ISSN:0094-8276    

DOI:10.1029/GL010i009p00773

年代:1983

数据来源: WILEY

摘要:

Antarctic meteorite ALHA81005, discovered in the Allan Hills region of Victoria Land, is a polymict anorthositic breccia which differs from other meteorites in mineralogical and chemical composition but is strikingly similar to lunar highlands soil breccias. The petrologic character and several independent lines of evidence identify ALHA81005 as a meteorite from the Moon. Two small clasts of probable mare basalt occur among the highlands lithologies in Thin Section 81005,22. This lunar specimen, which shows relatively minor shock effects, has generated new ideas on the types of planetary samples we may find on the Earth, and has added fresh excitement to the Antarctic meteorite program.

ISSN:0094-8276    

DOI:10.1029/GL010i009p00775

年代:1983

数据来源: WILEY

摘要:

MnO/FeO ratios in pyroxene, texture (abundant brown, swirly glass, in general typical of lunar regolith breccias), and overall composition (∼75% plagioclase) all indicate that Allan Hills A81005 is of lunar origin. It is presumably from a heretofore unsampled region of the Moon. It differs in detail from other regolith samples, e.g., it has exceptionally low contents of Na and KREEP. A pristine clast contains exceptionally coarse augite, compared to similar Apollo samples. ALHA81005 is not perceptibly more shocked than typical Apollo regolith breccias. Therefore, its discovery on Earth lends further credence to suggestions that SNC achondrites were derived by impact ejection from Mar

ISSN:0094-8276    

DOI:10.1029/GL010i009p00779

年代:1983

数据来源: WILEY

摘要:

Petrographic data and pyroxene compositions indicate that meteorite ALHA 81005 is a breccia from the terrae of the Earth's Moon. Thin section ALHA 81005,9 includes ferroan anorthositic clasts, a lone clast of Mg‐suite plutonic composition, fragments which are intermediate in composition between ferroan anorthosite and Mg‐suite plutonics, and a clast of very low‐titanium mare basalt. Fragments of norite and harzburgite have mineral compositions like ferroan anorthosite, and a clast of ferroan anorthosite has pyroxenes with lower molar Mg/(Mg+Fe) than in known pristine rocks. The Mg‐suite protoliths for the clasts of intermediate composition are inferred to be magnesian troctolites, spinel troctolites and feldspathic lherzolites. Although clasts of these lithologies are not present in ALHA 81005,9, mineral fragments from them are present. A single basaltic clast is of mare origin, based on the molar Mg/(Mg+Fe) ratio and Cr content of its pyroxenes. The composition of its plagioclase and the molar Ti/(Ti+Cr) ratios of its pyroxenes indicate that the clast is a fragment of very low‐titanium (VLT) mare basalt. If this basalt is significantly younger than the last basin‐forming impact event (≃ 3.9 × 109years ago), its presence probably constrains the source crater for ALHA 81005 to be within a hundred kilometers of a VLT ma

ISSN:0094-8276    

DOI:10.1029/GL010i009p00783

年代:1983

数据来源: WILEY

摘要:

Petrography and mineral compositions show that ALHA81005 is a lunar highland regolith breccia and is the first known lunar meteorite. Lithic clasts are abundant and most are members of the anorthosite‐norite‐troctolite highland suite. Plagioclase compositions in lithic clasts and single grains are calcic (An94‐98). Pyroxene compositions, Al‐Ti and MnO‐FeO relationships support a lunar highland origin. A non‐KREEPy source region is indicated, and the unexplored far side of the moon cannot be ruled out as a poten

ISSN:0094-8276    

DOI:10.1029/GL010i009p00787

年代:1983

数据来源: WILEY

摘要:

Meteorite ALHA 81005, a glassy regolith breccia, is beyond any reasonable doubt of lunar origin, according to its petrographic, chemical, and isotopic characteristics. The sample was shocked at most to 15 GPa during ejection and supports the possibility of some meteorites being of Martian origin. Most lithic fragments are feldspathic granulitic impactites, cataclastic anorthosites, and impact melts, all typical lunar lithologies. Mineral fragments are derived from plutonic troctolitic and noritic rocks, varied mare basalt‐like extrusive rocks, and the identified lithic fragment types. Neither petrographically nor chemically are there significant components in ALHA 81005 which were previously unknown. A mare basalt component restricts the origin of the sample: with remotely‐sensed data, which eliminates most frontside, as well as farside groundtrack regions, it makes the probability of ejection from Giordano Bruno, near the Moon's NE limb, far greater than from any other lunar cra

ISSN:0094-8276    

DOI:10.1029/GL010i009p00791

年代:1983

数据来源: WILEY

摘要:

Meteorite ALHA81005 is a shock‐compacted lunar highland regolith breccia. Besides glasses (fragments, spherules, matrix glass), chondrules (of ANT composition), and mineral fragments this new lunar sample contains principally three lithologies: 1) A pristine ferroan anorthosite suite consisting of anorthosites, norites, and one plagioclase peridotite. 2) A high‐Mg granulitic breccia suite representing variable mixtures of troctolitic and noritic precursor rocks. 3) A melt‐rock suite consisting of feld‐spathic basalts and metabasalts of a composition intermediate between (1) and (2). Most glass compositions and the chondrule compositions also project into this group. All lithologies and their derivatives are characteristically poor in alkalis. Neither a KREEP nor a mare basalt composition could be identified with certainty. ALHA81005 apparently comes from a highland area far from any mare basalt and KREEP

ISSN:0094-8276    

DOI:10.1029/GL010i009p00795

年代:1983

数据来源: WILEY

摘要:

The Antarctic meteorite ALHA 81005 has oxygen and silicon isotopic compositions identical with lunar highland rocks. The oxygen is distinctly unlike that in calcium‐rich achondrites. The isotopic data are entirely consistent with a lunar origin for the meteorit

ISSN:0094-8276    

DOI:10.1029/GL010i009p00799

年代:1983

数据来源: WILEY

摘要:

The isotopic abundances of the noble gases (He, Ne, Ar, Kr, Xe) are reported for Antarctic meteorite ALHA81005. It contains solar wind‐implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites. ALHA81005 also contains a large excess40Ar component which is identical to the component in lunar fines implanted from the lunar atmosphere. Large concentrations of cosmogenic21Ne,82Kr and126Xe in ALHA81005 indicate a total cosmic ray exposure age of ≥ 2×108years. The noble gas data alone are strong evidence for a lunar origin of this meteo

ISSN:0094-8276    

DOI:10.1029/GL010i009p00801

年代:1983

数据来源: WILEY

摘要:

Measurements of the10Be and26Al contents of ALHA 81005 constrain the length and conditions of its exposure to cosmic rays. Calculations based on one‐step irradiation models imply that the time spent by this object in space is shorter than that spent by most ‘asteroidal’ meteorites. On the other hand the results are readily consistent with a lunar origin for ALHA

ISSN:0094-8276    

DOI:10.1029/GL010i009p00804

年代:1983

数据来源: WILEY