# A Petrological and Microstructural Study of Ten Brachinites: A Cumulate Texture?

N. Meunier-Mili, M.-a. Kaczmarek, M. Bystricky

► To cite this version:

N. Meunier-Mili, M.-a. Kaczmarek, M. Bystricky. A Petrological and Microstructural Study of Ten Brachinites: A Cumulate Texture?. Journal of Geophysical Research. Planets, 2024, 129 (4), 10.1029/2023JE007998. [hal-04811935](https://hal.science/hal-04811935v1)

HAL Id: hal-04811935

https://hal.science/hal-04811935v1

Submitted on 29 Nov 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

**Key Points:**

* Petrology and microstructural analyses allow classification of the studied brachinites into two groups suggesting different igneous processes

* The brachinites display cumulate textures with magma flow and variable weak compaction intensities

* Olivine underwent early plastic deformation, and moderate to weak intensities of [010] axes normal to compaction point to relative brachinite locations

**Supporting Information:**

Supporting Information may be found in the online version of this article.

**Correspondence to:**

M.-A. Kaczmarek,
Mary-Alix.Kaczmarek@get.omp.eu

**Citation:**

Meunier-Mili, N., Kaczmarek, M.-A., & Bystricky, M. (2024). A petrological and microstructural study of Ten brachinites: A cumulate texture? *Journal of Geophysical Research: Planets*, 129, e2023JE007998.
https://doi.org/10.1029/2023JE007998

Received 28 JULY 2023

Accepted 21 MAR 2024

© 2024. The Authors.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

<figure><img src="image_3.png" /></figure>

# A Petrological and Microstructural Study of Ten Brachinites: A Cumulate Texture?

N. Meunier-Mili¹, M.-A. Kaczmarek¹ ID, and M. Bystricky² ID

¹Géosciences Environnement Toulouse (GET), CNRS-CNES-IRD-Université de Toulouse III, Observatoire Midi-Pyrénées, Toulouse, France, ²Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS-CNES-Université de Toulouse III, Observatoire Midi-Pyrénées, Toulouse, France

**Abstract** Brachinites are igneous, ultramafic and unrecciated primitive achondrites mainly composed of olivine and pyroxene, with a partial melt residue or cumulate origin that is still debated. This study presents a petrological and microstructural study of 10 brachinite meteorites to identify igneous and deformation processes responsible for their formation. Detailed microstructural analyses were performed using secondary electron microscopy, electron probe microanalysis, and electron backscatter diffraction. The olivine-spinel and two-pyroxene closure temperatures of these brachinites ranged from 814 ± 27 to 909 ± 20°C. Olivine [001] axes coincide with the elongation of olivine grains and the crystallographic preferred orientations (CPO) of clinopyroxene [001] axes, which led us to infer lineation as olivine [001] axes parallel to X for all samples. Olivine CPO displays a strong or medium concentration of [001] axes parallel to X and [010] axes parallel to Z pointing to a B-type fabric. Limited internal deformation of olivine grains and slip systems identified from low-angle boundary misorientation analyses are inconsistent with the CPO and grain misorientation distributions are close to those found in untextured rocks. Olivine B-type fabrics may therefore result not from plastic deformation but rather from rigid crystal rotation or preferential crystal growth during compaction. Olivine subgrain boundary misorientation axes imply limited activation of [001](100) and [100](001) slip systems, which could be due to primary plastic deformation during or after crystal settling. These new results reveal that brachinites developed a cumulate texture and accommodated only weak plastic deformation during early differentiation processes in the parent body.

**Plain Language Summary** Brachinite meteorites, rich in olivine and pyroxene, are classified as ultramafic and unrecciated primitive achondrites. However, the precise way in which they formed is still a subject of debate. This study conducted a thorough petrological and microstructural examination of 10 brachinites using scanning electron microscopy, microprobe, and electron backscatter diffraction. The findings reveal that the closure temperatures of the brachinites are between 814 ± 27 and 909 ± 20°C. Olivine crystal preferred orientations (CPO) indicate a B-type fabric [001](010), characterized by a strong to moderate concentration of [001] axes (slip direction) parallel to the lineation and [010] axes (slip plane) perpendicular to the foliation. Grain misorientation distributions resemble those found in untextured rocks (e.g., undeformed granular peridotite), implying that the B-type fabrics in olivine were a result of rigid crystal rotation or preferential crystal growth during cumulate formation or melt flow alignment and weak compaction. Olivine subgrain boundary misorientation axes suggest limited activation of [001](100) C-type and [100](001) E-type slip systems, which could be the result of compaction and primary plastic deformation during or after crystal settling. These new results indicate that brachinites developed a cumulate texture and accommodated only weak plastic deformation during early differentiation processes in the parent body.

## 1. Introduction

The microstructural and crystallographic study of natural rocks provides a window on the physical processes taking place during their formation and evolution. In particular, crystallographic preferred orientations (CPO) of minerals observed in microstructures are often the result of plastic deformation, and vary depending on deformation geometry and thermomechanical parameters and conditions (e.g., temperature, pressure, stress field, hydration, presence of melt). For instance, olivine CPO in mantle rocks help identify active deformation mechanisms and provide constraints on mantle flow (e.g., Skemer & Hansen, 2016). Similarly, the study of plastic deformation textures in primitive achondrites may help understand asteroidal and planetary early crustal and mantellic processes, since they are considered as either residues of partial melting or cumulates (Mittlefehldt
et al., 1998, 2022). Yet, surprisingly few studies up to now have focused on microstructures in meteorites (Daly et al., 2019; Griffin et al., 2022; Hasegawa et al., 2019; Ruzicka & Hugo, 2018; Tkalcec & Brenker, 2014; Tkalcec et al., 2013). One reason may be that shock-induced deformation often overprints older high-temperature deformation features and may reset the microstructure, erasing evidence of earlier processes (e.g., Langenhorst & Deutsch, 2012; Rubin, 2006; Stöffler et al., 1991).

Geochemistry, petrology and remote sensing studies have shown that olivine-rich differentiated meteorites should be more abundant in the world's meteorite collection, an observation called the Missing Mantle problem (Burbine et al., 1996) or the Great Dunite Shortage (Greenwood et al., 2015; Toplis et al., 2013). Among the primitive achondrite meteorites, the brachinites, a group of olivine-rich meteorites, are mostly unshocked (e.g., Keil, 2014). A study of their textures and microstructures may therefore provide important insight into differentiation and deformation processes in the early stages of the formation of planetary bodies.

The brachinite type-specimen, Brachina, was discovered in South Australia in 1974. Recent accurate dating using $^{53}$Mn-$^{53}$Cr systematics revealed that its formation occurred early in the solar system, about 4563.7 ± 0.9 Ma (Dunlap et al., 2016), making it one of the oldest known rocks. Currently, the world's collection contains 60 brachinites (https://www.lpi.usra.edu/meteor/metbull.php). They likely originated from one or several FeO-rich chondritic parent bodies (Day et al., 2019). However, there is no clear consensus on their formation, and they may represent either partial melt residues (Day et al., 2012; Goodrich et al., 2017) or igneous cumulates (Hasegawa et al., 2019; Mittlefehldt et al., 2003; Warren & Kallmeyn, 1989). The brachinite group includes 3 subgroups: (a) brachinites, (b) brachinite-like achondrites, and (c) ungrouped achondrites related to brachinites, described hereafter.

1. Brachinites are mainly small- to coarse-grained (0.5–2.5 mm) meteorites, wehrlitic in composition, highly dominated by Fe-rich olivine (70%–98%, $Fa_{<30}$), with clinopyroxene (3%–15%, mostly augite) and sometimes plagioclase (0%–10%). Orthopyroxene are found as submillimetric grains (0%–8%) or as micrometric grains (<50 µm) in a symplectic assemblage with FeO-oxides, FeO-hydroxides, and sulfur-rich opaque minerals. Minor minerals are chromite (<2%), Fe-sulfides as troilite (<5%) and Fe-Ni metals as taenite and kamacite (<5%), phosphates (<2%), and pentlandite (<1%). Brachinites are distinguishable from other meteorites by their low levels of $SiO_2$ and high levels of FeO and MgO.

2. Brachinite-like achondrites have similar mineralogical compositions to brachinites (olivine ~ 75–95 % and clinopyroxene ~ 0.5–10 %) and oxygen isotopic values close to brachinites ($δ^{17}O$ = [2.19; 2.99] and $δ^{18}O$ = [4.55; 7.04]; $δ^{17}O$ = [-0.03; 3.10] and $δ^{18}O$ = [2.37; 6.17] respectively) (Greenwood et al., 2012). They contain a higher proportion of orthopyroxene (>10%), and their silicates are more magnesian (olivine $Fa_{<30}$) than those in brachinites (Day et al., 2012).

3. Ungrouped achondrites related to brachinites have strong similarities with brachinites, and no obvious elements to rule them out of the group. They often include meteorites inadvertently classified in other meteorite groups (e.g., MIL 090206 and paired meteorites initially classified as ureilites) that share similar features to brachinites and are now thought to be brachinite-like meteorites (e.g., mineralogy, O isotopes, bulk composition, from Goodrich et al., 2017). They are rich in olivine (>70%), have similar modal compositions, and similar $δ^{17}O$, $δ^{18}O$, and $δ^{17}O$ values.

There are relatively few studies on brachinites compared for instance to ureilites or howardite-eucrite-diogenite (HED) meteorites. Brachinite petrology (Day et al., 2012; Gardner-Vandy et al., 2013; Goodrich et al., 2010, 2017; Irving et al., 2013; Keil, 2014; Mittlefehldt et al., 2003), geochemistry (Goodrich et al., 2010; Keil, 2014), and O isotope studies (Greenwood et al., 2012) have provided some clues regarding their nature and origin, but very few studies have focused on the petrofabrics (e.g., Hasegawa et al., 2019; Mittlefehldt et al., 2003). Brachinites may have formed on a parent body <~100 km radius (Keil, 2014) or 10's to 100's km in diameter (Day et al., 2019). They are thought to be either partial melt residues due to their igneous texture, modal mineral abundances and near-chondritic trace element abundances (Day et al., 2012; Gardner-Vandy et al., 2013; Goodrich et al., 2017; Keil, 2014), or cumulates based on grain morphologies, grain shape and crystal alignment (e.g., ALH 84025, NWA 11756, or MIL 090206; Goodrich et al., 2017; Mittlefehldt et al., 2003) and olivine CPO (e.g., NWA 6112, MIL 090206, MIL 090340, MIL 090405; Gruber et al., 2022; Hasegawa et al., 2019). This could be due to heterogeneity within the parent body (Day et al., 2019), and/or the possibility that brachinites come from several asteroid parent bodies, an interpretation strengthened by Mn/Mg ratios consistent with a classification of brachinites and brachinite-like achondrites along a continuous redox spectrum (Crossley
<caption>**Table 1**</caption>

Step Size Analysis and Modal Abundances (Modal %) of Mineral Phases

<table><thead><tr><th>Group</th><th>Sample</th><th>Shock stage</th><th>Step size (µm)</th><th>Olivine</th><th>Cpx</th><th>Opx</th><th>Opx-opq</th><th>Pl</th><th>Chr</th><th>Tro</th><th>Fe-Ni</th><th>Pho</th></tr></thead><tbody><tr><td rowspan="6">(G1)</td><td>Al H. 010</td><td rowspan="6">S2</td><td>11/2</td><td>68.83</td><td>4.66</td><td>-</td><td>25.79</td><td></td><td>0.73</td><td>&lt;0,1</td><td>-</td><td>-</td></tr><tr><td>Aridal 010-1</td><td>13</td><td>69.38</td><td>0.90</td><td>-</td><td>29.64</td><td>-</td><td>0.08</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Aridal 010-2</td><td>13</td><td>76.58</td><td>2.06</td><td>-</td><td>17.11</td><td>2.72</td><td>1.53</td><td>-</td><td>-</td><td>-</td></tr><tr><td>NWA 12545</td><td>10</td><td>73.26</td><td>3.72</td><td>-</td><td>22.04</td><td>-</td><td>0.96</td><td>-</td><td>-</td><td>0.02</td></tr><tr><td>Reid 013</td><td>10/1</td><td>95.20</td><td>3.14</td><td>-</td><td>&lt;0.1</td><td>0.30</td><td>1.25</td><td>-</td><td>-</td><td>-</td></tr><tr><td>NWA 4882</td><td>20/1</td><td>78.19</td><td>3.97</td><td>-</td><td>&lt;1</td><td>12.89</td><td>0.41</td><td>3.42</td><td>-</td><td>-</td></tr><tr><td rowspan="5">(G2)</td><td>NWA 4929</td><td rowspan="5">S2</td><td>10</td><td>92.24</td><td>5.19</td><td>0.29</td><td>-</td><td>0.13</td><td>0.28</td><td>0.22</td><td>0.25</td><td>0.01</td></tr><tr><td>NWA 7904</td><td>10</td><td>98.36</td><td>-</td><td>0.38</td><td>-</td><td>-</td><td>0.85</td><td>0.25</td><td>-</td><td>0.15</td></tr><tr><td>NWA 10932</td><td>15</td><td>85.00</td><td>2.52</td><td>8.44</td><td>-</td><td>-</td><td>0.35</td><td>0.45</td><td>1.89</td><td>1.36</td></tr><tr><td>NWA 7297</td><td>11</td><td>83.14</td><td>8.39</td><td>-</td><td>-</td><td>-</td><td>1.40</td><td>4.21</td><td>2.70</td><td>-</td></tr><tr><td>RaS 309</td><td>18</td><td>95.02</td><td>3.77</td><td>-</td><td>-</td><td>-</td><td>0.74</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>

Note. Al H. 010 = Al Huwaysah 010; RaS 309 = Ramlat as Sahmah 309; Cpx = clinopyroxene; Opx = orthopyroxene; Opx-opq = orthopyroxene-opaque assemblage; Pl = plagioclase; Chr = chromite; Tro = troilite; Pho = phosphate. Aridal 010-1 and Aridal 010-2 represent two pieces of the meteorite Aridal 010.

et al., 2020). Brachinites cosmic-ray exposure ages suggest several events for their ejection from their parent body (ies) (Beard et al., 2018 and references therein), but to date, there is not enough information to determine whether these are several ejection events on one parent body or isolated events on several parent bodies.

This study presents new petrological observations and petrofabric data on 10 brachinites or brachinite-like meteorites, obtained through optical microscopy, secondary electron microscopy (SEM), electron microprobe analysis (EMPA) and electron backscatter diffraction analysis (EBSD). The aim of this study is to characterize the textures in detail, identify the high temperature deformation processes that were activated in the brachinites' parent body(ies) and discuss the implications for the origin and petrogenesis of brachinites.

## 2. Materials and Methods

### 2.1. Sample Preparation and Preliminary Observations

Nine brachinites and one ungrouped achondrite related to brachinite (Al Huwaysah 010) were analyzed by optical and electron microscopy (Table 1) at Géosciences Environnement Toulouse. Four samples are polished thin sections and seven are rock chips mounted in epoxy (including two pieces of brachinite Aridal 010). Samples were first observed with an optical microscope and in a SEM JEOL JSM6360JLV with an accelerating voltage of 20 kV, 1 nA beam current and a working distance of 15 mm. The search for shock features was carried out using both optical and electron microscopy mainly in olivine and to a lesser extent in pyroxenes and plagioclase depending on modal abundances (Table 1).

### 2.2. Electron Backscattered Diffraction

After mechanical polishing, the sample surfaces were polished for an additional 1 hr 15 min in a colloidal silicate suspension using the vibratory polisher VibroMet2 (Buehler) and were then carbon coated (thickness of 15 nm). EBSD data were obtained using a SEM JEOL JSM-7100F TTLS LV equipped with a HKL Advanced Nordlys camera and the Aztec software from Oxford Instruments at the Center de Microcaractérisation Raimond Castaing (Université Paul Sabatier, Toulouse, France). Analyses were performed under an accelerating voltage of 20 kV, 7 nA beam current, a working distance of 15 mm, and a tilting of the sample of 70°. Identified phases were olivine, augite, enstatite, low-albite, whitlockite, troilite, chromite, kamacite, and taenite. Maps were acquired with step sizes varying from 2 to 20 µm depending on the grain size, and three detailed maps were acquired with either a 1 or 2 µm step size (Table 1).

EBSD data were reduced using the open source MTEX Matlab® toolbox (Bachmann et al., 2010; Hielscher & Schaeben, 2008). The first steps performed using MTEX were noise reduction and data set refining. It consists of removing wild-spikes (isolated misindexed pixels) and small isolated clusters of pixels (size varying between a
few pixels for accessory phases and up to 10 pixels for olivine) and defining them as non-indexed pixels. Then, part of non-indexed pixels are replaced (i.e., grain reconstruction) with neighbor grain orientations (typically, at least 6 indexed neighbors are required to make a good average measurement in noise reduction). Grain boundaries are considered to create new grains and a limit is established for boundary misorientations greater than 10°. In addition, the data set was smoothed to avoid “staircase effects” and to remove small remaining artifacts. Smoothing consists of not limiting the grain boundaries to the edges of pixels, which consistently reduces grain boundary lengths, resulting in more realistic measurements. Phase, inverse pole figure (IPF), misorientation, and grain size maps were constructed from data acquired for each sample. Grain shape and grain size parameters were extracted from the EBSD data. Mean grain sizes were calculated as the average of the diameters of the circles of equivalent area for each grain. Some accessory phases (particularly Fe-Ni metals, troilite and phosphates, sometimes chromite) were difficult to index with EBSD (due to weathering and/or grain size), and were mainly visible on energy dispersive spectrometry (EDS) maps. Therefore, the modal compositions for each sample were determined by combining phase maps and EDS maps using the software Image J and MTEX data.

2.2.1. Crystallographic Preferred Orientations and Sample Orientations

CPO of minerals such as olivine or pyroxene typically develop during magmatic and/or plastic deformation processes. Based on the crystal symmetry, the crystal orientation at each measurement point is automatically determined through EBSD analysis. CPO of a mineral in a microstructure are often represented as pole figures showing the orientations of the three major axes of the crystals (e.g., [100], [010], and [001] for olivine). Following the distribution pattern of these axes, it is possible to identify the processes responsible for its development, and in particular whether or not it is the result of plastic deformation. In the case of olivine, the main focus of this study, six major CPO patterns may develop by plastic deformation and the activation of different slip systems (Figure S1 in Supporting Information S1). For example, plastic deformation by dominant glide of dislocations in the [001] direction on the (010) plane results in a B-type [001](010) fabric. CPO is presented as one point per grain and is accompanied with the number of indexed grains (n). Contouring has been applied only to pole figures representing more than 120 grains (i.e., orientation density function). Contour lines correspond to multiples of uniform distribution (mud) and give quantitative information about orientations with similar densities. The J-index and M-index of contoured CPO is based on the orientation density function and the distribution of uncorrelated misorientation angles, respectively, and quantify its fabric strength (Bunge, 1982; Skemer et al., 2005). The M-index varies between 0 and 1 and the J-index varies between 0 and infinity, with the higher the value, the stronger the fabric.

As there is no real method to determine the primary orientation of meteorite samples, pole figures have been rotated to facilitate their comparison. It has frequently been noted that terrestrial mantle rocks with a similar mineralogy often have their lineation coinciding with pyroxene [001] axes parallel to olivine [100] or [001] (e.g., Kaczmarek et al., 2016). Here, olivine [001] and clinopyroxene [001] point maxima from meteorites Al Huwaysah 010, NWA 4929 and RaS 309 are parallel, suggesting that they represent the lineation. Hence, all CPO were rotated in order to orient [001] point maxima of olivine in the X direction (a supposed lineation) within the induced foliation plane (XY), with olivine [010] point maxima normal to the foliation, as is common in mantellic rocks (e.g., Tommasi et al., 2000).

2.2.2. Internal Deformation

Plastic deformation gives rise to a dispersion of crystallographic orientations within individual grains, sometimes
leading to the formation of low-angle boundaries. This dispersion, also called local misorientation, can be
interpreted as resulting from the accommodation of deformation through activation of one or several slip systems
and is an expression of the internal deformation. Hereafter, internal deformation is shown in Grain Reference
Orientation Deviation (GROD) maps displaying the difference in orientation between each indexed pixel of a
grain and the mean orientation of the grain. GROD maps were favored over Kernel Average Misorientation maps
(KAM, where the reference orientation is set as the average orientation of all neighboring pixels of the pixel being
analyzed) because they better highlight grain boundary sliding offsets and low-angle boundaries when internal
deformation is small. Although using mean grain orientation as a reference often leads to misorientation values
higher than 10° from one side of a grain to the other, the color mapping was set from 0° (blue) to 10° (red) to
highlight misorientations in grains with small amounts of internal deformation. Identification of the main slip
systems has been done by characterizing subgrain boundary misorientation axes (de Kloe, 2001; de Kloe et al., 2002; Ruzicka & Hugo, 2018).

Crystal Rotation Axis (CRA) plots represent the direction of rotational axes, also called misorientation axes, at grain boundaries or subgrain boundaries in crystal coordinates. Misorientation at grain boundaries allows the identification of processes such as grain sedimentation or accumulation, whereas main slip systems are inferred from misorientations at subgrain boundaries (de Kloe, 2001; de Kloe et al., 2002; Ruzicka & Hugo, 2018).

## 2.3. EMPA—Major Element Chemistry and Thermometry

Chemical analysis was conducted through wavelength-dispersive X-ray spectroscopy in the EMPA Cameca SXFive at the Center de Microcaractérisation Raimond Castaing (Université Paul Sabatier, Toulouse, France). The EMPA was calibrated with a 20 nA beam current and a 15 keV accelerating voltage. Surface analysis is 2 µm². Standards used for calibration are given in Table S1 in Supporting Information S1. Detection limits were <0.03 wt. % for TiO₂, <0.05 wt. % for Al₂O₃, SiO₂, MgO, and Cr₂O₃, and <0.1 wt. % for Na₂O, K₂O, CaO, MnO, FeO, and NiO. Major elemental analyses enabled the determination of chemical compositions of mineralogical phases and the calculation of equilibrium temperatures through various thermometers. Thermometers used were the olivine-chromite mineral thermometers from Wlotzka (2005) and Ballhaus et al. (1991), and the Ol-Ca exchange and two-pyroxene mineral thermometers from Köhler and Brey (1990) and Brey and Köhler (1990), respectively.

# 3. Results

## 3.1. Petrography

Shock features in these brachinites are the products of weak shock deformation consisting of few planar fractures and undulatory extinctions, mostly in olivine (Figure S2 in Supporting Information S1). Such features correspond to shock stages S2 or S3 (i.e., very weakly to weakly shocked) as suggested by the scheme of Stöffler et al. (1991). In addition, undulatory extinctions occur more frequently than planar fractures, suggesting that the shock stage in these brachinites is essentially S2. The absence of mosaicism and planar deformation features supports this hypothesis, as these features are high intensity shock markers corresponding to stages S4 and S5. Consequently, the microstructural study of these 10 samples was carried out under the assumption that the effects of shock on the microstructures were minor.

Based on petrographic observations and modal compositions of minerals a sorting in two groups is proposed in this study: (a) Group 1 (G1): brachinites rich in an assemblage of secondary micrometric orthopyroxene (Opx), Fe-oxides/Fe-hydroxides Fe-Ni metal and troilite (5 meteorites); (b) Group 2 (G2): brachinites with more than 80% volume (vol%) of olivine, free of assemblage and with presumed primary orthopyroxene crystals (5 meteorites) (Figures 1 and 2).

### 3.1.1. Group 1: Brachinites With Micrometric Orthopyroxene + Fe-Oxides/Fe-Ni Metal/Troilite Assemblage

Five of the studied meteorites (Al Huwaysah 010, Aridal 010, NWA 12545, Reid 013, and NWA 4882) present an assemblage of orthopyroxene, sulfides and metal specific to some brachinites (Goodrich et al., 2010, 2017; Rumble et al., 2008). They have a protogranular texture dominated by olivine (69–95 vol%, Figure 1a, Table 1), with a mean grain size ranging from 130 to 200 µm. The aspect ratios of olivine grains primarily fall within the range of 1–3 but occasionally reach values of 7–9. Aridal 010 shows some elongated and oriented olivine grains, as in NWA 7297 (described in the second group below) and in MIL 090206, 090340, and 090405 meteorites associated with brachinites (Goodrich et al., 2017; Hasegawa et al., 2019). The characteristic assemblage present in these meteorites is formed by micrometric grains of orthopyroxene (up to ~50 µm) intergrown with either Fe-oxide/Fe-hydroxide, Fe-Ni metal, troilite, or the three together (Figure 1d). The proportion of this assemblage varies in the four samples, from a large volume in Al Huwaysah 010 (>25 vol%, Figure 1b), Aridal 010 and NWA 12545 to very low amounts in Reid 013 and NWA 4882 (only observed at higher resolution ~1 µm) (Table 1). The assemblage fills olivine grain boundaries and cracks and is sometimes present within olivine grains but never within other phases (Figure 1). The assemblage in Al Huwaysah 010 is often accompanied by acicular Fe-oxide/Fe-hydroxide grains that are sometimes clustered (Figures 1b–1d),
<figure><img src="image_4.png" /><figcaption>**Figure 1.** (a) Phase map of Al Huwaysah 010 (step size analysis: 11 µm) from Group 1. Ol = olivine; Cpx = clinopyroxene; Opx = orthopyroxene; Pl = plagioclase; Chr = chromite; Opq = opaque. Opaque minerals are either Fe-oxides/Fe-hydroxides or misindexed Fe-Ni metal minerals (i.e., kamacite or taenite). (b) Zoom of top right corner area in (a) outlined by a white box (step size analysis: 2 µm). (c) Same area as in (b) shown as inverse pole figure—X map. Both olivine and orthopyroxene grain orientations are represented using a color key according to inverse pole figures of assumed stretching direction. (d) Backscattered electron image of area outlined by a white box in (a).</figcaption></figure>

which are suggested to be pseudomorphs resulting from the terrestrial weathering of metal and/or sulfides (Goodrich et al., 2017). At a higher resolution, accessory phases such as phosphate or chromite can be seen as mixed with the assemblage (as in NWA 12545, see also Goodrich et al., 2017; Singerling et al., 2013). These samples also contain plagioclase (up to 13 vol%), clinopyroxene (<5 vol%) and minor chromite (<1.5 vol%) (Table 1). Plagioclase occurs as millimetric oikocrysts in samples Al Huwaysah 010 and Aridal 010, with included round and small olivine grains (chadacrysts). In NWA 4882, plagioclase is distributed as small grains (mean ≈ 100 µm, up to 500 µm) and as an enriched lens enclosing millimetric and sub-millimetric automorphic grains (Figure S3 in Supporting Information S1). In addition, only a few small xenomorphic plagioclase grains (mean < 100 µm) are found in Reid 013 in an area where olivine grains are smaller (~50 µm) than in the rest of the sample (Figure S4 in Supporting Information S1). Accessory minerals are troilite (as traces or micrometric grains, <3.5 vol%) and phosphate (<1 vol%).
<figure><img src="image_5.png" /><figcaption>**Figure 2.** Maps of samples from Group 2. (a) Phase map of NWA 7297. Cpx = clinopyroxene; Opx = orthopyroxene; Chr = chromite; Tro = troilite; Pho = phosphate; Opq = opaque. (b) Same area as in (a) shown as grain size map, with grain size increasing from blue to red. Bold-contoured grains are those bigger than 450 µm (half the size of the biggest grain). Long axis orientations are represented as black straight lines. (c) Phase map of NWA 10932. (d) Phase map of RaS 309. The white ellipse highlights a layer of aligned and slightly elongated clinopyroxene grains.</figcaption></figure>

### 3.1.2. Group 2: Brachinites Free of Orthopyroxene Assemblage

The second group is constituted by samples NWA 4929, NWA 7297, NWA 7904, NWA 10932 and RaS 309. This group is defined by a high olivine content (83–98 vol%, Figures 2a, 2c, and 2d), the lack of orthopyroxene
<figure><img src="image_6.png" /><figcaption>**Figure 3.** Equilibrium temperatures in brachinites and associated meteorites separated according to our mineralogical G1 and G2. Circles correspond to Ol-Sp thermometers, triangles to Ol-Cpx thermometers, and squares to 2-px thermometers. Our measurements are represented in red solid symbols. Each color corresponds to a thermometer (see legend). Literature data are in open symbols, from Crossley et al. (2020), Day et al. (2015), Gardner-Vandy et al. (2013), Goodrich et al. (2006, 2010, 2017), Hasegawa et al. (2019), and Petaev et al. (1994).</figcaption></figure>

assemblage (contrary to brachinites in Group 1), orthopyroxene grains that are sometimes large (up to 8.5 vol%) and/or clinopyroxene (up to 8.5 vol%) (Table 1). The samples show a protogranular texture where the olivine mean grain size varies between 200 and 300 µm (e.g., Figure 2b, with a high proportion of green colored grains) with only a few grains exceeding 1 mm. Olivine grains have aspect ratios mostly within the range of 1–3 with maxima around 6–7, except in NWA 7297 and RaS 309 where aspect ratios reach a maximum around 9. Both NWA 7297 and RaS 309 have olivine grains with a slightly shape preferred orientation (SPO) (Figures 2b and 2d). Some olivine grains are sub-euhedral in NWA 10932 (Figure 2c).

NWA 10932 seems enriched in orthopyroxene (8.5 vol%) compared to the four others, but it has been reported that the amount of orthopyroxene can be up to 6.5 vol% in NWA 4929 (The Meteoritical Bulletin, No. 108, 2019), more than 1 vol% in NWA7297 (Crossley et al., 2020), or accessory in RaS 309 (N 101, Meteoritical Bulletin database, September 2012). Pyroxenes have mean grain sizes ranging from 170 to 250 µm. Some clinopyroxenes in RaS 309 are organized in layers with a weak shape preferred orientation (Figure 2d). NWA 4929 also contains small plagioclase grains (size ≈ 100 µm) in low proportions (0.13 vol%), clustered in a small area of the thin section. As in other brachinites, these five samples contain usual accessory minerals such as small amounts of chromite (<1.5 vol%), troilite (up to 4.2 vol% in NWA 7297), Fe-Ni metals (up to 2.7 vol% in NWA 7297), and phosphates (<1.5 vol%) (Table 1). On another note, the euhedral shape of olivine grains in NWA 7904 as well as its CPO (see Section 3.3) and the absence of opx-opaque assemblage differ from the paired meteorite NWA 12545, which led us to assign them to two different petrological groups.

## 3.2. Thermometry

Temperatures have been estimated using the olivine-spinel thermometers from Ballhaus et al. (1991) and Wlotzka (2005), and the olivine-augite Ca-exchange and two-pyroxene thermometers from Köhler and Brey (1990) and Brey and Köhler (1990), respectively. Olivine-spinel equilibrium temperatures were already determined for brachinites NWA 4882, NWA 7297, RaS 309, and Reid 013 in Crossley et al. (2020), hence measurements were done for the other 6 samples (Tables S2 and S3 in Supporting Information S1). The data are presented in Figure 3 along with data from previous work separated into two groups as defined for this study based
on the petrography. The estimated equilibrium temperatures are in the same range as those from previous studies on brachinites, as well as brachinite-like achondrites and associated ungrouped-achondrites (Crossley et al., 2020; Day et al., 2015; Gardner-Vandy et al., 2013; Goodrich et al., 2006, 2010, 2017; Hasegawa et al., 2019; Petaev et al., 1994) (Figure 3; Table S3 in Supporting Information S1).

Calculations using olivine-spinel thermometers ranged from 827 ± 31 to 835 ± 15°C and from 883 ± 15 to 909 ± 20°C using Ballhaus et al. (1991) and Wlotzka (2005), respectively (Figure 3). Globally, these equilibrium temperatures are similar to previous estimates with the same olivine-spinel thermometers (830°C–963°C). By contrast, studies using the thermometer from Sack and Ghiorso (1991) provide values that are significantly higher on average (1056 ± 22°C). Calculations with the olivine-augite Ca-exchange thermometer (Köhler & Brey, 1990) were made at a pressure of 1 kbar, since it is assumed that it is the maximum pressure inside an asteroid with a diameter of 100 km. They are lower than those from olivine-spinel thermometers, ranging from 814 ± 27°C to 843 ± 19°C (Figure 3). The Ol-Cpx thermometer from Köhler and Brey (1990) gives an intermediate value of 930°C for ungrouped achondrites related to brachinites MIL 090206 and MIL 090340 (Goodrich et al., 2017).

Equilibration temperatures using the two-pyroxene thermometer of Brey and Köhler (1990) were calculated only with supposed primary orthopyroxenes, leaving aside the micrometric pyroxene grains in the opx-opaque assemblage present in G1 brachinites. Thus, temperatures from associated primary clinopyroxenes and orthopyroxenes were obtained for samples NWA 4929 and NWA 10932 (excluding NWA 7904 because of its lack of clinopyroxene), yielding values of 868 ± 1°C and 853 ± 15°C, respectively (Figure 3). Two-pyroxene thermometers give lower equilibrium temperatures, comprised between 820 ± 20°C (Divnoe, thermometer from Nakamura et al., 2017) and 1080 ± 50°C (LEW 88763, thermometer from Andersen et al., 1993).

There is no disparity between the two groups either within this study or considering equilibrium temperatures for all brachinites and associated meteorites (Figure 3). However, there are some remarkable fluctuations when taking the brachinite group as a whole. For instance, Brachina is the only meteorite with an equilibrium temperature above 1250°C. This is also true when looking at fluctuations for a single meteorite, such as Hughes 026, which has a two-pyroxene equilibrium temperature with a large uncertainty (893 ± 84°C).

## 3.3. Crystallographic Preferred Orientations of Silicates

### 3.3.1. CPO From Group 1

The five meteorites from this group show olivine [001] axes with distinct concentration points parallel to (X), which are either nicely concentrated (e.g., sample Al Huwaysah 010, J-index = 3.05; M-index = 0.16; mud = 7) or more dispersed to almost random in the XY plane (e.g., sample NWA 12545, J-index = 1.40; M-index = 0.03; mud = 2.5, or NWA 4882, J-index = 1.03; M-index <0.01; mud = 1.5) (Figure 4). [010] axes show concentration points normal to the foliation plane, parallel to (Z), except for NWA 12545 and Reid 013 where there is no clear concentration point but vertical girdles in the (YZ) plane (Figure 4). Pole figures from NWA 4882 show only very weak dispersed concentration points of [010] normal to the foliation plane (XY) without any real distinctive pattern. In all samples, the [100] axes are more scattered. In the case of Al Huwaysah 010 and Aridal 010, they are weakly oriented normal to the lineation. In sample NWA 12545, the [100] axes display a weak point concentration parallel to (Z) (Figure 4). In contrast, [100] axes in Reid 013 and NWA 4882 do not display any specific orientation.

Clinopyroxene CPO shows concentration points of [001] axes sub-parallel to olivine [001] axes (Figure 4). For sample NWA 12545, [001] axes display a girdle sub-parallel to the foliation plane (XY), with a small concentration point parallel to (Y). In samples Al Huwaysah 010 (J-index = 3.14; M-index = 0.05; mud = 3.3) and NWA 12545 (J-index = 3.30; M-index = 0.03; mud = 3.5), clinopyroxenes have concentration points of [010] axes sub-parallel to (Z), and no specific pattern for the [100] axes. Several grains have a very similar orientation in Aridal 010 and Reid 013, and given their texture, they probably are oikocrysts.

Micrometric orthopyroxene CPO displays various orientations. In Al Huwaysah 010, both [100] and [001] axes show girdles within the (YZ) plane similar to [100] axes of olivine (Figure 4). The Al Huwaysah 010 and NWA 4882 [010] axes also have a well-defined concentration point parallel to olivine lineation on [001] axis (Figure 4). Pole figures constructed with data from both Aridal 010 samples and Reid 013 show orthopyroxene [001] axes that are oriented sub-parallel to (X) and olivine [001] axes.
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Pole figures of the crystallographic preferred orientations (CPO) of olivine, clinopyroxene and micrometric orthopyroxene in samples from Group 1. The data are displayed as equal-area stereographic lower hemisphere projections in the assumed reference frame (X: lineation; Z: normal to foliation), for [100], [010], and [001] axes. Data are represented using average Euler angles for each grain (one point per grain), and colored as mean uniform density distributions (mud) for contoured plots. Fabrics are quantified by J-index (Bunge, 1982) and M-index (Skemer et al., 2005).</figcaption></figure>

### 3.3.2. CPO From Group 2

In all samples, olivine [010] axes form strong concentration points parallel to (Z) (i.e., parallel to the pole of the foliation plane) (Figure 5). In addition, in samples NWA 4929, RaS 309, and NWA 10932, the [010] axes also have their concentration points underlined by weak girdles perpendicular to (X) (to a lesser extent in NWA 10932). Olivine [001] axes form either strong concentration points parallel to (X) (e.g., sample NWA 4929) or weaker concentration points parallel to (X) associated with a girdle in the foliation plane (XY) (e.g., sample RaS 309). Olivine [100] axes in NWA 4929, NWA 7297 and RaS 309 display very weak concentration points parallel to (Y). Olivine [100] axes in both NWA 7904 and NWA 10932 samples show weaker scattered distributions without any particular preferred orientation. Fabric strength varies from weak (NWA 10932: J-index = 1.45; M-index = 0.02; mud = 2.20) to moderately strong (NWA 4929: J-index = 2.46; M-index = 0.11; mud = 4.80). Clinopyroxene CPOs are very similar to olivine ones, albeit with a slight shift in orientation (Figure 5). Contouring of clinopyroxene pole figures from NWA 4929 and RaS 309 shows strong concentration points on [010] axes sub-parallel to (Z), and [001] axes subparallel to olivine [001] axes in the inferred lineation direction (X). The fabric on [100] axis is scattered. The numbers of clinopyroxene grains in NWA 7297 and orthopyroxene grains in NWA 10932 are too small to result in a measurable preferential orientation.

## 3.4. Internal Deformation of Olivine

### 3.4.1. Internal Deformation in Group 1

Olivine misorientation maps from the first group show variable amounts of internal deformation, but all display low angle boundaries (NWA 4882 and Reid 013; Figures 6a and 6b respectively). There is less misorientation in
Group 2

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Pole figures of the crystallographic preferred orientations (CPO) of olivine, clinopyroxene and orthopyroxene in samples from Group 2. The data are displayed as equal-area stereographic lower hemisphere projections in the assumed reference frame (X: lineation; Z: normal to foliation), for [100], [010], and [001] axes. Data are represented in the same way as in Figure 4.</figcaption></figure>

Al Huwaysah 010 and NWA 12545 (Figure S5 in Supporting Information S1), but several grains show intense homogeneous internal deformation (e.g., single colored grains). Low angle boundaries in Reid 013 are more common, well distinct and oriented in two directions at 90°. Smaller olivine grains in the fine grain zone in Reid 013 do not seem deformed, but a few bigger grains within that area show clear low angle boundaries. NWA 4882 is the most deformed brachinite in the first group (Figure 6a), with many grains showing intense internal deformation, particularly the longest olivine grain in the thin section. Many olivine grains contain low angle boundaries (misorientations ranging 2–10°) throughout the thin section without any well-defined pattern. Olivine grains in Aridal 010 show more internal deformation (Figure S6 in Supporting Information S1), and contain lower angle boundaries. Low angle boundaries are often oriented normal to the direction of elongation of olivine grains.
<figure><img src="image_9.png" /><figcaption>Figure 6.</figcaption></figure>
### 3.4.2. Internal Deformation in Group 2

All five brachinites from the second group show many low angle boundaries, sometimes with several orientations within one grain (frequently at 90°) (NWA 7297, NWA 4929, NWA 10932, and RaS 309; Figures 6c–6f respectively). However, they can be differentiated by the different amounts of internal deformation. NWA 10932 is less deformed but contains several olivine grains with high misorientations leading to low-angle boundaries. Most olivine grains in NWA 7904 show very low degrees of misorientation, and few grains show low angle boundaries (Figure S7 in Supporting Information S1). On the contrary, NWA 4929 is the brachinite showing the most amount of internal deformation (Figure 6d) with many grains strongly deformed (e.g., single colored grains) and containing numerous subgrain boundaries (misorientations of 2–10°). Low angle boundaries seem to have particular orientations, with a first family oriented northeast-southwest, and a second one at 90° oriented northwest-southeast. Samples NWA 7297 and RaS 309 are optically similar in the way internal deformation is distributed, but olivine grains in RaS 309 have on average more internal deformation (see Section 4.2). Only very few elongated grains show strong misorientations. Many grains display low angle boundaries that seem oriented perpendicularly to their long axis (e.g., in NWA 7297; Figure 2b, 5, 6c), with misorientations mainly smaller than 2°, thus showing fewer subgrain boundaries than what could be expected considering the high number of low angle boundaries. Both NWA 7297 and RaS 309 have olivine grains with low-angle boundaries apparently perpendicular to their elongation.

## 3.5. Misorientation Angles Distribution at Olivine—Olivine Grain Boundaries

The distributions of misorientation angles of olivine grains from G1 and G2 are shown in Figure 7. The random texture (bold black dotted-line) displays a concave profile between 0° and 90°, which is similar to profiles of samples NWA 4882, NWA 12545, Reid 013 from G1, and NWA 7904, NWA 10932 from G2. A second cluster formed by samples Aridal 010 from G1, and NWA 4929, NWA 7297 and RaS 309 from G2 displays convex profiles between 20° and 90° that depart from the untextured one. Indeed, misorientation angles of olivine grains from Al Huwaysah 010, for instance, are different from a random texture, with a higher number of grains between 20° and 60°, a convex profile, and a smaller number of grains between 60° and 90° (Figure 7). The further the profiles are from the untextured one between 20° and 60°, the smaller the peaks are at 90°. All the profiles similarly decreased at misorientation angles between 90° and 120°. There is no obvious discrepancy between Groups 1 and 2.

## 3.6. Crystal Rotation Axis Plot—Misorientation Axes

### 3.6.1. At Grain Boundaries

In Group 1, Al Huwaysah 010 and Aridal 010 samples display a strong concentration of [001] misorientation axes (mud around 3–3.5, Figure 8). There is a weaker secondary misorientation axis concentration for Aridal 010 close to [010]. The CRA patterns for the three other samples from G1 (NWA 4882, NWA 12545, Reid 013) are more scattered with lower mud (maximum at 1.5–2), all showing maxima centered between the three crystallographic axes. All samples from G1 have their misorientation axes minima close to [100].

The CRA patterns from G2 show a maximum for misorientation axes close to [010], with partial or complete girdles ranging between [010] and [001] and very few [100] misorientation axes (i.e., [0kl] misorientation axes, Figure 8). Distributions of [010] misorientation axes are particularly strong in NWA 7297, RaS 309 and NWA 7297 (from the strongest to the weakest, mud = 2.8; 2.2; 1.5). CRA patterns in NWA 7904 and NWA 10932 are more scattered with low maxima (mud <1.5). However, they display similar distributions of misorientation axes located preferentially around [010] and [001] with a lack of [100] misorientation axes.

**Figure 6.** Olivine Grain Reference Orientation Deviation (GROD) maps of five samples representing intracrystalline deformation. G1: (a) NWA 4882, (b) Reid 013; G2: (c) NWA 7297, (d) NWA 4929, (e) NWA 10932 and (f) RaS 309. Accessory phases are in the same colors as in Figures 1 and 2 but more transparent (see legend) to avoid confusion with GROD color mapping. Reference orientation is set as the mean orientation of each grain. White arrows point out deformation bands; Magenta arrows point out low-angle boundaries; Red arrows point out grain areas with high deviation from the reference orientation. The scale (0–10° in misorientation) has been set equal for all samples. Subgrain boundary misorientations are separated depending on their misorientation degree, depicting low (magenta) to intermediate and high (cyan) misorientations.
<figure><img src="image_10.png" /><figcaption>**Figure 7.** Uncorrelated distribution of misorientation angles at olivine—olivine grain boundaries from the 10 samples. The untextured profile (bold black dotted-line) corresponds to a random texture. Samples from Group 1 and Group 2 are plotted in blue and red, respectively.</figcaption></figure>

### 3.6.2. At Subgrain Boundaries

Crystal rotation axes for subgrain boundaries in olivine are somewhat similar in the whole data set, regardless of their attributed group: all the samples are characterized by misorientation axes with a [010] maximum except for Al Huwaysah 010 (Figure 9). NWA 12545, Reid 013, NWA 4882, and RaS 309 have only one concentration point along [010], while Aridal 010, NWA 7904, NWA 10932, and NWA 7297 have lower maxima along [010] and a small concentration point close to [001]. The Al Huwaysah 010 CRA plot shows a similar concentration point close to [010] but a more intense [100] concentration point is visible. NWA 4929 is the only sample with misorientation axes concentrated along [100], [010] as well as [001], but with a maximum close to [010] as in several samples (Figure 9).

## 4. Discussion

### 4.1. Comparison Between Olivine CPO in Brachinites and in Terrestrial or Experimentally Deformed Rocks

Crystallographic preferred orientations of olivine in the brachinite meteorites show clearly defined [001] point maxima parallel to X and either a girdle of [010] axes within the YZ plane (G1, Figures 4 and 10) or a strong [010] cluster parallel to Z (G2, Figures 5 and 10). This pattern is typical of a B-type CPO, a fabric which has been observed under many different conditions and different settings (e.g., Bernard et al., 2019). For instance, similar fabrics have been measured in terrestrial rocks in mantle xenoliths, abyssal peridotites (e.g., ophiolites) and orogenic massifs (e.g., Mizukami et al., 2004; Park & Jung, 2015; Skemer et al., 2006), in terrestrial cumulates (e.g., Boulanger et al., 2021), and more recently in three olivine-rich achondrites related to brachinites (Hasegawa et al., 2019).

In experimental studies, a B-type fabric often develops in olivine aggregates deformed by simple shear at high pressures (~2 GPa) and water contents (e.g., Jung & Karato, 2001), and was interpreted as resulting from simple shear with predominant dislocation glide in the [001] direction on the (010) plane, that is, the [001](010) slip system. Further studies have shown that under dry conditions, a change from dominant slip in the [100] direction (*a* slip) at low pressures to slip in the [001] direction (*c* slip) takes place at very high pressures (Couvy et al., 2004; Raterron et al., 2009) and B-type CPO may be promoted at high pressures (≥3 GPa, Jung et al., 2009). However, other experiments have highlighted that a B-type CPO does not always reflect dominant *c* slip. For instance, a B-type CPO observed in deformed partially molten olivine aggregates under conditions of reduced permeability was explained by dominant *a* slip, diffusion processes and back-rotation of the CPO due to melt segregation and strain
<figure><img src="image_11.png" /><figcaption>**Figure 8.** Grain boundary olivine Crystal Rotation Axes (CRA) plots for Groups 1 and 2. All plots share the same scale with a multiple of uniform distribution from 0 to 3.5 including the CRA associated with an untextured fabric.</figcaption></figure>

partitioning (Holtzman et al., 2003). A B-type CPO also formed during deformation of dry olivine-enstatite aggregates at low pressures due to interface-controlled diffusion creep assisted by rigid grain rotation and grain boundary sliding processes (Sundberg & Cooper, 2008).

However, the CPO does not necessarily reflect the implication of plastic deformation, and can be created in a deformation-free magmatic environment. B-type olivine CPO have been frequently identified, particularly in terrestrial cumulates, and are often associated with compaction processes (e.g., Benn & Allard, 1989; Boulanger et al., 2021; Cao et al., 2017; Henry et al., 2021; Yao et al., 2019). Typically, olivine grains contain little internal plastic deformation and the B-type fabric has often been labeled a “magmatic fabric” (e.g., Benn & Allard, 1989). Olivine crystals in a magmatic system undergo anisotropic growth along the [001] axis, and oriented anisotropic grain growth and rigid crystal rotation may result in [001] axes oriented preferentially in the direction of flow (Wen et al., 2018). During compaction in a crystal mush, a B-type fabric may therefore develop by olivine (010) planes orienting perpendicular to gravity-driven compaction and [001] axes stabilizing in the flow direction, with strain accommodated by limited internal deformation, and diffusion and grain boundary sliding processes (Yao et al., 2019).

## 4.2. Are Olivine CPO in Brachinites the Result of Plastic Deformation?

Plastic deformation in brachinites using dislocation creep processes is minor as demonstrated through GROD maps showing the distribution of the internal deformation in olivine grains (Figure 6). The most deformed sample
<figure><img src="image_12.png" /><figcaption>**Figure 9.** Crystal Rotational Axes (CRA) at olivine subgrain boundaries for Groups 1 and 2. All plots share the same scale, with a multiple of uniform distribution from 0 to 8. The box at the bottom includes the expected misorientation for an untextured fabric as well as the associated slip systems (e.g., A-type or B-type, refer to Figure S1 in Supporting Information S1 for details). Olivine inferred slip-systems in the CRA plots are based on low angle misorientation axes. Colors are coded to combine deformation and temperature: warmer from blue to green, yellow, orange, and red (see legend). Magenta for a + c slip indicates a non-existent relation to temperature. The plot is modified from Ruzicka and Hugo (2018), after de Kloe et al. (2002).</figcaption></figure>

is NWA 4929, where a few grains display strong internal deformation features (up to color code red in Figure 6d). The degree of internal deformation is uncorrelated with the petrology or the mineralogy of the samples (G1 or G2). In most samples, the uncorrelated distribution of misorientation angles at olivine—olivine grain boundaries is similar to the distribution expected for a random texture (Figure 7), which is consistent with a limited amount of internal deformation in olivine and suggests very limited plastic deformation.

If the olivine B-type CPO fabric measured in the brachinites is due to activation of the [001](010) slip system, one would expect the presence of numerous [100] subgrain misorientation axes in olivine grains (de Kloe, 2001; Ruzicka & Hugo, 2018; Skemer & Hansen, 2016). However, a detailed study of olivine subgrain misorientation axis distributions in these samples indicates that misorientation axes are mainly clustered near [010] for both G1 and G2 (Figures 9 and 10). A high concentration near [010] is usually indicative of the activation of E-type [100] (001) and C-type [001](100) slip systems (Figure 10). This is illustrated by sample RaS 309, where a high concentration of [010] misorientation axes (yellow grains, Figures 11a–11c) implies tilt boundaries formed by [100](001) edge dislocations (E-type), [001](100) edge dislocations (C-type), and/or twist boundaries formed by [100](010) and [001](010) screw dislocations (Figures 9–11). In some grains, several slip systems were identified (gray area Figure 11a), and this may cause a bias in the estimation of slip system activity in grain maps compared to counting subgrain boundaries of different types. In the 235 grains studied in sample Ras 309, only five subgrain boundaries were identified as formed by dominant activation of the B-type [001](010) slip system (Figure 11c). Analysis of only subgrain boundaries with high misorientations (mean misorientation ≥5°, Figure 11c) yields the same results as analysis of all subgrain boundaries. Overall, internal deformation features in olivine are limited,
<figure><img src="image_13.png" /><figcaption>**Figure 10.** Petrological and microstructural overview of the brachinites from Groups 1 and 2 of this study. Orientation density is represented from the weakest to the strongest as green, orange and red.</figcaption></figure>

and are not consistent with the observed B-type CPO. They are indicative of activation of [100](001) edge (E-type) or [100](010) and [001](010) screw dislocations (Figures 9–11).

Deformation in the brachinites likely took place under low stress, modest pressure, and low temperature conditions (~750–950°C, Figure 3), probably in the presence of melt, that is, conditions where activation of [100](001) may be expected or even favored (e.g., Bai et al., 1991). The limited internal deformation in olivine and pyroxene in the brachinites probably took place during compaction and primary plastic deformation. The compaction effect is not strong because crystallization of the brachinite cannot take place at large depths in a parent body with a presumed size smaller than 100 km in radius (Keil, 2014).

In all brachinite samples, the deformation processes taking place during formation of the low angle boundaries observed in the microstructures (Figure 6) were likely very minor. This is confirmed by looking at the CPO of grains with more internal deformation. Indeed, grains with a grain orientation spread (average of the misorientation angles to the mean orientation of the grain) greater than 2° (limit established for recrystallized grains, Wright et al., 2011) have CPO that are very similar to the CPO of the overall microstructure (Figure S8 in Supporting Information S1). This observation and the clear dichotomy between the observed CPO and the
<figure><img src="image_14.png" /><figcaption>Figure 11.</figcaption></figure>
misorientation axes data at low-angle boundaries strongly suggest that the olivine CPO is likely the result of magmatic processes rather than plastic deformation.

### 4.3. A Magmatic Gravity-Driven Accumulation Process Responsible for B-Type Olivine in Brachinites?

Poikilitic texture is typical of cumulate rocks and is almost ubiquitous in mafic/ultramafic igneous intrusions (Hunter, 1996; Wager et al., 1960). Evidence of a magmatic texture in brachinite meteorites is the occurrence of poikilitic texture with a few plagioclase oikocrysts in Aridal 010 and Al Huwaysah 010 meteorites (Figure S9 in Supporting Information S1) and a few pyroxene oikocrysts in sample NWA 10932 (Figure 2c). More frequently, brachinite meteorites display equilibrated textures with subhedral olivine grains and frequent 120° triple junctions (e.g., samples NWA 7297, NWA 4882, Reid 013, Figures 2 and 6), similar to what is commonly observed in texturally equilibrated terrestrial cumulate rocks (Cao et al., 2017; Hunter, 1996). In addition to equilibrated textures, a plagioclase-clinopyroxene lens (NWA 4882) and small interstitial plagioclase grains (Reid 013) are present within sub-monomineralic olivine lithologies, suggesting crystallization of magma within this layer (Figures S4 and S5 in Supporting Information S1, respectively).

Different types of cumulate textures are defined in the literature according to their mineralogy and the percentage of crystals relative to their groundmass (i.e., their melt abundance, Hall, 1987; Wager et al., 1960). For instance, orthocumulates require a high abundance of crystals from intercumulus liquid; adcumulates, which usually form when grown crystals have a composition similar to the intercumulus liquid at a constant temperature, result in equilibrated microstructures through grain growth (Wager et al., 1960). If an adcumulate also has poikilitic grains, it is called a heteradcumulate. All studied brachinites are dominated by olivine (Table 1) with homogeneous compositions (Gardner-Vandy et al., 2013; Goodrich et al., 2017; Keil, 2014), indicating that the bulk magma composition remained constant throughout the crystallization process (Wager et al., 1960). They contain only a few poikilitic grains and display an equilibrated texture. All together, these observations indicate that the brachinite texture is coherent with an adcumulate or heteradcumulate formation.

The microstructural analysis presented in the previous section indicates that the B-type CPOs are not due to solid-state plastic deformation but could be the result of magmatic processes. The question is how could magmatic processes lead to the formation of olivine B-type patterns? On the one hand, the concentration of olivine [001] axes (Figures 4 and 5) can be correlated with grain elongation and shape preferred orientation (Figure 2b), which are often linked to the direction of magmatic flow (Skemer & Hansen, 2016) or to anisotropic grain growth (Wen et al., 2018). The olivine grain boundary misorientation axes from Group 1 samples display a concentration on [001] (Figures 8 and 12). Grain boundary misorientation axes close to [001] have been interpreted in olivine aggregates originating from a settling context as resulting from physical aggregation on (001) and (021) planes (Figures 12a, 12c, 12e, and 12f) rather than oriented growth (Wieser et al., 2019). On the other hand, olivine [010] axis alignment parallel to Z as observed in the brachinites occurs ubiquitously in compaction processes during olivine grain accumulation (e.g., Cao et al., 2015, 2017; Yao et al., 2019), coinciding with [010] misorientation axes at grain boundaries and suggesting that (010) planes overlap (Figures 10 and 12d). In G2, the correlation between the orientation of olivine [010] axes and [010] misorientation axes at grain boundaries is also evident, both in terms of distribution and fabric strength (Figures 5, 8, and 10). Yao et al. (2019) have proposed that in a magma chamber, a weak B-type fabric may develop by anisotropic crystal growth during early compaction, and remain during the final stages of fast compaction and crystallization as strain is accommodated by grain boundary sliding (GBS) and diffusion processes. Interestingly, GBS and diffusion processes during deformation and dynamic recrystallization may lead to the formation of neoblasts with inherited orientations (Linckens et al., 2014). Compaction can thus preserve or even enhance a B-type CPO despite the absence of significant strain. During compaction, grain boundary misorientation axes are mainly parallel to [010], where (010) planes from neighboring grains remain

**Figure 11.** Slip system analysis in RaS 309. (a) Map of olivine grain and subgrain boundaries. The black-dotted box corresponds to Figure 6f (internal deformation map). Subgrain boundaries are colored according to the inferred main slip system activated in their formation, and grains are colored according to the most activated slip system taking their total subgrain boundaries into account. (b) Olivine subgrain misorientation axes in the whole thin section, represented as one point per pixel and one point per subgrain boundary. The third plot shows the colors associated with each “misorientation axis—slip system” pair and differentiates subgrain boundaries by their mean degree of misorientation. (c) Bar chart showing the proportion of each slip system inferred to have contributed to the formation of the subgrain boundaries in the whole thin section.
<figure><img src="image_15.png" /><figcaption>**Figure 12.** Schematic diagrams showing contacts between pairs of olivine crystals, adapted from Wieser et al. (2019). Contacts are shown on (001), (010), or (021) planes, with [010] or [001] misorientation axes according to misorientation axes at grain boundaries in brachinites in Figure 8.</figcaption></figure>

in contact and tend to overlay (Figure 12d). In the absence of any other kinetic process, (100) and (001) planes are usually free of any preferential orientation and result in a girdle CPO, as they are oriented normal to the [010] accumulation direction within the foliation/lineation plane.

A correlation between the amount of intracrystalline deformation (GROD maps, Figures 6 and 11a) and CPO fabric strength may also be established, as a sample located deeper will likely be more affected by compaction. Brachinites with strong CPO and high amounts of internal deformation in both groups, such as Al Huwaysah 010 or NWA 4929, probably record primitive plastic deformation and may have formed at greater depths than samples with weaker fabrics and less deformation features, such as Reid 013 or NWA 10932 (Figure 6).

## 4.4. Formation of the Brachinites in Their Asteroidal Parent(s) Body(ies)

The petrological and microstructural study of these brachinites suggests that they were formed by crystal accumulation accompanied by weak compaction and magmatic flow (Figure 10). Moreover, G1 and G2 brachinites may have recorded magmatic processes leading to their formation within different small reservoirs, sills, or dykes.
<figure><img src="image_16.png" /><figcaption>**Figure 13.** Schematic diagram of a petrogenetic model for G1 and G2 brachinites. Color coding of minerals is the same as in phase maps (green: olivine; blue: clinopyroxene; red: orthopyroxene; magenta: plagioclase). Accumulation, compaction and magmatic flow after melt crystallization led to their cumulate texture. G1 brachinites represent a small-scale heterogeneity with the percolation of a sulfide-rich melt as a late stage event. GRA 06128/9 and EET 99402/7 represent potential samples for the felsic crust of brachinites parent body.</figcaption></figure>

In the proposed model, G1 and G2 brachinites originate from two different reservoirs or settings (Figure 13), given the dichotomy between their CPO. The opx-opaque assemblage is interpreted as a late-stage event (e.g., Goodrich et al., 2017; Singerling et al., 2013), and its presence in group G1 suggests that G1 and G2 brachinites represent heterogeneities at a small scale within their parent body that may be correlated with olivine CPO. It is possible that percolation of the sulfide-rich material was heterogeneous as well, resulting in variations in the amount of assemblage within a larger reservoir.

The various fabric strengths and olivine shape preferred orientations (SPO) of brachinites (e.g., NWA 7297 and RaS 309, Figures 2b-2d), a consequence of variations in intensity of magmatic melt flow and compaction (Hasegawa et al., 2019; Nagahara & Ozawa, 1986; Shirley, 1986; Yao et al., 2019), can be used as a proxy to locate the samples within their reservoirs. On the one hand, concentrations of [001] axes in the direction of lineation in brachinites (e.g., Aridal 010 in G1) may be due to melt flow (Hasegawa et al., 2019; Mittlefehldt et al., 2003). On the other hand, (010) poles clustering perpendicular to foliation (Figure 10) is likely the result of accumulation and weak compaction (e.g., Yao et al., 2019). For both processes, the higher the concentration of [010] or [001] axes, the more the sample has been affected by the associated process. Hence, the amount of melt allowing alignment of [001] axes in the flow direction may have been higher in a brachinite with a strong concentration of olivine [001] axes than in one with a weaker [001] concentration. Compaction being highly related to depth, the stronger the [010] axis concentrations are in the CPO (e.g., NWA 7297, Figure 5), the deeper in the magma chamber the brachinites are likely to be (Figures 5 and 13). Al Huwaysah 010 and Aridal 010, located in the G1 reservoir, display the strongest [001] concentrations parallel to lineation, suggesting a high influence of magmatic flow leading to passive rotation of the olivine [001] axes in the flow direction (Figures 4 and 8). They also display a strong concentration of [010] axes, suggesting that both samples have undergone accumulation and compaction but to a lesser extent than magmatic flow (Figure 4). Accumulation in Aridal 010 should have been a bit stronger than in Al Huwaysah 010, considering its olivine [010] fabric strength (Figure 4) and its distribution of [010] misorientation axes at olivine grain boundaries (Figure 8). Overall, taking into account CPO fabric strengths and relative [010] concentrations, and SPO, the distribution from bottom to top in the reservoir of G1 brachinites should be structured as Aridal 010, Al Huwaysah 010, NWA 12545, Reid 013, and NWA 4882. Brachinite NWA 4882 is plagioclase-rich (13 vol%, Table 1), has more scattered olivine CPO and olivine grain rotation axes (Figures 4, 8 and 13), and may therefore have formed closer to the surface. In such a setting, NWA 4882 could represent an intermediary sample between brachinites and GRA 06128/9 and EET 99402/7, which are expected to be the felsic crust of the brachinite parent body according to their petrography and geochemical data (Figure 13, Day et al., 2012). By comparison, MIL brachinites, which have fabrics similar to Aridal 010 but stronger SPO (Day, et al., 2019; Gruber et al., 2022; Hasegawa et al., 2019), may be located below the same reservoir (Figure 13).
In Al Huwaysah 010, the orthopyroxene CPO from the assemblage displays unusual patterns with a strong concentration of [010] axes parallel to X and girdles on [100] and [001] axes in the YZ plane (Figure 4). The olivine CPO have a similar pattern but for different axes with olivine [001] axes parallel to the lineation and orthopyroxene [010], and girdles at 90° to the lineation on the other axes, suggesting that micrometric orthopyroxene crystals partially grew following the olivine crystal orientation axes (Figures 1 and 4). On the contrary, in Aridal 010 and Reid 013, orthopyroxene CPO from the assemblage display a strong concentration of [001] axes parallel to X and [100] axes subparallel to Z. This may suggest that they were affected by a common late event of sulfidization but with different input directions, either perpendicular or parallel to the lineation direction. The formation of the opx-assemblage is likely to be the result of high sulfide fluid/vapor percolation, and its high density suggests horizontal percolation rather than vertical percolation (Figure 13). The relationship between opx-assemblage and G1 brachinite texture could be due to the anisotropic texture with a strong SPO, where a fluid percolation could be facilitated.

In the second reservoir containing brachinites from the G2 group, similar observations (strength of CPO, internal deformation, SPO) point to brachinite NWA 7297, with the strongest olivine [010] concentrations in the CPO (Figures 5 and 10) and grain boundary rotation axes near [010] (Figure 8), as a sample coming from deeper in the reservoir (Figure 13). Brachinites RaS 309 and NWA 4929 may come from similar depths as NWA 7297 since they display similar [010] concentrations but have recorded more intense magmatic flow (stronger [001] concentrations in the CPO and weaker grain boundary olivine rotation axes near [010]) (Figures 5 and 8). This is strengthened by the occurrence of interstitial plagioclase and orthopyroxene grains in NWA 4929 (Figure S10 in Supporting Information S1), suggesting that a small amount of melt was trapped during compaction at shallow depths (Figure 13). Both samples NWA 10932 and NWA 7904 show an equal influence of melt flow and compaction (Figures 5, 6, and 13a; Figure S7 in Supporting Information S1). The euhedral shape of their olivine grains, the absence of significant internal deformation in olivine and weak olivine subgrain and grain boundary misorientation axes concentrations (Figures 6e and 8–10; Figure S7 in Supporting Information S1) suggest an environment favorable for grain growth under low stress, such as at the top of a magmatic reservoir (Figure 13).

The internal deformation state of minerals could also be another parameter to locate brachinites within their parent body and reservoir, as more strain is expected below a thicker lithostatic column as a consequence of compaction, for example, However, in the context of accumulation and compaction in a reservoir in the presence of inter-cumulus melt, little strain (e.g., Yao et al., 2019) and stress (Cao et al., 2017) are expected. Considering the estimated small size of the brachinite parent body (e.g., ~<100 km in radius from Keil, 2014 or 10's to 100's km in diameter from Day et al., 2019) and the proximity of the different samples, small variations in internal deformation are likely a consequence of a heterogeneous distribution of plastic deformation.

Our results highlight that the studied brachinites display a cumulate texture indicative of both magmatic flow and slight compaction with early plastic deformation. However, an important question concerns the cumulate or the restitic origin of brachinites, and whether or not the observed cumulate-like texture could in fact be a residual texture. It is noteworthy that, to date, microstructures and textures of restites remain unexplored, while studies on cumulate textures are rare (Boudier, 1991; Boulanger et al., 2021). In these studies, olivine CPO is very similar to brachinites olivine CPO despite the different scales of their parent bodies (Earth radius ~ 6,372 km vs. < brachinites parent body ~ 100 km in radius from Keil, 2014) inducing changes in pressure, stress and strain. Geochemical studies indicate that brachinite meteorites may constitute the residue of chondrites after 13%–30% melting (Day et al., 2012). Achondrite meteorites usually display porphyric or fine-grained textures without SPO (Krot et al., 2007). This contrasts with the studied brachinites which display SPO (Figure 2) and high concentrations of [001] axes parallel to the lineation (Figures 4 and 5) that are interpreted as resulting from magma flow. If brachinites display a restitic texture and are paracumulates (i.e., “mushy cumulate-like partial melt residues,” Warren & Kallemeyn, 1989, or Goodrich et al., 2004), the degree of partial melting must be sufficient to change the porphyric texture, reorient crystals, and promote olivine crystal growth within a magma flow. An experimental investigation into the partial melting of granite demonstrated that, within the range of 40%–60% partial melting, the solid network breaks down (Rosenberg & Handy, 2005). The highest estimated melting degree in brachinites is 30% (Day et al., 2012), close to the network breakdown. Brachinites with strong CPO and SPO could be samples with a higher degree of partial melting. The texture of chondrites is rarely characterized by the presence of automorphic grains as in the case of brachinites; however, Fe/Mn-Fe/Mg plots indicate that olivine in brachinites has a chondritic composition (Goodrich & Delaney, 2000; Goodrich et al., 2017). From a microstructural point of view, it seems difficult to start from a chondrite and create a brachinite as the pure residue of
partial melting. It suggests that several processes contribute to the formation of a cumulate texture in brachinites. Possibly, a large degree of partial melting led to the breakdown of the grain network. Moreover, olivine Fe/Mn and Fe/Mg compositions in brachinite are relatively constant and stay in the chondritic redox trend, suggesting no igneous crystallization (Goodrich et al., 2017). The presence of the melt, which is the product of chondrite melting, might have allowed growth and grain reorientation during melt flow.

## 5. Conclusions

Brachinites can be divided into two groups, those containing an opx-opaque assemblage (G1) and those which do not contain it (G2), representing different formation processes and possibly different reservoirs. Brachinites from both groups have olivine CPO similar to B-type fabrics [001](010), with a stronger orientation of [001] axis in G1 and a stronger orientation of [010] axis in G2. The limited internal plastic deformation in olivine grains and the discrepancy between olivine subgrain misorientation axes and the CPO indicate that the B-type CPO probably results from magmatic processes, in agreement with a cumulate texture. The magmatic processes may include preferential crystal growth, rigid crystal rotation during magmatic flow and strain accommodation by diffusion and grain boundary sliding during accumulation and compaction. Olivine [001] axis orientations parallel to the lineation mark the direction of magmatic flow and olivine [010] axis orientations indicate the direction of compaction. Plastic deformation, although limited, is almost systemic in all samples. Internal deformation features in olivine grains indicate the activity of the [100](001) E-type and [001](100) C-type slip systems. This deformation may represent early plastic deformation in the brachinite parent body. New Ol-Sp equilibrium temperatures for Al Huwaysah 010, Aridal 010, NWA 4929, NWA 7904, NWA 10932, and NWA 12545 are within the range of literature data, that is, 823 ± 14–909 ± 20°C, corresponding to temperatures favoring the activity of C- and E-type slip systems. Ol-Cpx and two-pyroxenes equilibrium temperatures for the samples are lower, that is, 814 ± 27–868 ± 1°C, but still high enough to activate the same slip systems. The opx-opaque assemblage distribution in G1 brachinites and their orthopyroxene CPO may represent small-scale heterogeneities.

## Data Availability Statement

All the data presented in this study are available on Zenodo.org (Meunier-Mili et al., 2023). All the data were processed using Matlab thanks to the MTEX toolbox version 5.7, (Bachmann et al., 2010; Hielscher & Schaeben, 2008). Scripts used for data processing were mainly based on the MTEX documentation and enhanced through community publications (Lopez-Sanchez et al., 2021; Mainprice et al., 2014).

## Acknowledgments

We would like to thank Edwin Gnos, Beda Hofmann, Jérôme Gataccecca and Rainer Bartoschewitz for the loan of meteorite samples. This manuscript was improved by constructive and thoughtful comments and reviews from editor L. Montesi and two anonymous reviewers. We also thank Fabienne de Parseval for the preparation of thin sections, Thierry Aigouy and Françoise Maubé for assistance with SEM analysis at the Geosciences Environnement Toulouse, and Sophie Gouy and Arnaud Proietti for help with EMPA and EBSD analysis, respectively, at the Centre de Microcaractérisation Raimond Castaing (Université Paul Sabatier, Toulouse). This work was partially supported by the Programme National de Planétologie (PNP) of CNRS/INSU, co-funded by CNES.

## References

Andersen, D. J., Lindsley, D. H., & Davidson, P. M. (1993). QUILF: A pascal program to assess equilibria among Fe-Mg-Mn-Ti oxides, pyroxenes, olivine, and quartz. *Computers & Geosciences*, *19*(9), 1333–1350. https://doi.org/10.1016/0098-3004(93)90033-2

Bachmann, F., Hielscher, R., & Schaeben, H. (2010). Texture analysis with MTEX-free and open source software toolbox. *Solid State Phenomena*, *160*, 63–68. https://doi.org/10.4028/www.scientific.net/SSP.160.63

Bai, Q., Mackwell, S. J., & Kohlstedt, D. L. (1991). High-temperature creep of olivine single crystals 1. Mechanical results for buffered samples. *Journal of Geophysical Research*, *96*(B2), 2441–2463. https://doi.org/10.1029/90JB01723

Ballhaus, C., Berry, R. F., & Green, D. H. (1991). High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen barometer: Implications for the oxidation state of the upper mantle. *Contributions to Mineralogy and Petrology*, *107*(1), 27–40. https://doi.org/10.1007/BF00311183

Beard, S. P., Weimer, D., Busemann, H., Maden, C., & Swindle, T. D. (2018). 21Ne cosmic-ray exposure ages of brachinites and brachinite-like achondrites. In *81st annual meeting of the meteorological society* (2018).

Benn, K., & Allard, B. (1989). Preferred mineral orientations related to magmatic flow in ophiolite layered gabbros. *Journal of Petrology*, *30*(4), 925–946. https://doi.org/10.1093/petrology/30.4.925

Bernard, R. E., Behr, W. M., Becker, T. W., & Young, D. J. (2019). Relationships between olivine CPO and deformation parameters in naturally deformed rocks and implications for mantle seismic anisotropy. *Geochemistry, Geophysics, Geosystems*, *20*(7), 3469–3494. https://doi.org/10.1029/2019GC008289

Boudier, F. (1991). Olivine xenocrysts in picritic magmas: An experimental and microstructural study. *Contributions to Mineralogy and Petrology*, *109*(1), 114–123. https://doi.org/10.1007/BF00687204

Boulanger, M., France, L., Ferrando, C., Ildefonse, B., Ghosh, B., Sanfilippo, A., et al. (2021). Magma-mush interactions in the lower oceanic crust: Insights from Atlantis bank layered series (Southwest Indian Ridge). *Journal of Geophysical Research: Solid Earth*, *126*(9). https://doi.org/10.1029/2021JB022331

Brey, G. P., & Köhler, T. (1990). Geothermobarometry in four-phase Lherzolites II. New thermobarometers, and practical assessment of existing thermobarometers. *Journal of Petrology*, *31*(6), 1353–1378. https://doi.org/10.1093/petrology/31.6.1353

Bunge, H.-J. (1982). Texture analysis in materials science: Mathematical models. In H.-J. Bunge (Ed.), *Texture analysis in materials science* (pp. 1–2). Butterworth-Heinemann. https://doi.org/10.1016/B978-0-408-10642-9.50006-4
Burbine, T. H., Meibom, A., & Binzel, R. P. (1996). Mantle material in the main belt: Battered to bits? *Meteoritics & Planetary Sciences*, 31(5), 607–620. https://doi.org/10.1111/j.1945-5100.1996.tb02033.x

Cao, Y., Jung, H., & Song, S. (2017). Olivine fabrics and tectonic evolution of fore-arc mantles: A natural perspective from the Songshugou dunite and harzburgite in the Qinling orogenic belt, central China. *Geochemistry, Geophysics, Geosystems*, 18(3), 907–934. https://doi.org/10.1002/2016GC006614

Cao, Y., Jung, H., Song, S., Park, M., Jung, S., & Lee, J. (2015). Plastic deformation and seismic properties in fore-arc mantles: A petrofabric analysis of the Yushigou Harzburgites, North Qilian Suture zone, NW China. *Journal of Petrology*, 56(10), 1897–1944. https://doi.org/10.1093/petrology/egv053

Couvy, H., Frost, D., Heidelbach, F., Nyilas, K., Ungár, T., Mackwell, S., & Cordier, P. (2004). Shear deformation experiments of forsterite at 11 GPa–1400°C in the multianvil apparatus. *European Journal of Mineralogy*, 16(6), 877–889. https://doi.org/10.1127/0935-1221/2004/0016-0877

Crossley, S. D., Ash, R. D., Sunshine, J. M., Corrigan, C. M., McCoy, T. J., Mittlefehldt, D. W., & Puchtel, I. S. (2020). Sulfide-dominated partial melting pathways in brachinites. *Meteoritics & Planetary Sciences*, 55(9), 2021–2043. https://doi.org/10.1111/maps.13558

Daly, L., Piazolo, S., Lee, M. R., Griffin, S., Chung, P., Campanale, F., et al. (2019). Understanding the emplacement of Martian volcanic rocks using petrofabrics of the nakhlite meteorites. *Earth and Planetary Science Letters*, 520, 220–230. https://doi.org/10.1016/j.epsl.2019.05.050

Day, J. M. D., Corder, C. A., Assayag, N., & Cartigny, P. (2019). Ferrous oxide-rich asteroid achondrites. *Geochimica et Cosmochimica Acta*, 266, 544–567. https://doi.org/10.1016/j.gca.2019.04.005

Day, J. M. D., Corder, C. A., Rumble, D., Assayag, N., Cartigny, P., & Taylor, L. A. (2015). Differentiation processes in FeO-rich asteroids revealed by the achondrite Lewis Cliff 88763. *Meteoritics & Planetary Sciences*, 50(10), 1750–1766. https://doi.org/10.1111/maps.12509

Day, J. M. D., Walker, R. J., Ash, R. D., Liu, Y., Rumble, D., Irving, A. J., et al. (2012). Origin of felsic achondrites Graves Nunataks 06128 and 06129, and ultramafic brachinites and brachinite-like achondrites by partial melting of volatile-rich primitive parent bodies. *Geochimica et Cosmochimica Acta*, 81, 94–128. https://doi.org/10.1016/j.gca.2011.12.017

de Kloe, R. (2001). Deformation mechanisms and melt Nano-structures in experimentally deformed olivine-orthopyroxene rocks with low melt fractions. PhD thesis *Geologica Ultraiectina* 201. (p. 173). Utrecht University.

de Kloe, R., Drury, M., & Farrer, J. K. (2002). Determination of activated slip systems in experimentally deformed olivine- orthopyroxene polycrystals using EBSD. *Microscopy and Microanalysis*, 8(S02), 680–681. https://doi.org/10.1017/S1431927602106404

Dunlap, D. R., Wadhwa, M., & Romaniello, S. J. (2016). 53Mn-53Cr Systematics of brachina revisited in high precision. In *47th lunar and planetary science conference*.

Gardner-Vandy, K. G., Lauretta, D. S., & McCoy, T. J. (2013). A petrologic, thermodynamic and experimental study of brachinites: Partial melt residues of an R chondrite-like precursor. *Geochimica et Cosmochimica Acta*, 122, 36–57. https://doi.org/10.1016/j.gca.2013.07.035

Goodrich, C. A., & Delaney, J. S. (2000). Fe/Mg–Fe/Mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies. *Geochimica et Cosmochimica Acta*, 64(1), 149–160. https://doi.org/10.1016/S0016-7037(99)00107-6

Goodrich, C. A., Kita, N. T., Spicuzza, M. J., Valley, J. W., Zipfel, J., Mikouchi, T., & Miyamoto, M. (2010). The Northwest Africa 1500 meteorite: Not a ureilite, maybe a brachinite. *Meteoritics & Planetary Sciences*, 45(12), 1906–1928. https://doi.org/10.1111/j.1945-5100.2010.01130.x

Goodrich, C. A., Kita, N. T., Sutton, S. R., Wirick, S., & Gross, J. (2017). The Miller Range 090340 and 090206 meteorites: Identification of new brachinite-like achondrites with implications for the diversity and petrogenesis of the brachinite clan. *Meteoritics & Planetary Sciences*, 52(5), 949–978. https://doi.org/10.1111/maps.12846

Goodrich, C. A., Scott, E. R. D., & Fioretti, A. M. (2004). Ureilitic breccias: Clues to the petrologic structure and impact disruption of the ureilite parent asteroid. *Geochemistry*, 64(4), 283–327. ISSN 0009-2819. https://doi.org/10.1016/j.chemer.2004.08.001

Goodrich, C. A., Wlotzka, F., Ross, D. K., & Bartoschewitz, R. (2006). Northwest Africa 1500: Plagioclase-bearing monomict ureilite or un-grouped achondrite? *Meteoritics & Planetary Sciences*, 41(6), 925–952. https://doi.org/10.1111/j.1945-5100.2006.tb00496.x

Greenwood, R. C., Barrat, J.-A., Scott, E. R. D., Haack, H., Buchanan, P. C., Franchi, I. A., et al. (2015). Geochemistry and oxygen isotope composition of main-group pallasites and olivine-rich clasts in mesosiderites: Implications for the “Great Dunite Shortage” and HED-mesosiderite connection. *Geochimica et Cosmochimica Acta*, 169, 115–136. https://doi.org/10.1016/j.gca.2015.07.023

Greenwood, R. C., Franchi, I. A., Gibson, J. M., & Benedix, G. K. (2012). Oxygen isotope variation in primitive achondrites: The influence of primordial, asteroidal and terrestrial processes. *Geochimica et Cosmochimica Acta*, 94, 146–163. https://doi.org/10.1016/j.gca.2012.06.025

Griffin, S., Daly, L., Piazolo, S., Forman, L., Cohen, B., Lee, M., et al. (2022). Can the magmatic conditions of the Martian Nakhlites be Discerned via investigation of clinopyroxene and olivine intracrystalline misorientations? *Journal of Geophysical Research: Planets*, 127(6). https://doi.org/10.1029/2021JE007082

Gruber, B. H., Nicklas, R. W., Day, J. M. D., Chin, E. J., Ren, M., & Bernard, R. E. (2022). Residual nature of brachinite-like achondrites: An electron backscatter diffraction (EBSD) and olivine trace element study. In *53rd lunar and planetary science conference*.

Hall, A. L. (1987). *Igneous petrology*. English Language Book Society/Longman.

Hasegawa, H., Mikouchi, T., Yamaguchi, A., Yasutake, M., Greenwood, R. C., & Franchi, I. A. (2019). Petrological, petrofabric, and oxygen isotopic study of five ungrouped meteorites related to brachinites. *Meteoritics & Planetary Sciences*, 54(4), 752–767. https://doi.org/10.1111/maps.13249

Henry, H., Kaczmarek, M.-A., Ceuleneer, G., Tilhac, R., Griffin, W. L., O'Reilly, S. Y., et al. (2021). The microstructure of layered ultramafic cumulates: Case study of the Bear Creek intrusion, Trinity ophiolite, California, USA. *Lithos*, 388–389, 106047. https://doi.org/10.1016/j.lithos.2021.106047

Hielscher, R., & Schaeben, H. (2008). A novel pole figure inversion method: Specification of the MTEX algorithm. *Journal of Applied Crystallography*, 41(6), 1024–1037. https://doi.org/10.1107/S0021889808030112

Holtzman, B. K., Kohlstedt, D. L., Zimmerman, M. E., Heidelbach, F., Hiraga, T., & Hustoft, J. (2003). Melt segregation and strain partitioning: Implications for seismic anisotropy and mantle flow. *Science*, 301(5637), 1227–1230. https://doi.org/10.1126/science.1087132

Hunter, R. H. (1996). Texture development in cumulate rocks. In *Developments in petrology* (Vol. 15). Oliver and Boyd: Elsevier. https://doi.org/10.1016/S0167-2894(96)80005-4

Irving, A. J., Kuehner, S. M., & Ziegler, K. (2013). Petrology and oxygen isotopic composition of brachinite-like achondrites northwest Africa 7388 and northwest Africa 7605, and evidence for late-stage reduction. In *44th lunar and planetary science conference*.

Jung, H., & Karato, S. (2001). Water-induced fabric transitions in olivine. *Science*, 293(5534), 1460–1463. https://doi.org/10.1126/science.1062235

Jung, H., Mo, W., & Choi, S. H. (2009). Deformation microstructures of olivine in peridotite from Spitsbergen, Svalbard and implications for seismic anisotropy. *Journal of Metamorphic Geology*, 27(9), 707–720. https://doi.org/10.1111/j.1525-1314.2009.00838.x
Kaczmarek, M.-A., Reddy, S. M., Nutman, A. P., Friend, C. R. L., & Bennett, V. C. (2016). Earth's oldest mantle fabrics indicate Eoarchaean subduction. *Nature Communications*, 7(1), 10665. https://doi.org/10.1038/ncomms10665

Keil, K. (2014). Brachinite meteorites: Partial melt residues from an FeO-rich asteroid. *Geochemistry, 74*(3), 311–329. https://doi.org/10.1016/j.chemer.2014.02.001

Köhler, T., & Brey, G. P. (1990). Calcium exchange between olivine and clinopyroxene calibrated as a geothermobarometer for natural peridotites from 2 to 60 kb with applications. *Geochimica et Cosmochimica Acta*, 54(9), 2375–2388. https://doi.org/10.1016/0016-7037(90)90226-B

Krot, A. N., Keil, K., Scott, E. R. D., Goodrich, C. A., & Weisberg, M. K. (2007). Classification of meteorites. In *Treatise on Geochemistry*. Elsevier.

Langenhorst, F., & Deutsch, A. (2012). Shock metamorphism of minerals. *Elements*, 8(1), 31–36. https://doi.org/10.2113/gselements.8.1.31

Linckens, J., Bruijn, R. H. C., & Skemer, P. (2014). Dynamic recrystallization and phase mixing in experimentally deformed peridotite. *Earth and Planetary Science Letters*, 388, 134–142. https://doi.org/10.1016/j.epsl.2013.11.037

Lopez-Sanchez, M. A., Tommasi, A., Ben Ismail, W., & Barou, F. (2021). Dynamic recrystallization by subgrain rotation in olivine revealed by electron backscatter diffraction. *Tectonophysics*, 815, 228916. https://doi.org/10.1016/j.tecto.2021.228916

Mainprice, D., Bachmann, F., Hielscher, R., & Schaeben, H. (2014). Descriptive tools for the analysis of texture projects with large datasets using *MTEX: Strength, symmetry and components* (Vol. 409). Geological Society, London, Special Publications. https://doi.org/10.1144/SP409.8

Meunier-Mili, N., Mary-Alix, K., & Misha, B. (2023). Supporting material for the article "insights on the brachinite parent body: A petrological and microstructural study of 10 brachinites [Dataset]. *Zenodo*. https://doi.org/10.5281/zenodo.8184073

Mittlefehldt, D. W., Bogard, D. D., Berkley, J. L., & Garrison, D. H. (2003). Brachinites: Igneous rocks from a differentiated asteroid. *Meteoritics & Planetary Sciences*, 38(11), 1601–1625. https://doi.org/10.1111/j.1945-5100.2003.tb00004.x

Mittlefehldt, D. W., Greenwood, R. C., Berger, E. L., Le, L., Peng, Z. X., & Ross, D. K. (2022). Eucrite-type achondrites: Petrology and oxygen isotope compositions. *Meteoritics & Planetary Science*, 57(2), 484–526. https://doi.org/10.1111/maps.13730

Mittlefehldt, D. W., McCoy, T. J., Goodrich, C. A., & Kracher, A. (1998). Chapter 4. Non-chondritic meteorites from asteroidal bodies. In J. J. Papike (Ed.), *Planetary materials* (pp. 523–718). De Gruyter. https://doi.org/10.1515/9781501508806-019

Mizukami, T., Wallis, S. R., & Yamamoto, J. (2004). Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum. *Nature*, 427(6973), 432–436. https://doi.org/10.1038/nature02179

Nagahara, H., & Ozawa, K. (1986). Petrology of Yamato-791493, lodranite: Melting, crystallization, cooling history, and relationship to other meteorites. *Memoirs of National Institute of Polar Research - Special Issue* (41), 181–205.

Nakamura, Y., Urata, K., Shibata, Y., & Kuwahara, Y. (2017). Effect of NaCrSi2O6 component on Lindsley's pyroxene thermometer: An evaluation based on strongly metamorphosed LL chondrites. *Meteoritics & Planetary Sciences*, 52(3), 511–521. https://doi.org/10.1111/maps.12808

Park, Y., & Jung, H. (2015). Deformation microstructures of olivine and pyroxene in mantle xenoliths in Shanwang, eastern China, near the convergent plate margin, and implications for seismic anisotropy. *International Geology Review*, 57(5-8), 629–649. https://doi.org/10.1080/00206814.2014.928240

Petaev, M. I., Barsukova, L. D., Lipschutz, M. E., Wang, M.-S., Ariskin, A. A., Clayton, R. N., & Mayeda, T. K. (1994). The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin. *Meteoritics*, 29(2), 182–199. https://doi.org/10.1111/j.1945-5100.1994.tb00671.x

Raterron, P., Amiguet, E., Chen, J., Li, L., & Cordier, P. (2009). Experimental deformation of olivine single crystals at mantle pressures and temperatures. *Physics of the Earth and Planetary Interiors*, 172(1–2), 1–2. https://doi.org/10.1016/j.pepi.2008.07.026

Rosenberg, C. L., & Handy, M. R. (2005). Experimental deformation of partially melted granite revisited: Implications for the continental crust. *Journal of Metamorphic Geology*, 23(1), 19–28. https://doi.org/10.1111/j.1525-1314.2005.00555.x

Rubin, A. E. (2006). Shock, post-shock annealing, and post-annealing shock in ureilites. *Meteoritics & Planetary Sciences*, 41(1), 125–133. https://doi.org/10.1111/j.1945-5100.2006.tb00197.x

Rumble, D., Irving, A. J., Bunch, T. E., Wittke, J. H., & Kuehner, S. M. (2008). Oxygen isotopic and petrological diversity among brachinites NWA 4872, 4874, 4882, 4969. How many ancient parent bodies. In *39th lunar and planetary science conference*.

Ruzicka, A. M., & Hugo, R. C. (2018). Electron backscatter diffraction (EBSD) study of seven heavily metamorphosed chondrites: Deformation systematics and variations in pre-shock temperature and post-shock annealing. *Geochimica et Cosmochimica Acta*, 234, 115–147. https://doi.org/10.1016/j.gca.2018.05.014

Sack, R. O., & Ghiorso, M. S. (1991). Chromian spinels as petrogenetic indicators: Thermodynamics and petrological applications. *American Mineralogist*, 76(5-6), 827–847.

Shirley, D. N. (1986). Compaction of igneous cumulates. *The Journal of Geology*, 94(6), 795–809. https://doi.org/10.1086/629088

Singerling, S. A., McCoy, T. J., & Gardner-Vandy, K. G. (2013). Possible evidence for sulfidization reactions in the miller range brachinites. *44th lunar and planetary science conference*.

Skemer, P., & Hansen, L. N. (2016). Inferring upper-mantle flow from seismic anisotropy: An experimental perspective. *Tectonophysics*, 668–669, 1–14. https://doi.org/10.1016/j.tecto.2015.12.003

Skemer, P., Katayama, I., Jiang, Z., & Karato, S. (2005). The misorientation index: Development of a new method for calculating the strength of lattice-preferred orientation. *Tectonophysics*, 411(1–4), 157–167. https://doi.org/10.1016/j.tecto.2005.08.023

Skemer, P., Katayama, I., & Karato, S. (2006). Deformation fabrics of the Cima di Gagnone peridotite massif, central Alps, Switzerland: Evidence of deformation at low temperatures in the presence of water. *Contributions to Mineralogy and Petrology*, 152(1), 43–51. https://doi.org/10.1007/s00410-006-0093-4

Stöffler, D., Keil, K., & Edward, R. D. S. (1991). Shock metamorphism of ordinary chondrites. *Geochimica et Cosmochimica Acta*, 55(12), 3845–3867. https://doi.org/10.1016/0016-7037(91)90078-J

Sundberg, M., & Cooper, R. F. (2008). Crystallographic preferred orientation produced by diffusional creep of harzburgite: Effects of chemical interactions among phases during plastic flow. *Journal of Geophysical Research*, 113(B12), B12208. https://doi.org/10.1029/2008JB005618

Tkalcec, B. J., & Brenker, F. E. (2014). Plastic deformation of olivine-rich diogenites and implications for mantle processes on the diogenite parent body. *Meteoritics & Planetary Sciences*, 49(7), 1202–1213. https://doi.org/10.1111/maps.12324

Tkalcec, B. J., Golabek, G. J., & Brenker, F. E. (2013). Solid-state plastic deformation in the dynamic interior of a differentiated asteroid. *Nature Geoscience*, 6(2), 93–97. https://doi.org/10.1038/ngeo1710

Tommasi, A., Mainprice, D., Canova, G., & Chastel, Y. (2000). Viscoplastic self-consistent and equilibrium-based modeling of olivine lattice preferred orientations: Implications for the upper mantle seismic anisotropy. *Journal of Geophysical Research*, 105(B4), 7893–7908. https://doi.org/10.1029/1999JB00411

Toplis, M. J., Mizzon, H., Monnereau, M., Forni, O., McSween, H. Y., Mittlefehldt, D. W., et al. (2013). Chondritic models of 4 Vesta: Implications for geochemical and geophysical properties. *Meteoritics & Planetary Sciences*, 48(11), 2300–2315. https://doi.org/10.1111/maps.12195
Wager, L. R., Brown, G. M., & Wadsworth, W. J. (1960). Types of igneous cumulates. *Journal of Petrology*, *1*(1), 73–85. https://doi.org/10.1093/petrology/1.1.73

Warren, P. H., & Kallemeyn, G. W. (1989). Allan Hills 84025: The second brachinite, far more differentiated than Brachina, and an ultramafic achondritic clast from L chondrite Yamato 75097. *Lunar and Planetary Science Conference Proceedings*, *19*, 475–486.

Wen, D.-P., Wang, Y.-F., Zhang, J.-F., & Jin, Z.-M. (2018). Anisotropic growth of olivine during crystallization in basalts from Hawaii: Implications for olivine fabric development. *American Mineralogist*, *103*(5), 735–741. https://doi.org/10.2138/am-2018-6174

Wieser, P. E., Vukmanovic, Z., Kilian, R., Ringe, E., Holness, M. B., Maclennan, J., & Edmonds, M. (2019). To sink, swim, twin, or nucleate: A critical appraisal of crystal aggregation processes. *Geology*, *47*(10), 948–952. https://doi.org/10.1130/G46660.1

Wlotzka, F. (2005). Cr spinel and chromite as petrogenetic indicators in ordinary chondrites: Equilibration temperatures of petrologic types 3.7 to 6. *Meteoritics & Planetary Sciences*, *40*(11), 1673–1702. https://doi.org/10.1111/j.1945-5100.2005.tb00138.x

Wright, S. I., Nowell, M. M., & Field, D. P. (2011). A review of strain analysis using electron backscatter diffraction. *Microscopy and Microanalysis: The Official Journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada*, *17*(3), 316–329. https://doi.org/10.1017/S1431927611000055

Yao, Z., Qin, K., Wang, Q., & Xue, S. (2019). Weak B-type olivine fabric induced by fast compaction of crystal mush in a crustal magma reservoir. *Journal of Geophysical Research: Solid Earth*, *124*(4), 3530–3556. https://doi.org/10.1029/2018JB016728