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1.
绝大部分的亚硝酸盐和氰化物属于钙钛矿型结构,但有部分化合物为“反”钙钛矿型结构,充填空洞A位的阳离子的拓扑体积为0。阴离子团NO2-和CN-的拓扑体积都近乎常数,分别为41.73Å3和40.03Å3,标准方差σn-1=1.516和σn-1=1.25。由此,进一步证明了原来的一套离子拓扑体积数值的普适性。“反”钙钛矿型结构中A位阳离子的平均半径rA>1.00Å时,三价阳离子会产生扩容效应,其扩容系数大约是其本身拓扑体积的2倍;正钙钛矿型结构中,当A位是由半径较大的Cs+充填时,Cs+也会产生扩容效应,其扩容系数约为24Å3。氰化物中结晶水分子的拓扑体积近乎常数,为24Å3或0。 相似文献
2.
Werner F. Giggenbach 《Geochimica et cosmochimica acta》1984,48(12):2693-2711
At very low fluid/rock mass ratios the hydrothermal alteration process corresponds to isochemical recrystallisation of the primary rock. The resulting full equilibrium assemblage with the composition of an average crustal rock contains the phases albite, K-feldspar, K-mica, biotite, quartz and (depending on temperature) epidote, prehnite or one of the Ca-zeolites. Relative Na+, K+, Mg2+ and Ca2+—solution activities in such a rock-dominated alteration system are uniquely fixed and provide useful reference points with regard to the degree of attainment of full fluid/rock equilibrium. With increasing fluid/rock mass ratios the composition of now increasingly fluid-dominated alteration assemblages is determined by the interplay of three major processes: hydrogen metasomatism as a function of CO2 reactivity increasing with the horizontal distance from major fluid upflow zones and leading to the formation of Al-enriched alteration assemblages; potassium metasomatism accompanied by silicification in or close to major fluid upflow zones leading to potassic and phyllic alteration; sodium, magnesium, calcium metasomatism associated with descending and heating solutions leading to propylytic alteration of recharge zones. Two new parameters, reactivity and exchangeability, determining the effectiveness of fluid components with respect to hydrothermal alteration are introduced. 相似文献
3.
绝大部分的亚硝酸盐和氰化物属于钙钛矿型结构,但有部分化合物为“反”钙钛矿型结构,充填空洞A位的阳离子的拓扑体积为0。阴离子团NO2-和CN-的拓扑体积都近乎常数,分别为41.73Å3和40.03Å3,标准方差σn-1=1.516和σn-1=1.25。由此,进一步证明了原来的一套离子拓扑体积数值的普适性。“反”钙钛矿型结构中A位阳离子的平均半径rA>1.00Å时,三价阳离子会产生扩容效应,其扩容系数大约是其本身拓扑体积的2倍;正钙钛矿型结构中,当A位是由半径较大的Cs+充填时,Cs+也会产生扩容效应,其扩容系数约为24Å3。氰化物中结晶水分子的拓扑体积近乎常数,为24Å3或0。 相似文献
4.
自然界中已发现的硫酸盐矿物主要是表生作用和热液后期的产物,均是在低温、低压条件下形成的。因此,对于硫酸盐化合物来说,由于其结晶条件相似,那么,各种离子(或离子团)在不同的硫酸盐化合物中是否占有大致相同的体积。 相似文献
5.
Ulf Hålenius 《Lithos》1982,15(3):249-251
Linear regression analysis of chemical and X-ray data on natural monoclinic chloritoids yields a general formula for the unit cell volume of the mineral: V = 337.2 ()3 + 814.1 (Å3), where r? is the mean ionic radius of the cations in the brucite-type layer. With this function as a basis, the unit cell volumes (V) and the densities (D) of the members of the pseudo-ternary system Fe-Ctd-Mn-Ctd-Mg-Ctd can be calculated. The V-D surface for reported compositions of natural chloritoids has also been defined. 相似文献
6.
Yamuna Singh R. Viswanathan P. S. Parihar P. B. Maithani 《Journal of the Geological Society of India》2013,81(1):79-90
X-ray diffraction (XRD) studies on the radioactive ore samples from various parts of Rajasthan and Haryana have revealed the presence of several uranium and other atomic mineral occurrences in the albitite belt of western India. The primary uranium minerals (PUMs) are uraninite and brannerite, whereas, the secondary uranium minerals (SUMs) show considerable speciations: phosphate, silicate, hydrous oxide hydrate, and vanadate. Multiple oxides (MOs) are davidite, fergusonite, aeschynite-(Y), microlite, samarskite, euxenite, betafite, and columbite-tantalite. The thorium minerals are huttonite, thorite, uranoan-thorite, thorianite, thorutite, and brabantite. The yttrium and REE-bearing minerals are xenotime, britholite, allanite, chevkinite, tritomite, and monazite. It is noted that the measured unit cell dimension (a0) of the investigated uraninites ranges from 5.4110 Å to 5.4646 Å. The highest unit cell dimension (5.4646 Å) represents a composition (or oxidation grade) of UO2.05, whereas, the lowest one (5.4110 Å) corresponds to a composition of UO2.54. Furthermore, it is also apparent that, with increase in oxidation grade, there is a concomitant decrease in unit cell dimension. As most of the values of ao of uraninites from the albitite belt are high (> 5.45 Å), it may be inferred that the overall temperature of formation of uraninites of the albitite belt was higher (ca. 400°C). However, the low values of a0 in certain localities could be due to the prevalence of relatively low and fluctuating temperature regimes locally (ca. 400°–100° C). Numerous occurrences of refractory, multiple oxides, and REE minerals, in association with uranium mineralisation, also support a high-temperature origin for the investigated uraninites. Binary data plots of unit cell dimension (a0) versus oxidation grade/composition (UO2+x) of uraninites (n = 36) suggest that the gross uranium mineralisation in the albitite belt of western India is mainly linked to regional metamorphism, anatexis, granitic intrusion, metasomatism, and contact metamorphosed granite-pegmatite aureoles and granite-related vein type with hydrothermal overprints, including redistribution of intrinsic sedimentary uranium and its concentration along suitable structural locales. These interpretations are consistent with the known gross geologic features of the albitite belt. Furthermore, the presence of marialite (calcian) in many places in the albitite belt also supports such a contention, as this mineral is known to be restricted to metamorphic and metasomatic environments. The speciation of secondary uranium minerals could be due to the higher oxidation of U4+ to U6+ in surface to near-surface conditions and its (U6+) remobilisation as uranyl ions. The combination of moving uranyl ions with available cations and anions en route caused re-precipitation of U as diversified assemblages of low-temperature uranyl minerals under suitable physicochemical conditions. 相似文献
7.
T. B. Pradeep Kumar Akhileshwar Tiwary Sohail Fahmi 《Journal of the Geological Society of India》2009,73(2):220-228
Mineralisation of uraninite and brannerite occurs in the albitised metasedimentary and intrusive igneous rocks of Kerpura-Tiwari-ka-bas
area in Sikar district, Rajasthan. Samples collected from well dumps contain 0.016 to 1.52% U3O8 with very low ThO2. The host rocks show wide variation in chemical composition due to varying degree of alkali metasomatism, associated alteration
and composition of protoliths. The spatial distribution of uranium in groundwater as well as rock samples from well dumps
indicates localisation of the uranium mineralisation along NNE-SSW and NWSE directions in Kerpura block. Petrographic and
lithogeochemical studies point towards close genetic relationship between alkali metasomatism and uranium mineralisation.
The mineralisation seems to be due to mobilisation of uranium and other LILEs by metasomatising fluids and their deposition
along shear zones at a later stage, which may not be spatially related to zones of intense albitisation. 相似文献
8.
《International Geology Review》2012,54(12):1074-1093
The mineral-fluid equilibria that govern silica redistribution by aqueous fluids in subduction zones were evaluated at constant pressure and temperature in the model system MgO-SiO2-H2O (MSH). At <20 kbar and <1000° C, model H2O-SiO2 fluids liberated via devolatilization in subducting crust will be buffered at or near quartz saturation along any specified subduction P-T path, whereas fluids in equilibrium with model metaperidotites, ranging from dunite to orthopyroxenite protoliths, have silica concentrations significantly below quartz saturation. Isothermalisobaric flow of fluid from the slab to the mantle wedge therefore drives metasomatic reactions that increase the bulk silica content of metaperidotites and decrease the silica content of the fluid. The potential for silica metasomatism increases with depth for all subduction paths and model bulk compositions. At a given depth, the capacity for silica metasomatism increases with temperature and with abundance of forsterite relative to enstatite. Water-rock ratios required to produce metasomatic mineral assemblages decrease with increasing pressure and temperature. Mineral assemblages diagnostic of silica metasomatism at shallow subduction levels require water-rock ratios of >100 moles fluid/cm3 rock; but at depth, flow of only several moles fluid/cm3 rock is sufficient to produce assemblages characteristic of silica metasomatism. Decreasing temperature with time in most subduction zones suggests that the potential for silica metasomatism is greatest at early stages of convergence. Subducted ultramafic rocks showing evidence of high-temperature silica metasomatism therefore may provide windows into early subduction processes. In general, temporal changes in subduction parameters favoring increasing temperatures will enhance the potential for silica metasomatism, whereas those leading to lower temperatures should be expected to decrease the capacity for silica transfer with time. 相似文献
9.
Metasomatism and fluid flow in ductile fault zones 总被引：8，自引：0，他引：8
Observed major element metasomatism in 5 amphibolite facies ductile fault zones can be explained as the inevitable consequence of aqueous fluid flow along normal temperature gradients under conditions of local chemical equilibrium. The metasomatism does not require the infiltration of chemically exotic fluids. Calculations suggest that metasomatized ductile fault zones are typically infiltrated by 105 moles H2O/cm2, fluid flow is in the direction of decreasing temperature, and fluids contain about 1.0 molal total chloride. Where available, stable isotopic alteration data confirm both flow direction and fluid fluxes calculated from major element metasomatism. The fluid fluxes inferred from metasomatism do not require large-scale fluid recirculation or mantle sources if significant lateral fluid flow occurs in the deep crust. Time-integrated fluid fluxes are combined with estimates of flow duration to constrain average flow rates and average permeabilities. Rocks in ductile fault zones are probably much more permeable during metasomatism (average permeabilities of 10-17 to 10-15 m2) than rocks normally are during regional metamorphism (10-21 to 10-18 m2). Estimated average fluid flow rates (3.5×10-3 to 0.35 m/yr) are insufficient, however, to significantly elevate ambient temperatures within ductile faults. Fluid flow in the direction of decreasing temperature may increase the ductility of silicate rocks by adding K to the rocks and thereby driving mica-forming reactions. 相似文献
10.
《International Geology Review》2012,54(3):187-194
Various processes of metasomatism, such as biotitization, aegiritization, and nephelinization, control the ultimate appearance of rocks just as much as magmatic stages of their development. These processes have been brought to light in small composite intrusions in the northern part of the Siberian shield. The aegiritization and nephilinization reconstitute melanocratic rocks with nonalkaline pyroxene into mesocratic rocks with alkaline pyroxene. Of great interest is the conversion of dolerite at the contact with an alkaline intrusion into a rich nepheline rock, which retains vestiges of a poikilophitic texture. The investigation showed that metasomatism is involved in formation of alkaline rocks. Such rocks as carbonates were evidently formed here through the metasomatism of alkaline and nepheline syenite. ---Auth. 相似文献
11.
湘东南汝城盆地火山岩的元素地球化学及源区性质讨论 总被引：12，自引：4，他引：12
湘东南汝城盆地火山岩系由辉绿岩、玄武岩和玄武质火山碎屑岩组成 ,属于低钾拉斑玄武岩系。玄武岩全岩K Ar年龄为 ( 12 8 4± 4 2 )Ma ,辉绿岩全岩K Ar年龄为 ( 112 1±3 2 )Ma。元素地球化学分析表明火山岩系具有同一岩浆源区 ,其形成以部分熔融方式为主。岩石微量元素出现大离子亲石元素Rb、Ba、Th、U的富集和高场强元素Ta、Nb、Ti的亏损。强不相容元素含量的比值表明岩浆源区明显偏离原始地幔组分 ,具有富集型地幔的特征。岩浆源区主要受到地壳物质混染以及来自消减残留板片析出流体的交代改造作用。 相似文献
12.
Thermal expansion data, determined by powder X-ray diffraction methods are presented for 11 members of the (Li,Na,K,Rb)8(Al6Si6O24)Cl2 solid solution series, 3 members of the (Na,K)8(Al6Si6O24)Br2 solid solution series and Na8(Al6Si6O24)I2. Only the latter showed a discontinuity in its expansion curve at 810° C wigh a mean linear expansion coefficient of 22.0×10?6 °C?1 below and 7.7×10?6 °C?1 above the discontinuity. The mean expansion coefficients from 0° to 500° C decrease gradually over the range of room temperature cell edges from 8.4 to 8.89 Å, then increase up to a cell edge of 9.01 Å above which they decrease sharply and extrapolate to a zero coefficient at 9.4 Å. These variations may be related to the expansion characteristics of the bonds between the cavity cations and cavity anions in different sodalites. The aluminosilicate-sodalites which show a discontinuity in their thermal expansion curves are those with large cavity anions, I? or SO 4 2? ; the discontinuity is believed to occur at the point when the x-coordinate of the cavity cation becomes 0.25. 相似文献
13.
P. GONCALVES E. OLIOT D. MARQUER J. A. D. CONNOLLY 《Journal of Metamorphic Geology》2012,30(7):703-722
Alpine deformation in the Grimsel granodiorite (Aar massif, Central Alps) at greenschist facies conditions (6.5 ± 1 kbar for 450°C ± 25°C) is characterized by the development of a network of centimetre to decametre localized shear zones that surround lenses of undeformed granodiorite. Localization of deformation is assumed to be the result of a first stage of extreme localization on brittle precursors (nucleation stage) followed by a transition to ductile deformation and lateral propagation into the weakly deformed granodiorite (widening stage). A paradox of this model is that the development of the ductile shear zone is accompanied by the crystallization of large amounts of phyllosilicates (white mica and chlorite) that maintains a weak rheology in the localized shear zone relative to the host rock so that deformation is localized and prevents shear zone widening. We suggest that chemical processes, and more particularly, the metamorphic reactions and metasomatism occurring during re‐equilibration of the metastable magmatic assemblage induced shear zone widening at these P–T–X conditions. These processes (reactions and mass transfer) were driven by the chemical potential gradients that developed between the thermodynamically metastable magmatic assemblage at the edge of the shear zone and the stable white mica and chlorite rich ultramylonite formed during the first stage of shear zone due to localized fluid infiltration metasomatism. P–T and chemical potential projections and sections show that the process of equilibration of the wall rocks (μ–μ path) occurs via the reactions: kf + cz + ab + bio + MgO + H2O = mu + q + CaO + Na2O and cz + ab + bio + MgO + H2O = chl + mu + q + CaO + Na2O. Computed phase diagram and mass balance calculations predict that these reactions induce relative losses of CaO and Na2O of ～100% and ～40% respectively, coupled with hydration and a gain of ～140% for MgO. Intermediate rocks within the strain gradient (ultramylonite, mylonite and orthogneiss) reflect various degrees of re‐equilibration and metasomatism. The softening reaction involved may have reduced the strength at the edge of the shear zone and therefore promoted shear zone widening. Chemical potential phase diagram sections also indicate that the re‐equilibration process has a strong influence on equilibrium mineral compositions. For instance, the decrease in Si‐content of phengite from 3.29 to 3.14 p.f.u, when white mica is in equilibrium with the chlorite‐bearing assemblage, may be misinterpreted as the result of decompression during shear zone development while it is due only to syn‐deformation metasomatism at the peak metamorphic condition. The results of this study suggest that it is critical to consider chemical processes in the formation of shear zones particularly when deformation affects metastable assemblages and mass transfer are involved. 相似文献
14.
The space group of an orthopyroxene (En86) from a deep crustal lunar rock (sample 76535) that was previously reported as having space group P21 ca has been re-examined on an automated X-ray diffractometer. In addition to diffractions violating the b-glide of the conventional space group, Pbca (0kl,k-odd) reported in the earlier study, diffractions violating the a-glide of Pbca are also present. Careful examination of both the a-glide- and b-glide-violations shows them to be sharp, with no evidence of diffuse streaks parallel to a *, and with consistent intensities at several rotations about ψ. Diffractions violating the b-glide are in registry with the host, however, those violating the a-glide appear to be out of registry and result from a cell with a slightly longer a of about 18.4 Å, consistent with previous electron diffraction studies. The most reasonable explanation for the observed space group violations is that both the a- and b-glide violations result from ordering of Ca into (100) Guinier-Preston (G-P) zones that possess orthopyroxene topology, but have space group P21/c and a cell of a=18.4 Å, b=8.83 Å, c=5.18 Å, and β=90.0°; whereas the Cadepleted host has space group Pbca and a cell of a= 18.230(6) Å, b = 8.828(2) Å, and c=5.1946(9) Å. In addition to the G-P zones which may compose 12% or more of the sample, the crystal contains (100) lamellae of pigeonite, and other samples from the same rock contain lamellae of augite. 相似文献
15.
16.
Jing Liu Xi Huang Juan Liu Weiqing Wang Wei Zhang Faqin Dong 《Environmental Earth Sciences》2014,72(6):2081-2090
Bone char has been used as a low-cost adsorbent for the removal of As(V) from waste water. The batch experiments show that the Langmuir isotherm describes well the adsorption behavior. The adsorption process follows a pseudo-second-order kinetic model. The column experiments were conducted at pH = 4 and 10 mg/L an initial concentration of As(V). The breakthrough curves were investigated for various conditions, such as different flow rates, column bed heights, adsorption cycles, coexisting cations and anions such as Mn2+, Al3+, PO4 3?, SO4 2? and SiO3 2?. The convection–diffusion equation was used to model the experimental transport data of As(V) for these conditions. It has been found that the coexisting cations can enhance As(V) immobilization and increase retardation factor (R f), and coexisting anions significantly decrease the diffusion coefficient (D L) of As(V). The secondary adsorption phenomena were observed in the breakthrough curves of column studies of As(V) with cations, especially Mn2+. The regeneration experiments using distilled water and 0.1 mol/L NaOH solution were done to evaluate the desorption degree. The total desorbed amounts from whole column for three experiments decreased from 8.98 to 7.67 mg and the desorption degrees increased from 0.51 to 0.71 unexpectedly, which indicates that the regeneration operation is feasible. Finally, the chemical analysis of column effluents and infrared spectroscopic analysis of absorbent both revealed that the ligand exchange and electrostatic interaction are the main removal mechanisms. 相似文献
17.
Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering
James W. Kirchner Clifford S. Riebe Kenneth L. Ferrier Robert C. Finkel 《Journal of Geochemical Exploration》2006,88(1-3):296
Understanding the evolution of geochemical and geomorphic systems requires measurements of long-term rates of physical erosion and chemical weathering. Erosion and weathering rates have traditionally been estimated from measurements of sediment and solute fluxes in streams. However, modern sediment and solute fluxes are often decoupled from long-term rates of erosion and weathering, due to storage or re-mobilization of sediment and solutes upstream from the sampling point. Recently, cosmogenic nuclides such as 10Be and 26Al have become important new tools for measuring long-term rates of physical erosion and chemical weathering. Cosmogenic nuclides can be used to infer the total denudation flux (the sum of the rates of physical erosion and chemical weathering) in actively eroding terrain. Here we review recent work showing how this total denudation flux can be partitioned into its physical and chemical components, using the enrichment of insoluble tracers (such as Zr) in regolith relative to parent rock. By combining cosmogenic nuclide measurements with the bulk elemental composition of rock and soil, geochemists can measure rates of physical erosion and chemical weathering over 1000- to 10,000-year time scales. 相似文献
18.
O. G. Savichev A. K. Mazurov I. I. Pipko V. I. Sergienko I. P. Semiletov 《Doklady Earth Sciences》2016,466(1):59-63
The discharge of major cations and dissolved organic carbon (Corg) with water of the Ob River and its tributaries along the natural zones within the Ob River basin was calculated, and the contribution of the underground component to the volumes of total discharge of the Ob River basin was estimated. It was demonstrated that the total chemical composition of river water and the geochemical discharge in the Ob River basin were consistent with the zoned hydroclimatic conditions controlling the character and duration of interaction in the water–rock system. It was established that the average ionic discharge of the Ob River increased from 6–7 × 106 t/year near Barnaul to 46–47 × 106 t/year near Salekhard; the discharge of dissolved Corg increased from 0.1 × 106 to 3.8 × 106 t/year. Multiple enrichment of underground waters of the Ob River in dissolved organic matter from the upper to the lower reaches was revealed. 相似文献
19.
高岭石-多水高岭石演化系列共包括四种矿物:结晶良好的高岭石、结晶差的或b轴无序的高岭石、7Å多水高岭石和10Å多水高岭石。我们将结晶良好的高岭石和10Å多水高岭石分别视为这一演化系列的两个端元矿物,其余两种矿物则是演化系列的中间矿物。该系列中的矿物同属于1:1型含水的层状铝硅酸盐矿物,因而它们的化学成分基本相同,主要差别是在晶体结构上由于单位结构层沿c轴彼此堆叠的方式而引起从有序向无序变化,同时层间键力的减弱引起水分子进入,促使层间水的含量逐渐增大。基于以上特征,这一系列中的四种类型矿物受热以后的热效应很灵敏,详细研究它们在加热脱水过程中的变化规律,可以加深对矿物特性的认识和鉴别。 相似文献
20.
《Applied Geochemistry》2004,19(4):575-591
The weathering rate of rocks and chemical dynamics of the Corumbataı́ River basin, São Paulo State, Brazil, were evaluated using major elements as natural tracers. This basin has serious environmental problems in terms of quality of surface and rainwater, which affect the determination of weathering rate. The Corumbataı́ River, downstream from Rio Claro City, receives several elements/compounds through anthropogenic activities, with only K, SO42− and alkalinity yielding positive flux values. The negative flux of some anions/cations can be attributed to atmospheric loading mainly related to anthropogenic inputs, providing K a value of 16.7 ton/km−2a−1 for the material removed by weathering in the Corumbataı́ River basin. This is equivalent to 26×106 kg of rock being removed each year by the Corumbataı́ River. The instantaneous flux was found to be a function of discharge, with the majority of dry residue (dissolved load) being transported during the summer (wet) months. The removed material in Corumbataı́ River basin derives mainly from two sub-basins (Cabeças River and Passa Cinco River), where the sandstones weather more easily than siltstones and claystones in the basin. 相似文献