Engineering topics

Jones, John H.

Publications and source records attributed to Jones, John H..

30 records · Page 2

NASA NTRS1993

Rubidium and cesium in the earth and the moon

The purpose of the study is to provide an alternative perspective on both the mass balance issue and on the issue of secular change in the Rb-Cs ratio in the earth mantle. In particular, it is argued that the apparent secular change in the Rb/Cs ratio may be simply an artifact of alteration of older rocks through weathering and/or metamorphism subsequent to formation. It is also shown that there is not necessarily a need for a hidden, undepleted reservoir, and the consistency of this result with other mass calculations is explored. New methods for estimating the Rb/Cs ratio of the bulk silicate earth are suggested.

Jones, John H.↗

NASA NTRS1993

Metal-silicate thermochemistry at high temperature - Magma oceans and the 'excess siderophile element' problem of the earth's upper mantle

Low-temperature metal-silicate partition coefficients are extrapolated to magma ocean temperatures. If the low-temperature chemistry data is found to be applicable at high temperatures, an important assumption, then the results indicate that high temperature alone cannot account for the excess siderophile element problem of the upper mantle. For most elements, a rise in temperature will result in a modest increase in siderophile behavior if an iron-wuestite redox buffer is paralleled. However, long-range extrapolation of experimental data is hazardous when the data contains even modest experimental errors. For a given element, extrapolated high-temperature partition coefficients can differ by orders of magnitude, even when data from independent studies is consistent within quoted errors. In order to accurately assess siderophile element behavior in a magma ocean, it will be necessary to obtain direct experimental measurements for at least some of the siderophile elements.

Capobianco, Christopher J.↗

NASA NTRS1993

Partial melting of ordinary chondrites: Lost City (H) and St. Severin (LL)

Eucrites and diogenites are examples of asteroidal basalts and orthopyroxenites, respectively. As they are found intermingled in howardites, which are inferred to be regolith breccias, eucrites and diogenites are thought to be genetically related. But the details of this relationship and of their individual origins remain controversial. Work by Jurewicz et al. showed that 1170-1180 C partial melts of the (anhydrous) Murchison (CM) chondrite have major element compositions extremely similar to primitive eucrites, such as Sioux County. However, the MnO contents of these melts were about half that of Sioux County, a problem for the simple partial melting model. In addition, partial melting of Murchison could not produce diogenites, because residual pyroxenes in the Murchison experiments were too Fe- and Ca-rich and were minor phases at all but the lowest temperatures. A parent magma for diogenites needs an expanded low-calcium pyroxene field. In their partial melting study of an L6 chondrite, Kushiro and Mysen found that ordinary chondrites did have an expanded low-Ca pyroxene field over that of CV chondrites (i.e., Allende), probably because ordinary chondrites have lower Mg/Si ratios. This study expands that of both Kushiro and Mysen and Jurewicz et al. to the Lost City (H) and St. Severin (LL) chondrites at temperatures ranging from 1170 to 1325 C, at an fO2 of one log unit below the iron-wuestite buffer (IW-1).

Jurewicz, Amy J. G.↗

NASA NTRS1993

Experimental partitioning of Zr, Ti, and Nb between silicate liquid and a complex noble metal alloy and the partitioning of Ti between perovskite and platinum metal

El Goresy et al.'s observation of Nb, Zr, and Ta in refractory platinum metal nuggets (RPMN's) from Ca-Al-rich inclusions (CAI's) in the Allende meteorite led them to propose that these lithophile elements alloyed in the metallic state with noble metals in the early solar nebula. However, Grossman pointed out that the thermodynamic stability of Zr in the oxide phase is vastly greater than metallic Zr at estimated solar nebula conditions. Jones and Burnett suggested this discrepancy may be explained by the very non-ideal behavior of some lithophile transition elements in noble metal solutions and/or intermetallic compounds. Subsequently, Fegley and Kornacki used thermodynamic data taken from the literature to predict the stability of several of these intermetallic compounds at estimated solar nebula conditions. Palme and Schmitt and Treiman et al. conducted experiments to quantify the partitioning behavior of certain lithophile elements between silicate liquid and Pt-metal. Although their results were somewhat variable, they did suggest that Zr partition coefficients were too small to explain the observed 'percent' levels in some RPMN's. Palme and Schmitt also observed large partition coefficients for Nb and Ta. No intermetallic phases were identified. Following the work of Treiman et al., Jurewicz and Jones performed experiments to examine Zr, Nb, and Ti partitioning near solar nebula conditions. Their results showed that Zr, Nb, and Ti all have an affinity for the platinum metal, with Nb and Ti having a very strong preference for the metal. The intermetallic phases (Zr,Fe)Pt3, (Nb,Fe)Pt3, and (Ti,Fe)Pt3 were identified. Curiously, although both experiments and calculations indicate that Ti should partition strongly into Pt-metal (possibly as TiPt3), no Ti has ever been observed in any RPMN's. Fegley and Kornacki also noticed this discrepancy and hypothesized that the Ti was stabilized in perovskite which is a common phase in Allende CAI's.

Jurewicz, Stephen R.↗

NASA NTRS1992

Estimation of high temperature metal-silicate partition coefficients

It has been known for some time that abundances of siderophile elements in the upper mantle of the Earth are far in excess of those expected from equilibrium between metal and silicate at low pressures and temperatures. Murthy (1991) has re-examined this excess of siderophile element problem by estimating liquid metal/liquid silicate partition coefficients reduces from their measured values at a lower temperature, implying that siderophile elements become much less siderophilic at high temperatures. Murthy then draws the important conclusion that metal/silicate equilibrium at high temperatures can account for the abundances of siderophile elements in the Earth's mantle. Of course, his conclusion is critically dependent on the small values of the partition coefficients he calculates. Because the numerical values of most experimentally-determined partition coefficients increase with increasing temperature at both constant oxygen fugacity and at constant redox buffer, we think it is important to try an alternative extrapolation for comparison. We have computed high temperature metal/silicate partition coefficients under a different set of assumptions and show that such long temperature extrapolations yield values which are critically dependent upon the presumed chemical behavior of the siderophile elements in the system.

Jones, John H.↗

NASA NTRS1991

Exploration of relationships between low-Ti and high-Ti pristine lunar glasses using an armalcolite assimilation model

The pristine glasses of Delano are the most primitive lunar basaltic magma compositions discovered to date. They are grouped into two (and possibly three) arrays: a low-alumina array and a high alumina array. These glasses are very olivine normative and are multiply saturated at pressures of approximately 20 kbar, implying a depth of origin of 400 to 500 km in the Moon. Thus, these glasses appear to be the best candidates for primitive partial melts of the upper lunar mantle. One of the most perplexing characteristics of the pristine glasses is a positive correlation between Ni and SiO2 within each array. This is contrary to the terrestrial experience, where Ni is observed to positively correlate with MgO and negatively correlate with SiO2. These systematics are believed to be due to the depletion of Ni by olivine fractionation. The difference between the lunar and terrestrial Ni vs. SiO2 trends may be partially ascribed to the Ti-rich component. In the case of the pristine glasses, SiO2 increases not because of olivine fractionation, but because they contain less of the high-Ti component. An attempt was made to model this variation in Ni and SiO2 with a simple assimilation-fractional crystallization (AFC) model. Silica and Ni both decreased dramatically as the AFC process proceeded. Only 15 to 20 percent AFC was necessary to produce the observed variation, and the SiO2 vs. Ni variation was modeled quite well. The D(Ni) for olivine/liquid in this model was taken to be 10 and the olivine was assumed to be Fe sub 80. However, the results of this model for Ti and Mg were less than satisfactory. It seemed difficult to achieve the high TiO2 contents of some glasses (16 to 17 wt. percent) by this method. Continual addition of ilmenite by AFC could indeed raise the titania concentrations to the necessary levels, but only by enriching the magma in FeO and greatly depleting the magma in MgO. An attempt was made to circumvent this problem by using armalcolite, (Fe, Mg)Ti2O5, in the AFC model, and the results are presented.

Jones, John H.↗

NASA NTRS1989

A three-component model for the bulk composition of the moon

A three-component model for the moon's bulk composition was developed on the basis of the results of Delano (1986) on lunar pristine glasses. This suite of models is based on the following two assumptions: (1) that the early moon differentiated into two primary reservoirs, a FeO-rich magma ocean and an olivine-rich residuum of about Fo(90); and (2) that this magma ocean then differentiated into an olivine-dominated cumulate, about equal to or greater than Fo(80), and a primitive liquid composition. Because serious uncertainties remain concerning the moon's complex differentiation history, this three-component model does not yield a single unique composition for the bulk silicate moon; instead, it yields a range of restricted compositions that are permitted within the conceptual framework of the model.

Jones, John H.↗

NASA NTRS1988

Speculations on the igneous history of Mars: Inferences from the SNC meteorites

In general, attempts to delineate an a priori sampling strategy for missions to terrestrial planets must be simple. In the case of the Moon, for example, the simplest and most obvious plan that to sample both the highly-cratered, high-albedo highlands and less-cratered, low-albedo mare--has proven very useful. However in the case of Mars, multiple missions and/or roving samplers may prove expensive or infeasible. Thus, we may be limited to collecting samples from a single site, and, consequently, consideration of sampling strategies for a Mars mission is more critical than for the more-accessible Moon.

Jones, John H.↗

NASA NTRS1987

Origin and evolution of the ureilite parent magmas - Multi-stage igneous activity on a large parent body

The minor-element/major-element trends among the ureilites were investigated using electron microprobe data on olivine and pigeonite cores in eight low-shock ureilites. The results show well-defined correlations between Fe/X (where X is one of the minor elements Mn, Cr, Ca, Al, Ti, P, or Ni) and Fe/Mg ratios. For the lithophile minor elements, these trends are linear, with positive slope, and pass through or near the origin, indicating various degrees of FeO reduction of the parent magmas. The trends shown by P and Ni are consistent with this interpretation and require, in addition, equilibrium crystallization of 20-27 mole pct metal. A model is proposed for generation and crystallization of ureilite parent magmas, which predicts that the ureilite parent body had a differentiated crust, did not have a core, and was at least 235 km in radius.

Goodrich, Cyrena Anne↗

NASA NTRS1987

Experimental geochemistry of Pu and Sm and the thermodynamics of trace element partitioning

An experimental study of the partitioning of Pu and Sm between diopside/liquid and whitlockite/liquid supports the hypothesis that Pu behaves as a light rare earth element during igneous processes in reducing environments. D-Pu/D-Sm is found to be about 2 for both diopsidic pyroxene and whitlockite, and the amount of fractionation would be decreased further if Pu were compared to Ce or Nd. Data indicate that temperature, rather than melt composition, is the most important control on elemental partitioning, and that P2O5 in aluminosilicate melts serves as a complexing agent for the actinides and lanthanides.

Jones, John H.↗

NASA NTRS1987

Core formation in the shergottite parent body and comparison with the earth

Abundances of elements in shergottite, nakhlite, and Chassigny meteorites which originated on a single planet, the shergottite parent body (SPB), were examined with the aim of elucidating the chemical conditions of metal separation and core formation in the SPB and of testing present models of planetary core formation. Using partition coefficients and the SPB mantle composition determined in earlier studies, the abundances of Ag, Au, Co, Ga, Mo, Ni, P, Re, S, and W were modeled, with free parameters being oxygen fugacity, proportion of solid metal formed, proportion of metallic liquid formed, and proportion of silicate that is molten. It is shown that the abundances of all elements (except Mo) could be reproduced using models with these four free parameters. In contrast to the SPB, an equivalent model used to predict element abundances in the earth's mantle was shown by Jones and Drake (1986) to be inadequate; there is at present no hypothesis capable of quantitatively reproducing the elemental abundances of the earth's mantle. The contrast suggests that these two terrestrial planets (assuming that the SPB is Mars) may have accreted or differentiated differently.

Treiman, Allan H.↗

NASA NTRS1986

Geochemical Constraints on Core Formation in the Earth

New experimental data on the partitioning of siderophile and chalcophile elements among metallic and silicate phases may be used to constrain hypotheses of core formation in the Earth. Three current hypotheses can explain gross features of mantle geochemistry, but none predicts siderophile and chalcophile element abundances to within a factor of two of observed values. Either our understanding of metal-silicate interactions and/or our understanding of the early Earth requires revision.

Jones, John H.↗