Analysis of Paleointensity Results Under Different Interpretation Approaches: A Case Study on the Korkhi Volcanic Sequence (Lesser Caucasus, Georgia)

International audienceAbstract In this study we focus on the investigation of the absolute intensity records of two volcanic subsequences, aiming to enrich the global paleointensity database for the last 5 Ma, which currently shows important dispersion. We present new absolute paleointensities obtained from the Plio‐Pleistocene volcanic sequence of Korkhi (Djavakheti Highland, Georgia) (41°27′31″N, 43°27′55″E). Korkhi is divided into two lava flow subsequences dated at 3.11 ± 0.20 Ma and 1.85 ± 0.08 Ma. Paleomagnetic directions previously published (Sánchez‐Moreno et al., 2018, https://doi.org/10.1029/2017GC007358 ) show a normal polarity in the lower Korkhi subsequence and a reverse‐to‐intermediate polarity in the upper Korkhi subsequence. The new paleointensity determinations are obtained through two different Thellier‐type protocols (Thellier‐Thellier and IZZI) and the corrected multispecimen method. We utilize different selection criteria and interpretation approaches (TTB, CCRIT, BiCEP and multimethod), and we make a critical evaluation on their application on complex magnetic behaviors, such as often found in volcanic rocks. Finally, we obtained a paleointensity of 70 μT in upper Korkhi and 14 paleointensities in lower Korkhi that vary between 5.2 and 37.2 μT. These results agree with a recently proposed non‐Geocentric Axial Dipole (GAD) hypothesis for the last ∼1.5 Ma (Cych et al., 2023, https://doi.org/10.1029/2023JB026492 ), and with low field strength for the 3–4 Ma

X-Ray Constraints on Wandering Black Holes in Stripped Galaxy Nuclei in the Halo of NGC 5128

International audienceAbstract A subset of galaxies have dense nuclei, and when these galaxies are accreted and tidally stripped, the nuclei can masquerade as globular clusters in the halos of large galaxies. If these nuclei contain massive central black holes, some may accrete gas and become observable as active galactic nuclei. Previous studies have found that candidate stripped nuclei rarely host luminous X-ray sources, but these studies were typically restricted to both the most massive candidate nuclei and the most luminous X-ray sources. Here we use new and archival Chandra and XMM-Newton data to search for X-ray emission in a near-complete sample of massive globular clusters and candidate stripped nuclei in the nearest accessible elliptical galaxy, NGC 5128. This sample has the unique advantage that the candidate stripped nuclei are identified dynamically via elevated mass-to-light ratios ( M / L V ). Our central result is that 5/22 ( 2 3 − 6 + 11 %) of the candidate stripped nuclei have X-ray sources down to a typical limit of L X ∼ 5 × 10 36 erg s −1 , a fraction lower than or comparable to that among massive clusters with normal M / L V (16/41; 3 9 − 7 + 8 %). Hence we confirm and extend the result that nearly all X-ray sources in stripped nuclei are likely to be X-ray binaries rather than active galactic nuclei. If the candidate stripped nuclei have black holes of typical masses ∼2 × 10 5 M ⊙ needed to explain their elevated M / L V , then they have typical Eddington ratios of ≲ 2 × 10 −6 . This suggests that it will be challenging to conduct an accretion census of wandering black holes around even nearby galaxies

Tracking lithospheric delamination and surface processes across the Messinian salinity crisis

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A Paleozoic history of Armorica recounted through anorogenic to vaugneritic magmatism

International audienceThe Plouaret-Commana-Huelgoat (PCH) vaugnerite-granite complex, emplaced at around 315 Ma on both sides of the North Armorican Shear Zone (NASZ) in the Armorican Massif (France), can be regarded as the "axial pivot" around which a large part of the history of the Armorican magmatism was revolving. Indeed, four main magmatic cycles can be distinguished in the Ordovician/Early Permian time-span over much of the considered areas, i.e. North and Central Armorican Domains (N/CAD): (1) several anorogenic mafic complexes (plutons, dykes and/or lavas) were successively emplaced from the Ordovician to Early Carboniferous; (2) near the Bashkirian/Moscovian time-boundary, when the N/CAD started to record the effects of the Variscan collision, magmatism became predominantly lamprophyric/vaugneritic (K-rich West-Armorican kersantites and PCH vaugnerites), prior to (3) the generalized granitic peak during the Moscovian-Kasimovian ages, in turn followed by (4) a K-rich intermediate magmatic activity, including again vaugnerites and the last granitic intrusions, during the late-/post-collision stages in the upper Pennsylvanian-Early Permian time-period. The sharp geochemical break evidenced in the present work between an early anorogenic magmatic group and a syn- to post-collisional system in the N/CAD emphasizes the original magmatic history recorded by part of Armorica, including probably the Central Iberian Zone (CIZ), during the nearly entire Paleozoic era compared to those commonly applied to the rest of the European Variscan orogen. This evolution is assumed to result from: (1) large-scale asthenospheric upheavals due to the downward straightening and retreat of variously plunging slabs during the Paleozoic times, (2) partial melting of metasomatized lithospheric/asthenospheric mantle due to fluid release from fragments of buried continental crust, and (3) crustal anatexis

Is the Symbiotic Recurrent Nova T CrB Late? Recent Photometric Evolution and Comparison with Past Pre-Outburst Behaviour

International audienceT CrB is a symbiotic recurrent nova that last erupted in 1946. Given its recurrence timescale of approximately 80 years, the next outburst is eagerly anticipated by the astronomical community. In this work, we analyse the optical light curves of T CrB, comparing recent photometric evolution with historical data to evaluate potential predictive indicators of nova eruptions. Although the "super-active" phases preceding both the 1946 and anticipated eruptions are strikingly similar, the subsequent photometric behaviour differs. We find that the decline in brightness observed in 2023, interpreted by some as a "pre-eruption dip", deviates from the deep minimum recorded prior to the 1946 event and does not reliably predict the eruption timing. Recent photometric and spectroscopic observations indicate that the system is returning to a high-accretion state. Given this, an eruption may be imminent, even without distinct precursors. While the next eruption of T CrB will be a major scientific event, its expected peak brightness of $V \sim 2$ mag highlights the importance of setting realistic public expectations for what will be a visually modest, yet astrophysically very significant, celestial event

Line Intensity Mapping Prediction from the Cosmic Dawn (CoDa). III. Simulation for Hα from Galaxies and the Intergalactic Medium During the Epoch of Reionization

International audienceThe evolution of large-scale structure, galaxies and the intergalactic medium (IGM) during the Epoch of Reionization can be probed by upcoming Line Intensity Mapping (LIM) experiments, which sample in redshift and direction without needing to resolve individual galaxies. We predict the intensity and sources of hydrogen Hα emission, dominated by radiative recombination following ionization by UV from the same massive stars that caused reionization, down to redshift 4.6, using the largest fully coupled, radiation-hydro simulation of galaxy formation and reionization to date, Cosmic Dawn (CoDa) III. We compute the mean intensity and VID versus redshift, including the relative contributions of galaxies and IGM. This will provide mock data to guide and interpret LIM experiments such as NASA’s SPHEREx and proposed CoDa Intensity Mapper

Betelgeuse, the Prototypical Red Supergiant

International audienceThe behavior of the bright red supergiant, Betelgeuse, is described with results principally from the past 6 years. The review includes imaging, photometry, and spectroscopy to record the Great Dimming of 2019–2020. This event was followed by a slow ongoing recovery from the massive surface mass ejection after which the stellar characteristics changed. Theoretical simulations address the cause of this episodic mass ejection and the optical Dimming. Recent publications evaluating the perplexing 2100 day periodicity in the star’s brightness and radial velocity provide evidence that Betelgeuse may harbor a companion object. Current attempts at direct detection of this companion are discussed. Betelgeuse provides a well-studied and meaningful example for supergiant stars in our Galaxy and others

The Aptian-Albian of the Costa Blanca (SE Spain): Implications for identifying the Aptian/Albian boundary in the neritic zone within the Tethys realm

International audienceThe Aptian-Albian interval of the Costa Blanca (SE Spain) has been studied to provide new insights into the evolution of the neritic domain of carbonate platforms in the Tethys. Three areas have been re-examined: Serra Gelada, Puig Campana, and Cabeçó d'Or. The biozonations of large benthic foraminifers (LBF) have been revised based on ammonite biostratigraphy. Updated ammonite datings and stratigraphic revisions reveal that several LBF and calcareous algae (CA) taxa previously attributed to the late Aptian actually originated in the early Albian. These findings correct and refine the calibration of LBF and CA biozones and ranges with standard ammonite zones. Furthermore, the identification of a significant local hiatus during the middle Albian at Cabeçó d'Or is likely linked to halokinesis

No Robust Sign of Human Influence in the Unprecedented Atmospheric Circulation of Summer 2018 Over Northern Europe

International audienceThe summer of 2018 was characterized by prolonged heatwaves over Northern Europe, associated with persistent atmospheric blocking, and an unusually northward jet stream location over Scandinavia. Whilst event attribution studies tend to focus on the change in probability or magnitude of the extreme temperatures themselves, we provide context to these studies by examining whether there are human induced trends in the atmospheric circulation that might affect the likelihood of similar extreme circulation patterns and associated heat waves occurring in the future. We examine trends and variability in summer jet latitude, blocking frequency and overall circulation pattern over the Scandinavian sector in a variety of reanalyses and climate model ensembles. Both the number of blocked days, and the average jet location for summer 2018 were unprecedented in the reanalyses, and rare in climate model simulations. We found no robust evidence of past or future externally forced changes in summer blocking frequency over Scandinavia in model simulations, whilst trends in circulation analogs were also largely insignificant. Trends in jet latitude were dependent on the time period examined, models included and other analysis choices. Overall, we found no robust evidence for systematic trends in average or extreme years toward Summer 2018-like conditions for any of the three indices, nor in the frequency of co-occurring extreme northward jet latitude and high blocking frequency. We conclude that Summer 2018s circulation can likely be explained by internal atmospheric variability.Plain Language Summary Northern Europe experienced prolonged heatwaves during the summer of 2018. These were associated with an unusually far north jet-stream location and persistent atmospheric blocking over Scandinavia-(i.e., high atmospheric pressure which persists for days to weeks, blocking the passage of other weather systems and contributing to the buildup of heat). Studies on heatwaves commonly seek to quantify how the probability or severity of the hot temperatures has changed due to human-induced climate change. However, it is also important to examine whether the likelihood of the atmospheric circulation patterns leading to such heatwaves has changed, since this may affect how often they occur in the future. We look for trends in summer jet stream location and blocking frequency over Scandinavia, as well as in the number of days with a similar overall circulation pattern to summer 2018 over Europe. We use a combination of climate model simulations and observational data sets (reanalyses). We find that Summer 2018 had the furthest north jet stream location and most blocked days over Scandinavia ever seen since the reanalysis records began in 1948. However, we found no convincing evidence for human-induced trends toward an increased likelihood of such a circulation pattern occurring.</div

Constraints on Fe-Ca metasomatism in mineralized mantle rocks: Insights from in-situ geochemistry and thermodynamic modeling

International audienceUltramafic-hosted seafloor massive sulfide deposits have been reported in present-day oceanic settings for nearly thirty years. However, the development of comprehensive genetic models that account for deep-seated hydrothermal processes is largely hindered by the limited availability of seafloor observations and their reliance on large-scale geophysical studies. The Platta nappe (Swiss Alps) preserves a Jurassic hydrothermal system (the Marmorera-Cotschen Hydrothermal System; MCHS), where Cu-Fe-Co-Zn-Ni mineralization is associated with Fe-Ca silicates (ilvaite, hydrogarnet, and diopside). Petrographic analyses and thermodynamic modeling indicate that Fe-Ca metasomatism occurred between 300 and 360 °C and at low fO2 (from FMQ −6 to +1), likely coeval with early-stage serpentinization. The composition of Fe-Ca silicates (Co, Ni, and REE contents, measured by in-situ LA-ICP-MS) indicates fluid-rock interaction from an ultramafic-dominated system to an open-system, involving fluids derived from both mafic and ultramafic rocks. Mineralogical and geochemical signatures of Fe-Ca silicates in the MCHS do not support genetic relationships with common rodingitization. Our results highlight that Fe-Ca metasomatism may be a widespread deep-seated alteration along mafic–ultramafic rock contacts or in mantle rocks modified through melt-rock interaction accompanying mantle exhumation