Engineering topics

Nyquist, L. E.

Publications and source records attributed to Nyquist, L. E..

At least 127 records · Page 7

NASA NTRS1994

Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513

Igneous clasts of basaltic eucrites are found in both howardites and polymict eucrites. We have studied the Rb-Sr and Sm-Nd isotopic systematics of a number of such clasts, of metamorphic grades 1-6, using the classification of Takeda and Graham. Here, we report Rb-Sr, (147)Sm-(143)Nd, and (145)Sm-(142)Nd studies of clast, 53 from Antarctic howardite EET87503. Although there is no evidence of disturbance of trace element systematics by Antarctic weathering, the Rb-Sr and conventional Sm-Nd isotopic systematics are severely disturbed, which we ascribe to thermal metamorphism. The Ar-Ar age spectrum shows ages ranging from approximately 3.85-3.55 Ga in an unusual 'down stairstep'. The (146)Sm-(142)Nd systematics, however, show the presence of live (146)Sm(t(sub 1/2) = 103 Ma), with (146)Sm/(144)Sm = 0.0061 +/- 0.0007 at the time of crystallization. This result is very similar to that previously obtained for basaltic clast, 18 from howardite EET87513 (paired with EET87503), which has concordant Rb-Sr and Sm-Nd ages of approximately 4.5 Ga. Thus, the two clasts are nearly the same age, and we conclude further than the EET87503,53 clast crystallized within 33 +/- 19 Ma of the LEW86010 angrite by comparing initial (146)Sm/(144)Sm to that of the angrite. We suggest that disturbances in the isotopic systematics of EET87503,53 are consanguineous with pyroxene homogenization.

Nyquist, L. E.↗

NASA NTRS1994

New data supporting a Sm-146,147-Nd-142,143 formation interval for the lunar mantle

Very small variations in Nd-142 abundance in SNC meteorites lunar basalts, and a terrestrial supracrustal rock, have been attributed to the decay of 103 Ma Sm-146 initially present in basalt source regions in varying abundances as a result of planetary differentiation. We previously interpreted variations in Nd-142 abundances in two Apollo 17 high-Ti basalts, three Apollo 12 low-Ti basalts, and two KREEP basalts as defining an isochron giving a formation interval of approximately 94 Ma for the lunar mantle. Here we report new data for a third Apollo 17 high-Ti basalt, two Apollo 15 low-Ti basalts, the VLT basaltic lunar meteorite A881757 (formerly Asuka 31), basalt-like KREEP impact melt rocks 14310 and 14078, and three terrestrial rock standards. Those lunar samples which were not exposed to large lunar surface thermal neutron fluences yield a revised mantle formation interval of 237 +/- 64 Ma.

Nyquist, L. E.↗

NASA NTRS1993

Ages of pristine noritic clasts from lunar breccias 15445 and 15455

The Rb-Sr and Sm-Nd isotopic ages were determined for two Apollo 15 pristine lunar breccias, 15445 and 15455, collected near Spur Crater on the Apennine Front. The analyses of mineral separates from two norite samples in breccia 15445 showed that the Sm-Nd isotopic system for both norites from the large Clast B of 15445 was well defined, yielding precise ages of 4.28 +/- 0.03 Ga and 4.46 +/- 0.07 Ga, suggesting that the Cast B is a mixture of two or more lithologies. The overall age results indicate that some Mg-suite rocks are as old as ferroan-anorthosite-suite rocks. Moreover, age data of three major crustal rocks (a Mg suite, a ferroan-anorthosite suite, and an evolved suite) show that they all have variable ages.

Shih, C.-Y.↗

NASA NTRS1993

Petrologic models of 15388, a unique Apollo 15 mare basalt

Mare basalt 15388, a feldspathic microgabbro from the Apennine Front, is chemically and petrographically distinct from Apollo 15 picritic, olivine-normative (ON), and quartz-normative basalts. The evolved chemistry, coarse texture, lack of olivine, and occurrence of cristobalite in 15388 argue for derivation by a late-stage magmatic process that is significantly removed from parental magma. It either crystallized from a magma evolved from the more mafic Apollo 15 basalts, or it crystallized from a currently unrepresented magma. Rb-Sr and Sm-Nd isotopic systematics yield isochron ages of 3.391 plus or minus 0.036 and 3.42 plus or minus 0.07 Ga, respectively, and epsilon(sub Nd) = 8.6 plus or minus 2.4, which is relatively high for Apollo 15 mare basalts. In contrast to chemical patterns of average Apollo 15 ON basalts and Apollo 15 picritic basalt, 15388 has a strongly positive LREE slope, high Ti, shallower HREE slope and a slightly positive Eu anomaly. These features argue against 15388 evolution by simple olivine fractionation of a parental ON or picritic basalt magma, although olivine is a dominant liquidus phase in both potential parents.

Hughes, S. S.↗

NASA NTRS1993

The Sm-(146,147)-Nd-(142,143) formation interval for the lunar mantle and implications for lunar evolution

Small anomalies in the isotopic abundance of Nd-142 have been measured for two A17 high-Ti basalts, ilmenite basalt 12056, olivine-pigeonite basalt 12039, feldspathic basalt 12038, and two KREEP basalts. These anomalies correlate with Sm-147/Nd-144 for the basalt source regions as calculated from initial Nd-143/Nd-144 ratios in the basalts, and are interpreted to be from decay of Sm-146 (t sub 1/2 = 103 Ma) in distinct lunar mantle reservoirs. A three-stage model for evolution of Nd-143/Nd-144 and Nd-142/Nd-144 yields reservoir Sm-147/Nd-144 ratios which, with the Nd-142/Nd-144 ratios in the basalts, form a 'mantle isochron' giving a lunar mantle formation interval of 94+2230 Ma (2c(rho)). Calculated reservoir Sm/Nd ratios are in the range expected from some earlier models of basalt petrogenesis. The isochron value of Nd-142/Nd-144 at Sm-147/Nd-144 sub CHUR = 0.1967 is within error limits of the average Nd-142/Nd-144 measured for an L6 chondrite, an H5 chondrite, and the Orgueil carbonaceous chondrite. Evolution of Nd-143 and Nd-142 for high-Ti basalt 70135 was modeled precisely, starting from chondritic relative REE and Nd-isotopic abundances and using the initial (Sm-146/Sm-144) sub 0 ratio inferred from a previous study of angrite LEW86010 as the initial solar system value of this parameter. We infer that the initial Sm/Nd ratio in precursor lunar materials was very nearly chondritic (within approximately 8 percent) prior to lunar differentiation.

Nyquist, L. E.↗

NASA NTRS1993

Chronology of lunar granite 12033,576: Resetting of Rb-Sr and K-Ca isochrons

Lunar granite 12033,576 is a subsample of the 'large' (approximately 1 g) felsite 12033,507 which was identified from a collection of 4-10 mm particles from the 12033 soil sampled from the north rim of Head Crater in the eastern part of Oceanus Procellarum. Discordant ages of approximately 3.6, approximately 0.8, approximately 3.9, and approximately 2.2 Ga for this lunar granite were obtained, respectively, by the K-Ca, Ar-39/Ar-40, and U-Pb zircon methods in previous studies and by the Rb-Sr method is this study. Assuming the granite crystallized approximately 3.9 Ga ago (zircon age) and was shocked by meteoritic impacts at 0.8 Ga ago (Ar-39-Ar-40 age), the intermediate apparent ages by the Rb-Sr and K-Ca methods can be interpreted as reset by diffusion of the parent and daughter nuclides. The Rb-Sr age is less resistant to resetting than the K-Ca age, but more resistant that the Ar-39/Ar-40 age.

Shih, C.-Y.↗

NASA NTRS1992

The isotopic record of lunar volcanism

Some fundamental aspects of lunar history which have been established as a result of the Apollo program of lunary exploration and contemporaneous Soviet lunar missions are summarized, with emphasis on the isotopic data which record lunar global evolution most directly. It is shown that some lunar anorthosites formed about 4.45 Ga ago, consistent with the early formation of an anorthositic lunar crust. Some 'Mg-suite' norites, troctolites, and dunites also formed approximately contemporaneously with the oldest anorthosites, but others are up to 200-300 Ma younger. More evolved rocks (granites and quartz-monzodiorites) also formed between about 4.4 and 4.0 Ga ago. KREEP basalt volcanism began at least 4.1 Ga ago, approximately contemporaneously with that of the ancient, mare-like basalts, and continued during the cataclysm. The isotopic data record an early primary lunar differentiation during which mare basalt sources formed, probably by crystallization of cumulus minerals from a lunar magma ocean.

Nyquist, L. E.↗

NASA NTRS1992

Rb-Sr and Sm-Nd chronology of an Apollo 17 KREEP basalt

The paper determines Sm-Nd and Rb-Sr mineral isochrons for an Apollo 17 KREEP (pigeonite) basalt clast from breccia 72275 collected from Boulder 1, Station 2 in the Valley of Taurus-Littrow. Sm-Nd analyses of the basalt yield a precise mineral isochron age of 4.08 +/-0.07 Ga for lambda(Sm-147) = 0.00654/Ga. The concordancy of Sm-Nd and Rb-Sr ages for the basalt suggests that it crystallized about 4.08 Ga ago. Distinct ages and initial Sr isotopic ratios for Apollo 17 KREEP basalts and Apollo 14 and 15 KREEP suggest that these two types of KREEP basalts were not derived from the same source. Apollo 17 KREEP basalts are contemporaneous with some Apollo 14 aluminous mare basalts. The ages and Sr and Nd isotopic data suggest that these two different types of basalts were produced from sources having similar Rb/Sr ratios but different Sm/Nd ratios.

Shih, C.-Y.↗

NASA NTRS1991

Cs-135 - Ba-135: A new cosmochronometric constraint on the origin of the Earth and the astrophysical site of the origin of the solar system

It is argued that if Cs-135 was indeed present in the early solar system at the level inferred from evidence presented here, then two major conclusions follow. (1) A supernova contributed newly synthesized r-process matter into the protosolar reservoir within approx. 5 Ma of the Cs/Ba fractionation recorded in LEW 86010; (2) The strong Cs depletion in the bulk Earth reservoir (Cs-133/Ba-135 approx. 0.1) took place very early in solar system history. If this volatile loss was pre-accretionary, then the accretionary chronology of the Earth is not constrained. However, if it is a consequence of accretion, then the very tight time constraint of approx. less than 5 Ma (rel. to LEW 86010) is obtained for accretion of most of the Earth's mass.

Harper, C. L.↗

NASA NTRS1991

Nd-142/Nd-144 in SNCs and early differentiation of a heterogeneous Martian mantle

Sm/Nd correlated variations in Nd-142/Nd-144 have been observed for mineral phases of achondrites from decay of live Sm-146 in the early solar system. Crystallization ages of shergottites-nakhlites-Chassigny (SNC) meteorites are less than or = 1.3 Ga, so variations of Nd-142/Nd-144 among mineral phases of the SNC's are not expected. However, if SNC's were derived from source reservoirs of differing Sm/Nd ratios, established while Sm-146 was still alive, and which remained isolated except for magma extraction, then variations in Nd-142/Nd-144 would exist among individual SNC meteorites. Rb-Sr and U-Pb isotopic data for the shergottites imply differentiation of their parent planet approximately 4.6 Ga ago. The confirmation of the conclusion that the nakhlites and shergottites were derived from different source regions, and that, consequently, the shergottite parent body (SPB) mantle was heterogeneous is presented.

Nyquist, L. E.↗

NASA NTRS1989

Chronology and complexity of early lunar crust

The petrology and chronology of early lunar crust is examined using the least equivocal of the available petrographic and age data on lunar rock samples, and the possible processes which produced the lunar crust are discussed. The results suggest that the lunar anorthositic crust was formed by about 120 Ma after the primary accretion of the moon at 4.56 Ga. At least some members of the diverse Mg-suites of rocks, such as norites, troctolites, and dunites, crystallized within a very few 100s of Ma after 4.56 Ga. A trace-element-rich material (KREEP) was formed by about 4.3 Ga ago, and this residue was subsequently reworked in melting and impact processes such that most samples which contain it have ages around 3.9-4.0 Ga. The findings also suggest that the onset of ferrous mare basalt volcanism began about 4.33 Ga, much earlier than was once assumed, and was still in process before the end of the most intense period of bombardment (3.9-4.0 Ga ago).

Dasch, E. J.↗

NASA NTRS1988

Chronology of early lunar crust

The chronology of lunar rocks is summarized. The oldest pristine (i.e., lacking meteoritic contamination of admixed components) lunar rock, recently dated with Sm-Nd by Lugmair, is a ferroan anorthosite, with an age of 4.44 + 0.02 Ga. Ages of Mg-suite rocks (4.1 to 4.5 Ga) have large uncertainties, so that age differences between lunar plutonic rock suites cannot yet be resolved. Most mare basalts crystallized between 3.1 and 3.9 Ga. The vast bulk of the lunar crust, therefore, formed before the oldest preserved terrestrial rocks. If the Moon accreted at 4.56 Ga, then 120 Ma may have elapsed before lunar crust was formed.

Dasch, E. J.↗

NASA NTRS1987

Isotopic analysis of basaltic fragments from lunar breccia 14321 - Chronology and petrogenesis of pre-Imbrium mare volcanism

Internal (mineral) Rb-Sr isochrons were determined for six Apollo 14 mare basalts of lunar breccia 14321. The ages of these fragments, which represent the time of crystallization of the respective mafic lavas, range from about 4.05 to 4.24, and, possibly, to 4.33 Ga and are among the oldest dates reported for mare basalts. For three of the fragments, internal Sm-Nd isochron data were collected and initial Nd isotopic composition was determined. The results are discussed with reference to the original source of these different basaltic fragments.

Dasch, E. J.↗

NASA NTRS1987

Geochronology of high-K aluminous mare basalt clasts from Apollo 14 breccia 14304

Two aluminous mare basalt clasts of high K abundances from Apollo 14 breccia 14304 (the 14304,127 and 14304,128 samples) were characterized with respect to the Rb and Sr concentrations and isotopic compositions, and the Rb-Sr, K-Ar, and Sm-Nd isotopic age determinations were carried out. The results suggest that these high-K basalts were melts derived from mantle material and that they have experienced about ten-fold Rb/Sr and K/La enrichments at approximately the time of crystallization.

Shih, C.-Y.↗

NASA NTRS1986

Rb-Sr and Sm-Nd internal isochron ages of a subophitic basalt clast and a matrix sample from the Y75011 eucrite

Rb-Sr and Sm-Nd dating studies of the Yamato polymict eucrite Y75011, which contains several coarse-grained mesostasis-rich basaltic clasts with subophitic texture which are representative of pristine lavalike basalts extruded on the surface of the Howardite-Eucrite-Diogenite (HED) parent body, are reported. The results show that moderately evolved basaltic lavas were produced very early in the history of the HED parent body. Their preservation as clasts in the polymict eucrites suggests derivation from a different geological setting on the parent body than that occupied by the more thermally metamorphosed monomict eucrites. It is suggested that the preservation of pristine clasts in polymict eucrites may be due to their impact excavation to the surface of the parent body away from heat sources concentrated within impact craters.

Nyquist, L. E.↗

NASA NTRS1986

Geochronology and petrogenesis of Apollo 14 very high potassium mare basalts

Rb-Sr, K-Ar, and Sm-Nd isotopic studies were undertaken for two Apollo 14 very high potassium (VHK) highly radiogenic mare basaltic clasts from breccias 14305 and 14168. Rb-Sr data indicate ages of 3.83 + or - 0.08 b.y., and 3.82 + or - 0.12 b.y. for samples 14305 and 14168 respectively, for lambda(Rb-87) = 0.0 139/b.y. Their corresponding initial Sr-87/Sr-86 ratios are nearly identical, as well as their Ar-39 to Ar-40 age spectra, and it is proposed that they were derived from the same flow. The Sm-Nd isotopic data of whole rock and mineral separates for the two VHK basalts define an internal isochrone age of 3.94 + or - 0.16 b.y. for lambda (Sm-147) = 0.00654/b.y. and an initial Nd-143/Nd-144 of 0.50673 + or - 21. The similarity in isotopic ages suggests that VHK basalts crystallized from a melt about 3.85 b.y. ago. VHK basalts show very large Rb/Sr fractionation but no significant Sm/Nd fractionation at the time of crystallization. The source material had a Rb/Sr ratio similar to those of Apollo 14 high-Al mare basalts and a nearly chrondritic Sm/Nd ratio. Basalt/granite interaction was found to be responsible for the extreme enrichments of Rb/Sr and K/La during the formation of VHK basalts. It is concluded that K, Rb-rich components of granitic wall rocks in the highland crust were selectively introduced into ascending hot high-Al mare basaltic magma upon contact.

Shih, C.-Y.↗

NASA NTRS1986

Redetermination of parameters for semi-empirical model for spallogenic He and Ne in chondrites

A semi-empirical model described previously satisfactorily reproduced a number of shielding-dependent variations in the relative production rates of spallogenic He and Ne in chondrites. However, data for cores of the Keyes and St. Severin meteorites showed a subsurface build-up in He-3 which was not predicted with the original model parameters and the model was not pursued. Renewed interest in the preatmospheric size of meteorites, spurred in part by the desirability of understanding the exposure history of the SNC meteorites, justifies redetermination of model parameters.

Nyquist, L. E.↗

NASA NTRS1985

Very high potassium (VHK) basalt - Complications in mare basalt petrogenesis

The first comprehensive report on the petrology and geochemistry of Apollo 14 VHK (Very High Potassium) basalts and their implications for lunar evolution is presented. The reported data are most consistent with the hypothesis that VHK basalts formed through the partial assimilation of granite by a normal low-Ti, high-Al mare basalt magma. Assimilation was preceded by the diffusion-controlled exchange of alkalis and Ba between basalt magma and the low-temperature melt fraction of the granite. Hypotheses involving volatile/nonvolatile fractionations or long-term enrichment of the source regions in K are inconsistent with the suprachondritic Ba/La ratios and low initial Sr-87/Sr-86 ratios of VHK basalt. An important implication of this conclusion is that granite should be a significant component of the lunar crust at the Apollo 14 site.

Shervais, J. W.↗