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1.
Abstract Petrogenetic grids for ultrahigh-pressure (UHP) metamorphism were calculated at different Xco2 conditions in the model system CaO-MgO-SiO2-CO2-H2O involving coesite (Co), diopside (Di), dolomite (Do), enstatite (En), forsterite (Fo), magnesite (Ms), quartz (Qz), talc (Tc), tremolite (Tr) using a published internally consistent thermodynamic data set. Two P-T grids at Xco2= 0.01 and 0.5 are described. In the calculated P-T grid at Xco2= 0.01, four out of 10 stable invariant points, Co-En-Ms-Tc, Co-Di-En-Tc-Tr, Co-Di-Ms-Tc-Tr and Di-En-Ms-Tc-Tr lie within the stability field of coesite. If the fluid phase has Xco2= 0.5, no invariant point is stable under UHP conditions. Some magnesite-bearing assemblages are stabilized by the following three reactions: Di + Ms = Do + Fo + CO2, Ms + Tr = Do + Fo + CO2+ H2O and Ms + Tc = Fo+ CO2+ H2O at Xco2= 0.01 and by reaction Ms + Tc = Fo + CO2+ H2O together with these three at Xco2= 0.5. Ten possible UHP assemblages for mafic and ultramafic compositions at very low Xco2 conditions include the following: Co-Do-Ms, Co-Di-Ms, Co-Di-Tc, Di-Ms-Tc, Di-En-Tc-, Di-En-Ms, Co-Di-En, Di-En-Fo, Di-Fo-Ms, Di-Do-Fo. Among them, talc-bearing assemblages are restricted to Xco2 < 0.02 and their high-P limit is 31.7 kb (749°C) at Xco2= 0.01. Dolomite-magnesite-silica assemblages have large P-T stability fields even if Xco2 is as low as 0.1, and could occur in cold subduction zones with very low geothermal gradients. Reported UHP coesite-dolomite assemblage is restricted only to a calc-silicate rock interlayered with marble where Xco2 is relatively higher; no such assemblage appears for mafic and ultramafic rocks with low Xco2 evidenced by the occurrence of diopside (or omphacite) at the expense of dolomite + coesite. The effect of Xco2 on the stability of coesite-dolomite-magnesite, diopside-enstatite-magnesite, diopside-talc assemblages is examined and the occurrence of coesite-dolomite, magnesite-bearing and talc-bearing assemblages in the Dabie UHP rocks are interpreted by employing the calculated P-T grids. 相似文献
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The enstatite-diopside solvus in the system Mg2Si2O6-CaMgSi2O6 has been experimentally determined within the pressure range 5–40 kbars and the temperature range 900–1500°C. Experiments involving reversal of the phase boundaries by unmixing from glass starting material and by reaction of pure clinoenstatite and diopside showed difficulty in achieving equilibration due to persistence of metastable, subcalcic clinopyroxene and to the sluggishness of reaction rate. The experimental data showed that the temperature dependence of the diopside limb is less than previously accepted. At 1500°C and 30 kbars subcalcic diopside found by Davis and Boyd (1966) is shown to be metastable with respect to enstatite and more calcic diopside of composition En42.3Di57.7. The solvus widens with increasing pressure between 5 and 40 kbars at 1200°C, but at 900°C the pressure effect on the solvus is very small. The stability relationships of the four pyroxenes, protoenstatite, enstatite, iron-free pigeonite and diopside are summarized, based on data from the literature and the present study. 相似文献
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Leonie E.A. Jones 《Physics of the Earth and Planetary Interiors》1977,15(1):77-89
The elastic moduli of single-crystal CaF2, SrF2 and BaF2 have been determined by the ultrasonic pulse superposition technique as a function of temperature from T = 298 to T = 650°K. These new data are consistent with other data obtained by ultrasonic pulse techniques in the region of room temperature and are superior to previous high-temperature data from resonance experiments. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range with the curvature in the same sense for all the moduli. Evaluation of the temperature derivatives of the elastic moduli at constant volume indicates that the dominant temperature effect is extrinsic for (?KS/?T)P and intrinsic for (?μ/?T)P, where KS and μ are the isotropic bulk and shear moduli, respectively. For the series CaF2SrF2BaF2, |(?c/?T)p| decreases with increasing molar volume for all moduli; however there are no theoretical or empirical grounds on which to derive a simple relationship between (?c/?T)P and crystallographic parameters. 相似文献
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The effectiveness of CO2 storage in deep saline aquifers and hydrocarbon reservoirs is governed, among other factors, by the interfacial tension between the injected CO2 and formation water (brine). Experimental data on CO2/water and CO2/NaCl solution have revealed that the interfacial tension depends on the pressure, temperature and water salinity. However, there is still a lack of data for other salts (such as MgCl2 and CaCl2) which are also present in aquifers and carbonate reservoirs. 相似文献
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Lin-Gun Liu 《Earth and Planetary Science Letters》1975,25(3):286-290
Co2SiO4 spinel has been found to disproportionate into its isochemically mixed oxides with rocksalt and rutile structures at pressures between 170 and 190 kbar and temperatures between 1400 and 1800°C in a diamond-anvil press. The exact disproportionation pressure is not certain due to transient increases in pressure during the local and rapid heating by a continuous YAG laser. The slope of the phase boundary between the spinel phase and the mixed oxides is calculated to be?33 ± 20bar/deg. This negative slope is consistent with the observed anomalously large entropy of CoO (relative to its isostructural oxides) in entropy vs.(MV)?1/2 systematics, whereM is the formula weight andV the molar volume. The sign of the slope for a phase boundary in the disproportionation of spinel depends on the values of entropy of the rocksalt oxides as well as the inverse character exhibited in the spinel phases. The normal entropy of MgO suggests that the phase boundary for the disproportionation of Mg2SiO4 spinel has positive slope. 相似文献
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The TiO2–K2O–P2O5 ternary diagram is proposed as a method of discriminating between oceanic and non-oceanic (continental) basalts. This diagram is effective for non-alkaline “primitive” basalts: fractionated rocks cannot be adequately discriminated. Suitable analyses are those which have total alkalies ≤ 20% in an (Fe2O3 + FeO)–MgO–(Na2O + K2O) diagram. The proposed dividing line separates 93% of 222 ocean-floor and ocean-ridge basalts into the oceanic field and > 80% of continental basalt analyses into the non-oceanic field. Two exceptions are the Tertiary basalts of Greenland and the Deccan Traps which have oceanic affinities. “Continental” suites displaying an oceanic affinity in the TiO2–K2O–P2O5 diagram may be a result of abortive attempts to generate new sea floor. Preliminary results for dike swarms and Archean basalts suggest preponderant oceanic affinities. Alteration and metamorphism of oceanic basalts generally occasion enrichment of K2O relative to TiO2 and P2O5. 相似文献
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Ian Jackson 《Physics of the Earth and Planetary Interiors》1976,13(3):218-231
The melting curves of the structural analogues SiO 2, BeF 2 and GeO 2 have been studied at pressures ?40 kbar in a piston-cylinder apparatus. The initial slopes dTm/dP of the β-quartz-liquid boundaries for SiO 2 and BeF 2 are ～35° while the slope of the rutile-liquid boundary for GeO 2 is approximately 32°C/kbar. These large values of dT/dP reflect the unusually low entropies of fusion for these compounds in which strong structural similarities exist between the crystalline phases and the melt. Implications for the extended phase diagram of silica are discussed and it is concluded that either: (1) a maximum exists on the coesite melting curve, or (2) estimates of the melting temperature of stishovite need to be revised upwards. 相似文献
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The melting curves of CaCO3 and MgCO3 have been extended to pressures of 36 kb by experiments in piston-cylinder apparatus. At 30 kb, the melting temperatures of calcite and magnesite are 1610°C and 1585°C, respectively. New data for the magnesite dissociation reaction permit the location of an invariant point for the assemblage magnesite + periclase + liquid + vapor near 26 kb-1550°C. New data are also presented for the calcite-aragonite transition at 800°C, 950°C and 1100°C. At pressures above 36–50 kb, calcite and magnesite melt at temperatures lower than the solidus of dry mantle peridotite. Natural and experimental evidence suggests that carbon dioxide in the Earth's mantle could be present in a variety of forms: (a) a free vapor phase, (b) vapor dissolved in silicate magma, (c) crystalline carbonate, (d) carbonatite liquid, (e) carbon-bearing silicate analogs, or (f) carbonato-silicates (such as scapolite, spurrite, tilleyite, and related compounds). 相似文献
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Lin-Gun Liu 《Earth and Planetary Science Letters》1975,26(3):425-433
Two synthetic end-members and two natural solid solutions of the system Mg3Al2Si3O12-Fe3Al2Si3O12 have been found to display successive phase transformations at increasingly high pressures when they were compressed in a diamond-anvil cell and heated with a YAG laser to temperatures of approximately 1400–1800°C. X-ray diffraction studies of the quenched samples show that the iron-rich garnets apparently first transform to a garnet-related high-pressure phase, then disproportionate into a mixture of magnesiowüstite plus an unknown phase(s). The latter phase(s) may further transform to a still denser unknown phase(s). The ultimate high-pressure phase may be a perovskite-like structure as was previously found for the magnesium-rich garnets. One of the unknown phases may be the high-pressure phase of Al2O3 · nSiO2 compounds. Magnesium-rich garnets display similar phase transformations as do the iron-rich garnets with the exception of the garnet-related high-pressure phase. These results disagree with a previous interpretation for the high-pressure phase of iron-silicate garnets recovered in shock-wave experiments reported by Ahrens and Graham (1972). 相似文献
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P. Kroopnick 《Earth and Planetary Science Letters》1974,22(4):397-403
13C and ΣCO2 data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ13C of the ΣCO2 in the deep water (～3000m) decreases from 1.7‰ in the North Atlantic to ?0.10‰ in the North Pacific. This change is attributed to the addition of about 158 μmoles of CO2 per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO2, while the remainder is attributed to dissolution of calcium carbonate.The δ13C of the dissolved CO2 in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO2 at a mean temperature of 16°C. The δ13C and ΣCO2 values of Antarctic surface water samples suggest that these waters are derived from a mixture of North Atlantic deep water and equilibrated surface water. 相似文献
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由于具有高效的CO2-浓缩机制,蓝藻在低CO2浓度条件下具有竞争优势。然而,随着大气中CO2浓度急剧增加,蓝藻CO2-浓缩机制如何响应的研究较少。因此,本文以常见水华蓝藻——微囊藻为研究对象,通过对滇池微囊藻水华动态及不同CO2-浓缩机制基因型进行监测,探讨蓝藻CO2-浓缩机制基因的微进化特征及其动态变化。同时,设置高(0.08%)、中(0.04%)、低(0.02%)CO2浓度(V/V)进一步揭示微囊藻不同CO2-浓缩机制基因微进化对CO2的竞争效应。结果表明:滇池无机碳浓度在4个采样点存在空间差异性,均呈现先降低后升高的趋势,并以HCO3-为主要无机碳存在形式。调查期间,东大河、观音山、洛龙河和生态所4个采样点的微囊藻均以sbtA基因型占绝对优势,相对丰度远高于bicA基因型。在不同水华时期,bicA基因型和sbtA基因型呈现相反的变化趋势,即从... 相似文献
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Eiji Ito Yoshito Matsui Kaichi Suito Naoto Kawai 《Physics of the Earth and Planetary Interiors》1974,8(4):342-344
Magnesium orthosilicate with spinel structure (γ-Mg2SiO4) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg2SiO4 and other γ-M2SiO4 spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg2SiO4 spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels. 相似文献
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Lin-Gun Liu 《Earth and Planetary Science Letters》1978,40(3):401-406
Gehlenite (Ca2Al2SiO7) has been found to transform to a new phase at pressures greater than 100 kbar and at about 1000°C, using a diamond-anvil pressure cell coupled with laser heating. The atoms of the new phase appear to be arranged in a perovskite-related structure similar to that described for Na2Ti3O7. The structure probably consists of layers of (Al2SiO7)4−, which are built up from blocks of edge-sharing (Al, Si)O6 octahedra and these blocks are joined by common octahedra corners. A small cubic unit cell with a = 3.719 ± 0.004 Å indexes completely the strong lines of the powder diffraction pattern, and a superlattice with a = 14.88 ± 0.02 Å satisfies all the observed weak lines in addition to the strong ones. However, the cell may be pseudocubic. The small cell contains a half of the gehlenite formula while the large cell contains 32 gehlenite formulae. Hence the molar volume for the new phase of Ca2Al2SiO7 is calculated to be 61.96 ± 0.20 cm3 at atmospheric pressure and room temperature. The new sodium titanate-type structure is probably more closely packed than an ordinary perovskite-type structure in which all octahedral corners are shared. This view is strongly supported by the very great density of this new phase, which is about 8% denser than the equivalent mixture of CaAl2O4 (calcium ferrite type) plus CaSiO3 (cubic perovskite type). The new phase is probably the most closely packed silicate known. Mg2SiO4 (spinel) was found to transform to an assemblage containing MgSiO3 (perovskite) plus MgO (periclase) at P-T conditions equivalent to the upper part of the lower mantle. By reacting with MgO, the perovskite modification of both MgSiO3 and MgSiO3 · xAl2O3 may adopt the sodium titanate structure at the still greater depths of the lower mantle. If the sodium titanate structures of Mg2(Al2Si)O7 and Mg2(MgSi2)O7 are present in the deep part of the lower mantle, MgO does not exist as a separate phase at the mantle-core boundary. This might be an obstacle to the possibility of dissolving these oxides (specifically the FeO component) in the molten Fe in the outer core as suggested by geophysical and geochemical studies of the earth's interior. The mechanism for developing the chemical plumes in the deep mantle proposed by Anderson does not appear to be consistent with studies of phase transformations in Ca-Al-rich compounds as outlined in this paper. 相似文献
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Expeditions during the summers of 2002 and 2003 implemented continuous monitoring of near-surface (2 m height) atmospheric
CO2 and H2O concentrations at the 4500 m elevation on Muztagata. The resultant data sets reveal a slight decrease of CO2 concentrations (of about 5 μmol·mol-1) and changes in the diurnal variations from the end of June to the middle August. The daily maximum CO2 concentrations occur between 02:30-05:30 AM (local time) and the minimum levels occur between 12:00-15:30 PM. The atmospheric
CO2 concentrations in the summer of 2002 were around 5 μmol·mol-1 lower than those during the same period of 2003, whereas the diurnal amplitude was higher. In contrast, we found that the
daily mean atmospheric H2O content in 2003 was much lower than that in 2002 and there exists a striking negative correlation between CO2 and H2O concentrations. We therefore suggest that the near-surface atmospheric CO2 concentration is affected not only by photosynthesis and respiration, but also by the air H2O content in the glaciated region around Muztagata. 相似文献
20.
MnO/TiO2/P2O5: a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis 总被引：4，自引：0，他引：4
Ellen D. Mullen 《Earth and Planetary Science Letters》1983,62(1):53-62
A ternary diagram using MnO, TiO2, P2O5 can discriminate between five petrotectonic environments of basaltic rocks (45–54% SiO2). Fields for mid-ocean ridge, island arc tholeiite, island arc calc-alkaline, ocean island tholeiite, and ocean island alkalic rocks were distinguished on the basis of 507 analyses from well-defined environments. Boninites plot within island arc fields. Continental tholeiites, such as the Columbia River basalts, are high in P2O5 relative to MnO and TiO2, and overlap portions of all five oceanic fields.MnO is depleted relative to TiO2 in mid-ocean ridge analyses and may be controlled by early fractionation of olivine and/or clinopyroxene under conditions of lowfO2. In island arc rocks, MnO is enriched relative to TiO2 due to early crystallization of titanomagnetite in a high-fO2 environment. Primitive mid-ocean ridge and arc tholeiites have similar MnO/TiO2/P2O5 ratios which indicate a grossly similar parent magma. Increasingly differentiated basaltic rocks are more easily classified by the diagram. High relative abundances of TiO2 and P2O5 in ocean island rocks are consistent with their derivation from a separate source.Despite the purported high mobility of MnO, the MnO/TiO2/P2O5 discriminant diagram may be applied to unspilitized and moderately spilitized zeolite to greenschist facies greenstones with good agreement between the environment determined by MnO/TiO2/P2O5 and by other means such as trace elements, REE, or field relations. 相似文献