CO₂ release due to impact devolatilization of carbonate: Results of shock experiments

Abstract

Abstract-A study of pure, single crystal calcite shocked to pressures from 9.0 to 60.8 GPa was conducted to address contradictory data for carbonate shock behavior. The recovered materials were analyzed optically and by transmission electron microscopy (TEM), as well as by thermogravimetry (TGA), X-ray diffraction (XRD), and Raman-spectroscopy. In thin section, progressive comminution of calcite is observed although grains remain birefringent to at least 60.8 GPa. TGA analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure (R = 0.77) and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range. XRD patterns of shocked Iceland spar samples produce peaks that are qualitatively and quantitatively less intense, more diffuse, and shift to lower o 2h. However, the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60.8 GPa. Raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening. TEM micrographs display progressively diminishing crystallite domain sizes. Selected area electron diffraction (SAED) patterns reveal no signatures of amorphous material. These data show that essentially intact calcite is recovered at shock pressures up to 60.8 GPa with only slight mass loss (~7%). This work suggests that the amount of CO 2 gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been (substantially) overestimated.

Shock metamorphism of planetary silicate rocks and sediments: Proposal for an updated classification system

“…; Hörz et al. ; Bell ). Although frequently studied in shock recovery experiments, no consensus has been reached so far regarding the onset or even nature of specific shock effects in carbonates.…”

“…This is illustrated in particular by disagreeing estimates for the shock pressure threshold that governs the onset of calcite decomposition or melting in experiments (see summaries in Osinski et al. ; Bell ), or by conflicting studies regarding the existence of carbonate impact melts in the impactites from Ries (Graup ; Osinski ; Stöffler et al. ) or Barringer Crater (Hörz et al.…”

The reaction of carbonates in contact with laser‐generated, superheated silicate melts: Constraining impact metamorphism of carbonate‐bearing target rocks

“…; Kurosawa et al. ; Bell ), (2) petrologic studies of impactites from terrestrial impact structures (Martinez et al. ; Graup ; Osinski and Spray ; Osinski et al.…”

“…So far, experiments with carbonates yielded contrasting results, illustrated in particular by disagreeing estimates for the shock pressure threshold that governs the onset of calcite decomposition (see summaries in Osinski et al. ; Bell ). Although different experimental techniques were used, these pressure estimates range from as low as some 20 GPa (e.g., Lange and Ahrens ; Kurosawa et al.…”

Researching the Earth—and a Few of Its Neighbors

“…More generally, the role of melting and devolatilization has been discussed and debated by Osinski et al (2008), Hörz et al (2015), and Bell (2016). Howard (2011) invoked volatiles in the shallow crust to enhance the dispersal of impact melts as tektites.…”