Petrogenesis of Glaucophane Schists

Some glaucophane schists are chemically indistinguishable fromgreenschists and epidote amphibolites. Provided all three rocktypes represent equilibrium assemblages, they must have formedunder differing physical conditions. The mineralogy of suchglaucophane schists taken in conjunction with experimental evidencesuggests that these rocks formed at low temperatures and atrelatively elevated pressures. The relatively high-pressure,low-temperature phases lawsonite, jadeitic pyroxene, and metamorphicaragonite are diagnostic of physical conditions attending thismetamorphism. Differential stress may aid in the attainmentof the appropriate mean pressure necessary for the productionof these phases. Graphic analysis and approximated thermodynamic calculationsindicate that relatively elevated pressures, or relatively lowtemperatures, or both, promote the formation of glaucophanein rocks of a wide range of bulk compositions while restrictingthe compositional range of albite-bearing rocks. It is concludedthat the coexistence of glaucophane with carbonate, calcium-aluminumsilicate or paragonite results from such physical conditions,and it is on the basis of these associations or, equally well,the presence of lawsonite, jadeitic pyroxene, or metamorphicaragonite that the blueschist facies should be defined. High pressures are not required for the production of glaucophaneitself. It is stable under physical conditions present in thegreenschist and epidote amphibolite facies in rocks deficientin CaO and rich in Na₂O and MgO relative to A1₂O₃. Such bulkcompositions might result from exchange of material betweenserpentinite and albite-bearing country rocks, and could accountfor glaucophane aureoles around, and inclusions of glaucophanerock within, some serpentinites.     

Melting Relationships in the System CaO-MgO-CO2-H2O, with Petrological Applications

Phase relationships on the vapor-saturated liquidus surfacein the system CaO-MgO-CO₂-H₂O have been deduced from data inthe systems CaO CO₂-H₂O, CaO-MgO-CO₂, and MgO-CO₂-H₂O, and frompreliminary experiments in the quaternary system. These areillustrated in composition tetrahedra, and in isobaric sectionsthrough the petrogenetic model. The univariant PT curve forthe beginning of melting lies between 625? C and 600? C in thepressure range 10 bars to 4 kilobars, in the presence of a vaporphase rich in H₂O. The curve is divided into three sectionsby two invariant points, each section having a different primarymagnesian phase involved in the melting reaction. Periclaseoccurs on the low-pressure section (less than about 1 kilobar),and with increasing pressure first brucite and then dolomitebecome stable on the liquidus. The pressure of the second invariantpoint, above which dolomite is stable on the liquidus, is notknown. The effect of FeO as an additional component is considered.Processes of crystallization resulting from changes in temperature,in pressure, and in the composition of the vapor phase are discussed.These processes are applied to the crystallization and differentiationof carbonatite magmas, and the reverse processes involving fusionare applied to the metamorphism of dolomites. Crystallizationdifferentiation of a carbonatite magma could produce the sequenceof intrusion observed at some carbonatite complexes: calcitics?vite, followed by ankeritic s?vite, and finally sideriticcarbonatite. Partial melting may occur during the thermal metamorphismof dolomites, but melting is unlikely during regional metamorphism.     

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Electrochemical strengthening of clayey sandy soils

Most previous studies and applications of electrochemical stabilization of soils through electroosmosis have been made on clayey soils. The object of this investigation was to find out if relatively small amounts of clay (1.5%–3.5%, by weight) present in a sandy soil would be enough for stabilization and strengthening to be possible. The results indicate increases of cohesion of the order of 100–200 lb./sq.ft. X-ray analyses of treated soils indicate that sheet structures of clays are reduced and silicates destroyed upon treatment by electroosmosis. Newly-formed minerals also cement the soil. These neoformations include gibbsite, limonite, calcite, hydrohematite, hydrogoethite (hydrolepidocrocite), hisingerite, allophane, allophanoid, gypsum, hematite, magnetite, nontronite, trona and natron (Na₂ CO₃, 10H₂O). The process seems to be irreversible.     

Reduction of hydroelastic responses of a very-long floating structure by a floating oscillating-water-column breakwater system

The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater.