layers, their lack of internal structures and extremely low Al, Ti and high-field-strength elements preclude an origin by silicification of sedimentary or volcanic precursors. Moreover, their reworking at the surface into slab conglomerates, and sediment-like contacts with black layers rule out a diagenetic origin. We propose a new model whereby the white layers were periodically deposited as precipitates of pure silica; and the micro-layering within the black layers formed by annual temperature fluctuations, favouring microbial activity in summer and inorganic silica precipitation in winter. Outcrop-scale alternation of B&W layers was associated with major, thousand-year-long climate events: white cherts represent massive silica precipitation resulting from changes in ocean circulation and temperature during cold intervals. © 2019 by the authors. Licensee MDPI, Basel, Switzerland. Article 2019 English 20763263 10.3390/geosciences9100424 Geosciences (Switzerland) 9 MDPI AG 10 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85073451902&doi=10.3390%2fgeosciences9100424&partnerID=40&md5=485230dc6fb0c315b84c85de2ca60329 Cited by: 5; All Open Access, Gold Open Access, Green Open Access Morgane Ledevin Nicholas Arndt Catherine Chauvel Etienne Jaillard Alexandre Simionovici article Lowe201934 Article 2019 10.1016/j.precamres.2019.02.024 Precambrian Research 327 34 – 46 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85062402999&doi=10.1016%2fj.precamres.2019.02.024&partnerID=40&md5=38780e6d8a5b223f56bb2d68056c90b4 Cited by: 14; All Open Access, Bronze Open Access Donald R. Lowe Nadja Drabon Gary R. Byerly article Kaźmierczak2019 Article 2019 10.1016/j.precamres.2019.105357 Precambrian Research 331 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85066813779&doi=10.1016%2fj.precamres.2019.105357&partnerID=40&md5=c1bc726537ec15772c50c826be113740 Cited by: 3 Józef Kaźmierczak Barbara Kremer article Drabon2019849 Article 2019 10.2110/jsr.2019.46 Journal of Sedimentary Research 89 849 – 874 9 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85075675350&doi=10.2110%2fjsr.2019.46&partnerID=40&md5=a10534e8d763733e0f7a950681f8b3ce Cited by: 19 Nadja Drabon Christoph E. Heubeck Donald R. Lowe article Greco201859 Article 2018 10.4435/BSPI.2018.04 Bollettino della Societa Paleontologica Italiana 57 59 – 74 1 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85047527946&doi=10.4435%2fBSPI.2018.04&partnerID=40&md5=b104cd16a9b0b25241f3f1645c6b42b9 Cited by: 13 Francesco Greco Barbara Cavalazzi Axel Hofmann Keyron Hickman-Lewis article Avice201882 We have analyzed ancient atmospheric gases trapped in fluid inclusions contained in minerals of Archean (3.3 Ga) to Paleozoic (404 Ma) rocks in an attempt to document the evolution of the elemental composition and isotopic signature of the atmosphere with time. Doing so, we aimed at understanding how physical and chemical processes acted over geological time to shape the modern atmosphere. Modern atmospheric xenon is enriched in heavy isotopes by 30–40‰ u−1 relative to Solar or Chondritic xenon. Previous studies demonstrated that, 3.3 Ga ago, atmospheric xenon was isotopically fractionated (enriched in the light isotopes) relative to the modern atmosphere, by 12.9 ± 1.2 (1σ) ‰ u−1, whereas krypton was isotopically identical to modern atmospheric Kr. Details about the specific and progressive isotopic fractionation of Xe during the Archean, originally proposed by Pujol et al. (2011), are now well established by this work. Xe isotope fractionation has evolved from 21‰ u−1 at 3.5 Ga to 12.9‰ u−1 at 3.3 Ga. The current dataset provides some evidence for stabilization of the Xe fractionation between 3.3 and 2.7 Ga. However, further studies will be needed to confirm this observation. After 2.7 Ga, the composition kept evolving and reach the modern-like atmospheric Xe composition at around 2.1 Ga ago. Xenon may be the second atmospheric element, after sulfur, to show a secular isotope evolution during the Archean that ended shortly after the Archean-Proterozoic transition. Fractionation of xenon indicates that xenon escaped from Earth, probably as an ion, and that Xe escape stopped when the atmosphere became oxygen-rich. We speculate that the Xe escape was enabled by a vigorous hydrogen escape on the early anoxic Earth. Organic hazes, scavenging isotopically heavy Xe, could also have played a role in the evolution of atmospheric Xe. For 3.3 Ga-old samples, Ar-N2 correlations are consistent with a partial pressure of nitrogen (pN2) in the Archean atmosphere similar to, or lower than, the modern one, thus requiring other processes than a high pN2 to keep the Earth's surface warm despite a fainter Sun. The nitrogen isotope composition of the atmosphere at 3.3 Ga was already modern-like, attesting to inefficient nitrogen escape to space since that time. © 2018 The Authors Article 2018 English 00167037 10.1016/j.gca.2018.04.018 Geochimica et Cosmochimica Acta 232 Elsevier Ltd 82 – 100 Archean; atmospheric chemistry; fluid inclusion; isotopic composition; isotopic fractionation; nitrogen isotope; paleoatmosphere; Proterozoic; xenon https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046634100&doi=10.1016%2fj.gca.2018.04.018&partnerID=40&md5=c9c15af7a45ae34a563becb53ff0585c Cited by: 69; All Open Access, Green Open Access, Hybrid Gold Open Access G. Avice B. Marty R. Burgess A. Hofmann P. Philippot K. Zahnle D. Zakharov article Byerly2018967 Article 2018 10.1130/G45276.1 Geology 46 967 – 970 11 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85055909624&doi=10.1130%2fG45276.1&partnerID=40&md5=76f46934e57685b28f0fee12e0d96316 Cited by: 29 Benjamin L. Byerly Donald R. Lowe Nadja Drabon Matthew A. Coble Dale H. Burns Gary R. Byerly article Mohr-Westheide20181516 The oldest known large bolide impacts onto Earth are represented by approximately 3.47–3.2 Ga old Archean spherule layers of the Barberton Greenstone Belt (BGB) in South Africa and the Pilbara craton in West Australia. These layers were recognized as impact deposits by their excessively high platinum group element (PGE) contents that are indicative of an extraterrestrial component. This was followed by measurements of extraterrestrial Cr isotopic ratios, in some cases. Recently, the extraterrestrial PGE signature in Archean spherule layers from the BGB was localized and positively associated with the presence of submicrometer PGE alloy micronuggets associated with Ni,Cr-rich spinel. The actual formation of these platinum group mineral (PGM) phases has, however, not yet been resolved. Primary meteoritic particles from the impacting body, the products of impact melting, or condensation from impact vapor plumes have all been proposed as possible genetic process. Resolving this requires detailed microanalytical investigation of the internal microchemical and microstructural compositions, textural characteristics, and crystallographic relationships between the different phases. Here, we report the results of a first transmission electron microscopy (TEM) study of six such PGE microparticles enclosed in Ni-Cr spinel or occurring in groundmass of Barberton spherule layers from the BARB5 ICDP drill core and from the CT3 exploration core. Results include a variety of chemical and structural PGM compositions that are difficult to explain by a single process, leading to the conclusion that several processes may have been involved in the formation of PGMs in Archean spherule layers from the BGB. There is evidence supporting formation of these PGMs by exsolution from the spinel host phase, precipitation from a melt phase, and condensation from a gas phase (of the impact vapor plume). © The Meteoritical Society, 2018. Article 2018 English 10869379 10.1111/maps.13109 Meteoritics and Planetary Science 53 University of Arkansas 1516 – 1536 7 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046454491&doi=10.1111%2fmaps.13109&partnerID=40&md5=3a8e670b05e87c05230e942d0e4b7853 Cited by: 3; All Open Access, Bronze Open Access T. Mohr-Westheide A. Greshake R. Wirth W.U. Reimold article Avice2017 Xenon (Xe) is an exceptional tracer for investigating the origin and fate of volatile elements on Earth. The initial isotopic composition of atmospheric Xe remains unknown, as do the mechanisms involved in its depletion and isotopic fractionation compared with other reservoirs in the solar system. Here we present high precision analyses of noble gases trapped in fluid inclusions of Archean quartz (Barberton, South Africa) that reveal the isotopic composition of the paleo-atmosphere at ≈3.3 Ga. The Archean atmospheric Xe is mass-dependently fractionated by 12.9±2.4 ‰ u-1 (± 2σ, s.d.) relative to the modern atmosphere. The lower than today 129 Xe excess requires a degassing rate of radiogenic Xe from the mantle higher than at present. The primordial Xe component delivered to the Earth's atmosphere is distinct from Solar or Chondritic Xe but similar to a theoretical component called U-Xe. Comets may have brought this component to the Earth's atmosphere during the last stages of terrestrial accretion. © 2017 The Author(s). Article 2017 English 20411723 10.1038/ncomms15455 Nature Communications 8 Nature Publishing Group Barberton; Mpumalanga; South Africa; argon; chlorine; inert gas; xenon; atmospheric chemistry; degassing; isotopic composition; isotopic fractionation; noble gas; paleoatmosphere; quartz; solar system; tracer; xenon; Archean; Article; astronomy; atmosphere; comparative study; fractionation; irradiation; thermodynamics; thermogenesis; volumetry https://www.scopus.com/inward/record.uri?eid=2-s2.0-85019584995&doi=10.1038%2fncomms15455&partnerID=40&md5=e0cd3f4dcecf1fcf9eb33f097fe9b4b3 Cited by: 48; All Open Access, Gold Open Access, Green Open Access Guillaume Avice Bernard Marty Ray Burgess article Schulz2017322 Archean spherule layers, resulting from impacts by large extraterrestrial objects, to date represent the only remnants of the early meteorite, asteroid, and comet bombardment of the Earth. Only few Archean impact debris layers have been documented, all of them embedded in the 3.23–3.47 billion year old successions of the Barberton Greenstone Belt (BGB) in South Africa and the Pilbara Craton in Western Australia. Some of them might be correlated with each other. Given the scarcity of Archean spherule deposits, four spherule layer intersections from the recently recovered BARB5 drill core from the central Barberton Greenstone Belt, analyzed in this study, provide an opportunity to gain new insight into the early terrestrial impact bombardment. Despite being hydrothermally overprinted, siderophile element abundance signatures of spherule-rich samples from the BARB5 drill core, at least in part, retained a meteoritic fingerprint. The impact hypothesis for the generation of the BARB5 spherule layers is supported by correlations between the abundances of moderately (Cr, Co, Ni) and highly siderophile (Re, Os, Ir, Pt, Ru and Pd) elements, whose peak concentrations and interelement ratios are within the range of those for chondrites. Rhenium-Osmium isotope evidence further support the impact hypothesis. Collectively, this study provides evidence for extraterrestrial admixtures ranging between ∼40 and up to 100% to three of the four analyzed BARB5 spherule layers, and a scenario for their genesis involving (i) impact of a chondritic bolide into a sedimentary target, (ii) varying admixtures of meteoritic components to target materials, (iii) spherule formation via condensation in an impact vapor plume, (iv) transportation of the spherules and sedimentation under submarine conditions, followed by (v) moderate post-impact remobilization of transition metals and highly siderophile elements. © 2017 Elsevier Ltd Article 2017 English 00167037 10.1016/j.gca.2017.05.040 Geochimica et Cosmochimica Acta 211 Elsevier Ltd 322 – 340 Australia; Barberton Greenstone Belt; Pilbara Block; Western Australia; Archean; Earth; geochemistry; impact; meteorite; Ocean Drilling Program; remobilization; rhenium-osmium dating; siderophile element; spherule https://www.scopus.com/inward/record.uri?eid=2-s2.0-85020705751&doi=10.1016%2fj.gca.2017.05.040&partnerID=40&md5=19aff9fd4e1ff958a4e64e382810dc5d Cited by: 12 Toni Schulz Christian Koeberl Ambre Luguet David Acken Tanja Mohr-Westheide Seda Ozdemir Wolf Uwe Reimold article Galić2017135 Multiple sulfur isotope variability in Archean sedimentary rocks provides constraints on the composition of the Earth's earliest atmosphere. The magnitude and sign of mass-independent anomalies reflect not only atmospheric processes, but also transformations due to the Archean marine sulfur cycle prior to preservation into sedimentary pyrite. The processes affecting the Archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear. Here we combine iron (Fe) and multiple sulfur (S) isotope data in individual pyrite grains with petrographic information and a one-dimensional reactive transport model, to investigate the sources of Fe and S in pyrite formed in a Paleoarchean sedimentary basin. Pyrites were selected from mudstones, sandstones and chert obtained from a drill core in the ca. 3.2 Ga Mapepe and Mendon Formations of the Fig Tree and Onverwacht Groups, respectively, in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa. Pyrite textures and δ56Fe distinguish early-diagenetic pyrite formed with pore-water ferrous iron (disseminated grains with average δ56Fepyrite = 0‰) from late-diagenetic pyrite formed through sulfidation of iron oxide minerals (layered and aggregate forms with average δ56Fepyrite = + 1‰). Mass dependent S isotope variability in pyrite was small (δ34Spyrite ranged from − 1.1 to + 3.3‰) with a correspondingly minor spread in Δ33Spyrite (ranging from + 0.3 to + 2.1‰) and Δ36Spyrite (ranging from − 3.08 to + 0.27‰) that indicates a lack of post-depositional re-working with other distinct sulfur sources. Our combined Fe and S isotope data are most readily explained with pyrite sulfide derived from microbial-reworking of solid elemental S. Iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed. The lack of a negative Δ33S signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis, consistent with low sulfate concentrations in the Paleoarchean ocean. © 2016 Article 2017 English 00092541 10.1016/j.chemgeo.2016.12.006 Chemical Geology 449 Elsevier B.V. 135 – 146 Barberton Greenstone Belt; Kaapvaal Craton; Ficus (angiosperm); Earth atmosphere; Iron; Iron oxides; Isotopes; Oxide minerals; Photolysis; Redox reactions; Sedimentary rocks; Sedimentology; Sulfur; Sulfur compounds; Composition of the Earth; Fe isotopes; Greenstone belts; Low sulfate concentrations; Multiple sulfur isotopes; Paleoarchean; Reactive transport modeling; S isotopes; Archean; iron; isotopic fractionation; pyrite; sediment chemistry; sedimentary rock; sulfate; sulfur; sulfur isotope; Pyrites https://www.scopus.com/inward/record.uri?eid=2-s2.0-85008214294&doi=10.1016%2fj.chemgeo.2016.12.006&partnerID=40&md5=973ba24b13c01b9d629a776f96b9cdc7 Cited by: 21; All Open Access, Green Open Access Aleksandra Galić Paul R.D. Mason José M. Mogollón Mariëtte Wolthers Pieter Z. Vroon Martin J. Whitehouse article Drabon2017803 Article 2017 10.1130/G39255.1 Geology 45 803 – 806 9 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85028516716&doi=10.1130%2fG39255.1&partnerID=40&md5=e60730039b9cff9f7bc24bb472101ced Cited by: 36 Nadja Drabon Donald R. Lowe Gary R. Byerly Jacob A. Harrington article Hofmann201747 Article 2017 10.1016/j.epsl.2017.01.008 Earth and Planetary Science Letters 462 47 – 54 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85010298650&doi=10.1016%2fj.epsl.2017.01.008&partnerID=40&md5=cb26fea0b20d5c80a194da2fd3d53863 Cited by: 12 Axel Hofmann Iain Pitcairn Allan Wilson article Garçon2017216 Knowing the composition, nature and amount of crust at the surface of the early Earth is crucial to understanding the early geodynamics of our planet. Yet our knowledge of the Hadean-Archean crust is far from complete, limited by the poor preservation of Archean terranes, and the fact that less attention has been paid to the sedimentary record that tracks erosion of these ancient remnants. To address this problem and get a more comprehensive view of what an Archean continent may have looked like, we investigated the trace element and Sm-Nd, Lu-Hf isotopic records of Archean metasedimentary rocks from South Africa. We focused our study on sandstone and mudstone from drill core in the Fig Tree Group (3.23–3.26 Ga) of the Barberton granite-greenstone belt, but also analyzed the 3.4 Ga Buck Reef cherts and still older (3.5–3.6 Ga) meta-igneous rocks from the Ancient Gneiss Complex, Swaziland. Based on principal component analysis of major and trace element data, the Fig Tree metasedimentary rocks can be classified into three groups: crustal detritus-rich sediments, Si-rich sediments and Ca-, Fe-rich sediments. The detritus-rich sediments have preserved the Sm-Nd and Lu-Hf isotopic signatures of their continental sources, and hence can be used to constrain the composition of crust eroded in the Barberton area in the Paleoarchean period. Based on Sm/Nd ratios, we estimate that this crust was more mafic than today, with an average SiO2 content of 60.5 ± 2 wt.%. This composition is further supported by isotopic mixing calculations suggesting that the sedimentary source area contained equal proportions of mafic-ultramafic and felsic rocks. This implies that the Archean crust exposed to weathering was more mafic than today but does not exclude a more felsic composition at depth. Neodymium and Hf crustal residence ages show that the eroded crust was, on average, ∼300–400 Ma older than the deposition age of the sediments, which highlights the importance of intracrustal reworking of older crust at ∼3.2 Ga in the Barberton area. The Si-rich sediments have slightly positive εNd (t=3.23Ga) but extremely radiogenic εHf (t=3.23Ga), up to +11. Based on analyses of 3.4 Ga Buck Reef cherts, we suggest that the radiogenic Hf isotopic signature of the Si-rich sediments can be accounted for by the old chert clasts or detrital silicified rock fragments present in the rocks. The latter have extremely high Lu/Hf ratios such that their εHf values would increase dramatically, by about +100 epsilon units every 100 Ma. In the Ca-, Fe-rich sediments, one sample contains carbonate that preserves the typical rare-earth element features of seawater precipitates. The initial Nd isotopic composition of this sample (εNd (t=3.23Ga) = +1.7) is within the range of previous estimates for Archean anoxic seawater. © 2017 Elsevier Ltd Article 2017 English 00167037 10.1016/j.gca.2017.03.006 Geochimica et Cosmochimica Acta 206 Elsevier Ltd 216 – 235 South Africa; Ficus (angiosperm); Archean; chert; continental crust; erosion; hafnium; lutetium; mudstone; neodymium isotope; samarium; sandstone; sedimentary rock https://www.scopus.com/inward/record.uri?eid=2-s2.0-85015881338&doi=10.1016%2fj.gca.2017.03.006&partnerID=40&md5=406ccb7c2f4643597a72cb526a1b79f7 Cited by: 22; All Open Access, Green Open Access M. Garçon R.W. Carlson S.B. Shirey N.T. Arndt M.F. Horan T.D. Mock article Kremer2017117 Article 2017 10.1016/j.precamres.2017.04.023 Precambrian Research 295 117 – 129 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85018649596&doi=10.1016%2fj.precamres.2017.04.023&partnerID=40&md5=cb3e2bf17710234c0022174a648e3ba8 Cited by: 21 Barbara Kremer Józef Kaźmierczak article Fritz20162441 A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (μXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The μXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3-poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism. © The Meteoritical Society, 2016. Article 2016 English 10869379 10.1111/maps.12736 Meteoritics and Planetary Science 51 University of Arkansas 2441 – 2458 12 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84990866317&doi=10.1111%2fmaps.12736&partnerID=40&md5=3619380019ac2201d6de67f714f91807 Cited by: 14; All Open Access, Bronze Open Access Jörg Fritz Roald Tagle Luisa Ashworth Ralf Thomas Schmitt Axel Hofmann Béatrice Luais Phillip D. Harris Desirée Hoehnel Seda Ozdemir Tanja Mohr-Westheide Christian Koeberl article Farber2016639 The 3.33 to 3.26 Ga Mendon Formation in the Palaeoarchaean Barberton greenstone belt, South Africa, forms the uppermost unit of the Onverwacht Group. It is dominated by ultramafic volcanic rocks interbedded with thin layers of cherty sediments that show pervasive alteration, including widespread serpentinisation, silicification and chert and quartz veining. The BARB4 drill core of the ICDP Barberton drilling project exposes a unique section through the Mendon Formation in the Manzimnyama Syncline. The komatiites are pervasively altered to an assemblage comprising quartz, chlorite, carbonate, talc, biotite, and, locally, plagioclase, K-feldspar, muscovite, amphibole, stilpnomelane and ankerite. The overlying sediments are made up of banded iron formations and rare beds of siliciclastic rocks. Though the altered komatiites are pervasively silicified, SiO, contents do not exceed 58 wt.%, and their major and trace element geochemistry is similar to other komatiitic rocks of the Mendon Formation, particularly those of the M2v-member. Quartz veins and, less commonly, quartz-carbonate and quartz-carbonate-plagioclase veins are found throughout the core. Overall, composition and texture of the veins differ from primary and early diagenetic veins found in silicified komatiites elsewhere in the Barberton greenstone belt. In the BARB4 drill core, the veins are generally coarse-grained, and the immediate wall rocks are locally foliated along the vein margins. In addition, the δ18O values of vein quartz range from 14.1 to 15.3%o, significantly lower than the values typically found in veins on the modern seafloor that formed during low temperature hydrothermal seafloor alteration (∼22 to 32%o). Fluid inclusions in vein quartz are homogeneous two-phase (L+V) aqueous inclusions that occur in trans- and intragranular trails and clusters. Intragranular and isolated fluid inclusions have a similar homogenisation temperature (Th) of 130 to 200°C, with most data ranging between 145 and 175°C. Salinities cluster in three different groups of high (20 to 27wt.% NaCl equiv.), medium (10 to 15wt.% NaCl equiv.) and low salinity (0.3 to 1.5wt.% NaCl equiv.). The composition and microthermometric characteristics of the fluid inclusions analysed within the drill core show similarities to those found in quartz veins in silicified komatiites of the Mendon Formation, which are interpreted to have been entrapped during metamorphism. P-T calculations based on fluid inclusion microthermometry reveal conditions of 230 to 400 MPa and 250 to 400°C. Similar conditions of 240 to 270°C have been obtained using oxygen isotope thermometry, assuming a metamorphic fluid with a δ180 value of 6%o. Collectively, the δ18O values, together with the texture and composition of the veins, are interpreted to indicate a metamorphic origin of the veins. The presence of high salinity inclusions indicates the occurrence of a highly saline fluid that locally mixed with the dominant lower salinity fluids. The high salinity might have been derived from fluid circulation through evaporites. © 2016 December Geological Society of South Africa. Article 2016 English 10120750 10.2113/gssajg.119.4.639 South African Journal of Geology 119 Geological Society of South Africa 639 – 654 4 Barberton Greenstone Belt; banded iron formation; fluid inclusion; greenstone belt; komatiite; metamorphism; petrology; quartz vein; ultramafic rock https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029700084&doi=10.2113%2fgssajg.119.4.639&partnerID=40&md5=1719e6002af7abf711c7995aff9cffc7 Cited by: 6 K. Farber A. Dziggel F.M. Meyer C. Harris article Montinaro2016177 Sedimentary and magmatic rocks and their distinct sulphur isotopic signatures indicate the sources and processes of sulphur cycling, in particular through the analysis of all four stable sulphur isotopes (32S, 33S, 34S and 36S). Research over the past 15 years has substantially advanced our understanding of sulphur cycling on the early Earth, most notably through the discovery of mass-independently fractionated sulphur isotopic signatures. A strong atmospheric influence on the early Archean global sulphur cycle is apparent, much in contrast to the modern world. Diverse microbially driven sulphur cycling is clearly discernible, but its importance for Earth surface environments remains to be quantified. © 2016 Cambridge University Press. Article 2016 English 14735504 10.1017/S1473550415000531 International Journal of Astrobiology 15 Cambridge University Press 177 – 185 3 Archean; magma; pyrite; sedimentary rock; stable isotope; sulfate; sulfur cycle; sulfur isotope https://www.scopus.com/inward/record.uri?eid=2-s2.0-84962128075&doi=10.1017%2fS1473550415000531&partnerID=40&md5=371e260cceee80debb0954123e5b0492 Cited by: 2 A. Montinaro H. Strauss article Puchtel20162168 Article 2016 10.1002/2016GC006324 Geochemistry, Geophysics, Geosystems 17 2168 – 2193 6 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84977541987&doi=10.1002%2f2016GC006324&partnerID=40&md5=4418a515b19f4d81585d07e8a773f454 Cited by: 109; All Open Access, Green Open Access Igor S. Puchtel Janne Blichert-Toft Mathieu Touboul Mary F. Horan Richard J. Walker article Puchtel20152369 The start of plate tectonics on Earth is one of the most controversial issues in modern geology, with proposed timings covering almost the entire history of our planet. On page 2387 of this issue (vol. 100, 2015), Blichert-Toft and co-authors report Sm-Nd and Lu-Hf isotopic and lithophile trace element data for early Archean komatiites from the Barberton Greenstone Belt (GB) in South Africa, and argue for the onset of plate tectonics on Earth as early as 3.5 Ga. The studied komatiites show a large decoupling of the two isotopic systems and lithophile trace element signatures that are most consistent with deep-water, pelagic sediments being present in the lower-mantle source of these lavas. Their conclusions have far-reaching implications for advancing our understanding of how the Earth system operated in the distant geological past. © Walter de Gruyter Berlin/Boston 2015. Article 2015 English 0003004X 10.2138/am-2015-5468 American Mineralogist 100 Walter de Gruyter GmbH 2369 – 2370 11-12 Barberton Greenstone Belt; Belt conveyors; Binary alloys; Earth (planet); Isotopes; Lutetium alloys; Neodymium alloys; Samarium alloys; Tectonics; Trace elements; Barberton; Conveyor belts; Element signatures; Greenstone belts; Hf isotope; Isotopic systems; Pelagic sediments; subduction; greenstone belt; hafnium; isotopic analysis; komatiite; lutetium; neodymium; plate tectonics; samarium-neodymium dating; subduction; Hafnium alloys https://www.scopus.com/inward/record.uri?eid=2-s2.0-84948823083&doi=10.2138%2fam-2015-5468&partnerID=40&md5=6f20fa7d73830bb0ea97cb1ef1f8f6c5 Cited by: 1 Igor S. Puchtel article Farber2015134 Pervasive silicification is a common phenomenon in Early Archaean volcano-sedimentary sequences, reflecting the interaction between Si-rich fluids and the Archaean oceanic crust. In the Palaeoarchaean Barberton greenstone belt, South Africa, the silicified zones locally contain abundant tourmaline. In order to constrain the source of fluids responsible for the alteration, six tourmaline-bearing samples from the 3.3. Ga Mendon Formation were investigated by in-situ analyses of mineral chemistry and boron isotopes. The samples comprise a silicified, finely laminated sedimentary chert and five highly altered and silicified komatiites. Electron microprobe analysis (EMPA) indicates that tourmaline is mostly dravitic, with one sample between dravite and Mg-foitite. Tourmaline has a weakly-developed patchy colour- and chemical zonation, with variations in Al, Fe and Mg composition. Some samples show strong zoning in Cr-concentration with Cr enrichment in the core, and locally the high-Cr domains are at contacts with other Cr-rich phases such as magnesiochromite and chromian muscovite ("fuchsite").Overall, the boron isotope composition (δ11B) ranges from -20.7 to +10.2‰. Two groups of tourmaline are distinguished based on the variation in δ11B ratios within single samples: 1) those with small (<4‰) range in δ11B values (spinifex-textured komatiites and silicified sediment), and 2) those with a large range in δ11B values of up to 18‰ (brecciated and foliated samples). Positive boron isotope values (+6 to +10‰) are found in one spinifex-textured komatiite and are interpreted as being derived from seawater interacting with Archaean oceanic crust in shallow hydrothermal systems. The intermediate boron isotope values (-5 to -8‰) found in all other samples are similar to MORB and may represent boron derived from the Archaean oceanic crust. The rare and exceptionally light boron isotope values (-10 to -21‰) were found in rims of group 2 tourmaline. These values cannot be produced by fractionation alone, and point to the presence of another fluid source. The source of the light boron has yet to be identified, but possible candidates are remobilized boron either derived from granitic crust or from marine evaporites that precipitated from seawater enriched in 10B. In any case, the isotopically light boron appears to have been present during seafloor hydrothermal alteration and deposition of the Mendon Formation at ca. 3.3Ga. © 2015 Elsevier B.V. Article 2015 English 00092541 10.1016/j.chemgeo.2015.10.009 Chemical Geology 417 Elsevier 134 – 147 Barberton Greenstone Belt; Chemical analysis; Clay alteration; Electron probe microanalysis; Isotopes; Magnesium; Mica; Microanalysis; Seawater; Secondary ion mass spectrometry; Sedimentology; Silicate minerals; Zoning; Boron isotopes; Greenstone belts; Hydrothermal alterations; Hydrothermal system; Marine evaporites; Mendon Formation; Tourmaline; Volcano-sedimentary sequences; Archean; boron isotope; concentration (composition); evaporite; hydrothermal alteration; igneous geochemistry; isotopic composition; isotopic fractionation; komatiite; oceanic crust; tourmaline; tracer; Boron https://www.scopus.com/inward/record.uri?eid=2-s2.0-84945118316&doi=10.1016%2fj.chemgeo.2015.10.009&partnerID=40&md5=0fd48e0c9def483071d211db33f23038 Cited by: 15 Katja Farber Annika Dziggel Robert B. Trumbull F. Michael Meyer Michael Wiedenbeck article Ledevin2015253 In the Barberton Greenstone Belt, South Africa, a 100-250 m thick complex of carbonaceous chert dikes marks the transition from the Mendon Formation to the Mapepe Formation (3260 Ma). The sub-vertical-to vertical position of the fractures, the abundance of highly shattered zones with poorly rotated angular fragments and common jigsaw fit, radial structures, and multiple injection features point to repetitive hydraulic fracturing that released overpressured fluids trapped within the shallow crust. The chemical and isotopic compositions of the chert favour a model whereby seawater-derived fluids circulated at low temperature (< 100-150 °C) within the shallow crust. From the microscopic structure of the chert, the injected material was a slurry of abundant clay-sized, rounded particles of silica, carbonaceous matter and minor clay minerals, all suspended in a siliceous colloidal solution. The dike geometry and characteristics of the slurry concur on that the chert was viscoelastic, and most probably thixotropic at the time of injection: the penetration of black chert into extremely fine fractures is evidence for low viscosity at the time of injection and the suspension of large country rock fragments in the chert matrix provides evidence of high viscosity soon thereafter. We explain the rheology by the particulate and colloidal structure of the slurry, and by the characteristic of silica suspensions to form cohesive 3-D networks through gelation. <br><br> Our results provide valuable information about the compositions, physical characteristics and rheological properties of the fluids that circulated through Archean volcano-sedimentary sequences, which is an additional step to understand conditions on the floor of Archean oceans, the habitat of early life. Article 2015 English 18699510 10.5194/se-6-253-2015 Solid Earth 6 Copernicus GmbH 253 – 269 1 Barberton Greenstone Belt; Complex networks; Fracture; Fracturing fluids; Gelation; Hydraulic fracturing; Hydraulic structures; Levees; Silica; Temperature; Viscosity; Colloidal structures; Isotopic composition; Microscopic structures; Multiple injections; Physical characteristics; Rheological behaviour; Rheological property; Volcano-sedimentary sequences; Archean; chert; dike; fracture; greenstone belt; isotopic composition; rheology; viscosity; Suspensions (fluids) https://www.scopus.com/inward/record.uri?eid=2-s2.0-84923332286&doi=10.5194%2fse-6-253-2015&partnerID=40&md5=ef1ddfa1609be50788d12b2b08dc99b1 Cited by: 9; All Open Access, Gold Open Access, Green Open Access M. Ledevin N. Arndt A. Davaille R. Ledevin A. Simionovici conference Koeberl2015310 The first 2.5 billion years of the terrestrial impact history are not documented by any impact structures. Only a few spherule layers of impact origin are known, most of them of late Archean to early Proterozoic age. In the Barberton Greenstone Belt (South Africa), several spherule horizons (layers S1 to S4, possibly up to S8, with ages between ∼3.5 and ∼3.2 Ga) are amongst the oldest deposits from large bolide impacts onto Earth. Impact evidence is limited to (highly) elevated siderophile element contents and Cr isotopic compositions. Other isotope tools, such as the 187Re-188Os radionuclide system in combination with high-precision concentration data for siderophile elements, might be useful to confirm the propositions regarding the presence of meteoritic components made so far. Two recently recovered drill cores from the central and northern Barberton area (CT3 and BARB5) with as many as 18 spherule layer intersections of Paleoarchean age (some of which may be due to tectonic duplication, some might correlate with the S2 to S4 layers) provide an outstanding opportunity to gain new insight into the early impact bombardment of Earth. We present new mineralogical, chemical, and 187Re-188Os isotope data on CT3 and BARB5 drill core samples. Spherules in most layers exhibit undeformed shapes and include vesicles. Sulfides frequently are present in both matrix and spherules. Osmium data reveal a trend between the spherule-free horizons (intercalating the spherule layers) and spherule-matrix aggregates. Whereas the former typically exhibit elevated 187Os/188Os ratios of up to ∼1.2 and low Os and Ir concentrations below several hundred ppt, spherule-matrix aggregates tend to be less radiogenic (down to subchondritic present day 187Os/188Os ratios) with Os and Ir concentrations as high as in chondrites. Chromium-Ir correlations for CT3 and BARB5 samples mirror earlier results on S1 to S4 layers and can be interpreted in favor of an impact origin of the here investigated spherule horizons. © 2015 The Authors. Conference paper 2015 English 18777058 10.1016/j.proeng.2015.04.052 Procedia Engineering 103 Elsevier Ltd Schonberg W.P. 310 – 317 Aggregates; Core drilling; Deposits; Drills; Iridium; Isotopes; Meteorites; Osmium; Archean; Greenstone belts; Highly siderophile elements; Osmium isotopes; spherules; Matrix algebra https://www.scopus.com/inward/record.uri?eid=2-s2.0-84991328147&doi=10.1016%2fj.proeng.2015.04.052&partnerID=40&md5=29574d04e0062b2c880d6de4140b0cfb Cited by: 11; All Open Access, Bronze Open Access Christian Koeberl Toni Schulz W. Uwe Reimold article Montinaro2015311 Mass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550-3215. Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different sample suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales.Variable but generally slightly positive δ34S values between -0.7 and +5.2‰, negative δ33S values between -0.50 and -0.09‰, and a negative correlation between δ34S and δ33S as well as between δ33S and δ36S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater.Barite from the Mapepe Formation displays positive δ34S values between +3.1 and +8.1‰ and negative δ33S values between -0.77 and -0.34‰. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, notably photolytic sulfate, whereas the positive δ34S values suggest bacterial sulfate reduction of the marine sulfate reservoir.Non-mineralized black shale samples from the presumed stratigraphic equivalent of the Mapepe Formation show positive δ34S values between 0.0 and +1.3‰ and positive δ33S values between +0.59 and +2.45‰. These results are interpreted to result from the reduction of photolytic elemental sulfur, carrying a positive δ33S signature.Positive δ34S values ranging from +0.7 to +3.5‰ and slightly negative δ33S values between -0.17 and -0.12‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source, but a contribution from recycled seawater sulfate, which would be indicative of submarine hydrothermal activity, cannot be ruled out.Massive and disseminated sulfides from the M'hlati prospect are distinctly different from massive and disseminated sulfide from the Bien Venue Prospect. They show negative δ34S values between -1.2 and -0.1‰ and positive δ33S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positive δ33S values, suggesting a connection with photolytic elemental sulfur.In conclusion, the sulfur isotope signatures in Paleoarchean rocks from the Barberton Greenstone Belt are diverse and indicate the incorporation of different sources of sulfur. For komatiites and tholeiites, barite and massive and possibly also disseminated sulfides from Bien Venue, multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin, while massive and disseminated sulfides from M'hlati and non-mineralized black shales are related to a second (photolytic elemental sulfur) end member. © 2015 Elsevier B.V. Article 2015 English 03019268 10.1016/j.precamres.2015.06.008 Precambrian Research 267 Elsevier 311 – 322 Barberton Greenstone Belt; Bacteria (microorganisms); Archean; black shale; hydrochemistry; isotopic fractionation; komatiite; oceanic crust; paleoceanography; reduction; seawater; sulfate; sulfur isotope https://www.scopus.com/inward/record.uri?eid=2-s2.0-84937920693&doi=10.1016%2fj.precamres.2015.06.008&partnerID=40&md5=cfbdbdc9eacfee8adddb68282340b1ea Cited by: 26; All Open Access, Bronze Open Access, Green Open Access Alice Montinaro Harald Strauss Paul R.D. Mason Desiree Roerdink Carsten Münker Ulrich Schwarz-Schampera Nicholas T. Arndt James Farquhar Nicolas J. Beukes Jens Gutzmer Marc Peters article Blichert-Toft20152396 To constrain the origin of komatiites from the Barberton Greenstone Belt, South Africa, we measured 147Sm-143Nd and 176Lu-176Hf compositions for 18 komatiites from core obtained during the International Continental Drilling Program in the Komati Formation of the Barberton Belt, as well as 33 komatiites from surface outcrops of the Komati, Hooggenoeg, and Weltevreden Formations, these latter for purposes of comparison between core and surface samples. Magmatic clinopyroxene from surface samples near the drill site was also analyzed. For the Lu-Hf isotope system, the Komati Formation core and surface samples including the clinopyroxene define a linear array whose slope corresponds to an age of 3426 ± 16 Ma (MSWD = 118; εHf(T) = +2.2), which is slightly younger than the accepted age of the rocks (3.48 Ga). The Sm-Nd isotope data for the same set of samples likewise fall along a linear array also yielding a younger age of 3339 ± 12 Ma (MSWD = 42; εNd(T) = +2.8). The high MSWD for both isotope systems indicate substantial scatter at variance with normal magmatic processes, likely implying element mobility disturbing even these relatively robust isotopic systems shortly after eruption of the lavas. The average initial εNd and εHf of the core samples at 3.48 Ga are +0.45 and +1.4, respectively, in overall accordance with the positive errorchron intercepts and a depleted mantle source at 3.5 Ga. In contrast, the clinopyroxene and their host rocks have strongly positive εHf(T) of about +5 and negative εNd(T) of about -2. Given the overall scatter of the whole-rock data, the most robust constraint on the composition of the komatiite source comes from the clinopyroxene. Their positive εHf(T) is in line with, though somewhat higher than other results from komatiites from the Komati Formation, but their negative εNd(T) is unexpected in that it indicates a source with long-term low Sm/Nd, which is at odds with its long-term high Lu/Hf. This signature is also found in the trace element compositions of some of the komatiites, such as moderately enriched LREE, negative Hf anomalies, and low Hf/Sm ratios. The origin of these features is uncertain but one possibility is that the discordance between the Hf and Nd isotope systems reflects the presence of deepsea sediments in the source of some of the Barberton komatiites. The possible presence of a surface component in an ancient deep mantle source has wide-ranging implications for mantle-crust interaction and dynamics in the early Earth and for constraining a minimum age for the onset of plate tectonics. © Walter de Gruyter Berlin/Boston 2015. Article 2015 English 0003004X 10.2138/am-2015-5325 American Mineralogist 100 Walter de Gruyter GmbH 2396 – 2411 11-12 Barberton Greenstone Belt; Binary alloys; Core samples; Gallium alloys; Hafnium; Infill drilling; Isotopes; Lutetium alloys; Neodymium; Samarium alloys; Trace elements; chert; Clinopyroxenes; Deep sea sediment; Greenstone belts; Hf isotope; International Continental Drilling Program; Invited Centennial article; Komatiites; Sm-Nd isotope; Archean; chert; clinopyroxene; deep-sea sediment; drilling; hafnium; isotopic composition; komatiite; neodymium; research program; Neodymium alloys https://www.scopus.com/inward/record.uri?eid=2-s2.0-84948776885&doi=10.2138%2fam-2015-5325&partnerID=40&md5=3310f90d2aacb0c1baf6bab6712e631a Cited by: 41 Janne Blichert-Toft Nicholas T. Arndt Allan Wilson Grace Coetzee article Farber2015150 In recent years, the role of Archaean seawater and hydrothermal fluid in the extensive silicification of Palaeoarchaean volcano-sedimentary successions has been a matter of considerable debate. In an attempt to constrain the conditions of silica precipitation, and the sources and chemical composition of the interacting fluids, we used fluid inclusion microthermometry, bulk crush-leach and oxygen isotope analyses of chert and quartz veins in silicified komatiites and sediments from the Barberton greenstone belt, South Africa. Chert vein margins consist of microcrystalline quartz and carbonaceous matter, whereas the vein centres are often filled with macrocrystalline quartz that contains abundant fluid inclusions.Oxygen isotope ratios of vein chert and macrocrystalline quartz vary from 18 to 21‰, with the macrocrystalline quartz having slightly higher δ18O values (0.7±0.3‰). The data are consistent with silica precipitation during low-temperature (≤100°C) hydrothermal processes on the Archaean seafloor. Macrocrystalline quartz contains homogeneous 2-phase (L+V) inclusions at room temperature with a relatively constant vapour fraction. The inclusions have a salinity of 3-11wt.% NaCl equiv. and homogenisation temperatures (Th) of 150-200°C. Whereas some of the inclusions form intragranular fluid inclusion clusters that appear to be primary, other inclusions form transgranular fluid inclusion trails and are clearly secondary. Both types of inclusions share the same microthermometric characteristics, indicating that fluid entrapment occurred during a later metamorphic event and not near the seafloor. The event likely coincided with regional deformation and metamorphism at 3.23Ga. Chlorite thermometry from vein host rocks reveals peak conditions of ~257±31°C. In conjunction with microthermometry, the data correspond to a crustal depth of 3-6km. A secondary origin of fluid inclusions is also consistent with the Cl/Br, Na/Cl and Na/K ratios of the macrocrystalline veins, which are similar to those found in metamorphic quartz veins. The fluid inclusions thus do not provide information on the conditions and temperatures during chert formation. While the fluids potentially carry the geochemical signature of modified Archaean seawater (i.e. hydrothermal fluid), characterised by low Cl/Br and Na/K ratios, and low Mg-contents, the fluid composition was likely modified during regional metamorphism. © 2015 Elsevier B.V. Article 2015 English 03019268 10.1016/j.precamres.2015.05.020 Precambrian Research 266 Elsevier 150 – 164 Barberton Greenstone Belt; Archean; chert; deformation mechanism; fluid inclusion; hydrothermal alteration; hydrothermal fluid; isotopic ratio; oceanic crust; oxygen isotope; paleoceanography; quartz vein; seawater; silicification https://www.scopus.com/inward/record.uri?eid=2-s2.0-84930674700&doi=10.1016%2fj.precamres.2015.05.020&partnerID=40&md5=b83af565e37104e974f5037738f97ec4 Cited by: 16 Katja Farber Annika Dziggel F. Michael Meyer Walter Prochaska Axel Hofmann Chris Harris article Puchtel2014394 Article 2014 10.1016/j.gca.2013.10.013 Geochimica et Cosmochimica Acta 125 394 – 413 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84888085933&doi=10.1016%2fj.gca.2013.10.013&partnerID=40&md5=f701a8ca3a198094fd1826f10b16752d Cited by: 83 Igor S. Puchtel Richard J. Walker Mathieu Touboul Euan G. Nisbet Gary R. Byerly article Puchtel201363 Article 2013 10.1016/j.gca.2013.01.016 Geochimica et Cosmochimica Acta 108 63 – 90 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84874454444&doi=10.1016%2fj.gca.2013.01.016&partnerID=40&md5=eaafdc482d8f7e610dac208b843bebcf Cited by: 119 I.S. Puchtel J. Blichert-Toft M. Touboul R.J. Walker G.R. Byerly E.G. Nisbet C.R. Anhaeusser article Grosch2013142 This study presents the first multiple sulfur isotope dataset on sulfides from the ca. 3.5-3.2 Ga Onverwacht Group in the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. In situ δ34SCDT and δ33S values of pyrite (n = 568) are reported from a wide range of hydrothermal, volcanic and sedimentary environments and are used to explore Mid-Archean biogeochemical sulfur cycling. Samples are from fresh drill core collected by the Barberton Scientific Drilling Project that intercepted cherts, metabasalts and sheared ultramafics of the ~3.3-3.35 Ga Kromberg Formation; the sedimentary units of the ~3.432 Ga Noisy formation; and the unconformably underlying metabasaltic pillow lavas of the ~3.472 Ga Hooggenoeg Formation.Pyrite in quartz-carbonate-veins in the lower diamictite of the Noisy sequence records the largest range and most negative δ34SCDT values so far reported from an Archean terrain (δ34SCDT = - 55.04 to +27.46‰). The Noisy sediments also contain detrital and diagenetic pyrites with a significant variation in δ33S of between -0.62 to +1.4‰ and δ34SCDT of between -7.00 and +12.6‰, interpreted to reflect tectonic exposure of these early sediments to atmospheric - shallow marine conditions. Early marine pyrites from the Kromberg Cherts also display strong positive δ33S values up to +2.50‰ with narrow range in δ34SCDT values (-6.00 to +1.50‰), whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values (~0‰). This study reveals a potential proto-tectonic control on atmospheric, geodynamic and hydrothermal environments available for early sulfate reducing and/or methanogenic microbes in the Paleoarchean.No evidence for microbial sulfate reduction or disproportionation was identified in the Kromberg Cherts, despite previous morphological claims for microbial life. Highly variable and negative δ34SCDT values were found in the Noisy turbidites and Hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono-sedimentary basins and in the Paleoarchean sub-seafloor, respectively. In light of current controversies surrounding sulfur isotope studies in similar-aged rocks of the Pilbara Craton (West Australia), we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the Paleoarchean earth. © 2013 Elsevier B.V. Article 2013 English 0012821X 10.1016/j.epsl.2013.06.035 Earth and Planetary Science Letters 377-378 142 – 154 Australia; Barberton Greenstone Belt; Pilbara Block; Western Australia; Biogeochemistry; Gallium; Geodynamics; Isotopes; Pyrites; Quartz; Sedimentology; Sulfur compounds; Tectonics; Disproportionations; Greenstone belts; Hydrothermal environment; Multiple sulfur isotopes; Scientific drilling; Sedimentary environment; Sulfate reduction; Sulfur cycling; anoxic conditions; Archean; atmosphere-biosphere interaction; biogeochemistry; chert; detrital deposit; early Earth; metabasalt; pyrite; seafloor; sulfur cycle; sulfur isotope; tectonics; Sulfur https://www.scopus.com/inward/record.uri?eid=2-s2.0-84883653190&doi=10.1016%2fj.epsl.2013.06.035&partnerID=40&md5=3d893062a8d7e549e43f74d763a289bd Cited by: 16 Eugene G. Grosch Nicola McLoughlin article Heubeck2013236 Thin and largely discontinuous volcanic tuff beds in the alluvial, fluvial, and marginal-marine siliciclastic strata of the Middle Archaean Moodies Group, Barberton Greenstone Belt (BGB), contain rare to abundant zircon. Dating of magmatic zircon grains from five tuff beds and one cross-cutting dike yield ages which span the entire spectrum of BGB history from ca. 3550. Ma to 3215. Ma and show variable degrees of post-depositional alteration until ca. 2500. Ma. The youngest pristine zircon grains in all tuff samples analyzed by CA-ID-TIMS (Chemical-Abrasion Ion-Dissolution Thermal Ion Mass Spectrometry) yield upper intercept and Concordia ages between 3227.6. ±. 0.3 and 3216. ±. 0.3. Ma, and those grains analyzed by LA-SF-ICP-MS (Laser Ablation-Sector Field-Inductively Coupled Plasma-Mass Spectrometry) and SHRIMP (Sensitive High-Resolution Ion Microprobe) yield ages between 3228. ±. 9 and 3214. ±. 9. Ma. Most of these ages are either identical (within error) or significantly older than a CA-ID-TIMS age of 3223.4. ±. 0.3. Ma, obtained from zircon grains of a tuff horizon of the Schoongezicht Formation at the top of the underlying Fig Tree Group. We interpret this age to mark the time of volcanic eruption, whereas the significantly older and overlapping ages of the stratigraphically higher Moodies tuff zircon grains point either to a high degree of magmatic inheritance and/or a detrital contribution from surrounding sedimentary rocks during or after ash-tuff deposition. The minimum age for deposition of Moodies Group sediments and deformation is provided by a LA-ICP-MS zircon U-Pb age of 3219. ±. 9. Ma obtained from an undeformed felsic dike which crosscuts folded Moodies strata. This age overlaps with a precise CA-ID-TIMS U-Pb zircon age of 3216.0. ±. 0.3. Ma obtained from a tuff horizon of the upper Moodies Group. Overall, the new age data collectively imply that the up to 3.7. km-thick, sandstone-dominated Moodies Group was deposited and deformed within <1-14. Ma, and that Moodies strata thus hold the potential to offer a temporal resolution comparable to active- and passive-margin Quaternary strata (~0.1-1. mm/a). © 2013 Elsevier B.V. Article 2013 English 03019268 10.1016/j.precamres.2013.03.021 Precambrian Research 231 236 – 262 Barberton Greenstone Belt; Ficus (angiosperm); alluvial deposit; Archean; deformation; deposition; dike; felsic rock; fluvial deposit; geochronology; sandstone; sedimentary rock; siliciclastic deposit; subsidence; tuff; zircon https://www.scopus.com/inward/record.uri?eid=2-s2.0-84877035734&doi=10.1016%2fj.precamres.2013.03.021&partnerID=40&md5=9382a2d81ef583f245319f7eb4641ad5 Cited by: 71 Christoph Heubeck Jonathan Engelhardt Gary R. Byerly Armin Zeh Bryan Sell Tim Luber Donald R. Lowe article Robin-Popieul20122191 The oldest well-preserved komatiites, and the type examples, are found in the Barberton Greenstone Belt in South Africa (3·5-3·3 Ga). All three komatiite types are present, commonly within the same stratigraphic unit. Al-depleted komatiites have low Al/Ti, relatively high concentrations of incompatible elements and depleted heavy rare earth elements (HREE); Al-undepleted komatiites have chondritic Al/Ti and flat HREE patterns; and Al-enriched komatiites have high Al/Ti, low concentrations of incompatible elements, enriched HREE and extremely depleted light rare earth elements. Based on a comprehensive petrological and geochemical study, we propose a new melting model for the formation of these magmas. The basis of the model is the observation, from published experimental studies, that at great depths (~13 GPa) the density of komatiitic liquid is similar to that of solid peridotite. At such depths, melting in a rising mantle plume produces near-neutrally buoyant komatiite melt that does not escape from the residual peridotite. As the source ascends to shallower levels, however, the pressure decreases and the density difference increases, eventually making melt escape possible. Al-depleted komatiites form first at about 13 GPa by equilibrium melting under conditions in which a large proportion of melt (30-40%) was retained in the source and the residue contained a high proportion of garnet (15%). Al-undepleted and Al-enriched komatiites form by fractional melting at intermediate to shallow depths after the escape of a large proportion of melt and after exhaustion of residual garnet. This model reproduces the chemical characteristics of all komatiite types in the Barberton belt and can probably be applied to komatiites in other parts of the world. © The Author 2012. Published by Oxford University Press. All rights reserved. Article 2012 English 14602415 10.1093/petrology/egs042 Journal of Petrology 53 2191 – 2229 11 Barberton Greenstone Belt; Archean; concentration (composition); geochemistry; komatiite; magma; mantle plume; modeling; peridotite; petrogenesis; petrology; rare earth element https://www.scopus.com/inward/record.uri?eid=2-s2.0-84867776716&doi=10.1093%2fpetrology%2fegs042&partnerID=40&md5=81e2e6b6920aab204c65b9decc0d9c7a Cited by: 94; All Open Access, Bronze Open Access Christophe C.M. Robin-Popieul Nicholas T. Arndt Catherine Chauvel Gary R. Byerly Alexander V. Sobolev Allan Wilson article sd-13-65-2012 2012 10.5194/sd-13-65-2012 13 65-71 https://sd.copernicus.org/articles/13/65/2012/