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1.
Daily charts of the aerial search effort (432 206 nautical miles) of the Union Whaling Company and 1 099 sightings of 10 497 whales were available from 628 flights off Durban between 1972 and 1975. Densities of whales were analysed by month and water depth distribution over the four-year period. Low observed densities of blue Balaenoptera musculus, right Eubalaena australis, sei B. borealis and humpback Megaptera novaeangliae whales most likely resulted from earlier whaling pressure. Seasonality of blue, sei and humpback whales was bimodal, indicative of winter migrations to the north of the Durban whaling grounds, whereas the unimodal seasonality of fin whales B. physalus and minke whales B. bonaerensis or B. acutorostrata suggest the offshore region as the northern terminus of their migrations. Sperm whales Physeter macrocephalus migrate northwards offshore of the KwaZulu-Natal coast in autumn/early winter and southwards in late winter/spring, with larger males migrating later than the smaller males and females. Killer whale Orcinus orca presence was coincident with that of offshore minke whales and the southward migrations of other baleen whales, whereas densities of animals deemed as bottlenose whale Hyperoodon planifrons suggest strong early and late summer seasonal abundance in the offshore region. Such extensive surveys offshore of the KwaZulu-Natal coast are unlikely to be repeated; hence, data-extraction of whaling records provides a valuable source of seasonal and distributional information for marine management. 相似文献
2.
Kjell P. Skjerlie Alberto E. Patiño Douce A. Dana Johnston 《Contributions to Mineralogy and Petrology》1993,114(3):365-378
We report the result of H2O-undersaturated melting experiments on charges consisting of a layer of powdered sillimanite-bearing metapelite (HQ36) and a layer of powdered tonalitic gneiss (AGC150). Experiments were conducted at 10 kbar at 900°, 925° and 950°C. When run alone, the pelite yielded 40 vol% strongly peraluminous granitic melt at 900°C while the tonalite produced only 5 vol% weakly peraluminous granitic melt. At 950°C, the pelite and the tonalite yielded 50 vol% and 7 vol% granitic melt, respectively. When run side by side, the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone. In the pelite, the melt abundance increased by 25 vol%. When run alone, biotite dehydration-melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt. When run side by side only garnet was produced in addition to granitic melt. Experiments of relatively short duration, however, also contained Al-rich orthopyroxene. We suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of Al2O3 in the melt, which lowers the temperature of the biotite dehydration-melting reaction. In the pelite, the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite-layer to the pelite-layer. This has the effect of changing the bulk composition of this layer in the direction of minimum-temperature granitic liquids. Our results show that rocks which are poor melt-producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase(s) and facilitate dehydration-melting. Because of this effect, the continental crust may have an even greater potential for granitoid melt production than previously thought. Our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks, which will be reflected in their isotopic and geochemical compositions. 相似文献
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4.
KP. Tiwari 《Journal of the Indian Society of Remote Sensing》1974,2(2):65-73
The use of panchromatic (black & white) aerial photographs on 1:15,000 scale for forest type mapping and evolving a suitable basis of volume stratification for man-made forests of Haldwani Division of U.P. is discussed. Forest types by species, height and density were identified and ground survey data collected in 0.1 hectare circular plots were used to evolve the basis of volume stratification by statistical analysis. The methodology used for pilot studies before regional surveys are undertaken is presented. 相似文献
5.
The structural behaviour of precast shear wall-diaphragm connection was compared with the monolithic connection under seismic loading. The monolithic connection was made by using U-bars connecting shear wall and slab, and the precast connection was made by using dowel bars in two steps. Firstly, U-shaped dowel bars from the precast shear wall lower panel and precast slab were connected by the longitudinal reinforcement, and screed concreting was done above the precast slab. Secondly, the shear wall upper panel was connected using the dowel bar protruding from the shear wall lower panel. The gap between the dowel bars and the duct was filled with non-shrink grout. The specimens were subjected to reverse cyclic loading at the ends of the slab. This study also aimed to develop a 3-D numerical model using ABAQUS software. The non-linear properties of concrete were defined by using the concrete damaged plasticity(CDP) model to analyse the response of the structure. The precast dowel connection between the shear wall and slab showed superior performance concerning ductility, strength, stiffness and energy dissipation. The developed finite element model exactly predicted the behaviour of connections as similar to that of experimental testing in the laboratory. The average difference between the results from finite element analysis and experimental testing was less than 20%. The results point to the conclusion that the shear resistance is provided by the dowel bars and the stiffness of the precast specimen is due to the diaphragm action of the precast slab. The damage parameter and the interaction between structural members play a crucial role in the modelling of precast connections. 相似文献
6.
Kre Kullerud Kjell Petter Skjerlie Fernando Corfu Jesús D. de la Rosa 《Precambrian Research》2006,150(3-4):183-200
A north to northwest trending mafic dyke swarm of gabbronoritic and gabbroic composition makes up a significant part of the Archean basement on the island of Ringvassøy in northern Norway. U–Pb geochronology of zircon and baddeleyite in a gabbronorite provides an age of emplacement of 2403 ± 3 Ma. Metamict zircon in a plagioclase phyric dyke yield data that are discordant but consistent with the age of the gabbronoritic dyke. Titanite indicates a metamorphic overprint at 1768 ± 4 Ma. The two types of dyke show some distinct chemical characteristics. They are both tholeiitic, enriched in LREEs and LILE elements but depleted in HFS elements including Nb. Their Nd isotopic composition yields Nd values of −1.5 to −1.8 for gabbronorites and −0.4 to +1.3 for the plagioclase phyric dykes. The chemical and isotopic constraints are typical of continental basalts.The Ringvassøy mafic dykes correlate broadly with a global Palaeoproterozoic magmatic event that formed extensive bimodal intrusive and extrusive suites in most Archaean cratons, including the northeastern Fennoscandian Shield. In detail, the 2403 ± 3 Ma Ringvassøy dykes postdated most episodes of magmatism at this time. On the regional scale there is a distinct trend from a 2505–2490 Ma suite present in the Kola Peninsula, over a second 2460–2440 Ma suite present both in Kola and further south in Karelia, to the 2403 Ma dykes on Ringvassøy. This variation suggests that the locus of maximum extension and magmatic activity may have been shifting with time. 相似文献
7.
Kjell Petter Skjerlie 《Contributions to Mineralogy and Petrology》1992,110(4):473-487
Obduction of the late Ordovician Solund-Stavfjord Ophiolite Complex (443±3 Ma), west Norwegian Caledonides, involved generation and high-level emplacement of granitic and granodioritic dikes and plutons. Initial 87Sr/86Sr ratios in the granites are low (0.7042–0.7059), suggesting either a mantle component or a Rb-poor crustal source. Initial Nd (Nd(t)) ranges from-0.8 to-8.8, indicating that the granites represent recycling of old crustal rocks, which is supported by Precambrian inheritance in zircons from two of the studied granites. I argue that the Rb-Sr and the Sm-Nd isotope systems are decoupled in the sense that the Sr-and the Nd-isotopes derive their dominant signals from two different sources, a mantle source and a crustal source respectively. The granites are metaluminous to peraluminous and typically have high Sr, Ba and Na2O/K2O ratios. SiO2 contents range from 66 to 74 wt%. REE abundances are highly variable; the La contents range from 80 to 200 times chondrite, and are inversely correlated with the contents of SiO2. The concentration of Nd in the granites decreases asymptotically with decreasing Nd(t) suggesting fractional crystallization of accessory phases and assimilation of continental crust. This argument is supported by the presence of partly dismembered xenoliths in the granites with Nd(t)-values that are significantly lower than Nd(t)-values in the host granite. The following models are suggested for the granites. When the ophiolite complex obducted, an outboard subduction zone approached the continental margin, and subduction-related magmas accumulated beneath the continental margin, and probably intruded the overlying eugeosynclinal deposits. The mantle-derived magmas most likely evolved to granitoid composition by assimilation of these eugeosynclinal sediments and by fractional crystallization of amphibole, feldspar, sphene, and allanite. Alternatively, but less likely, the heat content of the mantle-derived magmas caused extensive melting of immature graywackes and calc-alkaline volcaniclastic rocks in the deepest portions of the eugeosyncline. Either way, during ascent, the compositions of the granitic melts were modified by fractional crystallization of LREE-rich phases and by assimilation of continental metasediments. 相似文献
8.
Variations in basaltic geochemistry along a propagating rift of the late Ordovician marginal basin of the West Norwegian Caledonides 总被引：1，自引：0，他引：1
The late Ordovician Solund-Stavfjord ophiolite complex in the western Norwegian Caledonides records a multi stage seafloor spreading history of an Iapetus marginal basin and contains three structural domains with distinctive tectonomagmatic evolutionary paths. The NNE-trending Domain 1 consisting of high-level gabbro, sheeted dykes and extrusive rocks is interpreted to represent fossil oceanic crust developed along a spreading centre that propagated northwards into pre-existing oceanic crust in the marginal basin. Dyke swarms at the head of this inferred propagating rift range from primitive, high-MgO basalts to highly fractionated quartz-diorites. Southwards along-strike of Domain 1, the abundance of primitive basalts decreases and the proportion of FeTi-basalts increases to become predominant furthest behind the tip of the propagating rift. This geochemical evolution is comparable to that of the basalts of modern propagating rifts at the East Pacific Rise and the Galapagos spreading ridge. We suggest that the chemical variations of the metabasalts reflect changes in magma supply rates and in the increasing size of magma chamber(s) along-strike of the spreading centres. 相似文献
9.
The Lyngen gabbro (LG), defining the major part of the Lyngen magmatic complex, is characterised by layered gabbros of N-MORB affinity (western suite) and layered gabbronorites, quartz-bearing gabbros and diorites/quartz-diorites of IAT (island-arc tholeiite) to boninitic affinity (eastern suite). The boundary between the eastern and western suites is generally defined by a large-scale ductile shear zone of suboceanic origin, the Rypdalen shear zone (RSZ). Tonalites occur within the RSZ and in the eastern suite of the LG. Variations in field occurrence and chemical composition of the tonalites suggest that they represent two petrologically different groups. Tonalite intrusion (the Vakkas pluton) up to 5 km2 large occur in the eastern suite of the LG, and are characterised by high Y contents (average 26 ppm) and high K2O/Rb ratios (average 0.062) compared to tonalites on the RSZ. The Vakkas pluton has lightly concave REE (rare earth element) patterns with negative Eu-anomalies, and positive ND-values (+3.7 to +3.9). Geochemical modelling based on the REE and field evidence suggests that these tonalites may have formed by fractional crystallization from a boninitic parental magma. Tonalites related to the RSZ form irregular veins and dikes that net vein the shear zone. They are characterised by low Y contents (average 6 ppm), low K2O/Rb ratios (average 0.025), and highly variable contents of Na2O, K2O, Sr and Ba, compared to the Vakkas pluton. Tonalites related to the RSZ show substantial variation in the content of the LREEs. They possess low abundances of the HREEs, and absence of, or slightly positive Eu-anomalies. The tonalites have highly variable ND-values (−0.6 to −9.4), probably resulting from enrichment of Nd from an external source. Geochemical modelling suggests that the LREE-rich tonalites formed by H2O-rich partial melting of differentiated products from the eastern suite of the LG. The presence of B in the fluid phase is suggested by the presence of tourmaline-bearing tonalite pegmatites. Thus, the anatectic tonalites of this group could have been formed by water-excess melting of a variety of gabbroic cumulates of the LG. In the LG, LREE-depleted tonalites (ND-values +5.1) also occur, and these are best explained in terms of partial melting of gabbroic cumulates from the transition zone between the eastern and the western suites of the LG. 相似文献
10.
The Late Ordovician Solund-Stavfjord ophiolite in western Norway represents a remnant of the Iapetus oceanic lithosphere that developed in a Caledonian marginal basin. The ophiolite contains three structural domains that display distinctively different crustal architecture that reflects the mode and nature of magmatic and tectonic processes operated during the multi-stage seafloor spreading evolution of this marginal basin. Domain I includes, from top to bottom, an extensive extrusive sequence, a transition zone consisting of dike swarms with screens of pillow breccias, a sheeted dike complex, and plutonic rocks composed mainly of isotropic gabbro and microgabbro. Extrusive rocks include pillow lavas, pillow breccias, and massive sheet flows and are locally sheared and mineralized, containing epidosites, sulfide-sulfate deposits, Fe-oxides, and anhydrite veins, reminiscent of hydrothermal alteration zones on the seafloor along modern mid-ocean ridges. A fossil lava lake in the northern part of the ophiolite consists of a >65-m-thick volcanic sequence composed of a number of separate massive lava units interlayered with pillow lavas and pillow breccia horizons. The NE-trending sheeted dike complex contains multiple intrusions of metabasaltic dikes with one- and two-sided chilled margins and displays a network of both dike-parallel normal and dike-perpendicular oblique-slip faults of oceanic origin. The dike-gabbro boundary is mutually intrusive and represents the root zone of the sheeted dike complex. The internal architecture and rock types of Domain I are analogous to those of intermediate-spreading oceanic crust at modern mid-ocean ridge environments. The ophiolitic units in Domain II include mainly sheeted dikes and plutonic rocks with a general NW structural grain and are commonly faulted against each other, although primary intrusive relations between the sheeted dikes and the gabbros are locally well preserved. The exposures of this domain occur only in the northern and southern parts of the ophiolite complex and are separated by the ENE-trending Domain III, in which isotropic to pegmatitic gabbros and dike swarms are plastically deformed along ENE-striking sinistral shear zones. These shear zones, which locally include fault slivers of serpentinite intrusions, are crosscut by N20°E-striking undeformed basaltic dike swarms that contain xenoliths of gabbroic material. The NW-trending sheeted dike complex in the northern part of Domain II curves into an ENE orientation approaching Domain III in the south. The anomalous nature of deformed crust in Domain III is interpreted to have developed within an oceanic fracture zone or transform fault boundary.REE chemistry of representative extrusive and dike rocks from all three domains indicates N- to E-MORB affinities of their magmas with high Th/Ta ratios that are characteristic of subduction zone environments. The magmatic evolution of Domain I encompasses closed-system fractional crystallization of high-Mg basaltic magmas in small ephemeral chambers, which gradually interconnected to form large chambers in which mixing of primary magmas with more evolved and fractionated magma caused resetting of magma compositions through time. The compositional range from high-Mg basalts to ferrobasalts within Domain I is reminiscent of modern propagating rift basalts. We interpret the NE-trending Domain I as a remnant of an intermediate-spread rift system that propagated northeastwards (in present coordinate system) into a pre-existing oceanic crust, which was developed along the NW-trending doomed rift (Domain II) in the marginal basin. The N20°E dikes laterally intruding into the anomalous oceanic crust in Domain III represent the tip of the rift propagator. The inferred propagating rift tectonics of the Solund-Stavfjord ophiolite is similar to the evolutionary history of the modern Lau back-arc basin in the SW Pacific and suggests a complex magmatic evolution of the Caledonian marginal basin via multi-stage seafloor spreading tectonics. 相似文献