Denitrification and N₂O production in near-shore marine sediments     

Sbil Seitzinger  Scott Nixon  Michael E.Q. Pilson  Suzanne Burke 《Geochimica et cosmochimica acta》1980,44(11):1853-1860

Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N₂ from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N₂m^?2 hr^?1. This nitrogen flux is equal to approximately one-half of the NH⁺₄flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N₂ during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N₂O, but the amount of nitrogen involved was only about 0.2 μmol m^?2 hr^?1 at 23°C.  相似文献   

Magma mixing in the Aleutian arc: evidence from cognate inclusions and composite xenoliths     

Walter K. Conrad  Suzanne M. Kay  Robert W. Kay 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

The complexity of igneous processes in the Aleutian calc-alkaline magma series can be inferred from study of xenolithic fragments. Composite xenoliths and cognate inclusions provide direct evidence for magma—magma and wall-rock—magma mixing processes. Using distributions of Cr in clinopyroxene, compositional endmembers involved in mixing are identified within the xenoliths. The basaltic mixing endmember is more mafic than calc-alkaline lavas in the arc. Magma mixing and wall-rock assimilation within calc-alkaline basaltic to andesitic magmas is identified in phenocrystic assemblages as well as in xenoliths, and appears to be a widespread phenomenon in Aleutian calc-alkaline magmas.  相似文献   

Combined U-Pb dating and Sm-Nd studies on lower crustal and mantle xenoliths from the Delegate basaltic pipes, southeastern Australia     

Y. D. Chen  Suzanne Y. O'Reilly  W. L. Griffin  T. E. Krogh 《Contributions to Mineralogy and Petrology》1998,130(2):154-161

Mafic rocks dominate the lower crustal and upper mantle xenolith suites within the Jurassic Delegate basaltic diatremes in the Paleozoic Lachlan Fold Belt, SE Australia. Two upper mantle mafic xenoliths from the Delegate pipes, a garnet pyroxenite and a garnet granulite (equilibrated at 1060 and 1140 °C, and 40–50 km), yield garnet-clinopyroxene Sm-Nd ages of 160 ± 4 Ma and 153 ± 10 Ma, respectively. Both ages are indistinguishable from the time of eruption of the diatremes, and are interpreted as showing continuous isotopic equilibrium within the mantle of Sm and Nd between garnet + clinopyroxene at temperatures ≥ 1050 °C. A lower crustal, 2-pyroxene granulite xenolith (equilibrated at 810–850 °C and ca. 25 km) yields a clinopyroxene + plagioclase + whole rock Sm-Nd isochron ages of 283 ± 26 Ma. This age probably reflects partial resetting of the isotopic systems of much older granulite during slow cooling, or after a heating event in the lower crust associated with the Jurassic magmatic activity represented by the basaltic host rock. Metamorphic zircons from the 2-pyroxene granulite xenolith were dated by the U-Pb method at 398±2 and 391 ± 2 Ma. These ages are considered to date granulite facies metamorphic events in the lower crust of the region. The age gap between the granulite facies metamorphism and granitoid plutonism in the region (420–410 Ma) indicates that the dated granulite is unlikely to represent residue after partial melting and magma extraction that generated the regional granitoids. It is suggested that these ages may record a relatively slow cooling following the cessation of mafic magmatic intrusion that formed the xenolith protoliths and that was probably the heat source responsible for granite production. At about 25 km, this thermal relaxation accounts for the change from an olivine + plagioclase + 2-pyroxene gabbroic assemblage into the granulite facies 2-pyroxene + plagioclase + spinel field. Received: 17 May 1995 / Accepted: 24 March 1997  相似文献   

Distinguishing Natural Hydrocarbons from Anthropogenic Contamination in Ground Water     

Suzanne Lesage  Hao Xu  Kent S. Novakowski 《Ground water》1997,35(1):149-160

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Variation of magnetic directions within pillow basalts     

William Soroka  Suzanne Beske-Diehl 《Earth and Planetary Science Letters》1984,69(1):215-223

Relative directions of magnetization have been measured within individual pillow basalts collected from the Atlantic Ocean and Caribbean Sea. The angle between the magnetic directions was determined and is referred to as the directional difference. Although one pillow contained a directional difference of 44°, the remaining ten pillows had differences less than 14°. The maximum orientation and measurement error was 7°. Dispersion on the scale found in these fine-grained pillow basalts would not appreciably affect the magnetic anomaly pattern on the sea floor. We detected no reversals of magnetization despite the sometimes large and variable low-temperature oxidation. Comparison of directions within homogeneous segments of the pillow, viscous remanent magnetization (VRM) acquisition experiments, and alternating field (AF) demagnetization indicate a large portion of the dispersion was due to the acquisition of a viscous component in the larger grained, less oxidized portion of the pillows. Evidence from one variably weathered pillow suggests that extreme low-temperature oxidation may lead to the acquisition of a secondary component with high coercivities (20–80 mT). We could not determine whether this was a chemical remanent magnetization (CRM) or a VRM acquired by single domain grains near the superparamagnetic threshold. Hysteresis properties confirmed by microscopic examination indicated that the magnetic grain size in all the pillows was at least as small as pseudo-single domain.  相似文献   

Sr isotopic heterogeneity in primitive basaltic rocks,southeastern Australia: correlation with mantle metasomatism     

Suzanne Y. O'Reilly  W. L. Griffin 《Contributions to Mineralogy and Petrology》1984,87(3):220-230

Rb/Sr data for seven basaltic provinces (K-Ar ages 50-0 Ma) in southeastern Australia imply isotopic heterogeneities in the mantle sources. The total range of ⁸⁷Sr/ ⁸⁶Sr is 0.7031–0.7054. Effects of crustal contamination are negligible, since the rocks analyzed represent primary or primitive magma compositions. The inferred scales of heterogeneity range from <1 km for small intraprovince variations, to in the order of 100 km for the larger differences between provinces.Correlation of regional high ⁸⁷Sr/⁸⁶Sr in basaltic rocks with the presence of amphibole-bearing upper mantle xenoliths suggests that the degree of metasomatic activity in the underlying mantle is a major control on the Rb/Sr and ⁸⁷Sr/⁸⁶Sr values of mantle source volumes and partial melts derived from these. Xenolith data also indicate that both pervasive metasomatism and the presence of crystallized melts or cumulates as veins and dykes in mantle wall rock are possible mechanisms for metasomatic additions.Mantle isochrons can be constructed both within some provinces and between provinces. However, episodic metasomatism in the mantle source regions, with correlated enrichment in Rb/Sr and ⁸⁷Sr/⁸⁶Sr, can produce artificial isochrons which may have no relevance to mantle differentiation events.  相似文献   

Apatite as an indicator mineral for mineral exploration: trace-element compositions and their relationship to host rock type   总被引：7，自引：0，他引：7  

E. A. Belousova  W. L. Griffin  Suzanne Y. O'Reilly  N. I. Fisher 《Journal of Geochemical Exploration》2002,76(1):1056

Over 700 apatite grains from a range of rock types have been analysed by laser-ablation microprobe ICPMS for 28 trace elements, to investigate the potential usefulness of apatite as an indicator mineral in mineral exploration. Apatites derived from different rock types have distinctive absolute and relative abundances of many trace elements (including rare-earth elements (REE), Sr, Y, Mn, Th), and chondrite-normalised trace-element patterns. The slope of chondrite-normalised REE patterns varies systematically from ultramafic through mafic/intermediate to highly fractionated granitoid rock types. (Ce/Yb)_cn is very high in apatites from carbonatites and mantle-derived lherzolites (over 100 and over 200, respectively), while (Ce/Yb)_cn values in apatites from granitic pegmatites are generally less than 1, reflecting both HREE enrichment and LREE depletion. Within a large suite of apatites from granitoid rocks, chemical composition is closely related to both the degree of fractionation and the oxidation state of the magma, two important parameters in determining the mineral potential of the magmatic system. Apatite can accept high levels of transition and chalcophile elements and As, making it feasible to recognise apatite associated with specific types of mineralisation. Multivariate statistical analysis has provided a user-friendly scheme to distinguish apatites from different rock types, based on contents of Sr, Y, Mn and total REE, the degree of LREE enrichment and the size of the Eu anomaly. The scheme can be used for the recognition of apatites from specific rock types or styles of mineralisation, so that the provenance of apatite grains in heavy mineral concentrates can be determined and used in geochemical exploration.  相似文献   

Characterization of the subsurface architecture and identification of potential groundwater paths in a clay-rich floodplain using multi-electrode resistivity imaging     

Ander Guinea  Suzanne Hollins  Karina Meredith  Stuart Hankin  Dioni I. Cendón 《水文科学杂志》2018,63(6):909-925

The interaction between surface water and groundwater in clay-rich fluvial environments can be complex and is generally poorly understood. Airborne electromagnetic surveys are often used for characterizing regional groundwater systems, but they are constrained by the resolution of the method. A resistivity imaging survey has been carried out in the Macquarie Marshes (New South Wales, Australia) in combination with water chemical sampling. The results have enabled the identification of buried palaeochannels and the location of potential recharge points. The data have been compared with previously published airborne electromagnetic data in the same area. Deeper less conductive features suggest that there is a potential connection between the Great Artesian Basin and groundwater contained within the shallow sand aquifer. Even though the chemistry of the groundwater samples does not indicate interaction with the Great Artesian Basin, the observed discontinuity in the saprolite implies potential for this to happen in other locations.  相似文献   

Efficient reliability analysis of earth dam slope stability using extreme gradient boosting method     

Wang  Lin  Wu  Chongzhi  Tang  Libin  Zhang  Wengang  Lacasse  Suzanne  Liu  Hanlong  Gao  Lei 《Acta Geotechnica》2020,15(11):3135-3150

Acta Geotechnica - Reliability analysis approach provides a rational means to quantitatively evaluate the safety of geotechnical structures from a probabilistic perspective. However, it suffers...  相似文献   

Aggregate performance in managing marine ecosystems of 53 maritime countries     

Jacqueline Alder  Sarika Cullis-Suzuki  Vasiliki Karpouzi  Kristin Kaschner  Suzanne Mondoux  Wilf Swartz  Pablo Trujillo  Reg Watson  Daniel Pauly 《Marine Policy》2010

Fourteen indicators of marine living resource management performance by country, reflecting both their intention to sustainably use the resource within their Exclusive Economic Zones and the effectiveness of their policies, were developed and the performances of 53 maritime countries were assessed. Four rankings of the countries, which jointly account for over 95 percent of the world's marine fisheries landings, are presented here as aggregated scores of the fourteen indicators, using different schemes for weighting the indicators, each reflective of the management preferences identified by the Global Environment Outlook 4 (GEO4) future development scenarios: Market First; Policy First; Security First; and Sustainability First. The resulting rankings differed substantially between the weighting schemes for the top performing countries but less so for the countries performing poorly.  相似文献