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Coupled Ce-Nd isotope systematics and rare earth elements differentiation of the Moon
Abstract
138Ce/142Ce and 143Nd/144Nd isotope ratios of lunar samples are determined to constrain the petrogenetic differentiation and evolution of the moon. High-precision Ce–Nd isotope data, well-defined Rb–Sr isochrons, and rare earth elements (REE) abundances of lunar samples show that unexpectedly low La/Ce ratios of evolved lunar highland samples are preserved from at least 3.9 Ga. Precise analysis of REE abundances indicates that the low La/Ce ratio results from a depletion of La relative to other REE. This depletion can be seen in pristine KREEP basalts and Mg-suite rocks from 3.85 to 4.46 Ga. As REE abundances of all these samples are controlled by the presence of a KREEP component, the depletion was probably inherited from a late crystallization sequence of the lunar magma ocean related to the production of the original KREEP component.
... In this paper we present an improved analytical technique that includes chemical purification of Ce, and mass spectrometry measurements based on the technique reported by Willbold (2007). Our Ce isotope dataset includes two basaltic rock standards (BCR-2 and BHVO-2) and two Ce reference material solutions (AMES and JMC-304) documented in previous publications (Tanaka and Masuda, 1982;Shimizu et al., 1984Shimizu et al., , 1988Shimizu et al., , 1990Shimizu et al., , 1992Shimizu et al., , 1994Masuda et al., 1988;Amakawa et al., 1991;Makishima and Nakamura, 1991;Lee et al., 2001;Tanimizu and Tanaka, 2002;Hayashi et al., 2004;Tanimizu et al., 2004;Tazoe et al., 2007;Willbold, 2007). In a second part, we focus on the Lesser Antilles arc formed by the subduction of the Atlantic ocean lithosphere beneath the Caribbean plate for which a comprehensive set of geochemical data has already been published on both the arc lavas and the sediments present in front of the subduction zone (Carpentier et al., 2008(Carpentier et al., , 2009Labanieh et al., 2010Labanieh et al., , 2012. ...
... We have also measured the isotopic composition of the Johnson Matthey reference material, JMC-304, frequently used as the Ce isotope reference material in previous studies (Tanaka and Masuda, 1982;Shimizu et al., 1984Shimizu et al., , 1988Shimizu et al., , 1990Shimizu et al., , 1992Shimizu et al., , 1996Masuda et al., 1988;Amakawa et al., 1991;Makishima and Nakamura, 1991;Lee et al., 2001;Tanimizu and Tanaka, 2002;Hayashi et al., 2004;Tanimizu et al., 2004;Tazoe et al., 2007). The values published for this reference material display a large scatter. ...
... The values published for this reference material display a large scatter. One of the reasons is the different normalization values (Makishima and Nakamura, 1991) to 0.0225891 ± 26 (Tanimizu and Tanaka, 2002), which corresponds to $9 e-unit difference. Different batches of the JMC reference material (not reported in the publications) might have been used. ...
The La-Ce systematics has one of the longest half-lifes (T1/2 = 292.5 Ga) of radioactive decay systems used in isotope geochemistry. Variations of the 138Ce/142Ce ratio are expected to be small and the use of Ce as isotopic tracer requires a very precise measurement. Compared to Sm–Nd studies, the La–Ce decay system can provide additional information about the nature of sediments recycled in subduction zones, because unusually large Ce anomalies relative to the neighboring rare earth elements exist in marine sediments such as fish teeth or hydrothermal deposits. Here, we present a chemical purification technique for Ce, and mass spectrometric technique to perform accurate and reproducible analyses of Ce isotopes of natural samples. We report a large set of Ce isotope data including analysis of 2 Ce reference material solutions (AMES and JMC-304), 2 rock standards (BCR-2 and BHVO-2), 2 chondrites (the carbonaceous chondrite Allende and the enstatite chondrite Sahara 97072), 4 mid-ocean ridge basalts, 30 arc lavas from the Martinique Island and 5 oceanic sediments from DSDP-site 144 drilled on the Demerara rise. The long-term, external precision obtained on the AMES reference material is 80 ppm (2 s.d., 138Ce/142Ce = 0.0225732 ± 18, n = 89). However, we note an evolution of isotopic ratios measured in static mode over the duration of this study (33 months). When the reproducibility is calculated from the AMES reference material measured during the same analytical session, it averages 40 ppm. All the 138Ce/142Ce ratios have been normalized to the AMES value of 0.0225746 (measured in session 7, 2 s.d. = 14 ppm, n = 8), a session during which the chondritic value has been defined and the peak tailing was negligible. The 138Ce/142Ce ratio measured for the JMC-304 Ce reference reagent is 0.0225706 ± 9 (2 s.d. = 38 ppm, n = 10). The analytical precision on natural samples is improved by a factor of about 4 in relation to previous studies on island arcs ( Tanaka et al., 1987 and Shimizu et al., 1992). The 138Ce/142Ce ratios of the two chondrites are identical within uncertainty and similar to previous determinations done on other meteorites; the average value is 0.0225654 ± 7 (2 s.d. = 32 ppm). Martinique samples show a limited but significant range of variations for 138Ce/142Ce ratios (∼2 ε-units). The latter ratios correlate well with the Nd isotopes and define a binary mixing between a depleted mantle and subducted sediments that could be similar to those drilled at DSDP-site 144 (Leg 14). The Martinique lavas do not define a single curve in the εCe vs. εNd diagram, but a band. The apparent scattering can be explained by the involvement of sediments with different Ce isotope compositions and/or variations in the melting process itself such as the effect of melting on the light rare earth element ratios. The Ce isotopic signature of Martinique samples is dominated by the contribution of old terrigeneous sediments. However, according to our mixing models a low contribution of a few percent of marine sediment material in the source of the lavas is undetectable and therefore cannot be definitely excluded. Although the participation of marine sediments in this arc system is not demonstrated, our calculations show that the La–Ce system has a potential as geochemical tracer despite its very long half-life.
... " values fromTable 1 of Anders and Grevesse (1989) and k 1.36, a value that corrects to a volatile-free basis and yields absolute concentrations similar to those of ordinary chondrites (e.g., Nakamura, 1974; Wasson and Kallemeyn, 1988). This figure andFigure 10 show that low La/Ce ratios, with respect to the Ce-Sm slope, are characteristic of feldspathic, low-REE samples as well as REE-rich samples (Tanimizu and Tanaka, 2002). 4910 R. L. Korotev et al. among the lunar meteorites. ...
... In a recent paper Tanimizu and Tanaka (2002) argue that lunar KREEP-rich and magnesian-suite rocks are depleted in La with respect to Ce and Nd, but that ferroan anorthosite is not. The low-La/Ce effect observed by Tanimizu and Tanaka (2002) is also evident in the feldspathic lunar meteorites and the Apollo 16 comparison suite (Figs. 10a and 11), all of which are feldspathic and KREEP poor. ...
... The relative magnitude of the apparent depletion does not increase with increasing REE concentration (Fig. 10a), so the anomaly in the feldspathic samples can not be the result of admixture of KREEP-rich rocks to ferroan anorthosite. Our own observation, which differs slightly from the conclusion of Tanimizu and Tanaka (2002), is that most nonmare samples, except perhaps highly feldspathic ferroan anorthosite, appear to have low La (or high Ce) relative to the overall slope of the light REE (e.g.,Fig. 11). ...
We present new compositional data for six feldspathic lunar meteorites, two from cold deserts (Yamato 791197 and 82192) and four from hot deserts (Dhofar 025, Northwest Africa 482, and Dar al Gani 262 and 400). The concentrations of FeO (or Al2O3) and Th (or any other incompatible element) together provide first-order compositional information about lunar polymict samples (breccias and regoliths) and regions of the lunar surface observed from orbit. Concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft, although the derived concentrations have large uncertainties and some systematic errors compared to sample data. Within the uncertainties and errors in the concentrations derived from orbital data, the distribution of FeO and Th concentrations among lunar meteorites, which represent ∼18 source regions on the lunar surface, is consistent with that of 18 random samples from the surface. Approximately 11 of the lunar meteorites are low-FeO and low-Th breccias, consistent with large regions of the lunar surface, particularly the northern farside highlands. Almost all regoliths from Apollo sites, on the other hand, have larger concentrations of both elements because they contain Fe-rich volcanic lithologies from the nearside maria and Th-rich lithologies from the high-Th anomaly in the northwestern nearside. The feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands, and we provide such an estimate based on the eight most well-characterized feldspathic lunar meteorites. The variable but high (on average) Mg/Fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high-Mg/Fe feldspathic rocks such as magnesian granulitic breccia, not ferroan anorthosite. Geochemically, the high-Mg/Fe breccias appear to be unrelated to the mafic magnesian-suite rocks of the Apollo collection. Models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites.
... Recently the reproducibility of Ce isotopic analysis was improved (Tanimizu et al., 2004), and Tanimizu and Tanaka (2002) discussed the presence of a positive Ce anomaly in early lunar history using a newly determined decay constant for 138 La (Tanimizu, 2000). In this study, Ce and Nd isotopic ratios were determined and the concentrations of LREE were examined in Archean sedimentary rocks, which included ferruginous cherts, derived from the Barberton Greenstone Belt in South Africa. ...
... The R sample (T) and R CHUR (T) correspond to 138 Ce/ 142 Ce or 143 Nd/ 144 Nd for a sample and CHUR at time T (T = 0 for the present). A rock derived from CHUR changes its ε Ce and ε Nd values according to its LREE pattern with time, as shown schematically in Fig. 3 (Tanaka et al., 1987;Tanimizu and Tanaka, 2002); epsilon values of a LREE-enriched rock will evolve like the arrows of 'h' or 'g' in Fig. 3. ...
The origin of sedimentary rocks with negative Ce anomalies among several samples derived from the Barberton Greenstone Belt (3250 Ma), South Africa, was investigated using La–Ce and Sm–Nd isotopic systematics, together with light rare Earth element (LREE) abundances. Negative Ce anomalies were recognized in two sedimentary rocks, a banded ferruginous chert and a shale. Their Ce/Ce* values are 0.40 and 0.81, respectively. Initial Ce isotopic ratio calculated for the ferruginous chert, 138Ce/142Ce (3250 Ma) = 0.0225059, is far lower than CHUR value at 3250 Ma and even the value at Earth formation, 138Ce/142CeCHUR (4560 Ma) = 0.0225409. The calculated initial Ce isotopic ratio for the shale with a Ce anomaly is also lower than that of other rocks without Ce anomalies. These results indicate that the negative Ce anomalies were not inherited from an Archean redox change, but occurred following later episodes of alteration.Two possible formation models were examined to estimate a plausible occurrence age for the negative Ce anomalies. One is characterized by Ce extraction and the other is by an addition of La, Nd and Sm. Both models indicate that negative Ce anomalies arose before 1100 Ma. This study suggests that La–Ce isotopic systematics provides a unique tool to constrain the occurrence age of negative Ce anomalies observed in Archean sedimentary rocks and gives some hints about the redox condition in the Archean ocean and the evolution of the Earth.
... Particularly, the divalent oxidation state of Eu may result in fractionation during magmatic evolution in response to oxygen fugacity or other parameters of the magmatic system [4,5]. Reports on Sm -Nd and La -Ce radiogenic isotope systematics have documented REE concentrations in igneous rocks and have provided valuable constraints on the formation and evolution of early Earth and other planetary systems [6][7][8][9][10][11][12][13][14][15][16][17]. ...
... Rare earth elements (REEs), which exhibit similar physical and chemical properties, can provide insight into numerous geological and cosmic processes. [1][2][3][4][5][6] Among REEs, only Ce could be naturally oxidized from a trivalent state to a tetravalent state in oxidizing environments, and insoluble Ce(IV) results in Ce anomalies relative to other REEs(III) eventually. [7][8][9] The 138 La-138 Ce decay system is a highly useful tool for geochronology and a geochemical tracer of a diverse range of geological reservoirs on Earth, especially when combined with other popular isotope systems ( 147 Sm-143 Nd and 176 Lu-176 Hf). ...
The138La–138Ce isotope system has been regarded as a useful radiogenic tracer for geochronology studies. Compared to commonly-used CeO+ technique, the measurement of Ce isotope ratios as Ce+ is straighter and more advantageous, but it is challenging due to the severe isobaric interference of 138Ba on 138Ce and large variations in relative abundances of all Ce isotopes. In this study, a novel method has been developed for high-precision measurement of Ce isotope ratios by thermal ionization mass spectrometry (TIMS) as Ce+. A newly-developed film porous ion emitter (FPIE) was used to enhance the ionization of Ce as Ce+ ions. The employment of TaF5 as an activator significantly suppressed the Ba+ isobaric interference signal. 140Ce was proposed to be an alternative reference Ce isotope as there is no isobaric interference on 140Ce and complicated peak tailing correction can be avoided. The combinations of diverse amplifiers (10¹⁰ Ω, 10¹¹ Ω, 10¹² Ω and 1013 Ω) were used for the measurement of Ce isotope ratios as Ce+ and 137Ba was monitored simultaneously on a 1013 Ω amplifier for 138Ba interference correction. The reproducibility on Ce isotope ratios obtained was ca. 10-fold better than the previously published Ce+ results and even comparable with that obtained using the more laborious CeO+ techniques. The method was further applied for the analysis of reference rock samples and uranium ores of world-wide origin. The analytical results demonstrated that Ce isotope ratio could be a promising signature for the nuclear forensic investigation to identify the source of unknown nuclear materials.
... However, when the Ba interference is well controlled, the reproducibility obtained on the standard-spike mixture is d 142 Ce ¼ À0.083 AE 0.028&, which is better than the reproducibility obtained in oxide mode and in the methods proposed in the literature. 22,25 This value is slightly lower than the expected d 142 Ce value of 0. The main reason for this discrepancy is probably the fact that the correction procedure is different between metal and oxide analyses. ...
Techniques for the separation of Cerium (Ce) from silicate matrices and for the analysis of radiogenic (ε138Ce) and mass dependent (δ142Ce) Ce isotope variations by Thermal Ionisation Mass Spectrometer (TIMS)...
... Sm-Nd계는 지구 및 태양계의 생성 및 진화와 관 련하여 지구화학적-우주화학적으로 매우 유용하게 활 용되는 방사성 동위원소계이다 (Dickin, 2005;Bouvier et al., 2008;Caro and Bourdon, 2010 (Rollinson, 1993). 그리고Sm-Nd 동위 원소계를 이용한 암석의 연대측정 및 지각의 진화와 같은 지구화학적 연구활용은 열이온화 질량분석기 (Thermal Ionization Mass Spectrometer, TIMS), 다 중 검출기 유도결합플라즈마 질량분석기(MC-ICP-MS) 와 같은 분석 장비를 이용한 Nd, Sm의 동위원소비 측정에 의해 이루어진다 (Tanaka et al., 1987;Tanimizu and Tanaka, 2002;Makishima, 2008;Guo et al., 2010;Murphy et al., 2010). (Pin and Zalduegui, 1997;Míková and Denková, 2007;Tazoe et al., 2007;Hirahara et al.. 2009;Cheong and Kwon, 2010). ...
The rare earth element(REE)s play an important role in understanding of rock formation and evolution because of their similar geochemical behaviors. Sm and Nd are more useful than other REEs because Sm-Nd isotopic system has important applications for geochemical interpretation like age dating and crustal evolution. These studies require a chromatographic technique for Sm and Nd separation from the geological samples. Ln-resin method using 0.25 M HCl as the eluent is widely used for Nd separation. However, this technique has a disadvantage of the poor elemental selectivity that the Nd fraction contains Ce as a tailing of the previous fraction. This technical report is a comparison study on the effect of eluent concentration between 0.25 M HCl and 0.15 M HCl on the separation of Nd with Ln-resin method for improving the technique of Nd separation. The results showed that the separation of Ce and Nd using 0.15M HCl as the eluent was not effective compared to the separation using 0.25 M HCl. In this experiment, we could confirm that the dilution of eluent might not be effective on the high purity separation of Nd with Ln-resin method.
... These systems yield age information and initial ratio of the elements in granites and thus may be used as tools in understanding the origins of these rocks. Many studies showed that the application of the La-Ce and Sm-Nd isotope systematics in petrogenetic studies enabled the estimation of the light rare earth element (LREE) patterns in the source materials (Dickin, 1987(Dickin, , 1988Tanaka et al., 1987;Shimizu et al., 1988Shimizu et al., , 1990Tanimizu and Tanaka, 2002;Hayashi et al., 2004;Lee et al., 2010a). Based on the La-Ce and Sm-Nd isotope systems, Lee et al. (2010a) proposed that the REE tetrad patterns in Proterozoic leucogranite might be formed by magmatic fractionation during granite emplacement, rather than by metamorphism, alteration, or weathering. ...
Rare earth elements (REEs) have received considerable attention in
geochemistry and cosmochemistry because of their similar chemical
behaviors and their gradual changes in ionic radii. Compared with Sr,
REEs are relatively immobile during various kinds of geological
processes. As a result, Nd isotopes in the geologic systems are likely
to be changed less than Sr isotopes in the same geologic systems.
Recently, a unique and chemically coherent behavior of the rare earth
elements (REEs) called as "tetrad effect" from geological sample has
spawned considerable interest in geologic systems. The "tetrad" effect
consists of four separate curves, encompassing four points, La-Ce-Pr-Nd,
Pm-Sm-Eu-Gd, Gd-Tb-Dy-Ho and Er-Tm-Yb-Lu, with Gd being an element
common to the second and the third tetrad. One of the characteristic of
the granites with REE tetrad effect is that the Nd model ages (TDM) are
unreasonable because they are negative or extremely old. The Muamsa and
Weolaksan granites are Cretaceous granites with REE tetrad effect, which
occurs at the middle part of the Ogcheon belt, South Korea. In order to
survey Nd isotopic system in granites with REE tetrad effect, we
measured the whole Nd isotopic composition of the Muamsa and Weolaksan
granites with REE tetrad effect and without REE tetrad effect. As a
result, we could observe that the 143Nd/144Nd ratios of granites with
REE tetrad pattern range from 0.511907 to 0.511969, whereas those
without REE tetrad pattern range from 0.511885 to 0.511920. And in plots
of 87Rb/86Sr - 87Sr/86Sr and 147Sm/144Nd - 143Nd/144Nd diagrams,
granites with REE tetrad pattern plotted at higher values than those
without REE tetrad pattern. However, we could not find anomalies of Nd
isotopic composition except 143Nd/144Nd. This suggests that there was no
mixing or input of the materials with different Nd isotopic composition
during the formation of REE tetrad effect. Our data indicate that REE
tetrad effect might be product during differentiation of granitic magma
rather than hydrothermal water-rock interaction.
... These systems yield age information and initial ratio of the elements in granites and thus may be used as tools in understanding the origins of these rocks. Many studies showed that the application of the La-Ce and Sm-Nd isotope systematics in petrogenetic studies enabled the estimation of the light rare earth element (LREE) patterns in the source materials (Dickin, 1987(Dickin, , 1988Tanaka et al., 1987;Shimizu et al., 1988Shimizu et al., , 1990Tanimizu and Tanaka, 2002;Hayashi et al., 2004;Lee et al., 2010a). Based on the La-Ce and Sm-Nd isotope systems, Lee et al. (2010a) proposed that the REE tetrad patterns in Proterozoic leucogranite might be formed by magmatic fractionation during granite emplacement, rather than by metamorphism, alteration, or weathering. ...
... On the other hand, if La depletion relative to Ce (a negative La anomaly) is assumed, the negative La anomaly is calculated to be 20-32% from the ratio La/La* (La* is the normal abundance extrapolated from Ce and Nd). However, such a systematic La depletion is not readily understandable except for a few cases in lunar highland samples, which was explained by a late crystallization sequence of the lunar magma ocean (Tanimizu and Tanaka 2002). Under oxidizing conditions, Ce can exist in the (IV) oxidation state, therefore, we suspect that the data reflect the anomalous behavior of Ce compared to trivalent REE. ...
Abstract— The trace element distributions in the matrix of primitive chondrites were examined using four least-contaminated matrix specimens from the polished sections of the Allende (CV) meteorite. Analysis of rare earth element (REE), Ba, Sr, Rb, and K abundances by isotope dilution mass spectrometry revealed that the elemental abundances of lithophile elements except for alkali metals (K, Rb) in the specimens of the Allende matrix studied here are nearly CI (carbonaceous Orgueil) chondritic (∼1 × CI). Compared to refractory elements, all the matrix samples exhibited systematic depletion of the moderately volatile elements K and Rb (0.1–0.5 × CI). We suggest that the matrix precursor material did not carry significant amounts of alkali metals or that the alkalis were removed from the matrix precursor material during the parent body process and/or before matrix formation and accretion. The matrix specimens displayed slightly fractionated REE abundance patterns with positive Ce anomalies (CI-normalized La/Yb ratio = 1.32–1.65; Ce/Ce* = 1.16–1.28; Eu/Eu* = 0.98–1.10). The REE features of the Allende matrix do not indicate a direct relationship with chondrules or calcium-aluminum-rich inclusions (CAIs), which in turn suggests that the matrix was not formed from materials produced by the breakage and disaggregation of the chondrules or CAIs. Therefore, we infer that the Allende matrix retains the REE features acquired during the condensation process in the nebula gas.
... Similar results have been reported by Korotev et al. (2002). Light rare earth enrichments and negative Eu anomalies are typical of the lunar KREEP component , and LREE profiles with slight downward deflections in Ce have recently been identified in a variety of lunar mafic rocks (Tanimizu and Tanaka 2002). The concentrations of most REE in the NWA 773 olivine gabbro are similar to those of lunar meteorite Elephant Moraine 87521, which is thought to have a mare origin (Delaney 1989;Warren and Kallemeyn 1989), but NWA 773 has a much deeper Eu anomaly (Fig. 7). ...
Abstract— The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Carich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized.
The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergite-bearing symplectites.
The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heatproducing elements.
Rare Earth Elements (REEs) play an important role in interpretation of trace element behavior in geological systems. Changes in the shape of the normalized REE patterns measured from a suite of rocks can record fractionation or differentiation history of the magmatic source. In this paper, we report conjugate chondrite-normalized REE patterns from a felsic granulite in the Jirisan complex of southern Korea. Granulite bodies show systematic variation in REE patterns from north to the south. Rocks in the northern, middle and southern parts of the complex exhibit a range of REE patterns varying from
weak, M-type tetrad patterns with a large, negative Eu anomaly to W-type patterns with a slightly positive Eu anomaly. Systematic variation in REE patterns supports a possibility for the interpretation of fractionation from granitic melts related to movement of metamorphic or magmatic fluids.
The IUPAC (International Union of Pure and Applied Chemistry) Periodic Table of the Elements and Isotopes (IPTEI) was created to familiarize students, teachers, and non-professionals with the existence and importance of isotopes of the chemical elements. The IPTEI is modeled on the familiar Periodic Table of the Chemical Elements. The IPTEI is intended to hang on the walls of chemistry laboratories and classrooms. Each cell of the IPTEI provides the chemical name, symbol, atomic number, and standard atomic weight of an element. Color-coded pie charts in each element cell display the stable isotopes and the relatively long-lived radioactive isotopes having characteristic terrestrial isotopic compositions that determine the standard atomic weight of each element. The background color scheme of cells categorizes the 118 elements into four groups: (1) white indicates the element has no standard atomic weight, (2) blue indicates the element has only one isotope that is used to determine its standard atomic weight, which is given as a single value with an uncertainty, (3) yellow indicates the element has two or more isotopes that are used to determine its standard atomic weight, which is given as a single value with an uncertainty, and (4) pink indicates the element has a well-documented variation in its atomic weight, and the standard atomic weight is expressed as an interval. An element-by-element review accompanies the IPTEI and includes a chart of all known stable and radioactive isotopes for each element. Practical applications of isotopic measurements and technologies are included for the following fields: forensic science, geochronology, Earth-system sciences, environmental science, and human health sciences, including medical diagnosis and treatment.
The La-Ce isotope system has been rarely applied, mostly due to analytical difficulties. Recent technical refinements of mass spectrometers have overcome some of these technical limitations, but Ce isotope analyses still face considerable analytical challenges. These are mainly related to the low abundance of the minor isotopes ¹³⁶Ce and ¹³⁸Ce relative to the main isotopes ¹⁴⁰Ce and ¹⁴²Ce (¹³⁶Ce=0.19%, ¹³⁸Ce=0.25%, ¹⁴⁰Ce=88.45%, ¹⁴²Ce=11.11%). Hence simultaneous measurement of ion beams over a large dynamic range is required, resulting in large differences in count statistical uncertainty on the individual ion beams. In addition, the large abundance of ¹⁴⁰Ce introduces a tailing effect of the large ¹⁴⁰CeO ion beam onto the ¹³⁶CeO and ¹³⁸CeO ion beams, which requires adequate correction. Here, we present a chemical purification scheme and high-precision thermal ionization mass spectrometric (TIMS) method for analyzing CeO isotope ratios in silicate samples. The advantages and disadvantages of different mass spectrometric strategies for data acquisition by TIMS were evaluated, including the use of 10¹⁰, 10¹¹, and 10¹² Ω amplifiers and different strategies for the ¹⁴⁰CeO tail correction. An optimization scheme was developed for different on-peak and off-peak collection schemes, in combination with different tail and baseline correction methods. It is shown that, as long as the integration times for the on-peak, off-peak (half-mass), and baseline signals are adequately optimized for the employed collection scheme and tail correction method, different strategies yield Ce isotope ratios with similar precision of 20-40ppm (2 S.D.). In contrast to previous studies, we have acquired ¹⁴⁰CeO by using a 10¹⁰ Ω amplifier, and have determined a long-term average ¹⁴⁰Ce/¹⁴²Ce of=7.94319±2. Using a common ¹³⁶Ce/¹⁴²Ce=0.01688 for mass fractionation correction, the ¹³⁶Ce/¹³⁸Ce of the international rock reference materials BCR-1, BCR-2, and BHVO-2 of this study agree well with those recently reported, when all Ce isotope ratios are reported relative to a common ¹³⁸Ce/¹³⁶Ce=1.337366 for the average Ames Ce metal. In addition, Ce isotope ratios for several other widely available international rock reference materials (AGV-2, BE-N, BIR-1, DNC-1, W2A) are presented, and facilitate easy inter-laboratory comparison.
The ¹³⁸ La- ¹³⁸ Ce decay system (half-life 1.02x10 ¹¹ years) is a potentially highly useful tool to unravel information about the timing of geological processes and about the interaction of geological reservoirs on...
Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic (~800 Ma) Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of εCe(t) variation but limited εNd(t) range, which cause a deviation from the “crustal array” and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce* ratios but broadly proximate εCe(t) values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe(t) and Ce/Ce* is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies (TCe) for the intermediate-mafic samples infers that the alteration events took place >350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.
The cerium (Ce) anomaly observed in rare earth element (REE) patterns has been used to estimate the redox state of paleo-marine environments. Cerium is unique because it forms tetravalent cations under oxic conditions, in contrast to the other REEs that occur in a trivalent state. This characteristic leads to anomalously high or low Ce concentrations relative to neighboring REEs. However, the use of Ce anomaly as a paleo-redox proxy is not well calibrated. This study shows that coupling of the Ce anomaly and Ce stable isotope ratio (δ142Ce) is more quantitative redox proxy to distinguish suboxic and oxic redox conditions. Our results revealed a progressive enrichment in heavy Ce isotopes in consecutive formations of iron (Fe) and manganese (Mn) precipitate from hot spring water without any associated change in REE patterns. The δ142Ce values of Mn precipitates were approximately 0.35‰ heavier than those of the Fe precipitates, which was consistent with experiment-based predictions. The δ142Ce values of marine ferromanganese deposits with three different formation processes were hydrogenetic (+0.25‰) > diagenetic (+0.10‰) ⩾ hydrothermal (+0.05‰), which also reflects redox conditions of their formation environment. These observations suggest that the Ce stable isotope ratios yield more quantitative information regarding redox state than REE patterns alone. We thus suggest that this novel proxy can be successfully utilized to reconstruct marine redox states, particularly from slightly oxic to highly oxic conditions such as the Great Oxidation Event (GOE).
Element Ce shows variable valences in the nature, which accounts for the decoupling between La-Ce and Sm-Nd isotopic system. In addition to a radiometric application, the La-Ce system thus sheds new light on a set of studies such as crust recycling in mantle components, oxidation events during outer sphere evolution of the Earth and metallogenesis. This paper consists of two parts. The first part summarizes the application status of the La-Ce system, its analytical problem faced as well as developing trends in experimental technique and geological application. The second half describes a new chemical procedure for La-Ce separation and purification. Analytical results for some USGS standards and some gabbroic rocks from the Neoproterozoic Huangling complex, interior of the Yangtze craton, are also reported.
Lanthanum and cerium are low mobile rare earth elements, which can be used to trace the provenance of clastics, but there is lack of systematic research on the La-Ce isotopes of clastics. This paper reports the Ce isotopic compositions of Nanhuan-Sinian clastic rocks in Sixi, Eastern Three Gorges. These clastic rocks have 138Ce/142Ce values of 0.0225832 to 0.0225878, and show an increasing trend of εCe(t) values from 1.06 to 6.13, which coupled with the εNd(t) values. Combined with Nd isotopec compositions of the clastic rocks, it is suggested that the main provenance of Nanhuan-Sinian clastic rocks in Sixi, Eastern Three Gorges were from the Paleoproterozoic-Middle Proterozoic and even older crustal rocks and mixing with juvenile crustal rocks in different degrees.
A column chemistry is the most useful tools for isolating the elements of interest in isotope geochemistry. Here we introduce the chemical experimental procedure for Sm, Nd, La and Ce separation such as Teflon powder or Ln-resin method using HDEHP of KIGAM, KBSI, KOPRI and -HIBA(-Hydroxy Isobutyric acid) method of Nagoya University, Japan. This technical report will provide an useful information in selecting the experiment method for rare earth element isotope system study such as Sm-Nd and La-Ce isotope system.
Northwest Africa 479 (NWA 479) is a lunar meteorite recovered in 2000 from Morocco. This unbrecciated low-Ti basalt is paired with NWA 032. The texture of NWA 032/479 indicates a simple crystallization history and a fast cooling, followed by an impact event. The occurrence of high-pressure polymorphs of olivine (ringwoodite and wadsleyite) in shock-melt veins indicates shock-pressures of at least 20 GPa.Lithium abundances and isotopic compositions were measured by ion microprobe in pyroxene, olivine crystals, and magmatic inclusions. The δ7Li values in the magmatic inclusions indicate that the NWA 479 parental melt was enriched in 7Li (δ7Li = +15‰). The behavior of Li depicted by the phenocrysts is complex and is not controlled by their major element compositions. Li abundances and δ7Li values range respectively from 3.2 to 11.8 μg/g and +2.4 to +15.1‰ in olivine and from 2.8 to 18.4 μg/g and −0.2 to + 16.1‰ in pyroxene phenocrysts. Neither hot desert weathering, closed-system fractional crystallization, involvement of a low-δ7Li reservoir, degassing of NWA 479 parental melt, nor shock metamorphism correctly explain the Li distribution in the phenocrysts. We propose that the wide range of δ7Li values displayed by the phenocrysts results from the large diffusivity differences between 6Li and 7Li. It is shown that this difference is able to produce large isotopic heterogeneities in a very short time.
We report La–Ce and Sm–Nd isotopic data for leucogranites having tetrad rare earth element (REE) patterns at Imweon area in the northeastern Yeongnam Massif, South Korea. The leucogranites are strongly peraluminous (A/CNK=1.18–1.79) S-type granite generated by the partial melting of metasediments, which consist of quartz, K-feldspar, plagioclase, muscovite, biotite, garnet and sillimanite. The leucogranites have three types of chondrite-normalized REE patterns: one showing a tetrad REE pattern of M-type with a large negative Eu anomaly, another with slightly V-shaped REE pattern with a positive Eu anomaly, and third with an REE pattern of crustal type with an LREE-enriched and HREE-depleted pattern. U–Pb zircon ages and, Sm–Nd and Rb–Sr whole-rock ages from the leucogranites are 1853±15Ma −1859±14Ma (2σ), 1833±220Ma (2σ) with εNd(1.83Ga)=−6.6±5.5 (2σ) and 1740±71Ma (2σ) with initial 87Sr/86Sr=0.755±0.050 (2σ), respectively. These values suggest that the leucogranites were emplaced from magma formed by partial melting of the crustal material. In the εCe–εNd diagram, the present Ce and Nd isotopic compositions of the leucogranites with a tetrad REE pattern are plotted in the positive εNd and εCe field whereas those of the leucogranites without tetrad REE pattern are in the negative εNd and positive εCe field. The initial Ce isotope values of the leucogranites with a tetrad REE pattern are plotted in a range of −2.31
Radiogenic 138Ce/136Ce ratios in geological and cosmological materials are a valuable tracer and dating tool in geo- and cosmochemistry. However, the variation in global 138Ce/136Ce ratios is small (e.g., 0.03% in ocean island basalts). In addition, the isobaric interference of 138Ba and the influence of the dominant 140Ce ion beam (88.5%) on 138Ce (ca. 0.251%) during mass spectrometric analysis present an analytical challenge. Hitherto employed methods generally dismiss the influence of the 140Ce low-mass peak-tail on the accuracy of the determined 138Ce/136Ce ratios. Therefore, the reported reproducibility ranges only from 0.05 to 0.004% (2RSD). In this study, TIMS and MC-ICPMS are used to determine 138Ce/136Ce ratios in reference materials. The results show that only the measurement of Ce as an oxide species by TIMS, combined with the accurate monitoring and correction of the background between the acquired ion intensities, can yield accurate and reproducible 138Ce/136C ratios. This method achieves a more than two-fold improvement in reproducibility (0.002%; 2RSD) compared to reported methods. The identification and quantification of individual sources of error resulted in a combined standard uncertainty of 0.002% (2RSE) for the method. A comparison of published data for the CeO2 reference material JMC 304 reveals its isotopic heterogeneity. Therefore, a new reference material has been prepared from ultra-pure Ce metal from Ames Laboratory. It is now available for distribution. An initial characterization of the new reference material yielded a 138Ce/136C ratio of 1.33738 ± 0.000005 (2σmean; N = 35) as a working value.
Northwest Africa 773 is one of the more unusual lunar meteorites found in recent years because it contains a prominent clast lithology, which appears to be an olivine-rich cumulate and because it is a very-low-Ti (VLT) mare breccia with relatively high incompatible-trace-element concentrations and LREE/HREE enrichment. A lunar origin was verified by Fagan and coworkers on the basis of noble-gas contents, oxygen isotopes, and mineral compositions. Fagan et al. described two lithologies: (1) heterolithic impact breccia with a regolith component and (2) cumulus olivine gabbronorite. Here, we refer to these as the breccia (Bx) lithology and the olivine-cumulate (OC) lithology. The impact breccia components are predominantly volcanic (basaltic), and, in this context, the occurrence of the cumulus lithology is especially significant: is it related to the volcanic components or does it represent a deep-seated rock entrained by the basaltic magma as it rose to the surface? Elevated incompatible-element concentrations with more or less KREEP-like inter-element ratios and very-low-Ti concentrations distinguish both lithologies of this meteorite from Apollo mare basalts. Here, we summarize key compositional information (bulk and mineral), especially related to the OC lithology, to show that it formed at shallow depth and comes from a VLT ultramafic precursor that mixed with a KREEP-like trace-element component deep in the crust or upper mantle.
Although incomplete because of the imperfect and somewhat random sampling of rock types by the Apollo and Luna missions (1969–1976), the history of lunar magmatism has been reconstructed by numerous researchers over the past three decades. These reconstructions have illustrated the con-tinuous nature of lunar magmatism (from 4.6 to ∼2.0 Ga) and the large influence of early differentia-tion and catastrophic bombardment on lunar mantle dynamics, magmatism, and eruptive style. In this review, we group magmatism into multiple stages of activity based on sampled rock types and evaluate the models for each stage. Stage 1 is early lunar differentiation and associated magmatism. Partial melting of the Moon soon after accretion was responsible for producing an anorthositic crust and a differentiated lunar interior. The extent of lunar melting and mantle processing depends strongly on the mechanisms that induced melting. Estimates for the time over which melting and crystallization occurred range from tens to hundreds of millions of years. Stage 2 is the disruption of lunar magma ocean cumulates. Soon after the crystallization of most of the lunar magma ocean, the cumulate pile experienced gravitational overturn. This resulted in transport of late-forming cumulates into the deep lunar mantle and mixing of magma ocean cumulates on a variety of scales. Stage 3 is the post-magma ocean highland magmatism. Whereas the ferroan anorthositic crust was probably produced during the crystallization of a magma ocean, the slightly younger Mg suite and alkali suite plutonic rocks may have been generated by decompressional melting of early magma ocean cumulates during cumulate pile over-turn. A KREEP and crustal signature was incorporated into these primitive basaltic magmas through assimilation near the base of the lunar crust or through melting of a hybridized mantle. The alkali suite could represent either the differentiation products of Mg suite parental magmas or a separate, but contemporaneous episode of basaltic magmatism. Stage 4 is pre-basin volcanism. Sample analy-sis and remote sensing data indicate that early lunar volcanism (KREEP basalts and high-alumina basalts) was contemporaneous with periods of highlands plutonism and catastrophic bombardment of the lunar surface. The relationship between early stages of lunar volcanism and the contemporane-ous plutonism is not clear. The KREEP basalts may be volcanic equivalents to both the Mg suite and alkali suite. Stage 5 is the late remelting of magma ocean cumulates and eruption of mare basalts. Basin-associated eruption of mare basalts occurred during and following the late stages of cata-strophic bombardment. This volcanic activity was possibly an extension of the thermal event that initiated pre-basin volcanism. Mare basalts exhibit a wide range of composition resulting from near-surface fractionation of chemically distinct primary basaltic magmas. Most likely, mare basalts were produced by small to moderate degrees of partial melting of hybrid cumulate sources in the deep lunar mantle. Alternatively, the mixed chemical signatures observed in many mare basalts may be interpreted as indicating assimilation of late-stage, evolved cumulates by melts produced deep in the cumulate pile. The wide range of compositions exhibited by the mare basalts compared with earlier episodes of basaltic magmatism may reflect the thermal regime in the lunar mantle that limited the extent of partial melting and melt-source homogenization.
The history of lunar troctolite 76535 was investigated on the basis of information from the Sm-147-Nd-143 mineral isochron age, the Nd-143 evolution, extinct Pu-224, the Kr-81-Kr exposure age and the cosmic ray exposure record. It was found that the troctolite minerals last equilibrated 4.26 plus or minus 0.06 AE ago and that the Sm-Nd system became closed at this time. The rock remained at temperatures where the loss of radiogenic Ar-40 was small.
Sm-Nd whole rock measurements on a variety of KREEP-rich samples from different landing sites are reported. Despite a variation of Nd and Sm concentrations of almost a factor of 3, the Sm-Nd ratios, as well as the Nd-143/Nd-144 values, show an extremely close grouping. No systematic differences between samples from different landing sites are resolved. These results are taken to be indicative of a moon-wide process having been responsible for the generation of the KREEP source reservoir, 4.36 plus or minus 0.06 AE ago, as estimated from model age calculation.
The 138La β- decay constant was determined geophysically. The isotopic growths of 138Ce/142Ce and 143Nd/144Nd were examined from ancient igneous crystalline rocks. For the Ce isotope measurement, a newly developed dynamic multicollector technique was applied. The crystallization age of the rocks was calculated to be 2037 ± 13 Myr from the growth of 143Nd. From the age and the growth of 138Ce, λβ of 138La was estimated to be (2.37±0.10)×10-12 yr-1. This value is consistent with those of the latest two γ-ray counting data of lanthanum compounds within the analytical error.
Lunar breccia 15445, collected near the rim of Spur Crater, contains iron-rich olivine and ortho-pyroxene mineral clasts and two types of white lithic clasts. The dominant type (Type A) is composed principally of anorthite - magnesian orthopyroxene and appears to be a low-pressure cumulate from a magnesian, high-Al basalt. A minor type (Type B) is composed of olivine + chrome pleonaste + aluminous orthopyroxene + minor plagioclase. Type B clasts have affinities to terrestrial spinel peridotites and have a REE pattern unique for the moon. Considerations of the observed mineralogy and the trace element geochemistry suggest that garnet was originally a phase in this peridotite but was subsequently lost during subsolidus reequilibration. Hence, Type B clasts provide indirect evidence for the existence of garnet in the lunar interior.
A theoretical model is presented for the coupled evolution of cerium and neodymium isotopes in terrestrial rocks. Data presented for samples ranging from mid-ocean-ridge basalts to continental metamorphic rocks show that, while mantle-derived rocks are dispersed on a Ce-Nd diagram, continental crustal rocks form a clearly defined 'mantle array'. As analytical techniques improve, cerium isotopes will provide valuable constraints in studies of petrogenesis and crustal evolution.
Ce and Nd isotope ratios and REE contents of one carbonaceous chondrite (Murchison), 3 ordinary chondrites (Granès, Holbrook and Barwise) and 4 achondrites (Camel Donga, Juvinas, two pieces of Millbillillie) were measured. For the Ce isotope analysis of meteorite samples the new chemistry for extracting Ce from the gel formed after decomposition of ∼1-g chondrite sample with Mg content of 20% was developed with a recovery yield of 80%. The initial Ce isotope ratio of each meteorite sample was calculated with the assumption that the age of meteorite samples is 4.56 Ga, and the average value was obtained to be 138Ce/142Ce−0.0225321 ± 0.0000007 (2σ), which is considered to be the primordial Ce isotopic composition of the solar system. The average of the present-day Ce isotope ratios of the chondrites of this study and that previously published by Shimizu et al. is 0.0225653, which suggests that the estimation of the Ce isotope ratio of the present-day bulk Earth of 0.0225652 that was published by Makishima and Nakamura is convincing. The Ce isotope ratio of the present-day bulk Earth of 0.0225652 gives the 138La/142Ce ratio of the bulk Earth to be 0.00306 ± 0.00006 (2σ), which corresponds to La/Ce = 0.375 ± 0.007 (2σ). We propose that the La/Ce ratio of 0.375 represents that of the bulk Earth or CHUR.
The 138La β- decay constant was determined geophysically. The isotopic growths of 138Ce/142Ce and 143Nd/144Nd were examined from ancient igneous crystalline rocks. For the Ce isotope measurement, a newly developed dynamic multicollector technique was applied. The crystallization age of the rocks was calculated to be 2037±13 Myr from the growth of 143Nd. From the age and the growth of 138Ce, λβ of 138La was estimated to be (2.37±0.10)×10-12 yr-1. This value is consistent with those of the latest two γ-ray counting data of lanthanum compounds within the analytical error.
It is generally accepted that Cl chondrites contain most elements in
unfractionated, solar proportions, and thus are a good source of
solar-system abundances of the elements. This paper presents a table
compiling the most recent element abundances determinations for
chondrites.
The La-Ce data of Millbillillie are plotted in Figure 2. The age of Millbillillie #2 is 3.7 ± 2.0 Ga. The data for Millbillillie #2 do not fall on the 4.52 Ga reference isochron. There is a possibility that the La-Ce decay
system was reset. The fine-grained crystalline clast of Millbillillie #1 made a cluster due to the difficulty in mineral separation.
Two different trends between Millbillillie #1 and #2 are also recognized in Figure 2, as well as in the Sm-Nd decay system
(Figure 1a) and clearer than it. This fact indicates that Millbillillie is a polymict eucrite, too.
Now-extinct 146Sm ( was present in the early solar system, and lunar basalts might be expected to have inherited small anomalies in 142Nd abundances from mantle sources with variable Sm/Nd ratios established during the early global differentiation of the Moon. 142Nd/144Nd ratios were measured for several lunar basalts, and values of ϵNd142, (deviations from terrestrial 142Nd/144Nd in parts in 104) calculated for them. The ϵNd142ENa values show very small variations attributable to 146Sm decay. Neutron capture near the lunar surface also modified both the samarium and neodymium isotopic compositions of the basalt samples. The calculated neutron fluences range from ∼0 to ∼7.8 × 1016 n/cm2. Both thermal and epithermal neutron fluences were calculated from the Sm isotopic compositions of the basalts and used to correct the ϵNd142 values for neutron capture by neodymium. Well-resolved radiogenic enrichments ϵNd142 = +0.28 ± 0.11 and +0.17 ± 0.08 (2σ), respectively, were measured for lunar meteorite Asuka 881757 and Apollo 17 basalt 74255, respectively, for which the neutron fluences were nil. Basalts 70135 and 75075, which were exposed to small, measureable neutron fluences of ∼2.5 × 1015 and ∼7.7 × 1015 n/cm2, respectively, have neutron-corrected ϵNd142 values of +0.25± 0.15 and +0.29 ± 0.11, respectively. The average value of radiogenic ϵNd142 for the three high-Ti basalts from Apollo 17 is +0.22 ± 0.06. Neutron capture effects were greater for the other basalts, but can be corrected using the measured neutron fluences derived from the samarium isotopic data. The neutron-corrected ϵNd142 = +0.19 ± 0.20 for Apollo 12 ilmenite basalt 12056, consistent with its derivation from a highly depleted mantle source also. Three low-Ti basalts from Apollo 12 and Apollo 15 (12038, 15076, 15555), have neutron corrected ϵNd142 which are not resolved from zero, and average +0.04 ± 0.06. A fourth low-Ti basalt, 12039, has neutron-corrected ϵNd142 = +0.25 ± 0.12, but is subject to the largest neutron correction of ∼0.32 ϵ-units. KREEP basalt 14078 was exposed to only a small neutron fluence of ∼6.4 × 1015 n/cm2, and has a small deficit of 142Nd, corresponding to ϵNd142 = -0.11 ± 0.08. The average neutron-corrected ϵNd142 of three KREEP basalts is −0.05 ± 0.04. The ϵNd142 values of the basalts correlate with 147Sm/144Nd values for their source regions as calculated from their ages and initial ϵNd,churi,i142 values. 147Sm- 143Nd and 146Sm- 142Nd systematics were combined in a three-stage model yielding an isochron equation for the lunar mantle formation interval, which was calculated to be 238−40+56 Ma (2σ). Sm/Nd ratios for the source regions also are derived from the model and compare favorably with values from conventional geochemical models of mare basalt petrogenesis. If the Moon were formed by impact of a large, Mars-sized planetesimal with the Earth, the impact was early enough that the lunar mantle cooled to neodymium isotopic closure by ∼4.32 Ga ago. The bulk lunar ϵMoon142 evaluated from the mantle isochron at (147Sm/144Nd)chur = 0.1967 is −0.01 ± 0.03 (2σ), consistent with derivation of lunar and terrestrial neodymium from a common reservoir.
Isotopic composition of zirconium from eight zircon and two baddeleyite samples including meteoritic zircon have been measured using a laser ablation-multiple collector-inductively coupled plasma mass spectrometer (LA-MC-ICPMS). A frequency-quadrupled Nd-YAG UV laser (266 nm), which produces pit sizes of 10–15 μm was used to ablate solid samples. The resultant precisions of the 92Zr/90Zr, 94Zr/90Zr and 96Zr/90Zr isotopic ratio measurements for zircons and baddeleyites achieved by the present LA-MC-ICPMS technique were 0.01–0.02%, 0.02–0.03% and 0.03–0.04% (2σ, SD), respectively. The obtained Zr isotopic ratios for zircons and baddeleyites show an excellent agreement with those for chemical reagents (Merck AA standard solution, JMC ICP/DCP standard and JMC metallic Zr) obtained by the solution nebulisation technique; normalised to 91Zr/90Zr≡0.21814 [Nomura, M., Kogure, K., Okamoto, M., 1983. Isotopic abundance ratios and atomic weight of zirconium. Int. J. Mass Spectrom. Ion Phys., 50, 219–227.], the isotopic ratios for Merck reagent are 92Zr/90Zr=0.333935±0.000023, 94Zr/90Zr=0.339158±0.000048 and 96Zr/90Zr=0.054626±0.000010 (2σ, SD). Neither isotopic variation in 92Zr/90Zr ratio due to radiogenic contribution from 92Nb nor isotopic heterogeneity was found for all the zircon and baddeleyite samples.
High precision isotopic composition measurements of Sm have been carried out for two terrestrial and seven lunar samples from three Apollo sites. The lunar samples, selected to show a wide variation in cosmic ray exposure ages, have a wide range of enrichments in150Sm/154Sm (up to 0.8%) and depletions in149Sm/154Sm which are due to neutron capture. The ratio of the number of neutrons captured per atom by149Sm to157Gd is 0.9 and reflects a hardened lunar neutron spectrum. This ratio is in reasonable but not exact agreement with that obtained from the theoretical lunar neutron energy spectrum of Lingenfelter, Canfield and Hampel. The average composition for terrestrial samarium is144Sm :147Sm :148Sm :149Sm :150Sm :152Sm :154Sm = 3.074 : 14.995 : 11.243 : 13.820 : 7.380 : 26.739 : 22.749%.
Rb-Sr and Sm-Nd isotopic studies were undertaken of two Apollo 15 breccias, 15445 and 15455, collected near Spur Crater on the Apennine Front. Seven pristine lithic clasts including four norites, one anorthositic norite, one troctolitic anorthosite and one spinel troctolite, as well as a matrix sample of 15445, were analysed. In addition, a K-Ar age determination was also made for a plagioclase separate from a different anorthositic norite clast.Sm-Nd isotopic data of a pristine Mg-norite sample, 15445,17, from the large white Clast B of breccia 15445 yielded a precise internal isochron age of 4.46 ± 0.07 Ga for and an initial of 0.506058 ∓ 0.000078 (normalized to corresponding to an initial ϵNd of +0.71. However, Sm-Nd isotopic results of another Mg-norite sample, 15445,247, chipped from the same Clast B, about 1 cm away from 15445,17, yielded a significantly younger isochron age of 4.28 ± 0.03 Ga and a higher initial of 0.506246 ∓ 0.000037 corresponding to an initial ϵNd of −0.35. The Sm-Nd data indicate that Clast B is heterogeneous and contains at least two similar lithologies. The Rb-Sr isotopic systems were severely disturbed for both norites. No useful isochron ages were observed. The Sm-Nd age and ϵNd data for A-15 Mg-norites 15445,17 and 15445,247, A-17 Mgnorite 78236, and two Mg-gabbronorites 73255,27,45 and 67667 are clearly resolved from each other. Four distinct parental magmas are required for derivation of these two major groups of Mg-suite noritic rocks.The Rb-Sr isotopic system of an anorthositic norite clast, 15455,228, was slightly disturbed; and isotopic data defined an isochron age of 4.59 ± 0.13 Ga for or 4.55 ± 0.13 Ga for . The corresponding initial for the rock is 0.69899 ∓ 0.00006 and is in satisfactory agreement with the LUNI value of Nyquist et al. (1974). The Sm-Nd system is more disturbed than the Rb-Sr system for this rock. A tie-line between whole-rock samples and a pyroxene separate gives a Sm-Nd age of 4.53 ± 0.29 Ga, which is in nominal agreement with the Rb-Sr isochron age. The 39Ar40Ar age of a plagioclase separate of the rock has a weighted average value of ~ 3.83 Ga, suggesting that the age was reset by the Imbrium impact event. Probably, the Sm-Nd and Rb-Sr systems of the clast were also partly reset by this event.Our age results indicate that some Mg-suite rocks are as old as ferroan-anorthosite-suite rocks. Furthermore, 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. These observations are difficult to explain by the “magma ocean” hypothesis alone. Petrogenetic processes such as production of Mg-suite rocks by “serial magmatism” (Walker, 1983), of ferroan-anorthosite-suite rocks by “multiple diapiric intrusions” (Longhi and Ashwal, 1985), and evolved-suite rocks by “continuous magmatism” (Meyer et al., 1988, 1989) probably all played a role. These processes seem to be able to accommodate the wide ranges of ages and different origins observed for lunar crustal rocks.
We present compositions, including REEs determined by ion microprobe, of apatite and whitlockite in lunar rock assemblages rich in incompatible trace elements. Total concentrations of REE oxides in whitlockites range from 9–13 wt%, and those in apatites range from 0.15 to 1 wt%. Ratios of REE concentrations in whitlockite to those in coexisting apatite range from ~ 10 to 60. The distribution of Mg and Fe between apatite and whitlockite is correlated to that of coexisting mafic silicates: Magnesium is strongly preferred by whitlockite, and Fe is preferred by apatite. Incorporation of REEs in whitlockite is dominated by the coupled substitution of 2REE3+ in Ca(B) sites + vacancy in Ca(IIA) for 2Ca+2 in Ca(B) sites and (Ca2+,Na+) in Ca(IIA). Other substitutions account for only a small portion of the REEs in whitlockite over the observed concentration range; thus, REE concentrations become partially saturated as the primary substitution approaches its stoichiometric limit of two REEs per fifty-six oxygens, leading to reduced whitlockite/melt distribution coefficients e.g., decreasing from twenty-five to ten for Nd. The REE concentrations of lunar residual melts are not depleted by whitlockite crystallization in assemblages consisting mainly of other minerals in typical proportions. Distribution coefficients for the REEs in lunar apatite appear to be low and variable e.g., ~0.2–0.8 for Nd.
Ce(IV)-Ce(III) and Fe(III)-Fe(II) redox equilibria in Ca-Mg-Al-silicate melts have been individually measured with respect to the base composition, melt temperature, imposed oxygen fugacity, and multivalent element concentration (up to about 1.5 wt%). The mutual interaction of these two redox couples has been studied in analogous glasses which simultaneously contained iron and cerium. Analyses of Fe(III) concentrations in iron-cerium glasses by electron paramagnetic resonance and optical absorption spectroscopy indicate that Ce(IV) is stoichiometrically reduced by Fe(II) in the melt to produce Fe(III) and Ce(III) and that Ce(III)-O-Fe(III) complexes are formed in the melt. Consequently, it is concluded that cerium exists only as Ce(III) in basaltic magmas; cerium anomalies cannot be ascribed to the stabilization of Ce(IV) in magmas.
Initial positive ϵNd values of early Archean continental crust imply derivation from depleted (high ratio) mantle sources. A balancing enriched (low ratio) region is therefore required to exist contemporaneously somewhere on the Earth during the early Archean. The essentials of the mass balance involved are presented. It is shown that the enriched reservoir must contain a large proportion (∼ 30–70%) of the total Nd budget of the differentiated system, even if it was formed only shortly after the accretion of the Earth. This amount of Nd is comparable to or greater than the present-day continental inventory relative to the upper mantle. If this “enriched” reservoir was “continental crust,” the small proportion of surviving early Archean continent requires that nearly all of it was destroyed. However, surviving Archean metasediments and granites, in general, have primitive or depleted initial Sr and Nd isotopic compositions, and this does not suggest the existence of a large continental crust at this time. If the “enriched” reservoir was the result of early mantle melting, it is more likely to have consisted predominantly of basalt. It is shown that partial melting can yield appropriate fractionations and Nd depletions for the Archean depleted mantle if the melting was dominated by episodes with melt fractions in the range ∼2–10%. Such degrees of melting are far less than occur beneath spreading ridges today; for a hotter Archean mantle, melt fractions would be even greater than today. Therefore, there is considerable difficulty reconciling this with a plate tectonic regime in which isentropic melting due to plate spreading occurred to the near surface. Instead, we propose that no significant plate spreading occurred. In this case, an alkalic crust of basalt would be produced because any isentropic melting in the mantle would be of much more limited extent than occurs beneath ocean ridges. A crust built up serially in this way, rather than laterally, appears the most likely candidate for the enriched reservoir balancing the positive ϵNd values of the depleted mantle in the early to middle Archean.The existence of such a layer has important implications for the thermal and tectonic history of the Earth. Highly incompatible elements, including the heat-producing elements (K, Th, and U) would be concentrated there. Therefore, in spite of the greater overall global heat production, intrinsic radiogenic heating of the depleted mantle would have been low even during the earliest Archean. The present-day Urey ratio of the Earth (the ratio of radioactive heat production to heat loss from the Earth today) of 0.48 ± 0.12 therefore requires (1) sources of radiogenic heat in the deep mantle and (2) storage of this heat for > 1 Ga. Consequently, the mantle must be chemically layered with inefficient advective transport of material from the lower mantle to shallow levels.
New abundance tables have been compiled for Cl chondrites and the solar photosphere and corona, based on a critical review of the literature to mid-1988. The meteorite data are generally accurate to ± 5–10%. Significant discrepancies between Sun and meteorites occur only for Fe, Mn, Ge, Pb, and W; other well-determined elements agree to ±9% on the average. There is no evidence for group fractionations in Cl chondrites of cosmochemically similar elements (refractories, siderophiles, volatiles, etc.), but a selective fractionation of Fe cannot be ruled out. Abundances of odd-A nuclides between A = 65 and 209 show a generally smooth trend, with elemental abundances conforming to the slope defined by isotopic abundances. Significant irregularities occur in the NdSmEu region, however, suggesting that the abundance curve is dependably smooth only down to the ∼20% level.
A combined Sr and Nd isotopic study of 15 Apollo 17 high-Ti mare basalts was undertaken to investigate geochronological and compositional differences between previously identified magma types (A, B1, B2, and C). Whole-rock and mineral separates for one of the least-evolved Type B1 basalts, 70139, yield Sm-Nd and Rb-Sr isochron ages of 3.71 ± 0.12 Ga and 3.65 ± 0.13 Ga, respectively. A more-evolved, Type A basalt, 71539, exhibits a slightly older Sm-Nd isochron age of 3.75 ± 0.07 Ga and a Rb-Sr isochron age of 3.67 ±0.10 Ga. Although these two ages are non-resolvable by themselves, compilation of all available geochronological data allows resolution of Type A and B1/B2 ages at high levels of confidence (>99%). The most reliably dated samples, classified according to their geochemical type, yield weighted average ages of 3.75 ± 0.02 Ga for Type A (N = 4) and 3.69 ± 0.02 Ga for Type B1/B2 (N = 3) basalts. Insufficient geochronological data are available to place the rare, Type C basalts within this stratigraphy. We propose that age differences correlate with geochemical magma type, and that early magmatism was dominated by eruption of Type A basalts while later activity was dominated by effusion of Type B1 and B2 basalts.
The origin of the incompatible element-rich lunar component, KREEP, is in the Lunar Magma Ocean (LMO). The fractionated residual melt after crystallization of the LMO represents “urKREEP” (after Warren and Wasson, 1979). The percentage of this residual melt is low enough to be within the realm of silicate liquid immiscibility (SLI). This process has the ability to split the KREEP signature into K- and REEP-Fractions, which are manifest as lunar granite (K) and phosphate phases present in highland lithologies or as quartz ferrotroctolite in lunar soils (REEP). We envisage this as a localized, but significant process since only a small portion of urKREEP undergoes SLI. Norms of experimental and Apollo 15 basaltic immiscible glasses suggest that thevREEP-Fraction found in the lunar highlands has undergone post-SLI fractionation of at least fayalite. This significantly reduces the density of the REEP-Fraction and coupled with its low viscosity (10–15 poise), it can percolate upward, metasomatizing the lunar crust. The higher viscosity of the granitic melt (=∼30000 poise) inhibits its mobility, and it forms “pods” in the lower rust (as required for VHK basalt petrogenesis).
Lunar soils from all missions indicate that an early lunar differentiation process occurred in the interval 4.3–4.6 AE and resulted in the formation of a crust rich in K, Rb, U and Th. An attempt has been made to identify rocks which were formed during this early differentiation event.
Internal Rb-Sr isochrons were determined on four basaltic rocks and on a basaltic clast from a breccia from the Fra Mauro landing site. An internal isochron was determined for rock 12004 and yielded a value in agreement with previous results for basaltic rocks from the Apollo 12 site. The crystallization ages for Apollo 14 basalts are only 0.2 to 0.3 AE older than were found for mare basalts from the Sea of Tranquility. Assuming these leucocratic igneous rocks to be representative of the Fra Mauro site, it follows that there were major igneous processes active in these regions, and presumably throughout the highlands, at times only slightly preceding the periods at which the maria were last flooded.
The internal Sm-Nd systematics of lunar KREEP basalt 15386 and its implications for the evolutionary history of KREEP on the moon are reported. The age of the 15386 rocklet indicated by the measured Sm-Nd mineral isochron is consistent with the reported Rb-Sr and (Ar-39)-(Ar-40) ages of other KREEP-rich samples, which is interpreted as the time 15386 crystallized from a liquid on or near the lunar surface. This suggests that the eruption of these incompatible element-rich liquids was related to deep impact events during the final bombardment phase of the surface of the moon. It is concluded that the extremely narrow spread of Sm-Nd model ages for these samples around 4.36 AE, and the compatibility of this age with that indicated by the U-Pb and Rb-Sr systems, indicate that the source of later KREEP volcanism was produced in the closing stages of an early global scale lunar differentiation episode.
Sm-Nd isotopic data for mineral separates from the ferroan anorthosite 60025, which define a precise isochron of 4.44 + or - 0.02 Ga age, are discussed. This age is about 110 Myr younger than the formation of the first large solid objects in the solar nebula. If the moon is as old as the oldest meteorite, the relatively young age determined for 60025 implies that the magma ocean did not form synchronously with lunar formation or that the magma ocean required over 100 Myr to reach the stage of ferroan anorthosite crystallization. It is proposed that the accumulated body of radiogenic isotope data for lunar rocks permit the moon to be as young as 4.44-4.51 Ga. This is consistent with the idea that the materials that make up the moon were derived from the earth.
In most Archean cratons, cumulates of equant plagioclase megacrysts form anorthositic complexes, including those at Bad Vermilion Lake (Ontario). In this paper, partition coefficients (Ds) of REEs between natural high-Ca plagioclase megacrysts and their basaltic matrices were determined, using a multiple aliquot techique, and megacrystic plagioclases occurring in anorthosites were analyzed for the same components which, in conjunction with their Ds, were applied to calculations of melts in equilibrium with anorthosites. The REE's Ds were found to agree well with experimentally determined values and to predict equilibrium melts for Archean anorthosites that agree well with coeval basaltic flows and dikes. The Ds also appear to be valid for both the tholeiitic and alkali basalts over a wide range of mg numbers and REE concentrations. It is suggested that the moderately Fe-rich tholeiites that are hosts to plagioclase megacrysts in greenstone belts form the parental melts for megacrysts which make up the Bad Vermilion Lake Archean anorthositic complex.
Lunar sample 76535 is a coarse-grained troctolitic granulite. It is characterized by low REE concentrations and a positive Eu anomaly. Its original petrographic character has been disturbed by metamorphic reequilibration. Its chemical characteristics are those of an olivine-plagioclase cumulate. The amount of trapped parent liquid in the rock is estimated to be in the range of 8-16%. The REE concentrations of the parent liquid, if 16%, range from 13 times the chondritic value for Lu to 27 times for La. The parent liquid had no appreciable Eu anomaly.
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.
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.
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.
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.
87Rb-87Sr internal isochrons have been determined for six crystalline rocks from the Sea of Tranquillity, and all yield ages within the narrow range 3.65±0.06 × 109 yr. Differences in initial (87Sr/86Sr)I define at least two main rock groups which coincide with the two groups indicated by alkali content of the rocks. This demonstrates that at least two magnetic reservoirs were involved in the 3.65 × 109 yr event on the moon. The soil yields a model Rb-Sr age of 4.6 × 109 yr which suggests that it consists of an average over a variety of rock systems of different ages which represent a closed total system 4.6 × 109 yr old or the widespread existence of rocks of 4.6 × 109 yr age. A single peculiar rock fragment from the soil gives a model age of 4.4 × 109 yr. Initial Sr compositions for the lunar rocks and for soil fragments define a narrow range (0.6990-0.6994) whose lower limit is equal to the basaltic achondrite initial Sr. The moon, earth and basaltic achondrites represent planets with Rb/Sr much lower than in the sun. The moon and the basaltic achondrites must have separated from the solar nebula within a time interval of less than 4 × 106 yr. From consideration of Sr-Rb relations, if the moon formed by fission from the earth, it must have occurred prior to 4.4 × 109 yr ago.
Isotopic analysis of basaltic fragments from lunar breccia 14321
- Dasch
Water in ancient moon?
- Tanaka
The age of ferroan anorthosite 60025
- Carlson
A strontium and neodymium isotopic study of Apollo 17 high-Ti mare basalts
- Paces
Partitioning in REE-saturating minerals
- Jolliff
Partition coefficients for calcic plagioclase
- Phinney
The redox state of cerium in basaltic magmas
- Schreiber
Subcommission on geochronology
- Steiger
The origin of pristine KREEP
- Warren