The Mineralogy of the Yaringie Hill Meteorite—A New H5 Chondrite from South Australia

The mineralogy of the Yaringie Hill meteorite —A new H5 chondrite from South Australia

Item Type Article; text

Authors Tappert, R.; Foden, J.; Pring, A.

Citation Tappert, R., Foden, J., & Pring, A. (2009). The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite from South Australia. Meteoritics & Planetary Science, 44(11), 1687-1693.

DOI 10.1111/j.1945-5100.2009.tb01199.x

Publisher The Meteoritical Society

Journal Meteoritics & Planetary Science

Download date 03/10/2021 21:14:20

Item License http://rightsstatements.org/vocab/InC/1.0/

Version Final published version

Link to Item http://hdl.handle.net/10150/656634 Meteoritics & Planetary Science 44, Nr 11, 1687–1693 (2009) Abstract available online at http://meteoritics.org

The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite from South Australia

Ralf TAPPERT1*, John FODEN1, and Allan PRING2

1University of Adelaide, Geology and Geophysics, School of Earth and Environmental Sciences, Adelaide, South Australia 5005, Australia 2South Australian Museum, Science Centre, Adelaide, South Australia 5000, Australia *Corresponding author. E-mail: [email protected] (Received 26 May 2009; revision accepted 24 July 2009)

Abstract–The Yaringie Hill meteorite is a new H5 ordinary chondrite found in the Gawler Ranges, South Australia. The meteorite, which shows only minor signs of terrestrial weathering, is predominantly composed of olivine (Fa17.2), orthopyroxene (Fs15.1Wo1.1), and three distinct phases of nickeliferous iron metal (kamacite, taenite, tetrataenite). Other minerals include troilite, plagioclase (Ab81An16Or3), clinopyroxene (En52Wo42Fs6), chlorapatite, merrillite, ilmenite, and native copper. Three types of spinel with distinctive textures (coarse, skeletal aggregates, rounded aggregates) and with compositions close to the join MgAl2O4-FeCr2O4 are also present. Chondrules within the Yaringie Hill meteorite, which often have poorly defined boundaries, are placed in a recrystallized matrix. Shock indicators suggest that the meteorite experienced only weak shock metamorphism (S3).

INTRODUCTION nickeliferous iron metal. Minor phases are plagioclase, troilite, and clinopyroxene. Accessory minerals include The Yaringie Hill meteorite was found by entomologist Dr. chlorapatite, merrillite, ilmenite, spinel, and native copper. Peter Hudson, during a fauna survey of the South Australian Chondrules composed of olivine, pyroxene or both minerals Museum on October 18, 2006, in the Gawler Ranges, South occur throughout the meteorite. The chondrules include types Australia (32°04.972′S, 135°38.991′E; Fig. 1). The discovery with porphyritic, non-porphyritic (radial pyroxene, barred site is located about 15 km east of the eastern shore of Lake olivine, cryptocrystalline), and granular textures (see Gooding Acraman, which coincidentally marks the location of a large and Keil 1981). Chondrule sizes range from ~300 µm to a Neoproterozoic meteorite impact (Williams 1986). The maximum of ~4 mm. The largest chondrule consisted of Yaringie Hill meteorite is the first meteorite found within radially aligned barred olivine with interstitial feldspar the Gawler Ranges; however, nine other meteorites were (Fig. 3). The boundaries of the chondrules are often poorly recovered from the adjacent Eyre Peninsula to the south defined, and the interchondrule matrix is recrystallized. (Fig. 1). Weathering features of the Yaringie Hill meteorite are restricted to minor oxide rims around most of the metal and PHYSICAL DESCRIPTION AND PETROGRAPHY troilite grains, and staining of the adjacent silicate minerals. These weathering characteristics are consistent with stage W1 The Yaringie Hill meteorite was recovered as a single on the weathering scale devised by Wlotzka (1993). Meteorite mass and was entirely covered by a thin brownish-black finds with similar weathering characteristics, from regions fusion crust. The stone is roughly tetrahedral shaped with two with arid climate conditions comparable to South Australia, roughly planner faces at right angles to each other; the other were found to have terrestrial ages of less than 5000 years sides of the tetrahedron are less regular. The approximate (Jull et al. 1990; Wlotzka 1993). dimensions of the meteorite are 18 × 13 × 12 cm, and the original weight was 5.75 kg. A conspicuous feature of the MINERALOGY meteorite is a thin (~0.5 mm) vein of metal that crosscuts the entire specimen (Fig. 2). The interior of the meteorite is The composition of the mineral phases were analyzed light colored, with some patchy brown oxidized areas (Fig. 2). with a CAMECA SX-51 electron microprobe at the The Yaringie Hill meteorite is a recrystallized chondrite, University of Adelaide, using a 15 kV acceleration voltage predominantly composed of olivine, orthopyroxene, and and a beam current of 20 nA. Counting times for each

Fig 1. Map of the Eyre Peninsula and the Gawler Ranges (South Australia) with the location of the sites of the Yaringie Hill and other meteorite finds. element ranged from 40 to 60 seconds (including Clinopyroxene is a rare component of the Yaringie Hill background counts). Representative mineral analyses are meteorite. It occasionally occurs as distinct grains of up to presented in Table 1. 50 µm, but more commonly forms thin overgrowths (≤20 µm) Olivine occurs both within chondrules and as of larger orthopyroxene crystals. The average composition of granoblastic matrix grains. The average fayalite component clinopyroxene is En51.9, Wo42.0, Fs6.1. Minor elements include σ = ) % % of the olivines is Fa17.2 (range: Fa16.6–Fa19.4, 1 : 0.45, n 54 titanium (0.47 wt TiO2), aluminium (1.65 wt Al2O3), and % (Fig. 4). chromium (1.12 wt Cr2O3) (Table 1). Like olivine, orthopyroxene also occurs within Minerals belonging to the spinel group are chondrules and as granoblastic matrix grains. compositionally variable and show a range of textures. The Orthopyroxenes have an average ferrosilite content of Fs15.1 maximum size of all types of spinel group minerals is around σ = µ (range: Fs14.5–Fs15.9, 1 : 0.34, n 28), and an average 200 m. Most abundant are coarse Cr-spinels (Ramdohr σ wollastonite content of Wo1.1 (range: Wo0.6–Wo2.9, 1 : 0.53) 1973), which are rather uniform in composition (Fig. 6, Table (Fig. 4). 1), and commonly occur in association or as inclusion in Fe- Despite the fact that plagioclase feldspar comprises a Ni metal or troilite (Fig. 5B). Aggregate spinels, which often significant part of the matrix and of the interstitial phases of have distinctive skeletal crystal shapes (skeletal aggregate chondrules within the Yaringie Hill meteorite (Fig. 5A), spinels, Fig. 5C) are more variable in composition but have discrete and inclusion-free crystals of sizes >10 µm are lower chromium and iron and higher aluminium and uncommon. Most of the very fine-grained to magnesium contents than coarse Cr-spinels (Fig. 6, Table 1). cryptocrystalline feldspar forms intergrowths with other The skeletal aggregate spinels are commonly rimmed by fine-grained minerals. Compositionally the plagioclase plagioclase (Fig. 5C). Other spinels, which are also associated feldspar of the Yaringie Hill meteorite is oligoclase with an with plagioclase, form conspicuous rounded aggregates approximate average composition Ab81An16Or3 (Table 1). (rounded aggregate spinels, Fig. 5D). These spinels have even This feldspar composition falls into the range which is typical lower chromium and iron and higher aluminium and for H chondrites (Van Schmus and Ribbe 1968). magnesium contents. Rubin (2003) suggested that the The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite 1689

Fig. 2. Photograph of the Yaringie Hill meteorite after cutting. The prominent metal vein (white arrow) and a single large chondrule (black arrow) are visible on the cut surface. Scale bar is in centimeters.

Fig. 3. Photomicrograph (crossed polars) of a large chondrule (Ø ~4 mm) from the Yaringie Hill meteorite. The chondrule consists of radially aligned barred olivine, rimmed by coarse recrystallized matrix. 1690 R. Tappert et al.

Table 1. Representative compositions of minerals from the Yaringie Hill meteorite (analyses given in wt%). Orthopy- Spinel Spinel Olivine roxene Clinopy- Spinel (skeletal (rounded Mineral (n = 54) (n = 28) roxene Feldspar Apatite Merrillite Ilmenite (coarse) agg.) agg.) ≤ ≤ ≤ ≤ P2O5 0.04 0.04 0.04 0.04 41.2 46.4 – – – – SiO2 38.7 56.1 53.6 66.1 0.24 0.11 0.18 0.09 0.12 0.15 ≤ ≤ ≤ TiO2 0.06 0.13 0.47 0.04 0.04 0.04 54.8 1.47 1.09 0.21 ≤ ≤ ≤ ≤ Al2O3 0.04 0.18 1.65 22.7 0.04 0.04 0.04 6.11 14.7 40.9 ≤ V2O3 –– – – –– 0.04 0.92 0.47 0.29 ≤ ≤ ≤ ≤ ≤ Cr2O3 0.04 0.14 1.12 0.04 0.04 0.04 0.04 58.4 51.0 26.6 MgO 44.0 31.9 18.2 0.43 0.12 3.58 4.76 2.70 6.37 12.3 CaO ≤0.04 0.56 20.5 2.97 53.5 47.4 0.07 ≤0.04 0.07 0.07 MnO 0.46 0.49 0.27 ≤0.04 ≤0.04 ≤0.04 3.62 0.84 0.68 0.31 FeO 16.3 10.3 3.81 0.48 0.29 0.48 37.0 28.8 25.8 18.8 NiO ≤0.04 ≤0.04 ≤0.04 ≤0.04 ≤0.04 ≤0.04 0.13 ≤0.04 ≤0.04 ≤0.04 ZnO – – – – – – 0.05 0.47 0.43 0.63 ≤ ≤ Na2O 0.04 0.04 0.59 8.31 0.32 2.73 – – – – ≤ ≤ ≤ ≤ K2O 0.04 0.04 0.04 0.48 0.04 0.05 – – – – F – – – – 0.46 0.06 – – – – Cl – – – – 4.38 ≤0.04 – – – – Total 99.5 99.8 100.3 101.5 100.4 100.8 100.6 99.8 100.9 100.2 P 0.00 0.00 0.00 0.00 13.4 14.0 – – – – Si 2.95 3.96 3.89 2.86 0.09 0.04 0.02 0.01 0.01 0.01 Ti 0.00 0.01 0.03 0.00 0.00 0.00 3.98 0.12 0.08 0.01 Al 0.00 0.02 0.14 1.16 0.00 0.00 0.00 0.77 1.72 4.14 V – – – – – – 0.00 0.08 0.04 0.02 Cr 0.00 0.01 0.06 0.00 0.00 0.00 0.00 4.91 4.00 1.81 Mg 5.00 3.35 1.97 0.03 0.07 1.90 0.69 0.43 0.94 1.57 Ca 0.00 0.04 1.60 0.14 22.0 18.0 0.01 0.00 0.01 0.01 Mn 0.03 0.03 0.02 0.00 0.01 0.01 0.30 0.08 0.06 0.02 Fe2+ 1.04 0.60 0.23 0.02 0.09 0.14 2.99 2.57 2.14 1.35 Ni 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 Zn – – – – – – 0.00 0.04 0.03 0.04 Na 0.00 0.00 0.08 0.70 0.24 1.88 – – – – K 0.00 0.00 0.00 0.03 0.00 0.02 – – – – Cation tot. 9.04 8.02 8.02 4.92 35.9 36.0 8.00 8.99 9.03 8.99 [O] 12 12 12 8 56 56 12 12 12 12 association of such texturally variable, Al2O3 enriched spinels adjacent to metal or troilite grains. Merrillite also occurs and plagioclase in ordinary chondrites is the result of shock closely associated with chlorapatite, which is not uncommon melting processes. Molar Mg/(Mg+Fe) and Cr/(Cr+Al) ratios in ordinary chondrites (Van Schmus and Ribbe 1969, Jolliff demonstrate that all spinel types in the Yaringie Hill meteorite et al. 2006). Chlorapatite and merrillite in the Yaringie Hill fall close to the join chromite (FeCr2O4)—spinel s.s. meteorite are present in approximately equal abundance. (MgAl2O4) (Fig. 6). Concentrations of minor elements in Troilite is present as isolated grains of up to 0.5 mm spinel group minerals, which include titanium, vanadium, and within the matrix of the meteorite or, more commonly, zinc, were found to correlate with the FeCr2O4 (chromite) associated with metal phases. Smaller grains of troilite were component of the spinels (Table 1). also observed as inclusions in chondrules. Magnesian ilmenite is a rare constituent of the Yaringie Fe-Ni metal occurs as abundant anhedral grains of up to Hill meteorite and is present as anhedral grains (~50 µm) in ~0.5 millimeters and forms the prominent vein which close contact with metal grains. crosscuts the meteorite (Fig. 2). Three distinct metal phases Chlorapatite with chlorine concentrations of up to 5.5 wt% can be distinguished based on their nickel contents, which (Table 1) is present in the Yaringie Hill meteorite as subhedral have been determined for the cores of randomly selected to anhedral crystals of up to 200 µm. metal grains. Kamacite is the most abundant metal phase and An additional phosphate mineral in the Yaringie Hill has an average nickel content of 6.12 wt% (n = 47). The meteorite is merrillite, which also occurs as subhedral to prominent metal vein, which undulates around larger anhedral crystals of up to 200 µm. Merrillite is often found chondrules, is also primarily comprised of kamacite, but The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite 1691

Fig. 4. Average fayalite component of olivine versus average ferrosilite component of orthopyroxene of the Yaringie Hill meteorite and other ordinary chondrites from the Eyre Peninsula (Mason 1974; Wallace and Pring 1991a, 1991b). Compositional fields for H, L, and LL ordinary chondrites are based on Keil and Fredriksson (1964). Error bars represent the standard deviation (1σ) for individual point analyses. contains occasional troilite, coarse Cr-spinel, and fragments CLASSIFICATION of silicates. A less abundant metal phase in the Yaringie Hill meteorite is taenite, with nickel contents in the range 29.0 to Based on the magnesium-rich composition of the % 35.3 wt . A third metal phase, with markedly higher nickel ferromagnesian silicates —olivine (Fa17.2) and orthopyroxene % contents (47.0–50.4 wt Ni), has been identified as (Fs15.1Wo1.1)—the Yaringie Hill meteorite belongs to the H- tetrataenite (Clarke and Scott 1980). No obvious zoning or group of ordinary chondrites (Keil and Fredriksson 1964) intergrowths within individual metal grains have been noted. (Fig. 4). This classification is also consistent with the high Native copper is a rare component of the Yaringie Hill modal abundance of metal phases in the meteorite, the meteorite, occurring as small isolated grains (≤10 µm), either composition of the plagioclase feldspar (Van Schmus and surrounded by silicates or within metal phases. Ribbe 1968), and the composition of the coarse Cr-spinels (Bunch et al. 1967). The distinctive composition of the SHOCK METAMORPHISM ferromagnesian silicates suggests that the Yaringie Hill meteorite is not related to any of the other meteorites The result of shock metamorphism is evident in the described from the Eyre Peninsula (Fig. 4). undulatory extinction of olivine, pyroxene and plagioclase, as The microstructure of the Yaringie Hill meteorite, which well as in the presence of planar fractures in olivine crystals. shows chondrules with indistinct rims in a crystalline matrix, Based on the classification scheme of Stöffler et al. (1991), indicates that the meteorite experienced a pre-terrestrial this indicates that the Yaringie Hill meteorite is weakly shocked, metamorphic overprint. The scarcity of discrete plagioclase i.e., experienced shock stage S3. The presence of spinel- crystals, however, rules out that the Yaringie Hill meteorite plagioclase assemblages is also consistent with a shock stage belongs to the highest metamorphic class for ordinary of at least S3 (Rubin 2003). The peak pressure for shock chondrites (type 6), but rather suggests a type 5 classification stage S3 is estimated to be in the range 10–20 GPa (Stöffler in the petrographical classification scheme of Van Schmus et al. 1991). Other effects of shock metamorphism, possibly and Wood (1967). The type 5 classification of the Yaringie related to localized P-T excursions, include the presence of Hill meteorite is also consistent with the relatively low rare opaque melt veins. The prominent metal vein, which average wollastonite content of the orthopyroxenes (Wo1.1), cross-cuts the entire meteorite may also be the result of this since the wollastonite content was shown to correlate with the shock metamorphism. degree of metamorphic overprint and hence the petrographic 1692 R. Tappert et al.

Fig. 5. Backscattered electron (BSE) images of the Yaringie Hill meteorite. A) Chondrule with porphyritic orthopyroxene (light) and interstitial feldspar (dark). B) Coarse Cr-spinel inclusions in troilite. C) Skeletal spinel aggregate with plagioclase rim in matrix of ferromagnesian silicates. D) Rounded aggregate spinel with plagioclase in matrix of ferromagnesian silicates.

Fig. 6. Mg/(Mg + Fe) versus Cr/(Cr/Al) of accessory spinel in the Fig. 7. Isotherm diagram for spinels from the Yaringie Hill meteorite, Yaringie Hill meteorite. based on Wlotzka (2005). The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite 1693 type of chondrites (Scott et al. 1986). Chondrites belonging to Gooding J. L. and Keil K. 1981. Relative abundances of chondrule type 6 are expected to have average wollastonite contents of primary textural types in ordinary chondrites and their bearing on >1.6. The variability in the composition of olivine and conditions of chondrule formation. Meteoritics 16:17–43. Jolliff B. L., Hughes J. M., Freeman J. J., and Zeigler R. A. 2006. orthopyroxene provides additional support for the type 5 Crystal chemistry of lunar merrillite and comparison to other classification of the Yaringie Hill meteorite, because it meteoritic and planetary suites of whitlockite and merrillite. indicates some degree of unequilibration. American Mineralogist 91:1583–1595. Because of the unequilibrated nature of the silicates in Jull A. J. T., Wlotzka F., Palme H., and Donahue D. J. 1990. the Yaringie Hill meteorite, it was not possible to gain Distribution of terrestrial age and petrologic type of meteorites from western Libya. Geochimica et Cosmochimica Acta 54: meaningful temperature information using two-pyroxene 2895–2898. thermometry (e.g., Wells 1977; Lindsley 1983; Bertrand and Keil K. and Fredriksson K. 1964. The iron, magnesium, and calcium Mercier 1985). However, temperatures have been determined distribution in coexisting olivines and rhombic pyroxenes of using the olivine-spinel thermometer of Wlotzka (2005). The chondrites. Journal of Geophysical Research 69:3487–3515. resulting temperatures, which are in the range 640–830 °C, Lindsley D. H. 1983. Pyroxene thermometry. American Mineralogist 68:477–493. depend strongly on the textural type of the spinels (Fig. 7). Mason B. 1974. Notes on Australian meteorites. Records of the Coarse Cr-spinels indicate relatively low equilibration Australian Museum 29:169–186. temperatures of 640–700 °C. Temperature estimates for Ramdohr P. 1973. The opaque minerals in stony meteorites. skeletal aggregate spinels (685–782 °C) and rounded Amsterdam: Elsevier. 245 p. aggregate spinels (740–830 °C) are significantly higher (Fig. 7). Rubin A. E. 2003. Chromite-plagioclase assemblages as a new shock ° indicator; implications for the shock and thermal histories of Similar temperature discrepancies of 50–100 C between ordinary chondrites. Geochimica et Cosmochimica Acta 67: chromium-rich coarse spinel and more aluminous spinel 2695–2709. assemblages have been observed in other meteorites (Wlotzka Scott E. R. D., Taylor G. J., and Keil K. 1986. Accretion, 2005). Assuming aluminous spinel-plagioclase assemblages metamorphism, and brecciation of ordinary chondrites: Evidence are the result of shock induced melting, as proposed by Rubin from petrologic studies of meteorites from Roosevelt County, New Mexico. Proceedings, 17th Lunar and Planetary Science (2003), the higher temperature estimates for these spinels may Conference. Journal of Geophysical Research 91(B13):E115– reflect the temporarily increased heat flux during the shock E123. event. Coarse spinels, on the other hand, are more likely to Stöffler D., Keil K., and Scott E. R. D. 1991. Shock metamorphism reflect steady-state conditions during metamorphism. of ordinary chondrites. Geochimica et Cosmochimica Acta 55: 3845–3867. Van Schmus W. R. and Ribbe P. H. 1968. The composition and Acknowledgments—We thank Dr. Hudson for bringing the structural state of feldspar from chondritic meteorites. meteorite to the attention of the South Australian Museum, Geochimica et Cosmochimica Acta 32:1327–1342. and the Waterhouse Club of the South Australian Museum Van Schmus W. R. and Ribbe P. H. 1969. Composition of phosphate who funded the survey on which the meteorite was found. minerals in ordinary chondrites. Geochimica et Cosmochimica Additional financial support was provided by the Australian Acta 33:637–640. Van Schmus W. R. and Wood J. A. 1967. A chemical-petrologic Research Council (ARC), the Department of Primary classification for the chondritic meteorites. Geochimica et Industries and Resources of South Australia (PIRSA), and Cosmochimica Acta 31:747–765. Flinders Mines Ltd. The manuscript benefited from helpful Wallace M. and Pring A. 1991a. Geological note: The Streaky Bay reviews by A. Bevan and A. Ruzicka. meteorite, a new (L4) chondrite from South Australia. Australian Journal of Earth Sciences 38:247–248. Wallace M. and Pring A. 1991b. The Mangalo meteorite, a new (L6) Editorial Handling—Dr. Alex Ruzicka olivine-hypersthene chondrite from South Australia. Transactions of the Royal Society of South Australia 115:89–93. REFERENCES Wells P. R. A. 1977. Pyroxene thermometry in simple and complex systems. Contributions to Mineralogy and Petrology Bertrand P. and Mercier J. C. 1985. The mutual solubility of 46:129–139. coexisting ortho- and clinopyroxene: Toward an absolute Williams G. E. 1986. The Acraman impact structure: Source of geothermobarometer for the natural system? Earth and Planetary ejecta in Late Precambrian shales, South Australia. Science Science Letters 76:109–122. 233:200–203. Bunch T. E., Keil K., and Snetsinger K. G. 1967. Chromite Wlotzka F. 1993. A weathering scale for the ordinary chondrites. composition in relation to chemistry and texture of ordinary Meteoritics 28:460. chondrites. Geochimica et Cosmochimica Acta 31:1569–1582. Wlotzka F. 2005. Cr spinel and chromite as petrogenetic indicators in Clarke R. S. and Scott E. R. D. 1980. Tetrataenite—ordered FeNi, a ordinary chondrites: Equilibration temperatures of petrologic new mineral in meteorites. American Mineralogist 65:624–630. types 3.7 to 6. Meteoritics & Planetary Science 40:1673–1702.