Mean crustal velocity: a critical parameter for interpreting crustal structure and crustal growth     

Scott B. Smithson  Roy A. Johnson  Yun K. Wong 《Earth and Planetary Science Letters》1981,53(3):323-332

Mean crustal velocity is a critical parameter for genesis of continental crystalline crust because it is a function of mean crustal composition and therefore may be used to resolve continental crustal growth in space and time. Although the best values of mean crustal velocity are determined from wide-angle reflection measurements, most studied here necessarily come from vertical averages in crustal refraction determinations. The mode of 158 values of mean crustal velocity is 6.3 km/s, a velocity which corresponds to a mean crustal composition of granodiorite to felsic quartz diorite; Archean crust may be slightly more mafic. Mean crustal velocities range from 5.8 to 7.0 km/s. The lowest values invariably are found in thermally disturbed rift zones and the highest values correspond to velocities in gabbro. Velocities in island arcs may be as low as 6.0 km/s but are typically 6.5–6.9 km/s which corresponds to andesitic composition; estimates of island arc composition are andesitic. If values of mean crustal velocity are not biased, this observation suggests that continental crust did not grow simply by addition of island arc material. Possibilities are that crust formed from fusion of island arcs and was later changed to more felsic composition by addition of material from the mantle or that the late Archean episode of major crustal growth did not involve processes similar to younger island arcs. Some crustal blocks might be changed in composition and thickness by such processes as underplating, interthrusting, necking and sub-crustal erosion. Specially designed experiments are suggested to determine this parameter so critical for understanding genesis of continental crust.  相似文献   

A SIMPLE DERIVATION OF SEIGEL'S TIME DOMAIN INDUCED POLARIZATION FORMULA *     

A. Roy  M. Poddar 《Geophysical Prospecting》1981,29(3):432-437

It is advantageous to postulate the phenomenological equivalence of chargeability with a slight increase in resistivities rather than a similar reduction in the conductivities. Substitution of these increments in the expression for the total differential of apparent resistivity leads directly to Seigel's formula. Included also are (i) an equally simple demonstration that, for a homogeneously chargeable ground with arbitrary resistivity distribution, the apparent chargeability m_a, equals the true homogeneous value m, and (ii) a direct derivation of the completely general resistivity relation where the symbols have the usual meanings.  相似文献   

Some results of induced polarisation surveys for sulphide mineralisation in parts of Rajasthan and Gujarat,India     

P. C. Paul  Asok Kumar Roy  B. Sarkar 《Pure and Applied Geophysics》1978,116(6):1174-1190

Some results of induced polarisation surveys carried out for the exploration of sulphide mineralisation in parts of Rajasthan and Gujarat, employing both frequency-domain and time-domain techniques, are presented. A few typical examples of I.P. results along with borehole sections and results of conventional geophysical surveys have been incorporated. Frequency-domain and time-domain I.P. data have been compared for selected areas.Borehole data pertaining to several areas investigated have corroborated the I.P. results fairly well.  相似文献   

Multiphase magnetizations: Problems and implications     

J.L. Roy  P.L. Lapointe 《Physics of the Earth and Planetary Interiors》1978,16(1):20-37

Experiments combining different cleaning and analytical techniques indicate that multiphase magnetizations may be quite common. However, these may not be recognized because of limited experimental work. Alternating field (AF) cleaning is often the only treatment applied to igneous and metamorphic rocks; thermal and/or AF cleanings are usually the only treatments applied to sedimentary rocks. In many instances, AF and thermal treatments are limited to 100 mT and 550°C respectively. Investigations based on such limited cleaning often fail to detect some of the phases of magnetization contained in the rock. Failure to detect one or more phases means that valuable data are not recovered and the whole magnetic history of the rock has not been unfolded. Most importantly, the undetected phase might be the initial so that a secondary magnetization can easily be mistaken for the initial with an erroneous interpretation as a result. It is therefore imperative to recognize all phases of magnetizations and it possible to separate them.Procedures that have been used to recognize and unravel multiphase magnetizations are described. These procedures make use of chemical, thermal and AF cleaning treatments, two-stage demagnetization, vector analysis, slicing of specimens and vector diagrams. The combination used depends on the rock studied. For example, it is found that AF followed by thermal treatment can be very useful for the study of igneous rocks; chemical leaching is by far the most effective cleaning technique for the study of red beds. A three-phase model describing the magnetizations process of certain red beds is proposed. The slicing of specimens is used to explain intermediate directions with respect to field reversals. It is shown that graphical representation by vector diagrams can greatly facilitate the interpretation of the results. The examples show that, although a statistically well defined magnetization may be obtained after limited cleaning, it cannot be assumed to be the initial. One must ascertain that another magnetization has not remained undetected. This necessitates detailed and extensive experimental work using and devising new analytical procedures in an attempt to unfold the whole magnetic history of the rock. It is noted that tentative polar paths constructed from results obtained after inadequate experimental work cannot be up-graded by adding more data points of doubtful or unproven quality. The evolutionary process of polar paths is dependent upon increasing the reliability of palaeomagnetic results.  相似文献   

Paleomagnetic evidence of large fault displacement around the Po basin—Discussion     

Roy Kligfield  J. E. T. Channel   《Tectonophysics》1979,53(1-2)

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Organo-sulfur compounds in sediments of the Puget Sound basin     

Timothy S. Bates  Roy Carpenter 《Geochimica et cosmochimica acta》1979,43(8):1209-1221

Sediment samples from a variety of different environments were analyzed for organo-sulfur compounds (OSC) to provide the first characterization of the amounts and types of these compounds in sediments of the greater Puget Sound basin. A gas Chromatograph equipped with a sulfur specific flame photometric detector was used to quantify individual OSC. Compositions of OSC mixtures were essentially constant throughout the study area. Dibenzothiophene (DBT), its alkylated homologs, and an unknown compound were the predominant OSC in most samples. Concentrations of total OSC and DBT ranged from 4 to 60 and 0.4 to 2 μg/g organic carbon, respectively. The flux of OSC to the sediments at a station in central Puget Sound west of Seattle was approximately 140 ng/cm²/yr. The profile of total OSC concentration with depth showed three organic sulfur compounds that are apparently created in situ in the vicinity of where hydrogen sulfide production begins. The concentrations of the aromatic OSC were relatively constant with depth. Although several anthropogenic sources of OSC were identified, there was no evidence that OSC from these sources were accumulating in the sediments. The major source of the aromatic OSC in the sediments is apparently atmospheric input from natural sources such as forest fires.  相似文献   

Exploitation of the Gauribidanur array for seismic monitoring     

T.G. Varghese  F. Roy  B.S.S. Rao  M.P. Suryavanshi  R.N. Bharthur 《Physics of the Earth and Planetary Interiors》1979,18(2):87-94

The medium-aperture array at Gauribidanur is in continous operation since 1966. With the recent addition of a 12-bit 16-K computer its potential for the monitoring of underground explosions has improved considerably. The salient aspects of the monitoring system, the present and projected procedures for generation and dissemination of detection data and the long-term storage of data relevant to discrimination research are discussed. An attempt is also made to assess its detection efficiency in the light of the major features of site noise.  相似文献   

The early diagenesis of aliphatic hydrocarbons and organic matter in sedimentary particulates from Dabob Bay,Washington     

Fredrick G. Prahl  Joseph T Bennett  Roy Carpenter 《Geochimica et cosmochimica acta》1980,44(12):1967-1976

Aliphatic hydrocarbon compositions were quantitatively characterized in plankton, sediment trap-collected particulate materials and sediments from Dabob Bay using high resolution glass capillary gas chromatography. The average net accumulation of individual hydrocarbons measured in a 1-yr series of sediment traps was compared with the net accumulation of corresponding compounds measured in three depth intervals of ²¹⁰Pb-dated bottom sediments. Systematic and rapid decreases in the net accumulation of individual hydrocarbons were observed from the sediment traps to the sediments. Most pronounced decreases were measured for planktonically derived hydrocarbon constituents (e.g. pristane and two unsaturated compounds) which are rapidly remineralized at or near the sediment-water interface. Consequently, the amount of each compound measured in deposited sediments is not necessarily a quantitative indication of its initial flux to the sediments. The n-alkanes (C_25,27,29,31). characteristic of terrestrial plant waxes, are the predominant hydrocarbons measured by 4–6 cm depth in these sediments and show reasonably constant net accumulation below this interval.Significant diagenetic alteration of the bulk organic matter contained in the average sediment trap particulate material is also noted through comparison with bottom sediments on the basis of organic C/N and δ¹³C measurements. Organic matter elementally similar to marine plankton is preferentially remineralized upon deposition of the sedimentary particulates. The residual organic matter remaining and buried in the bottom sediments closely resembles terrestrial organic matter.  相似文献   

Measurements of Reaction Coefficients of NO2 and HONO on Aerosol Particles     

Roy M. Harrison  Gareth M. Collins 《Journal of Atmospheric Chemistry》1998,30(3):397-406

The reaction coefficients of nitrogen dioxide and nitrous acid with monodisperse sodium chloride and ammonium sulphate aerosols have been measured in a flow reactor at atmospheric pressure. These experiments were performed at relative humidities above and below the deliquescence points of both aerosols (r.h. 50 and 85%) at 279 K. The results for NO₂ afford a reaction coefficient in the range (2.8–10) × 10^-4 and for HONO, (2.8–4.6) × 10^-3. For both species, there appears to be an enhancement of the reaction coefficient on sodium chloride aerosol at 50% r.h. The results are compared with reaction coefficients determined by other experimental methods. A good agreement is found for both gases between this method and the coated denuder method previously developed in our research laboratories (Msibi et al., 1993) and with the majority of other published data for NO₂. In the case of HONO, our estimate of reaction coefficient is smaller than, or at the lower limits of the ranges reported by other published studies.  相似文献   

Analysis of the vajont slide — new approach   总被引：1，自引：0，他引：1  

R. Chowdhury 《Rock Mechanics and Rock Engineering》1978,11(1):29-38

SummaryAnalysis of the Vajont Slide — New Approach This paper is concerned with the analysis of the 1963 Vajont slide in Italy. Attention is drawn to the fact that numerous investigations have been consistently unsuccessful in explaining the slide. A new approach consistent with a progressive failure mechanism established by all comprehensive investigations is suggested in this paper. The analysis simulates the transformation of the slope from a condition of stability to one of limit-equilibrium and failure in a step-by-step process. It is shown that the enormous velocities calculated on the basis of external observations of the slide can be explained by the new analytical approach.

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ZusammenfassungAnalyse der Felsgleitung bei Vajont — Neuer Erklärungsversuch Dieser Artikel beschäftigt sich mit der Felsgleitung bei Vajont in Italien im Jahre 1963. Es wird darauf hingewiesen, daß es in einer Vielzahl anderer Untersuchungen bislang nicht möglich war, eine Erklärung für die Felsgleitung zu finden. Ein neues Modell, basierend auf dem Mechanismus des progressiven Zusammenbruchs wird vorgeschlagen. Die Untersuchung simuliert den Übergang des Hanges vom stabilen Zustand in ein Grenzgleichgewicht und schließlich den Zusammenbruch in einem Prozeß, der Schritt für Schritt abläuft. Es wird gezeigt, daß die enormen Geschwindigkeiten, die aufgrund von Beobachtungen berechnet wurden, im Rahmen dieses Modells erklärt werden können.

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RésuméAnalyse de l'éboulement de Vajont — Nouvelle approche Cette communication constitue une analyse de l'éboulement de Vajont (Italie) en 1963. On souligne le fait que les nombreuses enquêtes entreprises pour expliquer cet éboulement se sont montrées infructueuses. Cette communication propose une nouvelle approche conforme à un mécanisme progressif de défaillances établi par toutes les enquêtes compréhensives. L'analyse simule la transformation graduelle de la pente: de la stabilité à l'équilibre limité et enfin à la défaillance. On démontre que les vélocités énormes calculées à base des observations externes de l'éboulement peuvent s'expliquer par cette nouvelle approche analytique.

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Notation c unit effective cohesion - ø effective angle of shearing resistance (residual) - n proportion of the slip surface along which failure has progressed - K conjugate stress ratio for a slope - K ₀ ratio of effective horizontal normal stress to effective vertical normal stress in the slope With 3 Figures  相似文献