Crystal field stabilization energies of almandine-pyrope and almandine-spessartine garnets determined by FTIR near infrared measurements     

Charles A. Geiger  George R. Rossman 《Physics and Chemistry of Minerals》1994,21(8):516-525

The band positions of three partially overlapping Fe²⁺ spin-allowed transitions located between 4000 and 9000 cm^–1 in almandine-pyrope and almandinespessartine garnets solid solutions were measured using near-infrared (NIR) spectroscopy. The crystal field stabilization energies (CFSE) along both binaries were calculated assuming a splitting of 1100 cm^–1 for the lower orbitals. The CFSE show a slight increase along the almandine-spessartine binary from 3730 to 3810 cm^–1 and a larger increase from 3730 to 3970 cm^–1 for the almandine-pyrope binary. Dodecahedral Fe²⁺-site distortion increases with an increase in spessartine component and decreases with increasing pyrope component, in agreement with average dodecahedral site distortions determined from diffraction experiments. The excess CFSE's along both joins are negative. For the almandinespessartine binary they are small, but are about 3.5 times larger in magnitude along the join almandine-pyrope, where an interaction parameter of W= -2.9 KJ/mole has been derived from a symmetric mixing model. The excess CFSE are relatively small compared to the magnitudes of the excess enthalpies of mixing that have been assigned to garnet solid solutions. Moreover, they give no indication which could support the positive and asymmetric excess enthalpies of mixing that have been proposed for almandine-pyrope solid solutions.  相似文献   

The warming of the industrialized middle latitudes 1985–2050: Causes and consequences     

George M. Woodwell 《Climatic change》1989,15(1-2):31-50

The dominant influence on global climate for the indefinite future is expected to be a warming in the middle and high latitudes of both hemispheres. The speed of the warming is uncertain. The warming in winter may exceed 1.0 degree per decade. The warming in summer is expected to be less. The cause is the accumulation of infra-red absorptive gases, especially CO₂ and CH₄, in the atmosphere. The sources are the combustion of fossil fuels, the destruction of forests and their soils, and, possibly, the warming itself, which can be expected to stimulate decay of organic matter in soils. The warming in these latitudes is expected to be accompanied by increased precipitation as climatic zones migrate generally poleward. A 1 °C change in mean temperature is equivalent to a change in latitude of 100–150 km. The changes expected are rapid enough to exceed the capacity of forests to migrate or otherwise adapt. Forest trees will die at their warmer and drier limits of distribution more rapidly than forests can be regenerated in regions where climates become favorable. The destruction of forests will add further to the releases of C to the atmosphere. There is no equivalent countervailing storage that has been identified. The result suggests that a significant enhancement of the warming beyond current predictions is to be expected. An open-ended, accelerating warming of the Earth at rates that bring rapid changes in climatic zones, drive forests to impoverishment, and raise sea level rapidly is beyond the limits of simple adjustments of the human enterprise. Steps to stabilize the atmospheric composition seem inevitable. Because the total emissions of C to the atmosphere are not known, the current rate of transfer from the atmosphere to the oceans is uncertain. But whatever the current total release to the atmosphere, the annual atmospheric increase is about 3.0 G-tons of C as CO₂. At least three possibilities exist for reducing or eliminating the imbalance and moving toward long-term stability:

1. a reduction in the use of fossil fuels globally, now estimated as the source of about 5.6 G-tons of C annually;
2. a reduction or cessation of deforestation, now estimated as releasing 1–3 G-tons annually;
3. a vigorous program of reforestation that would remove from the atmosphere into storage in plants and soils about 1 G-ton of C annually for each 2 × 10⁶ km² tract reforested.

Further adjustments in emissions will be appropriate as experience accumulates. Such steps are appropriate now and possible. They will bring widespread ancillary benefits to the human enterprise.  相似文献   

Some models of the geomagnetic field in western Europe from 1960 to 1980     

George Backus  Sue Hough 《Physics of the Earth and Planetary Interiors》1985,39(4):243-254

Achache et al.'s averages over 10 west European observatories of the annual mean magnetic components X, Y, Z are studied from 1953 to 1979. A 1970 jerk is fitted to the data by least squares, and the fit is quantitatively compared with that of a polynomial having the same number of free parameters as the jerk (a quintic). A crude correction for the 11-y sunspot cycle is also attempted. The jerk and quintic are equally good fits to X, the jerk is clearly better for Y, and the quintic is modestly better for Z. The jerk amplitudes of X and Z but not Y depend heavily on whether a sunspot correction is made, and such a correction may be required to estimate the energy of the internal part of the jerk in the manner of Malin and Hodder. The sunspot correction to Y probably cannot be brought above the noise because it is small and highly correlated with both the jerk and the quintic. The sunspot corrections to X and Z are statistically significant but depend on whether the core signal is taken as a jerk or a quintic. Courtillot and Le Mouël's physical model for the jerk predicts that the jerk amplitudes of X, Y, Z will be proportional to the longitudinal derivatives of X, Y and Z. This prediction is roughly verified for the magnitudes but not the signs; it is just possible that the signs in X and Z are not statistically significant.  相似文献   

Tank damage during the may 1983 coalinga earthquake     

George C. Manos  Ray W. Clough 《地震工程与结构动力学》1985,13(4):449-466

The magnitude M = 6-5 Coalinga earthquake of 2 May 1983 caused intense ground shaking throughout the epicentral region. Unanchored cylindrical ground supported tanks located at six sites within this oil producing area were damaged; damages included elephant's foot buckling at the base of three moderate sized tanks, joint rupture and top shell buckling in one large old rivetted tank, bottom plate rupture of a relatively new welded tank and damage to the floating roofs of 11 tanks. Also oil spilled over the top of many tanks and secondary damages occurred in pipe connections, ladders, etc. In this paper an estimate is made of the intensity of ground motion at each of the tank sites, based on strong motion records made during the main shock and the strongest aftershock. Then response parameters specified by current codes are correlated with the damages observed at each tank site. Based on this comparison, it is concluded that current U.S. practice under-estimates the sloshing response of tanks with floating roofs and does not adequately address the uplifting mechanism of unanchored ground supported tanks.  相似文献   

Halite and sylvite as solid inclusions in high-grade metamorphic rocks     

Volkmar Trommsdorff  George Skippen  Peter Ulmer 《Contributions to Mineralogy and Petrology》1985,89(1):24-29

Solid inclusions of halite and sylvite, formed during regional and contact metamorphism have been identified by microscopy and by electron microprobe analysis in rocks from Campolungo, Switzerland and Cornone di Blumone, Italy. The solid inclusions occur in several of the major minerals crystallized during metamorphism and have been observed as idiomorphic crystals and dendrites. The compositions measured in 100 analyses from Campolungo, Switzerland and 40 analyses from Cornone di Blumone, Italy extend across the two-phase region in the system, KCl-NaCl, indicating that the salt inclusions are high temperature precipitates. In both localities compositionally zoned and unzoned crystals have been found. Measured compositions on the temperature maximum of the two-phase region indicate at least 500° C which can be compared with 500°±20° C determined by Mercolli (1982) and Walther (1983) from the Mg content of calcites from Campolungo. The solid inclusions have been trapped apart from CO₂-rich and saline, H₂O-rich fluid inclusions which have been described by Mercolli (1982) as the earliest preserved fluid inclusions in the rocks. The early precipitation of salt minerals at Campolungo indicates that fluids were saturated with NaCl and KCl at 500° C and pressures of 2,000 bars or higher. Similar relationships exist between solid and fluid inclusions in the rocks of Cornone di Blumone which formed at temperatures as high as 800° C and pressures between 0.5 and 1 kilobar (Ulmer 1983). The entrapment of halite and sylvite as solid inclusions preserves the composition of the minerals which may therefore be useful as geothermometers.  相似文献   

Apparent counter-gradient heat fluxes generated by atmospheric waves     

George Chimonas 《Boundary-Layer Meteorology》1985,31(1):1-12

In studies of turbulence, tower data are used to measure vertical fluxes of momentum and heat generated by correlations in the fluctuating fields. Similar time averages of wu and w may be computed for an interval of wave activity observed at an instrumented tower. However, it is shown that such measurements do not necessarily correspond to the conventional Reynold's stresses or vertical heat fluxes. And waves can appear to have non-zero and even countergradient fluxes when proper averages show no fluxes at all.These spurious fluxes are generated by the method of analysis, a Fourier series performed on a finite time interval. Any background disturbance that is not strictly confined to the interval will generate a spurious wave spectrum. In particular, long-period waves will generate terms that interfere with the true high frequency waves to give false wave fluxes. The theoretical findings of this paper provide a ready explanation of tower data that would otherwise appear to conflict with conventional wave theory.  相似文献   

Amino acids of the Murchison meteorite: II. Five carbon acyclic primary β-, γ-, and δ-amino alkanoic acids     

John R Cronin  Sandra Pizzarello  George U Yuen 《Geochimica et cosmochimica acta》1985,49(11):2259-2265

All ten of the possible five-carbon acyclic primary β-, γ-, and δ-amino alkanoic acids (amino position isomers of the valines) have been positively identified in hot-water extracts of the Murchison meteorite using combined gas chromatography-mass spectrometry (GC-MS) and ion exchange chromatography. With the exception of δ-aminovaleric acid, none of these amino acids has been previously reported to occur in meteorites or in any other natural material. The γ-amino acids (4-aminopentanoic acid, 4-aminc-2-meth-ylbutanoic acid, and 4-amino-3-methylbutanoic acid) are present at higher concentrations (about 5 nmol g^?1) than are the β-amino isomers (3-aminopentanoic acid, 3-amino-2-methylbutanoic acid, allo-3-amino-2-methylbutanoic acid, 3-amino-3-methylbutanoic acid, 3-amino-2-ethylpropanoic acid, and 3-amino-2,2-dimethylpropanoic acid) which are present at concentrations of 1–2 nmol g^?1. These amino acids are less abundant in the meteorite than either the corresponding α-amino acids or the four-carbon homologues. Thirty-six amino acids have now been positively identified in the Murchison meteorite, 17 of which are apparently unique to carbonaceous chondrites. The fact that the meteorite contains all possible five-carbon acyclic primary α-, β-, γ-, and δ-amino alkanoic acids is consistent with a synthetic process involving random combination of single-carbon precursors.  相似文献   

The frequency and periodicity of preserved turbidites in submarine fans as a quantitative record of tectonic uplift in collision zones     

George Devries Klein 《Tectonophysics》1985,119(1-4)

The frequency and periodicity of preserved graded turbidite cycles in submarine fans in the Coral Sea and Sea of Japan are correlated to times of tectonic uplift in response to major collisions in the Owen-Stanley Range of Papua and the Hida Range of Japan, respectively. Large frequencies and shorter-term periodicities of turbidites at DSDP Site 210 were coeval with early Pliocene maximum tectonic-uplift rates which occurred in the Owen-Stanley Range in response to obduction. Similarly, large frequencies and shorter-term periodicities of turbidites at Site 299 (Toyama Submarine Fan) were coeval with the late Pleistocene uplift in the Hida Range; this uplift of 1000 to 1500 m occurred in response to collision tectonics. In both cases, trends of increasing frequencies and towards shorter-term periodicities of preserved turbidite depositional events correlate to trends of increasing rates of tectonic uplift.The role of sea-level fluctuations on changing denudation rates in these two collision zones is secondary. At Site 210, larger frequencies and short-term periodicities of preserved turbidites were coeval with early Pliocene high stands of sea level, whereas at Site 299, Pleistocene sea-level fluctuations are considered minor because at low stands of sea level, both relief and denudation rates were increased by about ten to 14%. At Site 286 (New Hebrides Basin), Eocene turbidite deposition is coeval with high stands of sea level, whereas at Site 297 (Northern Shikoku Basin), turbidite deposition was coeval with both rising and falling sea level.Analysis of both frequency and periodicity of turbidites by fan subenvironment at Site 299 indicates a record of continuous deposition, and maintainance of frequency and periodicity trends controlled by tectonic uplift. Late Pleistocene channel and overbank deposits showed periodicity differences of less than 28% of an order of magnitude, whereas Miocene-Pliocene overbank and distal turbidite periodicities differed by a 19% order of magnitude. Greater differences in magnitude occurred between distal turbidites or early Pleistocene age and Pliocene age than between Miocene-Pliocene overbank and distal turbidite deposition with a magnitude difference of 860%. These findings suggest that shifting depocenters and differences in sedimentation history in subenvironments of submarine fans are secondary to the role of tectonic uplift in this particular case.The minimal rate of tectonic uplift required to generate deep-sea fan turbidities appears to be approximately 400 m/million years. This figure is tentative and is based on very few observation points.Frequency and periodicity of preserved turbidite cycles in submarine fans in active continental margins and ancient counterparts should provide an independent measurement of rates and timing of tectonic uplift, particularly in collision terrains. Because this sediment parameter is a record of a single process from a single source and a record of “event stratigraphy”, its usage is preferable over standard and bulk sediment accumulation rates determined from age depth curves.  相似文献   

Uplift and submarine formation of some Melanesian porphyry copper deposits: Stable isotope evidence     

Allan R. Chivas  James R. O&#x;Neil  George Katchan 《Earth and Planetary Science Letters》1984,68(2):326-334

Hydrogen and oxygen isotope analyses of sericites and kaolinites from four young porphyry copper deposits (Ok Tedi (1.2 Ma) and Yandera (6.5 Ma), Papua New Guinea; Koloula (1.5 Ma), Solomon Islands; and Waisoi (<5 Ma), Fiji) indicate that the fluids from which these minerals precipitated were of mixed magmatic and non-magmatic sources. The non-magmatic component of the fluid from the island arc deposits (Koloula, Waisoi) was ocean water.For Ok Tedi, the non-magmatic component was a meteoric water with an isotopic composition different from that of the present meteoric water in the region. The isotopic signature of the former meteoric water is consistent with a surface elevation of 200 m a.s.l. or less at the time of mineralization. The deposit was later exposed and supergene kaolinitization commenced at approximately 1200 m a.s.l. Uplift and erosion has continued to the present at which time the elevation of the exposed deposit is 1800 m a.s.l. This rate of uplift is consistent with that known from other geological evidence. If the rate of uplift were approximately constant during the last 1.2 Ma, the age of supergene enrichment can be dated at approximately 0.4 Ma B.P.Similarly, influx of meteoric water at Yandera occurred when the ground surface above the deposit was at an elevation of approximately 600 m a.s.l. The deposit's present elevation is 1600 m a.s.l. In this case a total uplift of approximately 2.2 km is indicated, with removal of 1.2 km of overburden by erosion.  相似文献   

Characteristics and origins of lee-side stratification sequences in late pleistocene drumlins,northern Ireland     

George F. Dardis  A. Marshall McCabe  W. Ian Mitchell 《地球表面变化过程与地形》1984,9(5):409-424

Spindle- and parabolic-shaped drumlins examined at fifty-five localities in northern Ireland possess stratification sequences on their lee-side flanks. These forms lack the distinctive steep stoss- and tapering lee-ends of classical drumlins and tend to occur in linear zones transverse to late Pleistocene ice-flow. In most cases (90 per cent) the stratified deposits infill embayments excavated in the lee-side of barkhanoid forms and, in the remainder (10 per cent), they are superimposed on the lee-side of whaleback forms. The stratification sequences developed as a result of sedimentation in interconnected subglacial water-filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form. Stratigraphic evidence indicates that the lee-side sequences developed during drumlin streamlining, which supports the view that subglacial hydraulic processes played an important role in drumlin formation.  相似文献