Helium in diamonds unravels over a billion years of craton metasomatism

Chemical events involving deep carbon- and water-rich fluids impact the continental lithosphere over its history. Diamonds are a by-product of such episodic fluid infiltrations, and entrapment of these fluids as microinclusions in lithospheric diamonds provide unique opportunities to investigate their nature. However, until now, direct constraints on the timing of such events have not been available. Here we report three alteration events in the southwest Kaapvaal lithosphere using U-Th-He geochronology of fluid-bearing diamonds, and constrain the upper limit of He diffusivity (to D ≈ 1.8 × 10−19 cm2 s−1), thus providing a means to directly place both upper and lower age limits on these alteration episodes. The youngest, during the Cretaceous, involved highly saline fluids, indicating a relationship with late-Mesozoic kimberlite eruptions. Remnants of two preceding events, by a Paleozoic silicic fluid and a Proterozoic carbonatitic fluid, are also encapsulated in Kaapvaal diamonds and are likely coeval with major surface tectonic events (e.g. the Damara and Namaqua–Natal orogenies)

Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability

Pyroxenites embedded in peridotite are often invoked as a major cause of short-length scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence. We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy, with depleted mantle compositions, representing a surface exposure of veined upper mantle, a potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and adjacent mantle rocks results in centimeter-scale chemical modifications in the host peridotites, systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host peridotite at greater than 0.1 m scale to acquire an isotopic heterogeneity larger than the range defined by the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites. Such pyroxenite-peridotite veined mantle domains may represent the enriched component rarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd variations in MORB

Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability

Pyroxenites embedded in peridotite are often invoked as a major cause of short-length scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence. We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy, with depleted mantle compositions, representing a surface exposure of veined upper mantle, a potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and adjacent mantle rocks results in centimeter-scale chemical modifications in the host peridotites, systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host peridotite at greater than 0.1 m scale to acquire an isotopic heterogeneity larger than the range defined by the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites. Such pyroxenite-peridotite veined mantle domains may represent the enriched component rarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd variations in MORB

Expedition 391 Preliminary Report : Walvis Ridge Hotspot: drilling Walvis Ridge, Southeast Atlantic Ocean, to test models of ridge hotspot interaction, isotopic zonation, and the hotspot reference frame

Hotspot tracks (quasilinear chains of seamounts, ridges, and other volcanic structures) provide important records of plate motions, as well as mantle geodynamics, magma flux, and mantle source compositions. The Tristan-Gough-Walvis Ridge (TGW) hotspot track, extending from the active volcanic islands of Tristan da Cunha and Gough through a province of guyots and then along Walvis Ridge to the Etendeka flood basalt province, forms one of the most prominent and complex global hotspot tracks. The TGW hotspot track displays a tight linear age progression in which ages increase from the islands to the flood basalts (covering ~135 My). Unlike Pacific tracks, which are simple chains of seamounts that are often compared to chains of pearls, the TGW track is alternately a steep-sided narrow ridge, an oceanic plateau, subparallel linear ridges and chains of seamounts, and areas of what appear to be randomly dispersed seamounts. The track displays isotopic zonation over the last ~70 My. The zonation appears near the middle of the track just before it splits into two to three chains of ridge- and guyot-type seamounts. The older ridge is also overprinted with age-progressive late-stage volcanism, which was emplaced ~30–40 My after the initial eruptions and has a distinct isotopic composition. The plan for Expedition 391 was to drill at six sites, three along Walvis Ridge and three in the seamount (guyot) province, to gather igneous rocks to better understand the formation of track edifices, the temporal and geochemical evolution of the hotspot, and the variation in paleolatitudes at which the volcanic edifices formed. After a delay of 18 days to address a shipboard outbreak of the coronavirus disease 2019 (COVID-19) virus, Expedition 391 proceeded to drill at four of the proposed sites: three sites on the eastern Walvis Ridge around Valdivia Bank, an ocean plateau within the ridge, and one site on the lower flank of a guyot in the Center track, a ridge located between the Tristan subtrack (which extends from the end of Walvis Ridge to the island of Tristan da Cunha) and the Gough subtrack (which extends from Walvis Ridge to the island of Gough). One hole was drilled at Site U1575, located on a low portion of the northeastern Walvis Ridge north of Valdivia Bank. At this location, 209.9 m of sediments and 122.4 m of igneous basement were cored. The latter comprised 10 submarine lava units consisting of pillow, lobate, sheet, and massive lava flows, the thickest of which was ~21 m. Most lavas are tholeiitic, but some alkalic basalts were recovered. A portion of the igneous succession consists of low-Ti basalts, which are unusual because they appear in the Etendeka flood basalts but have not been previously found on Walvis Ridge. Two holes were drilled at Site U1576 on the west flank of Valdivia Bank. The first hole was terminated because a bit jammed shortly after penetrating igneous basement. Hole U1576A recovered a remarkable ~380 m thick sedimentary section consisting mostly of chalk covering a nearly complete sequence from Paleocene to Late Cretaceous (Campanian). These sediments display short and long cyclic color changes that imply astronomically forced and longer term paleoenvironmental changes. The igneous basement yielded 11 submarine lava units ranging from pillows to massive flows, which have compositions varying from tholeiitic basalt to basaltic andesite, the first occurrence of this composition recovered from the TGW track. These units are separated by seven sedimentary chalk units that range in thickness from 0.1 to 11.6 m, implying a long-term interplay of sedimentation and lava eruptions. Coring at Site U1577, on the extreme eastern flank of Valdivia Bank, penetrated a 154 m thick sedimentary section, the bottom ~108 m of which is Maastrichtian–Campanian (possibly Santonian) chalk with vitric tephra layers. Igneous basement coring progressed only 39.1 m below the sediment-basalt contact, recovering three massive submarine tholeiite basalt lava flows that are 4.1, 15.5, and >19.1 m thick, respectively. Paleomagnetic data from Sites U1577 and U1576 indicate that their volcanic basements formed just before the end of the Cretaceous Normal Superchron and during Chron 33r, shortly afterward, respectively. Biostratigraphic and paleomagnetic data suggest an east–west age progression across Valdivia Bank, becoming younger westward. Site U1578, located on a Center track guyot, provided a long and varied igneous section. After coring through 184.3 m of pelagic carbonate sediments mainly consisting of Eocene and Paleocene chalk, Hole U1578A cored 302.1 m of igneous basement. Basement lavas are largely pillows but are interspersed with sheet and massive flows. Lava compositions are mostly alkalic basalts with some hawaiite. Several intervals contain abundant olivine, and some of the pillow stacks consist of basalt with remarkably high Ti content. The igneous sequence is interrupted by 10 sedimentary interbeds consisting of chalk and volcaniclastics and ranging in thickness from 0.46 to 10.19 m. Paleomagnetic data display a change in basement magnetic polarity ~100 m above the base of the hole. Combining magnetic stratigraphy with biostratigraphic data, the igneous section is inferred to span >1 My. Abundant glass from pillow lava margins was recovered at Sites U1575, U1576, and U1578. Although the igneous penetration was only two-thirds of the planned amount, drilling during Expedition 391 obtained samples that clearly will lead to a deeper understanding of the evolution of the Tristan-Gough hotspot and its track. Relatively fresh basalts with good recovery will provide ample samples for geochemical, geochronologic, and paleomagnetic studies. Good recovery of Late Cretaceous and early Cenozoic chalk successions provides samples for paleoenvironmental study

How double volcanic chains sample geochemical anomalies from the lowermost mantle

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Displaced helium and carbon in the Hawaiian plume

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Nourriture, cuillères, ornements... Les témoignages d'une exploitation variée des mollusques marins à Ayios Mamas (Chalcidique, Grèce)

Une grande quantité de restes d\u27animaux datée du milieu de l\u27Âge du Brome à la période byzantine a été mise au jour lors de nouvelles fouilles à Ayios Marnas, dans le nord de la Grèce. L\u27un des aspects de la stratégie de subsistance, particulièrement à l\u27époque de l\u27Âge du Bronze Moyen, était l\u27exploitation des ressources marines. L\u27utilisation des mollusques marins est analysée et discutée de manière détaillée. Ils ont pu être exploités pour la seule consommation, ou bien pour servir également d\u27éléments de décoration, de récipients, d\u27objets de magie ou encore pour la production de la pourpre.Large quantifies of animal remains, dating from the Bronze Age to the Byzantine period, were excavated at Ayios Marnas (northern Greece). During the Middle Bronze Age in particular, the exploitation of marine molluscs formed one aspect of the subsistence strategy practised there. Amongst the questions discussed are whether these molluscs were used not only as food but also as elements of decoration, as receptacles, as magical objects or even as sources for purple-dye production.</p

Le rôle de la chasse dans le pastoralisme néolithique pré-céramique et ses implications écologiques : l’exemple de Basta (Jordanie)

La fouille du site PPNB final de Basta (près de Petra, Jordanie) a livré une grande quantité de restes animaux, principalement des moutons et des chèvres domestiques. La question discutée ici est de savoir à quel point la chasse des gazelles, des équidés, des cervidés et autres ongulés sauvages jouait toujours un rôle crucial dans la vie des éleveurs qui occupaient Basta il y a 9000 ans. Le possible impact de ces activités sur la faune de la région de Petra est examiné. De plus, l’article analyse les facteurs qui peuvent avoir influé sur la fiabilité des considérations écologiques et économiques tirées des données ostéologiques présentées ici.Excavations at Late PPNB Basta (near Petra, Jordan) have yielded a large amount of animal remains mainly from domesticated sheep and goats. It is discussed in how far the hunting of gazelles, equids, cervids and other wild ungulates still played a crucial role in the life of the pastoralists, inhabiting Basta 9000 years ago. The possible impact of these activities on the fauna in the Greater Petra region is discussed. In addition, the paper focusses on those factors that might influence the reliability of ecological and economical considerations, ascertained from the osteological data presented here.</p

Le Néolithique moyen et le site de Platia Magoula Zarkou. Le point sur les recherches archéozoologiques en Thessalie (Grèce)

L’important village en tell de Platia Magoula Zarkou, situé près de la rivière Peneios, dans le nord de la Thessalie, est connu pour ses poteries néolithiques et son modèle réduit de maison accompagné de figurines. À la faveur des recherches archéologiques approfondies menées sur ce site, d’importantes quantités d’ossements animaux ont été collectées (n = 11623). Elles renvoient à une période comprise entre le Néolithique moyen et l’âge du Bronze moyen (n = 2477), en particulier sur les informations permettant la restitution de la gestion des troupeaux et l’exploitation des ressources naturelles durant cette période. Les résultats sont confrontés aux connaissances actuelles concernant l’économie et la vie sociale dans cette région de Grèce, au Néolithique moyen.The substantial settlement mound of Platia Magoula Zarkou, located near the Peneios river in the north of Thessaly, is famous for its Neolithic pottery and for a house-model with figurines. During extended archaeological research at this site, large amounts of animal remains have been excavated (n = 11.613). They cover periods from the Middle Neolithic to the Middle Bronze Age. These assemblages crucially enlarge the body of archaeozoological data for Thessaly. In this paper the main emphasis will be put on Middle Neolithic material (n = 2477), in particular on the reconstruction of livestock management and the exploitation of natural resources, practised by the inhabitants of the Magoula during this very period. The results are evaluated against the background of present archaeological knowledge on Middle Neolithic economy and social life in this part of Greece.</p

Ẏoung formation age of a mantle plume source

The Ninetyeast Ridge hotspot track displays strontium, neodymium and lead isotope variations over time that reflect simple radioactive decay in the plume source rather than a change in the mantle components present. The lead isotope variations indicate that the time spent by the plume source in a non-convecting mantle boundary layer was only a few hundreds of millions of years, contrary to the conventional view of individual plume sources as old (1-3 Gyr) or persistent features.SCOPUS: ar.jinfo:eu-repo/semantics/publishe