摘要:

Experimentally determined steady state flow properties and processes of important rock‐forming materials are reviewed in reference to those of metals and ceramics and to physical conditions in the earth's crust and upper mantle. Dislocation motion controls the creep rate over a wide range of steady state conditions in the experiments, and the observation that the same processes have operated during natural deformations permits extrapolations of the mechanical data. Under these conditions, strain rate is related to stress raised to the power 2–9, depending on the material and conditions, and the resulting flow stresses and equivalent viscosities are compared at a representative geological strain rate of 10−14/s. The results are applied in brief discussions of diapirism, growth of folds, and flow in the upper m

ISSN:8755-1209    

DOI:10.1029/RG014i003p00301

年代:1976

数据来源: WILEY

摘要:

Melting experiments on mare basalts are complicated by technical problems. The quality of the experimental results can be evaluated from the following criteria: (1) attainment of equilibrium (except in rate studies), (2) acceptable monitoring and control of pressure and temperature, (3) acceptable control of oxygen fugacity, and (4) preservation of constant bulk composition of the sample; i.e., reaction of the sample with its container must be controlled within narrow limits. Melting experiments in vacuum and in controlled gas atmospheres confirm petrologic and geochemical observations that most of the chemical variety among the (olivine normative) low‐Ti basalts is due to fractionation of olivine plus or minus minor spinel. The chemical variety among the high‐Ti basalts is likewise controlled by near‐surface fractionation processes, but the low‐K and high‐K groups cannot be interrelated in such a manner. Crystallization experiments have also shown that porphyritic textures can sometimes be produced by a single‐stage cooling history. High‐pressure studies indicate that the low‐Ti suite originated by partial melting of an olivine‐pyroxenite mantle at depths ranging from 200 to 350 km (to 500 km including green glass). It is generally agreed that a spectrum of low‐Ti parental magmas could be produced over this depth interval, the most olivine normative liquids originating at greatest depths. Experimental results suggest that the high‐Ti suite (and orange glass) formed by partial melting of an intrinsically Ti rich olivine‐pyroxenite mantle at depths similar to those at which the low‐Ti suite is produced. Alternatively, the high‐Ti basalts can be interpreted as hybrid liquids whose petrogenesis involves the assimilation of subcrustal Ti‐rich material by parental magmas of low‐Ti type and origin. The Ti‐rich zone is believed to have formed during an early differentiation event. Isotopic data indicate a prior differentiation histo

ISSN:8755-1209    

DOI:10.1029/RG014i003p00361

年代:1976

数据来源: WILEY

摘要:

The earth's core, at a pressure of between 1.3 and 3.7 Mbar and a temperature between 3000° and 5000°C, consists primarily of Fe‐Ni in the inner core and molten Fe alloyed with from 8 to 20% of a light element, most likely S or Si, giving an average atomic number for the elements in the outer core of about 23. If the core accreted before the mantle, then the apparent disequilibrium of some elements with respect to core and mantle is explained, but it is difficult to explain the presence of appreciable quantities of a light element that are required in the core. Alternatively, the core formed by melting, coalescence, and subsequent collapse of metallic particles in a protoearth that was relatively homogeneous initially. Such collapse would raise the temperature of the earth as much as 2300°K. Silicon must be present in the core if (Fe + Mg)/Si>1 in the mantle and if that ratio for the bulk earth lies within the limits set by the sun and chondrites. If Si is present, the apparent chemical disequilibrium between metallic Si in the core and Fe2+and Fe3+in the mantle must be explained. Arguments for S in the core based on the abundance of S in rocks of crustal and mantle origin appear to have little foundation; however, there are strong geochemical and cosmochemical arguments justifying the presence of S in the core if the earth accreted at relatively low temperatures. The intriguing speculation that the bulk of the earth's potassium is present in the outer core, thus providing energy for core and mantle, remains to be tested by more partitioning experiments. A number of explanations exist to explain the apparent disequilibrium of some elements between core and mantle; however, none is satisfactory. The core formed soon after the earth accreted; in fact, the age generally taken as the age of the earth probably represents the time of core forma

ISSN:8755-1209    

DOI:10.1029/RG014i003p00375

年代:1976

数据来源: WILEY

摘要:

Rare gas abundances in various terrestrial materials can be classified into three distinct fractionation patterns: type 1 shows a progressive enrichment in the heavier gases (shales, natural gases, holocrystalline submarine basalts, seawater and groundwater), type 2 shows a large enrichment of Ne and a slight apparent enrichment of Xe (glassy margins of submarine basalts, a subaerial basalt, an olivine xenolith from Hawaii), and type 3 shows large enrichments of Ne, Kr, and Xe relative to Ar (thucolite and a shale sample). The type 1 pattern is formed by the low‐temperature adsorption of rare gases usually via the rare gases dissolved in seawater. The type 2 pattern is interpreted as a combination of high‐temperature diffusion, solubility, and bulk melting in the mantle. The type 3 pattern probably represents a hybrid pattern. These patterns are consistent with an earth‐atmosphere evolution model which assumes (1) that the present rare gas abundances in the atmosphere closely approximate the rare gas inventory of the whole earth except for xenon and (2) that the average rare gas abundance pattern in the solid earth is roughly similar to that in the atmosphere except f

ISSN:8755-1209    

DOI:10.1029/RG014i003p00385

年代:1976

数据来源: WILEY

摘要:

The near‐Martian plasma measurements carried out by means of charged particle traps aboard the Mars 2, 3, and 5 satellites are reviewed. The planetary bow shock was observed; in a number of satellite passes near the planet the boundary of the obstacle that causes the bow shock was crossed. Arguments supporting the existence of an intrinsic magnetic field of Mars and of the possible existence of a quasi‐isotropic plasma zone in the Martian magnetic tail are given. The behavior of the plasma and magnetic field at the obstacle boundary gives evidence favoring a magnetic nature for the obstacle (i.e., favoring the existence of a Martian magnetosphe

ISSN:8755-1209    

DOI:10.1029/RG014i003p00391

年代:1976

数据来源: WILEY

摘要:

A major problem encountered in trying to model the current system associated with a polar magnetic substorm from ground‐based magnetic observations is the difficulty of adequately evaluating the earth's induction effects. Two methods for simulating these effects are reviewed here. Method 1 simply reduces the earth to a perfect conductor and leads to very simple field equations. Method 2 considers the earth as a ‘horizontally’ layered body of finite conductivity but requires a large amount of computational time. The performances of both methods are compared when the substorm current system can be approximated by an infinitely long electrojet flowing over a flat earth. In this case it appears that for most substorm modeling problems it is sufficient to treat the earth as a perfect conductor. The depth of this perfect conductor below the earth's surface should be selected in function of the source frequency co

ISSN:8755-1209    

DOI:10.1029/RG014i003p00403

年代:1976

数据来源: WILEY

摘要:

Recent quantitative magnetospheric field models contain many features not found in earlier models. Magnetopause models which include the effects of the dipole tilt have been presented. More realistic models of the tail field include tail currents which close on the magnetopause, cross‐tail currents of finite thickness, and cross‐tail current models which model the position of the neutral sheet as a function of tilt. Finally, models have attempted to calculate the field of currents distributed in the inner magnetosphere. As the purpose of a magnetospheric model is to provide a mathematical description of the field that reasonably reproduces the observed magnetospheric field, several recent models have been compared with the observed ΔB(Bobserved‐Bmain field) contours. Models containing only contributions from magnetopause and tail current systems are able to reproduce the observed quiet time field only in an extremely qualitative way. The best quantitative agreement between models and observations occurs when currents distributed in the inner magnetosphere are added to the magnetopause and tail current systems. However, the distributed current models are valid only for zero tilt. Even the models which reproduce the average observed field reasonably well may not give physically reasonable field gradients. Three of the models evaluated contain regions in the near tail in which the field gradient reverses direction. One region in which all the models fall short is that around the polar cusp, though most can be used to calculate the position of the last closed field line reasonabl

ISSN:8755-1209    

DOI:10.1029/RG014i003p00411

年代:1976

数据来源: WILEY

摘要:

This report reviews the findings on pollutant emissions, removal processes, and pollutant concentrations, as well as some aspects of climatic change. It is shown that emissions from agricultural burning in the tropics exceed significantly U.S. annual emission rates. The direct anthropogenic global particle production amounts to about 7% of that naturally produced. More than 70% of the man‐made particles are in the form of gaseous precursors. The anthropogenic contribution to the total global particle production is about 15%. Natural emissions of particulates and CO, CO2, CH4, H2S, NO2, and NH3exceed man‐made emissions by orders of magnitude. Only SO2is produced predominantly by human activities. Emission estimates, especially those of CO, CO2, CH4, NH3, and N2O, differ greatly among the different investigators. The major removal processes of particulate and gaseous pollutants in the troposphere and stratosphere are reviewed. Trends and current levels of particulate and gaseous pollutants for urban and background stations are discussed. The tropospheric and stratospheric global monitoring programs are outlined. The discussion of changes in the upper atmosphere centers around stratospheric aerosols CO2, CO, CH4, H2O, and O3. The relative effects of nuclear tests, SST flights, and propellants and refrigerants are discussed. Recent hypotheses of ozone destruction by chlorofluoromethanes and bromines are presented. Next evidence of climatic change is given. Natural and man‐made external causes of climatic change, including fluctuations in solar emission, orbital changes, changes in CO2, dust, and land use, and internal causes of climatic change, which include Antarctic ice surges, decreases in ocean salinity, and almost intransitivity, are discussed. All these factors are interrelated via complicated feedback mechanisms. Hypotheses concerning the physical causes, the time scales, and the initial stages of ice ages are reviewed. It appears that major ice ages seem to occur every 100,000 yr and that after an interglacial interlude we are on the brink of a period of colder climate. It has been estimated that the mean temperature of the planetary atmosphere in its surface layers has decreased by about 0.3°C since the 1940's despite an 11% increase of CO2above the nineteenth century preindustrial level of 290 ppm. It appears that the natural climatic cooling trend is roughly 3 times more powerful than the present influence of CO2. However, in the near future, far‐reaching adverse climatic and ecological consequences can be expected because the CO2increase is too rapid for the regulatory mechanisms of the oceans. The impact of an increasing aerosol loading cannot be assessed reliably yet. The net effect will probably be small or one of warming. Presently, the heat release of the order of 15–20 TW from global energy production is still relatively small. But with the continuation of the present energy growth rate, within one generation, waste heat production may reach 100–300 TW, an amount found sufficient in natural processes to cause climatic changes. Some problems related to land use changes are also discussed, especially overgrazing, which may lead to desertification, and tropical deforestation, which may alter the atmospheric

ISSN:8755-1209    

DOI:10.1029/RG014i003p00429

年代:1976

数据来源: WILEY