Quantification of shock in enstatite chondrites using micro-X-ray diffraction

Abstract

Enstatite chondrite meteorites are chemically and isotopically related to the precursors of inner Solar System planetesimals, and bear evidence of shock metamorphism which reflects events in enstatite chondrite evolution. Here, we build upon a micro-X-ray diffraction (micro-XRD)-based method to relate strain-related mosaicity (SRM) to petrographic shock stage. Making use of the peak pressure ranges estimated for the petrographic shock stages, we are able to provide quantitative constraints on the peak shock pressures recorded in enstatite (MgSiO₃). Full-width at half-maximum measurement of X-ray diffraction maxima distributed along the Debye rings (ΣFWHMχ) are a proxy for SRM in enstatite grains. Eleven Antarctic enstatite chondrites spanning all documented shock stages (S1−S5), petrologic types, and metamorphic grades, are used to establish a linear correlation P (GPa) = 4.62 × ΣFWHMχ + 0.57; with R² = 0.92 between estimated peak shock pressure and ΣFWHMχ. Enstatite lattice planes (020), (610) and (131) show similar ΣFWHMχ values where meaningful comparisons can be made, suggesting that enstatite has, within measurement error, an isotropic response to shock deformation along its three crystal axes. The (610) reflection is particularly productive at all shock stages and could be used exclusively for future peak pressure studies, under the assumption that enstatite is isotropic to shock deformation. This 2D XRD method enables the estimation of peak shock pressures up to at least 30 GPa in enstatite chondrites and for other enstatite-rich meteorites.

Graphical abstract

Keywords

enstatite chondrite / shock metamorphism / shoch stage / pressure calibration / X-ray diffraction

1 Introduction

The mineral enstatite (orthopyroxene with ideal endmember composition MgSiO₃) is prevalent in planetary materials, including enstatite chondrites, ungrouped enstatite-rich chondrites, aubrites (enstatite achondrites), Martian regolith breccias and diogenites (Rubin, 2015 and references therein; Agee et al., 2013), as well as in some terrestrial rocks. In this contribution, we advance a universally applicable quantification of enstatite shock metamorphism, making it possible for future work to investigate the impact processing histories not only for enstatite chondrites but also for differentiated asteroids and other enstatite-bearing planetary materials. On an asteroidal scale, shock-induced features in enstatite constrain parent body disruption mechanisms in the early inner Solar System (Rubin et al., 1997), as well as the shock deformational environment experienced by different enstatite-bearing asteroidal populations over the evolution of the inner Solar System.

Enstatite chondrites (ECs) are chemically and isotopically similar to the Earth-Moon system, making them plausible analogs for the precursor materials of inner Solar System planetesimals (e.g., Keil, 1989; Lin, 2022). Formed under highly reducing conditions in the early solar nebula, ECs are characterized by dominant enstatite (MgSiO₃) with minimal FeO content (< 1.0 wt.%), exotic sulfides (e.g., oldhamite, niningerite), and silicon-bearing metal alloys, reflecting oxygen fugacities lower than those of any other chondrite group (Weisberg and Kimura, 2012). Representing only ~2% of meteorite falls, ECs offer critical insights into condensation processes under sulfur-rich, oxygen-poor conditions (Lin, 2022), planetary differentiation in reducing environments (Ebel and Alexander, 2011), and the preservation of highly reduced phases during asteroidal processing (Wang and Lipschutz, 2005). Notably, EC impact melts and reduced assemblages serve as key petrological analogs for interpreting Mercury’s surface processes, linking shock barometry to volatile loss and differentiation. This connection is supported by their similar mineralogies (e.g., Fe-metal-rich and FeO-poor silicate compositions) and low oxygen fugacity, as evidenced by MESSENGER data (Nittler et al., 2011; Udry et al., 2019; Lin, 2022).

Like all solid bodies in our Solar System, the parent bodies of enstatite chondrites have undergone shock-induced metamorphism during hypervelocity impact events (e.g., Rubin et al., 1997; Rubin, 2015), with the resultant deformation microstructures in enstatite acting as a mineralogical record of the impact histories of parent bodies of ECs. These impacts generate unique shock metamorphic signatures in ECs due to their distinctive mineralogy. For instance, enstatite develops irregular fractures, undulatory extinction, planar fractures (PF), and {100} lamellae below 15 GPa. At higher pressures (> 25−30 GPa), enstatite shows optical mosaicism and melting, with possible transition to polymorph majorite (garnet structure) (Rubin et al., 1997; Stöffler et al., 2018). Whole-rock melting occurs at even higher pressures (> 70−75 GPa). Although high-pressure phases such as bridgmanite have been identified in ordinary chondrites at estimated pressures of ~24 GPa and temperatures of 2300 K (Tschauner et al., 2014), they have not yet been observed in ECs. Moreover, recent in situ shock experiments indicate that enstatite undergoes disordering into a non-crystalline structure starting at ~80 GPa—well below equilibrium melting—rather than forming expected high-pressure phases like bridgmanite (Hernandez et al., 2020).

There is notably some uncertainty associated with the shock pressures assigned to the different shock stages by Rubin et al. 1997. The onset of crystal deformation is affected by the temperature of the sample at the time of impact, as demonstrated by Schmitt (2000) for H6 chondrite Kernouvé. Furthermore, increased sample porosity plays a role in reducing shock deformation recorded in minerals (Schmitt, 2000; Stöffler et al., 2018). Orthopyroxene appears more resistant to crystal plastic deformation than olivine, as evidenced by the of onset of mosaicism in pyroxene at higher pressures than in olivine, according to the experimental observations by Schmitt (2000). He observed weak mosaicism of olivine occurring from 10−15 GPa to 20−25 GPa with strong mosaicism of olivine occurring starting at 20−25 GPa, whereas weak mosaicism in orthopyroxene was observed above 25−30 GPa (high target temperature experiments) and at 30−35 GPa (low target temperature experiments). Stöffler et al. (2018 Table 2) have also tabulated differences between the deformation behavior of olivine and pyroxene, noting that pyroxene is more resilient to peak shock pressure.

Building on earlier studies such as that of Hörz and Quaide (1973), Izawa et al. (2011) demonstrated a relationship between the degree of shock observable in cross-polarized transmitted light microscopy (optical mosaicism in single crystals) and the broadening of X-ray diffraction maxima along the direction of the Debye rings, or strain-related mosaicity (SRM), measured using in situ micro-X-ray diffraction (micro-XRD) with a 2-dimensional detector (Flemming, 2007). SRM is demonstrated by in non-uniformly strained single crystals, which produce an orientationally-related near-continuous array of diffracted X-rays, observed as “streaking” along the Debye ring in the 2D XRD image (Hörz and Quaide, 1973). In meteorites and impact rocks, this non-uniform deformation in crystals is manifested as a smoothly-varying (curved) crystal structure, or more commonly, as structurally misoriented subdomains within the single crystal, developed in response to impact-related shock pressures.

Subsequent to Flemming (2007) and Izawa et al. (2011), numerous investigators have expanded and improved upon the analysis of SRM, enabling qualitative (shock stage) and quantitative (peak shock pressure) assessment of shock recorded in minerals, including plagioclase (e.g., Cao et al., 2025), clinopyroxene (Jenkins et al., 2019a; Cao et al., 2022 ), and olivine (e.g., Rupert et al., 2020), with applications spanning terrestrial (e.g., Pickersgill et al., 2015), Lunar (e.g., Pickersgill et al., 2015; Li et al., 2025), Martian (e.g., Jenkins et al., 2019b), and asteroidal (e.g., Li et al., 2021) materials.

Despite these developments, there has yet to be a quantitative assessment of the relationship between peak shock pressure and SRM as recorded by 2-dimensional XRD of enstatite. This gap critically limits our ability to decipher shock records in ECs, which are among the most reduced meteorite groups (Lin, 2022). This study aims to address this gap by reassessing the signatures of shock recorded in enstatite grains from 11 Antarctic ECs spanning all documented petrographic shock stages (S1−S5) using the micro-XRD method. We quantify shocked-induced metamorphism, through full-width at half-maximum (FWHMχ) measurements along Debye rings, establishing a proxy measurement of peak shock pressure recorded in meteoritic enstatite, for shock stages 1−5, using peak shock pressures estimated by Rubin (1997) and reiterated by Izawa et al. (2011) and Rubin (2015).

2 Methods

2.1 Micro-XRD

Micro-X-ray diffraction (micro-XRD) patterns were acquired from multiple targets on polished thin sections of 11 enstatite chondrite meteorites, previously reported in Izawa et al. (2011). The meteorites in this study include EH and EL chondrites of all available petrologic grades (Type 3 to 7) and shock stages (S1 to S5) and are dominated by near end-member orthoenstatite. Micro-XRD data were collected using the Bruker AXS D8 Discover microdiffractometer at Western University, using Cu Kα radiation (λ = 1.5418 Å, 40 kV, 30 mA) with a 500 μm nominal beam diameter, an XYZ sample stage with microscope for target selection, and a Bruker Hi-STAR two-dimensional detector in “coupled scan” mode using general area diffraction detector system (GADDS) software to detect the diffracted X-rays (e.g., Flemming, 2007). Enstatite peaks were identified and indexed using International Centre for Diffraction data (ICDD) card 019-0768, in the orthorhombic crystal system with Space Group Pbca (61).

Two-dimensional micro-XRD images from the original study of Izawa et al., (2011) were re-processed by fitting each observable reflection of the (020), (610), and (131) enstatite lattice planes with one or more peaks, from each of which a full-width at half-maximum of the peak integrated along the Debye ring (i.e., FWHMχ) was obtained. In contrast to the original study by Izawa et al. (2011), where FWHMχ was extracted directly from Bruker EVA software with only normal distribution single peak fitting of complex streaked diffraction spots, this new reprocessing enhances the precision of the analysis of complex peaks as shown in Fig. 1. The (020), (610) and (131) lattice planes were chosen due to their distinct d-spacing, which avoids overlap with coexisting phases, especially plagioclase feldspar, and because they can form a 3-dimensional basis set, which in principle allows assessment of strain along all crystallographic axes in enstatite.

The FWHMχ values were determined using Renishaw’s Raman WiRE software (version 4.2) by performing background subtraction and peak fitting employing a Gaussian-Lorentzian function. Figure 1 shows examples of FWHMχ analyses for the (610) reflection, comparing a low-shock simple diffraction streak fitted with a single peak with a higher-shock complex streak, fitted with multiple peaks. For diffraction profiles exhibiting complex peak shapes, multi-peak fitting was applied, and the cumulative strain-related mosaicity (SRM) was quantified as the term ΣFWHMχ, defined as the sum of FWHMχ values across all resolved peaks (n ≥ 1). For consistency, the term ΣFWHMχ (where n ≥ 1 represents the number of fitted peaks), is used throughout, whether derived from a single peak or multiple overlapping peaks. This provides a standardized metric for X-ray intensity dispersion in the χ dimension, ensuring cross-sample comparability. It is worth noting that because the parameter ΣFWHMχ pertains to intensity of diffracted X-rays distributed along the Debye rings, it is independent of the X-ray wavelength. Therefore, ΣFWHMχ values measured with different instrument configurations and source characteristics are highly inter-comparable, provided that the analysis methods are consistent between data sets.

2.2 Peak shock pressure estimation

To ensure robust and reliable peak shock pressure estimates, we adopted a conservative approach for assigning pressure ranges to each shock stage (S1−S5), based on Rubin (1997Table 1). For example, for the S4 shock stage, Rubin (1997) indicated that peak shock pressures fall below the range of 25−30 GPa, while S3 pressures are below 10−15 GPa. This implies that S4 pressures span from the upper boundary of S3 (10−15 GPa) to the maximum of S4 (25−30 GPa). To account for this variability and ensure our estimates are conservative, we defined the S4 pressure range as 15−30 GPa, using the midpoint of 22.5 GPa and a standard deviation of ± 7.5 GPa (half the range width). This wider range deliberately encompasses the full range of possible pressures for S4, from the lower boundary adjacent to S3 (15 GPa) to the upper limit of 30 GPa. By choosing this broader range, we prioritize caution over precision, acknowledging the inherent uncertainties in shock pressure estimation. This methodology enhances the reliability of our results by avoiding underestimation of uncertainties, particularly for higher shock stages like S3 to S5.

The assigned values and error bars for each shock stage are: S1: 0 5 GPa, represented as 2.5±2.5 GPa; S2: 5−10 GPa, represented as 7.5±2.5 GPa; S3: 10−15 GPa, represented as 12.5±2.5 GPa; S4: 15−30 GPa, represented as 22.5±7.5 GPa; S5: 30−60 GPa, represented as 45±15 GPa.

3 Results

Figure 2 displays representative examples of shocked enstatite grains, showcasing microscopic images alongside their corresponding 2D XRD images. Comprehensive microscopic images and corresponding 2D XRD images for all analyzed enstatite grains are available in the supplementary materials (Figs. S1 to S11).

The average of all ΣFWHMχ measurements for all detectable reflections (196 total reflections over 3 lattice planes (see supplemental spreadsheet S1) are shown in Table 1 and Fig. 3(a), where they are compared with peak shock pressure estimates based on petrographic shock stage classifications (Rubin, 1997). Figures 3(b)−3(d) show the ΣFWHMχ measurements for the (020), (610), and (131) lattice planes, respectively. These measured ΣFWHMχ values show significant dispersion consistent with a heterogeneous distribution of peak shock pressure (Fig. 4(a)). The estimated peak shock pressures correspond to the petrographic shock stages assigned to each meteorite (Rubin, 1997 and 2015), where petrographic observations of shock metamorphism in enstatite were tied to experimentally shocked samples. Figure 4(b) illustrates the cumulative frequency (%) of lattice planes within each shock stage versus ΣFWHMχ for each individual Miller index. This plot quantifies the proportion of grains with ΣFWHMχ values ≤ a given threshold, highlighting the heterogeneity in shock deformation features among samples classified at the same shock stage.

We next determine a linear fit of our observed ΣFWHMχ values versus the range of peak shock pressure drawn from the S shock stages defined by Rubin (1997 and 2015) for the enstatite chondrites (Fig. 5). Because only three reflections could be successfully fit in S5 sample PCA 91020, it was not included in the linear fitting of ΣFWHMχ versus peak shock pressure, as the concept of standard deviation is nearly meaningless in such a small S5 data set.

4 Discussion

The previously established (Izawa et al., 2011) correlation between shock level and FWHMχ (which is exported from EVA software with single peak fitting) holds, but is subject to large errors and is strongly affected by the lack of strong reflections in the S5 sample PCA 91020. The S5 sample produced only three reflections, preventing robust statistical analysis, necessitating its exclusion from quantitative analysis of a relationship between ΣFWHMχ and peak shock pressure. Interestingly, the ΣFWHMχ values for the S5 meteorite are quite large, larger than values seen in the S1 to S4 meteorites, suggesting that the relationship of increased ΣFWHMχ with increasing shock pressure should be definable in the future with more S5 measurements. In this work, the linear relationship presented here should be considered valid for ΣFWHMχ values < 10°. By applying a linear fit to the average ΣFWHMχ over shock stages S1−S4, corresponding roughly to peak shock pressure range of 4−30 GPa, we have established an empirical linear relationship between strain-related mosaicity (SRM) in terms of ΣFWHMχ measured by micro-XRD and peak shock pressure as follows (Fig. 4):

(1){\mathit{P}(\mathrm{G}\mathrm{P}\mathrm{a})=4.62\times \mathrm{\Sigma }\mathrm{F}\mathrm{W}\mathrm{H}\mathrm{M}\chi +0.57;\mathrm{w}\mathrm{i}\mathrm{t}\mathrm{h}\mathit{R}}^2=\mathrm{0.92.}

This relation is conservatively assessed as valid for ΣFWHMχ < 10° corresponding to a pressure range of at least 4−30 GPa. It is possible that the linear relation described here holds to higher pressures (e.g., S5 ranges from 30 to 60 GPa), but we urge conservatism in the application of this apparent linear relationship until further measurements can be added to constrain enstatite shock response at higher peak pressures. Similarly, this work on enstatite may hold for low-Ca orthorhombic pyroxenes with greater Fe/Mg or Ca/Mg ratios, but further investigation is required to test this.

It is well-known that shock effects in geological materials are heterogeneously distributed across a wide range of spatial scales (e.g., Cao et al., 2025; Fritz et al., 2017). This is reflected by the large dispersion in measured ΣFWHMχ values both within individual meteorites (Izawa et al., 2011) and across the overall data set (Figs. 4(a)–(b)). An advantage of the micro-XRD methodology lies in its capacity to interrogate substantial material volumes during analysis, thereby yielding an overall measurement that more accurately represents the peak shock pressure experienced by the bulk meteorite compared to spatially limited techniques.

Enstatite deformation is highly complex but is commonly associated with twinning and the formation of twinned and interlayered orthoenstatite and clinoenstatite lamellae stacked along the [010] crystallographic axis (e.g., Coe and Muller, 1973; Leroux, 2001). In this study, we have measured ΣFWHMχ corresponding to the lattice planes (020) with 19 reflections, (610) with 117 reflections, and (131) with 63 reflections, across all shock stages S1 to S5. Izawa et al. (2011) found no significant FWHMχ distinction between the enstatite (020), (610) and (131) planes, suggesting that shock deformation is isotropic across all three enstatite crystal axes. In our multi-peak fitting analysis, we also find no clear distinction between lattice planes within their measurement error (Fig. 6), but note that this analysis is limited by the relatively few reflections obtained from the enstatite (020) plane. Our results suggest that the ΣFWHMχ values increase most consistently on the well-represented (610) plane, with a similar increase seen on the (131) plane for shock stages S1 to S3 (Fig. 6; Supplementary data S1). The low ΣFWHMχ values for the (131) and (020) planes in S4 are represented by relatively few reflections (5 and 1, respectively) from two meteorites, and so may not be adequately representative of S4 compared with the values obtained from the (610) plane (39 reflections). Given the excellent representation by the (610) plane (119 reflections/196 total), future use of this 2D XRD method for shock pressure determination could focus on the (610) plane, assuming that enstatite shock deformation is isotropic along all three crystal axes.

While the results of the present study show that the qualitative relationship between FWHMχ and shock stage/estimated peak shock pressure established by Izawa et al. (2011) is valid, it is notable that the average ΣFWHMχ values at each shock stage/pressure determined by peak fitting are consistent with this from Izawa et al. (2011) for lower shock stages S1 to S3, but become significantly larger for S4. In the initial Izawa et al. (2011) study, many composite peaks were approximated as single features, leading to FWHMχ values that were too low or too high, and some peaks with low signal-to-noise and high FWHMχ in Izawa et al. (2011) were not included in the present analysis. We therefore recommend that attempts to relate strain-related mosaicity (SRM) to shock stage, and subsequent quantitative estimates of peak shock pressure rely on the revised peak fitting method presented in this study.

5 Conclusions and future work

This study quantifies the relationship between strain-induced mosaicity (via ΣFWHMχ in 2D XRD images) and shock stage, using 196 enstatite reflections from 11 enstatite chondrite meteorites. Shock stage for a bulk meteorite, while an oversimplification, is a useful parameter for understanding petrogenesis and placing constraints on the geological history of the sample. In the peak shock pressure range of 4−30 GPa (S1 to S4), we have established an empirical linear relationship between ΣFWHMχ and peak shock pressure:

(1)\begin{array}{c}{\mathit{P}(\mathrm{G}\mathrm{P}\mathrm{a})=4.62\times \mathrm{\Sigma }\mathrm{F}\mathrm{W}\mathrm{H}\mathrm{M}\chi +0.57;\mathrm{w}\mathrm{i}\mathrm{t}\mathrm{h}\mathit{R}}^2=\mathrm{0.92.}\end{array}

This relationship is applicable to enstatite-bearing terrestrial and extraterrestrial materials, offering a non-destructive tool for shock stage estimation. Insofar as shock stage can be related to peak shock pressure, our results can provide a first quantitative estimate of the peak shock pressure experienced by enstatite-bearing rocks. A comparison of enstatite (020), (610) and (131) lattice planes at each shock level shows that their ΣFWHMχ values overlap within error, suggesting that shock deformation is isotropic across all three enstatite crystal axes. However, the large dispersion in ΣFWHMχ values and low number of measurements corresponding to the (020) plane make this a preliminary inference at this time.

This study has also revealed useful directions for future study. Of the 703 known enstatite chondrites as of this writing, only a few possess established shock stages and almost none have estimated peak shock pressures. The micro-XRD/ΣFWHMχ method can provide a fast and non-destructive means for shock assessment (along with phase identification), which can enable population studies of the shock state of large groups of meteorites. In particular, the enstatite (610) lattice plane appears to be productive at all shock stages, thus providing a basis for further shock pressure determinations based on (610) alone, assuming that enstatite shock is isotropic along all crystal axes.

While the present study has investigated the low and intermediate shock levels (S1−S4), we have few data for shock stage S5 (estimated peak shock pressure 30−60 GPa) and none for higher shock levels. Furthermore, the peak shock pressures used here lack a firm experimental basis. There is an urgent need to study enstatite samples from shock experiments with well-constrained peak shock pressures to develop an enstatite pressure calibration, expanding upon the relationship found in this study to relate observed strain-related mosaicity to experimentally determined peak shock pressures rather than shock stages. Cross-calibration between multiple minerals, e.g., enstatite, olivine, and plagioclase, is also an important future direction both to evaluate consistency between different mineral shock barometers and to elucidate the differences in shock response in different minerals within the same target rocks.

Rubin (2015) observed a correlation between petrologic type and shock stage among chondrite groups which supports collisional heating as the mechanism primarily responsible for chondrite metamorphism (e.g. Rubin, 1995). An alternative perspective, suggested by the experimental work of Schmitt (2000), is that pre-collisional heating (thermal metamorphism) of chondritic materials will influence shock metamorphism. Collision into heated materials will result in deformation at lower peak shock pressures than expected for the equivalent cold chondritic materials. The presence of deformation features in olivine or pyroxene is also a function of target rock temperature at the time of impact. Independent evidence of target rock temperature is desirable to more clearly apply peak shock pressures found in cold temperature experimental work to the meteorite record. Mineral reactions and textures, such as those involving troilite or FeNi metal (Schmitt, 2000), can provide insights into the temperature of the host rock during impact event. Further work is necessary in this regime.

References

[1] Agee C B, Wilson N V, McCubbin F M, Ziegler K, Polyak V J, Sharp Z D, Asmerom Y, Nunn M H, Shaheen R, Thiemens M H, Steele A, Fogel M L, Bowden R, Glamoclija M, Zhang Z, Elardo S M (2013). Unique meteorite from early Amazonian Mars: water-rich basaltic breccia Northwest Africa 7034.Science, 339(6121): 780–785

[2] Cao , F. , Flemming , R. L., Izawa , M. R. M., Jaret , S. J., Johnson , J. R. (2025). Micro X‐Ray Diffraction Observations and Calibration of Experimentally Shocked Plagioclase Feldspars: Comparison With Raman Spectroscopic Observations.J Geophys Res: Planets, 130(5): e2024JE008574

[3] Cao F, Flemming R L, Izawa M R M, Loiselle L, Di Cecco V E, Moriguti T, Okuchi T, Moser D E, Tait K T, Houde V L, Hyde B C, Agee C B, Osinski G R, Irving A J (2022). Shock Effects in Lithic and Crystal Clasts in Martian Regolith Breccias. IMA Lyon. Abs#1678

[4] Coe R S, Muller W F (1973). Crystallographic orientation of clinoenstatite produced by deformation of orthoenstatite.Science, 180(4081): 64–66

[5] Ebel D S, Alexander C M O (2011). Equilibrium condensation from chondritic porous IDP enriched vapor: Implications for Mercury and enstatite chondrite origins.Planet Space Sci, 59(15): 1888–1894

[6] Flemming R L (2007). Micro X-ray diffraction (μXRD): a versatile technique for characterization of Earth and planetary materials.Can J Earth Sci, 44(9): 1333–1346

[7] Fritz J, Greshake A, Fernandes V A (2017). Revising the shock classification of meteorites.Meteorit Planet Sci, 52(6): 1216–1232

[8] Hernandez J -A , Morard G, Guarguaglini M, Alonso-Mori R, Benuzzi-Mounaix A, Bolis R (2020). Direct Observation of Shock-Induced Disordering of Enstatite Below the Melting Temperature. Geophys Res Lett, 47(15): e2020GL088887

[9] Hörz F, Quaide W L (1973). Debye-scherrer investigations of experimentally shocked silicates.Moon, 6(1−2): 45–82

[10] Izawa M R M, Flemming R L, Banerjee N R, McCausland P J A (2011). Micro-X-ray diffraction assessment of shock stage in enstatite chondrites: μXRD assessment of enstatite chondrite shock.Meteorit Planet Sci, 46(5): 638–651

[11] Jenkins L E, Flemming R L, Burchell M, Harriss K, Peslier A, Christoffersen R, Fritz J, Meyer C (2019a). Creating calibration curves to determine shock pressure in clinopyroxene using lattice strain and strain related mosaicity. GSA annual meeting, Phoenix, AZ. ID: 338044.

[12] Jenkins L E, Flemming R L, McCausland P J A (2019b). Quantitative in situ XRD measurement of shock metamorphism in Martian meteorites using lattice strain and strain-related mosaicity in olivine.Meteorit Planet Sci, 54(4): 902–918

[13] Keil K (1989). Enstatite meteorites and their parent bodies.Meteoritics, 24(4): 195–208

[14] Leroux H (2001). Microstructural shock signatures of major minerals in meteorites.Eur J Mineral, 13(2): 253–272

[15] Li Y, McCausland P J A, Flemming R L (2021). Quantitative shock measurement of olivine in ureilite meteorites.Meteorit Planet Sci, 56(7): 1422–1439

[16] Li Y, McCausland P J A, Flemming R L, Osinski G R (2025). Petrology and shock history of hybrid lunar feldspathic–troctolitic breccia Northwest Africa 11515.Meteorit Planet Sci, 60(2): 347–370

[17] Lin Y (2022). Enstatite chondrites: condensation and metamorphism under extremely reducing conditions and contributions to the Earth.Prog Earth Planet Sci, 9(1): 1–16

[18] Nittler L R, Starr R D, Weider S Z, McCoy T J, Boynton W V, Ebel D S, Ernst C M, Evans L G, Goldsten J O, Hamara D K, Lawrence D J, McNutt R L Jr, Schlemm C E II, Solomon S C, Sprague A L (2011). The major-element composition of Mercury’s surface from MESSENGER X-ray spectrometry.Science, 333(6051): 1847–1850

[19] Pickersgill A E, Flemming R L, Osinski G R (2015). Toward quantification of strain-related mosaicity in shocked lunar and terrestrial plagioclase by in situ micro-X-ray diffraction.Meteorit Planet Sci, 50(11): 1851–1862

[20] Rubin A E (1995). Petrologic evidence for collisional heating of chondritic asteroids.Icarus, 113(1): 156–167

[21] Rubin A E (2015). Impact features of enstatite-rich meteorites.Chem Erde, 75(1): 1–28

[22] Rubin A E (1997). Mineralogy of meteorite groups.Meteorit Planet Sci, 32(2): 231–247

[23] Rubin A E, Scott E R D, Keil K (1997). Shock metamorphism of enstatite chondrites.Geochim Cosmochim Acta, 61(4): 847–858

[24] Rupert A N, McCausland P J A, Flemming R L (2020). Ordinary chondrite shock stage quantification using in situ 2‐D X‐ray diffraction of olivine.Meteorit Planet Sci, 55(10): 2224–2240

[25] Schmitt R T (2000). Shock experiments with the H6 chondrite Kernouvé: Pressure calibration of microscopic shock effects.Meteorit Planet Sci, 35(3): 545–560

[26] Stöffler D, Hamann C, Metzler K (2018). Shock metamorphism of planetary silicate rocks and sediments: Proposal for an updated classification system.Meteorit Planet Sci, 53(1): 5–49

[27] Tschauner O, Ma C, Beckett J R, Prescher C, Prakapenka V B, Rossman G R (2014). Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite.Science, 346(6213): 1100–1102

[28] Udry A, Wilbur Z E, Rahib R R, McCubbin F M, Vander Kaaden K E, McCoy T J, Ziegler K, Gross J, DeFelice C, Combs L, Turrin B D (2019). Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury.Meteorit Planet Sci, 54(4): 785–810

[29] Wang M S, Lipschutz M E (2005). Thermal metamorphism of primitive meteorites—XII. The enstatite chondrites revisited.Environ Chem, 2(3): 215

[30] Weisberg M K, Kimura M (2012). The unequilibrated enstatite chondrites.Chem Erde, 72(2): 101–115

RIGHTS & PERMISSIONS

The Author(s). Published by Higher Education Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0)