Experimental abiotic alteration of igneous and manufactured glasses     

Martin R. Fisk  Jean-Louis Crovisier  José Honnorez 《Comptes Rendus Geoscience》2013,345(4):176-184

Pits in ocean basalt glass are often attributed to the activity of microorganisms, however, neither the mechanism of formation of pits in glass nor the involvement of microorganisms have been confirmed by experimentation. Experimental abiotic corrosion of basalt glass with 1% hydrofluoric acid (HF), a proxy for more slowly acting organic acids, produces pits that are similar in size, shape, and distribution to pits found in basalt glass collected from the ocean floor and basalt glass incubated with microorganisms. This pit formation by HF etching was demonstrated by comparing secondary electron images taken before and after the acid treatment. The formation of pits by abiotic corrosion of basalt glass is an alternate hypothesis for the origin of these features, and the interpretation of these features as biomarkers may require a resolution of these alternative hypotheses.  相似文献   

Intra-oceanic settings of the western Mexico Late Jurassic-Early Cretaceous arc sequences. Implications for the Pacific-Tethys geodynamic relationships during the Cretaceous     

Marc Tardy  Henriette Lapierre  Jean-Louis Bourdier  Christian Couloni  R. Juventino Martinezr  H. Enrique Ortiz 《Geodinamica Acta》2013,26(3):174-185

Abstract

The Guerrero suspect terrane composed of Late Jurassic-Early Cretaceous sequences, extends from Baja California up to Acapulco and is considered to be coeval with the Late Mesozoic igneous and sedimentary arc sequences of the Greater Antilles, Venezuela and Western Cordillera of Colombia. New geological, petrological and geochemical data from central and southern Mexico, led us to propose a new model for the building of the Alisitos-Teloloapan arc. This arc, partly built on the Pacific oceanic lithosphere and partly on continental fragments, could be related to the subduction of an oceanic basin - the Arperos basin - under the Paleo-Pacific plate. This subduction was dipping southwest.

At the beginning of the magmatic activity of the oceanic segment of this arc, depleted tholeiitic basalts were emitted in a submarine environnement below the CCD. While subduction was going on, the arc magmas evolved from LREE depleted tholeiites to slightly LREE enriched tholeiites and then, to calc-alkaline basalts and andesites enriched in LREE and HFSE. Concurrently, the arc sedimentary environment changed from deep oceanic to neritic with the deposition of Aptian-Albian reefal limestones, at the end of the arc building. In the continent-based segment, the arc magmas are exclusively differentiated calc-alkaline suites depleted in HREE and Y, formed of predominantly siliceous lavas and pyroclastic rocks, emitted in a sub-aerial or shallow marine environment.

Thus, taking into account this above mentioned model, the Cretaceous volcanic series, accreted to the margins of cratonal America, in Colombia, Venezuela, Greater Antilles and Mexico, could be related to the same west-south-west dipping subduction of oceanic basins, fringing the North and South American continental cratons and connected directly with the inter-American Tethys. While the subduction was proceeding, this magmatic arc drifted towards the North and South American cratons and finally, collided with the continental margins at different periods during the Cretaceous.  相似文献   

Le magmatisme basique calcoalcalin d'âge dévono-dinantien du nord du Massif Central,témoin d'une marge active hercynienne: arguments géochimiques et isotopiques Sr/Nd     

Christian Pin  Jean-Louis Paquette 《Geodinamica Acta》2013,26(1):63-77

Abstract

Samples of volcanic rocks from the main outcrops of Devono-Dinantian series in northern Massif-Central have been studied for Sr and Nd isotopes and immobile incompatible trace elements. In addition, two intrusive bodies of dioritic composition have been dated at 365 ± 3 Ma (Aydat) and 360 ± 1 Ma (Beaumont-Huriel), using the U/Pb zircon method. Together with geochemical data, these ages show that all the studied rocks belong to the same igneous episode. Based on trace element and radiogenic isotopes (⁸⁷Sr/⁸⁶Sr_i from 0,7041 to 0,7057; εNd_i from +1.5 to +5.0), the Late Devonian and Early Carboniferous igneous rocks bear distinct similarities with magmas produced in modern active margin settings. Combined with independent evidence for the occurrence of Devonian oceanic lithosphere in the northern branch of the Variscides, these geochemical affinities suggest that southward subduction of oceanic crust prevailed during the Late Devonian in northern Massif-Central. As a corollary, it appears that true continent-continent collision did not occur before Early Carboniferous times. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.  相似文献   

Coupes équilibrées à travers le massif subalpin de la Chartreuse     

Jean-Louis Mugnier  Réjane Arpin  François Thouvenot 《Geodinamica Acta》2013,26(2):125-137

Résumé

Pour étudier la tectonique des chaînes subalpines du Nord, et proposer un modèle cinématique régional, nous avons utilisé les résultats d’une expérience géophysique réalisée en 1985, et les observations géologiques de surface publiées à ce jour. Ces données ont été analysées de manière à préciser le style tectonique, le positionnement des failles par rapport aux horizons stratigraphiques et le schéma de branchement des failles. La construction simultanée d’une coupe interprétative, d’une coupe restaurée et d’une carte de branchement des failles a permis d’estimer l’amplitude du raccourcissement par la méthode des coupes équilibrées. Au niveau du Nord de la Chartreuse, la valeur minimale du raccourcissement global est de 14 km, 4 km étant associés au système chevauchant du Jura et 10 km à celui du massif des Bornes et des Bauges. Compte tenu des imprécisions existant sur les données utilisées, trois modèles cinématiques, qui correspondent à une plage de raccourcissement comprise entre 14 et 25 km, sont proposés.  相似文献   

In situ heavy metals (copper, lead and cadmium) in different plankton compartments and suspended particulate matter in two coupled Mediterranean coastal ecosystems (Toulon Bay, France)     

Rossi N  Jamet JL 《Marine pollution bulletin》2008,56(11):1862-1870

We monitored the concentrations of copper, lead and cadmium in seawater, in suspended particulate matter (SPM) and in bacteria, phyto- and zooplankton communities separated from abiogenic particles, over a one year cycle in two coupled Mediterranean coastal ecosystems (Little Bay (LiB) and Large Bay (LaB)). Metals were present in seawater in the order Cu > Pb > Cd in both bays and showed important variations within the same month than among months. In LiB, their concentrations were between 0.62 and 2.82 μg Cu l⁻¹, 0.16 and 19 μg Pb l⁻¹ and 0.007 and 0.14 μg Cd l⁻¹, respectively, whereas in LaB, they were between 0.23 and 2.11 μg Cu l⁻¹, 0.09 and 0.76 μg Pb l⁻¹ and not detected and 0.65 μg Cd l⁻¹. SPM play an important role on metal adsorption, especially for copper. Bioaccumulation factors showed that bacteria and phytoplankton accumulate metals whereas zooplankton tends to biodiminish them in the plankton food web.  相似文献   

The region on the core–mantle boundary where a geostrophic velocity field can be determined from frozen-flux magnetic data     

George E. Backus  Jean-Louis Le Mouël 《Geophysical Journal International》1987,88(1):321-322

  相似文献   

Mn-Cr systematics of the early Solar System revisited     

A. Trinquier  J.-L. Birck  C. Göpel 《Geochimica et cosmochimica acta》2008,72(20):5146-5163

We have reinvestigated the Mn-Cr systematics in a number of primitive meteorites, differentiated planetesimals and terrestrial planets in order to address the chronology of the early stages of protoplanetary disk evolution and planetary formation. Our analytical procedure is based on the assumption of terrestrial abundances for ⁵⁰Cr and ⁵²Cr only; recognizing that a data reduction scheme based on Earth-like ⁵⁴Cr/⁵²Cr abundances in all meteorites is not tenable. Here we show that initial ε_⁵³Cr compositions of ⁵⁴Cr-rich and ⁵⁴Cr-poor acid leach fractions in the primitive carbonaceous chondrite Orgueil differ by 0.9ε, reflecting primordial mineral-scale heterogeneity. However, asteroidal processing effectively homogenized any ε_⁵³Cr variations on the planetesimal scale, providing a uniform present-day solar ε_⁵³Cr=0.20±0.10. Thus, our ⁵³Mn-⁵³Cr data argue against the previously suggested ⁵³Mn heliocentric gradient. Instead, we suggest that inner Solar System objects possessed an initially homogeneous ⁵³Mn/⁵⁵Mn composition, which determined by two independent means is estimated at (6.28 ± 0.66) × 10⁻⁶. Our revised Mn-Cr age for Ste. Marguerite (SM) metamorphism of 4562.9 ± 1.0 Ma is identical to the Pb-Pb age of SM phosphates. Using this age, we confirm that mantle differentiation of the eucrite parent body occurred 4564.9 ± 1.1 Ma ago, and revise the time interval between this event and CAI formation to 2.2 ± 1.1 Ma. We also constrain metamorphism in carbonaceous chondrites of type 2 and 3 to have occurred between 1 and 6 Ma after CAI formation. The ⁵³Mn-⁵³Cr correlation among chondrites, planetesimals and terrestrial planets (the eucrite parent body, Mars and Earth) provides evidence for Mn/Cr fractionation within the protoplanetary disk recorded by all precursor materials of the terrestrial planets and primitive asteroids. This fractionation appears to have occurred within 2 Ma of CAI formation.  相似文献   

Modeling of the transport and deposition of tungsten in the scheelite-bearing calc-silicate gneisses of the Montagne Noire,France     

François Gibert  Bernard Moine  Jacques Schott  Jean-Louis Dandurand 《Contributions to Mineralogy and Petrology》1992,112(2-3):371-384

Scheelite-bearing calc-silicate gneisses (CSG) oceur in the Montagne Noire within a series of dominant micaschists. Detailed petrographical and mineralogical studies reveal three successive stages of metamorphism and hydrothermal alteration: (1) stage 1, a regional metamorphism at 550°C and 4.5 kb where no mineralization is formed; (2) stage 2a, a hydrothermal alteration at 500 to 450°C and 4 to 3 kb which is characterized by an intense sericitization of feldpars and deposition of Sn in Sn-bearing cale-silicates; and (3) stage 2b, a hydrothermal alteration characterized by the crystallization of idocrasegrossular in CSG with concomittant precipitation of scheelite. Tungsten was transported through the micaschist environment and deposited as scheelite only in the CSG of stage 2b at relatively low pressures. To characterize the mechanism of tungsten transport, tungsten speciation at high P-T and scheelite solubility in aqueous solations buffered by the CSG and by the micaschists assemblages were calculated. It was found that H₂WO ₀ ⁴ , HWO _- ⁴ and WO _2- ⁴ are the dominant tungsten aqueous species in H₂O–NaCl (one molal) solutions at 500°C and 2–4 kb. Calculations also indicate that scheelite deposition is controlled by decreasing pressure and increasing activity of aqueous calcium in this system. This is consistent with the petrographical and mineralogical observations. The consequences of the presence of volatiles (N₂, CH₄, CO₂) in the regional fluids were examined by determining the effect of N₂ on tungsten speciation and scheelite solubility. The addition of N₂ (up to 10 mol%) to the mineralizing fluids results in a marked increase in H₂WO ₀ ⁴ and HWO _- ⁴ concentrations relative to WO _2- ⁴ and in a large decrease of scheelite solubility. This mechanism favours scheelite precipitation and accounts for the commonly observed association of W (and Sn) deposits with graphitic series generating mixed volatiles fluids.  相似文献   

Sedimentation, distribution and diagenesis of organic matter in a recent carbonate environment, Abu Dhabi, U.A.E.     

Fabien Kenig  Alain Y. Huc  Bruce H. Purser  Jean-Louis Oudin 《Organic Geochemistry》1990,16(4-6)

In the modern hypersaline carbonate lagoon and sabkha sedimentary environments of Abu Dhabi (United Arab Emirates), three types of organic matter originate respectively from microbial mat, Avicennia mangrove, and Halodule lagoonal seagrass. The study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo-sedimentary facies based on geochemical and sedimentological criteria. This permits the construction of an organo-sedimentary sequence which expresses the Holocene sedimentary record involving a transgressive and a regressive sequence. The various organic facies occur in both sequences.Heterogeneity within the individual organic facies reflects several factors, including sedimentation dynamics, mineral matrix, oxidation and reduction, and selective organic and mineral diagenesis. These parameters are discussed in terms of depositional environment and location within the organo-sedimentary sequence. Changes in distribution, quantity, and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates.  相似文献   

Cadmium bioconcentration in the echinoid Paracentrotus lividus: Influence of the cadmium concentration in seawater     

Michel Warnau  Jean-Louis Teyssié  Scott W. Fowler 《Marine environmental research》1997,43(4):303-314

Uptake and loss kinetics of cadmium were studied in Paracentrotus lividus exposed for 24 d to different stable Cd concentrations (0 to 1.14 μg Cd l⁻¹) and ¹⁰⁹Cd tracer added to seawater. The whole-body uptake kinetics were linear over the time course of the experiment. The whole-body ¹⁰⁹Cd concentration factor was independent of the stable Cd concentration in ambient seawater. Bioconcentration of Cd in whole individuals and their body compartments was directly proportional to the Cd concentration added to the seawater. The echinoid digestive tract wall showed the highest degree of Cd uptake. Whole-body loss kinetics were described by a 2-component exponential equation. The loss kinetics were similar for each of the treatments examined. Cadmium was found to display a long biological half-life in echinoid tissues; the major fraction (73 to 85%) of the Cd taken up by echinoids was eliminated following a loss component whose biological half-life was of the order of 1 year, regardless of the absolute Cd concentration accumulated by the echinoid. Paracentrotus lividus is suggested as a valuable biomonitor of Cd, particularly where knowledge of Cd concentration variations over long-term is of interest.  相似文献