Mn-Cr systematics of carbonates in CM chondrites: Implications for the timing and duration of aqueous alteration     

Simone de Leuw  Alan E. Rubin  John T. Wasson 《Geochimica et cosmochimica acta》2009,73(24):7433-2751

CM chondrites contain carbonates and other secondary minerals such as phyllosilicates, sulfides, sulfates, oxides and hydroxides that are believed to have formed by aqueous alteration reactions on their parent asteroid. We report in situ Mn-Cr isotope measurements in the highly aqueously altered CM2.1 chondrites QUE 93005 and ALH 83100 using secondary ion mass spectrometry (Cameca ims-1270 ion microprobe). The ⁵³Cr excesses are correlated with the ⁵³Mn/⁵⁵Mn ratio and result from the in situ decay of ⁵³Mn, a short-lived radioisotope with a half-life of 3.7 Ma. If we assume that carbonate grains in samples QUE 93005 and ALH 83100 are cogenetic, then the excesses define initial ⁵³Mn/⁵⁵Mn ratios ((⁵³Mn/⁵⁵Mn)₀) of (4.1 ± 1.2) × 10⁻⁶ and (5.1 ± 1.7) × 10⁻⁶, respectively. These values are comparable to those in carbonates from other CM chondrites as reported in the literature. Initial ⁵³Mn/⁵⁵Mn ratios for calculated model isochrones for individual carbonate grains range from (3.8 ± 1.4) × 10⁻⁶ to (4.8 ± 2.1) × 10⁻⁶ for QUE 93005 and from (3.1 ± 1.6) × 10⁻⁶ to (1.3 ± 0.5) × 10⁻⁵ for ALH 83100. A possible interpretation for the ranges in (⁵³Mn/⁵⁵Mn)₀ could be that alteration in individual CM chondrites was episodic and occurred over an extended period of time. However, isochrones based on the entire set of carbonate grains in each of the CM chondrites imply that the degree of aqueous alteration is roughly correlated with the age of carbonate formation in CM chondrites of different subtypes and that alteration on the CM parent asteroid started contemporaneously with or shortly after CAI formation and lasted at least 4 Ma.  相似文献   

Changes of the susceptibility to lava flow invasion induced by morphological modifications of an active volcano: the case of Mount Etna,Italy     

Tarquini  Simone  Favalli  Massimiliano 《Natural Hazards》2010,54(2):537-546

Changes of the susceptibility to lava flow invasion at Mount Etna are quantified by using lava flow simulations on four Digital Elevation Models documenting the morphostructural modifications of the volcano in the time interval 1986–2007. The probabilistic code DOWNFLOW is used to derive the areas invaded by several thousands of lava flows obtaining, for each DEM, maps of the susceptibility to lava flow invasion and of the lava flow hazard. These maps show, for the first time, the evolution of these surficial properties with time, and render a quantitative image of the effects of topographic changes on the preferential lava flow drainage paths. The results illustrate how the emplacement of new lava flows and the growth of scoria cones affect the probability of inundation by lava flows. We conclude that the persistent activity of this volcano requires a frequent updating of the topography for a reliable lava flow hazard assessment.  相似文献   

Toarcian–Aalenian (Early–Middle Jurassic) radiolarian fauna from the Los Molles Formation,Neuquén Basin,Argentina: Taxonomy and paleobiogeographic affinities     

Karlos Guilherme Diemer Kochhann  Simone Baecker-Fauth  Ignacio Pujana  Ariane Santos da Silveira  Gerson Fauth 《Journal of South American Earth Sciences》2011,31(2-3):253-261

This paper reports the occurrence of a Toarcian–Aalenian (Early–Middle Jurassic) radiolarian fauna in the Los Molles Formation, Neuquén Basin, Argentina, as well as comments on its paleobiogeographic affinities. The micropaleontologic analysis was carried out in fine-grained rocks from a turbiditic section of the Los Molles Formation. These samples were first chemically processed using only hydrogen peroxide (H₂O₂), and afterward treated with acetic (CH₃COOH) and hydrofluoric (HF) acids. The first chemical procedure permitted the recovery of only few spongy spumellarians, while the second one enabled to recover more diversified radiolarian assemblages. In general, the studied fauna presents low diversity and abundance, with a strong dominance of spumellarians over nassellarians. The fauna is composed by the genera Paronaella, Homoeoparonaella, Praeconocaryomma, Archaeocenosphaera, Orbiculiformella, Praeparvicingula, and some unidentified spumellarians and nassellarians. According to paleobiogeographic models, the studied Toarcian–Aalenian fauna presents a mid to high latitude affinity. It is possible to infer from those data a bipolar distribution of some taxa, such as Praeparvicingula and probably Praeconocaryomma, between the Northern and Southern hemispheres since the Early Jurassic (Toarcian).  相似文献   

Hindcast of oil-spill pollution during the Lebanon crisis in the Eastern Mediterranean, July-August 2006   总被引：2，自引：0，他引：2  

Coppini G  De Dominicis M  Zodiatis G  Lardner R  Pinardi N  Santoleri R  Colella S  Bignami F  Hayes DR  Soloviev D  Georgiou G  Kallos G 《Marine pollution bulletin》2011,62(1):140-153

MOON (Mediterranean Operational Oceanography Network http://www.moon-oceanforecasting.eu) provides near-real-time information on oil-spill detection (ocean color and SAR) and predictions [ocean forecasts (MFS and CYCOFOS) and oil-spill predictions (MEDSLIK)]. We employ this system to study the Lebanese oil-pollution crisis in summer 2006 and thus to assist regional and local decision makers in Europe, regionally and locally. The MEDSLIK oil-spill predictions obtained using CYCOFOS high-resolution ocean fields are compared with those obtained using lower-resolution MFS hydrodynamics, and both are validated against satellite observations. The predicted beached oil distributions along the Lebanese and Syrian coasts are compared with in situ observations.The oil-spill predictions are able to simulate the northward movement of the oil spill, with the CYCOFOS predictions being in better agreement with satellite observations. Among the free MEDSLIK parameters tested in the sensitivity experiments, the drift factor appears to be the most relevant to improve the quality of the results.  相似文献   

Unraveling the hidden origin and migration of plagioclase phenocrysts by in situ Sr isotopes: the case of final dome activity at Nisyros volcano,Greece     

Eleonora?BraschiEmail author  Lorella?Francalanci  Simone?Tommasini  George?E.?Vougioukalakis 《Contributions to Mineralogy and Petrology》2014,167(3):988

This contribution reports a detailed study on in situ Sr isotope analyses, along with textural and compositional characteristics, of plagioclase phenocrysts occurring in the rhyodacitic dome-lavas and associated mafic enclaves, erupted during the last magmatic activity at Nisyros volcano (Greece). Dome-lavas and enclaves have a paragenesis dominated by plagioclase. We recognize five different types of plagioclase based on their specific textures and composition. Dome-lava plagioclases (Type-1) are mainly large (1–5 mm), subhedral, clear, and poorly zoned crystals with low An content (An_25–35). The plagioclase phenocrysts (Type-4 and Type-5) and groundmass microlites crystallizing in the enclaves, and found in dome-lavas as xenocrysts, have high An content (An_75–95). In both dome-lavas and enclaves, two other types of plagioclase do also occur: (1) plagioclase phenocrysts with size and core composition similar to those of Type-1 having a dusty sieve zone (DSZ) at the rims (Type-2); (2) plagioclases with a DSZ affecting the entire crystal but a thin rim (Type-3). The drilled plagioclases have ⁸⁷Sr/⁸⁶Sr negatively correlated with their An content. Low An cores of Type-1 and Type-2 have quite homogeneous ⁸⁷Sr/⁸⁶Sr (0.7044–0.7046), whose values are more radiogenic than their host magmas (0.70403–0.70408) and similar to those of the previous Upper Pumice (UP) rhyolite magma (0.70438–0.70456). The DSZs of Type-2 and Type-3 show lower and scattered ⁸⁷Sr/⁸⁶Sr (0.70397–0.70426) with intermediate and variable An content. High An cores of Type-4 and Type-5 have the least radiogenic Sr isotope composition (0.70379) in equilibrium with that measured in the enclaves (0.70384–0.70389). We demonstrate that Type-1 plagioclase crystallizes in the previous UP rhyolitic magmas representing the silica-rich magma from which the dome-lava melts derived by open system evolutionary processes (e.g., mixing, mingling, and crystal migration), caused by successive refilling of mafic enclave-forming magma. The Type-2 plagioclase derives from entrainment of Type-1 into the still molten enclave magma. The DSZs originated in response to the interaction between the low An plagioclase and the enclave mafic melt in which dissolution and re-crystallization acted together as function of the interaction time. Type-1 and Type-2 plagioclases record, therefore, a long-lived timescale of events starting from their crystallization in the UP rhyolite. Instead, the different width of DSZs (Type-2 and Type-3) seems to indicate short different interaction timescales between the single crystals and the enclave melt (from few hours to some 40 days). These microanalytical data contribute to the understanding of the origin of the rhyodacitic dome-lavas at Nisyros volcano and to set robust constraints on the dynamics of mingling/mixing processes in terms of crystal exchange pathways and enclave disaggregation.  相似文献   

A Simulation Method for Semicollisional Plasmas     

Filippo Pantellini  Simone Landi 《Astrophysics and Space Science》2001,277(1-2):149-152

We present a one dimensional kinetic simulation model which can be used to simulate the stationary state of a semicollisional plasma. Results of a simple simulation are presented and compared to Fokker-Planck calculations. The model is particularly well suited for the diluted solar atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Weak lensing by galaxies in groups and clusters – I. Theoretical expectations     

Xiaohu Yang  H. J. Mo  Frank C. van den Bosch  Y. P. Jing  Simone M. Weinmann  M. Meneghetti 《Monthly notices of the Royal Astronomical Society》2006,373(3):1159-1172

Three of the six southern Clube Areas that were mainly observed at the European Southern Observatory and whose principal results are given in Paper XVI are marginally observable from Haute-Provence. Additional measurements obtained on several observing runs there enabled orbits to be determined (in most cases rather poorly, owing to the paucity of data) for 30 of the newly discovered spectroscopic-binary systems; they are presented in this paper. One object, HD 33978, seems to be of such significance that special efforts have been made, largely by Drs J. Andersen and H. Lindgren, to obtain additional radial-velocity measurements. That system is shown to be a double-lined binary with a period of only 10.67 d despite one of its components being a late-type giant. The giant star has a projected rotational velocity of almost 40 km s⁻¹; it could be expected to exhibit RS CVn-type photometric variations, which have not yet been observed, in addition to the 'ellipsoidal variation', discovered by Hipparcos , which occasioned its designation as VV Lep.  相似文献   

Properties of galaxy groups in the Sloan Digital Sky Survey – II. Active galactic nucleus feedback and star formation truncation     

Simone M. Weinmann  Frank C. van den Bosch  Xiaohu Yang  H. J. Mo  Darren J. Croton  Ben Moore 《Monthly notices of the Royal Astronomical Society》2006,372(3):1161-1174

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Correction to: CrystalMom: a new model for the evolution of crystal size distributions in magmas with the quadrature-based method of moments     

Simone?ColucciEmail authorView author&#;s OrcID profile  Mattia?de’?Michieli Vitturi  Patrizia?Landi 《Contributions to Mineralogy and Petrology》2018,173(4):32

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Latitudinal Trends and Drivers in the CO2–Carbonic Acid System of Papahānaumokuākea Marine National Monument     

Andrea K. Kealoha  Samuel E. Kahng  Fred T. Mackenzie  Simone R. Alin  Randall K. Kosaki  Russell E. Brainard  Christopher D. Winn 《Aquatic Geochemistry》2015,21(6):535-553

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