The problematic past     

Elizabeth Griffin 《Astronomy& Geophysics》2001,42(2):2.25-2.26

Elizabeth Griffin argues for international action to rescue astronomical observations from decay and obsolescence.  相似文献   

Empirical predictors of annual bed load travel distance,and implications for salmonid habitat restoration and protection     

Timothy J. Beechie 《地球表面变化过程与地形》2001,26(9):1025-1034

Measurements of annual travel distance (L_b) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r² = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce L_b. Longer cumulative duration of bed load transporting flows in a year appears to increase L_b. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with L_b (r² ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to L_b (r² < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short‐term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.  相似文献   

The role of H2O during crystallization of primitive arc magmas under uppermost mantle conditions and genesis of igneous pyroxenites: an experimental study   总被引：2，自引：4，他引：2  

Othmar Müntener  Peter B. Kelemen  Timothy L. Grove 《Contributions to Mineralogy and Petrology》2001,141(6):643-658

Exposed, subduction-related magmatic arcs commonly include sections of ultramafic plutonic rocks that are composed of dunite, wehrlite, and pyroxenite. In this experimental study we examined the effects of variable H₂O concentration on the phase proportions and compositions of igneous pyroxenites and related ultramafic plutonic rocks. Igneous crystallization experiments simulated natural, arc magma compositions at 1.2 GPa, corresponding to conditions of the arc lower crust. Increasing H₂O concentration in the liquid changes the crystallization sequence. Low H₂O concentration in the liquid stabilizes plagioclase earlier than garnet and amphibole while derivative liquids remain quartz normative. Higher H₂O contents (>3%) suppress plagioclase and lead to crystallization of amphibole and garnet thereby producing derivative corundum normative andesite liquids. The experiments show that alumina in the liquid correlates positively with Al in pyroxene, as long as no major aluminous phase crystallizes. Extrapolation of this correlation to natural pyroxenites in the Talkeetna and Kohistan arc sections indicates that clinopyroxenes with low Ca-Tschermaks component represent near-liquidus phases of primitive, Si-rich hydrous magmas. Density calculations on the residual solid assemblages indicate that ultramafic plutonic rocks are always denser than upper mantle rocks in the order of 0.05 to 0.20 g/cm³. The combination of high pressure and high H₂O concentration in the liquid suppresses plagioclase crystallization, so that ultramafic plutonic rocks form over a significant proportion of the crystallization interval (up to 50% crystallization of ultramafic rocks from initial, mantle-derived liquids). This suggests that in subduction-related magmatic arcs the seismic Moho might be shallower than the petrologic crust/mantle transition. It is therefore possible that calculations based on seismic data have overestimated the normative plagioclase content (e.g., SiO₂, Al₂O₃) of igneous crust in arcs.  相似文献   

The Dublin Gulch intrusion-hosted gold deposit, Tombstone plutonic suite, Yukon Territory, Canada   总被引：1，自引：0，他引：1  

Terri L. Maloof  Timothy Baker  John F. Thompson 《Mineralium Deposita》2001,36(6):583-593

The Dublin Gulch intrusion is a member of the Tombstone plutonic suite, a linear belt of middle Cretaceous intrusions that extend across the Yukon Territory. Like many of the intrusions in this suite, the Dublin Gulch intrusion is associated with several different zones of gold and tungsten mineralization, within and immediately adjacent to the intrusion. The Eagle zone (50.3 Mt @ 0.93 g/t gold), located in the southwestern part of the Dublin Gulch intrusion, hosts the most significant concentration of gold in the area. The gold occurs in a broadly east-west-striking, steeply south-dipping series of sheeted veins. The veins consist of early quartz-scheelite-pyrrhotite-pyrite-arsenopyrite, and are associated with K-feldspar-albite alteration envelopes. These grade out to and are overprinted by sericite-carbonate-chlorite alteration. The same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold. The gold occurs with molybdenite, lead-bismuth-antimony sulfosalts, galena, and bismuthinite. Gold correlates strongly with bismuth (r²=0.9), a relationship common to several intrusion-related gold deposits, but has a poor correlation with all other elements. Tungsten and molybdenum have a weak inter-element correlation (r²=0.55) and paragenetically pre-date the majority of gold precipitation. Lead, zinc, copper, silver, antimony, and arsenic have moderate to strong inter-element correlations (0.58 to 0.93). The change from tungsten-bearing mineralization through to gold-bismuth-rich ores with elevated syn- to post-ore lead, zinc, copper, silver, antimony, and arsenic can be grossly correlated with a change in hydrothermal fluid composition. Early scheelite-bearing quartz contains primary CO₂-rich fluid inclusions, which are post-dated by secondary inclusions with higher salinities (up to 15 wt% NaCl equiv.) and less CO₂. These latter inclusions are interpreted to coincide with the later gold-bismuth and base metal mineralization. The favored genetic model is one in which early CO₂-rich fluids exsolved from a magma with an initially high CO₂ content, but progressively became more saline and H₂O-rich as the system evolved.  相似文献   

Aircraft wind measurement considering lift-induced upwash     

Timothy L. Crawford  Ronald J. Dobosy  Edward J. Dumas 《Boundary-Layer Meteorology》1996,80(1-2):79-94

Flow distortion is a universal consideration in the measurement of wind. Usually the distortion results from deflection of the flow by the support. Instruments mounted on airplanes, however, experience an additional deflection associated with lift, which changes rapidly and continuously during flight. In front of the airplane, this deflection appears as upwash. Characteristic upwash contamination ranges from 0.5 to 2.5 m s^-1, depending on wing loading, flight speed, and forward distance from the wing to the measurement location. On pressure-radome installations the distance from the wing is usually small and the potential for upwash contamination large. Sensors mounted at the end of long probes attached to smaller airplanes with light wing loading are less susceptible to upwash contamination. Since wing loading also depends on the local vertical wind velocity the upwash velocity is directly correlated with vertical wind velocity. Generally, empirical corrections are derived from flight tests. We develop a simple method from principles of aerodynamics which explains these corrections in terms of upwash. The applicability of our approach to moderate upwash is demonstrated with data collected from the NOAA Long-EZ research airplane. More severe upwash conditions require a more sophisticated correction beyond the scope of this paper, but basically derived from the same principles.Oak Ridge Associated Universities, assigned to NOAA/ATDD  相似文献   

Laboratory Data Reporting Standards: We Need Them Now     

Timothy M. Cosgrave 《Ground Water Monitoring & Remediation》1992,12(3):5-6

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Preface     

Thomas D. Demchuk  Jane C. Shearer  Timothy A. Moore 《International Journal of Coal Geology》1995,28(2-4)

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Parageneses of garnet in granulite-facies rocks,Lofoten-Vesteraalen,Norway     

W. L. Griffin  K. S. Heier 《Contributions to Mineralogy and Petrology》1969,23(2):89-116

Garnet occurs widely as a secondary mineral in the granulite-facies rocks of the Lofoten-Vesteraalen islands of North Norway. The garnet-forming reactions may be inferred from the resulting textures and are interpreted as being retrograde reactions. Microprobe analyses show that garnets with high proportions of CaO and MgO occur in coronas around olivine grains in anorthosites, whereas the most iron-rich garnets formed by reaction between plagioclase and the very iron-rich pyroxenes of some monzonitic (mangeritic) rocks. Garnets ranging in composition between these extremes formed by reactions involving biotite, plagioclase and magnetite. Textural features indicate that these reactions have been induced by oxidation of the biotite; the liberated water has converted the pyroxenes to amphibole. The net effect of the reactions is to transform the granulite-facies assemblages to amphibolite-facies assemblages.The secondary garnet is nearly ubiquitous in the granulites of the outer Lofoten islands, which may show no other signs of retrogression. On Langöy in Vesteraalen garnet occurs only within a zone of strongly retrograded gneisses. Differences in bulk composition do not satisfactorily explain the distribution of secondary garnet. This distribution, and the observed oxidation textures, imply widespread penetration of the Lofoten granulites by a transient oxidizing fluid. On Langöy these fluids apparently affected only the narrow retrograded zone. The model suggests that the 1700 to 1800 m.y. Rb/Sr date obtained by Heier and Compston (1969) for the Lofoten granulites represents the time of oxidation, whereas the 2800 m.y. date for the Langöy granulites represents the original granulite-facies metamorphism.Publication number 3 in the Norwegian Geotraverse Project.  相似文献   

Lherzolite nodules from the Fen alkaline complex,Norway     

W. L. Griffin 《Contributions to Mineralogy and Petrology》1973,38(2):135-146

The alkaline ultrabasic rooks (damkjernite) of the Fen alkaline complex contain abundant rounded inclusions of spinel lherzolite, closely similar in composition and mineralogy to the nodules found in many undersaturated basaltic rocks. Clinopyroxene compositions indicate crystallization at P=10–13 KB, T=1200–1250° C. A model involving partial melting in a rising diapir of mantle peridotite allows interpretation of the nodules either as mantle fragments or as cognate cumulates, and suggests that crustal thinning in the Oslo area possibly began as early as 500–600 m.y. ago. The presence of the nodules indicates that the damkjernite did not pause for intracrustal differentiation during its rapid ascent to the surface. The crustal contamination suggested by recent Sr-isotope studies may have occurred during differentiation at the base of the continental crust.Contribution No. 62 in The Norwegian Geotraverse Project.  相似文献   

Setting the stage: ultralumnous galaxies in a cosmological context     

Timothy M. Heckman 《Astrophysics and Space Science》1999,266(1-2):3-10

I will try to put the ultraluminous galaxy phenomenoninto a broad cosmological context. Viewed from this perspective,the significance of ultraluminous galaxies and the `starburstvs. monster' debate becomes clear. Ultraluminous galaxiesare fascinating in their own right, allow detailedstudy of the processes by which massive spheroids were builtand the IGM was heated and polluted, and resemble the mostluminous and dustiest galaxies at high-redshift. Ultraluminous galaxieswere apparentlyfar more common at z 3 than today. Recentinventories in the local universe of the cumulative effect of nuclear burning(metal production)and of monster-feeding (compact dark objects in galactic nuclei)imply that either stars ormonsters could have generated the observed far-IR cosmic background.The starburst vs. monster debate has global, as well as localimportance.  相似文献