Comparative petrology, geochemistry, and petrogenesis of evolved, low-Ti lunar mare basalt meteorites from the LaPaz Icefield, Antarctica     

James M.D. Day  Lawrence A. Taylor  Allan D. Patchen  D. Graham Pearson 《Geochimica et cosmochimica acta》2006,70(6):1581-1600

New data is presented for five evolved, low-Ti lunar mare basalt meteorites from the LaPaz Icefield, Antarctica, LAP 02205, LAP 02224, LAP 02226, LAP 02436, and LAP 03632. These basalts have nearly identical mineralogies, textures, and geochemical compositions, and are therefore considered to be paired. The LaPaz basalts contain olivine (Fo_64-2) and pyroxene (Fs₃₂Wo₈En₆₀ to Fs_84-86Wo₁₅En_2-0) crystals that record extreme chemical fractionation to Fe-enrichment at the rims, and evidence for silicate liquid immiscibility and incompatible element enrichment in the mesostasis. The basalts also contain FeNi metals with unusually high Co and Ni contents, similar to some Apollo 12 basalts, and a single-phase network of melt veins and fusion crusts. The fusion crust has similar chemical characteristics to the whole rock for the LaPaz basalts, whereas the melt veins represent localized melting of the basalt and have an endogenous origin. The crystallization conditions and evolved nature of the LaPaz basalts are consistent with fractionation of olivine and chromite from a parental liquid similar in composition to some olivine-phyric Apollo 12 and Apollo 15 basalts or lunar low-Ti pyroclastic glasses. However, the young reported ages for the LaPaz mare basalts (∼2.9 Ga) and their relative incompatible element enrichment compared to Apollo mare basalts and pyroclastic glasses indicate they cannot be directly related. Instead, the LaPaz mare basalts may represent fractionated melts from a magmatic system fed by similar degrees of partial melting of a mantle source similar to that of the low-Ti Apollo mare basalts or pyroclastic glasses, but which possessed greater incompatible element enrichment. Despite textural differences, the LaPaz basalts and mare basalt meteorite NWA 032 have similar ages and compositions and may originate from the same magmatic system on the Moon.  相似文献   

Microearthquakes at the puhagan geothermal field, Philippines — A case of induced seismicity     

C.J. Bromley  C.F. Pearson  D.M. Rigor Jr.  PNOC-EDC   《Journal of Volcanology and Geothermal Research》1987,31(3-4)

The Puhagan area in Southern Negros is the only known Philippine geothermal field where there is a clear correlation between increased levels of local seismicity, and the development and early production phases of a geothermal power project. During commissioning of the Palinpinon I power plant in May 1983, a large increase in the microseismic event rate, occasionally exceeding 100 events per day, was noted. This seismic activity is characterized by swarms of events lasting from several hours to a month, separated by long periods of reduced activity. The largest events have local magnitudes of 2.4. Because the swarms appear to be triggered by both reinjection and production of fluids, it is difficult to relate them to a single triggering mechanism.An epicenter study was conducted during July to October 1983, using a simplified joint determination algorithm modified for a uniform velocity structure. The vast majority of the hypocenters occur in a narrow zone with a WNW lineation in the production sector of the field (correlating with a known fault trace) with very little activity in the reinjection sector (1 km to the north). First motions suggest activity has been induced on several non-parallel faults in the area, however, a majority of the events are consistent with normal faulting or oblique slip on steeply dipping NW-SE-trending planes.  相似文献   

Potassium-argon ages and strontium isotope ratio measurements from volcanic rocks in northeastern Nigeria     

Norman Kennedy Grant  David C. Rex  Samuel J. Freeth 《Contributions to Mineralogy and Petrology》1972,35(4):277-292

The Cenozoic volcanic activity in northeastern Nigeria began with the intrusion into the Benue trough of a trachyte-phonolite suite of plugs 22-11 m.y. ago. Later activity, which was more widespread and dominantly basaltic in character, began some 7 m.y. ago and has continued until very recent times. It resulted in basaltic plugs and lava plateaux within the Benue trough, and cinder cones and lavas on the Jos Plateau.The initial ⁸⁷Sr/⁸⁶Sr ratios of nine of the fifteen analyzed basic and alkalic rocks lie in the range 0.7025–0.7032, and the highest ratio measured is 0.7129.The main group of trachytes and phonolites are considered to be fractional melts derived from the upper mantle, modified in small part by potassium feldspar crystal fractionation. Two Sr-rich phonolite plugs may have a separate origin from the main group of trachytes and phonolites.The Cenozoic volcanic activity in northeastern Nigeria is probably related to the nearby Cameroun volcanic line. The concentration of plugs within the Benue trough may reflect internal adjustments along old lines of weakness within the African lithosphere plate, in response to synchronous changes affecting the plate's external dimensions and internal structure, such as the growth of the Red Sea and the Gulf of Aden, and the volcanism of the east African rift valley.  相似文献   

Eddy correlation measurements of CO2, latent heat,and sensible heat fluxes over a crop surface   总被引：14，自引：0，他引：14  

Dean E. Anderson  Shashi B. Verma  Norman J. Rosenberg 《Boundary-Layer Meteorology》1984,29(3):263-272

Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO₂ sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO₂ were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO₂ fluxes were near 1.0 mg m^–2 (ground area) s^–1.The eddy correlation technique was also employed in this study to measure nocturnal CO₂ fluxes caused by respiration from plants, soil, and roots. These CO₂ fluxes ranged from - 0.1 to - 0.25 mg m^–2s^–1.From the data collected over mature soybeans, a relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m^–2 s^–1. The light compensation point was found to be about 160 Ei m^–2 s^–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.  相似文献   

Metamorphic incongruent solution,diffusion and pressure solution stripes     

Norman Fry 《Lithos》1982,15(3):183-190

The formation of pressure solution stripes is discussed on the basis of previosly published observations and of local chemical equilibria between solution and solid phases. Chemically driven mineral reactions can be localized at early sites of nucleation and be enhanced by stresses to create patterns of cleavage stripes. These reactions cause transport of material over distances greater than single grains. They provide suitable sites and suitable chemistry for later incongruent pressure solution, potentially a much faster process than congruent pressure solution discussed in previous literature. Neither reaction nor straightforward incongruent pressure solution explains the solution of quartz, commonly observed at cleavage stripes. Quartz pressure solution is explicable on certain assumptions about diffusivities and the effects of stresses. This involves interaction between quartz and the established incongruent solution of other minerals, an overall process termed ‘interdependent pressure solution’. Electrical potential differences will be greatest during early mineral reactions, a feature which may provide a means to corroborate the chemical role in initiating ‘pressure solution stripes’.  相似文献   

Compendium of seashells: Tucker R. Abbot and Peter S. Dance, 1982. E. P. Dutton,New York. 411 pp. 4200 colour illustrations. Price US$50.00, £19.95. ISBN 0 525 93209 0     

Norman Tebble 《Marine pollution bulletin》1983,14(6):239-240

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A strontium isotope and trace element profile through the Partridge River Troctolite,Duluth complex,Minnesota     

Norman K. Grant  Philip A. Molling 《Contributions to Mineralogy and Petrology》1981,77(3):296-305

Initial ⁸⁷Sr/⁸⁶Sr ratios down a 2,315 foot-long core (DDH-295) through the Partridge River Troctolite are lower in the depth range 710–1,410 feet (0.70443±22) than in the underlying and overlying rocks (0.70500±18). These initial ratio variations define three zones (I, II, and III) thought to be three intrusive units within the troctolite. The best estimate of the Rb-Sr age of the troctolite is 1,050±105 m.y. The olivine compositions and the abundances of the incompatible trace elements Zr, Y, and Rb show identical variations down the core, with downward repetitions of olivine iron-enrichment and incompatible trace element enrichments. Discontinuities in the olivine compositions and incompatible trace element abundances match the initial ⁸⁷Sr/⁸⁶Sr ratio discontinuities in the core. The strontium isotope data imply that involatile components of the Proterozoic Virginia Formation and other Archaean rocks were not significantly assimilated by the troctolites, for only three out of the twenty-three initial ⁸⁷Sr/⁸⁶Sr ratios depart from normal magmatic values. These three anomalous ratios are not systematically related to the Cu-Ni sulphide mineralization and may be the result of secondary calcite in the troctolite. The strontium isotope systematics of the Virginia Formation xenoliths and underlying hornfelses are highly disturbed as a result of Rb loss. The apparently inverted fractionation sequences in the troctolites are interpreted in terms of downward increases in intercumulus liquid in repeated magma batches and controlled by plagioclase flotation. The amount of intercumulus liquid is estimated to range from 7 to 61 weight per cent. The Cu-Ni sulphides are concentrated in the lower 250 feet of zone I (immediately above the Virginia Formation) and through 400 feet of core across the contact between zones I and II, more than 750 feet above the base. Because the sulphide-bearing troctolites are not systematically related to disturbances in the magmatic initial ⁸⁷Sr/⁸⁶Sr ratios, the mineralization probably involved the volatile transfer of sulphur derived from dehydration reactions in the underlying Virginia Formation.  相似文献   

Origin of CFB Magmatism: Multi-tiered Intracrustal Picrite-Rhyolite Magmatic Plumbing at Spitzkoppe, Western Namibia, during Early Cretaceous Etendeka Magmatism     

Thompson  R. N.; Riches  A. J. V.; Antoshechkina  P. M.; Pearson  D. G.; Nowell  G. M.; Ottley  C. J.; Dickin  A. P.; Hards  V. L.; Nguno  A.-K.; Niku-Paavola  V. 《Journal of Petrology》2007,48(6):1119-1154

Early Cretaceous tholeiitic picrite-to-rhyolite dykes aroundSpitzkoppe, western Namibia, are part of the extensive HentiesBay–Outjo swarm, penecontemporaneous with 132 Ma Etendekalavas 100 km to the NW. Although only intermediate to rhyoliticdykes contain clinopyroxene phenocrysts, the behaviour of Ca,Al and Sc in the dyke suite shows that liquidus clinopyroxene—togetherwith olivine—was a fractionating phase when MgO fell to9 wt %. Both a plot of CIPW normative di–hy–ol–ne–Qand modelling using (p)MELTS show that a mid-crustal pressureof 0·6 GPa is consistent with this early clinopyroxenesaturation. Sr, Nd, Hf and Pb isotope variations all show trendsconsistent with AFC contamination (assimilation linked to fractionalcrystallization), involving Pan-African Damara belt continentalcrust. The geochemical variation, including isenthalpic AFCmodelling using (p)MELTS, suggests that the picrites (olivine-richcumulate suspensions) were interacting with granulite-faciesmetamorphic lower crust, the intermediate compositions withamphibolite-facies middle crust, and the rhyolitic dykes (anda few of the basalts) with the Pan-African granites of the uppercrust. The calculated densities of the magmas fall systematicallyfrom picrite to rhyolite and suggest a magmatic system resemblinga stack of sills throughout the crust beneath Spitzkoppe, withthe storage and fractionation depth of each magma fraction controlledby its density. Elemental and isotopic features of the 20 wt% MgO picrites (including Os isotopes) suggest that their parentalmelts probably originated by fusion of mid-ocean ridge basalt(MORB) source convecting mantle, followed by limited reactionwith sub-continental lithospheric mantle metasomatized justprior to the formation of the parental magmas. Many of the distinctivefeatures of large-volume picritic–basaltic magmas maynot be derived from their ultimate mantle sources, but may insteadbe the results of complex polybaric fractional crystallizationand multi-component crustal contamination. KEY WORDS: flood basalts; Spitzkoppe; picrite; trace elements; hafnium isotopes; Etendeka  相似文献   

Climate change drives coherent trends in physics and oxygen content in North American lakes     

Michelle E. Palmer  Norman D. Yan  Keith M. Somers 《Climatic change》2014,124(1-2):285-299

Using a 25-year record of monitoring data, we show that recent climate change has affected the thermal properties and oxygen content of seven lakes in south-central Ontario, Canada, and five lakes in north-central Wisconsin, USA. Coherent patterns in autumnal lake warming were driven by increased autumn air temperature in both lake districts. Temperature increases were restricted to the epilimnion and metalimnion of the lakes, resulting in increased thermal stability of the water column. Mixing depths also decreased over the study period. Shallower mixing depths in the Ontario lakes were due to climate-driven increases in lake-water dissolved organic carbon concentrations. Collectively, changes in the thermal regime of the lakes suggest autumn mixing of the water column may be delayed. Metalimnetic oxygen also increased in the Wisconsin lakes, perhaps in response to increased algal production as lake thermal regimes changed. The response of individual lakes to climate change was modified by lake chemistry in the Ontario lake district and by lake chemistry and morphometry in the Wisconsin lake district. Our results demonstrate coherent lake response to climate change and highlight the importance of both regional and local factors in regulating individual lake response to global climate change.  相似文献   

Observations of the Early Morning Boundary-Layer Transition with Small Remotely-Piloted Aircraft   总被引：1，自引：1，他引：0  

Norman Wildmann  Gerrit Anke Rau  Jens Bange 《Boundary-Layer Meteorology》2015,157(3):345-373

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