Density calculations for silicate liquids. I. Revised method for aluminosilicate compositions

Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature T_r, is given by $\text{V}{}_{\mathrm{r}}\text{= ∑X}{}_{\mathrm{i}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{i}}\text{+ X}{}_{\mathrm{A}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$, where the summation is taken over all oxide components except A1₂O₃, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is the composition-dependent apparent partial molar volume of Al₂O₃. The thermal expansion coefficient of aluminosilicate liquids is given by $\text{α = ∑X}{}_{\mathrm{i}}\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}\text{+ X}{}_{\mathrm{A}}\text{}\text{?}\text{ga}{}_{\mathrm{A}}{}^{\mathrm{o}}$, where $\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}$ terms are constants independent of temperature and composition, and $\text{}\text{?}\text{ga}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is a composition-dependent term representing the effect of Al₂O₃ on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = V_rexp[α(T-T_r)], where T_r = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 $\text{cc}\text{mole}$ and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is discussed in terms of several possible interpretations of the structural role of Al³⁺ in aluminosilicate melts.     

Polymetamorphic relations in iron ores from the Iron Quadrangle,Brazil: The correlation of oxygen isotope variations with deformation history

This study deals with the oxygen isotope composition of hematite-rich ore bodies in the Iron Quadrangle, Brazil. The area studied can be divided into two different regions: a western (W) zone of greenschist facies assemblages and an eastern (E) zone of amphibolite facies with transitions into granulite facies assemblages.The ¹⁸O values of 136 quartz-iron oxide pairs have been determined and temperatures of formation have been calculated. The ¹⁸O values of quartz vary between +6 and 20 except one value near +23, whereas the iron oxides fall between –4 and +10, with nearly 80% of the iron oxide values between –0.5 and 4.0. The regional distribution of the ¹⁸O values is as follows: in the W-region 85% of the quartz are >12, whereas in the E-region only 46% fall in this range, In contrast to quartz the iron oxides do not show any regional differences.The variation of oxygen isotope fractionations between quartz and iron oxides is obviously related to the complex deformation history of the iron ores. Samples with a primary schistosity (S₁) only represent peak metamorphic conditions. In the E-region the (S₁) high temperatures >700° C seem to correspond to orogenic events in the Archaen basement 2,700 m.y. ago. In the W-region S₁-temperatures between 460° and 560° C seem to represent peak metamorphic conditions of the Proterozoic Minas metamorphism 2,000 m.y. ago. Iron ores which have been overprinted by later deformation events are selectively reset to lower isotopic temperatures. The more closely spaced the schistosity planes the larger the extent of a temperature lowering.The genetic processes associated with these hematite-rich ore bodies appear to be sedimentary-metamorphic rather than metasomatic processes. Furthermore, there is no evidence for secondary leaching by weathering solutions.     

Precambrian phosphorites in the Bijawar rocks of Hirapur-Bassia areas,sagar district,madhya pradesh,India

The Precambrian phosphorites of Bijawar Group of rocks show characteristics of a epicontinental sea with restricted and very shallow marine environment of formation along some shoals, which existed during the iron-rich Precambrian times. These phosphorite deposits located in the Hirapur-Bassia areas show extensive leaching of carbonate and phosphate minerals during episodes of weathering. X-ray diffraction studies indicated that carbonate-flourapatite is the major apatitic phase in these phosphorites while crandallite developed on the surface outcrops. There is a general tendency for the depletion of CO₂ in these apatites leading to formation of flourapatite. This CO₂ is an indicator of hidden weathering in the rocks. Major and trace element determinations of phosphorite have been used to indicate various correlation factors responsible for the concentration of elements in these Precambrian leached phosphorites.The paper is a contribution to the aims and objectives of IGCP Project 156The paper is dedicated to Prof. Dr. R. C. Misra, who as a teacher and guide had been a source of inspiration to the senior author for the last two decades     

Chronology and development of the 1980 earthquake at El Asnam (Algeria): a postscript

Radiocarbon dating has now confirmed the alluvial chronology that was used in assessing the extent of deformation during the 1980 El Asnam earthquake. It also supports the suggestion that earlier movements were related to a hypocentre further to the east.     

Intercomparison of210Pb measurements at GEOSECS station 500 in the northeast Pacific

During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for²¹⁰Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured²¹⁰Pb results.The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%.The SIO experiments show that (1) the two scavenging methods employed (Fe(OH)₃ and Co-APDC co-precipitation) yield identical²¹⁰Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in²¹⁰Pb loss or contamination.The²¹⁰Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum²¹⁰Pb concentration around 500 m depth, marking the penetration depth of the flux of excess²¹⁰Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The²¹⁰Pb/²²⁶Ra activity ratio decreases monotonically from about 1 at the²¹⁰Pb minimum to about 0.5 near the bottom. The particulate²¹⁰Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate²¹⁰Pb profiles.     

210Pb in the Pacific: the GEOSECS measurements of particulate and dissolved concentrations

We report here on particulate and dissolved²¹⁰Pb profiles at 16 stations, and on total²¹⁰Pb profiles at 3 stations, all occupied during the Pacific GEOSECS expedition. Comparison with measurements at Yale on GEOSECS library samples indicates that during separation of particulate lead from dissolved lead, our filtered water samples suffered some loss of²¹⁰Pb in the filtration system; this effect appears to have reduced the dissolved²¹⁰Pb activities by ～ 20% in stations where the water was filtered. However, for these first Pacific data on the²¹⁰Pb distribution between the two phases, this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved²¹⁰Pb distributions.The dissolved²¹⁰Pb profiles in general vary geographically, following the²²⁶Ra profiles. In deep water,²²⁶Ra increases northward and eastward from the southwest Pacific, from ～ 22dpm/100kg, to over 40 dpm/100 kg in the northeast Pacific. Our dissolved²¹⁰Pb profiles show a similar increase in deep water, varying from about 10 to 20 dpm/100 kg along this line, and are commonly characterized by a mid-depth maximum. This²¹⁰Pb maximum reflects the mid-depth²²⁶Ra maximum of the Pacific Deep Water observed along the western boundary current.In surface water at low latitudes there is a significant²¹⁰Pb flux from the atmosphere, which produces a²¹⁰Pb/²²⁶Ra activity ratio generally greater than unity. This flux penetrates as deep as 600 m, as indicated by an “induced”²¹⁰Pb minimum caused by the surface maximum. The surface water²¹⁰Pb excess decreases toward high southern latitudes and vanishes in the Circumpolar region.The particulate²¹⁰Pb profiles show a general increase with depth, from ～ 0.3dpm/100kg in subsurface water to ～ 1.5dpm/100kg in bottom water, with or without a mid-depth maximum that reflects the²²⁶Ra or dissolved²¹⁰Pb maximum. The particulate²¹⁰Pb normally comprises about 2% of the total²¹⁰Pb in subsurface water, and this fraction increases to about 10% near the bottom. As the filtration loss is not taken into account, the fraction of particulate²¹⁰Pb quoted here is an upper limit. Since the particulate matter concentrations are quite uniform in the water column below a few hundred meters, the²¹⁰Pb activity of the particulate matter also increases with depth. The particulate matter has a²¹⁰Pb concentration of ～ 100dpm/g in subsurface water, but the concentration increases to ～ 500dpm/g or more toward the bottom. This indicates that there is a cumulative adsorption of Pb onto the suspended particles as they are sinking through the water column.     

Orientation of the stress field from breakouts in a crystalline well in a seismic active area

The orientation of the regional stress field in the Swabian Jura was determined from borehole breakouts caused by stress accumulation at the borehole wall. The analysis is based on caliper data recorded in the Urach 3 geothermal well within an intervall of about 1450 m. The azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes.     

Mögliche Massnahmen zur Restaurierung des Sempachersees

Since 1954 average orthophosphate and total phosphorus concentrations have increased twenty and eightfold respectively in Lake Sempach. It is demonstrated that the lake is not in steady state with its phosphorus loading and that the net deposition rate of phosphorus is not linearly related to the phosphorus content of the lake. This implies that linear steady state one-box models are unsuitable to describe the phosphorus balance of this lake. Applying a nonlinear dynamic lake model we predict that the defined water quality goals ([P] ⩽30 mg m⁻³, [O₂ ⩾4 mg m⁻³]) can only be achieved within the next 15 years if the external phosphorus loading is reduced by at least 50% and simultaneously lake-internal measures, such as hypolimnion areation or hypolimnion siphoning are carried into effect.      

Case study of Pampa,Texas, multicell storms

Analysis of the Pampa, Texas, multicell storms showed prestorm environmental conditions of a strong horizontal convergence of moisture, mixing ratio 12 g/kg at the 850 mb level in the Texas Panhandle areas and strong winds with shear veering with height. Rapid-scan satellite imagery showed that the clouds penetrated above the tropopause and cloud-top temperatures were at least 4 to 9° C colder than the temperature of the tropopause. This formation and collapsing of high-mass-density overshooting cloud tops above the tropopause is characteristic of tornadoes in the middle portion of the United States.