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1.
M. Manzoni 《Tectonophysics》1979,60(3-4):169-188
The magnetization of Lower Permian rocks from Sila has a mean direction D = 56.5°, I= +20.4° with 95 = 9.1° after correction for Upper Neogene tilting. A further correction for the attitude of the nappes after their Middle Miocene emplacement establishes paleolatitudes consistent with those from the Lower Permian Tethys. The remarkable internal consistency of the data has not supported the distinction of units with opposite vergences within the Sila crystalline nappes. The declination indicates that the Sila massif has rotated counter-clockwise by about 90° relative to the Apennines, Sardinia and the Southern Alps and therefore the well-known Apenninic rotation alone does not account for the total change of direction in tectonic transport. Accordingly, the structural trends of tectonic phases older than the emplacement time of the Calabrian nappes should no longer be referred to present-day geographic coordinates. The post-Late Cretaceous motion relative to the north Calabrian Apennines enhances the geotectonic role of the northern boundary of the Calabrian—Peloritan arc, since its sinistral-shear character permits both tectonic transport from the west and counter-clockwise motion during tectonic transport.  相似文献   

2.
The paleomagnetism of Upper Cretaceous magmatic rocks from 47 collecting sites (172 samples, 692 specimens) in the Apuseni Mountains was studied. After AF cleaning, characteristic magnetizations were identified for various collecting areas in the study zone, which defined a few spatial and temporal units for which paleomagnetic poles could be derived statistically. At 21 sampling sites the paleomagnetic directions showed a high level of intrasite and intersite consistency, with a mean direction of If = −38° and Df = −100°, with 95 = 6°. The paleomagnetic results show that to reach their present-day position the Apuseni Mountains moved to the north, around 14° with respect to Europe, or around 25° with respect to the geographic poles, between the Campanian and, probably, Late Miocene, while a clockwise rotation, of around 80°, was taking place.  相似文献   

3.
To verify paleomagnetic proof for megatectonic translation in the Tethys a large collection of samples from a key area, the Bolzano Quartz Porphyry Plateau in the Southern Alps, was examined. Their natural remanent magnetization was analyzed with thermal, and mainly alternating field demagnetization. The result is a well-established paleomagnetic direction of D: 150° and I: −19.5° (95 = 4.9), obtained from 152 samples from 39 sites distributed over 12 volcanic units. It is argued that the inclination of this result is not significantly different from that which can be extrapolated for the Southern Alps from Early Permian paleomagnetic directions of the stable European shield. Consequently it is concluded that a paleomagnetic indication for megatectonic translation of the Southern Alps is virtually absent. But a large counterclockwise deviation of the declination is evident, and is easily explained by a counterclockwise rotation of 50° of the Southern Alps with respect to stable Europe. Since the paleomagnetic direction of the Early Permian volcanics of the Southern Alps fits in reasonably well with the (poorly known) Early Permian paleomagnetic pattern of Africa, a coherence between both regions is presumed.  相似文献   

4.
Garnet–melt trace element partitioning experiments were performed in the system FeO–CaO–MgO–Al2O3–SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (DGrt/Melt). DGrt/Melt, measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal–melt partition coefficients from elastic moduli. Nature 372, 452–454], which describes partitioning of an element i with radius ri and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus EX(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838–847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3+) and EX(3+) as a function of garnet composition (X) and pressure (P):
r0(3+) [Å]=0.930XPy+0.993XGr+0.916XAlm+0.946XSpes+1.05(XAnd+XUv)−0.005(P [GPa]−3.0)(±0.005 Å)
EX(3+) [GPa]=3.5×1012(1.38+r0(3+) [Å])−26.7(±30 GPa)
Accuracy of these equations is shown by application to the existing garnet–melt partitioning database, covering a wide range of P and T conditions (1.8 GPa<P<5.0 GPa; 975°C<T<1640°C). DGrt/Melt for all 3+ elements entering the X-site (REE, Sc and Y) are predicted to within 10–40% at given P, T, and X, when DGrt/Melt for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. DSmGrt/Melt/DNdGrt/Melt) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3+) for garnets ranges from 0.939±0.005 to 0.953±0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet–melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting DGrt/Melt for these elements as a function of P, T and X.  相似文献   

5.
A preliminary study of paleomagnetism and rock magnetism has been done on 55 eclogite samples collected from the Chinese Continental Scientific Drilling (CCSD) site at the Maobei (毛北) area, Donghai (东海) County, Jiangsu (江苏) Province. Also the isothermal remanence, hysteresis loop, magnetic fabric, thermal susceptibility were measured, and analyses were made by electron-probe and scanning electric microscope on some samples synchronously. The result indicates that there are two groups of stable remanence, the normal and reversed magnetization. The remanence orientations are: D=94.3o, I=-29.1o and D=273.7o, I=15.4o, respectively. The magnetization intensity and the density of the samples which carry the normal magnetization are very different from those bearing reversed magnetization. The magnetic anisotropy is weak, and the minimum axis is hardly determined. The isothermal remanence and the hysteresis loop show that the magnetic carriers of the eclogite are likely SD (single domain) and PSD (pseudo-single domain) magnetite. According to the magnetic property, the cause of formation of magnetic carriers, the mechanism of the remanence, and the significance for the tectonics are discussed.  相似文献   

6.
Strontium chemical diffusion has been measured in albite and sanidine under dry, 1 atm, and QFM buffered conditions. Strontium oxide-aluminosilicate powdered sources were used to introduce the diffusant and Rutherford Backscattering Spectroscopy (RBS) used to measure diffusion profiles. For the 1 atm experiments, the following Arrhenius relations were obtained:
Sanidine (Or61), temperature range 725–1075°C, diffusion normal to (001): D=8.4 exp(−450±13 kJ mol−1/RT) m2s−1. Albite (Or1), temperature range 675–1025°C, diffusion normal to (001): D=2.9 × exp(−224±11 kJ mol−1/RT) m2s−1.
The alkali feldspars in this and earlier work display a broad range of activation energies for Sr diffusion, which may be a consequence of the thermodynamic non-ideality of the alkali feldspar system and/or the mixed alkali effect.  相似文献   

7.
Status report on stability of K-rich phases at mantle conditions   总被引：1，自引：0，他引：1  
George E. Harlow  Rondi Davies 《Lithos》2004,77(1-4):647-653
Experimental research on K-rich phases and observations from diamond inclusions, UHP metamorphic rocks, and xenoliths provide insights about the hosts for potassium at mantle conditions. K-rich clinopyroxene (Kcpx–KM3+Si2O6) can be an important component in clinopyroxenes at P>4 GPa, dependent upon coexisting K-bearing phases (solid or liquid) but not, apparently, upon temperature. Maximum Kcpx content can reach 25 mol%, with 17 mol% the highest reported in nature. Partitioning (K)D(cpx/liquid) above 7 GPa=0.1–0.2 require ultrapotassic liquids to form highly potassic cpx or critical solid reactions, e.g., between Kspar and Di. Phlogopite can be stable to about 8 GPa at 1250 °C where either amphibole or liquid forms. When fluorine is present, it generally increases in Phl upon increasing P (and probably T) to about 6 GPa, but reactions forming amphibole and/or KMgF3 limit F content between 6 and 8 GPa. The perovskite KMgF3 is stable up to 10 GPa and 1400 °C as subsolidus breakdown products of phlogopite upon increasing P. (M4)K-substituted potassic richterite (ideally K(KCa)Mg5Si8O22(OH,F)2) is produced in K-rich peridotites above 6 GPa and in Di+Phl from 6 to 13 GPa. K content of amphibole is positively correlated with P; Al and F content decrease with P. In the system 1Kspar+1H2O K-cymrite (hydrous hexasanidine–KAlSi3O8·nH2O–Kcym) is stable from 2.5 GPa at 400 to 1200 °C and 9 GPa; Kcym can be a supersolidus phase. Formation of Kcym is sensitive to water content, not forming within experiments with H2O2O>Kspar. Phase X, a potassium di-magnesium acid disilicate ((K1−x−n)2(Mg1−nMn3+)2Si2O7H2x), forms in mafic compositions at T=1150–1400 °C and P=9–17 GPa and is a potential host for K and H2O at mantle conditions with a low-T geotherm or in subducting slabs. The composition of phase-X is not fixed but actually represents a solid solution in the stoichiometries □2Mg2Si2O7H2–(K□)Mg2Si2O7H–K2Mg2Si2O7 (□=vacancy), apparently stable only near the central composition. K-hollandite, KAlSi3O8, is possibly the most important K-rich phase at very high pressure, as it appears to be stable to conditions near the core–mantle boundary, 95 GPa and 2300 °C. Other K-rich phases are considered.  相似文献   

8.
We have studied the influence of Ca-Tschermaks (Calcium Tschermaks or CaTs) content of clinopyroxene on the partitioning of trace elements between this phase and silicate melt at fixed temperature and pressure. Ion probe analyses of experiments carried out in the system Na2O–CaO–MgO–Al2O3–SiO2, at 0.1 MPa and 1218°C, produced crystal-melt partition coefficients (D) of 36 trace elements (Li, Cl, Sc, Ti, V, Cr, Fe, Co, Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, In, Sn, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta and W), for clinopyroxene compositions between 10 and 32 mol% CaTs. Partition coefficients for 2+ to 5+ cations show, for each charge, a near parabolic dependence of log D on ionic radius of the substituting cation, for partitioning into both the M1 and M2 sites of clinopyroxene. Fitting the results to the elastic strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452–454] we obtain results for the strain-free partition coefficients of theoretical cations (D0), with site radius r0, and for the site's Young's Modulus (E).

In agreement with earlier data our results show that increasing ivAl concentration in cpx is matched by increasing D, EM1, EM2 and D0 for tri-, tetra- and pentavalent cations. The degree of fractionation between chemically similar elements (i.e. Ta/Nb, Zr/Hf) also increases. In contrast, D values for mono-, di- and hexavalent cations decrease with increasing ivAl in the cpx. The large suite of trace elements used has allowed us to study the effects of cation charge on D0, r0 and E. We have found that D0 and r0 decrease with increasing cation charge, e.g. r0=0.66 Å for 4+ cations and 0.59 Å for 5+ cations substituting into M1. Values of EM1 and EM2 increase with cation charge as well as with increasing ivAl content. The increase in EM2 is linear and close to the trend set by Hazen and Finger [Hazen, R.M., Finger, L.W., 1979. Bulk modulus-volume relationship for cation–anion polyhedra. J. Geophys. Res. 84 (10) 6723–6728] for oxides. EM1 values are much higher and do not fit the trend predicted by the Hazen and Finger relationship.  相似文献   


9.
J.J. Schott  A. Peres 《Tectonophysics》1987,140(2-4):179-191
The paleomagnetic analysis of the Permo-Triassic redbeds outcropping in the western part of the Cantabric Chain and the small Mesozoic basin from the Asturias shows that these formations have a history of complex magnetization. Only a few sites did not experience the remagnetization processes and retained original directions. The most reliable results yield a paleomagnetic pole located at: lat. 49° N, long. 217° E (n = 11, 95 = 3.7°), which is suggested as reliable Permo-Triassic data for the Iberian plate. Two remagnetization phases are recognized: a moderate phase predating the folding gave rise to a first overprinting. It is connected with the distension which occurred in the Pyreneo-Cantabrian region during the upper Jurassic-lower Cretaceous. The main remagnetization phase which occurred after the folding is dated from the lower Tertiary, and can be related to the compression induced on the northern boundary of Iberia from upper Cretaceous onwards. In some cases this phase led to a complete replacement of the primary magnetization.

Previously published data, which were at the time interpreted as being European-like in direction, are attributed to this phase. Hence, our results do not support the hypothesis of a micro-plate called “le Danois block”, which was suggested in order to explain these results. We believe that there is no paleomagnetic evidence supporting the existence of a complicated boundary between Europe and Iberia during the mid-Cretaceous opening of the Bay of Biscay.  相似文献   


10.
Partitioning coefficients between olivine and silicate melts   总被引：3，自引：0，他引：3  
J.H. Bdard 《Lithos》2005,83(3-4):394-419
Variation of Nernst partition coefficients (D) between olivine and silicate melts cannot be neglected when modeling partial melting and fractional crystallization. Published natural and experimental olivine/liquidD data were examined for covariation with pressure, temperature, olivine forsterite content, and melt SiO2, H2O, MgO and MgO/MgO + FeOtotal. Values of olivine/liquidD generally increase with decreasing temperature and melt MgO content, and with increasing melt SiO2 content, but generally show poor correlations with other variables. Multi-element olivine/liquidD profiles calculated from regressions of D REE–Sc–Y vs. melt MgO content are compared to results of the Lattice Strain Model to link melt MgO and: D0 (the strain compensated partition coefficient), EM3+ (Young's Modulus), and r0 (the size of the M site). Ln D0 varies linearly with Ln MgO in the melt; EM3+ varies linearly with melt MgO, with a dog-leg at ca. 1.5% MgO; and r0 remains constant at 0.807 Å. These equations are then used to calculate olivine/liquidD for these elements using the Lattice Strain Model. These empirical parameterizations of olivine/liquidD variations yield results comparable to experimental or natural partitioning data, and can easily be integrated into existing trace element modeling algorithms. The olivine/liquidD data suggest that basaltic melts in equilibrium with pure olivine may acquire small negative Ta–Hf–Zr–Ti anomalies, but that negative Nb anomalies are unlikely to develop. Misfits between results of the Lattice Strain Model and most light rare earth and large ion lithophile partitioning data suggest that kinetic effects may limit the lower value of D for extremely incompatible elements in natural situations characterized by high cooling/crystallization rates.  相似文献   

11.
The absolute abundance of the chromium isotopes in chromite   总被引：1，自引：0，他引：1  
Isotopic assays have been made on the chromium in eighteen chromite samples from countries responsible for 81 per cent of the chromite production between 1900 and 1950. The use of mixtures of separated isotopes to determine the accuracy indicates that the measurements are absolute. On the basis of these assays, the natural abundances of the chromium isotopes in atoms per cent are: Cr50 = 4·352 ± 0·024, Cr52 = 83·764 ± 0·036, Cr53 = 9·509 ± 0·027, Cr54 = 2·375 ± 0·018. where the limits cited represent 3β. No variation in the isotopic composition of the chromium in any of the chromites examined was found within the stated limits.

The chemical atomic weight, computed on the basis of these abundance values and the latest accepted values for the masses of the involved isotopes, is 51·9985 ± 0·0013.  相似文献   


12.
The dissolution and precipitation rates of boehmite, AlOOH, at 100.3 °C and limited precipitation kinetics of gibbsite, Al(OH)3, at 50.0 °C were measured in neutral to basic solutions at 0.1 molal ionic strength (NaCl + NaOH + NaAl(OH)4) near-equilibrium using a pH-jump technique with a hydrogen-electrode concentration cell. This approach allowed relatively rapid reactions to be studied from under- and over-saturation by continuous in situ pH monitoring after addition of basic or acidic titrant, respectively, to a pre-equilibrated, well-stirred suspension of the solid powder. The magnitude of each perturbation was kept small to maintain near-equilibrium conditions. For the case of boehmite, multiple pH-jumps at different starting pHs from over- and under-saturated solutions gave the same observed, first order rate constant consistent with the simple or elementary reaction: .

This relaxation technique allowed us to apply a steady-state approximation to the change in aluminum concentration within the overall principle of detailed balancing and gave a resulting mean rate constant, (2.2 ± 0.3) × 10−5 kg m−2 s−1, corresponding to a 1σ uncertainty of 15%, in good agreement with those obtained from the traditional approach of considering the rate of reaction as a function of saturation index. Using the more traditional treatment, all dissolution and precipitation data for boehmite at 100.3 °C were found to follow closely the simple rate expression:

Rnet,boehmite=10-5.485{mOH-}{1-exp(ΔGr/RT)}, with Rnet in units of mol m−2 s−1. This is consistent with Transition State Theory for a reversible elementary reaction that is first order in OH− concentration involving a single critical activated complex. The relationship applies over the experimental ΔGr range of 0.4–5.5 kJ mol−1 for precipitation and −0.1 to −1.9 kJ mol−1 for dissolution, and the pHm ≡ −log(mH+) range of 6–9.6. The gibbsite precipitation data at 50 °C could also be treated adequately with the same model:Rnet,gibbsite=10-5.86{mOH-}{1-exp(ΔGr/RT)}, over a more limited experimental range of ΔGr (0.7–3.7 kJ mol−1) and pHm (8.2–9.7).  相似文献   


13.
We report Sr, Nd and Pb isotopic compositions of mid-Proterozoic anorthosites and related rocks (1.45-1.65 Ga) and of younger olivine diabase dikes (1.4 Ga) from two complexes on either side of the Grenville Front in Labrador. Anorthositic or diabasic samples from the Mealy Mountains (Grenville Province) and Harp Lake (Nain-Churchill Provinces) complexes have very similar major, minor and trace element compositions, but distinctly different isotopic signatures. All Mealy Mountains samples have ISr = 0.7025−0.7033, εNd = +0.6 to +5.6 and Pb isotopic compositions consistent with derivation from a mantle source depleted with respect to Nd/Sm and Rb/Sr. Pb isotopic compositions for the Mealy Mountains samples are slightly more radiogenic than model mantle compositions. All Harp Lake samples have ISr = 0.7032−0.7066, εNd = −0.3 to −4.4 and variable, but generally unradiogenic 207Pb/204Pb and 206Pb/204Pb compared to model mantle, suggesting mixing between a mantle-derived component and a U-depleted crustal contaminant. Crustal contaminants are probably a variety of Archean high-grade quartzofeldspathic gneisses with low U/Pb ratios and include a component that must be isotopically similar to the early Archean (>3.6 Ga) Uivak gneisses of Labrador or the Amitsoq gneisses of west Greenland. This would imply that the ancient gneiss complex of coastal Labrador and Greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the Labrador Trough. If Harp Lake and Mealy Mountains samples were subjected to the same degree of contamination, as suggested by their chemical similarities, then the Mealy contaminants must be much younger, probably early or middle Proterozoic in age. The Labrador segment of the Grenville Front, therefore, appears to coincide with the southern margin of the Archean North Atlantic craton and may represent a pre mid-Proterozoic suture.  相似文献   

14.
As a result of the collapse of a mine tailing dam, a large extension of the Guadiamar valley was covered with a layer of pyritic sludge. Despite the removal of most of the sludge, a small amount remained in the soil, constituting a potential risk of water contamination. The kinetics of the sludge oxidation was studied by means of laboratory flow-through experiments at different pH and oxygen pressures. The sludge is composed mainly of pyrite (76%), together with quartz, gypsum, clays, and sulphides of zinc, copper, and lead. Trace elements, such as arsenic and cadmium, also constitute a potential source of pollution. The sludge is fine grained (median of 12 μm) and exhibits a large surface (BET area of 1.4±0.2 m2 g−1).

The dissolution rate law of sludge obtained is r=10−6.1(±0.3) [O2(aq)]0.41(±0.04) aH+0.09(±0.06) gsludge m−2 s−1 (22 °C, pH=2.5–4.7). The dissolution rate law of pyrite obtained is r=10−7.8(±0.3) [O2(aq)]0.50(±0.04) aH+0.10(±0.08) mol m−2 s−1 (22 °C, pH=2.5–4.7). Under the same experimental conditions, sphalerite dissolved faster than pyrite but chalcopyrite dissolves at a rate similar to that of pyrite. No clear dependence on pH or oxygen pressure was observed. Only galena dissolution seemed to be promoted by proton activity. Arsenic and antimony were released consistently with sulphate, except at low pH conditions under which they were released faster, suggesting that additional sources other than pyrite such as arsenopyrite could be present in the sludge. Cobalt dissolved congruently with pyrite, but Tl and Cd seemed to be related to galena and sphalerite, respectively.

A mechanism for pyrite dissolution where the rate-limiting step is the surface oxidation of sulphide to sulphate after the adsorption of O2 onto pyrite surface is proposed.  相似文献   


15.
Experiments in which cleavage nepheline samples were reacted with aqueous solutions at fixed pH's and temperature were carried out in the laboratory. The chemistry of the solution as a function of time was monitored, as well as the chemistry of the nepheline surfaces.

At 25°C, Al derived from the nepheline stays in solution due to slow precipitation kinetics of Al(OH)3. At 60° and 80°C, precipitation of Al(OH)3 is so rapid that Al concentration in solution is below 0.05 ppm. This indicates that precipitation kinetics favour the formation of bauxite deposits in tropical regions (i.e. T25°C), but not in temperate regions.

Precipitation products on the surface of the nepheline fragments at 60° and 80°C depend on the pH. At pH 3.0, an amorphous aluminium silicate (proto-kaolinite?) is formed. At pH>7.0, the precipitated phase contains, in addition to Al and Si, high amounts of Na and K (proto-muscovite?). The optimum pH for the formation of bauxite is in the range 5–7. These results are in agreement with thermodynamic calculations.  相似文献   


16.
Spinel-sapphirine-corundum-rutile parageneses in metapelitic xenoliths from the lamprophyric Popes Harbour dyke are enclosed by feldspathic (±rare quartz) haloes that embay aluminosilicates and biotite. These feldspathic haloes contain plagioclase (An20–40) and/or an alkali or ternary (hypersolvus) feldspar, and show a variety of igneous and devitrification textures, suggesting an anatectic origin. The spinel-bearing parageneses are interpreted as the refractory residue formed by the incongruent melting of biotite, aluminosilicates and associated phases.

Equilibration temperatures of these assemblages are estimated from an empirical sapphirine-spinel Mg---Fe exchange thermometer derived from literature data on both silica-saturated and undersaturated sapphirine granulites. Linear regression (R=0.81) of the calibrant data yields the expression T(°C) = [800 + (228*InKd)] − 273 where

Kd=(XspFe/XspMg)/(XsaFe/XsaMg)

Precision is estimated at ± 100°C, but will likely be less for highly oxidized sapphirine granulites owing to (1) errors in the stoichiometric estimation of XFe3+ from microprobe data and (2) the formation of magnetite at the expense of spinel or sapphirine, leading to an increase in XMg in either or both phases during cooling. Application of this expression to the reduced (graphite-bearing) Popes Harbour xenoliths yields T of 725–795°C. Anatexis is attributed to thermal metamorphism by the lamprophyric magma prior to and/or during entrainment of xenolith material in the dyke. Higher-T assemblages were quenched before the xenoliths attained thermal equilibrium with the magma, consequently prograde reaction textures and compositional zoning patterns are preserved.  相似文献   


17.
贵州三都早奥陶世同高组下燕高页岩段的生物标志化合物   总被引：8，自引：1，他引：8  
许玩宏  沈平 《沉积学报》1997,15(3):72-77
本文着重报道了贵州三都早奥陶世同高组下燕高页岩段生物标志化合物特征，首次在采自该层位的样品中检出丰富的正烷烃、链状类异戊二烯烷烃、萜类化合物及甾类化合物。测试结果显示:正烷烃图谱呈双驼峰形，碳数分布为ｎＣ１５～ｎＣ３５，以ｎＣ１８为主峰碳，ｎＣ２９为次主峰碳，Ｃ－２１/Ｃ＋２２为０.７７～１.０２，ＯＥＰ为０.９４～１.０４；植烷占优势，Ｐｒ/Ｐｈ为０.４０～０.４６；藿烷碳数为Ｃ２７～Ｃ３５，以Ｃ３０占优势，Ｃ２７＋Ｃ２９＜Ｃ＋３１；仅见碳数分布为Ｃ２０～Ｃ２９的长链三环二萜烷，以Ｃ２８为主峰碳；甾烷丰度顺序为Ｃ２９甾烷＞Ｃ２７甾烷＞Ｃ２８甾烷，同时检出了孕甾烷和４－甲基甾烷。生物标志化合物显示出还原环境特点，且可能主要来自藻类。  相似文献   

18.
We have conducted acid–base potentiometric titrations and U(VI) sorption experiments using the Gram negative, facultatively anaerobic bacterium Shewanella putrefaciens. Results of reversed titration studies on live, inactive bacteria indicate that their pH-buffering properties result from the equilibrium ionization of three discrete populations of functional groups. Carboxyl (pKa=5.16±0.04), phosphoryl (pKa=7.22±0.15) and amine (pKa=10.04±0.67) groups most likely represent these three resolvable functionalities, based on their pKa values. Site densities for carboxyl, phosphoryl and amine groups on the bacterial surface were approximately 31.7 μmol sites/g bacteria (0.35±0.02 sites/nm2), 8.95 μmol/g (0.11±0.007 sites/nm2) and 38.0 μmol/g (0.42±0.008 sites/nm2), respectively, based on an estimated bacterial specific surface area of 55 m2/g. Sorption experiments showed that U(VI) can reversibly complex with the bacterial surface in the pH 2–8 interval, with maximum adsorption occurring at a pH of 5. Sorption is not strongly sensitive to ionic strength (NaCl) in the range 0.02–0.10 M. The pH and ionic strength dependence of U(VI) sorption onto S. putrefaciens is similar to that measured for metal-oxide surfaces and Gram positive bacteria, and appears to be similarly governed by competitive speciation constraints. Measured U(VI) sorption is accounted for by using two separate adsorption reactions forming the surface complexes >COO–UO2+ and >PO4H–UO2(OH)2. Using S. putrefaciens as a model organism for dissimilatory metal-reducing Gram negative anaerobes, our results extend the applicability of geochemical speciation models to include bacteria that are capable of reductively solubilizing or precipitating a wide variety of environmentally and geologically important metals and metallic species.  相似文献   

19.
D. A. Carswell  R. N. Wilson  M. Zhai 《Lithos》2000,52(1-4):121-155
As is typical of ultra-high pressure (UHP) terrains, the regional extent of the UHP terrain in the Dabieshan of central China is highly speculative, since the volume of eclogites and paragneisses preserving unequivocal evidence of coesite and/or diamond stability is very small. By contrast, the common garnet (XMn=0.18–0.45)–phengite (Si=3.2–3.35)–zoned epidote (Ps38–97)–biotite–titanite–two feldspars–quartz assemblages in the more extensive orthogneisses have been previously thought to have formed under low P–T conditions of ca. 400±50°C at 4 kbar. However, certain orthogneiss samples preserve garnets with XCa up to 0.50, rutile inclusions within titanite or epidote and relict phengite inclusions within epidote with Si contents p.f.u. of up to 3.49 — overlapping with the highest values (3.49–3.62) recorded for phengites in samples of undoubted UHP schists. These and other mineral composition features (such as A-site deficiencies in the highest Si phengites, Na in garnets linked to Y+Yb substitution and Al F Ti−1 O−1 substitution in titanites) are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated UHP schists and eclogites. Re-evaluated garnet–phengite and garnet–biotite Fe/Mg exchange thermometry and calculated 5 rutile+3 grossular+2SiO2+H2O=5 titanite+2 zoisite equilibria indicate that the orthogneisses may indeed have followed a common subduction-related clockwise P–T path with the UHP paragneisses and eclogites through conditions of Pmax at ca. 690°C–715°C and 36 kbar to Tmax at ca. 710°C–755°C and 18 kbar, prior to extensive re-crystallisation and re-equilibration of these ductile orthogneisses at ca. 400°C–450°C and 6 kbar. The consequential conclusion, that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these Dabieshan orthogneisses with undoubted UHP lithologies, has far-reaching implications for the interpretation of controversial gneiss–eclogite relationships in other UHP metamorphic terrains.  相似文献   

20.
The relationship between the breakup of eastern Gondwanaland and the Kerguelen plume activity is a subject of debate. The Cona mafic rocks are widely exposed in the Cona area of the eastern Himalaya of south Tibet, and are studied in order to evaluate this relationship. Cona mafic rocks consist predominantly of massive basaltic flows and diabase sills or dikes, and are divided into three groups. Group 1 is composed of basaltic flows and diabase sills or dikes and is characterized by higher TiO2 and P2O5 content and OIB-like trace element patterns with a relatively large range of Nd(T) values (+ 1.84 to + 4.67). A Group 1 diabase sill has been dated at 144.7 ± 2.4 Ma. Group 2 consists of gabbroic sills or crosscutting gabbroic intrusions characterized by lower TiO2 and P2O5 content and “depleted” N-MORB-like trace element patterns with relatively higher, homogeneous Nd(T) values (+ 5.68 to + 6.37). A Group 2 gabbroic diabase dike has been dated at 131.1 ± 6.1 Ma. Group 3 basaltic lavas are interbedded with the Late Jurassic–Early Cretaceous pelitic sediments; they have compositions transitional between Groups 1 and 2 and flat to slightly enriched trace element patterns. Sr–Nd isotopic data and REE modeling indicate that variable degrees of partial melting of distinct mantle source compositions (enriched garnet–clinopyroxene peridotite for Group 1 and spinel-lherzolite for Group 2, respectively) could account for the chemical diversity of the Cona mafic rocks. Geochemical similarities between the Cona mafic rocks and the basalts probably created by the Kerguelen plume based on spatial–temporal constraints seem to indicate that an incubating Kerguelen plume model is more plausible than a model of normal rifting (nonplume) for the generation of the Cona mafic rocks. Group 1 is interpreted as being related to the incubating Kerguelen plume–lithosphere interaction; Group 2 is likely related to an interaction between anhydrous lithosphere and rising depleted asthenosphere enriched by a “droplet” originating from the Kerguelen plume, while Group 3 may be attributed to thermal erosion resulting in the partial melting of lithosphere during the long-term incubation of a magma chamber/pond at a shallow crustal level. The Cona mafic rocks are probably related to a progressively lithospheric thinning beneath eastern Gondwanaland from 150–145 Ma to 130 Ma. Our new observations seem to indicate that the Kerguelen plume may have started its incubation as early as the latest Jurassic or earliest Cretaceous period and that the incubating Kerguelen plume may play an active role in the breakup of Greater India, eastern India, and northwestern Australia.  相似文献   

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