Laboratoire de Géologie de Lyon : Terre, Planètes et Environnement

The Sierra del Convento mélange in southeastern Cuba is one of a limited number of jadeite jade occurrences worldwide. This exhumed, pervasively serpentinized fossil subduction interface hosts tectonic blocks up to several tens of meters in scale that were reworked during intense metasomatism. The flat-lying mélange spans a 300 m thick vertical exposure, progressing from a block-rich lower portion toward a block free, serpentinite-dominated upper region. We conducted structurally-controlled sampling of blocks and matrix to produce a spatially-resolved geochemical and microstructural profile through the thickness of the Convento mélange. Pale green, nearly pure jadeitite constitutes the dominant block population in the southern part of this mélange, and may contain up to 30% epidote and/or white mica by volume. Minor metasedimentary and metamafic block populations, recording variable degrees of HP metamorphism, coexist alongside the jade blocks. We report a newly identified metre-scale zoning within the jadeitite bodies, consistent with that documented in other jade localities. Green jadeitite locally occurs surrounding an older core of zoisitite containing relict jadeite crystals rimmed by omphacite. Green jade is cross-cut by fractures infilled by dark-colored brecciated jade, which is in turn rimmed by a late, pyroxene-free rind composed mainly of weakly foliated phengite + albite ± epidote. The latter facies occupies a similar position to chloritite blackwalls previously described from the Convento jade occurrence. All jade varieties except for these latest phengite-albite rinds and chloritite blackwalls are cross-cut by fractures infilled by jadeite and omphacite. Parts of the main jade bodies exhibit prismatic radial and comb jadeite microstructures, consistent with descriptions of P-type jade, which precipitate directly into open fractures from hydrothermal fluids. However, Convento jade contains paragonite with up to 2 wt.% K2O and jadeite-omphacite exsolution domains brecciated into jigsaw-like fragments recemented by jadeite and/or omphacite. These observations are consistent with at least part of the jade in the Sierra del Convento mélange representing near-total high-temperature metasomatic replacement of high-pressure anatectic trondhjemite protoliths, which originated as partial melts of garnet amphibolite at ~15 kbar, resembling an R-type (replacement) jade paragenesis. To overcome the considerable ambiguity inherent to geochronology datasets from HP igneous and metasomatic rocks from this locality (105 to 115 Ma, U-Pb zircon), we are conducting detailed multi-mineral and multi-system geochronology, including further U-Pb on zircon, titanite, and apatite, Ar/Ar on white mica, and Rb-Sr on white mica. This multi-chronometric approach will establish relative and numerical chronology for the diverse jade facies of the Convento occurrence, resolving timescales of the multiple associated fluidization events within the subduction channel.

Earth’s interior plays a fundamental role in the long-term evolution of the surface, climate, and biosphere. However, Earth's mantle evolution remains largely ambiguous, as imaging techniques are limited to present-day observations and geochemical or geological constraints apply to a non-global scale. Plate tectonic reconstructions coupled with convection models could provide constraints on the evolution of mantle structure. In this study, we employ both fully self-consistent and kinematically constrained mantle convection models[1]. The mantle rheology is temperature-, pressure-, phase-, and stress-dependent, with the latter represented through pseudo-plasticity. The novelty of this work lies in employing a composite rheology with “realistic” rheological parameters[2] in a fully three-dimensional geometry. By using both fully self-consistent models and plate-driven models, we aim to address the discrepancies in terms of long-term convective and tectonic behaviour that arise when forcing plate velocities onto the surface. The latter is done by imposing time-dependent surface velocity boundary conditions provided by a plate tectonic reconstruction[3].To evaluate the extent to which the models reproduce plate-like tectonics, we explore several independent constraints. In particular, we compute slab sinking rates and compare them to estimates inferred from seismic tomography[4]. Slab sinking rates in self-consistent models provide insight into the mantle’s rheology. For example, sinking rates that are lower than those based on tomographic and geological data may indicate an overly viscous mantle. Our results show that the slab sinking rate is generally higher in models with imposed plate velocities compared to fully self-consistent models. Furthermore, a tessellation algorithm[5] will be applied to the surface of the models to detect plates in the self-consistent models with plate-like behaviour. Based on these results, a plate-size frequency distribution can be calculated and compared to present-day Earth[6]. Results show that low yield stresses generate too many small plates, and too few large plates [Fig. 1]. In order to generate Earth-like plate tectonics, yield stress needs to be sufficiently high to reproduce the plate-size frequency distribution of present-day Earth, but also sufficiently low to facilitate a long-term mobile lid regime.[1] Tackley, P. J. (2008). Phys. Earth Planet. Inter. 171, 1–4.[2] Tackley, P. J., Ammann, M., Brodholt, J. P., Dobson, D. P., & Valencia, D. (2013). Icarus 225, 50–61.[3] Merdith, A. S., Williams, S. E., Collins, A. S., et al. (2021). Earth-Sci. Rev. 214, 103477.[4] Van der Meer, D. G., van Hinsbergen, D. J. J., & Spakman, W. (2018). Tectonophysics 723, 309–448.[5] Janin, A., Coltice, N., Chamot-Rooke, N., & Tierny, J. (2025). Nat. Geosci. 18, 1041–1047.[6] Bird, P. (2003). Geochem. Geophys. Geosyst. 4, 2001GC000252.

In its past, Mars experienced a warmer and wetter climate than on present days. Many uncertainties remain about the early climate of Mars, for instance on the nature of gas species included in the greenhouse warming or the duration of the warm episodes. Most existing reconstructions of Martian paleo-topography either rely on idealised assumptions, large-scale isostatic corrections, or limited regional reconstructions, and therefore do not explicitly integrate stratigraphic information on buried Noachian terrains. As a result, it is uncertain how paleo-topography impacted the early climate, and the development of the valley network.For the first time, we present a global reconstruction of the Noachian paleo-surface using constraints from geological mapping, and craters central peaks mineralogy and morphology. Starting from the present-day Mars Orbiter Laser Altimeter topography, we removed all the terrains younger than Noachian, based on the geological map from Tanaka et al., 2014. That includes the large areas from the lowlands in the northern hemisphere, the Tharsis bulge, recent impact basins, craters with inner sedimentary deposits, and the Noachian surfaces extensively affected by post-Noachian tectonic activity such as Valles Marineris and outflow channels. We used the mineral detections in the central peaks of impact craters and the central peak morphologies to describe the buried terrains and find the boundary between Noachian (lowest layer) and post-Noachian terrains (shallower layer). Phyllosilicates-bearing central peaks and massive morphologies are considered as evidence for excavated Noachian material, while mafic detections without hydrated minerals associated to layers morphologies are interpreted as post-Noachian units. We estimated the stratigraphic uplift for each impact to infer the original depth of the excavation, allowing us to define upper and lower bounds of the Noachian surface. The points are interpolated using a kriging interpolation technique to produce global envelopes, and the Noachian paleo-surface is defined taking the spatial mean of the lower and upper envelopes.Unlike previous products, this reconstruction directly links surface elevation to independently derived stratigraphic and mineralogical constraints, providing a physically grounded estimate of Noachian topography rather than a purely geometric or isostatic correction of present-day relief. Future refinements of the paleo-surface will include the effects of the true polar wander and lithospheric flexure effects due to the surface loading, particularly for the Tharsis region. This resulting dataset is designed to be used as a common boundary condition for climate, hydrological, erosional, and thermal models. We expect the paleo-surface to allow more realistic simulations of early Mars and a reassessment of the environmental conditions under which valley networks formed. Tanaka, K. L. et al. (2014). The digital global geologic map of Mars: Chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history. Planetary and Space Science, 95, 11-24.

Abstract. The North African desert margin is considered one of the most sensitive areas to future climate changes. Improved knowledge about Holocene climatic variability and environmental responses on millennial to centennial scale will help to refine scenarios related to future climate changes. During the last two decades, the recovery and compilation of Holocene records from the subtropical North Atlantic and the Mediterranean realms have improved our knowledge about the millennial-scale variability of the Western Mediterranean palaeoclimate and the Saharan dust cycle. However, the understanding on periodicities as well as potential coupling and forcing mechanisms remains poor. To detect periodicities in Holocene climatic variability and geomorphological processes, we use a Holocene sediment record from Lake Sidi Ali in the semiarid to sub-humid Middle Atlas with a robust 210Pb /137Cs and pollen-concentrates-based 14C chronology. We use a high-resolution core scanning-XRF record, in order to distinguish between lake-internal (e.g., chemical precipitation) and lake-external (e.g., detrital input) processes. Redfit and Wavelet time series analyses reveal distinct periodicities of millennial to centennial scale. By a correlation analysis of extracted, highly significant, frequency analysis spectra, three XRF-based “Redfit Proxy Groups” (RPGs) which potentially reflect different hydro-climatic forcing mechanisms were derived. Subsequently, we integrated environmental and climatic proxies from the same core (Cedrus pollen abundance, magnetic susceptibility, δ18O and δ13C values of ostracod shells, grain-size endmembers and total organic carbon) and used their wavelet domain to improve the interpretation. Finally, we identified two main periodicity regimes that affected, on the one hand, the hydrological regime and, on the other hand, the lake productivity and catchment erosion dynamics. For RPG 1 (Ca, Sr, Ca/Ti, Sr/Ti), we identified 2 ky and 1 ky periodicities, which we interpret as precipitation/evaporation related proxies in the context of North Atlantic and solar forcing. For RPG 2 (Fe, Ti, K, Si/Ti), we observe 3.5 ky and 1.5 ky periodicities, which we interpret as driven by lake productivity or detrital input.

Two new species of honeyguides (Indicatoridae) are described from the Lower Pliocene Upper Varswater Formation at Langebaanweg, South Africa. One of these species is referred to the genus Indicator, as Indicator sp. (taxon A), and comparable in size to the Lesser Honeyguide (I. minor). It is represented by a partial coracoid as well as 12 humeri, eight carpometacarpi, and two tarsometatarsi. The second species is slightly smaller than the Least Honeyguide (I. exilis). It is known from a fragmentary proximal humerus, a carpometacarpus and two tarsometatarsi, and cannot be referred to a particular genus of modern Indicatoridae, hence it is referred to Indicatoridae indet. (taxon B). Both species form the as yet earliest record of honeyguides in Africa and the world, and confirm the presence of woodland with mature trees suitable for cavity-nesting species at Langebaanweg during the Early Pliocene.

<strong class="journal-contentHeaderColor">Abstract.</strong> The El Salvador Fault Zone (ESFZ) accommodates most of the differential motion between the Central America Volcanic Forearc and the Chort&iacute;s block in Central America. By combining recent Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations, we develop the first kinematic block model for El Salvador that jointly inverts both data types. The model refines previous regional studies by resolving slip partitioning within the ESFZ and its continuations in Guatemala and the Gulf of Fonseca. Our preferred model predicts total slip rates of about 14 mm yr⁻&sup1; across the central ESFZ, distributed between a northern branch (5&ndash;8 mm yr⁻&sup1; dextral, 3&ndash;7 mm yr⁻&sup1; normal) and a southern branch (2&ndash;6 mm yr⁻&sup1; dextral). Dextral motion decreases toward the Jalpatagua Fault in Guatemala and toward the San Miguel Fault in eastern El Salvador, increasing again along the Marrabios Fault in Nicaragua. Subduction coupling beneath El Salvador appears weak (&Phi;&asymp;0.2) and confined to shallow depths, strengthening westward into Guatemala. These results highlight a strongly coupled volcanic arc and a weakly coupled subduction interface. Future seafloor geodetic measurements and new radar satellite missions could improve constraints on slab coupling and crustal deformation processes in this seismically active region.

This manuscript reports the deposition of holotypes of fossil species of Radiolarian described by Patrick De Wever in the Micropaleontology collections of the Muséum national d’Histoire naturelle (MNHN), Paris. They belong to the Université Claude Bernard Lyon 1 and are deposited in the MNHN because of their fragility, impossibility to remove from SEM stubs where they are mixed with MNHN specimens and to maintain the integrity of the collection (sediments, processed residues, picked specimens). They correspond to 91 species described from Permian to Cretaceous deposits worldwide, in 13 scientific articles published between 1981 and 1995. In order to inform the scientific community of the institutional localisation of this important collection, an annotated alphabetic list by genera is provided, including the original citation for each species, type locality, age, collection number, and subsequent re-attributions and synonymizations. The adjustment of one collection number has been necessary because of a duplicated number. Ce manuscrit rapporte le dépôt d’holotypes d’espèces fossiles de Radiolaires décrits par Patrick De Wever dans les collections de Micropaléontologie du Muséum national d’Histoire naturelle (MNHN), Paris. Ces holotypes appartiennent à l’Université Claude Bernard Lyon 1 et sont déposés au MNHN en raison de leur fragilité, de l’impossibilité de les retirer des plots MEB où ils sont mélangés aux spécimens du MNHN, et pour conserver l’intégrité de la collection (sédiments, résidus traités, spécimens prélevés). Ils correspondent à 91 espèces décrites des dépôts du Permien au Crétacé à travers le monde, dans 13 articles scientifiques publiés entre 1981 et 1995. Afin d’informer la communauté scientifique de la localisation institutionnelle de cette importante collection, une liste alphabétique annotée par genre est fournie, incluant la citation originale de chaque espèce, la localité type, l’âge, le numéro de collection, ainsi que les éventuelles réattributions et synonymisations ultérieures. L’ajustement d’un numéro de collection a été nécessaire en raison d'un numéro dupliqué.

• Deconvolution of mass-independent Mo isotope signatures provides a new tool to decipher the history of geological samples. • Molybdenum isotope anomalies caused by the nuclear field shift (NFS) effect were detected in natural samples. • The Mo mass-independent anomalies observed in uranium ores result from natural processes associated with their geological settings. • The Mo isotope signatures deconvoluted in samples of natural ores and industrially produced uranium ore concentrates provide an efficient tracer of their geographic origin. • Mass-independent anomalies have a potential for a broader range of applications in other areas of geochemistry. Mass-independent isotope fractionation (MIF) has only been documented for a limited number of heavy elements (such as Hg, Tl and U) and has thus received limited attention for intermediate mass elements such as Mo. Conversely, mass-dependent isotope fractionation (MDF) of various isotope systems has become one of the most common tools in geochemistry as a means of deciphering processes that have shaped our planet. MDF signatures have provided fruitful insights by establishing a correspondence between a given process and specific isotope ratios. However, they are hampered by some limitations, notably because several processes can yield the same isotope signature or because superimposed effects can complicate interpretations. In this study, we identified Mo isotope mass-independent signatures resulting from, first, nuclear field shift effects, and second, fissiogenic isotopic anomalies in natural samples of uranium ores, as well as in industrially produced uranium ore concentrates. Furthermore, most MDF signatures yield residual anomalies after correction of instrumental mass bias using an exponential law, leading to a third signature (though an apparent MIF). The three types of mass-independent signatures were successfully deconvoluted and result in a powerful tracer that is shown to discriminate the origin of several ore deposits, from studying the isotope composition of uranium ores or uranium concentrates. These isotope effects discovered in natural uranium ores are produced by generic geochemical processes that have been described in many other environments. Thus, the identification of these effects opens the possibility of extending the search for mass-independent isotope signatures in natural samples with numerous isotope tracers in a broad number of applications such as environmental geochemistry or nuclear forensics.

Geological data of the region indicate that the Canary Islands have not been connected to the mainland before. However, fossil evidence suggests some kind of faunal exchange with Africa during the late Neogene. After extensive field work during past years, a re-evaluation of the fossil remains of the first terrestrial vertebrates that settled and thrived on the Canary Islands is presented, with special attention to the long-debated identity of birds that laid large-sized eggs, reported some decades ago on Lanzarote Island. The age of the eggshell-bearing deposits has been recently updated as Early Pliocene (ca. 4 Ma). The dispersal mode of these terrestrial birds to reach the island was an unsolvable challenge in previous studies because the regional geography of the sea bottom was neglected, as well as the chronological succession of events in the formation of the Canary Eastern Ridge, which increased attention to a unique case of arrival of ratites on an island never before united with the mainland. The few animals found in northern Lanzarote (ratites, snakes, turtles, terrestrial snails and bite marks on eggshells pointing to a jagged and unknown large predator) probably made the sea crossing from the mainland in different ways. Two scenarios are contemplated. In both, the circumstances facilitating the faunal transit from Africa to the Canaries ceased after the early Pliocene, around 4 Ma, since these animals have never managed to cross the Canary Channel again.