Petrology and Mineralogy of the Ningqiang Carbonaceous Chondrite

Meteoritics & Planetary Science 44, Nr 5, 763–780 (2009) Abstract available online at http://meteoritics.org

Petrology and mineralogy of the Ningqiang carbonaceous chondrite

Ying WANG1 and Weibiao HSU1, 2*

1Laboratory for Astrochemistry and Planetary Sciences, Lunar and Planetary Science Center, Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China 2Faculty of Earth Science, China University of Geosciences, Wuhan 430074, China *Corresponding author. E-mail: [email protected] (Received 08 August 2008; revision accepted 07 March 2009) Supplementary material is available online at http://meteoritics.org/Online%20Supplements.htm

Abstract–We report detailed chemical, petrological, and mineralogical studies on the Ningqiang carbonaceous chondrite. Ningqiang is a unique ungrouped type 3 carbonaceous chondrite. Its bulk composition is similar to that of CV and CK chondrites, but refractory lithophile elements (1.01 × CI) are distinctly depleted relative to CV (1.29 × CI) and CK (1.20 × CI) chondrites. Ningqiang consists of 47.5 vol% chondrules, 2.0 vol% Ca,Al-rich inclusions (CAIs), 4.5 vol% amoeboid olivine aggregates (AOAs), and 46.0 vol% matrix. Most chondrules (95%) in Ningqiang are Mg- rich. The abundances of Fe-rich and Al-rich chondrules are very low. Al-rich chondrules (ARCs) in Ningqiang are composed mainly of olivine, plagioclase, spinel, and pyroxenes. In ARCs, spinel and plagioclase are enriched in moderately volatile elements (Cr, Mn, and Na), and low-Ca pyroxenes are enriched in refractory elements (Al and Ti). The petrology and mineralogy of ARCs in Ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes. We found 294 CAIs (55.0% type A, 39.5% spinel-pyroxene-rich, 4.4% hibonite-rich, and several type C and anorthite-spinel- rich inclusions) and 73 AOAs in 15 Ningqiang sections (equivalent to 20 cm2 surface area). This is the first report of hibonite-rich inclusions in Ningqiang. They are texturally similar to those in CM, CH, and CB chondrites, and exhibit three textural forms: aggregates of euhedral hibonite single crystals, fine-grained aggregates of subhedral hibonite with minor spinel, and hibonite ± Al,Ti-diopside ± spinel spherules. Evidence of secondary alteration is ubiquitous in Ningqiang. Opaque assemblages, formed by secondary alteration of pre-existing alloys on the parent body, are widespread in chondrules and matrix. On the other hand, nepheline and sodalite, existing in all chondritic components, formed by alkali-halogen metasomatism in the solar nebula.

INTRODUCTION Ningqiang fell on 25 June 1983 in Ningqiang County, Shanxi Province of China. It shares similar petrologic and Chondrites consist mainly of chondrules (<5–80 vol%), mineralogic characteristics with oxidized CV and CK refractory inclusions (<0.01–13%), metallic Fe-Ni (<0.01– chondrites (Kallemeyn and Rubin 1987; Kallemeyn et al. 70%) and fine-grained matrix material (<0.1–95%) (Scott and 1991), but exhibits unique features that differ from any known Krot 2005). Chondrules, refractory inclusions and metallic subtype of carbonaceous chondrites. Ningqiang has a lower Fe-Ni formed in the early solar system by high-temperature abundance of Ca,Al-rich inclusions (CAIs) and a higher processes, such as condensation, evaporation and melting. abundance of amoeboid olivine aggregates (AOAs) than Matrix, which rims other components and fills interstices typical CV3 chondrites (Rubin et al. 1988). As a result, among them, formed under low-temperature conditions. Ningqiang has lower abundances of refractory lithophiles Chondrites are the oldest rocks in the solar system and than CV and CK chondrites (Rubin et al. 1988). In Ningqiang, preserve rich information about the origin and evolution of the abundances of moderately volatile lithophile and the early solar system. Studies on different types of chondrites siderophile/chalcophile elements are similar to those of CO expand our knowledge about the variety and distribution of chondrites, but the highly volatile elements are higher than chondritic components in the early solar system, and enable those of COs (Kallemeyn 1996). The carbon content of us to link chondrite groups with asteroid classes. Ningqiang, close to the range of CM2 and CR2 chondrites, is

763 © The Meteoritical Society, 2009. Printed in USA. 764 Y. Wang and W. Hsu significantly higher than that of CV and CK chondrites dissolved by 10 vol% hydrochloric acid (HCl) at 70 °C. Then (Kallemeyn 1996). The bulk oxygen isotopic composition of the solution was set to 100 ml in a volumetric flask for ICP- Ningqiang is more 16O-rich than Allende, a typical CV3 AES measurement. Lithium tetraborate was used as an chondrite (Weisberg et al. 1996). Thermoluminescence (TL) internal standard. GSD-6 (aquatic sediment) and GSR-2 characteristics of Ningqiang are similar to those of CV (andesite) from the National Research Center for Certified chondrites (Guimon et al. 1995). Ningqiang has been Reference Materials were used as an external standard and a classified as a CV anomalous, CK anomalous, and finally an comparison standard, respectively. The optimal operating ungrouped carbonaceous chondrite (Rubin et al. 1988; conditions for the instrument were summarized by Wu et al. Kallemeyn et al. 1991; Kallemeyn 1996). (2007). Ningqiang is such a unique chondrite that it has invoked Minor and trace element concentrations of Ningqiang great interest among researchers (Rubin et al. 1988; Kimura were determined with a Finnigan Element II high-resolution et al. 1997; Lin and Kimura 1997, 2000; Nakamura et al. inductively coupled plasma mass spectrometer (ICP-MS) at 2003; Zolensky et al. 2003). The first occurrences of Ca-rich Nanjing University, China. 50 mg of Ningqiang powders armalcolite and geikielite in a meteorite, and the second were digested in a capped Teflon beaker with mixed acids of ° occurrence of phase T (an unidentified titanium mineral concentrated HF and HNO3 at a temperature of ~190 C for series) were reported in plagioclase-olivine inclusions of 24–48 hours. After total dissolution, the sample was exposed Ningqiang (Lin and Kimura 1997). A dark inclusion in to the air and evaporated to almost dryness. Finally, the % Ningqiang contains highly primitive solar nebular material residue was redissolved by 5 ml 30 vol HNO3, and then % (Zolensky et al. 2003) and high concentrations of heavy diluted to 15 ml in 3 HNO3. Rhodium of 10 ppb was spiked primordial rare gases (Nakamura et al. 2003). However, in the as an internal standard. The instrument was optimized with various works recently carried out on Ningqiang, detailed multi-elemental standard solutions. The analytical procedures petrologic and mineralogic studies were still limited. Works were described by Jiang et al. (2004). Samples of Allende of Rubin et al. (1988) and Kimura et al. (1997) are among the meteorite were treated and analyzed in the same way for most comprehensive petrologic and mineralogic studies on comparison. Ningqiang, but were merely done on 3 and 2 sections, respectively. With the advantage of a large amount of the type Petrography and Mineralogy specimen in house, we have initiated a series of studies on the Ningqiang chondrite (Hsu et al. 2003, 2006; Wang et al. 2006, All Ningqiang sections were examined with a Nikon 2007). To gain a deeper insight into this unique meteorite and E400 POL optical microscope and a Hitachi S-3400N a better understanding of the variety of materials in the early scanning electron microscope (SEM) equipped with an solar system, we made extensive petrologic and mineralogic OXFORD INCA7021 energy dispersive spectroscopy (EDS). observations on Ningqiang. In this work, the mineral To search for refractory inclusions and Al-rich chondrules, chemistry, petrology, and bulk composition of Ningqiang are automatic X-ray mapping analyses were carried out on each reported. section with a resolution of 2–5 µm/pixel. Back scattered electron (BSE) images were obtained at an accelerating SAMPLES AND EXPERIMENTS voltage of 15 kV. Elemental maps were mixed by INCA software using an RGB color scheme. Modal abundances of Six polished thick sections and nine polished thin Ningqiang components were estimated from BSE images and sections (equivalent to 20 cm2 surface area) were prepared for X-ray elemental maps by pixel-counting with a commercial petrographic and mineralogical observations. About 1.5 g of software, assuming that area fractions equal to volume fresh fragments were sampled randomly from the interior and percentages. crushed in an agate mortar into ~200 mesh powders for bulk In situ compositional analyses were performed with chemical analyses. electron microprobes (EMPs) at China University of Geosciences, Wuhan (JEOL JXA-8100M), and Nanjing Bulk Chemistry University (JEOL JXA-8800M). Working conditions are as following: 15 kV accelerating voltage, 10–20 nA beam Major element concentrations of Ningqiang were current, focused beam for mineral analyses, and defocused measured with a mono-channel scanning inductively coupled beam of 10–20 µm diameters for bulk chemical analyses of plasma atomic emission spectrometer (ICP-AES, model various chondritic components. Both synthetic (NBS) and JY38S) at the State Key Laboratory for Mineral Deposits natural mineral standards were used. ZAF corrections were Research, Nanjing University, China. Mixed powders of applied. The detection limits for the analyzed elements are (in 0.1000 g Ningqiang and 0.2500 g lithium tetraborate wt%): sulfur, cobalt, chlorine, and K2O, 0.01; Na2O, MgO, (Li2B4O7) in a graphite crucible were heated in a muffle furnace CaO, Al2O3, phosphorus and nickel, 0.02; Cr2O3, FeO, and at 1000 °C for ~15 minutes. After melting, the sample was MnO, 0.03; TiO2 and SiO2, 0.04. Petrology and mineralogy of the Ningqiang carbonaceous chondrite 765

RESULTS up to 5.5 mm. The mean diameter is ~550 µm (average of 122 chondrules), smaller than those of CV (1.0 mm) and CK Bulk Composition (0.7 mm) chondrites (Brearley and Jones 1998). Various types of chondrules are present, such as barred olivine (BO), radical Averages of duplicate analyses of Ningqiang determined pyroxene (RP), porphyritic, granular, cryptocrystalline, and by ICP-AES and ICP-MS are listed in Table 1. Abundances of compound (Fig. 2). Porphyritic chondrules (Fig. 2a) are the most major elements (except P) obtained in this work are most abundant. Granoblastic chondrules (Fig. 2b) are rare. RP within ±5% of the range of previous analyses, and chondrules consist of radiating needles of inter-layered abundances of other elements are within ±20% except the enstatite and diopside. BO chondrules are often enclosed by trace elements of Zn, Rb, Y, Tb, Tm, Pb, and U (Chai et al. later-formed porphyritic ones, thus occurring as compound 1986; Rubin et al. 1988; Wang and Lin 2007). The chondrules (Fig. 2d). Many chondrules are surrounded by discrepancies may result from analytical uncertainties and/or fine-grained accretionary rims (Fig. 2d). Chondrules with sample heterogeneity. Relative to Ningqiang, the analyses of coarse-grained igneous rims are much less common in Allende show higher abundances in nearly all refractory Ningqiang (~5% of all chondrules) than in CV3 chondrites lithophile elements except La (0.48 ppm in Ningqiang versus (~50%) (Rubin 1984). 0.44 ppm in Allende), Pr (0.17 versus 0.17 ppm), and Eu (0.10 Most chondrules in Ningqiang are Fe-poor type I versus 0.10 ppm). chondrules. They are mainly composed of forsteritic olivine The CI-, Mg-normalized elemental abundance pattern of (mean Fa4.5, Table A1 [all supplementary material is available Ningqiang is shown in Fig. 1. It is clear that the bulk online at http://meteoritics.org/Online%20Supplements.htm]) composition of Ningqiang is distinct from those of CV or CK and/or low-Ca pyroxenes (defined as pyroxenes with Wo <15; chondrites, and closer to the latter. Ningqiang is depleted in mean En96.7Wo2.1, Table A2) with minor phases such as high- refractory lithophile elements (1.01 × CI on average) relative Ca pyroxenes (Wo > 15), plagioclase, oxides (magnetite, to CK (1.20 × CI) and CV (1.29 × CI) groups. The rare earth spinel and chromite), Fe,Ni metals, and sulfides. Only four element (REE) pattern of Ningqiang shows an enrichment of Fe-rich type II chondrules were found in this work. One is light REEs [(La/Lu)CI = 1.21], while REE patterns of CV (1.05) composed of granular olivine (Fa23.0) and Fe-rich enstatite and CK (1.09) chondrites are nearly flat. Moderately volatile (En76.5Wo5.0, Table A2); and the other consists of euhedral to lithophile elements (Mn, K, and Zn) are depleted in subhedral zoned olivine (Fa23.0) phenocrysts and accessory Ningqiang relative to those in CV and CK chondrites, chromite, Fe,Ni metal and sulfides. The third one is composed although Na is slightly enriched (1.11 × CK; 1.06 × CV). The of more ferrous olivine with a Fa value up to ~45. The last one refractory to moderately volatile siderophile and chalcophile is a barred olivine chondrule with a mean Fa of 10.8. elements in Ningqiang show a roughly volatility-controlled Opaque minerals in chondrules appear as discrete grains, abundance pattern similar to that of the average CV. The opaque nodules (Fig. 2a), or complex opaque assemblages abundances of W, Fe, Sn, Bi, and Pb are higher in Ningqiang (Fig. 2b–d). Modal abundances of opaque minerals in than in CV and CK chondrites, while abundances of other chondrules vary from almost 0 to over 50 vol%. elements are relatively lower. The exceptionally high content Mesostasis in most Ningqiang chondrules exhibits of Fe in our analyses of Ningqiang could be due to the over- varying textures and compositions (Fig. A1 [available online sampling of metallic grains. at http://meteoritics.org] and Table A3). It appears as patches of devitrified holocrystalline minerals (Fig. A1a), or contains Petrography microcrystalline to glassy phases with lamellar, dendritic or worm-like textures (Fig. A1b–d). Some glassy phases have All chondritic components are present in Ningqiang, compositions close to pure minerals. For example, glass-1, -2, including ferromagnesian and Al-rich chondrules, CAIs, and -3 in Fig. A1c have anorthite-, Al-rich diopside (Al- % AOAs, dark inclusions, opaque assemblages, matrix and diopside, defined as diopside with Al2O3 > 8 wt )-, and matrix-like fine-grained rims. Modal analyses of Ningqiang hedenbergite-like compositions, respectively (Table A3). The reveal 47.5 vol% chondrule, 2.0 vol% CAI, 4.5 vol% AOA and major mineral phases in mesostasis are anorthite, Al-diopside % % 46.0 vol matrix. The chondrule abundance of Ningqiang is (with Al2O3 up to 10.4 wt ) and pigeonite. Minor amounts of close to that of the CV group (45%) but much higher than that nepheline and sodalite replaced anorthite and anorthitic of the CK group (15%); the matrix content is close to that of glasses. Bulk compositions of mesostasis vary from Ca, Al- CVs (40%) but much lower than that of CKs (75%); the rich to Si, Mg-rich within a given chondrule and among refractory inclusion abundance is intermediate between those different chondrules (Table A3). of CVs (10%) and CKs (4%) (Brearley and Jones 1998). Al-Rich Chondrules Ferromagnesian Chondrules Three Al-rich chondrules (ARCs) were found in this Chondrules in Ningqiang are well-defined round to study. Two are plagioclase-olivine-rich chondrules similar to subround objects, ranging in size from several tens of microns those reported by Lin and Kimura (1997); the third (Fig. 3) is 766 Y. Wang and W. Hsu

Table 1. Bulk chemistry of Ningqiang, CV and CK chondrites (in ppm except as noted). This work* From literature Ningqiang Allende Ningqiang(1) Ningqiang(2) Ningqiang(3) CV(4) CK(5) Si (%) 17.19 15.6 Ti (%) 0.078 0.081 0.082 0.098 Al (%) 1.47 1.54 1.45 1.69 1.75 1.61 Fe (%) 27.49 24.5 22.40 26.5 23.5 23.6 Mn (%) 0.15 0.159 0.146 0.146 0.145 0.146 Mg (%) 15.82 15.1 16.00 14.71 14.5 14.8 Ca (%) 1.65 1.61 1.60 1.73 1.90 1.72 Na (%) 0.38 0.376 0.370 0.343 0.33 0.319 K(%) 0.025 0.032 0.023 0.031 0.031 0.028 P(%) 0.092 0.10 0.099 Sc 9.06 10.78 9.71 9.63 12.1 11.4 11.0 V 91.48 109.33 85 71 80.8 96 96 Cr (%) 0.324 0.344 0.364 0.394 0.370 0.360 0.366 Co 566 553 679 619 763 655 637 Ni 11405 12103 13600 13300 12700 13400 12700 Cu 85.0 81.1 91 110 100 Zn 86.7 81.8 131 123 116 98 Ga 6.18 5.85 6.2 6 5.5 Rb 1.51 1.32 1.18 1.25 Sr 11.82 12.33 11.08 16.1 15.3 Y 2.00 2.30 2.87 2.4 Zr 6.77 7.20 7.33 8.3 Nb 0.45 0.50 0.49 (0.54) Mo 1.53 2.72 2.10 Cd 0.11 0.25 0.373 Sn 0.71 1.26 0.90 Cs 0.10 0.10 0.08 0.095 Ba 5.93 5.57 5.06 4.9 La 0.48 0.44 0.397 0.45 0.64 0.486 0.462 Ce 1.17 1.21 1.15 1.72 1.290 Pr 0.17 0.17 0.18 0.200 Nd 0.85 0.88 0.90 0.88 0.990 Sm 0.24 0.27 0.242 0.28 0.30 0.295 0.284 Eu 0.10 0.10 0.098 0.11 0.16 0.113 0.108 Gd 0.34 0.35 0.39 0.415 Tb 0.051 0.057 0.068 0.065 Dy 0.37 0.44 0.44 0.475 Ho 0.089 0.093 0.10 0.110 Er 0.26 0.31 0.30 0.315 Tm 0.041 0.044 0.052 0.045 Yb 0.29 0.30 0.275 0.31 0.20 0.322 0.311 Lu 0.041 0.046 0.041 0.048 0.052 0.048 0.044 Hf 0.17 0.20 0.21 0.194 Ta 0.036 0.037 (0.032) W 0.24 0.28 0.190 Pb 1.69 2.00 1.09 1.4 Bi 0.060 0.047 0.048 Th 0.080 0.067 0.065 0.060 U 0.026 0.024 0.014 0.017 *Results of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P are from ICP-AES analysis; results of other elements are from ICP-MS analysis. Literature: (1) Rubin et al. 1988; (2) Wang and Lin 2007; (3) Chai et al. 1986; (4) Wasson and Kallemeyn 1988; (5) Kallemeyn et al. 1991. mainly composed of spinel, plagioclase, and aluminous- In NQ-PMO-0024 ARC-1, the core is dominated by lathy enstatite (Al-enstatite). They are spheroidal objects (>1 mm) anorthite (up to 1 mm long, An85.9) and euhedral olivine with igneous textures, and exhibit distinct core-mantle (150–300 µm, Fa0.8) phenocrysts, with minor dendritic structures. pigeonite and diopside overgrowing on anorthite. The mantle Petrology and mineralogy of the Ningqiang carbonaceous chondrite 767

Fig. 1. Mg- and CI-normalized bulk elemental abundance patterns of Ningqiang, in comparison with CV and CK chondrites. The black vertical line divides lithophile elements from siderophile and chalcophile ones. The dashed lines separate elements into refractory, main component, moderately volatile, and highly volatile categories from the left to the right. The cosmochemical classification of elements and the CI elemental abundances are from Palme and Jones (2005).

Fig. 2. Backscattered electron (BSE) images of chondrules in Ningqiang. Various types of chondrules present in Ningqiang: a) porphyritic olivine (PO); b) granoblastic porphyritic olivine (GPO); c) cryptocrystalline (C), and d) compound chondrule. Opaque assemblages (OAs) and fine-grained rims (FGRs) are prevalent. Abbreviations: Ch, chondrule; BO, barred olivine. µ is composed of euhedral to subhedral olivine (Fa2.2) and (<40 m, Fa8.5). Anorthite is relatively concentrated in the core, pigeonite grains (En90.9Wo7.7), with pigeonite partly corroded while olivine is abundant in the mantle. Olivines are usually by diopside. In NQ-PMO-0024 ARC-2, two major minerals partly replaced by enstatite and diopside. µ are lathy anorthite (<200 m, An87.4) and granular olivine In NQ-PMO-0026 ARC (Fig. 3), the core is composed of 768 Y. Wang and W. Hsu

Table 2. Types of CAIs in Ningqiang. Type Mineralogy Number % Hib-free Mel-sp-perv ± di-an-ol ± 33 11.2 CTA hed-ne-sod ± metal-mt-sulfide-noble metal alloy Hib-bear- Hib-mel-perv ± sp-di-ol ± 6 2.0 ing CTA ne Hib-free Mel-sp-perv ± di-an-ol ± 47 16.0 FTA hed-ne-sod ± metal-mt-sulfide-noble metal alloy Hib-bear- Hib-sp-mel ± perv ± sod-ne 3 1.0 ing FTA Type A Mel-sp ± perv-di-an-hib-ol 73 24.8 fragment ± hed-ne-sod ± metal-mt- sulfide SPI Sp-di ± perv-ol ± hed-ne- 116 39.5 sod ± metal-mt-sulfide-noble metal alloy ASI An-sp-di ± metal-sulfide 2 0.7 Type C An-sp-di-aug-pig-ne 1 0.3 Hib-rich Hib ± perv-di-mel-sp ± hed- 13 4.4 ne-sod ± metal-mt-sulfide Total 294 100 Abbreviations: hib, hibonite; mel, melilite; perv, perovskite; di, diopside; hed, hedenbergite; ne, nepheline; sod, sodalite; metal, FeNi metal; mt, magnetite; sulfide, FeNi sulfide; aug, augite; pig, pigeonite.

anorthite and mesostasis (Fig. 3b–c). A few olivine grains with round and corroded surfaces are embedded in Al-enstatite. Comparing with ARCs from other chondrites, NQ-PMO-0026 ARC is characterized by its enrichment in Al-enstatite and spinel, and the scarcity of olivine and high-Ca pyroxene.

Amoeboid Olivine Aggregates (AOAs) A total of 73 AOAs were found in Ningqiang, accounting for ~20% of the refractory inclusions. They are irregularly- shaped loose to compact aggregates with sizes ranging from ~100 µm to over 4 mm (Fig. A2). Subhedral to anhedral forsteritic olivine (Fa8.1) encloses accessory anorthite (An99.3), Al-diopside, and Al,Ti-rich diopside (Al,Ti-diopside, i.e., fassaite, defined as diopside with Al2O3 > 8 wt% and Fig. 3. BSE images of the NQ-PMO-0026 Al-rich chondrule (ARC) TiO2 > 3%; with up to 15.0 wt% Al2O3 and 4.4% TiO2) in Ningqiang. The ARC is mainly composed of aluminous-enstatite (Fig. A2b). Spinel is rare in most Ningqiang AOAs, and (Al-en), anorthite, and spinel poikilitically enclosed by Al-en, only occurs as diopside-rimmed nodules in a few spinel- anorthite and mesostasis. Regions outlined in (a) are shown in detail in (b) and (c). Abbreviations: an, anorthitic plagioclase; ol, olivine; rich AOAs (Fig. A2d). Secondary minerals, such as fayalitic sp, spinel; meso, mesostasis. olivine, nepheline, sodalite and hedenbergite, are present. Opaque minerals are rare. anorthite (An87.6), spinel, Al-enstatite (En97.5Wo1.3, with up to 10.9 wt% Al2O3, Table A2) and interstitial mesostasis. The Ca, Al-Rich Inclusions mantle contains Al-enstatite and minor olivine (Fa4.7), metals, A total of 294 CAIs were found in Ningqiang. They sulfides, hedenbergite, nepheline and sodalite. The estimated display a wide range of petrologic types (Table 2). The modal abundances are (in vol%): anorthite, 33; spinel, 25; melilite-rich type A and spinel-pyroxene-rich (SPIs) Al-enstatite, 25; mesostasis, 6; olivine, 1; opaque and secondary inclusions are the most abundant, accounting for 55.0% and minerals, 10. Al-enstatite crystals are radially oriented in the 39.5% of all CAIs observed, respectively. Hibonite-rich mantle, and are intergrown with anhedral anorthite in the core. inclusions account for 4.4%. Type B (melilite-Al,Ti- The longest Al-enstatite lath is ~800 µm long and traverses diopside-anorthite-spinel-rich) inclusions, which are largely almost the entire core. Spinel grains are euhedral to subhedral confined to CV3 chondrites (MacPherson 2005), are (5–15 µm) and poikilitically enclosed by Al-enstatite, basically absent from the sections, although two unusual Petrology and mineralogy of the Ningqiang carbonaceous chondrite 769

Fig. 4. BSE images of fluffy and compact type A inclusions (FTAs and CTAs) in Ningqiang. a–b) An irregularly shaped FTA composed of loose melilite grains with minor perovskite enclosed. c–d) A CTA with Wark-Lovering rims (W–L rims) composed of spinel, melilite, perovskite, diopside, forsteritic and fayalitic olivines. e–f) A CTA composed mainly of sinuous spinel-melilite intergrowths with minor perovskite and noble metal alloys, and mantled by W-L rims. Regions outlined in (a), (c) and (e) are shown in detail in (b), (d), and (f), respectively. Abbreviations: fo, forsteritic olivine; fa, fayalitic olivine.

type B inclusions were reported in Ningqiang by Lin and with fine-grained spinel included (Figs. 5a–b). Loose SPIs are Kimura (2000). CAIs from Ningqiang have smaller sizes aggregates of individual objects that have a spinel core and a than those from CV3 chondrites. Most are tens to hundreds diopside shell (Fig. 5c). Some spinel-dominated compact of microns. Only a few inclusions with fluffy textures reach SPIs are composed of spinel nodules with narrow diopside millimeter sizes. rims. Accessory minerals include perovskite, olivine, and Type A inclusions have two varieties: fluffy (FTA) noble metal alloys (Fig. 5d). Melilite is essentially absent. and compact (CTA) (Fig. 4). FTAs are composed of Type C CAIs are rare in all chondrites (MacPherson loose melilite grains (5–20 µm) with or without perovskite 2005). We only found one fragment (~140 µm) of a type C (Figs. 4a–b). FTA also contains separate aggregates of CAI in this study. Typical type C inclusions normally have melilite + spinel + diopside ± hibonite. CTAs are composed of ophitic or subophitic textures (Brearley and Jones 1998; Lin blocky melilite with enclosed spinel + perovskite ± Al,Ti- and Kimura 1998), but this fragment is composed of blocky diopside ± hibonite (Figs. 4c–d), or of sinuous spinel-melilite anorthite and overgrowing anhedral spinel and pyroxene. intergrowths (Figs. 4e–f). In rare hibonite-bearing type A Pyroxene varies in composition from pigeonite to diopside inclusions, hibonite occurs as euhedral to subhedral platy and Al-diopside. crystals embedded in spinel and melilite. Anorthite-spinel-rich inclusion (ASI) is a rare type CAI Spinel-pyroxene-rich inclusions (SPIs) have compact or reported by Lin and Kimura (1998) in Ningqiang. Two ASIs loose textures and vary from pyroxene-dominated to spinel- were found here. Both are irregularly shaped, fluffy dominated (Fig. 5). Compact SPIs are mostly blocky diopside aggregates of concentric nodules composed, from center to 770 Y. Wang and W. Hsu

Fig. 5. BSE images of spinel-pyroxene-rich inclusions (SPIs) in Ningqiang. a–b) A compact-textured SPI composed of Al-diopside, Al,Ti- diopside, and spinel with forsteritic and fayalitic olivine rims. c) A loose-textured SPI composed of spinel and diopside rims. d) A SPI composed of spinel, Al,Ti-diopside, perovskite, noble metal alloy, and an Al-diopside rim. Region outlined in (a) is shown in detail in (b).

Hibonite-rich CAIs commonly occur in (but are not unique to) CM chondrites (MacPherson 2005), and were also found in Ningqiang. The inclusions vary from ~20 to 400 µm in size, and have three different types: (1) aggregates of euhedral hibonite crystals set in matrix (Fig. 7a) or mantled by multilayered rims (Fig. 7b); (2) irregularly shaped fine-grained aggregates of subhedral to anhedral hibonite with minor spinel grains (Fig. 7c–d); (3) hibonite ± Al,Ti-diopside ± spinel spherules, which had probably crystallized from melt droplets (Fig. 7e–f). Corundum, a rare mineral in hibonite-rich CAIs from CM chondrites, was not found in Ningqiang. There are a few inclusions in Ningqiang that only contain a small proportion of refractory minerals and hence are not real CAIs in the sense of bulk composition. The inclusion in NQ-PMO-0030 is a special example which contains Sc-, Zr-, Y-rich minerals (Fig. A3). In this irregularly-shaped 600 × 900 µm inclusion, about 90 vol% is fayalitic olivine, and 10 vol% is composed of Y-bearing perovskite, IMA 2007– 027 (Sc4Zr3O12, a new mineral approved in 2007; Burke and Hatert 2007), Sc-rich Al,Ti-diopside, Al-diopside, and noble metal alloys. Fine-grained IMA 2007–027 (<2 µm) and noble metal alloys (sub-µm) are enclosed in Y-bearing perovskite Fig. 6. BSE images of an anorthite-spinel-rich inclusion (ASI) in and Sc-rich Al,Ti-diopside. Sc-rich Al,Ti-diopside and Al- Ningqiang. The ASI is composed of numerous concentric objects diopside form 2–5 µm wide rims around Y-bearing perovskite. formed by spinel, anorthite and diopside from the center to the rim. Fayalitic olivine (Fa ) is located outside the diopside layer Region outlined in (a) is shown in detail in (b). ~50 and constitutes the main part of the inclusion. rim, of spinel, anorthite, and diopside (Fig. 6). The sinuous Many CAIs in Ningqiang have experienced multi-stage subtype of ASI observed by Lin and Kimura (1998) was not formation processes and are surrounded by Wark-Lovering found. rims (W-L rims; Wark and Lovering 1977). In multilayered Petrology and mineralogy of the Ningqiang carbonaceous chondrite 771

Fig. 7. BSE images of hibonite-rich inclusions in Ningqiang. a) Single crystals of euhedral hibonite embedded in matrix. b) A compact aggregate of euhedral hibonite plates mantled by a discontinuous layer of melilite and Al-diopside, two continuous layers of diopside and fayalitic olivine from center to rim. c–d) A loose aggregate of fine-grained subhedral to anhedral hibonite and accessory spinel. e) A subround inclusion composed of Al,Ti-diopside and hibonite. f) A fragment of a subround inclusion composed of spinel, hibonite and an Al-diopside rim.

W-L rims, spinel usually occurs in the innermost layer. Perovskite is surrounded by a rim of ilmenite. Fe content is Melilite partly replaced by anorthite appears in the second, higher in rims of spinel grains than in their cores. Calcic and calcic pyroxenes varying from Al,Ti-diopside outwards pyroxenes were altered to ferrous augite and hedenbergite. to diopside are present in the outmost layer (Fig. 4c–f). In Forsteritic olivine was corroded by fayalitic one. Alkali, some W-L rims, perovskite is enclosed in spinel and/or halogen-rich minerals, nepheline and sodalite, are present melilite. Forsterite is dispersed in diopside, and a layer of widely in Ningqiang CAIs. forsteritic and/or fayalitic olivine accompanied by opaque phases overlies the pyroxene layer (Fig. 4d). Most CTAs have Opaque Assemblages diopside rims or multilayered W-L rims (Fig. 4c–f), but W-L Opaque assemblages (OAs), also termed “Fremdlinge” rims are rare in SPI, FTA, and hibonite-rich inclusions and (El Goresy et al. 1978), are components relatively restricted to were not found in other petrologic types of CAIs. CV3 chondrites (Brearley and Jones 1998). However, we Opaque minerals in Ningqiang CAIs include magnetite, found numerous round to oblate OAs in chondrules and Fe,Ni metals and sulfides. Sub-µm metal alloy grains of Ru, matrix of Ningqiang (Figs. 2 and 8). The OAs range in size Re, Os, Ir, and Pt as well as Mo, Y and W are present. from 10 to 600 µm, and most are larger than 100 µm. OAs in Fremdlinge (El Goresy et al. 1978), rich in noble metal Ningqiang are mainly composed of awaruite, magnetite, elements and normally occurring in CAIs of CV3 chondrites pyrrhotite and pentlandite with minor amounts of whitlockite, (Brearley and Jones 1998), is absent in Ningqiang CAIs. phosphoran-olivine and pyroxene. They are mostly Evidence of secondary alteration processes is ubiquitous intergrowing anhedral crystals (Fig. 8a), and their relative in Ningqiang CAIs. Melilite was partly replaced by anorthite. abundances are variable among OAs. Trace amounts of nano- 772 Y. Wang and W. Hsu sized platinum-group metal alloys are included in magnetite inclusions (Fig. A5a). The matrix has heterogeneous grain grains (Fig. 8b). Some OAs in matrix are surrounded by an sizes and porosities, and therefore exhibits darker and lighter olivine layer. OAs in Ningqiang are petrographically similar appearances under reflected light. As shown in Figs. A5b–c, to those previously reported in CV3 chondrites. The main the dark matrix has a coarser mean grain-size and higher difference is that OAs are absent in Ningqiang CAIs but porosity than the light one. The distribution of minerals in present in CAIs from CV3 chondrites. matrix, especially opaque and volatile-rich minerals, is quite uneven, and thereby the compositions of matrix are highly Dark Inclusions variable (Table A4). The matrix surrounding an AOA in NQ- Dark inclusions (DIs) are commonly present in PMO-0024 contains abundant nepheline grains and a few carbonaceous chondrites, especially CVs and CRs. They are metals and sulfides (Figs. A5d). The composition of the angular clasts with dark or fine-grained appearances. They matrix is richer in Na, K, Al and much lower in Fe, Ni, and S display a considerable diversity in textures (A, A/B, B, and C; than that of the average matrix (Table A4). Brearley and Jones 1998). Type A DIs resemble the host Monomineralic grains in Ningqiang matrix are mainly chondrites and consist of chondrules, CAIs, etc. embedded in olivine (Fa0.2–53.8), enstatite, pigeonite, spinel, awaruite, a fine-grained matrix. Type B contains no chondrules and pyrrhotite and pentlandite, which range in size from 20 to CAIs, but consists largely of aggregates of fine-grained over 200 µm (Fig. A5e). Most grains had experienced fayalitic olivine, usually embedded in a matrix of somewhat secondary alteration processes. finer-grained olivine. Type A/B DIs are intermediate between Most chondrules, AOAs, CAIs and monomineralic type A and B. Type C consists exclusively of fine-grained grains in Ningqiang are surrounded by fine-grained rims material without chondrules, CAIs, or mineral fragments. DIs (FGRs), which are matrix-like materials composed of µm to may have been derived from multiple sources and/or have sub-µm fayalitic olivine, pyroxene, magnetite, Fe,Ni-metal experienced complex formation or alteration histories (Krot and sulfides. FGRs have thicknesses from 20 up to 400 µm, et al. 1995). and are thicker at embayments and thinner at projections. Three DIs (0.3–1 mm) were found in Ningqiang matrix. FGRs have bulk compositions similar to that of the mean They are all type C DIs composed of fine-grained materials matrix, but are slightly enriched in Na and Al and depleted in (Fig. A4). Two DIs in NQ-PMO-1021 are dominated by Mg and Ca (Table A4). diopside (<6 µm), with accessory hedenbergite, fayalitic olivine and nepheline (Figs. A4a–b). The NQ-PMO-1012 DI Mineral Chemistry is highly enriched in alkalis and halogens. It is composed of abundant subhedral to anhedral nepheline (15 vol%) and The Fa histogram of olivines (Fig. 9) shows that the sodalite (10 vol%), porous diopside (30%), platy fayalitic majority of olivine in Ningqiang is Mg-rich (Fa < 10), with a % µ olivine crystals (10 ), and sub- m matrix-like mesostasis few having compositions spreading up to Fa60. Olivines in (35 vol%) (Figs. A4c–d). All three DIs show irregular type I chondrules, ARCs and AOAs are mostly forsteritic contacts with the host and have continuous to discontinuous (Fa < 10). Fayalitic olivines (Fa > 10) typically occur in type rims composed of fayalite, hedenbergite, magnetite and II chondrules, at edges around forsterite grains, in the outmost Fe,Ni-sulfides. Bulk compositions of DIs are distinctly layer of W-L rims, and in matrix. The most ferrous olivine different from those of Ningqiang matrices. DIs have higher (Fa58.3) is observed in matrix. The nearly pure endmember contents of Na, K, Ca, Al, Ti, Si, Cl and lower contents of Fe, fayalite as reported in some CV3 chondrites (Hua and Buseck Ni and S than Ningqiang matrices (Table A4). The 1995) was not found here. As shown in Table A1, olivines % compositions of DIs in this study differ significantly from that have very low minor element concentrations (TiO2 <0.1 wt , % % % of the one previously reported in Ningqiang (Zolensky et al. Al2O3 <0.2 , CaO ~0.2–0.5 , Cr2O3 ~0.05–0.2 , and MnO 2003). Our DIs contain more secondary alteration ~0.1–0.4%). Olivines from CAIs contain the highest contents % % components than the previous one. of Al2O3 (0.21 ) and CaO (0.51 ). Olivines from matrix are relatively enriched in MnO (0.37%). Olivines from OAs are Matrix, Monomineral Grains and Fine-Grained Rims fayalitic (Fa42–59) and extraordinarily enriched in phosphor Matrix in Ningqiang is mainly composed of fine-grained (0.2–3.9%), which has been described in detail in our fayalitic olivine (Fa45.7–58.3), with minor high-Ca pyroxenes, previous work (Wang et al. 2006, 2007). Ni-rich metal, Fe,Ni-sulfide, magnetite, nepheline and sodalite The Fs histogram of low-Ca pyroxenes has a peak at Fs0–2, (Fig. A5). Fayalite grains are mostly sub-µm and anhedral in with a tail extending to Fs21 (Fig. 10). Low-Ca pyroxenes shape. Euhedral platy fayalite crystals, as observed in vary in composition from enstatite to pigeonite (Table A2). Ningqiang DIs and in matrices of CV3 chondrites (Brearley Enstatite occurs widely, and has a much higher content of and Jones 1998), are basically absent in Ningqiang matrix. FeO in type II (Fs18.5) than in type I (Fs1.2) chondrules. Low- Matrix in Ningqiang is highly heterogeneous. It usually Ca pyroxenes have variable amounts of Cr2O3 (0.2–1.2%), disperses interstitially among other chondritic components, Al2O3 (0.2–10.9%), TiO2 (0.1–2.3%), and MnO (0.03–0.5%). but can occupy an area up to ~40 mm2 free of chondrules or Low-Ca pyroxenes from ARCs are more enriched in Cr, Al and Petrology and mineralogy of the Ningqiang carbonaceous chondrite 773

Ti than those from other chondritic components (Table A2). Pigeonite is enriched in Al and Ti relative to enstatite. But Al- enstatite (En97.5Wo1.3) in an ARC contains up to 10.1% Al2O3, 1.9% TiO2 and 0.8% Cr2O3 on average. High-Ca pyroxenes in Ningqiang are mainly diopside with minor hedenbergite and augite. Diopside contains highly % % variable amounts of Al2O3 (0.1–32 ) and TiO2 (0.05–19 ) (Fig. 11, Table A5), and thereby was divided arbitrarily into % categories of diopside (Al2O3 < 8 ), Al-rich diopside (Al2O3 > % % % 8 ) and Al,Ti-rich diopside (Al2O3 > 8 , TiO2 > 3 ). Diopside and Al-diopside occur in all petrographic % % components, but Al,Ti-diopside (Al2O3 12–34 , TiO2 3.9–19 ) only occurs in AOAs, type A, spinel-pyroxene-rich and hibonite-rich CAIs. High-Ca pyroxenes in chondrules are % % much more enriched in Cr2O3 (0.2–1.8 ) and MnO (0.03–0.5 ) than those from AOAs, SPIs, type A and hibonite-rich % % inclusions (Cr2O3 < 0.3 , MnO < 0.06 ); high-Ca pyroxenes from anorthite-spinel-rich and type C inclusions have % % intermediate contents of Cr2O3 (0.2–0.4 ) and MnO (0.1–0.2 ) (Fig. 11, Table A5). Na2O contents of high-Ca pyroxenes are uniformly low (<0.8%). Plagioclase is essentially anorthitic and free of potassium % (Table A6). It contains minor amounts of MgO (0.05–0.9 ) Fig. 8. BSE images of opaque assemblages (OAs) in Ningqiang. a) A and FeO (0.1–1.6%). Plagioclase grains from chondrules are spheroidal OA in a chondrule composed of magnetite, pyrrhotite and more sodic (An82.0–93.7) than those from refractory inclusions awaruite with minor amounts of olivine and whitlockite. b) An Os- (An ). rich alloy grain (~150 nm) enclosed by magnetite in the OA from a 98.2–99.6 compound chondrule. Abbreviations: mt, magnetite; aw, awaruite; Most melilite in Ningqiang is Al-rich and in the range of pyrr, pyrrhotite; whit, whitlockite. Åk0–12 (Fig. 12, Table A7). The most Mg-rich melilite found is Åk24, occurring in a fragment of a type A inclusion. Melilite % % contains very low amounts of Na2O (<0.5 ), TiO2 (<0.2 ) and FeO (<1.4%). Melilites from hibonite-bearing type A and hibonite-rich inclusions tend to have lower Åk contents than those from the less refractory, hibonite-free type A inclusions (Fig. 12, Table A7). % Spinels are mainly MgAl2O4 with minor Na2O (<0.1 ), % % % MnO (<0.2 ), CaO (<1.1 ) and TiO2 (0.1–1.5 ) (Table A8). A few Cr,Fe-rich varieties occur in Ningqiang Type II % chondrules, including a chromite with up to 40 Cr2O3 and % % % 31 FeO and a spinel with 28 Cr2O3 and 18 FeO. In % MgAl-spinels, the contents of Cr2O3 (0–3.7 ) and FeO % (0.2–23 ) are also variable. Cr2O3 contents in spinels decrease from 3.5% in ARCs to 0.6–1.3% in ASI and type C inclusions, and to <0.2% in AOA, SPI and type A inclusions. Spinels are more ferrous in the rims than in the Fig. 9. Histogram of fayalite (Fa) contents (in mol%) of olivine in cores of grains; and fine-grained and isolated spinels tend to Ningqiang. be more ferrous than coarse-grained ones. Hibonite contains 0.5–7.4% TiO2, 0.3–6.2% MgO, and The Y-bearing perovskite in an olivine-dominated inclusion % 0.2–2.6% FeO (Table A8). It shows large variations in TiO2, contains ~5.5 wt Y2O3. MgO, and Al2O3, and has higher abundances of Ti and Mg Grossite is rare in Ningqiang. The only occurrence we in type A CAIs than in hibonite-rich inclusions (Fig. 13). The found is in a CAI fragment coexisting with spinel and % content of Al varies inversely with contents of Mg and Ti, perovskite. Grossite is nearly pure CaAl4O7 with only 0.05 % % indicating a coupled substitution of Al by Ti+Mg (Fig. 13). MgO, 0.1 TiO2, and 0.7 FeO (Table A8). Perovskite contains minor amounts of MgO (<0.3%), IMA 2007-027 (Sc4Zr3O12) is a new mineral found in Al2O3 (0.4–1.6%), FeO (0.05–0.4%) and SiO2 (<0.7%) (Table A8). Allende meteorite by Chi Ma (Burke and Hatert 2007). We 774 Y. Wang and W. Hsu

Fig. 10. Histogram of ferrosilite (Fs) contents (in mol%) of low-Ca pyroxene in Ningqiang.

also found IMA 2007-027 in an inclusion of Ningqiang. Based on EDS analyses, IMA 2007-027 in Ningqiang % % % contains 55.4 wt ZrO2, 35.5 wt Sc2O3, 6.6 wt TiO2, and 2.5 wt% CaO, and the chemical formula is (Sc3.28Zr2.87Ti0.53Ca0.28)Σ6.96O12. Compositions of some accessory minerals are listed in Table A9. Sodalite contains 0.3–0.6% MgO, 0.6–3.1% CaO, % % % 0.3–0.6 FeO, and <0.03 K2O. Nepheline contains 1.5–1.9 % % % K2O, 0.1–1.1 MgO, 1.1–1.8 CaO and 0.4–2.0 FeO. % Magnetite has minor amounts of Cr2O3 (0.6–2.7 ), MgO % % % (0.2–0.6 ) and Al2O3 (0.2–1.7 ). Whitlockite contains 44.5 % % % % CaO, 44.3 P2O5, 4.7 FeO, 2.6 Na2O and 3.4 MgO. Compositions of metals and sulfides in Ningqiang are listed in Table A10. Fe,Ni metals are present in three forms: kamacite (Fe 87–94%, Ni 5.0–12%, Co 0.7–0.9%), taenite (Fe 50%, Ni 47%, Co 0.2%), and awaruite (Fe 31–34%, Ni 63– 66%, Co 1.8–2.7%). Awaruite appears widely in all chondritic components, while kamacite and taenite are much less Fig. 11. Concentrations (in wt%) of Al O versus Cr O (a), MnO (b), abundant. Sulfides are pyrrhotite, troilite, mackinawite, and 2 3 2 3 and TiO2 (c) in high-Ca pyroxenes in chondrules and refractory pentlandite, with pyrrhotite the most abundant. Pentlandite inclusions from Ningqiang. has higher cobalt contents (0.4–0.8%) than other sulfides (<0.2%). In a chondrule, a pentlandite grain coexisting with (1.09) and CV (1.05) chondrites, but previous analyses % magnetite contains 7.2 wt Co. yielded nearly flat REE patterns of Ningqiang ([La/Lu]CI = 1.00, Rubin et al. 1988; [La/Lu]CI = 0.97, Wang and Lin DISCUSSION 2007). This could have resulted from the sample heterogeneity. The mean abundances of moderately volatile Chemical and Petrological Comparison of Ningqiang with lithophile elements are low in Ningqiang (0.34 × CI), CV and CK Chondrites compared to CK (0.36 × CI) and CV (0.39 × CI). Ningqiang has 47.5 vol% chondrules with a mean From the perspective of bulk composition, Ningqiang diameter of 0.55 mm, whereas CV group meteorites have has an affinity with CV and CK chondrites, and is more 45 vol% chondrules with a larger mean diameter of 1.0 mm, closely related to the CK group. Abundances of refractory and CKs contain only 15 vol% chondrules with a mean lithophile elements in Ningqiang are distinctly depleted diameter of 0.7 mm (Brearley and Jones 1998). Most relative to CV and CK chondrites: Ningqiang (1.01 × CI) chondrules in Ningqiang have porphyritic textures; the

Ningqiang contains 6.5 vol% of refractory inclusions, including AOAs, type A, spinel-pyroxene-rich, hibonite-rich, anorthite-spinel-rich, and type C CAIs. Melilite-rich type A inclusions are the most abundant, followed by SPIs, AOAs, hibonite-rich inclusions and other minor varieties. In comparison, CV and CK chondrites contain 10 vol% and 4 vol% refractory inclusions, respectively. Refractory inclusions in Ningqiang have smaller sizes than those in CVs. They are mostly tens to hundreds of microns; only ~5% reach up to >1 mm. Type A and spinel-pyroxene-rich inclusions are commonly present in Ningqiang and CV chondrites but rarely occur in CK chondrites. Types B and C inclusions, common in CVs, are rare in Ningqiang and CK chondrites (Scott and Krot 2005). Hibonite-rich inclusions, which are absent in CK chondrites, account for 4.5% of CAIs in Ningqiang. Fig. 12. Histogram of åkermanite contents (in mol%) of melilite in Anorthite-spinel-rich inclusion, a rare type of CAI reported CAIs from Ningqiang. by Lin and Kimura (1998), finds two other representatives here in Ningqiang. Ningqiang contains 46 vol% of matrix which is dominated by fayalitic olivine (Fa46–58) with minor high-Ca pyroxenes, Ni-rich metal, Fe,Ni-sulfide, magnetite, nepheline and sodalite. This mineral assemblage is similar to that of CV chondrites, although fayalitic olivines in CVs have a more variable and less ferrous composition of Fa30–60 (Brearley and Jones 1998). Some fayalite grains in CV matrices are platy crystals (up to 20 µm in length) (Brearley and Jones 1998), whereas those in Ningqiang are fine-grained anhedral grains. CK chondrites contain much more amounts of matrix (75 vol%) than Ningqiang. CK matrices commonly contain coarse- grained (mostly 20–100 µm) plagioclase grains (Scott and Krot 2005), which are basically absent in Ningqiang. FGRs that are present in most carbonaceous chondrites except CH Fig. 13. Composition of hibonite in type A and hibonite-rich CAIs and CB groups (Scott and Krot 2005), are relatively abundant from Ningqiang, plotted in terms of cations per formula unit (19 in Ningqiang enclosing various kinds of coarse-grained oxygens). components. Opaque minerals in Ningqiang generally occur as account for 6.3% and <1%, respectively (Scott and Krot subround nodules inside chondrules, discrete phases in 2005). Chondrules in Ningqiang are predominantly Mg-rich. matrix, and complex OAs within chondrules and matrix. Only 4 Fe-rich Type II chondrules were found in 15 sections. Refractory inclusions contain few opaque phases. Opaque This indicates that Type II chondrules account for <1% of all minerals in Ningqiang are mainly magnetite, awaruite and chondrules. Similarly, the proportion of type I chondrules are pyrrhotite, which are similar to those in oxidized CV >95% in CV chondrites (Scott and Krot 2005). About 5% chondrites (Brearley and Jones 1998). As for CK chondrites, chondrules in Ningqiang are surrounded by coarse-grained magnetite, often containing exsolution lamellae of ilmenite rims, compared to ~50% in CV chondrites (Rubin 1984) and and spinel, is the dominate opaque phase, and Fe,Ni metal is zero in CK group (Krot et al. 2005). extremely rare (Brearley and Jones 1998). Sulfides in CKs Al-rich chondrules, which are common in all include not only pyrrhotite, troilite and pentlandite but also carbonaceous chondrites, are also present in Ningqiang. Two pyrite, millerite and chalcopyrite. The latter two are virtually ARCs found in NQ-PMO-0024 are plagioclase-olivine rich absent in Ningqiang. OAs, which are characteristic of CV with minor low- and high-Ca pyroxenes. The other ARC in chondrites and are basically absent in CK chondrites, exist NQ-PMO-0026 is characterized by high abundances of widely in Ningqiang. In some OAs and CAIs, trace amounts spinel, Al-enstatite, and anorthite. It is essentially free of of refractory metal (Ru, Re, Os, Ir, Pt, Mo, Y, and W) alloys olivine and clinopyroxene. This mineral assemblage is are present. relatively rare in ARCs, and resembles to that of a compound In summary, the chemical and petrological features of ARC from Allende meteorite (Akaki et al. 2007). Ningqiang are similar but not identical to those of both CV 776 Y. Wang and W. Hsu and CK group chondrites; therefore we suggest that from CAIs. Low-Ca pyroxenes are more enriched in Al and Ti Ningqiang be classified as an ungrouped carbonaceous than those from ferromagnesian chondrules. This suggests chondrite. that the formation of ARCs could have involved mixing and melting of refractory and ferromagnesian chondrule Petrogenesis of ARCs in Ningqiang: Implications for materials. During these processes, spinel and anorthite Genetic Link between Ferromagnesian Chondrules and incorporated moderately volatile elements (Na, Cr and Mn), CAIs and pyroxenes refractory elements (Al and Ti). Furthermore, moderately volatile elements, which condense or evaporate in ARCs are intermediate between CAIs and the range of 650–1350 K in an equilibrium mix of solar ferromagnesian chondrules in bulk chemistry, mineralogy and composition (Yin 2005), are sensitive indicators for thermal isotopic compositions, and hence play an important role in events. The high content of moderately volatile elements in revealing their petrogenetic relationship. ARCs in Ningqiang phases from Ningqiang ARCs requires a rapid cooling rate to are texturally and mineralogically similar to those of CV3 prevent considerable evaporation from high temperature melt chondrites (Sheng et al. 1991; Krot et al. 2002). They and/or efficient recondensation if there is any evaporation probably have a similar origin. (Galy et al. 2000). The experimentally determined range of Several models have been proposed for the petrogenesis cooling rates for typical once-molten type B CAIs is 2–50 K/h of ARCs. Bischoff et al. (1989) suggested that ARCs formed (Stolper and Paque 1986), far below the rate of 100–1000 K/h from Al-rich melt fractions ejected from partly molten Mg, for chondrules (Lofgren 1996). Recondensation during Fe-rich chondrules during collisions. MacPherson and Huss chondrule formation is rapid and efficient (Zanda et al. 2002). (2000) proposed that ARCs originated from partial Therefore, it is inferred that ARCs are genetically related to evaporation from ferromagnesian chondrule precursors. normal chondrules, i.e., forming via astrophysical events that These two models are incompatible with many observations. produced chondrules, instead of the melted CAIs. (4) Al-rich 16 % For example, ARCs are O-enriched relative to enstatite (with up to 10.9 wt Al2O3) in a Ningqiang ARC is ferromagnesian chondrules (Russell et al. 2000), suggesting a very rare mineral phase. According to Rubin (2004), Al-rich that they are not simply derived from ferromagnesian orthopyroxene crystallized from a melt with a high bulk chondrules. Relict CAIs occur in ARCs (Krot et al. 2004). Al2O3 content when quenching of the precursor droplet ARCs are relatively enriched in moderately volatile elements caused a kinetic failure of a normal Al-rich phase to (Krot et al. 2002). ARCs have highly fractionated bulk REE crystallize. Therefore, the presence of Al-enstatite further abundances (Misawa and Nakamura 1996). There are no large supports the conclusion that ARCs were formed by rapid (>1‰ amu−1) mass dependent isotopic fractionations of Mg cooling processes. This has been proven by the recent study or O in ARCs (Galy et al. 2000), arguing against a history by Tronche et al. (2007). They concluded from isothermal and involving evaporation. dynamic crystallization experiments that the formation The most attractive model is that ARCs formed from conditions of ARCs are consistent with those inferred for precursors consisting of a heterogeneous mixture of ferromagnesian chondrules. ferromagnesian chondrules and refractory materials via We suggest that ARCs in Ningqiang also formed from processes that produced normal chondrules (Krot et al. 2002, hybrid precursors of ferromagnesian chondrules mixed with 2004), i.e., a flash heating event followed by rapid cooling refractory materials. The precursors had experienced high- and crystallization. ARCs in Ningqiang reveal several pieces temperature melting, and subsequent rapid cooling and of evidence that support this argument. (1) All ARCs in crystallization. Among all types of refractory inclusions in Ningqiang have round to subround morphologies and igneous Ningqiang, the type C and anorthite-spinel-rich inclusions textures resembling normal chondrules. This indicates that composed of anorthite, spinel, pigeonite and diopside are ARCs must have formed from molten droplets floating freely closely related to ARCs. The mineral chemistry of the type C in space. (2) ARCs in Ningqiang are composed of spinel, CAI and ASIs is very similar to that of ARCs. The high-Ca anorthite, olivine, pyroxene, Fe,Ni metal, magnetite and pyroxene in the type C CAI and ASIs has amounts of Cr2O3 sulfide. Spinel and anorthite are typical minerals of some and MnO closer to those of ARCs than high-Ca pyroxenes CAIs, and other phases are commonly observed in from AOAs, SPIs, type A and hibonite-rich CAIs (Fig. 11, ferromagnesian chondrules. The mineral assemblage of Table A5). The Cr2O3 content of spinel and the anorthitic ARCs suggests that precursor materials are most likely to be component of plagioclase in the type C CAI and ASIs are mixtures of CAIs and ferromagnesian chondrules. Relict closer to those in ARCs than those in other refractory CAIs and AOAs were found within ARCs of Acfer 094, inclusions (Tables A6, A8). Therefore, type C and anorthite- Adelaide, CV, and CR chondrites (Krot et al. 2001, 2002, spinel-rich inclusions are the most probable refractory 2004). (3) Mineral phases in Ningqiang ARCs have different precursors to Ningqiang ARCs. minor element concentrations compared to their counterparts The petrogenesis of ARCs requires the presence of from CAIs and ferromagnesian chondrules. Spinel is enriched Ca,Al-rich materials in the chondrule-forming region of the in Cr and Mn and anorthite is enriched in Na relative to those protoplanetary disk. This suggests a probable overlapping of Petrology and mineralogy of the Ningqiang carbonaceous chondrite 777 the formation of ferromagnesian chondrules and CAIs in time such as 26Al. However, previous studies revealed that hibonite and/or space. Isotopic studies have revealed that some from many hibonite-rich CAIs in CM chondrites lacks chondrules and CAIs formed contemporaneously (Itoh and evidence of high 26Al content (MacPherson 2005), and that Yurimoto 2003; Bizzarro et al. 2004). On the other hand, Al- hibonite-rich inclusions in CB chondrites are 16O-poor (Scott Mg and O isotopic studies on chondrules with relict CAIs and Krot 2005). Therefore, further isotopic work on hibonite- indicate that the CAI component formed in a 16O-rich gaseous rich CAIs in Ningqiang is highly desired. reservoir before their host chondrules, which originated in a 16O-poor gas (Krot et al. 2006). Therefore, we suggest that Anorthite-Spinel-Rich Inclusion: A Link between Type A ferromagnesian chondrules and CAIs may have overlapping and Type C CAIs formation regions, in which ARCs formed and sampled the least refractory, anorthite-rich CAIs (type C and ASIs) and Fe, Anorthite-spinel-rich inclusions are a rare type of CAI, Mg-rich chondrules. In this sense, the occurrence of ARCs is and they seem to be largely confined to Ningqiang. The ASIs expected to be related to that of the refractory inclusions, reported by Lin and Kimura (1998) are composed of a spinel- specifically the least refractory ones. According to Krot nodule-rich core, a spinel-anorthite-Ca-pyroxene mantle, and (2000), the anorthite-rich ARCs are common in CV (5–10 per a melilite-spinel crust. ASIs were classified into two thin section) and CR (3–5 per thin section) but rare in CH subtypes: a fluffy one with loose texture and abundant voids (1 found) chondrites, which is relevant to their modal and a sinuous one with compact texture and much less voids. abundances of refractory inclusions (10 vol%, 0.5%, and ASIs found in this work, however, have simple textures. They 0.1%, respectively) (Scott and Krot 2003). We found only are fluffy aggregates of spinel nodules rimmed successively 3 ARCs in 15 sections, comparable with not only the low by anorthite and diopside, which closely resemble the core of abundance of CAIs in Ningqiang (2 vol%), but also the rarity fluffy ASIs observed by Lin and Kimura (1998). Furthermore, of anorthite-rich inclusions among all CAIs. Specifically, the melilite, perovskite, hedenbergite, and feldspathoids there is only 1 type C inclusion and 9 ASIs in a total of present in those ASIs are virtually absent here. 124 CAIs observed by Lin and Kimura (2003), and there is 1 Lin and Kimura (1998) proposed that ASIs were formed type C inclusion and 2 ASIs in ~300 CAIs based on our by alteration of spinel-rich type A inclusions with melilite and observation. spinel reacting with the nebular gas to produce anorthite and Ca-pyroxene. This is consistent with oxygen isotopic Hibonite-Rich CAIs in Ningqiang characteristics of component minerals in ASIs (Guan et al. 2005). And according to Lin and Kimura (1998), sinuous We report here the first occurrence of hibonite-rich CAIs ASIs were not formed directly from type A inclusions, but in Ningqiang. Thirteen hibonite-rich inclusions were found in indirectly from mild heating of fluffy ASIs. Based on our our sections, accounting for 4.5% of all CAIs. Hibonite-rich observations, however, there are two classes of type A CAIs in Ningqiang exhibit three different textural forms: as inclusions that are likely to be precursors of ASIs: one is the aggregates of euhedral hibonite single crystals; as fine- fluffy aggregate of spinel-rich nodules rimmed by melilite, grained aggregates of subhedral hibonite with minor spinel; the other is the compact inclusion composed of sinuous and as hibonite ± Al,Ti-diopside ± spinel spherules. These spinel-melilite intergrowths (Fig. 4e–f). It is very likely that inclusion types are also found in CM, CH, CB chondrites, and fluffy and sinuous ASIs derived directly from the former and an ungrouped chondrite Acfer 094. CAIs consisting of the latter class of inclusions, respectively, via alteration euhedral hibonite single crystals in Ningqiang closely processes described by Lin and Kimura (1998). resemble PLACs (platy hibonite crystals) in CM chondrites Based on the similarities of modal and bulk compositions (Ireland 1988). Spinel-hibonite CAIs (SHIBs) that usually of ASIs and type C inclusions, ASIs were proposed to be occur in CM chondrites are also present in Ningqiang. Round precursors of type C inclusions (Lin and Kimura 1998). Our to subround hibonite-Al,Ti-diopside inclusions in Ningqiang work shows that ASIs have mineralogical characteristics are texturally similar to pyroxene-hibonite spherules similar to those of type C inclusions, supporting this occurring in CH, CB, and the Acfer 094 chondrites (Krot et al. suggestion. Spinels from these two types of inclusions have % 2004; Scott and Krot 2005). similar Cr2O3 contents (0.6–1.3 wt ), which is intermediate The existence of hibonite-rich inclusions in Ningqiang between those (3.5%) of ARCs and those (<0.2%) of AOAs, and their textural similarities with those from CM, CH, CB, SPIs and type A inclusions. Plagioclases from ASIs and the and the Acfer 094 chondrites add further evidence to the type C inclusion have a narrow range of composition (An98.2–99.2). suggestion that Ningqiang is a unique carbonaceous High-Ca pyroxenes from these inclusions have similar chondrite. contents of Cr2O3 (0.2–0.3%) and MnO (0.1–0.2%), different Hibonite is one of the most refractory minerals which from those of chondrules (Cr2O3 0.9–1.2% and MnO 0.1–0.3%) −3 condensed early from the solar nebula (at a pressure of 10 and those of other refractory inclusions (Cr2O3 < 0.08% and atm) at ~1735 K (Fegley 1991). It was expected to be 16O-rich MnO < 0.06%). Therefore, the rare ASIs in Ningqiang could and have high initial abundances of short-lived radionuclides, be a genetic link between type A and C inclusions. 778 Y. Wang and W. Hsu

Secondary Alteration Processes in Ningqiang: Both in the three oxygen isotope diagram, and vary by 16 ‰ in Nebular and Asteroidal δ18O. Magnetite grains have consistently higher ∆17O values than their adjacent olivine grains. The petrology, mineralogy Evidence for secondary alteration processes is ubiquitous and O-isotopic compositions of OAs in Ningqiang indicate in Ningqiang. Forsteritic olivines and low-Ca pyroxenes were that they were neither direct nebular condensates, nor crystals altered to fayalitic olivines around grain peripheries and/or crystallized from chondrule melts, but a low-temperature along cracks. Amorphous to crystalline chondrule mesostasis alteration product within an asteroidal environment (Hsu and plagioclase were replaced by nepheline and sodalite. et al. 2006; Wang et al. 2007). Some primary high-Ca pyroxenes were altered to ferrous Observations in Ningqiang indicate that secondary varieties. In CAIs, melilite was partly replaced by anorthite; alteration processing can occur in different environments and/ perovskite was corroded by a thin rim of ilmenite; spinel was or times, i.e., in the solar nebular prior to accretion and in distinctly enriched in FeO along peripheries. Fe-rich metals asteroids after accretion, and in a number of different ways were widely oxidized to magnetite and sulfidized to form including at least oxidation, sulfidation, aqueous alteration, Fe,Ni-sulfides. Opaque assemblages mainly composed of and metasomatism. Components of Ningqiang had been awaruite, magnetite, pyrrhotite, pentlandite, and minor altered by both nebular and asteroidal secondary processes in whitlockite are widespread in Ningqiang chondrules and various ways. matrix. Other secondary alteration products include hedenbergite and minor wollastonite and kirschsteinite. The CONCLUSIONS secondary mineralogy of Ningqiang is quite similar to that of oxidized-CV3 chondrites, including that of OAs. We have carried out detailed chemical, petrological and Nevertheless, some secondary phases, such as phyllosilicates mineralogical studies on the Ningqiang carbonaceous found in chondrules, CAIs and matrices of oxidized CV3 chondrite. Ningqiang bears many similarities with typical CV chondrites (e.g. Mokoia, Bali, and Kaba; Brearley and Jones and CK chondrites, but is distinct from them in various 1998), were not encountered in Ningqiang, which indicates aspects. It should be considered as an ungrouped type 3 that the extent of aqueous alteration in Ningqiang is less carbonaceous chondrite. severe than those of most oxidized CV3 chondrites. The bulk chemical composition of Ningqiang is close to Sodalite and nepheline are widely present in chondrules, those of CV and CK chondrites, but is distinctly depleted in CAIs, AOAs, DIs and matrix in Ningqiang. Sodalite and refractory lithophile elements. Abundances of moderately nepheline are not primary phases, but were formed by alkali- volatile lithophile elements (except Na) are depleted in halogen metasomatism of anorthite and anorthite-normative Ningqiang relative to CV and CK chondrites. glasses in chondritic components (Krot et al. 1995). Whether Ningqiang is composed of 47.5 vol% chondrules, the alteration process occurred in the nebula or on asteroids is 2.0% CAIs, 4.5% AOAs and 46.0% matrix, texturally a long-standing issue (Kimura and Ikeda 1995; Krot et al. resembling CV3 chondrites, but with a relatively low 1995). Our observations support a nebular environment. The abundance of refractory inclusions. Chondrules in Ningqiang overall abundance of sodalite and nepheline in Ningqiang is are mostly Mg-rich type I, with a mean diameter of 500 µm. very low (<<1 vol%), and their distribution is highly About 95% chondrules have porphyritic textures, and 5% are heterogeneous. The sharpest contrast lies in the NQ-PMO- mantled by coarse-grained rims. 1012 DI. The DI contains 25 vol% nepheline and sodalite, but The abundance of ARCs in Ningqiang is very low. Only its surrounding matrix has much less nepheline and sodalite three ARCs were found in 15 sections. They are texturally (<1 vol%). Matrix is mainly composed of fine mineral grains, and mineralogically similar to those from other carbonaceous with high porosity and permeability. If nepheline and sodalite chondrite groups (CV, CO, CR, etc.) and consist of forsteritic were formed by secondary alteration processes in an olivine, anorthitic plagioclase, spinel, low- and high-Ca asteroidal environment, matrix should be more susceptible to pyroxenes, and minor opaque minerals. One ARC has a rare alteration than any other components, and thereby contain mineral combination with 33 vol% plagioclase, 25% spinel, more nepheline and sodalite grains. Our petrographic 25% Al-enstatite, and only 1% olivine. The petrology and observation is consistent with oxygen isotopic compositions mineralogy of ARCs in Ningqiang are compatible with the of Ningqiang sodalite, which fall along the CCAM line on the formation of ARCs by melting of hybrid precursors of three-oxygen isotope diagram (Guan et al. 2005), indicating ferromagnesian chondrules mixed with refractory materials, that sodalite formed in a nebular environment. and subsequent rapid cooling and crystallizing of melt Different from the origin of nepheline and sodalite, droplets. however, OAs in Ningqiang formed by aqueous alteration of Ningqiang has a distinct population of refractory preexisting metal alloys within a planetary body. According inclusions, which can be divided into type A (55.0% in all to our previous work (Hsu et al. 2006), O-isotopic CAIs), spinel-pyroxene-rich (39.5%), anorthite-spinel-rich compositions of magnetite in Ningqiang OAs fall on a (0.7%), type C (0.3%), and hibonite-rich (4.4%) Ca,Al-rich regression line with a slope of 0.51 and a mean ∆17O of −2.9 ‰ inclusions, and amoeboid olivine aggregates (accounting for Petrology and mineralogy of the Ningqiang carbonaceous chondrite 779

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