Seismic surface-wave dispersion: A world-wide survey

Summary By means of the long-period records at Uppsala and Kiruna of thirteen specially selected earthquakes, the Love and Rayleigh wave dispersion is determined for all oceans and all continents except for South America. The observations have given information on crustal structure along several paths, not investigated earlier; in other cases, they have confirmed earlier results. The methods are discussed. The results for oceanic areas are summarized in the following table: The observations demonstrate the oceanic structure of the central Arctic area as well as the complete similarity of the Atlantic and Pacific bottom structure. Continental dispersion curves are determined for very long paths over Euro-Asia and for the hitherto longest path over North America as well as for a path crossing Africa. These observations indicate an average crust about 10–15 km thicker along the Euro-Asiatic path than along the North American path, whereas there is perfect agreement between the North American and the African continent. A shear-wave velocity of 4.3–4.4 km/sec is obtained for the upper part of the mantle under the continents. Further conclusions must await the computation of a greater number of theoretical dispersion curves.

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Zusammenfassung Mittels der langperiodischen Registrierungen in Uppsala und Kiruna von dreizehn speziell ausgewählten Erdbeben ist die Dispersion der Love-und Rayleigh-Wellen für alle Ozeane und alle Kontinente mit Ausnahme von Süd-Amerika bestimmt worden. Die Beobachtungen haben in mehreren Fällen Auskunft über die Krusten-Struktur längs Wellenwege gegeben, die nie früher untersucht worden sind; in anderen Fällen haben sie frühere Resultate bestätigt. Die Methoden werden diskutiert. Die Resultate für ozeanische Gebiete sind in der folgenden Tabelle zusammengefasst: Die Beobachtungen beweisen sowohl die ozeanische Struktur des zentralen Teiles des arktischen Gebietes als auch die vollständige Gleichheit der atlantischen und pazifischen Krusten-Struktur. Kontinentale Dispersionskurven sind für sehr lange Wellenwege über Euro-Asien und für den bisher längsten Wellenweg über Nord-Amerika bestimmt worden. Diese Beobachtungen zeigen, dass die mittlere Krusten-Dicke 10–15 km grösser längs des euro-asiatischen Weges ist als längs des nordamerikanischen Weges; dagegen zeigen die Beobachtungen für Nord-Amerika und Afrika sehr gute Übereinstimmung. Eine Transversalwellen-Geschwindigkeit von 4.3–4.4 km/sek wird für den oberen Teil des Erdmantels unter den Kontinenten gefunden. Weitere Schlussfolgerungen müssen die Berechnung einer grösseren Anzahl theoretischer Dispersionskurven erwarten.

     

Strike and dip of crustal boundaries — A method and its application

Summary If for a point on the earth's surface, the apparent (moveout) seismic velocities have been determined for a number of profiles in different directions, a possibility is offered to calculate true strike and dip of crustal boundaries. In the present paper the theory is developed, partly for a sloping Mohorovii discontinuity only, partly for sloping Conrad and Mohorovii discontinuities with parallel strikes. The theory for the sloping Mohorovii discontinuity is applied to field measurements at a place about 30 km west of Uppsala performed in June 1969. With a crustalP-wave velocity of 6.3 km/sec, a good fit to the observations is obtained for aPn-velocity of 8.55 km/sec and a downdip of Moho of 7.2° in the direction S 3.8° E. These numerical values are not the most important output of this paper. On the other hand, the testing of the method appears far more important, and also that improvements can be suggested in the experimental procedure in future applications of this method.     

Lumbering operations,lake humification and consequences for the structure of the lake foodweb: A case study using the LakeWeb-model for Lake Stora Kröntjärn,Sweden

This work presents a scenario to demonstrate how a given lake (Lake Stora Kröntjärn, Sweden) would respond to changes in colour related to lumbering operations in its watershed. The questions posed are: How would lake colour values increase, for how long would such increases last and how would this influence the production and biomasses of key functional organisms in the lake? The work is based on a comprehensive lake ecosystem model, LakeWeb, which accounts for production, biomasses, predation, abiotic/biotic interactions of nine key functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), two types of fish (prey and predatory), as well as zoobenthos, macrophytes and benthic algae. The LakeWeb-model has been calibrated and critically tested using empirical data and regressions for many lakes and it can capture typical functional and structural patterns in lakes. To obtain results like these by traditional field-work in one or more lakes would be very demanding (in terms of money, persons and time). It has been shown that single tributary peaks in colour concentrations are often "drowned" in weekly mean lake values. The lumbering operations must be extensive and continue for a long time to cause significant increases in tributary colour values in order to significantly influence fundamental lake foodweb structures. This means that it is often realistic to assume that lumbering activities do not strongly influence lake foodweb structures. The LakeWeb-model with the given mass-balance model for lake colour can be a useful tool to assess situations when this might not be valid.     

Alkaline ultramafic lamprophyres and associated carbonatite dykes from the Kalix area,northern Sweden

Alkahne ultramafic lamprophyres and associated carbonatite dykes form north-south trending dyke swarms. The lamprophyres are sub-divided into micaceous, picritic and breccia varieties. Carbonatites sensu stricto (beforsites) occur very subordinate.The dykes of the Kalix area show great similarities to petrographically related rocks from other Scandinavian occurrences (Sokli, Alnö and Fen). Major differences are found in their tectonic setting (regularly striking dyke swarms) and the REE-pattern (distinctly negative cerium anomalies).The following petrogenetic model is advanced for the Kalix dykes: (1) partial melting of upper mantle material, (2) Intrusion into a crustal magma chamber, fractional crystallization, (3) Interactions between crystallized material and the volatile phase (light REE depletion, oxidation of cerium), (4) Intrusion in fracture zones under horizontal tension.

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Zusammenfassung Alkalin-ultrabasiscbe Lamprophyre und begleitende KarbonatitgÄnge bilden nordsüdlidi streichende GangschwÄrme. Die Lamprophyre zeigen gewisse Ähnlichkeiten zu alnöitischen und kimberlitischen Gesteinen; sie wurden unterteilt in glimmerreiche und pikritische Lamprophyre sowie Brekzien. Karbonatite im engeren Sinn treten nur sehr untergeordnet auf; sie sind als Beforsite charakterisiert.Die Ganggesteine des Kalix-Gebiets weisen gro\e Ähnlichkeiten mit petrographiscb verwandten Gesteinen von anderen skandinavischen Vorkommen (Sokli, Alnö und Fen) auf. GrundsÄtzliche Unterschiede finden sich vor allem im tektonischen Auftreten (ziemlich konstant streichende GangschwÄrme) und im Verteilungsmuster der seltenen Erden (deutlich negative Cer-Anomalien).Die Bildung der Kalix-GÄnge wird folgenderweise erklÄrt: (1) Partielle Aufschmelzung des oberen Mantels, (2) Intrusion der Schmelze in eine krustale Magmakammer, gefolgt von fraktionierter Kristallisation, (3) Reaktion zwischen vorzugsweise kristallisiertem Material und der volatilen Phase (Entarmung an leichten seltenen Erden, Oxidation des Cers), (4) Intrusion in Bruchzonen, die horizonteller Dehnung ausgesetzt sind.

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Résumé Des lamprophyres alcalins ultrabasiques accompagnés de carbonatites forment des essaims de dykes de direction nord-sud. Les lamprophyres se subdivisent en variétés micacée, picritique ainsi que brÊchique. Les carbonatites sensu stricto sont rares et sont plutÔ des beforsites.Les dykes de la région de Kalix présentent de grandes similitudes avec des roches pétrographiquement apparentées d'autres localités Scandinaves (Sokli, Alnö et Fen). Les différences essentielles sont dues à leur situation tectonique (essaims de dykes de direction régulière) ainsi qu'à la distribution des Terres Rares (anomalie négative distincte de cérium).Le modèle pétrogénétique suivant est proposé pour les dykes de Kalix: (1) fusion partielle de matériau du manteau supérieur, (2) intrusion dans une chambre magmatique de l'écorce et cristallisation fractionnée, (3) interaction entre le material déjà cristallisé et la phase volatile (appauvrissement des éléments légers des Terres Rares, oxydation du cérium), (4) intrusion le long de zones de fracture dans des conditions d'extension horizontale.

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Mineral zoning as a record of P,T history of Precambrian eclogites and schists in western Tasmania

Ferromagnesian minerals, particularly garnet but also phengite, omphacite and talc, from eclogites and surrounding schists from the Lyell Highway-Collingwood river area, western Tasmania are compositionally zoned.In rocks which have suffered little secondary alteration the Mg-value ($\text{100 Mg}\text{Mg+Fe}{}^{\mathrm{++}}$) of granets increases from core to rim, while the Mg-value of the most important coexisting ferromagnesian phases (clinopyroxene, phengite and talc in different assemblages) decreases from core to rim. CaO decreases from core to rim in garnet. MnO may show little or no variation in garnet, or decrease from core to rim.When compared with experimental data, the zoning of these minerals can be uniquely explained by growth during changing P,T conditions. The eclogites and the surrounding schists have the same prograde P,T history.When determining the K_D-values of garnet and its coexisting ferromagnesian phases it is important to consider secondary rim alterations as well as the prograde zoning of the mineral.     

Temperature and pressure dependence of Fe-Mg partitioning between garnet and phengite,with particular reference to eclogites

Experimental data combined with data from natural rocks have been used to calibrate a geothermometer based on the distribution of Fe²⁺ and Mg between coexisting garnets and phengites. The pressure effect on the K _D -value appears to be considerable. The calculated thermometer is expressed as $$T(K) = \frac{{3685 + 77.1P(kb)}}{{InK_D + 3.52}}.$$ The use of this \(K_{D_{(FeO/MgO)} }^{ga + ph}\) geothermometer on eclogites with low Fe₂O₃ content, gives P-T values which are in good accordance with those obtained by other methods. The problems that arise when Fe³⁺ is present in larger amounts, are discussed.     

Talc-garnet-kyanite-quartz schist from an eclogite-bearing terrane,Western Tasmania

Talc-garnet-kyanite-quartz schist occurs in an eclogite-bearing terrane in the Precambrian of Western Tasmania. It is argued that this rock was formed at a pressure of ? 10 kb and a temperature of 600°±20° C. Chemical zoning in the garnet and talc preserves evidence of increasing temperature during growth of the major minerals.     

Biodiversity and invasibility: Distribution patterns of invasive plant species in the Himalayas,Nepal

Invasive plant species are exerting a serious threat to biological diversity in many regions of the world. To understand plant invasions this study aims to test which of the two plant invasiveness hypotheses; ‘low native diversity' vs. ‘high native diversity', is supported by the regional distribution patterns of invasive plant species in the Himalayas,Nepal. This study is based on data retrieved from published literatures and herbarium specimens. The relationship between invasive plant species distribution patterns and that of native plant species is elucidated by scatter plots, as well as by generalized linear models. The native plant species and invasive plant species have similar distribution patterns and the maximum number of invasive plant species is found in the same altitudinal range where the highest richness for native tree species is found. There is a clear trend of higher invasive plant richness in regions where native tree species richness is relatively high.Consequently, the native plant richness is highest in the central phytogeographic region, followed by the eastern and the western regions, respectively. The invasive plant species also follows a similar trend.Additionally, the invasive plant species richness was positively correlated with anthropogenic factors such as human population density and the number of visiting tourists. This study supports the hypothesis that ‘high native diversity' supports or facilitates invasive plant species. Further, it indicates that nativeand invasive plant species may require similar natural conditions, but that the invasive plant species seem more dependent and influenced by anthropogenic disturbance factors.