Research ArticlePLANETARY SCIENCE

Boom boom pow: Shock-facilitated aqueous alteration and evidence for two shock events in the Martian nakhlite meteorites

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Science Advances  04 Sep 2019:
Vol. 5, no. 9, eaaw5549
DOI: 10.1126/sciadv.aaw5549
  • Fig. 1 Distribution of deformation and aqueous alteration in MIL 03346.

    (A) Transmitted light image of the MIL 03346 thin section. The dominant augite phenocrysts impart the green color, whereas mesostasis is black. Areas where the mesostasis has been altered are red brown, and they correlate with the location of the deformed regions in (B). The black box indicates the area analyzed by EBSD in (B) to (D). (B) GROD angle EBSD map showing that deformation occurs in regions ~2 mm in size that are separated by 1- to 3-mm undeformed areas. Undeformed crystals are shown in blue, whereas increasing internal deformation is highlighted by a progression of green through yellow to red. (C) Band contrast EBSD map showing diminished band contrast [lower electron backscatter pattern (EBSP) quality] as darker regions that correlate with the deformed regions of (B). The blue polygons indicate the location of areas of altered mesostasis, which also correlate with deformed regions in (B). The red dashed line is the orientation of the foliation described by Daly et al. (4). The white box and labels indicate the sites where high-resolution backscattered electron (BSE) images and energy dispersive x-ray spectroscopy (EDS) images were acquired for Fig. 5 (A to C). (D) Inverse pole figure map highlighting the distribution of twinned augite crystals. Mechanical twins, whose boundaries are shown as yellow lines, occur exclusively within the deformed areas of (B). Simple twin boundaries are shown as white lines and occur throughout the sample. See fig. S3 for a high-resolution version of this image.

  • Fig. 2 Distribution of deformation and aqueous alteration in Lafayette.

    (A) Transmitted light image of the thin section. The dominant augite phenocrysts impart the green color. Areas where the mesostasis has been altered are red brown, and they correlate with the location of the deformed regions in (B). The black box indicates the area analyzed by EBSD in (B) to (D). (B) GROD angle EBSD map showing that deformation occurs in regions ~2 mm in width with undeformed areas between 1 and 3 mm in size. Undeformed crystals are shown in blue, whereas increasing internal deformation is highlighted by a progression of greens through yellow to red. (C) Band contrast EBSD map showing diminished band contrast (lower EBSP quality) as darker regions that correlate with the deformed regions of (A). The blue polygons indicate the location of altered mesostasis, which correlates with deformed regions in (B). The red dashed line is the orientation of the foliation described by Daly et al. (4). The white box and labels indicate the sites where high-resolution BSE images and EDS images acquired for Fig. 5 (D to H). The yellow box indicates the region of Lafayette modeled in the numerical simulation in (E). (D) Inverse pole figure map highlighting the distribution of twinned augite. Mechanical twins, whose boundaries are shown as yellow lines, occur exclusively in the vicinity of the deformed regions of (B). Simple twin boundaries are shown as white lines and occur throughout the sample. See fig. S4 for a high-resolution version of this image. (E) Results from numerical simulation of the local pressure distribution from the passage of a 10-GPa horizontal compressive (left) and horizontal tensile (right) shock wave. The modeled area of Lafayette highlighted in (C). High-pressure spikes are associated with regions of high mesostasis abundance (black polygons); high-pressure loci are associated with mesostasis-phenocryst contacts. The pattern of deformation mirrors the foliation (red dashed line) and regions of abundant shock-related deformation [high GROD, fracturing, and (100) twinning] in Lafayette.

  • Fig. 3 Microstructures of undeformed areas exhibiting simple twinning and no lattice bending.

    High-resolution (0.5- to 1.5-μm step size) EBSD Euler maps of different simple mirror twin varieties in Lafayette augite phenocrysts. (A) Simple mirror twins parallel to (100). Insets are three-dimensional (3D) representations of the twins. (B) Complex variety of simple twinning parallel to (100). In all maps, simple and mechanical twins are highlighted by yellow and red lines, respectively.

  • Fig. 4 Microstructural characteristics of deformed areas including shock-related mechanical twinning, continuous crystal lattice bending, and high frequency of fractures.

    High-resolution (0.5- to 1.5-μm step size) EBSD maps of Lafayette. (A) Euler map of a typical mechanical twin parallel to (001). The inset shows the 3D representation of the twins. (B) Euler map of chevron-like mechanical twinning parallel to (001) developed in an augite phenocryst with preexisting mirror twinning. (C) Euler map of mechanical twins that are discontinuous/displaced by fractures. (D) Euler image of bent mechanical twins. (E) Texture component map of the same area imaged in (D) indicating that the deformation in both the twin and the crystal is related to continuous crystal plastic deformation. The colors represent increasing degrees of misorientation away from the + symbol. Simple twins and mechanical twins are highlighted by yellow and red lines, respectively.

  • Fig. 5 The nature and distribution of mesostasis alteration within Lafayette and MIL 03346 meteorites.

    BSE and EDS images of mesostasis alteration in Lafayette (A to F) and MIL 03346 (G to I). (A) BSE image of an area that contains both pristine and altered mesostasis. Augite is mid-gray, olivine (Ol) is white, orthopyroxene (Opx) is light gray, and pristine mesostasis is dark gray. (B) Al Kα x-ray map of (A). Areas of pristine mesostasis are white as they have retained Al. Mesostasis in the middle and upper right of the field of view has been altered with loss of Al. (C) BSE image of an area of mesostasis surrounded by augite (Aug) that has been completely altered to siderite (Sd) and phyllosilicate. (D) Si Kα x-ray map of (C). Phyllosilicate is light gray, and siderite (Sd) is black. (E) Ca Kα x-ray map of (C). Siderite (Sd) is light gray, and phyllosilicate is black. (F) A representative vein of alteration products in olivine (Ol) comprising siderite (Sd) that is crosscut by bands and rosettes of phyllosilicate (Phy). (G) An area containing pristine mesostasis (Mes) with fayalite laths (Fa) that is juxtaposed with altered mesostasis containing hematite (Hem, white), the low-Z phase (dark gray), and high-Z phase (light gray). Grains of augite (Aug) are unaltered. (H) An area of altered mesostasis containing grains of hematite (Hem, white) that are rimmed by bands of the low-Z phase (dark gray) and high-Z phase (light gray). (I) An area of pristine mesostasis (Mes) containing glass (dark gray) and titanomagnetite (TiM) crystals (white). Unaltered grains of augite (Aug) and an olivine (Ol) grain that is host to several veins of iddingsite (mid-gray) are also shown. Parts of the olivine grain that have a lower Z may be laihunite (Lh).

  • Table 1 Chemical compositions of the alteration assemblages in MIL 03346 in weight % (wt %) ± 1 SD.

    Olivine-hosted
    iddingsite
    Mesostasis alteration products
    Low-ZHigh-ZHematite
    Na2O0.17 ± 0.060.38 ± 0.240.43 ± 0.200.06 ± 0.08
    MgO3.26 ± 0.143.27 ± 0.400.83 ± 0.700.11 ± 0.09
    Al2O31.35 ± 0.563.50 ± 0.591.29 ± 0.660.91 ± 0.25
    SiO245.53 ± 1.2746.09 ± 1.4320.06 ± 5.121.02 ± 0.98
    S0.23 ± 0.060.28 ± 0.071.14 ± 0.490.03 ± 0.13
    K2O0.08 ± 0.070.28 ± 0.210.05 ± 0.070.01 ± 0.04
    CaO0.12 ± 0.100.16 ± 0.240.57 ± 0.430.24 ± 0.24
    TiO20.07 ± 0.070.04 ± 0.070.04 ± 0.073.01 ± 1.38
    MnO0.54 ± 0.080.40 ± 0.070.81 ± 0.670.07 ± 0.13
    FeO32.63 ± 1.0830.11 ± 1.4553.89 ± 2.4887.13 ± 2.16*
    Total83.98 ± 1.5684.51 ± 1.6579.11 ± 4.1892.59 ± 0.70
    n17291841

    *96.81 wt % as Fe2O3, giving a total of 102.28 wt %.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaaw5549/DC1

      Fig. S1. Figures of the numerical impact model run at different angles of the principal stress axis and the anisotropy of the microstructures, i.e., the foliation and mesostasis-phenocryst distribution.

      Fig. S2. Representation of the numerical mesh used for the simulations shown.

      Fig. S3. High-resolution inverse pole figure map of MIL 03346 highlighting the distribution of twinned augite crystals.

      Fig. S4. High-resolution inverse pole figure map of Lafayette highlighting the distribution of twinned augite crystals.

    • Supplementary Materials

      This PDF file includes:

      • Fig. S1. Figures of the numerical impact model run at different angles of the principal stress axis and the anisotropy of the microstructures, i.e., the foliation and mesostasis-phenocryst distribution.
      • Fig. S2. Representation of the numerical mesh used for the simulations shown.
      • Fig. S3. High-resolution inverse pole figure map of MIL 03346 highlighting the distribution of twinned augite crystals.
      • Fig. S4. High-resolution inverse pole figure map of Lafayette highlighting the distribution of twinned augite crystals.

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