Hot pressing of polycrystals of high-pressure phases of mantle minerals in multi-anvil apparatus

In the 1960s, E. Schreiber and his colleagues pioneered the use of hot-pressed polycrystalline aggregates for studies of the pressure and temperature dependence of the elastic wave velocities in minerals. We have extended this work to the high-pressure polymorphs of mantle minerals by developing techniques to fabricate large polycrystalline specimens in a 2000-ton uniaxial split-sphere apparatus. A new cell assembly has been developed to extend this capability to pressures of 20 GPa and temperatures of 1700°C. Key elements in the new experimental design include: a telescopic LaCrO₃ forT>1200°C; Toshiba Tungaloy grade F tungsten carbide anvils; and the use of homogeneous glasses or seeded powder mixtures as starting material to enhance reactivity and maximize densities. Cell temperatures are linearly related to electrical power to 1700°C and uniform throughout the 3 mm specimens. Pressure calibrations at 25°C and 1700°C are identical to 15 GPa. Cylindrical specimens of the beta and spinel phases of Mg₂SiO₄, stishovite (SiO₂-rutile), and majorite-pyrope garnets have been synthesized within their stability fields in runs of 1–4 hr duration and recovered at ambient conditions by simultaneously decompressing and cooling along a computer-controlledP-T path designed to preserve the high-pressure phase and to relax intergranualar stress in the polycrystalline aggregate. These specimens are single-phased, fine-grained (<5 micron), free of microcracks and preferred orientation, and have bulk densities greater than 99% of X-ray density. The successful fabrication of these high-quality polycrystalline specimens has made possible experiments to determine the pressure dependence of acoustic velocities in the ultrasonics laboratory of S. M. Rigden and I. Jackson at the Australian National University.CHiPR: NSF Science and Technology Center for High Pressure Research.     

The stress release hypothesis of magma formation

The possibility of magma formation due to the release of stresses in the Crust and Upper Mantle of the Earth is examined for both tensile and compressive failure. The correlation of volcanic activity with shallow and intermediate focus earthquakes is examined in the light of new experimental data on the strength of rocks, and recent theories of the thermal history of the Earth. It is found that in association with earthquakes, granitic magmas may be generated between depths of approximately 15 and 50 kilometers; basaltic magmas between 50 and 100 kilometers; while duntic magmas are unlikely to be generated in this manner.     

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Computation of 5-day temperature normals in western Europe and the Mediterranean area

Summary UsingCraddock's method of representing the annual temperature variation by a two-term harmonic form fitted to monthly means, the harmonic coefficients of 63 stations in western Europe and around the Mediterranean Sea, as well as the 5-day normals for 24 Mediterranean stations, were computed and tabulated. In addition, some of the harmonic coefficients were charted and isoplethed, showing very distinctly the influence of continentality and topography. These charts, together withCraddock's charts for northern and northwestern Europe, provide fairly complete coverage of Europe and the Mediterranean area.This paper was prepared in the offices of the Technical Support Division of the 2d Weather Wing, United States Air Force, as a matter of routine business. The information contained herein was presented at the 5th Meeting of the Italian Society of Geophysics and Meteorology by Dr.Ingrid Weiss (Genoa: 23–25 April 1957). Since the paper is of general interest to all meteorologists of the Mediterranean area, it is published here with the permission of the originating agency as «Mémoire No. 3 du Centre International de Recherches sur la Météorologie de la Méditerranée (CIRMM)».     

Petrogenesis of oceanic granites from the Aves Ridge in the Caribbean Basin

A genetic model proposed for granitic rocks dredged from the Aves Rise involves a sodium-enriched hydrothermal fluid phase, shallow emplacement, and significant derivation of components from the upper mantle. Megascopic observations of serially slabbed sections of the rock samples show that aggregates of plagioclase phenocrysts concentrate into channel-like mats. The presence of a late-stage, hydrothermal fluid is suggested by crystal-lined cavities in the plagioclase aggregates.     

The petrology of chondrules in the sharps meteorite

Correlated petrographic and microprobe studies of 96 chondrules in the Sharps (H-3) chondrite indicate that chondritic material had a highly varied pre-accumulation history. Some chondrules, chiefly excentroradial and barred types, appear to be quenched droplets. Others, including most of the metal poor microporphyritic type, appear to have crystallized more slowly and are thought to be fragments of pre-existing rock. Although chondrules of all types show various effects similar to those produced by shock, such effects are most conspicuous in metal-rich chondrules and least conspicuous in spherical chondrules. It is concluded that shock was involved in the origin of chondrules and not simply a secondary effect.It is proposed that chondrules were formed by shock processes during the accumulation of nebular dust into asteroid-sized bodies. Olivine-rich microporphyritic chondrules are thought to be due to complete melting of large masses of target material; metal-rich chondrules represent shock melting and partial vaporization; and spherical, pyroxene-rich chondrules are interpreted as condensates from shock-generated vapor.