Continental- Margin Structure of Northeast China and Its Adjacent Areas

The continental margin of Northeast China and its adjacent areas is composed of two tectonic belts. The inner belt is a collage made up of fragments resulting from breakup of an old land with the north part related to the evolution of the Palaeo-Asian Ocean and the south part to the evolution of the Palaeo - Pacific Ocean. The outer belt is a Mesozoic terrane, which is a melange made up of fragments of the Late Palaeozoic to Early Mesozoic oceanic crust and the Late M esozoic trench accumulations.There existed another ocean-the Palaeo - Pacific Ocean during the period from the closing of the Palaeo-Asian Ocean to the opening of the modern Pacific Ocean or from the Devonian to Jurassic, and the ocean-floor spreading of the Palaeo - Pacific Ocean led to the formation of the above-mentioned tectonic belts. The development of the strike-slip fault system after the Late Jurassic and the formation of an epicontinental volcano -plutonic rock belt in the Late Cretaceous to Early Tertiary are attributed to the i     

Long-term deformation and fluid-enhanced mass transport in a Variscan peridotite shear zone in the Ivrea Zone,northern Italy: a microtextural,petrological and geochemical study of a reactivated shear zone

The microtextural, petrological and geochemical study of a ductile shear zone in the phlogopite peridotite of Finero/Ivrea Zone (northern Italy) reveals the long-term deformation of this zone. The zone is divided into a protomylonitic and an ultramylonitic part. Both parts reflect different periods of deformation, although the orientation of the mineral lineations does not change. In the coarse-grained part (period 1) the deformation started under granulite facies conditions (about 775°C). Olivine, ortho- and clinopyroxene and phlogopite recrystallized dynamically. In the ultramylonitic part relics of the granulite facies event and evidence for a continuous or two-stage deformation history under amphibolite facies (minimum 640°C) to upper greenschist facies conditions (maximum 520°C) are preserved (period 2). Amphibolite facies conditions are indicated by olivine recrystallization, the monoclinization of orthopyroxene porphyroclasts and the recrystallization and chemical changes of clinopyroxene. The greenschist facies final stage of period 2 is characterized by decreased X _{CO 2} and the syntectonic formation of antigorite, tremolite and phlogopite at the expense of recrystallized and porphyroclastic olivine and pyroxene. Between both deformation periods a short break in deformation continuity is probable. Continuous deformation or reactivation in shear zones of the Ivrea Zone has not been described so far. During the granulite facies shearing, small amounts of channelized fluid flow led to a slight mass transfer. The shear zone shows a moderate enrichment of Na, Ba, Cu, Cs, H₂O and CO₂ and a small loss of P. The mass balance of the ultramylonite indicates a significant increase in mass transport. A mass gain can be inferred for H, Na, K, Ba, Al, Ti, P, S, Cs, Sr, Rb, C, Zn, Zr, S, Sc, light rare earth elements, Nb, Cl and Au. The zone is depleted in Ca, Cu, Co, F and Ni. Si, Mg, Cr, Mn, Y, Nb and V are constant within analytical error. Deformation and fluid infiltration led to a change in volume which increases during the granulite facies event by 5.7% and during the lower temperature phase by 3.3%. The calculated fluid to rock ratios by standard equations results in unrealistically high values. For the interpretation of highly deformed rocks with drastic grain size reduction it is therefore necessary to consider the enhanced diffusion, which is mainly controlled by the increased grain boundary surface.     

Application of limited fuzzy clusters to anomaly recognition in complex geological environments

In stream sediment and soil surveys, samples represent mixtures of components from different geological environments. Such mixed samples are misclassified when using conventional “hard” cluster methods. In fuzzy clustering, each sample is allowed to belong to several clusters. Similar to element concentrations, these cluster contributions can be displayed in contour maps (e.g. kriging maps). The amount of an element that is explained by the cluster contribution and element residuals can be calculated. The modified fuzzy clustering algorithm called “limited fuzzy clusters” used in this paper avoids negative residuals.Stream sediment data of Sierra de San Carlos, Tamaulipas, Mexico are used to demonstrate the possibilities of limited fuzzy clustering in geochemical exploration and mapping. From the different drainage systems, 681 stream sediment samples were taken and analyzed for 24 elements. A nineteen-element data set was used to calculate limited fuzzy clusters and element residuals. The contribution values for the clusters and element residuals are displayed in contour maps. All geological units were outlined by the cluster contributions. Extended anomalies are characterized by their own cluster. Small anomalies are clearly identified from the element residuals.     

Systematic errors in the medium range prediction of the Asian summer monsoon circulation

The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM) of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August) of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988). Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became more intense with the introduction of changes in the operational forecasting system. Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10). The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts to improve the formulations of physical processes for further reduction of systematic forecast errors.     

Simulation of cyclones using synthetic data

A number of sensitivity experiments have been conducted to investigate the influence of using synthetic data on cyclone forecasts by a global spectral model. Some well known vortices have been used and the generated wind and pressure profiles are compared. It is found that the Rankine vortex and Holland’s vortex show the best representation of cyclonic circulation. Hence these two vortices are used in the sensitivity studies to simulate two cyclones, one of May 1979 and the other of August 1979. For this purpose the FGGE level-III b data set, produced at ECM WF, UK is used. Synthetic temperature and humidity data are also introduced to make the cyclones more realistic. With the use of Holland’s vortex the system is found to move faster than with the Rankine vortex. Also, the tracks of the cyclones simulated with Rankine vortex are found to be on the left side of the observed track while that of Holland’s vortex is on the right side of the observed track. However, substantial filling up of the systems are noticed with introduction of diabatic initialization of the mass and velocity fields and the forecasts of both the vortices behave differently. It is suggested that proper selection of synthetic vortex, initialization scheme and resolution of the model are very important for better forecast of cyclones.     

Schwerestörungen im östlichen Mittelmeer nach Messungen mit einem Askania-Seegravimeter

Zusammenfasung Das Gebiet der großen Schwereanomalien um Kreta wurde Ende 1961 durch kontinuierlich vermessene Gravimeterprofile genauer untersucht. Zusammen mit den Ergebnissen früherer Pendelmessungen im U-Boot konnte ein detaillierter Isanomalenplan der Freiluftschwere des gesamten östlichen Mittelmeeres (Tafel 3) gewonnen werden. Daraus wurden die Bougueranomalien und die isostatischen Anomalien berechnet und in farbigen Kartendarstellungen (Tafel 4 und 5) wiedergegeben.Der Vergleich zwischen zwei gleichzeitig eingesetzten Askania-Seegravimetern (Abb. 3) ergibt eine Instrumentengenauigkeit von etwa 2 mgal für die in Fahrt gemessenen Schwerewerte. Hierzu kommen mittlere Fehler von etwa 5–6 mgal aus Unsicherheiten in der Positionsbestimmung (Eötvöseffekt), der Geländekorrektion und der isostatischen Kompensation. Somit sind die Freiluftanomalien auf etwa ±6 mgal, die Bougueranomalien auf etwa ±8 mgal und die isostatischen Anomalien auf etwa ±10, mgal genau anzugeben. Bei der Größe der Anomalien, die positive und negative Werte bis zu 200 mgal annehmen können ist diese Genauigkeit durchaus zufriedenstellend.Die gravimetrische Vermessung zeigt, daß das östliche Mittelmeer zum großen Teil den Gleichgewichtszustand noch nicht erreicht hat. Die Ausgleichsbewegungen sind in den einzelnen Teilgebieten verschieden weit fortgeschritten, am wenigsten in der Umgebung von Kreta.Die heutige Morphologie dieses Gebietes hat sich wahrscheinlich durch Aufsteigen des Meeresbodens im Ägäisraum und Absinken außerhalb des Inselbogens Kythera-Kreta-Rhodos entwickelt. Wenn man annimmt, daß vor Einsetzen dieser Bewegung Isostasie herrschte, müßte das Meer im Mittel etwa 1500 m tief gewesen sein.Aus der Kombination der Schwereanomalien mit der heutigen Morphologie in der dem Inselbogen vorgelagerten Ringzone (blau II auf Tafel 6) ergibt sich eine mittlere Gesteinsdichte von etwa 3,0 g/cm³. Zwischen diesem Gebiet und dem in fast vollkommenem Gleichgewichtszustand befindlichen südöstlichen Levantemeer (grün IV, Tafel 6) liegt eine Übergangszone (rot III, Tafel 6), die sich — ebenso wie die Ägäis — durch einen nicht ausgeglichenen Dichteüberschuß von etwa 2,1 g/cm³ auszeichnet.

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Gravity anomalies in the Eastern Mediterranean as measured with the Graf-Askania sea gravimeter

Summary At the end of 1961, the area round the isle of Crete distinguished by large gravity anomalies was subjected to thorough investigations and for this purpose continuous gravity profiles were run. The material of the above research and the results of former submarine pendulum measurements were included in a detailed isogam map of free-air anomalies of the whole Eastern Mediterranean (plate 3). From this map the Bouguer anomalies and the isostatic anomalies were derived and represented on coloured maps (plates 4 and 5).A comparison of two Askania sea gravimeters (fig. 3) operated simultaneously, demonstrates an instrumental accuracy of about 2 mgals for the gravity values measured from the ship underway. In addition, there resulted mean errors of about 5–6 mgals from uncertainties in the determination of the position (Eötvös effect), in the terrain correction, and in the isostatic compensation. The freeair anomalies are thus to be stated with an accuracy of about ±6 mgals, the Bouguer anomalies with an accuracy of about ±8 mgals and the isostatic anomalies with about ±10 mgals. Considering the fact, that the anomalies can assume positive and negative values of up to 200 mgals, this accuracy is completely sufficient.The measurement of gravity shows that the Eastern Mediterranean has, to a great extent, not yet reached the state, of equilibrium. The movements of compensation have developed differently in the individual parts of the area; the least advance is found in the area of the isle of Crete.The present morphology of this area has probably developed from an uplifting of the sea bottom of the Aegean Sea and a depression outside the island arc Kithira-Crete-Rhodes. Taking into account that before the beginning of this movement isostasy prevalied, the medium depth of the water must have been about 1500 metres.The combination of gravity anomalies with the present morphology of the ring zone extending in front of the three islands of kithira, Crete and Rhodes (bule II on plate 6) results in a mean density of the substratum of about 3,0 g/cm³. The extreme south-east of the Mediterranean, however, is in almost complete equilibrium (green IV, on plate 6). Between these two zones (blue II and green IV on plate 6) lies a transition zone (red III on plate 6) showing — like the Aegean Sea — an unbalanced density contrast of about 2,1 g/cm³.

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Anomalies de presanteur en Méditerranée orientale, suivantles enregistrements avec le gravimètre de mer Askania

Résumé Vers la fin de 1961, les parages autour de la Candie, marqués de grandes anomalies de pesanteur, ont été l'objet des enregistrements précis et continus de l'intensité de gravité, exécutés à bord d'un navire en route. Les résultats de ces recherches ainsi que ceux des mesures pendulaires antérieures faites à bord d'un sous-marin, pouvaient être réunis sur une carte montrant en détail les courbes iso-anomales des anomalies totales mesurées de toute la Méditerranée orientale (planche 3). On se servait de cette carte pour en déduire les anomalies d'après Bouguer et les anomalies isostatiques pour les représenter sur des cartes multicolores (planches 4 et 5).La comparaison de deux gravimètres de mer Askania (fig. 3), actionnés simultanément, faisait la preuve d'une précision d'enregistrement de 2 mglas environ pour les valeurs gravimétriques mesurées à bord d'une navire en route. De plus, il faut tenir compte des erreurs moyennes d'environ 5–6 mgals dues aux déterminations un peu insécures de la position (effet d'Eötvös) et aux insécurités de la correction du terrain et de la compensation isostatique. On doit, donc, indiquer les anomalies totales mesurées à ±6 mgals environ, près, les anomalies de Bouguer à ±8 mgals environ près et les anomalies isostatiques à ±10mgals environ près. Tenant compte du fait que les anoamlies peuvent atteindre de valeurs positives ou négatives jusqu' à 200 mgals, cette précision est bien satisfaisante.Les enregistrements gravimétriques montrent que la Méditerranée orientale est encore loin d'avoir atteint son état d'équilibre. Les mouvements de compensation ont fait des progrès inégaux dans les diverses parties de la Méditerranée orientale; le moindre progrès a été constaté aux alentours de la Candie.La morphologie actuelle de cette région paraît être le résultat d'un soulevèment du fond de la mer Egée et d'un affaisement du fond au dehors, du cordon des îles de Cythérée, de Candie et de Rhodes. Lorsqu'on suppose que le commencement de ces mouvements était précédé d'un état d'isostasie, la profondeur moyenne de la mer aurait été de 1500 mètres environ.De l'association des anomalies de pesanteur avec la morphologie actuelle de la région circulaire, qui s'étend devant, le cordon des îles de Cythérée, de Candie et de Rhodes (no. II, bleu, planche 6) résulte une densité moyenne du substratum d'environ 3,0 g/cm³. La partie de l'extrème sud-est de la Mediterranée (no. IV, vert, planche 6) se trouve, cependant, dans un état d'istostasie presque parfait. Entre ces deux zones (nos. II, bleu, et IV, vert, planche 6) s'étend une zone de transition (no. III, rouge, planche 6) qui est, comme la mer Egée, caractérisée par un excès non-compensé de densité de 2,1 g/cm³ environ.

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Inhalt eines Vortrages, gehalten auf der 25. Jahrestagung der Deutschen Geophysikalischen Gesellschaft im April 1963 in Bochum.     

Age levels of Precambrian orogenic cycles of India

The paper reviews critically the present status of knowledge on the Precambrian orogenic cycles of India. The Precambrian age data obtained by Pb-U-Th, alpha-helium and Rb-Sr methods are presented cycle-wise, and the degree of dependability of each determination is indicated. The following cycles have so far been delineated — Dharwar (2300±100 M. Y.), Eastern Ghats (1625±75 M. Y.), Mahanadi (1350±200 M. Y.?), Satpura (955±40 M. Y.), Delhi (735±30 M. Y.) and Kishengarh (580±20 M. Y.) and it is shown that these cycles have equivalents in several parts of the world. These results are discussed in relation to the tectonics of India. A comprehensive programme of dating the Precambrian geological formations of India is suggested.     

On love waves in inhomogeneous anisotropic elastic solids

Summary This paper consists of two parts. In the first part, the existence of Love waves in non-homogeneous and transversely-isotropic elastic layer over-lying a semi-infinite isotropic elastic solid has been investigated. The frequency equation for such waves has been derived. Numerical calculations giving the velocity of such waves has been made for different layer thicknesses. In the second part, a characteristic frequency equation has been calculated considering the lower boundary of the layer to be rigid. A numerical calculations has been made in this case also to represent the variation of wave number with velocity for different mode number.     

Biogeochemistry of the rare-earth elements in aquatic macrophytes of Linsley Pond,North Branford,Connecticut

Aquatic plants, water, lake mud, soils and rocks from Linsley Pond were analyzed for all the naturally occurring elements of the periodic table which could be detected by optical and X-ray emission spectroscopy. In the course of this study, it was noted that all the rare earths of even atomic number were detected; of the odd-numbered members of the group only La and Pr were found. The others were presumably present in amounts below detection. These elements relative to their concentration in the soils and rocks of the basin are absorbed by plants, giving an enrichment of about one hundred fold relative to Al on a dry weight basis. Samarium is present in excess of Nd in the rooted emergent plants but not in the submerged rooted or rootless ones. There is some suggestion of a fractionation of the rare earths in different parts of the plants. A comparison of the relative accumulation of trace elements with their content in the sediment suggests that Y, La, Ce, Pr, Sm, Dy, Er and Yb may be essential trace elements.     

Ambiguity in the electromagnetic interpretation due to a conducting halo surrounding the target

Summary Using the electromagnetic response of a two-layer spherical model it is shown that the estimate of the depth, radius, conductivity and magnetic contrast of a spherical conductor through the multifrequency or multi-time measurements is dependent upon the electrical and geometrical parameters of the conducting halo surrounding the target. The results identify the corrections or ambiguity in the interpretation depending upon whether some knowledge about the halo is available or not.National Geophysical Research Institute, Hyderabad-7, A.P., India.-NGRI Contribution No. 72–364.