Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their relation to enstatite chondrites, primitive enstatite achondrites, and aubrites

Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their

relation to enstatite chondrites, primitive enstatite achondrites, and aubrites

Deon VAN NIEKERK1*, Klaus KEIL1, and Munir HUMAYUN2

1Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology,

University of Hawai‘i at Manoa, Honolulu, Hawai‘i 96822, USA2National High Magnetic Field Laboratory, Department of Earth, Ocean & Atmospheric Science,

Florida State University, Tallahassee, Florida 32310, USA*Corresponding author. E-mail: [email protected]

(Received 20 December 2012; revision accepted 11 November 2013)

Abstract–Queen Alexandra Range (QUE) meteorite 94204 is an anomalous enstatitemeteorite whose petrogenesis has been ascribed to either partial melting or impact melting.We studied the meteorite pairs QUE 94204, 97289/97348, 99059/99122/99157/99158/99387,and Yamato (Y)-793225; these were previously suggested to represent a new grouplet. Wepresent new data for mineral abundances, mineral chemistries, and siderophile trace elementcompositions (of Fe,Ni metal) in these meteorites. We find that the texture and compositionof Y-793225 are related to EL6, and that this meteorite is unrelated to the QUEs. Themineralogy and siderophile element compositions of the QUEs are consistent withpetrogenesis from an enstatite chondrite precursor. We caution that potential re-equilibration during melting and recrystallization of enstatite chondrite melt-rocks make itunreliable to use mineral chemistries to assign a specific parent body affinity (i.e., EH or EL).The QUEs have similar mineral chemistries among themselves, while slight variations intexture and modal abundances exist between them. They are dominated by inclusion-bearingmillimeter-sized enstatite (average En99.1–99.5) with interstitial spaces filled predominantlyby oligoclase feldspar (sometimes zoned), kamacite (Si approximately 2.4 wt%), troilite(≤2.4 wt% Ti), and cristobalite. Siderophile elements that partition compatibly between solidmetal and liquid metal are not enriched like in partial melt residues Itqiy and Northwest Africa(NWA) 2526. We find that the modal compositions of the QUEs are broadly unfractionatedwith respect to enstatite chondrites. We conclude that a petrogenesis by impact melting, notpartial melting, is most consistent with our observations.

INTRODUCTION

There are several types of enstatite-rich meteorites:Enstatite chondrites, impact-melt breccias, and totalimpact melts are mostly undifferentiated, while enstatiteachondrites (aubrites) are mostly differentiated silicate-rich rocks. Intermediate to these types of meteorites areprimitive enstatite achondrites, which are partlydifferentiated.

Several anomalous enstatite-rich meteorites fromthe Queen Alexandra Range (QUE) in Antarctica areknown. There are many interpretations with respectto the petrogenesis of, and the relationships between,the QUE meteorites. These meteorites and their

Meteoritical Bulletin Database classifications are: QUE97289/97348 (anomalous aubrite), QUE 99059/99122/99157/99158/99387 (anomalous enstatite meteorite), andQUE 94204 (EH7). QUE 97289/97348 was noted to besimilar to LEW 88055 (Antarctic Meteorite Newsletter1999), which is classified as an ungrouped ironmeteorite, but thought by Casanova et al. (1993) topotentially be related to aubrites. Weisberg et al. (1997)studied QUE 94204 and concluded that it is an EHmelt-rock that crystallized from an internally derivedmelt on its parent body (i.e., it was melted by heat thatcame from within the parent body from radioactivenuclide decay). They point out that there aremineralogic similarities between QUE 94204 and Ilafegh

Meteoritics & Planetary Science 49, Nr 3, 295–312 (2014)

doi: 10.1111/maps.12248

295 © The Meteoritical Society, 2014.

009, which was shown by McCoy et al. (1995) to be atotal impact-melt rock. Lin and Kimura (1998) concludedthat QUE 94204 and Y-793225 share petrographic andmineralogic characteristics that set them apart from otherenstatite chondrite melt rocks and assigned them to a newgrouplet, intermediate between EH and EL. Burbineet al. (2000) hypothesized, based on roughly chondriticcompositions, that QUEs 94204 and 97289/97348 mightbe impact-melt rocks. Izawa et al. (2011) studied QUE94204 and concluded that it probably represents aprimitive enstatite achondrite similar to NWA 2526 (Keiland Bischoff 2008), which is a partial melt residue.

We present results from a petrographic andmineral-chemistry study that characterizes the QUEmeteorites, examines relationships between them,explores potential relationships with other types ofenstatite meteorites, and considers their petrogenesis.We also present siderophile element abundances for themetal in these QUE meteorites obtained by laserablation ICP-MS.

SAMPLES AND ANALYTICAL TECHNIQUES

We studied polished thin sections from Y-793225and QUEs 94204, 97289, 97348, 99059, 99122, 99157,99158, 99387. Direct study of LEW 88055 was notpossible because the small size of the meteorite (1.7 g)prevented a loan of the sample material.

We studied the thin sections with a petrographicmicroscope and a backscattered electron (BSE) detectoron a JEOL5900 LV scanning electron microscope(SEM) at the University of Hawaii. We identified thephases optically and with a Thermo ElectronNanoTrace energy-dispersive spectrometer (EDS) fittedon the SEM. We used the EDS with an acceleratingpotential of 20 kV. We carried out the X-ray elementalmapping of thin sections (not QUE 99158) for 19chemical elements at a theoretical resolution of3 lm per pixel, although the actual resolution wasfound to be approximately 10 lm per pixel in some (notall) instances. Due to the large size of all phases in therocks, we do not anticipate that the lower resolutionhad significant impact on the modal abundancedeterminations. We determined the modal abundancesof minerals (vol%) from the X-ray maps with Multispecimage data analysis software (Biehl and Landgrebe2002); digital point counting similar to this has beendone by others (Maloy and Treiman 2007; Van Niekerkand Keil 2011). The procedure involved making three-element overlay maps for a diverse combination ofelements to identify phases; confirming the identities ofphases on these maps by BSE images and EDSanalyses; and producing a supervised classification mapwith point counting statistics for each meteorite, using a

minimum Euclidean distance algorithm. We used astatistical indicator (overall class performance) in thesoftware to assess the quality of, and if necessary refine,the supervised training. We visually compared the finalclassification map with the three-element overlay mapsto ensure accuracy.

We obtained quantitative elemental analyses ofmineral chemistry on a JEOL JXA-8500F electronmicroprobe analyzer (EMPA) at the University of Hawaiiusing 20 kV accelerating potential, beam currents of 15and 25 nA, and beam sizes of 1 and 2 lm. We used theelectron imaging mode to position the beam for analysis,to avoid analyzing small inclusions potentially not visiblein reflected light. Counting times for all elements were30 s for K-a peaks and 30 s for backgrounds. We usedthe well-characterized natural and synthetic standards.Na was analyzed first in the sequence on its assignedspectrometer. The data were collected and processed withProbe for Windows software version 8.4.7. We usedautomated ZAF procedures (the Armstrong/Love Scottdefault option that includes a /qz absorption correction)to correct for differential matrix effects. Interferencecorrections were applied to Co for interference by FeK-b, and to Mn for interference by Cr K-b. We excludeddata with totals below 98.5% and above 101.5% fromour data tables.

For three of the meteorites, we performed laserablation ICP-MS (LA-ICP-MS) analyses of Fe,Ni metalin thin section at the Plasma Analytical Facility of theNational High Magnetic Field Laboratory, FloridaState University, using a New Wave UP193FX excimerlaser ablation system coupled to an Element XR(Humayun et al. 2007), using normal Ni sampler andskimmer cones. We performed spot analyses using a50 lm spot size with a 5 s dwell time, except for asingle line scan on coarse metal in QUE 99122, whichwas analyzed with a 25 lm spot scanned at 10 lm s�1

across 933 lm length; 20 Hz laser repetition rate; 100%laser power output with 2 GW cm�2 irradiance. Forstandards, we used iron meteorites North Chile(Filomena, IIA) for Cu, Ga, Ge, As, W, and Au(Wasson et al. 1998); Hoba (IVB) for Ru, Rh, Pd, Re,Os, Ir, and Pt (Walker et al. 2008); and NIST SRM1263a for Cu, As, Mo, W, and Au (Campbell et al.2002; Campbell and Humayun 2005). We obtainedrelative sensitivity factors for Fe, Co, and Ni from allthree standards. Fe served as internal standard. Wedetermined Ni interferences on Ru using a pure Nimetal; this amounted to 12–15% corrections. Blankcorrections were 0–5% for all elements, except Mo,which was approximately 30%. Typical precision was3–5%, except for Mo (6%) and Re (7%).

We collected Raman spectra (for identification ofsilica polymorphs) in “single spectrum mode” with a

296 D. van Niekerk et al.

Witec Alpha300-R confocal Raman microscope linkedto a 532 nm Nd:YAG excitation laser and a UHTS-300spectrometer at the University of Hawaii. The laserpower at objective magnification 50 was 10 mW. Thespectrometer was equipped with a diffraction grating of600 lines mm�1 that provided a spectral resolution of<3 cm�1 and that dispersed the signal onto athermoelectrically cooled charged-coupling device. Aspectral measurement consisted of the average of fiveacquisitions of 5 s each. We used a Si wafer withRaman shift centered at 520 cm�1 for calibration.

RESULTS

Petrography

Modal abundances of phases in the meteorites westudied are listed in Table 1; grain sizes and textures arecompared in Fig. 1.

Enstatite meteorite parent bodies are commonlyassumed to be anhydrous. Thus, a lack of aqueousalteration on the parent bodies leads to the preservationof their highly reduced mineralogies. However, enstatite

Table 1. Mineral abundances.

Meteoritesa MET WMET SCH TRO NIN WOL DAU ENS OLI SIL FEL AGL

Y-793225(vol%) 5.1 17.3 0.5 4.1 0 0 0.8 60.0 0 0.9 11.3 0

(vol%)b 9.4 0 0.6 4.8 0 0 0.9 70.0 0 1.1 13.2 0(wt%)b 20.2 0 1.2 6.0 0 0 0.9 61.2 0 0.8 9.7 0(vol%)c 3.0 20.6 0.5 4.8 <0.1 0 0.9 66.9 0 0.3 3.0 0

QUE 94204(vol%) 5.7 18.6 0.5 2.2 0.1 0.7 0.3 60.5 0 2.1 9.0 0.3(vol%)b 10.4 0 0.6 2.6 0.1 0.8 0.4 71.6 0 2.5 10.6 0.4

(wt%)b 22.3 0 1.2 3.3 0.1 0.6 0.4 62.2 0 1.8 7.8 0.3QUE 97289(vol%) 3.3 24.7 0.3 1.3 0 1.8 0.4 57.4 0 0.9 9.9 0(vol%)b 9.4 0 0.4 1.6 0 2.3 0.5 72.2 0 1.1 12.5 0

(wt%)b 20.6 0 0.8 2.0 0 1.7 0.5 64.2 0 0.8 9.4 0QUE 97348(vol%) 1.9 16.2 0.1 2.1 0.3 5.4 0.2 59.3 0 1.7 12.7 0.1

(vol%)b 5.4 0 0.1 2.4 0.3 6.2 0.2 68.5 0 2.0 14.8 0.1(wt%)b 12.7 0 0.2 3.3 0.4 4.8 0.2 64.9 0 1.5 11.9 0.1QUE 99059

(vol%) 18.5 7.9 1.3 6.0 1.1 3.3 0.8 55.2 0 1.5 4.4 <0.1(vol%)b 21.2 0 1.4 6.4 1.2 3.5 0.9 59.1 0 1.6 4.7 <0.1(wt%)b 38.9 0 2.4 6.8 1.1 2.1 0.8 44.0 0 1.0 2.9 <0.1QUE 99122

(vol%) 31.6 7.2 0.6 3.0 1.2 1.1 0.2 46.4 0 3.0 5.5 0.2(vol%)b 34.8 0 0.6 3.2 1.3 1.2 0.2 49.4 0 3.2 5.9 0.2(wt%)b 56.6 0 0.9 3.0 1.1 0.6 0.2 32.5 0 1.7 3.3 0.1

QUE 99157(vol%) 0.9 15.0 1.2 2.1 <0.1 5.4d 0.3 64.6 0 0.7 8.6 1.2d

(vol%)b 3.9 0 1.4 2.4 <0.1 6.2d 0.3 73.8 0 0.8 9.8 1.4d

(wt%)b 9.1 0 3.1 3.3 <0.1 4.8d 0.3 69.9 0 0.6 7.8 1.1d

QUE 99387(vol%) 2.5 10.6 0.2 3.1 0.4 2.4 0.4 68.0 0 0.7 10.2 1.5d

(vol%)b 4.7 0 0.2 3.4 0.4 2.6 0.4 74.6 0 0.8 11.3 1.6d

(wt%)b 11 0 0.4 4.6 0.5 2.0 0.4 70.3 0 0.6 9.0 1.2d

MET = Fe,Ni metal; WMET = weathered metal; SCH = schreibersite; TRO = troilite; NIN = niningerite; WOL = Ca-rich weathering products,

presumably of oldhamite; DAU = daubr�eelite; ENS = enstatite; OLI = olivine; SIL = silica (cristobalite); FEL = feldspar; AGL = aluminum-

alkali-rich silica glass.aArea (mm2) of rock counted in thin section. Y-793225 (26), QUE 94204 (95), QUE 97289 (88), QUE 97348 (70), QUE 99059 (44), QUE 99122

(58), QUE 99157 (34), QUE 99387 (40.6). Void and crack space are excluded from these values.bWeathered metal reconstituted as unweathered metal (see text for explanation).cModes recalculated from Lin and Kimura (1998) to include weathering products (20.6%) that were reported in their text, but not included in

calculation of the modes reported in their data table.dThis is an upper estimate (could be up to double the true amount).

Anomalous QUE enstatite meteorites 297

chondrite “finds” (as opposed to “falls”) may sufferrapidly from terrestrial aqueous alteration; this may altertheir modal compositions. Metal and oldhamite areparticularly vulnerable. Thus, the present abundances ofminerals in the weathered meteorites do not reflect theoriginal abundances on their parent bodies. We reportdata in Table 1 that not only reflect the modalcompositions of the presently weathered meteorites (invol%) but also the estimated modal compositions of thepreweathered meteorites as they would have existed ontheir parent bodies (in vol% and wt%). Izawa et al.

(2011), using micro X-ray diffraction on QUE 94204,identified goethite as the weathering product of metal.Goethite’s unit cell volume is approximately six timesgreater than that of kamacite’s (i.e., a volume increaseoccurs during weathering). We counted the Fe-richweathering products (assumed to be goethite) of metal invol% and then corrected the weathered metal abundancefor volume and density differences between kamaciteand goethite ([weathered metal/~6) + metal], thenrenormalized). Thus, in Table 1, the second line of vol%of each meteorite, as well as the wt%, represents the

Fig. 1. Comparison of rock textures with red-green-blue (S-Mg-Al) ka X-ray map mosaics of meteorite thin sections. Blackinside the rocks are metal and accessory minerals. a) Y-793225. b) Queen Alexandra Range (QUE) 94204; most grains/crystalsthat appear to be individual entities are, in fact, so. They have uniform extinction under crossed polars. c) QUE 99387. d) QUE99059; the large individual masses of enstatite have uniform extinction under crossed polars. e) QUE 99122. f) QUE 99157. Thelarge individual masses of enstatite have uniform extinction under crossed polars.


estimated preterrestrial unweathered mineral abundances.We consider the preweathered metal abundances that wereport to be upper limit estimates, because some degree ofvolume increase may have been canceled out by Femobilization in thin veins. The same type of correctionsoutlined for metal were not done for weatheredoldhamite, because oldhamite has multiple weatheringproducts, which are indistinguishable on X-ray maps,thus making unit cell adjustments impractical.

We could not determine graphite abundance fromthe X-ray maps, but petrography indicates that itseldom occurs and when it does, it is present in traceamounts and occurs in kamacite.

Y-793225The meteorite does not contain any chondrules. The

various minerals are homogeneously distributedthroughout the enstatite-dominated matrix (70 vol%preweathering), but with a few larger-than-averageaggregates of plagioclase here and there (Fig. 1a).Minerals are anhedral to subhedral; enstatite (50–300 lm; Lin and Kimura 1998) does not occur as thelarge elongated euhedral crystals protruding into metal/sulfide that are usually found in enstatite chondriteimpact-melt rocks. The texture of the rock is similar tothat of a petrologic type 6 meteorite; Lin and Kimura(1998) made the same observation.

Lin and Kimura (1998) found that, compared withenstatite chondrite melt-rocks they studied, Y-793225 hadmuch less plagioclase (3.8 versus approximately 11 vol%,respectively). We found approximately 11 vol%plagioclase (Fig. 1a) in postweathering (i.e., current)abundance; our observations therefore differ significantlyfrom those of Lin and Kimura (1998). In Appendix S1,we argue that our data are more representative, andtherefore conclude that Y-793225 is not depleted inplagioclase.

Silica (1.1 vol%) occurs interstitially to enstatite andis heterogeneously distributed throughout the rock.

Schreibersite (0.6 vol%) is associated with metal (5.1 vol%).Daubr�eelite (0.9 vol%) predominantly occurs adjacent totroilite (4.8 vol%) in sulfide assemblages (blebs); it is alsosometimes exsolved as fine lamellae inside troilite. Linand Kimura (1998) found trace amounts of alabandite(one grain) and perryite; we found none. We found thatY-793225 does not contain oldhamite, and Ca-rich veinsthat are often found in enstatite meteorites and might beweathering products of oldhamite (Van Niekerk and Keil2011) are absent. Thus, this meteorite may never havecontained oldhamite. Olivine and diopside (present inaubrites) were not found.

Queen Alexandra Range MeteoritesGeneral Petrography: None of the QUE meteorites

contain chondrules, and none of them contain olivine ordiopside, which are found in aubrites.

All of the enstatite crystals in these meteorites arepolysynthetically twinned. Polysynthetic twinning inenstatite meteorite orthopyroxene is usually a very fine(micron- to submicron-sized) intergrowth of clino- andorthopyroxene (e.g., McCoy et al. 1995; Haack et al.1996; Rubin et al. 1997); in this case, clinopyroxenewould be a minor component. The fine clinopyroxenewould only be readily identifiable by a transmissionelectron microscope.

Some of the QUEs are more similar to one anotherthan others, in terms of texture and modalcompositions. QUEs 94204, 97289, 97348, 99158, and99387 have a texture that resembles that of slowlycooled magmatic rocks and are dominated by large(approximately 1 mm) equigranular crystals of enstatitewith less abundant minerals filling in the interstices(Figs. 1b, 1c, and 2a).

Queen Alexandra Ranges 99059 and 99122 containthe same minerals as the five aforementioned QUEs, buttheir mineral abundances and textures differ. Notably,they have more metal, less plagioclase (by a factor oftwo), and less enstatite; QUE 99059 contains less metal

Fig. 2. Fe,Ni metal in the Queen Alexandra Range (QUE) meteorites. In these backscattered electron images, metal is white(silicates are dark gray; sulfides and iron oxide are lighter shades of gray). a) QUE 94204. b) QUE 99122.


than 99122, but more enstatite (they have almost the sameamount of plagioclase). Their textures are not ashomogenous as those of QUEs 94204, 97289, 97348,99158, and 99387, because metal, enstatite, and plagioclaseare unevenly distributed and have heterogeneous crystal/grain sizes with irregular outlines and embayments(Figs. 1d, 1e, and 2b). Enstatite is approximately 1–2 mmsized. QUEs 99059 and 99122 do not have the even-sizedinterstitial space between enstatite crystals that QUEs94204, 97289, 97348, 99158, and 99387 have.

Queen Alexandra Range 99157 contains the sameminerals as the other QUEs, but its mineral abundancesand texture differ. It contains the least metal of theQUEs (although similar to QUEs 97348 and 99387). Itstexture is dominated by a range of enstatite crystalsizes; the largest enstatite crystal that we observed in theQUEs occurs in this meteorite (approximately 2 by3 mm). The enstatites are less dramatically embayedthan those in QUEs 99059 and 99122 (Fig. 1f). QUE99157 lacks the large patches of metal that QUEs 99059and 99122 contain.

Note that the modes referred to below arepreweathering (i.e., parent body) abundances.

Enstatite: Enstatite in the QUEs occurs as mm-sizedcrystals (Figs. 1b and 1c) with small inclusions (Figs. 3aand 3b). The inclusions are individual entities; that is,they are not part of curvilinear trails of minute metaland sulfide inclusions as described by Izawa et al.(2011) in enstatite of QUE 94204. They consistof (1) optically isotropic Al-alkali-rich silica glass(0.4–1.6 vol%) with minor Al-alkali-poor domains(there is no glass in QUE 97289), (2) plagioclase, (3)troilite with minor daubr�eelite/niningerite, (4)unweathered metal and iron oxide, and (5) crystallinesilica. Excluding the glass, all these phases are alsofound (in greater abundance) outside enstatite. Exceptfor plagioclase and glass, the different inclusion phasesoften occur together in a single inclusion.

Queen Alexandra Range 94204, 97289, 97348, 99158,99387, and 99157 contain 68.5–74.6 vol% enstatite.QUEs 99059 and 99122 contain 49.4–59.1 vol%.

Plagioclase: Plagioclase in the QUEs predominantlyoccurs interstitially to enstatite and conforms to itsoutlines. Inclusions in enstatite are a minor occurrence.In QUEs 99059, 99122, and 99157, plagioclase alsooccurs as thin bands between enstatite and metal, andfills into embayments in the enstatite. In QUEs 94204,97289, 97348, 99158, 99387, and 99157, plagioclasecontent ranges from 9.8–14.8 vol%, and in QUEs 99059and 99122, from 4.7–5.9 vol%.

Fe,Ni metal: Fe,Ni metal occurs interstitially toenstatite while conforming to its outlines (Fig. 2a), andfilling embayments in it. In QUEs 99059 and 99122, the

metal (21.2–34.8 vol%) completely envelops someenstatite grains and occurs as large patches comparableto the sizes of enstatite crystals (Fig. 2b). Modalabundances in QUEs 94204, 97289, 97348, 99158, and99387 range from 4.7 to 10.4 vol%; there is a factor oftwo less metal in QUEs 97348 and 99387 than in 94204and 97289. QUE 99157 has 3.9 vol% metal. Iron oxide(weathered metal) surrounds some metal assemblagesand troilite; it is common as thin veins permeatingthroughout the rock in between enstatite grain/crystalboundaries. Thinner veins meander through feldspar insome meteorites.

Silica: A silica phase (0.8–3.2 vol%) is irregularlydistributed throughout the meteorites. In QUEs 97348and 99059, we identified it as cristobalite (see RamanSpectroscopy section); Izawa et al. (2011) identifiedcristobalite in QUE 94204 with micro X-ray diffraction.The silica sometimes contains small (a few lms) K-Na-Al-rich silicate inclusions. In QUE 97348, the silicaoccurs interstitially to enstatite, as well as alongenstatite grain/crystal faces (and conforms to theenstatite outline), and separates metal and enstatitefrom each other (Fig. 3c). This is less often the case inthe QUEs 94204, 97289, 99158, and 99387 where silicaoften occurs as anhedral grains interstitial to enstatiteand intergrown with plagioclase. In QUE 99059, silica ismostly associated with plagioclase; in QUE 99122, itoccurs both intergrown with plagioclase, and in thinbands between enstatite and metal (conforming to theenstatite morphology).

Troilite: Troilite (1.6–6.4 vol%) predominantlyoccurs interstitially to enstatite and often conforms tothe outlines of enstatite crystals and fills intoembayments in the enstatite. It often is in contact withmetal and enstatite, and sometimes with plagioclase.

Ca-rich weathering products: Ca-Fe-sulfate and Ca-Fe-oxide are present and they sometimes contain“islands” of iron oxide and sometimes rare millerite(NiS). Izawa et al. (2011) identified gypsum and calcitein QUE 94204 by micro X-ray diffraction. The Ca-richmaterial (0.8–6.2 vol%) is present in all the meteoritesand occurs in two morphologies: (1) interstitial toenstatite and conforming to the morphologies ofsurrounding minerals (Fig. 3d), and (2) as thin,meandering veins throughout the rock. In QUE 99387,some of it occurs inside inclusions in enstatite. TheCa-rich material is probably a weathering product ofoldhamite.

Daubr�eelite and niningerite:Daubr�eelite (0.2–0.9 vol%)and niningerite (0.1–1.3 vol%) are found either exsolvedas lamellae in troilite, or as discrete grains within oradjacent to troilite (Figs. 3e and 3f). QUE 97289 containsno niningerite.


Schreibersite: Schreibersite (0.1–1.4 vol%) is associatedwith metal and, sometimes, iron oxide, either asindividual grains or as thin bands that separate metal andenstatite (the thin bands are discontinuous).

Micro-Raman Spectroscopy of Silica

Micro-Raman spectroscopy of the silica phase inQUEs 97348 and 99059 (Fig. 4) reveals that it is the

Fig. 3. Backscattered electron images of mineral assemblages. (MET = Fe,Ni metal; CRI = cristobalite (silica); ENS = enstatite;FEL = feldspar (plagioclase); TRO = troilite; DAU = daubr�eelite; NIN = niningerite; AGL = aluminum-alkali-rich silica glass;WEA = weathered (iron oxide). a) An inclusion of plagioclase feldspar, troilite with exsolved daubr�eelite, and cristobalite(silica) in an enstatite crystal in QUE 99157. b) An inclusion of troilite and aluminum-alkali-rich silica glass in the sameenstatite crystal as (a). c) Interstitial cristobalite (silica) in QUE 94204. d) Interstitial Ca-Fe-rich weathering products of,presumably, oldhamite in QUE 94204. e) A coassemblage of troilite, daubr�eelite, and niningerite in QUE 99387. f) Acoassemblage of troilite (with exsolved daubr�eelite) and weathered niningerite (with finely exsolved troilite lamellae) in QUE99122.


polymorph cristobalite. Cristobalite can be of either thea- or b-varieties; the former is tetragonal and the lattercubic. The cristobalite in the QUEs is not opticallyisotropic under crossed polars, and is thus not cubic.The cristobalite in the QUEs is thus of the a-variety.

Mineral Chemistry

Average mineral compositions for the QUEs arepresented in Tables 2–6.

Enstatite: The average compositions of enstatite inall the meteorites are similar (Table 2); they are all Mg-rich (range of averages En99.1–99.5). The Fe-content ofQUEs 94204, 97348, and 99157 might be slightlyoverestimated in our analyses, relative to the otherQUEs, due to secondary excitation of nearby metalinclusions. The pyroxene contains trace to minoramounts of Al2O3 (0.04–0.64 wt%). It does not containdetectable Na, K, Ti, Mn, or Cr. The small (a few lmto tens of lm) inclusions of Al-alkali-rich silica glasstypically have high or low analytical totals, and thusmost analyses were excluded from Table 5. Note,however, that excluded analyses are otherwise identicalto the presented analyses (overestimation of Si often ledto high totals). The glass contains major amountsof Na2O (approximately 2 wt%), K2O (approximately6 wt%), and Al2O3 (approximately 13 wt%); it does notcontain Ca. There is no compositional variationbetween the different meteorites.

Plagioclase: Feldspar (Table 2) in all the QUEs issodic plagioclase—predominantly oligoclase (definedas Ab90-Ab70)—with Na2O averaging approximately8–9 wt% and ranging approximately 7–10.5 wt%. Thereis a small variation in average Ab composition betweenthe meteorites, but no correlation with textural variation.The plagioclase contains minor K2O (0.2–0.7 wt%) and

FeO (0–0.9 wt%). The FeO-content is highest toward theedges of grains where they are separated from adjacentminerals by thin weathering veins, as well as inside grainswhere weathering veins and cracks cut through. Thehighest FeO might thus be a result of secondaryexcitation of Fe X-rays. The true FeO of the plagioclasemight approach 0.06 wt%. Izawa et al. (2011) found nozoned plagioclase in QUE 94204; we did, however.Plagioclase is sometimes zoned, both in inclusions and ininterstitial settings, with higher Ca/lower Na cores andlower Ca/higher Na rims (Fig. 5).

Fe,Ni metal: The average major and minor elementcompositions of metal (Table 3), as well as the ranges ofcomposition, are similar in the different meteorites. Thereis no correlation between composition and texturalvariation, and inclusions in enstatite have the samecomposition as interstitial metal. Metal predominantlyhas the composition of kamacite (Ni <7.5 wt%), but afew high-Ni domains exist; the Ni-content of the metalranges continuously from approximately 5 to 15 wt%with one analysis at approximately 18 wt%. There is nograin size effect; that is, smaller grains do not have higherNi-contents than larger grains, as is often the case inchondrites. The kamacite has lower Si-content (Siapproximately 2.0–2.6 wt%) than the high-Ni domains(Si approximately 2.6–3.4 wt%; one analysis at 4 wt%).The metal contains minor Co (0.31–0.40 wt%). Kamacitegrains are predominantly unzoned; in many cases, thecomposition of kamacite varies irregularly across a givengrain (in these cases Ni- and Si-variation are correlated).We found one case of minor zoning; the Ni- andSi-contents decrease slightly toward the interior of akamacite grain. Metal does not contain Cr (the detectionlimit was 0.01 wt%).

Siderophile element abundances in metal fromQUEs 94204, 97289, and 99122 are presented inTable 4. The individual analyses within each meteoriteare very similar and element abundances in the metalshow correlated variations. Metal from QUE 99122exhibits higher Ge, Ru, Rh, Re, Os, Ir, and Ptabundances; similar Co, Cu, Ga, As, Mo, Pd, and Wabundances; and lower Au abundances, than metalfrom the other two QUE meteorites. Cu and Ni arecorrelated; QUE 99122 contains the largest variation inCu (23%). Some metal grains, particularly in QUE97289, exhibit higher W abundances than other metalgrains by up to a factor of three. However, such high-Wmetals otherwise have identical siderophile elementpatterns to the normal-W metal grains. The cause of theanomalous W-values is not understood and those valueswere excluded from the curves in Fig. 6. In Fig. 6., theaverage CI- and Ni-normalized siderophile elementpatterns of the meteorites are compared with each otherand with average patterns from bulk EH and EL

Fig. 4. Raman spectra of silica compared with cristobalite. Inthis wave number range, a single band is diagnostic of thecristobalite polymorph. Cristobalite from Downs (2006).


chondrite metal (Kong et al. 1997). Patterns for metalfrom QUE 94204 and QUE 97289 are identical. Thepatterns of the compatible elements (Re, Os, Ir, Ru, Pt,Rh) for all three meteorites are similar, or slightlydepleted, with respect to EH/EL metal. Au, As, Ga,and Ge are lower than EH bulk metal, but similar toEL bulk metal.

Schreibersite: Schreibersite compositions are similarbetween the different meteorites (Table 3). Schreibersitecontains 64–69 wt% Fe, 16.5–21.5 wt% Ni, and minoramounts of Si (0.13–0.23 wt%) and Co (0.13–0.17 wt%).

Silica: Cristobalite analyses from several meteoriteshad totals unsuitable for presentation, due tooverestimation of SiO2, and were excluded fromTable 5. The cristobalite in all the meteorites containsAl2O3 (1.8–2.91 wt%). Cristobalite has an open crystalstructure compared with that of quartz, and as a resultcommonly contains Al in Al-saturated systems; alkali andalkali earth elements balance the charge deficiencycreated by replacement of Si4+ by Al3+ (Deer et al.

1992). In the QUEs, cristobalite contains minor amountsof Na2O (0.4–0.5 wt%) and K2O (approximately0–0.3 wt%). It also contains trace to minor amounts ofFeO (0.06–0.25 wt%).

Troilite: Troilite in all QUEs is similar incomposition (Table 6). There is no chemical differencebetween troilite inside and outside of inclusions. Troilitecontains 0.7–2 wt% Cr, and notably, 0.7–2.4 wt% Ti.The high Cr-content of QUEs 99059, 99122, and 99157might be due to beam overlap on, or secondaryexcitation of, micron- to submicron-sized daubr�eelitelamellae (e.g., Figs. 3a and 3f). The Ti-contents in theQUE troilites are higher than those of enstatitechondrites (<0.8 wt%; Keil 1968), and comparable tosome aubrites (0.46–5.7 wt%; Keil 2010). A 500 lmmicroprobe traverse across a troilite in QUE 99059shows no zoning of any elements.

Daubr�eelite: The composition of daubr�eelite in allthe QUEs is similar (Table 6). The daubr�eelites contain1–2.6 wt% Mn, making it manganoan daubr�eelite.

Table 2. Average composition (wt%) of enstatite and plagioclase.a

Enstatite Plagioclase

QUE94204

QUE97289

QUE97348

QUE99387

QUE99059

QUE99122

QUE99157

QUE94204

QUE97289

QUE97348

QUE99059

QUE99122

QUE99157

n = 16 n = 37 n = 46 n = 38 n = 11 n = 13 n = 21 n = 9 n = 13 n = 14 n = 36 n = 34 n = 40

SiO2 58.9 59.3 58.9 59.5 59.5 59.9 60.1 SiO2 62.0 61.3 61.3 61.7 63.7 62.1Al2O3 0.12 0.14 0.08 0.06 0.08 0.07 0.09 Al2O3 23.2 24.1 23.9 24.3 22.8 23.5FeOb 0.34 0.14 0.29 0.15 0.13 0.09 0.31 FeOb 0.1 0.2 0.3 0.1 0.2 0.2

MgO 40.8 40.7 40.4 40.0 41.0 40.9 40.0 MgO n.d. n.d. n.d. n.d. n.d. n.d.CaO 0.21 0.20 0.23 0.21 0.24 0.20 0.27 CaO 4.34 4.98 5.01 5.05 3.33 4.76Na2O n.d. n.d. n.d. n.d. n.d. n.d. n.d. Na2O 8.80 8.37 8.24 8.40 9.16 8.53

K2O n.d. n.d. n.d. n.d. n.d. n.d. n.d. K2O 0.47 0.37 0.39 0.38 0.52 0.46Total 100.4 100.5 99.9 99.9 101.1 101.2 100.8 Total 98.9 99.2 99.1 99.9 99.7 99.6

Wo 0.4 0.4 0.4 0.4 0.4 0.4 0.5 Ab 76.5 78.0 73.1 73.4 80.8 74.4En 99.1 99.4 99.2 99.4 99.4 99.5 99.1 An 20.8 19.3 24.6 24.4 16.2 23.0Fs 0.5 0.2 0.4 0.2 0.2 0.1 0.4 Or 2.7 2.7 2.3 2.2 3.0 2.6

n.d. = not detected.aMn, Cr, Ti are below detection.bSee text for discussion.

Fig. 5. Examples of zoning (rim to rim) in feldspar. a) Queen Alexandra Range (QUE) 99059; interstitial setting. b) QUE 94204;interstitial setting. c) QUE 99157; inclusion in Fig. 3a.


Table

3.Averagecomposition(w

t%)ofFe,Nimetalandschreibersite.

Metal

Schreibersite

QUE

94204

QUE

97289

QUE

97348

QUE

99387

QUE

99122

QUE

99157

QUE

94204

QUE

99387

QUE

99059

QUE

99122

QUE

99157

KAM

H-N

iKAM

H-N

iKAM

H-N

iKAM

H-N

iKAM

H-N

iKAM

H-N

in=8

n=2

n=27

n=2

n=9

n=2

n=13

n=3

n=36

n=7

n=10

n=1

n=3

n=4

n=2

n=2

n=2

Fe

91.8

80.0

90.2

84.7

91.2

87.0

90.4

84.4

92.4

85.9

89.6

76.8

68.4

66.8

64.9

65.6

65.5

Ni

6.77

16.7

6.64

11.5

7.31

10.8

6.21

11.58

6.15

11.5

6.14

17.7

17.1

19.8

20.7

19.8

20.5

Co

0.37

0.34

0.33

0.33

0.37

0.35

0.38

0.36

0.37

0.35

0.36

0.32

0.15

0.14

0.15

0.15

0.13

Si

2.46

3.59

2.47

2.93

2.40

2.81

2.29

2.94

2.26

2.85

2.45

4.12

0.17

0.20

0.15

0.18

0.19

P0.05

0.52

0.08

0.24

0.05

0.17

0.02

0.16

0.04

0.27

0.03

0.37

13.8

13.7

13.7

13.6

13.9

Total

101.4

101.2

99.7

99.7

101.3

101.1

99.3

99.4

101.2

100.9

98.6

99.4

99.6

100.6

99.6

99.3

100.2

KAM

=kamacite;H-N

i=high-N

i.


Table

4.Elementalanalyses(ppm)ofFe,Nimetal.

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

99122

QUE

94204

Fe

906000

916000

911000

914000

912000

913000

917000

920000

921000

914000

923000

920000

917000

913000

921000

Co

3710

3760

3780

3880

3690

3850

3680

3810

3800

4000

3770

3980

3860

3860

4040

Ni

89500

80000

84400

81400

83500

83000

79200

76300

74700

81200

72600

75800

78400

82500

74400

Cu

177

188

214

207

199

170

162

142

109

130

123

123

109

140

136

Ga

42

48

49

47

46

45

44

43

45

48

45

45

45

46

49

Ge

107

105

109

105

106

106

107

100

106

114

108

109

109

108

98

As

10.4

9.8

10.0

9.4

9.7

9.7

9.2

9.5

10.2

10.1

9.9

10.2

9.5

10.0

9.6

Mo

2.54

2.80

2.95

2.78

2.85

2.57

2.56

2.58

2.46

2.39

2.24

2.62

2.40

2.60

2.72

Ru

3.93

3.69

3.78

3.73

3.65

3.61

3.61

3.43

3.91

4.03

3.96

3.83

3.85

4.03

3.17

Rh

0.73

0.68

0.69

0.68

0.73

0.66

0.63

0.66

0.71

0.70

0.70

0.66

0.70

0.73

0.64

Pd

3.21

2.82

2.88

2.83

3.03

2.98

3.01

2.74

2.62

2.90

2.97

2.95

2.77

3.01

2.85

W0.54

0.52

0.55

0.51

0.49

0.51

0.45

0.46

0.54

0.51

1.86

0.56

0.56

0.55

0.48

Re

0.28

0.24

0.22

0.21

0.25

0.26

0.23

0.23

0.24

0.24

0.20

0.27

0.23

0.23

0.24

Os

2.90

2.75

2.62

2.57

2.60

2.72

2.76

2.52

2.85

2.83

2.77

2.79

2.96

2.75

2.26

Ir2.63

2.55

2.39

2.43

2.38

2.54

2.36

2.31

2.43

2.76

2.69

2.61

2.60

2.57

2.09

Pt

5.47

5.04

4.94

5.18

4.96

5.00

5.04

4.67

5.24

5.44

4.98

5.21

5.19

5.36

4.35

Au

1.09

1.03

1.04

1.04

1.03

0.96

1.04

1.01

0.93

1.14

1.06

1.03

1.01

1.08

1.28

QUE

94204

QUE

94204

QUE

94204

QUE

94204

QUE

94204

QUE

94204

QUE

94204

QUE

97289

QUE

97289

QUE

97289

QUE

97289

QUE

97289

QUE

97289

QUE

97289

QUE

97289

Fe

906000

917000

927000

922000

912000

918000

920000

930000

909000

923000

923000

924000

925000

934000

926000

Co

3740

3750

3940

3760

3930

3900

4030

3770

3580

3840

3680

3720

3720

3450

3730

Ni

89900

79100

69000

74100

84200

77700

75600

66300

87300

73200

73100

72000

71200

61800

69600

Cu

171

129

98

117

128

129

133

115

178

123

128

129

110

111

108

Ga

48

45

47

46

47

47

46

44

47

48

47

48

46

46

48

Ge

98

93

102

99

95

95

93

92

95

99

97

97

97

92

92

As

10.1

9.9

9.0

10.0

10.4

10.5

9.8

9.6

10.7

10.8

10.0

10.9

10.2

11.2

10.3

Mo

2.40

2.54

2.84

2.57

2.56

3.07

2.66

2.19

2.46

2.43

2.67

2.53

2.36

2.49

2.30

Ru

3.24

3.03

3.15

3.11

3.27

3.17

3.27

2.69

2.72

3.29

3.08

3.21

3.26

3.02

3.36

Rh

0.64

0.60

0.59

0.62

0.60

0.67

0.68

0.52

0.51

0.70

0.66

0.59

0.59

0.56

0.53

Pd

3.67

2.95

2.75

2.96

3.29

2.97

2.83

2.67

3.66

3.01

2.68

2.90

2.79

2.55

2.82

W0.45

0.50

0.45

0.44

0.44

0.50

0.47

0.38

2.39

0.49

0.45

0.47

0.45

1.31

1.32

Re

0.17

0.15

0.16

0.18

0.19

0.22

0.24

0.19

0.20

0.20

0.20

0.22

0.19

0.19

0.18

Os

2.34

1.91

1.83

1.93

2.29

2.27

2.38

1.92

1.88

2.06

2.12

2.00

2.12

1.92

2.00

Ir2.07

1.85

1.70

1.76

2.09

2.01

2.12

1.74

1.74

1.97

1.93

1.85

1.93

1.78

1.81

Pt

4.23

4.07

3.90

4.10

4.45

4.19

4.15

3.69

3.74

4.45

4.25

4.13

4.19

3.82

3.94

Au

1.15

1.24

1.31

1.24

1.23

1.10

1.15

1.16

1.09

1.11

1.06

1.17

1.10

1.09

1.00


Niningerite: Analyses of niningerite commonly havelow totals (low- to mid-90s). The niningerite has beenpartially oxidized during terrestrial weathering (this isoptically observable by microscopy in some cases), andthe low totals are the result of unanalyzed oxygen (whichis evident on oxygen X-ray maps). Because Fe is locallyremoved from sulfides during weathering (e.g., Rosso andVaughan 2006), the composition of niningerite mighthave changed and thus the composition might not berepresentative of unweathered niningerite; we thereforedo not include analyses with low totals in the averagecompositions (Table 6). A microprobe traverse across alarge grain in QUE 99122 shows that there is no zoningof Fe, Mg, or Mn. In unweathered cases, niningeritecontains a large amount of Mn (approximately 20 wt%)and some Cr (0.5–1.5 wt%).

DISCUSSION

Relationships between the Meteorites

The QUE MeteoritesThe fact that so many anomalous enstatite-rich

meteorites come from only one geographic location onthe Antarctic ice sheet implies that they fell together(i.e., they are paired). Minor petrographic differencesbetween the meteorites must represent small-scaleheterogeneities from a single parent body.

Y-793225 and the QUE MeteoritesY-793225 and the QUEs do not have the same

mineralogy. Enstatite in the QUE meteorites commonlycontains Al-alkali-rich silica glass inclusions, whereasenstatite in Y-793225 does not. The QUEs probablycontained oldhamite, but Y-793225 never did. This isevident because the QUEs and Y-793225 have similarmodal abundances of weathered metal, and hencesimilar degrees of weathering (thus, if all thesemeteorites contained oldhamite, one would expectweathering effects on oldhamite to be the same), butY-793225 lacks weathered oldhamite, whereas the QUEscontain it.

The QUEs and Y-793225 have dissimilar texturesand grain sizes (Figs. 1a, 1b, and 7). This indicates that

they have different petrogenetic histories. As stated inthe Results section, Y-793225 texturally resembles ametamorphic type 6 chondrite, and probably is one.

Lin and Kimura (1998) suggested that severalcompositional similarities between QUE 94204 andY-793225 indicate that they should belong to a newgrouplet, but below we show that Y-793225 is probablyan anomalous EL6. The compositional similarities theycite include the Mn-rich compositions of daubr�eelite, theTi-rich compositions of troilite, and the Ca-richcompositions of plagioclase. We briefly compare thesecompositions in Y-793225 with those of EL6s fromKeil (1968) and Kimura and Lin (1999). TheMn-compositions of the daubr�eelite (0.97–2.56 wt%) inY-793225 are similar to those of EL6 chondrites (1.41–3.67 wt%;). The average Mn-content is similar to that ofPillistfer (1.86 versus 1.53 wt%, respectively). Theaverage Ti-content of troilite (1.07 wt%) in Y-793225 isoutside the range of averages of EL6 (0.55–0.77 wt%)and EHs reported by Keil. The Ca-content of plagioclase(average 2.34 wt% CaO) in Y-793225 is enrichedcompared to EH chondrites (average 0.43 wt% CaO),but falls within the EL6 range of 1.96–3.61 wt% CaO;the value for Y-793225 is similar to that of Ufana andY-793258 (2.81 and 2.89 wt% CaO). The Mg-Mn-Femonosulfide composition for QUE 94204 lies slightly inthe niningerite (Mg-dominant; characteristic of EHs) sideof the solid solution series, while that for Y-793225 liesslightly in the alabandite (Mn-dominant; characteristic ofELs) side (see Fig. 8). Furthermore, we point out thattrace amounts of Zn in Y-793225 daubr�eelite (Lin andKimura 1998) are characteristic of the ELs (daubr�eelitein EHs often bears several percent Zn; Keil 1968). Onthese lines of evidence, we conclude that Y-793225 ispossibly an EL6 and that it is unrelated to the QUEmeteorites.

Rubin and Wasson (2011) concluded that Y-793225has an anomalous EH composition, based on the EH-like Si-content of kamacite. Their bulk rock siderophileand chalcophile element data, however, demonstrate anEL-like composition. Thus, while we agree that the highSi-content of the kamacite is anomalous for EL6,almost all other chemical fingerprints point toward anaffinity with the EL parent body.

Table 5. Compositions (wt%) of glass and cristobalite (silica).

SiO2 Al2O3 FeO MgO Na2O K2O Total

GlassQUE 99059 (n = 2) 77.9 12.9 n.d. n.d. 2.15 6.18 99.1

CristobaliteQUE 99059 (n = 4) 97.5 2.2 0.2 n.d. 0.44 0.13 100.5QUE 97348 (n = 1) 95.7 2.91 0.3 0.03 0.47 0.01 99.4

n.d. = not detected.


Comparison of the QUE Meteorites to Other Enstatite

Meteorites

There are general similarities between the QUEsand other anomalous enstatite meteorites (HappyCanyon, Zaklodzie, NWA 4301, Ilafegh 009, LEW88055, Mt. Egerton, Shallowater) and the aubrites.However, there are differences that make it difficult torelate them to each other in a petrogenetic sense, andthus it is likely that they come from distinct parentbodies (e.g., Keil 2010). Still, the possibility remainsthat some of these meteorites could come from a singleparent body on which melting and localized re-equilibration during crystallization gave rise to spatiallyheterogeneous lithologies. We compare these meteoritesto the QUEs in Appendix S2. We find that HappyCanyon, Zaklodzie, and NWA 4301 are similar to eachother, and probably constitute a new grouplet.

NWA 2526 and ItqiyNWA 2526 (Keil and Bischoff 2008) and Itqiy

(Patzer et al. 2001) are coarse-grained achondriticenstatite meteorites whose textures look remarkablysimilar to those of QUEs 94204, 97289, 97348, 99158,and 99387. The similarities between NWA 2526and QUE 94204 were pointed out by Izawa et al.(2011). NWA 2526 consists predominantly of enstatite(85 vol%), metal (10 vol%), and weathering products.A striking difference between NWA 2526 and the QUEsis that the former contains no plagioclase, and only

trace amounts of troilite, whereas the QUEs contain anabundance of both. The Si-content and siderophile traceelement patterns of metal in NWA 2526 are differentfrom those of the QUEs. NWA 2526 metal contains onaverage 5 wt% Si versus approximately 2.4 wt% in theQUEs. The NWA 2526 metal is enriched in compatiblesiderophile elements (Re, Os, Ir, Ru) relative to CI,whereas the QUEs are depleted (Fig. 6). Itqiy appearsto be identical to NWA 2526 in many respects,

Table 6. Average compositions (wt%) of sulfides.

n Fe Cr Mn Ti Ni Mg S Total

Atomic proportionsbased on 1 S

Fe Mn, Cr Mg

Troilitea

QUE 94204 4 60.8 1.18 0.05 1.68 0.05 n.d. 37.1 100.8QUE 97289 4 59.5 0.80 0.04 2.01 0.03 n.d. 36.7 99.1QUE 97348 3 61.1 0.90 0.06 1.59 0.06 n.d. 37.0 100.8

QUE 99387 5 59.7 0.91 0.04 1.54 0.04 n.d. 37.4 99.6QUE 99059 16 60.6 1.34 0.09 1.25 0.04 n.d. 37.2 100.5QUE 99122 6 60.5 1.57 0.08 0.80 0.02 n.d. 37.4 100.3

QUE 99157 5 58.1 1.57 0.07 1.66 0.06 n.d. 37.5 99.0Daubr�eeliteQUE 94204 3 17.0 35.4 2.28 0.10 n.d. n.d. 44.5 99.3

QUE 99387 3 18.1 35.2 1.92 0.10 n.d. n.d. 44.9 100.3QUE 99059 3 17.4 35.3 2.18 0.10 n.d. n.d. 44.7 99.6QUE 99122 3 18.3 34.9 1.68 0.06 n.d. n.d. 44.3 99.2

QUE 99157 4 18.8 33.8 2.08 0.15 n.d. n.d. 44.3 99.2NiningeriteQUE 99387 2 17.8 1.22 22.8 n.d. n.d. 13.5 43.8 99.1 0.23 0.33 0.41QUE 99059 1 20.7 0.51 21.8 n.d. n.d. 13.1 43.0 99.1 0.28 0.30 0.40

n.d. = not detected.aSee text for discussion of Cr.

0.0

0.5

1.0

1.5

2.0

2.5

W Re Os Ir Ru Pt Rh Mo Ni Co Pd Fe Au As Cu Ga Ge

Ni-,

CI-n

orm

aliz

ed a

bund

ance

s

QUE 99122QUE 94204QUE 97289NWA 2526Bulk EH metalBulk EL metal

Fig. 6. Mean siderophile trace element patterns of Fe,Nimetal. NWA 2526 from Humayun et al. (2009). Bulk EH andEL metal from Kong et al. (1997).


although it has less Si in metal (average Si = 3.1 wt%).Both NWA 2526 and Itqiy have been interpreted asresidues of partial melting that lost plagioclase-richliquids (Patzer et al. 2001; Keil and Bischoff 2008).Siderophile trace element patterns of NWA 2526 andItqiy are enriched in elements that act compatibly in thepresence of solid-liquid metal; that is, Re, Os, Ir, Ru,and Pt are interpreted to have remained in the solidresidue during partial melting (Patzer et al. 2001;Humayun et al. 2009). In contrast, the trace elementpatterns of metal (and presence of plagioclase andtroilite) in the QUEs do not support their petrogenesisas partial melt residues.

Petrogenesis of the QUE Meteorites

Features that Indicate that the QUE Meteorites AreMelt-Rocks

The QUE meteorites are melt-rocks that representcrystallization products of complete or near-completemelts. This is evident because of the following:

The orthocumulate-like texture of several of theQUEs is characteristic of rocks that crystallized frommagma. These meteorites are probably not crystal-

settled cumulates, but they resemble rocks thatcrystallized from liquids and are dominated by largeequigranular crystals of a major mineral, whereas lessabundant lower temperature minerals fill in theinterstitial space.

The normal zoning of plagioclase feldspar isconsistent with crystallization from a liquid.

Cristobalite is the highest-temperature (low-pressure) polymorph of the silica minerals (e.g., Deeret al. 1992). b-cristobalite has a primary stability fieldbetween molten silica (1726 °C) and tridymite(1470 °C). b-Cristobalite will thus crystallize directlyfrom a liquid at high temperature. It inverts uponcooling to a-cristobalite at approximately 250 °C. Thepresence of a-cristobalite in the QUEs is consistent withinitial crystallization of silica at high temperature andinversion at lower temperature.

Inclusions of Al-alkali-rich silica glass, troilite, andmetal inside enstatite are commonly observed inenstatite meteorites that crystallized from completemelts. For example, Ilafegh 009 (total impact melt;McCoy et al. 1995) and Bishopville (aubrite; Fuchs1974) among others. Likewise, inclusions of sulfides andmetal inside the QUE enstatite are consistent withimmiscible liquids being trapped during crystallizationof a silicate liquid.

The QUE Meteorites Are Mostly Unfractionated Melts(And Thus Probably Formed by Impact Melting)

Partial melting caused by metamorphism fractionatesmodal abundances of minerals. In ordinary chondritepartial melting, local melt migration via veins starts at>5% melting, while efficient extraction of melt takesplace at roughly 10–20% melting (McCoy et al. 1997).Metal and troilite are the first to start melting, followed

Fig. 7. Comparison of grain sizes and textures between a) Y-793225 and b) QUE 94204. Metal in white; silicates in darkgray; sulfides and iron oxide in light gray; graphite in black.

QUE 94204 QUE 99059 QUE 99387 Y-793225 Blithfield Itqiy Norton County

Alabandite

NiningeriteKeilite

Mn,Ca,Cr

Fe Mg

Fig. 8. Compositions (atom%) of monosulfides in meteoritesfrom this study compared to other enstatite meteorites.Y-793225 from Lin and Kimura (1998); QUE 94204 fromWeisberg et al. (1997); Blithfield from Rubin (1984); Itqiyfrom Patzer et al. (2001); Norton County from Okada et al.(1988); and Wheelock et al. (1994).


by plagioclase. Upon melt extraction, troilite andplagioclase are almost absent from the residue. Incontrast, impact melting is understood to preservechondritic modal abundances, because impact melts coolquickly at high temperature (e.g., Keil 2007) and thusprevent segregation of metal and silicate (e.g., Ilafegh009). The modal abundances of plagioclase, troilite, andmetal can thus be used to determine if fractionation, andhence partial melting, took place or not.

In Table 7, we summarize modal abundancedata for plagioclase, troilite, and metal. For EL3 andEL6 chondrites, as well as impact melts, plagioclaseranges from approximately 10 to 15 vol%, troilite has alarge range with perhaps bimodal populations at

approximately 4 vol% and 10 vol%, and metal averagesapproximately 10 vol%. QUEs 94204, 97289, 97348,and 99387 have plagioclase contents that are within10–15 vol%. They are thus unfractionated in terms ofplagioclase. Their troilite abundances are slightly belowthe 4 vol% baseline. Their metal contents are bimodalapproximately 5 vol% (QUEs 97348 and 99387) andapproximately 10 vol% (QUEs 94204 and 97289). Theyhave slightly fractionated metal content, but note it issimilar to the EL3 impact-melt breccia MAC 02839.QUEs 99059 and 99122 have a depleted plagioclasecontent by a factor of approximately two, troilite that isunfractionated, and metal that is enriched by factors ofapproximately two and three. QUE 99157 hasunfractionated plagioclase, slightly fractionated troilite,and depleted metal by a factor of approximately three.

Some of the QUEs are clearly unfractionatedrelative to enstatite chondrites, and must thereforerepresent isochemical, total-melt rocks. The meteoritesthat do show slightly fractionated mineralogy remainbroadly chondritic (much more so than residues ofpartial melting like NWA 2526 and Itqiy; see Table 7).The fact that the QUEs have essentially chondriticmodal abundances, while at the same time being totalor near-total melt-rocks, means that they cannot beproducts of partial melting. They must be impact melts.

The textures of QUEs 94204, 97289, 97348, 99158,and 99387 indicate that, after rapid initial cooling(possibly indicated by captured melt inclusions insideenstatite), slow cooling and annealing must have takenplace. The textures of QUEs 99059 and 99122 are more“chaotic,” but the large enstatites must also haveundergone slow cooling and annealing.

Finally, note that Izawa et al. (2011) argued thatQUE 94204 is a highly metamorphosed and partiallymelted (residue) similar to NWA 2526 (Keil andBischoff 2008). We have shown in the above sectionswhy we believe that QUE 94204 and the other QUEsare products of impact melting. In Appendix S3, wediscuss Izawa et al. (2011) interpretations of thepetrology of QUE 94204 and offer counterarguments.

The Identity of the Chondrite Precursor to the QUE

Meteorites

Meteoriticists often try to link enstatite chondrite-related meteorites to EH or EL parent bodies based on theSi-contents of kamacite, the identity of monosulfidephases, and the compositions of other minerals. There is,however, a complication that renders any suchclassification of melt-rocks (such as the QUEs) unreliable.Given that chondrites form as unequilibrated rocks, it isinevitable that repartitioning of elements will occur duringmelting and subsequent crystallization (i.e., thermal re-

Table 7. Modal abundances (vol%) in enstatitemeteorites, of minerals that are first to melt andfractionate during partial melting.a

Plagioclase Troilite Metal

EL3 impact-melt brecciasb

MAC 02839 14.9 4.1 6.7EET 90299 14.7 4.1 15.2

QUE 94594 4.8 2.6 9.5Grein 002 10.5 10 13.8

Impact meltsc

Ilafegh 009 9.7 6.5 12.7

Y-8414 11.9 5.2 10.1Y-86004 10.4 15.2 10.8Y-82189 9.7 11.8 12.9

Petrologic type 6d

Y-793225 13.2 4.8 9.4Jajh deh Kot Lalu 14.4 3.3 6.2

Residues of partial meltinge

NWA 2526 0 <1 10–15

Itqiy 0 <1 14.3–22

QUE meteoritesd

QUE 94204 10.6 2.6 10.4QUE 97289 12.5 1.6 9.4

QUE 97348 14.8 2.4 5.4QUE 99387 11.3 3.4 4.7QUE 99059 4.7 6.4 21.2QUE 99122 5.9 3.2 34.8

QUE 99157 9.8 2.4 3.9aFor literature data where weathered metal abundances were

reported, we reconstructed the weathered metal as unweathered

metal, as described in the text and Table 1.bMAC, QUE, and EET from Van Niekerk and Keil (2011); Grein

002 from Patzer et al. (2004).cIlafegh 009 recalculated from McCoy et al. (1995) wt% data with

bulk density from Macke et al. (2010). Note that the metal mode

includes minor schreibersite; Yamato meteorites from Lin and

Kimura (1998).dY-793225 & QUE meteorites from this study; JdKL from Van

Niekerk and Keil (2011).eNWA 2526 from Keil and Bischoff (2008); Itqiy from Patzer et al.

(2001) and the Meteoritical Bulletin Database.


equilibration) on the parent body. Changes in the oxygenfugacity may also occur in this manner, and alter thecompositions of phases. For example, McCoy et al. (1999)observed that during partial melting experiments onIndarch, SiO2 in melts was reduced by C from the matrix,leading to an increased Si-content of the metal.

The identity of the monosulfide phase (niningerite/alabandite) may also no longer be an accurate indicatorof the precursor parent body’s identity. Weisberg et al.(1997) note that QUE 94204 monosulfide compositionsare unique. There are, in fact, other meteorites thatcontain monosulfides similar to QUE 94204 (Fig. 8) withMg:Mn close to 1. Blithfield (EL6 and/or impact-meltbreccia) contains monosulfides that range in compositionfrom very low Mg:Mn (alabandite) to slightly >1:1 Mg:Mn (barely niningerite). Norton County (aubrite)contains monosulfides that range in composition fromvery high Mg:Mn (niningerite) to slightly >1:1 Mg:Mn(barely niningerite). Itqiy, which is a partial melt residue(Patzer et al. 2001), contains monosulfides (with Cr- andCa-contents of several percent) that plot both in thealabandite and niningerite fields. The point is that, inmelt-rocks, the composition of the monosulfide phasereflects the post-melting cooling rate (Skinner and Luce1971; Keil 2007) as well as the extent to which Mnhas equilibrated between enstatite and sulfides (Rubin2008); extreme ranges in alabandite and niningeritecompositions within a single meteorite (as pointed outabove for Blithfield, Norton County, and Itqiy) attest tothis. It is thus evident that alabandite in ELs orniningerite in EHs may be compositionally altered duringmelting and resolidification to the extent that the newcomposition may overlap the alabandite/niningeritephase boundary (i.e., Mg:Mn = 1).

Thus, the fact that the QUEs have a similar Si-content of metal as well as niningerite in common withEHs, and manganoan daubr�eelite in common with ELs,does not necessarily mean that the precursors to thesemeteorites represent a new grouplet intermediate to EHsand ELs. The compositions of the phases probablyreflect thermal re-equilibration on the parent body,which could have been EH-like, EL-like, or ofpreviously unsampled composition.

Bulk compositions of the QUEs calculated bymodal abundance and mineral chemistry fall slightlyoutside of the EH and EL fields in Mg/Si versus Al/Sispace. No firm conclusions can be drawn, when takinganalytical uncertainties into account, with respect to theprecursor parent body’s identity.

SUMMARY AND CONCLUSIONS

We presented new data for QUE 94204, and datafor QUEs 97289/97348/99122/99157/99158/99387 for the

first time. We also presented new data for Y-793225,which has previously been suggested to form a newgrouplet with QUE 94204. We conclude that Y-793225and QUE 94204 are unrelated, and that aside from theSi-content of its kamacite and Ti in troilite, Y-793225resembles an EL6.

Petrographically, QUE 94204 is similar to QUEs97289, 97348, 99158, and 99387. QUEs 99059 and99122 are similar. QUE 99157 is slightly different fromthe others. Despite minor differences in texture andmodal abundances, these meteorites are all probablypaired. The differences can probably be ascribed toheterogeneous (“messy”) melting and crystallization.The mineral chemistries of the meteorites are essentiallythe same, as are the trace element compositions of thekamacite.

QUE 94204 has previously been interpreted as aresidue of partial melting, based on certain observationsand a textural comparison to NWA 2526. The strongestand most direct evidence that NWA 2526 is a productof partial melting is a fractionated composition with acomplete absence of plagioclase (and essentially troilite).QUE 94204, however, is unfractionated. The traceelement composition of its metal also stands in contrastto the residue signature of metal compositions in NWA2526. While some other QUEs are slightly fractionated,they are still broadly chondritic, and their siderophiletrace element patterns support the same petrogenesis asQUE 94204. In keeping with the principle of parsimony,we have to ask which is more likely? That partialmelting produced a large volume of melt that wasunaccompanied by significant melt extraction, or thatthe broadly unfractionated compositions are the resultof impact melting and crystallization, which preservedchondritic mineral proportions? We think that thecharacteristics of the QUEs are best explained byisochemical crystallization of a total impact melt withan initially rapid cooling rate followed by subsequentlyslower cooling. Note that the textures of the QUEs aredifferent from those of other impact melts (e.g., Ilafegh009); this may merely indicate different postimpactcooling histories. It is possible that in the QUEs heatingby live radionuclides may have eased melting by impactand facilitated slower cooling after rapid initial cooling.The precursor material of the QUEs was a type ofenstatite chondrite, but an exact parent body cannot bededuced with certainty. In terms of a taxonomicclassification of these paired finds, Izawa et al. (2011)made a case that “primitive enstatite achondrite” isappropriate and independent of petrogenesis. We agreethat this is a desirable term in a descriptive sense. Wecaution, however, that in practice the term “primitiveachondrite” often has the connotation of “residue ofpartial melting,” which we contend is inappropriate for


the QUEs. Therefore, “anomalous enstatite meteorite”could be considered an alternative.

Acknowledgments—We thank the following persons andinstitutions for providing meteorite sections: Curationstaff, NASA Johnson Space Center and SmithsonianInstitution; Dr. Ralph Harvey and ANSMET; NationalInstitute of Polar Research, Japan; Dr. Tony Irving,University of Washington. We thank Drs. Gary Huss,Jeff Taylor, and David Muenow (sadly, he passed awayduring 2013) for discussions and informal reviews ofportions of the manuscript. We thank the associateeditor Dr. Cyrena Goodrich and reviewers Drs.Timothy McCoy, Alan Rubin, Jason Herrin, and ananonymous reviewer for their professional reviews. TheNASA cosmochemistry program is thanked for supportthrough grants to Klaus Keil (NNX08AE08G) andMunir Humayun (NNX10AI37G). This is HawaiiInstitute of Geophysics and Planetology publication no.2023 and School of Ocean and Earth Science andTechnology publication no. 9036.

Editorial Handling—Dr. Cyrena Goodrich

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SUPPORTING INFORMATION

Additional supporting information may be found inthe online version of this article:

Appendix S1: Modal abundance of plagioclase inY-793225.

Appendix S2: Comparison of the Queen AlexandraRange meteorites to other anomalous meteorites.

Appendix S3: Arguments against a metamorphicand partial melting origin of the Queen AlexandraRange meteorites.


Documents

Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their relation to enstatite chondrites, primitive enstatite achondrites, and aubrites