Sm-Nd for Norite 78236 and Eucrite Y980318/433: Implications for Planetary and Solar System Processes

Here, we compare Sm-147-Nd-143 and Sm-146-Nd-142 data for lunar norite 78236 to those for approximately 4.54-4.56 Ga old cumulate eucrite Yamato 980318/433 and show that the norite data are compatible with its derivation from an isotopic reservoir similar to that from whence the eucrite pair came. Thus, lunar-like Sm-Nd isotopic systematics are not unique to the Earth-Moon system

Dating Melt Rock 63545 By Rb-Sr and Sm-Nd: Age of Imbrium; Spa Dress Rehearsal

Apollo 16 sample 63545 was initially described as one of a group of 19 generally rounded, fine-grained, crystalline rocks that were collected as rake samples [1]. This 16 g "rocklet" was collected at Station 13 on the ejecta blanket of North Ray Crater at the foot of Smoky Mountain [2]. Originally classified as a Very High Alumina (VHA) basalt on geochemical grounds [3], it was later argued to be an impact melt rock [4]. Here we report a Rb-Sr and Sm-Nd isotopic study that shows that some portions of the rock failed to reach isotopic equilibrium on last melting in agreement with the impact melt rock interpretation. Nevertheless, by omitting mineral fractions that are discordant with the majority of the data, we arrive at the time of last melting as 3.88 plus or minus 0.05 Ga ago. This age is in agreement with the Ar-39/Ar-40 plateau age of 3839 plus or minus 23 Ma [5], if the latter is adjusted for the ~1.4-1.8% revision in the age of the hornblende monitor [6]. This investigation was undertaken in part as proof-of-concept for SPA-basin sample return

Redetermination of the Sm-Nd Age and Initial (Epsilon)Nd of Lunar Troctolite 76535: Implications for Lunar Crustal Development

Lunar troctolite 76535 is an old lunar rock predating the era of the lunar cataclysmic bombardment, but its radiometrially determined ages have been discordant [1-3]. The most recent multi-chronometer study [4] gave preferred ages of 4226+/-35 Ma and 4236+/-15 Ma from a Pb-207/Pb-206 isochron and an U-Pb upper concordia intercept, resp. We derive an age of 4323+/-64 Ma from Sm-Nd data reported by [4] for the bulk rock and three mineral separates. They derived an age of approx.4.38 Ga from combined Rb-Sr data [3,4] by omitting data for olivine separates. Ar-39-Ar-40 ages of approx.4.2 Ga are summarized by [5]. New Sm-147-Nd-143 data presented here give an age of 4335+/-71 Ma in agreement with the Sm-Nd age from [4], whereas Sm-146-Nd-142 data give a model age T(sub LEW) = 4439+/-22 Ma. Further, initial (Epsilon)Nd-143 for 76535 conforms to the Nd-143 evolution expected in an urKREEP [6] reservoir, consistent with inheritance of urKREEP Sm-Nd systematics via assimilation. We show that urKREEP Sm-Nd systematics require the lunar initial (Epsilon)Nd-143 to exceed the Chondritic Uniform Reservoir (CHUR) value [7], but are consistent with evolution from initial (Epsilon)Nd-143 like that of the HED meteorite parent body as defined by a 4557+/-20 Ma internal isochron for the cumulate eucrites Y-980433 and Y- 980318 [8]

Mn-53-Cr-53 Systematics of R-Chondrite NWA 753

Chondrules and chondrites are interpreted as objects formed in the early solar system, and it is important to study them in order to elucidate its evolution. Here, we report the study of the Mn-Cr systematics of the R-Chondrite NWA753 and compare the results to other chondrite data. The goal was to determine Cr isotopic and age variations among chondrite groups with different O-isotope signatures. The Mn-53-Cr-53 method as applied to individual chondrules [1] or bulk chondrites [2] is based on the assumption that 53Mn was initially homogeneously distributed in that portion the solar nebula where the chondrules and/or chondrites formed. However, different groups of chondrites formed from regions of different O-isotope compositions. So, different types of chondrites also may have had different initial Mn-53 abundances and/or Cr isotopic compositions. Thus, it is important to determine the Cr isotopic systematics among chondrites from various chondrite groups. We are studying CO-chondrite ALH83108 and Tagish Lake in addition to R-Chondrite NWA753. These meteorites have very distinct O-isotope compositions (Figure 1)

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

Prospects for Chronological Studies of Martian Rocks and Soils

Chronological information about Martian processes comes from two sources: Crater-frequency studies and laboratory studies of Martian meteorites. Each has limitations that could be overcome by studies of returned Martian rocks and soils. Chronology of Martian volcanism: The currently accepted chronology of Martian volcanic surfaces relies on crater counts for different Martian stratigraphic units [1]. However, there is a large inherent uncertainty for intermediate ages near ~2 Ga ago. The effect of differing preferences for Martian cratering chronologies [1] is shown in Fig. 1. Stoeffler and Ryder [2] summarized lunar chronology, upon which Martian cratering chronology is based. Fig. 2 shows a curve fit to their data, and compares to it a corresponding lunar curve from [3]. The radiometric ages of some lunar and Martian meteorites as well as the crater-count delimiters for Martian epochs [4] also are shown for comparison to the craterfrequency curves. Scaling the Stoeffler-Ryder curve by a Mars/Moon factor of 1.55 [5] places Martian shergottite ages into the Early Amazonian to late Hesperian epochs, whereas using the lunar curve of [3] and a Mars/Moon factor ~1 consigns the shergottites to the Middle-to-Late Amazonian, a less probable result. The problem is worsened if a continually decreasing cratering rate since 3 Ga ago is accepted [6]. We prefer the adjusted St ffler-Ryder curve because it gives better agreement with the meteorite ages (Fig

Early Petrogenesis and Late Impact(?) Metamorphism on the GRA 06128/9 Parent Body

Initial studies of GRA06128 and GRA06129 (hereafter GRA 8 and GRA 9) suggested that these alkalic meteorites represent partial melts of a parent body of approximately chondritic composition. A SM-147-Nd-143 isochron age of 4.545 +/- 0.087 Ga was found for GRA 8, but plagioclase (oligoclase) plus whole rock and leachate samples gave an apparent secondary age of approximately 3.5 Ga. The approximately 4.54 Ga age was interpreted to be the crystallization age of GRA 8; the approximately 3.5 Ga as an upper limit to a time of metamorphism. Here we extend Sm-Nd and Rb-Sr analyses to GRA 9

Observations on the vibration of axially-tensioned elastomeric pipes conveying fluids

A study of the effect of axial tension on the vibration of a single-span elastomeric pipe clamped at both ends conveying fluid has been carried out both experimentally and theoretically. A new mathematical model using a penalty function technique and the method of kinematic correction and fictitious loads has been developed. The influence of flowing fluid and axial tension on natural frequencies and mode shapes of the system has been described using this model and compared with experimental observations. Linear and non-linear dynamic response of the harmonically excited pipe has also been investigated for varying flow velocities and initial axial tensions

Sm-Nd and Rb-Sr Ages for MIL 05035: Implications for Surface and Mantle Sources

The Sm-Nd and Rb-Sr ages and also the initial Nd and Sr isotopic compositions of MIL 05035 are the same as those of A-881757. Comparing the radiometric ages of these meteorites to lunar surface ages as modeled from crater size-frequency distributions as well as the TiO2 abundances and initial Sr-isotopic compositions of other basalts places their likely place of origin as within the Australe or Humboldtianum basins. If so, a fundamental west-east lunar asymmetry in compositional and isotopic parameters that likely is due to the PKT is implied

Concordant Rb-Sr and Sm-Nd Ages for NWA 1460: A 340 Ma Old Basaltic Shergottite Related to Lherzolitic Shergottites

Preliminary Rb-Sr and Sm-Nd ages reported by [1] for the NWA 1460 basaltic shergottite are refined to 336+/-14 Ma and 345+/-21 Ma, respectively. These concordant ages are interpreted as dating a lava flow on the Martian surface. 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 lherzolitic shergottites and basaltic shergottite EETA79001, lithology B. We also examine the suggestion that generally "young" ages for other Martian meteorites should be reinterpreted in light of Pb-207/Pb-206 - Pb-204/Pb-206 isotopic systematics [2]. Published U-Pb isotopic data for nakhlites are consistent with ages of approx.1.36 Ga. The UPb isotopic systematics of some Martian shergottites and lherzolites that have been suggested to be approx.4 Ga old [2] are complex. We nevertheless suggest the data are consistent with crystallization ages of approx.173 Ma when variations in the composition of in situ initial Pb as well as extraneous Pb components are considered