3.1 Ga crystallization age for magnesian and ferroan gabbro lithologies in the Northwest Africa 773 clan of lunar meteorites

Shaulis, Barry; Righter, M.; Lapen, T. J.; Jolliff, Bradley L.; Irving, A. J.

doi:10.1016/j.gca.2017.06.031

Cited by 20 publications

(61 citation statements)

References 46 publications

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“…Pb-Pb baddeleyite [5] NWA 773 2865±31 (2σ) Sm-Nd Whole rock [18] 2670±10 (2σ) Ar-Ar Whole rock [17] NWA 3160 2650±40 (2σ) Ar-Ar Whole rock [36] NWA 3170 3118±14 (95% conf.) Pb-Pb baddeleyite [5] NWA 7007 3106±22 (95% conf.) Pb-Pb baddeleyite [5] 3100±16 (95% conf.)…”

Section: Discussionunclassified

“…The weighted mean age of 207 Pb/ 206 Pb of phosphate is (3119 ± 18) Ma (MSWD = 2.1, Figure 7), which is the same as baddeleyite. By comparing these ages with the crystallization ages http://engine.scichina.com/doi/10.1007/s11432-019-2809-3 of the gabbro lithology of NWA 773 clan of meteorites (Table 4 [4,5,17,18,24,25,36]), it is concluded that the age of NWA 6950 is nearly the same.…”

Section: U-pb Chronology Of Baddeleyite and Phosphatementioning

confidence: 99%

“…Northwest Africa (NWA) 6950 is a 1649 g lunar meteorite, whose lithology is magnesian gabbro with thin black shock veins. It is inferred to be paired with other lunar meteorites called the NWA 773 clan [4,5], which is a group of paired or petrogenetically related stones that include NWA 773, NWA 2977, NWA 2700, NWA 2727, NWA 3160, NWA 7007, and etc. [6][7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…In recent years, NWA 773 and its paired meteorites have received extensive attention from planetary chemists because they are significantly different from Apollo and Luna samples and other lunar meteorites [13]. Scientists studying the Apollo and Luna samples, generally conclude that the volcanic eruption of the mare basalts lasts from 3900 Ma to ∼3150 Ma, after which there is no large-scale volcanic activity [5,[14][15][16]. However, in recent years, studies on the age of crystallization of lunar meteorites have modified this conclusion [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

“…The NWA 773 clan is 30-40 Ma younger than the youngest Apollo samples (about ∼3. 16 Ga, 12051 and 12065 samples [5,15]), and provides new opportunities to study the formation and evolution of lunar magmas [20][21][22][23]. Moreover, compared to other younger lunar meteorites such as LAP 02205/NWA 4734, the gabbro clast of NWA 773 has unique geochemical characteristics including KREEP-like rare earth element (REE) patterns, but at lower concentrations [13].…”

Section: Introductionmentioning

confidence: 99%

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Petrography and chronology of lunar meteorite Northwest Africa 6950

Bao

Shi

Anderson

et al. 2020

Sci. China Inf. Sci.

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Northwest Africa (NWA) 6950 is an olivine-gabbro lunar meteorite that has a distinctly different petrographic texture from other lunar basalts. In this contribution, we report the petrography, mineralogy, and U-Pb geochronology of baddeleyite and phosphate in this lunar meteorite and make a comparison with other NWA 773 paired meteorites. NWA 6950 consists mainly of coarse-grained olivine, pyroxene, and plagioclase, with minor ilmenite, chromite, troilite, baddeleyite, taenite, and apatite. The abundant rounded to euhedral olivine has a limited Fo ranging from 68 to 69. Pyroxenes include both augite and pigeonite, with a narrow range of Mg#=71-80, and composition, respectively, En 46-52 Fs 12-16 Wo 32-41 and En 58-68 Fs 19-28 Wo 7-20. Plagioclase is mainly anhedral, conforming to the crystal margins of olivine and pyroxene. The plagioclase grains are elongated and several hundreds of microns in length. Raman spectra shows that plagioclase has been transformed into maskelynite, which is very calcic (An 87-95) with low sodium and very low potassium (Ab 4-9 Or 0.6-3.7). The weighted mean 207 Pb/ 206 Pb ages of baddeleyite and phosphate measured using a sensitive high resolution ion micro probe (SHRIMP II) are 3119 ± 16 Ma (n = 9, MSWD = 2.5) (mean squared weighted deviates, MSWD) and 3119 ± 18 Ma (n = 15, MSWD = 2.1), respectively, giving the crystallization age of the meteorite. NWA 6950 has similar mineral compositions, geochemical characteristics, and an almost identical age of crystallization to the magnesian gabbro of the NWA 773 clan. We conclude that NWA 6950 and NWA 773 are paired meteorites, which crystallize at ca. 3119 Ma, and represent magmatic activities in the KREEP (potassium (K), rare earth elements (REE) and phosphorus (P) rich lunar material) region of the Moon.

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