Are assemblages of black bream (Acanthopagrus butcheri) in different estuaries genetically distinct?

Samples of the estuarine-spawning teleostAcanthopagrus butcheri were collected from nine estuaries and a coastal lake, located in the Pilbara and South-western drainage divisions of Western Australia and distributed along a coastline covering a distance of nearly 2,000 km. The patterns of allozyme variation in these samples were used to explore the extent to which there was variation in the genetic compositions of black bream assemblages in geographically-isolated estuarine systems, and whether or not any such variation could be related to the geographical location or type of estuary. Although only three of 36 scorable loci (Gpi-1, Ldh andMdh-2) exhibited variation that could be used for analysis, there was considerable variation in allele frequencies at these loci among the different samples (mean F_ST=0.166). Much of the detected variation was attributable to differences between the samples collected from the two drainage divisions, which are located in very different climatic regions. Furthermore, the genetic compositions of samples from neighbouring estuaries were typically more similar to each other than to those of samples collected from more distantly-located systems. However, the assemblages in one west coast and two south coast estuaries, that are closed to the ocean for extensive periods of time during the year, all showed very similar genetic compositions. Nevertheless, it is crucial to recognise that, pairwise comparisons of samples collected from the different estuaries, both within and between the two drainage divisions, almost invariably showed statistically significant differences in allele frequencies at one or more loci. Thus, our results indicate that the local populations of black bream in individual estuaries are genetically distinct, which is probably a consequence of both a limited movement by individuals between estuaries and the effects of differences in regional and local environmental conditions.     

Amelioration of soil fertility by woody perennials in cropping fields: evaluation of three tree species in the semi-arid zone of Nigeria

Soil was sampled from cropping fields in radial patterns from beneathAcacia albida, Parkia bigloboza(Jacq.) Benth. andEucalyptus camaldulensisDehnh. near Zaria, Nigeria. Results of analysis show a significant coarsening of soil texture and a decrease in organic matter and cation exchange capacity with increasing distance from all three tree species at a depth of 0–15 cm. Concentrations of nitrogen and some exchangeable cations decreased significantly with increasing distance from beneath acacia and parkia, and soil pH decreased with increasing distance from eucalyptus. The implication of the results for land management are discussed in relation to increasing productivity and soil use sustainability.     

Effects of early season defoliation ofAnthyllis cytisoides(a Mediterranean browse species) on further herbivore attack

To determine if defoliation of a woody plant affects foraging by folivorous insects, we examined the infection rate (number of leaves damaged per total number of leaves sampled on marked stems) ofAnthyllis cytisoidesunder three experimental treatments: 10, 50 and 90% plant defoliation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoliation by increasing total vegetative length of the stem and total inflorescence length. This response is most evident in young individuals.Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds—chewing, mining, or sucking insects. We found that increased defoliation elicited increased resistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attack by chewing insects declines with defoliation for all plant age classes; only sucking insects which feed on the oldest plants reduce feeding rate with plant defoliation. Finally, mining insects present the opposite trend in young and senescent plants.     

Fluid inclusion evidence for the physicochemical conditions of sulfide deposition in the Olympias carbonate-hosted Pb-Zn(Au, Ag) sulfide ore deposit, E. Chalkidiki peninsula, N. Greece

The Olympias Pb-Zn(Au, Ag) sulfide ore deposit, E. Chalkidiki, N. Greece, is hosted by marbles of the polymetamorphic Kerdilia Formation of Paleozoic or older age. The geologic environment of the ore also comprises biotite-hornblende gneisses and amphibolites intruded by Tertiary pegmatite-aplite dikes, lamprophyre dikes, the 30-Ma Stratoni granodiorite, and porphyritic stocks. Only limited parts of the deposit display shear folding and brecciation; most of it is undeformed. Microthermometry of fluid inclusions in gangue syn-ore quartz indicates three types of primary and pseudosecondary inclusions: (1) H₂O-rich, 1–18 wt.% NaCl equivalent, <3.6 mol% CO₂; (2) H₂O-CO₂ inclusions, <4wt.% NaCl equivalent, with variable CO₂ contents, coexisting in both undeformed and deformed ore; (3) aqueous, highsalinity (28–32 wt,% NaCl equivalent) inclusions found only in undeformed ore. Type 2 inclusions are differentiated into two sub-types: (2a) relatively constant CO₂ content in the narrow range of 8–15 mol% and homogenization to the liquid phase; (2b) variable CO₂ content between 18 and 50 mol% and homogenization to the vapor phase. Type 1 and 2b inclusions are consistent with trapping of two fluids by unmixing of a high-temperature, saline, aqueous, CO₂-bearing fluid of possible magmatic origin, probably trapped in type 2a inclusions. Fluid unmixing and concomitant ore mineralization took place at temperatures of 350 ± 30 °C and fluctuating pressures of less than 500 bar, for both undeformed and deformed ores. The wide salinity range of type 1 inclusions probably represents a complex effect of salinity increase, due to fluid unmixing and volatile loss, and dilution, due to mixing with low-salinity meteoric waters. High solute enrichment of the residual liquid, due to extreme volatile loss during unmixing, may account for high salinity type 3 inclusions. The Olympias fluid inclusion salinity-temperature gradients bear similarities to analogous gradients related to Pb-Zn ores formed in “granite”-hosted, low-T distalskarn, skarn-free carbonate-replacement and epithermal environments.     

Composition of hydrous melts in equilibrium with quartz eclogites

Summary Compositions of the hydrous melts in equilibrium with garnet, omphacitic clinopyroxene and quartz have been investigated experimentally at 28.5 and 35 kbar. They are represented by silica-rich liquids (> 70% SiO₂) with low MgO, FeO and CaO contents. The removal of ca 10–15% of the magma of this composition may be sufficient to convert quartz eclogite formed after subduction of altered MORB into a quartz-free bimineralic eclogite assemblage, which is a common type of xenoliths in kimberlites.At 28.5 kbar the solidus temperature is between 700 and 750° C in the system quartz eclogite—water, and the high pressure amphibole-out boundary lies at ca 25 kbar in accord with the previous studies.

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Die Zusammensetzung wasserhältiger Schmelzen im Gleichgewicht mit Quarz-Eklogiten

Zusammenfassung Um Prozesse zu simulieren, die bei der Subduktion von Ozeanbodenbasalten durch partielle Anatexis im Stabilitätsfeld von Eklogiten ablaufen, wurde die Zusammensetzung wasserhältiger Schmelzen in Gleichgewicht mit Granat, Omphacit und Quarz bei 28.5 und 35 Kbar experimentell untersucht. Diese Schmelzen sind reich an SiO₂ (> 70 Gew%) und arm an Mg0, Fe0 and CaO. Die Extraktion von ca. 10–15% derartiger Schmelzen würde genügen, um quarzführende Eklogite, die durch die Subduktion von alteriertem MORB Material entstanden sind, in quarzfreie bimineralische Eklogite umzuwandeln wie sie häufig als Xenolithe in Kimberliten beobachtet werden.Im System Quarz-Eklogit-Wasser liegt die Solidustemperatur bei 28.5 Kbar zwischen 700 und 750°C. Die obere Stabilitätsgrenze von Amphibol liegt in diesem Temperaturbereich bei ca. 25 Kbar.

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With 1 Figures     

Using Hydrogeochemical Methods To Evaluate Complex Quaternary Subsurface Stratigraphy Block Island,Rhode Island,USA

One of the major problems in hydrogeologic investigations of glaciated regions is the determination of complex stratigraphic relationships in the subsurface where insufficient information is available from drilling and geophysical records. In this paper, chemical characteristics of groundwater were used to identify stratigraphic changes in glacial deposits that were previously inferred on Block Island, Rhode Island, USA, an emergent remnant of the late Wisconsinan terminal moraine, located approximately 16 km south of the Rhode Island mainland. Two chemically distinct water types are recognized on the island: 1) high-iron, characterized by dissolved silica levels in excess of 20 mg/L, bicarbonate greater than 30 mg/L and dissolved iron ranging from 1-20 mg/L; and 2) low-iron, characterized by dissolved silica levels below 16 mg/L, bicarbonate less than 30 mg/L, and less than 0.3 mg/L dissolved iron. The spatial distribution of iron-bearing minerals and organic matter and the resulting redox conditions are believed to control the occurrence of high-iron groundwater. The high-iron waters occur almost exclusively in the eastern half of the island and appear to coincidence with the presence of allochthonous blocks of Cretaceous-age coastal-plain sediments that were incorporated into Pleistocene-age deposits derived from the Narragansett Bay-Buzzard's Bay lobe of the Late Wisconsinan Laurentide ice sheet. The low-iron waters occur in the western half of the island, where the occurrence of these Cretaceous-age blocks is rare and the sediments are attributed to a sublobe of the Hudson-Champlain lobe of the Late Wisconsinan ice-sheet. RÉSUMÉ: L'un des principaux problèmes dans les études hydrogeologiques des régions qui ont été englacées est la définition des relations stratigraphiques complexes sous la surface, lá où les informations fournies par les forages et par la géophysique sont insuffisantes. Dans l'exemple traité, les caractéristiques chimiques de l'eau souterraine sont utilisées pour identifier les variations stratigraphiques dans les dépôts glaciaires qui avaient auparavant été supposées, sur l'île de Block (Rhode Island), restes émergeant d'une moraine terminale du Wisconsinien récent, situé à environ 16 km au sud de Rhode Island. Deux types d'eau chimiquement distincts ont été reconnus dans l'île: 1) à fortes teneurs en fer, caractérisées par des concentrations en silice supérieures à 20 mg/L, en bicarbonates supérieures à 30 mg/L et en fer comprises entre 1 et 20 mg/L; et 2) à faibles teneurs en fer, marquées par des concentrations en silice inférieures à 16 mg/L, en bicarbonate inférieures à 30 mg/L et en fer dissous inférieures à 0.3 mg/L. La distribution spatiale des minéraux riches en fer et de la matière organique et les conditions redox résultantes contrôlent probablement la présence de fer dans les eaux souterraines à fortes concentrations. Les eaux à fortes teneurs en fer sont connues presque exclusivement dans la moitié orientale de l'île et semblent coïncider avec la présence de blocs allochtones provenant des sédiments côtiers crétacés, introduits dans les formations pléistocènes liées au lobe glaciaire des baies de Narragansett et du Busard de la calotte glaciaire laurentide du Wisconsinien récent. Les eaux à faibles teneurs en fer apparaissent dans la moitié occidentale de l'île, là où ces blocs de Crétacé sont rares et où les sédiments sont attrbués à une digitation du lobe de l'Hudson-Champlain de la calotte glaciaire du Wisconsinien récent. RESUMEN: Uno de los mayores problemas en la investigación hidrogeológica en regiones glaciares es la determinación de las complejas relaciones estratigráficas en el subsuelo, donde la información procedente de registros de perforaciones y de geofísica no es suficiente. En este artículo, se han usado las características químicas del agua subterránea para identificar unos cambios estratigráficos que se habían predicho previamente en unos depósitos glaciares en Block Island, Rhode Island (Estados Unidos), un remanente emergente de la morrena terminal del Winsconsiniense tardío, situada unos 16 km al sur de la Rhode Island continental. En la isla se encuentran dos tipos de agua distintos: 1) de alto contenido en hierro, caracterizada por niveles de sílice disuelto superando los 20 mg/L, bicarbonatos por encima de 30 mg/L y hierro disuelto oscilando entre 1-20 mg/L; y 2) de bajo contenido en hierro, caracterizada por niveles de sílice disuelto inferiores a 16 mg/L, bicarbonatos por debajo de 30 mg/L y menos de 0.3 mg/L de hierro disuelto. La distribución espacial de los minerales ricos en hierro y de la materia orgánica, así como las condiciones redox resultantes se supone que condicionan la presencia de aguas de alto contenido en hierro. Estas aguas aparecen casi exclusivamente en la mitad oriental de la isla y parecen coincidir con la presencia de bloques alóctonos de sedimentos costeros, de edad cretácica, que se incorporaron a los depósitos de edad pleistocena procedentes del lóbulo de la Bahía de Narragansett-Bahía de Buzzard, correspondiente a la capa glaciar del Winsconsiniense-Lauréntido tardío. Las aguas de bajo contenido en hierro aparecen en la mitad occidental de la isla, donde la presencia de estos sedimentos de edad cretácica es rara y los sedimentos se suponen procedentes de un sublóbulo del lóbulo de Hudson-Camplain, correspondiente a la capa glaciar del Winsconsiniense tardío.     

Melting of albite and dehydration of brucite in H2O–NaCl fluids to 9 kbars and 700–900°C: implications for partial melting and water activities during high pressure metamorphism

 The melting reaction: albite_(solid)+ H₂O_(fluid) =albite-H₂O_(melt) has been determined in the presence of H₂O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H₂O–CO₂ fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X _(H2O) ) melting relations in the two systems are almost coincident. By contrast, H₂O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 ^°C higher in H₂O–NaCl brines than in H₂O–CO₂ fluids for X _(H2O) =0.8 and ∼100 ^°C higher for X _(H2O) =0.5. The melting temperature of albite in H₂O–NaCl fluids of X _(H2O)=0.8 is ∼100 ^°C higher than in pure water. The P–T curves for albite melting at constant H₂O–NaCl show a temperature minimum at about 5 kbar. Water activities in H₂O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H₂O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but may be due to the presence of low a _(H2O) brines. Received: 17 March 1995/Accepted: 9 April 1996     

A calderas field at the Marifil Formation, new volcanogenic interpretation, Norpatagonian Massif, Argentina

Major volcanogenic structures within the Marifil Formation allowed to determine the location of a claderas field that spreads along 400 kilometers. This field has at least three large calderas with diameters near to 100 kilometers, recognizable by regional distribution of associated dikes and rhyolite lava flows present at the caldera border that separates a monotonous ignimbritic plateau from a depressed (150 meters) inner volcanic collapsed caldera. The Marifil ignimbritic plateau cover more than 50,000 square kilometers with thicknesses that reach 800 meters. Associated with these plateau ignimbrites there is an important fluorite mineralization.     

Effects of heat/water flow interaction on compacted bentonite: Preliminary results

Compacted bentonite blocks have been heated and hydrated in a stainless steel cell in order to simulate, in the laboratory, the conditions of the clay barrier in a high-level radioactive waste repository. Temperature distributions at different times, rate of hydration, final water content and dry density have been measured. Some chemical parameters, as electrical conductivity in an aqueous extractable amorphous silica, have also been obtained. For the periods of time considered (up to 2500 h), the hydration process is not affected by the thermal gradient, the high suction of the bentonite being the critical factor in the initial water uptake of the clay barrier. A remarkable saline environment has been detected near the heater, due to salt migration towards dried areas. This phenomenon should be taken into account in further investigations of the mechanical and geochemical behaviour of the clay barrier.