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941.
O. V. Verkhodanov A. I. Kopylov Yu. N. Pariiskii N. S. Soboleva A. V. Temirova O. P. Zhelenkova 《Astronomy Reports》2002,46(7):531-542
BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m R <23.5m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (~20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8. 相似文献
942.
The Petrology and Geochemistry of Calc-Alkaline Andesites on Shodo-Shima Island, SW Japan 总被引:3,自引:3,他引:3
Petrographical and geochemical characteristics of calc-alkalineandesites on Shodo-Shima Island, SW Japan, having bulk compositionslargely identical to the continental crust, are presented. Thefollowing petrographic observations suggest a role for magmamixing in producing such andesite magmas: (1) two types of olivinephenocrysts and spinel inclusions, one with compositions identicalto those in high-Mg andesites and the other identical to thosein basalts, are recognized in terms of NiMg and CrAlFe3+relations, respectively; (2) the presence of orthopyroxene phenocrystswith mg-number >90 suggests the contribution of an orthopyroxene-bearinghigh-Mg andesite magma to production of calc-alkaline andesites;(3) reversely zoned pyroxene phenocrysts may not be in equilibriumwith Mg-rich olivine, suggesting the involvement of a differentiatedandesite magma as an endmember component; (4) the presence ofvery Fe-rich orthopyroxene phenocrysts indicates the associationof an orthopyroxene-bearing rhyolitic magma. Contributions fromthe above at least five endmember magmas to the calc-alkalineandesite genesis can also provide a reasonable explanation ofthe PbSrNd isotope compositions of such andesites. KEY WORDS: calc-alkaline andesites; high-Mg andesites; magma mixing; continental crust; SW Japan 相似文献
943.
Quantitative analysis of variations in depositional sequence thickness from submarine channel levees 总被引:2,自引:0,他引:2
Abstract Thickness variations across‐levee and downchannel in acoustically defined depositional sequences from six submarine channel‐levee systems show consistent and quantifiable patterns. The thickness of depositional sequences perpendicular to the channel trend, i.e. across the levee, decreases exponentially, as characterized by a spatial decay constant, k. Similarly, the thickness of sediment at the levee crest decreases exponentially down the upper reaches of submarine channels and can be characterized by a second spatial decay constant, λ. The inverse of these decay constants has units of length and defines depositional length scales such that k?1 is a measure of levee width and λ?1 is a measure of levee length. Quantification of levee architecture in this way allowed investigation of relationships between levee architecture and channel dimensions. It was found that these measures of levee e‐folding width and levee e‐folding length are directly related to channel width and relief. The dimensions of channels and levees are thus intimately related, thereby limiting the range of potential channel‐levee morphologies, regardless of allocyclic forcing. A simple sediment budget model relates the product of the levee e‐folding width and e‐folding length to through‐channel volume discharge. A classification system based on the quantitative downchannel behaviour of levee architecture allows identification of a ‘mid‐channel’ reach, where sediment is passively transferred from the through‐channel flow to the levees as an overspilling flow. Downstream from this reach, the channel gradually looses its control on guiding turbidity currents, and the resulting flow can be considered as an unconfined or spreading flow. 相似文献
944.
Basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins. In southern Ontario, the basement consists of complexly structured mid-Proterozoic (ca. 1.2 Ga) crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of Paleozoic sedimentary strata. Reactivation of basement structures is suspected to control the location of Paleozoic fault and fracture systems, but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement. New aeromagnetic- and gravimetric-lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of Paleozoic fault and fracture systems. Lineament mapping was facilitated by reprocessing and digital image enhancement (micro-levelling, regional residual separation, derivative filtering) of existing regional gravity and aeromagnetic datasets. Reprocessed images identify new details of the structural fabric of the basement below southern Ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones. Linear zones parallel the projected trends of mid-Proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area, and are interpreted as zones of shearing and basement faulting. Mapped aeromagnetic and gravity lineaments show similar trends to Paleozoic faults and fracture networks and broad zones of seismicity in southern Ontario. These new data support an ‘inheritance model’ for Paleozoic faulting, involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata. 相似文献
945.
Bryan G. Mark Geoffrey O. Seltzer Donald T. Rodbell Adam Y. Goodman 《Quaternary Research》2002,57(3):287
Moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the Huancané Valley on the west side of the Quelccaya Ice Cap and the Upismayo Valley on the northwest side of the Cordillera Vilcanota. The fastest rates of deglaciation (39×10−5 to 114×10−5 km3 yr−1 and 112×10−5 to 247×10−5 km3 yr−1 for each valley, respectively) were calculated for the most recent paleoglaciers, corresponding to the last few centuries. These results are consistent with observations in the Venezuelan Andes showing high rates of deglaciation since the Little Ice Age. These rates also fall within the range of 20th century rates of deglaciation measured on the Quelccaya Ice Cap (29×10−5 to 220×10−5 km3 yr−1, Brecher and Thompson, 1993; Thompson, 2000). These results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century. Equilibrium line altitude (ELA) depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the Quelccaya Ice Cap and 170 m for the Cordillera Vilcanota. Maximum ELA depressions are lower than previously published: <500 m for the Cordillera Vilcanota and <400 m for the Quelccaya Ice Cap. These lower values could imply a topographic control over paleoglacier extent. 相似文献
946.
Darrell S. Kaufman Gary O'Brien Jim I. Mead Jordon Bright Paul Umhoefer 《Quaternary Research》2002,58(3):329
One of the most intriguing episodes in the Quaternary evolution of the Grand Canyon of the Colorado River, Arizona, was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge. Stratigraphic evidence for these deep lava-dammed lakes is expectedly sparse. Possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake. At two of the sites the sediment was associated with late Quaternary spring-fed pools and marshes. Water-lain silt and sand at lower Havasu Creek was deposited 3000 cal yr ago. The deposit contains an ostracode assemblage similar to that living in the modern travertine-dammed pools adjacent to the outcrop. The second deposit, at Lees Ferry, formed in a spring-fed marsh 43,000 cal yr ago, as determined by 14C and amino acid geochronology. It contains abundant ostracode and mollusk fossils, the richest assemblages reported from the Grand Canyon to date. Our interpretation of these sediments as spring-fed deposits, and their relative youth, provides an alternative to the conventional view that deposits like these were formed in deep lava-dammed lakes that filled the Grand Canyon. 相似文献
947.
Amphiboles were synthesized from bulk compositions prepared along the join Ca1.8Mg5.2Si8O22(OH)2–Ca1.8Mg3Ga4Si6O22(OH)2 hydrothermally at 750–850 °C and 1.0–1.8 GPa, and along the join Ca2Mg5Si8O22F2–Ca2Mg3Ga4Si6O22F2, anhydrously at 1000 °C and 0.7 GPa to document how closely the tschermak-type substitution is obeyed in these analogues
of aluminous amphiboles. Electron-microprobe analyses and Rietveld X-ray diffraction structure refinements were performed
to determine cation site occupancies. The extent of Ga substitution was found to be limited in both joins, but with the fluorine
series having about twice the Ga content (0.6 atoms per formula unit, apfu) of the hydroxyl-series amphiboles (0.3 apfu).
The tschermak-type substitution was followed very closely in the hydroxyl series with essentially equal partitioning of Ga
between tetrahedral and octahedral sites. The fluorine-series amphiboles deviated significantly from the tschermak-type substitution
and, instead, appeared to follow a substitution that is close to a Ca-pargasite substitution of the type: [6]Ga3++2[4]Ga3++1/2[A] Ca2+ = [6]Mg2++2[4]Si4++1/2[A]□. Infrared spectroscopy revealed an inverse correlation between the intensity of the OH-stretching bands and the Ga content
for the hydroxyl- and fluorine-series amphiboles. The direct correlation between the Ga and F content and inverse relationship between the Ga and
OH content may be a general phenomenon present in other minerals and suggests, for example, that high F contents in titanite
are controlled by the Al content of the host rock and that there may be similar direct Al–F correlations in tschermakitic
amphiboles. Evidence for the possibility that Al (Ga) might substitute onto only a subset of the tetrahedral sites in tschermakitic
amphiboles was sought but not observed in this study.
Received: 5 March 2001 / Accepted: 31 July 2001 相似文献
948.
We have investigated a well-ordered sample of natural Cr-bearing dickite from Nowa Ruda (Lower Silesia, Poland) using electron
paramagnetic resonance (EPR) at X- and Q-band frequencies (9.42 and 33.97 GHz, respectively) and optical diffuse reflectance
spectroscopy. The observation of the spin-forbidden transitions at 15500 and 14690 cm−1 allows us to unambiguously identify the major contribution of octahedrally coordinated Cr3+ ions in the optical spectrum. The X- and Q-band EPR spectra show two superposed Cr3+ signals. The corresponding fine-structure parameters were determined at room temperature and 145 K. These results suggest
the substitution of Cr3+ for Al3+ in equal proportions in the two unequivalent octahedral sites of the dickite structure. In kaolin group minerals, the distortion
around Cr3+ ions (λ≈ 0.2–0.4) in Al sites is significantly less rhombic than that observed around Fe3+ ions (λ≈ 0.6–0.8).
Received: 29 June 2001 / Accepted: 22 October 2001 相似文献
949.
I. E. Paukov N. K. Moroz Yu. A. Kovalevskaya I. A. Belitsky 《Physics and Chemistry of Minerals》2002,29(4):300-306
The heat capacity of paranatrolite and tetranatrolite with a disordered distribution of Al and Si atoms has been measured
in the temperature range of 6–309 K using the adiabatic calorimetry technique. The composition of the samples is represented
with the formula (Na1.90K0.22Ca0.06)[Al2.24Si2.76O10]·nH2O, where n=3.10 for paranatrolite and n=2.31 for tetranatrolite. For both zeolites, thermodynamic functions (vibrational entropy, enthalpy, and free energy function)
have been calculated. At T=298.15 K, the values of the heat capacity and entropy are 425.1 ± 0.8 and 419.1 ±0.8 J K−1 mol−1 for paranatrolite and 381.0 ± 0.7 and 383.2 ± 0.7 J K−1 mol−1 for tetranatrolite.
Thermodynamic functions for tetranatrolite and paranatrolite with compositions corrected for the amount of extraframework
cations and water molecules have also been calculated. The calculation for tetranatrolite with two water molecules and two
extraframework cations per formula yields: C
p
(298.15)=359.1 J K−1 mol−1, S(298.15) −S(0)=362.8 J K−1 mol−1. Comparing these values with the literature data for the (Al,Si)-ordered natrolite, we can conclude that the order in tetrahedral
atoms does not affect the heat capacity. The analysis of derivatives dC/dT for natrolite, paranatrolite, and tetranatrolite has indicated that the water- cations subsystem within the highly hydrated
zeolite may become unstable at temperatures above 200 K.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
950.
L. Vočadlo K. S. Knight G. D. Price I. G. Wood 《Physics and Chemistry of Minerals》2002,29(2):132-139
The thermal expansion and crystal structure of FeSi has been determined by neutron powder diffraction between 4 and 1173?K. No evidence was seen of any structural or magnetic transitions at low temperatures. The average volumetric thermal expansion coefficient above room temperature was found to be 4.85(5)?×?10?5?K?1. The cell volume was fitted over the complete temperature range using Grüneisen approximations to the zero pressure equation of state, with the internal energy calculated via a Debye model; a Grüneisen second-order approximation gave the following parameters: θD=445(11)?K, V 0=89.596(8)?Å3, K 0′=4.4(4) and γ′=2.33(3), where θD is the Debye temperature, V 0 is V at T=0?K, K 0′ is the first derivative with respect to pressure of the incompressibility and γ′ is a Grüneisen parameter. The thermodynamic Grüneisen parameter, γth, has been calculated from experimental data in the range 4–400?K. The crystal structure was found to be almost invariant with temperature. The thermal vibrations of the Fe atoms are almost isotropic at all temperatures; those of the Si atoms become more anisotropic as the temperature increases. 相似文献