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1.
Eirik Sundvor 《Marine Geophysical Researches》1971,1(3):303-313
A seismic refraction survey along nine profiles has been carried out on the Norwegian continental shelf in the area between Andøya and Fugløybanken (69°–71°N). In all but one of the profiles the shelf is found to be covered with layered sediments. Average velocities are 1.85, 2.20, 2,55, 3.25, and 3.90 km/s probably representing sediments of Cenozoic and Mesozoic ages. An average velocity of 5.25 km/s represents a basement, which probably is the seaward continuation of the onshore Caledonian rocks. Except for an apparent depressional area just north of Andøya the sedimentary layers appear to dip towards the shelf edge. On the outer part of the shelf the 2.20 km/s layer appears at the sea-floor while more complex structures are found on the inner part of the shelf.Publication No. 3 in NTNF's Continental Shelf Project. 相似文献
2.
Ingi Olafsson Eirik Sundvor Olav Eldholm Kjersti Grue 《Marine Geophysical Researches》1992,14(2):137-162
Analysis in both the x—t and —p domains of high-quality Expanded Spread Profiles across the Møre Margin show that many arrivals may be enhanced be selective ray tracing and velocity filtering combined with conventional data reduction techniques. In terms of crustal structure the margin can be divided into four main areas: 1) a thicker than normal oceanic crust in the eastern Norway Basin; 2) expanded crust with a Moho depth of 22 km beneath the huge extrusive complex constructed during early Tertiary breakup; 3) the Møre Basin where up to 13–14 km of sediments overlie a strongly extended outer part with a Moho depth at 20 km west of the Ona High; and 4) a region with a 25–27 km Moho depth between the high and the Norwegian coast. The velocity data restricts the continent-ocean boundary to a 15–30 km wide zone beneath the seaward dipping reflector wedges. The crust west of the landward edge of the inner flow is classified as transitional. This region as well as the adjacent oceanic crust is soled by a 7.2–7.4 km s–1 lower crustal body which may extend beneath the entire region that experienced early Tertiary crustal extension. At the landward end of the transect a 8.5 km s–1 layer near the base of the crust is recognized. A possible relationship with large positive gravity anomalies and early Tertiary alkaline intrusions is noted. 相似文献
3.
The abundance of coexisting structural units in K-, Na-, and Li-silicate melts and glasses from 25° to 1654°C has been determined with in-situ micro-Raman spectroscopy. From these data an equilibrium constant, Kx, for the disproportionation reaction among the structural units coexisting in the melts, Si2O5(2Q3)SiO3(Q2)+SiO2(Q4), was calculated (Kx is the equilibrium constant derived by using mol fractions rather than activities of the structural units). From ln Kx vs l/T relationships the enthalpy (Hx) for the disproportionation reaction is in the range of-30 to 30 kJ/mol with systematic compositional dependence. In the potassium and sodium systems, where the disproportionation reaction shifts to the right with increasing temperature, the Hx increases with silica content (M/Si decreases, M=Na, K). For melts and supercooled liquids of composition Li2O·2SiO2 (Li/Si=1), the Hx is indistinguishable from 0. By decreasing the Li/Si to 0.667 (composition LS3) and beyond (e.g., LS4), the disproportionation reaction shifts to the left as the temperature is increased. For a given ratio of M/Si (M=K, Na, Li), there is a positive, near linear correlation between the Hx and the Z/r2 of the metal cation. The slope of the Hx vs Z/r2 regression lines increases as the system becomes more silica rich (i.e., M/Si is decreased). Activity coefficients for the individual structural units, i, were calculated from the structural data combined with liquidus phase relations. These coefficients are linear functions of their mol fraction of the form i=a lnX
i+b, where a is between 0.6 and 0.87, and X
i is the mol fraction of the unit. The value of the intercept, b, is near 0. The relationship between activity coefficients and abundance of individual structural units is not affected by temperature or the electronic properties of the alkali metal. The activity of the structural units, however, depend on their concentration, type of metal cation, and on temperature. 相似文献
4.
M. A. Bouhifd G. Gruener B. O. Mysen P. Richet 《Physics and Chemistry of Minerals》2002,29(10):655-662
Premelting effects in gehlenite (Ca2Al2SiO7) have been studied by Raman spectroscopy and calorimetry, and in gehlenite and pseudowollastonite (CaSiO3) by electrical conductivity. The enthalpy of premelting of gehlenite is 17.3 kJ mol−1 and represents 9% of the reported enthalpy of fusion, which is in the range of the reported fraction of other minerals. The
Raman and electrical conductivity experiments at high temperatures, for gehlenite and pseudowollastonite, show that the premelting
effects of both compositions are associated with enhanced dynamics of calcium atoms near the melting point. This conclusion
agrees with the results obtained for other minerals like diopside, but contrasts with those found for sodium metasilicate
in which the weaker bonding of sodium allows the silicate framework to distort near the melting temperature and deform in
such a way to prefigure the silicate entities present in the melt.
Received: 30 April 2002 / Accepted: 7 August 2002
Acknowledgements We thank Y. Linard for help with DSC measurements and two anonymous reviewers for their constructive comments. This work
has been partly supported by the EU Marie-Curie fellowship contract no. HPMF-CT-1999-00329, the CNRS-Carnegie Institution
of Washington program PICS no.192, and the NSF grants EAR-9614432 and EAR-9901886 to B.O.M. 相似文献
5.
P. B. Tomascak Eirik J. Krogstad Richard J. Walker 《Contributions to Mineralogy and Petrology》1996,125(1):45-59
Neodymium and lead isotope and elemental data are presented for the Sebago batholith (293±2 Ma), the largest exposed granite
in New England. The batholith is lithologically homogeneous, yet internally heterogeneous with respect to rare earth elements
(REE) and Nd isotopic composition. Two-mica granites in the southern/central portion of the batholith (group 1) are characterized
by REE patterns with uniform shapes [CeN/YbN (chondrite normalized) = 9.4–19 and Eu/Eu* (Eu anomaly) = 0.27–0.42] and ɛ
Nd(t) = −3.1 to −2.1. Peripheral two-mica granites (group 2), spatially associated with stromatic and schlieric migmatites,
have a wider range of total REE contents and patterns with variable shapes (CeN/YbN = 6.1–67, Eu/Eu* = 0.20–0.46) and ɛ
Nd(t) = −5.6 to −2.8. The heterogeneous REE character of the group 2 granites records the effects of magmatic differentiation
that involved monazite. Coarse-grained leucogranites and aplites have kinked REE patterns and low total REE, but have Nd isotope
systematics similar to group 2 granites with ɛ
Nd(t) = −5.5 to −4.7. Rare biotite granites have steep REE patterns (CeN/YbN = 51–61, Eu/Eu* = 0.32–0.84) and ɛ
Nd(t) = −4.6 to −3.8. The two-mica granites have a restricted range in initial Pb isotopic composition (206Pb/204Pb = 18.41–18.75; 207Pb/204Pb = 15.60–15.68; 208Pb/204Pb = 38.21–38.55), requiring and old, high U/Pb (but not Th/U) source component. The Nd isotope data are consistent with magma
derivation from two sources: Avalon-like crust (ɛ
Nd>−3), and Central Maine Belt metasedimentary rocks (ɛ
Nd<−4), without material input from the mantle. The variations in isotope systematics and REE patterns are inconsistent with
models of disequilibrium melting which involved monazite.
Received: 8 December 1995 / Accepted: 29 April 1996 相似文献
6.
7.
A general model for the structural state of iron in a variety of silicate and aluminosilicate glass compositions in the systems Na2O-Al2O3-SiO2-Fe-O, CaO-Al2O3-SiO2-Fe-O, and MgO-Al2O3-SiO2-Fe-O is proposed. Quenched melts with variable Al/Si and NBO/T (average number of nonbridging oxygens per tetrahedrally coordinated cation), synthesized over a range of temperatures and values of oxygen fugacity, are analyzed with57Fe Mössbauer spectroscopy. For oxidized glasses with Fe3+/∑Fe>0.50, the isomer shift for Fe3+ is in the range ~0.22–0.33 mm/s and ~0.36 mm/s at 298 K and 77 K, respectively. These values are indicative of tetrahedrally coordinated Fe3?. This assignment is in agreement with the interpretation of Raman, luminescence, and X-ray,K-edge absorption spectra. The values of the quadrupole splitting are ~0.90 mm/s (298 K and 77 K) in the Na-aluminosilicate glasses and compare with the values of 1.3 mm/s and 1.5 mm/s for the analogous Ca- and Mg-aluminosilicate compositions. The variations in quadrupole splittings for Fe3+ are due to differences in the degree of distortion of the tetrahedrally coordinated site in each of the systems. The values of the isomer shifts for Fe2+ ions in glasses irrespective of Fe3+/∑Fe are in the range 0.90–1.06 mm/s at 298 K and 1.0–1.15 mm/s at 77 K. The corresponding range of values of the quadrupole splitting is 1.75–2.10 mm/s at 298 K and 2.00–2.35 mm/s at 77 K. The temperature dependence of the hyperfine parameters for Fe2+ is indicative of noninteracting ions, but the values of the isomer shift are intermediate between those values normally attributable to tetrahedrally and octahedrally coordinated Fe2+. The assignment of the isomer-shift values of Fe2+ to octahedral coordination is in agreement with the results of other spectral studies. For reduced glasses (Fe3+/∑Fe≈<0.50), the value of the isomer shift for Fe3+ at both 298 K and 77 K increases and is linearly correlated with decreasing Fe3+/∑Fe in the range of \(f_{O_2 } \) between 10?3 and 10?6 atm when a single quadrupole-split doublet is assumed to represent the absorption due to ferric iron. The increase in value of the isomer shift with decreasing \(f_{O_2 } \) is consistent with an increase in the proportion of Fe3+ ions that are octahedrally coordinated. The concentration of octahedral Fe3+ is dependent on the \(T - f_{O_2 } \) conditions, and in the range of log \(f_{O_2 } \) between 10?2.0 and 10?5 a significant proportion of the iron may occur as iron-rich structural units with stoichiometry similar to that of inverse spinels such as Fe3O4, in addition to isolated Fe2+ and Fe3+ ions. 相似文献
8.
Bjørn Mysen 《Earth》1984,20(3):251-252
9.
The anionic structure of magmatic liquids has been estimated at 1 atm and at pressures corresponding to those of the upper mantle. These estimates are based predominantly on spectroscopic data on binary metal oxide-silica and ternary metal oxide-silica-alumina melts. Structural information on melt compositions in aluminate-silica joins has been used to provide detailed information on the role of Al3+ in natural magma at atmospheric and high pressure.Regardless of pressure, andesitic melts may be described as combinations of chain, sheet, and three-dimensional network units. Nearly all Al3+ in the magmatic liquid resides in the three-dimensional network units. This Al3+ is locally charge-balanced with Na+, K+, Ca2+, and Mg2+. In the latter two cases, Al3+ and Si4+ are ordered, whereas for Na+ and K+, Si4+ and Al3+ are randomly mixed. Solution of water in natural magma results in the formation of new nonbridging oxygens in addition to OH groups attached to Si4+ and metal cations.On the basis of determined solution mechanisms of CO2 and H2O in silicate melts, thermodynamic properties of HO+CO2, fluids and hydrous silicate melts and melting phase relations in peridotite-H2O-CO2, systems, it is found that natural andesitic magma in equilibrium with spinel Iherzolite in the upper mantle (10–20 kbar) must contain at least 5–7 wt.% H2O. Andesitic magma with 5–7 wt.% H2O in solution may be described as a mixture of Al-free three-dimensional units, sheets, and chains with a small proportion (less than 10%) of monomers. 相似文献
10.
Bjørn Mysen 《Contributions to Mineralogy and Petrology》1975,52(2):69-76
The iron-magnesium distribution coefficient, $$K'_D = (X_{\Sigma {\text{FeO}}} /X_{{\text{MgO}}} )^{{\text{olivine}}} (X_{{\text{MgO}}} /X_{\Sigma {\text{FeO}}} )^{{\text{liquid}}} ,$$ has frequently been used as a means of testing whether experimental and natural silicate liquids could have been in equilibrium with olivine of mantle composition. It is shown here that this K′ D decreases with increasing oxygen fugacity (xxx) for a hydrous partial melt in equilibrium with a natural spinel peridotite assemblage under pressure and temperature conditions corresponding to those of the upper mantle (from 0.52 at the xxx of the iron-wüstite buffer to 0.04 at the xxx of the magnetite-hematite buffer). K′ D also increases with increasing pressure, with decreasing temperature, and probably with increasing Mg/(Mg+∑ Fe) of the parental peridotite, suggesting that $$K_D = (X_{{\text{FeO}}} /X_{{\text{MgO}}} )^{{\text{olivine}}} (X_{{\text{MgO}}} /X_{{\text{FeO}}} )^{{\text{liquid}}}$$ also increases with increasing pressure and decreasing temperature. Thus, unless these four variables (P, T, xxx, silicate composition) are known for a natural magma, K′ D and probably K D are variables, and the Mg/(Mg+∑ Fe) of such a magma cannot be correlated to that of the parent. The K D determined at 1 atm pressure by Roeder and Emslie has frequently been used to test whether the Mg/(Mg+∑ Fe) ratios of experimentally formed liquids at high pressure in equilibrium with olivine of known Fo content represent the equilibrium Mg/(Mg+Fe2+) of this liquid, assuming that ∑Fe=Fe2+ and that K′ D does not vary with P, T, and composition of the system. Published data demonstrate that the oxygen fugacities of the experimental designs employed by different laboratories vary between those of the magnetite-hematite and magnetite-wüstite buffers (6 orders of magnitude), resulting in K′ D between 0.04 and 0.31 at 1050° C and 15 kbar, for example. Thus, published arguments as to whether the quenched liquids represent equilibrium compositions based on iron-magnesium partitioning are inadequate. The effects of P, T, xxx, and the composition of the starting material must also be considered. 相似文献