Apollo 17 KREEPy basalt: A rock type intermediate between mare and KREEP basalts

The Apollo 17 KREEPy basalt is a unique lunar volcanic rock, observed only as clasts in the light friable breccia matrix (72275) of Boulder 1, Station 2 at Taurus-Littrow. Its status as a volcanic rock is confirmed by the absence of any meteoritic contamination, a lack of cognate inclusions or xenocrystal material, and low Ni contents in metal grains.The basalt was extruded 4.01 ± 0.04 b.y. ago, approximately contemporaneously with the high-alumina mare basalts at Fra Mauro; shortly afterwards it was disrupted, probably by the Serenitatis impact, and its fragments emplaced in the South Massif. The basalt, which is quartz-normative and aluminous, is chemically and mineralogically intermediate between the Apollo 15 KREEP basalts and the high-alumina mare basalts in most respects. It consists mainly of plagioclase and pigeonitic pyroxene in approximately equal amounts, and 10–30% of mesostatis. Minor phases outside of the mesostatis are chromite, a silica mineral, Fe-metal, and rare olivine; the mesostatis consists primarily of ilmenite, Fe-metal, troilite, and ferroaugite, set in a glassy or microcrystalline Si-rich base.Chemical and isotopic data indicate that an origin by partial melting of a distinct source region is more probable than hybridization or contamination of magmas, and is responsible for the transitional composition of the basalt. The moon did not produce two completely distinct volcanic groups, the KREEP basalts and the mare/mare-like basalts; some intermediate rock types were generated as well. A corresponding spectrum of source regions must exist in the interior of the moon.     

Al depth profile in Apollo 15 drill core

Cosmic-ray-produced²⁶Al (t_1/2 = 7.05 × 10⁵ years) has been measured in the Apollo 15 long core (surface to 390 g/cm²—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for²⁶Al production can be calculated to be 122 g/cm² (150–400 g/cm² region) after normalizing the data to average chemical composition. The⁵³Mn (t_1/2 = 3.7 × 10⁶ years) production profile in deep cores was also compiled to date. The half-attenuation length for⁵³Mn production was calculated to be 123 g/cm² (150–400 g/cm² region).     

Lunar glass compositions: Apollo 16 core sections 60002 and 60004

Approximately 500 glasses between 1 mm and 125 μm in size have been analyzed from fourteen samples from the Apollo 16 core sections 60002 and 60004. The majority of glasses have compositions comparable to those found in previous studies of lunar surface soils; however, two new and distinct glass compositions that are probably derived in part from mare material occur in the core samples. The major glass composition in all samples is that of Highland Basalt glass, but it also appears that high-K Fra Mauro Basalt (KREEP) glass is more common at the Apollo 16 site than was previously thought. The relative abundance of glasses within the core samples is random in distribution: each sample is characterized by a particular assemblage and distribution of the constituent glass compositions.     

Be andCl depth profiles in an Apollo 15 drill core

Cosmic-ray-produced¹⁰Be (t_1/2 = 1.6 × 10⁶ years) and³⁶Cl (t_1/2 = 3.0 × 10⁵ years) have been measured in the Apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry. From these experiments, the half-attenuation length for¹⁰Be production and³⁶Cl production were calculated to be 120 g/cm² and 132 g/cm² (150–400 g/cm² region). The measured half-attenuation length for¹⁰Be is slightly longer than that predicted by the Reedy-Arnold theoretical model. The flatter and somewhat deeper maximum seen in the³⁶Cl profile compared to the¹⁰Be,²⁶Al and⁵³Mn profiles can be explained by production from secondary thermal neutrons on³⁵Cl.     

Isotopic and REE studies of lunar basalt 12038: implications for petrogenesis of aluminous mare basalts

We report Sr, Nd, and Sm isotopic studies of lunar basalt 12038, one of the so-called aluminous mare basalts. A precise internal Rb-Sr isochron yields a crystallization age of 3.35±0.09 AE and initial⁸⁷Sr/⁸⁶Sr=0.69922?2 (2σ error limits, 1AE=10⁹ years, λ(⁸⁷Rb)=0.0139AE^?1). An internal Sm-Nd isochron yields an age of 3.28±0.23AE and initial¹⁴³Nd/¹⁴⁴Nd=0.50764?28. Present-day¹⁴³Nd/¹⁴⁴Nd is less than the “chondritic” value, i.e. ?(Nd, 0)=?2.3±0.4 where ?(Nd) is the deviation of¹⁴³Nd/¹⁴⁴Nd from chondritic evolution, expressed as parts in 10⁴. At the time of crystallization ?(Nd, 3.2AE)=1.5±0.6.We have successfully modeled the evolution of the Sr and Nd isotopic compositions and the REE abundances within the framework of our earlier model for Apollo 12 olivine-pigeonite and ilmenite basalts. The isotopic and trace element features of 12038 can be modeled as produced by partial melting of a cumulate mantle source which crystallized from a lunar magma ocean with a chondrite-normalized REE pattern of constant negative slope. Chondrite-normalized La/Yb=2.2 for this hypothetical magma ocean pattern. A plot of I(Sr) versus ?(Nd) for the Apollo 12 basalts clearly shows the influence of varying proportions of olivine, clinopyroxene, orthopyroxene, and plagioclase in the basalt source regions. A small percentage of plagioclase (～5%) in the 12038 source apparently is responsible for low I(Sr) and ?(Nd) in this basalt. Aluminous mare basalts from Mare Crisium (Luna 24) and by inference Mare Fecunditatis (Luna 16) occupy locations on the I(Sr)-?(Nd) plot similar to that of 12038, implying that some basalts from three widely separated lunar regions came from plagioclase-bearing source regions. A summary of model calculations for mare basalts shows a record of lunar mantle solidification during the period when REE abundances in the lunar magma ocean increased from ～20× chondritic to >100× chondritic. Although there is a general trend from olivine to clinopyroxene-dominated source regions with progressive magma ocean evolution, significant mineralogical heterogeneities in mantle composition apparently formed at any given stage of evolution, as evidenced in particular by the three Apollo 12 magma types.     

Trapped solar and cosmogenic noble gas abundances in Apollo 15 and 16 deep drill samples

Abundances and isotopic compositions of all the stable noble gases have been measured in 19 different depths of the Apollo 15 deep drill core, 7 different depths of the Apollo 16 deep drill core, and in several surface fines and breccias. All samples analyzed from both drill cores contain large concentrations of solar wind implanted gases, which demonstrates that even the deepest layers of both cores have experienced a lunar surface history. For the Apollo 15 core samples, trapped⁴He concentrations are constant to within a factor of two; elemental ratios show even greater similarities with mean values of⁴He/²²Ne= 683±44,²²Ne/³⁶Ar= 0.439±0.057,³⁶Ar/⁸⁴Kr= 1.60±0.11·10³, and⁸⁴Kr/¹³²Xe= 5.92±0.74. Apollo 16 core samples show distinctly lower⁴He contents,⁴He/²²Ne(567±74), and²²Ne/³⁶Ar(0.229±0.024), but their heavy-element ratios are essentially identical to Apollo 15 core samples. Apollo 16 surface fines also show lower values of⁴He/²²Ne and²²Ne/³⁶Ar. This phenomenon is attributed to greater fractionation during gas loss because of the higher plagioclase contents of Apollo 16 fines. Of these four elemental ratios as measured in both cores, only the²²Ne/³⁶Ar for the Apollo 15 core shows an apparent depth dependance. No unambiguous evidence was seen in these core materials of appreciable variations in the composition of the solar wind. Calculated concentrations of cosmic ray-produced²¹Ne,⁸⁰Kr, and¹²⁶Xe for the Apollo 15 core showed nearly flat (within a factor of two) depth profiles, but with smaller random concentration variations over depths of a few cm. These data are not consistent with a short-term core accretion model from non-irradiated regolith. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. The lack of large variations in solar wind gas contents across core layers is also consistent with appreciable pre-accretion irradiation. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmogenic gases below ～65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper ～70 cm of the core. Cosmogenic gas concentrations of several Apollo 16 fines and breccias are consistent with ages of North Ray Crater and South Ray Crater of ～50·10⁶ and ～2·10⁶ yr, respectively.     

Primitive neon and helium isotopic compositions of high-MgO basalts from the Kerguelen Archipelago,Indian Ocean

The geochemical characteristics of mildly alkalic basalts (24–25 Ma) erupted in the southeastern Kerguelen Archipelago are considered to represent the best estimate for the composition of the enriched Kerguelen plume end-member. A recent study of picrites and high-MgO basalts from this part of the archipelago highlighted the Pb and Hf isotopic variations and suggested the presence of mantle heterogeneities within the Kerguelen plume itself. We present new helium and neon isotopic compositions for olivines from these picrites and high-MgO basalts (6–17 wt.% MgO) both to constrain the enriched composition of the Kerguelen plume and to determine the origin of isotopic heterogeneities involved in the genesis of Kerguelen plume-related basalts. The olivine phenocrysts have extremely variable ⁴He / ³He compositions between MORB and primitive values observed in OIB (∼90,000 to 40,000; i.e., R / R_a ∼8 to 18) and they show primitive neon isotopic ratios (average ²¹Ne / ²¹Ne_ext ∼0.044). The neon isotopic systematics and the ⁴He / ³He ratios that are lower than MORB values for the Kerguelen basalts clearly suggest that the Kerguelen hotspot belongs to the family of primitive hotspots, such as Iceland and Hawaii. The rare gas signature for the Kerguelen samples, intermediate between MORB and solar, is apparently inconsistent with mixing of a primitive component with a MORB-like source, but may result from sampling a heterogeneous part of the mantle with solar ³He / ²²Ne and with a higher (U, Th) / ³He ratio compared to typically high R / R_a hotspot basalts such as those from Iceland and Hawaii.     

Metal-olivine associations and NiCo contents in two Apollo 12 mare basalts

Olivine crystals in mare basalts 12004,8 and 12022,12 are normally zoned with Cr-poor rims. The Ni content of rare 2–10-μm metal inclusions in olivine decreases markedly as Fe/Mg in their immediate olivine hosts increases. Each metal grain appears to have been enclosed by late olivine almost immediately after it crystallized. The fractionation trend for the olivine and metal contrasts with the subsolidus equilibration trend for pallasites. For the basalts, not even local equilibration of Fe, Ni and Co at metal/olivine interfaces can be detected by microprobe. Ni and Co concentrations range from about 300 ppm in olivine cores to about 70 ppm in rims. The limits of detection, at 95% confidence, are 36 ppm (Ni) and 25 ppm (Co). The distribution of Ni and Co in olivine, like that of Mg and Cr, records the depletion of these elements in the melt.Fractional solidification models, using the Ni and Co concentrations of the whole rock, and Ni and Co concentrations of the earliest formed olivine, metal and “opaques” as initial compositions, allow metal and olivine compositions to be predicted if the order of crystallization is known. Conversely the order of crystallization can be established if known olivine and metal compositions are reproduced. Calculated Ni and Co contents for metal and olivine in these basalts correspond to observed concentrations only where metal precipitation is delayed until the liquid has crystallized 4–5 wt.% olivine.     

Particle track record in Apollo 15 deep core from 54 to 80 cm depths

Particle track measurements have been made in nearly 500 individual grains from 13 levels in the 54–80 cm depth range of the Apollo 15 deep core. They reveal a wide range of track densities at all depths and some systematic variations within layers, indicating that both predepositional mixing and subsequent layering are present and that separate sub-layers exist within larger regions where no sub-layers are visible. Minimum track densities are inferred to be useful measures of maximum residence times for undisturbed layers. Using the observed minimum track densities we conclude that the average deposition rate in this section of soil column was ≥ 0.4 cm/million years.     

南极湖泊沉积物中有机硫组成及其与铁硫化物的联系

本文利用有机硫硫同位素组成(δ34Sorg)及活性铁的黄铁矿化度(DOP)和硫化度(DOS)研究了南极阿德雷岛受企鹅活动影响的Y2湖和未受影响的菲尔德斯半岛燕鸥湖YO沉积物中有机硫的来源组成及其与铁硫化物的联系.结果 表明,Y2沉积物1～15 cm较低的δ34Sorg指示有机质硫化形成的贫34S成岩有机硫(Sdiag)...     

Chemical composition of boulder-2 rocks and soils,Apollo 17, station 2

Forty-two elements have been measured via INAA and RNAA in six samples of five rocks from a 2-m tan-gray boulder-2 breccia (South Massif), in four soils from the South Massif and a valley soil. The chemical composition of the four metaclastic rocks corresponds to “high alumina” (52% Pl) and medium-K KREEP-type rocks. Rock 72335,2 is a medium K anorthositic gabbro (74% Pl). Both the North and South Massifs appear to be medium-K KREEP in composition and thus may represent a single stratigraphic unit of the Serenitatis basin event. Four soils of the South Massif are identical in composition to medium-K KREEP; they are more feldspathic and lower in LIL trace elements relative to the boulder-2 rocks. The valley soil 75081 is like the 10084 soil; both soils are high in TiO₂ and both are deficient in KREEP. Th and U give a sharp distinction between the valley and highland soils. The South Massif rocks and soils contain siderophiles at the 2–4% Cl level and show an ancient meteoritic pattern. Five samples of the four rocks have Ir/Au ratios of ± 0.02 which we assign to the Serenitatis basis planetesimal. The valley soil at Camelot Crater has low siderophiles (1% Cl). Our systematic study of four shadowed and exposed soils does not support the labile hypothesis for Cd, In, Tl and Zn. We observe no volatile (atmophile) movement from the South Massif highland soils to the valley soil 75081. The volatiles Cs and Tl appear to have been fractionated in the boulder-2 rocks during cratering, brecciation and metamorphic processes. The uniform ratio of FeO/MnO = 80–85, observed for all previous mare and highland sites, also holds for the Taurus-Littrow site.     

Inert gases from Apollo 11 and Apollo 12 fines: Reversals in the trends of relative element abundances

On the basis of the⁴He/²⁰Ne ratios in feldspathic particles from Apollo 11, basaltic fragments from Apollo 11, and magnetic separates from Apollo 12 fines, one expects the former to have the highest, and the Apollo 12 material to have the lowest⁸⁴Kr/¹³²Xe ratios. This is not the case; the⁸⁴Kr/¹³²Xe ratios from sample 12070 are substantially greater than those from the feldspathic and basaltic fragments in 10084. The trend-reversal in the feldspathic particles could be due to the trapping of genuine primordial lunar Kr and Xe. The reversal in the Apollo 11 basaltic fragments might be due to periodicnear-quantitative loss of the lighter gases by impact heating, with the Apollo 11 fines containing a relatively large proportion of strongly heated fragments.     

Content and behavior of fluorine in Japanese quaternary volcanic rocks and petrogenetic application

Fluorine contents in about 160 representative Quaternary volcanic rocks and 15 hornblende and biotite phenocrysts in a calc-alkali series in Japan have been determined by a selective ion-electrode method. Tholeiites have the lowest contents and the narrowest range (58–145 ppm), while alkali basalts have the highest contentws and the widest range (301–666 ppm), high-alumina basalts have intermediate values (188–292 ppm). F contents in basalts clearly increase from east to west across the Japanese Islands, as do alkalies, P₂O₅ REE, U, Th and H₂O.The volcanic rocks studied are divided into two groups on the basis of F: (1) witt, increasing % SiO₂ or advancing fractionation, F contents show either progressive enrichment; or (2) with increasing fractionation, F contents show rather constant values. The former is produced by fractionation of anhydrous phases from basalt to mafic andesite magmas; the tholeiite series of Nasu volcanic zone (outer zone), northeastern, Japan is a typical example. The latter group is derived through separation of amphibole-bearing phases from basaltic magmas at various depths from upper mantle (about 30 km) to upper crust; the alkali series in southwestern Japan and the calc-alkali series of Chokai volcanic zone (inner zone), northeastern Japan, are examples.     

Oxygen isotope variations in marginal basin and ocean-ridge basalts

Oxygen isotope analyses have been made on 27 tholeiitic basalts from the Lau and Mariana marginal ocean basins and from mid-ocean ridges. The ¹⁸O values are related to the extent of hydration by submarine weathering as indicated by H₂O^? and total water content. Extrapolation to zero H₂O^? content gives a δ¹⁸O value of 5.5‰ on the SMOW scale for unaltered marginal basin basalts, in exact agreement with the oxygen isotope “signature” of ocean-ridge tholeiites. Three alkali basalts from seamount provinces also fit the tholeiite relationship. A Lau Basin gabbro has the tholeiitic ¹⁸O content, but an Indian Ocean gabbro is unusually light (δ¹⁸O = 4.0 for whole rock, plagioclase, and amphibole), and resembles the low -¹⁸O Iceland basalts. The basalt data confirm petrologic and chemical evidence for origin of marginal basins by extensional processes with production of basalts from depleted mantle material isotopically identical to the source of ocean-ridge tholeiites.