Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages     

L.E. Nyquist  J. Wooden  B. Bansal  H. Wiesmann  G. McKay  D.D. Bogard 《Geochimica et cosmochimica acta》1979,43(7):1057-1074

  相似文献   

Ultrabasic magmas and high-degree melting of the mantle   总被引：1，自引：0，他引：1  

Nicholas T. Arndt 《Contributions to Mineralogy and Petrology》1977,64(2):205-221

As the degree of melting of mantle peridotite increases, the liquids that are formed become more basic and less viscous, and the spacing between residual crystals increases. The settling velocities of residual crystals in partial melts consequently will increase by several orders of magnitude, from 9.4 × 10^–4 cm/s to 4.3 × 10^–1 cm/s for a 1 cm olivine grain, as the proportion of liquid increases from 15 to 60%.To produce an ultrabasic komatiitic magma from a source with commonly assumed mantle composition requires 50 to 80% melting. Before this degree of melting can be reached, a highly fluid picritic magma produced by 30 to 50% melting will segregate from the source. Ultrabasic magmas probably form by a sequential melting process and are derived from a residuum composed of refractory minerals and trapped liquid left by previous episodes of partial melting and magma extraction. Trace element concentrations in ultrabasic komatiite lavas are consistent with this theory.  相似文献   

Occurrence ofSpartina macrodetritus in Bay of Fundy waters     

Donald C. Gordon  Nicholas J. Prouse  Peter J. Cranford 《Estuaries and Coasts》1985,8(3):290-295

Suspended macrodetritus (>600 μm) from extensiveSpartina alterniflora marshes is widespread in the Cumberland Basin region of the macrotidal upper Bay of Fundy. The average concentration is about 5 mg C per m³ and most is found in the lower two-thirds of the water column. The total amount in the Basin at high tide is approximately 8 metric tonnes of organic carbon which is less than 1% of the annual net aerial primary production of the fringingS. alterniflora marshes. The high visibility ofSpartina detritus in Cumberland Basin is caused by the extreme tides (average tidal range about 11 m) which export marsh vegetation and distribute it widely about the estuary, and by the pronounced turbidity which has been shown to limit phytoplankton growth.  相似文献   

Determination of the strain ellipsoid from measurements on any three sections     

Nicholas J. Milton 《Tectonophysics》1980,64(1-2)

An ellipsoid is defined by, and may be re-constructed from, any three sections through it. In the field, calculation of the strain ellipsoid from general sections (two-dimensional strain ellipses determined from measured strain markers) is complicated by the fact that, due to experimental error and/or strain inhomogeneity, the three ellipses may not come from the same ellipsoid. The ellipses must first be adjusted to make them compatible. A method is suggested by which an adjustment ellipse is determined analytically for each of the three sections. Application of these adjustment ellipses makes the three sections compatible, and the strain ellipsoid may be determined. The principal axes of the ellipsoid are derived from the ellipsoid matrix by eigenvector analysis. Examples are given of practical applications of this method.  相似文献   

“Rare-earth and other trace element contents and the origin of minettes.” A critical comment on a paper by Bachinski and Scott (1979)     

Nicholas M.S. Rock 《Geochimica et cosmochimica acta》1980,44(9):1385-1388

  相似文献   

Comment on “Two Paleoproterozoic (Statherian) siliciclastic metasedimentary sequences in central Wisconsin: The end of the Penokean Orogeny and cratonic stabilization of the southern Lake Superior region” [Precamb. Res. 157 (2007) 188–202]     

Nicholas Van Wyck   《Precambrian Research》2008,164(3-4):233-235

  相似文献   

Interaction of magma with sedimentary wall rock and magnetite ore genesis in the Panzhihua mafic intrusion,SW China   总被引：10，自引：0，他引：10  

Clément Ganino  Nicholas T. Arndt  Mei-Fu Zhou  Fabrice Gaillard  Catherine Chauvel 《Mineralium Deposita》2008,43(6):677-694

In southwestern China, several large magmatic Fe–Ti–V oxide ore deposits are hosted by gabbroic intrusions associated with the Emeishan flood basalts. The Panzhihua gabbroic intrusion, a little deformed sill that contains a large titanomagnetite deposit at its base, concordantly intrudes late-Proterozoic dolostones. Mineralogical and chemical studies of the contact aureole in the footwall dolostones demonstrate that the metamorphism was largely isochemical but released large quantities of CO₂ as the rocks were converted to marble and skarns during intrusion of the gabbroic magma. Petrological modelling of the crystallization of the intrusion, using H₂O-poor Emeishan basalt as parent magma, shows that under normal conditions, Fe–Ti oxides crystallize at a late stage, after the crystallization of abundant olivine, clinopyroxene and plagioclase. In order for titanomagnetite to separate efficiently to form the ore deposit, this mineral must have crystallized earlier and close to the liquidus. We propose that CO₂-rich fluids released during decarbonatization of sedimentary floor rocks passed up through the magma. Redox equilibria calculations show that when magma with the composition of Emeishan basalt is fluxed by a CO₂-rich gas phase, its equilibrium oxygen fugacity (fO₂) increases from the fayalite–magnetite–quartz buffer (FMQ) to FMQ + 1.5. From experimental constraints on magnetite saturation in basaltic magma under controlled fO₂, such an oxidizing event would allow magnetite to crystallize near to the liquidus, leading to the formation of the deposit.  相似文献   

The July 2007 rock and ice avalanches at Mount Steele, St. Elias Mountains, Yukon, Canada   总被引：1，自引：0，他引：1  

Panya S. Lipovsky  Stephen G. Evans  John J. Clague  Chris Hopkinson  Réjean Couture  Peter Bobrowsky  Göran Ekström  Michael N. Demuth  Keith B. Delaney  Nicholas J. Roberts  Garry Clarke  Andrew Schaeffer 《Landslides》2008,5(4):445-455

A large rock and ice avalanche occurred on the north face of Mount Steele, southwest Yukon Territory, Canada, on July 24, 2007. In the days and weeks preceding the landslide, several smaller avalanches initiated from the same slope. The ice and rock debris traveled a maximum horizontal distance 5.76 km with a maximum vertical descent of 2,160 m, leaving a deposit 3.66 km² in area on Steele Glacier. The seismic magnitude estimated from long-period surface waves (M _s) is 5.2. Modeling of the waveforms suggests an estimated duration of approximately 100 s and an average velocity of between 35 and 65 m/s. This landslide is one of 18 large rock avalanches known to have occurred since 1899 on slopes adjacent to glaciers in western Canada. We describe the setting, reconstruct the event chronology and present a preliminary characterization of the Mount Steele ice and rock avalanches based on field reconnaissance, analysis of seismic records and an airborne LiDAR survey. We also present the results of a successful dynamic simulation for the July 24 event.  相似文献   

Lateral Chloride Migration from a Landfill in a Fractured Clay-Rich Glacial Deposit   总被引：1，自引：0，他引：1  

L. D. McKay  D. J. Balfour  J.A. Cherry 《Ground water》1998,36(6):988-999

  相似文献   

Hydrologic history of the Mississippi and Lower Missouri Rivers based upon a refined specific‐gauge approach     

Abebe A. Jemberie  Nicholas Pinter  Jonathan W. F. Remo 《水文研究》2008,22(22):4436-4447

A refined specific‐gauge approach was developed to quantify changes over time in hydrological response on 3260 km of the Mississippi River system using long‐term data observed at 67 hydrologic measurement stations. Of these stations, 49 were unrated (stage‐only) stations, for which over 2 000 000 ‘synthetic discharges’ were generated based on measured discharge values at nearby rated stations. The addition of these synthetic discharges nearly tripled the number of stations in the study area for which specific‐gauge analysis could be performed. In order to maintain spatial homogeneity across such a broad study area, discharges were normalized to multiples of mean daily flow (MDF). Specific‐gauge analysis calculates stage changes over time for invariant discharge conditions. Two discharges were analysed: low‐flow and flood conditions at each station. In order to avoid the large errors associated with extrapolation of annual rating curves, a new ‘enhanced interpolation’ technique was developed that calculates continuous specific‐stage time series, even for rare discharges. Thus enhanced, specific‐gauge analysis is a useful reconnaissance tool for detecting geomorphic and hydrologic trends over time. Results show that on the Middle Mississippi River and Lower Missouri River, flood stages increased at all stations in spite of widespread incision of the river bed. On the Lower Mississippi River, both low‐flow and flood stages decreased, mainly the result of artificial meander cutoffs in the late 1920s and 1930s, except downstream of Natchez, MS, where net aggradation was observed. On the Upper Mississippi River, the specific‐gauge trends were dominated by emplacement of navigational dams and impoundment of slackwater pools. On all four river reaches, these results document hydrologic responses to the different engineering toolkits used on the different portions of the Mississippi River system during the past 75–150 years. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献