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881.
The primary objective of this research was to determine if vesicular-arbuscular (VA) mycorrhizal fungi are associated with the roots of common plant species found in North Carolina salt marshes. Root samples of Spartina alterniflora, S. patents, S. cynosuroides, Distichlis spicata, and Juncus roemerianus were collected from eight salt marsh sites. With the exception of S. alterniflora, all plant species were mycorrhizal. A greenhouse experiment was conducted to determine whether unfavorable soil conditions or inherent resistance by the plant inhibited development of mycorrhizal infection in field-collected S. alterniflora. Spartina alterniflora and S. patens were grown from seeds in soil collected from a pure stand of S. alterniflora (soil A) or a mixed stand of S. patens and D. spicata (soil P). Seedlings were harvested weekly for 8 wk, and roots were evaluated for infection by mycorrhizal fungi. Seedlings of S. patens were infected when grown for 2 wk in either soil A or soil P, indicating that soil collected from stands of S. alterniflora did not inhibit mycorrhizal infection in a susceptible host. Percent root length infected in S. patens was always greater in soil P than in soil A. Seedlings of S. alterniflora were not infected by mycorrhizal fungi in either soil A or soil P. Results of the greenhouse study indicate that S. alterniflora may be resistant to infection by vesicular-arbuscular mycorrhizal fungi. 相似文献
882.
The results from a recent North—South gravity traverse across eastern Timor show that the Bouguer gravity field is characterized by a strong, 6 mGal/km, gradient on the north coast. This gradient appears to be a fundamental feature of Timor and of the Outer Banda Arc. Preliminary computer models suggest that, to a first approximation, the gradient is due to a vertical fault at the north coast of Timor separating oceanic crust from continental crust. The fit between the computed and observed gradient can be improved significantly by assuming a northward-dipping lithospheric slab, north of Timor. The model further indicates that the Australian continental crust extends at least as far as the north coast of Timor. 相似文献
883.
Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REE's.The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments. Large ion lithophile trace element abundance patterns confirm the origin of the glasses by total shock melting of metasediments. 相似文献
884.
885.
The stable isotopic composition of coral skeletons: control by environmental variables 总被引:1,自引:0,他引:1
Sandra M. Weil Robert W. Buddemeier Stephen V. Smith Peter M. Kroopnick 《Geochimica et cosmochimica acta》1981,45(7):1147-1153
The reef corals Pocillopora damicornis and Montipora verrucosa were cultured under various controlled temperature and light conditions. The corals were analyzed for growth rate, tissue pigment content and skeletal 13C and 18O. Coral skeletal δ13C values varied with light dose and correlated with changes in zooxanthellar pigment. The δ13C values of skeletal aragonite seem to be modified by oxidation of photosynthetically produced organic matter.Functionally significant relationships between coral skeletal δ18O values and temperature have been determined. The temperature coefficients of the δ18O values [?4.4°C (%.)?1] are similar to the first order coefficient in the equilibrium paleotemperature equation, but the δ18O values have taxonomically consistent offsets from equilibrium. The offsets may be attributed to the coral metabolism with slight but statistically significant differences between the two genera. Environmental and metabolic variables other than temperature have little or no effect on skeletal δ18O. 相似文献
886.
887.
The results of a detailed microstructural and microchemical study of a slate from the Chewton area, Victoria, Australia are reported in which it was found that cleavage developed from microcrenulations. Phyllosilicates in P-domains differed in their chemistry from those in Q-domains and were concentrated in the P-domains by localized metamorphic reactions which were aided by mechanical rotation and solution processes. Wide, dark cleavage lamellae, often taken as evidence for the passive concentration of insoluble minerals, appear to have had a similar origin. The P-domains exhibited two types of microstructure, one which was consistent with annealing and the other with deformation within the domain. Cataclasites had formed along some P-domains, suggesting that they had become preferential sites for late phase brittle deformation. 相似文献
888.
Hubert Staudigel Karlis Muehlenbachs Stephen H. Richardson Stanley R. Hart 《Contributions to Mineralogy and Petrology》1981,77(2):150-157
18O and87Sr/86Sr isotopic data from smectites, calcites, and whole rocks, together with published isotopic age determinations, alkali element concentration data and petrographic observations suggest a sequential model of ocean floor alteration. The early stage lasts about 3 m.y. and is characterized by palagonite and smectite formation, and solutions with a large basaltic component, increasing with temperature which varies from 15° to 80° C at DSDP site 418A. Most carbonates are depositedafter this stage from solutions with a negligible basaltic Sr component and temperatures of 15° to 40° C. Water of seawater Sr and O isotopic composition is shown to percolate to at least 500 m into the basaltic basement. No evidence was found for continuing exchange of strontium or oxygen after 3 m.y.Lamont-Doherty Geological Observatory Contribution number 3199 相似文献
889.
Jay D. Bass Robert C. Liebermann Donald J. Weidner Stephen J. Finch 《Physics of the Earth and Planetary Interiors》1981,25(2):140-158
Hydrostatic compression data for a number of high-pressure phases of oxides and silicates, which have been studied independently by acoustic techniques, have been analyzed by least-squares fitting of the Birch-Murnaghan equation of state to determine the zero-pressure bulk modulus K0 and its pressure derivative K′0 for each material. The standard deviations of K0 and K′0 so determined are generally underestimated unless the experimental errors in the measurements of volume and pressure are explicitly included. When the values of K0 determined from the acoustic and compression techniques are consistent, test results for quartz and rutile demonstrate that constraining K0 to be equal to the acoustic value significantly improves both the accuracy and the precision of K′0 obtained from the compression data. Similar analyses for high-pressure phases (e.g., pyrope garnet and silicate spinels) indicate that by combining the acoustic and P-V data, the standard deviation of K′0 is typically reduced by a factor of three. Thus, we conclude that this approach does allow precise determinations of K′0 even when neither technique alone is able to resolve this parameter. For some materials, however, the P-V and acoustic experiments do not define mutually consistent values of K0, invalidating any combination of these data. The compression data for stishovite clearly exhibit run to run effects, and we infer that systematic errors are present in some of the P-V data which are responsible for many of the interlaboratory inconsistencies. Such systematic biases in the P-V data can at least be partially compensated for by performing several duplicate experimental runs. 相似文献
890.
Herbert E. Huppert R. Stephen J. Sparks 《Contributions to Mineralogy and Petrology》1981,75(3):279-289
This paper describes a fluid dynamical investigation of the influx of hot, dense ultrabasic magma into a reservoir containing lighter, fractionated basaltic magma. This situation is compared with that which develops when hot salty water is introduced under cold fresh water. Theoretical and empirical models for salt/water systems are adapted to develop a model for magmatic systems. A feature of the model is that the ultrabasic melt does not immediately mix with the basalt, but spreads out over the floor of the chamber, forming an independent layer. A non-turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion. Both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock. The convection continues until the two layers have almost the same temperature. The compositions of the layers remain distinct due to the low diffusivity of mass compared to heat. The temperatures of the layers as functions of time and their cooling rate depend on their viscosities, their thermal properties, the density difference between the layers and their thicknesses. For a layer of ultrabasic melt (18% MgO) a few tens of metres thick at the base of a basaltic (10% MgO) magma chamber a few kilometres thick, the temperature of the layers will become nearly identical over a period of between a few months and a few years. During this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling. Olivines only settle after the two layers have nearly reached thermal equilibrium. At this stage residual basaltic melt segregates as the olivines sediment in the lower layer. Depending on its density, the released basalt can either mix convectively with the overlying basalt layer, or can continue as a separate layer. The model provides an explanation for large-scale cyclic layering in basic and ultrabasic intrusions. The model also suggests reasons for the restriction of erupted basaltic liquids to compositions with MgO<10% and the formation of some quench textures in layered igneous rocks. 相似文献