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   

Tarawera 1886, New Zealand — A basaltic plinian fissure eruption     

George P.L. Walker  Stephen Self  Lionel Wilson 《Journal of Volcanology and Geothermal Research》1984,21(1-2)

New Zealand's biggest and most destructive volcanic eruption of historical times was that of Tarawera in 1886. The resulting scoria fall has a dispersal very similar in extent to that of the Vesuvius A.D. 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type. A new estimate of the volume (2 km³) is significantly greater than previous estimates. The basalt came mainly from a 7-km length of fissure, and emission and exit velocity were fairly uniform along at least 4 km of it, this is one of the few documented examples of a plinian eruption from a fissure vent. Primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min⁻¹. A model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1.5–3%. Violent phreatic explosions occurred in the southwestern extension of the fissure across the Rotomahana geothermal field, and it is thought that some of the water responsible for the power of the plinian eruption came from this source, though its amount was not sufficient to turn the eruption into a phreatoplinian one.  相似文献   

A world model of soil carbon dioxide: A reply     

George A. Brook  Elgene O. Box 《地球表面变化过程与地形》1984,9(1):85-87

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Hydrogen speciation in synthetic quartz   总被引：1，自引：0，他引：1  

Roger D. Aines  Stephen H. Kirby  George R. Rossman 《Physics and Chemistry of Minerals》1984,11(5):204-212

The dominant hydrogen impurity in synthetic quartz is molecular H₂O. H-OH groups also occur, but there is no direct evidence for the hydrolysis of Si-O-Si bonds to yield Si-OH HO-Si groups. Molecular H₂O concentrations in the synthetic quartz crystals studied range from less than 10 to 3,300 ppm (H/Si), and decrease smoothly by up to an order of magnitude with distance away from the seed. OH^? concentrations range from 96 to 715 ppm, and rise smoothly with distance away from the seed by up to a factor of three. The observed OH^? is probably all associated with cationic impurities, as in natural quartz. Molecular H₂O is the dominant initial hydrogen impurity in weak quartz. The hydrolytic weakening of quartz may be caused by the transformation H₂O + Si-O-Si → 2SiOH, but this may be a transitory change with the SiOH groups recombining to form H₂O, and the average SiOH concentration remaining very low. Synthetic quartz is strengthened when the H₂O is accumulated into fluid inclusions and cannot react with the quartz framework.  相似文献   

Mixed valence of iron in minerals with cation clusters     

Georg Amthauer  George R. Rossman 《Physics and Chemistry of Minerals》1984,11(1):37-51

The valence and distribution of iron in vivianite, lazulite, babingtonite, rockbridgeite, acmite, aegirine-augite, hedenbergite, and ilvaite were studied with optical and Mössbauer spectroscopy. Optically activated intervalence charge transfer between Fe²⁺ and Fe³⁺ in neighboring sites through common edges or faces is observed in all these minerals irrespective of the polymerization of the iron-oxygen polyhedra ranging from finite clusters to infinite structural units. However, a distinct decrease occurs in the energy of the corresponding optical absorption band with increasing number of Fe²⁺ and Fe³⁺ ions involved in the charge transfer process. Thermally activated electron delocalization between Fe²⁺ and Fe³⁺ occurs only if Fe²⁺ and Fe³⁺ occupy crystallographically equivalent or geometrically very similar neighboring sites which share common edges to form extended structural units such as the ribbon in ilvaite. If the Fe-O polyhedra form finite clusters of two, three, or four polyhedra (e.g., in vivianite, lazulite, and babingtonite, respectively) no thermally-activated mixed-valence states of iron are observed. In aegirine, extended regions of the M1 chain are statistically occupied by Fe²⁺ and Fe³⁺ giving rise to thermally-activated electron delocalization in addition to the intervalence band in the optical absorption spectrum. The intensity of the optical intervalence absorption has been measured in a number of systems: ? values range from 60 to 210.  相似文献