The mantled gneiss domes of Kuopio (Finland): Interfering diapirs

Finite strain data from the Kuopio mantled gneiss domes are described. Synclines located between two domes have flattening-type strains while those situated between more than two domes exhibit constrictional strains. Cleavage trajectory patterns show that cleavage tends to parallel the dome boundaries and encloses characteristic points termed “cleavage triple points”, at junctions of synclines. The stretching lineation is generally steeply plunging in a mean southwest direction. Folds range from inclined to reclined. Their asymmetry is apparently related to irregularities in the cover-basement boundary. Two shear components of the deformation have been deduced from available data. The major one is steeply plunging and is well exhibited by cleavage fans, steeply plunging lineations and finite-strain gradients. The second shear component is horizontal, as deduced from asymmetric folds and other small-scale structures, and is controlled by bosses and dimples in the cover-basement boundaries.The described structural features are explained in terms of interference between progressively inflating neighbouring diapirs. Furthermore, some of these features, such as cleavage triple points, flattening between two domes and constriction between three or more domes, and horizontal shear components controlled by cover-basement boundary irregularities, could be used as criteria of diapirism. A model of progressive dome interference is presented in which each dome inflates and interacts with neighbours. Such a model could possibly be applied to other orogenic situations with closely spaced diapirs, e.g., Archean greenstone belts or granite-rich orogenic belts.     

Micro-topographic change on calcarenites,grand Cayman Island,West Indies

Changes in micro-topography, as a result of varying erosion rates, have been monitored on a calcarenite ridge on Grand Cayman Island, West Indies, using a traversing model of the micro-erosion meter. Erosion takes place through the solution of a calcitic cement and ‘solutional disintegration’ results in a rapid change of micro-relief. Where a protective crust is present, surface lowering is slower and also more uniform; thus the original relative relief is maintained.     

Metal binding capacity of selected maine surface waters

Concentrations of Ca, Cd, Cu, Fe, and Pb and binding capacities for Cd, Cu, and Pb were determined for water samples collected from 12 lakes in southwestern Maine using atomic absorption and ion-selective electrodes, respectively. Surface waters in this area are soft and characterized by low pH. Some lakes were highly colored with refractory organics, whereas others had very low organic carbon concentrations. Both Cu and Pb concentrations were positively correlated with organic carbon content. Copper and Pb binding capacities were significantly correlated with organic carbon content, whereas Cd binding capacity was positively correlated with pH, but not with organic carbon. Surface water binding capacity for Pb was greater than that for Cu or Cd. More than 99% of the Ca from all waters studied was removed onto cationic exchange resins. Less than 1% of the total Cu existed as cationic species in highly humic waters, whereas as much as 65% existed as cationic species in less huic waters. Conversely, more than 99% of the Cd present in humic waters existed as cationic species, whereas as little as 50% existed as cationic species in less humic, more alkaline waters. These correlative studies indicate that binding by organic carbon is important for both Cu and Pb in this area and must be considered in models of trace metal speciation. However, Cd binding in the same waters is not correlated with organic carbon, which does not need to be considered in speciation models for Cd.     

Postglacial forest patterns associated with till and outwash in northcentral Upper Michigan

Pollen analysis of lake sediments reveals that small areas of till and outwash in northcentral Upper Michigan have influenced plant distributions throughout postglacial time. Each substrate has different textural characteristics. Modern forest communities form a mosaic, with jack pine woodlands occupying the medium sands of the Yellow Dog Plains outwash and white pine-hardwood communities on both till and outwash soils in the Michigamme Highlands to the south.The analysis of modern pollen samples from 21 lakes within the area indicates that pollen can be used to study the distribution of local vegetation in relation to substrate type. Fossil pollen from three of the lakes documents the character of ancient forest on Yellow Dog outwash, Michigamme outwash, and Michigamme till.Unique boreal communities occupied each area immediately after deglaciation. Between 8000 and 7000 y.a., white pine and maples migrated into the study area and replaced jack pine in forests on the Highlands, but not on the Plains. Jack pine has continued to occupy the Plains since early postglacial time. White pine reached highest densities on Michigamme outwash, and deciduous trees increased primarily on till during the presumably dry climates which existed 8000-5000 yr BP. As the climate became more mesic, forests on the Highlands changed, so that by 3000 yr BP the communities on Michigamme outwash and till were indistinguishable on the basis of pollen. Present-day forest patterns of the area became established at that time.Pollen influx rates, measured at each lake, generally support interpretations based on pollen percentages and were similar to values reported elsewhere. Variations in influx values are within the range expected for the method.     

From subduction to transform motion: a seabeam survey of the Hellenic trench system

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.     

Kepone®: Toxicity and bioaccumulation in blue crabs

Two long-term studies were conducted to determine toxicity, uptake and depuration of Kepone in blue crabs (Callinectes sapidus). In the first, Kepone was administered to crabs in seawater (0.03 or 0.3 μg Kepone/I) or food (eastern oyster,Crassostrea virginica, containing 0.25 μg/g Kepone). Uptake of Kepone in 28 days was primarily through the contaminated oysters. When these crabs were held in Kepone-free seawater and fed Kepone-free oysters for 28 days, no loss of the insecticide was evident. There were adverse effects on molting and survival in crabs fed oysters that contained 0.25 μg/g Kepone. A second study was conducted to determine: (1) the depuration of Kepone over a 90-day period in blue crabs fed oysters from the James River, Virginia (containing 0.15 μg/g Kepone); and (2) the effects of Kepone on molting and survival of blue crabs fed James River oysters or laboratory-contaminated oysters that contained 0.15 or 1.9 μg/g Kepone. Crabs fed Kepone-contaminated oysters followed by a diet of Kepone-free oysters for 90 days had detectable concentrations of the insecticide in tissues. Also, blue crabs that ate oysters containing Kepone in concentrations similar to those found in oysters from the James River, died or molted less frequently than crabs fed Kepone-free oysters meats.     

Propagation of an accreting plate boundary: a discussion of new aeromagnetic data in the Gulf of Tadjurah and southern Afar

A detailed aeromagnetic survey of the Republic of Djibouti and immediate surroundings was performed in 1977. This paper summarizes the reduction techniques which are used in order to produce a magnetic anomaly map and discusses the accuracy of this map, which is presented as an insert at a scale of 1/250,000. Two distinct magnetic styles are recognized: linear anomalies with both large amplitude and short wavelength, considered to be typical of oceanic lithosphere, contrast with areas of lower-amplitude longer-wavelength anomalies, which are found mostly in the northern part of the survey. This quiet zone of subdued magnetic style is thought to have undergone major tectonic deformation in the last millions of years. The general morphology of magnetic anomalies is interpreted in terms of a propagating crack model, as proposed by Courtillot [23]. The crack propagates westwards at approximately 3 cm/yr and the crack tip is thought to lie close to Lake Asal, both on the basis of the magnetic data and of other geophysical evidence. The land section of the survey is a central topic of this paper and is interpreted in terms of the crack propagation model in the light of other available geological, geochemical and geophysical data.