53Mn–53Cr chronology of Ca–Fe silicates in CV3 chondrites

Accepted Manuscript Mn-53Cr Chronology of Ca-Fe Silicates in CV3 Chondrites

53

Glenn J. MacPherson, Kazuhide Nagashima, Alexander N. Krot, Patricia M. Doyle, Marina A. Ivanova PII: DOI: Reference:

S0016-7037(16)30557-9 http://dx.doi.org/10.1016/j.gca.2016.09.032 GCA 9944

To appear in:

Geochimica et Cosmochimica Acta

Received Date: Accepted Date:

26 February 2016 26 September 2016

Please cite this article as: MacPherson, G.J., Nagashima, K., Krot, A.N., Doyle, P.M., Ivanova, M.A., 53Mn-53Cr Chronology of Ca-Fe Silicates in CV3 Chondrites, Geochimica et Cosmochimica Acta (2016), doi: http://dx.doi.org/ 10.1016/j.gca.2016.09.032

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53

1

Mn-53Cr CHRONOLOGY OF Ca-Fe SILICATES IN CV3 CHONDRITES

2 3 4 5

Glenn J. MacPherson1, Kazuhide Nagashima2, Alexander N. Krot2, Patricia M. Doyle3, and

6

Marina A. Ivanova1

7 8 9 10 11

1

12

USA. ([email protected])

13

2

14

96822, USA.

15

3

US National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20560,

Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI

Department of Geological Sciences, University of Cape Town, Rondebosch, 7701, RSA.

16 17 18 19 20 21 22

Submitted to: Geochimica et Cosmochimica Acta February 28, 2016

23

Revised September 8, 2016

24 25 1

26

This study is dedicated to our late colleague and friend Dr. Ian D. Hutcheon, who pioneered the

27

use of 53Mn-53Cr systematics in secondary minerals as a means of dating aqueous alteration in

28

chondritic meteorites.

29

ABSTRACT

30

High precision secondary ion mass-spectrometry (SIMS) analyses of kirschsteinite

31

53

32

(CaFeSiO4) in the reduced CV3 chondrites Vigarano and Efremovka yield well resolved

33

excesses that correlate with

34

radionuclide

35

52

36

sensitivity factor. The inferred initial ratio (53Mn/55Mn)0 in chondritic kirschsteinite is

37

(3.71±0.50)×10‒6. When anchored to

38

ages of the D’Orbigny angrite, this ratio corresponds to kirschsteinite formation 3.2ା଴଼ ି଴.଻ Ma after

39

CV Ca-, Al-rich inclusions. The kirschsteinite data are consistent within error with the data for

40

aqueously-formed fayalite from the Asuka 881317 CV3 chondrite as reported by Doyle et al.

41

(2015), supporting the idea that Ca-Fe silicates in CV3 chondrites are cogenetic with fayalite

42

(and magnetite) and formed during metasomatic alteration on the CV3 parent body.

43

Concentrically-zoned crystals of kirschsteinite and hedenbergite indicate that they initially

44

formed as near end-member compositions that became more Mg-rich with time, possibly as a

45

result of an increase in temperature.

53

55

Cr

Mn/52Cr, demonstrating in situ decay of the extinct short-lived

Mn. To ensure proper correction for relative sensitivities between

55

Mn+ and

Cr+ ions, we synthesized kirschsteinite doped with Mn and Cr to measure the relative 53

Mn-53Cr relative and U-corrected

207

Pb-206Pb absolute

46 47

1. INTRODUCTION

48

The matrices and fine-grained accretionary rims in CV3 (Vigarano type) carbonaceous

49

chondrites are characterized by the presence of secondary assemblages that include various

50

combinations of magnetite, ferroan olivine (Fa50‒100), Ca- rich clinopyroxene [diopside

51

(CaMgSi2O6) – hedenbergite (CaFeSi2O6) solid solution], andradite garnet (Ca3Fe2Si3O12), and

52

kirschsteinite (CaFeSiO4; the Fe-rich end member of a solid solution series with monticellite,

53

CaMgSiO4). Beginning with Krot et al. (1995), this assemblage generally is interpreted as a

54

result of metasomatic alteration on the CV3 parent body. Krot et al. (1998a) showed that the 2

55

diverse combinations of the above minerals in different CV3s are a result of different local

56

conditions, such as oxygen fugacity, temperature, and fluid chemistry, during metasomatic

57

alteration. For example, relatively oxidizing conditions favor andradite and magnetite over

58

fayalite and hedenbergite. Most of this earlier work was focused on both the Allende-like and

59

Bali-like oxidized-subgroup CV3s (CV3oxA and CV3oxB), and little work was done on reduced-

60

subgroup CV3s (CV3red). Later, MacPherson and Krot (2014) showed that kirschsteinite is a

61

characteristic constituent of the CV3red chondrites, whereas magnetite and andradite are

62

characteristic of the CV3ox chondrites. Hedenbergite-rich pyroxene and ferroan olivine occur in

63

all subgroups.

64

Constraining the chronology of meteorite metamorphism and metasomatism is important

65

both for understanding early parent body processes and also for constraining the accretion age of

66

the parent body. The 53Mn-53Cr short-lived isotope system (53Mn decays to

67

of

68

http://www.nndc.bnl.gov) has proven particularly useful in this regard (e.g., Hutcheon and

69

Phinney, 1996; Endreβ et al., 1996; Hutcheon et al., 1998; see Doyle et al., 2015 for additional

70

references). The diversity of assemblages in the various CV3 meteorites (e.g., CV3ox vs. CV3red)

71

imply not only a complex process but possibly a complex chronology as well. To date the only

72

chronology studies of CV3 metasomatism have been Mn-Cr isotopic analyses of fayalite in

73

several CV3 meteorites (Hutcheon et al., 1998; Hua et al., 2005; Jogo et al., 2009; Doyle et al.,

74

2015). In order to more fully explore the chronology of CV3 metasomatism, we initiated a

75

project to analyze Mn-Cr isotopes in the Ca-Fe silicates (hedenbergite, andradite, and

76

kirschsteinite) in both CV3ox and CV3red meteorites. Our main goals are to determine if there are

77

any resolvable age differences between the Ca-Fe-rich secondary phases in CV3ox vs. CV3red

78

meteorites, whether there is any evidence for an evolutionary sequence within the individual

79

assemblages of either CV3ox or CV3red, and to constrain the timing of accretion of the CV3

80

parent body.

3.7

Ma;

National

Nuclear

Data

Center,

Brookhaven

53

Cr with a half-life

National

Laboratory;

81

We report here the first such isotopic analyses of Ca-Fe silicates in chondrites. Andradite

82

and hedenbergite both lacked sufficiently high 55Mn/52Cr ratios to yield any resolved excesses of

83

radiogenic

84

differences between CV3ox vs. CV3red meteorites or among the phases within individual

53

Cr, so we were unable in this first study to evaluate either possible chronologic 3

53

Cr excesses that correlate with

55

Mn/52Cr,

85

assemblages. However, kirschsteinite yielded large

86

corresponding to its formation 3−4 Ma after CAIs and thus confirming a parent body origin. The

87

inferred kirschsteinite ages are contemporaneous with secondary fayalite in the Asuka 881317

88

CV3oxB (based on its containing nearly pure fayalite; e.g. Krot et al., 2004; Jogo et al., 2009)

89

chondrite, which was analyzed by secondary ion mass-spectrometry (SIMS) using (for the first

90

time) matrix-matched standards (Doyle et al., 2015). Both data sets require accretion of the CV3

91

parent body less than 3–4 million years after CV3 CAI formation.

92

Preliminary data were given in MacPherson et al. (2015); the data reported herein have

93

been revised owing to the use of a new Mn-Cr relative sensitivity factor that was derived from

94

synthetic kirschsteinite.

95

2. METHODS

96 97

2.1. Scanning electron microscopy (SEM) studies

98

Polished sections of the CV3 chondrites Allende, Efremovka, and Vigarano were studied

99

at the Smithsonian using a FEI NOVA NanoSEM 600 field-emission gun SEM, equipped with a

100

Thermo-Noran energy-dispersive silicon-drift X-ray spectrometer (EDS). Prior to SIMS

101

analysis, crystals suitable for analysis were identified and documented at high resolution using

102

back-scattered electron (BSE) imaging. The crystals were also analyzed via EDS X-ray analysis

103

in order to determine phase identification. Because phase identification via stoichiometry was

104

the primary goal, all mineral phases were identified by semi-quantitative analyses using a

105

standard-less ZAF correction procedure. Operating conditions were 15 KeV accelerating voltage

106

and ~ 0.1 nA beam current. Acquisition times were 60 seconds, resulting in total count rates on

107

the order of 7,000–8000 counts per second at 20-25% dead time. Stoichiometry for all phases is

108

uniformly good and phase identification is unambiguous in all cases. All the kirschsteinite EDS

109

data shown graphically in this paper conforms to the requirements (0.95< Ca per 4 oxygens

110

<1.05) and (1.95< total cations per 4 oxygens <2.05). All positive detections for Mn and Cr

111

were confirmed by ensuring that peaks were visible on the raw spectra. On this basis, a realistic

112

detection limit of 0.2 wt. % oxide is estimated for both elements.

113

2.2. SIMS measurements 4

Manganese-chromium isotope analyses were collected in situ in the polished sections via

114

16

O−

115

SIMS, using the Cameca ims-1280 ion probe at the University of Hawai‘i. A 13 keV

116

primary beam, using a 100 pA current, was focused into a ~3×4 µm2 spot. The positive

117

secondary ions were accelerated with 10 kV, and a ~50 eV energy window was used. The 52Cr+

118

and

119

(EMs), followed by the measurement of

120

Counting times were 45 s and 2 s for chromium isotopes and 55Mn+, respectively, in each cycle.

121

The mass resolving power was set to ~4,300 for

122

analytical conditions allowed

123

including 52CrH+. The analysis area was pre-sputtered using a focused beam for 6 minutes, after

124

which isotopic data were collected over 125 cycles (~1.8 hours). The chromium count rate often

125

showed rapid decrease with time during the first 20−30 cycles, which might be due to surface

126

contamination, so the first 25 cycles of all analyses were discarded.

53

Cr+ isotopes were measured simultaneously using multicollector electron multipliers

52

Cr+,

53

55

Mn+ on the monocollector EM by peak-jumping.

Cr+, and

55

52

Cr+, and ~6,100 for

53

Cr+ and

55

Mn+. These

Mn+ to be separated from interfering species,

Corrections were made for both the EM background and dead time. Chromium-isotope and

127 128

55

129

lowest number of total counts of the denominator (52Cr+) is ~2,000 among all measurements and

130

corresponds to a bias of <0.1‰ (Ogliore et al., 2011). The measured

131

corrected for instrumental mass fractionation determined by repeat analysis of synthetic glass of

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Ca-Fe-olivine composition Fa85La15 (see Appendix A for an explanation of composition

133

nomenclature), which is assumed to have a terrestrial

134

(Papanastassiou, 1986). The reported uncertainties (2σ) in chromium-isotope ratio and 55Mn/52Cr

135

ratio include both the internal precision of an individual analysis and the external reproducibility

136

(two standard deviation (2SD)) on the preceding and/or succeeding standard measurements of

137

similar pit shape.

138

Mn+/52Cr+ ratios were calculated using the total number of counts (Ogliore et al., 2011). The

Differences in the ionization efficiencies for

55

Mn+ and

52

53

53

Cr+/52Cr+ ratios were

Cr/52Cr ratio of 0.113459

Cr+ are corrected for by using a

139

relative sensitivity factor (RSF), defined as [(55Mn+/52Cr+)SIMS/(55Mn/52Cr)true]. The RSF is

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determined using standards for which the “true” value is measured independently using electron

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microprobe analysis (EPMA). It has been shown that for olivine compositions in both the Ca-Fe

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and Mg-Fe systems, the Mn-Cr RSF is composition dependent (McKibbin et al., 2013; Doyle et

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al., 2015). The preliminary data reported in MacPherson et al. (2015) used a RSF derived from a 5

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Mn- and Cr-doped fayalitic glass (Fa85La15), as there were no Mn- and Cr-bearing kirschsteinites

145

available (synthetic or natural). Since then we successfully synthesized Mn- and Cr-bearing

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kirschsteinite, and determined new RSFs based on this material. The original isotopic data have

147

accordingly been corrected using those new RSFs, and the new values reported in this paper.

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Details of the sample synthesis and determination of the RSFs are given in Appendices A and B.

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Additional details about determination of RSFs for the ims-1280 ion probe at Hawai‘i are given

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in Doyle et al. (2016).

151

We have not yet synthesized appropriate garnet or pyroxene standards, nor could we find

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suitable natural material (containing appreciable Mn and Cr) in the US National Mineral

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Collection at the Smithsonian. In the case of pyroxene, this ended up not being an issue because

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initial isotopic analyses of the hedenbergite showed that the Mn/Cr ratios are too low to give

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resolvable 53Cr excesses anyway. We do report some preliminary data for hedenbergite, but these

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are shown for illustration only; they were not considered in calculating the initial

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ratio. We did not attempt to analyze andradite at all. We hope to be successful in our future

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attempts to analyze these two minerals if a new radio frequency plasma ion source for the O-

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primary beam (e.g., Malherbe et al., 2016) becomes available for the ims-1280. This source

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provides higher beam density, smaller source diameter, and a smaller energy dispersion than the

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current duoplasmatron source. This translates into a smaller spot size for the same beam current,

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thus enabling the measurement of small grains (<5 µm) that we were not able to measure in this

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study. The higher beam density also helps to obtain better counting statistics and may allow us to

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acquire meaningful 53Cr isotopic data for phases having 55Mn/52Cr ratios less than ~1,000−2,000.

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Synthetic doped pyroxene and garnet standards will then to enable us to acquire high precision

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53

Mn/55Mn

Cr isotopic data for andradite and hedenbergite.

167 168

3.

SAMPLE DESCRIPTION

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Ca-Fe silicates occur in all CV3 chondrite components (CAIs, chondrules and matrices) but

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especially are concentrated in the accretionary rims and matrices surrounding CAIs. We

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therefore studied Ca-Fe silicates near four CAIs that we previously studied in detail: one in

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Allende, two in Vigarano, and one in Efremovka. The two Vigarano samples are from the 6

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Smithsonian collection and are denoted by their USNM thin section numbers: USNM 1623-5

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and USNM 447-5. Efremovka 48E is a thick section from the Russian collection at the

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Vernadsky Institute, Moscow. For the Efremovka and Vigarano samples, the thin section number

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is the same as the CAI number. Allende TS25 is a thin section from the collection of CAIs

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studied by Larry Grossman at the University of Chicago, now in the possession of the Field

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Museum. By convention in Grossman’s group, all interesting objects in each thin section were

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given individual Feature (F) numbers, so TS25-F1 is the dominant large CAI in the middle of

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TS25.

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Vigarano USNM 1623-5 (Fig. 1) is a forsterite-bearing Type B CAI from the reduced

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lithology of the Vigarano breccia, and is notable for being a FUN inclusion (containing

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Fractionation and Unidentified Nuclear isotopic effects). The inclusion was described in detail

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by Davis et al. (1991) and its bulk isotopic properties were reported by Loss et al. (1994).

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Kirschsteinite grains in the vicinity of 1623-5 are exceptionally large and euhedral (Figs. 4a, b),

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and occur both as grains attached directly to the CAI exterior and as “horizons” within layering

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in the associated accretionary rim. The crystals are strongly zoned from cores of nearly end-

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member kirschsteinite to rims of kirschsteinite65-monticellite35, with small irregular hedenbergite

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crystals occurring locally along the crystal edges (Fig. 4a). Some of the kirschsteinite crystals

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enclose small grains of metallic iron (Fig. 4a).

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Vigarano USNM 477-5 (Fig. 2) is a large fluffy Type A CAI, also from the reduced

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lithology of Vigarano, and was studied and described by MacPherson et al. (2003). The

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kirschsteinite near this object differs in its occurrence from that around Vigarano 1623-5,

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occurring here as numerous but small dispersed grains in the surrounding accretionary rim and

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locally filling cavities within the CAI itself (Figs. 4c−e).

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Efremovka 48E (Fig. 3) is a large hibonite-rich compact Type A inclusion, 7×10 mm in

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size. The inclusion consists of gehlenitic melilite (Åk0.9–36), hibonite that is concentrated in the

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CAI core, spinel, pyroxene (Al2O3 up to 22 wt. %, TiO2 – up to 11 wt. %), and anorthite. The

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inclusion is surrounded by an irregular Wark-Lovering rim, and also an accretionary rim that

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contains small tight clumps of kirschsteinite and hedenbergite crystals. The kirschsteinite in

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Efremovka 48E is texturally different from that in Vigarano. The crystals are smaller on average, 7

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un-zoned, and compacted together into clumps. Figure 4f shows one such small clump in the

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region immediately surrounding the CAI. It is intergrown with small crystals of iron-rich calcic

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pyroxene, but the temporal relationship between the two phases is unclear.

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Allende TS25-F1 is a ~ 2 cm long Type A CAI that has been described previously (and

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illustrated) by MacPherson and Grossman (1984), Cosarinsky et al. (2008) and MacPherson and

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Krot (2014). It contains abundant euhedral andradite crystals around its periphery that commonly

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enclose wollastonite (Figs. 4g, h). Analogous to the kirschsteinite in Vigarano 1623-5, the

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pyroxene in the accretionary rim of TS25-F1 is zoned. In most cases the zoning is from iron-rich

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cores to iron-poor rims (Fig. 4g), but in some cases the zoning is more complex (Fig. 4h).

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Figure 5 illustrates the essential chemical variations in kirschsteinite from CV3 chondrites,

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including in this case Leoville and other Efremovka sections that we examined as part of this

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study. The most striking feature is that the kirschsteinite in Vigarano has a much greater

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variation in the range of Fe-Mg variation than does that in either Leoville or Efremovka. This is

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consistent with the lack of any visible zonation in BSE images of the latter, unlike the very

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prominent zoning visible in some of the Vigarano kirschsteinite. There are no significant

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differences in MnO and Cr2O3 contents in kirschsteinite between Vigarano and the other

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meteorites at the level of detection (about 0.2 wt. % for both elements). In all cases, MnO is at or

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above the obvious detection limit (visible peak) of EDS, and Cr2O3 is below it.

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4.

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53

RESULTS

Cr excesses could only be resolved where

55

Mn/52Cr ratios were greater than

223

~1,000−2,000. Kirschsteinite from Vigarano and Efremovka yielded high 55Mn/52Cr ratios, up to

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~21,000 with well resolved δ53Cr excesses, although some had much lower 55Mn/52Cr ratios and

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no resolved δ53Cr excesses. All analyses of hedenbergite yielded

226

consequently no

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analyses (all phases) gave resolved 53Cr excesses.

53

55

Mn+/52Cr+ <1,000 and

Cr excesses were resolved for this phase. Ultimately, about one half of our

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Table 1 gives our isotopic data for kirschsteinite and hedenbergite, and Table 2 summarizes

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the isochron slopes and intercepts for individual and combined samples. Figure 6a shows the 8

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Mn-Cr evolution diagram for the full range of Mn/Cr ratios, and Figure 6b shows in detail the

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data for kirschsteinite and hedenbergite with low Mn/Cr ratios. The hedenbergite data were not

232

used in any of the regressions. The most data were obtained from the accretionary rim

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surrounding 1623-5; only a few analyses from the other two meteorites yielded sufficiently high

234

55

235

an initial ratio (53Mn/55Mn)0 of (3.71±0.50)×10–6. Using Mn-Cr and Pb-Pb data from the

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D’Orbigny angrite to derive an absolute time anchor (Brennecka and Wadhwa, 2012; Glavin et

237

al., 2004; Connelly et al., 2012), this ratio corresponds to 3.2ା଴.଼ ି଴.଻ Ma after formation of the CV

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CAIs. An unconstrained isochron for Vigarano 1623-5 alone yields a slightly higher (albeit

239

within error) and less precise value owing to lack of any data at 55Mn/52Cr < 4,000, (53Mn/55Mn)0

240

= (4.46±2.00)×10‒6, which corresponds to approximately 2.2 Ma after CAI formation. However,

241

if the same data for 1623-5 are forced through the intercept at δ53Cr = 0, we obtain (53Mn/55Mn)0

242

= (3.66±0.61)×10‒6, which is indistinguishable from the slope given by all data combined.

Mn/52Cr ratios. A Model-1 ISOPLOT (v. 3.7) fit with correlated errors to all of the data gives

5. DISCUSSION

243 244 245 246

5.1. Chronology of Ca-Fe silicates and implications for the accretion age of CV3 parent body Ours is the first 53Mn-53Cr data to be obtained from Ca-Fe silicates in CV3 meteorites, and 53

Mn/55Mn ratio derived from our combined data corresponds to kirschsteinite

247

the initial

248

formation 3.2ା଴.଼ ି଴.଻ Ma after CV CAIs. Doyle et al. (2015) reported Mn-Cr isotopic data for pure

249

fayalite from the Asuka 881317 CV3 chondrite. Unlike previous Mn-Cr isotopic measurements

250

of fayalite that are now known to be inaccurate, Doyle et al. (2015) used properly matched

251

standards. Their data are plotted along with ours on Figure 6a for comparison, and trend along a

252

line of somewhat lower slope than ours, corresponding to (53Mn/55Mn)0 = (3.07±0.44)×10−6.

253

Statistically, that value is marginally within error of ours but, taken at face value and again using

254

the D’Orbigny angrite as an absolute time anchor, corresponds to Asuka 881317 fayalite

255

formation 4.2ା଴.଼ ି଴.଻ Ma after CV3 CAIs.

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These ages of formation relative to CAIs are strongly indicative of a parent-body origin for

257

the kirschsteinite and fayalite in these CV3 chondrites. Krot et al. (1998, 2001) argued that the

258

assemblage of magnetite + ferroan olivine + Ca-Fe silicates in CV3 chondrites is the product of 9

259

fluid-assisted metasomatism and metamorphism on the asteroid parent body. Krot et al. (2000,

260

2013) and Doyle et al. (2015) later expanded that interpretation to unequilibrated ordinary, CO3

261

and CO3-like carbonaceous chondrites. MacPherson and Krot (2014) showed that the differing

262

mobile element contents (e.g., alkalis, oxidized iron) of CV3ox vs. CV3red chondrites correlate

263

with differences in impact-controlled porosity and permeability. They concluded from this

264

correlation that the differing secondary mineral assemblages in CV3ox vs. CV3red chondrites must

265

likewise reflect local porosity and permeability differences, thus supporting the idea that these

266

assemblages formed during aqueous metasomatism.

267

Our data thus indicate not only that the Ca-Fe silicates from the reduced CV3 chondrites

268

did indeed form during a parent body process, but did so coevally with the fayalite. This in turn

269

supports the hypothesis of Krot et al. (1998, 2001) that the assemblage of magnetite + ferroan

270

olivine + Ca-Fe silicates in CV3 chondrites is a cogenetic one that collectively formed during

271

fluid-assisted metasomatism and metamorphism on the asteroid parent body.

272

Finally, by definition, parent body metasomatism must have occurred after accretion of

273

that parent body. Thus, accepting that the metasomatism model is correct, our kirschsteinite

274

isotopic data constrain the accretion of the CV3 parent body to have occurred less than 3–4

275

million years after CAI formation. This is consistent with the thermal modelling calculations of

276

Doyle et al (2015) for the L, CO and CV chondrite parent bodies, based on the constraints of

277

Mn-Cr isotopic measurements of fayalitic olivine. They estimated the accretion ages of the

278

respective parent bodies to be on the order of 1.8–2.5 million years after CAI formation. Fujiya

279

et al. (2012) made similar calculations for the CM parent body, based on Mn-Cr isotopic

280

measurements of carbonates. Their estimated accretion age for the CM parent body was ~3.5

281

million years after CAI formation. Although their Mn-Cr data were anchored to another angrite

282

(LEW 86010) instead of D’Orbigny, their thermal evolution modeling ruled out accretion of the

283

CM parent body less than ~ 3 million years after CAI formation. It is important to stress that all

284

of these estimates supersede earlier estimates based on Mn-Cr measurements, because those

285

earlier measurements did not use proper standards from which to calculate relative sensitivity

286

factors.

10

287 288 289

5.2. Relative conditions of formation of Ca-Fe-rich silicates in CV3red vs. CV3ox: Chemistry and time Because the hedenbergite from Allende did not yield resolved excess

53

Cr, we cannot

290

address the question of whether the Ca-Fe silicate assemblages of CV3ox chondrites differ in age

291

from those in CV3red chondrites. We can, however, make some general inferences about the

292

different conditions under which these contrasting assemblages formed and even about the time

293

evolution within each assemblage. These inferences are based on interpreting our textural

294

observations in the context of thermodynamic calculations made by Krot et al. (1998a, 2001) and

295

Hu et al. (2011), which show how the relative stabilities of magnetite, fayalite, and Ca-Fe

296

silicates are controlled by factors such as temperature, PH2O, fluid composition, and oxygen

297

fugacity (fO2).

298

Krot et al. (1998a) calculated the stability fields of magnetite, fayalite, hedenbergite, and

299

andradite in terms of temperature, Fe2+/Ca2+ ions in aqueous solution, fO2 (expressed as H2O/H2)

300

and silica activity in aqueous solution (aSiO2). For example, Figure 7a (modified from Krot et

301

al., 1998a) shows that elevated temperatures stabilize magnetite and andradite relative to

302

hedenbergite and fayalite whereas high calcium activity (low Fe2+/Ca2+) favors hedenbergite and

303

andradite relative to fayalite and magnetite. Krot et al. (1998a) also showed that oxidizing

304

conditions favor andradite and magnetite over fayalite and hedenbergite, whereas elevated aSiO2

305

has the opposite effect. However, because Krot and co-workers were specifically focused on

306

mineral assemblages in the oxidized CV3 meteorites, they did not include kirschsteinite in their

307

calculations. Hu et al. (2011) did include kirschsteinite, albeit not in the context of secondary

308

minerals in CV3 chondrites. Figures 7b and 7c are reproduced in modified form from Hu et al.

309

(2011), and show (respectively) temperature vs. fO2 and fO2 vs. aSiO2. They showed that

310

kirschsteinite is restricted to low fO2 and low aSiO2 (highlighted blue fields in Figs. 7b and 7c)

311

relative to magnetite and hedenbergite respectively. In this context, the differences between the

312

CV3red and. CV3ox chondrites can be interpreted as due to differing physico-chemical

313

environments of alteration. Complications exist however. For example, CV3oxA chondrites

314

contain the four-phase assemblage andradite + hedenbergite + magnetite + ferroan olivine

315

(Fa40‒60), which is unexpected based on Figure 7a. Thus this may not be a stable (equilibrium)

316

assemblage. The coexistence of hedenbergite and kirschsteinite in CV3red chondrites requires 11

317

elevated temperatures combined with low fO2 (Fig. 7b). The simultaneous requirement for a very

318

restricted range of aSiO2 implied by Figure 7c apparently is eased at temperatures above 400 oC

319

(Figs. 7b, c; Hu et al., 2011). The above evidence suggests that the phase assemblage in the

320

CV3oxA chondrites formed under more oxidizing conditions and higher aSiO2 than did the

321

assemblage in the CV3red chondrites. Although elevated temperature favors magnetite and

322

andradite over hedenbergite and fayalite, even higher temperature coupled with low fO2 favors

323

kirschsteinite over magnetite and, presumably, andradite. There are no reaction relationships to

324

indicate whether the CV3red chondrites could have evolved from the CV3ox chondrites or vice

325

versa but, in the model of MacPherson and Krot (2014), the primary cause of the difference

326

between the two was a large difference in the fluid/rock ratio that in turn was controlled by

327

permeability differences. In this model, the differences between the CV3red and CV3ox chondrites

328

are original and do not reflect an evolutionary sequence from one to the other.

329

None of this is to say that both assemblages did not evolve. There is evidence in both that

330

they did evolve, just not in the direction of one another. The kirschsteinite crystals in Vigarano

331

are chemically-zoned, with the crystal rims being sufficiently Fe-poor relative to the crystal cores

332

as to make the zoning readily apparent via BSE imaging (Figs. 4a, d). This zoning is not apparent

333

in Efremovka. Hedenbergite crystals in Allende (but not in Vigarano) also show magnesium-rich

334

rims (Fig. 4h), and MacPherson and Krot (2014) illustrated hedenbergite crystals from Leoville

335

with similar diopside-rich rims. Such zoning might be due to rising temperatures (by analogy

336

with zoning in ferroan olivine: Jogo et al., 2009). Alternatively, under the very low water/rock

337

ratios (~0.1–0.2) estimated for CV3 metasomatism (Doyle et al., 2015), local iron depletion from

338

the fluid due to growth of the Ca-Fe silicates might also have played a role. More indicative is

339

the replacement of wollastonite by andradite and hedenbergite in Allende (Fig. 4g). The upper

340

right portion of Figure 7c indicates that decreasing fO2 and or increasing aSiO2 will destabilize

341

wollastonite (+ magnetite) in favor of hedenbergite. Hu et al. (2011) did not include andradite in

342

their calculations but, as andradite is part of the new (replacing wollastonite) assemblages along

343

with hedenbergite, it seems likely that decreasing fO2 was a less important factor than increasing

344

aSiO2. Thus there is clear evidence that conditions did evolve in both CV3red and CV3ox

345

chondrite alteration regions, but both were evolving in the same direction of increasing

346

temperature, or increasing aSiO2, or some combination of the two. 12

347

Constraining the temporal relationship between the secondary assemblages in CV3red and

348

CV3ox chondrites, will require both the preparation of additional synthetic standards (garnet) and

349

improvement in SIMS techniques. In particular, the use of a radio frequency plasma ion source

350

for the oxygen primary beam would significantly improve counting statistics and allow us to

351

acquire meaningful 53Cr isotopic data for phases having 55Mn/52Cr ratios less than ~1,000−2,000.

352

5.3 Comments related to the special nature of Vigarano 1623-5

353

As noted previously, Vigarano 1623-5 is a FUN inclusion whose unusual isotopic

354

properties set it and similar objects apart from all other CAIs. This begs the question, can the

355

kirschsteinite in the accretionary rim surrounding Vigarano 1623-5 – and the associated Mn-Cr

356

data – be considered as representative of even just the reduced CV3 chondrites? Both FUN and

357

non-FUN CAIs ultimately ended up being accreted into a single object, the CV3 parent body, but

358

it does not necessarily follow that all CAIs acquired their accretionary rims in the same place or

359

at the same time. There is also the possibility that the nearby CAI might have imparted its

360

isotopic signature to the kirschsteinite in the surrounding accretionary rim. However, the Mn-Cr

361

isotopic data from kirschsteinite in the vicinity of Vigarano 1623-5 are in no way unusual

362

relative to the isotopic data from the other CAIs in this study or even relative to the fayalite data

363

from Asuka 881317. Indeed Loss et al. (1994) reported that the chromium isotopes in the

364

Vigarano 1623-5 CAI itself were among the least unusual (“FUN-like”, relative to other

365

elements) for that CAI. Because the Mn-Cr isotope data from Vigarano 1623-5 are

366

indistinguishable from the Vigarano 477-5 and Efremovka 48E data, we conclude that the

367

kirschsteinites from the accretionary rim surrounding Vigarano 1623-5 formed out of the same

368

isotopic reservoir as did those surrounding the other CAIs in this study. That reservoir was

369

independent of the isotopic composition of the CAI itself.

370

6. CONCLUSIONS

371

High precision SIMS analyses of Mn and Cr isotopes in kirschsteinite from Vigarano and

372

Efremovka yield well resolved 53Cr excesses from the in situ decay of extinct 53Mn, which was

373

present at an initial ratio 53Mn/55Mn = (3.71±0.50)×10‒6. This ratio corresponds to kirschsteinite

374

formation (3.2ା଴.଼ ି଴.଻ ) Ma after CV CAIs, which is approximately the same age as fayalite from the

375

Asuka 881317 CV3 chondrite (Doyle et al., 2015). Based on this age we conclude that the 13

376

formation of kirschsteinite, like fayalite, took place on the CV3 parent body during metasomatic

377

alteration. For analytical reasons we are not yet able to establish any relative age difference

378

between CV3red and CV3ox chondrite alteration, but it is reasonably clear from other evidence

379

that one assemblage did not form from the other. They formed independently. Both CV3red and

380

CV3ox chondrite alteration assemblages evolved subsequent to their formation and in similar

381

ways, leading to the Fe-bearing silicates becoming progressively more Mg-rich. This likely was

382

due to progressive depletion of oxidized iron in the evolving fluid phase or increasing

383

temperature, or a combination of both.

384 385

Acknowledgements: We gratefully acknowledge detailed and constructive reviews by Dr.

386

Seann McKibbin and two anonymous reviewers, which significantly improved the paper. This

387

work was supported by National Aeronautics and Space Administration (NASA)

388

Cosmochemistry grants NNX11AD43G (GJM, PI), and NNX10AH76G (ANK, PI), NASA

389

Emerging Worlds grants NNX15AH68G (GJM, PI) and 14-EW14-2-0049 (ANK, PI), and South

390

African National Research Foundation grant no. 88191 (PMD, PI).

391

14

392 393

References

394

Brennecka G. A. and Wadhwa, M. (2012) Uranium isotope compositions of the basaltic angrite

395

meteorites and the chronological implications for the early Solar System. Proc. Nat. Acad.

396

Sci. 109, 9299−9303.

397

Connelly J. N., Bizzarro M., Krot A. N., Nordlund Å., Wielandt D., Ivanova M. A. (2012) The

398

absolute chronology and thermal processing of solids in the solar protoplanetary disk.

399

Science 338:651−655.

400

Cosarinsky M., Leshin L. A., MacPherson G. J., Guan Y., and Krot A. N. (2008) Chemical and

401

oxygen isotopic compositions of accretionary rim and matrix olivine in CV chondrites:

402

Constraints on the evolution of nebular dust. Geochim. Cosmochim. Acta 72, 1887–1913.

403

Davis A. M., MacPherson G. J., Clayton R. N., Mayeda T. K., Sylvester P., Grossman L, Hinton

404

R.W., and Laughlin J.R. (1991) Melt solidification and late-stage evaporation in the

405

evolution of a FUN inclusion from the Vigarano C3V chondrite. Geochim. Cosmochim. Acta

406

55, 621–638.

407

Davis A. M., Alexander C. D., Ciesla F. J., Gounelle M., Krot A. N., Petaev M. I., and Stephan

408

T. (2014). Samples of the Solar System: recent developments. Protostars and Planets VI,

409

809−831.

410

Doyle P. M., Jogo K., Nagashima K., Krot A. N., Wakita S., Ciesla F. J., and Hutcheon I. D.

411

(2015) Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies

412

recorded by fayalite. Nature Comm. 6, 1‒10.

413

Doyle P. M., Jogo K., Nagashima K., Huss G. R., and Krot A. N. (2016) Mn-Cr relative

414

sensitivity factor in ferromagnesian olivines defined for SIMS measurements with a Cameca

415

ims-1280 ion microprobe: Implications for dating secondary fayalite. Geochim. Cosmochim.

416

Acta 174, 102−121.

417 418 419

Endreβ M., Zinner E, and Bischoff A (1996) Early aqueous activity on primitive meteorite parent bodies. Nature 379: 701–703. Fujiya W., Sugiura N., Hotta H., Ichimura K. and Sano Y. (2012) Evidence for the late formation 15

420 421 422

of hydrous asteroids from young meteoritic carbonates. Nature. Comm. 3, 1–6. Glavin D. P., Kubny A., Jagoutz E., and Lugmair G. W. (2004) Mn–Cr isotope systematics of the D’Orbigny angrite. Meteorit. Planet. Sci. 39, 693–700.

423

Hu J., Mao S., Du G., Wu Y., and Zhang P. (2011) A new thermodynamic analysis of the

424

intergrowth of hedenbergite and magnetite with Ca-Fe-rich olivine American Mineralogist,

425

96, 599–608.

426

Hua J., Huss G. R., Tachibana S., and Sharp T. G. (2005) Oxygen, silicon, and Mn–Cr isotopes

427

of fayalite in the Kaba oxidized CV3 chondrite: Constraints for its formation history.

428

Geochim. Cosmochim. Acta 69, 1333–1348.

429 430

Hutcheon I. D. and Phinney D. L. (1996) Radiogenic 53Cr* in Orgueil carbonates: Chronology of aqueous activity on the CI parent body. Lunar and Planetary Science 27: 577–578.

431

Hutcheon I. D., Krot A. N., Keil K., Phinney D. L., and Scott E. R. D. (1998) 53Mn–53Cr dating

432

of fayalite formation in the CV3 chondrite Mokoia: Evidence for asteroidal alteration.

433

Science 282, 1865–1867.

434

Jogo K., Nakamura T., Noguchi T., and Zolotov M. Y. (2009) Fayalite in the Vigarano CV3

435

carbonaceous chondrite: Occurrences, formation age and conditions. Earth Planet. Sci. Lett.

436

287, 320–328.

437

Kita N. T., Huss G. R., Tachibana S., Amelin Y., Nyquist L. E., and Hutcheon I. D. (2005)

438

Constraints on the origin of chondrules and CAIs from short-lived and long-lived

439

radionuclides. In Chondrites and the Protoplanetary Disk (eds. A. N. Krot, E. R. D. Scott

440

and B. Reipurth). pp. 558–587.

441

Krot A. N., Scott E. R. D., and Zolensky M. E. (1995) Mineralogical and chemical modification

442

of components in CV3 chondrites: Nebular or asteroidal processing? Meteoritics 30: 748–

443

775.

444

Krot A. N., Petaev M. I., Zolensky M. E., Keil K., Scott E. R. D., and Nakamura K. (1998a)

445

Secondary calcium-iron minerals in the Bali-like and Allende-like oxidized CV3 chondrites

446

and Allende dark inclusions. Meteoritics 33, 623−645. 16

447

Krot A N., Petaev M. I., Scott E. R. D., Choi B-K., Zolensky M. E., and Keil K. (1998b)

448

Progressive alteration in CV3 chondrites: More evidence for asteroidal alteration. Meteorit.

449

Planet. Sci. 33, 1065–1085

450

Krot A. N., Brearley A. J., Petaev M. I., Kallemeyn G. W., Sears D. W. G., Benoit P. H.,

451

Hutcheon I. D., Zolensky M. E., and Keil K. (2000) Evidence for in situ growth of fayalite

452

and hedenbergite in MacAlpine Hills 88107, ungrouped carbonaceous chondrite related to

453

CM-CO clan. Meteorit. Planet. Sci. 35, 1365−1387.

454 455

Krot A. N., Petaev M. I., Meibom A., and Keil K. (2001) In situ growth of Ca-rich rims around Allende dark inclusions. Geochem. Internation. 36, 351−368.

456

Krot A. N., Petaev M. I., and Bland P. A. (2004) Multiple formation mechanisms of ferrous

457

olivine in CV carbonaceous chondrites during fluid-assisted metamorphism. Antarct.

458

Meteorite Res. 17, 153-171.

459

Krot A. N., Hutcheon I. D., Brearley A. J., Pravdivtseva O. V., Petaev M. I., and Hohenberg C.

460

M. (2006) Timescales and settings for alteration of chondritic meteorites. Meteorites and the

461

Early Solar System II, 525−553.

462

Krot A. N., Doyle P., and Nagashima K. (2013) Secondary fayalite, hedenbergite, and magnetite

463

in the CO3.0−3.1 carbonaceous chondrites Y-81020, EET 90043, and MAC 88107. Lunar

464

Planet. Sci. XLIV, Lunar Planet. Inst., Houston. Abstr. #1754.

465

Loss R. D., Lugmair G. W., MacPherson G. J., and Davis A. M. (1994) Isotopically distinct

466

reservoirs in the solar nebula: Isotope anomalies in Vigarano meteorite inclusions.

467

Astrophys. J. 436, L193−L196.

468 469 470 471 472 473

MacPherson G.J. and Grossman L. (1984) Fluffy Type A inclusions in the Allende meteorite; Geochim. Cosmochim. Acta 48, 29−46. MacPherson G. J., Huss G. R., and Davis A. M. (2003) Extinct 10Be in Type A CAIs from CV Chondrites. Geochim. Cosmochim. Acta 67, 3165−3179. MacPherson G. J. and Krot A. N. (2014) Distribution of Ca-Fe-silicates in CV3 chondrites: Controls by parent-body compaction. Meteorit. Planet. Sci. 49, 1250–1270. 17

474

MacPherson G. J., Nagashima K., Krot A. N. and Ivanova M.A. (2015) 53Mn-53Cr compositions

475

of Ca-Fe silicates in CV3 chondrites. Lunar Planet. Sci. XLVI, Lunar Planet. Inst.,

476

Houston. Abstr #2760.

477

Malherbe J., Penen F., Isaure M.-P., Frank J., Hause G, Dobritzsch D., Gontier E., Horréard F.,

478

Hillion F., and Schaumlöffel D. (2016) A New Radio Frequency Plasma Oxygen Primary

479

Ion Source on Nano Secondary Ion Mass Spectrometry for Improved Lateral Resolution and

480

Detection of Electropositive Elements at Single Cell Level. Anal. Chem. 88, 7130−7136

481

McKibbin S. J., Ireland T. R., Amelin Y., O’Neill H. S. C., and Holden P. (2013) Mn–Cr relative

482

sensitivity factors for secondary ion mass spectrometry analysis of Mg-Fe-Ca olivine and

483

implications for the Mn-Cr chronology of meteorites. Geochim. Cosmochim. Acta 110,

484

216−228.

485

Ogliore R. C., Huss G. R., and Nagashima K. (2011) Ratio estimation in SIMS analysis. Nuclear

486

Instruments and Methods in Physics Research Section B: Beam Interactions with Materials

487

and Atoms 269, 1910−1918.

488 489 490

Papanastassiou D. A. (1986) Chromium isotopic anomalies in the Allende meteorite. Astrophys. J. 308, L27−L30. Papanastassiou D. A., Wasserburg G. J. and Bogdanovski O. (2005) The

53

Mn–53Cr system in

491

CAIs: an update. Lunar Planet. Sci. XXXVI. Lunar and Planetary Inst., Houston. Abstract

492

#2198.

493 494 495 496

Rosman K. J. R. and Taylor P. D. P. (1998) Isotopic compositions of the elements 1997. Pure and Applied Chemistry 70, 217−235. Zolotov M. Yu., Mironenko M. V., and Shock E. (2006) Thermodynamic constraints on fayalite formation on parent bodies of chondrites. Meteorit. Planet. Sci. 41, 1775–1796

497

18

498

Figure Captions

499

Figure 1. BSE image of the FUN CAI Vigarano 1623-5, a forsterite-bearing Type B inclusion.

500

The highlighted rectangles show the locations of the detailed images shown in Figures 4a−b,

501

which contain the analyzed kirschsteinite crystals.

502

Figure 2. BSE image of the Fluffy Type A CAI Vigarano 477-5. The highlighted rectangles

503

show the locations of the detailed images shown in Figures 4c−e, which contain the analyzed

504

kirschsteinite crystals.

505

Figure 3. BSE image of the Compact Type A CAI, Efremovka 48E. The highlighted rectangle,

506

emphasized by the arrow, shows the location of the detailed image shown in Fig. 4f, which

507

contain the analyzed kirschsteinite crystals.

508

Figure 4. (a-f) Backscattered electron images of kirschsteinite (Kir) and hedenbergite (Hd)

509

crystals in the matrices (Mtx) and accretionary rims (AR) surrounding CAIs from Vigarano,

510

Efremovka, and Allende. The kirschsteinite in Vigarano 1623-5 is strongly zoned from nearly

511

pure kirschsteinite cores to rims with ~ 65% of the monticellite component. (g-h) Backscattered

512

electron images of andradite (And), wollastonite (Wo), and hedenbergite (Hd) crystals in the

513

matrix and accretionary rim surrounding the Allende CAI TS25-F1. Note that the andradite and

514

hedenbergite envelop and likely are replacing wollastonite. The pyroxene crystals in (g) are

515

strongly zoned from hedenbergite cores to diopside-rich rims, but in (h) the zoning pattern is

516

complex. Other abbreviations: Di: diopside; Hib: hibonite; Mel: melilite; Met: metal.

517

Figure 5. Bulk (left) and minor element (right) compositions of kirschsteinite. All analyses by

518

EDS. The detection limit (dashed vertical line) is the same for both MnO and Cr2O3, putting all

519

Cr2O3 analyses below detection limit and most MnO analyses above it. Data shown include

520

analyses of kirschsteinite from additional thin sections of Allende and also Leoville, although

521

these were not analyzed by SIMS.

522

Figure 6. (a) 55Mn/52Cr vs. δ53Cr for kirschsteinite crystals in the accretionary rims around three

523

CAIs in Vigarano and Efremovka. The combined data define a correlation line corresponding to

524

initial 53Mn/55Mn ratio of (3.71±0.50) ×10‒6. Data for Asuka 881317 fayalite (Doyle et al., 2015)

525

are shown for comparison. (b) Similar to (a), but showing an enlargement of the region near the 19

526

origin and with the addition of low Mn/Cr data. Hedenbergite data from Efremovka 48E and

527

Allende TS25-F1 is shown for reference only and is plotted in terms of uncorrected 55Mn+/52Cr+

528

ion ratios, because the relative sensitivity factor for this phase is not known

529

Figure 7. Thermodynamic stability diagrams for the system Ca-Fe-Si-O. (a) Diagram showing T

530

vs. log (Fe2+/Ca2+) in aqueous solution, showing the relative stability of the phases fayalite,

531

andradite, magnetite (Mag), and hedenbergite. Note that andradite (highlighted red field) is

532

stable at higher temperatures than is hedenbergite. Kirschsteinite is not present on this diagram

533

because it is only stable at lower activities of silica than that used for this calculation (see Fig.

534

7c). Reproduced in modified form from Krot et al. (2000). (b) A schematic but geometrically-

535

correct (in the manner of Schreinemakers) graph of T vs. log fO2 for the system Ca-Fe-Si-O.

536

Note that the assemblage kirschsteinite + hedenbergite + fayalite (highlighted blue field) requires

537

relatively high temperature and low fO2. (c) A graph of log a (SiO2) vs. log fO2 for the system

538

Ca-Fe-Si-O, showing that kirschsteinite (highlighted blue field) is stabilized by low silica

539

activity and low fO2. Wo: wollastonite; other abbreviations as used previously. (b) and (c) are

540

reproduced in modified form from Hu et al. (2011) with permission from the Mineralogical

541

Society of America.

542

20

Table 1. Kirschsteinite Mn-Cr isotopic data. ±2σ

RSF used

19532

1055

A4-sp2

24299

A2-sp5

22455

Mineral

Meteorite

Sample

Meas #

Kirschsteinite

Vigarano

1623-5

A4-sp4

Vigarano

Efremovka

c

Hedenbergite

Efremovka

Vig477-5

E48

E48

55

raw Mn+/52Cr+

55

Mn/52Cr

±2σ

1.74

11243

2027

2358

1.74

13987

1629

1.74

12926

d

53

Cr/52Cr

52

Crtotal ctsa

±2σ

δ53Cr

±2σ

0.1483

0.0177

307

156

2934

0.25

2763

0.1586

0.0245

398

216

2349

0.33

2413

0.1686

0.0156

486

138

3859

0.10

ρb

A2-sp6

27019

2193

1.73

15631

3035

0.1699

0.0216

497

190

2181

0.40

A1-sp4

15053

1196

1.74

8665

1642

0.1475

0.0156

300

138

5152

0.32

A1-sp3

17942

1091

1.74

10328

1885

0.1473

0.0142

298

125

4242

0.28

A6-sp2

8414

878

1.74

4843

974

0.1215

0.0176

71

155

2474

0.24

A8-sp1

17156

1661

1.74

9876

1950

0.1502

0.0164

324

144

3111

0.15

A4-sp3

3110

125

1.74

1790

316

0.1219

0.0074

74

65

11282

-0.06

A3-sp3

158

18

1.74

91

19

0.1133

0.0016

-2

14

221400

0.04

A5-sp2

488

68

1.74

281

62

0.1122

0.0033

-11

29

65790

0.04

AA-sp2

32959

1964

1.74

18972

3454

0.1877

0.0205

654

180

2002

0.14

AA-sp8

657

34

1.74

378

68

0.1165

0.0024

27

21

82672

0.00

AA-sp6

90

7

1.71d

52

10

0.1128

0.0014

-6

12

313222

-0.04

AA-sp5

480

16

n.d.

n.d.

n.d.

0.1144

0.0033

9

29

20000

n.d.

0.1162

0.0042

24

37

26925

n.d.

Allende TS25-F1 A7F-sp3 721 12 n.d. n.d. n.d. 55 + 52 + All errors are 2σ, including reproducibility of standard measurements except for raw Mn / Cr ion ratios. a sum of all counts per run. b correlation coefficient on 53Cr/52Cr vs. 55Mn/52Cr among cycles. c Not used for calculation of initial 53Mn/55Mn ratio. d RSF factors are different because of fewer cycles during analysis. See Appendix B 2.4.2

21

Table 2. Summary isochron slopes.

(53Mn/55Mn)0 (x10-6)

±2σ

(53Cr/52Cr)0

±2σ

δ53Cr0

±2σ

MSWD

all combined

3.71

0.50

0.11296

0.00090

-4.4

8.0

0.72

Vigarano

Vig 1623-5

4.46

2.03

0.10329

0.02209

-89.7

194.7

0.41

Vigarano

Vig 477-5

4.65

4.41

0.11251

0.00158

-8.3

13.9

1.30

Vigarano

Vig 1623-5 + 477-5

3.65

0.56

0.11265

0.00138

-7.1

12.2

0.52

Efremovka

E48

4.09

1.21

0.11316

0.00119

-2.6

10.5

3.10

Meteorite

Sample

Vigarano+Efremovka

All regressions were made with an IsoPlot model-1 fit with correlated errors.

22

Figure 1.

24

Figure 2.

25

Figure 3. 26

Figure 4.

27

Figure 5.

28

Figure 6.

29

Figure 7

30

Appendix A: Synthesis of Fe- and Ca-rich silicate standards (including kirschsteinite) Four synthetic standards were prepared using a 1 atm vertical gas-mixing furnace at the University of Hawai‘i at Mānoa (UH). Appendix Figure A1 shows the compositions of our experimental charges in the system Mg2SiO4-Ca2SiO4-Fe2SiO4., along with the associated nomenclature. The preparation of liquidus phase fayalite (Fa99) is described by Doyle et al. (2015). The Fe-, Ca-rich olivine composition (Fa85La15) that was used in a preliminary study (MacPherson et al., 2015) was synthesized using a mixture of pre-dried CaCO3 and the oxide mixture (Fe2SiO4) from which Fa99 was produced. For the kirschsteinite synthesis reported here, stoichiometric mixtures of pre-dried SiO2, Fe2O3, MgO, CaCO3, MnCO3 and Cr2O3 were ground by hand under ethanol in an agate pestle and mortar. The powders were mixed with a polyvinyl alcohol solution and mounted on platinum loops. Mixtures of H2 and CO2 were used to control the oxygen fugacity (fO2), which was monitored using a SIRO2 C700+ solid-electrolyte oxygen sensor. The conditions were ~iron-wüstite (IW) +0.7 to +0.8 (Table A1). Up to four compositions were loaded during a single run, and temperatures ranged between 1143 and 1214°C such that the bulk composition was sub-solidus, completely molten or within the liquidus envelope for Fe-Ca-olivines (Mukhopadhyay and Lindsley, 1983). The temperature was monitored using an S-type thermocouple. The samples were held at dwell temperature for either 2 or ~19 hours, after which they were quenched into water. Appendix A Figure A2a is a photograph of one of the run products, showing amber-colored kirschsteinite crystals concentrated at the bottom of the charge with black glass above; Figure A2b is a BSE image of a polished grain mount made from this charge. Portions of the run products were mounted in epoxy resin, either as one-inch round disks or in stainless steel bullet pucks. The polished samples were characterized using the University of Hawai‘i (UH) JEOL JXA-8500F field emission electron microprobe. Linear drift corrections were applied (where necessary) to calcium, magnesium, silicon, iron and manganese contents using samples measured approximately two hours apart. The drift correction for CaO was calibrated using CaO-rich minerals and appears to overestimate the CaO contents for samples with negligible CaO. For example, the CaO content of Fa99 (UH standard NN14) was amended from below the detection limit (<0.01 wt% CaO) to 0.62±0.25 wt% CaO after the drift correction. 31

Two samples with end-member kirschsteinite compositions were prepared: one was a homogeneous glass and the other contained liquidus phase crystals. The compositions of the synthesized samples (measured from areas surrounding the ion probe pits) are listed in Supplementary Table A2. Although there is not a complete solid solution between fayalite and larnite, the samples will be referred to according to their Fa-La-Forsterite (Fo) number. Samples with Fo1 (or less) will be referred to in Appendix B simply by their Fa-La number. Appendix A References: Doyle P. M., Jogo K., Nagashima K., Krot A. N., Wakita S., Ciesla F. J., and Hutcheon I. D. (2015) Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite. Nature Comm. 6, 1‒10. MacPherson G. J., Nagashima K., Krot A. N. and Ivanova M.A. (2015) 53Mn-53Cr compositions of Ca-Fe silicates in CV3 chondrites. Lunar Planet. Sci. XLVI, Lunar Planet. Inst., Houston. Abstr #2760. Myers J. and Eugster H. P. (1983) The system Fe-Si-O: Oxygen buffer calibrations to 1,500K. Contrib. Miner. Petrol. 82, 75‒90. Mukhopadhyay D.K. and Lindsley D. H. (1983) Phase-relations in the join kirschsteinite (CaFeSiO4) – fayalite (Fe2SiO4). Amer. Mineral. 68, 1089‒1094.

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Appendix Table A1 Summary of synthesis conditions. Experiment Dwell Hours at log ∆IW Product o Number T ( C) dwell T fO2 UH190912 1200 19 -11.0 0.7 Liquidus phase UH230414 1143 18 -11.7 0.8 Glass UH191015 1187 20 -11.2 0.7 Liquidus phase UH201015 1215 2 -10.8 0.8 Glass

Stoichiometry

Composition

Fe2.0Si1.0O4 Ca0.3Fe1.7Si1.0O4 Ca1.0Fe0.9Si1.0O4 Ca0.9Fe1.0Si1.0O4

Fa99 * Fa85La15 Fa48La51Fo1 Fa50La49Fo1

Notes: ∆IW calculated relative to the iron-wüstite buffer curve defined by Myers and Eugster (1983). Uncertainties on measurements of temperature (T) and fO2 are ± 3−4 oC and ± 0.04 fO2 log units, respectively. The standard deviation on the log fO2 during the last ~2 h of synthesis for UH230414, UH191015 and UH201015 is 0.01, 0.04 and 0.08 log units. *Fa99 was described by Doyle et al. (2015); includes 1 mole% forsterite.

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Appendix Table A2 Composition of crystals and glasses with Fe,Ca-olivine stoichiometry Sample SiO2 CaO MgO 1σ FeO(tot) 1σ 1σ 1σ * Fa99 29.26 ±0.28 0.62 ±0.25 0.44 ±0.05 69.41 ±0.30 Fa85La15 28.83 ±0.29 8.19 ±0.15 0.09 ±0.05 60.87 ±0.69 * Fa48La51 (xstl) 31.47 ±0.23 29.79 ±0.11 0.38 ±0.03 35.42 ±0.22 * Fa50La49 (glass) 32.89 ±0.12 27.68 ±0.05 0.28 ±0.04 36.06 ±0.13 # = number of analyses. *

Includes 1 mole% forsterite.

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MnO 0.70 0.67 0.94 0.71

1σ ±0.01 ±0.01 ±0.01 ±0.01

Cr2O3 0.10 0.04 0.08 0.08

1σ ±<0.01 ±<0.01 ±0.01 ±0.01

Total 100.54 98.68 98.08 97.70

1σ ±0.63 ±1.14 ±0.48 ±0.19

# 19 9 23 16

Appendix Figure A1. Compositions of experimental charges in the system Mg2SiO4-Ca2SiO4Fe2SiO4. Abbreviations: La – larnite; Fo – forsterite; Fa – fayalite. “Larnite” is a familiar notation used throughout this work to refer to the composition Ca2SiO4-with no intended implication for a specific polymorph.

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Appendix Figure A2. (a) Optical image of the run product showing golden crystals of kirschsteinite (the liquidus phase) that have settled to the bottom of the charge; (b) BSE image of a polished section of the run product, showing kirschsteinite and glass.

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Appendix B: Manganese-chromium relative sensitivity factor for kirschsteinite 2.4.1 Compositional dependence The RSF measured on Fa85La15 is ~0.1 higher than that measured on Fa99, and the RSFs for Fa48La51

(Xll)

and Fa50La49

(glass)

are ~0.3 higher than that measured on Fa99 (Suppl. Table B1).

Although analytical procedures and instrumentation can affect the RSF value and behavior (Doyle et al., 2016), the general trend for RSFs measured on Fe,Ca-bearing olivine compositions appears to be similar for Cameca and SHRIMP (reverse geometry) ion microprobes. Indeed, the RSF measured using a SHRIMP instrument (McKibbin et al., 2013) increases from 1.06 for fayalite (Fa100) to 1.41 for low-Ca kirschsteinite (~Fa58La35Fo7) when the RSF is recalculated as RSFmeasured/true. 2.4.2 RSF reconciliation Preliminary data reported in MacPherson et al. (2015) used a RSF derived from a Mn- and Cr- doped glass of fayalitic composition (Fa85La15) as there were no Mn- and Cr-bearing kirschsteinite samples available (synthetic or natural). In 2015, Mn-Cr isotope data were collected from Fa48La51 (Xll), Fa50La49 (glass), Fa85La15, and Fa99 using the 2014 SIMS measurement protocol. The 2015 Mn-Cr isotope measurements for Fa99 and Fa85La15 were made alongside the SIMS pits created in 2014, and the RSFs measured on Fa99 during the two sessions are within uncertainty (Appendix B, Table B1, Fig. B1), differing by only 0.04. Similarly, the RSF measured on Fa85La15 between sessions differed by only 0.02. The SIMS pit-shape in Fe-rich olivine compositions does influence the Mn-Cr RSF (Doyle et al., 2016). The pit sizes and shapes for the 2014 and 2015 sessions are very similar, which is consistent with the small variation in RSF between the sessions. A RSF for end-member kirschsteinite composition was calculated using a bootstrap method, assuming that the variation in RSFs between kirschsteinite, and Fa99 and/or Fa85La15 was a constant percent. Using an average of the relative differences for Fa99 and Fa85La15, the estimated RSFs for the 2014 session are 1.73±0.44 and 1.75±0.40 for Fa48La51

(Xll)

and Fa50La49

(glass),

respectively. We took an average of the estimated RSFs for Fa48La51 (Xll) and Fa50La49 (glass), and 38

used it (1.74±0.30) to correct the 55Mn+/52Cr+ ratios of kirschsteinite in Vigarano and Efremovka. The revised values are reported in this paper. Two measurements (Vigarano 1623-5 A2-sp6 and Efremovka E48 AA-sp6) have smaller numbers of cycles (69 and 51, respectively) than the nominal 100 cycles, because of sudden increases of Cr count rates likely due to breaching the base of the grains. Since Mn/Cr RSF is time-dependent, RSFs of these two measurements were determined based on 69 and 51 cycles of the standard data.

Appendix B References: Doyle P. M., Jogo K., Nagashima K., Huss G. R., and Krot A. N. (2016) Mn-Cr relative sensitivity factor in ferromagnesian olivines defined for SIMS measurements with a Cameca ims-1280 ion microprobe: Implications for dating secondary fayalite. Geochim. Cosmochim. Acta 174, 102−121. MacPherson G. J., Nagashima K., Krot A. N. and Ivanova M.A. (2015) 53Mn-53Cr compositions of Ca-Fe silicates in CV3 chondrites. Lunar Planet. Sci. XLVI, Lunar Planet. Inst., Houston. Abstr #2760. McKibbin S. J., Ireland T. R., Amelin Y., O’Neill H. S. C., and Holden P. (2013) Mn–Cr relative sensitivity factors for secondary ion mass spectrometry analysis of Mg-Fe-Ca olivine and implications for the Mn-Cr chronology of meteorites. Geochim. Cosmochim. Acta 110, 216−228.

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Appendix Table B1 55Mn+/52Cr+, 55Mn/52Cr(true) and Mn-Cr RSF for Fe,Ca-olivine stoichiometry Year Sample # 55Mn+/52Cr+ ±2SD 55Mn/52Cr(true)a Fa99* 3 12.41 0.32 8.44 2014 Fa85La15 17 34.78 1.51 22.14 est. kirschsteinite† Fa99* 4 12.03 0.29 8.44 Fa85La15 2 34.98 0.20 22.50 2015 Fa48La51* (Xll) 8 24.11 3.66 14.26 * Fa50La49 (glass) 4 17.97 1.33 10.49

crystals and glasses with ±2SD 0.71 2.09 0.71 4.51 2.35 1.82

RSF 1.47 1.57 1.74 1.43 1.55 1.69 1.71

±2σ 0.13 0.16 0.30 0.12 0.31 0.38 0.32

# = number of analyses. Uncertainties are either 2 standard deviation (2SD) or 2σ uncertainty including uncertainties from electron microprobe and secondary ion mass spectrometry measurements. * Includes 1 mole% forsterite. † Estimated RSF for end-member kirschsteinite composition (~Fa50La50) for 2014 measurement session. a The (55Mn/52Cr)true ratio is calculated from electron microprobe analyses, assuming 83.789% of Cr is 52Cr (Rosman and Taylor, 1998).

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Appendix Figure B1. RSF for crystals and glasses having Fe-, Ca-olivine stoichiometry. The data point for Fa50La50 (est) is not based on measurements of an actual sample but rather is an estimated value for end-member kirschsteinite (see text).

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