The corrosion of basaltic dykes in evaporites: Ar–Sr–Nd isotope and rare earth elements evidence     

《Chemical Geology》1999,153(1-4):259-279

The corrosion of basaltic dykes from central Germany which intruded during the Tertiary into rock and potash salts of Upper Permian age (Zechstein) has been studied. The corrosion behavior of these glassy basalts can serve as a natural analogue for the long-term corrosion expected for nuclear waste glasses in a salt repository. Our data demonstrate mobility and fractionation of the rare earth elements (REE) during a postintrusive circulation of salt brines. The processes controlling this behavior of the REE were dissolution and reprecipitation of phosphates. The K–Ar data document the synintrusive assimilation of a salt phase followed by a postintrusive fluid circulation in the peripheral parts. This circulation removed the assimilated salt and imported highly radiogenic salt Ar which was integrated into newly formed sheet silicates. The central part of the dyke was not affected by this circulation and could retain a mantle gas phase. The Sr isotope data document a synintrusive assimilation of salt Sr and a strong exchange with salt fluids during the postintrusive corrosion which was strongest in a zone next to the chilled dyke margins. This locally stronger alteration is probably due to different cooling and shrinking rates of the basalt at the margins and in the core of the dyke which led to the formation of a highly permeable fractured zone.  相似文献   

Sorption of inorganic 14C on to calcite,montmorillonite and soil     

《Applied Geochemistry》1998,13(1):43-47

Although ¹⁴C occurs naturally, it is also a waste product of the nuclear industry, and can be important because of its long half-life, high mobility as an anion, and ready incorporation into biota. Some aqueous inorganic species are anionic with migration minimally retarded by most geological and soil materials. Substantial retardation is expected when calcite is present, but there are few data to quantify this effect. The present study measured partition coefficient values, R_d (concentration on solids divided by concentration in liquids), of 8–85 l kg⁻¹ for a series of calcite materials and for a carbonated soil. In contrast, R_d was zero for montmorillonite. The series of calcite materials varied in particle size. In order to investigate the effects of particle size, dissolution and degassing of ¹⁴C and ¹²C were monitored as pH was slowly decreased. The change in pH with addition of acid was strongly affected by particle size, as expected, but there was no systematic effect of particle size on the relative dissolution rates of ¹⁴C vs ¹²C, or on R_d. Apparently, surface area was not a limiting factor in the interaction of ¹⁴C with these materials. The ¹⁴C in soil behaved most like the very fine calcite, indicating that the specific surface of the soil carbonate was similar to that of the very fine calcite.  相似文献   

On the use of the Radon Transform in studying nearshore wave dynamics     

《Coastal Engineering》2014

In the nearshore, describing the complex individual wave dynamics remains a key challenge. In this paper we test the ability of the Radon Transform to produce estimates of individual wave celerities and to separate incoming and outgoing waves conserving the temporal characteristics. The Radon Transform is a projection of a two-dimensional field into polar space. Oblique features such as propagating crests in a spatio-temporal space are identified with density peaks in the polar space. In this paper, the Radon Transform is applied to synthetic test cases including a wide range of beach slopes and wave conditions. The Radon Transform shows good skills at estimating individual celerity and separating incoming and outgoing components with a relative RMS error lower than 10%, even a standing wave node. The accuracy is fairly insensitive to wave characteristics whereas the main limitations rise from the sampling scheme and are the number and density of wave gauges. The distance between gauges should be less than one third of the shortest wavelength, while the set of gauges should cover more than one third of the longest wavelength.  相似文献   

Alternative representation of planetary perturbations     

Carol Williams 《Celestial Mechanics and Dynamical Astronomy》1987,43(1-4):35-35

An attempt is made to find a representation of planetary perturbations which does not require a Fourier expansion. For the planetary type three body problem a sequence of canonical transformations is given based on Landen transformations coupled with a rescaling of the time. The expansion is carried out to the order 2 in the Hamiltonian.  相似文献   

Cryogenic carbonates in cave environments: A review     

Karel k  Bogdan P. Onac  Aurel Peroiu 《Quaternary International》2008,187(1):84

Cryogenic cave carbonate (CCC) represents a specific type of speleothem. Its precipitation proceeds at the freezing point and is triggered by freezing-induced concentration of solutes. Compared to classical speleothems (stalagmites, flowstones), CCC occurs as accumulations of loose uncemented aggregates. The grain sizes range from less than 1 μm to over 1 cm in diameter. Karst groundwater chemistry and its freezing rate upon entering the cave are responsible for highly variable grain morphology. Rapid freezing of water results in the formation of CCC powders with grain size typically below 50 μm. Slow freezing of water in caves (usually in systems where the CO₂ escape is partly restricted; e.g., ice covered water pools) results in the formation of large mineral grains, with sizes from less than 1 mm to about 20 mm. The range of carbon and oxygen stable isotope compositions of CCC is larger than for a typical carbonate speleothem. Rapid freezing of water accompanied by a quick kinetic CO₂ degassing results in large ranges of δ¹³C of the CCC powders (between –10‰ and +18‰ PDB). Slow freezing of water, with a restricted CO₂ escape results in gradual increase of δ¹³C values (from −9‰ to +6‰ PDB; data ranges in individual caves are usually much more restricted), accompanied by a δ¹⁸O decrease of the precipitated carbonate (overall range from −10‰ to −24‰ PDB). These unusual trends of the carbonate δ¹⁸O evolution reflect incorporation of the heavier ¹⁸O isotope into the formed ice. New isotope data on CCC from three Romanian ice caves allow better understanding of the carbon and oxygen isotope fingerprint in carbonates precipitated from freezing of bulk water. CCCs are proposed as a new genetic group of speleothems.  相似文献   

Texture development during progressive deformation of hematite aggregates: Constraints from VPSC models and naturally deformed iron oxides from Minas Gerais,Brazil     

《Journal of Structural Geology》2016

We show that naturally-deformed hematite from the Quadrilátero Ferrífero Province, Minas Gerais, Brazil, develops CPOs by dislocation creep, strongly influenced by basal plane parallel glide, even when this is not the favored slip system. Characterization of microstructure and texture, particularly intragranular misorientations, of naturally deformed hematite aggregates by EBSD allowed us to determine the importance of different slip systems, and confirm dislocation creep as the dominant deformation mechanism. Viscoplastic self-consistent (VPSC) models were constructed to constrain the slip systems required to operate for the observed CPO to develop, and its rheological implications. Changes in the CRSS ratio of hematite prism and basal slip systems and deformation regime lead to the development of distinct patterns of hematite crystallographic orientations. The basal slip-dominated simple shear model is the only one that can develop quasi-single-crystal CPO of the kind observed in highly deformed rocks from Quadrilátero Ferrífero. Comparison between naturally deformed hematite aggregates and VPSC models shows that CPO development of hematite is strongly influenced by a highly viscoplastic anisotropy through dislocation creep on hematite basal plane. Nonetheless, our results demonstrate that even the unfavorable slip systems should be regarded when the bulk rheology of mineral aggregates is evaluated.  相似文献   

Evolution of the lithospheric mantle during passive rifting: Inferences from the Alpine–Apennine orogenic peridotites     

《Gondwana Research》2016

This paper presents an updated review of recent field/structural and petrologic/geochemical studies on orogenic peridotites from the Alpine–Apennine ophiolites (NW Italy). Results provide determinant constraints to the evolution of the lithospheric mantle during passive rifting of the fossil Ligurian Tethys oceanic basin.The pre-rift, spinel lherzolites precursors, preserved in the mantle section of the Ligurian ophiolites, were resident in the lithosphere along an intermediate geothermal gradient (T about 1000 °C, P compatible with spinel-peridotite facies). Passive rifting by far-field tectonic forces induced whole-lithosphere extension and thinning (the a-magmatic stage). After significant thinning of the lithosphere, the passively upwelling asthenosphere underwent decompression melting along the axial zone of extension. Silica-undersaturated melt fractions infiltrated via diffuse/focused porous-flow through the lithospheric mantle under extension (the magmatic stage) and underwent pyroxenes-dissolving/olivine-crystallizing interaction with the percolated host peridotite.Pyroxenes assimilation and olivine deposition modified the melt compositions into silica-saturated. These derivative liquids migrated to shallower, plagioclase-peridotite facies levels, where they stagnated and impregnated/refertilized the lithospheric mantle. Melt thermal advection by melt infiltration heated to temperatures higher than 1200 °C the lithospheric mantle column above the melting asthenosphere.The syn-rift magmatic and tectonic processes induced significant rheological softening/weakening that destabilized the lithospheric mantle of the Europe–Adria plate along the axial zone of extension. The presence of destabilized lithospheric mantle between the future continental margins played a determinant role in promoting the geodynamic evolution from pre-oceanic rifting to oceanic spreading.The active upwelling of hotter/deeper asthenosphere inside the destabilized axial zone promoted transition to active rifting, enhancing continent break-up. Asthenosphere underwent partial melting and formed aggregated MORB liquids that migrated inside high-porosity dunite channels. The MORB liquids formed olivine-gabbro intrusions and pillowed lava flows (the oceanic crustal rocks).This paper evidences the primary role of mantle destabilization by melt infiltration in the geodynamic evolution of the Ligurian Tethys rifting.  相似文献   

人类活动对港湾岸线及景观变迁影响的比较研究————以中国象山港与美国坦帕湾为例   总被引：3，自引：0，他引：3  

刘永超  李加林  袁麒翔  史小丽  浦瑞良  杨磊  卢雪珠 《地理学报》2016,71(1):86-103

利用多时期遥感数据,以10年为时间步长,提取1985-2015年4个时期中国象山港和美国坦帕湾的岸线空间位置,长度和曲折度以及港湾地区景观构型,多样性和破碎度等信息,构建海岸人工化和港湾景观人工干扰指标,探讨人类活动对港湾岸线,景观演变的影响.结果表明:① 近30年来,象山港和坦帕湾自然岸线长度不断缩减,人工岸线长度呈先增后稳定的态势.由于两地人类活动方式的差异,象山港局部岸段形态发生剧烈变化,岸线曲折度不断变小;而坦帕湾岸线形态变化较小,岸线曲折度几乎保持不变.② 1985-1995年,象山港海岸人工化不断加强,1995年以后有所减弱,但人类活动的影响范围逐渐变大,几乎遍及整个港湾海岸.1985-2015年,坦帕湾海岸人工化强度虽有加强,但增幅缓慢,海岸人类活动也主要集中于各沿海城市区域.③ 1985-2005年,象山港和坦帕湾各人工化强度等级样区景观平均斑块面积总体呈减少趋势,但2005-2015年,象山港各强度样区景观平均斑块面积变化趋势不一,坦帕湾各强度样区变幅则较为平稳.④ 1985-2005年,象山港各强度样区景观多样性指数逐渐增大,而坦帕湾变化不一;2005-2015年,两港湾人工化强度由弱至强,景观多样性指数先增后减.⑤ 1985-2005年,象山港和坦帕湾不同人工化强度样区,景观破碎度指数逐渐增大;2005-2015年,两港湾景观破碎度指数呈减小趋势.  相似文献   

Intertidal Invertebrate and Algal Communities on the Rocky Shores of the Bay of Morbihan, Kerguelen (South Indian Ocean)   总被引：3，自引：0，他引：3  

John M.  Lawrence James B.  McClintock 《Marine Ecology》1987,8(3):207-220

Abstract. Both the emergent surfaces and tide pools of the rocky intertidal shores of the Bay of Morbihan, Kerguelen are depauperate in number of macroinvertebrate and macroalgal species. Diversity (H') was high and similar for macroinvertebrates in tide pools from the high to low intertidal and on the emergent surface exposed at extreme low-tide when calculated in terms of numbers of individuals. H' was lower when calculated in terms of energy and twice as high for the tide pool in the high intertidal than the lower tide-pools and the emergent surface. H' for macroalgae was 0 in the highest tide-pool and highest in the lower tide-pools. The density/species-rank curves for the macroinvertebrates and the macroalgae are logarithmic but vary in linearity. Algal biomass was 37 % of the macroinvertebrate biomass on the emergent surface at the extreme low-tide, but 106% in the highest tide-pool. Twenty-three months after denudation of the tide pools, the ratios of total densities of the macroinvertebrates (ind m^-2) to the original densities were 48 % for the pool in the high intertidal, 25 % for the middle tide-pool, and 4 % for the pool in the low intertidal. The diversity indexes for the macroinvertebrates were similar to the original ones. Recolonization at Kerguelen is slow and shows an intertidal gradient. The composition of the rocky intertidal community at Kerguelen results from the rigorous physical environment and the small number and functional types of species. In the absence of major predators on macroinvertebrates and of herbivores on macroalgae, interaction among the species present seems to be competitive in nature.  相似文献   

Environmental history,palaeoecology and human activity at the early Neolithic forager/cultivator site at Kuahuqiao,Hangzhou, eastern China     

James B. Innes  Yongqiang Zong  Zhongyuan Chen  Chun Chen  Zhanghua Wang  Hui Wang 《Quaternary Science Reviews》2009,28(23-24):2277-2294

The date and location of the adoption of rice cultivation by foraging cultures in China are of considerable current interest but its understanding is hampered by lack of information regarding its palaeoenvironmental context. We present detailed multi-proxy palaeoecological research at the earliest-dated site of rice cultivation in the coastal littoral of east China which has revealed the precise environmental setting of this early Neolithic settlement and its incipient cultivation at ca 7750 cal BP. Regional and local environmental changes governed the character of the site and the duration of human activity. After an episode of marine conditions, natural hydrological succession and terrestrialisation of the site preceded fire clearance of marsh fen-carr alder scrub that prepared the ground for cultivation and then maintained a reedswamp-type wet grassland in which rice was grown. Cropping of Typha stands may have formed part of the subsistence base before the site was overwhelmed by marine inundation ca 7200 cal BP, after which rice cultivation spread to Neolithic sites of Hemudu type elsewhere in the coastal lowlands. We suggest that integrated multi-proxy palaeoecological studies are vitally important for the full understanding of such key wetland archaeological sites.  相似文献