Microdistribution of primordial Ne and Ar in fine‐grained rims,matrices, and dark inclusions of unequilibrated chondrites—Clues on nebular processes     

Nadia VOGEL  Rainer WIELER  Addi BISCHOFF  Heinrich BAUR 《Meteoritics & planetary science》2003,38(9):1399-1418

Abstract— The low temperature fine‐grained material in unequilibrated chondrites, which occurs as matrix, rims, and dark inclusions, carries information about the solar nebula and the earliest stages of planetesimal accretion. The microdistribution of primordial noble gases among these components helps to reveal their accretionary and alteration histories. We measured the Ne and Ar isotopic ratios and concentrations of small samples of matrix, rims, and dark inclusions from the unequilibrated carbonaceous chondrites Allende (CV3), Leoville (CV3), and Renazzo (CR2) and from the ordinary chondrites Semarkona (LL3.0), Bishunpur (LL3.1), and Krymka (LL3.1) to decipher their genetic relationships. The primordial noble gas concentrations of Semarkona, and—with certain restrictions—also of Leoville, Bishunpur, and Allende decrease from rims to matrices. This indicates a progressive accretion of nebular dust from regions with decreasing noble gas contents and cannot be explained by a formation of the rims on parent bodies. The decrease is probably due to dilution of the noble‐gas‐carrying phases with noble‐gas‐poor material in the nebula. Krymka and Renazzo both show an increase of primordial noble gas concentrations from rims to matrices. In the case of Krymka, this indicates the admixture of noble gas‐rich dust to the nebular region from which first rims and then matrix accreted. This also explains the increase of the primordial elemental ratio 36Ar/ 20Ne from rims to matrix. Larger clasts of the noble‐gas‐rich dust form macroscopic dark inclusions in this meteorite, which seem to represent unusually pristine material. The interpretation of the Renazzo data is ambiguous. Rims could have formed by aqueous alteration of matrix or—as in the case of Krymka—by progressive admixture of noble gas‐rich dust to the reservoir from which the Renazzo constituents accreted. The Leoville and Krymka dark inclusions, as well as one dark inclusion of Allende, show noble gas signatures different from those of the respective host meteorites. The Allende dark inclusion probably accreted from the same region as Allende rims and matrix but suffered a higher degree of alteration. The Leoville and Krymka dark inclusions must have accreted from regions different from those of their respective rims and matrices and were later incorporated into their host meteorites. The noble gas data imply a heterogeneous reservoir with respect to its primordial noble gas content in the accretion region of the studied meteorites. Further studies will have to decide whether these differences are primary or evolved from an originally uniform reservoir.  相似文献   

Elastic properties and stability of coexisting 3T and 2M 1 phengite polytypes     

Nadia Curetti  Davide Levy  Alessandro Pavese  Gabriella Ivaldi 《Physics and Chemistry of Minerals》2006,32(10):670-678

The elastic properties of coexisting natural 3T and 2M ₁ phengite samples (Cima Pal, Sesia Zone; Val Savenca; Western Alps, Italy) with similar chemical compositions have been studied by room temperature–high pressure powder diffraction, using synchrotron radiation on the ID9A beam-line at ESRF (Grenoble, France). The P–V curves have been modelled by the Birch–Murnaghan model; a third-order expansion fitted to the experimental data yields for 3T and 2M ₁ K ₀=60.4(±0.7) GPa, K′=5.79(±0.11) at V ₀=703.8851 ų, and K ₀=57.3(±1.0) GPa, K′=6.97(±0.24) at V ₀=938.8815 ų, respectively. The relative stability of 3T vs. 2M ₁ has been explored as a function of pressure and temperature in terms of configuration and deformation contributions to the Gibbs energy, using the elastic properties determined here and other thermodynamic parameters from earlier investigations. The results presented agree with the hypothesis of stability of the 3T polytype in the high pressure regime.  相似文献   

Internal erosion of chemically reinforced granular materials: a mathematical modeling approach     

Tony Khalil  Nadia Saiyouri  Bogdan Muresan  Pierre‐Yves Hicher 《国际地质力学数值与分析法杂志》2013,37(5):491-502

Internal erosion (IE) affects the stability of natural and reinforced materials by causing instability within their granular structure. The dislodgement and transport of eroded particles affect both the particulate concentration of eroding fluid and the pore network of eroded material. In this study, we examined these modifications using a transport model with a finite element code. First, IE tests on chemically reinforced sand columns were performed to obtain information about eroded material loss of mass, particulate concentration of effluent, porosity and permeability modifications, and existing IE stages. Second, based on experimental results, a mathematical one‐dimensional model has been formulated to monitor the evolution and spatial distribution of erodible solids, fluidized particles, porosity, permeability, and seepage stresses. The model consists of a set of coupled nonlinear differential equations solved in sequence. It provides valuable information about the extent and the dynamics of structural changes, which can be used to estimate an IE time for the hydraulic work to reach failure. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Isotopic and elemental fractionation of solar wind implanted in the Genesis concentrator target characterized and quantified by noble gases     

Veronika S. HEBER  Roger C. WIENS  Amy J. G. JUREWICZ  Nadia VOGEL  Daniel B. REISENFELD  Heinrich BAUR  Kevin D. McKEEGAN  Rainer WIELER  Donald S. BURNETT 《Meteoritics & planetary science》2011,46(4):493-512

Abstract– We report concentrations and isotopic compositions of He, Ne, and Ar measured with high spatial resolution along a radial traverse of a silicon carbide (SiC) quadrant of the Genesis mission concentrator target. The Ne isotopic composition maps instrumental fractionation as a function of radial position in the target: the maximum observed isotopic fractionation is approximately 33‰ per mass unit between the center and periphery. The Ne fluence is enhanced by a factor of 43 at the target center and decreases to 5.5 times at the periphery relative to the bulk solar wind fluence. Neon isotopic profiles measured along all four arms of the “gold cross” mount which held the quadrants in the concentrator target demonstrate that the concentrator target was symmetrically irradiated during operation as designed. We used implantation experiments of Ne into SiC and gold to quantify backscatter loss and isotopic fractionation and compared measurements with numerical simulations from the code “stopping and range of ions in matter.” The ²⁰Ne fluence curve as a function of radial distance on the target may be used to construct concentration factors relative to bulk solar wind for accurate corrections for solar wind fluences of other light elements to be measured in the concentrator target. The Ne isotopic composition as a function of the radial distance in the SiC quadrant provides a correction for the instrumental mass‐dependent isotopic fractionation by the concentrator and can be used to correct measured solar wind oxygen and nitrogen isotopic compositions to obtain bulk solar wind isotopic compositions.  相似文献   

Structural evolution of a 2M 1 phengite mica up to 11 GPa: an in situ single-crystal X-ray diffraction study     

G. Diego Gatta  Nicola Rotiroti  Paolo Lotti  Alessandro Pavese  Nadia Curetti 《Physics and Chemistry of Minerals》2010,37(8):581-591

The structural evolution at high pressure of a natural 2M ₁-phengite [(K_0.98Na_0.02)_Σ=1.00(Al_1.55Mg_0.24Fe_0.21Ti_0.02)_Σ=2.01(Si_3.38Al_0.62)O₁₀(OH)₂; a = 5.228(2), b = 9.057(3), c = 19.971(6)Å, β = 95.76(2)°; space group: C2/c] from the metamorphic complex of Cima Pal (Sesia Zone, Western Alps, Italy) was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to ~11 GPa. A series of 12 structure refinements were performed at selected pressures within the P range investigated. The compressional behaviour of the same phengite sample was previously studied up to ~25 GPa by synchrotron X-ray powder diffraction, showing an irreversible transformation with a drastic decrease of the crystallinity at P > 15–17 GPa. The elastic behaviour between 0.0001 and 17 GPa was modelled by a third-order Birch–Murnaghan Equation of State (BM-EoS), yielding to K _T0 = 57.3(10) GPa and K′ = ?K _T0/?P = 6.97(24). The single-crystal structure refinements showed that the significant elastic anisotropy of the 2M ₁-phengite (with β(a):β(b):β(c) = 1:1.17:4.60) is mainly controlled by the anisotropic compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P shows a negative slope, Fitting the P–V(K-polyhedron) data with a truncated second-order BM-EoS we obtain a bulk modulus value of K _T0(K-polyhedron) = 26(1) GPa. Tetrahedra and octahedra are significantly stiffer than the K-polyhedron. Tetrahedra behave as quasi-rigid units within the P range investigated. In contrast, a monotonic decrease is observed for the octahedron volume, with K _T0 = 120(10) GPa derived by a BM-EoS. The anisotropic response to pressure of the K-polyhedron affects the P-induced deformation mechanism on the tetrahedral sheet, consisting in a cooperative rotation of the tetrahedra and producing a significant ditrigonalization of the six-membered rings. The volume of the K-polyhedron and the value of the ditrigonal rotation parameter (α) show a high negative correlation (about 93%), though a slight discontinuity is observed at P >8 GPa. α increases linearly with P up to 7–8 GPa (with ?α/?P ≈ 0.7°/GPa), whereas at higher Ps a “saturation plateau” is visible. A comparison between the main deformation mechanisms as a function of pressure observed in 2M ₁- and 3T-phengite is discussed.  相似文献   

Influence of Electrokinetic Process on Compressibility Behaviour of Salt Affected Soils     

Hadjadj  Fatima Zohra  Laredj  Nadia  Maliki  Mustapha  Missoum  Hanifi 《Geotechnical and Geological Engineering》2022,40(8):4159-4170

Geotechnical and Geological Engineering - The improvement of salt affected lands is a major environmental challenge in arid and semi arid regions all over the world. Electrokinetic treatment is one...  相似文献   

Palaeoecological evidence of changes in vegetation and climate during the Holocene in the pre‐Polar Urals,northeast European Russia     

Seija Kultti  Minna Vliranta  Kaarina Sarmaja‐Korjonen  Nadia Solovieva  Tarmo Virtanen  Tommi Kauppila  Matti Eronen 《第四纪科学杂志》2003,18(6):503-520

This study investigated Holocene tree‐line history and climatic change in the pre‐Polar Urals, northeast European Russia. A sediment core from Mezhgornoe Lake situated at the present‐day alpine tree‐line was studied for pollen, plant macrofossils, Cladocera and diatoms. A peat section from Vangyr Mire in the nearby mixed mountain taiga zone was analysed for pollen. The results suggest that the study area experienced a climatic optimum in the early Holocene and that summer temperatures were at least 2°C warmer than today. Tree birch immigrated to the Mezhgornoe Lake area at the onset of the Holocene. Mixed spruce forests followed at ca. 9500–9000 ¹⁴C yr BP. Climate was moist and the water level of Mezhgornoe Lake rose rapidly. The hypsithermal phase lasted until ca. 5500–4500 ¹⁴C yr BP, after which the mixed forest withdrew from the Mezhgornoe catchment as a result of the climate cooling. The gradual altitudinal downward shift of vegetation zones resulted in the present situation, with larch forming the tree‐line. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Holocene environments and climate in the Mongolian Altai reconstructed from the Hoton-Nur pollen and diatom records: a step towards better understanding climate dynamics in Central Asia   总被引：1，自引：0，他引：1  

Natalia Rudaya  Pavel Tarasov  Nadezhda Dorofeyuk  Nadia Solovieva  Ivan Kalugin  Andrei Andreev  Andrei Daryin  Bernhard Diekmann  Frank Riedel  Narantsetseg Tserendash  Mayke Wagner 《Quaternary Science Reviews》2009,28(5-6):540-554

This study presents the results of the palynological and diatom analyses of the sediment core recovered in Hoton-Nur Lake (48°37′18″N, 88°20′45″E, 2083 m) in 2004. Quantitative reconstruction of the Holocene vegetation and climate dynamics in the semiarid Mongolian Altai suggests that boreal woodland replaced the primarily open landscape of northwestern Mongolia at about 10 kyr BP (1 kyr = 1000 cal yr) in response to a noticeable increase in precipitation from 200–250 mm/yr to 450–550 mm/yr. A decline of the forest vegetation and a return to a predominance of open vegetation types occurred after 5 kyr BP when precipitation sums decreased to 250–300 mm/yr. Prior to 11.5 kyr BP diatom concentrations are relatively low and the lake is dominated by planktonic Cyclotella and small Fragilariaceae, suggesting the existence of a relatively deep and oligotrophic/mesotrophic lake. The great abundance of Staurosirella pinnata from the beginning of the record until 10.7 kyr BP might imply intensified erosion processes in the catchment and this is fully consistent with the presence of scarce and dry vegetation and the generally arid climate during this period. From about 10.7 kyr BP, more planktonic diatom taxa appeared and increased in abundance, indicating that the lake became more productive as diatom concentration increased. This change correlates well with the development of boreal woodland in the catchment. Decrease in precipitation and changes in the vegetation towards steppe are reflected by the rapid increase in Aulacoseira distans from about 5 kyr BP. The Holocene pollen and diatom records do not indicate soil and vegetation cover disturbances by the anthropogenic activities, implying that the main transformations of the regional vegetation occurred as a result of the natural climate change. Our reconstruction is in agreement with the paleomonsoon records from China, demonstrating an abrupt strengthening of the summer monsoon at 12 kyr BP and an associated increase in precipitation and in lake levels between 11 and 8 kyr BP, followed by the stepwise attenuation of the monsoon circulation and climate aridization towards the modern level. The records from the neighboring areas of Kazakhstan and Russia, situated west and north of Hoton-Nur, demonstrate spatially and temporally different Holocene vegetation and climate histories, indicating that the Altai Mountains as a climate boundary are of pivotal importance for the Holocene environmental and, possibly, habitation history of Central Asia.  相似文献   

Maximum entropy method: an unconventional approach to explore observables related to the electron density in phengites     

Marcello Merli  Alessandro Pavese  Nadia Curetti 《Physics and Chemistry of Minerals》2009,36(1):19-28

The maximum entropy method (MEM) is used here to get an insight into the electron density [ρ(r)] of phengites 2M ₁ and 3T, paying special attention to the M1-formally empty site and charge distribution. Room temperature single crystal X-ray diffraction data have been used as experimental input for MEM. The results obtained by MEM have been compared with those from conventional structure refinement which, in turn, has provided the prior-electron density to start the entropy maximization process. MEM reveals a comparatively non-committal approach, able to produce information related to the M1-site fractional occupancy, and yields results consistent with those from the difference Fourier synthesis, but free of the uncertainties due to the abrupt truncation of the series. The charge distribution is investigated by means of the notion of ‘‘site basin’’, i.e., those site-centered volumes delimited by a surface such as ∇ρ·n = 0. In particular, we observe: (1) the overall partitioning of the basin total charge between cation and anion sites, and the interlayer site charge seems to depend on sample composition, and (2) the apical-oxygen plane total basin charge and hydroxyl basin charge are presumably related to the polytype. The MEM-determined electron density does not allow full exploration of the critical points for very complex structures as micas, insofar as conventional room temperature experimental diffraction data are used.  相似文献   

Impact of rock-water interactions and recharge on water resources quality of the Agadir-Essaouira basin,southwestern Morocco     

Al Yacoubi Latifa  Bouchaou Lhoussaine  Jaillard Etienne  Masrour Moussa  Ait Brahim Yassine  El Mouden Ahmed  Schneider Jana  Reichert Barbara 《Arabian Journal of Geosciences》2017,10(7):169

The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of δ¹⁸O and δ²H suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units.  相似文献