Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution

Mantle heterogeneities beneath the South Atlantic: a Nd-Sr-Pb isotope study along the Mid-Atlantic Ridge (3°S-46°S)

We report on 55 Nd and Sr isotope analyses of Mid-Atlantic Ridge (MAR) basalt glasses from 3°S to 46°S, using the same samples on which Pb and He isotope ratios were reported earlier (Hanan et al. [1] and Graham et al. [2]). Eighteen new Pb, Sr, and Nd isotope analyses are also reported on basalt glasses from 17 stations from the same region.87Sr86Sr ratios range from 0.70212 to 0.70410 and143Nd144Nd from 0.51285 to 0.51331. The along-ridge long wavelength87Sr86Sr variation delineated by light-REE depleted basalts increases progressively southward toward Tristan da Cunha. Short wavelength, spike-like, positive87Sr86Sr anomalies composed of light-REE enriched basalts are found opposite the Tristan, St. Helena, and Circe (Ascension) hotspots (as for the Pb isotopes). The short and long wavelength143Nd144Nd variations anti-correlate with those of87Sr86Sr. The 17 new Pb isotope analyses confirm both the short and long wavelength trends previously reported by Hanan et al. [1]. These spatial variations, as well as the variations in Nd-Sr-Pb isotopic space fully confirm the mantle plume-ridge interaction model and upper mantle mixing conditions beneath the South Atlantic inferred previously on the basis of Pb isotopic data only (Hanan et al. [1]). However, in Nd-Sr isotopic subspace the Circe and the St. Helena mixing vector are not distinguishable. The short wavelength Nd-Sr-Pb-He anomalies suggest recent lateral sublithospheric channeled flows from these off-ridge plumes to the migrating MAR axis. The long wavelength variations reflect a broad pollution of the asthenosphere by Pb and Sr radiogenic, isotope-rich, mantle material, which has been partly depleted of incompatible elements relatively recently. This broad pollution may be related to the partial melting and dispersion of the Tristan and St. Helena plume heads into the subcontinental asthenosphere, prior to the opening of the South Atlantic. In this two-stage model, the mixing relations in Nd-Sr-Pb space further require that the incompatible element depletion and dispersion of the St. Helena plume into the asthenosphere occurred before that of the Tristan plume head. We emphasize that this two-stage model is based pur tested.</p

Ages radiométriques K/Ar des éléments ophiolitiques de la nappe des Gets (Haute-Savoie, France)

Ophiolitic material from the nappe des Gets has been dated by conventional K/Ar and by total fusion 40Ar/39Ar methods. These ophiolites appear to belong to two. temporally distinct, magmatic episodes: — The first, of Lower to Middle Jurassic age. includes the gabbros and diabases associated with serpentinites. — The second, of Maastrichtian age. includes albite-chlorite diabases formed in submarine basaltic eruptions which probably occurred at about the same time as flysch sedimentation in Albian-Cenomanian times. Therefore, the age measured is considered to date a metamorphic event only. Finally, it should be noted that the albite-chlorite diabases from the col de la Ramaz zone seem to have ages older than other albite-chlorite diabases.Les éléments ophiolitiques de la nappe des Gets ont été datés par les variantes 40K/40Ar et 40Ar/39Ar (fusion totale). Ces ophiolites paraissent appartenir à deux épisodes magmatiques temporellement distincts: — Un premier, auquel se rattachent des gabbros et des diabases associés à des serpentinites, dont l'âge est jurassique inférieur à moyen. — Un second, auquel correspondent des diabases albito-chloritiques provenant d'épanchements basaltiques sous-marins, dont l'âge est vraisemblablement proche de celui de la sédimentation, albienne-cénomanienne, du flysch. L'âge maestrichtien mesuré est considéré comme datant un épisode métamorphique ultérieur. Enfin, il semble justifié de singulariser les diabases albito-chloritiques de la zone du col de la Ramaz dont l'âge paraît plus grand que celui des autres diabases albito-chloritiques.</p

Géochimie isotopique des basaltes de la ride médio-océanique de l'Atlantique Equatorial

A major, 1000-km long geochemical anomaly culminating at 1.7°N is observed in basalts erupted along the axis of the Mid-Atlantic Ridge across the Equatorial fracture zones. The anomaly is probably caused by the Sierra Leone mantle plume now in off-ridge position. The aseismic Sierra Leone and Ceara Rise reflect the activity of this hotspot in the past, when it was centered over the ridge axis.</p

Mantle plume-ridge interactions in the Central North Atlantic: a Nd isotope study of Mid-Atlantic Ridge basalts from 30°N to 50°N

We report on Nd isotopes and Sm and Nd contents of 46 fresh Mid-Atlantic Ridge basalts over the Azores swell from 30°N to 50°N. The latitudinal ¹⁴³Nd/¹⁴⁴Nd and Sm/Nd profiles anti-correlate with the ⁸⁷Sr/⁸⁶Sr profile previously established [1]. Sharp minima in ¹⁴³Nd/¹⁴⁴Nd, identical in value, are found at the 46°N, 43°N, 39°N, and 35°N short-wavelength geochemical anomalies previously recognized, as well as the 1100 km long gradient south of the Azores platform. A single binary mixing line is observed in ¹⁴³Nd/¹⁴⁴Nd vs. ⁸⁷Sr/⁸⁶Sr space, suggesting that the incompatible element-rich mantle sources underlying these four short-wavelength anomalies have a similar long-term origin. However, at a given ¹⁴³Nd/¹⁴⁴Nd (or ⁸⁷Sr/⁸⁶Sr), the MORB population from 40.5°N to 50°N is systematically lower in incompatible elements and their ratios, such as La/Sm, Nd/Sm, Cl/F and Rb/Sr, than the 40.5°N-30°N population. The required fractionation must be relatively recent. But the bulk chemistry of these MORB rules out that it was generated directly under the ridge by large varying degrees of partial melting of passive heterogeneities embedded in the depleted asthenosphere. An earlier, but not too distant, metasomatic enrichment or depletion event is required. A small 1–2% melt fraction removal by fractional decompression melting of a wet garnet lherzolite, at its wet solidus, can readily account for the depletion of the 46°N and 43°N relative to the 39°N mantle sources. We speculate that the short-wavelength 46°N, 43°N and 39°N anomalies were caused either by: (1) a family of plumes with the same long-term origin and thermal boundary layer source; or (2) by the detachment of blobs from a single bending plume converging with the MAR axis at 39°N and preferentially discharging southwestward along the spreading axis. In either case, the rising plumes, or the detached blobs, at 46°N and 43°N occurred on the east flank of the MAR below the thick lithosphere. The plume-derived material reaching the MAR axis at these latitudes would be residual in nature (mantle restite), as a result of an early removal in intraplate settings of small melt fractions, directly over the points where the plumes are rising, or over where the blobs detached from the bending plume. The previously proposed model invoking a separate off-ridge plume (Great Meteor) captured by the westward migrating MAR is retained for explaining the 35°N MAR anomaly and the related Great Meteor-Corner Seamount-New England Seamount hotspot track [2–4]

Hafnium, neodymium, and strontium isotope and parent-daughter element systematics in basalts from the plume-ridge interaction system of the Salas y Gomez Seamount Chain and Easter Microplate.

International audienc

La microplaque de l'île de Pâques (Pacifique Sud Oriental): variations isotopiques Pb-Sr-Nd

Dredged basalt samples from the Easter Island microplate show a very large local variety of isotope data with e.g. Nd values between 0.51328 and 0.51285. In the eastern branch they differ considerably from normal East Pacific Ridge values. 206Pb/204Pb, 87Sr/86Sr and 143Nd/144Nd ratios from the Easter island microplate (EMP) are intermediate between Sala y Gomez and MORB.</p

The volcanic activity in Syria and Lebanon between Jurassic and Actual

Chemical compositions of lavas from the Dead Sea Rift System volcanism indicate a typical intraplate setting during the period between Jurassic and Actual. Whole rock Potassium-Argon geochronology on 43 basalts reveals a strong and general activity between Berriasian and Valanginian times and also a constant activity during the Tertiary but with a large gap between 16 and 8 Ma. The volume and timing of the volcanism is controlled by the left-lateral mouvement along the Rift