Petrology and geochemistry of feldspathic impact-melt breccia Abar al’ Uj 012,

the first lunar meteorite from Saudi Arabia

Marianna M�ESZ�AROS1,2*, Beda A. HOFMANN2,3, Pierre LANARI3, Randy L. KOROTEV4,Edwin GNOS5, Nicolas D. GREBER3, Ingo LEYA1, Richard C. GREENWOOD6, A. J. Timothy

JULL7, Khalid AL-WAGDANI8, Ayman MAHJOUB8, Abdulaziz A. AL-SOLAMI8, andSiddiq N. HABIBULLAH8

1Space Research and Planetary Sciences, University of Bern, Sidlerstrasse 5, Bern 3012, Switzerland2Natural History Museum Bern, Bernastrasse 15, Bern 3005, Switzerland

3Institute of Geological Sciences, University of Bern, Baltzerstrasse 1 + 3, Bern 3012, Switzerland4Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis,

One Brooking Drive, St. Louis, Missouri 63130, USA5Natural History Museum of Geneva, 1, route de Malagnou CP 6434, Geneva 6 1205, Switzerland

6Planetary Sciences and Space Research, Open University, Milton Keynes MK7 6AA, UK7National Science Foundation Arizona AMS Laboratory, University of Arizona, 1118 East Fourth Street, Tucson,

Arizona 85721, USA8Saudi Geological Survey, P.O. Box 54141, Jeddah 21514, Kingdom of Saudi Arabia

*Corresponding author. E-mail: marianna.meszaros@space.unibe.ch

(Received 18 November 2015; revision accepted 08 June 2016)

Abstract–Abar al’ Uj (AaU) 012 is a clast-rich, vesicular impact-melt (IM) breccia,composed of lithic and mineral clasts set in a very fine-grained and well-crystallized matrix.It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside.Bulk composition (31.0 wt% Al2O3, 3.85 wt% FeO) is close to the mean of feldspathiclunar meteorites and Apollo FAN-suite rocks. The low concentration of incompatible traceelements (0.39 ppm Th, 0.13 ppm U) reflects the absence of a significant KREEPcomponent. Plagioclase is highly anorthitic with a mean of An96.9Ab3.0Or0.1. Bulk rock Mg#is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 � 5.2 kyr. AaU012 contains a ~1.4 9 1.5 mm2 exotic clast different from the lithic clast population whichis dominated by clasts of anorthosite breccias. Bulk composition and presence of relativelylarge vesicles indicate that the clast was most probably formed by an impact into aprecursor having nonmare igneous origin most likely related to the rare alkali-suite rocks.The IM clast is mainly composed of clinopyroxenes, contains a significant amount ofcristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast showssimilarities in texture and modal mineral abundances with some Apollo pigeonite basalts, ithas lower FeO and higher SiO2 than any mare basalt. It also has higher FeO and lowerAl2O3 than rocks from the FAN- or Mg-suite. Its lower Mg# (59) compared to Mg-suiterocks also excludes a relationship with these types of lunar material.

INTRODUCTION

Lunar meteorites are unique and play an importantrole in our understanding of the Moon’s history due totwo main reasons (1) most of the lunar meteorites arepolymict breccias (Korotev et al. 2003) and thereforesample a much wider variety of lunar rocks than

samples of the Apollo and Luna collections, (2) lunarmeteorites likely represent various source locations fromall over the Moon (Warren and Kallemeyn 1991), whilethe Apollo and Luna missions were restricted to a muchsmaller area representing only ~4.4% of the surface ofthe Moon (Warren et al. 2005). Since 1979, when thefirst lunar meteorite was discovered in Antarctica, about

Meteoritics & Planetary Science 51, Nr 10, 1830–1848 (2016)

doi: 10.1111/maps.12693

1830© The Meteoritical Society, 2016.

242 other meteorites (representing ~118 falls) wereclassified as lunar meteorites (as of February 2016;meteorites.wustl.edu). A large portion of thesemeteorites were discovered in Northern Africa (~56%)and on the Arabian Peninsula (~29%). The others arefrom Antarctica (~14%) and Australia (~1%)(meteorites.wustl.edu).

Korotev (2012) proposed six main features to betaken into account during the classification of lunarmeteorites (1) the ratio of plagioclase to olivine pluspyroxene; (2) the ratio of olivine to pyroxene, whichcorrelates with whole-rock Mg#; (3) the albite contentof plagioclase; (4) the relative abundance of KREEP;(5) the relative abundance of ilmenite (in basalticmeteorites); and (6) the amount of siderophile elements,which correlates with the fraction of chondriticcomponent in brecciated lunar meteorites.

The concentrations of Al and Fe (expressed asoxides, Al2O3 and FeO) are first-order classificationparameters, upon which lunar meteorites are dividedinto three main compositional types (1) feldspathiclunar meteorites with high Al2O3 (>25 wt%) and lowFeO (<7 wt%), (2) meteorites with intermediate Fe andAl concentration (7–17 wt% FeO; 13–20 wt% Al2O3),and (3) basaltic meteorites with low Al2O3 (<12 wt%)and high FeO (>17 wt%) (Korotev et al. 2003, 2009;Korotev 2005). Thorium along with other incompatibleelements, for example, K, REE, P, and U are used asindicators for the presence of a KREEP component andare thus useful in the classification of lunar rocks aswell as in the identification of their source regions(Korotev et al. 2003). Two important siderophileelements in lunar geochemistry are Ni and Ir, as theirconcentrations give an indication about the proportionof extralunar material in lunar breccias. While all lunarmeteorites contain traces (<0.1 wt%) of indigenousmetallic iron, brecciated lunar meteorites also containFeNi derived mainly from chondritic meteorites(Korotev 2005). Asteroidal contamination of brecciatedlunar meteorites can be as high as 1–2 wt% andtherefore contributes up to 99% of the highlysiderophile elements (Korotev et al. 2003).

On Earth, meteorites are exposed to variousterrestrial effects, which change the original mineralogy,chemical composition, and usually also their physicalproperties. The most important factors in meteoriteweathering are (1) climate (precipitation, dailytemperature fluctuations, wind), (2) local geology (hostsoil or bedrock, salt minerals, topography), (3) theinitial composition of the meteorite (mineralogy,chemistry, porosity) (Al-Kathiri et al. 2005), and (4) theduration of time a meteorite was exposed to weathering(Floss and Crozaz 2001). The terrestrial alteration ofchondritic meteorites discovered both in hot and cold

deserts, is well studied and described in literature (e.g.,Lee and Bland 2004; Al-Kathiri et al. 2005; Bland et al.2006; Zurfluh et al. 2011). According to the investigationof chondrites, the two major contaminants, Sr and Ba,most likely derive from the local soil meteorites lie on(Al-Kathiri et al. 2005; Zurfluh et al. 2011), andconcentrations of these elements are thought to becorrelated with the terrestrial ages of the meteorites(Nazarov et al. 2004; Al-Kathiri et al. 2005; Zurfluhet al. 2011).

AaU 012 was discovered on January 31, 2012. It isthe first lunar meteorite found in Saudi Arabia. Thefind location (22�240 N, 48�420 E) is situated on anUpper Tertiary limestone plateau on the northwesternboundary of the Rub’ al-Khali sand sea, a geologicalsetting similar to, but ~750 km northwest to the Dhofardense collection area of Oman, where many lunarmeteorites were found. The meteorite is a crystallineimpact-melt (IM) breccia, of which two fittingfragments were found in close proximity (Fig. 1). Itlacks a fusion crust, and has a total mass of 122.78 g.In this paper, we present a detailed study about themineralogy, petrology, and chemical composition ofAaU 012, and compare this meteorite with similar lunarmeteorites (Table 1) and some Apollo samples.

ANALYTICAL METHODS

Two polished thin sections of the lunar meteoriteAaU 012 were prepared at the University of Bern(Department of Geology) for optical and scanningelectron microscopy (SEM) in order to characterizemineralogy, texture, and chemical composition. The twopolished thin sections, S12-011.1.1. (area ~51 mm2;Fig. 2a) and S12-011.2.1 (area ~476 mm2; Fig. 2b) wereexamined at the Natural History Museum, Bern with a

Fig. 1. The two fitting parts of AaU 012 as found in the field(field number: S12-011) during the Saudi-Swiss meteoritesearch campaign in 2012. The scale bar is 5 cm.

Petrology and geochemistry of Abar al’ Uj 012 1831

polarized light microscope (Leica DM4500P). Bothtransmitted and reflected light were used to determinethe main mineral phases and to study the texture of thewhole-rock and certain clasts. Backscattered electron(BSE) and secondary electron (SE) images as well asqualitative and semiquantitative mineral analyses of thethin sections were obtained at the University of Bern(Institute of Geological Sciences) using an EVO 50scanning electron microscope equipped with an EDAXApollo X energy dispersive X-ray analysis system.

Quantitative analyses of minerals in both thinsections were done at the University of Bern (Instituteof Geological Sciences) with a JEOL JXA-8200 electronprobe microanalyzer (EPMA) equipped with fivewavelength dispersive spectrometers. Minerals wereanalyzed by using beam conditions of 15 keV and 20nA, a spot size of 2–3 lm, and the following syntheticand natural standards: anorthite (SiO2, Al2O3, CaO),

albite (Na2O), ilmenite (FeO, TiO2), forsterite (MgO),and orthoclase (K2O). Counting times were 10–60 s.CITZAF correction was used to calculate the oxideweight percentage compositions.

Quantitative X-ray mapping of an IM clast (foundin thin section S12-011.2.1) was performed with thesame instrument. An area of 1.4 9 1.5 mm2 waschemically mapped. Eight semiquantitative X-ray mapshave been measured in two passes (Si, Al, Ca, Na, K,and Ti, Mn, Mg, Fe) using five wavelength dispersivespectrometers. The analytical conditions were 15 keVaccelerating voltage, 100 nA specimen current, 1 lmbeam, 200 ms dwell times, and 2 lm step size, resultingX-ray maps with sizes of 700 9 750 pixels. Prior tomapping, conventional quantitative spot analyses weremeasured on the same area. CITZAF correction andsame mineral standards were used as for mineralanalysis in the bulk rock. X-ray maps and spot analyseswere processed using the program XMAPTOOLS 2.1.4(Lanari et al. 2013, 2014). Pixels were classified intodifferent masks based on their chemical compositions:silica, plagioclase, pyroxene, and vesicles. Thisclassification was performed using the automaticprocedure described in Lanari et al. (2014). Thisfunction classifies all the pixels of the image andgenerates a mask image. X-ray maps of each phase havebeen transformed into maps of oxide weight percentagecomposition using the spot analyses as internalstandards (procedure described in De Andrade et al.2006). The quality of the standardization was tested bydisplaying the map of the sum of oxide weightpercentage analyses and by plotting the compositions ofthe internal standards versus the composition of thecorresponding pixel on the standardized map. Thestandardized maps for all the minerals were thencorrected for density difference and merged to yieldentire standardized maps for SiO2, TiO2, Al2O3, FeO,MgO, Na2O, CaO, and K2O (Lanari 2015). The localcomposition of the IM clast was determined by selectinga spatial range of pixels and calculating the averagecomposition.

Raman spectra were obtained by using aJobinYvon LabRAM-HR800 instrument, an integratedRaman microprobe consisting of an Olympus BX41confocal microscope coupled to an 800 mm focal-lengthspectrograph. A frequency-doubled Nd-YAGcontinuous-wave laser with an excitation wavelength of532.12 nm (green) was used. All measurements wereperformed with the 1009 objective and without filter.The spectra were recorded with the software LabspecTMv. 4.14.

Major and minor oxide compositions weremeasured by inductively coupled plasma-massspectrometry after fusion/acid digestion (FUS-ICP-MS),

Table 1. List of feldspathic lunar meteorites used forcomparison with AaU 012 in this work.

Meteorite Type Reference

Dho 081/280/910 FB/RB Korotev (2012) andreferences thereinDho 301/304

(paired with Dho 025)

RB

Dho 302 IMBDho 490/1084 FBDho 1428 RB

Dho 1436/1443 IMBDho 1627 IMBJaH 348 IMB

Shis�r 160 RBShis�r 161 RBShis�r 162 IMB

Shis�r 166 IMBKalahari 008(paired with

Kalahari 009)

RB Korotev et al. (2009) andreferences therein

NWA 4936/5406 FBDho 489 (pairedwith Dho 303)

IMB Korotev et al. (2006)

PCA 02007 RBDaG 262 RB Warren et al. (2005)DaG 400 IMB

Dho 025 (pairedwith Dho 301/304)

RB

Dho 026/457-468 IMB/GB

NWA 482 IMBQUE 93069/94269 RBALHA 81005 RB Wieczorek et al. (2006)

and references thereinMAC 88104/88105 RBY-791197 RBY-82192/82193/86032 FB

FB = fragmental breccia, RB = regolith breccia, IMB = impact-melt

breccia, GB = granulitic breccia.

1832 M. M�esz�aros et al.

and also by analyzing fused beads with EPMA (EMPA-FB). In addition, some major and minor oxides (FeO,CaO, and Na2O) were also measured by instrumentalneutron activation analysis (INAA). The ICP-MSmeasurement was done by Activation Laboratories(ActLabs, Ontario, Canada), using an aliquot of 1.63 g,splitted into two subsamples (reported data are theaverage of the two subsamples, error is 2r). The EPMAmeasurement of fused beads, made from two of theINAA subsamples, was done at Washington Universitywith the technique described in Zeigler et al. (2005).Each bead was analyzed 10 times (reported data are theaverage of the two subsamples, error is 2r). Traceelements (including REE) were measured by FUS-ICP-MS and INAA. For the INAA measurement eightsamples were prepared, each ~30 mg of weight (reporteddata are the mass-weighted mean of the eightsubsamples, error is 1r), at Washington University,using a method described in Korotev et al. (2006).

The oxygen stable-isotopic composition wasmeasured at the Open University, using the techniquedescribed in Greenwood et al. (2014), and the terrestrial14C age of a 99.5 mg sample was measured by AMS atThe University of Arizona using the method describedby Jull et al. (2010).

Bulk density was determined by measuring thebuoyancy of isopropanol-saturated samples inisopropanol using Archimedes’ principle, after saturationof open porosity in vacuum. The open porosity wasdetermined by mass increase after saturation inisopropanol. For the measurement a 97.2 and a 5.9 gsample was used. Both samples were measured two times(n = 4).

RESULTS

Macroscopic Description and Petrography

AaU 012 consists of two fitting fragments. Themeteorite has a middle gray color (N4.5 2/1, GSARock-Color Chart), the surface is shiny and no fusioncrust is preserved, indicating significant wind erosion.The wind-polished surface shows an irregular pockedmorphology with some clasts standing out from thematrix, while others are eroded, demonstrating a quitevariable erosion resistance of the different lithologiestoward the blowing sand (Figs. 3a and 3b).

AaU 012 is highly vesicular and clast-rich (Figs. 3cand 3d). Spheroidal, mm-sized vesicles can be seen onthe surface. Some vesicles are completely or partly filledwith yellowish, very fine-grained (sand/silt-sized)terrestrial mineral assemblage. On the surface of therock, black and white lithic or mineral clasts, typicallyless than 2 mm in size, are also visible, but somefeldspathic clasts are up to ~7 mm in size. Themeteorite is crosscut by a fracture, up to ~1 mm inwidth, and is filled with similar terrestrial material asvesicles, and also with grains of quartz sand with atypical diameter of 0.3 mm. Broken surfaces are stainedwith yellowish, and in some places also with reddishbrown terrestrial alteration products, a mixture ofcalcite and sand/silt-sized material. Thinner fracturesare filled with a yellowish, very fine-grained assemblageof terrestrial minerals. This material can be seen onbroken surfaces as well, along which the meteorite fellinto pieces. There are broken surfaces, which are notcovered with the terrestrial material, on these surfaces

Fig. 2. Photomicrographs of the two thin sections of AaU 012. a) S12-011_TS1 and b) S12-011_TS2. The clast-rich and vesicularnature of the meteorite is well visible on both images.

Petrology and geochemistry of Abar al’ Uj 012 1833

small, white, gray, and brownish clasts or mineralfragments are recognizable. The size of these clasts isusually 1–2 mm, but can reach up to 5 mm.

Measured bulk density (including closed porosity) of2.72 � 0.03 g cm�3 is somewhat lower than of pureanorthosite (2.76 g/cm�3), indicating some porosity, whichis consistent with the vesicular nature of the sample. Thegrain density calculated from the mineral mode is2.84 � 0.02 g cm�3. Together with the bulk density, thisyields 4.2 � 0.7 vol% closed porosity and a total porosityof ~5.9 vol%. Some vesicles are filled with terrestrialminerals, which reduce the open porosity to ~1.7 vol%.

MatrixAaU 012 is a clast-rich feldspathic breccia. Clast-

poor parts of the matrix are built up of plagioclaseplatelets. The cross-section of these crystals is typically

8 lm in width and 15 lm in length, but can reach70 lm. Vesicles are abundant, and appear in differentsizes in the thin sections, from a few lm up to 1 mm.Figures 4a–c show the fine crystalline matrix and thevesicular nature of AaU 012. Regolith components, likeagglutinates or glass spherules were not observed.

Lithic ClastsThe lithic clasts are subrounded/rounded, typically

with smooth margins, indicating that clasts werepartially resorbed by the melt. Their size ranges from afew 100 lm up to 6.8 mm. Average clast size is ~2 mm.The lithic clast population is dominated by clasts ofanorthosite breccias, which consist mainly of plagioclasewith minor mafic silicates embedded in amicrocrystalline matrix. Plagioclase grains in these clastsare usually polycrystalline, show mosaicism, and are

Fig. 3. a) The main fragment of AaU 012. The meteorite has a middle gray color, fusion crust is absent. A crack filled withterrestrial minerals crosscuts the sample in the middle. The size of the piece is 60 mm. b, c) show the clastic nature of AaU 012.b) The backside of the main fragment with the crack running down in the middle of the sample. White mineral and/or lithicclasts are well visible on the broken surface. d) A relatively large (d ~0.8 mm) vesicle surrounded by several microvesicles (only afew tens of lm in size). Note the homogeneous and microcrystalline nature of the matrix.

1834 M. M�esz�aros et al.

resorbed, or partly recrystallized as a consequence ofheating by the shock. Beside the average lithic clastpopulation, a single clast of a pyroxene- andcristobalite-rich IM clast was also identified (Figs. 4dand 4e; see below).

Mineral ClastsThe most common mineral clasts are plagioclase

with minor pyroxene and olivine. Most of these clasts

are partially resorbed, and are polycrystalline or showmosaicism due to the shock. The size of these clastsranges from a few 10s of lm up to ~1 mm. Traceminerals are troilite, FeNi metal, and spinel.

Bulk Composition

Bulk composition of AaU 012 was measured withFUS-ICP-MS, EPMA-FB, and INAA. The results of

Fig. 4. A photomicrograph (a), BSE images (b, d, e), and a secondary electron image (c) of AaU 012. a) The two largest vesicles(left ~1 mm, and right ~500 lm) are surrounded by the microcrystalline matrix. Picture was taken with crossed polars. b, c)Close-ups of the matrix. Note the microcrystalline, acicular plagioclase crystals and the abundant microvesicles. d, e) Thevesicular impact-melt (IM) clast in AaU 012 consists of euhedral/subhedral pyroxene crystals embedded in a microcrystallinemixture of minerals. The mesostasis consists of euhedral, mainly zoned pyroxene crystals (middle gray); elongated/acicularplagioclase laths (dark gray); and between these minerals, a mixture of opaque minerals (white) and cristobalite (black).

Petrology and geochemistry of Abar al’ Uj 012 1835

the three different methods are in good agreement(Table 2), the small differences can derive from sampleheterogeneity. Compositional data for lunar meteoritespresented in the literature are usually obtained byEPMA-FB (for major and minor oxides) and INAA(for trace elements); therefore, in order to make a bettercomparison between AaU 012 and other lunarmeteorites, we provide and discuss our results obtainedwith these two methods. Detailed results are listed inTable 3.

Mean Al2O3 and FeO concentrations are 31.0 wt%and 3.85 wt%, respectively. AaU 012 has a bulk Mg#of 63, whole-rock FeO/MnO is 76, and Ca# (Ca/[Ca+Na]) is 98. According to the bulk composition,AaU 012 has a normative mineralogy of ~88.5 vol%plagioclase, ~5.5 vol% pyroxene, ~5.6 vol% olivine. and~0.4 vol% trace minerals. Concentrations of the twoincompatible elements Th and U are low, 0.39 and0.13 ppm, respectively. The two siderophile elements, Niand Ir. have concentrations of 131 ppm and 5.1 ppb,respectively. Sr and Ba are thought to be goodindicators of terrestrial weathering in hot desert regions(e.g., Al-Kathiri et al. 2005). Sr content is 271 ppm, andBa is 410 ppm, both with high standard deviations (115for Sr and 267 for Ba).

Bulk oxygen isotopic composition of the meteoriteis d17O +2.86&, d18O +5.46&, D17O +0.02&. The 14Cactivity is 1.15 � 0.70 dpm kg�1, corresponding to aterrestrial age of 33.4 � 5.2 kyr assuming a saturatedactivity of 65.2 dpm kg�1.

Major Silicate Composition

The chemical composition of the major silicatephases was measured by EPMA. Results are shown inTable 4.

PlagioclaseThe composition of feldspar was measured in

109 points, and data prove a highly anorthitic natureof the sample. All measured feldspar grains areplagioclase. Anorthite shows a narrow compositionalrange throughout the sample, especially in the matrix.Average plagioclase compositions are An96.8 � 0.9

Ab3.0 � 0.9 in lithic clasts, An97.0 � 0.7Ab2.9 � 0.7 inmineral clasts, and An96.8 � 0.4Ab3.0 � 0.4 in the matrix.

OlivineOlivine composition was measured in 53 points.

Mean Mg# (Fo) in the matrix, lithic, and mineral clastsare 73, 72, and 65 mol%, respectively. Mean FeO/MnOratios of the mineral clasts and the matrix are both 91,while olivine in the lithic clasts has somewhat lowermean FeO/MnO ratio of 86, with a wide variation of75–121.

PyroxenesPyroxene compositions were measured in 34 points

altogether, out of which 19 measurements wereperformed in the IM clast (see next section). Due to thesmall grain size of the matrix, only one single-grainmeasurement on pyroxene was obtained. Meancompositions of augite in the lithic and mineral clastsare En42.7Fs18.2Wo39.2 and En42.8Fs18.7Wo38.5,respectively. Pigeonite has also a very similarcomposition in the lithic and mineral clasts, with anaverage of En61.1Fs26.9Wo12.1 and En62.4Fs30.1Wo7.5,respectively. Low-Ca pyroxene in the matrix is richer inFe than in lithic and mineral clasts, although these dataare not representative, because of the low number ofmeasurements performed on low-Ca-pyroxenes. MeanMg# of pyroxenes varies between 63 and 71 andaverage FeO/MnO ratios have a variation of 45–60.

Petrography and Chemical Composition of the Impact-

Melt Clast

A single clast, different than any other clast in themeteorite was identified (Figs. 4d and 4e). The clast isrich in pyroxene and SiO2, has a size of about1.4 mm 9 1.5 mm, and possesses porphyritic texture.This special clast contains four relatively large vesicles,and a few smaller ones. The diameter of the largevesicles ranges from 100 to about 300 lm, while the sizeof the small vesicles is only a few tens of lm. The clast

Table 2. Major and minor oxide composition of AaU012.

Oxide (wt%) ICP-MS EPMA-FB INAA

SiO2 44.6 � 0.6 44.0 � 0.2 n.d.TiO2 0.20 � 0.00 0.17 � 0.01 n.d.

Al2O3 28.9 � 0.3 31.0 � 0.3 n.d.FeO 5.04 � 0.13 3.85 � 0.12 3.94 � 0.11MnO 0.07 � 0.00 0.05 � 0.01 n.d.MgO 3.86 � 0.03 3.70 � 0.17 n.d.

CaO 17.0 � 0.2 17.0 � 0.1 16.5 � 0.1Na2O 0.46 � 0.00 0.31 � 0.01 0.31 � 0.00K2O 0.10 � 0.00 0.04 � 0.00 n.d.

P2O5 0.05 � 0.01 0.03 � 0.01 n.d.Total 100.2 100.2 –Mg# 58 63 –Ca# 97 98 –FeO/MnO 75 76 –

ICP-MS data are the mean of two subsamples (error is 2r). EPMA-

FB data are the mean of two subsamples (made from two of the

INAA subsamples) measured ten times each (error is 2r). INAA

data are the mass-weighted mean of eight subsamples (error is 1r).Mg# (Mg/[Mg+Fe]), Ca# (Ca/[Ca+Na]) and FeO/MnO were

calculated from molar oxide values. n.d. = not detected.

1836 M. M�esz�aros et al.

is predominantly composed of pyroxene. The euhedralto subhedral porphyritic pyroxene crystals are 400–1000 lm in size, and surrounded by a microcrystalline

mesostasis, which also consists mainly of pyroxene andplagioclase. The porphyritic pyroxenes are slightlyzoned, while pyroxenes in the mesostasis have thin

Table 3. Bulk composition of AaU 012 compared to feldspathic lunar meteorites, the lunar surface andfeldspathic upper crust, and Apollo FAN-suite rocks.

Oxides (wt%)AaU 012(EPMA-FB) Shis�r 166 NWA 482 Dho 026 IMBs

Feldspathicmeteorites

Lunarsurface FUpCr

FANsuite

SiO2 44.0 44.6 44.9 44.8 44.7 44.5 44.7 44.9 44.8

TiO2 0.17 0.19 0.18 0.28 0.21 0.24 0.22 0.22 0.19Al2O3 31.0 29.3 29.1 29.0 28.7 28.4 28.2 28.5 30.1FeO 3.85 4.13 3.90 4.06 4.14 4.33 4.40 4.00 3.89MnO 0.05 0.05 0.06 0.06 0.07 0.07 0.06 0.06 0.06

MgO 3.70 3.97 4.13 4.07 4.49 4.82 5.40 5.30 3.20CaO 17.0 17.1 16.7 16.9 16.9 16.8 16.3 16.4 17.5Na2O 0.31 0.32 0.38 0.30 0.32 0.33 0.35 0.34 0.32

K2O 0.04 0.04 0.04 0.04 0.06 0.03 0.03 0.02 0.02P2O5 0.03 0.04 n.d. n.d. 0.13 0.14 0.03 0.02 0.02Total 100.2 99.7 99.5 99.7 99.7 99.7 99.7 99.8 100.1

Mg# 63 63 65 64 66 67 69 70 60FeO/MnO 76 83 65 63 63 65 70 67 65

Trace elements

(ppm) (ICP-MS) (INAA)

Sc 8.0 7.3 7.9 7.1 7.6 8.0 8.1 8.0 8.0

Cr 530 557 605 510 570 615 648 660 630Co 12 17 14 15 16 16 17 17 10Ni 130 131 141 170 134 146 169 185 16

Sr 242 271 210 127 497 602 612 150 151Y 8.5 n.d. n.d. n.d. n.d. n.d. n.d. 9.0 9.0Zr 37 35 38 29 35 41 42 35 35Sb b.d. 0.005 0.014 0.006 0.038 0.046 0.067 n.d. n.d.

Cs b.d. 0.043 0.022 0.052 0.078 0.078 0.067 n.d. n.d.Ba 226 410 83 30 391 265 205 33 33La 2.93 2.52 2.57 1.55 2.76 3.06 2.90 2.30 2.40

Ce 6.9 6.8 6.7 3.5 6.2 7.4 7.2 6.0 6.0Pr 0.95 n.d. n.d. n.d. n.d. n.d. n.d. 0.80 0.80Nd 4.1 3.8 4.2 2.5 3.8 4.4 4.4 3.6 3.7

Sm 1.20 1.21 1.22 1.14 1.14 1.36 1.31 1.10 1.10Eu 0.698 0.744 0.744 0.790 0.760 0.798 0.806 0.780 0.790Gd 1.32 n.d. n.d. n.d. n.d. n.d. n.d. 1.30 1.30Tb 0.25 0.26 0.25 0.17 0.25 0.28 0.28 0.23 0.23

Dy 1.60 n.d. n.d. 1.30 1.55 1.54 1.60 1.50 1.50Ho 0.32 n.d. n.d. 0.21 0.33 0.31 0.33 0.33 0.33Er 0.94 n.d. n.d. n.d. n.d. n.d. n.d. 0.90 0.90

Tm 0.14 n.d. n.d. n.d. n.d. n.d. n.d. 0.14 0.14Yb 0.97 0.94 0.96 0.67 0.90 1.04 1.07 0.89 0.90Lu 0.151 0.133 0.140 0.097 0.127 0.145 0.151 0.130 0.130

Hf 0.9 0.89 0.93 0.60 0.81 0.97 1.01 0.80 0.80Ta 0.05 0.11 0.12 0.09 0.11 0.13 0.13 0.11 0.11Ir* n.d. 5.1 5.2 5.9 15.5 6.2 7.4 7.5 0.0

Au* n.d. 1.8 6.7 2.8 12.5 9.0 6.7 2.8 0.6Th 0.50 0.39 0.42 0.23 0.36 0.44 0.47 0.37 0.39U 0.16 0.13 0.14 0.05 0.13 0.19 0.19 0.16 0.16

Bulk chemical compositions of impact-melt breccias (IMBs) and feldspathic meteorites (including IMBs) were calculated from literature data

reported until 2012 (altogether 44 specimens). Values for lunar surface and lunar feldspathic upper crust (FupCr) are from Korotev et al.

(2003), and values of Apollo FAN-suite rocks are from Wieczorek et al. (2006). For other references see Table 1.

*values in ppb. n.d. = not detected, b.d. = below detection.

Petrology and geochemistry of Abar al’ Uj 012 1837

Table

4.Compositionofmajorsilicate

phasesin

AaU

012measuredbyEPMA.

Plagioclase

Olivine

Augite(W

o>20)

Pigeonite(W

o5–20)

Low-C

apyroxene

(Wo<5)

LC

MC

MX

LC

MC

MX

LC

MC

IMclast

LC

MC

IMclast

LC

MC

MX

SiO

244.8

44.3

45.2

38.2

36.3

38.3

51.4

50.3

50.8

52.5

53.5

54.0

54.3

54.3

53.6

TiO

2b.d.

b.d.

0.08

b.d.

b.d.

0.05

1.08

0.64

1.30

0.60

0.15

0.45

0.42

0.25

0.15

Al 2O

334.6

35.1

33.6

0.15

0.09

0.22

3.07

2.53

2.76

2.71

0.66

1.11

0.78

0.86

0.33

Cr 2O

3b.d.

b.d.

b.d.

0.19

b.d.

0.12

0.77

1.21

0.39

0.40

0.44

0.38

0.24

0.29

0.14

FeO

0.42

0.18

0.91

25.3

31.1

24.5

10.8

11.5

15.6

16.8

19.1

15.7

18.2

17.8

23.1

MnO

b.d.

b.d.

b.d.

0.29

0.34

0.27

0.24

0.24

0.27

0.32

0.34

0.32

0.35

0.33

0.39

MgO

0.25

b.d.

0.52

36.2

32.3

37.0

14.4

14.7

14.4

21.3

22.3

22.1

24.9

25.0

21.9

CaO

19.6

19.8

19.3

0.56

0.29

0.47

18.4

18.4

14.4

5.81

3.71

6.67

1.52

1.72

1.32

Na2O

0.34

0.33

0.33

b.d.

b.d.

b.d.

b.d.

0.06

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

K2O

b.d.

b.d.

0.03

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

0.05

b.d.

b.d.

b.d.

b.d.

NiO

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

b.d.

Total

100.0

99.7

99.9

100.9

100.4

101.0

100.2

99.4

99.9

100.4

100.3

100.6

100.7

100.5

100.9

An

96.8 (93.4–

98.6)

97.0 (95.4–

98.5)

96.8 (96.2–

97.4)

Ab

3.0 (1

.4–

6.3)

2.9

(1.4–

4.3)

3.0 (2

.4–

3.6)

Or

0.1 (0

.0–

0.5)

0.1

(0.0–

0.3)

0.2 (0

.1–

0.3)

Mg#

72 (6

1–8

0)

65

73 (6

3–8

6)

71(65–7

6)

70

62(28–7

4)

70(64–7

5)

67(62–7

3)

71(54–7

8)

71

71(65–7

9)

63

FeO

/

MnO

86 (7

5–1

21)

91 (8

9–9

3)

91 (7

0–1

01)

45(43–4

8)

48

56(48–7

1)

52(48–5

9)

56(54–5

8)

50(43–5

7)

52

53(50–5

8)

60

En

42.7 (42.3–4

3.0)

42.8

42.7 (19.3–5

2.6)

61.1 (59.8–6

2.9)

62.4 (58.1– 6

7.2)

61.7 (43.3–7

1.8)

68.7

69.0 (62.2–7

6.2)

61.1

Fs

18.2 (13.4–2

2.9)

18.7

26.4 (16.5–5

0.2)

26.9 (20.9–3

4.3)

30.1 (25.4–3

6.1)

24.7 (20.0–3

7.2)

28.3

27.6 (20.9–3

3.6)

36.2

Wo

39.2 (34.8–4

3.6)

38.5

30.9 (20.3–3

6.6)

12.1 (5.7–1

8.9)

7.5

(5.8–9

.2)

13.5 (5.9–2

0.0)

3.0

3.4 (2

.9–4

.2)

2.7

n52

40

17

27

224

21

74

312

13

1

Alloxides

are

given

inwt%

.An,Ab,Or,

En,Fs,

andWoare

given

inmol%

.Mg#ofolivines

equals

withtheirforsterite

content.Data

inparentheses

are

rangevalues.LC

=lithic

clasts,MC

=mineralclasts,MX

=matrix,IM

=im

pact-m

eltclast,n=number

ofanalyses,b.d.=below

detection.

1838 M. M�esz�aros et al.

(1–2 lm) Fe-rich rims (Figs. 4e, 5c, and 5d). Accordingto the chemical composition (see below), pyroxenes arepigeonite and augite. The clast contains relatively largeamounts of a SiO2 phase, identified as cristobalite byRaman spectroscopy. Cristobalite is not homogenous,inclusions of very fine (<10 lm in size) pyroxenecrystallites are distributed in it.

Modal mineral abundances of the clast wereestimated from the mask image generated byXMAPTOOLS (Fig. 5a). Trace minerals, like ilmenite,troilite, spinel, and zircon, which were analyzedpreviously by spot analysis, could not be visualized on

the map because of their tiny grain size and smallamount. The following phase proportions wereextracted from the mask image: ~59.5 vol% pyroxene,~19.5 vol% plagioclase, and ~7.8 vol% cristobalite. Theproportion of the vesicles (~13.3 vol%) was subtractedfrom the total, and then the amount of the real mineralphases was normalized to 100%, which led to a modalmineralogy of 68.6 vol% pyroxene, 22.5 vol%plagioclase, and 9.0 vol% cristobalite.

Chemical composition of the pyroxenes is listed inTable 4. Augite is less calcic in this clast than in otherlithic and mineral clasts of the meteorite, and has a

Fig. 5. Modal mineral and X-ray elemental maps of the impact-melt (IM) clast created with XMAPTOOLS. a) Map showingthe mineral distributions of the clast. Dark gray (1) marks pyroxenes, light gray (2) marks plagioclase, black (3) markscristobalite, and white (4) marks the vesicles. b) CaO map showing an augite crystal on the lower right part of the clast, and anaugite intergrowth with pigeonite in the middle upper part. CaO map also shows that the mesostasis of the clast is relatively richin plagioclase. c) FeO map shows the zonation in the porphyritic pyroxene crystals, and the distinct iron-rich rims of thepyroxenes building up the mesostasis of the clast. d) MgO map. Porphyritic pigeonites have Mg-rich cores and are moremagnesian than pyroxenes in the mesostasis.

Petrology and geochemistry of Abar al’ Uj 012 1839

mean composition of En42.7Fs26.4Wo30.9. The averagecomposition of pigeonite is En61.7Fs24.7Wo13.5, which isvery similar to the pigeonite composition found in otherlithic clasts. Mg# and FeO/MnO ratio of pigeonite andaugite in the clast are 71 and 50, and 62 and 56,respectively (Table 4). Bulk composition of the IM clastis listed in Table 5. Bulk Mg# of the clast is 59 andaverage An content of plagioclase is 88.7 mol%.

DISCUSSION

A Typical Piece of the Lunar Feldspathic Crust

St€offler et al. (1980) created a consistentclassification for lunar highland rocks (including thebreccias) and their nomenclature is still in use. Tayloret al. (1991) gave a definition for IM lunar rocks:“Crystalline melt breccias are coherent rocks thatcontain obvious clastic material in a finer grainedgroundmass that has formed by the crystallization of asilicate melt,” which was produced by meteoroidimpacts to the Moon. Impact related melts form in thezone of the impact-craters where the shock pressurereaches or even exceeds 80 GPa (H€orz et al. 1991).During the formation of such breccias, a large portionof the target material undergoes total melting anddegassing (Taylor et al. 1991). In crystalline IM rocks,the abundance of vesicles and the cooling rate can becorrelated, because rapid cooling allows a large amountof gas bubbles to “freeze in” the melt (Lucey et al.2006). Crystalline IM breccias contain various amountsof clasts. As the amount of the clastic material

increases, the matrix becomes more glassy (Lucey et al.2006).

To estimate the crater size and the position of AaU012 in the IM body is difficult if not impossible. Themicrocrystalline matrix, the abundant vesicles and lithicclasts can suggest two possibilities (1) if the impactcrater was large, then AaU 012 most likely originatesfrom the outer zone of the impact melt; (2) if the IMbody was relatively small, an origin from a more centralpart is also possible. In both cases, the melt cooledrelatively rapidly to preserve the vesicles, but slowenough that the matrix could crystallize.

Table 3 shows the bulk composition of AaU 012compared to other, compositionally similar feldspathiclunar meteorites, to the mean composition of the lunarsurface and feldspathic upper crust (FUpCr), and to theaverage composition of the Apollo ferroan anorthositic-suite (FAN) rocks. Values of the lunar surface (upperfew meters) and feldspathic upper crust (upper fewkilometers) are based on some feldspathic lunarmeteorites (Korotev et al. 2003).

With 31.0 wt% Al2O3 and 3.85 wt% FeO, AaU 012fits well among the feldspathic lunar meteorites (Al2O3

>25 wt%, FeO <7 wt%; Korotev et al. 2003, 2009;Korotev 2005) (Fig. 6), and the values are within theranges given for the Apollo FAN-suite rocks (Al2O3

26.2–35.6 wt%, FeO 0.2–6.6 wt%; Wieczorek et al.[2006] and references therein). Normative plagioclasecontent (~88.5 vol%) of the meteorite is higher, butclose to the mean value of the feldspathic upper crust(~83 vol%; Korotev et al. 2003). Bulk Mg# variesbetween 57 and 77 among feldspathic lunar meteorites

Table 5. Chemical composition of the impact-melt (IM) clast of AaU 012 and other lunar rock types.

Oxide(wt%)

AaU012

IMclast

Marebasalts Mg-suite FAN-suite

Alkali-suite

KREEPbasaltsAnorthosite QMD/MG Granite Norite Gabbronorite

SiO2 54.8 37.8–49.2 37.5–52.0 41.9–45.4 43.4–53.0 44.9–56.9 65.0–74.2 46.9–49.9 49.4–51.2 48.0–52.8TiO2 1.15 0.36–13.0 0.03–1.03 0.01–0.40 0.04–1.99 1.11–2.60 0.26–4.60 0.36–2.30 0.36–4.60 1.03–2.23Al2O3 7.76 5.30–13.8 1.30–28.7 26.2–35.6 26.8–35.9 6.40–12.6 8.80–18.5 10.6–24.4 7.19–28.3 13.3–16.4Cr2O3 b.d. 0.16–0.96 0.02–0.38 0.00–0.10 0.00–0.05 0.05–0.37 0.00–0.25 0.08–0.24 0.09–0.39 0.29–0.48FeO 13.6 15.5–22.7 2.25–17.1 0.15–6.56 0.26–4.25 10.8–26.2 2.32–14.2 4.30–12.4 6.90–17.2 9.20–15.5MnO b.d. 0.20–2.20 0.03–0.20 0.00–0.09 0.01–0.06 0.18–0.28 0.02–0.17 0.12–0.14 0.10–0.26 0.14–0.23MgO 11.0 5.67–20.0 6.90–45.4 0.14–8.30 0.15–8.30 2.68–8.64 0.07–10.7 4.40–15.9 5.10–12.4 6.80–10.5CaO 10.2 6.31–12.7 1.10–15.9 15.2–20.4 12.3–19.6 8.30–12.9 0.50–9.70 8.40–16.4 9.10–15.7 7.10–11.1Na2O 0.26 0.06–0.65 0.02–0.91 0.18–0.57 0.47–2.14 0.46–1.41 0.19–1.90 0.78–0.91 0.29–1.21 0.29–0.89K2O 0.36 0.01–0.80 0.00–0.23 0.01–0.11 0.07–1.05 0.60–2.17 0.37–8.60 0.43–0.98 0.11–1.90 0.25–0.67P2O5 b.d. n.d. 0.03–0.11 0.01–0.05 n.d. 0.29–4.98 n.d. n.d. n.d. 0.46–0.70Sum 99.1 – – – – – – – – –BulkMg#

59 33–62 68–90 43–74 36–87 26–54 5–62 57–73 48–73 47–65

Composition data of different lunar rock types are from Wieczorek et al. (2006) and references therein. QMD/MG = quartz-monzodiorite and

monzogabbro, b.d. = below detection, n.d. = no data.

1840 M. M�esz�aros et al.

(Lucey et al. 2006), and with Mg# of 63, AaU 012 fitswell in this range. AaU 012 has a bulk FeO/MnO ratioof 76, which is higher than the values of the referenceslisted in Table 3, except Shis�r 166, which also has ahigh FeO/MnO ratio of 83.

Th and U concentrations of AaU 012 (0.39 and0.13 ppm, respectively) are comparable with the meanof the feldspathic lunar breccias, and are close to theaverage values of the lunar surface and the feldspathicupper crust. The low concentrations of theseincompatible elements exclude the presence of asignificant KREEP component. Based on the Irconcentration of 5.1 ppb in AaU 012, we estimated acontribution of ~0.8 wt% chondritic material in themeteorite (25 ppb Ir = ~4 wt% chondritic material;Wasson et al. 1975; Korotev 2005). The amount ofextralunar material in feldspathic breccias ranges from0.2 wt% (Dho 489) to 2.7 wt% (PCA 02007). AaU 012contains less chondritic component compared to theaverage of feldspathic lunar meteorites (1.2 wt%), andplots between the mean values of the lunar surface andthe feldspathic upper crust (Fig. 7). Figure 7 also showsthat different types of lunar breccias contain variableamounts of meteoritic material without any correlationbetween the different groups of feldspathic breccias(e.g., regolith breccias, IM breccias, fragmental breccias,etc.).

Feldspathic lunar meteorites have lowconcentrations of incompatible elements, especially rareearth elements (Korotev 2005). Eu2+ substitutes for Cain plagioclase, and hence all feldspathic lunar meteorites

have strong positive Eu anomalies (Fig. 8). AaU 012has a mean Eu concentration of 0.744 ppm, which isidentical to the Eu concentration of Shis�r 166. Sc-Smplots are usually used to classify and show pairings oflunar meteorites (e.g., Korotev et al. 2012; Korotev andIrving 2013, 2014, 2015). Sc and Sm data of AaU 012were previously reported by Korotev and Irving (2015).We depicted AaU 012 in the Sc-Sm space along withmeteorites selected for comparison in this work (Fig. 9).The plot shows that AaU 012 is well in the field of thefeldspathic lunar meteorites, close to Shisr 166, NWA482 and Dho 026, and other IM breccias. Bulk oxygenisotopic composition of d17O +2.86&, d18O +5.46&,D17O +0.02& of AaU 012 is also typical for lunarmeteorites (d17O +2.91&, d18O +5.59&, D17O +0.01&;Clayton and Mayeda 1996).

In feldspathic lunar meteorites the normativeanorthite content of plagioclase varies in a narrowrange, typically between 95 and 97 mol% (Korotevet al. 2003). With an average An content of 96.9 mol%of plagioclase, AaU 012 clearly belongs to the group ofthe highly feldspathic lunar breccias. Lunar olivineshave an average FeO/MnO ratio of 89, with a largevariation of 60–120 (Nazarov et al. 2009). AaU 012olivines have the same mean FeO/MnO ratio of 89,with a variation of 70–121 (Table 4). The mean FeO/MnO ratio of lunar low-Ca pyroxene (Wo <5%) is 54,with a variation between 30 and 80, while pyroxeneswith Wo >5% (pigeonite and augite) have a muchlarger variation, typically 20–100, depending stronglyfrom the Mg# and Ca-content of the minerals (Nazarov

2

3

4

5

6

7

25 27 29 31 33 35

FeO

t(w

t%)

Al2O3 (wt%)

AaU 012Shişr 166NWA 482Dho 026IMBsOther feldspathic lunar meteoritesLunar surfaceFUpCrApollo FAN Suite

Fig. 6. The plot depicts the feldspathic lunar meteorites in theAl2O3-FeO space with the mean Al2O3/FeO ratios of the lunarsurface, the feldspathic upper crust, and the Apollo FAN suiterocks. AaU 012 is a typical feldspathic breccia, lying close tothe mean values of the Apollo FAN-suite rocks. For references,see Table 1, and for the average Al2O3 and FeO concentrationsof meteorites and Apollo samples plotted here, see Table 3.IMBs = impact-melt breccias, FUpCr = feldspathic upper crustof the Moon.

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300 350 400

Ir (p

pb)

Ni (ppm)

RBIMB/GBIMBFBFB/RBAaU 012Lunar surfaceFUpCr

Fig. 7. Ni-Ir plot showing a linear trend in brecciatedfeldspathic lunar meteorites. AaU 012 plots between the meanvalues of the feldspathic upper crust and the lunar surface. Forreferences, see Table 1, and for the mean Ni and Irconcentrations plotted here see Table 3. RB = regolith breccia,IMB/GB = impact-melt breccia/granulitic breccia, IMB =impact-melt breccia, FB = fragmental breccia, FB/RB =fragmental breccia/regolith breccia, FUpCr = feldspathic uppercrust of the Moon.

Petrology and geochemistry of Abar al’ Uj 012 1841

et al. 2009). AaU 012 low-Ca pyroxenes and pigeoniteshave FeO/MnO of 54, and augites have FeO/MnO of46 (Table 4).

Clast of a Mare Basalt or Impact-Melt of an Alkali-Suite

Precursor?

Clasts of mare basalts were previously reportedfrom a number of feldspathic lunar breccias (e.g.,Robinson et al. [2012] and references therein). Based on

textural and mineralogical similarities with somepigeonite basalts of the Apollo 12 and 15 collections,the pyroxene- and silica-rich clast in AaU 012 was alsodescribed as mare basalt previously (M�esz�aros et al.2014). Having the bulk composition data (Table 5),conducted by EPMA X-ray mapping and corrected forunequal host-phase density, we can exclude a marebasalt origin for this clast, as it has lower FeO (13.6 wt%)and higher SiO2 (54.8 wt%) concentration than anyother mare basalts (Fig. 10). The lower FeO contentalso results in a higher Mg# of 59 than the average ofmare basalts (46). Although some Apollo olivine,ilmenite, and very high-K basalts have Mg# comparablewith that of the clast, these type of mare basalts havehigher MgO, TiO2, or K2O concentrations.

The clast was most likely formed from a nonmareigneous precursor. A relationship with the Mg-suiterocks can be also excluded, as those type of lunar rockshave much higher Mg# (>68). Another argumentagainst a Mg-suite origin is that those rocks also havehigher Al2O3 concentration (usually >13.2 wt%), exceptdunites, which have Al2O3 <1.5 wt%. The clast hashigher SiO2 and FeO and much lower Al2O3 contentthan the FAN rocks (Table 5).

The composition of the clast is most comparablewith some rare Apollo samples from the alkali-suite(Figs. 11 and 12), rocks that are enriched in SiO2 as aconsequence of the presence of free silica in the form ofglass, cristobalite, or tridymite (Korotev 2005). Anothercharacteristic feature of these rocks is the presence of arelatively sodic plagioclase typically with An82 � 8

(Lucey et al. 2006). With An88.7, the clast of AaU 012fits in this range. In Table 5 we also list the bulkcomposition of different types of alkali-suite rocks.Lunar granites have much higher SiO2 contents

2

3

4

5

6

7

8

9

10

11

12

La Ce Nd Sm Eu Tb Dy Ho Yb Lu

otdezila

mronsnoitartnecnocEER

vola

�le-

free

CI c

hond

rite

Rare earth elements in order of increasing atomic number

FUpCrLunar surfaceFeldspathic lunar meteoritesIMBsDho 026 (457-468)NWA 482Shişr 166AaU 012

Fig. 8. CI-normalized REE-plot for AaU 012 compared toother feldspathic lunar meteorites, and to the average of thelunar surface and feldspathic upper crust. Pr, Gd, Y, Er, andTm are not plotted, because no data were available in theliterature for these elements. For references, see Table 1, andfor the mean REE concentrations plotted here, see Table 3.FUpCr—feldspathic upper crust of the Moon, IMBs—impact-melt breccias.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

4 6 8 10 12 14

Sm (p

pm)

Sc (ppm)

AaU 012Shişr 166Dho 026NWA 482IMBsOther feldspathic lunar meteoritesLunar surface and FUpCr

Fig. 9. Sc-Sm plot of AaU 012 and comparison to data ofother feldspathic lunar meteorites with similar composition.For references, see Table 1, and for the mean Sc and Smconcentrations plotted here, see Table 3.

12

14

16

18

20

22

24

35 40 45 50 55 60

FeO

(wt%

)

SiO2 (wt%)

Mare basaltsAaU 012 IM clast

Fig. 10. The impact-melt (IM) clast of AaU 012 compared tomare basalts in the SiO2-FeO space. This clast was previouslydescribed as a mare basalt, but based on its chemicalcomposition, for example, lower FeO and higher SiO2

concentrations, a mare basalt origin can be ruled out. Data ofmare basalts are from Wieczorek et al. (2006).

1842 M. M�esz�aros et al.

(Fig. 12) and also a different mineralogy with relativelyhigh amounts of K-feldspar and silica. Accordingto the low Al2O3 (7.76 wt%) and relatively high FeO(13.6 wt%) concentration, the clast cannot be an alkalianorthosite as well (Fig. 12), because these rocks havesignificantly higher Al2O3 concentration (>26.8 wt%)and lower amounts of FeO (<4.3 wt%). The low modalplagioclase content of 22.5 vol% makes it also unlikelyfor the clast being anorthosite, as these rocks havemodal plagioclase usually >60 vol% (Wieczorek et al.[2006] and references therein). Quartz-monzodioritesand monzogabbros usually have lower Mg# (<41) thanthe clast, and also contain significant proportions ofsilica-phase and K-feldspar, similarly to granites(Wieczorek et al. 2006).

We also included data of KREEP basalts inTable 5, as some of the alkali-suite rocks are thought tobe related to KREEP (e.g., Neal et al. 1989; Jolliff1991; Marvin et al. 1991; Snyder et al. 1992, 1994;Jolliff et al. 1993). These rocks have higher Al2O3

concentration (>13.3 wt%), but some have comparableamounts of FeO, SiO2, Na2O, and K2O with the clast.Moreover, the Mg# of the clast is in the range ofKREEP basalts (47–65). Although major and minorelements are in good agreement, without incompatibletrace element analysis of the clast, a KREEP origincannot be confirmed.

Bulk composition of the clast corresponds to anormative mineralogy of 24.7 vol% plagioclase, 2.6 vol%orthoclase, 25.0 vol% high-Ca pyroxene (augite),34.2 vol% pigeonite, 12.0 vol% silica (cristobalite), and1.5 vol% ilmenite. The calculated normative mineralogy(and also modal mineralogy obtained by X-raymapping) is consistent with our microscopic

observations that olivine is absent from the clast. Sincenormative mineralogy reflects only the hypotheticalmineral proportions in a rock, it is not useful to makerelevant comparison between rocks, as modal mineralabundances can deviate from the normative ones.

Although the clast is relatively small and thereforemight be not representative, the above mentionedobservations, like higher SiO2 and lower FeOconcentrations, and also higher Mg# compared to marebasalts, the higher SiO2 and FeO, and lower Al2O3

compared to FAN-suite rocks, the lower Mg# and alsolower Al2O3 concentration compared to Mg-suite rocks,all suggest that the clast most likely originates from thealkali-suite. Due to the lower Al2O3 content comparedto alkali anorthosites and KREEP basalts, the highMg# compared to the QMD/MG rocks, the lower SiO2

concentration compared to lunar granites, the presenceof relatively sodic plagioclase, and the high proportionof modal pyroxenes (68.6 vol%), mainly clinopyroxenes,and finally, the presence of large vesicles, the clast couldbe an IM clast most likely with an alkali norite orgabbronorite precursor. Although the Al2O3 and Na2Oconcentrations are somewhat lower than values reportedin the literature for these types of rocks, the lowamount of plagioclase in the clast can explain thisdifference.

Most of these rare alkali-suite norites (2.8 g ofApollo rocks) and gabbronorites (0.2 g of Apollo rocks)were collected during the Apollo 14 mission (Wieczoreket al. 2006), which landed north of the Fra Mauro

20

30

40

50

60

70

80

90

40 45 50 55 60 65 70

Mg#

SiO2 (wt%)

FAN-suite

Mg-suite

Alkali-suite + KREEP-basalts

AaU 012 IM clast

Fig. 11. SiO2-Mg# plot of pristine nonmare igneous rocks.The impact-melt (IM) clast of AaU 012 plots among thealkali-suite rocks, as it has lower Mg# than the magnesium-suite rocks, and higher SiO2 content than the ferroananorthositic-suite rocks. Data of pristine nonmare lunar rocksare from Wieczorek et al. (2006).

40

50

60

70

80

90

100

5 10 15 20 25 30 35

SiO

2(w

t%)

Al2O3 (wt%)

Alkali anorthosites Alkali norites Alkali gabbronoritesMonzogabbros Quartz-monzodiorites GranitesKREEP-basalts AaU 012 IM clast

Fig. 12. Alkali-suite rocks in the Al2O3-SiO2 space aresubdivided into three different groups (1) rocks with >60 wt%SiO2 and <25 wt% Al2O3 are lunar granites, (2) those with<60 wt% SiO2 and >25 wt% Al2O3 are alkali anorthosites,and (3) rocks that have <60 wt% SiO2 and <25 wt% Al2O3

are rocks like alkali norites and gabbronorites, monzodioritesand quartz-monzogabbros, KREEP basalts. The impact-melt(IM) clast found in AaU 012 plots in the latter group. Dashedlines mark the boundary of the subgroups of alkali-suite rocksdefined by SiO2 (60 wt%) and Al2O3 (25 wt%). Data foralkali-suite rocks are from Wieczorek et al. (2006).

Petrology and geochemistry of Abar al’ Uj 012 1843

crater, about 550 km south of the large basin of MareImbrium (Hiesinger and Head 2006).

Terrestrial Age and Weathering

A correlation between weathering grade andterrestrial residence times of chondritic meteorites(mainly ordinary chondrites) from hot deserts wasshown by many authors (e.g., Jull et al. 1990; Blandet al. 1998; Al-Kathiri et al. 2005). Weathering scales,to define the degree of terrestrial alteration, are basedmainly on the weathering rate of FeNi metal and Fe-sulfides (e.g., Wlotzka 1993), two minerals that are mostsusceptible to weathering in terrestrial environments.Lunar meteorites contain no or only trace amounts ofthese minerals, consequently they can survive muchlonger times in terrestrial environments than chondrites(and iron meteorites), therefore the weathering scalescannot be applied for lunaites, and a correlationbetween the terrestrial age and the weathering gradecannot be defined so well as for ordinary chondrites.Terrestrial ages of lunar meteorites range between <10to ~500 ka. For more details, see table 2 in Jull (2006).The 14C age of AaU 012 was determined to be33.4 � 5.2 kyr.

We compared Sr and Ba concentrations, as possibleindicators of terrestrial weathering, of AaU 012 to

other feldspathic lunar meteorites, of which Sr and Badata were available. Data are listed in Table 6 andplotted on Fig. 13. In general, Sr and Ba concentrationsare higher and more variable in hot desert lunarmeteorites than in finds collected on Antarctica.Average Sr and Ba concentrations in hot desertmeteorites are 713 ppm and 251 ppm, respectively,while in Antarctic lunar breccias are only 150 ppm and32 ppm, respectively. Among meteorites from differenthot desert regions, Omani meteorites are the mostenriched in Sr compared to lunar meteorites discoveredin other hot desert areas. All feldspathic lunarmeteorites having Sr >1000 ppm were found in Oman.AaU 012 is more enriched in Ba than in Sr, it has a Sr/Ba ratio of 0.7. Only a few other meteorites have a Sr/Ba ratio less than 1.0, for instance, DaG 400 (0.4) andDho 468 (0.9).

Table 7 shows the U/Th and Ba/La ratios of AaU012 and other feldspathic meteorites from hot and colddesert regions, along with some reference materials.These ratios were proposed by Warren et al. (2005) towork as good weathering proxies in lunaites. Antarcticmeteorites differ significantly in their terrestrial mineralassemblage from hot desert finds, because they lacksuch minerals like barite, gypsum, and carbonates (Leeand Bland 2004), the main carriers of U and Ba in hotdesert environments. Because of this difference, we can

Table 6. Sr and Ba concentrations of AaU 012, and hot and cold desert feldspathic lunar meteorites.

Hot desert meteorites Antarctic meteorites

Meteorite Sr Ba Sr/Ba Meteorite Sr Ba Sr/Ba Meteorite Sr Ba Sr/Ba Meteorite Sr Ba Sr/Ba

AaU 012 271 410 0.7 Dho 1436 1407 269 5.2 Dho 466 310 220 1.4 QUE

93069 A

140 42 3.3

DaG 262 A 176 240 0.7 Dho 1443 1319 130 10.1 Dho 467 300 165 1.8 QUE93069 B

154 42 3.5

DaG 262 B 209 117 1.8 Dho 1627 1363 291 4.7 Dho 468 1260 1340 0.9 QUE

94269

147 35 4.2

DaG 400 300 820 0.4 Dho 025 1410 110 12.8 Dho 489 700 238 2.9 ALHA81005

136 29 4.7

Dho 081 178 13 13.7 Dho 026 497 391 1.3 JaH 348 330 48 6.9 MAC88104/5

152 32 4.8

Dho 280 279 42 6.6 Dho 457 209 81 2.6 Kalahari

008

200 46 4.3 Y-791197 150 26 5.8

Dho 910 169 13 13.0 Dho 458 254 168 1.5 NWA 482 127 30 4.2 Y-82192/3 161 25 6.4Dho 301 3738 597 6.3 Dho 459 540 430 1.3 NWA

4936/5406

198 167 1.2 Y-86032 168 26 6.5

Dho 304 3904 1438 2.7 Dho 461 350 109 3.2 Shis�r 160 248 68 3.6 PCA02007

147 34 4.3

Dho 302 413 98 4.2 Dho 462 206 79 2.6 Shis�r 161 1106 273 4.1Dho 490 432 90 4.8 Dho 463 890 350 2.5 Shis�r 162 961 47 20.4Dho 1084 775 39 19.9 Dho 464 630 121 5.2 Shis�r 166 210 83 2.5

Dho 1428 543 48 11.3 Dho 465 670 320 2.1

Sr and Ba concentrations are in ppm. For references see Tables 1 and 3.

1844 M. M�esz�aros et al.

assume that Antarctic lunar meteorites preserved thepristine concentrations of these elements.

Mean U/Th and Ba/La ratios of Antarctic lunarmeteorites (U/Th = 0.27 � 0.02, Ba/La = 14.8 � 1.3)are equal or close to the values of unaltered lunarmeteorites (U/Th = 0.28, Ba/La = 12.0; Warren et al.2005), the lunar regolith (U/Th = 0.28; Lucey et al.2006), and the lunar surface (U/Th = 0.269 � 0.007;Yamashita et al. 2010). In Table 7, we have listed themean U/Th and Ba/La ratios of hot desert lunarbreccias as well, which were reported until 2012 and forwhich U, Th, Ba, and La data were available (Table 3).These ratios for hot desert lunar meteorites are muchhigher compared to meteorites from Antarctica, or thelunar surface and the feldspathic upper crust.

Although Dho 025 is the oldest known feldspathiclunar meteorite, with a terrestrial age of 500–600 ka(Nishiizumi and Caffee 2001), its U/Th ratio is lower(U/Th = 0.41) than the average of the feldspathic lunarmeteorites discovered in hot deserts (U/Th = 0.53 � 0.08). The Ba/La ratios of Dho 025 is alsonot conspiciously high (Ba/La = 36.7) compared to theaverage of hot desert lunar breccias (Ba/La = 101.5 � 20.8), and is much lower than the Ba/Laratio of AaU 012 (Ba/La = 162.7), which has a youngerterrestrial age than Dho 025. These data suggest thatweathering proxies like U/Th and Ba/La ratios have aweak correlation with the duration of time a meteoritewas exposed to terrestrial weathering, or can only beused for feldspathic lunar meteorites discovered in thesame find location with the same geological setting andclimate. If this is the case, AaU 012 cannot becompared with other feldspathic breccias in respect of

terrestrial weathering, as it is the only lunar meteoritefound in Saudi Arabia so far.

Comparison with Shis�r 166

Compositionally AaU 012 and Shis�r 166 are verysimilar (see Table 3), but only a source-crater or launchpairing is possible, because the two meteorites werefound ~700 km apart. Two or more meteorites can besource or launch paired if their texture and/orcomposition are very similar, and their ejection times(the cosmic-ray exposure age plus the terrestrial age) arethe same. Unfortunately, Shis�r 166 is poorly described.A short description of the meteorite was published inWeisberg et al. (2010), and detailed bulk chemical datacan be found in Korotev (2012).

Both meteorites are vesicular and clast-rich IMbreccias. The main textural difference between the twois that Shis�r 166 has a matrix of recrystallized glass,consisting of submicroscopic crystallites and containingshock-melt veins, clearly different from AaU 012, whichhas a microcrystalline matrix and no shock-melt veinswere identified in it. Textural differences do not rule outa source or launch pairing, and can only indicate thatthe two meteorites were formed in different zones of theIM, but originate from the same impact crater and werelaunched by the same impact event.

The two meteorites have a very similar bulkcomposition. Bulk Mg# for both meteorites is 63. TheirFeO/MnO ratio is somewhat different, 76 for AaU 012and 83 for Shis�r 166, but both are higher than theaverage of feldspathic lunar meteorites (65). Shis�r 166has a mean plagioclase composition of An96.7Or0.2,which is very close to AaU 012’s An96.9Or0.1.

To test for a possible launch pairing of AaU 012and Shis�r 166, noble gas measurements and

10

100

1000

10000

10 100 1000 10000

Ba (p

pm)

Sr (ppm)

AaU 012

Oman

North Africa

Antarc�ca

Kalahari 008

Fig. 13. Sr-Ba plot of feldspathic lunar meteorites fromdifferent collection regions. Hot desert meteorites containmore Ba and Sr than cold desert meteorites, and Omanimeteorites are more enriched in Sr than hot desert meteoritesfrom other find locations. AaU 012 has one of the highest Baconcentration for a given Sr content among hot desertfeldspathic lunar meteorites. For references, see Table 1 andfor Sr and Ba values plotted here, see Table 6.

Table 7. U/Th and Ba/La ratios of AaU 012,feldspathic lunar meteorites, and some referencematerials.

U/Th Ba/La

Antarctic meteorites 0.27 � 0.02 14.8 � 1.3Hot desert meteorites 0.53 � 0.08 101.5 � 20.8Unaltered lunar meteorites 0.28 12.0

AaU 012 0.33 162.7Shis�r 166 0.33 32.3Dho 025 0.41 36.7

NWA 482 0.23 19.4Lunar surface 0.269 � 0.007 –Lunar regolith 0.28 –

Data for Antarctic and hot desert meteorites, Shisr 166, Dho 025,

and NWA 482 are from references listed in Table 1. Data of

unaltered lunar meteorites are from Warren et al. (2005), lunar

surface from Yamashita et al. (2010), and lunar regolith from Lucey

et al. (2006).

Petrology and geochemistry of Abar al’ Uj 012 1845

measurement regarding the terrestrial age of Shis�r 166are planned.

CONCLUSIONS

Based on the presented analytical data, we draw thefollowing conclusions:1. The oxygen isotopic composition (d17O +2.86&,

d18O +5.46&, D17O +0.02&) along with thehighly anorthitic nature (i.e., the 88.5 vol%normative plagioclase and 96.9 mol% anorthitecontent of plagioclase) provide the strongestevidence of a lunar origin for AaU 012.

2. According to the textural properties (i.e., clasticnature, microcrystalline matrix, vesicles, lack ofregolith components), AaU 012 can be classified asa clast-rich, crystalline IM breccia. The largenumber of vesicles and the microcrystalline matriximply a cooling fast enough to “freeze in” the gasbubbles, but slow enough to have a crystallinematrix, that is, the source location of AaU 012could be in the outer zones of a large IM body, orit could have crystallized even in the center of asmall IM body, otherwise the matrix would becoarser grained, and probably vesicles also couldhave enough time to gas out from the melt in amore central position of a large IM body, or thematrix would be glassy due to a faster cooling inthe outer parts of a smaller IM body.

3. AaU 012 has a bulk composition (31.0 wt% Al2O3,3.85 wt% FeO) typical of feldspathic lunar highlandmeteorites. Bulk Mg# of 63 is in the range offeldspathic lunar meteorites (57–77), and it iscomparable with mean of the FAN-suite rocks (60),which are the most typical rocks on the lunar farsidehighlands. Bulk FeO/MnO of 76 is higher than themean of feldspathic lunar breccias (65).

4. The low Th and U concentrations (0.39 and0.13 ppm, respectively) show the absence of asignificant KREEP component, which indicates thatthe source location was probably not in the vicinityof the Procellarum KREEP Terraine or the SouthPole Aitken-basin.

5. The low concentration of chondritic component(� 0.8 wt%) in AaU 012 implies an origin in somedepth below the surface, as it is lower than valuesmeasured for the lunar surface (1.2 wt%).

6. The clinopyroxene- and cristobalite-rich clast ofAaU 012 is compositionally similar to some alkali-suite samples of the Apollo collection. According toits geochemistry, modal mineral composition andvesicular nature, we conclude that the clast could bean IM rock with precursor material related to thealkali norites and gabbronorites. A derivation of the

IM clast from the Procellarum KREEP terrainappears unlikely. The bulk geochemistry of AaU012 shows very low concentrations of incompatibleelements (including Th, U), demonstrating theabsence of a significant KREEP component in thebulk rock. A KREEPy nature of the IM clastwould therefore mean that it represents anexceedingly rare component within AaU 012, whichis very unlikely, though not impossible.

7. The very similar chemical composition of AaU 012and Shis�r 166, another feldspathic IM breccia fromthe Moon, indicates that the two meteorites couldbe source or launch paired.Summarizing all the observations and conclusions,

we propose that AaU 012 is a typical lunar crystallineIM breccia. Chemical composition implies a KREEP-free source and ferroan anorthositic affinity for thewhole-rock, indicating a lunar farside highland originfor AaU 012. A possible launch pairing with thelunar IM breccia Shis�r 166 needs to be checked, andfor this purpose future noble gas measurements areplanned.

Acknowledgments—We thank Drs. Zohair Nawab,Abdullah al Attas, and Saleh al Ghamdi, SaudiGeological Survey, for their kind support of thefieldwork. Moreover, we thank Axel Wittmann for theEPMA-FB measurements, and reviewers of the paper,Dr. Paul Warren, Yangting Lin, and Alex Ruzicka fortheir constructive comments. This study was supportedby the Swiss National Science Foundation, grants200020-137924 and 200021-143966.

Editorial Handling—Dr. Alex Ruzicka

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