Multilevel Modular Mesocrystalline Organization in Red Coral

International audienceBiominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nm. Thus, the transition from imperfect crystallographic order at mm scale to nearly perfect single crystalline domains at nm scale is progressive. The concept of 'mesocrystal' involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of 'multilevel modularity'. This modularity has potential implications for the origin of complex biomineral shapes in nature. A multilevel modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow

Early stages of development in Mediterranean red coral (Corallium rubrum): The key role of sclerites

Corals are ecosystem engineers whose tree-like structures give three-dimensional complexity to the habitat. Their population dynamics are affected by recruitment and juvenile survival. Therefore, several defense strategies, such as the formation of hard skeletons and/or spicules, have evolved to protect these vulnerable stages. The family Coralliidae, to which “precious corals” belong, represent an exception in the order Scleralcyonacea, as they form hard CaCO3 skeletons and small CaCO3 structures, the sclerites. The skeletogenesis of Corallium species is relatively well documented in adult colonies but remains poorly known in the early stages of the development of new colonies. To shed light on the timing of Corallium rubrum’s early skeleton formation and the role of sclerites, we focused on the first 4-years of life, applying different techniques, from scanning electron microscopy to synchrotron tomography and laser ablation inductively coupled plasma-mass spectrometry. Our results show that: 1) the first visible sclerites in the primary polyp appear at least 12 days after larval settlement, which is associated with a high CaCO3 production rate (4.5 ± 2.3 μg of CaCO3 per day). Furthermore, growth rings are visible in the sclerites, showing that fully matured sclerites grow fast, probably in 3 to 4 days. 2) Sclerites are the only biomineral product in the first year of life of C. rubrum’s colonies. 3) The evidence of a consolidated axial skeleton, intended as the inner part of the skeleton characteristic of the adult red coral (the medullary zone, MZ), is recorded for the first time in 2-year-old colonies. 4) The annular zone (AZ) around the medullary zone starts forming not before four years after settlement. Thus, primary polyp builds a deformable armor made of only sclerites during the first year. This shelter provides mechanical protection from abrasion and predation to early settled colonies. After two years, settlers are firmly and mineralogically attached to the substratum, which makes them less vulnerable to predation than younger recruits that are not anchored by the skeleton

Growth Kinetics and Distribution of Trace Elements in Precious Corals

The concentration and spatial distribution of major (Ca, Mg) and trace elements (Na, Sr, S, Li, Ba, Pb, and U) in different Corallium skeletons (C. rubrum, C. japonicum, C. elatius, C. konojoi) have been studied by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). EMP data show positive Na-Mg and negative Na-S and Mg-S correlations in all skeletons. LA-ICPMS data display additional Sr-Mg, Li-Mg, and U-Mg positive correlations. Medullar zones in the skeletons, corresponding to fast growing zones, are systematically richer in Mg, Na, Sr, Li, and U and poorer in S than the surrounding slow growing zones. These spatial distributions are mostly interpreted in terms of growth kinetics combined with steric effects influencing the incorporation of impurities in biogenic calcites. This interpretation is in agreement with available experimental data on kinetic effects on the incorporation of elements in calcite. At a different scale, annual growth rings in annular slow growing zones show oscillations in Mg, Na, Sr, and S. These chemical oscillations probably result from growth rate variations: fast growth would produce rings enriched in Mg, Sr, and Na, while slow growth would produce rings enriched in Ca, S and organic matter. From previous studies in C. rubrum, the Mg-rich rings would develop during the spring to fall period while the S-rich rings would form immediately after (late fall and winter). Analytical traverses performed in annular zones of different Corallium skeletons indicate that Mg, Na, Sr, Li, and U decrease from core to rim. This observation indicates that radial growth rate decreases as the colony gets older. Contrary to Mg, Na, Sr, Li, S, and U, barium and lead concentrations are identical in medullar and annular zones and appear independent of growth kinetics. Thus, concentrations in Corallium skeletons could provide indications on Ba and Pb contents in the oceans. Barium and lead concentrations are higher in Mediterranean than in Pacific precious corals, these two elements can be used to discriminate C. rubrum from C. japonicum, and contribute enforcing regulations on the trade of precious corals

The retrogressive breakdown of orthopyroxene in an intermediate charnockite from Saleix (French Pyrénées)

An intermediate charnockite from the Saleix granulitic slice shows a primary paragenesis involving perthitic K-feldspar, plagioclase An 30, hypersthene with minor amount of quartz and greatly subordinate clinopyroxene, garnet (and zircon, apatite, rutile, titanomagnetite). During total pressure and temperature decreases, and more especially P H₂O increase, related to crustal thinning, orthopyroxene broke down giving a complex corona involving four well specified rims of actinolite, quartz, biotite, secondary plagioclase. Chemical compositions of the phases are used to balance the reaction with a petrological mixing model. A multivariant reaction of the following form can be balanced : Opx + Kf + Pl I + W ↔ Act + Bi + Pl II + Q. In that reaction, the imbalance in the elements Ba, Cr, Ti and CI is immediately obvious. On the contrary, only the introduction of a volumetric constraint proves that the reaction was not strictly isochemically in equilibrium with respect to major elements. A part of the reaction can be explained only in terms of metasomatism. The excellent correlation between K and Cl in the amphiboles suggests that K was present in a chlorine enriched fluid phase. The simplified reaction Hb + Bi + Q → Opx + Kf + Pl + W has been suggested by de Waard (1965) to account for the diagnostic appearance of orthopyroxene and the tendency for hornblende and biotite to disappear concomitantly. The charnockitic rock from Saleix displays a good exemple of a "frozen" comparable (but retrogressive) reaction which can be considered as an important indicator of the transition from granulite-facies to amphibolite-facies assemblages during retrogressive metamorphism.Une charnockite intermédiaire de l'écaille granulitique de Saleix présente une paragenèse primaire composée de feldspath potassique perthitique, plagioclase An 30, hypersthène, quartz et de quelques rares cristaux de clinopyroxène, grenat (zircon, apatite, rutile, titanomagnétite). Au cours d'une diminution de la pression totale, de la température et plus spécialement d'une augmentation de la pression partielle d'eau, en rapport avec un amincissement crustal, l'orthopyroxène se déstabilise pour donner une structure réactionnelle complexe comprenant quatre couronnes d'actinote, quartz, biotite et plagioclase secondaire. Les compositions chimiques des minéraux sont utilisées pour équilibrer la réaction à l'aide d'un modèle de mélange. Une réaction de la forme suivante peut être proposée : Opx + Fk + Pl I + eau ↔ Act + Bi + Pl II + Q Dans cette réaction, les éléments Ba, Cr, Ti et Cl ne peuvent de toute évidence pas être équilibrés. Par ailleurs, seule l'introduction d'une contrainte volumique démontre que la réaction n'est pas strictement isochimique du point de vue des éléments majeurs. Une partie de la réaction ne peut s'expliquer qu'en terme de métasomatisme. L'excellente corrélation K/Cl dans l'actinote suggère que le potassium était présent dans une phase fluide enrichie en chlore. La réaction simplifiée Hb + Bi + Q → Opx + Fk + Pl + eau a été proposée par de Waard (1965) pour prendre en compte l'apparition de l'orthopyroxène et la disparition concomitante de la hornblende et de la biotite. La charnockite de Saleix offre un excellent exemple d'une réaction "figée" comparable (mais rétromorphique) qui peut être considérée comme un bon indice de la transition faciès granulite - faciès amphibolite durant la rétromorphose et pour ce type de composition chimique.Vielzeuf Daniel. The retrogressive breakdown of orthopyroxene in an intermediate charnockite from Saleix (French Pyrénées). In: Bulletin de Minéralogie, volume 105, 6, 1982. pp. 681-690

Orthopyroxene and cordierite secondary assemblages in the granulitic paragneisses from Lherz and Saleix (French Pyrenees)

The paragneisses from the Pyrenean granulitic slices associated with lherzolites show a primary paragenesis composed of kyanite, garnet, perthitic potash feldspar, quartz, plagioclase, rutile, graphite, indicating conditions of crystallization towards the base of the crust. During pressure decrease related to isostatic uplift, this assemblage breaks down. The two following divariant reactions occur during the retrogressive metamorphism : Gt + Q → Opx + Cd      (1) Gt + Fk + H₂O → Cd + Bi + Q.    (2) According to the presence or absence of H₂O, reaction (1) occurs within the garnet whereas reaction (2) takes place around the garnet margins. The reactions take place under slightly different P.T. and pH₂O conditions owing to local chemical equilibria, and they induce a retrograde Fe — Mg zoning in the garnet. Mineral compositions, together with experimental and topological data, indicate pressures in the range of 5.5 to 6.5 Kbar and temperatures of about 750 °C. The kinetic and thermodynamic conditions did not permit complete equilibration. However, the late crystallization of andalusite in some samples indicates that recrystallization continued to lower pressures and temperatures.Dans les Pyrénées, les paragneiss des écailles granulitiques associées structuralement aux lherzolites montrent une paragenèse primaire à disthène, grenat, feldspath potassique perthitique, quartz, plagioclase, rutile et graphite, suggérant des conditions de cristallisation à la base de la croûte. Au cours d'une diminution de pression attribuée à une remontée isostatique, cet assemblage s'est déstabilisé. Les deux réactions divariantes suivantes se sont produites au cours de cette rétromorphose : Gt + Q → Opx + Cd     (1) Gt + Fk + H₂O → Cd + Bi + Q.    (2) En relation avec la présence ou l'absence d'eau, la réaction (1) a joué à l'intérieur du grenat, tandis que la réaction (2) s'est produite à sa périphérie. Le développement de ces réactions montre l'existence de micro-équilibres ; elles ont induit un zonage rétrograde en fer et magnésium dans le grenat. La composition des minéraux, l'approche topologique et les résultats expérimentaux récents indiquent des pressions comprises entre 5,5 et 6,5 Kbar et une température de 750 °C. La cinétique des réactions n'a pas permis un rééquilibrage total. La cristallisation tardive d'andalousite dans quelques échantillons montre que la recristallisation s'est poursuivie à plus basses pressions et températures.Vielzeuf Daniel. Orthopyroxene and cordierite secondary assemblages in the granulitic paragneisses from Lherz and Saleix (French Pyrenees). In: Bulletin de Minéralogie, volume 103, 1, 1980. pp. 66-78

The retrogressive breakdown of orthopyroxene in an intermediate charnockite from Saleix (French Pyrénées)

An intermediate charnockite from the Saleix granulitic slice shows a primary paragenesis involving perthitic K-feldspar, plagioclase An 30, hypersthene with minor amount of quartz and greatly subordinate clinopyroxene, garnet (and zircon, apatite, rutile, titanomagnetite). During total pressure and temperature decreases, and more especially P H₂O increase, related to crustal thinning, orthopyroxene broke down giving a complex corona involving four well specified rims of actinolite, quartz, biotite, secondary plagioclase. Chemical compositions of the phases are used to balance the reaction with a petrological mixing model. A multivariant reaction of the following form can be balanced : Opx + Kf + Pl I + W ↔ Act + Bi + Pl II + Q. In that reaction, the imbalance in the elements Ba, Cr, Ti and CI is immediately obvious. On the contrary, only the introduction of a volumetric constraint proves that the reaction was not strictly isochemically in equilibrium with respect to major elements. A part of the reaction can be explained only in terms of metasomatism. The excellent correlation between K and Cl in the amphiboles suggests that K was present in a chlorine enriched fluid phase. The simplified reaction Hb + Bi + Q → Opx + Kf + Pl + W has been suggested by de Waard (1965) to account for the diagnostic appearance of orthopyroxene and the tendency for hornblende and biotite to disappear concomitantly. The charnockitic rock from Saleix displays a good exemple of a "frozen" comparable (but retrogressive) reaction which can be considered as an important indicator of the transition from granulite-facies to amphibolite-facies assemblages during retrogressive metamorphism.Une charnockite intermédiaire de l'écaille granulitique de Saleix présente une paragenèse primaire composée de feldspath potassique perthitique, plagioclase An 30, hypersthène, quartz et de quelques rares cristaux de clinopyroxène, grenat (zircon, apatite, rutile, titanomagnétite). Au cours d'une diminution de la pression totale, de la température et plus spécialement d'une augmentation de la pression partielle d'eau, en rapport avec un amincissement crustal, l'orthopyroxène se déstabilise pour donner une structure réactionnelle complexe comprenant quatre couronnes d'actinote, quartz, biotite et plagioclase secondaire. Les compositions chimiques des minéraux sont utilisées pour équilibrer la réaction à l'aide d'un modèle de mélange. Une réaction de la forme suivante peut être proposée : Opx + Fk + Pl I + eau ↔ Act + Bi + Pl II + Q Dans cette réaction, les éléments Ba, Cr, Ti et Cl ne peuvent de toute évidence pas être équilibrés. Par ailleurs, seule l'introduction d'une contrainte volumique démontre que la réaction n'est pas strictement isochimique du point de vue des éléments majeurs. Une partie de la réaction ne peut s'expliquer qu'en terme de métasomatisme. L'excellente corrélation K/Cl dans l'actinote suggère que le potassium était présent dans une phase fluide enrichie en chlore. La réaction simplifiée Hb + Bi + Q → Opx + Fk + Pl + eau a été proposée par de Waard (1965) pour prendre en compte l'apparition de l'orthopyroxène et la disparition concomitante de la hornblende et de la biotite. La charnockite de Saleix offre un excellent exemple d'une réaction "figée" comparable (mais rétromorphique) qui peut être considérée comme un bon indice de la transition faciès granulite - faciès amphibolite durant la rétromorphose et pour ce type de composition chimique.Vielzeuf Daniel. The retrogressive breakdown of orthopyroxene in an intermediate charnockite from Saleix (French Pyrénées). In: Bulletin de Minéralogie, volume 105, 6, 1982. pp. 681-690

Existence d'un fragment de « complexe stratifié » (pyriclasites et anorthosites) associé à la série granulitique du port de Saleix (Pyrénées ariégeoises)

A part of a layered intrusion involving pyriclasites, garnet bearing pyriclasites and anorthosites has been discovered in the granulitic basement from Saleix. Field evidences as well as petrological and mineralogical studies supported by experimental data indicate conditions of primary crystallization from tholeiitic melt towards the base of the crust followed by a recrystallization in the granulite facies near 7-9 kbar and 750-800 °C. This outcrop related to basic granulites associated with the surrounding « kinzigites », could be considered as the upper part of a magmatic complex after the example of Balmuccia (Western Alps, where dunites, harzburgites and pyroxenites complete down the magmatic sequence). Occurrence of the same kind of petrological association at Castillon authorizes a close comparison between the latter area and the outcropping basement at Saleix and suggests a period of intense magmatic activity towards the base of the crust.Un fragment de complexe basique stratifié comportant pyriclasites, pyriclasites à grenat et anorthosites, a été mis en évidence au sein des formations granulitiques de Saleix. Les relations spatiales sur le terrain, les études pétrographiques et minéralogiques appuyées sur les données expérimentales, indiquent que cette intrusion a cristallisé à la base de la croûte, à partir d'un liquide tholéiitique, et a recristallisé dans les conditions du faciès des granulites vers 7-9 kbar et 750-800 °C. Cet affleurement, qui paraît être en relation avec les granulites basiques étroitement associées aux « kinzigites », pourrait représenter la partie supérieure d'un ensemble magmatique comparable à celui de Balmuccia (où dunites, harzburgites et pyroxénites complètent vers le bas la série magmatique). L'existence d'une association similaire dans le Castillon justifie une comparaison étroite entre ce dernier massif et l'écaille de Saleix et indique, pour l'unité structurale ainsi définie, une période d'intense activité magmatique à la base de la croûte.Vielzeuf Daniel. Existence d'un fragment de « complexe stratifié » (pyriclasites et anorthosites) associé à la série granulitique du port de Saleix (Pyrénées ariégeoises). In: Bulletin de Minéralogie, volume 103, 2, 1980. pp. 287-296

Le vase et le microscope : origine et développement d'une connaissance scientifique du corail rouge de Méditerranée (XVIe-XXIe s.)

International audienceRed coral, an emblematic product of the Mediterranean, has been studied by naturalists and scientists since antiquity. Previously classified in the mineral world, Corallium rubrum integrated the world of life at the initiative of Ferdinando di Marsigli and Jean-André Peyssonnel during the eighteenth century. In 1864, Henri de Lacaze-Duthiers published a Natural History of Coral, a major contribution to the physiology of this cnidarian. After tracing the emergence of scientific knowledge concerning the red coral, this study proposes a critical analysis of the work of Henri de Lacaze-Duthiers by bringing its contributions into line with contemporary research.Produit emblématique de la Méditerranée, le corail rouge intéresse naturalistes et savants depuis l’Antiquité. Longtemps rangé dans le monde minéral, Corallium rubruma intégré tardivement le monde du vivant sous l’impulsion des recherches de Ferdinando di Marsigli et de Jean-André Peyssonnel au xviiie siècle. En livrant en 1864 à la communauté scientifique son ouvrage Histoire naturelle du corail, Henri de Lacaze-Duthiers a permis une avancée importante des connaissances de la physiologie de ce cnidaire. Cette étude, après avoir retracé la longue gestation d’une connaissance scientifique du corail rouge, propose une relecture de l’œuvre de ce biologiste français du xixe siècle, en mettant ses apports en écho avec les avancées de la recherche contemporaine

Etude expérimentale des relations de phases dans les métasédiments à haute pression et haute température. Application à la croûte continentale subductée

Des expériences ont été réalisées à partir d'un métagrauwacke et d'une métapélite saturée en silicate d'alumine dans un vaste domaine P-T (P=0,5-0,8 GPa; T=750-1000C) pour étudier les relations de phases dans les roches subduites et les variations de composition des minéraux. Pour le grauwacke , l'assemblage minéralogique phg + cpx + grt + qtz/ coes est stable à P>2,3 GPa, alors que l'assemblage bt +pl + grt + qtz est stable entre 0,5 et 2,0 GPa. pour T<900C,contrairement aux roches basiques , la phg demeure stable à UHP. La présence d'un minéral hydraté lors du pic de P et durand l'exhumation a d'importantes conséquences sur la fusion partielle et la rétromorphose.Contrairement aux roches basiques , l'apport de fluide pas indispensable à la rétromorphose et à la fusion des roches acides subduites puis exhumées. L'examen des principales unités métamorphiques de ultra-haute pression confirme le rôle de la fusion partielle lors de l'exhumation dans la plupart d'entre elles.CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Growth kinetics and distribution of trace elements in precious corals

Vielzeuf, Daniel ... et al.-- 18 pages, 9 figures, 3 tables, supplementary material https://www.frontiersin.org/articles/10.3389/feart.2018.00167/full#supplementary-materialThe concentration and spatial distribution of major (Ca, Mg) and trace elements (Na, Sr, S, Li, Ba, Pb, and U) in different Corallium skeletons (C. rubrum, C. japonicum, C. elatius, C. konojoi) have been studied by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). EMP data show positive Na-Mg and negative Na-S and Mg-S correlations in all skeletons. LA-ICPMS data display additional Sr-Mg, Li-Mg, and U-Mg positive correlations. Medullar zones in the skeletons, corresponding to fast growing zones, are systematically richer in Mg, Na, Sr, Li, and U and poorer in S than the surrounding slow growing zones. These spatial distributions are mostly interpreted in terms of growth kinetics combined with steric effects influencing the incorporation of impurities in biogenic calcites. This interpretation is in agreement with available experimental data on kinetic effects on the incorporation of elements in calcite. At a different scale, annual growth rings in annular slow growing zones show oscillations in Mg, Na, Sr, and S. These chemical oscillations probably result from growth rate variations: fast growth would produce rings enriched in Mg, Sr, and Na, while slow growth would produce rings enriched in Ca, S and organic matter. From previous studies in C. rubrum, the Mg-rich rings would develop during the spring to fall period while the S-rich rings would form immediately after (late fall and winter). Analytical traverses performed in annular zones of different Corallium skeletons indicate that Mg, Na, Sr, Li, and U decrease from core to rim. This observation indicates that radial growth rate decreases as the colony gets older. Contrary to Mg, Na, Sr, Li, S, and U, barium and lead concentrations are identical in medullar and annular zones and appear independent of growth kinetics. Thus, concentrations in Corallium skeletons could provide indications on Ba and Pb contents in the oceans. Barium and lead concentrations are higher in Mediterranean than in Pacific precious corals, these two elements can be used to discriminate C. rubrum from C. japonicum, and contribute enforcing regulations on the trade of precious coralsThis work has been supported by the Centre National de la Recherche Scientifique (CNRS), by the Institut National des Sciences de l’Univers (INSU) through grant INTERRVIE 2017 to DV, by the Agence Nationale pour la Recherche (ANR) through ANR CoRo 2011-2015, by the Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants, and by the European Union COST action TD0903Peer Reviewe