Engineering topics

Warren, P. H.

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

At least 19 records

NASA NTRS1993

Consortium reports on lunar meteorites Yamato 793169 and Asuka 881757, a new type of mare basalt

Consortium studies on lunar meteorites Yamato 793169 and Asuka 881757 (formerly Asuka-31) were performed to characterize these new samples from unknown locations in the lunar mare. Both meteorites are coarse-grained mare rocks having low Mg/Fe ratios (bulk mg'=30-35) and low TiO2 (1.5-2.5 percent in homogenized bulk samples). They are intermediate between VLT and low-Ti mare basalts. Although these meteorites are not identical to each other, their mineral and bulk compositions, isotopic systematics, and crystallization ages are remarkably similar and distinct from those of all other mare basalts. They appear to represent a new type of low-Ti mare basalt that crystallized at about 3.9Ga. These meteorites are inconsistent with the canonical correlation between the TiO2 contents and ages of mare basalts and suggest that our knowledge of lunar volcanism is far from complete.

Yanai, Keizo↗

NASA NTRS1991

Pristine moon rocks - Apollo 17 anorthosites

New chemical analyses and petrographic descriptions for 10 previously unanalyzed Apollo 17 rock samples are provided. Attention is focused on several that appear to be pristine. All samples were analyzed in INAA using a procedure based on that of Kallemeyn et al. (1989). One sample was found to be unambiguously pristine, and is the first pristine ferroan-anorthositic suite (FAS) sample from Apollo 17. It exhibits extremely low-mg(asterisk) mafic silicates, coupled with relatively sodic plagioclase. It has an unusually high augite/low-Ca pyroxene ratio and contains incompatible trace elements at levels unprecedentedly high compared to FAS anorthosites from the Apollo 14, 15, 16 sites. It is inferred that 74114.5, and Apollo 17 anorthosites in general, formed at a relatively late stage in the evolution of the primordial magmasphere.

Warren, P. H.↗

NASA NTRS1990

Pristine moon rocks - An alkali anorthosite with coarse augite exsolution from plagioclase, a magnesian harzburgite, and other oddities

Results are presented on the analyses of 18 samples of pristine rocks obtained from the primarily mare Apollo 12 site and from the primarily highland Apollo 14 site, as well as samples from the nonmare Apollo 15 site. It was found that, while two of anorthosites from Apollo 12 were similar in composition to most other anorthosites from the west-central near region, the texture of an alkali anorthosite featured a long and narrow crystal of augite surrounded by a single crystal of plagioclase, clearly suggesting that the augite formed by exsolution out of the plagioclase. Another Apollo 12 rocklet was an unusual magnesian harzburite, with subequal amounts of enstatite and olivine, traces of Cr-Fe spinel, and FeNi metal, but no plagioclase; the bulk composition was found to be remarkably Ir-rich (53 percent) for a pristine rock, and the texture was also unusual. Apollo 14 samples included several uncommonly Al-rich and REE-poor impact melt breccias.

Warren, P. H.↗

NASA NTRS1990

Pomozdino - An anomalous, high-MgO/FeO, yet REE-rich eucrite

A new chemical analysis and petrographic data for the Pomozdino basaltic achondrite are presented. Earlier indications that Pomozdino is a eucrite and that it is a monomict breccia with an anomalous, REE-rich, yet high-MgO/FeO bulk composition, are confirmed. Characteristics such as texture, composition, and REE concentration are examined and compared to those in other publications. A model for the origin of this meteorite, as a partial cumulate with an uncommonly high content of trapped liquid, is found to be preferable. Two alternatives of the origin are suggested, one of which implies that the parent melt is roughly similar in composition to Stannern. The other considers Pomozdino as a possible primary partial melt, derived from a source region far more magnesian than generally envisaged for the sources of primary eucritic partial melts. It is concluded that at least some Stannern-like eucrites were involved in fractional crystallization, and thus do not represent primary partial melts.

Warren, P. H.↗

NASA NTRS1989

Allan Hills 84025 - The second brachinite, far more differentiated than brachina, and an ultramafic achondritic clast from L chondrite Yamato 75097

New bulk-compositional and petrographic data tend to confirm that dunitic-wehrlitic meteorite ALH84025 is a second brachinite. It is suggested here that ALH84025 originated as an olivine heteradcumulate, whereas Brachina, or ALH84025, originated as an olivine orthocumulate. The tendency for pyroxenes among brachinites to be high-Ca may be a consequence of a relatively low MgO/FeO ratio, and/or high Na/Ca and K/Ca ratios in the bulk parent body. New data for a 2.5-cm dunite-melatroctolite clast from L6 chondrite Y75097 are reported. This clast has experience depletion of middle REE, except for a large (+) Eu anomaly. The clast as a whole is enriched in phosphates, but almost exclusively in its least-metamorphosed 'core' portion, whereas the analyzed samples represent phosphate-poor portions. It is suggested that this bizarre assemblage probably originated as an achondrite containing cumulus olivine, plagioclase, and phosphate, not necessarily all from a single igneous source rock.

Warren, P. H.↗

NASA NTRS1989

Workshop on Moon in Transition: Apollo 14, KREEP, and Evolved Lunar Rocks

Lunar rocks provide material for analyzing lunar history and now new evaluation procedures are available for discovering new information from the Fra Mauro highlands rocks, which are different from any other lunar samples. These and other topics were discussed at this workshop, including a new evaluation of the nature and history of KREEP, granite, and other evolved lunar rock types, and ultimately a fresh evaluation of the transition of the moon from its early anorthosite-forming period to its later stages of KREEPy, granitic, and mare magmatism. The summary of presentations and discussion is based on notes taken by the respective summarizers during the workshop.

Taylor, G. J.↗

NASA NTRS1986

Alkali norite, troctolites, and VHK mare basalts from breccia 14304

Six pristine rocks, two mare basalts, and four nonpristine highlands rocks were separated from breccia 14304 for consortium study. The pristine highlands rocks include representatives of the Mg troctolite-anorthosite and alkali suites of the Apollo 14 site. Two troctolite clasts have olivine and plagioclase compositions similar to one group of Apollo 14 troctolites and one also contains spinel. Incompatible element abundances in one are similar to those of 14305 troctolites, although the heavy rare earth elements pattern is distinct among Apollo 14 troctolites. Alkali lithologies include an alkali anorthosite and an alkali norite, the latter having a pristine igneous texture and resembling alkali gabbronites from Apollo 14 and 67975 in mineralogy and mineral compositions. It is suggested that Apollo 14 alkali lithologies and PO4-bearing Mg anorthosites formed from Mg-rich magmas that assimilated various amounts of material rich in P and REE. Another pristine clast from 14304 is an Mg-gabbronorite. The two mare basalt clasts are very high potassium basalts, whose parent magmas could have formed from a typical low-Ti, high-Al basaltic magmas by assimilation of K-rich material. Nonpristine 14304 clasts include melt-textured anorthosites and an augite-rich poikilitic melt rock.

Goodrich, C. A.↗

NASA NTRS1986

A potpourri of pristine moon rocks, including a VHK mare basalt and a unique, augite-rich Apollo 17 anorthosite

The anorthosite fragment, 76504,18, the first of the Apollo 17's pristine anorthosites, was found to have: (1) a higher ratio of high-Ca pyroxine to low-Ca pyroxene, (2) higher Na in its plagioclase, (3) higher contents of incompatible elements, and (4) a higher Eu/Al ratio in comparison to ferroan anorthosites. With a parent melt having a negative Eu anomaly, 76504,18 closely resembles a typical mare basalt. This anorthosite was among the latest to be formed by plagioclase flotation above a primordial magmasphere; typical mare basalt regions accumulated at about the same time or even earlier. Another fragment 14181c, a very high potassium basalt, was studied and found to be similar to typical Apollo 14 mare basalt though it has a K/La ratio of 1050. It is suggested that this lithology formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderphile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination.

Warren, P. H.↗

NASA NTRS1986

Anorthosite assimilation and the origin of the Mg/Fe-related bimodality of pristine moon rocks - Support for the magmasphere hypothesis

The geochemical bimodality of pristine rocks led to proposals that a major fraction of the crust (the Mg rich suite) formed in cumulates in numerous intrusions slightly younger than the magmasphere. It is suggested that assimilation helped to engender the bimodal patterns. Mass/energy balance calculations indicate that large proportions of plagioclase were probably assimilated from the older (Magmasphere-generated) ferroan anorthosite crust by most of the Mg-rich intrusive melts. The magmasphere, in the absence of assimilation probably did not yield appreciable plagioclase until fractional crystallization of mafic silicates had diminished the melt mg ratio to about 0.42. However, assuming identical melt composition, an Mg-rich intrusion assimilating ferroan anorthosite would have reached plagioclase saturation at a much higher mg, about 0.66. It is suggested that the current version of the magmasphere hypothesis (ferroan anorthosites = magmasphere flotation cumulates; Mg-rich rocks = products of younger, localized intrusions) is the only plausable mechanism for engendering the Mg/Fe-relate bimodality.

Warren, P. H.↗

NASA NTRS1985

Origin of howardites, diogenites and eucrites - A mass balance constraint

Two petrogenetic models for the noncumulate-basaltic parts of howardite meteorites are discussed. A mass balance constraint is developed which indicates that more than half of the basaltic components in howardites formed as residual liquids from fractional crystallization of melts that had earlier produced diogentelike pyroxene cumulate components. Other model constriants involving scandium trends, clustering near olivine-pyroxene-plagioclase peritectic, and MgO/(MgO + FeO) ratios are discussed.

Warren, P. H.↗

NASA NTRS1985

Megaregolith thickness, heat flow, and the bulk composition of the moon

Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25 percent higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83 percent of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) mantle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.

Rasmussen, K. L.↗

NASA NTRS1985

Earth's primordial differentiation, and its after-effects

The case for massive primordial melting on the Earth is circumstantial (i.e., based mainly on lunar evidence), but nonetheless compelling. The term magma ocean is probably a hyperbole. Among other things, ocean implies the system is virtually 100% liquid, with a mainly gas/liquid upper surface, and a water like viscosity of the order .01 poise. The preferred term for this phenomenon is magmasphere.

Warren, P. H.↗

NASA NTRS1985

Primordial magmaspheres and their lasting consequences

The lunar magmasphere is a useful but potentially misleading analog for the earliest evolution of other planetary objects. A significant fraction of the lunar magmasphere became a crust rich in buoyant cumulus plagioclase. Another significant fraction became a series of ultramafic cumulates (the mare basalt sources) complementary to the anorthosite. These events predetermined all subsequent lunar evolution. Empirically, the Moon was big enough to produce a magmasphere. Beyond a depth limit of roughly 200 km, nearly independent of the size of the planet, the remainder of the magmasphere will probably at all times be a single convective, and therefore essentially non-differentiating layer. The fraction of the mantle contained in the outer 200 km is of course inversely related to planet size. Compared to the Moon the Earth's mantle comprises a volume of 40 x greater and a pressure range 30 x greater. Steeper dP/dZ, favoring garnets and pyroxenes, also works to dampen differentiation in larger planets. One long term consequence of the Earth's magmasphere was probably a depletion of H2O in much of the mantle. Because water is a flux for mantle convection, anhydrous parts of the mantle probably had anomalously thick lithospheres and hot asthenospheres.

Warren, P. H.↗

NASA NTRS1985

Geochemical confirmation of the lunar magmasphere hypothesis

The lunar magmasphere (or magma ocean) hypothesis was originally conceived to account for the enrichment of cumulus plagioclase (Al and Ca) in the main (highlands) portion of the crust. The great age of the highlands, and the complementary pattern of Eu anomalies between the highlands and the younger mare basalts, helped convince most specialists that the magmasphere hypothesis is correct. Doubts persist, however, particularly among physicists concerned about heat sources. It was shown in 1976 that a plot of Na/Ca vs. Mg/Fe for pristine highlands cumulates manifests a profound bimodality: One group, the Mg-rich rocks, plots along a normal igneous trend of inverse correlation between Na/Ca and Mg/Fe; the other group, the ferroan anorthosites (FAN), features low Na/Ca and low Mg/Fe. Only the FAN group can be plausibly linked to plag. flotation over the magmasphere.

Warren, P. H.↗

NASA NTRS1985

The magma ocean concept and lunar evolution

The model of lunar evolution in which the anorthositic plagioclase-rich oldest crust of the moon is formed over a period of 300 Myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies. Consideration is given to the classification of lunar rocks, the evidence for primordial deep global differentiation, constraints on the depth of the molten zone, the effects of pressure on mineral stability relationships, mainly-liquid vs mainly-magmifer ocean models, and the evidence for multiple ancient differentiation episodes. A synthesis of the model of primordial differentiation and its aftereffects is presented, and the generalization of the model to the earth and to Mars, Mercury, Venus, and the asteroids is discussed.

Warren, P. H.↗

NASA NTRS1985

The origin of pristine KREEP: Effects of mixing between ur KREEP and the magmas parental to the MG-rich cumulates

The magnesium/incompatible elements paradox is explained by a model that considers not only the magmasphere, but also its aftermath. A systematic mixing of primitive magnesium rich material with residual liquid is discussed as a method to account for the paradox that KREEP basalts, despite their high incompatible element contents, have moderate magnesium ratios. The KREEP basalts are compared with mare basalts.

Warren, P. H.↗

NASA NTRS1984

Pristine rocks (8th Foray) - 'Plagiophile' element ratios, crustal genesis, and the bulk composition of the moon

Eu/Al, Sr/Al, Eu/Sr, and similar ratios among pristine lunar nonmare lithologies with implications for nonmare petrogenesis and for the bulk composition of the moon are examined. On a plot of Eu/Al versus mg, ferroan anorthosites are separated from all other pristine nonmare rocks by a considerable gap. A nonrandom process must be invoked to account for the gap in the spectrum of ratios. A single magma probably cannot account for even the Mg-rich pristine rocks subset, based on diversity of plagiophile ratios among samples with similar mg ratios. Plagiophile ratios also constrain the bulk composition of the moon. Plagiophile ratios among ferroan anorthosites exactly match those expected under a model in which ferroan anorthosites formed by flotation of plagioclase cumulates over a primordial 'magmasphere'. Ratios among nonvolatile elements confirm that the moon formed out of materials akin to chondritic meteorites.

Warren, P. H.↗

NASA NTRS1984

Megaregolith thickness, heat flow, and the bulk composition of the Moon

Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25% higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83% of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) matle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.

Warren, P. H.↗