Experimentelle und Analytische Planetologie
Stoßwelleneffekte in Sulfaten: Natur - Experiment - Modellierung
One of the widely accepted killing mechanisms of the KT biota includes global atmosphere and hydrosphere
deterioration by the shock-induced release of SOx gases from sulfate-bearing target sequences of the
Chicxulub impact crater. The decomposition of anhydrite is currently inferred mainly from thermodynamic
considerations and lacks systematic experimental confirmation. In addition only a limited amount of data is
available on the shock behavior of anhydrite. Therefore we have conducted an experimental study on the solid-state
shock behavior of anhydrite. Starting material consisting of massive polycrystalline anhydrite was shock-loaded by
the multiple reverberation method at the NASA-JSC. Peak shock pressures range from 4 to 64 GPa. Recovered
samples were examined by optical microscopy, scanning (SEM) and transmission electron microscopy (TEM), and
X-ray powder diffraction.
Numerous defects are produced in target
material in response to shock compression and/or release. These include twinning, dislocations and melting. The
unit-cell dimensions vary by less than 0.15 rel.% over the studied range of shock pressures. Neither high-pressure
polymorphs nor decomposition products were found. Melting suggests that complete devolatilization proposed by
several models is not necessarily a major process, even at very high shock pressures. Melting as an important process
of response of anhydrite to shock compression during cratering is also supported by recent thermodynamic
calculations. The newly developed
techniques for shock experiments with high-explosive set-ups (100 GPa; T=900 K), are in addition used to simulate
successfully shock- and post-effects in the central uplift of the world's oldest and largest impact structure, Vredefort,
South Africa.
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