# Gallium isotopic evidence for the fate of moderately volatile elements in planetary bodies and refractory inclusions

Chizu Kato, Frédéric Moynier

► To cite this version:

Chizu Kato, Frédéric Moynier. Gallium isotopic evidence for the fate of moderately volatile elements in planetary bodies and refractory inclusions. Earth and Planetary Science Letters, 2017, 479, pp.330-339. 10.1016/j.epsl.2017.09.028. insu-02917183

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1 Gallium isotopic evidence for the fate of moderately volatile

2 elements in planetary bodies and refractory inclusions

3

4 Chizu Kato<sup>a,*,1</sup> and Frédéric Moynier<sup>a,b</sup>

5

6 <sup>a</sup>Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité,

7 CNRS UMR 7154, Paris, France

8 <sup>b</sup>Institut Universitaire de France, 75005, Paris, France

9

10 *Corresponding author email address: kato@ipgp.fr

11 Present address: <sup>1</sup>Division of Sustainable Energy and Environmental Engineering,

12 Graduate school of Engineering, Osaka University, Suita, Osaka, 565-0871 Japan

13

14

15 Abstract

16 The abundance of moderately volatile elements, such as Zn and Ga, show variable
17 depletion relative to CI between the Earth and primitive meteorite (chondrites) parent
18 bodies. Furthermore, the first solar system solids, the calcium-aluminium-rich inclusions
19 (CAIs), are surprisingly rich in volatile element considering that they formed under high
20 temperatures. Here, we report the Ga elemental and isotopic composition of a wide
21 variety of chondrites along with five individual CAIs to understand the origin of the
22 volatile elements and to further characterize the enrichment of the volatile elements in
23 high temperature condensates. The δ<sup>71</sup>Ga (permil deviation of the <sup>71</sup>Ga/<sup>69</sup>Ga ratio from
24 the Ga IPGP standard) of carbonaceous chondrites decreases in the order of CI > CM >
25 CO > CV and is inversely correlated with the Al/Ga ratio. This implies that the Ga budget
26 of the carbonaceous chondrites parent bodies were inherited from two component mixing
27 of a volatile rich reservoir enriched in heavy isotope of Ga relative to the Ga isotope
28 composition of volatile poor. Calcium-aluminum-rich inclusions are enriched in Ga and
29 Zn compared to the bulk meteorite and are both highly isotopically fractionated with
30 δ<sup>71</sup>Ga down to -3.56 ‰ and δ<sup>66</sup>Zn down to -0.74 ‰. The large enrichment in the light
31 isotopes of Ga and Zn in the CAIs implies that the moderately volatile elements were
32 introduced in the CAIs during condensation in the solar nebula as opposed to secondary
33 processing in the meteorite parent body and supports a change in gas composition in
34 which CAIs were formed.
35
36

35

36

1. Introduction

38

39 Volatile elements control many fundamental characteristics of the terrestrial planets,
40 including their ability to develop and sustain life as well as the geochemical properties
41 that make each planet unique. The asteroid belt is like a cold chamber of relics from the
42 earliest stage of the solar system, and thanks to Jupiter's gravitational perturbation we
43 have free sample delivery in the form of meteorites (Walsh et al. 2011). Among these
44 meteorites, chondrites have not undergone planetary differentiation. A major unresolved
45 issue is the widespread volatile elements depletion observed in terrestrial planets and in
46 meteorites (e.g. Halliday and Porcelli 2001, Palme and O'Neill 2003). In particular,
47 carbonaceous chondrites show a volatile depletion trend in the order CI > CM > CO > CV, which has challenged the scientific community for decades.

49 Calcium-Aluminum rich Inclusions (CAIs), together with chondrules and matrix, are the main components of meteorites. Calcium-Aluminum-rich Inclusions are formed at high-temperature (e.g. Grossman et al. 2002) and represent the first solids of the Solar System with U-corrected Pb-Pb absolute age of 4567.30 ± 0.16 million years (Connelly et al. 2012). However, CAIs show large enrichment in moderately volatile elements (e.g. Zn, Ga, refs: Chou et al. 1976; Bischoff et al. 1987; Sylvester et al. 1993) whose origin is debated between being introduced by secondary aqueous alteration of the CAIs on the meteorite parent body or by gas-solid exchange in the solar nebula prior to the formation of the parent body.

58 Volatilization is known to fractionate isotopes; therefore, comparing the isotopic compositions of volatile elements is a very powerful tool to understand the origin of volatile element abundance variations, especially to distinguish between aqueous alteration and volatilization for the origin of the volatile element excesses in CAIs (e.g. Luck et al. 2005). In this work, we will focus on the Ga isotopic composition of bulk meteorites and CAIs.

64 Gallium is a moderately volatile element with a 50% volatile temperature of 968 K (Lodders 2003). It has two isotopes, <sup>69</sup>Ga and <sup>71</sup>Ga, with natural elemental abundances of 60.1 % and 39.9 %, respectively (Machlan et al 1986). Gallium is moderately siderophile as shown by its enrichment in iron meteorites (up to 100 ppm) compared to chondritic meteorites (5~10 ppm; Lodders and Fegley 1998). In addition, its abundance varies by about two orders of magnitude between iron meteorite groups which depends
on many factors but the most important is due to its volatility and Ga concentration has been widely used to classify iron meteorites (e.g. Wai and Wasson 1979).

The Ga concentration of the bulk silicate Earth (BSE) falls on the terrestrial volatility trend, suggesting that despite its moderately siderophile behavior, large quantities of Ga was not segregated into the Earth's core (McDonough 2003). Two possible scenarios can explain this apparent lithophilic behavior of Ga during Earth's formation: 1) A fraction of the Ga was partitioned into the Earth's core and later the mantle has been replenished in Ga by a late veneer together with other volatile elements (e.g. Albarède, 2009), and coincidentally Ga falls on the volatile trend defined by lithophile volatile elements, or 2) under the pressure and temperature condition of mantle/core segregation Ga behaved as a lithophile element (e.g. Blanchard et al. 2015). In addition, similar to other moderately volatile elements, Ga is progressively depleted from the CI (~10 ppm) to the CV (~6 ppm) chondrites groups (Lodders and Fegley 1998) and the Earth's mantle is further depleted (~3.9 ppm; McDonough 1990).

Early studies measured the isotopic composition in metallic Ga, as a representative of terrestrial Ga, as well as in some iron meteorites (De Laeter 1972; Inghram and Hess 1948), however at the analytical precision of these studies, no isotopic variations were found. With the advent of Multi-Collector Inductively-Coupled-Plasma Mass-Spectrometer (MC-ICP-MS), Ga isotopic compositions of terrestrial samples were re-investigated (Zhang et al. 2016; Yuan et al. 2017; Kato et al. 2017; Kato and Moynier 2017). In particular, Kato et al. (2017) measured the Ga isotopic composition of a large variety of terrestrial igneous samples with a precision of 0.05 ‰ and showed that igneous processes does not fractionate Ga isotopes by more than the analytical precision and estimated the $\delta^{71}$Ga (permil deviation of the $^{71}$Ga/$^{69}$Ga ratio compared to the IPGP Ga
standard) of the mantle to be 0.00 ± 0.05 ‰. In addition, Kato and Moynier (2017) have
shown that the Moon is enriched in the heavier isotopes of Ga compare to Earth,
suggesting volatile element loss by evaporation following the giant impact at the origin
of the Moon.

Here, we present the Ga isotopic composition of a series of carbonaceous
chondrites (CI, CM CO, CV and CBa), along with enstatite (EH and EL) and ordinary
chondrites (L, LL, H) in order to understand 1) the volatile element history of the
chondrites parent body, and 2) the origin of the apparent excess of Ga in the Earth's
mantle. We also measured the isotopes of the moderately volatile elements Ga and Zn in
CAIs from Allende CV3 meteorite to test the possible origin of moderately volatile
element excesses. By investigating the magnitude of isotopic fractionation it is possible
to determine its source, as aqueous alteration processes produce limited isotopic
fractionation of Zn (on the order of 0.2 ‰ for CM chondrites that are highly aqueous
altered chondrites; see Luck et al. 2005), Ga isotopes are unlikely to be affected by
aqueous alteration as well; however, if Ga was incorporated into the CAIs within the solar
nebula, evaporation/condensation processes should produce large isotopic fractionation
(e.g. Davis et al. 1990).

111

## 2. Samples and Methods

113 **2.1. Samples**

The analyzed chondrite groups were, in order of volatile element enrichment, CI
(Y980115), CM (Cold Bokkeveld, Murchison, LON 94101, Jbilet Winselwan), CO
(Lancé, Ornans, Felix), CV (Allende, Vigarano) and CBa (Gujba). The ordinary
chondrites studied were QUE 97030 (H3.4), LAR 06392 (H5), ALHA81030 (L3.4),
118 ALHA76001 (L6), EET 83213 (LL3.7), LAP 02266 and LAP 02266 (LL4) are all
119 meteorites collected in Antarctica (find). Eight enstatite chondrites were studied: Kota-
120 Kota, Qingzhen, Sahara 97072 (all EH3) Indarch and Abee (EH4), St Mark's (EH5), LON
121 94100 and Hvittis (EL6). Calcium-aluminium-rich inclusions were all from Allende, C1,
122 C2 and C3 are fine-grained CAIs, whereas C4, and C18 are coarse-grained CAIs and are
123 all described in details in Sossi et al. (2017). Reproducibility of the entire methodology
124 (sample dissolution, chemical purification, mass-spectrometry) was investigated through
125 total procedural replicates, and to reaffirm that no isotopic fractionation is induced by the
126 chemical purification, samples were passed through the chemistry multiple extra times
127 following the same approach as in Kato et al. (2017).

128

## 2.2 Sample preparation and chemical purification

130 All bulk meteorites were powdered with an agate mortar and pestle, and the weight
131 of each sample processed through chemistry was estimated in order to obtain
132 approximately 1µg of Ga (5mg to 100mg of bulk sample depending on the Ga
133 concentration). The largest CAIs were selected and sampled from their host meteorite by
134 crushing and collected by tweezers under a microscope and powdered for chemical
135 purification. The glassy matrix was sampled by tweezers upon crushing from a section
136 free of visible inclusions. All samples were dissolved in Teflon beakers on hot plates in
137 a mixed solution of HNO₃ and HF (3:1) at 120 °C for 72 hours. After dissolution, samples
138 were passed through a three-step chemical purification: 1) first step to separate Ga and
139 Fe from major elements, 2) second step to separate Ga from Fe and 3) third step to remove
140 the isobaric interference element Ba from Ga. The doubly ionized ¹³⁸Ba has the same
141 mass over charge ratio as ⁶⁹Ga⁺, which would result as an isobaric interference. The
achieved yield was above 95 % and the final analytical blank (<0.02 ng) was negligible,
as shown in details along with the Ga purification method described in Kato et al. (2017).

The Zn isotopic composition of the CAIs were measured on the Zn obtained from the Ga
separation on which we applied the method detailed in Kato et al. (2015).

146

147 **2.3 Isotopic measurement**

Gallium and Zn concentrations and isotope ratio were analyzed on a Thermo
Fisher Scientific Neptune Plus multi-collector inductively-coupled-plasma mass-
spectrometer (MC-ICP-MS) at either Washington University in St. Louis, USA or at the
Institut de Physique du Globe de Paris (IPGP), France (see Kato et al. 2017 for details on
the Ga isotopic measurements and Moynier and Le Borgne 2015 for Zn isotopic
measurements). Samples were dissolved and diluted in a 0.1 N HNO₃ solution to match
the concentration of the standard, and were introduced into the plasma source through an
ESI APEX HF sample introduction system for Ga, a double-pass glass cyclonic spray
chamber introduction system was used for Zn. A blank solution of 0.1 N HNO₃ was
measured in the beginning of each sequence and a blank correction was applied. A jet
sampler cone and a H skimmer cone was used. Peak centers were taken after tuning and
baselines were measured before each measurement. Each analysis was composed of 25
cycles of 8.3 seconds, and was done in low-resolution mode. Gallium and Zn isotopic
variations are reported as per mil deviations from the Ga IPGP standard (Aldrich, catalog
number 35623-9, Lot no. 00226LX) for Ga and JMC-Lyon standard for Zn. The Ga IPGP
standard is used instead of the international standards NIST SRM 3119a which is ~1.4‰
fractionated compared to the bulk silicate Earth (see data and discussion in Kato et al.
2017). Delta notations are as shown in Equations 1 and 2, with x = 66 or 68. The
166 analytical precision on the δ⁷¹Ga is estimated as the 2 standard deviation (2 s.d.) from the
167 replicated measurements for each sample. Samples for which we were only able to
168 perform one or two measurements we used the 2 s.d. estimated in Kato et al. (2017) of
169 0.05 ‰. For δ⁶⁶Zn, we use the 2 s.d. precision estimated in Mahan et al. (2017) of 0.05 ‰.
170 The Ga concentrations were estimated from the MC-ICP-MS intensity by comparing a
171 Ga standard with a known concentration.

172

173

$$
\delta^{71}\text{Ga} = \left[ \frac{\left( \frac{^{71}\text{Ga}}{^{69}\text{Ga}} \right)}{\left( \frac{^{71}\text{Ga}}{^{69}\text{Ga}} \right)_{\text{Ga IPGP standard}}} - 1 \right] \times 1000 \text{ (Eq. 1)}
$$

174

$$
\delta^{x}Zn = \left[ \frac{\left( \frac{xZn}{^{64}Zn} \right)}{\left( \frac{xZn}{^{64}Zn} \right)_{\text{JMC-Lyon standard}}} - 1 \right] \times 1000 \text{ (Eq. 2)}
$$

175

3. Results

176

3.1 Evaluation test of reproducibility

177 Accuracy and reproducibility of our method is detailed in Kato et al. (2017). Here,
178 we provide several additional tests to further validate the method (see supplementary
179 materials, Table S1). Full procedural replicates of Murchison (Murchison A, B, D, E, and
180 F), Allende (Allende A, B and D), Indarch (Indarch A, B and D), Lancé (Lancé A and B),
181 Sahara 97072 (Sahara 97072 A and B) and LON 94100 (LON 94100 A and B) were
182 measured for their isotopic ratio. All replicated samples agreed within error of
183 approximately 0.05 ‰ except for Murchison and Vigarano which had a scatter of ±
184 0.14 ‰ (2 s.d.) and ± 0.16 ‰ (2 s.d.) respectively. This large scatter is due to one irregular
185 measurement for Vigarano A2 (δ⁷¹Ga = -0.60 ‰), whilst when analyzed again, the same
186 sample had a value of δ⁷¹Ga = -0.37 ‰, which is closer to the other portion of the divided
187 Vigarano, Vigarano A1 ave (δ⁷¹Ga = -0.37 ‰). A single irregular isotopic measurement
out of four measurements of Murchison B2, and the sole analysis of Murchison A also resulted in the large scatter. To test the precision, a single sample was divided into several aliquots and passed through different columns from the second step of the chemistry. Murchison B and Allende D were divided into three aliquots (Murchison B1, B2, B3, Allende D1, D2, D3). Murchison D, Allende A, Allende B, Vigarano A, LAR 06392 A, ALHA 81030 A, EET 83213 A and LAP 02266 A, were divided into two aliquots and passed through separate columns (number at the end of the sample name indicates the column number, such as Murchison D1 and D2). All measurements agreed within ± 0.11 ‰ (2 s.d.) except for Murchison D1 and D2, and Vigarano A1 and A2. Finally, several samples (ALHA 81030 A1 (4) and A2 (4), EET 83213 A1 (4) and A2 (4)) were passed four times through the second step of the chemical purification to test the possibility of isotopic fractionation during the most sensitive stage of the chemical separation. We did not observe any isotopic difference created by the extra pass through the column, and the Ga concentration was not modified during the extra procedure (Table S1) confirming that no Ga is lost during this procedure (Kato et al. 2017). These different procedural replicates further confirm the robustness of the method.

204

## 3.2 Gallium isotopic and elemental composition of the chondrites

Isotopic and elemental results are shown in Table 1 and S1 in supplementary materials and Figure 1. All bulk chondrites were isotopically lighter compared to BSE estimate from Kato et al. (2017), except for LON 94101 (CM2, $\delta^{71}$Ga = 0.13 ± 0.04 ‰, 2 s.d.) and Gujba (CBa, $\delta^{71}$Ga = 0.02 ± 0.07 ‰, 2 s.d.). Compared to the other three CM2 chondrites (Murchison, Cold Bokkeveld, Jbilet Winselwan), LON 94101 had an isotopically heavy signature. Since this was obtained from a single dissolution, further
measurements of LON 94101 is needed to verify this value and this sample is not included
in the discussion of the CM chondrites.

Carbonaceous chondrites exhibit a range of δ<sup>71</sup>Ga from -0.43 ± 0.16 ‰ (2 s.d.) to
0.02 ± 0.07 ‰ (2 s.d.), with Ga concentrations varying between 1 to 10 ppm. The
concentration values are in agreement with previous studies (see Lodders and Fegley
1998 for review). There was no clear correlation between the Ga isotopic compositions
and Ga concentrations for each meteorite, but each petrological type showed a discernable
δ<sup>71</sup>Ga signature. CVs were the isotopically lightest (Allende δ<sup>71</sup>Ga = -0.42 ± 0.03 ‰, 2
s.d. and Vigarano δ<sup>71</sup>Ga = -0.43 ± 0.16 ‰, 2 s.d.), followed by COs (Lancé δ<sup>71</sup>Ga = -0.25
± 0.06 ‰, 2 s.d., Ornans δ<sup>71</sup>Ga = -0.20 ± 0.02 ‰, 2 s.d., and Felix δ<sup>71</sup>Ga = -0.09 ± 0.02 ‰,
2 s.d.), CMs (Murchison δ<sup>71</sup>Ga = -0.12 ± 0.14 ‰, 2 s.d., Cold Bokkeveld δ<sup>71</sup>Ga = -0.12
± 0.00 ‰, 2 s.d.) CI (Y980115 δ<sup>71</sup>Ga = -0.07 ± 0.09 ‰, 2 s.d.) and CBa (δ<sup>71</sup>Ga = 0.02 ±
0.07 ‰, 2 s.d.). The Ga concentration is most enriched in CI with a value of 10 ppm,
followed by similar average concentrations of CMs 5.4 ppm, CVs 4.1 ppm and COs 3.8
ppm and CBa with 1.0 ppm, which are all in agreement with previous studies (e.g.
Lodders and Fegley 1998, Rubin et al. 2003).

Ordinary chondrites show a wide range of isotopic composition with δ<sup>71</sup>Ga from
-0.13 ± 0.06 to -1.12 ± 0.02 ‰, and Ga concentrations from 2 to 29 ppm. QUE 97030 has
the highest concentration of Ga out of all of the samples measured with 29 ppm and the
lowest δ<sup>71</sup>Ga value (δ<sup>71</sup>Ga = -1.12 ‰) of all ordinary chondrites. No correlation was
observed between the Fe metallic amount (H, L, LL) and isotopic composition nor the Ga
concentration.

Enstatite chondrites exhibit a range of δ<sup>71</sup>Ga = -0.43 ± 0.06 to -0.05 ± 0.05 ‰ with
Ga concentrations between 2 to 23 ppm. Although all six EH samples show different
236 petrological classifications, they are all enriched in Ga compared to EL, with the two
237 groups covering similar ranges in Ga isotope compositions.

238

239 **3.3 Gallium and Zinc isotopic compositions of CAIs**

240 Calcium-aluminium-rich inclusions C1, C2, C3, C4, C18 and the glassy matrix
241 from the vicinity of C4 were measured for their Ga isotopic composition, while only CAIs
242 C1, C2, C3 had enough Zn to be analyzed for Zn isotopic composition. Zinc isotopes
243 were distributed along a mass dependent fractionation line (see supplementary materials,
244 Figure S1) and therefore only δ66Zn will be discussed below. Isotopic and elemental
245 results are shown in Table 2, and Figure 2a and 2b. The CAIs were normalized to CI
246 isotopic compositions of Zn (δ66Zn = 0.48 ‰; Luck et al. 2005), and Ga (δ71Ga = -0.07 ‰;
247 Y980115), with δ71GaCI = δ71Ga sample - δ71Ga chondrite and δ66ZnCI = δ66Zn sample - δ66Zn chondrite, ranged from δ71GaCI = -3.49 to +0.70 ‰, with Ga concentrations varying from 3
248 to 18 ppm, and δ66ZnCI = -1.23 to -0.19 ‰ with Zn concentrations between 91 to 702 ppm
249 (Table 2). The enrichment in the lightest isotopes of Zn in CAIs compared to bulk
250 meteorites confirms previous results from one Allende CAI (δ66Zn = -2.65 ‰, Luck et al.
251 2005 and Murchison δ66Zn = -0.64 ‰ Moynier et al. 2007). The Allende matrix has a
252 similar Ga elemental abundance to C4 and to the bulk Allende.
253

254

255 **4. Discussion**

256 **4.1 Mass-dependent isotope fractionation of Ga**

257 The chondrites and the CAIs show variations in δ71Ga. However, since Ga has
258 only two isotopes, it is not possible to attribute the variations in Ga isotopic ratios to
259 solely mass-dependent isotope fractionation. Inheritance of nucleosynthetic differences
260 or irradiations by cosmic rays may also be a source of isotopic variations. However, we
261 do not consider these effects to be major sources because multi-isotopic elements of
262 similar masses and volatility (e.g. Zn, Ge) do not show any nucleosynthetic effects larger
263 than 50 ppm in meteorites or CAIs (Moynier et al. 2009; Luais et al. 2003) which is within
264 our analytical uncertainties makes irradiation a very unlikely source of isotopic variations.
265 We will therefore only consider mass-dependent isotopic fractionation as the source of
266 Ga isotopic variability in the following discussion.

267

268 **4.2 Isotopic composition of carbonaceous chondrites and the origin of the volatile**
269 **element depletion**

270 Volatile enrichment of carbonaceous chondrites is in the order of CI > CM > CO
271 > CV, with CI the most enriched in volatile elements, and CV the most depleted, CO and
272 CV switch position in the trend depending on the volatility of the element (Kallemeyn
273 and Wasson 1981). Gallium behaves similarly to Al during magmatic differentiation due
274 to their comparable ionic radii, valence and ionization potential (De Argollo and Schilling
275 1978) and therefore the Al/Ga ratio is not much fractionated during igneous processes.
276 On the other hand, Al is a refractory element (Tc=1653 K, Lodders 2003) and the Al/Ga
277 ratio should vary according to volatility processes. The isotopic composition of the
278 carbonaceous chondrites is negatively correlated with Al/Ga ratios (Figure 3). This is
279 consistent with what has been observed previously for other moderately elements such as
280 Zn and Cu, that show similar isotopic patterns (e.g. Luck et al. 2003; 2005; Pringle et al.
281 2017) and therefore δ<sup>71</sup>Ga correlates with δ<sup>66</sup>Zn and δ<sup>65</sup>Cu<sub>CI</sub> (δ<sup>65</sup>Cu<sub>CI</sub> = δ<sup>65</sup>Cu<sub>sample</sub> -
282 δ<sup>65</sup>Cu<sub>CI chondrite</sub>) and Δ<sup>17</sup>O in carbonaceous chondrites (Figure 4a, 4b and 4c). All these
observations points against a volatile depletion by evaporation processes, which would
produce a reverse trend with enrichment in heavy isotopes positively correlated with the
Al/Ga ratio. Instead, this trend may reflect a two-component mixing of a volatile rich
isotopically heavy reservoir and a volatile poor isotopically light reservoir, that would
also be isotopically different for O isotopes (e.g. Clayton and Mayeda 1999). Selenium
and Cd, which are more volatile than both Zn and Ga, and strongly chalcophile do not
show isotopic variations between carbonaceous chondrites (e.g. Wombacher et al. 2008;
Baker et al. 2010; Vollstaedt et al. 2016). As already suggested by Vollstaedt et al. (2016),
this implies a decoupling between the elements with possibly the most volatile (and most
chalcophile) elements, such as Se, S and Cd, being present in only the volatile rich phase.
Contrary to carbonaceous chondrites, the δ<sup>71</sup>Ga values of ordinary and enstatite
chondrites are not correlated to that of δ<sup>65</sup>Cu<sub>CI</sub>, or Δ<sup>17</sup>O values (Figure 4b and 4c). The
correlation between carbonaceous chondrites, and the absence of correlation for ordinary
chondrites has been observed before between δ<sup>65</sup>Cu and δ<sup>66</sup>Zn (Luck et al. 2003), and
between δ<sup>66</sup>Zn and Δ<sup>17</sup>O (Luck et al. 2005). In order to form this trend, Luck et al. (2003)
proposed a mixing between the nebular gas and the “refractory component” represented
by the CVs, which are depleted in Δ<sup>17</sup>O. In this model, the refractory component
interacted with the Δ<sup>17</sup>O rich nebula gas, to form the rich end member of the ordinary
chondrites while not changing the δ<sup>71</sup>Ga significantly.

Ordinary chondrites are chondrule-rich compared to other chondrites groups, have
a larger isotopic range (δ<sup>71</sup>Ga = -0.15 ‰ down to -1.12 ‰ compared to -0.43 to +0.13‰
for carbonaceous chondrites). Their generally light isotope enrichment suggests that
chondrules must be isotopically light compared to the matrix as already observed for
individual chondrules for Zn (Pringle et al. 2017, Bollard et al. 2017) and suggested based
307 on the bulk composition for other moderately volatile elements (e.g. Sn: Bourdon et al.
308 2017 Rb: Pringle and Moynier 2017, Cd: Wombacher et al. 2008 and Ag: Schönbächler
309 et al. 2008). Pringle et al. (2017) suggested that the isotopically light Zn composition of
310 individual chondrules were due to the separation of isotopically heavy sulphides from the
311 chondrules or their precursors, while the Cd and Ag isotope systematics in ordinary
312 chondrites were explained to be result of multiple series of evaporation and condensation,
313 as well as open system metamorphism on the parent body (Schönbächler et al. 2008;
314 Wombacher et al. 2008).

315 The δ⁶⁶Zn and δ⁷¹Ga of ordinary and enstatite chondrites show a general
316 correlation (Figure 4a). More data acquired in both isotopic systems would be needed to
317 further interpret this correlation, but this possibly suggests that both Zn and Ga were
318 transported by similar mechanisms in these meteorites during thermal metamorphism on
319 the ordinary and enstatite parent bodies.

320

321 **4.3 Implication on the origin of Earth's mantle gallium**

322 The present estimate of the Ga isotopic composition of the BSE (δ⁷¹Ga = 0.00 ±
323 0.06 ‰, 2 s.d., Kato et al. 2017) is isotopically heavier than any known chondrite group.
324 This suggests that either the material that accreted to form the Earth had a Ga isotopic
325 composition distinct from any known chondrites groups or that the isotopic composition
326 of the bulk Earth is chondritic and some processes have isotopically fractionated the Ga
327 of the BSE. Since all chondrite groups are isotopically lighter than the BSE, it seems
328 unlikely that only the material that formed the Earth was enriched in the heavy isotopes.
329 In addition, enstatite chondrites, which have similar isotopic composition (at a precision
330 < 50 ppm) than the BSE for any elements (e.g. Cr, Ni, Sr, O; see Moynier and Fegley
331 2015) are also isotopically lighter than the BSE by 200 ppm; the only exception being Si
332 for which the difference is explained by the partitioning of isotopically light Si in the
333 metal during nebular condensation associated possibly with volatile related processes (e.g.
334 Savage and Moynier 2013, Pringle et al. 2014). Since Ga is both moderately siderophile
335 and volatile, either volatility processes and/or metal-silicate partitioning could
336 isotopically fractionate it.

337 Evaporation would result in the preferential loss of the light Ga isotope and
338 therefore leaving a high δ<sup>71</sup>Ga value in the residue. On a δ<sup>71</sup>Ga vs Al/Ga diagram, the
339 BSE plots in the direction of an evaporation trend from the carbonaceous chondrites
340 (Figure 3); i.e. that the Earth is depleted in Ga and enriched in the heavy isotope. However
341 for Zn, which is more volatile compared to Ga (Tc=726K for Zn, vs Tc=968K for Ga;
342 Lodders 2003), the bulk Earth is depleted in the heavier isotopes compared to chondrites,
343 and therefore plot on a reverse trend compared to what evaporation would produce, which
344 has been taken as evidence that Zn was not lost from Earth by evaporation (Albarède
345 2009). Unlike for the lithophile element Zn (Wang et al. 2016), it is however possible that
346 a complementary fraction of the terrestrial Ga with light isotope enrichment is stored in
347 the Earth's core, which would decrease the Al/Ga ratio of the bulk Earth and could explain
348 the mismatch of the Ga isotopic composition of the BSE with the enstatite chondrites and
349 the difference to the Zn isotopes.

350 The position of Ga on the volatile depletion trend (e.g. Palme and O'Neill 2003)
351 defined by lithophile elements, however, suggests minor partitioning of Ga into the
352 Earth's core. High-temperature and high-pressure experiments have shown that the
353 metal/silicate partitioning of Ga depends on the oxygen fugacity and on the nature and
354 abundance of light elements present in the metal phase, wherein the existence of light
elements such as C, S, O, and Si in the core lowers the D<sub>Ga</sub> (the metal-silicate partition coefficient) (Blanchard et al. 2015). Considering the analytical uncertainties associated with the composition of Ga in the BSE and its position on the volatility trend, up to a maximum of 30 % of the Ga could be partitioned into the Earth's core (Corgne et al. 2008). Using this maximum value (that is equivalent to have D<sub>Ga</sub>~1; see Blanchard et al. 2015), reduces the Al/Ga ratio of the bulk Earth to ~ 2/3 compared to the BSE and leaves the bulk Earth closer to the carbonaceous chondrite trend, albeit not on it (see figure 3).
In order to plot on the volatility trend, we would need a D<sub>Ga</sub>~4 which is out of the possible ranges (see Blanchard et al. 2015). This would imply that the Ga isotopic composition and abundance is, unlike Zn, largely controlled by nebular processes.

An alternative scenario is that the δ<sup>71</sup>Ga of the BSE is not representative of the bulk Earth and that Ga isotopes were fractionated during core/mantle differentiation. In this case, if the bulk Earth has a chondritic isotopic composition, the core must be isotopically light. Considering a fraction of Ga in the core of 30 % (Corgne et al. 2008), the Ga isotopic composition of the core should be ~0.60 ‰. Isotopic fractionation between metal and silicate during partitioning experiments for elements have shown that the metal phase can be either isotopically heavy (Ni: Lazar et al. 2012), light (Mo: Hin et al. 2013, Si: Shahar et al. 2009) or not fractionated (Fe: Poitrasson et al. 2009, Zn: Mahan et al. 2017). Currently there are no experiments of Ga isotopic fractionation during metal silicate differentiation, and high-temperature high-pressure experiments of metal silicate partitioning will be needed to test whether Ga isotopes were fractionated and possibly quantify the abundance of Ga into the core.

377

## 4.4 Gallium and Zn enrichment in the CAIs
Even though CAIs have been formed at high temperature in a refractory element rich regions of the solar nebula, the enrichment in moderately volatile elements such as Zn and Ga in CAIs are common features (Chou et al. 1976; Bischoff et al. 1987; Sylvester et al. 1993). Here, we confirm this enrichment with CAIs having up to 18ppm of Ga and 702ppm of Zn, which is higher than even bulk CI chondrites (9.48 ppm Ga and 303 ppm Zn; Barrat et al. 2012). The origin of the Ga and Zn enrichment is puzzling, since they are both more abundant in the CAIs that in the rest of the meteorite. The large isotopic enrichment in both light Zn and Ga, may help to shed light on this origin of those volatile elements.

Leaching experiments suggest that moderately volatile elements tend to be enriched in the rims, compared to the inner part or bulk of the CAI, or even the bulk meteorite itself (Chou et al. 1976; Bischoff et al. 1987; Sylvester et al. 1993). This suggests that the moderately volatile elements have been introduced in the samples after crystallization of the inclusions. This introduction of volatile elements could occur either in the solar nebula by gas/solid exchanges with the gas, or on the parent-body of the meteorite by secondary processes such as aqueous alteration. Since CAIs have concentrations of both Ga and Zn higher than the host meteorite (6 ppm of Ga and 110 ppm of Zn in Allende, Lodders and Fegley 1998), it seems unlikely that aqueous alteration would have specifically enriched the rim of the CAIs. Furthermore, rims of chondrules are not specifically enriched in volatile elements compared to the inner part of the chondrule or bulk Allende (Rubin and Wasson 1987) as would be expected if the redistribution were from the matrix to CAIs and chondrules. It should be noted, that Na is also highly enriched in some CAIs, due to the crystallization of secondary minerals such as nepheline and sodalite, which are formed by late stage iron-alkali-halogen
403 metasomatic alteration of primary high temperature minerals (e.g. Krot et al. 1995).

404 However, unlike Na or Cl, Ga is an insoluble element known from its low concentration

405 in thermal waters (e.g. Wood and Samson 2006), which dismisses the possibility of fluid

406 assisted mobilization which is commonly seen for Na-Cl rich inclusions (e.g. Wasserburg

407 et al. 2011). In addition, the degree of isotopic fractionation (>3 ‰ for Ga and >2 ‰ for

408 Zn) is far larger than that observed for any low-temperature processes affecting Zn

409 isotopes (e.g. Pons et al. 2016) and is more in line with what is observed to volatile related

410 processes (e.g. Moynier et al. 2010, Kato et al. 2015). Therefore, the high concentration

411 of both Ga and Zn in the CAIs, the fact that these elements are concentrated at the rim,

412 and the very large isotopic fractionation - much larger than what would be excepted by

413 alteration, suggests that the process of enrichment of Ga and Zn occurred prior to the

414 incorporation of the CAIs in the parent body of the Allende meteorite, as suggested for

415 Cd and Zn in Wombacher et al. (2008). We will now discuss the origin of the light isotope

416 enrichment observed in the fine grain CAIs.

417 The isotopically light CAIs (C1, C2 and C3) are fine grained CAIs with group II

418 (Sossi et al. 2017) or ultra refractory depleted REE patterns, which is usually interpreted

419 as being produced by condensation of a nebular gas that was already depleted in refractory

420 elements and enriched in volatile elements. These CAIs are considered to be the most

421 primitive CAIs (e.g. Boynton 1975; Kornacki and Fegley 1986). The isotopically heavier

422 CAIs (C4 and C18) are coarse grain CAIs with group V REE pattern (Sossi et al. 2017),

423 which suggests secondary melting, which are associated with evaporation of the volatile

424 elements. Therefore, the heavy Ga isotope composition of coarse grain CAIs is consistent

425 with secondary heating and melting events, which would have evaporated Ga and

426 enriched the residue in the heavy isotopes compared to fine grain CAIs. In the following
427 part of the discussion, we will focus on the origin of the light isotopic composition of the
428 fine grain CAIs.

429 The variations in the Ga isotopic composition together with the variation in
430 concentration suggests that after their condensation, the CAIs have had secondary
431 interactions with the gas of the nebula. The changes in Ga isotopic composition suggest
432 that either the composition of the gas changes with time in the CAI forming region or that
433 the CAIs have been transported within a heterogeneous gas. Similar results were observed
434 for O isotopes (Simon et al. 2011; 2016). Simon et al. (2011, 2016) found that the mineral
435 layered sequence surrounding the CAI, the Wark-Lovering (WL) rim, has different
436 isotopic composition compared to the interior, suggesting a gas-solid exchange within a
437 solar nebula isotopically heterogeneous in oxygen (Simon et al. 2011). In addition, Mg
438 isotopic data suggests that CAIs must have been transported to oxidized region less than
439 300,000 yrs after their formation (Simon et al. 2005). It should be pointed out that there
440 are also CAIs with no isotopic difference between the WL rim and the interior (e.g.
441 Bodénan et al. 2014).

442 The simplest explanation of the extremely light Ga and Zn isotopic signatures,
443 together with heterogeneous O isotopes across WL rim is that, following condensation,
444 CAIs were transported to a cooler and volatile-rich zone of the nebula, where gas
445 condensed at the surface of the CAI. During condensation, the Ga and Zn isotopes were
446 fractionated between the nebular gas and the condensing phases. Due to the limited size
447 of the CAIs, Zn isotopic analysis was possible in only 3 (C1, C2, and C3). It is therefore
448 difficult to combine both datasets in the discussion. However, we note the three CAIs are
449 enriched in the light isotopes of both Zn and Ga with C2 and C3 being the most enriched
450 in the light isotopes for both elements in this suit of CAIs, followed by the slightly heavier
451 Cl.

452 Following a Rayleigh distillation, and the condensation of isotopically heavy
453 solids, the nebular gas will evolve in a direction to become isotopically lighter. The
454 Rayleigh distillation equation controlling the Ga and Zn isotopic composition of the
455 condensates and the gas can be written as Equation. 3, 4, 5, and 6 for the delta value of
456 the condensate and gas phase.

$$
457 \qquad \delta^{71}Ga_{condensate} = \alpha(\delta_0 + 1000)F^{\alpha-1} - 1000 \quad (\text{Eq. 3})
$$

$$
458 \qquad \delta^{71}Ga_{gas} = (\delta_{0} + 1000)F^{\alpha-1} - 1000 \quad (\text{Eq. 4})
$$

$$
459 \qquad \delta^{66}Zn_{condensate} = \alpha(\delta_0 + 1000)F^{\alpha-1} - 1000 \quad (\text{Eq. 5})
$$

$$
460 \qquad \delta^{66}Zn_{gas} = (\delta_0 + 1000)F^{\alpha-1} - 1000 \quad (\text{Eq. 6})
$$

461 Where δ<sup>71</sup>Ga<sub>condensate</sub> and δ<sup>66</sup>Zn<sub>condensate</sub> represent the isotopic composition of the
462 instant condensate, δ<sup>71</sup>Ga<sub>gas</sub> and δ<sup>66</sup>Zn<sub>gas</sub> is the isotopic composition of the gas, δ<sub>0</sub> is
463 the initial isotopic composition of the gas, and F is the fraction of the <sup>69</sup>Ga or <sup>64</sup>Zn in the
gas. The α is the isotopic fractionation factor that, in the absence of experimental
464 determination, will be approximated as the square root of the heavy isotope over the light
465 isotope (kinetic isotopic fractionation factor). It should be noted however, that
466 experiments have shown that residues of evaporation experiments in vacuum follow a
467 Rayleigh distillation law with an isotopic fractionation factors slightly different from the
468 square root of the mass ratio (e.g. Richter et al. 2002). If we use Ga as an example, the
469 major species of Ga among the condensing nebular gas phase at 968K (T<sub>50</sub>) is, in order
470 of abundance, GaOH(g), GaCl(g), GaBr(g) and Ga(g) at both 10<sup>-4</sup> and 10<sup>-6</sup> atm solar
471 nebula pressures (Wai and Wasson 1979). When the most abundant isotope is used for
472 the Ga species, the fractionation factors are for Ga<sup>16</sup>O<sup>1</sup>H: √<span style="text-decoration: overline;">87.93/85.93</span> = 1.0116,
473 Ga<sup>35</sup>Cl: √<span style="text-decoration: overline;">105.89/103.89</span> = 1.0096, Ga<sup>79</sup>Br: √<span style="text-decoration: overline;">149.84/147.84</span> = 1.0067,
474
Ga:√70.93/68.93 = 1.0144, although the real gas would have been a mix of these species. Utilizing the Rayleigh distillation, it is then possible to predict both isotopically light and heavy condensates, as observed in the CAIs, along with high Ga and Zn concentrations depending on the fraction of Ga and Zn condensed from the gas. This scenario can reproduce the isotopic composition of the CAIs C1, C2, C3 and C18 (see Figure 5a and 5b). In this model we consider the starting gas phase has a chondritic composition (δ⁷¹Ga₄, δ⁶⁶Zn₄ = 0‰). As the gas condenses, the heavier isotope favorably condenses on to the surface of the CAIs, resulting for the gas to become isotopically lighter. The condensed material would be removed from the gas and avoids further reactions. As the fraction of the element in the gas phase continues to decrease due to condensation, the isotopic composition of the gas phase becomes continuously lighter, causing condensates formed from that gas to become isotopically lighter compared to previously condensed phases (Figure 5a and 5b).

Alternatively, it has been proposed that isotopically light condensates may result from the different velocities of isotopes in the gas (Richter 2004), however, this effect has not been observed experimentally and the sticking probability of the isotopes at the surface of the solids would likely also play a strong role in the isotopic fractionation (Moynier et al. 2006). Moreover, high temperature condensation experiments of Mg by Uyeda et al. (1991) found isotopically heavy condensates. However, the Ga and Zn isotopic composition of the CAIs could also be explained by the formation of light condensates due to kinetic effects following Richter (2004) formalism.

Both mechanisms of isotopic fractionation, can predict the various isotopic compositions of the fine-grained CAIs. Gallium and Zn isotopes show that these elements must have been introduced by gas/CAIs interactions in an evolving solar nebula,
499 consistently with what is observed for oxygen isotopes (Simon et al. 2011).

500

501

502 **5. Conclusions**

503 We have measured the Ga isotopic composition of carbonaceous, enstatite and
504 ordinary chondrites and the Ga and Zn concentrations and isotopic composition of six
505 CAIs from Allende. Carbonaceous chondrites fall on a negative correlation on a δ<sup>71</sup>Ga vs
506 Al/Ga ratio suggesting that Ga behaves similarly to Zn, Cu and O (Clayton and Mayeda
507 1999; Luck et al. 2003; Luck et al. 2005). On the other hand, Ga isotopes in ordinary and
508 enstatite chondrites do not correlate with δ<sup>65</sup>Cu and Δ<sup>17</sup>O, but with δ<sup>66</sup>Zn. The origin of
509 the correlation between δ<sup>71</sup>Ga and Al/Ga ratio cannot be evaporation/condensation
510 processes and reflects the mixing of two components, one which is depleted in Ga with
511 light isotope enrichment and another enriched in Ga with heavy isotope enrichment.

512 CAIs are enriched in the moderately volatile elements Ga and Zn, which are
513 concentrated in the rim (Chou et al. 1976; Bischoff et al. 1987; Sylvester et al. 1993). To
514 explain the REE patterns, the enrichment of Ga and Zn compared to the bulk meteorite,
515 and the large isotopic fractionations recorded in the CAIs, condensation of the moderately
516 volatile elements from the nebular after the formation of the CAIs is most likely the cause.
517 The condensing nebular gas rich in Ga and Zn followed a Rayleigh distribution model,
518 which will form a condensate rich in Ga and Zn concentration, and have fractionated
519 isotopic compositions. For the coarse grained CAIs, which have similar concentrations
520 and isotopic compositions as the bulk meteorite, secondary heating of a previously
521 formed CAI may have resulted in the depletion in concentration and depletion of the light
522 isotope, consistent with their thermal history.
523

524

Acknowledgements

525

526

527

528

529

530

531

532

533

534

535

536

537

FM acknowledges funding from the European Research Council under the H2020
framework program/ERC grant agreement #637503 (Pristine), as well as the financial
support of the UnivEarthS Labex program at Sorbonne Paris Cité (ANR-10-LABX-0023
and ANR-11-IDEX-0005-02), and the ANR through a chaire d'excellence Sorbonne Paris
Cité. Parts of this work were supported by IPGP multidisciplinary program PARI, and by
Region Île-de-France SESAME Grant no. 12015908. Discussions with Julien Foriel and
Paolo A. Sossi were highly informative. We would also like to thank Katharina Lodders,
Bruce Fegley Jr., Ingrid Blanchard and Hugh O'Neill. We also thank Brandon Mahan for
proof-reading the manuscript.
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733
734 Table Captions

735 Table 1

736 Average Ga isotopic value and Ga concentrations of the chondrites. Error bars represent

737 2 s.d. for δ<sup>71</sup>Ga, 30 % estimation for Ga concentration.

738

739 Table2

740 Gallium and Zn isotopic components of CAIs corrected to the CI value and their

741 elemental abundances. Reproducibility of the for Ga measurements are 0.06 ‰ (Kato et

742 al. 2017), 0.05 ‰ for Zn (Mahan et al. 2017).

743

744 Figure captions

745 Figure 1

746 Gallium isotopic composition versus Ga concentration for chondrites. The horizontal line

747 represents the estimated BSE δ<sup>71</sup>Ga value (Kato et al. 2017).

748

749 Figure 2

750 a) Gallium isotopic composition versus Ga concentration in CAIs. b) Zinc isotopic

751 composition versus Zn concentration in CAIs.

752

753 Figure 3

754 Gallium isotopic composition versus Al/Ga ratio of selected carbonaceous chondrites, the

755 bulk silicate Earth and the bulk Earth composition with 30 % of the Ga budget in the core.

756 Red arrow shows the direction in which the bulk Earth value would move compared to

757 the BSE if the difference between the Ga concentrations between BSE and CI meteorites
758 was caused by core formation (i.e. if 30 % of the Ga budget resides in the core).

759 Aluminum concentrations for the carbonaceous chondrites are from Kallemeyn and
760 Wasson (1981), BSE Al concentrations from Moynier and Fegley (2015).

761

762 Figure 4

763 a) Gallium isotopic composition of carbonaceous, ordinary and enstatite chondrites
764 compared to δ⁶⁶Zn. Sample δ⁶⁶Zn values were obtained from Luck et al. (2005) and

765 Moynier et al. (2011). Correlation line has been drawn for CC, EC and OC combined. b)

766 Gallium isotopic composition of carbonaceous, ordinary and enstatite chondrites
767 compared to δ⁶⁵Cu. Sample δ⁶⁵Cu values were obtained from Luck et al. (2003) and

768 Savage et al. (2015), and corrected to CI value. c) Gallium isotopic composition of
769 carbonaceous, ordinary and enstatite chondrites compared to Δ¹⁷O. Sample Δ¹⁷O values

770 were obtained from Clayton et al. (1984 and 1991) and Clayton and Mayeda (1999). If
771 exact sample was not available, average of same class type was used.

772

773 Figure 5

774 Rayleigh distillation model for condensation/evaporation of Ga (a) and Zn (b). The
775 isotopic components of the CAIs are shown on the Rayleigh distillation curve. The square

776 root of the respective masses for ⁷¹Ga/⁶⁹Ga and ⁶⁶Zn/⁶⁴Zn were used as the fractionation
777 factor for an example (this provides a maximum estimate). The F on the x-axis represents

778 the fraction of the gas that has been condensed. Solid line represents the condensate phase,
779 dotted line represents the gas phase. The gas phase starts from a chondritic composition

780 (δ⁷¹GaCl, δ⁶⁶ZnCl = 0‰).

781
<table><caption>782 Table 1</caption><thead><tr><th>Sample names</th><th>δ<sup>71</sup>Ga (‰)</th><th>2 s.d.</th><th>Ga (ppm)</th><th>n</th><th>Type</th></tr></thead><tbody><tr><td>Y980115</td><td>-0.07</td><td>0.09</td><td>10.2</td><td>3</td><td>CI</td></tr><tr><td>Lancé</td><td>-0.25</td><td>0.06</td><td>3.9</td><td>2</td><td>CO3.5</td></tr><tr><td>Ornans</td><td>-0.20</td><td>0.02</td><td>4.1</td><td>2</td><td>CO3.4</td></tr><tr><td>Felix</td><td>-0.09</td><td>0.02</td><td>3.3</td><td>4</td><td>CO3.3</td></tr><tr><td>Cold Bokkeveld</td><td>-0.122</td><td>0.004</td><td>5.1</td><td>2</td><td>CM2</td></tr><tr><td>LON 94101</td><td>0.13</td><td>0.04</td><td>2.9</td><td>6</td><td>CM2</td></tr><tr><td>Jbilet Winselwan</td><td>-0.08</td><td>0.06*</td><td>7.9</td><td>1</td><td>CM2</td></tr><tr><td>Murchison</td><td>-0.12</td><td>0.14</td><td>5.6</td><td>5</td><td>CM2</td></tr><tr><td>Allende</td><td>-0.42</td><td>0.03</td><td>4.3</td><td>3</td><td>CV3</td></tr><tr><td>Vigarano</td><td>-0.43</td><td>0.16</td><td>3.9</td><td>2</td><td>CV3</td></tr><tr><td>Gujba</td><td>0.02</td><td>0.07</td><td>1.0</td><td>3</td><td>CBa</td></tr><tr><td>QUE 97030</td><td>-1.12</td><td>0.02</td><td>29.4</td><td>4</td><td>H3.4</td></tr><tr><td>LAR 06392</td><td>-0.13</td><td>0.06</td><td>3.5</td><td>2</td><td>H5</td></tr><tr><td>ALHA81030</td><td>-0.31</td><td>0.01</td><td>5.1</td><td>2</td><td>L3.4</td></tr><tr><td>ALHA76001</td><td>-1.01</td><td>0.06</td><td>1.8</td><td>2</td><td>L6</td></tr><tr><td>EET 83213</td><td>-0.61</td><td>0.02</td><td>4.8</td><td>4</td><td>LL3.7</td></tr><tr><td>LAP 02266</td><td>-0.27</td><td>0.03</td><td>4.8</td><td>2</td><td>LL4</td></tr><tr><td>Kota-Kota</td><td>-0.21</td><td>0.07</td><td>15.5</td><td>3</td><td>EH3</td></tr><tr><td>Qingzhen</td><td>-0.34</td><td>0.06</td><td>23.0</td><td>3</td><td>EH3</td></tr><tr><td>Sahara 97072</td><td>-0.25</td><td>0.05</td><td>17.5</td><td>2</td><td>EH3</td></tr><tr><td>Indarch</td><td>-0.14</td><td>0.04</td><td>10.8</td><td>3</td><td>EH4</td></tr><tr><td>Abee</td><td>-0.24</td><td>0.05</td><td>12.7</td><td>2</td><td>EH4</td></tr><tr><td>St Mark's</td><td>-0.05</td><td>0.05</td><td>15.4</td><td>3</td><td>EH5</td></tr><tr><td>LON 94100</td><td>-0.14</td><td>0.04</td><td>7.8</td><td>2</td><td>EL6</td></tr><tr><td>Hvittis</td><td>-0.43</td><td>0.06*</td><td>2.0</td><td>1</td><td>EL6</td></tr></tbody></table>

<footnote>* = 2 s.d. error from Kato et al. 2017 was used due to single measurement.</footnote>
<table><caption>784 Table 2</caption><thead><tr><th>Sample names</th><th>δ<sup>71</sup>GacI<br>(‰)</th><th>Ga<br>(ppm)</th><th>δ<sup>66</sup>ZnC1<br>(‰)</th><th>Zn<br>(ppm)</th><th>n</th><th>Type</th><th>REE<br>group</th></tr></thead><tbody><tr><td>C1</td><td>-0.85</td><td>16</td><td>-0.19</td><td>91</td><td>1</td><td>Fine</td><td>II</td></tr><tr><td>C2</td><td>-3.49</td><td>16</td><td>-0.76</td><td>685</td><td>1</td><td>Fine</td><td>II</td></tr><tr><td>C3</td><td>-3.36</td><td>13</td><td>-1.23</td><td>702</td><td>1</td><td>Fine</td><td>II</td></tr><tr><td>C4</td><td>-0.40</td><td>3</td><td>n/d</td><td>n/d</td><td>1</td><td>Coarse</td><td>V</td></tr><tr><td>CAI 18 ave</td><td>0.70</td><td>18</td><td>n/d</td><td>n/d</td><td>2</td><td>Coarse</td><td>V</td></tr><tr><td>BSE</td><td>0.07<sup>a</sup></td><td>4<sup>b</sup></td><td>-0.20</td><td>53.5<sup>c</sup></td><td></td><td></td><td></td></tr><tr><td>CI</td><td>0.00</td><td>10</td><td>0.00<sup>d</sup></td><td>307<sup>d</sup></td><td>3</td><td></td><td></td></tr><tr><td>Allende</td><td>-0.35</td><td>4</td><td>-0.15</td><td>117<sup>d</sup></td><td>3</td><td></td><td></td></tr><tr><td>Matrix of Allende</td><td>0.12</td><td>3</td><td>n/d</td><td>n/d</td><td>1</td><td></td><td></td></tr></tbody></table>

a = Kato et al. 2017, b = McDonough 1990, c = Palme and O'Neill 2003, d = Luck et al. 2005.
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807

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815 Figure 5a

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