Engineering topics

Warren, Paul H.

Publications and source records attributed to Warren, Paul H..

35 records · Page 2

NASA NTRS1991

The MacAlpine Hills lunar meteorite and implications of the lunar meteorites collectively for the composition and origin of the moon

The MAC88104/105 meteorite, a lunar highlands regolith breccia, is described. The rock and a number of its component clasts are characterized. One of the clasts is considered to be a rare pristine nonmare rock containing extraordinarily Fe-rich (Fo40) olivine; the other has silicate compositions that extend the range of the Mg-suite in the direction of the high-mg* end of the ferroan-anorthositic suite. For the major element composition of the crust, the highlands meteorites confirm that the two low-Th central nearside sites, Luna 20 and Apollo 16, are approximately representative. The high Al2O3 composition indicated for the upper crusts supports the magmasphere hypothesis. For the trace-element composition of the crust, the highlands meteorites indicate that the central nearside Apollo and Luna sites are in several respects grossly unrepresentative.

Warren, Paul H.↗

NASA NTRS1991

Megaregolith insulation and the duration of cooling to isotopic closure within differential asteroids and the moon

Global cooling of the moon and large (R = 40-250 km) asterodis, was modeled, starting at or near the solidus. A crucial factor in determining the prevailing interval (Ic) of cooling between igenous crystallization and isotopic closure, for any given depth in the crust, is the extent to which the body is insulated by a regolith/megaregolith layer of porous, fragmental impact debris. Given plausible assumptions regarding the thicknesses of such layers on the moon and the eucrite parent asteroid (and regarding the radius of the eucrite asteroid), the results indicate that deep-crustal regions tend to remain above the Nd and Sr isotopic closure temperature for intervals that are long in comparison to the precision of modern Nd- and Sr-based age measurements, and in comparison to suggested chronologic scenarios of global differentiation. Ic intervals of as long as 100 my may be common among available samples of primordial, deep-crustal cumulates from both bodies. Chronologies for the gross solidification of the moon and the eucrite asteroid should allow for the possibility that any single age for a coarse-grained 'plutonic' or cumulate-textured rock might be many tens of millions of years younger than the igneous crystallization age.

Warren, Paul H.↗

NASA NTRS1991

The moon

Moon research is reviewed for the 1987-1990 time period. Particular attention is given to lunar meteorites, remote sensing and photogeology, impact cratering and impact breccias, soils, cores, and regolith breccias, mare magmatism, origin of the crust, bulk composition and origin of the moon.

Warren, Paul H.↗

NASA NTRS1990

Effects of regolith/megaregolith insulation on the cooling histories of differentiated asteroids

The cooling histories of differentiated asteroids are calculated employing a variety of thermal-conductivity structures to simulate the potential insulating effects of regolith and megaregolith layers on the cooling rate. It was found that a combination of relatively thick megaregolith and regolith can potentially reduce the core cooling rate by more than a factor of 10 below the rate predicted by models with conventional thermal conductivity structure. Thus, differences in cratering (regolith production) histories may have resulted in radically different cooling rates for asteroids of similar radius, or in similar cooling rates from asteroids of different radius.

Haack, Henning↗

NASA NTRS1990

In quest of lunar regolith breccias of exotic provenance - A uniquely anorthositic sample from the Fra Mauro (Apollo 14) highlands

Bulk compositions of 21 Apollo regolith breccias were determined using an INAA procedure modified from that of Kallemeyn et al. (1989). With one major exception, namely, the 14076,1 sample, the regolith breccias analyzed were found to be not significantly different from the surfaces from which they were collected. In contrast, the 14076,1 sample from the Fra Mauro (Apollo 14) region is a highly anorthositic regolith breccia from a site where anorthosites are extremely scarce. The sample's composition resembles soils from the Descartes (Apollo 16) highlands. However, the low statistical probability for long-distance horizontal transport by impact cratering, together with the relatively high contents of imcompatible elements in 14076,1 suggest that this regolith breccia originated within a few hundred kilometers of the Apollo 14 site. Its compositional resemblance to ferroan anorthosite strengthens the hypothesis that ferroan anorthosite originated as the flotation crust of a global magmasphere.

Jerde, Eric A.↗

NASA NTRS1989

Elephant Moraine 87521 - The first lunar meteorite composed of predominantly mare material

This paper presents the results of trace-element analyses and detailed petrography obtained for the Elephant Moraine 87521 meteorite (EET87521) found recently in Antarctica. Its high values found for the Fe/Mn ratio and the bulk-Co content indicate that the EET87521 is not, as was originally classified, a eucrite. Moreover, its low Ga/Al and Na/Ca ratios exclude the possibility that it is an SNC meteorite. These and other characteristics (e.g., a very low Ti content) of the EET87521 suggest its affinity with very-low-Ti high-alumina varieties of lunar mare basalt.

Warren, Paul H.↗

NASA NTRS1989

Geochemistry of polymict ureilite EET83309, and a partially-disruptive impact model for ureilite origin

Bulk-compositional data for the EET83309 polymict ureilite were obtained using INAA and radiochemistry procedures and electron probe analysis. It was found that the EET83309 has a bulk composition indistinguishable from ordinary ('monomict') ureilites for all elements except light-middle REEs (which are present in much higher concentrations), suggesting that polymict ureilites are mixtures of ordinary ureilites which were mixed on a very small number of parent bodies. Despite the light-REE enrichments, polymict ureilites are nearly devoid of basaltic (Al-rich) material. It is suggested that the missing basalt may have been blown off the parent body by a partially disruptive collision with a large C-rich projectile. This impact model of ureilite origin reconciles many paradoxical aspects of ureilite composition.

Warren, Paul H.↗

NASA NTRS1989

Lunar meteorites - Siderophile element contents, and implications for the composition and origin of the moon

Data for 10 siderophile elements in all of the known lunar meteorites except for Y793274 are reported. Bulk compositional data for Ni, Ge, Cd, Re, Os, Ir, and Au were obtained from radiochemical neutron activation analysis (Warren et al., 1986). Data for Fe, Co, and Zn, and additional data for Ni, Ir, and Au were obtained by instrumental neutron activation analysis (Kallemeyn et al., 1988). Except for the case of Au in Y791197, there was good agreement between the results obtained by the two methods. The differences observed between the lunar-meteoritic regolith samples and central nearside highlands regolith samples are discussed.

Warren, Paul H.↗

NASA NTRS1989

Preliminary examination of the Yamato-86032 lunar meteorite. II - Major and trace element chemistry

Results of the chemical composition analysis of Yamato-86032, found in Antarctica in 1986, are summarized. The meteorite may be classified as an anorthositic breccia, but its trace element composition is different from the composition of the other known lunar meteorites. The major element chemistry of Y-86032 is similar to the other lunar meteorites, except for the iron content, which is lower by a factor of about 1.4. The abundances of incompatible and lithophile elements such as Zr, Hf, Ta, Th, or the REEs are very low and comparable to Y-82192/3. Other elements, in particular Fe, Ti, Sc, Cr, Mn, and Co, have lower abundances in Y-86032 than in Y-82192/3. Variations between individual analysis demonstrate that the rock itself is heterogeneous.

Koeberl, Christian↗

NASA NTRS1988

Growth of the continental crust: A planetary-mantle perspective

The lack of earth rocks older than about 3.8 Ga is frequently interpreted as evidence that the earth formed little or no subduction-resistant continental crust during the first 700 My of its history. Such models obviously imply that the pre-3.8 Ga earth was covered entirely or almost entirely by smoothly subducting oceanic crust. On the other hand, the thermal regime of the early earth probably tended to cause the oceanic crust at this time to be comparatively thin and comparatively mafic. The present earth is covered by about 50 percent oceanic crust, averaging about 7 km in thickness, and 41 percent continental crust, averaging roughly 40 km in thickness. Thus continentless-early-earth models would seem to imply a total mass of crust less than 1/3 that of the present day earth. Possible explanations are examined.

Warren, Paul H.↗

NASA NTRS1988

The origin of pristine KREEP - Effects of mixing between UrKREEP and the magmas parental to the Mg-rich cumulates

The fact that pristine KREEP basalts generally have bulk-rock molar MgO/(MgO+FeO) ratios lower than average for the lunar crust despite their extraordinarily high incompatible element contents is discussed. Pristine KREEP basalts also have primitive Ni contents compared to mare basalts with comparable REE contents. It is suggested that these facts can be explained through mixing between ancient KREEP precursor materials and primitive Mg-rich melts. Finite-difference models of this mixing, followed by anorthosite assimilation and fractional crystallization provide satisfactory fits to the composition of these basalts. It is suggested that this is a further confirmation of the magmasphere hypothesis.

Warren, Paul H.↗

NASA NTRS1987

Mars regolith versus SNC meteorites - Possible evidence for abundant crustal carbonates

Viking XRF data of the Martian regolith are compared with data of typical igneous rocks of the earth, Moon, eucrite parent asteroid, and shergottite, nakhlite, and Chassigny (SNC) meteorites. It is suggested that regolith's low Ca/Si ratio, with respect to igneous rocks with similar (Mg + Fe)/Si ratios, is not a result of simple mixing of SNC-like rocks with other igneous rocks, but rather is due to the removal of Ca from the regolith as Ca-carbonate. Formation of a mass of carbonate equivalent to a 20-m-thick global shell could account for the removal of 1000 mbar of CO2 from the Martian atmosphere. This Ca/Si ratio is consistent with the hypothesis that the Martian climate was once far warmer and wetter than at present.

Warren, Paul H.↗

NASA NTRS1987

Pristine moon rocks - A 'large' felsite and a metal-rich ferroan anorthosite

Results of elemental analyses, performed either by instrumental neutron activation analysis (NAA) or radiochemical NAA, of 19 lunar rock samples obtained by the Apollo 15, 17, and 12 missions are presented. Two of the samples are most extraordinary: 'large' (1 g) felsite from Apollo 12 and a pristine ferroan anorthosite from Apollo 15. The felsite is mainly a graphic intergrowth of K-feldspar and a silica phase, with about 6 pct plagioclase and 1 pct each of ferroaugite, ilmenite, and fayalitic olivine. The Fe-metal content of ferroan anorthosite is 1.2 wt pct in the thin section studied (but, based on mass balance for Co and Ni, must have been lower in the chip used for bulk-rock analysis); the measured bulk-rock concentrations of siderophile elements Re, Os, and Ir are far higher than previously observed among pristine lunar anorthosites. These results underscore the uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon's crust.

Warren, Paul H.↗

NASA NTRS1987

A potpourri of regolith breccias - 'New' samples from the Apollo 14, 16, and 17 landing sites

Compositional (by INAA) and petrographic studies were performed among the smaller rocks (not analyzed previously) from the Apollo 14, 16, and 17 sites as part of a search for regolith samples exotic to the small traverse areas associated with these missions. Of the 40 samples studied, 31 were regolith breccias. Among these, three of the Apollo 14 samples proved to be compositionally unique, particularly the 14315 sample, which is radically different from all other Apollo 14 regolith materials (lower Mg and Fe, far higher Al and far lower REE abundances), and is probably exotic to the Apollo 14 traverse area. Among 10 samples from Apollo 17, all but one proved to be typical Apollo 17 regolith breccia. However, the 72504,10 sample is more than 99 percent pure pyroclastic glass, compositionally identical to the Apollo 17 orange glass obtained at a location 4 km away, attesting to the widespread distribution of orange glass deposits.

Jerde, Eric A.↗

NASA NTRS1987

Composition and origin of Nuevo Laredo Trend eucrites

The new bulk-rock analyses reported for the ALHA81001, Lakangaon and Nuevo Laredo eucritic meteorites indicate that the first of these resembles Ibitira in possessing lower Na concentrations than any other eucrite, while the other two are the lowest-Mg/Fe of all eucrites. The present data and those seen in the literature suggest that most of the ostensible Main Group eucrites actually belong to the Nuevo Laredo Trend, which is characterized by limited variations of incompatible element contents despite considerable variations in Mg/(Mg+Fe) ratio and V content.

Warren, Paul H.↗

NASA NTRS1987

Mars regolith versus SNC meteorites: Evidence for abundant crustal carbonates

Viking XRF analyses are compared with those for terrestrial and lunar basalt samples, and eucritic meteorites (of possible Mars origin). The comparison indicates depletion of Ca relative to Si in the Mars regolith. It is suggested that carbonate formation during a warmer, wetter epoch early in Mars' history could have been responsible.

Warren, Paul H.↗

NASA NTRS1986

Megaregolith insulation, internal temperatures, and bulk uranium content of the moon

Finite-difference models are used to study the effects of insulation by the megaregolith on lunar thermal evolution. Results indicate that the megaregolith has two important influences on heat flow: (1) Because the megaregolith is exceptionally thin in mare regions, heat passes more readily through them than through highland regions, and even flows laterally from the highland toward the mare. As a result, heat flow is exceptionally high along a boundary between highland and mare regions. (2) On a global scale, megaregolith insulation combined with lithosphere insulation causes slow cooling, which as a cumulative effect results in high present-day mantle temperatures and heat flow. Assuming that the global mean megaregolith thickness is 2 km, a heat flow of 12 mW/sq m is best matched by models with bulk moon U contents of 20-21 ng/g. Independent constraints on lunar internal temperatures derived from magnetic and tectonic data are best matched by models with about 14 ng/g U. Thus the bulk moon U content is roughly 17 ng/g. These results imply that the bulk moon contents of U, and related refractory lithophile elements such as Th, Al, Ca, etc., must be considerably lower than commonly assumed.

Warren, Paul H.↗