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1.
Lanthanide tetrad effects are often observed in REE patterns of more highly evolved Variscan peraluminous granites of mid-eastern Germany (Central Erzgebirge, Western Erzgebirge, Fichtelgebirge, and Northern Oberpfalz). The degree of the tetrad effect (TE1,3) is estimated and plotted vs. K/Rb, Sr/Eu, Eu/Eu1, Y/Ho, and Zr/Hf. The diagrams reveal that the tetrad effect develops parallel to granite evolution, and significant tetrad effects are strictly confined to highly differentiated samples. Mineral fractionation as a cause for the tetrad effect is not supported by a calculated Rayleigh fractionation, which also could not explain the fractionation trends of Sr/Eu and Eu/Eu1. The strong decrease of Eu concentrations in highly evolved rocks suggests that Eu fractionates between the residual melt and a coexisting aqueous high-temperature fluid. Mineral fractionation as a reason for the tetrad effect is even more unlikely as REE patterns of accessory minerals display similar tetrad effects as the respective host rocks. The accessory minerals inherit the REE signature of the melt and do not contribute to the bulk-rock tetrad effect via mineral fractionation. These results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts: ionic radius and charge, which commonly control the element distribution between mineral and melt, are no longer the exclusive control. The tetrad effect and the highly fractionated trace element ratios of Y/Ho and Zr/Hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence. This distinct trace element behavior and the common features of magmatic-hydrothermal alteration suggest the increasing importance of an aqueous-like fluid system during the final stages of granite crystallization. The positive correlation of TE1,3 with bulk-rock fluorine contents hints at the importance of REE fluorine complexation in generating the tetrad effect. As the evolution of a REE pattern with tetrad effect (M-type) implies the removal of a respective mirroring REE pattern (W-type), the tetrad effect identifies open system conditions during granite crystallization.  相似文献   

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The effect of the group IA and VIIA ions, as well as Mg2+, and the molecules H2O, CO2, H3O+ and OH? on the energy of the Si-O bond in a H6Si2O7 cluster has been calculated using semiempirical molecular orbital calculations (CNDO/2). Three types of elementary processes, i.e. substitution, addition, and polymerization reactions have been used to interpret data on the dynamic viscosity, surface tension and surface charge, hydrolytic weakening, diffusivity, conductivity, freezing point depression, and degree of polymerization of silicates in melts, glasses, and aqueous solutions. As a test of our calculational procedure, observed X-ray emission spectra of binary alkali silicate glasses were compared with calculated electronic spectra. The well known bondlength variations between the bridging bond [Si-O(br)] and the non-bridging bond [Si-O(nbr)] in alkali silicates are shown to be due to the propagation of oscillating bond-energy patterns through the silica framework. A kinetic interpretation of some results of our calculations is given in terms of the Bell-Evans-Polanyi reaction principle.  相似文献   

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The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO2 is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and O18O16 pore water ratios also decrease.The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and O18O16 composition of the silicate phases are in agreement with these interpretations.The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O18 and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.  相似文献   

11.
Dualite has been found at Mount Alluaiv, the Lovozero Pluton, the Kola Peninsula in peralkaline pegmatoid as sporadic, irregularly shaped grains up to 0.3–0.5 mm across. K-Na feldspar, nepheline, sodalite, cancrinite, aegirine, alkaline amphibole, eudialyte, lovozerite, lomonosovite, vuonnemite, lamprophyllite, sphalerite, and villiaumite are associated minerals. Dualite is yellow, transparent or translucent, with conchoidal fracture. The new mineral is brittle, with vitreous luster and white streaks. The Mohs hardness is 5. The measured density is 2.84(3) g/cm3 (volumetric method); the calculated density is 2.814 g/cm3. Dualite dissolves and gelates in acid at room temperature. It is nonfluorescent. The new mineral is optically uniaxial and positive; ω = 1.610(1), ɛ = 1.613(1). Dualite is trigonal, space group R3m. The unit cell dimensions are a = 14.153(9), c = 60.72(5) ?, V = 10533(22) ?, Z = 3. The strongest reflections in the X-ray powder pattern [d, ? (I,%)(hkl)] are as follows: 7.11(40)(110), 4.31(50)(0.2.10), 2.964(100)(1.3.10), 2.839(90)(048), 2.159(60)(2.4.10, 0.4.20), 1.770(60)(2.4.22, 4.0.28, 440), 1362(50)(5.5.12, 3.0.42). The chemical composition (electron microprobe, H2O calculated from X-ray diffraction data) is as follows, wt %: 17.74 Na2O, 0.08 K2O, 8.03 CaO, 1.37 SrO, 0.29 BaO, 2.58 MnO, 1.04 FeO, 0.79 La2O3, 1.84 C2O3, 0.88 Nd2O3, 0.20 Al2O3, 51.26 SiO2, 4.40 TiO2, 5.39 ZrO2, 1.94 Nb2O5, 0.58 Cl, 1.39 H2O,-O = 0.13 Cl2; they total is 99.67. The empirical formula calculated on the basis of 106 cations as determined by crystal structure is (Na29.79Ba0.1K0.10)Σ30(Ca8.55Na1.39REE1.27Sr0.79)Σ12 · (Na3.01Mn1.35Fe0.872+Ti0.77)Σ6(Zr2.61Nb0.39)Σ3 (Ti2.52Nb0.48)Σ3(Mn0.82Si0.18)Σ1(Si50.77Al0.23)Σ51 O144[(OH)6.54(H2O)1.34·Cl0.98]Σ8.86). The simplified formula is Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3 MnSi51O144 (OH,H2O,Cl)9). The name dualite is derived from Latin dualis (dual) alluding to the dual taxonomic membership of this mineral, which is at the same time zirconosilicate and titanosilicate. The crystal structure is characterized by two module types (alluivite-like and eudialyte-like) alternating along a threefold axis with a doubled c period relative to eudialyte and close chemical affinity to rastsvetaevite (Khomyakov et al., 2006a) and labyrynthite (Khomyakov et al., 2006b). According to the authors’ crystal chemical taxonomy of the eudialyte group, the new mineral belongs to one of three subgroups characterized by a 24-layered structural framework. Dualite is a mineral formed during the final stages of peralkaline pegmatite formation. The type material of dualite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? A.P. Khomyakov, G.N. Nechelyustov, R.K. Rastsvetaeva, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, Pt CXXXVI, No. 4, pp. 68–73. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 8, 2005.  相似文献   

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The enthalpies of solution of La2O3, TiO2, HfO2, NiO and CuO were measured in sodium silicate melts at high temperature. When the heat of fusion was available, we derived the corresponding liquid-liquid enthalpies of mixing. These data, combined with previously published work, provide insight into the speciation reactions in sodium silicate melts. The heat of solution of La2O3 in these silicate solvents is strongly exothermic and varies little with La2O3 concentration. The variation of heat of solution with composition of the liquid reflects the ability of La(III) to perturb the transient silicate framework and compete with other cations for oxygen. The enthalpy of solution of TiO2 is temperature-dependent and indicates that the formation of Na-O-Si species is favored over Na-O-Ti at low temperature. The speciation reactions can be interpreted in terms of recent spectroscopic studies of titanium-bearing melts which identify a dual role of Ti4+ as both a network-former end network-modifier. The heats of solution of oxides of transition elements (Ni and Cu) are endothermic, concentration-dependent and reach a maximum with concentration. These indicate a charge balanced substitution which diminishes the network modifying role of Na+ by addition of Ni2+ or Cu2+. The transition metal is believed to be in tetrahedral coordination, charge balanced by the sodium cation in the melts.  相似文献   

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高锰酸盐指数(CODMn)、硝酸根(NO-3)、铵根(NH+4)是判断水体是否受到三氮污染的重要指标。对于测定这三个指标的水样保存方式和时间,地质行业标准和国内外主要国家标准间存在明显差异。地质行业标准规定地下水样品原水室温保存,CODMn和NH+4在3天内测定;NO-3在20天内测定;国家标准和美国标准推荐样品硫酸酸化,避光或冷藏保存,在2~7天内完成CODMn和NO-3和1~7天内完成NH+4测试。为了分析各类标准在样品保存要求上的差异对检测结果的影响,确保检测数据能真实地反映水体污染状况,找寻简便的保存方式,本文在广州地区采集地下水,按照地质行业标准与国家标准进行处理和保存,并在不同时间段对三个指标进行测试。分析验证结果表明:地质行业标准与国家和美国标准关于水样的保存方法均非常可靠。地质行业标准主要针对静态地下水,保存方法相对宽松;国家标准和美国标准适用范围除了地下水,还包括动态的地表水和废水,采样对象成分更为复杂,更不稳定,更容易受外界影响发生变化,故保存条件高于地质标准。在广州地区,采用原水室温避光保存水样,CODMn、NH+4保存时间可为5天,NO-3保存时间可为30天;采用酸化水室温保存水样,CODMn、NO-3和NH+4保存时间可长达30天。这两种方式均比地质行业标准和国家标准推荐的有效时间长,且原水和酸化水室温保存方式相对于冷藏保存方式更为方便。本文提出,如果采集的水样能方便、快速送达实验室,可采用原水保存;如果不能在短时间内送达实验室检测,可采用硫酸酸化保存。  相似文献   

14.
Phosphoinnelite, an analogue of innelite with P > S, has been found in a peralkaline pegmatite vein crosscutting calcite carbonatite at the phlogopite deposit, Kovdor pluton, Kola Peninsula. Cancrinite (partly replaced with thomsonite-Ca), orthoclase, aegirine-augite, pectolite, magnesioarfvedsonite, golyshevite, and fluorapatite are associated minerals. Phosphoinnelite occurs as lath-shaped crystals up to 0.2 × 1 × 6 mm in size, which are combined typically in bunch-, sheaf-, and rosettelike segregations. The color is yellow-brown, with vitreous luster on crystal faces and greasy luster on broken surfaces. The mineral is transparent. The streak is pale yellowish. Phosphoinnelite is brittle, with perfect cleavage parallel to the {010} and good cleavage parallel to the {100}; the fracture is stepped. The Mohs hardness is 4.5 to 5. Density is 3.82 g/cm3 (meas.) and 3.92 g/cm3 (calc.). Phosphoinnelite is biaxial (+), α = 1.730, β = 1.745, and γ = 1.764, 2V (meas.) is close to 90°. Optical orientation is Z^c ∼ 5°. Chemical composition determined by electron microprobe is as follows (wt %): 6.06 Na2O, 0.04 K2O, 0.15 CaO, 0.99 SrO, 41.60 BaO, 0.64 MgO, 1.07 MnO, 1.55 Fe2O3, 0.27 Al2O3, 17.83 SiO2, 16.88 TiO2, 0.74 Nb2O5, 5.93 P2O5, 5.29 SO3, 0.14 F, −O=F2 = −0.06, total is 99.12. The empirical formula calculated on the basis of (Si,Al)4O14 is (Ba3.59Sr0.13K0.01)Σ3.73(Na2.59Mg0.21Ca0.04)Σ3.04(Ti2.80Fe 0.26 3+ Nb0.07)Σ3.13[(Si3.93Al0.07)Σ4O14(P1.11S0.87)Σ1.98O7.96](O2.975F0.10)Σ3.075. The simplified formula is Ba4Na3Ti3Si4O14(PO4,SO4)2(O,F)3. The mineral is triclinic, space group P or P1. The unit cell dimensions are a = 5.38, b = 7.10, c = 14.76 ?; α = 99.00°, β = 94.94°, γ = 90.14°; and V = 555 ?3, Z = 1. The strongest lines of the X-ray powder pattern [d, ? in (I)(hkl)] are: 14.5(100)(001), 3.455(40)(103), 3.382(35)(0 2), 2.921(35)(005), 2.810(40)(1 4), 2.683(90)(200, 01), 2.133(80)( 2), 2.059(40)(204, 1 3, 221), 1.772(30)(0 1, 1 7, 2 2, 2 3). The infrared spectrum is demonstrated. An admixture of P substituting S has been detected in the innelite samples from the Inagli pluton (South Yakutia, Russia). An innelite-phosphoinnelite series with a variable S/P ratio has been discovered. The type material of phosphoinnelite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? I.V. Pekov, N.V. Chukanov, I.M. Kulikova, D.I. Belakovsky, 2006, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2006, No. 3, pp. 52–60. Considered and recommended by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, May 9, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 4, 2005 (proposal 2005-022).  相似文献   

15.
Determinations of 40Ar39Ar ages are reported for seven severely shock-heated chondrites. Shaw gives a plateau age of 4.29 Gyr. Louisville, Farmington, and Wickenburg give well-defined intercept ages of 0.5–0.6 Gyr. Orvinio, Arapahoe, and Lubbock show complex 40Ar39Ar release curves, with age minima of 0.7–1.0 Gyr. Degassing times of 0.5–1.0 Gyr are suggested for these meteorites. Most severely shocked chondrites were apparently not totally degassed of 40Ar by the event, but retained from ~ 2 to ~45% of their 40Ar. When calculated values of the diffusion parameter, Da2, for Ar are examined in Arrhenius plots, they show two distinct linear relationships, which apparently correspond to the degassing of different mineral phases with distinct KCa ratios and different average temperatures for Ar release. The experimentally determined values of Da2 for the high temperature phase of several severely shocked chondrites are ~10?7 to 10?5sec?1 for their determined shock-heating temperatures of ~950°C to ~ 1200°C. The inferred reheating temperatures, Da2 values, and fraction of 40Ar loss during the reheating event for these seven chondrites suggest post-shock cooling rates and burial depth of ~ 10?2 10?4°C/sec and ~0.5–2m, respectively. For three chondrites these cooling rates agree with those determined from Ni diffusion in metal grains: for five chondrites the cooling rates derived from 40Ar and Ni disagree by a factor of ~105. It is suggested that five of these severely shocked chondrites were part of large ejecta blankets containing hot material and cold clasts with a distribution of sizes and that the cooling rate of this ejecta appreciably decreased as a function of time.  相似文献   

16.
Abstract Petrological, oxygen isotope and 40Ar/39Ar studies were used to constrain the Tertiary metamorphic evolution of the lower tectonic unit of the Cyclades on Tinos. Polyphase high-pressure metamorphism reached pressures in excess of 15 kbar, based on measurements of the Si content in potassic white mica. Temperatures of 450–500° C at the thermal peak of high-pressure metamorphism were estimated from critical metamorphic assemblages, the validity of which is confirmed by a quartz–magnetite oxygen isotope temperature of 470° C. Some 40Ar/39Ar spectra of white mica give plateau ages of 44–40 Ma that are considered to represent dynamic recrystallization under peak or slightly post-peak high-pressure metamorphic conditions. Early stages in the prograde high-pressure evolution may be documented by older apparent ages in the high-temperature steps of some spectra. Eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation. Oxygen isotope thermometry of four quartz–magnetite pairs from greenschist samples gives temperatures of 440–470° C which cannot be distinguished from those deduced for the high-pressure event. The exhumation and overprint is documented by decreasing ages of 32–28 Ma in some greenschists and late-stage blueschist rocks, and ages of 30–20 Ma in the lower temperature steps of the Ar release patterns of blueschist micas. Almost flat parts of Ar–Ar release spectra of some greenschist micas gave ages of 23–21 Ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism. Oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a δ18O-enriched fluid. Rather, the compositions indicate that fluid to rock ratios were very low, the isotopic compositions being primarily controlled by those of the protolith rocks. We assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid. A quartz–magnetite sample from a contact metamorphic skarn, taken near the Miocene monzogranite of Tinos, gave an oxygen isotope temperature of 555° C and calculated water composition of 9.1%. The value of δ18O obtained from this water is consistent with a primary magmatic fluid, but is lower than that of fluids associated with the greenschist overprint, which indicates that the latter event cannot be directly related to the monozogranite intrusion.  相似文献   

17.
While many coastal ecosystems previously supported high densities of seagrass and abundant bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have collectively contributed to the decline of these important resources. Despite improvements in wastewater treatment in some watersheds and subsequent reduced nutrient loading to neighboring estuaries, seagrass and bivalve populations in these locations have generally not recovered. We performed three mesocosm experiments to simultaneously examine the contrasting effects of nutrient loading and historic suspension-feeding bivalve densities on the growth of eelgrass (Zostera marina), juvenile bivalves (northern quahogs, Mercenaria mercenaria; eastern oysters, Crassostrea virginica; and bay scallops, Argopecten irradians), and juvenile planktivorous fish (sheepshead minnow, Cyprinodon variegatus). High nutrient loading rates led to significantly higher phytoplankton (chlorophyll a) levels in all experiments, significantly increased growth of juvenile bivalves relative to controls with lower nutrient loading rates in two experiments, and significantly reduced the growth of eelgrass in one experiment. The filtration provided by adult suspension feeders (M. mercenaria and C. virginica) significantly decreased phytoplankton levels in all experiments, significantly increased light penetration and the growth of eelgrass in one experiment, and significantly decreased the growth of juvenile bivalves and fish in two experiments, all relative to controls with no filtration from adult suspension feeders. These results demonstrate that an appropriate level of nutrient loading can have a positive effect on some estuarine resources and that bivalve filtration can mediate the effects of nutrient loading to the benefit or detriment of different estuarine resources. Future ecosystem-based approaches will need to simultaneously account for anthropogenic nutrient loading and bivalve restoration to successfully manage estuarine resources.  相似文献   

18.
In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of ML 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude Mw 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes.Eight small earthquakes (3.0  ML < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 1012–5.04 × 1015 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.  相似文献   

19.
Four natural gypsum rock samples were prepared and certified for major elements and some trace elements by the Analytical Group of Domtar Inc., Research Centre in Senneville (Montréal), Québec, Canada with the cooperation of Domtar Gypsum Products Laboratory in Caledonia, Ontario, Canada. The analytical round-robin results received from 29 participating laboratories were statistically evaluated, summarized, and form the basis of this paper. These certified reference materials are primarily intended as calibration standards for the determination of major and minor elements in gypsums and gypsum related minerals and products. As certified gypsum rock samples were not available on the North-American or world markets, these may be particularly important not only to the gypsum and cement industries, but also to geochemists, geologists and analysts of minerals and ores.  相似文献   

20.
Basaltic glasses included in olivine phenocrysts from Kilauea volcano contain concentrations of H2O, CO2, and S similar to glassy Kilauean basalt dredged from the deep sea floor and greater than vesicular, subaerial Kilauean basalt. Our result contrasts with earlier reports that inclusions of basaltic glass in phenocrysts have little or no H2O and large ratios of CO2H2O. Our analysed inclusions of glass are larger than 100 micrometers thick and similar in chemical composition to the host glass surrounding the olivine crystals indicating that the trapped melts are representative of the bulk liquid from which the crystals grew. Crystallization of about 2–8% of olivine from the melts after they were trapped is indicated by slight departures from the experimentally established equilibrium distribution of Mg and Fe between olivine and liquid. The measured concentrations of CO2 correspond to phenocryst crystallization pressures of about 1.3 kbar for a subaerial basalt and about 5 kbar for a submarine basalt, consistent with geophysical models of Kilauea volcano. The compositions of volcanic gas predicted from our analyses are consistent with restored compositions of actual Kilauean gases. The rate of sulfur emission predicted from our analyses is greater than the sulfur dioxide emission rate observed during repose, but probably consistent with total degassing including eruptive episodes. The concentrations of H2O, K2O, Cl, and P in parental Kilauean basalt can be derived from upper mantle phlogopitic mica, pargasitic amphibole and apatite with compositions close to those of natural primary minerals in ultramafic xenoliths from continental kimberlites, or solely from apatite and phlogopitic mica with H2OK2O near 0.47 ± 0.03, slightly higher than the range of values reported. The amounts of phlogopitic mica and pargasitic amphibole contributing volatiles to Kilauean tholeiite is about 10 percent by mass of the parental liquid, or about 5% if the source does not include amphibole. In view of an estimated 20% of partial melting of mantle source rock to produce Kilauean tholeiites, there may be about 2 weight percent of mica plus amphibole in part of the mantle beneath Kilauea, or about 1 weight percent of phlogopitic mica if amphibole is absent.  相似文献   

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