Chemical composition,volatile components,and trace elements in melts of the Karymskii volcanic center,Kamchatka, and Golovnina volcano,Kunashir Island: Evidence from inclusions in minerals

Melt inclusions were examined in phenocrysts in basalt, andesite, dacite, and rhyodacite from the Karymskii volcanic center in Kamchatka and dacite form Golovnina volcano in Kunashir Island, Kuriles. The inclusions were examined by homogenization and by analyzing glasses in more than 80 inclusions on an electron microscope and ion microprobe. The SiO₂ concentrations in the melt inclusions in plagioclase phenocrysts from basalts from the Karymskii volcanic center vary from 47.4 to 57.1 wt %, these values for inclusions in plagioclase phenocrysts from andesites are 55.7–67.1 wt %, in plagioclase phenocrysts from the dacites and rhyodacites are 65.9–73.1 wt %, and those in quartz in the rhyodacites are 72.2–75.7 wt %. The SiO₂ concentrations in melt inclusions in quartz from dacites from Golovnina volcano range from 70.2 to 77.0 wt %. The basaltic melts are characterized by usual concentrations of major components (wt %): TiO₂ = 0.7–1.3, FeO = 6.8–11.4, MgO = 2.3–6.1, CaO = 6.7–10.8, and K₂O = 0.4–1.7; but these rocks are notably enriched in Na₂O (2.9–7.4 wt % at an average of 5.1 wt %, with the highest Na₂O concentration detected in the most basic melts: SiO₂ = 47.4–52.0 wt %. The concentrations of volatiles in the basic melts are 1.6 wt % for H₂O, 0.14 wt % for S, 0.09 wt % for Cl, and 50 ppm for F. The andesite melts are characterized by high concentrations (wt %) of FeO (6.5 on average), CaO (5.2), and Cl (0.26) at usual concentrations of Na₂O (4.5), K₂O (2.1), and S (0.07). High water concentrations were determined in the dacite and rhyodacite melts: from 0.9 to 7.3 wt % (average of 15 analyses equals 4.5 wt %). The Cl concentration in these melts is 0.15 wt %, and those of F and S are 0.06 and 0.01 wt %, respectively. Melt inclusions in quartz from the dacites of Golovnina volcano are also rich in water: they contain from 5.0 to 6.7 wt % (average 5.6 wt %). The comparison of melt compositions from the Karymskii volcanic center and previously studied melts from Bezymyannyi and Shiveluch volcanoes revealed their significant differences. The former are more basic, are enriched in Ti, Fe, Mg, Ca, Na, and P but significantly depleted in K. The melts of the Karymskii volcanic center are most probably less differentiated than the melts of Bezymyannyi and Shiveluch volcanoes. The concentrations of water and 20 trace elements were measured in the glasses of 22 melt inclusions in plagioclase and quartz from our samples. Unusually high values were obtained for Li concentrations (along with high Na concentrations) in the basaltic melts from the Karymskii volcanic center: from 118 to 1750 ppm, whereas the dacite and rhyolite melts contain 25 ppm Li on average. The rhyolite melts of Golovnina volcano are much poorer in Li: 1.4 ppm on average. The melts of the Karymskii volcanic center are characterized by relative minima at Nb and Ti and maxima at B and K, as is typical of arc magmas.     

Paleogeographic regionalization of Triassic seas based on conodontophorids

Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic     

Geochemical characterization of surface waters and groundwater resources in the Managua area (Nicaragua,Central America)

This paper reports new geochemical data on dissolved major and minor constituents in surface waters and ground waters collected in the Managua region (Nicaragua), and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area. The peculiar geological features of the study site, an active tectonic region (Nicaragua Depression) characterized by active volcanism and thermalism, combined with significant anthropogenic pressure, contribute to a complex evolution of water chemistry, which results from the simultaneous action of several geochemical processes such as evaporation, rock leaching, mixing with saline brines of natural or anthropogenic origin. The effect of active thermalism on both surface waters (e.g., saline volcanic lakes) and groundwaters, as a result of mixing with variable proportions of hyper-saline geothermal Na–Cl brines (e.g., Momotombo geothermal plant), accounts for the high salinities and high concentrations of many environmentally-relevant trace elements (As, B, Fe and Mn) in the waters. At the same time the active extensional tectonics of the Managua area favour the interaction with acidic, reduced thermal fluids, followed by extensive leaching of the host rock and the groundwater release of toxic metals (e.g., Ni, Cu). The significant pollution in the area, deriving principally from urban and industrial waste-water, probably also contributes to the aquatic cycling of many trace elements, which attain concentrations above the WHO recommended limits for the elements Ni (∼40 μg/l) and Cu (∼10 μg/l) limiting the potential utilisation of Lake Xolotlan for nearby Managua.     

Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers

Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1× or (4) 10× the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.     

GEOPHYSICAL STUDIES OF WATER LEAKAGES FROM RESERVOIRS*

Considerable water leakages from reservoirs make it difficult to attain the planned storage capacity. In some cases water leakages give rise to suffusion followed by catastrophes. Until recently methods for locating water leakages were extremely imperfect. Geophysical methods offer good prospects in this direction. For solving these problems, it is effective to use streaming potential measurements, water flow rate observations and thermometry. Laboratory experiments were carried out in connection with the fact that water leakages from reservoirs are characterized by negative anomalies of natural currents; the more filtration discharge, the higher these anomalies are. As a result, the relationship governing the intensity of streaming potential and sand granulometric composition, electrolyte concentrations and other factors were revealed. To determine the velocity of water flowing to leakage sites, a special device, based on the relationship between the temperature of a heated body and its resistance, is applied. This device simultaneously makes it possible to measure the water medium temperature. Observations at reservoir sites were effected by moving along the reservoir non-polarizable potential electrodes and water velocity devices. Recordings were carried out automatically by the recording device of the logging apparatus. Under the conditions of ice cover on water surfaces, measurements were made through separate points by digging holes in the ice cover. Practical field observations were carried out at reservoir sites located in regions where fissured massive rocks as well as loose sediments predominate. In the first case field experiments were carried out in alpine reservoirs, in Armenia. The major water leakages were found to be concentrated on the right bank of the reservoir. In this connection it was not only possible to locate water leakage sites, but also to evaluate their relative intensity. These data were used for planning antifiltration measures. In the second case water leakages from a reservoir located in Uzbekistan in the submontane part of the Pamirs were studied. Streaming potential anomalies and high benthonic flow rates made it possible to discover high filtrations in the base and walls of the dam. Further perfection of these methods should not only permit the determination of water leakage sites and their relative intensity, but also filtration discharges in absolute units.     

THE DELINEATION OF THE BEDROCK CONFIGURATION OF PART OF PORT JACKSON,NEW SOUTH WALES,WITH A BOOMER SYSTEM*

A high resolution Boomer system was used to investigate the bedrock configuration of part of Port Jackson, New South Wales. The continuous reflection profiling technique was successful in delineating a channel incised in bedrock under a thickness of up to 60 m. of unconsolidated sediment covered by up to 20 m. of water.     

THOUGHTS ON MAPPING BY PHOTOGRAMMETRY

Topics of immediate practical interest formed the basis of the Address. Particular emphasis was placed upon problems of point transfer, pre-marking of ground control points, aerial triangulation by observation of independent models, and the status of photogrammetric operators.