Major and trace elements have been determined in spinel lherzolite, spinel pyroxenite and garnet websterite xenoliths from the Hoggar and in their host basanites and nephelinites. Transition metal and REE abundances do not support a genetic link between these ultramafic rocks and the lavas erupted at the surface. Mineral chemistry and textures suggest a complex evolution and subsolidus re-equilibration in the range 800–1, 000°C. High-density CO2 fluid-inclusions define minimum pressures of 10–12kb. Thus the ultramafic xenoliths came from a relatively low pressure regime within an inhomogeneous lithospheric mantle segment characterized by a disturbed geotherm.
An attempt was made to determine both elemental and isotopic abundances of rare gases in natural gases by means of a conventional quadrupole mass spectrometer (QMS). Elemental abundances and isotopic ratios of Ar, Kr and Xe on the atmospheric concentration level were successfully measured by the present method. Reproducibility of 10–20% was obtained for 4He, 20Ne, 36Ar, 84Kr and 132Xe measurements. Isotopic ratios of Ar, Kr and Xe were determined within about 2% experimental errors, except for 78Kr/84Kr, 124Xe/132Xe and 126Xe/132Xe. Sensitivity and reproducibility of the measurements were examined by repeating runs of the atmospheric air. In order to verify the applicability of the present method to terrestrial natural gas analyses, eight typical samples of natural gases in Japan, with differences in major compositions, were measured. The values observed by a QMS in this work are generally in good agreement with those obtained by magnetic deflection mass spectrometers. Enrichment of radiogenic 40Ar was observed in some CO2-rich natural gas samples. Observed Kr and Xe isotopic ratios in N2-rich gases and CH4-rich gases coincided with the atmospheric ratios within experimental error.
The distribution pattern of the chemical elements of the Earth's surface indicates that the bulk composition of the Earth as a whole is similar to that of volatile-depleted CI chondrites. On the basis of the above bulk composition of the Earth, the known chemical composition of the Earth's crust, and the well accepted compositional model for the upper mantle, the chemical compositions of the lower mantle and the core have been calculated. It has been found that the silica content (the most abundant chemical component of the mantle) of the lower mantle is about 20wt% more enriched than the upper mantle. Furthermore, the iron content of the lower mantle is likely to be depleted relative to that of the upper mantle, since iron is chemically incompatible with the major mineral phase in the lower mantle, which is probably composed of 95 wt% of silicates with perovskite modifications. The possible stable mineral assemblages of the various parts of the mantle are given. It has also been calculated that the outer core contains about 15wt% of a light element, which is in line with, but independent of, previous estimates based primarily on geophysical constraints. Various reasons suggest that oxygen is the major light element in the core. The simple and direct correlations in the abundances of the major and minor elements, and in the general distribution of the chemical elements between the Earth and CI chondrites suggest a comparatively simple model for the origin of the Earth. Only some volatile and light elements in the CI composition were volatilized and escaped from the accreting Earth. The core of the Earth was developed by high-pressure disproportionation reactions in iron-rich silicates simultaneously with accretion.
Ca, Sr and Ba contents of various volcanic rocks (basalts, andesites, dacites and a granitic xenolith) from the Higashi-Izu monogenetic volcano group, the Izu Peninsula, Japan, have been determined by an ICP-OES method. The results indicate that the monogenetic volcano group makes a Sr/Ca-Ba/Ca systematics which is similar to that defined by a stratovolcano. The SB systematics suggests that there are two different high alumina basalt magmas in the Higashi-Izu monogenetic volcano group: one (basalt I) is a primitive basalt magma derived from the mantle with rather small degree of partial melting and the other (basalt II) is a mixture of the primitive basalt magma and a cumulus phase enriched in plagioclase. The high alumina basalt series (basalt (I)-andesite-dacite series) is considered to be established, not by crystal fractionation process in magma chamber, but by assimilation process of the primary basalt magma with the granitic crust. The crust under the Izu Peninsula may have a chemical composition similar to that of the dacite(I) from Kawagodaira.
The concentration profiles of 9Be, 10Be and 230Thexc have been measured in two oceanic sediment cores from near Antarctica in the Pacific. The 10Be and 9Be depth profiles in eleven Pacific cores investigated so far by our group have been summarized, and the variations of 10Be flux, 9Be concentration and 10Be/9Be atomic ratio from core to core are discussed in the light of a scavenging process of the beryllium isotopes.