Discovery of Naturally Etched Fission Tracks and Alpha-Recoil Tracks in Submarine Glasses: Reevaluation of a Putative Biosignature for Earth and Mars

Figure 8

Petrographic and SEM study of white (K-Al-Si)-rich devitrified zones (in thin section). (a–f) Photomicrographs in plane polarized light, highlighting development of “lip-shaped” (K-Al-Si)-rich devitrified zones along late (f₂) fractures (a–c), as well as halos around some plagioclase crystals (d–f). (a, b): sample DSDP-418A-75-3[120–123]; (d, e): sample DSDP-418A-68-3[40–43]; (c, f): sample DSDP-418A-72-4[13–15]. (g–i) SEM (BSE) images of a polished thin section of sample DSDP-418A-68-3[40–43], highlighting white (K-Al-Si)-rich devitrified zones. Note: palagonitization of basaltic glass along early (f₁) fractures (a, d, g, and h) and the stepwise/punctuated “cracking” of basaltic glass (from through in (g, h) and from f₁ through f₂ in (a, d, g, and h)), inferred based on the pattern of termination of successively younger fractures against older ones. (j) SEM EDS spectra for white (K-Al-Si)-rich devitrified zones (see petrographic context in (a, i)), showing abundant Si, Al, and K—consistent with microcrystalline K-feldspar ± quartz or cristobalite. cf: corrosion front; D: white (K-Al-Si)-rich devitrified zones; f₁ (including ): early fractures along which palagonite is rooted; f₂: late fractures along which white (K-Al-Si)-rich devitrified zones are rooted; FG: fresh basaltic glass; GP: granular palagonite ART alteration; gt: minor granular corrosion texture associated with devitrified zones; H: halos of white (K-Al-Si)-rich devitrified zones around plagioclase; ip: initial palagonite; P: palagonite; plg: plagioclase.

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