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Rubidium-strontium isotope measurements of Lemumbo igneous monocline associated acid and basic rocks to determine earth mantle or crust origin
Movement of earth mantle and geographic poles
Magnesium silicate crystal structure, discussing transformations under high pressure, crystallochemistry and implications for physics of earth mantle
Equation of state measurements of earth materials by shock wave techniques, applying to olivine for earth mantle constitution problem
Crystal-chemical and geophysical implications concerning earth mantle phase transitions from beta magnesium silicate crystal structure
Elastic seismic waves attenuation in polycrystalline ceramics and rocks by grain boundary relaxation, noting strong frequency dependence of earth mantle internal friction
The paper presents chemical and petrologic data relating the Allan Hills (ALHA) 77005 achondrite from Antarctica and explores their petrogenetic relationship with the shergottites. Petrologic similarities with the latter in terms of mineralogy, oxidation state, inferred source region composition, and shock ages suggest a genetic relationship, also indicated by volatile to involatile element ratios and abundances of other trace elements. ALHA 77005 may be a cumulate crystallized from a liquid parental to materials from which the shergottites crystallized or a sample of peridotite from which shergottite parent liquids were derived. Chemical similarities with terrestrial ultramafic rocks suggest that it provides an additional sample of the only other solar system body with basalt source origins chemically similar to the upper earth mantle.
The two-dimensional surface deformation, gravity field, and geoid are calculated from the temperature fields of a number of numerical models of constant-viscosity three-dimensional convective flows, heated from within and from below. The surface deformation and the geoid are insensitive to the short-wavelength features of the temperature variation; the gravity field is less smooth, although it still does not clearly indicate the narrowness of the upwelling and downwelling regions at large Rayleigh numbers. The results indicate that the convective upwelling beneath regions showing positive geoid and residual depth anomalies is more localized than the horizontal extent of these features would suggest. The results are relevant to attempts to understand the behavior of the earth mantle.
Thermal convection in the earth mantle is investigated by means of numerical simulations. The mantle models comprise two horizontal layers of viscous incompressible fluid (with identical or differing properties) separated by a fixed horizontal interface; an isothermal, fixed-heat-flux, or insulating lower boundary; and heat supplied either from below or internally (in the lower layer only, equally in both layers, or primarily in the upper layer). The mathematical formulation of the models is explained, and results for linear stability and finite-amplitude convection are presented in extensive tables and graphs and discussed in detail. Particular attention is given to the presence of thermal coupling without interface distortion in many cases, the predominance of long-wavelength cells in the finite-amplitude models, and the large (50 percent) temperature difference across the interface in all cases.
Measurements of the concentration of rare gases and trace elements in oceanic basalts provided a new information concerning the structure if the Earth mantle and its evolution. The results set important constraints that need to be incorporated into any comprehensive understanding of the early history of the planets. Some of the highlights of these results are described and an indication is given how they are derived.
The effect of an increase of viscosity in the earth-mantle's transition zone between 420 and 670 km on the geophysical signatures induced by postglacial rebound was analyzed using a self-gravitating model consisting of an elastic lithosphere, a three-layer viscoelastic mantle, and an inviscid core. Results show that the horizontal displacements and velocities as well as the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone. The findings indicate that geodetic data on intraplate deformation can be used to put constraints on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle.
Measurements made on materials from Earth, Mars, comets, and meteorites of Mg/Si, Al/Si, oxygen, Os, D/H, Ar/H2O, and Kr/Xe ratios, all lead to the conclusion that no primitive material similar to Earth mantle material is currently represented in our meteorite collections. Additional information is contained in the original extended abstract.
Two main processes were responsible for the composition of this atmosphere: chemical evolution of the volatile fraction of the accretion material forming the planet and the delivery of gasses to the planetary surface by impactors during the late heavy bombardment (LHB). The amount and composition of the volatile fraction influences the outgassing of the Earth mantle during the last planetary formation period. A very weakened form of outgassing activity can still be observed today by examining the composition of volcanic gasses. An enlightenment of the second process is based on the sparse records of the LHB impactors resulting from the composition of meteorites, observed cometary comas, and the impact material found on the Moon. However, for an assessment of the influence of the outgassing on the one hand and the LHB event on the other, one has to supplement the observations with numerical simulations of the formation of volatiles and their incorporation into the accretion material which is the precursors of planetary matter, comets and asteroids. These simulations are performed with a combined hydrodynamic-chemical model of the solar nebula (SN). We calculate the chemical composition of the gas and dust phase of the SN. From these data, we draw conclusions on the upper limits of the water content and the amount of carbon and nitrogen rich volatiles incorporated later into the accretion material. Knowing these limits we determine the portion of major gas compounds delivered during the LHB and compare it with the related quantities of the outgassed species.
The similarities in siderophile abundances strongly suggest that the Moon was derived from the Earth's mantle after the Earth's core had formed. The energy required to remove material from the Earth's mantle and place it into geocentric orbit can be supplied most readily by impact processes during accretion of the Earth. Impacts of late-accreting, high-velocity planetismals would evaporate many times their masses of mantle material. These gases would be accompanied by a massive spray of shock-melted silicate droplets. It is suggested that the gases produced from such near-equatorial impacts were rapidly spun out into equatorial geocentric orbit. The evaporated material was selectively recondensed, and, accompanied by the shock melted, devolatilized silicate droplets, accreted to form a sediment ring of Earth-orbiting planetismals. This sediment ring also captured a significant proportion of Earth-bound planetismals. The Moon was formed by accretion from planetismals comprising the sediment ring.
The considered investigation is concerned with a reexamination of the question of the distribution of siderophile elements in the earth's upper mantle, taking into account a more unified data base which is now available. A comprehensive suite of ultramafic inclusions was collected as part of the Basaltic Volcanism Study Project and has been analyzed by instrument neutron activation analysis for major, minor, and some lithophile trace elements. In addition, 18 of these rocks and the important sheared garnet lherzolite PHN 1611 have been analyzed by means of radiochemical neutron activation analysis for 7 siderophile elements (Au, Ge, Ir, Ni, Os, Pd, and Re) and 9 volatile elements (Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn). The siderophile element data reveal interesting inter-element correlations, which were not apparent from the compiled abundance tables of Ringwood and Kesson (1976) and Chou (1978).
The fortnightly Mf ocean tide is the largest of the long-period tides (periods between 1 week and 18.6 years), but Mf is still very small, generally 2 cm or less. All long-period tides are thought to be near equilibrium with the astronomical tidal potential, with an almost pure zonal structure. However, several lines of evidence point to Mf having a significant dynamic response to forcing. We use a combination of numerical modeling, satellite altimetry, and observations of polar motion to determine the Mf ocean tide and to place constraints on certain global properties, such as angular momentum. Polar motion provides the only constraints on Mf tidal currents. With a model of the Mf ocean tide in hand, we use it to remove the effects of the ocean from estimates of fortnightly variations in length-of-day. The latter is dominated by the earth's body tide, but a small residual allows us to place new constraints on the anelasticity of the earth's mantle. The result gives the first experimental confirmation of theoretical predictions made by Wahr and Bergen in 1986.
Radiochemical neutron activation analysis was used to determine the nine volatile elements Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn in 19 ultramafic rocks, consisting mainly of spinel and garnet lherzolites. A sheared garnet lherzolite, PHN 1611, may approximate undepleted mantle material and tends to have a higher volatile element content than the depleted mantle material represented by spinel lherzolites. Comparisons of continental basalts with PHN 1611 and of oceanic ridge basalts with spinel lherzolites show similar basalt: source material partition factors for eight of the nine volatile elements, Sb being the exception. The strong depletion of Te and Se in the mantle, relative to lithophile elements of similar volatility, suggests that 97% of the earth's S, Se and Te may be in the outer core.
A variety of evidence suggests that at least some hotspots are formed by quasi-cylindrical mantle plumes upwelling from deep in the mantle. Such plumes are modeled in cylindrical, axisymmetric geometry with depth-dependent, Newtonian viscosity. Cylindrical and sheet-like, Cartesian upwellings have significantly different geoid and topography signatures. However, Rayleigh number-Nusselt number systematics in the two geometries are quite similar. The geoid anomaly and topographic uplift over a plume are insensitive to the viscosity of the surface layer, provided that it is at least 1000 times the interior viscosity. Increasing the Rayleigh number or including a low-viscosity asthenosphere decreases the geoid anomaly and the topographic uplift associated with an upwelling plume.