On the mechanical interaction between a growing porphyroblast and its surrounding matrix     

C. C. Ferguson  P. K. Harvey  G. E. Lloyd 《Contributions to Mineralogy and Petrology》1981,75(4):339-352

Whether or not a growing porphyroblast can displace its surrounding matrix is an important but contentious issue affecting the interpretation of metamorphic textures. As an alternative to treating the problem in terms of force of crystallization, this paper examines the mechanics of porphyroblast-matrix interaction using a different and much simpler conceptual framework. New microstructural evidence for matrix displacement is then presented and analysed in detail. This evidence, from a hornfelsed metagreywacke, consists of dome-shaped accumulations of muscovite and graphite, each dome being attached to (and concave towards) a rhombdodecahedral face of a garnet porphyroblast. Muscovite within the domes shows a dimensional preferred orientation subparallel to the dome outlines while, in the matrix away from the domes, there is no preferred orientation.Our model for the origin of the mica domes envisages muscovite and graphite being swept ahead of, and mechanically accumulated onto, the growing garnet faces as they advance through the matrix. Rigorous testing of this model provides strong evidential support for matrix displacement by growing porphyroblasts. A new analysis is provided of the conditions under which matrix grains are included or displaced by porphyroblasts. It is concluded that matrix grain displacement may be very common, although the special combination of circumstances necessary to produce a diagnostic microstructural pattern probably occurs very rarely.  相似文献   

Dating of post-glacial landforms in the central howgills     

A. M. Harvey  F. Oldfield  A. F. Baron  G. W. Pearson 《地球表面变化过程与地形》1981,6(5):401-412

Little is known of Holocene landform development in Upland Britain. This paper describes a site at Middle Langdale in the Howgill Fells of Cumbria where large, but now stabilized and inactive gullies cut through periglacial material. At the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor. On these sediments and buried by the debris cones is a well-developed organic soil from which two ¹⁴C dates have been obtained in an attempt to estimate the age range of the soil. These dates range from 2580±55 years BP for the fine particulate fraction from the base of the organic horizon to 940±95 years BP for fossil rootlets from the uppermost organic layer, immediately below the overlying debris cones. The pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a Juncus marsh with birch, alder and hazel nearby. The pollen, from the surrounding upland area suggests woodland on the valley sides, dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present. The magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil. The evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation, although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period. The evidence then points to major geomorphological changes; a wave of soil erosion, gully development and debris cone deposition, perhaps following the Scandinavian introduction of sheep farming in the tenth century A.D.  相似文献   

Uptake of radioactivity by marine sediments and implications for monitoring metal pollutants     

J.A Hetherington  B.R Harvey 《Marine pollution bulletin》1978,9(4):102-106

The value of studying artificially-produced radionuclides in the marine environment is discussed in the wider context of monitoring sediments for other metal pollutants. Differences in the dispersion of selected radionuclides discharged from the same known source are used to illustrate the sort of changes in phase or speciation which must occur with other metal pollutants, but which cannot be demonstrated directly because of the multiplicity of sources. Various chemical and physical procedures are discussed which can be applied to a study of heavy metal associations with marine sediments, as are questions such as the existence, or otherwise, of mechanisms for the slow release of adsorbed material from the buried sediment back into the water column. Suggestions are made as to how radionuclide studies may be helpful in answering questions such as these, which are considered to be vital for the meaningful interpretation of sediment analyses.  相似文献   

Compaction of Argillaceous Sediments (Developments in Sedimentology 16): H.H. Rieke III and G.V. Chilingarian. Elsevier, Amsterdam, 1974, 424 pp., Dfl. 85.00     

Ralph E. Grim 《Journal of Geochemical Exploration》1975,4(3):389-390

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A study of the Rima Sirsalis lunar magnetic anomaly     

L.J. Srnka  J.L. Hoyt  J.V.S. Harvey  J.E. McCoy 《Physics of the Earth and Planetary Interiors》1979,20(2-4):281-290

The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10⁻³ G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10⁻⁵ – 10⁻⁴ G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length.  相似文献   

An aircraft study of turbulence dissipation rate and temperature structure function in the unstable marine atmospheric boundary layer     

C. W. Fairall  Ralph Markson  G. E. Schacher  K. L. Davidson 《Boundary-Layer Meteorology》1980,19(4):453-469

The dissipation rate of turbulent kinetic energy, , and the temperature structure function parameter, C _T ², have been measured over water from the near surface (Z = 3 m) to the top of the boundary layer. The near surface values of and C _T ² were used to calculate the velocity and temperature Monin-Obukhov scaling parameters u _* and T _*. The data collected during unstable lapse rates were used to evaluate the feasibility of extrapolating the values of and C _T ² as a function of height with empirical scaling formulae. The dissipation rate scaling formula of Wyngaard et al. (l971 a) gave a good fit to an average of the data for Z < 0.8 Z _i. In the surface layer the scaling formula of Wyngaard et al. (1971b) disagreed with the C _T ² values by as much as 50%. This disagreement is due to an unexpected reduction in the measured values of C _T ² forZ < 30 m. At this point it is not clear if the discrepancy is a unique property of the marine boundary layer or if it is simply some unknown instrumental or analytical problem. The mixed layer scaling results were similar to the overland results of Kaimal et al. (1976).  相似文献   

Depositional environments of some Pleistocene coastal terrace deposits,southwestern Oregon—case history of a progradational beach and dune sequence     

Ralph E. Hunter 《Sedimentary Geology》1980,27(4):241-262

Pleistocene coastal terrace deposits exposed in sea cliffs near Gold Beach, Oregon can be divided into four stratigraphic units: a basal gravelly unit and three overlying sandy units, each with mud beds, a paleosol, or the modern soil in its uppermost part. The gravelly unit consists of gravel and sand in its lower part, sand, in part pebbly or cobbly, in its middle part, and mud and sand in its upper part. Black sand and transported pieces of wood are common in the middle part of the unit, and wood is common in the mud. This unit is interpreted as a progradational deposit including environments ranging from lower forebeach at the base to backbeach flats and streams at the top.The main sandy parts of the sandy units are made up of a crossbedded sand facies, the dominant structure in which is medium-scale crossbedding, and an irregularly bedded sand facies, which is locally pebbly and is dominated by scour-and-fill structures. Deciding between shallow marine and eolian interpretations of the sandy units proved exceptionally difficult until modern analogues were found in the fine details of the internal structures. Largely on the basis of such structural details, the crossbedded sand facies is interpreted as the product of small eolian dunes, and the irregularly bedded sand facies is interpreted as deposits of interdune ephemeral streams, ephemeral ponds, and wet to dry subaerial flats. The mud beds and paleosols at the tops of the sandy units represent times of temporary stabilization of the dune field.  相似文献   

Letter to the Editor     

Ralph L. Seiler 《Ground water》1998,36(5):710-710

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Stranded tar on Florida beaches: September 1979–October 1980     

G.C. Romero  G.R. Harvey  D.K. Atwood 《Marine pollution bulletin》1981,12(8):280-284

Amounts of tar stranded on Florida beaches were determined periodically over one year (September 1979–October 1980). Results show that tar fouling of southeast Florida beaches is an order of magnitude greater than the rest of the state. This may result from the extensive ship traffic in the Straits of Florida. There is no evidence that any Florida beaches received increased amounts of tar as a result of the 1979 Ixtoc-1 blowout in the southern Bay of Campeche. There is also no evidence that the amounts of tar on southeast Florida beaches have increased over amounts measured in API studies conducted in 1958 and 1971.  相似文献   

Design of Ground–Water Level Observation–Well Programs     

Ralph C. Heath 《Ground water》1976,14(2):71-77

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