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NWA 4485

Lunar Mafic, Th-rich, Impact-Melt Breccia
(KREEP-melt regolith breccia)
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Found Summer of 2006
no coordinates recorded Two paired stones weighing 64.3 g (NWA 4472) and 188 g (NWA 4485) were found in the Algerian desert and subsequently purchased by separate collectors (G. Hupé and S. Ralew, respectively). A portion of each was submitted for analysis to the University of Washington in Seattle (S. Kuehner and A. Irving) and Washington University in St. Louis (R. Korotev), and the meteorite was classified as a unique KREEP-rich, basaltic melt breccia.

This is a polymict breccia composed of clasts from diverse lunar locations including mare basalt, High-Mg Suite (HMS), High-Alkali Suite (HAS), ferroan anorthosite (FAN), and impact-melt lithologies dispersed in the matrix. The KREEP-bearing assemblages are composed of granophyric textured clasts consisting of intergrowths of silica and K-feldspar, together with the high-temperature mineral zirconium oxide, or baddeleyite, and the Fe(Zr,Y)Ti-silicate known as tranquillityite, a mineral first recognized as a late-stage fractional crystallization product in Apollo 11 and 12 basalts. Other mineral fragments identified in NWA 4485 include olivine, pyroxene, plagioclase, ilmenite, chromite, K-feldspar, apatite, merrillite, silica, Fe-metal, and FeS, most reflecting derivation from a KREEP-rich precursor magma (Arai et al., 2009) referred to as urKREEP. The investigators observed that some of these KREEP basalt clasts exhibit chemical zoning and thick exsolution lamellae, attesting to slower cooling conditions at a deeper location compared to the Apollo mare basalts. The matrix also contains a variety of glasses, some containing vesicles and others taking the form of spherules enriched in P and K. In their study of apatite grains in NWA 4472, the pairing to NWA 4485, Tartèse et al. (2014) found that they contain moderate amounts of water, in the range of 2,000–6,000 ppm. Associated isotopic studies on the apatite demonstrated elevated δ37Cl values compared to terrestrial values, which suggests this meteorite has retained its original lunar isotopic signature. Moreover, they recognized that the δD values are consistent with lunar rocks associated with HMS, HAS, and KREEP-rich basalts.

The bulk composition of NWA 4485 reflects a high REE abundance with a strong negative Eu anomaly, with overall incompatible element abundances in the range of the only known KREEP-rich lunaites—the impact-melt breccias Sayh al Uhaymir 169 and Dhofar 1442. SaU 169 contains ~4.0 b.y. old clasts containing very high-K KREEP which best reflect the composition of primordial urKREEP (Lin et al. 2010). Basaltic clasts in NWA 4472/4485 sample low-Ti to very low-Ti source regions and exhibit a range of metamorphic textures. Some of these are fayalite-rich, quenched-textured glass thought to be derived from impact melting of mare basalt lithologies. Also present are a variety of feldspathic impact-melt, fragmental, and granulitic breccias, as well as metal clasts and glass spherules, all consistent with lithification within the lunar regolith.

The composition of NWA 4472/4485 is similar to that of the Th-rich, mafic, LKFM (low-K Fra Mauro) impact-melt breccias recognized from the Apollo collection; specifically, group-C melt breccias of Apollo 15, group-1S melt breccias of Apollo 16, and the aphanitic and poikilitic impact-melt breccias of Apollo 17 (Korotev 2000). The four constituents of the LKFM material—KREEP norite, forsteritic dunite, feldspathic upper crust, and FeNi-metal—are thought to be the likely products of a basin-sized impact into the ancient ‘Great Lunar Hot Spot’, which created the Imbrium basin within the Th-rich Procellarum KREEP Terrane (PKT) (Korotev, 1999). The impactor is thought to have been an iron meteorite that mixed upper mantle dunite with KREEP-contaminated Mg-rich magma, and incorporated clasts of ferroan anorthositic upper crust. The LKFM composition is unique to the PKT, and with its high FeO (noritic) composition and incompatible element abundances (>10 ppm Sm; 5.9–7.9 ppm Th), NWA 4472/4485 is likely derived from this nearside region (Joy et al., 2008). Other possible source locations are northwest of Sinus Iridium within the Jura mountains, northwest of Sinus Roris at Herschel crater, regions of the Mons Alpes formation in western Mare Imbrium, regions of the Apennine mountains near Mons Caucasus and Mons Bradley near Apollo 15, and regions near the craters Ptolemaeus and Lalande, the latter suggested to be the source location of SaU 169.

Calzada-Diaz et al. (2015) compared compositional and age data from a large number of lunar meteorites with elemental remote sensing data obtained by the Lunar Prospector gamma ray spectrometer, primarily for Fe, Ti, and Th, to better constrain the meteorite’s source regions. For the KREEP-rich basaltic melt breccia NWA 4485/4472, plausible ejection sites were identified near the John Herschel crater and in Mons Caucasus, having a composition consistent with ejecta from the Imbrium basin (see image below).
Image credit: A. Calzada-Diaz et al.
MAPS, vol. 50, #2, p. 220 (2015)
‘Constraining the source regions of lunar meteorites using orbital geochemical data’
(http://dx.doi.org/10.1111/maps.12412)
Establishment of a thorough chronological history of this lunar rock following the initial basin-forming impact, and including the time spent on the lunar surface, in Moon–Earth transit, and in terrestrial residence has begun (Joy et al., 2009). Cosmogenic Ar–Ar data are indicative of a ~300 m.y. near-surface residence as part of the ancient lunar regolith. The Pb–Pb and U–Pb ages were calculated from the phosphates fluorapatite and merrillite in matrix and basalt clasts, as well as from zircon grains in the KREEP basalt component (Joy et al., 2011). The ages found within this regolith breccia reflect a diversity of lithic fragments with a wide range of crystallization ages (~4.35–3.94 b.y.); the younger ages in this range are consistent with those of Apollo KREEPy mare basalts possibly dating the formation of Mare Imbrium, while the oldest ages were derived from a matrix apatite grain and might reflect the crystallization of the HAS lithology. The lower Ar–Ar apparent age of 1.7–2.2 b.y. obtained for trapped solar wind Ar is thought to reflect a recent impact-resetting event which could represent the consolidation of the NWA 4472/4485 meteorite components.

A more thorough treatment of the chemical classification of lunar meteorites can be found on the WUSL—Lunar Meteorites website, including information on the other (unpaired) KREEP-rich meteorites SaU 169 and Dhofar 961/960/925/SaU 449, the KREEPy clast bearing meteorites Calcalong Creek and Y-983885, and the KREEP basalt meteorites comprising the NWA 733 pairing group, the LAP pairing group, and Dhofar 287a.

NWA 4472/4485 contains Sr and Ba indicative of terrestrial weathering. Both portions of the meteorite also contain high Br concentrations, suggesting that they were contaminated by seawater. The photo of NWA 4485 shown above is a 0.32 g partial slice, while that pictured below is the uncut mass as found (both photos courtesy of Chladni’s-Heirs.com).

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Photo courtesy of Chladni’s-Heirs.com


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NWA 482

Lunar Feldspathic Breccia
(crystalline impact-melt)
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Purchased January 9, 2001
no coordinates recorded An oriented lunar meteorite weighing 1,015 g was originally found by a Berber nomad in late 2000 during a desert search, probably in Algeria. It was later sold in Morocco to a group of American meteorite collectors. Although much of the fusion crust on this meteorite has been replaced by desert varnish, the interior shows little sign of terrestrial weathering. Northwest Africa 482 is a polymict, crystalline impact-melt breccia, consisting of scattered white clasts of anorthosite within a fine-grained matrix of anorthitic plagioclase (An96.3), olivine, pigeonite, and augite, with rare troilite, FeNi-metal (Ni-rich), ilmenite, and whitlockite. Besides anorthosite clasts, other clast types that are present include troctolite, anorthositic troctolite, troctolitic anorthosite, and pleonaste spinel. No KREEP, regolith, Mg-suite, or mare components have been observed (Daubar et al., 2002), and thus a lunar far side origin is considered more favorable.

The rock was melted and brecciated, and clasts were introduced during a severe shock event, possibly occurring ~3.75 b.y. ago. Isotopic composition and elemental abundance studies indicate that the impactor component in the NWA482 impact melt breccia had a bulk composition comparable to an EH chondrite (Puchtel et al., 2008). Thereafter, the rock experienced a moderate shock event, possibly occurring ~2.4 b.y. ago, which resulted in shock melting and the formation of the black, vesiculated, shock-melt veins and melt pockets in the form of quenched glass. Ultimately, this rock was ejected from the Moon in a separate impact event, likely responsible for some of the shock veins. This lunaite has a relatively high porosity of ~13% (Warren et al., 2005). A more comprehensive treatment of this special meteorite is maintained by the owners at LunarRock.com.

Northwest Africa 482 is similar to sample #65015 that was returned by Apollo 16 from the lunar highlands, which is thought to be a sample of ancient lunar highlands, probably 4.4–4.5 b.y. old. However, in contrast to the Apollo samples, NWA 482 is derived from a KREEP-deficient terrane, more consistent with a location on the far side of the Moon. However, since an impact-melt breccia could be formed at a significant depth beneath the large-ion-lithophile contaminated regolith, its low-Th, low-Fe signature by itself is not an adequate determinant for either a nearside or a farside origin for this type of lunar meteorite (R. Korotev).

Calzada-Diaz et al. (2015) compared compositional and age data from a large number of lunar meteorites with elemental remote sensing data obtained by the Lunar Prospector gamma ray spectrometer, primarily for Fe, Ti, and Th, to better constrain the meteorite’s source regions. For the crystalline impact-melt breccia NWA 482, plausible ejection sites were identified in the Feldspathic Highland Terrane on the farside (see image below).
Image credit: A. Calzada-Diaz et al.
Meteoritics & Planetary Science, vol. 50, p. 222 (2015) Noble gas studies indicate that NWA 482 records the longest residence in the lunar regolith observed to date—2.07 (±0.42) b.y—which occurred at a depth of >2.8 m (>500 g/cm² [shielding depth] divided by 1.8 g/cm³ [ave. regolith density]) (Lorenzetti et al., 2005). Northwest Africa 482 has a cosmic-ray exposure age of 280 t.y., and it arrived on Earth 8.6 (±1.3) t.y. ago (Nishiizumi, 2003). According to Nishiizumi and Caffee (2010), this relatively long Moon–Earth transit time would be consistent with a launch from a depth of >5.6 m. They determined that shallower launches from depths of <1–4.7 m correspond to the shortest transit times of <0.1 m.y. Through studies of cosmogenic nuclides, its pre-atmospheric diameter was calculated to be ~11–14 cm, while the presence of 26Al is indicative of relatively low ablation, removing 1–1.5 cm from its surface.

The specimen of NWA 482 pictured above is a 0.29 g partial slice displaying intricate microbrecciation. The top photo below shows the slice from which the above specimen was removed, while the bottom photo below shows a close-up of the large shock vein within the slice.

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Photos courtesy of Anne Black—Impactika Meteorites The photos below show the complete oriented main mass exhibiting flow lines in the thin remnant crust or weathering rind. On the right is what might be the most beautiful photo taken of this awesome lunaite, showing a large cut face. A sizable portion of this rare meteorite has been donated for scientific study.

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Photos courtesy of Jim Strope—darksideofthemoon.com


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Dho 908

Lunar Feldspathic Breccia
(impact-melt)
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Found January 2003
19° 19.9′ N., 54° 47.0′ E. Nine individual stones, having a total combined weight of 245.46 g and exhibiting heterogeneous compositions, were recovered by a German expedition searching in Wadi Quitbit within the Dhofar dense collection area of Oman. The expedition was searching within the strewnfield in which the lunar pairing group of Dhofar 303, 305, 306, 307, 309, 310, 311, 730, 731, 489 (found 24 km away), 908, 909, 911 (comprising nine separate stones), 950, and 1085 was recovered. Terrestrial weathering has produced significant staining from hematite (R. Korotev).

The finder of the individual Dhofar 908 stone, Norbert Classen, adopted the term ‘Rosetta Stone’ to describe this 81 g lunaite due to its having three distinct lithologies that link the diverse finds Dhofar 302, 303, 305, 306, 307, 309, 310, 311, 730, 731, and 489 together; most of these other stones represent only one of the three lithologies. Importantly, Dhofar 908 established a clear pairing relationship among all of these separate finds (see photo below).

Following the analysis at the Institut für Planteologie in Münster, these meteorites were classified as lunar feldspathic breccias, specifically, impact-melt breccias. Interestingly, the lunar feldspathic fragmental breccia that comprises the individual stones Dhofar 081, 280, 910, and 1224, was found in the western half of this same strewnfield, which encompasses an area of 1.4 × 1.2 km—an astounding case of overlapping lunar strewnfields.

Cosmogenic nuclide studies of Dhofar 908 based on 10Be and 26Al have enabled the determination of the excavation depth on the Moon (>6 m), the Moon–Earth transit time (4 ±1 t.y.), and the terrestrial age (~300 t.y.) (Nishiizumi and Caffee, 2006). Sm–Nd data yield a crystallization age of 4.31 (±0.07) b.y., and might reflect derivation from magnesian troctolitic-anorthosite precursor material from plutons that intruded into the early ferroan crust after solidification of the lunar magma ocean (Nyquist et al., 2010). Gross et al. (2012) have presented evidence found in most feldspathic highlands meteorites that a global lunar magma ocean did not form, and they lack features of such a scenario; i.e., they contain no ferroan anorthosites, KREEP, or Mg-suite rocks. Instead, anorthosite intrusions rise continuously in diapirs, resulting in compositional diversity among the crustal regions.

An Ar–Ar age for the mostly troctolitic matrix material of Dhofar 908 was found to be 4,256 (±20) m.y., taking into consideration evidence for solar wind Ar trapped during residence on the lunar surface. This age may reflect material derived from an old basin within early-formed anorthositic crust on the lunar farside in which low Th and FeO exist (Karouji et al., 2010). The crustal asymmetries that exist between the farside and nearside can be explained by the tilted convection model. A potential ejection site for the Dhofar pairing group is considered to be the Derichlet-Jackson basin.

Studies of Dhofar 489, a member of the pairing group, revealed the presence of unique magnesian anorthosite clasts and a spinel troctolite clast. Its bulk analysis is highly depleted in Th (proxy for ITEs) and FeO (Takeda et al., 2007). In addition, studies of the paired stone Dhofar 309 revealed clasts of anorthosite and troctolite composition, considered to be metamorphosed and annealed crystalline rocks associated with an impact-melt pool. A reddish-orange clast found in these samples has a crystalline texture and contains plagioclase crystals and rounded olivine grains; it is thought to be an impact-melt clast derived from spinel troctolite, but which includes a pyroxene component derived from norite.

Studies of the paired Dhofar 307 led to the discovery of magnesian anorthositic granulite clasts, originally derived from impact melts, some of which contain large olivine fragments embedded in a glassy plagioclase matrix (Takeda et al., 2008, 2010). These olivine fragments may represent ejected mantle rock from the massive impact that created the largest impact crater in the Solar System, the South Pole–Aitken basin, located on the lunar farside. These magnesian anorthositic granulite clasts may be ancient (up to 4.3 b.y.), and are thought to represent basaltic plutons which were emplaced into plagioclase-rich crust following solidification of the lunar magma ocean. The bulk compositions of the anorthositic granulite clasts (FeO ~4.5 wt%; Al2O3 ~28 wt%; Th <1 ppm) are similar to those calculated for the Feldspathic Highlands Terrane (FHT) on the lunar farside. The magnesian anorthosite clasts represent a distinct geochemical lunar component that is widespread across the lunar surface (Treiman et al., 2010). These clasts contain too much magnesium to be related to the Ferroan Anorthosite Suite (FAN) components, and are too feldspathic and lacking in KREEP to be related to the Mg-Suite components, both of which are typical contaminates in lunar breccias recovered from the nearside of the Moon.

Since Dhofar 908 and its pairing group represent a quickly cooled impact-melt breccia that could have formed at a significant depth beneath a regolith, which could potentially have been contaminated with incompatible elements, its low-Th, low-FeO signature taken by itself is not an adequate determinant for either a nearside or a farside origin for this type of lunar meteorite (R. Korotev). However, when these analyses are considered together, along with the possible discovery of a norite component, it can be inferred that the origin of this pairing group is most likely the lunar farside—possibly from the area of the South Pole–Aitken basin, or perhaps the FHT at the northern portion of the lunar farside.

An alternative formation scenario has been proposed by Takeda et al. (2008, 2010) in which a large impact into magnesian anorthosites, likely on the northern farside, excavated a basin at least 80 km in diameter and produced an extensive melt sheet. Deep-seated lithologies present in the meteorite were excavated as well. Rapid cooling and subsequent impact gardening within this basin led to the final consolidation of this brecciated rock. A large basin containing many craters in which the Dhofar 908 breccia may have formed is the Dirichlet-Jackson basin, located in the low-Th region of the farside. The mineralogy, chemistry, and petrology of the various members of this pairing group indicate that they were all derived from a common precursor lithology, one having a spinel troctolite composition consistent with a location at a significant depth (>5 m) within the crust.

The specimen pictured above is a 0.143 g very thin partial slice from the main mass of Dhofar 908. The photo below shows the main mass of Dhofar 908, the first stone to be found, weighing 81.43 g. Dhofar 908 was exported by permit from the Ministry of Commerce and Industry, Sultanate of Oman. The bottom photo is a beautiful 0.61 g thin slice from the Dhofar 908 main mass showing three separate lithologies (3.1 cm in longest dimension). <!–Click to see a high resolution photo of a 2.54 g complete slice of this meteorite, courtesy of the finder, Norbert Classen. –> standby for dhofar 908 photo
Photo courtesy of Norbert Classen
dhofar 908
click on photo for a magnified view

Three Lithologies:
left: IMB clast-poor lithology
top: mature regolith w/ dark matrix
bottom: IMB clast-rich lithology
Photo courtesy of Stephan Kambach


For additional information on the magnesium-rich granulites, read the PSRD article by Linda Martel—‘Unraveling the Origin of the Lunar Highlands Crust’, Sept. 2010.