Application of new thermodynamic data to grossular phase relations     

Dexter Perkins III  Eric J. Essene  Edgar F. Westrum Jr.  Victor J. Wall 《Contributions to Mineralogy and Petrology》1977,64(2):137-147

Recent low temperature, adiabatic calorimetric heat capacity measurements for grossular have been combined with DSC measurements to give entropies up to 1000 K. In conjunction with enthalpy of solution values for grossular, these data have yielded H _f ^o (298.15K) and G _f ^o (298.15K) values of –1583.2 ± 3.5 and –1496.74 ± 3.7 kcal mol^–1 respectively. For 15 reactions in the CaO-Al₂O₃-SiO₂-H₂O system, thermodynamically calculated P-T curves have been compared with experimental reversals and have shown good agreement in most cases. Calculations indicate that gehlenite is probably totally disordered. Estimates of zoisite and lawsonite entropies are consistent with the phase equilibrium and grossular data, but estimates of the entropies of pyrope and andradite show large discrepancies when compared with experimental reversals.Contribution no. 600 from the Mineralogical Laboratory, The Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, Michigan 48109, USA  相似文献   

Distribution of viral and bacterial pathogens in a coastal canal community     

Charles P. Gerba  Sagar M. Goyal  Eric M. Smith  Joseph L. Melnick 《Marine pollution bulletin》1977,8(12):279-282

Significant concentrations of human enteric viruses and bacteria were found to be present in the water and sediment of a coastal canal community into which secondarily treated sewage was being discharged.  相似文献   

Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity,and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite     

L.Niel Plummer  Eric T. Sundquist 《Geochimica et cosmochimica acta》1982,46(2):247-258

We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are $\text{0.038 ± 0.002}$ and $\text{0.173 ± 0.010}$, respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.  相似文献   

Phase relations inferred from field data for mn pyroxenes and pyroxenoids     

Philip E. Brown  Eric J. Essene  Donald R. Peacor 《Contributions to Mineralogy and Petrology》1980,74(4):417-425

Electron microprobe analysis of manganese silicates from Balmat, N.Y., has helped elucidate phase relations for Mn-bearing pyroxenes and pyroxenoids. A compilation of these data along with published and unpublished analyses for phases plotting on the CaSiO₃-MgSiO₃-MnSiO₃ and CaSiO₃-FeSiO₃-MnSiO₃ faces of the RSiO₃ tetrahedron has constrained the subsolidus phase relations. For the system CaSiO₃-FeSiO₃-MnSiO₃, the compositional gaps between bustamite/hedenbergite, bustamite/ rhodonite and rhodonite/pyroxmangite are constrained for middle-upper amphibolite facies conditions and extensive solid solutions limit possible three phase fields. For the CaSiO₃-MgSiO₃-MnSiO₃ system much less data are available but it is clear that the solid solutions are much more limited for the pyroxenoid structures and a continuum of compositions is inferred for clinopyroxenes from diopside to kanoite (MnMgSi₂O₆) for amphibolite facies conditions (T=650° C). At lower temperatures, Balmat kanoites are unstable and exsolve into C2/c calciumrich (Ca_0.68Mn_0.44Mg_0.88Si₂O₆) and C2/c calciumpoor (Ca_0.12Mn_1.02Mg_0.86Si₂O₆) phases. At temperatures of 300–400° C the calcium-poor phase subsequently has undergone a transformation to a P2₁/c structure; this exsolution-inversion relationship is analogous to that relating augites and pigeonites in the traditional pyroxene quadrilateral. Rhodonite coexisting with Mn-clinopyroxenes is compositionally restricted to Mn_0.75–0.95Mg_0.0–0.15Ca_0.05–0.13SiO₃. For the original pyroxene+rhodonite assemblage, the Mg and Ca contents of the rhodonite are fixed for a specific P (6kbars)-T (650° C)-X(H₂O)-X(CO₂) by the coexistence of talc+quartz and calcite+quartz respectively.Contribution No. 363, from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor MI 48109, USA  相似文献   

Seasonal oxygen depletion in Chesapeake Bay     

Jay L. Taft  W. Rowland Taylor  Eric O. Hartwig  Randy Loftus 《Estuaries and Coasts》1980,3(4):242-247

The spring freshet increases density stratification in Chesapeake Bay and minimizes oxygen transfer from the surface to the deep layer so that waters below 10 m depth experiece oxygen depletion which may lead to anoxia during June to September. Respiration in the water of the deep layer is the major factor contributing to oxygen depletion. Benthic respiration seems secondary. Organic matter from the previous year which has settled into the deep layer during winter provides most of the oxygen demand but some new production in the surface layer may sink and thus supplement the organic matter accumulated in the deep layer.  相似文献   

The thermodynamic properties and phase relations of some minerals in the system CaO-AI2O3-SiO2-H2O     

Dexter Perkins  Edgar F. Westrum  Eric J. Essene 《Geochimica et cosmochimica acta》1980,44(1):61-84

The heat capacities of lawsonite, margante, prehnite and zoisite have been measured from 5 to 350 K with an adiabatic-shield calorimeter and from 320 to 999.9 K with a differential-scanning calorimeter. At 298.15 K, their heat capacities, corrected to end-member compositions, are 66.35, 77.30, 79.13 and 83.84 cal K^?1 mol^?1; their entropies are 54.98, 63.01, 69.97 and 70.71 cal K^?1 mol^?1, respectively. Their high-temperature heat capacities are described by the following equations (in calories, K, mol): Lawsonite (298–600 K): Cp° = 66.28 + 55.95 × 10^?3T ? 15.27 × 10⁵T^?2 Margarite (298–1000 K): Cp° = 101.83 + 24.17 × 10^?3T ? 30.24 × 10⁵T^?2 Prehnite (298–800 K): Cp° = 97.04 + 29.99 × 10^?3T ? 25.02 × 10⁵T^?2 Zoisite (298–730 K): Cp° = 98.92 + 36.36 × 10^?3T ? 24.08 × 10⁵T^?2 Calculated Clapeyron slopes for univariant equilibria in the CaO-Al₂O₃-SiO₂-H₂O system compare well with experimental results in most cases. However, the reaction zoisite + quartz = anorthite + grossular + H₂O and some reactions involving prehnite or margarite show disagreements between the experimentally determined and the calculated slopes which may possibly be due to disorder in experimental run products. A phase diagram, calculated from the measured thermodynamic values in conjunction with selected experimental results places strict limits on the stabilities of prehnite and assemblages such as prehnite + aragonite, grossular + lawsonite, grossular + quartz, zoisite + quartz, and zoisite + kyanite + quartz. The presence of this last assemblage in eclogites indicates that they were formed at moderate to high water pressure.  相似文献   

Geological walks around St. Paul's     

Eric Robinson  Clive Bishop 《Proceedings of the Geologists' Association. Geologists' Association》1980,91(4):241-260

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Global volcanism and tectonism on Mercury: comparison with the Moon     

Pierre G. Thomas  Philippe Masson  Luce Fleitout 《Earth and Planetary Science Letters》1982,58(1):95-103

Both morphologic and tectonic studies indicate that Mercury and the Moon have quite different internal histories, despite their apparently similar morphologies. The evaluation of the volcanic surfaces indicates a decreasing volcanism on Mercury at the largest impacting time, despite short and local reactivations. On the Moon, the basaltic volcanism was increasing at the same time and continued for 1 billion years. That indicates a strongly different thermal evolution for these two planetary bodies.A widespread graben pattern is present on the Moon, with a statistical dominance of radial or tangential orientation with respect to the Imbrium basin, thus suggesting a relation between this major basin and the expansion of the Moon.Azimuthal studies show that the compressive structures, observed on the stereographic covered surface of Mercury are not randomly oriented, but seem radial towards the Caloris basin, thus indicating a possible influence of this largest basin on Mercurian contraction.The qualitative and quantitative formulations of these tectonic perturbations induced by large basins will be developed in a companion paper [1].  相似文献   

An analytical electron microscopic study of a pyroxene-amphibole intergrowth     

Andrew M. Isaacs  Philip E. Brown  John W. Valley  Eric J. Essene  Donald R. Peacor 《Contributions to Mineralogy and Petrology》1981,77(2):115-120

Samples of a garnet granulite from the mafic border units of the Lake Chatuge, Georgia alpine peridotite body were found to contain lamellar intergrowths of a pargastic amphibole in augite having the typical appearance of an exsolution feature. Single crystal X-ray diffraction, optical, electron microprobe and conventional and analytical electron microscopic studies have provided data limiting the compositions and structures of the coexisting phases. Individual lamellae of both materials are from 0.5 to 2.0 m in width with the lamellar interface parallel to {0 1 0}. The formulae of the minerals, as determined by a combination of electron microprobe and analytical electron microscopy, are (Na_0.1Ca_1.0Mg_0.6Fe³⁺ _0.3)(Si_1.8Al_0.2)O₆ for the pyroxene and Na_0.7Ca_1.9(Mg_2.1Fe²⁺ _1.4Fe³⁺ _0.5Ti_0.1Cr_0.1Al_0.8)(Si_5.9Al_2.1) O₂₂(OH)₂ for the amphibole. Several other studies have described intergrowths similar to those observed in this work, in general favoring exsolution as the formation mechanism for the intergrowths. In the Lake Chatuge samples however, replacement of pyroxene by amphibole is in part indicated by continuous gradation of amphibole lamellae into amphiboles rimming the clinopyroxenes.Contribution No. 368 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan  相似文献   

Petrogenetic model for the origin of carbonatites   总被引：1，自引：0，他引：1  

Eric A.K. Middlemost 《Lithos》1974,7(4):275-278

The petrological significance and distribution of igneous carbonatites is discussed. Particular attention is paid to the relationship that exists between carbonatites and volcanism in East Africa. Using a simple model of a carbonatite-nephelinite-ijolite volcanic complex it was discovered that all the peralkaline and carbonatitic rocks found in such a complex could be derived from a single primary nephelinitic magma. The origin of such a primary magma, and the subsequent evolution carbonatitic sub-magmas, is examined.  相似文献