摘要:

Major‐element analyses of several thousand glasses from all of the Apollo landing sites have resulted in the identification of 25 groups of pristine (i.e., volcanic) glass. The nickel in these pristine glasses is shown to be indigenous, not meteoritic contamination, and to be correlated with Mg. The chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts. The pristine glasses support the view that assimilative processes [Ringwood and Kesson, 1976] involving two cumulate systems in the differentiated mantle operated during mare petrogenesis. The reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses. Data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history. Alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasse

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D201

年代:1986

数据来源: WILEY

摘要:

Rb‐Sr, K‐Ar, and Sm‐Nd isotopic studies were undertaken for two Apollo 14 very high potassium (VHK) mare basaltic clasts from breccias 14305 and 14168. The samples are distinctly more radiogenic than other lunar mare basalts. Rb‐Sr data for the whole rock and mineral separates determine internal isochrons corresponding to essentially identical ages of 3.83 ± 0.08 b.y. and 3.82 ± 0.12 b.y. for samples 14305 and 14168, respectively, for λ(87Rb) = 0.0139 (b.y.)−1. Their corresponding initial87Sr/86Sr ratios are indistinguishable and are 0.6995 ± 0.0005 and 0.6997 ± 0.0004, respectively. The39Ar–40Ar age spectra for the two samples are very similar and give identical plateau ages of 3.85 ± 0.02 b.y. for 14305 and 3.85 ± 0.05 b.y. for 14168. The identical Rb‐Sr and K‐Ar isotopic results for the two rocks indicate that they could be derived from the same flow. The Sm‐Nd isotopic data of whole rock and mineral separates for the two VHK basalts define an internal isochron age of 3.94 ± 0.16 b.y. for λ(147Sm) = 0.00654 (b.y.)−1and an initial143Nd/144Nd of 0.50673 ± 21. The averaged model age, relative to the chondritic initial143Nd/144Nd of 0.505893 for the basalts is 4.56 ± 0.04 b.y. The concordance of Rb‐Sr, K‐Ar, and Sm‐Nd ages strongly suggests that VHK basalts crystallized from a melt ∼3.85 b.y, ago. The Rb‐Sr and Sm‐Nd isotopic data indicate that VHK basalts show very large Rb/Sr fractionation but no significant Sm/Nd fractionation at the time of crystallization. The source material for these basalts had a Rb/Sr ratio similar to those of Apollo 14 high‐A1 mare basalts and a nearly chondritic Sm/Nd ratio. Extreme enrichments of Rb/Sr and K/La during the formation of VHK basalts can be adequately explained by an assimilation model that involves basalt/granite interaction. K, Rb‐rich components of granitic wall rocks in highland crust were selectively introduced into ascending hot high‐A1 mare basaltic magma upon contact. A similar crustal assimilation process has been frequently observed in terrestrial, mantle‐derived

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D214

年代:1986

数据来源: WILEY

摘要:

Partition coefficients were determined for Gd, Lu, Hf, and Zr among ilmenite, armalcolite, and synthetic high‐Ti mare basaltic melts at temperatures from 1122° to 1150°C, and at oxygen fugacities of IW × 100.5, by in situ analysis with the electron microprobe, using samples doped to percent concentration levels. Coefficients for Zr were also measured for samples containing 600–1600 ppm Zr, using a special high‐sensitivity electron microprobe technique. In addition, coefficients were determined for Hf and Zr between chromian ulvospinel and melt, for Hf between pigeonite and melt, and for Lu between olivine and melt by microprobe analysis of samples doped to percent levels. Recommended values for ilmenite are D(Gd) = 0.006, D(Lu) = 0.09, D(Hf) = 0.42, and D(Zr) = 0.33. Recommended values for armalcolite are D(Gd) = 0.006, D(Lu) = 0.046, D(Hf) = 1.5, and D(Zr) = 0.9. Values measured using the microprobe are in general agreement with values measured by analyzing mineral separates from the sanle run products by isotope dilution at the USGS Isotope Lab in Denver. Agreement between microprobe and ID is within 3% for Hf, and within 10% for Zr. For Lu, the ID results were 15–35% lower than the microprobe values. The source of this disagreement has not been identified. Parition coefficients measured in this study and the collaborative ID study confirm the general results of earlier measurements. D values for ilmenite are less than 0.01 for the LREE (light rare earth element), are around 0.1 for the HREE (heavy rare earth elements), and are several times greater than this for Zr and Hf. These results constitute the first simultaneous experimental measurement of ilmenite distribution coefficients for the three important elements Lu, Hr, arid Zr in mare basalt

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D229

年代:1986

数据来源: WILEY

摘要:

Hf, Zr, and REE partition coefficients between ilmenite and coexisting liquid were determined under near‐lunar conditions. Ilmenite was synthesized at 1125°C under low oxygen fugacity (fo2=10−12.4) from glass of a high‐Ti mare basalt composition, doped with 50–100 μg/g of REE and Hf, and 500–1000 μg/g of Zr. The partition coefficients (D) of ilmenite for Hf and Zr, obtained by isotope dilution analysis, are 0.41 and 0.33, respectively. These values are significantly lower than those of ilmenite (3.0 and 1.8, respectively) from a kimberlite megacryst (Fujimaki et al., 1984a). DREEfor the synthesized ilmenite are slightly smaller than those of ilmenite from the kimberlite megacryst, and the DLuis 0.056. These results suggest that ilmenite may have played an important role in the Lu‐Hf evolution of lunar mare basalts. Using newly determined DLuand DHffor ilmenite, the Lu‐Hf evolution or lunar cumulates and the coexisting magma was examined for several different crystallization sequences by a model calculation. The Lu‐Hf variation trend of most high‐Ti mare basalts is well explained by a small degree (less than 5%) of partial melting of the cumulates. However, a higher degree of partial melting is required to explain the variation of very low‐Ti basalts, green glass, and Apollo 12 low‐Ti basalts. Apollo 15 low‐Ti basalts could not be produced by simple partial melting, but may require chromi

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D239

年代:1986

数据来源: WILEY

摘要:

Based on the chemical data for 30 elements for 17 highland fragments (3–35 mg) from 6 suites of Apollo 12 coarse fines, 11 chemical highland groups (6 with negative Eu anomalies and 5 with positive Eu anomalies) are identified in the Apollo 12 fragments. The highland chemical groups are represented by a range of petrographic types. Among the chemical groups four are newly recognized. One group is very high‐K (VHK) KREEP‐La at 520× (chondrite) with a negative Eu anomaly at 50×. The other three new chemical groups have positive Eu anomalies and these are as follows: a poikilitic/granulitic rock with La at 130×; anorthosite with La at 30X and Eu at 90×, and anorthosite with La at 12× and Eu at 25×. The Apollo 12 highland suite is dominated by high‐K KREEP and is similar to the Apollo 14 highland suite. The presence of high‐K KREEP explains the relatively high LIL contents in the Apollo 12 soils. The plutonic suite data appear to show a trend in Eu anomaly versus longitude, i.e., eastern (Apollo 11) and western (Apollo 12 and 14) plutonic (ANT) rocks, as suggested byWarren et al.[1981]. Several parent magmas are suggested to explain the wide variety of plutonic and other highland suites observed at the Apollo

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D251

年代:1986

数据来源: WILEY

摘要:

Lunar granulites are breccias with metamorphic textures. They are not pristine, having been contaminated with meteoritic siderophiles. Nonetheless, they constitute an abundant class of highlands rocks that are important because they are ancient and KREEP‐free. They may represent our best samples of the early lunar crust. The granulites can be divided into ferroan and magnesian groups, and each group can be subdivided on the basis of mineral composition and REE concentrations. Textural and compositional data show that some of the granulites (especially 67215 and 67415) may be derived from distinct anorthositic norite precursors, while some other granulites (79215, 78155) are clearly polymict. Even the polymict granulites probably had anorthositic norites as their dominant precursors, and not anorthosites, norites, or troctolites. The granulites have compositions similar to those of the two lunar meteorites, one of which (Yamato‐791197) is ferroan, the other (ALHA81005) magnesian. These meteorites are soil breccias from an unknown location distant from the Apollo landing sites and contain anorthositic norites as abundant clasts. Compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands, as determined by remote sensing, than do those of any other returned lunar samples. The predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from Apollo missi

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D263

年代:1986

数据来源: WILEY

摘要:

All of the Apollo 16 regolith breccias (18 specimens) have been characterized in terms of their petrography, grain‐size distribution, porosity, major and trace element composition, noble gas contents, and ferromagnetic resonance properties. These breccias vary significantly with respect to their density and porosity, with the more dense breccias showing significant shock damage. The regolith breccias resemble the soils in grain‐size distribution and in the relative proportions of major petrological components, except agglutinates. Many of the breccias are compositionally different from the Apollo 16 soils in that they lack an important mafic component present in the soils. Although some groupings occur, the petrologic and chemical compositions of the regolith breccias do not correlate with the station location of the samples. All but one of the breccias show some evidence of irradiation at the lunar surface (solar gases, measurable FMR, agglutinates), and analyses made on grain‐size separates from two disaggregated breccias indicate that this irradiation occurred before compaction when the breccia material was finely disseminated on the surface. However, the concentrations of surface irradiation parameters (solar gases, FMR, agglutinates) for most breccias are far less than seen in any lunar soils or in regolith breccias from other Apollo missions. Several breccias also contain unusually high trapped40Ar/36Ar ratios of ∼8–12 and a significant fission Xe component in excess of that expected from in situ production. These observations suggest that the surface irradiation of these breccias occurred as early as 4×109years ago. We conclude that most of the Apollo 16 regolith breccias were not formed from any known Apollo 16 soil. They appear to be well‐comminuted material that contains ancient regolith developed during the late stage heavy bombardment of the moon when large impacts were much more common relative to small impacts so that regoliths did not have time to significantly mature before being diluted by fresh ejecta and buried. This ancient megaregolith is significantly different from more recent lunar regolith but may be similar to asteroidal regoliths from which some brecciated meteorites

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D277

年代:1986

数据来源: WILEY

摘要:

Twelve clasts were separated from breccia 14304 for consortium study: six pristine highlands rocks, two mare basalts, and four nonpristine highlands rocks. The pristine highlands rocks include representatives of the magnesian troctolite‐anorthosite and alkali suites, the two most common subgroups of the Mg suite found at the Apollo 14 site. Two troctolite clasts have olivine (∼Fo 90) and plagioclase (∼An 94) compositions similar to one group of Apollo Htroctolites. One also contains spinel (Mg′66–85). Incompatible element abundances in one are similar to those of 14305 troctolites, although the HREE (heavy rare earth elements) pattern is distinct among Apollo 14 troctolites. A dunite clast (∼Fo 89) may be an unrepresentative piece of a troctolite. Alkali lithologies include an alkali anorthosite and an alkali norite, which is a rock type not previously described. The alkali norite has a pristine igneous texture and contains inverted pigeonite (Mg′ 64), plagioclase (An82), K‐feldspar, ternary feldspar, REE‐rich phosphates, and silica. It resembles alkali gabbronorites from Apollo 14 and 67975 in mineralogy and mineral compositions. Alkali lithologies and phosphate‐bearing magnesian anorthosites from Apollo 14 may have formed from Mg‐rich magmas that assimilated various amounts of material rich in P and REE. This material could be a fractionated derivative of urKREEP. Another pristine clast from 14304 is an Mg‐gabbronorite. The two mare basalt clasts are very high potassium (VHK) basalts. They have 4 mg/g K and K/La ratios of 580 and 700. The parent magmas of VHK basalts could have formed from typical low‐Ti, high‐Al basaltic magmas by assimilation of K‐rich material. This material could also be a fractionated derivative or urKREEP. Nonpristine 14304 clasts include melt‐textured anorthosites and an augite‐rich poikilitic melt rock. The latter is probably polymict, but its major com

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D305

年代:1986

数据来源: WILEY

摘要:

Analysis of previously unstudied Apollo lithic fragments continues to yield surprising results. Among this year's samples is a small anorthosite fragment, 76504,18, the first pristine anorthosit e found from Apollo 17. This unique lithology strongly resembles the main type of Apollo anorthosites (ferroan anorthosites), but 76504, 18 has a far higher ratio (about 9) of high‐Ca pyroxene to low‐Ca pyroxene, higher Na in its plagioclase, higher contents of incompatible elements such as REE, and a higher Eu/Al ratio. Assuming that 76504, 18 is a cumulate with less than 45% trapped liquid, its parent melt probably had a negative Eu anomaly. In all these respects, 76504,18 seems more likely than (other) ferroan anorthosites to be closely related to typical mare basalts. Apparently this anorthosite was among the latest to form by plagioclase flotation above a primordial magmasphere; typical mare basalt source regions probably accumulated at about the same time or even earlier. Another previously unstudied fragment, 14181c, is a VHK (very high potassium) basalt that is similar in most respects to typical (“aluminous”) Apollo 14 mare basalt but has a K/La ratio of 1050. This lithology probably formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderophile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contam

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D319

年代:1986

数据来源: WILEY

摘要:

The lunar magma ocean (or magmasphere) hypothesis, always controversial, has required considerable revision in recent years. The geochemical bimodality of pristine rocks, epitomized by a diagram of Na/(Na + Ca) versus mg′ ratio, has led to proposals that a major fraction of the crust (the Mg‐rich suite) formed as cumulates in numerous intrusions slightly younger than the magmasphere. The precise origin of the bimodality has been elusive, however. One previous suggestion was that Na was lost as a volatile before the ferroan anorthosites crystallized from the magmasphere, whereas the Mg‐rich intrusives retained all of their original Na. However, this model cannot fully explain the bimodality, because the same bimodal pattern is manifested by plotting Eu/Al (a ratio of involatile elements) versus mg′ ratio. Assimilation probably helped to engender the bimodal patterns. Mass/energy balance calculations indicate that large proportions of plagioclase were probably assimilated from the older (magmasphere‐generated) ferroan anorthosite crust by most of the Mg‐rich intrusive melts. The magmasphere, in the absence of assimilation, probably did not yield appreciable plagioclase (the ferroan anorthosite crust) until fractional crystallization of mafic silicates had diminished the melt mg′ ratio to about 0.42. However, assuming identical initial melt composition, an Mg‐rich intrusion assimilating ferroan anorthosite (and perhaps also a small proportion of urKREEP) would have reached plagioclase saturation at much higher mg′, about 0.66. The current version of the magmasphere hypothesis (ferroan anorthosites = magmasphere flotation cumulates; Mg‐rich rocks = products of slightly younger, localized intrusions) appears to be the only plausible mechanism for engendering the Mg/Fe

ISSN:0148-0227    

DOI:10.1029/JB091iB04p0D331

年代:1986

数据来源: WILEY