A “chondritic” eucrite parent body: inference from trace elements

A total of 33 elements (Ag, Al, Au, Bi, Br, Cd, Ce, Co, Cr, Cs. Eu, Fe, Ge, Hf, Ir, Lu, Na, Ni, Os, Pd, Rb, Re, Sb, Se, Se, Si, Sm, Tb, Te, Tl, U, Yb and Zn) were analyzed by radiochemical and instrumental neutron activation in four eucrites: Juvinas (brecciated), Ibitira (vesicular, unbrecciated) and Moore County and Serra de Magé (cumulate, un brecciated).When arranged in order of volatility. Cl—normalized abundance patterns allow nebular and planetary effects to be distinguished. The stepped lithophile pattern reveals the dominance of nebular processes; in Ibitira, refractory elements (Hf, Lu, Tb, Ce, Sm, Yb, U, Eu) are (13.1 ± 0.7) × Cl chondrites; volatile elements (Rb. Cs, Br, Bi) are (6.0 + 1.5) × 10^?2 Cl. The depletion of Tl seems inherent to the eucrite parent body and is mirrored in the chalcophile elements by the marked deficit of Te relative to Se; apparently volatiles were accreted as a fractionated C3-like component. Consistent but subtle Cl-normalized abundance differences between eucrites (Serra de Magé < Moore County < Juvinas < Ibitira) result from crystal/liquid differentiation; Ibitira approximates the composition of an undifferentiated eucrite magma. The siderophile pattern retains little sign of nebular processes, but reflects planetary metal-silicate partition.The bulk composition of the eucrite parent body closely resembles that of H-chondrites, except for two features: moderately volatile elements (e.g. Na, K. Rb) are very much lower, apparently due to the accretion of more chondrule-like material; the metallic Fe-Ni content is only ~13%, even though total iron is very similar.     

Timing of metal–silicate differentiation in the Eagle Station pallasite parent body

The time of the metal–silicate differentiation of the Eagle Station pallasite (ESP) parent body was investigated using the ²⁶Al–²⁶Mg short-lived chronometer (half-life of 0.72 Myr). The Mg isotope ratios were measured in ESP olivines by both MC–SIMS and HR-MC–ICPMS, allowing us to check the consistency between the results given by two different analytical protocols and data reduction processes. Results show that the two datasets are consistent, with a (δ²⁶Mg*)_av. value of –0.003 (± 0.005)‰ (2 s.e., n = 89). Such a value, associated with data from the ¹⁸²Hf–¹⁸²W short-lived systematics (half-life of 8.9 Myr), indicates an ESP parent body metal–silicate differentiation occurring most likely at least at ∼ 2 Ma, but possibly 4 Ma, after CAI formation. From the ²⁷Al/²⁴Mg ratios measured in ESP olivines using MC–SIMS, the duration of the olivine crystallization process was inferred to have lasted over ∼ 275 kyr if the core has differentiated as early as 2 Ma after CAIs, while in the case of a core differentiation occurring 4 Ma after CAIs, the silicate–silicate differentiation should have lasted for another 4 Myr.     

Minerals of the Fe–Ni–Co–Cu–S System in Picrite Intrusions of the Southern Urals: Signatures of Liquation and Differentiation of the Sulfide Melt

Doklady Earth Sciences - New data on the minerals of the Fe–Ni–Co–Cu–S system in the differentiated intrusions of the Southern Urals are presented. Based on a detailed study...     

Melting of Fe–Ni–Si and Fe–Ni–S alloys at megabar pressures: implications for the core–mantle boundary temperature

High pressure melting behavior of three Fe-alloys containing 5 wt% Ni and (1) 10 wt% Si, (2) 15 wt% Si or (3) 12 wt% S was investigated up to megabar pressures by in situ X-ray diffraction and laser-heated diamond anvil cell techniques. We observe a decrease in melting temperature with increasing Si content over the entire investigated pressure range. This trend is used to discuss the melting curve of pure Fe. Moreover, our measurements of eutectic melting in the Fe–Fe₃S system show a change in slope around 50 GPa concomitant with the fcc–hcp phase transition in pure solid iron. Extrapolations of our melting curve up to the core–mantle boundary pressure yield values of 3,600–3,750 K for the freezing temperature of plausible outer core compositions.     

Sound velocity and elastic properties of Fe–Ni and Fe–Ni–C liquids at high pressure

The sound velocity (V _P) of liquid Fe–10 wt% Ni and Fe–10 wt% Ni–4 wt% C up to 6.6 GPa was studied using the ultrasonic pulse-echo method combined with synchrotron X-ray techniques. The obtained V _P of liquid Fe–Ni is insensitive to temperature, whereas that of liquid Fe–Ni–C tends to decrease with increasing temperature. The V _P values of both liquid Fe–Ni and Fe–Ni–C increase with pressure. Alloying with 10 wt% of Ni slightly reduces the V _P of liquid Fe, whereas alloying with C is likely to increase the V _P. However, a difference in V _P between liquid Fe–Ni and Fe–Ni–C becomes to be smaller at higher temperature. By fitting the measured V _P data with the Murnaghan equation of state, the adiabatic bulk modulus (K _S0) and its pressure derivative (K _S ^′ ) were obtained to be K _S0 = 103 GPa and K _S ^′  = 5.7 for liquid Fe–Ni and K _S0 = 110 GPa and K _S ^′  = 7.6 for liquid Fe–Ni–C. The calculated density of liquid Fe–Ni–C using the obtained elastic parameters was consistent with the density values measured directly using the X-ray computed tomography technique. In the relation between the density (ρ) and sound velocity (V _P) at 5 GPa (the lunar core condition), it was found that the effect of alloying Fe with Ni was that ρ increased mildly and V _P decreased, whereas the effect of C dissolution was to decrease ρ but increase V _P. In contrast, alloying with S significantly reduces both ρ and V _P. Therefore, the effects of light elements (C and S) and Ni on the ρ and V _P of liquid Fe are quite different under the lunar core conditions, providing a clue to constrain the light element in the lunar core by comparing with lunar seismic data.     

Severity–duration–frequency curves in the mitigation of drought impact: an agricultural case study

Severity–duration–frequency (SDF) curves are very useful in the analysis of drought phenomena. Station-level information obtained from SDF curves can be interpolated to obtain severity maps for fixed return period, in order to jointly analyse the spatial variability of drought characteristics (e.g. severity, duration and frequency). This approach is limited because the severity is usually quantified through indices that use hydrological and meteorological data, depending on the type of requirements. Therefore, drought indices can only reflect hydrological conditions, but are unable to quantify economic losses associated with droughts. In other words, SDF curves do not allow effective quantification of the impact expected with a certain return period. This paper proposes the methodology drought economic risk assessment (DERA) as an approach that emphasizes the importance of the relationship between a generic drought index (which quantifies water deficit) and the economic impact of the failure to meet water demand. Using integrated SDF curves, this relationship enables drought severity and corresponding impacts to be mapped. This procedure was applied to agricultural droughts (sunflower crop) in Umbria Region (central Italy). The agricultural drought impact variable was identified by sunflower yield (Y); the economic impact variable by net benefit depletion (EL); and the drought index by Relative Severity Index (RSI), which is quantifiable by a soil–water balance model. The relationships Y = g(RSI) and EL = f(Y) were specifically determined. Using DERA, it was possible to derive curves for SDF, impact–duration–frequency, and economic losses–duration–frequency (ELDF), which were then used to map severity, impact and economic losses for the assigned return period and duration. From the ELDF curves, further information was obtained by mapping critical drought durations for the assigned return period and economic loss threshold. The case study supports the potential of the proposed approach, both in the planning and real-time management of drought effects.     

A Raman spectroscopic study of Fe–Mg olivines

End-member synthetic fayalite and forsterite and a natural solid-solution crystal of composition (Mg_1.80,Fe_0.20)SiO₄ were investigated using Raman spectroscopy. Polarized single-crystal spectra were measured as a function of temperature. In addition, polycrystalline forsterite and fayalite, isotopically enriched in ²⁶Mg and ⁵⁷Fe, respectively, were synthesized and their powder spectra measured. The high-wavenumber modes in olivine consist of internal SiO₄ vibrations that show little variation upon isotopic substitution. This confirms conclusions from previous spectroscopic studies that showed that the internal SiO₄ vibrations have minimal coupling with the lower-wavenumber lattice modes. The lowest wavenumber modes in both forsterite and fayalite shift in energy following isotopic substitution, but with energies less than that which would be associated with pure Mg and Fe translations. The low-wavenumber Raman modes in olivine are best described as lattice modes consisting to a large degree of mixed vibrations of M(2) cation translations and external vibrations of the SiO₄ tetrahedra. The single-crystal spectra of forsterite and Fo₉₀Fa₁₀ were recorded at a number of temperatures from room temperature to about 1200 °C. From these data the microscopic Grüneisen parameters for three different A_g modes for both compositions were calculated, and also the structural state of the solid solution crystal was investigated. Small discontinuities observed in the wavenumber behavior of a low-energy mixed Mg/T(SiO₄) mode between 700 and 1000 °C may be related to minor variations in the Fe–Mg intracrystalline partitioning state in the Fo₉₀Fa₁₀ crystal, but further spectroscopic work is needed to clarify and quantify this issue. The mode wavenumber and intensity behavior of internal SiO₄ vibrations as a function of temperature are discussed in terms of crystal field and dynamic splitting and also ₁ and ₃ coupling. Crystal-field splitting increases only very slightly with temperature, whereas dynamical-field splitting is temperature dependent. The degree of ₁–₃ coupling decreases with increasing temperature.     

Effects of terrigenic He components on tritium–helium dating: A case study of shallow groundwater in the Saijo Basin

Dating using a combination of ³H and ³He is believed to be the most practical method for estimating the short residence time of shallow groundwater. However, this method must estimate tritiogenic ³He alone and tends to overestimate the residence time of groundwater, if terrigenic ³He from the mantle cannot be excluded from the total dissolved ³He. We demonstrate the exclusion of terrigenic ³He in the Saijo Basin, where mantle He is easily released along the major active fault, Median Tectonic Line. The ³He/⁴He ratios suggest that the west bank of the Kamo River, which lies within the basin, has experienced greater emanations of mantle He than the east bank. We estimate the residence times to be 1.1–96 years by the proposed exclusion method.     

A study of outburst activity of Z and in 2000–2010

We present the results of our study of the classical symbiotic star Z And during its period of activity in 2000–2010. In this period, the system experienced a series of six outbursts, for three of which high-resolution spectra were obtained and analyzed. These observations provided information about the system’s behavior during the entire activity period, rather than during an individual outburst. In particular, we found a fundamental difference between the first outburst, which initiated the activity period, and subsequent outbursts, namely, the presence of bipolar collimated optical outflows for some of the outbursts. We propose a model that can explain all the spectroscopic phenomena observed during this series of outbursts, as well as previous series of outbursts of Z And, and suggest that similar scenarios may be valid for other classical symbiotic stars.     

The interaction of tectonics,climate and eustasy in controlling dolomitization: A case study of Cenomanian–Turonian,shallow marine carbonates of the Iberian Basin

During the Cretaceous, high global sea-level and low latitudinal temperature variations led to the growth of epeiric carbonate platforms. Platform-scale dolomitization of these platforms is not common, reflecting the low Mg/Ca ratio of seawater and a humid climate. This study describes the processes governing pervasive dolomitization of a land-attached carbonate platform within the Iberian Basin. Dolomite is planar to sub-planar with a geochemical signature consistent with dolomitization from penesaline seawater. Dolomitization was most pervasive during a 1 Myr period in the middle Cenomanian, by repeated reflux of seawater from brine pools formed on the top of a southward-prograding carbonate platform. Tilting and structural reorganization in the Upper Cenomanian led to a reversal in polarity of the platform, and dolomitization was restarted by the northward reflux of seawater. Rising relative sea-level and oceanic acidification led to back-stepping of the platform such that the supply of dolomitizing fluids was cut off. In the Lower Turonian, pervasively dolomitized rudist rudstone facies in the south of the study area indicate that dolomitization restarted, either penecontemporaneously or later, from highly evaporated Campanian–Maastrichtian seawater. A systematic increase in dolomite crystal size up-section ties broadly, but not entirely, to stratigraphy. It is possible that these textural differences reflect changes in fluid chemistry, limestone permeability or precursor rock texture. However, the lack of stratigraphic conformance, and the preservation of the earliest-formed dolomite only in the oldest sediments, could indicate a progressive recrystallization of early-formed dolomite through repeated reflux of brines. As such, the succession appears to preserve a fossilized record of dolomite recrystallization through time during the Cenomanian–Turonian. The results of this study therefore provide a record of the progressive dolomitization of a carbonate platform and demonstrate the important interplay of climate and basin-scale tectonics on dolomite distribution and crystallinity.     

Mesozoic and Cenozoic structural deformation in the NW Tarim Basin,China: a case study of the Piqiang–Selibuya Fault

The Piqiang–Selibuya Fault is the most significant fault in the NW Tarim Basin, China. It has attracted increasing attention because of the discovery of a series of oil (gas) fields in and around the fault zone. The structural characteristics and evolution of the Piqiang–Selibuya Fault remain controversial. Field geological surveys and seismic data interpretation reveal that the fault has experienced three stages of activity. The thicknesses of the Permian and Miocene strata on opposing sides of the fault are clearly different, and these reveal that the fault has experienced two stages of significant thrusting. The first stage took place at the end of the Triassic and was associated with the Qiangtang Block amalgamated to the south margin of Eurasia. The second stage occurred at the end of the Miocene and might have been caused by the northwards overthrusting of the Pamir. These two stages of thrusting led to the lower–middle Cambrian detachment layer in the eastern part of the Keping thrust belt being 2 km shallower than in the western part. Since the Pliocene, the southern Tien Shan orogenic belt has been reactivated and thrust towards the interior of the Tarim Basin, and a series of ENE–WSW-trending thrust sheets have formed in the Keping thrust belt. Because of the different depth of the detachment layer on the opposing sides of the Piqiang–Selibuya Fault, the number and spacing of thrust sheets formed to the east of the fault differ from those to the west. This dissimilar deformation led to the strike–slip displacement on the Piqiang–Selibuya Fault. The three stages of fault activity record three important tectonic events in the NW Tarim Basin. Qualitative analysis of this activity helps us better understand the influence of the far-field effect of the collisions that occurred on the southern margin of the Eurasia plate on the structural deformation of the NW Tarim Basin.     

P–T paths and modeling the evolution of metapelitic mineral assemblages in the MnNCKFMASH system: A case of Northern Ladoga area

Phase equilibria in medium-grade metapelites of the Northern Ladoga area are calculated with the pseudosection method and Theriak/Domono software on the basis of zoning in garnets. It is shown that garnet in the staurolite-bearing parageneses crystallized at 520–600°C against the background of a pressure release from 7.0 to 3.5–4.0 kbar. The evolution of the mineral composition of rocks in the course of porphyroblast formation is discussed, placing special emphasis on the comparative analysis of P–T paths of garnet growth under decompression conditions.     

Determination of PCB-contaminated sites in Belarus： A case study

PCBs belong to POPs of priority concern in Belarus due to the large amount of PCBs, long period of PCB and PCB-containing equipment usage and possibilities of PCBs dissemination in the environment. From the point of health risk assessment the revealing of PCBs contaminated sites is very important. The greatest amounts of PCBs in Belarus are used in electrical equipment; therefore experimental work was conducted on the territories where PCB-containing electrical equipment is installed or stored. About 20 sub-stations with capacitors and 2 places with transformers were investigated. More than 200 soil and bottom sediments were collected and analyzed. 6 individual PCBs congeners （PCB-28, PCB-52, PCB-138, PCB-153, PCB-180 and PCB-203） were detected by gas chromatography and chromatography mass spectrometry. PCBs contents in the soils of the territories, where electrical equipment is used and stored, come up to milligrams or sometime grams per kilogram. Maximum concentrations of PCBs （2-21 g/kg） were tracked in the soil near destroyed capacitors and transformers as a consequence of PCB leakage. The highest concentrations of PCBs are found in topsoil layer. In some cases high PCB concentrations are fixed at the depth of 50 cm. In several cases PCB leakage can be easily noticed due to dark color. Low chlorinated PCBs prevail in the soils of the places where capacitors are installed or stored, and high chlorinated PCBs are noticed where transformers are stored. As a rule, contaminated areas are rather local （typical spot is less than a square meter）. Nevertheless, they are potentially sources of secondary ground and surface water, as well as bottom sediments pollution. Moreover, spreading of PCBs beyond the places of PCB-containing equipment usage or storage occurs： the sum of 6 PCBs at the distance of 100-150 m from capacitor battery comes up to 0.35-4.6 mg/kg in the soil. Soils at practically all investigated sub-stations are polluted with PCBs. In most cases high concentrations of PCBs are revealed. On the whole, spatial structure of PCB contamination soil is extremely heterogeneous.     

Carbon isotope systematics of the Cambrian–Vendian aquifer system in the northern Baltic Basin: Implications to the age and evolution of groundwater

Groundwater in the Cambrian–Vendian aquifer system has a strongly depleted stable isotope composition (δ¹⁸O values of about −22‰) and a low radiocarbon concentration, which suggests that the water is of glacial origin from the last Ice Age. The aim of this paper was to elucidate the timing of infiltration of glacial waters and to understand the geochemical evolution of this groundwater. The composition of the dissolved inorganic C (DIC) in Cambrian–Vendian groundwater is influenced by complex reactions and isotope exchange processes between water, organic materials and rock matrix. The δ¹³C composition of dissolved inorganic C in Cambrian–Vendian water also indicates a bacterial modification of the isotope system. The corrected radiocarbon ages of groundwater are between 14,000 and 27,000 radiocarbon years, which is coeval with the advance of the Weichselian Glacier in the area.     

Spatial–temporal differences in disaster perception and response among new media users and the influence factors: a case study of the Shouguang Flood in Shandong province

Natural Hazards - When human beings cannot avoid extreme climate disasters, it is widely accepted to take measures to address climate change. Research on ordinary people’s perception of...     

A photometric study of the polar MT draconis in 2005–2009

We have obtained data on various brightness states of the polar MT Dra over five years of observations, including the first multicolor photometry for this close binary. We confirm the known orbital period, which has remained constant over 17 years, which is unusual for cataclysmic binaries. Our observations in October 2006 demonstrated a transition of the polar to its low brightness state within one day.     

Visible and “invisible” forms of gold and silver in the crystallization products of melts in the Fe–S–Ag–Au system: experimental data

The forms of Au and Ag occurrence in the crystallization products of melts in the Fe–S–Ag–Au system depending on the proportions of Fe/S and Ag/Au have been studied at (Fe + S)/(Ag + Au) = 0.1. It is shown that the S-rich systems with S/Fe = 2 contain Au–Ag sulfides and Au–Ag alloys. The systems depleted in S with S/Fe = 1 contain only Au–Ag alloys. The results of XPS provide evidence for the sulfide and metallic components of Au and Ag among the crystallization products of melts in the system studied at S/Fe = 2 and a metallic component with S/Fe = 1. According to the data of electron microprobe analysis, the content of “invisible” forms of noble metals in pyrite and pyrrhotite is < 0.024 wt % for Au and <0.030 wt % for Ag; the contents of “invisible” Au and Ag in troilites are 0.040 ± 0.013 wt % Au and 0.079 ± 0.016 wt % Ag.     

A crystallographic and m?ssbauer spectroscopy study of Fe

The crystal chemistry of garnet solid solutions on the Fe ₃ ²⁺ Al₂Si₃O₁₂-Fe ₃ ²⁺ Fe ₂ ³⁺ Si₃O₁₂ (almandine-“skiagite”) and Ca₃Fe ₂ ³⁺ Si₃O₁₂-Fe ₃ ²⁺ Fe ₂ ³⁺ Si₃O₁₂ (andradite-“skiagite”) joins have been investigated by single-crystal X-ray structure refinements and M?ssbauer spectroscopy. Together, these two solid solution series encompass the complete range in Fe³⁺/ΣFe from 0.0 to 1.0. All garnets are isotropic and were re0fined in the Ia d space group. Small excess volumes of mixing are observed in andradite-“skiagite” solid solutions (W _v =1.0±0.2 cm³ mol^-1) and along the almandine-“skiagite” join (W _v =-0.77±0.17cm³ mol^-1). The octahedral (Al, Fe³⁺)-O bond lengths show a much greater variation across the almandine-skiagite join compared to the andradite-skiagite garnets. The dodecahedral (X)-O bond lengths show the opposite behaviour. In andradite-“skiagite” solid solutions, the octahedral site passes from being flattened to elongated parallel to the 3 axis of symmetry with increasing “skiagite” content. A perfect octahedron occurs in a composition of ≈35 mol% “skiagite”. The occupancy of the neighboring dodecahedral sites has the greatest effect on octahedral distortion and vice versa. The M?ssbauer hyperfine parameters of Fe²⁺remain constant in both solid solutions. The hyperfine parameters of Fe³⁺ (at room temperature: centre shift=0.32–0.40 mm/sec, quadrupole splitting (QS)≈0.21–0.55 mm/ sec) indicate that all Fe³⁺ is in octahedral coordination. The Fe³⁺ parameters are nearly constant in almandine-“skiagite” solid solutions, but vary significantly across the andradite-“skiagite” join. The structural unit that contributes to the electric field gradient of the octahedral site is different from that of the coordinating oxygen polyhedron, probably involving the neighboring dodeca-hedral sites.     

Advances in research of the time scales of porphyry deposits: A case study of the Yulong porphyry Cu-Mo deposit in the eastern TibetSCIEI北大核心CSCD

精确限定多期次岩浆-热液活动的时间尺度一直是剖析斑岩矿床形成过程的热点和难点。借助矿物的高精度同位素定年、热力学数值模拟以及石英的钛扩散模型等方法,斑岩矿床中岩浆-热液活动的时间尺度已经被限定在几万年之内。本文以三江特提斯超大型玉龙斑岩铜(钼)矿床为例,重点识别含矿热液脉中普遍存在的石英,利用钛元素的扩散年代学方法,精确限定斑岩矿床中多期岩浆-热液流体活动的时间尺度。扩散模型表明玉龙斑岩矿床热液活动的时间尺度为32000~870000年,有力支持了超大型斑岩矿床可以在几万至几十万年甚至更短时间内形成的观点。此外,为避免钛扩散模型产生较大的误差,需要在精确测定石英中钛含量的基础上,结合矿床地质背景或其他实验方法合理地估测温度和压力条件。研究认为,将矿物的高精度同位素定年与元素的扩散年代学相结合,可以在更为精细的尺度上完善斑岩矿床岩浆-热液活动的时间框架。