Seismotectonics of the Papua New Guinea—Solomon Islands region

Earthquakes for the period 1964–1973 are relocated by the method of Joint Hypocenter Determination in order better to resolve the configuration and the structure of the New Guinea—New Britain—Solomon Islands region. Focal mechanism solutions are integrated with the seismicity and interpreted closely with it. A zone of subduction exists beneath New Britain and the Solomon Islands, a zone of left-lateral strike-slip movement extends from New Ireland to New Guinea. The zone of seismicity in northern New Guinea has developed as a result of a continent—island-arc collision in late Oligocene—Miocene times and does not exhibit a well-developed inclined seismic zone. It is proposed that plate tectonics theory does not apply rigorously, but slip-line field theory allows the presentation of a new geodynamic model for this region.     

Partition of trace elements in co-existing biotite,muscovite and potassium feldspar of granitic rocks,northern Portugal

Chemical analyses are given for Na, K, and trace elements of muscovite and potassium feldspar of granitic rocks. The distribution of trace elements in co-existing minerals suggests that equilibrium was attained and that muscovite is a primary mineral. These observations and the comparison of the trace-element chemistry of megacrysts and groundmass potassium feldspars of porphyritic rock types lead to the conclusion that the megacrysts are in face phenocrysts which crystallized in equilibrium with the other minerals of the rock.The ranges of values of the distribution coefficients K_D(Rb/K) and K_D(Cs/K) in mineral pairs confirm other observations on the equilibrium among various minerals. However, application of experimental data on the temperature effect on K_D leads to results conflicting with the petrologic observations. The possible influence of other factors on K_D is analyzed and among these factors the composition of the feldspar and the solidus-liquidus temperature interval may play a dominant role.     

Organic geochemistry of Walvis Bay diatomaceous ooze—I. Occurrence and significance of the fatty acids

Diatomaceous ooze of the shelf off Walvis Bay (S.W. Africa) was analysed for lipid material. The lipids from the sediment consist of a mixture of hydrocarbons, alcohols, ketones, fatty acids, sterols, carotenoid pigments and chlorophylls. The total fatty acid mixture has been analysed by capillary gas chromatography mass spectrometry and shown to consist of straight chain, iso-, anteiso- and isoprenoid acids. The environmental setting of the S.W. African shelf (Walvis Bay) makes it possible to discuss these fatty acids as markers for the fate of organic matter. The acids in the sediment point to a generation during passage of algal lipids through levels of microbial activity either on or slightly above the burial surface.     

Rare-earth data on monzonoritic rocks related to anorthosites and their bearing on the nature of the parental magma of the anorthositic series

Major and trace elements have been determined in monzonoritic rocks (hypersthene-monzodiorite or jotunite) from two intrusions belonging to the South Rogaland anorthositic complex (Norway). The rare-earth abundance pattern reveals no Eu anomaly, or only a very small one. This fact together with field observations suggest that these rocks represent the parental magma of the anorthositic suite. High Ti and P abundances, low Si content, high Fe/Mg and K₂O/SiO₂ ratios are characteristics of the major element geochemistry. Absolute amounts of some trace elements abundances vary distinctly between the two intrusions. K/Rb ratios as high as 1700 are observed. Partial fusion of upper mantle kaersutite is proposed as a possible mechanism of magma generation. Partition coefficients between plagioclase phenocrysts and liquid are determined.     

Island-arc and underthrust-plate geometry

Geophysical data describing the geometry of underthrust crustal plates at the island arcs are fitted to the relation for strain-free buckling of a thin spherical shell as given by Frank (1968). Agreement of this relation with the data is notable for extensive arcs of large radius. The geometry associated with arcs of smaller radius is less strongly constrained and the dip of descending plates at arcs of small radius is greater than that predicted by the buckling relation. The data have implications concerning the growth of island arcs and the direction in which they may develop.     

The abundance of cadmium and zinc in meteorites

A stable isotope dilution technique using solid source mass spectrometry has been used to accurately determine Cd and Zn in a wide range of materials. The abundance of Cd has been determined in 19 iron, 28 stone and 1 stony-iron meteorites, together with a number of other samples. The abundance of Zn has also been determined for most of these samples. This has enabled the relationship between Cd and Zn to be examined in iron and stone meteorites. The abundance pattern of Zn in iron meteorites supports the existence of chemical groups.     

One dimensional elastic wave propagation in a non-homogeneous conical rod

Summary A one dimensional problem concerning the wave propagation in a non-homogeneous conical rod having its cross-section directly proportional to the square of the distance from a chosen point is considered in this paper. One end of the rod is subjected to a pressure step while the other end is stress free and the pulse shape is examined when the propagation speed of the wave has a particular continuous distribution over the entire rod.