The iron record of asteroidal processes in carbonaceous chondrites     

A. Garenne  P. Beck  G. Montes‐Hernandez  L. Bonal  E. Quirico  O. Proux  J.L. Hazemann 《Meteoritics & planetary science》2019,54(11):2652-2665

The valence of iron has been used in terrestrial studies to trace the hydrolysis of primary silicate rocks. Here, we use a similar approach to characterize the secondary processes, namely thermal metamorphism and aqueous alteration, that have affected carbonaceous chondrites. X‐ray absorption near‐edge structure spectroscopy at the Fe‐K‐edge was performed on a series of 36 CM, 9 CR, 10 CV, and 2 CI chondrites. While previous studies have focused on the relative distribution of Fe⁰ with respect to oxidized iron (Fe_ox = Fe²⁺ + Fe³⁺) or the iron distribution in some specific phases (e.g., Urey–Craig diagram; Urey and Craig 1953), our measurements enable us to assess the fractions of iron in each of its three oxidation states: Fe⁰, Fe²⁺, and Fe³⁺. Among the four carbonaceous chondrites groups studied, a correlation between the iron oxidation index (IOI = [2(Fe²⁺) + 3(Fe³⁺)]/[Fe_TOT]) and the hydrogen content is observed. However, within the CM group, for which a progressive alteration sequence has been defined, a conversion of Fe³⁺ to Fe²⁺ is observed with increasing degree of aqueous alteration. This reduction of iron can be explained by an evolution in the mineralogy of the secondary phases. In the case of the few CM chondrites that experienced some thermal metamorphism, in addition to aqueous alteration, a redox memory of the aqueous alteration is present: a significant fraction of Fe³⁺ is present, together with Fe²⁺ and sometimes Fe⁰. From our data set, the CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR chondrites, the three oxidation states of iron coexist. Even in the least‐altered CR chondrites, the fraction of Fe³⁺ can be high (30% for MET 00426). This observation confirms that oxidized iron has been integrated during formation of fine‐grained amorphous material in the matrix (Le Guillou and Brearley 2014; Le Guillou et al. 2015; Hopp and Vollmer 2018). Last, the IOI of CV chondrites does not reflect the reduced/oxidized classification based on metal and magnetite proportions, but is strongly correlated with petrographic types. The valence of iron in CV chondrites therefore appears to be most closely related to thermal history, rather than aqueous alteration, even if these processes can occur together (Krot et al. 2004; Brearley and Krot 2013).  相似文献   

Comparison of methods used for computing the impact of sound on the marine environment     

Schecklman S  Houser D  Cross M  Hernandez D  Siderius M 《Marine environmental research》2011,71(5):342-350

Concern about the impact of sound on marine mammals has increased over the last decade, causing governments to take a more rigorous look at the potential impact of activities that introduce sound into the ocean. Environmental Impact Statements (EIS's) can be prepared using differing analysis methods to estimate the impact on marine mammals. To assess consistency in assessment methods, differences in the base assumptions were investigated; in particular, differences that arise between assumptions of dynamic marine mammals (animat method) and static distributions of marine mammals (static distribution method). Using several ocean environment scenarios and species, it is demonstrated that differences consistently arise between the two methods. The static distribution method underestimates the number of behavioral harassments compared with the animat method. Repeating many simulations with the animat method provides a robust risk assessment, provides a measure of variability, and allows the probability of "spurious events" to be estimated.  相似文献   

Landscape and climate change threats to wetlands of North and Central America   总被引：1，自引：1，他引：0  

William J. Mitsch  Maria E. Hernandez 《Aquatic Sciences - Research Across Boundaries》2013,75(1):133-149

North and Central America has a combined total of 2.5 million km² of wetlands, with 51 % in Canada, 46 % in the USA, and the remainder in subtropical and tropical Mexico and Central America. Loss rates are well known for the conterminous USA and for parts of Canada but poorly understood for Mexico and Central America. Wetlands of North America continue to be threatened due to drainage for agriculture and urban development, extreme coastal and river management, water pollution from upstream watersheds, peat mining, waterfowl management, and more recently climate change. Human use of wetlands in this region are many, including receiving ecosystem services such as water purification, flood regulation, climate regulation, and direct provisioning benefits for many cultures living in and among wetlands, especially in the Louisiana Delta and in Mexico and Central America. Climate change affects will cause wetland impacts on coastal wetlands due to sea level rise and on inland wetlands due to changes in precipitation, air temperature, and river discharges. Wetlands, in turn, have a major role in the storage of carbon in boreal regions of Canada and with carbon sequestration in temperate and tropical wetlands of the Americas.  相似文献   

A Virgo high-resolution Hα kinematical survey – II. The Atlas     

L. Chemin  C. Balkowski †  V. Cayatte †  C. Carignan †  P. Amram †  O. Garrido  O. Hernandez †  M. Marcelin †  C. Adami  A. Boselli  J. Boulesteix 《Monthly notices of the Royal Astronomical Society》2006,366(3):812-857

A catalogue of ionized gas velocity fields for a sample of 30 spiral and irregular galaxies of the Virgo cluster has been obtained by using 3D optical data. The aim of this survey is to study the influence of high-density environments on the gaseous kinematics of local cluster galaxies. Observations of the Hα line by means of Fabry–Perot interferometry have been performed at the Canada–France–Hawaii Telescope, European Southern Observatory 3.6-m telescope, Observatoire de Haute-Provence 1.93-m telescope and Observatoire du mont Mégantic telescope at angular and spectral samplings from 0.4 to 1.6 arcsec and 7 to 16 km s⁻¹. A recently developed, automatic and adaptive spatial binning technique is used to reach a nearly constant signal-to-noise ratio (S/N) over the whole field of view, allowing us to keep a high spatial resolution in high-S/N regions and extend the detection of signal in low-S/N regions. This paper is part of a series and presents the integrated emission-line and velocity maps of the galaxies. Both Hα morphologies and kinematics exhibit signs of perturbations in the form of, for example, external filaments, inner and nuclear spiral- and ring-like structures, inner kinematical twists, kinematical decoupling of a nuclear spiral, streaming motions along spiral arms and misalignment between kinematical and photometric orientation axes.  相似文献   

Chemical evolution models of local dwarf spheroidal galaxies     

Leticia Carigi  Xavier Hernandez  Gerard Gilmore 《Monthly notices of the Royal Astronomical Society》2002,334(1):117-128

We calculate chemical evolution models for four dwarf spheroidal (dSph) satellites of the Milky Way (Carina, Ursa Minor, Leo I and Leo II) for which reliable non-parametric star formation histories have been derived. In this way, the independently-obtained star formation histories are used to constrain the evolution of the systems we are treating. This allows us to obtain robust inferences on the history of such crucial parameters of galactic evolution as gas infall, gas outflows and global metallicities for these systems. We can then trace the metallicity and abundance ratios of the stars formed, the gas present at any time within the systems and the details of gas ejection, of relevance to enrichment of the galaxies environment. We find that galaxies showing one single burst of star formation (Ursa Minor and Leo II) require a dark halo slightly larger that the current estimates for their tidal radii, or the presence of a metal-rich selective wind that might carry away much of the energy output of their supernovae before this might have interacted and heated the gas content, for the gas to be retained until the observed stellar populations have formed. Systems showing extended star formation histories (Carina and Leo I), however, are consistent with the idea that their tidally-limited dark haloes provide the necessary gravitational potential wells to retain their gas. The complex time structure of the star formation in these systems remains difficult to understand. Observations of detailed abundance ratios for Ursa Minor strongly suggest that the star formation history of this galaxy might in fact resemble the complex picture presented by Carina or Leo I, but localized at a very early epoch.  相似文献   

Simulation-optimization model for water management in hydraulic fracturing operations     

E. A. Hernandez  V. Uddameri 《Hydrogeology Journal》2015,23(6):1247-1265

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Inland aeolian deposits of south‐west France: facies,stratigraphy and chronology     

Pascal Bertran  Mark D. Bateman  Marion Hernandez  Norbert Mercier  Dominique Millet  Luca Sitzia  Jean‐Pierre Tastet 《第四纪科学杂志》2011,26(4):374-388

Archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of Pleistocene aeolian deposits in south‐west France. A chronological framework for deposition has been obtained using both radiocarbon (n = 24) and luminescence (n = 26) dating. It shows that aeolian transport was very active during the Late Pleniglacial, between 15 and ～23 ka, leading to sand emplacement over a 13 000‐m² area at the centre of the basin. The Pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east. Subsequent aeolian phases, at ca. 12 ka (Younger Dryas) and 0.8–0.2 ka (Little Ice Age), correspond to the formation of more localized and higher, mainly parabolic dunes. At the southern and eastern margins of the coversand area, aeolian dust accumulated to form loess deposits, the thickness of which reaches ～3 m on the plateaus. Luminescence dates together with interglacial‐ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial–interglacial cycles. The chronology of sand and loess deposition thus appears to be consistent with that already documented for northern Europe. This suggests that it was driven by global climate changes in the northern hemisphere. The relatively thin aeolian deposits (and particularly loess) in south‐west France is thought to reflect both a supply‐limited system and a moister climate than in more northern and continental regions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A dimensional study of disc galaxies     

X. Hernandez  B. Cervantes-Sodi 《Monthly notices of the Royal Astronomical Society》2006,368(1):351-360

We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies.  相似文献   

Evidence for high silicic melt circulation and metasomatic events in the mantle beneath alkaline provinces: the Na–Fe-augitic green-core pyroxenes in the Tertiary alkali basalts of the Cantal massif (French Massif Central)     

S. Pilet  J. Hernandez  B. Villemant 《Mineralogy and Petrology》2002,76(1-2):39-62

Summary ?Na–Fe augitic green-core pyroxenes (hereafter called GCPX) are common in the silica-undersaturated basaltic rocks of many magmatic alkaline provinces. In the Cantal massif, green-core pyroxenes occur in nearly all the Supracantalian basalts (9.5 to 2 Ma), in contrast to the Infracantalian basalts (13 to 9.5 Ma) where they are rarely observed. An electron microprobe study demonstrates that the GCPX crystallized from evolved melts at intermediate to high pressures. Both Supra- and Infracantalian basalts show major and trace-element compositions similar to those of Ocean Island Basalts (OIB). However, the Supracantalian basalts exhibit an additional enrichment in Nb and Ta which we ascribe to a metasomatic event in the magma source. This enrichment could be related to the remobilization of metasomatic Ta and Nb-rich oxides located on grain boundaries in mantle peridotites (Bodinier et al., 1996). The hypothesis of the percolation of Si and K-rich metasomatic melts through the mantle is invoked to explain the deposition of these Ta–Nb oxides. On the basis of mineralogical and geochemical arguments, we suggest a relationship between these melts, the timing of the percolation and the formation of GCPX observed in Cantal basalts. We propose that GCPX crystallized in a melt differentiated by “percolative fractional crystallization” (PFC –Harte et al., 1993), a process which would account for the similar major-element composition of the GCPX and pyroxenes observed in the phonolites of the Cantal massif. Amphibolitic siliceous metasomatic veins in peridotite xenoliths recently described by Wulff-Pedersen et al. (1999) contain augites similar in composition to the GCPX in Cantal basalts, in addition to Nb-rich oxides. This confirms the genetic relationship between metasomatic melts, GCPX and Nb-rich oxide parageneses. GCPX would therefore seem to be linked to a metasomatic event which took place both/either during and/or between the two main stages of basaltic outpouring, and is consequently contemporaneous with the volcanism. We suggest that this process may represent a common mechanism in many alkaline provinces, where asthenospheric upwelling generates silicic metasomatizing liquids by PFC. This metasomatic process is inferred to deposit accessory phases within the lithospheric mantle, a process followed by the subsequent inheritance of this metasomatic imprint by the younger basalts. Received February 2, 2001; revised version accepted September 24, 2001  相似文献   

Potassium enrichment by magma mixing and vapor exsolution: an example in the miocene volcanism of eastern Morocco     

J. Hernandez 《Bulletin of Volcanology》1982,45(4):385-399

Miocene volcanism in eastern Morocco is comprised of potash rich calc-alkalic and alkaline rocks. In the southern part of the area, at the base of the Guilliz massif, basic inclusions are found in latites. From a petrological, geochemical and mineralogical study of both latites and their inclusions, it appear that the inclusions represent a basic liquid quenched in the latitic magma, inside the magma chamber. As a result of the drop in pressure and crystallization, a K-rich vapour phase separated from the inclusion-forming liquid and percolated the latitic magma, increasing the K₂O content of the latter and possibly triggering eruptions. The mixing process between the two magmas seems supported by density and viscosity estimations. Calculations show that for temperatures ranging from 700 °C to 1000 °C and H₂O contents from 1.6 to 5%, the inclusion forming liquid is less dense than the latitic liquid and can therefore ascend into the latitic magma by interface disequilibrium and flotation.  相似文献