Petrology, chemistry, and isotopic compositions of the Lunar highland regolith breccia Dar AL Gani 262

Details Petrology, chemistry, and isotopic compositions of the Lunar highland regolith breccia Dar AL Gani 262 Petrology, chemistry, and isotopic compositions of the Lunar highland regolith breccia Dar AL Gani 262

Nov 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33.1243b&link_type=abstract

Meteoritics & Planetary Science, vol. 33, no. 6, pp. 1243-1257.

Computer Science

25

Scientific paper

Lunar meteorite Dar al Gani 262 (DG 262) found in the Libyan part of the Sahara is a mature, anorthositic regolith breccia with highland affinities. The origin from the Moon is undoubtedly indicated by its bulk chemical composition, radionuclide concentrations, noble gas, nitrogen, and oxygen isotopic compositions and petrographic features. Dar al Gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to QUE93069. About 52 vol% of the studied thin sections of Dar al Gani 262 consist of fine-grained (smaller than ?100 microns) constituents, and 48 vol% is mineral and lithic clasts and impact melt veins. The most abundant clast types are feldspathic fine-grained to microporphyritic crystalline melt breccias (50.2 vol%; includes recrystallized melt breccias), whereas mafic crystalline melt breccias are extremely rare (1.4 vol%). Granulitic lithologies are 12.8 vol%, intragranularly recrystallized anorthosites and cataclastic anorthosites are 8.8 and 8.2 vol%, respectively, and (devitrified) glasses are 2.7 vol%. Impact melt veins (5.5 vol% of the whole thin sections) cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure. Mafic crystalline melt breccias are very rare in Dar al Gani 262 and similar in abundance to those in QUE93069. The extremely low abundance of mafic components and the bulk composition may constrain possible areas of the Moon from which the breccia was derived. The source area of Dar al Gani 262 must be a highland terrain lacking significant mafic impact melts or mare components. Based on radionuclide activities an irradiation position of DG 262 on the Moon at a depth of 55-85 g/cm3 and a maximum transit time to Earth less than 0.15 Ma is suggested. Dar al Gani 262 contains high concentrations of solar wind implanted noble gases. The isotopic abundance ratio 40Ar/36Ar < 3 is characteristic of lunar soils. The terrestrial weathering of DG 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of Ca, Ba, Cs, Br, and As. There is also a large amount of terrestrial carbon and some nitrogen in the sample, released at low temperatures during stepped heating. High concentrations of Ni, Co, and Ir indicate a significant meteoritic component in the lunar surface regolith from which DG 262 was derived.

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