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1.
In this paper we investigate two major issues: (1) What are chondrules, and (2) why do they exist? We review the literature pertaining to each question and explore answers. We discuss the diversity of chondrules, especially with regard to their igneous textures and compositions. We review the constraints that have been placed experimentally on the thermal histories of chondrules and list those fundamental properties that all chondrule formation models must explain quantitatively in order to be considered predictive, quantitative models. We provide background on the three major classes of chondrule formation models currently being discussed, and scrutinize each with respect to how well they adhere to the experimental constraints placed on chondrule formation. Finally, we list several unresolved issues that are now or will soon be at the forefront of chondrule research. 相似文献
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Magnetisation measurements were performed on the synthetic analogue of stannite, Cu2FeSnS4, in order to characterise the antiferromagnetic transition at low temperature, evidenced by Bernardini et al. (2000). Temperature and field dependence of the material were checked by means of static magnetisation measurements, carried out scanning the magnetic fields up to 12 T and temperatures in the range 1.4–20 K, while ac susceptibility data were collected at different frequencies ranging from 1.8 to 510 Hz. Both static and dynamic magnetisation data, performed above and below the Néel temperature, 6.1(2) K, confirm stannite to order antiferromagnetically at a long-range scale. Moreover, an increase of both the magnetic anisotropy and the exchange interaction, with respect to the Mn-analogue (Fries et al. 1997), has been observed. 相似文献
5.
Gerald R. North 《GeoJournal》2007,70(1):27-31
An Inconvenient Truth provides an opportunity to examine the differences between scientific statements and the mixed statements made by politicians.
The Gore movie is a powerful example of the latter. There are some inaccuracies and exaggerations in the film, but on the
whole it represents mainstream scientific views on global warming. This essay looks into the state of the art of climate change
research including its scientific underpinnings. Climate science is in a state of ‘normal science’ as discussed by Kuhn. There
is a large body of scientists who are adherents to the paradigm and there does not appear to be any serious alternative at
this time. 相似文献
6.
Lucinid bivalves dominate the infauna of tropical seagrass sediments. While the effect of seagrass on lucinids has been studied,
the reverse effect has largely been ignored. Lucinids can alter porewater chemistry (i.e., increase porewater nutrients by
suspension feeding and decrease porewater sulfides by oxygen introduction and bacterial oxidation), which can potentially
change seagrass productivity and growth morphology. To observe correlations between porewater chemistry and lucinid presence,
a field survey and laboratory microcosm experiment were conducted. Survey sampling sites with lucinids had significantly lower
sulfide and higher ammonium concentrations than sampling sites without lucinids. There was no difference in phosphate concentration
among sampling sites. Both lucinid species used in the microcosm experiment (Ctena orbiculata andLucinesca nassula) significantly lowered sulfide concentrations in the sediment porewater. Microcosm and field survey results were incorporated
into a sulfide budget. In seagrass sediments, lucinids remove 2–16% of the total sulfide produced. Sulfide is a major stressor
to both plants and animals in Florida Bay sediments; this removal may be important to maintaining seagrass productivity and
health. Oxygen introduction into sediments byC. orbiculata was estimated in a dye experiment.C. orbiculata were added to small tubes containing sieved mud and incubated in a bath of seawater with a Rhodamine WT. Rhodamine WT accumulation
in the sediment was measured. A first order estimate showed that oxygen introduction can account for less than 5% ofC. orbiculata sulfide removal. 相似文献
7.
John W. Nielsen-Gammon 《GeoJournal》2007,70(1):21-26
The movie An Inconvenient Truth is a powerful portrayal of global warming and its impacts. The main scientific argument presented in the movie is for the
most part consistent with the weight of scientific evidence, but with some of the main points needing updating, correction,
or qualification. The detailed argument relies almost entirely on past and current evidence and neglects almost all information
that can be gained from computer models, perhaps because such information would be difficult for a lay audience to grasp,
believe, or connect with emotionally. This places an undue weight on current events as signs of ongoing climate change: some
such events are apparently not related at all to climate change, while for other specific events the role of global warming
is difficult or impossible to establish. 相似文献
8.
A new version of the STRUCTON (2009) computer model is proposed for the simulation of the molecular mass distributions (MMD)
characterizing the diversity of anions in silicate melts depending on their polymerization and temperature. In contrast to
earlier versions, the new version of the model accounts for disproportionation reactions of Q
n
species and makes use of their proportions in the statistical simulations of the origin of real Si-O complexes. The new potentialities
of the STRUCTON program package are illustrated by its application to studying the structural-chemical characteristics of
melts in the Na2O-SiO2 system along its liquidus line, including the points of eutectics and phase transitions at 0.333 ≤ $
N_{SiO_2 }
$
N_{SiO_2 }
< 0.500. This problem is solved with the use of a temperature-composition dependence of polymerization constants K
p
Na in the Toop-Samis approximation. The variations in K
p
Na were proved to be as large as three orders of magnitude due to both the temperature effect at a constant composition and
the composition effect at a constant temperature. The results of the MMD simulations on the liquidus show that the concentration
of the SiO44− ion strongly decreases, and the proportion of chain species increases compared to those at a stochastic distribution. The
concentration of the Si2O76− anion reaches its maximum (∼42%) at 40 mol % in the liquid, i.e., the composition of Na6Si2O7. At $
N_{SiO_2 }
$
N_{SiO_2 }
> 0.40, this ion dominates over the SiO44− monomer. More silicic melts with $
N_{SiO_2 }
$
N_{SiO_2 }
≥ 0.45, are dominated by (Si
n
O3n
)3n− ring species, and the concentrations of these species are related as (Si3O9)6− > (Si4O12)8− > (Si5O15)10−. The maximum concentration of these flat rings also occurs near the composition of stoichiometric metasilicate with Si/O
= 0.333. The comparison of the dependence of the average size of anions i
av and the average number of their species on depolymerization indicates that a change in the proportion of Q
n
species in melt at decreasing temperature results in structural restyling and an increase in the average size of Si-O complexes.
The average number of anion species thereby decreases compared to that in a stochastic MMD. The results presented in this
publication direct the progress in the thermodynamic theory of silicate melts to a new avenue that makes use of the capabilities
and advantages of the ion-polymer model, the theory of associated solutions, spectroscopic data, and the experimental study
of variations in oxide activities depending on composition and temperature. 相似文献
9.
The long-term variability of rainfall in the Soummam watershed (NE Algeria) has been analysed over the past 108 years using continuous wavelet method in order to identify the interannual modes controlling the rainfall variability. Statistical analyses of rainfall timeseries have shown its distribution following five periods of time, limited by a series of discontinuities around 1935, 1950, 1970 and 1990. The continuous wavelet transform have demonstrated different low frequency modes: 2–4, 4–8, 8–16 and 16–32 years.The annual band is expanded during the full study period with some pics around 1905, 1920–1935 and 1960; it shows a negative long-term trend, in particular since the period 1970–1990 when a major change has been identified. Then, the relationships between climate patterns of North Atlantic Oscillation (NAO) and Southern Oscillation Index (SOI) and the hydrological variability in the frequency domain have been investigated; they have shown a mean explained variance of 40 and 24 %, respectively. Such variances are less obvious for the annual mode and increase for the interannual frequencies. The coherence suffer from high perturbations since the period 1970–1990 when the NAO (SOI) shifts from negative (positive) phases to positive (negative) ones. Such anomalies are responsible for significant changes of rainfall variability, emphasising the global warming effects. 相似文献
10.
《Resource Geology》2018,68(3):209-226
Shin‐Otoyo, Suttsu, Teine, Date, Chitose, and Koryu are sites rich in precious and base metal Miocene–Pleistocene epithermal deposits, and located in southwestern Hokkaido, Japan. The deposits are predominantly hosted by the Green Tuff Formation of Middle Miocene age. Ore petrographic study of these deposits shows the occurrence of variable quantities of Cu–As–Sb–Ag–Bi–Pb–Te sulfosalt minerals. Determination of mineralogical and chemical compositions of the sulfosalt minerals was undertaken to elucidate the time and spatial changes of the sulfide‐sulfosalt minerals. Various types of sulfosalt minerals identified from gold–silver and base metal quartz–sulfide veins represented some sulfosalt mineralization phases, such as the Cu–Fe–Sn–S phase of mawsonite and stannite; Cu–(As,Sb)–S phase of tetrahedrite–tennantite and luzonite–famatinite series minerals; (Cu,Ag)–Bi–Pb–S phase of emplectite, pavonite, friedrichite, aikinite, and lillianite–gustavite series minerals; (Ag,Cu)–(As,Sb)–S phase of proustite–pyrargyrite and pearceite–polybasite series minerals; and Bi–Te–S phase of tetradymite and kawazulite minerals. There are some trends in the paragenetic sequence of sulfosalt mineralization in southwestern Hokkaido (in complete or partial) as follows: sulfide → Cu–Fe–Sn–S → (Cu,Ag)–Bi–Pb–S → (Bi–Te–S) → Cu–(As,Sb)–S → ([Ag,Cu]–[As,Sb]–S). The formation of sulfosalt minerals is characterized by the introduction of some elements such as Sn, Bi, and Te at an earlier stage and an increase or decrease of some elements such as As and Sb, followed by the introduction of Ag at the later stage of ore mineral paragenesis sequence. Mineral composition of the Chitose and Koryu deposits are slightly different from those of Shin‐Otoyo, Suttsu, Teine, and Date due to their lack of Sn (tin) and Bi (bismuth) mineralization. The variable concentrations and relationships are not simply with redistributed trace elements from the original sulfide minerals of chalcopyrite, pyrite, galena, and sphalerite. Some heavier elements were also introduced during the replacement reaction, which is consistent with the occurrence of their associated minerals. 相似文献
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Weili Wang Luofu Liu Zhenxue Jiang Ningning Zhong Ying Wang Ping Wang Lin Wu Jianghui Meng Jieli Zhou Yongqiang Guo 《中国地球化学学报》2011,30(4):405-414
The Western Depression of the Liaohe Basin is the major exploration area of the Liaohe Oilfield, and its main source rocks consist of the third and fourth members of the Shahejie Formation (Es3 and Es4). These source rocks are widely distributed in the depression, with semi-deep lake and fan delta as the main sedimentary facies, brown oil shale and black gray-dark gray mudstone as the main rocks, and a total thickness of 270-1450 m. The kerogens are mainly of the types I and IIA, and partly of the type IIB and least of the type III. The Ro values range from 0.4%-0.8%, indicating an evolution stage from immature to mature. The maturity of Es4 source rocks is rela-tively high, reaching the early mature stage, but their distribution and thickness are lower than those of Es3. Besides, according to biomarker analysis, it is thought that the source rocks of Es3 and Es4 are characterized by mixed input, and most of the source rocks were formed in the brackish water-saline and strongly oxygen-free environment. Fur-thermore, the Qingshui, Niuxintuo and Chenjia sags are believed to possess greater potential for hydrocarbon gen-eration and expulsion, for they are source rocks with a larger thickness, have higher organic carbon contents, belong to better organic matter types and possess higher maturities. 相似文献
13.
The segregation of ten isovalent impurities (Al3+ Cr3+, Eu3+, Gd3+, Ho3+, La3+, Lu3+, Nd3+, Tb3+, Y3+) to the and the (0001) surfaces of haematite (-Fe2O3) have been studied using atomistic simulation where the forces between the atoms are modelled using the Born model of solids. Segregation is found to be energetically favoured in virtually every case. The results for the surface show that the most favourable impurity surface concentration is 33.33%. The (0001) surface has two possible terminations, one terminated by iron atoms and the other by oxygen. No minimum is calculated for the Fe termination of the (0001) surface at low temperatures, but when the effect of raising the temperature is considered, an energy minimum is found, also at 33.33% impurity coverage. In contrast, the O terminated (0001) surface has a minimum in the segregation energy for between 16.67 and 33.33% depending on the cation being considered. 相似文献
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食盐析出实验对盐湖盆地沉积研究的启示 总被引：1，自引：0，他引：1
将物理模拟实验结果与地震、岩芯资料相结合,对东濮凹陷盐岩沉积的古地理位置、成因机制提出新的认识。研究认为:洼陷带的边缘、中央隆起带等浅水部位是盐岩沉积较早的部位,可以沉积厚度大、粒度小的单盐层,而靠近湖盆中心,矿物结晶时间充分,沉积的盐岩粒度大,单盐层厚度可大可小,甚至可以缺失,盐岩沉积的古地理位置受古盐度影响明显;盐湖盆地绝大多部分地区,湖水有一定深度时便已形成湖底盐层,湖水变浅时盐层已具备一定厚度,保证了其下部泥页岩的还原环境,盐岩沉积后基本保持了原有的构造形态,其上可以再次接受泥页岩沉积;湖盆边缘的渗滤带在湖水退去以后仍可以沉积盐岩,该处盐层最薄、粒度细小,下部地层常见氧化环境标志。 相似文献
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Steven Tufts Author Vitae 《Geoforum》2004,35(1):47-58
Toronto’s quest to host the Summer Olympic Games has dominated both contemporary planning discourse and practice. For some, the pursuit of the games embodies Toronto’s transformation into a ‘competitive’ global city. Relatively unexplored in this discourse are the contradictory roles that labour plays in contemporary urban development. I argue that the new labour geography can provide some interesting insights into such processes. Specifically, labour geographers have given workers with divergent interests greater agency in shaping economic landscapes and have noted the multi-scalar organisation of labour. The paper looks at the contradictory and conflicting positions held by different labour unions in Toronto toward the city’s bid to host the 2008 Olympics. The case study suggests that labour is an active agent in processes shaping contemporary Toronto and support the bid for complex reasons ranging from the promise of jobs to potential future organising opportunities. 相似文献
18.
舒德干 《《地质学报》英文版》2018,92(2):II-II
正Dear Authors and Readers:First of all,on behalf of the new Editorial Board,I would like to express our sincere appreciation for your continuing support of our journal.This journal,founded in 1922,is the oldest geological journal in China.As the flagslhip journal of the Geological Society of China,it has become more and nmore influcntial in earth scicences in China and beyond.The journal is now indexed by SCI,CA and more than 20 other databases,with an impact factor varying between 1.58 and 2.15 from year to year.It is co-publishd by the Gcoloigical Society of 相似文献
19.
《《地质学报》英文版》2017,91(3):II-II
<正>Dear Authors and Readers:First of all,on behalf of the new Editorial Board,I would like to express our sincere appreciation for your continuing support of our journal.This journal,founded in 1922,is the oldest geological journal in China.As the flagship journal of the Geological Society of China,it has become more and more influential in earth sciences in China and beyond.The journal is now indexed by SCI,CA and more than 20 other databases,with an impact 相似文献
20.
《《地质学报》英文版》2017,91(5):II-II
<正>Dear Authors and Readers:First of all,on behalf of the new Editorial Board,I would like to express our sincere appreciation for your continuing support of our journal.This journal,founded in 1922,is the oldest geological journal in China.As the flagship journal of the Geological Society of China,it has become more and more influential in earth sciences in China and beyond.The journal is now indexed by SCI,CA and more than 20 other databases,with an impact factor varying between 1.58 and 2.15 from year to year.It is co-published by the Geological Society of 相似文献