Petrogenesis of lunar meteorite Northwest Africa 2977: Constraints from in situ microprobe results

Zhang, Ai‐Cheng; Hsu, Weibiao; Floss, C.; Li, Xian‐Hua; Li, Qiuli; Liu, Yang; Taylor, L. A.

doi:10.1111/j.1945-5100.2010.01131.x

Cited by 39 publications

(77 citation statements)

References 47 publications

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“…However, most evidences for old impact events on the Earth would have been lost due to weathering and plate movement. Recent studies report high-pressure polymorphs of olivine, wadsleyite and ringwoodite together with those of silica in lunar meteorites 10,57,58 . These high-pressure polymorphs in lunar meteorites, overlooked over the years, might be a new clue for understanding the meteorite bombardments that has occurred on the early Moon and Earth.…”

Section: Discussionmentioning

confidence: 99%

Discovery of seifertite in a shocked lunar meteorite

et al. 2013

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Many craters and thick regoliths of the moon imply that it has experienced heavy meteorite bombardments. Although the existence of a high-pressure polymorph is a stark evidence for a dynamic event, few high-pressure polymorphs are found in a lunar sample. a-PbO 2 -type silica (seifertite) is an ultrahigh-pressure polymorph of silica, and is found only in a heavily shocked Martian meteorite. Here we show evidence for seifertite in a shocked lunar meteorite, Northwest Africa 4734. Cristobalite transforms to seifertite by high-pressure and -temperature condition induced by a dynamic event. Considering radio-isotopic ages determined previously, the dynamic event formed seifertite on the moon, accompanying the complete resetting of radio-isotopic ages, is B2.7 Ga ago. Our finding allows us to infer that such intense planetary collisions occurred on the moon until at least B2.7 Ga ago.

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Section: Discussionmentioning

confidence: 99%

Discovery of seifertite in a shocked lunar meteorite

et al. 2013

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“…Previous studies, including our work, have used minerals and textures to conclude that the OC of NWA 2977 is part of the NWA 773 clan (Bunch et al 2006;Nagaoka et al 2010Nagaoka et al , 2011Zhang et al 2011). In addition to their petrologic affinities, NWA 2977 and NWA 773 both have bulk rock chemical compositions with similar KREEP-like REE patterns (Fagan et al 2003;Jolliff et al 2003;Nyquist et al 2009;Zhang et al 2011). The pairing of NWA 2977 with NWA 773 is supported further by similar isotopic ages that are relatively young for lunar rocks.…”

Section: Introductionmentioning

confidence: 99%

“…Lunar meteorite NWA 2977 is an OC that is texturally and mineralogically similar to the OC clasts found in the NWA 773 clan (e.g., Bunch et al 2006;Fagan et al 2003;Jolliff et al 2003;Zhang et al 2011).…”

Section: Introductionmentioning

confidence: 99%

“…The radiogenic isotope data from the NWA 773 OC include a 147 Sm/ 143 Nd age of 2.993 ± 0.032 Ga (Borg et al 2009), an 40 Ar-39 Ar step-heating age of approximately 2.91 Ga (Fernandes et al 2003), and 207 Pb analyses of baddeleyite crystals indicating an age of 3.131 ± 0.012 Ga (Shaulis et al 2013). The radiogenic ages of NWA 2977 include whole-rock ages of 2.77 ± 0.04 Ga for Ar-Ar (Burgess et al 2007), 3.10 ± 0.05 Ga for Nd-Sm, 3.29 ± 0.11 Ga for Rb-Sr (Nyquist et al 2009), and 3.12 ± 0.01 Ga for Pb-Pb baddeleyite (Zhang et al 2011). Therefore, the similarities in texture, mineralogy, whole-rock geochemistry, and radiogenic age support the inference that NWA 2977 and NWA 773 are paired (Bunch et al 2006;Nagaoka et al 2010Nagaoka et al , 2011Zhang et al 2011).…”

Section: Introductionmentioning

confidence: 99%

“…The radiogenic ages of NWA 2977 include whole-rock ages of 2.77 ± 0.04 Ga for Ar-Ar (Burgess et al 2007), 3.10 ± 0.05 Ga for Nd-Sm, 3.29 ± 0.11 Ga for Rb-Sr (Nyquist et al 2009), and 3.12 ± 0.01 Ga for Pb-Pb baddeleyite (Zhang et al 2011). Therefore, the similarities in texture, mineralogy, whole-rock geochemistry, and radiogenic age support the inference that NWA 2977 and NWA 773 are paired (Bunch et al 2006;Nagaoka et al 2010Nagaoka et al , 2011Zhang et al 2011). Breccias of the NWA 773 clan contain a variety of mafic clasts, including the OC (Bunch et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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Mineralogy and petrology of lunar meteorite Northwest Africa 2977 consisting of olivine cumulate gabbro including inverted pigeonite

et al. 2015

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Lunar meteorite Northwest Africa (NWA) 2977 is identified as an olivine cumulate gabbro (OC), consisting of coarse cumulate olivine crystals up to 1 mm with low-Ca and high-Ca pyroxenes, plagioclase, and interstitial incompatible element-rich pockets of K-feldspar, Ca-phosphates, ilmenite, and troilite. These minerals and textures are similar to those of the OC clasts of the NWA 773 clan of meteorites. NWA 2977 contains a variety of pyroxene textures and compositions including augite, pigeonite, and rare orthopyroxene, all having exsolution lamellae. Some of the orthopyroxene has abundant augite lamellae with compositions indicating formation by inversion of pigeonite. This pigeonite was inverted at 1140°C according to the pigeonite eutectoid reaction (PER) temperatures. Inverted pigeonite has not been found previously in the NWA 773 clan of meteorites. The presence of inverted pigeonite indicates that NWA 2977 cooled more slowly than most other OC clasts of the NWA 773 clan. The relatively slow cooling of NWA 2977 can be explained by formation in a deeper level of the original igneous body of the NWA 773 clan OC lithology.

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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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Petrogenesis of lunar meteorite Northwest Africa 2977: Constraints from in situ microprobe results

Cited by 39 publications

References 47 publications

Discovery of seifertite in a shocked lunar meteorite

Discovery of seifertite in a shocked lunar meteorite

Mineralogy and petrology of lunar meteorite Northwest Africa 2977 consisting of olivine cumulate gabbro including inverted pigeonite

Petrography and chronology of lunar meteorite Northwest Africa 6950

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