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Project III

Microscale shock processes in sandstone

continuation of TP-7 

Project director:

Reimold, Wolf Uwe, Berlin
Schmitt, Ralf Thomas, Berlin
Langenhorst, Falko, Jena

Research staff:

Astrid Kowitz (PhD student, MfN Berlin)

Summary

Within the Multidisciplinary Experimental and Modelling Impact Research Network (MEMIN) this project focuses on micro- to nanoscale shock effects in porous sandstone and quartzite. Some topics of the previous project “Low-grade shock metamorphism of quartz in porous and wet sedimentary target rocks” will be extended within this project to include the (i) study of the influence of water saturation on the calibration and classification of progressive shock metamorphism in sandstone, and (ii) an application of the newly developed shock calibration and classification system for porous, quartz-rich lithologies to the natural impact craters BP, Oasis (both located in Lybia) and Santa Marta (Brazil) formed in sandstone targets. The major focus of this project is to address some specific questions regarding the formation of selected shock features in quartz: (a) The formation of planar deformation features (PDF) in quartz and the relationship to host crystal orientation will be investigated on experimentally shocked sandstone and quartzite samples. Especially the dependence of PDF formation with respect to the target quartz orientation has previously been insufficiently investigated for experimentally as well as naturally shocked samples, but might be of great importance for the verification of the existing models of PDF formation. (b) Dauphiné and Brazil twinning in quartz can be induced by high shear stresses in impact events. Experimentally shocked samples will be analyzed to unravel whether twinning can be used as a diagnostic shock indicator and barometer for quartz-bearing rocks in the low-pressure regime. This study is the first experimental attempt to understand the role and significance of mechanical twinning in shocked quartz. Additionally a pilot study for the investigation of localized shock melting in this system is proposed. Shock-melting of quartz at extremely high temperatures as indicated by the associated melting of rutile was observed in the shock recovery experiments in localized fracture zones associated with shearing. This experimentally generated melt is possibly an analog to naturally occurring thin pseudotachylitic breccia veins in impact craters.