The Lithium, Boron and Beryllium content of serpentinized peridotites from ODP Leg 209 (Sites 1272A and 1274A): Implications for lithium and boron budgets of oceanic lithosphere   总被引：2，自引：0，他引：2  

Flurin Vils  Laure Pelletier  Othmar Müntener 《Geochimica et cosmochimica acta》2008,72(22):5475-5504

Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 μg g⁻¹) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 μg g⁻¹), depleted in Li (most values below 1 μg g⁻¹) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 μg g⁻¹), H₂O and Cl contents and to lower Li contents (0.07-3.37 μg g⁻¹) of peridotites, implying that—contrary to alteration of oceanic crust—B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at 1 and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of 1 m × 1 m × thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li.  相似文献   

Geodetic accuracy of the Macrometer model V-1000     

Y. Bock  R. I. Abbot  C. C. Counselman  S. A. Gourevitch  R. W. King  A. R. Paradis 《Journal of Geodesy》1984,58(2):211-221

The Macrometer Model V-1000 is a geodetic positioning instrument that uses the radio signals broadcast by the GPS satellites. The Macrometer is the only GPS user equipment commercially available that does not require any of the GPS codes. The Model V-1000 receives only the 19-cm wavelength signals from GPS although similar instruments, built for the U.S. Air Force Geophysics Laboratory, receive both the 19-and the 24-cm wavelengths. In this paper we summarize the results of two years of field testing of the V-1000. This instrument, observing four or five satellites fof a few hours, yields a point position accurate within several meters in each coordinate: latitude, longitude and ellipsoidal height. All three components of the relative position vector between a pair of points can be determined within 2 parts per million of the distance, given a similar schedule of observations. This accuracy has been obtained for intersite distances from one kilometer to several thousand kilometers. Macrometer is a trademark of Aero Service Division, Western Geophysical Company of American, 8100 Westpark Drive, Houston, Texas, 77063, U.S.A.  相似文献   

Coniferization of the mixed‐wood boreal forests under warm climate     

Ccile C. Remy  Dominic Senici  Han Y. H. Chen  Yves Bergeron  Martin Lavoie  Laure Paradis  Adam A. Ali 《第四纪科学杂志》2019,34(7):509-518

Mixed‐wood boreal forests are characterized by a heterogeneous landscape dominated by coniferous or deciduous species depending on stand moisture and fire activity. Our study highlights the long‐term drivers of these differences between landscapes across mixed‐wood boreal forests to improve simulated vegetation dynamics under predicted climate changes. We investigate the effects of main climate trends and wildfire activities on the vegetation dynamics of two areas characterized by different stand moisture regimes during the last 9000 years. We performed paleofire and pollen analyses in the mixed‐wood boreal forest of north‐western Ontario, derived from lacustrine sediment deposits, to reconstruct historical vegetation dynamics, which encompassed both the Holocene climatic optimum (ca. 8000–4000 a bp ) and the Neoglacial period (ca. 4000 a bp ). The past warm and dry period (Holocene climatic optimum) promoted higher fire activity that resulted in an increase in coniferous species abundance in the xeric area. The predicted warmer climate and an increase in drought events should lead to a coniferization of the xeric areas affected by high fire activity while the mesic areas may retain a higher broadleaf abundance, as these areas are not prone to an increase in fire activity. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

Detailed Analysis of Solar Data Related to Historical Extreme Geomagnetic Storms: 1868 – 2010     

Laure Lefèvre  Susanne Vennerstrøm  Mateja Dumbović  Bojan Vršnak  Davor Sudar  Rainer Arlt  Frédéric Clette  Norma Crosby 《Solar physics》2016,291(5):1483-1531

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The Revised Brussels–Locarno Sunspot Number (1981 – 2015)     

Frédéric Clette  Laure Lefèvre  Marco Cagnotti  Sergio Cortesi  Andreas Bulling 《Solar physics》2016,291(9-10):2733-2761

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Mapping waterholes and testing for aridity using a remote sensing water index in a southern African semi-arid wildlife area     

Zorodzai Dzinotizei  Amon Murwira  Fadzai M. Zengeya  Laure Guerrini 《国际地球制图》2013,28(11):1268-1280

Abstract

Waterholes are a key resource that influences wildlife distribution in semi-arid ecosystems. Mapping waterholes can guide intervening decisions for supplementing water resources and managing wildlife distribution patterns. Although remote sensing provides a key to mapping distribution of waterholes, efficiency of existing remotely sensed methods for detecting waterholes have to be evaluated and even new ones developed. In this study, we evaluated performance of the Modified Normalized Difference Water Index (MNDWI) and Superfine Water Index (SWI) at selected optimum thresholds. Kappa results indicated that MNDWI detects waterholes better than SWI. We further validated MNDWI detected waterholes by testing response of waterhole area to temporal rainfall variability and waterhole persistence to spatial rainfall variability. Extent of MNDWI-detected waterholes varied in relation to temporal rainfall variability (p < 0.05). Waterhole persistence was not associated with spatial rainfall variability which could be explained by differences in waterhole types or low spatial rainfall variability.  相似文献   

Hydrocarbons in coastal sediments from the Mediterranean sea (Gulf of Fos area, France)   总被引：2，自引：0，他引：2  

Mille G  Asia L  Guiliano M  Malleret L  Doumenq P 《Marine pollution bulletin》2007,54(5):566-575

Sedimentary hydrocarbons have been studied quantitatively and qualitatively in 11 coastal stations located in the Gulf of Fos (French Mediterranean coast). Hydrocarbon levels ranged from 10 to 260 mg kg(-1) sed. dry weight. A new parameter "NAR" (Natural n-alkane ratio) is proposed to evaluate the contribution of terrestrial inputs of hydrocarbons in the sediments. The origins of hydrocarbons are multiple: terrestrial inputs, biogenic, pyrolytic (industry emissions mainly steel and iron industries, ship and road traffic). Generally, the main source of contamination is not petroleum. Several ratios between parent polycyclic aromatic hydrocarbons show that the sources of hydrocarbons in the sediments are generally much more pyrolytic than petrogenic.  相似文献   

A low δLi lower crustal component: Evidence from an alkalic intraplate volcanic series (Chaîne des Puys, French Massif Central)     

Cdric Hamelin  Hans-Michael Seitz  Jean-Alix Barrat  Laure Dosso  Ren C. Maury  Marc Chaussidon 《Chemical Geology》2009,266(3-4):205-217

The intraplate volcanic suite of the Chaîne des Puys (French Massif Central) shows a complete petrologic range, from alkali basalts to trachytes. The significant variations of trace elements and radiogenic isotopes along the series strongly support the occurrence of crustal assimilation associated with fractional crystallization (AFC). The least contaminated basalts are clearly related to a HIMU-type reservoir (²⁰⁶Pb/²⁰⁴Pb > 19.6; ⁸⁷Sr/⁸⁶Sr < 0.7037; ε_Nd > + 4). The behavior of radiogenic isotopes suggests that the most likely crustal contaminants are meta-sediments located in the lower crust.The Li isotopic compositions of the lavas range from high δ⁷Li (> + 7‰) in basalts to lighter values in more evolved lavas (down to δ⁷Li ≈ 0‰). The mantle component, expressed in the least evolved lavas, has a heavy Li isotopic signature, in good agreement with previous δ⁷Li measurements of OIB lavas with HIMU affinities. The evolution of Li isotopic compositions throughout the volcanic series is in agreement with the AFC model suggested by the Sr–Nd–Pb isotopic systems. Although the behavior of Li isotopes during assimilation processes is currently poorly constrained, our calculations suggest that at least a portion of the lower crust beneath the Chaîne des Puys is characterized by a light Li isotopic composition (δ⁷Li < − 5‰).  相似文献   

Emergent geomorphic–vegetation interactions on a subalpine alluvial fan          下载免费PDF全文

Stuart N. Lane  Laure Borgeaud  Pascal Vittoz 《地球表面变化过程与地形》2016,41(1):72-86

Following perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co‐development of geomorphic processes with ecosystems over very short through to very long (evolutionary) timescales. Alpine environments have been a particular focus of this co‐development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co‐develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across‐fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil–vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Microanalysis of carbon isotope composition in organic matter by secondary ion mass spectrometry     

Laure Sangély  Marc Chaussidon  Vincent Huault 《Chemical Geology》2005,223(4):179-195

An analytical procedure has been developed for the in situ measurement of carbon isotope composition of organic matter, with a spatial resolution of 20-30 μm, using a Cameca IMS 1270 ion microprobe. Instrumental mass fractionation (IMF) of carbon isotopes was observed to be independent of primary ion beam intensity and sputtering time, but did depend on vacuum conditions and on the chemical composition of the sample. To evaluate such “matrix effects”, a set of 9 standards representative of the natural chemical variability of organic matter was prepared, with H/C atomic ratios and organic carbon contents (C_org) ranging between 0.04 and 1.74 and between 41 and 100 wt.%, respectively. Under the analytical conditions tested, IMF was not found to be influenced by the presence of silicate mineral impurities in the organic matter, but variations in IMF up to 5‰ were observed over the set of standards with the magnitude of IMF negatively correlated to the H/C ratios of samples. Aliphaticity ratios determined using Fourier transform infrared microspectroscopy provided an in situ estimation of H/C ratios with a spatial resolution barely exceeding that of the ion microprobe and permit a correction for matrix effects with a standard error of ± 0.2‰ (1σ). Taking into account all sources of uncertainty, ion microprobe δ¹³C were accurately determined with a ± 0.7‰ (1σ) total uncertainty. The mechanism for the matrix effect of H/C ratios upon IMF is still to be determined but it is likely related to the difference in proportion of atomic vs. molecular carbon ions observed between samples of different H/C ratios.  相似文献