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151.
Mn-activated cathodoluminescence can be used in several fields of carbonate petrography. It may, for instance, be possible to recognize
- cement sequences and their correlation (Tab. 1, Figs. 1, 2, 4; Tab. 2, Fig. 1)
- growth fabrics of skeletons (Tab. 2, Figs. 2, 3, 4; Tab. 3, Figs. 1, 2)
- dolomitisation processes and problems (Tab. 1, Figs. 1, 2; Tab. 4, Fig. 2)
- transformation paths from Mg-calcite to calcite and from aragonite to calcite (Tab. 2, Fig. 1; Tab. 3, Figs. 3, 4; Tab. 4, Fig. 1)
- growth structures in certain types of ooids (Tab. 1, Fig. 4; Tab. 3, Fig. 3; Tab. 4, Fig. 1)
- reworked skeletal particles (Tab. 3, Fig. 4)
- phantom grains and fossil-outlines in a micro- or macrocrystalline groundmass (Tab. 4, Figs. 2, 3)
- healed fissures crossing micro- or macrocrystalline carbonate rocks (Tab. 4, Fig. 4).
152.
A simple inexpensive photometer designed for Winkler titration end-point detection is described. The precision of replicate dissolved oxygen measurements using this instrument was 0.06–0.22%. This high precision is needed to measure the small changes in dissolved oxygen concentration for determining the respiration rate of small aquatic organisms. Other recommendations for improving precision are also presented. 相似文献
153.
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
154.
Erik W. Grafarend Ivan I. Mueller Haim B. Papo Burghard Richter 《Journal of Geodesy》1979,53(3):195-213
Modern high accuracy measurements of the non-rigid earth are to be referred to four-dimensional, i.e., time- and space-dependent
reference frames. Geodynamic phenomena derived from these measurements are to be described in a terrestrial reference frame
in which both space- and time-like variations can be monitored. Existing conventional terrestrial reference frames (e.g. CIO,
BIH) are no longer suitable for such purposes.
The ultimate goal of this study is the establishment of a reference frame, moving with the earth in some average sense, in
which the geometric and dynamic behavior of the earth can be monitored, and whose motion with respect to inertial space can
also be determined.
The study is conducted in several parts. In the first part problems related to reference directions are investigated, while
subsequent parts deal with positions, i.e., with reference origins and scale. Only the first part is treated in this paper.
The approach is based on the fact that reference directions at an observation point on the earth surface are defined by fundamental
vectors (gravity, earth rotation, etc.), both space and time variant. These reference directions are interrelated by angular
parameters, also derived from the fundamental vectors. The interrelationships between these space- and time-variant angular
parameters are illustrated in a commutative diagram, tower of triads, which makes the derivation of the various relationships
convenient. In order to determine the above parameters from observations using least squares techniques, a model tower of
triads is also presented to allow the formation of linear observation equations. Although the model tower is also space and
time variant, its variations are described by adopted parameters representing our current knowledge of the earth. 相似文献
155.
Compressional (VP) and shear (VS) wave velocities and the dependent elastic constants have been determined by the pulse transmission technique to 6 kb confining pressure at room temperature and to 700° C at 6 kb confining pressure for eleven basalts from the Faeroe Islands. The Faeroe basalts investigated are tholeiitic, they clearly lie within the tholeiitic area, and display a pronounced trend of iron enrichment from rocks with an M/M + F ratio of 0.5 to rocks with an M/M + F ratio of about 0.25. The mean VP and VS for eleven specimens are 5.57 km/sec and 3.18 km/sec, respectively. Velocity—density relations for the basalts might be more appropriately described by non-linear solutions than by linear relations commonly used for basalts. In general, VP and VS remain unaffected by temperature up to 300° C. At higher temperature the changes in wave velocities are influenced by metamorphic processes and are, therefore, somewhat erratic. In zeolite-bearing specimens an abrupt velocity decrease around 350°C is observed, which correlates well with a drastic compaction of bulk volume. Additional experiments on cold-pressed zeolite powder clearly indicate that the sharp velocity decrease in the basalts is related to dehydration of zeolite minerals. Partial-melting processes, which occur within vesicules and pore-spaces at distinctly higher temperatures have no additional effect on wave velocity. Comparison with field data reveals that, without exception, the velocities at 0.5 kb confining pressure display the same range that has been commonly noted in refraction data for Layer 2. There are no significant differences in wave velocities and the pressure—temperature dependence in samples recovered from the upper, middle, and lower basalt series in the Faeroe Islands. 相似文献
156.
Jorge A. Mendiguren Frank M. Richter 《Physics of the Earth and Planetary Interiors》1978,16(4):318-326
Intraplate stresses in middle South America are not negligible. We report thrust-faulting mechanisms for five intraplate earthquakes, which indicate a dominant horizontal deviatoric compressional stress oriented in a NW-SE direction. We conclude that this state of stress is due to forces connected with spreading on the Mid Atlantic Ridge and resistive forces exerted by the Caribbean plate to the north and the Nazca plate to the west. The existence and nature of the resistive forces is inferred from earthquake mechanisms and geological evidence presented in other studies. All the available intraplate stress data for Nazca and South America indicate that both plates are under deviatoric compression generated at spreading centers. The absence of tensional earthquake focal mechanisms, particularly in the Nazca plate near the trench, suggests that the forces associated with the gravitational sinking of subducted lithosphere are locally compensated. We present a simple numerical calculation of a non-subducting plate to show how the compressional deviatoric stresses in middle South America can be used to estimate an upper bound of about 1021 P for the viscosity of the mantle. 相似文献
157.
Diffusion of ions in sea water and in deep-sea sediments 总被引:3,自引:0,他引:3
Sandra Gregory 《Geochimica et cosmochimica acta》1974,38(5):703-714
The tracer-diffusion coefficient of ions in water, Dj0, and in sea water, , differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective or Dj0 values. The tracer diffusion coefficients of ions in deep-sea sediments, Dj,sed., can be related to by , where θ is the tortuosity of the bulk sediment and a a constant close to one. 相似文献
158.
Zusammenfassung Die glasführenden Gesteine von Köfels, Tirol, wurden petrologisch untersucht. Sowohl Elektronenstrahl-Mikrosondenanalysen der Phasen als auch chemische Pauschalanalysen einiger Gesteine werden angegeben.Das Vorhandensein von Cr- und Si-führendem Nickeleisen, Lechatelierit, Kalifeldspatglas, Fe-reichen Gläsern, Olivin sowie die kräftigen Inhomogenitäten in der Glasphase sind nur durch eine Impakt-Entstehung dieser Gesteine erklärbar.
Mit 7 Abbildungen 相似文献
Impactites from Koefels, Tyrol, Austria
Summary The glass-bearing rocks from Koefels, Tyrol, have been investigated petrologically. Electron-microprobe Analyses of the phases and chemical bulk analyses of some rocks are presented.The presence of Cr- and Si-bearing nickel-iron, lechatelierite, potassium-feldspar-glass, olivine, as well as the pronounced inhomogenities of the glasses strongly suggest an impact origin of these rocks.
Mit 7 Abbildungen 相似文献
159.
Willem van der Velden James Baker Sandra de Maesschalck Thea van Meerten 《International Journal of Earth Sciences》1982,71(1):171-181
The Grythytte field sequence forms a NNW belt of acid-basic metavolcanic and metasedimentary rocks. The geology shows characteristics of a dynamic process of trough-forming and infilling which to a large extent post-dates the Hjulsjö volcanoplutonic complex situated to the east. In the latter complex acid metapyroclastics strike around a centre of granite and granophyre, which cut and are cut by basic sills and dykes. Field and petrochemical evidence points to a distinct bimodal magmatism that ist manifested during one short phase of a rifting period.
Zusammenfassung Die Grythytte Schichtenfolge bildet einen NNW verlaufenden Gürtel aus sauren und basischen Metavulkaniten und Metasedimenten. Die geologischen Befunde weisen auf einen dynamischen Entstehungsprozeß von Grabenbildung und Füllung hin. Im weiter östlich gelegenen vulkanisch-plutonischen Hjulsjö-Komplex streichen älteren metamorphen pyroklastischen Gesteine rund ein Granit-Granophyr Zentrum. Dieser Komplex durchschneidet und wird durchschnitten von basischen Sills und Gängen. Feldgeologische und geochemische Untersuchungen weisen deutlich auf einen bimodalen Magmatismus hin, der während einer kurzen Phase der Grabenbildung stattfand.
Résumé La séquence de Grythytte forme une ceinture de roches métavolcaniques et métasédimentaires de direction NNO. La géologie fait apparaître les caractéristiques d'un processus dynamique de formation de fosse et de remplissage, qui s'est produit, pour la plus grande partie, après la formation du complexe volcano-plutonique de Hjulsjö situé à l'Est. Dans ce dernier complexe des produits pyroclastiques acides sont disposés autour d'un centre granitoïde et granophyrique, qui à son tour recoupe et est recoupé par des sills et des dykes basiques. Les observations de terrain et les faits pétrochimiques indiquent un procèssus magmatique distinctement bimodal qui s'est manifesté pendant une phase courte dans une période de «rifting».
Grythytte , NNW . . Hjulsj -- . . , , .相似文献
160.
Sandra García-Bustos Jimmy Landín Ricardo Moreno A.S.E. Chong Maurizio Mulas Mónica Mite 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(1):56-68
ABSTRACTIn this work, we have studied the largest earthquake magnitudes on the Ecuadorian coast by using the principles of Extreme Value Analysis based on its two approaches: Block Maxima and Peaks-over-Threshold. First, before modelling the recorded earthquakes, the K-means clustering technique was applied to determine a classification according to the level of magnitude of the earthquakes. Then, models based on the Extreme Value theory of earthquake magnitudes were developed for each of the four clusters that were found, and finally, the best-fitted models were those known as Fréchet and Gumbel ones. The zone with the greatest earthquake magnitudes on the Ecuadorian coast is located between the north of the province of Manabí and the south of the province of Esmeraldas, with a return period of 50 years for an earthquake with magnitude greater than 7.7 MW. 相似文献