Phase behaviors of albite, jadeite and nepheline have been studied in the diamond-anvil press employing YAG laser heating from about 100 to 280 kbar and at about 1000°C. Incorporating earlier work, the sequences of phase transformations with increasing pressure are as follows:
where the percentages are the decreases in zero-pressure volume from one to the other. Both NaAlSi3O8 hollandite and NaAlSiO4 (CaFe2O4-type) are new sodium aluminosilicates. The latter is the most likely host for sodium in the earth's lower mantle. High-pressure phases or phase assemblages revealed in albite and jadeite by static experiments are poorly defined by shock-wave studies of albitite and jadeite to about 900 and 1200 kbar respectively. 相似文献
The phase assemblages of monticellite (CaMgSiO4) were investigated in the pressure range 80–300 kbar at about 1000°C in a diamond-anvil cell with laser heating. Incorporating earlier work, the following phase transformations are found: where the percentages give the decreases in zero-pressure volume for the new assemblage. If merwinite is a stable mantle mineral phase, even in very small quantities (～1 mole percent), the results imply that olivine might decrease substantially in amount in the lower part of the Earth's upper mantle. This study also suggests that the observed seismic discontinuities in the mantle should not be entirely attributed to high-pressure polymorphism or decompositions of individual mineral species, and that some discontinuities may result from chemical reactions between the individual phases. 相似文献
The kinetics of metamorphism of the Staroe Boriskino C2 chondrite heated at 450°C in an inert atmosphere of helium flow was investigated. After being heated at 450°C during 160 minutes one specimen was moreover heated for 10 minutes at 500°C. The phase distribution was determined by means of Mössbauer spectroscopy, X-ray diffraction analysis, and electron probe microanalysis.The material changes rapidly (1–2 minutes). As a result of dehydration, the iron of the phyllosilicate is oxidized, the charge compensation being realized through the removal of iron and magnesium cations with the formation of magnetite and forsterite. Upon 10 minutes additional heating at 500°C iron appears in the olivine structure, the degree of iron oxidation declines, and magnetite disappears. Possible trends of change of C2 chondrite material are:
Highlights? Four distinct groundwater classes resulted from the fuzzy c-means clustering method. ? Both geogenic and anthropogenic processes affect the groundwater quality in the area. ? Salinization in the area is due to seawater intrusion and dissolution of evaporites. ? Near the coastal zone, the groundwater level is lowered 2–5 m below the sea level. ? Ancient subsurface hydrological features act as conduits for groundwater flow. 相似文献
Scattering by a slightly-rough core-mantle boundary (CMB) with small-scale radial variations of up to a few hundred metres, has been an attractive (though non-unique) interpretation of at least part of the precursors to PKIKP. Here it is shown that a slightly-rough CMB has an observable effect on PKKP as well, if the signal-to-noise ratio is sufficiently high. The effect may be observed as precursive arrivals and is due to back-scattering at CMB. This work was prompted by observations by Chang and Cleary at LASA of “PKKP” and precursors from the Novaya Zemlya explosions. NORSAR data from several source regions are presented here; small-scale radial variations of 100–200 metres are inferred from these data, although in some regions the CMB appears to be much smoother. On the other hand, the LASA data are anomalous and suggest much larger topography in the sampled region of the CMB. Both large- and small-scale topography must be dynamically produced, if current estimates of the viscosity of the lower mantle (～1022 Poise) are correct. 相似文献
The concept of a time-depth correlation between tectonic earthquakes at depth beneath some volcanoes, and their eruptions, developed by the author since 1962, has been confirmed by new observations and successful prediction of renewed volcanic activity in New Zealand.Regular earthquake migrations are observed along the Benioff zone, and volcanic eruptions are found to be related to these seismic migrations beneath the volcanoes, as follows: Therefore, in island arcs and continental margins, volcanic activity is the result of two processes occurring beneath the volcanoes: (1) a “tectonic process”, a migration of strain release along the downgoing lithosphere, of which the earthquakes are the manifestation; (2) a “magmatic process”, a relatively fast vertical ascent of magmatic material from the deep root of the volcano, where the observed shocks may be the starting signal from this level.The rate of migration of tectonic earthquakes increases with depth in the upper mantle.An empirical time relationship between the earthquakes occurring at depth beneath a volcano and its eruptions, has been successfully tested for renewed activity at White Island in New Zealand, over the period 1977–1978. 相似文献
The system Mg2SiO4MgOH2O was investigated at pressures between 85 and 160 kbar and at temperatures between 750 and 1200°C. In runs for a gel with Mg/Si ratio of 3 and with 4.0 wt.-percent H2O, a dense hydrous magnesian silicate, denoted phase B by Ringwood and Major, was found at pressures from about 100 kbar to at least 160 kbar in the whole temperature range studied. In the following table the crystallographic parameters and chemical formula of phase B, determined in this study, are compared with those of the other dense hydrous silicates in Mg2SiO4MgOH2O.
Ultrasonic data for the velocities of the ilmenites MgTiO3 and CoTiO3 have been determined as a function of pressure to 7.5 kbar at room temperature for polycrystalline specimens hot-pressed in a piston-cylinder apparatus at pressures up to 30 kbar. Titanate and germanate ilmenites define divergent isostructural trends on a Birch diagram of bulk sound velocity (υφ) vs. density (ρ). On a υφ vs. mean atomic weight () diagram, however, all of the ilmenite consistent with a single . Elasticity systematics for isostructural sequences are used to e the bulk modulus (2.09 Mbar) and bulk sound velocity (7.4 km/sec) of MgSiO3-elmenite. 相似文献
Grain-growth kinetics in wadsleyite was investigated using a multianvil high-pressure apparatus. Fine-grained wadsleyite aggregates were synthesized by isostatic hot-pressing and were subsequently annealed under high pressure and temperature in a controlled chemical environment. Wadsleyite samples show normal grain-growth characterized by a log-normal grain-size distribution following the relation, where n is a constant, L the grain-size at time t, L0 the grain-size at time t = 0 and k is a rate constant that depends on temperature T and chemical environments (fO2: oxygen fugacity in Pa, COH: water content in H/106Si) as:
Neutral winds in the lower thermosphere (95–) measured during the March equinox period (1991–1992) by ground-based incoherent scatter radars at Arecibo (18°N), Millstone Hill (42.5°N), and Sondrestrom (67°N) and by the space-based wind imaging interferometer (WINDII) are compared and show overall good agreement but some differences. At 18°N, the wind field in the altitude region of 95– displays prevailing upward propagating diurnal tides with wavelengths of about . The diurnal structure is affected by the semidiurnal tide resulting in regular minima separated by 11–. At altitudes above , the diurnal tide dominant wind structure changes to the semidiurnal tide dominant structure as illustrated clearly by WINDII data with coverage. Winds at 42.5°N and 67°N show similar structures in which winds at 105– are generally anti-sunward. Daytime ISR winds show prevailing upward propagating semidiurnal tides with wavelengths of 35–. Winds from WINDII reveal the existence of the in situ thermospheric diurnal tide with amplitudes comparable to those of the semidiurnal tide. The superimposition of the two tides result in a wind field stronger during daytime than during nighttime at mid- and high-latitudes. Geomagnetic influence on neutral winds is negligible at low- and mid-latitudes under solar quiet conditions, but is observed at high-latitudes, where wind vectors follow a clockwise one-cell pattern at altitudes above about in geomagnetic coordinates. Most recent simulations for the three latitudes provided by the NCAR thermosphere/ionosphere/mesosphere electrodynamics general circulation model are compared to the observations. The results at low- and mid-latitudes agree well with the observed winds in both wind structures and magnitudes, and reveal details of wave transition. Simulations for high-latitudes are less satisfactory, and require further improvements. 相似文献
