The Second Nature of Geography: Hartshorne as Humanist*     

Craig S. Campbell 《The Professional geographer》1994,46(4):411-417

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A three dimensional boundary fitted coordinate hydrodynamic model,part I: Development and testing     

J. Craig Swanson  Malcolm Spaulding  Jan-Petter Mathisen  Øystein O. Jenssen 《Ocean Dynamics》1989,42(3-6):169-186

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The influence of vertical stratification on continental shelf circulation     

Peter D. Craig 《Ocean Dynamics》1989,42(3-6):215-230

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Submarine exhalative gold mineralization at the London-Virginia Mine,Buckingham County,Virginia     

Margaret Mangan  J. R. Craig  J. D. Rimstidt 《Mineralium Deposita》1984,19(3):227-236

Low grade submarine exhalative gold mineralization occurs at the London-Virginia deposit in central Virginia Piedmont. The deposit consists of a series of localized but conformable units — basal garnetiferous-chlorite schist, magnetite schist, quartz-muscovite schist, ferruginous quartzite, and chlorite-biotite schist — which represent a mixture of submarine epiclastic volcanic debris and exhalative chemical sediments. Finely disseminated gold occurs dispersed with minor amounts of pyrite, sphalerite, chalcopyrite, galena, and tennantite in the ferruginous quartzite and quartz-muscovite schist. The deposit is believed to have formed by processes analogous to those currently active in the Atlantis II Deep of the Red Sea. Silicarich, hypersaline brines discharged through fractures in the sea floor and ponded in a local basin. Epiosodic influx of clastic debris and extensive deposition of hydrothermal silica diluted the concentration of sulfides and gold to produce a low-grade, siliceous mineralized zone. Emanation from the exhalative vent was terminated when the basin was capped by a lava flow. Subsequent regional greenschist grade metamorphism has recrystallized the silica into a granular quartzite and produced minor remobilization of the gold and sulfides.  相似文献   

Introduction     

H. Craig 《Earth and Planetary Science Letters》1984,71(2):354-355

We have recently measured the concentrations of W and Mo in a large number of terrestrial samples using a new neutron activation analysis method and from these data we have estimated the abundance of these elements in the mantle. The new Mo mantle abundance of 59 ppb is much lower, the W mantle abundance of 10 ppb is somewhat lower than previous estimates. The concentrations of W in some ocean floor basalts are much lower than previously reported. The good correlation of W with U confirms the highly incompatible behavior of W and the good correlation of Mo with Nd indicates a moderately incompatible nature for Mo.The new data on W and Mo provide important constraints regarding the possible mechanisms of core formation and accretion because W and Mo are refractory elements under reducing conditions which would have accreted in the Earth in chondritic proportions, unaffected by volatility. The Mo/W ratio of 5.9 in the mantle is less than a factor of two lower than the chondritic ratio of 9.8. The ratio of Mo to W is a sensitive indicator for metal or sulfide fractionation, because Mo is more siderophile and more chalcophile than W. This tightly limits the amount of metal or sulfide segregation from the mantle to less than 0.1% since the end of accretion. The data for the moderately siderophile elements Mo, W, Co and Ni suggest that core formation in the Earth was essentially complete after 85–95% of the Earth had accreted.  相似文献   

Sources of magnetic susceptibility in a slate     

Graham Borradaile  John Mothersill  Don Tarling  Craig Alford 《Earth and Planetary Science Letters》1986,76(3-4)

Magnetic susceptibility and its anisotropy in the Borrowdale Volcanic slates at Kentmere in the English Lake District are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite-ripidolite composition. In units of 10⁻⁶ cgs/g, the principal susceptibilities for the slates are 9.61; 9.42; 8.69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11.57; 11.22 and 9.15. Because the magnetic susceptibility is carried by a tightly packed, matrix-forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility.  相似文献   

GEOSECS AtlanticSi profiles     

B.L.K. Somayajulu  R. Rengarajan  D. Lal  R.F. Weiss  H. Craig 《Earth and Planetary Science Letters》1987,85(4)

Measurements of five cosmogenic³²Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO₂ extracted range from 2 to 54 g; the amounts of water from which SiO₂ was extracted range between 540 kg and 270, 000 kg. In additon, SiO₂ recovered from four surface particulate composites (64°N to 61°S) were also analyzed for³²Si.³²Si measurements were made by milking and counting the daughter activity, ³²P. The net³²P activities range from 0.7 to 6.8 cph; typical errors in measurements of the³²P activities are 20–30%.The³²Si concentrations vary from 0.6 dpm/10⁶ kg of water in the North Atlantic surface waters to 235 dpm/10⁶ kg at 400 m depth in the circumpolar waters. The vertical profiles of³²Si at the five Atlantic stations approximately follow the Si profiles but the depth gradients are different. This would be expected also considering the in-situ release mechanisms due to dissolution and advection/diffusion from the bottom waters. Except for the circumpolar station 89, where the Si and³²Si profiles show the effect of marked vertical mixing (nearly depth independent profiles), the profiles show the following features: (1) specific activities of³²Si (³²Si/SiO₂ ratios) are lowest at intermediate depths, and (2) on an average the surface specific activities are higher, by 2–4 times, than the bottom water values. These data are consistent with generation of the highest specific activity³²Si waters at the surface, where Si concentrations are lowest and precipitation adds cosmogenic³²Si scavenged from the troposphere. Rapid removal of biogenic silica to the water-sediment interface, without much dissolution during transit, leads to the second regime of high³²Si specific activities.The³²Si inventories in the water column in the latitude belt 27°N-27°S are in the range (1–1.4) × 10⁻² dpm³²Si/cm², which is consistent with the expected fallout of cosmogenic³²Si. However, the³²Si column inventories south of 40°S are higher by a factor of 5–7, whereas the corresponding Si inventories increase by only a factor of 3. This excess³²Si in the Southern Ocean cannot be explained by direct fallout from the stratosphere or by melting of Antarctic snow and ice. Instead, this excess is maintained primarily by the southward deep-water transport of³²Si dissolved from sinking particulates.  相似文献   

Helium isotopes and mantle volatiles in Loihi Seamount and Hawaiian Island basalts and xenoliths     

W. Rison  H. Craig 《Earth and Planetary Science Letters》1983

We examine in this paper the use of helium isotope ratios for the study of hotspot volcanism along age-progressive island volcanic chains. The Hawaiian Islands are the original “high ³He” hotspot, with ³He/⁴He ratios as high as 32 × the atmospheric ratio; in the Pacific they stand out against the surrounding sea of MORB (rather uniformly 8 × atmospheric) which fills the entire Pacific with the exception of the Macdonald-Mehetia-Samoa axis in the South Pacific. The recent availability of a variety of alkalic and tholeiitic glasses from the U.S. Geological Survey and our own dredge hauls has prompted us to look first at isotopic variability within a single fresh and new volcano which is probably sitting directly atop a mantle plume. Thus we have looked in some detail at the total helium in glass pillow rims, at He in the enclosed vesicles, and at He in the glass itself, in both tholeiitic and alkalic lavas, and also at helium in associated phenocrysts and xenoliths. The measured ³He/⁴He ratios range from atmospheric to 30 × atmospheric, but we see clear evidence that the highly vesiculated lavas suffer exchange of He between the thin glass walls of vesicles and ambient seawater, so that we observe a post-eruptive isotopic disequilibrium between glass and gas phases. The primary effect is the very large loss of initial He content during eruptive vesiculation, which results in quite large isotopic effects from small additions of ambient He (of the order of 0.02 μcc He per gram of basalt; corresponding to a “water/rock ratio” of 0.5). Phenocrystic He in olivines verifies that the gas-phase He is not affected by vesicularities up to about 5%. Alkali basalt He appears to be independent of vesicularity up to values as high as 35%; this He is somewhat lower in ³He/⁴He ratio, but matches precisely the associated xenolithic He. However, from the present data we cannot exclude the possibility that diffusive exchange with seawater has affected the He ratio in alkalic vesicles.On the large scale, along the 10% of the Hawaiian chain available for subaerial sampling, we find high ³He/⁴He ratios (24 × atmospheric) in 5.5 × 10⁶-year-old lavas on Kauai. Maximum values of the ratio so far observed are in the pre-erosional Kula basalts on Maui, confirming the previous results of Kaneoka and Takaoka. Hawaii, where these high values were first observed is now seen to range from MORB ratios at Mauna Loa to only 15 × R_A at Kilauea fumaroles. Most xenolithic He so far measured is MORB He, but Loihi xenoliths have high values and are quite different in this respect. Finally, we discuss also the hydrogen and carbon isotope results on Loihi lavas, and show that these elements resemble MORB and appear not to show a distinctive plume signature.  相似文献   

²¹⁰Pb in the Pacific: the GEOSECS measurements of particulate and dissolved concentrations     

Y. Chung  H. Craig 《Earth and Planetary Science Letters》1983,65(2):406-432

We report here on particulate and dissolved²¹⁰Pb profiles at 16 stations, and on total²¹⁰Pb profiles at 3 stations, all occupied during the Pacific GEOSECS expedition. Comparison with measurements at Yale on GEOSECS library samples indicates that during separation of particulate lead from dissolved lead, our filtered water samples suffered some loss of²¹⁰Pb in the filtration system; this effect appears to have reduced the dissolved²¹⁰Pb activities by ～ 20% in stations where the water was filtered. However, for these first Pacific data on the²¹⁰Pb distribution between the two phases, this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved²¹⁰Pb distributions.The dissolved²¹⁰Pb profiles in general vary geographically, following the²²⁶Ra profiles. In deep water,²²⁶Ra increases northward and eastward from the southwest Pacific, from ～ 22dpm/100kg, to over 40 dpm/100 kg in the northeast Pacific. Our dissolved²¹⁰Pb profiles show a similar increase in deep water, varying from about 10 to 20 dpm/100 kg along this line, and are commonly characterized by a mid-depth maximum. This²¹⁰Pb maximum reflects the mid-depth²²⁶Ra maximum of the Pacific Deep Water observed along the western boundary current.In surface water at low latitudes there is a significant²¹⁰Pb flux from the atmosphere, which produces a²¹⁰Pb/²²⁶Ra activity ratio generally greater than unity. This flux penetrates as deep as 600 m, as indicated by an “induced”²¹⁰Pb minimum caused by the surface maximum. The surface water²¹⁰Pb excess decreases toward high southern latitudes and vanishes in the Circumpolar region.The particulate²¹⁰Pb profiles show a general increase with depth, from ～ 0.3dpm/100kg in subsurface water to ～ 1.5dpm/100kg in bottom water, with or without a mid-depth maximum that reflects the²²⁶Ra or dissolved²¹⁰Pb maximum. The particulate²¹⁰Pb normally comprises about 2% of the total²¹⁰Pb in subsurface water, and this fraction increases to about 10% near the bottom. As the filtration loss is not taken into account, the fraction of particulate²¹⁰Pb quoted here is an upper limit. Since the particulate matter concentrations are quite uniform in the water column below a few hundred meters, the²¹⁰Pb activity of the particulate matter also increases with depth. The particulate matter has a²¹⁰Pb concentration of ～ 100dpm/g in subsurface water, but the concentration increases to ～ 500dpm/g or more toward the bottom. This indicates that there is a cumulative adsorption of Pb onto the suspended particles as they are sinking through the water column.  相似文献   

Total mercury,methyl mercury and sulphide in river carron sediments     

P.J. Craig  P.A. Moreton 《Marine pollution bulletin》1983,14(11):408-411

Total mercury, methyl mercury and sulphide contents of River Carron sediments (Lothian, Scotland) have been determined. Total mercury concentrations are comparable to other mercury polluted estuaries in the UK, but the methyl mercury values for low-sulphide Carron sediments are generally higher. It has been found that methyl mercury levels are initially in direct proportion to the sulphide concentrations of the sediments but beyond sulphide concentrations of 1.8 mg g^?1 the methyl mercury levels decline sharply.  相似文献