# Impact-induced chemical fractionation as inferred from hypervelocity impact experiments with silicate projectiles and metallic targets

Clément Ganino, Guy Libourel, Akiko Nakamura, Suzanne Jacomet, Olivier

Tottereau, Patrick Michel

► To cite this version:

Clément Ganino, Guy Libourel, Akiko Nakamura, Suzanne Jacomet, Olivier Tottereau, et al. Impact-induced chemical fractionation as inferred from hypervelocity impact experiments with silicate projectiles and metallic targets. Meteoritics and Planetary Science, 2018, 53 (11), pp.2306-2326. 10.1111/maps.13131. hal-02196123

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# Impact-induced chemical fractionation as inferred from hypervelocity impact experiments with silicate projectiles and metallic targets

Clément GANINO<sup>1*</sup>, Guy LIBOUREL<sup>2,3</sup>, Akiko M. NAKAMURA<sup>4</sup>, Suzanne JACOMET<sup>5</sup>, Olivier TOTTEREAU<sup>6</sup>, and Patrick MICHEL<sup>2</sup>

**Abstract**—Hypervelocity impacts are common in the solar system, in particular during its early phases when primitive bodies of contrasted composition collided. Whether these objects are chemically modified during the impact process, and by what kind of processes, e.g., chemical mixing or gas–liquid–solid fractionation, are still pending questions. To address these issues, a set of impact experiments involving a multielemental doped phonolitic projectile and a metallic target was performed in a 3–7 km s<sup>-1</sup> range of impact speeds which are typical of those occurring in the asteroid belt. For each run, both texture and chemistry of the crater and the ejecta population have been characterized. The results show that the melted projectiles largely cover the craters at all speeds, and that melted phonolitic materials are injected into fractures in the crater in the metallic target. Ejecta are generally quenched droplets of silicate impact melt containing metal beads. Some of these beads are extracted from the target, but we propose that some of the Fe metal beads are the result of reduction of FeO. A thin FeO-SiO<sub>2</sub>-rich condensate layer is found at the edge of the crater, suggesting that a limited amount of vapor formed and condensed. LA-ICP-MS analyses suggest, however, that within analytical uncertainties, no volatility-controlled chemical fractionation of trace elements occurred in the ejecta. The main chemical fractionation during impact at such velocities and energies are the result of projectile-target mixing.

## INTRODUCTION

Impact cratering is considered to be one of the most important geological processes in the history of our planetary system (Melosh 1989; French 1998). Impact craters are indeed omnipresent on the surfaces of both asteroids and planetary bodies. They result from collisions between two bodies at speeds in excess of a few km s<sup>-1</sup>. Typical impact velocities depend on the location in the solar system, along with the precise details of the relative orbits of the respective bodies and

their mutual gravitational influence. While impacts are distributed over a wide range of speeds in the solar system (Le Feuvre and Wieczorek 2011), most impact speeds are in the range of 1–30 km s<sup>-1</sup> for the inner solar system. For instance, mean collision speeds in the asteroid belt are about 5 km s<sup>-1</sup> (Bottke et al. 1994), falling to around 1 km s<sup>-1</sup> in the vicinity of Pluto (Greenstreet et al. 2015). For the Earth–Moon system, average velocities are much higher, between 15 and 25 km s<sup>-1</sup> (Oberst et al. 2012). Typical impact speeds also depend on the stage of the solar system evolution

<footnote n="1"><sup>1</sup>Université Côte d'Azur, OCA, CNRS, Géoazur, 250 rue Albert Einstein, Sophia-Antipolis, 06560 Valbonne, France</footnote>

<footnote n="2"><sup>2</sup>Université Côte d'Azur, OCA, CNRS, Lagrange, Boulevard de l'Observatoire, CS 34229, 06304 Nice Cedex 4, France</footnote>

<footnote n="3"><sup>3</sup>Hawai'i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai'i at Mānoa, Honolulu, Hawai'i 96821, USA</footnote>

<footnote n="4"><sup>4</sup>Graduate School of Science, Kobe University, 1-1 Rokkoudai-cho, Nada-ku, Kobe 657-8501, Japan</footnote>

<footnote n="5"><sup>5</sup>MINES ParisTech, PSL—Research University, CEMEF—Centre de mise en forme des matériaux, CNRS, UMR 7635, Sophia-Antipolis, France</footnote>

<footnote n="6"><sup>6</sup>CRHEA, CNRS UPR 10, Sophia Antipolis, France</footnote>

<footnote>*Corresponding author. E-mail: ganino@unice.fr</footnote>

<footnote>(Received 08 June 2017; revision accepted 07 May 2018)</footnote>
at which impacts occurred, i.e., during protoplanetary disk, debris disk, planet migration phases, or now. Very likely, the so-called “Grand Tack” scenario (Walsh et al. 2011), in which Jupiter temporarily entered the asteroid belt region before migrating back outward, might have resulted in collisions at higher velocities than during the current era.

High-speed impacts have been widely studied for their role in catastrophic disruptions, concentrating mainly on their outcome on the target. The interaction between target and projectile during natural impact events and experimental hypervelocity impacts, on the other hand, has rarely been studied (Kelly et al. 1974; Gibbons et al. 1976; Horz et al. 1989; Evans et al. 1992; Mittlefehldt et al. 1992, 2005; Ebert et al. 2011, 2013, 2014; Wozniakiewicz et al. 2011; Hamann et al. 2013, 2016a, 2017). This is in part due to the complexity of such kind of experimental studies, and also linked to the fact that during large impact events, the projectile is melted or vaporized so that, at best, only small fragments survive (e.g., Mittlefehldt et al. 1992).

On the other hand, it is reasonable to expect that, in the frame of highly energetic, violent, and ultrafast impact events, phase transformations accompanied by various chemical fractionation processes (e.g., induced during melting and subsequent quenching, or evaporation and subsequent condensation, etc.) can occur as pressure and temperature reach extreme values. An example is the gas-associated spheroidal precipitates described in lunar regolith breccia 14076 (Warren 2008) compositions highly depleted in refractory oxides (Al₂O₃ and CaO) and which are interpreted as resulting from condensation from an impact vapor plume. Nevertheless, kinetically, the time scale of an impact is of the order of seconds or less, which might constitute a strong limitation in the completion of chemical fractionation from melting/evaporation and other classical magmatic processes known from Earth and other planetary bodies that are closer to equilibrium conditions.

Laboratory experiments and theoretical models have demonstrated that collisions can lead to different types of sticking, bouncing, and fragmentation (e.g., Güttler et al. 2010; Jutzi et al. 2015) depending on impact speed, porosity, and on the relative size of the involved bodies. In most of these processes, a mass transfer and a degree of mixing (as solid fragments and as impact melts derived from projectile and target) is expected. However, previous studies suggest that the process of projectile-target mixing and the formation of impactite is very complex and far from being understood (Evans et al. 1992; Mittlefehldt et al. 1992, 2005; Wozniakiewicz et al. 2011; Koeberl et al. 2012; Ebert et al. 2013, 2014; Hamann et al. 2013, 2016b).

Element fractionation during impact melting is, for instance, documented in impact melts from the Wabar crater where a complex vapor fractionation process produced siderophile element abundances in the impact melts that differ from those of the projectile (Mittlefehldt et al. 1992). On the other hand, siderophile element ratios in the impact melts from Meteor Crater are mostly unchanged from those of the projectile, although depletion in Au has been ascribed to loss of volatile Au halides (Mittlefehldt et al. 2005). Aside from these studies, several experimental studies have focused on impact-induced element fractionation processes. Ebert et al. (2013, 2014) described physical and chemical mixing of sandstone-derived impact melts with metallic impact melts derived from projectiles made of steel or the Campo del Cielo iron meteorite. Specifically, Ebert et al. (2013, 2014) described significant interelement fractionation, i.e., selective enrichment of Fe in the silicate melt, and enrichment of Ni and Co in coexisting projectile melt spherules. In addition, Ebert et al. (2014) observed that Cr (and V) of the projectile droplets preferentially partitioned into the silicate melt with respect to Fe, yielding Cr/Fe well above the target and projectile ratios. Hamann et al. (2013) focused on the impact glass from the Wabar crater, Saudi Arabia and demonstrated that meteoritic Fe was selectively mixed with high-silica target melt at high temperatures due to selective oxidation. Subsequent fractionation occurred during quenching of the melt by unmixing due to liquid immiscibility separating iron-rich and silica-rich melts. Rowan and Ahrens (1994) focused on basalt-molybdenum interactions during shock experiments and described the in situ reduction of FeO in the shocked melted basalt. Hamann et al. (2016a, 2016b) investigated the chemical interaction between Cu-bearing aluminum projectiles and quartz sand targets in hypervelocity impact experiments and redox reactions between Cu-bearing Al alloy and SiO₂ (forming Al₂O₃ melt and silicon as euhedral crystals, or spherical droplets).

These results illustrate that chemical fractionation processes, at least associated to redox reaction, occur during the short time scales of an impact and are various and complex. However, bridging the gap between impact experiments and natural observations is challenging because the impact energies are extremely different: the maximum impact velocities currently obtained for macroscopic (mm-sized) projectiles in the laboratory are limited to 6–8 km s⁻¹, resulting in low impact energy. Thus, impact energies in experiments are typically in the 10⁻¹ to 10² J range (Ebert et al. 2014), whereas those calculated for small natural craters such as Wabar or Meteor Crater are about 10⁷ kJ (Melosh and Collins 2005). Laser heating experiments (Hamann
et al. 2016a, 2016b; Ebert et al. 2017) produce superheated melts that thermodynamically, texturally, and mineralogically resemble impact melts formed during adiabatic decompression. Such experiments may extend attainable temperatures in experiments to ranges corresponding to impacts in the velocity range of 4–20 km s⁻¹, and may contribute to the study of time scales and magnitudes of petrogenetic processes in impact melts. A limitation is the absence of high shock pressures in these experiments, which remain complementary to hypervelocity experiments.

In the previous hypervelocity experiments mentioned above, chemical fractionation during melting and mixing of projectile and target material was only described for a limited number of chemical components. Consequently, the aim of this study was thus to extend the investigation of interelement fractionation to a larger set of chemical components that range from refractory to siderophile to highly volatile elements, and to explore chemical fractionation associated with impacts at speeds typical of those occurring in the asteroid belt (some 5 km s⁻¹). In order to test unambiguously the occurrence of any chemical fractionations while remaining close to the context of solar system collisions and respecting the experimental constraints, our strategy has been to perform impact experiments by shooting a projectile made of trace element-doped phonolitic (Table 1) glass beads onto a steel (Table 2) target. The phonolitic glass is used as a proxy of silicate material that is the major composition of most undifferentiated meteorite. Fifteen elements, representing a large spectrum of different chemical affinities from refractory to siderophile and to highly volatile elements, have been added to the phonolite composition (Table 1) to facilitate the recognition of any chemical fractionation. For each experiment, both the crater and the ejecta—the latter recovered using aluminum witness plates—have been characterized by scanning electron microscopy (SEM) techniques and analyzed by energy dispersive spectroscopy (EDX) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS).

## EXPERIMENTS AND ANALYTICAL TECHNIQUES

### Experiments

The projectile composition (Table 1) has been selected to be close to that of a phonolitic lava (55–60 wt% SiO₂ and ~15 wt% Na₂O+K₂O), a composition that maximizes the alkali (volatile) element contents. Crystal-free natural phonolitic glassy chips were ground in a mortar to a fine powder at CRPG-SARM Nancy. Fifteen trace elements (Ba, Ce, Cs, Co, Ga, La, Nb, Rb, Sc, Sr,

<table><caption>Table 1. ICP-MS analyses of the bulk composition (wt%) of the phonolitic projectile.</caption><thead><tr><th></th><th>Bulk projectile (n = 4)</th><th>2σ</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>57.5</td><td>1.1</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>13.8</td><td>0.3</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub></td><td>4.06</td><td>0.20</td></tr><tr><td>MnO</td><td>0.11</td><td>0.00</td></tr><tr><td>MgO</td><td>4.52</td><td>0.07</td></tr><tr><td>CaO</td><td>4.62</td><td>0.09</td></tr><tr><td>Na<sub>2</sub>O</td><td>6.03</td><td>0.30</td></tr><tr><td>K<sub>2</sub>O</td><td>7.92</td><td>0.11</td></tr><tr><td>TiO<sub>2</sub></td><td>1.11</td><td>0.02</td></tr><tr><td>Total</td><td>99.63</td><td>1.4</td></tr><tr><td>Ba</td><td>900</td><td>14</td></tr><tr><td>Ce</td><td>824</td><td>28</td></tr><tr><td>Co</td><td>641</td><td>83</td></tr><tr><td>Cs</td><td>737</td><td>23</td></tr><tr><td>Ga</td><td>322</td><td>49</td></tr><tr><td>La</td><td>745</td><td>5</td></tr><tr><td>Nb</td><td>685</td><td>7</td></tr><tr><td>Rb</td><td>839</td><td>19</td></tr><tr><td>Sc</td><td>342</td><td>4</td></tr><tr><td>Sr</td><td>753</td><td>12</td></tr><tr><td>Ta</td><td>983</td><td>25</td></tr><tr><td>V</td><td>569</td><td>16</td></tr><tr><td>Y</td><td>850</td><td>6</td></tr><tr><td>Yb</td><td>842</td><td>28</td></tr><tr><td>Zr</td><td>670</td><td>4</td></tr></tbody></table>

L.D. = limit of detection.

<table><caption>Table 2. Nominal composition (wt%) of the steel from the target and the aluminum ejecta catcher.</caption><thead><tr><th></th><th>Target</th><th>Ejecta catchers</th></tr></thead><tbody><tr><td>Si</td><td>0.15–0.35</td><td>0.14–0.25</td></tr><tr><td>Al</td><td></td><td>98.32–98.35</td></tr><tr><td>Fe</td><td></td><td>0.09–0.1</td></tr><tr><td>Mn</td><td>0.6–0.9</td><td>0.04–0.06</td></tr><tr><td>Mg</td><td></td><td>0.74–0.75</td></tr><tr><td>Ca</td><td></td><td>0.03</td></tr><tr><td>Na</td><td></td><td>0.39–0.49</td></tr><tr><td>K</td><td></td><td>0.07</td></tr><tr><td>Ti</td><td></td><td>0.04–0.05</td></tr><tr><td>P</td><td>&lt;0.03</td><td></td></tr><tr><td>C</td><td>0.33–0.38</td><td></td></tr><tr><td>S</td><td>&lt;0.03</td><td></td></tr><tr><td>Cu</td><td>&lt;0.3</td><td></td></tr><tr><td>Ni</td><td>&lt;0.25</td><td></td></tr><tr><td>Cr</td><td>0.9–1.2</td><td></td></tr><tr><td>Mo</td><td>0.15–0.3</td><td></td></tr></tbody></table>

Ta, V, Y, Yb, and Zr) ranging in concentrations from 300 to 1000 ppm were then added as oxides to this powder. The obtained mixture was then homogenized, and remelted 5 min at 1400 °C in a Gero muffle furnace using
<figure><img src="image_2.png" /><figcaption>Fig. 1. a) Experimental setup; (b) steel cylinder used as target with the resulting impact crater (here after impact from experiment n1); (c) aluminum ejecta catcher with macroscopic craters and scratches (scars) (1 cm × 1 cm); (d–f) high-speed video camera images of the impact during experiment n0 (d) after the shoot, (e) 12 µs after impact, and (f) 16 µs after impact. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

amorphous carbon crucible for making, after quenching (~100 °C s⁻¹), a dozen 2–5 mm homogeneous glassy spherical beads (Fig. S1 in supporting information). Four of them were selected to define the bulk chemical composition of the starting material (Table 1; see below), and the remaining ones were used as projectiles for the set of hypervelocity impact experiments described here. The targets consist in a SCM 435 steel cylinder of 5–6 cm radius and 3–4 cm height; minor element abundances, as provided by the supplier, are given in Table 2. Ejecta were collected on witness made of aluminum (Fig. 1; composition as provided by the supplier is given in Table 2), allowing convenient detection of silica- and/or iron-rich ejecta.

The impact experiments were performed using a 7 mm bore two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS) in Japan. Projectiles were all shot vertically to the target surface using a plastic sabot (Kawai et al. 2010). The range of impact speeds is between 3 and 7 km s⁻¹, allowing the determination of the scaling of the results with impact speed (see Table 3). A square aluminum witness plate (28 cm width) with a central hole (4 cm in diameter) allowing the passage of the projectile was placed in front of the target. Smaller aluminum plates (1 cm width) were fixed on the large aluminum witness plate and were

<table><caption>Table 3. Experimental setup.</caption><thead><tr><td>Exp. number</td><td>Impact velocity (km s<sup>-1</sup>)</td><td>Mass of the projectile (g)</td><td>Energy (J)</td></tr></thead><tbody><tr><td>n3</td><td>3.39</td><td>0.033</td><td>190</td></tr><tr><td>n1</td><td>4.9</td><td>0.037</td><td>444</td></tr><tr><td>n4</td><td>6.88</td><td>0.03</td><td>710</td></tr><tr><td>n0</td><td>6.89</td><td>0.08</td><td>1899</td></tr></tbody></table>

used for the analyses. The distance between the witness plate that collected the ejecta and the target surface was about 10 cm (see Fig. 1). All the experiments were performed under vacuum condition (<10 Pa).

A total of five experiments were performed with increasing impact speed (from 3.39 to 6.89 km s⁻¹) and different projectiles mass (from 0.03 to 0.08 g), resulting in impact energies that ranged from 190 to 1899 J (see Table 3). The trajectories of the projectile and the ejecta were captured with a high-speed video camera (frame rate of 4 µs) that monitored the experiments.

## Scanning Electron Microscopy

Backscattered electron (BSE) imaging of the resulting craters (Fig. 2) and ejecta (Fig. 3) as well as major element analysis was done using a Philipps FEI XL30
<figure><img src="image_3.png" /><figcaption>Fig. 2. SEM images of the targets after impact. a) BSE image of an orthogonal section of the major crater of experiment n0. b) SE vertical view of the major crater on the target of experiment n4. c) BSE image of impact melt covering the crater bottom. d) EDX-chemical map of impact melt covering the crater bottom. e) BSE image of fractures filled with impact melt containing beads of metal. f) BSE image of a detail of the metal beads contained in the impact melt covering the bottom of the crater. g) BSE image of the edge of the crater covered by a 10 µm thick condensate deposit (fayalite–ferrosilite composition). h) BSE image of an amorphous or poorly crystallized condensate covering the impact melt at the crater wall. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig. 3. BSE-SEM images of the aluminum ejecta catcher. a) Crater containing ejecta (quenched droplets of impact melt). b–d) Complex sequences of secondary craters and ejecta coatings. e, f) EDX-SEM chemical map (red = Fe; yellow = Si+O) combined with EDS image of the ejecta catcher showing the diversity of ejecta, their cumulation, and their textures including metal beads (f). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

ESEM with a LaB6 cathode and a BRUKER Quantax 655 detector, operated at 20 kV and 200 nA beam current at CEMEF-Mines ParisTech in Sophia Antipolis (France). EDX was used for semiquantitative point analyses. We assume an analytical precision of 1 wt% (Table 4).

Excitation volume is uncertain but close to 1 µm³. Therefore, the ejecta analysis does not cover the bulk of the ejecta but rather corresponds to a “point” (1 µm³) analysis. If the ejecta were homogenous, it would provide information on the bulk of the ejecta. In the case of heterogeneous ejecta, which is generally observed (Figs. 3e and 3f), these analyses have to be

interpreted as mixing between the different endmembers. In the case of very flat ejecta samples (thickness <1 µm), it is likely that there is a contribution from the aluminum ejecta catcher. For this reason, any conclusion on the behavior of aluminum is speculative with this experimental setup and has to consider the possible contribution of the witness plates.

## Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

We analyzed trace element compositions in 112 ejecta by means of laser ablation ICP-MS. Due to analytical
<table><caption>Table 4. EDX-SEM major element compositions (wt%) of the ejecta, impact melt, and condensate layer.</caption><thead><tr><th></th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>FeO</th><th>MgO</th><th>CaO</th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>TiO<sub>2</sub></th></tr></thead><tbody><tr><td>ejecta n3-001</td><td>48.3</td><td>16.5</td><td>5.17</td><td>5.10</td><td>5.12</td><td>8.51</td><td>10.5</td><td>0.75</td></tr><tr><td>ejecta n3-002</td><td>48.3</td><td>16.7</td><td>3.63</td><td>5.35</td><td>5.16</td><td>8.87</td><td>11.0</td><td>0.95</td></tr><tr><td>ejecta n3-003</td><td>50.1</td><td>17.0</td><td>4.10</td><td>4.84</td><td>5.46</td><td>5.83</td><td>11.6</td><td>1.12</td></tr><tr><td>ejecta n3-004</td><td>49.5</td><td>17.5</td><td>2.91</td><td>6.01</td><td>4.66</td><td>9.38</td><td>9.34</td><td>0.79</td></tr><tr><td>ejecta n3-005</td><td>50.7</td><td>18.3</td><td>2.85</td><td>4.31</td><td>6.47</td><td>4.16</td><td>12.0</td><td>1.24</td></tr><tr><td>ejecta n3-006</td><td>51.8</td><td>19.9</td><td>1.12</td><td>5.94</td><td>3.82</td><td>8.70</td><td>8.21</td><td>0.56</td></tr><tr><td>ejecta n3-007</td><td>48.6</td><td>21.8</td><td>2.53</td><td>5.29</td><td>4.81</td><td>6.44</td><td>9.77</td><td>0.69</td></tr><tr><td>ejecta n3-008</td><td>46.8</td><td>22.2</td><td>3.62</td><td>4.01</td><td>6.88</td><td>3.70</td><td>11.6</td><td>1.18</td></tr><tr><td>ejecta n3-009</td><td>47.5</td><td>22.9</td><td>2.28</td><td>4.26</td><td>6.38</td><td>4.52</td><td>11.1</td><td>1.13</td></tr><tr><td>ejecta n3-010</td><td>51.3</td><td>25.0</td><td>0.15</td><td>4.80</td><td>2.73</td><td>6.47</td><td>8.61</td><td>0.93</td></tr><tr><td>ejecta n3-011</td><td>53.4</td><td>25.5</td><td>0.13</td><td>3.88</td><td>1.70</td><td>6.55</td><td>8.41</td><td>0.46</td></tr><tr><td>ejecta n3-012</td><td>45.3</td><td>32.7</td><td>1.39</td><td>2.86</td><td>5.00</td><td>1.58</td><td>10.4</td><td>0.77</td></tr><tr><td>ejecta n3-013</td><td>34.7</td><td>32.2</td><td>6.55</td><td>7.69</td><td>4.82</td><td>2.47</td><td>10.9</td><td>0.65</td></tr><tr><td>ejecta n3-014</td><td>39.4</td><td>34.0</td><td>4.48</td><td>1.75</td><td>6.34</td><td>1.38</td><td>11.5</td><td>1.18</td></tr><tr><td>ejecta n3-015</td><td>22.7</td><td>31.2</td><td>10.6</td><td>2.29</td><td>10.0</td><td>4.21</td><td>16.9</td><td>2.07</td></tr><tr><td>ejecta n3-016</td><td>40.1</td><td>36.2</td><td>3.42</td><td>0.54</td><td>4.68</td><td>0.18</td><td>13.6</td><td>1.40</td></tr><tr><td>ejecta n3-017</td><td>41.8</td><td>38.8</td><td>1.31</td><td>4.44</td><td>3.15</td><td>5.22</td><td>4.65</td><td>0.61</td></tr><tr><td>ejecta n3-018</td><td>35.8</td><td>49.7</td><td>0.85</td><td>1.77</td><td>2.11</td><td>2.77</td><td>6.36</td><td>0.59</td></tr><tr><td>ejecta n3-019</td><td>31.1</td><td>54.6</td><td>0.66</td><td>2.59</td><td>1.65</td><td>3.52</td><td>5.30</td><td>0.59</td></tr><tr><td>ejecta n1-001</td><td>48.3</td><td>16.2</td><td>5.83</td><td>5.56</td><td>5.21</td><td>7.83</td><td>10.29</td><td>0.84</td></tr><tr><td>ejecta n1-002</td><td>52.5</td><td>17.2</td><td>1.85</td><td>5.72</td><td>4.94</td><td>7.09</td><td>9.75</td><td>0.95</td></tr><tr><td>ejecta n1-003</td><td>50.4</td><td>17.3</td><td>1.64</td><td>5.60</td><td>4.80</td><td>8.61</td><td>10.71</td><td>0.96</td></tr><tr><td>ejecta n1-004</td><td>50.4</td><td>17.5</td><td>2.98</td><td>6.31</td><td>3.91</td><td>9.93</td><td>8.19</td><td>0.80</td></tr><tr><td>ejecta n1-005</td><td>50.4</td><td>17.5</td><td>5.99</td><td>4.86</td><td>4.75</td><td>5.64</td><td>10.17</td><td>0.72</td></tr><tr><td>ejecta n1-006</td><td>50.8</td><td>18.4</td><td>2.54</td><td>5.94</td><td>4.42</td><td>8.23</td><td>9.19</td><td>0.52</td></tr><tr><td>ejecta n1-007</td><td>48.6</td><td>19.2</td><td>1.11</td><td>6.96</td><td>3.16</td><td>13.4</td><td>7.16</td><td>0.41</td></tr><tr><td>ejecta n1-008</td><td>48.7</td><td>19.3</td><td>2.10</td><td>5.64</td><td>4.24</td><td>9.35</td><td>9.96</td><td>0.76</td></tr><tr><td>ejecta n1-009</td><td>49.0</td><td>19.4</td><td>1.15</td><td>7.12</td><td>3.02</td><td>12.7</td><td>7.29</td><td>0.28</td></tr><tr><td>ejecta n1-010</td><td>48.4</td><td>19.4</td><td>2.71</td><td>5.64</td><td>4.81</td><td>8.50</td><td>9.71</td><td>0.81</td></tr><tr><td>ejecta n1-011</td><td>50.1</td><td>19.8</td><td>0.54</td><td>7.27</td><td>2.78</td><td>12.66</td><td>6.35</td><td>0.43</td></tr><tr><td>ejecta n1-012</td><td>51.0</td><td>20.2</td><td>1.67</td><td>6.23</td><td>3.93</td><td>8.29</td><td>8.16</td><td>0.58</td></tr><tr><td>ejecta n1-013</td><td>48.5</td><td>20.3</td><td>4.14</td><td>6.20</td><td>3.05</td><td>9.60</td><td>7.90</td><td>0.37</td></tr><tr><td>ejecta n1-014</td><td>50.5</td><td>21.8</td><td>0.40</td><td>7.59</td><td>2.45</td><td>11.3</td><td>5.93</td><td>0.13</td></tr><tr><td>ejecta n1-015</td><td>48.3</td><td>21.6</td><td>0.37</td><td>8.20</td><td>1.72</td><td>14.5</td><td>5.04</td><td>0.26</td></tr><tr><td>ejecta n1-016</td><td>51.0</td><td>22.5</td><td>0.44</td><td>8.00</td><td>2.38</td><td>10.2</td><td>5.34</td><td>0.21</td></tr><tr><td>ejecta n1-017</td><td>50.3</td><td>23.8</td><td>0.87</td><td>6.20</td><td>2.75</td><td>8.88</td><td>6.90</td><td>0.34</td></tr><tr><td>ejecta n1-018</td><td>49.8</td><td>24.0</td><td>1.07</td><td>5.79</td><td>3.46</td><td>7.49</td><td>7.94</td><td>0.40</td></tr><tr><td>ejecta n1-019</td><td>48.9</td><td>24.8</td><td>0.64</td><td>5.92</td><td>2.89</td><td>9.40</td><td>7.12</td><td>0.36</td></tr><tr><td>ejecta n1-020</td><td>51.6</td><td>26.1</td><td>1.05</td><td>4.65</td><td>4.02</td><td>4.04</td><td>7.92</td><td>0.55</td></tr><tr><td>ejecta n1-021</td><td>48.7</td><td>27.9</td><td>1.93</td><td>5.02</td><td>3.39</td><td>5.68</td><td>6.81</td><td>0.61</td></tr><tr><td>ejecta n1-022</td><td>48.5</td><td>29.4</td><td>0.74</td><td>3.71</td><td>4.05</td><td>2.99</td><td>10.1</td><td>0.55</td></tr><tr><td>ejecta n1-023</td><td>43.1</td><td>31.1</td><td>1.81</td><td>5.87</td><td>2.84</td><td>8.76</td><td>6.24</td><td>0.24</td></tr><tr><td>ejecta n4-001</td><td>54.4</td><td>22.5</td><td>2.87</td><td>5.91</td><td>4.15</td><td>4.57</td><td>5.01</td><td>0.52</td></tr><tr><td>ejecta n4-002</td><td>55.7</td><td>19.8</td><td>3.13</td><td>6.48</td><td>4.11</td><td>4.89</td><td>5.18</td><td>0.73</td></tr><tr><td>ejecta n4-003</td><td>54.0</td><td>20.0</td><td>3.31</td><td>7.30</td><td>3.94</td><td>6.20</td><td>4.79</td><td>0.42</td></tr><tr><td>ejecta n4-004</td><td>55.6</td><td>23.8</td><td>3.72</td><td>4.33</td><td>4.14</td><td>2.73</td><td>5.02</td><td>0.67</td></tr><tr><td>ejecta n4-005</td><td>50.0</td><td>16.9</td><td>3.98</td><td>5.76</td><td>4.45</td><td>8.56</td><td>9.72</td><td>0.70</td></tr><tr><td>ejecta n4-006</td><td>53.6</td><td>20.5</td><td>4.60</td><td>7.12</td><td>4.46</td><td>4.43</td><td>4.79</td><td>0.55</td></tr><tr><td>ejecta n4-007</td><td>54.8</td><td>19.5</td><td>4.70</td><td>5.12</td><td>5.24</td><td>3.07</td><td>6.49</td><td>1.04</td></tr><tr><td>ejecta n4-008</td><td>54.7</td><td>18.6</td><td>5.53</td><td>6.12</td><td>4.47</td><td>4.32</td><td>5.57</td><td>0.70</td></tr><tr><td>ejecta n4-009</td><td>53.0</td><td>18.9</td><td>6.04</td><td>6.44</td><td>5.05</td><td>4.18</td><td>5.63</td><td>0.73</td></tr><tr><td>ejecta n4-010</td><td>52.6</td><td>19.0</td><td>6.42</td><td>5.86</td><td>4.94</td><td>4.02</td><td>6.23</td><td>0.88</td></tr><tr><td>ejecta n4-011</td><td>50.9</td><td>20.6</td><td>7.83</td><td>4.69</td><td>6.23</td><td>1.91</td><td>6.64</td><td>1.22</td></tr><tr><td>ejecta n4-012</td><td>45.1</td><td>19.5</td><td>8.13</td><td>4.67</td><td>5.74</td><td>6.05</td><td>9.96</td><td>0.82</td></tr></tbody></table>
<table><caption>Table 4. Continued. EDX-SEM major element compositions (wt%) of the ejecta, impact melt, and condensate layer.</caption><thead><tr><th></th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>FeO</th><th>MgO</th><th>CaO</th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>TiO<sub>2</sub></th></tr></thead><tbody><tr><td>ejecta n4-013</td><td>49.2</td><td>16.8</td><td>8.22</td><td>5.02</td><td>4.78</td><td>5.91</td><td>9.28</td><td>0.79</td></tr><tr><td>ejecta n4-014</td><td>48.9</td><td>14.8</td><td>10.1</td><td>4.70</td><td>4.68</td><td>6.17</td><td>9.85</td><td>0.76</td></tr><tr><td>ejecta n4-015</td><td>47.3</td><td>16.5</td><td>10.4</td><td>5.68</td><td>4.50</td><td>7.12</td><td>7.81</td><td>0.64</td></tr><tr><td>ejecta n4-016</td><td>43.6</td><td>27.2</td><td>12.7</td><td>5.34</td><td>4.10</td><td>2.70</td><td>3.64</td><td>0.65</td></tr><tr><td>ejecta n4-017</td><td>48.1</td><td>20.5</td><td>13.6</td><td>7.04</td><td>4.08</td><td>3.80</td><td>2.45</td><td>0.39</td></tr><tr><td>ejecta n4-018</td><td>49.1</td><td>18.3</td><td>14.8</td><td>5.92</td><td>4.52</td><td>3.10</td><td>3.67</td><td>0.70</td></tr><tr><td>ejecta n4-019</td><td>45.9</td><td>21.0</td><td>16.6</td><td>6.14</td><td>4.02</td><td>2.97</td><td>2.86</td><td>0.53</td></tr><tr><td>ejecta n4-020</td><td>42.3</td><td>26.5</td><td>16.7</td><td>3.19</td><td>5.31</td><td>0.69</td><td>4.47</td><td>0.91</td></tr><tr><td>ejecta n4-021</td><td>42.1</td><td>14.1</td><td>21.1</td><td>4.91</td><td>3.79</td><td>6.52</td><td>6.94</td><td>0.49</td></tr><tr><td>ejecta n4-022</td><td>34.6</td><td>20.8</td><td>32.9</td><td>5.05</td><td>2.87</td><td>1.78</td><td>1.54</td><td>0.48</td></tr><tr><td>ejecta n0-001</td><td>62.0</td><td>18.7</td><td>2.21</td><td>4.33</td><td>4.55</td><td>2.1</td><td>6.1</td><td>n.m.</td></tr><tr><td>ejecta n0-002</td><td>55.7</td><td>16.5</td><td>7.28</td><td>4.48</td><td>5.33</td><td>3.01</td><td>7.73</td><td>n.m.</td></tr><tr><td>ejecta n0-003</td><td>56.1</td><td>16.2</td><td>7.98</td><td>4.37</td><td>5.41</td><td>2.16</td><td>7.82</td><td>n.m.</td></tr><tr><td>ejecta n0-004</td><td>55.9</td><td>16.4</td><td>7.58</td><td>4.25</td><td>6.03</td><td>2.39</td><td>7.48</td><td>n.m.</td></tr><tr><td>ejecta n0-005</td><td>52.9</td><td>16.0</td><td>11.4</td><td>4.47</td><td>4.92</td><td>3.19</td><td>7.08</td><td>n.m.</td></tr><tr><td>ejecta n0-006</td><td>60.5</td><td>15.9</td><td>3.18</td><td>2.78</td><td>5.55</td><td>2.89</td><td>8.71</td><td>0.55</td></tr><tr><td>ejecta n0-007</td><td>61.8</td><td>18.2</td><td>2.15</td><td>3.56</td><td>4.31</td><td>2.37</td><td>7.01</td><td>0.55</td></tr><tr><td>ejecta n0-008</td><td>59.1</td><td>15.8</td><td>7.24</td><td>2.73</td><td>4.8</td><td>2.62</td><td>7.09</td><td>0.57</td></tr><tr><td>ejecta n0-009</td><td>54.0</td><td>15.6</td><td>14.1</td><td>2.45</td><td>5.26</td><td>1.80</td><td>5.94</td><td>0.84</td></tr><tr><td>ejecta n0-010</td><td>53.3</td><td>15.9</td><td>5.99</td><td>5.11</td><td>5.26</td><td>5.71</td><td>7.40</td><td>1.33</td></tr><tr><td>ejecta n0-011</td><td>42.5</td><td>11.3</td><td>24.8</td><td>4.07</td><td>4.36</td><td>6.23</td><td>5.95</td><td>0.80</td></tr><tr><td>ejecta n0-012</td><td>48.5</td><td>14.7</td><td>13.2</td><td>5.09</td><td>4.53</td><td>6.92</td><td>6.04</td><td>0.98</td></tr><tr><td>ejecta n0-013</td><td>48.1</td><td>14.1</td><td>12.2</td><td>4.91</td><td>5.02</td><td>6.91</td><td>7.71</td><td>1.09</td></tr><tr><td>ejecta n0-014</td><td>49.2</td><td>14.7</td><td>10.2</td><td>4.87</td><td>5.14</td><td>6.77</td><td>8.04</td><td>1.15</td></tr><tr><td>ejecta n0-015</td><td>43.5</td><td>12.7</td><td>19.9</td><td>5.31</td><td>4.40</td><td>8.32</td><td>5.11</td><td>0.76</td></tr><tr><td>ejecta n0-016</td><td>51.0</td><td>15.7</td><td>6.59</td><td>5.34</td><td>5.37</td><td>7.18</td><td>7.61</td><td>1.21</td></tr><tr><td>ejecta n0-017</td><td>51.3</td><td>15.7</td><td>6.36</td><td>5.28</td><td>5.33</td><td>6.99</td><td>7.83</td><td>1.20</td></tr><tr><td>impact melt crater 01</td><td>30.8</td><td>4.9</td><td>51.9</td><td>1.08</td><td>5.02</td><td>1.56</td><td>4.78</td><td>n.m.</td></tr><tr><td>impact melt crater 02</td><td>44.9</td><td>13.0</td><td>21.1</td><td>4.41</td><td>4.14</td><td>5.75</td><td>6.67</td><td>n.m.</td></tr><tr><td>impact melt crater 03</td><td>46.4</td><td>13.2</td><td>18.9</td><td>4.43</td><td>4.48</td><td>5.55</td><td>7.09</td><td>n.m.</td></tr><tr><td>impact melt crater 04</td><td>44.0</td><td>12.4</td><td>23.4</td><td>4.16</td><td>4.44</td><td>4.76</td><td>6.84</td><td>n.m.</td></tr><tr><td>impact melt crater 05</td><td>46.4</td><td>13.4</td><td>18.3</td><td>4.63</td><td>4.40</td><td>6.02</td><td>6.89</td><td>n.m.</td></tr><tr><td>impact melt crater 06</td><td>47.7</td><td>11.9</td><td>21.0</td><td>3.86</td><td>4.37</td><td>4.89</td><td>6.20</td><td>n.m.</td></tr><tr><td>condensate n0-01</td><td>23.8</td><td>n.m.</td><td>73.4</td><td>n.m.</td><td>2.83</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate-n0-02</td><td>39.6</td><td>n.m.</td><td>58.6</td><td>n.m.</td><td>1.81</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate n0-02</td><td>25.4</td><td>n.m.</td><td>73.3</td><td>n.m.</td><td>1.34</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate-n0-03</td><td>26.1</td><td>n.m.</td><td>72.3</td><td>n.m.</td><td>1.62</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate n0-03</td><td>22.6</td><td>n.m.</td><td>74.8</td><td>n.m.</td><td>2.62</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate-n0-04</td><td>24.0</td><td>n.m.</td><td>72.8</td><td>n.m.</td><td>3.25</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate n0-04</td><td>29.7</td><td>n.m.</td><td>68.5</td><td>n.m.</td><td>1.83</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr><tr><td>condensate-n0-05</td><td>31.6</td><td>n.m.</td><td>66.7</td><td>n.m.</td><td>1.66</td><td>n.m.</td><td>n.m.</td><td>n.m.</td></tr></tbody></table>

n.m. = not measured.

constraints associated with the laser ablation setup, the smallest ejecta (with a surface <10 µm × 10 µm) were not analyzed, but we selected samples covering a large size distribution (from about 100 µm² to more than 50,000 µm²).

Trace element compositions of ejecta were measured at LMV Clermont-Ferrand using a ICP-MS Thermo Element XR equipped with a laser Excimer 193 nm Resonetics M-50E with adjustable impact diameter (3–133 µm). Depending on the size of the analyzed ejecta,

the laser totally ablated it and the analyses can be considered as a bulk composition. This is not the case for all ejecta and especially for the biggest for which the analyses still have to be considered as “point” analyses that are representative of the bulk only if the ejecta is homogeneous, which is not the case (e.g., Figs. 3e and 3f). Four internal standards were used (610, 612, BR, VS-N), and the data were normalized to the mean Ca content measured with EDX-SEM in the population of ejecta. Laser ablation ICP-MS composition were also
<table><caption>Table 5. LA-ICP-MS trace element composition (ppm) of the ejecta and projectile.</caption><thead><tr><th></th><th>Ba</th><th>Ce</th><th>Co</th><th>Cs</th><th>Fe</th><th>Ga</th><th>La</th><th>Mn</th><th>Nb</th><th>Rb</th><th>Sc</th><th>Sr</th><th>Ta</th><th>V</th><th>Y</th><th>Yb</th><th>Zr</th></tr></thead><tbody><tr><td>n3 ejecta 01</td><td>528</td><td>478</td><td>414</td><td>439</td><td>17926</td><td>174</td><td>442</td><td>332</td><td>402</td><td>505</td><td>179</td><td>443</td><td>442</td><td>395</td><td>439</td><td>485</td><td>411</td></tr><tr><td>n3 ejecta 02</td><td>498</td><td>456</td><td>396</td><td>412</td><td>18421</td><td>188</td><td>438</td><td>560</td><td>374</td><td>444</td><td>194</td><td>425</td><td>474</td><td>368</td><td>437</td><td>486</td><td>394</td></tr><tr><td>n3 ejecta 03</td><td>542</td><td>499</td><td>291</td><td>321</td><td>20523</td><td>159</td><td>463</td><td>782</td><td>398</td><td>367</td><td>187</td><td>466</td><td>511</td><td>373</td><td>484</td><td>527</td><td>436</td></tr><tr><td>n3 ejecta 04</td><td>522</td><td>500</td><td>155</td><td>398</td><td>16580</td><td>190</td><td>446</td><td>376</td><td>375</td><td>425</td><td>192</td><td>460</td><td>475</td><td>380</td><td>452</td><td>527</td><td>384</td></tr><tr><td>n3 ejecta 05</td><td>539</td><td>453</td><td>376</td><td>471</td><td>18699</td><td>164</td><td>449</td><td>492</td><td>417</td><td>517</td><td>177</td><td>451</td><td>488</td><td>375</td><td>467</td><td>493</td><td>435</td></tr><tr><td>n3 ejecta 06</td><td>529</td><td>460</td><td>382</td><td>450</td><td>18354</td><td>183</td><td>442</td><td>426</td><td>406</td><td>484</td><td>177</td><td>461</td><td>470</td><td>380</td><td>465</td><td>486</td><td>416</td></tr><tr><td>n3 ejecta 07</td><td>530</td><td>479</td><td>372</td><td>467</td><td>17742</td><td>183</td><td>455</td><td>412</td><td>412</td><td>507</td><td>182</td><td>456</td><td>479</td><td>390</td><td>468</td><td>493</td><td>418</td></tr><tr><td>n3 ejecta 08</td><td>529</td><td>476</td><td>371</td><td>397</td><td>18279</td><td>201</td><td>448</td><td>319</td><td>382</td><td>454</td><td>172</td><td>438</td><td>435</td><td>376</td><td>445</td><td>486</td><td>406</td></tr><tr><td>n3 ejecta 09</td><td>536</td><td>471</td><td>400</td><td>435</td><td>18669</td><td>188</td><td>456</td><td>336</td><td>410</td><td>503</td><td>177</td><td>457</td><td>464</td><td>381</td><td>462</td><td>504</td><td>429</td></tr><tr><td>n3 ejecta 10</td><td>556</td><td>486</td><td>398</td><td>434</td><td>19489</td><td>208</td><td>470</td><td>332</td><td>416</td><td>509</td><td>187</td><td>459</td><td>477</td><td>392</td><td>473</td><td>524</td><td>442</td></tr><tr><td>n3 ejecta 11</td><td>543</td><td>498</td><td>344</td><td>425</td><td>22669</td><td>193</td><td>454</td><td>363</td><td>404</td><td>471</td><td>177</td><td>456</td><td>468</td><td>381</td><td>452</td><td>488</td><td>410</td></tr><tr><td>n3 ejecta 12</td><td>552</td><td>510</td><td>367</td><td>447</td><td>17878</td><td>175</td><td>476</td><td>325</td><td>415</td><td>499</td><td>183</td><td>450</td><td>486</td><td>395</td><td>471</td><td>524</td><td>438</td></tr><tr><td>n3 ejecta 13</td><td>542</td><td>496</td><td>368</td><td>438</td><td>18686</td><td>204</td><td>469</td><td>429</td><td>420</td><td>476</td><td>178</td><td>474</td><td>478</td><td>379</td><td>481</td><td>496</td><td>422</td></tr><tr><td>n3 ejecta 14</td><td>535</td><td>476</td><td>337</td><td>458</td><td>20430</td><td>215</td><td>447</td><td>391</td><td>396</td><td>487</td><td>168</td><td>449</td><td>458</td><td>376</td><td>443</td><td>477</td><td>400</td></tr><tr><td>n3 ejecta 15</td><td>548</td><td>532</td><td>352</td><td>441</td><td>16306</td><td>151</td><td>448</td><td>379</td><td>395</td><td>468</td><td>176</td><td>454</td><td>485</td><td>387</td><td>464</td><td>493</td><td>424</td></tr><tr><td>n3 ejecta 16</td><td>530</td><td>461</td><td>371</td><td>428</td><td>16761</td><td>183</td><td>448</td><td>375</td><td>398</td><td>473</td><td>182</td><td>443</td><td>453</td><td>362</td><td>456</td><td>488</td><td>410</td></tr><tr><td>n3 ejecta 17</td><td>536</td><td>503</td><td>471</td><td>426</td><td>17311</td><td>171</td><td>462</td><td>335</td><td>403</td><td>486</td><td>181</td><td>456</td><td>459</td><td>386</td><td>467</td><td>505</td><td>425</td></tr><tr><td>n3 ejecta 18</td><td>539</td><td>495</td><td>399</td><td>418</td><td>17462</td><td>189</td><td>457</td><td>330</td><td>396</td><td>481</td><td>176</td><td>446</td><td>457</td><td>385</td><td>464</td><td>512</td><td>421</td></tr><tr><td>n3 ejecta 19</td><td>515</td><td>440</td><td>360</td><td>388</td><td>18208</td><td>198</td><td>420</td><td>304</td><td>367</td><td>460</td><td>170</td><td>431</td><td>414</td><td>375</td><td>443</td><td>481</td><td>402</td></tr><tr><td>n3 ejecta 20</td><td>552</td><td>486</td><td>422</td><td>460</td><td>17484</td><td>171</td><td>450</td><td>396</td><td>420</td><td>511</td><td>179</td><td>448</td><td>480</td><td>380</td><td>462</td><td>487</td><td>418</td></tr><tr><td>n3 ejecta 21</td><td>544</td><td>448</td><td>419</td><td>435</td><td>19630</td><td>245</td><td>432</td><td>515</td><td>374</td><td>490</td><td>165</td><td>460</td><td>456</td><td>405</td><td>437</td><td>487</td><td>397</td></tr><tr><td>n3 ejecta 22</td><td>555</td><td>570</td><td>116</td><td>517</td><td>14876</td><td>141</td><td>501</td><td>358</td><td>445</td><td>567</td><td>196</td><td>466</td><td>555</td><td>414</td><td>493</td><td>533</td><td>468</td></tr><tr><td>n3 ejecta 23</td><td>545</td><td>515</td><td>312</td><td>448</td><td>16197</td><td>168</td><td>469</td><td>379</td><td>410</td><td>479</td><td>181</td><td>459</td><td>486</td><td>388</td><td>475</td><td>512</td><td>423</td></tr><tr><td>n3 ejecta 24</td><td>567</td><td>533</td><td>278</td><td>489</td><td>15891</td><td>132</td><td>504</td><td>357</td><td>437</td><td>533</td><td>196</td><td>459</td><td>542</td><td>404</td><td>501</td><td>550</td><td>467</td></tr><tr><td>n3 ejecta 25</td><td>565</td><td>517</td><td>274</td><td>539</td><td>16052</td><td>153</td><td>488</td><td>389</td><td>427</td><td>591</td><td>187</td><td>460</td><td>532</td><td>397</td><td>481</td><td>524</td><td>454</td></tr><tr><td>n3 ejecta 26</td><td>532</td><td>518</td><td>372</td><td>422</td><td>16574</td><td>180</td><td>453</td><td>352</td><td>393</td><td>479</td><td>174</td><td>452</td><td>460</td><td>365</td><td>452</td><td>499</td><td>407</td></tr><tr><td>n3 ejecta 27</td><td>538</td><td>496</td><td>425</td><td>424</td><td>16049</td><td>166</td><td>463</td><td>322</td><td>394</td><td>483</td><td>179</td><td>444</td><td>448</td><td>375</td><td>464</td><td>507</td><td>425</td></tr><tr><td>n3 ejecta 28</td><td>550</td><td>501</td><td>305</td><td>433</td><td>15926</td><td>168</td><td>461</td><td>317</td><td>399</td><td>504</td><td>182</td><td>445</td><td>451</td><td>390</td><td>457</td><td>507</td><td>417</td></tr><tr><td>n3 ejecta 29</td><td>556</td><td>526</td><td>283</td><td>465</td><td>19085</td><td>210</td><td>476</td><td>358</td><td>411</td><td>503</td><td>181</td><td>472</td><td>483</td><td>397</td><td>467</td><td>497</td><td>429</td></tr><tr><td>n3 ejecta 30</td><td>567</td><td>484</td><td>381</td><td>431</td><td>16807</td><td>176</td><td>453</td><td>425</td><td>398</td><td>466</td><td>178</td><td>455</td><td>476</td><td>374</td><td>466</td><td>489</td><td>415</td></tr><tr><td>n3 ejecta 31</td><td>555</td><td>535</td><td>387</td><td>459</td><td>17248</td><td>196</td><td>473</td><td>347</td><td>398</td><td>498</td><td>173</td><td>461</td><td>481</td><td>383</td><td>470</td><td>523</td><td>415</td></tr><tr><td>n3 ejecta 32</td><td>557</td><td>544</td><td>365</td><td>469</td><td>17288</td><td>203</td><td>470</td><td>546</td><td>410</td><td>504</td><td>171</td><td>454</td><td>504</td><td>379</td><td>462</td><td>508</td><td>415</td></tr><tr><td>n3 ejecta 33</td><td>539</td><td>486</td><td>225</td><td>400</td><td>16727</td><td>197</td><td>451</td><td>335</td><td>385</td><td>436</td><td>166</td><td>457</td><td>462</td><td>364</td><td>446</td><td>493</td><td>389</td></tr><tr><td>n3 ejecta 34</td><td>545</td><td>478</td><td>378</td><td>453</td><td>18740</td><td>197</td><td>450</td><td>339</td><td>400</td><td>512</td><td>189</td><td>449</td><td>472</td><td>386</td><td>445</td><td>490</td><td>406</td></tr><tr><td>n1 ejecta 01</td><td>495</td><td>467</td><td>237</td><td>385</td><td>41325</td><td>136</td><td>441</td><td>391</td><td>403</td><td>453</td><td>179</td><td>409</td><td>427</td><td>371</td><td>429</td><td>474</td><td>419</td></tr><tr><td>n1 ejecta 02</td><td>498</td><td>425</td><td>395</td><td>421</td><td>20074</td><td>208</td><td>485</td><td>335</td><td>373</td><td>483</td><td>173</td><td>437</td><td>415</td><td>363</td><td>432</td><td>456</td><td>402</td></tr><tr><td>n1 ejecta 03</td><td>507</td><td>427</td><td>377</td><td>435</td><td>19934</td><td>186</td><td>427</td><td>362</td><td>380</td><td>488</td><td>176</td><td>437</td><td>436</td><td>358</td><td>435</td><td>463</td><td>402</td></tr><tr><td>n1 ejecta 04</td><td>490</td><td>432</td><td>281</td><td>383</td><td>17691</td><td>132</td><td>412</td><td>336</td><td>386</td><td>441</td><td>170</td><td>422</td><td>415</td><td>357</td><td>422</td><td>437</td><td>390</td></tr><tr><td>n1 ejecta 05</td><td>525</td><td>440</td><td>345</td><td>397</td><td>19925</td><td>164</td><td>433</td><td>350</td><td>379</td><td>458</td><td>178</td><td>449</td><td>428</td><td>368</td><td>437</td><td>494</td><td>393</td></tr><tr><td>n1 ejecta 06</td><td>519</td><td>407</td><td>364</td><td>383</td><td>19489</td><td>168</td><td>405</td><td>323</td><td>385</td><td>475</td><td>171</td><td>445</td><td>419</td><td>367</td><td>412</td><td>455</td><td>383</td></tr><tr><td>n1 ejecta 07</td><td>489</td><td>411</td><td>351</td><td>372</td><td>18769</td><td>181</td><td>405</td><td>314</td><td>366</td><td>461</td><td>170</td><td>434</td><td>388</td><td>366</td><td>411</td><td>436</td><td>379</td></tr><tr><td>n1 ejecta 08</td><td>514</td><td>428</td><td>330</td><td>364</td><td>17403</td><td>153</td><td>437</td><td>336</td><td>357</td><td>408</td><td>174</td><td>437</td><td>448</td><td>344</td><td>456</td><td>500</td><td>413</td></tr><tr><td>n1 ejecta 09</td><td>515</td><td>449</td><td>370</td><td>402</td><td>19140</td><td>185</td><td>439</td><td>320</td><td>386</td><td>443</td><td>182</td><td>453</td><td>440</td><td>356</td><td>445</td><td>492</td><td>408</td></tr><tr><td>n1 ejecta 10</td><td>487</td><td>417</td><td>381</td><td>371</td><td>17753</td><td>179</td><td>429</td><td>345</td><td>366</td><td>416</td><td>169</td><td>427</td><td>405</td><td>352</td><td>415</td><td>435</td><td>376</td></tr><tr><td>n1 ejecta 11</td><td>502</td><td>423</td><td>362</td><td>402</td><td>19467</td><td>171</td><td>442</td><td>346</td><td>381</td><td>438</td><td>171</td><td>439</td><td>425</td><td>356</td><td>428</td><td>460</td><td>401</td></tr><tr><td>n1 ejecta 12</td><td>567</td><td>475</td><td>290</td><td>447</td><td>20113</td><td>169</td><td>461</td><td>721</td><td>376</td><td>485</td><td>193</td><td>488</td><td>437</td><td>342</td><td>484</td><td>512</td><td>380</td></tr><tr><td>n1 ejecta 13</td><td>513</td><td>413</td><td>337</td><td>388</td><td>18716</td><td>151</td><td>456</td><td>435</td><td>374</td><td>430</td><td>169</td><td>460</td><td>441</td><td>338</td><td>439</td><td>464</td><td>398</td></tr><tr><td>n1 ejecta 14</td><td>493</td><td>402</td><td>314</td><td>392</td><td>16874</td><td>131</td><td>394</td><td>425</td><td>371</td><td>409</td><td>162</td><td>438</td><td>421</td><td>328</td><td>387</td><td>423</td><td>362</td></tr><tr><td>n1 ejecta 15</td><td>523</td><td>433</td><td>319</td><td>398</td><td>17331</td><td>150</td><td>437</td><td>380</td><td>375</td><td>429</td><td>177</td><td>455</td><td>435</td><td>341</td><td>446</td><td>470</td><td>386</td></tr><tr><td>n1 ejecta 16</td><td>516</td><td>419</td><td>274</td><td>393</td><td>17920</td><td>140</td><td>410</td><td>336</td><td>368</td><td>455</td><td>166</td><td>428</td><td>421</td><td>344</td><td>400</td><td>436</td><td>385</td></tr><tr><td>n1 ejecta 17</td><td>555</td><td>466</td><td>274</td><td>313</td><td>41328</td><td>134</td><td>459</td><td>645</td><td>363</td><td>342</td><td>182</td><td>454</td><td>445</td><td>312</td><td>474</td><td>511</td><td>400</td></tr><tr><td>n1 ejecta 18</td><td>479</td><td>363</td><td>295</td><td>258</td><td>55074</td><td>152</td><td>356</td><td>616</td><td>340</td><td>420</td><td>170</td><td>409</td><td>387</td><td>338</td><td>421</td><td>418</td><td>377</td></tr><tr><td>n1 ejecta 19</td><td>518</td><td>443</td><td>333</td><td>356</td><td>19777</td><td>150</td><td>446</td><td>389</td><td>377</td><td>406</td><td>181</td><td>460</td><td>453</td><td>359</td><td>451</td><td>487</td><td>412</td></tr><tr><td>n1 ejecta 20</td><td>542</td><td>458</td><td>338</td><td>386</td><td>19488</td><td>164</td><td>490</td><td>346</td><td>383</td><td>437</td><td>177</td><td>446</td><td>439</td><td>362</td><td>447</td><td>493</td><td>409</td></tr></tbody></table>
<table><caption>Table 5. *Continued.* LA-ICP-MS trace element composition (ppm) of the ejecta and projectile.</caption><thead><tr><th></th><th>Ba</th><th>Ce</th><th>Co</th><th>Cs</th><th>Fe</th><th>Ga</th><th>La</th><th>Mn</th><th>Nb</th><th>Rb</th><th>Sc</th><th>Sr</th><th>Ta</th><th>V</th><th>Y</th><th>Yb</th><th>Zr</th></tr></thead><tbody><tr><td>n1 ejecta 21</td><td>537</td><td>471</td><td>367</td><td>434</td><td>21096</td><td>187</td><td>467</td><td>347</td><td>406</td><td>492</td><td>186</td><td>453</td><td>470</td><td>377</td><td>462</td><td>512</td><td>430</td></tr><tr><td>n1 ejecta 22</td><td>519</td><td>445</td><td>378</td><td>394</td><td>19321</td><td>182</td><td>450</td><td>373</td><td>395</td><td>442</td><td>187</td><td>461</td><td>468</td><td>362</td><td>454</td><td>499</td><td>424</td></tr><tr><td>n1 ejecta 23</td><td>517</td><td>424</td><td>367</td><td>334</td><td>20448</td><td>173</td><td>436</td><td>463</td><td>380</td><td>373</td><td>174</td><td>439</td><td>463</td><td>317</td><td>458</td><td>515</td><td>397</td></tr><tr><td>n1 ejecta 24</td><td>568</td><td>487</td><td>308</td><td>351</td><td>19456</td><td>138</td><td>528</td><td>827</td><td>374</td><td>395</td><td>194</td><td>483</td><td>538</td><td>340</td><td>502</td><td>565</td><td>429</td></tr><tr><td>n1 ejecta 25</td><td>542</td><td>456</td><td>345</td><td>393</td><td>23291</td><td>144</td><td>458</td><td>499</td><td>384</td><td>431</td><td>174</td><td>461</td><td>474</td><td>374</td><td>442</td><td>513</td><td>398</td></tr><tr><td>n1 ejecta 26</td><td>571</td><td>463</td><td>356</td><td>506</td><td>21606</td><td>179</td><td>456</td><td>632</td><td>417</td><td>554</td><td>170</td><td>464</td><td>471</td><td>380</td><td>423</td><td>475</td><td>376</td></tr><tr><td>n1 ejecta 27</td><td>494</td><td>401</td><td>347</td><td>419</td><td>16142</td><td>171</td><td>415</td><td>585</td><td>361</td><td>466</td><td>160</td><td>432</td><td>429</td><td>337</td><td>404</td><td>452</td><td>364</td></tr><tr><td>n1 ejecta 28</td><td>445</td><td>383</td><td>313</td><td>545</td><td>37853</td><td>242</td><td>378</td><td>953</td><td>321</td><td>608</td><td>167</td><td>397</td><td>368</td><td>352</td><td>390</td><td>407</td><td>337</td></tr><tr><td>n1 ejecta 29</td><td>535</td><td>455</td><td>377</td><td>424</td><td>18114</td><td>183</td><td>464</td><td>368</td><td>390</td><td>460</td><td>180</td><td>456</td><td>476</td><td>363</td><td>455</td><td>503</td><td>415</td></tr><tr><td>n1 ejecta 30</td><td>593</td><td>454</td><td>248</td><td>583</td><td>13910</td><td>149</td><td>409</td><td>596</td><td>324</td><td>591</td><td>146</td><td>436</td><td>356</td><td>309</td><td>365</td><td>423</td><td>270</td></tr><tr><td>n1 ejecta 31</td><td>582</td><td>374</td><td>225</td><td>1828</td><td>18892</td><td>339</td><td>395</td><td>1166</td><td>303</td><td>2067</td><td>154</td><td>402</td><td>398</td><td>410</td><td>356</td><td>422</td><td>339</td></tr><tr><td>n1 ejecta 32</td><td>552</td><td>446</td><td>234</td><td>375</td><td>15229</td><td>137</td><td>447</td><td>566</td><td>356</td><td>390</td><td>172</td><td>445</td><td>420</td><td>335</td><td>435</td><td>481</td><td>357</td></tr><tr><td>n1 ejecta 33</td><td>562</td><td>528</td><td>288</td><td>395</td><td>17985</td><td>150</td><td>481</td><td>381</td><td>396</td><td>461</td><td>186</td><td>460</td><td>468</td><td>387</td><td>454</td><td>518</td><td>417</td></tr><tr><td>n1 ejecta 34</td><td>577</td><td>491</td><td>377</td><td>437</td><td>17892</td><td>181</td><td>488</td><td>1406</td><td>415</td><td>466</td><td>187</td><td>484</td><td>495</td><td>364</td><td>468</td><td>532</td><td>409</td></tr><tr><td>n4 ejecta 01</td><td>542</td><td>503</td><td>368</td><td>397</td><td>20714</td><td>164</td><td>470</td><td>439</td><td>396</td><td>417</td><td>179</td><td>461</td><td>496</td><td>366</td><td>482</td><td>507</td><td>425</td></tr><tr><td>n4 ejecta 02</td><td>537</td><td>514</td><td>383</td><td>442</td><td>22854</td><td>186</td><td>452</td><td>420</td><td>395</td><td>470</td><td>171</td><td>459</td><td>468</td><td>368</td><td>449</td><td>491</td><td>409</td></tr><tr><td>n4 ejecta 03</td><td>488</td><td>379</td><td>166</td><td>396</td><td>13365</td><td>113</td><td>361</td><td>816</td><td>157</td><td>414</td><td>142</td><td>412</td><td>199</td><td>164</td><td>394</td><td>403</td><td>212</td></tr><tr><td>n4 ejecta 04</td><td>500</td><td>471</td><td>296</td><td>608</td><td>230913</td><td>267</td><td>430</td><td>2020</td><td>363</td><td>626</td><td>161</td><td>428</td><td>493</td><td>335</td><td>455</td><td>491</td><td>414</td></tr><tr><td>n4 ejecta 05</td><td>763</td><td>660</td><td>440</td><td>477</td><td>26828</td><td>227</td><td>651</td><td>931</td><td>507</td><td>512</td><td>231</td><td>638</td><td>660</td><td>434</td><td>684</td><td>726</td><td>556</td></tr><tr><td>n4 ejecta 06</td><td>616</td><td>535</td><td>366</td><td>407</td><td>26066</td><td>187</td><td>510</td><td>666</td><td>438</td><td>406</td><td>189</td><td>494</td><td>537</td><td>371</td><td>490</td><td>576</td><td>449</td></tr><tr><td>n4 ejecta 07</td><td>580</td><td>460</td><td>379</td><td>461</td><td>34999</td><td>197</td><td>433</td><td>624</td><td>407</td><td>477</td><td>171</td><td>444</td><td>483</td><td>363</td><td>423</td><td>495</td><td>385</td></tr><tr><td>n4 ejecta 08</td><td>545</td><td>501</td><td>299</td><td>428</td><td>89373</td><td>150</td><td>462</td><td>710</td><td>423</td><td>485</td><td>181</td><td>448</td><td>475</td><td>386</td><td>465</td><td>497</td><td>431</td></tr><tr><td>n4 ejecta 09</td><td>518</td><td>471</td><td>384</td><td>469</td><td>24606</td><td>201</td><td>422</td><td>410</td><td>364</td><td>518</td><td>163</td><td>443</td><td>419</td><td>349</td><td>427</td><td>445</td><td>366</td></tr><tr><td>n4 ejecta 10</td><td>479</td><td>416</td><td>326</td><td>484</td><td>35220</td><td>171</td><td>372</td><td>588</td><td>311</td><td>484</td><td>146</td><td>374</td><td>383</td><td>362</td><td>399</td><td>402</td><td>336</td></tr><tr><td>n4 ejecta 11</td><td>534</td><td>472</td><td>386</td><td>436</td><td>17602</td><td>176</td><td>432</td><td>355</td><td>373</td><td>496</td><td>168</td><td>432</td><td>448</td><td>355</td><td>434</td><td>488</td><td>413</td></tr><tr><td>n4 ejecta 12</td><td>520</td><td>486</td><td>294</td><td>354</td><td>332583</td><td>153</td><td>449</td><td>1852</td><td>360</td><td>373</td><td>175</td><td>395</td><td>437</td><td>377</td><td>420</td><td>481</td><td>382</td></tr><tr><td>n4 ejecta 13</td><td>559</td><td>445</td><td>383</td><td>471</td><td>23597</td><td>212</td><td>460</td><td>495</td><td>391</td><td>501</td><td>176</td><td>445</td><td>457</td><td>399</td><td>442</td><td>465</td><td>398</td></tr><tr><td>n4 ejecta 14</td><td>539</td><td>454</td><td>362</td><td>407</td><td>22350</td><td>183</td><td>442</td><td>501</td><td>373</td><td>434</td><td>173</td><td>440</td><td>430</td><td>367</td><td>436</td><td>478</td><td>380</td></tr><tr><td>n4 ejecta 15</td><td>545</td><td>460</td><td>363</td><td>436</td><td>25194</td><td>216</td><td>433</td><td>681</td><td>343</td><td>478</td><td>170</td><td>454</td><td>392</td><td>340</td><td>414</td><td>462</td><td>358</td></tr><tr><td>n4 ejecta 16</td><td>501</td><td>447</td><td>334</td><td>268</td><td>64679</td><td>146</td><td>423</td><td>565</td><td>370</td><td>304</td><td>171</td><td>436</td><td>449</td><td>319</td><td>477</td><td>468</td><td>398</td></tr><tr><td>n4 ejecta 17</td><td>580</td><td>529</td><td>367</td><td>393</td><td>57040</td><td>196</td><td>483</td><td>502</td><td>425</td><td>435</td><td>182</td><td>510</td><td>508</td><td>337</td><td>499</td><td>564</td><td>460</td></tr><tr><td>n4 ejecta 18</td><td>544</td><td>470</td><td>364</td><td>457</td><td>42276</td><td>181</td><td>451</td><td>632</td><td>370</td><td>471</td><td>176</td><td>419</td><td>466</td><td>364</td><td>435</td><td>495</td><td>399</td></tr><tr><td>n4 ejecta 19</td><td>552</td><td>467</td><td>396</td><td>438</td><td>19224</td><td>170</td><td>456</td><td>378</td><td>395</td><td>469</td><td>178</td><td>449</td><td>455</td><td>374</td><td>442</td><td>503</td><td>415</td></tr><tr><td>n4 ejecta 20</td><td>546</td><td>438</td><td>358</td><td>380</td><td>35420</td><td>166</td><td>431</td><td>599</td><td>339</td><td>374</td><td>165</td><td>424</td><td>436</td><td>350</td><td>403</td><td>481</td><td>345</td></tr><tr><td>n4 ejecta 21</td><td>547</td><td>422</td><td>262</td><td>431</td><td>47152</td><td>168</td><td>405</td><td>1081</td><td>261</td><td>434</td><td>150</td><td>453</td><td>308</td><td>243</td><td>419</td><td>466</td><td>288</td></tr><tr><td>n4 ejecta 22</td><td>506</td><td>427</td><td>399</td><td>446</td><td>33217</td><td>206</td><td>440</td><td>526</td><td>360</td><td>499</td><td>170</td><td>427</td><td>423</td><td>362</td><td>418</td><td>454</td><td>369</td></tr><tr><td>n4 ejecta 23</td><td>481</td><td>326</td><td>236</td><td>527</td><td>15958</td><td>183</td><td>328</td><td>1157</td><td>198</td><td>560</td><td>123</td><td>383</td><td>239</td><td>220</td><td>331</td><td>387</td><td>210</td></tr><tr><td>n4 ejecta 24</td><td>111</td><td>116</td><td>102</td><td>94</td><td>98</td><td>111</td><td>119</td><td>112</td><td>107</td><td>109</td><td>113</td><td>131</td><td>115</td><td>112</td><td>112</td><td>113</td><td>112</td></tr><tr><td>n0 ejecta 01</td><td>569</td><td>483</td><td>484</td><td>423</td><td>88764</td><td>249</td><td>473</td><td>709</td><td>424</td><td>546</td><td>180</td><td>503</td><td>497</td><td>365</td><td>501</td><td>503</td><td>441</td></tr><tr><td>n0 ejecta 02</td><td>592</td><td>491</td><td>537</td><td>869</td><td>76151</td><td>380</td><td>433</td><td>891</td><td>413</td><td>950</td><td>166</td><td>455</td><td>548</td><td>638</td><td>418</td><td>464</td><td>422</td></tr><tr><td>n0 ejecta 03</td><td>524</td><td>490</td><td>439</td><td>305</td><td>19669</td><td>201</td><td>449</td><td>343</td><td>383</td><td>357</td><td>177</td><td>450</td><td>453</td><td>294</td><td>450</td><td>486</td><td>412</td></tr><tr><td>n0 ejecta 04</td><td>536</td><td>491</td><td>432</td><td>327</td><td>19818</td><td>196</td><td>457</td><td>334</td><td>383</td><td>378</td><td>178</td><td>452</td><td>451</td><td>303</td><td>453</td><td>490</td><td>422</td></tr><tr><td>n0 ejecta 05</td><td>530</td><td>462</td><td>443</td><td>260</td><td>20439</td><td>215</td><td>445</td><td>386</td><td>393</td><td>307</td><td>181</td><td>452</td><td>450</td><td>259</td><td>451</td><td>481</td><td>420</td></tr><tr><td>n0 ejecta 06</td><td>516</td><td>462</td><td>423</td><td>368</td><td>22991</td><td>189</td><td>438</td><td>352</td><td>387</td><td>443</td><td>174</td><td>436</td><td>449</td><td>347</td><td>444</td><td>494</td><td>410</td></tr><tr><td>n0 ejecta 07</td><td>520</td><td>436</td><td>405</td><td>363</td><td>20590</td><td>185</td><td>440</td><td>367</td><td>371</td><td>415</td><td>176</td><td>436</td><td>421</td><td>340</td><td>452</td><td>462</td><td>388</td></tr><tr><td>n0 ejecta 08</td><td>539</td><td>493</td><td>423</td><td>422</td><td>24611</td><td>214</td><td>455</td><td>402</td><td>409</td><td>507</td><td>190</td><td>471</td><td>467</td><td>364</td><td>471</td><td>502</td><td>435</td></tr><tr><td>n0 ejecta 09</td><td>525</td><td>465</td><td>422</td><td>325</td><td>22626</td><td>192</td><td>451</td><td>332</td><td>383</td><td>371</td><td>183</td><td>449</td><td>451</td><td>318</td><td>453</td><td>501</td><td>425</td></tr><tr><td>n0 ejecta 10</td><td>545</td><td>450</td><td>407</td><td>304</td><td>21456</td><td>174</td><td>431</td><td>327</td><td>384</td><td>371</td><td>179</td><td>443</td><td>435</td><td>297</td><td>443</td><td>482</td><td>420</td></tr><tr><td>n0 ejecta 11</td><td>533</td><td>466</td><td>365</td><td>247</td><td>36669</td><td>153</td><td>457</td><td>435</td><td>385</td><td>276</td><td>176</td><td>433</td><td>470</td><td>258</td><td>450</td><td>494</td><td>403</td></tr><tr><td>n0 ejecta 12</td><td>535</td><td>477</td><td>391</td><td>315</td><td>40235</td><td>172</td><td>456</td><td>387</td><td>388</td><td>354</td><td>181</td><td>447</td><td>462</td><td>321</td><td>456</td><td>511</td><td>423</td></tr><tr><td>n0 ejecta 13</td><td>534</td><td>461</td><td>393</td><td>281</td><td>32408</td><td>176</td><td>445</td><td>369</td><td>373</td><td>321</td><td>180</td><td>443</td><td>442</td><td>288</td><td>451</td><td>493</td><td>415</td></tr><tr><td>n0 ejecta 14</td><td>531</td><td>447</td><td>323</td><td>232</td><td>37510</td><td>131</td><td>458</td><td>377</td><td>369</td><td>262</td><td>187</td><td>446</td><td>446</td><td>226</td><td>439</td><td>494</td><td>412</td></tr><tr><td>n0 ejecta 15</td><td>518</td><td>435</td><td>393</td><td>365</td><td>25335</td><td>184</td><td>427</td><td>335</td><td>374</td><td>417</td><td>173</td><td>435</td><td>418</td><td>345</td><td>427</td><td>460</td><td>394</td></tr><tr><td>n0 ejecta 16</td><td>530</td><td>465</td><td>433</td><td>379</td><td>49360</td><td>206</td><td>453</td><td>384</td><td>400</td><td>470</td><td>182</td><td>471</td><td>481</td><td>355</td><td>454</td><td>493</td><td>429</td></tr></tbody></table>
<table><caption>Table 5. *Continued*. LA-ICP-MS trace element composition (ppm) of the ejecta and projectile.</caption><thead><tr><th></th><th>Ba</th><th>Ce</th><th>Co</th><th>Cs</th><th>Fe</th><th>Ga</th><th>La</th><th>Mn</th><th>Nb</th><th>Rb</th><th>Sc</th><th>Sr</th><th>Ta</th><th>V</th><th>Y</th><th>Yb</th><th>Zr</th></tr></thead><tbody><tr><td>n0 ejecta 17</td><td>532</td><td>462</td><td>416</td><td>375</td><td>18660</td><td>194</td><td>461</td><td>332</td><td>393</td><td>462</td><td>178</td><td>472</td><td>456</td><td>338</td><td>450</td><td>504</td><td>423</td></tr><tr><td>n0 ejecta 18</td><td>502</td><td>452</td><td>413</td><td>365</td><td>21110</td><td>189</td><td>444</td><td>365</td><td>384</td><td>443</td><td>169</td><td>463</td><td>466</td><td>323</td><td>455</td><td>484</td><td>414</td></tr><tr><td>n0 ejecta 19</td><td>508</td><td>441</td><td>396</td><td>357</td><td>21311</td><td>214</td><td>428</td><td>428</td><td>375</td><td>448</td><td>167</td><td>450</td><td>479</td><td>318</td><td>432</td><td>482</td><td>392</td></tr><tr><td>n0 ejecta 20</td><td>543</td><td>466</td><td>377</td><td>291</td><td>29140</td><td>178</td><td>433</td><td>350</td><td>383</td><td>330</td><td>171</td><td>440</td><td>439</td><td>277</td><td>444</td><td>484</td><td>410</td></tr><tr><td>Projectile 1</td><td>510</td><td>447</td><td>431</td><td>383</td><td>30452</td><td>205</td><td>446</td><td>342</td><td>381</td><td>476</td><td>164</td><td>453</td><td>435</td><td>341</td><td>429</td><td>485</td><td>402</td></tr><tr><td>Projectile 2</td><td>538</td><td>434</td><td>449</td><td>390</td><td>32849</td><td>221</td><td>425</td><td>340</td><td>383</td><td>478</td><td>172</td><td>452</td><td>453</td><td>355</td><td>438</td><td>497</td><td>399</td></tr><tr><td>Projectile 3</td><td>533</td><td>461</td><td>463</td><td>394</td><td>39532</td><td>200</td><td>464</td><td>404</td><td>402</td><td>509</td><td>178</td><td>480</td><td>479</td><td>373</td><td>464</td><td>507</td><td>421</td></tr><tr><td>Projectile 4</td><td>501</td><td>449</td><td>410</td><td>381</td><td>39112</td><td>187</td><td>427</td><td>488</td><td>380</td><td>408</td><td>167</td><td>420</td><td>459</td><td>339</td><td>419</td><td>465</td><td>381</td></tr><tr><td>Projectile 5</td><td>518</td><td>454</td><td>419</td><td>422</td><td>37710</td><td>201</td><td>440</td><td>459</td><td>371</td><td>457</td><td>168</td><td>444</td><td>446</td><td>354</td><td>423</td><td>469</td><td>389</td></tr><tr><td>Projectile 6</td><td>536</td><td>481</td><td>419</td><td>432</td><td>24611</td><td>200</td><td>443</td><td>432</td><td>371</td><td>479</td><td>176</td><td>447</td><td>452</td><td>356</td><td>445</td><td>487</td><td>397</td></tr><tr><td>Projectile 7</td><td>508</td><td>427</td><td>407</td><td>445</td><td>25667</td><td>224</td><td>399</td><td>717</td><td>348</td><td>488</td><td>160</td><td>439</td><td>409</td><td>375</td><td>412</td><td>448</td><td>379</td></tr><tr><td>Projectile 8</td><td>546</td><td>475</td><td>431</td><td>307</td><td>29786</td><td>187</td><td>465</td><td>353</td><td>392</td><td>342</td><td>185</td><td>456</td><td>477</td><td>288</td><td>450</td><td>502</td><td>421</td></tr><tr><td>Projectile 9</td><td>535</td><td>474</td><td>439</td><td>324</td><td>30434</td><td>207</td><td>460</td><td>371</td><td>396</td><td>367</td><td>183</td><td>454</td><td>478</td><td>299</td><td>451</td><td>494</td><td>412</td></tr><tr><td>Projectile 10</td><td>522</td><td>464</td><td>429</td><td>236</td><td>36660</td><td>150</td><td>465</td><td>344</td><td>376</td><td>278</td><td>192</td><td>438</td><td>449</td><td>272</td><td>440</td><td>494</td><td>407</td></tr><tr><td>Projectile 11</td><td>526</td><td>449</td><td>354</td><td>209</td><td>36612</td><td>145</td><td>448</td><td>352</td><td>358</td><td>243</td><td>182</td><td>434</td><td>461</td><td>176</td><td>424</td><td>470</td><td>412</td></tr><tr><td>Projectile 12</td><td>518</td><td>434</td><td>415</td><td>383</td><td>27950</td><td>187</td><td>431</td><td>316</td><td>370</td><td>418</td><td>175</td><td>434</td><td>415</td><td>346</td><td>429</td><td>486</td><td>393</td></tr><tr><td>Projectile 13</td><td>549</td><td>460</td><td>411</td><td>258</td><td>50549</td><td>169</td><td>443</td><td>393</td><td>377</td><td>264</td><td>189</td><td>449</td><td>440</td><td>278</td><td>455</td><td>495</td><td>416</td></tr><tr><td>Projectile 14</td><td>532</td><td>432</td><td>391</td><td>290</td><td>27659</td><td>196</td><td>431</td><td>313</td><td>355</td><td>316</td><td>179</td><td>425</td><td>455</td><td>303</td><td>426</td><td>482</td><td>381</td></tr><tr><td>Projectile 15</td><td>504</td><td>426</td><td>376</td><td>289</td><td>34898</td><td>169</td><td>422</td><td>314</td><td>359</td><td>327</td><td>181</td><td>423</td><td>425</td><td>307</td><td>430</td><td>470</td><td>391</td></tr><tr><td>Projectile 16</td><td>579</td><td>449</td><td>468</td><td>307</td><td>54295</td><td>229</td><td>455</td><td>422</td><td>407</td><td>358</td><td>201</td><td>476</td><td>516</td><td>310</td><td>482</td><td>500</td><td>418</td></tr><tr><td>Projectile 17</td><td>541</td><td>454</td><td>418</td><td>331</td><td>32756</td><td>187</td><td>445</td><td>365</td><td>386</td><td>380</td><td>184</td><td>444</td><td>476</td><td>313</td><td>447</td><td>490</td><td>415</td></tr><tr><td>Projectile 18</td><td>525</td><td>448</td><td>405</td><td>263</td><td>25002</td><td>175</td><td>444</td><td>325</td><td>361</td><td>291</td><td>177</td><td>447</td><td>422</td><td>287</td><td>434</td><td>486</td><td>386</td></tr><tr><td>Projectile 19</td><td>522</td><td>454</td><td>429</td><td>370</td><td>23304</td><td>207</td><td>436</td><td>337</td><td>396</td><td>480</td><td>168</td><td>481</td><td>448</td><td>335</td><td>486</td><td>506</td><td>429</td></tr><tr><td>Projectile 20</td><td>515</td><td>431</td><td>322</td><td>234</td><td>56242</td><td>119</td><td>423</td><td>406</td><td>379</td><td>243</td><td>182</td><td>470</td><td>420</td><td>261</td><td>477</td><td>491</td><td>433</td></tr></tbody></table>

measured for 20 points on the surface of a projectile (Table 5).

In addition to the laser ablation analyses, we analyzed the bulk composition of four projectiles to investigate the heterogeneity associated with the formation of this glass (Table 1). Major element oxide concentrations were measured by the CRPG laboratory in Nancy (France), using a Jobin-Yvon JY 70 inductively coupled plasma atomic emission spectrometer. The analytical method is similar to the one described by Govindaraju and Mevelle (1987). Details about analytical procedures and uncertainties are available at http://www.crpg.cnrs-nancy.fr/SARM/index.html. Most trace elements data are represented normalized to the composition of the projectile (mean from four analyses).

## RESULTS

### Description of the Target

All experimental runs resulted in a typical bowl shape crater (Fig. 2a). The diameter of the crater are 6.2, 8.5, 8.0, and 9.8 mm for the experiments n3 (190 J), n1 (444 J), n4 (710 J), and n0 (1899 J), respectively, suggesting a weakly positive correlation between the impact speed or the kinetic energy. Crater bottoms are

partially or totally mantled by a mixture of silicate glass (melted projectile; Figs. 2c and 2d) that represent quenched impact melt and metallic materials in various proportions (e.g., Fig. 2f). We observed numerous concentric fractures at the bottom and on each side of the craters (Figs. 2a and 2d). These cracks are deep and injected by impact melt that was likely emplaced during excavation stage (Fig. 2e).

We prepared a target (n0) sample for observations in the median plan of the crater, orthogonal to the surface of the target in order to monitor modifications at the bottom of the crater as well as crack propagations (Fig. 2). Strikingly, the geometry of fractures is typical of that found in natural impact craters in rocks (e.g., Kumar and Kring 2008), despite the rheology of our target (steel) is that of a ductile material and largely differs from the rheology of classical (brittle) rocks. The silicate glass formed by the quench of the melted projectile that covers the impact crater and injects most fractures (Fig. 2e) contains numerous small iron-rich metal beads (Fig. 2f). This impact melt also contains many spherical vesicles (Fig. 2c) that were not present initially in the projectile. The external edge of the n0 crater is covered by a 10 µm thick iron-silicate amorphous or poorly crystalline oxide layer (Figs. 2g and 2h). This layer has a fayalite to ferrosilite composition (Table 4) and its
location (at the edge below the metal flaps) as well as its layered and continuous aspect make us interpret it as resulting probably from the condensation of the vapor plume after the impact (see discussion). These condensates also coat some places within the crater (Fig. 2h) but they are relatively rare and absent going out of the crater away from the crater rim.

## Description of the Ejecta

The Al witness plates designed to collect the ejecta contain abundant impact pits, relatively abundant craters and ejecta, as well as some scars (Fig. 3). Some of these scars are linear but others have very curved trajectories.

The proportion of silicate ejecta coming from the projectile and iron metal-rich ejecta coming from the target is highly variable depending where the ejecta catcher is located. A few large iron-rich ejecta particles are responsible for the largest craters on the ejecta catcher (Fig. 1c). Roughly, we observed a nearly circular (Fig. 1a) ejecta field resulting from a conical ejecta blast where silicate ejecta were mostly inside the cone and iron ones near the sides of the cone. We cannot observe significant differences in the witness plates of the four experiments. We acquired a large-scale mosaic of X-ray chemical maps acquired on the Al witness plate, sampling the inner part of the impact ejecta field from experiment n4 (Figs. S2–S4 in supporting information). On these maps, using ImageJ, we counted about 40% generally small (1–10 µm) iron-rich ejecta versus 60% generally larger (5–50 µm) silicate ejecta. Like for the impact melt observed on the target, the ejecta contain numerous small iron metal beads (Figs. 3e and 3f).

## Structural Modification of the Target

During the formation of the crater, the steel target was deformed (e.g., folded crater rim). A significant mass was excavated and collected as ejecta and possibly as condensates. The surface of the target was injected and covered with the melted projectile, which changed drastically the bulk composition of the first micrometers of the target surface. Because of the coating, the surface is now composed of silicate impact melt instead of iron metal.

## Major Element Composition of the Ejecta and of the Impact Melt Covering the Crater

Ejecta are very heterogeneous between silicate-rich projectile composition, iron target, and aluminum contamination from the ejecta catchers as three endmembers (Fig. 4).

Low-velocity shots (n3 and n1) produced mainly projectile-dominated ejecta, as they closely follow mixing trends between the projectile and Al witness plate. On the other hand, the high-velocity shots (n4 and especially n0) show mixing between projectile and target composition. Moreover, most are large droplets of solidified silicate liquid that contain various amounts of small iron metal beads (Figs. 3e and 3f). Point analyses (Table 4) have to be interpreted considering this heterogeneity: the point analyses are sampling an equivalent ionization region of about 1 µm³, a volume that can include or exclude metal beads (some of which are not visible because they are below the surface) and a possibly significant contribution from the Al witness plate composition.

Aluminum has a high level of enrichment in some ejecta (up to 54.6 wt% versus ~13.4 wt% in the projectile), as expected when analyzing a thin sample with contribution from the aluminum ejecta catchers. This contribution may be related to the small thickness of the ejecta and is particularly important for the experiments with the lowest impact energies (Figs. 4a and 4b). In the high-velocity experiments (n4 and n0), some ejecta are strongly enriched in iron (up to 32.9 wt% FeOtot in the ejecta versus 4.14 wt% Fe₂O₃tot equivalent to ~3.73 wt% FeOtot in the projectile). We note that some point analyses of ejecta show a very low Fe content, together with a limited contamination from the Al-catcher. Here mixing between the three endmembers (projectile–target–Al-catcher) cannot result in such composition.

The composition of the impact melt covering the crater in experiment n0 is comparable to the composition of the ejecta (Table 4).

Composition of other elements is generally close to the nominal composition of the projectile within a 5% error-bar. It evolves passively following the dilution/concentration associated to the enrichment/depletion in iron and contribution of aluminum from the ejecta catcher (Fig. 4).

## Trace Element Analyses

Trace element analyses of four bulk projectiles show their composition is very homogeneous (Table 1; Fig. 5a) demonstrating that the process involved in the formation of our starting material resulted in glassy beads with identical trace element contents. Contrary to this, the 20 analyses of another bead using LA-ICPMS show a larger spread, especially for volatile elements. The trace element pattern normalized to the mean bulk of the projectile is relatively flat (Fig. 5b), but the absolute compositions are significantly lower than expected. The precise position of the pattern is
<figure><img src="image_5.png" /><figcaption>Fig. 4. Major element composition of the ejecta of the experiments n3, n1, n4, n0 (sorted with increasing energy of impact), and of the projectile. a) Triangular Ca-Fe-Al plot. b) Triangular Si-Fe-Al plot. c) Si versus Al plot. d) Si versus Fe plot. Data are in atom%. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

dependent on the normalization and as mentioned above, here we used the mean Ca content measured with EDX-SEM. This measurement is unfortunately poorly constrained because it is semiquantitative. For the discussion, we will avoid interpretation of absolute composition and will focus on the slope and spread of our analyses. Tracking subtle trends, the projectile analyses display a limited depletion in volatile element resulting in a global negative slope (Zr/Rb generally >1; see Figs. 6a and 6b). This slope is related to a depletion in the volatile element only (Ba to Rb; Fig. 6c) and the refractory element remains unfractionated (Fig. 6).

The chemical composition of the ejecta collected from the experiment n3 (lowest energy) normalized to

the measured composition of the projectile displays a nearly flat pattern (Fig. 5c) when elements are sorted by increasing volatility (Lodders 2003). The spread of the 34 analyses is slightly more important for volatile elements (Co, Ga, Rb, and Cs). The ejecta collected from the experiment n1 display a very similar pattern of trace element composition, an outlier having extreme enrichment in Ga, Rb, and Cs. The 33 other spectra are nearly perfectly flat. n4 also present a population of flat spectra, but the spread of composition is more pronounced here. An unique pattern is especially low and represents an outlying measured composition. Nevertheless, even for this pattern, there is no continuous slope expected for a volatility-controlled
<figure><img src="image_6.png" /><figcaption>Fig. 5. Trace element composition of the projectile and ejecta. a) Bulk composition of four beads of phonolitic glass prepared as projectile determined by ICP-MS. b) LA-ICP-MS analyses of a projectile normalized to the mean bulk composition. c–f) LA-ICP-MS analyses of the ejecta collected on the ejecta catcher in experiment n3, n1, n4, and n0 normalized to the mean bulk composition of the projectiles. The elements are sorted according to volatility (Lodders 2003). (Color figure can be viewed at wile.yonlinelibrary.com.)</figcaption></figure>

fractionation and it is nearly flat except unexplained interelement fractionation (e.g., when comparing Ga and Sc to Rb and Cs). The ejecta from the highest energy experiment (n0) display relatively flat pattern

too, with larger spread of the data as in all other cases. When looking into detail on the trace element pattern of all these patterns (Fig. 6), it appears that the ejecta share similarities with the projectile composition
<figure><img src="image_7.png" /><figcaption>Fig. 6. (a) Zr/Rb versus Zr, (b) Zr/Rb versus Rb, (c) Zr/Rb versus Ba/Rb, and (d) Zr/Sr versus Ba/Rb diagrams comparing the composition of ejecta from experiment n3, n1, n4, n0 with the composition of the projectile. (Color figure can be viewed at wile yonlinelibrary.com.)</figcaption></figure>

analyzed with LA-ICP-MS (Fig. 5b): a generally slightly negative slope mainly supported by a depletion in volatile elements. As these specificities are not observed for bulk analyses (Fig. 5a), they are the result of an analytical technique bias.

To identify fractionation trends independent to the analytical technique, we normalized the mean composition of the ejecta to the mean composition of the projectile measured with LA-ICP-MS. We calculated the error propagation and plotted the 2σ error bars. The results show here that there is no chemical fractionation with volatility whatever the impact energy and speed of the projectile within the ranges of these experiments.

Finally, LA-ICP-MS analyses (Table 5) provide a duplicate of iron content for the population of ejecta that confirms the results from EDX analyses. Again, when compared to the measured composition of the projectile, most ejecta are moderately depleted in iron in all

experiments but a few are found to be highly enriched in experiments performed at the highest impact velocities.

# DISCUSSION

## Time Scale Associated with the Cratering Process

The shock process and the accompanying release to ambient pressure occur on a very short time scale, and there is not enough time for chemical diffusion to produce the observed textures and chemical variations. Under our conditions, pressures are expected between 50 and more than 100 GPa (see tables 4.1 and 4.2 in Melosh 1989) and the shock wave-compression maximum temperature can be roughly estimated at 2500 to more than 3000 K using iron metal Hugenoit curve (Ahrens et al. 1998). Assuming a ductile behavior for the steel target, it is remarkable that this set of
experiments produced impact craters in every aspect similar to natural impact craters on geological (fragile) rock targets showing characteristic cross sections (Fig. 2a) with an impact melt layer glazing a shocked/ compressed and fractured basement (Melosh 1989; French 1998).

The systematic occurrence of vesicles and metal- bleb-bearing impact melts in craters, the collections of metallic- and phonolitic-dominated ejecta on the witness plates, as well as the existence of iron-silicate amorphous or poorly crystalline condensates on the external part of the flap of the crater confirm that melting, degassing, reduction, evaporation, and condensation are some of the physical/chemical processes involved in hypervelocity impacts. A rough estimate of the duration of contact and compression stage is approximately 2L/V, where L is the dimension of the projectile and V is the impact velocity (Melosh 1989). The diameter of the projectile being 2.8, 2.97, 2.77, and 3.8 mm in our experiments, durations of 1.7, 1.2, 0.8, and 1.1 µs for experiments n3, n1, n4, and n0, respectively, can be calculated. Adding a few other µs for the completion of the excavation and the modification stages of impact crater formation gives the order of magnitude of the duration of the impact crater formation together with the time for launching the ejecta and collecting them on the Al witness plates. Such an exceptionally short-lived duration emphasizes the intricacy of the problem to be solved.

## Impact Melt Properties

### *Crater Surface Coating*

During the impact, a significant portion of the melted projectile largely sticks to and covers the inside walls of the impact crater, forming a thin layer of impact melt. A smaller amount is injected into the concentric cracks of the crater and the remaining is ejected as small droplets, some of which being quenched and collected on Al witness plates.

Owing to the cross section cut through the impact crater of the experiment n0 (Fig. 2a), estimates of the different materials produced by hypervelocity impacts are thus possible. For a very conservative averaged thickness of ~10 µm layer of melted projectile covering the crater (Fig. 2f), one can calculate that the 5 mm diameter quasi-hemispheric crater is covered by ~3.1 mm³ of melted projectile. This volume represents close to 10% of that of the projectile (29.6 mm³). The remaining ~90% are either ejected out of the crater together with target material, or injected into the cracks in the metal target at the bottom of the crater, or evaporated/recondensed (Figs. 2g and 2h)—the latter portion being negligible in all cases.

### *Formation of Iron Metal Bead*

The processes involved in the formation of the abundant small iron beads remain unequivocal. At least a part of them were separated from the melted target material and participated in an emulsion with the silicate liquid. Figure 2f clearly shows the incorporation of tiny iron metallic spherules into the impact melt. Examples are described in natural craters where iron metal sphere is also observed disseminated in silicate impact melt (e.g., Meteor Crater and Wabar, respectively, described by Mittlefehldt et al. [2005] and Hamann et al. [2013]). A second hypothesis is that some of these metal beads would result from the reduction of FeO from the phonolitic impact melt into Fe metal. With this process, we expect that after the separation of immiscible iron and silicate melts, the remaining silicate liquid would have lower iron content than the initial phonolitic composition. This assertion is supported by some local iron depletion in both the phonolitic impact melt and the ejecta. Figures 4a and 4b show that most compositions observed in the ejecta are the result of the mixing between three endmembers (projectile-target-aluminum from the ejecta catchers), but many of them display an iron-poor composition that cannot be explained by a simple contamination from the ejecta catcher. Here we propose that part of the iron beads formed by the immiscible separation of iron metal liquid after reduction of FeO from the starting phonolitic material. When analyzing the ejecta using EDX-SEM, in some cases, the “point” analyses sampled the residual silicate melt (without or with few metal beads) with extracted iron explaining low concentration. The ubiquitous occurrence of vesicles in the impact melt further hints that the reduction processes obey to a general reaction of the type:

$$FeO_{(phonolite)} = Fe_{(metal)} + 1/2O_{2(gas)}$$

Even some vesicles might simply reflect boiling of the melt or volatilization of most volatile components in the starting phonolitic material. We propose then that the metal beads formed by the two abovementioned process. As the two origins are expected to form similar composition (nearly pure iron beads) and as the iron beads are very small and cannot be analyzed ruling out the possible contribution of surrounding silicate liquid, we failed to estimate the relative importance of reduction versus separation of melted target material.

Redox reactions are already documented during shock/impact experiments (Rowan and Ahrens 1994; Ebert et al. 2014) and natural impactites (Hamann et al. 2013) and are here confirmed as occurring within the impact time scale. Such process is observed in tektites and other types of impact glasses that are reduced
compared with the precursor target material (Lukanin and Kadik 2007). High temperatures (>2000 °C) reached at a certain stage of decompression are required for the occurrence of reduction reactions involving iron, the complete melting, and partial evaporation of the impact melt. In the present set of experiments, the reduction of shocked glass may be also attributed to the high temperature of the impact process. In the Ellingham diagram, the slope of the plots dΔG/dT is positive for all metals, with ΔG always becoming more negative with lower temperature. Since these reactions are exothermic, they occur at lower temperatures. At high temperature, the sign of ΔG may invert and the oxide can spontaneously reduce to the metal. Then, for a given redox condition, the higher the temperature, the more reducing the conditions.

Other possible concomitant reducers include C and Si from the steel target. When reacting with the projectile, they produce transient reducing conditions in the impact melt in the vicinity of the C/CO at high temperature according to the following reactions:

$$C_{(\text{steel})} + \text{FeO}_{(\text{phonolite})} = \text{Fe}_{(\text{metal})} + \text{CO}_{(\text{gas})}$$

In addition to the possible contribution of the melted target, shock-induced reduction of impact melt, i.e., here at the IW buffer curve or below, should thus be considered a viable mechanism for the formation of metallic phases.

## Chemical Modification of the Impact Melt

The composition of the ejecta normalized to the composition of the projectile (Fig. 7) displays a flat spectrum. In the frame of uncertainty related to this kind of experiment and analytical procedure, we did not observe any chemical fractionation controlled by volatility in the ejecta, whatever the impact energy and speed of the projectile. Contrary to what is observed in Joule melting experiment where volatile elements are strongly fractionated (e.g., Floss et al. 1996), and contrary to what is described in experiments involving high-temperature pulse heating of silicate (Gerasimov et al. 2005) here no clear fractionation trend from volatility is observed (Fig. 7). It is very likely that the instantaneity of the impact limits the evaporation and avoids fractionation from volatility. The duration of the impact plus the relaxation time is very short (order of magnitude is ~1 µs; see calculation above), and not enough to promote significant vaporization through diffusion in the silicate liquid of the impact melt. These few 10⁻⁶ s are for instance three orders of magnitude lower than the few 10⁻³ s experienced in laser pulse experiments where some fractionation is described

(Gerasimov et al. 2005). With diffusivity in the order of 10⁻¹⁰ m² s⁻¹ for most major elements in silicate melts (Eisenhüttenleute and Allibert 1995), the characteristic length for diffusivity (l = √Dt) is about 0.03 µm. The extremely low mobility of elements at such time scale provides, as a first approximation, a satisfactory explanation to the inefficient vaporization and the absence of significant volatility-controlled fractionation.

This result has however to be nuanced. As already mentioned, we observe in addition to the impact melt (n0 experiment), a thin layer of condensates (1–10 µm), especially at the edge of the crater (Fig. 2g) and also in other locations covering the impact melt (Fig. 2h). This feature unambiguously indicates the occurrence of a furtive vapor phase during this impact process. Instantaneous condensates being not representative of the bulk vapor, we have very little information about the vapor phase composition. Our analyses of the amorphous or poorly crystallized condensates indicate high Si, Fe, and O contents and a bulk composition varying from fayalite (Fe₂SiO₄) to ferrosilite (Fe₂Si₂O₆). Such compositions show that the vapor has been at least formed from the major elements at the point of impact, namely Si and O from the phonolitic projectile and Fe from the metallic target. This allows us to set corresponding partial pressures of this vapor phase, PSiO(g), PFe(g), and PO₂(g), the latter being supposedly closed to oxygen fugacity imposed by the IW buffer curve or slightly below (see 5.2). This vapor with a scarce and very thin thickness of the Si-Fe-O-rich amorphous or poorly crystallized condensates is, however, not supposed to weight too much in a mass balance calculation nor in any volatilization processes (Fig. 5). Our result suggests therefore that while a vapor phase was present at least during the n0 (the most energetic) impact experiment, its mass abundance per time unit must be negligible.

## Mixed Ejecta Spray

The whole ejected material includes both the excavated ejecta from the steel target and the ejecta coming from the projectile. Precise quantification of the material excavated from the target from the collected ejecta on the witness plates is so far impossible, since a few large steel ejecta with grazing angles and constituting probably the main mass (see the first images with the very high-speed camera, Fig. 1) have not been collected. Nevertheless, from the diameters of the craters and assuming a hemispheric shape, we estimate that the excavated volume is about 124, 321, 268, and 493 mm³ for experiments n3, n1, n4, and n0, respectively. With the hypothesis that 90% of the volume of the projectile was ejected, the population of ejecta consists of 4–9 vol% ejecta from the phonolitic projectile and 91–96 vol% ejecta from the target. As
<figure><img src="image_8.png" /><figcaption>Fig. 7. Mean trace element composition of ejecta from experiment (a) n3, (b) n1, (c) n4, (d) n0 normalized to the mean composition of the projectile measured with LA-ICP-MS. Error bars are 1σ standard deviation. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

explained, the population of collected ejecta comprises both fragments of metal excavated from the target and silicate pieces of the projectile. The intense cratering of the target as well as the screening and scratching of our ejecta catcher show the complexity of the ejecta trajectories.

The ejecta catchers show both quenched droplets from silicate ejecta from the impact melt, and quenched iron droplets that were formed by the reduction of FeO in the projectile or directly separated from the target. Our current experimental setting prevents us from performing a global description of the distribution of silicate versus metallic ejecta, especially because we can observe only a small portion of the ejecta that is not necessarily representative of the entire blast. Nevertheless, during the blast, these two chemically and physically contrasted types of materials (silicate and metallic droplets) travel together from the target to the ejecta catchers as a dual spray. Mixing occurs between the two types of droplets, resulting in the formation of silicate ejecta including small iron spheres (Fig. 3f).

## Mechanical Mixing of Target and Projectile Material as the Main Source of Chemical Change

As many ejecta contain beads of metal, our analyses show a large scatter for iron (and to a lesser extend manganese) contents. It is noteworthy that the mean composition of the silicate ejecta analyzed with EDX-SEM is sometimes depleted in iron, independently from a simple dilution that could be linked to aluminum contribution by the ejecta catchers. This depletion cannot be explained by uncertainty of EDX measurements (±1 wt%). For instance, ejecta n3-010 and ejecta n3-011 have, respectively, 0.15 and 0.13 ± wt% FeO (versus 4.06 wt% Fe₂O₃ equivalent to ~3.65 wt% FeOₜt in the projectile) and limited contribution of aluminum from the ejecta catcher (25.0 and 25.5 wt% Al₂O₃ versus 13.8 wt% Al₂O₃ in the projectile).

Nevertheless, we interpret the contrasted iron composition of ejecta as the result of a random sampling of iron-depleted silicate ejecta without metal bead (lowest iron contents) or metal bead-rich (highest
iron contents). The inhomogeneity produced by silicate-iron metal melt unmixing shares similarities with the silicate liquid immiscibility common in the evolution of natural impact melts (Hamann et al. 2017). In our experiments, the chemical heterogeneity is shared between EDX-SEM (“point”) analyses and ICP-MS (“bulk” in some case) analyses, illustrating that ejecta are heterogeneous (beads are not uniformly distributed in the ejecta) and of contrasted bulk compositions. This chemical heterogeneity is the result of the mechanical mixing of the melted projectile and the melted target ejecta (explaining high Fe contents) and of unmixing of iron liquid after reduction of FeO in the impact melt (explaining low Fe content in the residual impact melt).

We interpret these contrasted chemical compositions in a magmatic perspective. In the low-velocity experiments (n3 and n1), from the primitive composition of the projectile, the silicate liquid forming the ejecta sometimes lacks a significant portion of FeO that was reduced into the iron metal beads. Contrary to that, for the high-velocity experiments (n4 and n3), the silicate liquid was in some cases highly contaminated by iron metal from the target. Three distinct compositions can hence be produced, i.e., (1) the primitive composition of the projectile (FeO = ~4 wt%), (2) the composition of the silicate liquid depleted from iron after reduction and unmixing of iron melt, and (3) the composition of the silicate liquid doped in Fe from the target. If the redox conditions would allow oxidation of these iron metal beads into FeO and their incorporation into the silicate liquid, this third composition would be abnormally enriched in iron. We computed the temperature at liquidus and crystallization sequences for these compositions using MELTS (Ghiorso and Sack 1995; Asimow and Ghiorso 1998). From the primitive phonolitic composition ($T_{liquidus}$ = 1281 °C, crystallization sequence computed with MELTS = spinel, leucite, olivine...), the composition of some ejecta evolved to iron-rich foidite ($T_{liquidus}$ = 1379 °C, crystallization sequence = leucite, spinel, olivine...) and iron-poor phonolite ($T_{liquidus}$ = 1284 °C, crystallization sequence = spinel, olivine, leucite). We show here that the major element heterogeneity results in a large temperature range for liquidus (1281 °C to 1379 °C) and different crystallization sequences. If not quenched, the droplets of silicated liquid that formed the ejecta would have developed very contrasted mineralogy. Depending on the cooling rate, largely related to its volume, the impact melt can crystallize and form a magmatic rock or be quenched as a glass.

To scale one, our experiments mimic impact cratering of (micro-) meteorites on metallic targets, and in this sense, may resemble processes at work on metallic (M-type) asteroids, like (16) Psyche. We can

expect that the surface of such bodies could be more or less coated by glassy or partially crystallized impact melts from the various impacting (micro-) meteorites, mostly chondritic. This feature could have important implications on the spectral signature of these objects, which may give information on the veneer rather than the main body composition.

However, more numerical and modeling works need to be done to extrapolate this kind of small (laboratory-scale) impacts to larger (beyond laboratory-scale) impact cratering, which would greatly contribute to our better understanding of the formation and evolution of metallic asteroid surfaces. Laser experiments could bridge part of this gap (Ebert et al. 2017). If our results can be extrapolated to larger object such as asteroids, they confirm (after Kelly et al. 1974; Gibbons et al. 1976; Horz et al. 1989; Mittlefehldt et al. 1992, 2005; Evans et al. 1992; Wozniakiewicz et al. 2011; Ebert et al. 2011, 2013, 2014; Hamann et al. 2013, 2016a, 2016b, 2017) that high-speed collisions between two distinct objects result in impact melt and ejecta, which compositions correspond to mixtures between the two colliding objects acting as geochemical endmembers, and having a large variety of liquidus temperature and crystallization sequences (i.e., contrasted mineralogy). The high-velocity experiments presented here provide evidence that the mechanical mixing of colliding objects depends on the impact energy.

Impact energy and especially impact velocity is primarily governing the amount of vaporization of the projectile and part of the target. In the case of the Moon, impact of micrometeorites at typical velocities >15 km s⁻¹ results in bulk vaporization. It forms a gas phase, induces chemical fractionation, and produces agglutinates (Jolliff et al. 2000; Warren 2008). Limited impact velocities in the laboratory (<7 km s⁻¹) are insufficient to induce significant impact vaporization and measurable chemical fractionation from volatility. Another important conclusion can be drawn from this observation: that ~5 km s⁻¹ impacts of micrometeoroids into the regoliths of Main Belt asteroids likely will not induce chemical fractionation. This in turn suggests that one might readily reconstruct chemical signatures of the impactors from interelement ratios (e.g., Koeberl 1998; Tagle and Hecht 2006; Koeberl et al. 2012; Goderis et al. 2013), which should be preserved in these regoliths (Daly and Schultz 2016, 2018).

## CONCLUSIONS

Melting of phonolitic-like glass projectiles occurred during high-velocity impact experiments on a steel target. The impact melt largely covered the craters and was injected into fractures in the crater bottom. Contrary to what is observed in Joule melting experiments where
volatile elements are fractionated with respect to refractory elements, here no fractionation trend is observed. This result contrasts with what is observed for higher energy impact in laser experiments or in some natural impactite samples. Limited impact velocities in the experiments were insufficient to readily induce impact vaporization, especially involving materials like iron and silicate. The absence of measurable chemical fractionation from volatility might also result from the instantaneity of the impact (a few µs), which prevents efficient bulk diffusion of volatile elements in the melt before quenching. The unique chemical modification here is the various Fe contents of the ejecta. They are the result of two processes, i.e., (1) the mechanical removal and mixing of impact melt from the projectile and from the target—a process highly dependent on the energy of impact—and (2) the in situ high-temperature reduction of the impact melt followed by separation of metallic Fe from the silicate impact melt.

In a planetary science perspective, the possible coating of iron asteroid surfaces by micrometeorites can be critical (if significant) for the spectroscopic studies of these bodies: microimpacts may coat the surface with projectile material, preventing trustable conclusions from spectroscopy on the nature of the body. Finally, shock-induced reduction of impact melt should be considered a viable mechanism for the formation of metallic phases.

*Acknowledgments*—This manuscript benefits from a constructive and detailed review from Christopher Hamann and an anonymous reviewer. The authors thank Olivier Devidal for help in the LA-ICP-MS analyses. We are grateful to S. Hasegawa for technical support related to the experiments using a two-stage light-gas gun at ISAS. Acknowledgment also goes to T. Omura who helped the preparation of the high-speed impact experiments. This research was supported by the Hypervelocity Impact Facility (former facility name: the Space Plasma Laboratory), ISAS, JAXA, Japan. C. G. acknowledges support from PNP-INSU program from the CNRS, and CSI-from the Université de Nice Sophia Antipolis. P. M. and G. L. acknowledge support from the French space agency CNES.

*Editorial Handling*—Dr. Christian Koeberl

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**Fig. S2:** EDX-chemical map of Fe intensities of an Al-ejecta catcher of experiment n0.

**Fig. S3:** EDX-chemical map of Si intensities of an Al-ejecta catcher of experiment n0.

**Fig. S4:** EDX-chemical map of Mg intensities of an Al-ejecta catcher of experiment n0.