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1.
Hirokazu Fujimaki 《Contributions to Mineralogy and Petrology》1986,94(1):42-45
Concentration ratios of Hf, Zr, and REE between zircon, apatite, and liquid were determined for three igneous compositions: two andesites and a diorite. The concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient. Although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients, those for the apatite in the diorite may deviate from the partition coefficients. The HREE partition coefficients between zircon and liquid are very large (100 for Er to 500 for Lu), and the Hf partition coefficient is even larger. The REE partition coefficients between apatite and liquid are convex upward, and large (D=10–100), whereas the Hf and Zr partition coefficients are less than 1. The large differences between partition coefficients of Lu and Hf for zircon-liquid and for apatite-liquid are confirmed. These partition coefficients are useful for petrogenetic models involving zircon and apatite. 相似文献
2.
Atlantic tomcod larvae, hatching in late February and early March 1975 and 1976 into a regime of accelerating river flows, were moved rapidly downriver from milepoint 42–54 (MP 0 is the estuary mouth) to the most seaward reaches of the estuary. This resulted in a spatiotemporal distribution markedly different from that of other Hudson River fish species. Peak tomcod density on posthatch sampling dates was observed most frequently at the George Washington Bridge station (MP 11). Correlation between movements of the 1.0‰ salt front and movements of the age-0 tomcod population was high (r=0.82); and may have been enhanced by high freshwater flows. The population epicenter was always seaward of the 1.0‰ salt front and mean distance between the two was 16–17 km. Moved by tidal and freshwater flows, the tomcod population oscillated between MP 0 and MP 43 during March–May 1973–1976. Location of the population epicenter after mid march was predicted (r2=0.76) to be seaward of the Tappan Zee Bridge (MP 30) when freshwater flows were greater than 450 m3 s?1. During flow regimes greater than 1,290 m3 s?1, the epicenter was predicted to be seaward of the George Washington Bridge (MP 11). An optimum-allocation sampling design for age-0 tomcod showed that 58% of the total effort from mid March to early June should be directed to the river region between MP 0 and MP 24, a region largely ignored in previous studies. *** DIRECT SUPPORT *** A01BY066 00013 相似文献
3.
A range of mineral magnetic measurements have been carried out on archaeological sediments from Orkney and Cyprus. In a soil profile from Orkney, a magnetic enhancement factor of over 200 is observed in susceptibility data between the bedrock and a Norse sediment. The magnetic enhancement is associated with an increase in superparamagnetic grains probably caused by burning. Until now it has proved difficult to confirm the presence of superparamagnetic grains in natural samples using room temperature magnetic measurements. However, clear differences are to be found between the hysteresis loops of various magnetic domain states, including superparamagnetism. An algorithm has been developed to unmix hysteresis loops in terms of constituent domain states of ferrimagnetic iron oxides. Unmixing 128 hysteresis loops of archaeological sediments has shown that the dominant domain state in all sediments is superparamagnetic. Remarkably uniform superparamagnetic grain sizes of between 80 and 95 Å were found for all 128 sediments. © 1999 John Wiley & Sons, Inc. 相似文献
4.
Five seismic events occurred between August 1979 and May 1980 in the Belchatow trench area in central Poland, where large brown-coal deposits have been surface-mined since 1976. The three largest shocks had a local magnitudeML = 3.5 , seismic momentMo = 1.5 · 1014 N-m and source radiusr = 350m , approximately. The tremors had maximum intensity between 5 and 6, and from the magnitude—intensity—depth relation, the focal depth was estimated to be between 1 and 5 km.
The Belchatow tremors are the manifestation of an unusual type of induced seismicity, i.e., seismicity connected with surface mining. The removal of overburden and extensive ground-water withdrawal by the mining operations seem to be direct factors responsible for stress concentration, although preexisting tectonic stress might be the most important indirect factor responsible for the origin of these events. 相似文献
5.
As an extinct group, the origin, diversification and relationships of Cambrian lobopods have long been one of the most hotly-debated subjects. Lobopods used to be regarded as closely related to modern onychophorans and tardigrades, but the similarities are based on the few species of Cambrian lobopods and often on a fairly general level. With the discovery of new creatures and based on new observations on fossil lobopods, we consider that Cambrian lobopods show great diversity and reveal a close relationship between Cambrian lobopods and arthropods. In addition, comparison between the dorsal spines of Cambrian lobopods and small shelly fossils suggest that Cambrian lobopods might have originated from the Meishucun radiation and diversified in the Qiongzhusi radiation. 相似文献
6.
Mahfuzur Rahman Chen Ningsheng Golam Iftekhar Mahmud Md Monirul Islam Hamid Reza Pourghasemi Hilal Ahmad Jules Maurice Habumugisha Rana Muhammad Ali Washakh Mehtab Alam Enlong Liu Zheng Han Huayong Ni Tian Shufeng Ashraf Dewan 《地学前缘(英文版)》2021,12(6):16-35
Bangladesh experiences frequent hydro-climatic disasters such as flooding.These disasters are believed to be associated with land use changes and climate variability.However,identifying the factors that lead to flooding is challenging.This study mapped flood susceptibility in the northeast region of Bangladesh using Bayesian regularization back propagation(BRBP)neural network,classification and regression trees(CART),a statistical model(STM)using the evidence belief function(EBF),and their ensemble models(EMs)for three time periods(2000,2014,and 2017).The accuracy of machine learning algorithms(MLAs),STM,and EMs were assessed by considering the area under the curve-receiver operating char-acteristic(AUC-ROC).Evaluation of the accuracy levels of the aforementioned algorithms revealed that EM4(BRBP-CART-EBF)outperformed(AUC＞90％)standalone and other ensemble models for the three time periods analyzed.Furthermore,this study investigated the relationships among land cover change(LCC),population growth(PG),road density(RD),and relative change of flooding(RCF)areas for the per-iod between 2000 and 2017.The results showed that areas with very high susceptibility to flooding increased by 19.72％between 2000 and 2017,while the PG rate increased by 51.68％over the same period.The Pearson correlation coefficient for RCF and RD was calculated to be 0.496.These findings highlight the significant association between floods and causative factors.The study findings could be valuable to policymakers and resource managers as they can lead to improvements in flood management and reduction in flood damage and risks. 相似文献
7.
Raman spectra of aqueous systems containing sulfur dioxide, elemental sulfur and sulfate indicate that the equilibrium between these species is catalyzed by elemental sulfur. Therefore, dynamic equilibrium can be expected under conditions prevalent on Venus, on Io and in epigenic sulfur deposits. 相似文献
8.
Petrogenetic modeling of the Recent lava succession of Santa Barbara and Pico Alto volcanoes and associated basaltic lavas
indicates that there are two discrete lava series present, one erupted from the axial rift linking the two central volcanoes
and one associated with monogenetic cones scattered around the flanks of Santa Barbara. The felsic lavas of both volcanoes
are peralkaline and appear to be derived from associated basalts by fractional crystallization of an assemblage including
essential amphibole. Trace element abundances in the felsic lavas, particularly those of Sr and REE, cannot be reconciled
with an origin through partial melting of basaltic material at the base of the volcanic pile. The difference between the comenditic
and pantelleritic differentiation trends of Santa Barbara and Pico Alto is attributed primarily to FO2 control of the crystallizing assemblage, probably related to thermal dissociation of magmatic water in the Santa Barbara
magma chamber. This effect may be augmented by minor differences in parent basaltic compositions, the Pico Alto pantellerites
being derived from the rift basalts whereas the Santa Barbara comendites are derived from the off-rift basalts. A compositional
gap between 54 and 64% silica content in the lavas is not present if the suite is extended to include co-magmatic hypabyssal
xenoliths, leading to the inference that the gap in this and other bimodal suites results solely from a relative inability
of magma of intermediate composition to erupt. 相似文献
9.
Terrestrial geochemistry of Cd,Bi, Tl,Pb, Zn and Rb 总被引：1，自引：0，他引：1
About 2000 common magmatic, metamorphic and sedimentary rocks and rockforming minerals contained in 465 individual samples have been analyzed for 6 trace metals and potassium with high precision, mainly by combined distillation and AAS methods. Estimates of average abundances in the continental crust are: 98 ppb Cd. 82 ppb Bi. 490 ppb Tl, 14.8 ppm Pb, 77 ppm Zn and 98 ppm Rb (K/Rb: 223). These averages are close to the mean concentrations of the 6 elements in sedimentary and in low to medium grade metamorphic rocks. In relation to the upper mantle the earth's crust has very effectively accumulated Rb, Pb, Tl (and Bi). Cd and Zn are equally distributed between the upper and lower crust. Bi, Tl, Rb, Pb and K are accumulated in the upper relative to the lower continental crust by factors between 3.5 and 1.4. This is mainly due to higher concentrations in granites and lower abundances in granulites relative to gneisses and schists. The five metals form large ions with bulk coefficients less than one for the partition between metamorphic rocks and anatectic granitic melts. The major hosts of Rb, Tl, Pb and Bi in rocks are minerals with 8- to 12-coordinated sites such as mica, K-feldspar, plagioclase etc. (except for some preference of Bi for sphene and apatite). As examples of significant correlations those of Pb with Tl, K, Bi and Rb in mafic rocks and of Bi with K, Rb, Tl and Pb in sedimentary rocks can be reported. In granites and gneisses hydroxyl containing Fe2+-Mg-silicates are major host minerals for Zn and Cd. Except in some carbonate rocks Cd has no preference for Ca minerals. 相似文献
10.
A. R. Crawford 《Tectonophysics》1974,22(1-2)
A detailed examination of a Gondwanaland re-assembly of Peninsular India and part of East Antarctica permits several conclusions to be drawn largely from data from the Indian coastal belt, which includes Ceylon. These are that original major granulite metamorphism probably occurred at about 2000 m.y., and that the sinuosity of the granulite belt, now split into two coastal belts, is a later distortion, outlined by anorthosite occurrences in India, which probably occurred between 720 and 450 m.y. Brief mention is made of the continuation of this belt into Madagascar, and of the problem of what lay between Western Australia and India in Gondwanaland. 相似文献
11.
J. A. Whitehead 《Estuaries and Coasts》1998,21(2):281-293
Simple theoretical box-models and laboratory experiments demonstrate that an estuary subjected to freshwater flux and heating or cooling can possess more than one stable, stationary state if a well-defined set of forcing conditions are present. Two types of estuaries can develop such multiple temperature-salinity states. The same may be true of continental shelves and marginal seas. One type receives freshwater runoff from land but is cooled in the winter. The second has net freshwater loss from evaporation but also receives strong solar heating. Criteria are found which define the conditions needed for multiple states. It is shown that under most conditions, the density difference vetween estuary and ocean would be dominated by salinity if the inlet is sufficiently small (such as inland seas). In contrast, if the inlet is sufficiently wide and atmospheric cooling and heating is sufficiently great, the density difference would be dominated by temperature. Multiple states lie between these extremes. One of the multiple states is dominated by the salinity difference between estuary and ocean, the other by temperature difference. Each state is stable. 相似文献
12.
Geoff A. Wilson 《Geoforum》2012,43(6):1218-1231
This article investigates the impacts of globalization processes on community resilience. It argues that theoretical concepts such as transition theory can provide a lens through which resilience pathways at community level can be better understood, and proposes a framework focused on a social resilience approach for understanding community resilience as the conceptual space at the intersection between economic, social and environmental capital. It argues that certain types of communities are losing resilience through increased embeddedness into globalized pathways of decision-making, while other communities may be gaining resilience, although not one system is either totally resilient or totally vulnerable. Striking the right ‘balance’ between communities and their scalar interactions with the global level is key for maximization of community resilience: while too much isolation of a community may be bad in light of over-dependency on local resources, skills and people, ‘over-globalization’, with possible loss of autonomy and identity, may be equally fraught with problems. In particular, relocalized communities have, so far, not shown much tangible success, as almost all members of the relocalization process at community level are simultaneously embedded within the global capitalist system through their dependencies on global economic processes. 相似文献
13.
《Chemical Geology》2006,225(1-2):1-15
Microprobe monazite dating has been increasingly used to constrain the timing of deformation and metamorphism because of the potential to date very small monazite domains (down to 5 μm or less) in structural and petrologic context. This paper presents an analytical strategy, presentation format, and error considerations for microprobe monazite dating. The strategy involves high-resolution compositional mapping to delineate compositional domains within monazite crystals. Then for each compositional domain, a series of Th, U and Pb analyses are made, and a single date and error are calculated. The number of analyses in each domain is determined by the desired statistical precision of the date. Results from several monazite grains are typically combined and, along with textural relationships, are used to build an argument that the dates constrain the age of a deformation or metamorphic event. The total error involves three components: short-term random error (dominated by counting statistical uncertainty), short-term systematic error (uncertainty in background correction, conductive coating variation, and calibration), and long-term systematic error (uncertainty in standard composition, mass absorption factors, decay constants, etc.). In homogeneous compositional domains, short-term random errors (2σ) of less than 10 m.y. can be obtained from five to ten analyses. However, short-term systematic error, mainly background estimation uncertainty, would typically result in a doubling of the magnitude of random error. Microprobe dates are presented as a single Gaussian probability distribution for each domain, along with representative compositional maps. It is recommended that a consistency standard be analyzed during each analytical session and the results be reported along with those from the unknown. This proposed strategy and format are compatible with those of other geochronological techniques; they incorporate analytical limitations associated with trace, as opposed to major element, microprobe analysis, and will allow better comparisons to be made between labs and between different geochronological techniques. 相似文献
14.
The comparison of pollen diagrams and their inferred vegetational histories are an important component of palaeoecological research. Radiocarbon-dated pollen profiles from three cores taken from two adjacent mires located in northern Cumbria, Bolton Fell Moss and Walton Moss, have been used to reconstruct the Late Holocene vegetation history between the Bronze Age and the present day. The profiles have been interpreted in the light of available archaeological and historical records and, although the pollen records are broadly similar, there are some notable differences between them, particularly during Iron Age and medieval times. Dissimilarities between the diagrams are explored numerically, and the statistical and palynological results are discussed in relation to pollen representativity. The results suggest that it may be advantageous to construct more than one pollen diagram from a mire, or even adjacent mires, as extra-local pollen may be a more important part of the pollen rain than previously envisaged. © 1998 John Wiley & Sons, Ltd. 相似文献
15.
锡林浩特岩群是内蒙古中东部锡林郭勒微地块内原锡林郭勒杂岩的重要组成部分,由一套片麻岩夹层状斜长角闪岩、磁铁石英岩和变粒岩等变质岩组成,形成于中元古代［1］。岩群中片麻岩样品显示轻稀土元素富集的中等分异特征((La/Yb)N=4.71~7.97),斜长角闪岩具有平坦型((La/Yb)N=0.74~0.95)和轻稀土元素微弱富集型((La/Yb)N=1.06~3.63)两种稀土元素配分模式。在微量元素N MORB标准化图解中,斜长角闪岩显示出洋中脊玄武岩和岛弧玄武岩的过渡类型特征。同时结合岩相学和岩石地球化学图解分析,推断片麻岩原岩为富含泥质的亚杂砂岩,而斜长角闪岩原岩为一套具有拉斑质到钙碱性过渡型特征的玄武岩;变质沉积岩形成于活动大陆边缘大陆岛弧环境;变质基性火山岩形成于岛弧弧后盆地。二者指示锡林浩特岩群形成于活动大陆边缘体系。 相似文献
16.
Pools,riffles, and channelization 总被引：2，自引：0，他引：2
Edward A. Keller 《Environmental Geology》1978,2(2):119-127
The addition of regularly spaced deeps (pools) and shallows (riffles) that provide a variety of flow conditions, areal sorting
of stream-bed material, cover for wildlife, and a positive aesthetic experience, may be desirable in many channel projects.
Such designs will reduce adverse environmental impacts of stream channel modifications.
Analysis of variance for pool-to-pool spacing data suggests that there is no significant difference with respect to channel
width between pools that form in natural streams and those in streams affected by a variety of human uses. Short of channelization,
which changes the channel width, pools and riffles, within limits, are not particularly sensitive to environmental stress.
Experiments in Gum Branch near Charlotte, North Carolina, support the hypothesis that channel form and process evolve in harmony
and that manipulation of cross-channel morphology can influence the development of desired channel processes. Planned manipulation
of its channel form induced Gum Branch to develop as desired. Morphologic stability consisting of incipient point bars, pools,
and riffles was maintained over a period of high magnitude flood events, only to be degraded later by a wave of sediment derived
from upstream construction and stream-bank failures. Thus, environmentally desirable channel morphology in urban streams cannot
remain stable if changes in the sediment load or storm-water runoff exceed the limits of the stream's ability to make internal
adjustments while maintaining morphologic stability. 相似文献
17.
The oceans play an important role in the geochemical cycle of methyl bromide (CH3Br), the major carrier of O3-destroying bromine to the stratosphere. The quantity of CH3Br produced annually in seawater is comparable to the amount entering the atmosphere each year from natural and anthropogenic sources. The production mechanism is unknown but may be biological. Most of this CH3Br is consumed in situ by hydrolysis or reaction with chloride. The size of the fraction which escapes to the atmosphere is poorly constrained; measurements in seawater and the atmosphere have been used to justify both a large oceanic CH3Br flux to the atmosphere and a small net ocean sink. Since the consumption reactions are extremely temperature-sensitive, small temperature variations have large effects on the CH3Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The net CH3Br flux is also sensitive to variations in the rate of CH3Br production. We have quantified these effects using a simple steady state mass balance model. When CH3Br production rates are linearly scaled with seawater chlorophyll content, this model reproduces the latitudinal variations in marine CH3Br concentrations observed in the east Pacific Ocean by Singh et al. [1983] and by Lobert et al. [1995]. The apparent correlation of CH3Br production with primary production explains the discrepancies between the two observational studies, strengthening recent suggestions that the open ocean is a small net sink for atmospheric CH3Br, rather than a large net source. The Southern Ocean is implicated as a possible large net source of CH3Br to the atmosphere. Since our model indicates that both the direction and magnitude of CH3Br exchange between the atmosphere and ocean are extremely sensitive to temperature and marine productivity, and since the rate of CH3Br production in the oceans is comparable to the rate at which this compound is introduced to the atmosphere, even small perturbations to temperature or productivity can modify atmospheric CH3Br. Therefore atmospheric CH3Br should be sensitive to climate conditions. Our modeling indicates that climate-induced CH3Br variations can be larger than those resulting from small (+/- 25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs. Future measurements of marine CH3Br, temperature, and primary production should be combined with such models to determine the relationship between marine biological activity and CH3Br production. Better understanding of the biological term is especially important to assess the importance of non-anthropogenic sources to stratospheric ozone loss and the sensitivity of these sources to global climate change. 相似文献
18.
Accessory minerals are thought to play a key role in controlling the behaviour of certain trace elements such as REE, Y, Zr, Th and U during crustal melting processes under high-grade metamorphic conditions. Although this is probably the case at middle crustal levels, when a comparison is made with granulite-facies lower crustal levels, differences are seen in trace element behaviour between accessory minerals and some major phases. Such a comparison can be made in Central Spain where two granulite-facies terranes have equilibrated under slightly different metamorphic conditions and where lower crustal xenoliths are also found. Differences in texture and chemical composition between accessory phases found in leucosomes and leucogranites and those of melanosomes and protholiths indicate that most of the accessory minerals in melt-rich migmatites are newly crystallized. This implies that an important redistribution of trace elements occurs during the early stages of granulite-facies metamorphism. In addition, the textural position of the accessory minerals with respect to the major phases is crucial in the redistribution of trace elements when melting proceeds via biotite dehydration melting reactions. In granulitic xenoliths from lower crustal levels, the situation seems to be different, as major minerals show high concentration of certain trace elements, the distribution of which is thus controlled by reactions involving final consumption of Al-Ti-phlogopite. A marked redistribution of HREE–Y–Zr between garnet and xenotime (where present) and zircon, but also of LREE between feldspars (K-feldspar and plagioclase) and monazite, is suggested. 相似文献
19.
Heinz -Günter Stosch 《Contributions to Mineralogy and Petrology》1981,78(2):166-174
The partitioning of divalent (Co, Ni) and trivalent (Sc, Cr) trace elements between olivine, ortho- and clinopyroxene and spinel from spinel peridotite xenoliths has been investigated. These peridotites cover a wide range in modal composition from dunite to primitive lherzolites and have equilibrated in the upper mantle between >900° C and <1,200° C.The distribution of Co and Ni shows only minor variation through the whole sequence. In contrast, Sc partitioning between ortho- and clinopyroxene and olivine and clinopyroxene as well as Cr partitioning between olivine and clinopyroxene or olivine and orthopyroxene display high but systematic variations which can be assigned to dependences upon equilibration temperatues. Empirical temperature calibrations are given for Sc-orthopyroxene/clinopyroxene, Sc-olivine/clinopyroxene and Cr-olivine/clinopyroxene which, in principle, may permit to estimate equilibration temperatures not only for lherzolites or harzburgites but for orthopyroxene-free peridotites, too.Sc and Ni partition coefficients between spinel and mantle silicate minerals are primarily dependent upon the major element composition of spinel (e.g. Cr and Al) although a temperature dependence can still be identified. Probably such compositional effects are not observed for trace element partitioning between pyroxenes and olivine or ortho- and clinopyroxene only for the reason that in normal spinel peridotites these minerals show much less variation in major element composition than their coexisting spinels. 相似文献
20.
四川汶川地震诱发滑坡与峰值速度的关系 总被引：1，自引：0，他引：1
利用汶川地震诱发的滑坡资料和得到的地震动数据,对地震诱发滑坡与峰值速度的关系进行了分析,得到一些基本认识：①地震诱发滑坡与地震动峰值速度(PGV)存在明显的正相关性,可以利用PGV作为判别地震滑坡的判据;②汶川地震龙门山震区可以触发地震滑坡的PGV下限约为0.5m/s;③龙门山震区可以触发地震滑坡的PGV上限约为1.5m/s;④建立了汶川地震龙门山震区PGV衰减关系,可用以估计地震滑坡致灾的范围。利用地震动参数研究地震诱发滑坡具有很好的一致性,可以克服应用烈度时存在的不足。上述研究结果可以应用于震后灾害快速评估工作中,为应急救援方案的制定提供参考信息。 相似文献