Origin of mineral chemical stratification in the mantle section of the Table Mountain massif (Bay of Islands Ophiolite, Newfoundland, Canada)   总被引：3，自引：0，他引：3  

Gü  nter Suhr  Paul T. Robinson 《Lithos》1994,31(3-4):81-102

Mineral chemical data have been collected from the 6 km thick mantle section of the Table Mountain massif (Bay of Islands Ophiolite Complex, Newfoundland). The samples chosen represent the geochemical background, i.e. exclude samples from the vicinity of bands, dykes and pods of dunites and pyroxenites within the host harzburgites and (rare) lherzolites. Three large mineral-chemical domains can be distinguished as a function of depth below the crustal gabbros. The intermediate mantle section (2–5 km beneath the gabbros) has a very depleted geochemical pattern with Cr# [100Cr/(Cr + Al)] in spinel > 44, low Ti. The basal kilometer of the mantle section shows a steep geochemical gradient towards less depleted mineral chemistries (Cr# as low as 10). Both the intermediate and basal mantle rocks fit into a progressive partial melting trend. The top of the mantle section (0–2 km below the gabbros) shows Cr# between 30 and 44, but also higher Ti and ferric iron in spinel, and Na in clinopyroxene. Microstructural evidence for melt-related clinopyroxene is locally preserved and, in one area, plagioclase lherzolites occur. The topmost mantle section is considered to have been affected by melt infiltration. The geochemical variation is larger than elsewhere, suggesting that melt-infiltration, or at least the process of trapping of melt, was heterogeneous. In most melt-infiltrated harzburgites, plagioclase is absent. Other peridotites show good microstructural evidence for melt-infiltration but little chemical evidence to substantiate it. Both features are discussed and can be explained by a variety of processes demonstrating the complexity of melt-infiltration.  相似文献   

Employment Survey of Geography Graduates from New Zealand Universities     

Chris Cocklin  James Robinson 《New Zealand geographer》1994,50(1):53-55

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Sulphur and sulphate-oxygen isotopes and the origin of the silvermines deposits,Ireland     

P. G. Coomer  B. W. Robinson 《Mineralium Deposita》1976,11(2):155-169

New sulphur and sulphate-oxygen isotope measurements for the main discordant and stratiform lead-zinc-barite orebodies at Silvermines Co. Tipperary, allow reappraisal of previously offered differing interpretations (Graham, 1970; Greig et al., 1971) of the bearing of sulphur isotopes on the genesis of this important Irish deposit. The following aspects of the data are confirmed: barite ³⁴ S-values range from 17–21, similar to lower Carboniferous seawater sulphate: stratiform sulphide lens pyrites have ³⁴ S-values ranging from –13 to –36; vein sulphide ³⁴ S-values range from –8 to 4; sulphide ³⁴ S-values increase upwards and outwards respectively in the related discordant and stratiform G orebodies; galena-sphalerite isotope palaeotemperatures are not too consistent, ranging from 40 to 430°C (using the calibration of Czamanske and Rye (1974). New facts are as follows: barite ¹⁸O-values range from –13 to –17, stratiform barites ranging from 13 to 14.5; sulphides separated from a single stratiform ore lens hand specimen usually have ³⁴ S_sl > ³⁴ S_ga > ³⁴ S_py; the outward decrease in ³⁴ S-values in the stratiform G orebody is confined to the first few hundred feet only; pyrite ³⁴ S-values progressively increase downwards through one stratiform sulphide orebody; yet variations of 13 occur within a single colloform pyrite structure from another stratiform orebody. It is concluded that there were at least two sources of sulphur, seawater sulphate and deep-seated sulphur. The former was the dominant source of all sulphate and, via biogenic reduction, of the sulphur in the bulk of the stratiform sulphide. The latter was the source of the sulphur in the vein sulphides. There was minimal isotopic interaction between the cool seawater sulphate and the warm unwelling ore fluid sulphur species, even though the latter precipitated under near isotopic equilibrium conditions when the temperature dropped and/or the pH and Eh increased. The lack of isotopic equilibrium between pyrite and ore sulphides in the stratiform ore lenses may result from the latter having precipitated slightly later than the former because of solubility relationships. Overall the present isotopic evidence supports considerable geological evidence favoring a syngenetic origin for the stratiform Silvermines orebodies.  相似文献   

Book review     

G. D. Robinson 《Boundary-Layer Meteorology》1977,12(4):511-511

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The effect of surface texture on the determination of the surface hardness of rock using the schmidt hammer     

R. B. G. Williams  D. A. Robinson 《地球表面变化过程与地形》1983,8(3):289-292

The Schmidt hammer is employed by geomorphologists as a convenient field instrument for measuring the hardness of rock surfaces. Field trials indicate that the readings obtained are a function of not only the hardness of the surfaces but also their texture. Smooth planar surfaces give much higher readings than rough or irregular surfaces. This makes interpretation of the results particularly difficult when the hammer is used to measure the hardness of natural rock surfaces that have been roughened by weathering.  相似文献   

Geological walks around the city of London—Royal Exchange to Aldgate     

Eric Robinson 《Proceedings of the Geologists' Association. Geologists' Association》1982,93(3):225-246

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The origin, deposition, and alteration of the organic material in Green River shale     

W. E. Robinson 《Organic Geochemistry》1979,1(4):205-218

Characteristics of the organic material in Green River Formation shale suggest that this material was derived from algae that grew in ancient Eocene lakes. The basin depressions for these nonmarine lakes were formed by the uplifting of the Rocky Mountain ranges. Large quantities of soluble salts flowed into these basins from the mountain streams, increasing the salinity of the lake waters until they became chemically stratified. In the upper, relatively fresh-water section of the lakes, abundant quantities of microscopic algae and other biota grew. Lesser amounts of terrestrial plant life remains were supplied in the form of wind- or water-borne spores and in the form of water-soluble organic materials entering the in-flowing waters. The lower section of the lake waters became highly reducing and stagnant because of lack of seasonal oxidative turnovers, thus providing ideal conditions for the accumulation and preservation of the organic debris from the lake biota.Precipitation of mineral carbonates and silicates from the highly saline waters provided most of the minerals that were co-deposited with the organic matter. Carbon dioxide, which evolved from the aquatic plant life, probably influenced mineral carbonate precipitation. During the life span of a few million of years the characteristics of the lake waters varied considerably and had significant effect upon the composition of both the inorganic and organic constituents of the Green River shale.Sixty to seventy-five core samples from each of three basins of the Green River Formation were analyzed for changes in both the organic and inorganic constituents. Considerable differences in the organic components of the soluble bitumen and of the insoluble kerogen were evident. Some of these differences appeared to be related to depth of burial and some to source material and the environment of the lake waters. Compositional differences relative to lithologic differences in the sediments of the three basins were found.  相似文献   

A note on convection in the earth's mantle     

J.L. Robinson 《Earth and Planetary Science Letters》1974,21(2):190-193

In the present note a boundary-layer model of thermal convection throughout the mantle is outlined. It is shown that recent criticisms of mantle-wide convection by A.E. Ringwood do not apply to this model. The phase transitions discussed by Ringwood are consistent with the model, and in fact provide an additional driving force for the convective motion. It is further noted that the model offers explanations of the core-mantle coupling hypothesized by R. Hide from consideration of correlations between the earth's magnetic and gravity fields, and of the appearance in several parts of the world of pairs of trenches separated by distances of the order of 2000 km.  相似文献   

Meridional eddy flux of enthalpy in the Southern Hemisphere during the IGY     

John Ball Robinson Jr. 《Pure and Applied Geophysics》1970,80(1):319-334

Summary From meteorological IGY data for the calendar year 1958, the mean meridional eddy transport of enthalpy was evaluated for the Southern Hemisphere. Levels chosen for the study were 1000, 850, 700, 500, 400, 300, 200, 150 and 100 mb. Data from 84 Southern Hemisphere and 25 equatorial Northern Hemisphere stations were used. Yearly mean quantities related to meridional eddy enthalpy flux were computed and analyzed.It was found that around 40° S there is a double-maximum zone of poleward, meridional, transient eddy enthalpy flux, the stronger transport occurring at 850 mb, and the weaker near 200 mb. The countergradient transient eddy flux regions in the low latitude mid-troposphere and in the middle and upper latitude lower stratosphere, found in previous Northern Hemisphere investigations, were observed to exist in the Southern Hemisphere also. The standing eddy heat transport, as expected, was very weak except at high latitudes where Antarctic continentality effected a large double-maximum poleward flux centered near the surface and in the lower stratosphere. The total vertically integrated enthalpy transport by the eddies was found to be poleward everywhere, reaching a maximum between 35° and 40° S.  相似文献   

Diatom evidence on Wisconsin and Holocene events in the Bering Sea     

Constance Sancetta  Stephen W. Robinson 《Quaternary Research》1983,20(2):232-245

Previous work on surface (modern) sediments has defined diatom species which appear to be good indicators of various oceanographic/ecologic conditions in the North Pacific Ocean and marginal seas. Three long cores from the eastern and northern sides of the Aleutian Basin show changes in species assemblage which can be interpreted in terms of changes in the ocean environment during the last glaciation (Wisconsin) and the Holocene. The early and late Wisconsin maxima were times of prolonged annual sea-ice cover and a short cool period of phytoplankton productivity during the ice-free season. The middle Wisconsin interstade, at least in the southern Bering Sea, had greater seasonal contrast than today, with some winter sea-ice cover, an intensified temperature minimum, and high spring productivity. Variations in clastic and reworked fossil material imply varying degrees of transport to the basin by Alaskan rivers. The results of Jousé from the central Bering Sea generally correspond with those presented here, although there are problems with direct comparison.  相似文献