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Nyquist, L. E.

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

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Derivation of Apollo 14 High-Al Basalts from Distinct Source Regions at Discrete Times: New Constraints

Apollo 14 basalts occur predominantly as clasts in breccias, but represent the oldest volcanic products that were returned from the Moon [1]. These basalts are relatively enriched in Al2O3 (11-16 wt%) compared to other mare basalts (7-11 wt%) and were originally classified into 5 compositional groups [2,3]. Neal et al. [4] proposed that a continuum of compositions existed. These were related through assimilation (of KREEP) and fractional crystallization (AFC). Age data, however, show that at least three volcanic episodes are recorded in the sample collection [1,5,6]. Recent work has demonstrated that there are three, possibly four groups of basalts in the Apollo 14 sample collection that were erupted from different source regions at different times [7]. This conclusion was based upon incompatible trace element (ITE) ratios of elements that should not be fractionated from one another during partial melting (Fig. 1). These groups are defined as Group A (Groups 4 & 5 of [3]), Group B (Groups 1 & 2 of [3]), and Group C (Group 3 of [3]). Basalt 14072 is distinct from Groups A-C.

Neal, C. R.↗
NASA NTRS2006

Initial Isotopic Heterogeneities in ZAGAMI: Evidence of a Complex Magmatic History

Interpretations of Zagami s magmatic history range from complex [1,2] to relatively simple [3]. Discordant radiometric ages led to a suggestion that the ages had been reset [4]. In an attempt to identify the mechanism, Rb-Sr isochrons were individually determined for both fine-grained and coarse-grained Zagami [5]. Ages of approx.180 Ma were obtained from both lithologies, but the initial Sr-87/Sr-86 (ISr) of the fine-grained lithology was higher by 8.6+/-0.4 e-units. Recently, a much older age of approx.4 Ga has been advocated [6]. Here, we extend our earlier investigation [5]. Rb-Sr Data: In [5] we applied identical, simplified, procedures to both lithologies to test whether a grain-size dependent process such as thermally-driven subsolidus isotopic reequilibration had caused age-resetting. Minerals were separated only by density. In the present experiment, purer mineral separates were analysed with improved techniques. Combined Rb-Sr results give ages (T) = 166+/-12 Ma and 177+/-9 Ma and I(subSr) = 0.72174+/-9 and 0.72227+/-7 for the coarse-grained and fine-grained lithologies, respectively. ISr in the fine-grained sample is thus higher than in the coarse-grained sample by 7.3+/-1.6 e-units. The results for the coarse-grained lithology are in close agreement with T = 166+/-6 Ma, ISr = 0.72157+/-8 for an adjacent sample [7] and T = 178+/-4 Ma, ISr = 0.72151+/-5 [4, adjusted] for a separate sample. Thus, fine-grained Zagami appears on average to be less typical of the bulk than coarse-grained Zagami.

Nyquist, L. E.↗
NASA NTRS2006

Sm-Nd Age and Nd- and Sr- Isotopic Evidence for the Petrogenesis of Dhofar 378

Dhofar 378 (hereafter Dho 378) is one of the most ferroan lithologies among martian meteorites, resembling the Los Angeles basaltic shergottite in lithology and mineral chemistry, although it is more highly shocked than Los Angeles. All plagioclase (Pl) grains in the original lithology were melted by an intense shock in the range 55-75 GPa. Clinopyroxenes (Cpx) sometimes show mosaic extinction under a microscope showing that they, too, experienced intense shock. Nevertheless, they zone from magnesian cores to ferroan rims, reflecting the original lithology. Cpx grains also often contain exsolution lamellae, showing that the original lithology cooled slowly enough for the lamellae to form. Because all plagioclase grains were melted by the intense shock and subsequently quenched, the main plagioclase component is glass (Pl-glass) rather than maskelynite. Like Los Angeles, but unlike most basaltic shergottites, Dho 378 contains approximately equal modal abundances of Cpx and Pl-glass. The grain sizes of the original minerals were comparatively large (approximately 1 mm). The original plagioclase zoning has been severely modified. Following shock melting, the plagioclase melts crystallized from the outside inward, first forming outer rims of Cpx-Pl intergrowths (approximately 10 micrometers) followed by inner rims (10's to 100 micrometers) of An(sub 40-50) feldspar, and finally Pl-gl cores of compositions An(sub 33-50) with orthoclase compositions up to Or(sub 12).

Nyquist, L. E.↗
NASA NTRS2005

Three-System Isotopic of Lunar Norite 78238: Rb-Sr Results

The duration of lunar magma ocean (LMO) crystallization is poorly constrained (Fig. 1). Three techniques employed to determine the age of LMO solidification are 1) dating ferroan anorthosites (FANs), thought to be primary cumulates from the LMO, 2) calculating model ages for KREEP, the most incompatible element enriched material that remained after approx.99.5% of the LMO crystallized [1], and 3) constraining the age of the oldest KREEP-rich magnesium suite (Mg-suite) or alkali suite rock. Dating FANs is difficult because the samples are essentially monomineralic and contain low abundances of many elements used in isotopic dating. In addition, the young ages determined for some FANs may be related to impact metamorphism, potentially making FANs non-ideal for dating the age of LMO crystallization (e.g., [2]). Model ages for KREEP formation are dependent on the assumptions of the initial isotopic composition and parent/daughter ratio of the source. However, lunar rocks are susceptible to isotopic resetting and volatile element loss during shock, and are therefore unlikely to yield consistent model LMO crystallization ages (e.g., [3]). Rocks from the Mg-suite contain KREEP, indicating that they formed after LMO crystallization, and have old ages that indicate they formed almost immediately after the LMO crystallized (Fig. 1). Therefore, precisely dating the oldest Mg-suite rock is a promising way to constrain the age of LMO solidification.

Edmundson, J.↗
NASA NTRS2005

Age of Lunar Meteorite LAP02205 and Implications for Impact-Sampling of Planetary Surfaces

We have measured the age of lunar meteorite LAP02205 by the Rb-Sr and Ar-Ar methods. Sm-Nd analyses are in progress. The Rb-Sr and Ar-Ar ages indicate a crystallization age of approx. 3 Ga. Comparing the ages of LAP02205 and other lunar mare basaltic meteorites to mare surface ages based on the density of impact craters shows no significant bias in impact- sampling of lunar mare surfaces. Comparing the isotopic and geochemical data for LAP02205 to those for other lunar mare basalts suggests that it is a younger variant of the type of volcanism that produced the Apollo 12 basalts. Representative impact-sampling of the lunar surface

Nyquist, L. E.↗
NASA NTRS2005

Crystallization Age and Source Signature of Chassigny

Chassigny is the Martian dunite composed of cumulate olivine (92%), chromite (1.4%), pyroxene (5%) and interstitial feldspar (1.7%). Although nakhlites (clinopyroxenite) are less intensely affected by shock metamorphism, Chassigny has been subjected to a peak shock pressure of about 35 GPa. The cosmic-ray exposure age of Chassigny (11.3 +/- 0.6 Ma) is comparable to those of nakhlites, suggesting launch pairing of these meteorites. Prior chemical and isotopic studies of Chassigny suggest that the meteorite crystallized approx. 1.3 Ga ago and is closely related to nakhlites. Nevertheless, compared to other Martian meteorites there are limited isotopic data for Chassigny. To examine the relationship of Chassigny to nakhlites, we have undertaken new Rb-Sr and Sm-Nd isotopic studies. Here we present the new Sm-Nd isotopic data for Chassigny and discuss the nature of its source materials.

Misawa, K.↗
NASA NTRS2005

Rb-Sr and Sm-Nd Isotopic Studies of Lunar Highland Meteorite Y86032 and Lunar Ferroan Anorthosites 60025 and 67075

Lunar meteorite Yamato (Y) 86032 is a feldspathic breccia containing anorthositic fragments similar to ferroan anorthosite (FAN) clasts commonly found in Apollo 16 highland rocks. Previous Ar-39-Ar-40 analyses of a grey anorthositic clast (,116 GC) in Y86032 revealed an old degassing age of 4.39 plus or minus 0.06 Ga, which is as old as crystallization ages of some FANs e.g. 60025, 67016 and 67215, as determined by the more robust Sm-Nd radiometric method. The calculated initial Nd value for the clast is -1.8 plus or minus 0.3 for the age. The old age and its negative initial Nd value indicate that Y86032 contains components of the primitive lunar crust related to the lunar magma ocean (LMO). We undertook further Rb-Sr and Sm-Nd isotopic investigation of three major lithologies in the meteorite as described in the mineralogical and petrological studies. Ar-39-Ar-40 analyses of these component lithologies are presented in this volume. Also, we analyzed two Apollo 16 FANs, 60025 and 67075, to compare their ages and isotopic signatures to Y86032. Y86032 probably came from a feldspathic highland terrane (FHT) on the northern farside highlands, a locality not sampled by the Apollo and Luna missions.

Shih, C.-Y.↗
NASA NTRS2004

Rb-Sr and Sm-Nd Isotopic Studies of Shergottite Y980459 and a Petrogenetic Link Between Depleted Shergottites and Nakhlites

Y980459 was found near the Minami-Yamato Nunataks, Antarctica in 1998 and was recently classified as an olivine-bearing shergottite. It petrographically resembles many other olivine-phyric shergottites mostly found in hot deserts, e.g. DaG476/489, SaU005/094, Dohfar 019, NWA 1068/1110, NWA 1195 and EETA 79001 lith.A. However, Y980459 is unique among these meteorites in several respects. It is apparently very fresh and only weakly shocked. Also, it completely lacks plagioclase, but contains abundant residual volcanic glass. This group of olivine-phyric shergottites is characterized by variable crystallization ages from approx.172 Ma to approx.575 Ma and ejection ages from approx.1 Ma to approx.20 Ma. They probably represent volcanic melts originated from the deep Martian mantle. We performed Rb-Sr and Sm-Nd isotopic analyses on Y980459 to determine its crystallization age and compared its age and isotopic signatures with those obtained from other olivine-phyric shergottites and QUE 94201, the other Antarctic olivine-free shergottite. QUE 94201 and some olivine-phyric shergottites e.g. DaG, SaU, Doh and EETA lith A have similar depleted-LREE patterns and are herein referred to as depleted shergottites. A petrogenetic model correlating depleted shergottites and nakhlites is also proposed. Preliminary Rb-Sr and Sm-Nd isotopic data for Y980459 were presented earlier at the NIPR, Japan, in 2003.

Shih, C.-Y.↗
NASA NTRS2004

Rb-Sr and Sm-Nd Isotope Systematics of Shergottite NWA 856: Crystallization Age and Implications for Alteration of Hot Desert SNC Meteorites

Nakhlite NWA 998 was discovered in Algeria in 2001, and is unique among the six known members of this group of Martian meteorites in containing significant modal orthopyroxene. Initial petrologic and isotopic data were reported by Irving et al. This 456 gram stone consists mainly of sub-calcic augite with subordinate olivine and minor orthopyroxene, titanomagnetite, pyrrhotite, chlorapatite, and intercumulus An(sub 35) plagioclase. We report here preliminary results of radiogenic isotopic analyses conducted on fragmental material from the main mass.

Brandon, A. D.↗
NASA NTRS2004

Sm-Nd Age and Initial Sr-87/Sr-86 for Yamato 980318: An Old Cumulate Eucrite

The complex pyroxene exsolution texture of the Moore County cumulate eucrite was interpreted by Miyamoto and Takeda as indicating initial cooling at 160 C/Ma followed by a sudden temperature rise and final cooling at 0.35 C/yr. They suggested initial cooling at a depth of approx. 8 km near the base of Vesta s crust, followed by impact excavation to its surface. Young Sm-Nd ages of approx. 4456, 4460, and 4410 Ma, respectively, for the Moore County, Moama, and Serra de Mag cumulate eucrites are puzzling because closure to Nd isotopic exchange would occur in only a few Ma at the above initial cooling rate. The exception to young ages among the cumulate eucrites is EET87520, with a 147Sm-147 - Nd-143 age of 4547-4598 Ma. We report here initial results of a combined mineralogical/chronological study of the Yamato 980318 feldspar-cumulate eucrite.

Nyquist, L. E.↗
NASA NTRS2004

The Origin and Impact History of Lunar Meteorite Yamato 86032

Yamato (Y) 86032 is a feldspathic lunar highland breccia having some characteristics of regolith breccia. The absence of KREEP components in the matrix in Y86032 indicates that these meteorites came from a long distance from Mare Imbrium, perhaps from the far-side of the moon. One ferroan anorthosite (FAN) clast in Y86032 has a very old Ar-Ar age of approximately 4.35-4.4 Ga. The negative Nd of this clast may suggest a direct link with the primordial magma ocean. The facts indicate that Y86032 contains components derived from a protolith of the original lunar crust. Detailed petrologic characterization of each component in this breccia is essential to understand the early impact history and origin of the lunar highland crust. We made a large slab (5.2 x 3.6 cm x 3-5 mm) of Y86032 to better understand the relationship of various lithologies and their petrologic origin.

Yamaguchi, A.↗
NASA NTRS2004

Crystallization Age of NWA 1460 Shergottite: Paradox Revisited

We have determined the Rb-Sr age of basaltic shergottite NWA 1460 to be 312 +/- 3 Ma, and the Sm-Nd age to be 352 +/- 30 Ma. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the Iherzolitic shergottites and basaltic shergottite EETA79001, lithology B. The new ages of NWA 1460 and other recently analyzed Martian meteorites leads us to reexamine the paradox that most of the Martian meteorites appear to be younger from the majority of the Martian surface. This paradox continues to pose a challenge to determining a reliable Martian chronology.

Nyquist, L. E.↗
NASA NTRS2004

Constraints on the Origin of Chondrules and CAIs from Short-lived and Long-lived Radionuclides

In order to understand the timing of events in the early solar system, we rely on the radio-nuclide-based chronometers applied to materials in primitive meteorites. Because the time scale of early-solar system evolution was on the order of a few million years (Myr), we focus on so-called "short-lived radionuclides" with mean lives of less than 10 Myr (Table 1), as well as on the long-lived U-Pb system where high precision 207Pb-206Pb ages are applied. Note that the validity of some systems as chronometers (e.g., Be-B, Fe-Ni) has yet to be established. We summarize literature data for chondrules and CAIs and discuss how these chronometers constrain formation time scales in the early solar system.

Kita, N. T.↗
NASA NTRS2003

Crystallization and Alteration Ages of the Antarctic Nakhlite Yamato 000593

Nakhlites are unbrecciated, olivine-bearing clinopyroxenites that probably came from Mars. A total of eight nakhlites have been identified, including five recent finds: two samples (104 g and 456 g) from the hot desert of Morocco (NWA 817 and NWA 998), and three samples, a total weight of approx.15 kg, from the Yamato Mountains of Antarctica (Y000593, Y000749 and Y000802). Preliminary isotopic results for Y000593 have been given by Shih et al.. In this report, we present Rb-Sr and Sm-Nd isochron data for Y000593 and discuss the age correlation with other nakhlites and the timing of aqueous alteration on Mars.

Musawa, K.↗
NASA NTRS2003

Age and Petrogenesis of Picritic Shergottite NWA1068: Sm-Nd and Rb-Sr Isotopic Studies

NWA 1068 is a 577g picritic shergottite found in the Moroccan Sahara in 2001. The meteorite resembles several other picritic shergottites, e.g. EETA79001B, DaG476, SaU005 and Dho019, in major-element chemistry and mineralogy, but it differs significantly from these meteorites in REE distribution pattern. It has a slightly LREE-depleted pattern commonly shared by some olivine-free basaltic shergottites, e.g. Shergotty, Zagami and Los Angeles, but not QUE94201. Detailed geochemical and mineral-petrological studies were given in. We performed Rb-Sr and Sm-Nd isotopic analyses on this rock to determine its crystallization age and to study the petrogenetic relationship between this meteorite and other basaltic and pricritic shergottites.

Shih, C.-Y.↗
NASA NTRS2002

Isotopic Constraints on the Origin of Lunar Ferroan Anorthosites

Ferroan anorthosites have whole rock Nd isotopic compositions that are too radiogenic to have crystallized from a chondritic magma ocean. Mechanisms to disturb the whole rock Sm-Nd isotopic compositions are explored. Additional information is contained in the original extended abstract.

Borg, L. E.↗