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Revision and recalibration of existing shock classifications for quartzose rocks using low-shock pressure (2.5-20 GPa) recovery experiments and mesoscale numerical modeling

: Kowitz, A.; Güldemeister, N.; Schmitt, R.T.; Reimold, W.-U.; Wünnemann, K.; Holzwarth, A.


Meteoritics & planetary science 51 (2016), Nr.10, S.1741-1761
ISSN: 1086-9379
ISSN: 0026-1114
Fraunhofer EMI ()

A combination of shock recovery experiments and numerical modeling of shock deformation in the low-shock pressure range from 2.5 to 20 GPa for two dry sandstone types of different porosity, a completely water-saturated sandstone, and a well-indurated quartzite provides new insights into strongly heterogeneous distribution of different shock features. (1) For nonporous quartzo-feldspathic rocks, the traditional classification scheme (Stöffler 1984) is suitable with slight changes in pressure calibration. (2) For water-saturated quartzose rocks, a cataclastic texture (microbreccia) seems to be typical for the shock pressure range up to 20 GPa. This microbreccia does not show formation of PDFs but diaplectic quartz glass/SiO2 melt is formed at 20 GPa (~1 vol%). (3) For porous quartzose rocks, the following sequence of shock features is observed with progressive increase in shock pressure (1) crushing of pores, (2) intense fracturing of quartz grains, and (3) increasing formation of diaplectic quartz glass/SiO2 melt replacing fracturing. The formation of diaplectic quartz glass/SiO2 melt, together with SiO2 high-pressure phases, is a continuous process that strongly depends on porosity. This experimental observation is confirmed by our concomitant numerical modeling. Recalibration of the shock classification scheme results in a porosity versus shock pressure diagram illustrating distinct boundaries for the different shock stages.