Structure and viscosity of rhyolitic composition melts     

Michael F. Hochella  Gordon E. Brown 《Geochimica et cosmochimica acta》1984,48(12):2631-2640

The average local structure of a rhyolitic composition glass has been determined at 25°C using X-ray radial distribution analysis (RDA) and quasi-crystalline modelling and is best described as similar to that in a stuffed framework composed principally of six-membered rings of Si and Al tetrahedra (basically a stuffed tridymite-like model). Using this model it is possible to calculate a density (2.41 g/cm³) which compares well with the measured density (2.40 g/cm³); a structural model based on four-membered rings (an albite-like model) results in a substantially higher calculated density (2.60 g/cm³). We suggest that the rhyolite glass structural model is appropriate for rhyolitic melts, based on evidence from the recent literature. New viscosity data for an anhydrous rhyolite composition measured between 1200°C and 1500°C are presented and interpreted in terms of our proposed structural model and previous melt structure models for the major normative components of rhyolite. A mechanism for diffusion and viscous flow in framework silicate melts (including rhyolite composition) is proposed on the basis of recent molecular orbital calculations and molecular dynamics simulations of silicate and fluoride melts.  相似文献   

Preface     

Gordon McBean  Erik Rasmussen 《Dynamics of Atmospheres and Oceans》1987,10(4)

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Developments in soil mechanics and foundation engineering vol. 2: Stress–strain modelling of soils,edited by P. K. Banerjee and R. Butterfield,Elsevier Applied Science Publishers, 1985. No. of pages: 280. Price: £36     

S. F. Brown 《地震工程与结构动力学》1986,14(2):323-323

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MINI-MACtm—A new generation dual—Band surveyor     

Ladd  Jonathan W.  Welshe  Robert G.  Brown  Alison  Sturza  Mark 《Journal of Geodesy》1986,60(3):221-228

Summary Litton Divisions presently produce both high accuracy GPS surveyors and low—cost GPS navigation sets. Aero Service'sMACROMETER ^R Interferometric Surveyors, have become the standard against which GPS surveying equipment is measured. Litton Aero Products has developed a highly digitized, low costL ₁,C/A code GPS card set. The integration of these technologies had led to the development of a low-cost, high-precision, GPS survey system which can be configured with or without a codelessL ₂ capability. TheMINI-MAC surveying system is the first member of the new generation of GPS survey systems resulting from this joint development. The system design is described in this paper, and initial survey test results using a prototypeMINI-MAC surveying system are presented.  相似文献   

INDUSTRIAL PHOTOGRAMMETRY: NEW DEVELOPMENTS AND RECENT APPLICATIONS   总被引：3，自引：0，他引：3  

C. S. Fraser  D. C. Brown 《The Photogrammetric Record》1986,12(68):197-217

Over the past decade, photogrammetry has been increasingly applied as a precise three dimensional measuring tool in industrial and engineering works. Analytical photogrammetry is now routinely employed in tasks of measurement as diverse as machine tool inspection and fixture checking, structural deformation monitoring, the provision of control databases to guide industrial robots and the measurement of structures in earth orbit. Traditional photogrammetric techniques and instrumentation are usually inappropriate for industrial work and the development of complete, fully integrated close range photogrammetric systems has recently gained considerable impetus. This paper details some of the significant new developments in industrial photogrammetry, with particular reference to technological advances in the Simultaneous Triangulation and Resection System (STARS) designed by Geodetic Services, Inc. for industrial photograininetry. Practical aspects of industrial measurement are also presented in a review of some of the varying tasks that GSI has carried out in recent years. Emphasis is placed on demonstrating the flexibility, accuracy, reliability and economy of photogrammetry, as well as the progress made in automating this measurement technique.  相似文献   

Dependence of Effective Porosity on Fracture Continuity in Fractured Media     

Matthew J. Gordon 《Ground water》1986,24(4):446-452

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Quantitative chemical characterization of vitrinite concentrates using pyrolysis-gas chromatography. Rank variation of pyrolysis products     

J.T. Senftle  S.R. Larter  B.W. Bromley  J.H. Brown 《Organic Geochemistry》1986,9(6)

A series of hand-picked vitrinite samples from the Lower Kittanning Seam, Pennsylvania have been examined using quantitative pyrolysis-gas chromatography. These vitrinites ranged in rank from 0.59 to 1.71% reflectance, a rank range from high volatile C bituminous to low volatile bituminous. High molecular weight pyrolysis products included alkyl aromatic and phenolic compounds. Attempts have been made to correlate the pyrolysis product composition to rank parameters including vitrinite reflectance, volatile matter yield, carbon content, atomic H/C ratio and Rock-Eval determined T_max. Total yield of phenols was found to be strongly and inversely rank related. A clear relationship between C₈ alkyl-benzene yield and rank was not found for the sample set.  相似文献   

A petrographic and fluid inclusion comparison of silver-poor and silver-rich zinc-lead ores,N.E. Washington State     

Philip E. Brown  Gaafar A. Ahmed 《Mineralium Deposita》1986,21(2):156-163

Many of the zinc-lead deposits of NE Washington State are poorly known examples of Mississippi Valley Type (MVT) mineralization. This study compares inclusion fluids from the Josephine Breccia ores with the later cross-cutting sulfide-bearing quartz veins. The breccia ores are cemented mainly by open space fillings of dolomite, sphalerite, quartz, galena, jasperoid and calcite. Replacement is of minor importance. Ore and gangue deposition occurred over the range 150–250 °C with most of the temperatures less than 200 °C. The aqueous brines typically contain 17–23 equivalent weight percent NaCl with often substantial amounts of Ca and/or Mg chlorides. Homogenization temperatures do not delineate any cooling or paragenetic sequence. The cross-cutting vein quartz contains CO₂-rich inclusions with overall densities usually less than 0.7 g/cc and homogenization temperatures from 250–325 °C. Sulfur isotope analyses yield two populations with the quartz vein ores being lighter (<13 permil CDT) than the average for the conformable ores. The later veins are not remobilized MVT sulfides but represent a separate, high-silver period of mineralization.  相似文献   

Production and pelagic dissolution of biogenic silica in the Southern Ocean     

David M. Nelson  Louis I. Gordon 《Geochimica et cosmochimica acta》1982,46(4):491-501

Vertical distributions of particulate silica, and of production and dissolution rates of biogenic silica, were determined on two N-S transects across the Pacific sector of the Antarctic Circumpolar Current during the austral spring of 1978. Particulate silica profiles showed elevated levels in surface water and near the bottom, with low (35–110 nmol Si · 1^?1) and vertically uniform values through the intervening water column. Both the particulate silica content of the upper 200 m and the production rate of biogenic silica in the photic zone increased from north to south, reaching their highest values near the edge of the receding pack ice. A significant, but variable, fraction (18–58%) of the biogenic silica produced in the surface layer was redissolving in the upper 90–98 m. Net production of biogenic silica in the surface layer (production minus dissolution) was proceeding at a mean rate of ca. 2 mmol Si · m^?2 · day^?1. This is ca. 4 times greater than the most recent estimate of the mean accumulation rate of siliceous sediments beneath the ACC. We estimate, based on mass balance, that the mean dissolution rate of biogenic silica in subsurface water column in the Southern Ocean is 1.2–2.9 mmol Si · m^?2 · day^?1.  相似文献   

Oxygen isotope geothermometry and stability of lawsonite and pumpellyite in the Shuksan Suite,North Cascades,Washington     

E. H. Brown  J. R. O'Neil 《Contributions to Mineralogy and Petrology》1982,80(3):240-244

Metamorphic temperatures of 330°–400° C are inferred for rocks from the Shuksan blueschist terrane in the North Cascades, Washington. The temperatures are calculated from ¹⁸O fractionations between coexisting quartz and magnetite using the equations of Bottinga and Javoy (1973). Pressures of approximately 7 kilobars are indicated by the Jadeite content of clinopyroxene coexisting with quartz+albite. Published experimental and theoretical studies of the stability of lawsonite and pumpellyite are consistent with the oxygen isotope temperatures and occurrence of these minerals in the Shuksan Suite.  相似文献