Advances in Polar Science  2014, Vol. 25 Issue (1): 17-25

  The article information

XIE Lanfang, CHEN Hongyi, MIAO Bingkui, XIA Zhipeng, YAO Jie
Petrography and mineralogy of new lunar meteorite MIL090036
Advances in Polar Science, 2014, 25(1): 17-25
10.13679/j.advps.2014.1.00017

Article history

Received: 15 December 2013
Accepted: 4 March 2014
Petrography and mineralogy of new lunar meteorite MIL090036
XIE Lanfang1, 2, CHEN Hongyi1, 2, MIAO Bingkui1, 2 , XIA Zhipeng1, 2, YAO Jie1, 2    
1 Guangxi Scientific Experiment Center of Mining, Metallurgy and Environment, Guilin University of Technology, Guilin 541004, China;
2 Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin 541004, China
Received 15 December 2013; accepted 4 March 2014
Corresponding author: MIAO Bingkui (email: miaobk@glut.edu.cn)
Abstract: MIL090036 is a previously unknown meteorite (a feldspathic lunar breccia) that was discovered in Antarctica. The detailed petrography and mineralogy of this meteorite forms the subject of this paper. It has a typical clastic texture that consists of various types of rock debris (e.g. anorthosite, gabbroic anorthosite, gabbro, regolith breccia, troctolite, microporphyritic crystalline impact melt and compound clasts), mineral crystal fragments (e.g. pyroxenes, plagioclase, olivine and ilmenite) and feldspathic glass clasts. The fine-grained recrystallized minerals and mineral clasts are cemented together in a glassy groundmass. The anorthite content of plagioclase in the gabbro (An81-83) and anorthosite (An88-93) both have relatively low calcium content compared to those from other breccias (An90-98). The pyroxene composition (Fs12-35 Wo3-44 En22-79) in the rock debris, crystal mineral clasts and anorthositic glass clasts are relatively iron-deficient compared to those from gabbro debris with melt glass (Fs37-65 Wo10- 29 En21-49) and groundmass (Fs18-69 Wo3-45 En14-50). In contrast, the pyroxene grains in the gabbroic anorthosite display a narrow compositional range (Fs24-27 Wo7-14 En59-69). Olivine grains in mineral fragments and the groundmass have a wider compositional range (Fo57-79) than those in the rock debris (Fo67-77). The Fe/Mn ratio in olivine is in the range of 47 to 83 (average 76) and 76 to 112 (average 73) in pyroxenes, and hence classify within the lunar field. The characteristics of texture, mineral assemblage and compositions suggest that MIL090036 possibly originated from a region beyond that of the Apollo and Luna samples. Further study of MIL090036 is therefore likely to lead to a better understanding of the geological processes on the Moon and the chemical composition of the lunar crust.
Keywords: Lunar meteorite    MIL090036    Lunar breccias    Petrography    Mineralogy    

1 Introduction There are currently three main ways to gather compositional information of the lunar crust: Remote sensing,lunar sampling and collection of lunar meteorites[1, 2]. While remote sensing providesa “bird’s eye view” of the EPMAUser Moon,the precisionof the data is limited and cannot be used to research microscopic characteristics of the lunar crust,such as microstructure and micromorphology. Apollo and Luna samplingprograms collectedabundant lunar samples from different sites on the surface of the Moon over an area of only 5.4%-8.8% of the total surface[3]. Such in-situ sampling is costly and has not yet retrieved specimens from the far side of the Moon.

An importantsource of material that is representative of the lunar crust is lunar meteorites that were ejected from the surface of the Moon and captured by the gravitational field of the Earth.Compared with remote sensing and direct sampling,the collection and sampling of lunar meteorites found on Earth provideus a cost-effectiveway to study lunar material,which is likely more representative of the composition of the Moon’s crust[3, 4].

MIL090036 is a newly discovered lunar meteorite that was found in the Antarctic Miller Range Ice Field by the 2009-2010 ANSMET Program (Antarctic Search for Meteorites). Based on previous studies that included optical microscopy,resonance neutron activation analysis,electron microprobe analysis and cosmogenic nuclide studies,MIL090036 is a clast-rich,feldspathic breccia with a glassy- groundmass,and is mineralogically and petrologically similar to samples from the Apollo 16 sampling site[5, 6]. Cosmogenic nuclide studies show that the meteoritehas a 0.1-0.2 Ma terrestrial age[7]. We present a detailed petrographic and mineralogical study of MIL090036 which aims to better understand the composition of the Moon’s crust.

2 Sample and analytical methods MIL090036 which weighs 245 g,has a smooth surface with no fusion crust evident. Its interior structure is clearly brecciated with gray clasts dispersed in a dark groundmass[8]. The studied 30-μm-thick thin-section (MIL090036,26) was provided by NASA (Figure 1) and was petrographically assessed using optical microscopy. Mineral compositions were analyzed using a JEOL JXA-8230electron microprobe at the Guangxi Key Laboratory of Hidden Metallic Ore DepositsExploration in the Guilin University of Technology. Theaccelerating voltages during the analysis of metal,silicate and oxide minerals were 20 kV,15 kV and 15 kV,respectively. The beam current was 20 nA with a beam spot size of 5 μm,except for analysis of some very small mineral grains analyzed with a beam spot size of 1 μm. Bulk elemental composition was subsequently quantified using a 200 μm defocused electron beam,with data then normalized to 100%. Calibration of the samples was done against standards: silicates and metal minerals were calibrated against natural silicate and metal minerals respectively,and troilite was calibrated against oxide and sulfide. The measuring time of all the element-characteristic peaks and backgrounds were 10 s and 5 s,respectively with all raw analytical data corrected by the traditional ZAF method.

Figure 1 Transmitted-light photomicrograph of thin-section
3 Petrography MIL090036,26 has a feldspathic lunar breccia texture (Figure s 1-2) mainly composed of various types of lithic clasts (anorthosite,gabbroic anorthosite,gabbro,regolith breccia,troctolite,microporphyritic crystalline impact melt and compound clasts,Figure 3),mineral clasts (pyroxenes,plagioclase,olivine,with minor ilmenite) and glass clasts which are mainly plagioclase. The matrix is composed of fine-grained plagioclase,pyroxenes,and minor olivine,ilmenite and glass. The content of plagioclase and pyroxene in the matrix reaches 60 vol.%.

Figure 2 Backscattered electron (BSE) image of thin-section MIL090036, 26. Clasts discussed in the text are shown in white squares: Anorthosite clasts (a); Gabbroic anorthosite clasts (b); Troctolite clasts (c);Homeocrystalline gabbor clasts (d); Gabbro clasts with glass (e); Polymictclasts (f); Microporphyritic crystalline impact melt breccia(g); Glass melt breccia (hi); Regolith clasts (j); Kamacite graint (k); Pyroxenecrystalloclastic (l).
Figure 3 Frequency distributionof breccias in MIL090036,26, which are greater than 0.1 mm in size.

The main brecciasof MIL090036,26 are composed of anorthosite clastsand gabbroic anorthosite clasts (0.1-0.5 mm in size). The lithic clasts are mainly composed of plagioclase and pyroxene,with olivine as the main constituent of the troctolite clasts. Plagioclases in both mineral and lithic clasts have the same characteristics-clear mineral boundaries and a strongly broken texture. Plagioclase in the glassy clasts has no observedbroken characteristic (Figure 4). The pyroxenes vary texturallybetween clasts: pyroxene in lithic and glass clasts are euhedral-subeuhedral-anhedral,while in mineralclasts they are subeuhedral-euhedral,and most show exsolution textures (Figure 4i). Ilmenite was discovered in nearly all types of clasts,as well as minor amounts of troiliteand ferronickel. Ilmenite,troilite and ferronickel are randomly distributed with a “star-like” appearance in the various clasts. Further characteristics of the clasts are summarized in Table 1.

Figure 4 Backscattered electron images of the typical clasts in MIL090036, 26 (ap = apatite; pl = plagioclase; ilm = ilmenite;pyx = pyroxene; ol = olivine).Anorthosite clasts (a); Gabbroic anorthosite clasts (b); Troctolite clasts (c); Homeocrystalline gabbro clasts (d); Gabbro clasts with glass (e); Polymict clasts (f); Microporphyritic crystalline impact melt breccias(g); Glass melt breccias (hi); Regolith clasts (j); Kamacite grain(k); Crystalloclastic pyroxene (l).
Table 1 The characteristics of various breccias in MIL090036, 26
Clast typeNumberFormStructureMineral mode content and composition
PlagioclasePyroxeneOlivineOther minerals
vol.% mineralvol.% mineralvol.% mineralvol.%
Anorthosite55angularmassive broken 97-99An88-95----trace ilmenite
Gabbroic
anorthosite
54subroundedgranoblastic77-82An95-9716-30Fs19-26Wo5-12En57-62 1-5Fa30-33ilmenite1-3
Troctolite4subangular granoblastic50-63An91-935-11Fs12-23Wo8-40En31-52 23-35Fa26-28ilmenite, troilitr
1-3
Gabbro5subangular
angular
equigranular
porphyritic
29An95-9838Fs25-28Wo7-13En63-68
Fs37-65Wo5-35En21-49
--FeNi, troilite,
ilmenite 1-3
glass 26, ilmenite 3,
apatite 3
Polymict clast 2angularheterogranular52-59An95-9844-48Fs22-24Wo5-35En45-79--ilmenite 1-2
Regolith clast21subroundedheterogranular 58-63 An93-9735-39Fs13-24Wo3-36En29-810-2Fa24-30ilmenite 1-3
Microporphyritic
crystalline impact
melt breccia
22angularmicrophyric30-37An91-9755-62Fs19-23Wo5-50En19-54 0-3Fa22-24ilmenite 1-3
Plagioclase3angularmonocrystal100An90-95 -----
Pyroxene18subangularmonocrystal --100Fs26-48Wo2-33En19-54---
Olivine2angularmonocrystal----100Fa21-31-
Ilmenite2subangular monocrystal ------ilmenite 98-100,
FeNi, troilite 0-2
Feldsparthic glass
clast
10subroundedporphyritic 25-65An93-990-14Fs12-27Wo5-46En29-720-3Fa28-30glass 25-65,
ilmenite, FeNi,
troilite 0-3

The matrix of MIL090036,26 is glassy and contains fine-grained recrystallized plagioclase,pyroxene,olivine,ilmenite,quartz and other opaque minerals (<30 μm in size),these minerals comprise approximately 60 vol.% of the matrix and have similar characteristics within mineral clasts,except for being of a smaller size.

4 Mineral chemistry 4.1 Plagioclase The plagioclases in MIL090036,26 are predominantly anorthitic (An81-98,avg. An92) with 91% of An exceeding 90 mol% in all tested grains. Plagioclase with An81-83 compositions are found in the homeocrystalline gabbro lithic clasts (Figure 4d) and plagioclase with average An90 are found in the anorthosite lithic clasts (Figure 4a). Plagioclase in other clasts have average compositions of An >90 (Figure 5). The K2O content of plagioclase is in the range of 0.11%- 0.32% and Na2O in the range of 0.11%-0.53%,except in the anorthosite lithic clast (1.10%) and gabbro lithic clast (2.14%).Representative analyses are presented in Table 2.

Figure 5 Anorthite (An) content in various clasts.
Table 2 Representative analyses(wt.%) of the main mineralsin various clastsin MIL090036, 26
a b c d e f g
pl ol pyx pl ol pl pyx pyx pyx pl pyx ilm pl pyx pl ol pyx
Note: ol=olivine, pl=plagioclase, pyx=pyroxene, FeNi=FeNi metal, ilm=ilmenite, Q=quartz , min=mineral, mix=matrix, bd=below detectable limit.
Na2O 1.10 0.02 0.10 0.41 0.04 1.01 0.36 2.52 0.03 2.14 0.12 bd 0.30 0.51 0.31 0.02 0.02
Al2O3 30.0 0.61 5.41 34.1 0.03 32.2 1.21 1.03 0.82 30.6 0.51 0.22 34.6 14.2 34.4 1.11 1.70
MgO 0.11 34.7 20.2 0.02 38.3 0.21 23.5 22.8 22.1 0.08 6.60 0.69 0.18 15.69 0.02 38.5 20.2
ZnO bd bd bd bd bd bd bd bd bd bd bd 0.11 bd bd bd bd bd
K2O 0.11 bd bd 0.09 bd 0.28 0.02 0.40 bd 0.31 0.12 bd bd 0.11 bd bd 0.02
FeO 0.19 29.9 14.2 0.20 25.8 0.22 7.8 17.3 22.4 0.39 34.9 46.9 0.40 11.5 0.31 20.7 21.1
MnO bd 0.59 0.28 0.21 0.31 bd bd 0.02 0.62 0.10 0.50 0.59 bd 0.21 bd 0.21 0.62
Cr2O3 bd bd 0.30 bd 0.14 bd 0.02 0.09 0.22 0.11 bd 0.21 bd 0.23 bd 0.02 0.54
PbO bd 0.12 bd 0.02 bd bd bd 0.02 0.04 bd bd 0.02 0.10 bd bd bd bd
V2O3 bd bd 0.02 0.13 bd bd bd 0.11 bd 0.10 0.04 0.10 bd 0.03 bd bd bd
CaO 20.6 0.02 6.50 20.7 0.21 19.7 20.5 6.4 2.22 20.2 7.20 0.41 20.9 10.8 20.5 0.70 5.33
NiO bd 0.10 bd bd bd bd bd bd bd bd bd bd 0.09 bd bd bd bd
TiO2 bd bd 0.71 0.12 0.11 0.10 0.02 0.10 0.54 0.10 0.70 52.0 bd 1.80 bd 0.12 0.41
BaO bd 0.11 bd bd bd bd 0.10 bd bd bd bd bd 0.02 bd 0.11 0.02 bd
P2O5 bd bd bd bd bd bd bd bd bd bd bd bd bd 0.22 bd bd bd
SiO2 46.3 33.4 52.8 43.8 33.3 46.5 47.9 50.4 52.4 45.3 49.7 0.62 44.7 44.7 42.9 38.9 50.7
Total 98.3 99.5 100.7 99.8 98.2 100.2 99.5 100.4 101.2 99.5 100.2 102.0 101.5 99.8 98.7 100.2 100.5
Fa/Fs/An 90 31 24 96 27 90 12 26 34 83 62 95 21 98 23 33
Fo/Wo/Ab 9 69 14 3 73 8 42 12 4 16 16 5 25 2 77 10
g h i j min mix
FeNi ol pl pyx FeNi ilm pl glass ol pl pyx ol pyx pl ol pyx Q
Na2O 0.10 0.02 0.36 0.02 0.10 bd 0.28 0.49 0.02 0.51 0.30 0.02 0.02 0.30 bd 2.11 bd
Al2O3 1.41 0.11 18.4 2.60 1.40 2.11 36.5 25.7 0.08 36.8 9.11 bd 0.50 22.7 0.81 0.62 0.21
MgO 1.43 34.4 7.53 16.8 1.44 3.50 0.31 8.80 38.2 0.12 20.8 34.6 16.0 6.71 26.6 16.1 bd
ZnO 0.11 0.08 bd bd 0.13 bd bd bd 0.04 bd bd bd bd bd 0.02 0.02 bd
K2O bd bd bd bd bd 0.01 bd bd 0.11 bd 0.10 bd bd 0.02 bd 0.28 bd
FeO 81.7 26.2 12.6 7.9 81.7 39.7 0.32 5.62 24.2 0.31 13.4 27.4 28.1 9.90 35.8 14.0 0.10
MnO 0.11 0.31 0.26 0.28 0.10 0.58 0.02 0.02 0.40 0.12 0.11 0.20 0.34 0.10 0.31 0.10 0.10
Cr2O3 0.10 0.40 0.31 0.82 0.10 0.54 bd 0.10 0.31 bd 0.49 0.10 0.10 0.23 bd 0.02 bd
PbO 0.09 bd bd 0.07 0.08 0.21 bd bd bd bd bd 0.03 bd bd bd bd bd
V2O3 bd 0.10 bd bd bd 0.21 bd bd bd bd bd bd bd bd bd bd bd
CaO 1.51 0.62 14.4 21.0 1.52 2.84 20.2 15.1 0.54 20.3 7.52 0.18 2.30 14.9 0.22 14.7 0.10
NiO 7.44 bd bd bd 7.44 bd bd bd bd bd bd bd bd bd bd bd bd
TiO2 0.10 bd 0.59 1.88 0.10 42.8 0.11 0.60 0.02 0.10 1.74 bd 1.00 0.62 0.10 0.11 0.20
BaO bd bd bd 0.09 bd bd bd bd bd bd 0.02 bd bd bd bd bd bd
P2O5 bd bd bd bd bd 0.02 bd bd bd 0.02 bd bd bd bd bd bd bd
SiO2 3.62 38.4 45.2 45.4 3.61 6.62 43.6 44.1 39.0 43.6 45.4 36.7 50.3 45.4 35.0 53.5 97.4
Total 97.5 100.7 99.8 97.0 97.5 99.2 101.4 100.5 100.2 101.8 98.7 99.2 98.8 100.8 98.9 101.1 98.2
Fa/Fs/An 29 97. 12 98 26 97 22 30 47 98 29 22
Fo/Wo/Ab 71 3 42 2 74 3 16 70 5 2 71 30
4.2 Olivine The chemicalcomposition data indicates that the olivine grains are mainly peridot and hyalosiderite in the forsterite-fayalite series.The compositional range of olivine (Fo67-77) in the lithic clasts is narrower than that in the mineral grains and matrix(Fo57-79)(Figure 6). The Fe and Mn content of olivine ismostly consistent with that of lunar material (Figure 7).

Figure 6 Forsterite (Fo) content in various clasts.
4.3 Pyroxene There are a variety of pyroxene compositions evident in MIL090036,26 (Figure 8). Pyroxene in lithic and glass clasts occurs predominantly as augite,pigeonite and minor calciumaugite. Ferroaugite and calcium-deficient iron augite (Fs37-65 Wo10-29 En21-49) were discovered only in gabbro clasts with glass (Figure 4e). Pigeonite is the sole pyroxene variety recognizedin gabbroic anorthosite (Fs19-26 Wo5-12 En57-62) (Figure 4b) with partiallydevitrified and homeocrystalline gabbroic lithic clasts (Fs25-28 Wo7-13 En63-68) (Figure 4d). Pyroxene in the feldsparglass (Figure 4h) occurs in a wide rangeof compositions,with augite,ferroaugite and pigeonite recognized. Similarly,pyroxenein microporphyritic impact melt breccias(Figure 4g),regolith breccia clasts (Figure 4j),and troctoliteclasts (Figure 4c) has a wide range of compositions,from augite to calcium-deficient augite to pigeonite (components in order are: Fs19-23 Wo5-50 En31-62,Fs13-24 Wo3-36 En29-81,Fs12-23Wo8-40 En31-52). Pyroxene in the matrix occurs predominantly as ferroaugite and pigeonite; relatively enriched in Fe comparedto pyroxene in the lithic clasts (Figure 8). The Fe and Mn contents of the pyroxenesare mostly similar to lunar material(Figure 7).

Figure 7 Fe and Mn contents of pyroxene and olivine in MIL090036, 26[9].
Figure 8 Quadrilateral diagram of pyroxenecompositions occurringin MIL090036, 26: gabbroic anorthosite clasts (b); troctolite clasts (c); gabbro clasts (d); gabbro clasts with some glass (e); polymict clasts (f); microporphyritic crystalline impact melt breccia (g); glass melt breccia (h); regolith clasts(j).
4.4 Other minerals All of the ferronickel in MIL090036,26 is in the form of kamacite.Minor amounts of Al,Ti,Fe were found in quartz,as well as some chromiteinclusions.

4.5 Bulk composition The bulk chemistrytest results are presented in Table 3. The result is basically accordance with the previous results of other sections especially for the major elements,e.g. Fe,Mg,Al. And we calculatedthe ratios of Fe/Mn and (FeO+MgO)/ Al2O3 are 83 and 0.4,respectively. Both of the plots in compositional fields associated with the lunar highlands of the Moon (Figure s9-10).

Table 3 Bulk composition in MIL090036
TiO2Al2O3Cr2O3FeOMnOMgOCaONa2OK2OP2O5SO3SiO2
MIL090036,260.4726.10.225.010.065.5116.50.630.080.010.1545.1
MIL090036,12[5]28.33.02<0.013.5315.70.01
MIL090036,13[5]27.24.12<0.014.3314.80.01
MIL090036[7]0.5927.44.820.68
MIL090036[6]3.75—5.540.55—0.72
MIL090036[8]26.3
Figure 9 Bulk Fe/Mn compositional diagram for lunar meteorites[3].
5 Discussion 5.1 The lunar originof MIL090036 There are four main lines of evidence that MIL09036 originated from the Moon:

(1) The large number of varyingclasts discovered in this specimen—the rock-forming minerals,including plagioclase,pyroxene,olivine and ilmenite are characteristic of other lunar breccias [3].

(2) The anorthitecomponent of the plagioclase (An90-98) is consistent with that found in other lunar meteorites (An90-100),but is not consistentwith plagioclase composition in howardite-eucrite-diogenite (HED) achondrites (An80-100) [10].

(3) Mafic mineralsin rock from theEarth,Moon,Mars,and asteroids have distinct Fe to Mn rations,our pyroxene and olivinechemistry data support a lunar origin for MIL090036.

(4) The bulk chemistryof Fe/Mn and (FeO+MgO)/ (Al2O3) ratios also support the lunar highland origin for MIL090036,26 (Figure s 9-10).

Figure 10 Bulk (FeO+MgO)/Al2O3 compositional diagram for lunarmeteorites[3].
5.2 Meteorite type As discussed,MIL090036 is predominantly composed of various clasts,and has a fine-grained crystalline,glassy matrix. The clasts (>0.1mm in size) are mainly lithic and feldspathic and predominantly fine- to very fine-grained. Both Fe/Mn and (FeO+MgO)/(Al2O3) ratios support a lunar highland origin for MIL090036.

The bulk chemistryof MIL090036,26 (Al2O3 26.1%; FeO 5.01%)is comparable to lunar highland anorthosite (Al2O3 25-30 wt%; FeO 3-6 wt%)[11],indicating that MIL090036 is a lunar feldspathic breccia. According to Stöffler classification criteria[12],such as texture,structure,grain-size and petrography and chemistry of matrix and clasts,MIL090036 can be further classified as a plagioclase polymict breccia.

5.3 Provenance determination of MIL090036 MIL090034,MIL090070and MIL090075,also feldspathic breccias,were collected in the Miller Range of Antarctica at the same time as MIL090036. Petrographic and geochemical studies have shown that MIL090034,MIL090070 and MIL090075 came from the same meteorite[7]. Compared withMIL090036 the former three meteorites have lower FeO and Na2O contents and higher Al2O3 content. All four meteorites are clast-rich,feldspathic breccias. However MIL090034,MIL090070,MIL090075 mainly contain weathered breccia clasts,with very low anothosite,gabbroic anorthosite and clast content compared with MIL090036. A concentration of 1.7 ppm of Th was determined in MIL090036,compared with 0.3 ppm,0.3 ppm and 1.1 ppm in MIL090034,MIL090070 and MIL090075,respectively[6]. While MIL090034,MIL090070 and MIL090075 have negative Eu anomaliesit can be noted that MIL090036 has a positiveEu anomaly,comparableto feldspathic lunar meteoriteNWA4936 and samples from Apollo 16[8]. The chemical-petrographic type of MIL090036 shares certain characteristics with the samples of Apollo16,such as the feldspathic breccia character that basically consistent with 50 samples from Apollo16 mission[13]. However,MIL090036 is more deficient in aluminum (Figure 11) and has a different modal abundanceof pyroxene and feldsparto samples collected by both the Apollo 16 and Luna missions (Table 4).

Figure 11 Major element composition of MIL090036, 26 in comparison to Apollo16 samples[7].
Table 4 Modal mineralogy of MIL090036, 26
plagioclaseolivine pyroxenequartz opaque
mineral
MIL090036 632.8340.10.3
Apollo16[14] 692.628.2-0.1

It is evidentfrom the above that,although MIL090036 is a clearlya lunar meteorite,it originates from an area outside of that sampled by both the Apollo and Luna missions.

5.4 The significance of lunar meteorite MIL090036 MIL090036 is a plagioclase polymict lunar breccia consistingof fine-grained material originating from near the lunar surface. After strong impact,consequent breccia formation and mixing,this lunar breccia can be considered to be more representative of the average geochemical and mineralogical composition of the Moon than other unbrecciated rock from the same area[3]. It is also in itself a record of the early meteorite impacts of the Moon[15].

Given that MIL090036likely originated from an area outside of that sampledby the Apollo and Luna missions,it will provide significantsupplementary opportunity forresearch of the lunar crust,particularly in terms of understanding the spatial distribution of rock types within thelunar crust.

According to previous reports,MIL090036 contains higher concentrations of incompatible elements than other feldspathic lunar meteorites; the 1.7 ppm Th content indicates a possibleKREEP component in clasts of this meteorite[6] (KREEP = potassium,rare earth elements,phosphorous). Given that the meteorite is a breccia mixture,of a varietyof source materials,no KREEP clasts were found in this study; however,their existencecannot be precluded. If the KREEP componentcan be proved,it would not only provide an indicationof the distance between meteorite source area and the Imbrium Basin center[16],but may also provide evidence for an abundant extra-terrestrial rare earth element resource.

Acknowledgements This study was supported by the Natural Science Foundation of China (Grant no. 41173077) and the Director Fund of Guangxi Key Laboratoryof Hidden Metallic Ore Deposits Exploration (Grant no. 13-A-01-02). Sample was provided by National Aeronautics and Space Administration (NASA)Johnson Space Center. Resource-sharing Platform of Polar Samples (http://birds.chinare.org.cn)maintained by Polar Research Institute of China(PRIC) and Chinese National Arctic & Antarctic Data Center(CN-NADC) offers help in the process of this thesis writing.

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