Sanna Alwmark
Biträdande universitetslektor
Estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz-Sources of error and recommendations
Författare
Summary, in English
Planar deformation features (PDFs) in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks. They can also be used for estimating average shock pressures that quartz-bearing rocks have been subjected to. Here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of PDF orientations in quartz. These include a comparison between manual and automated methods of indexing PDFs, an evaluation of the new stereographic projection template, and observations regarding the PDF statistics related to the c-axis position and rhombohedral plane symmetry. We further discuss the implications that our findings have for shock barometry studies. Our study shows that the currently used stereographic projection template for indexing PDFs in quartz might induce an overestimation of rhombohedral planes with low Miller-Bravais indices. We suggest, based on a comparison of different shock barometry methods, that a unified method of assigning shock pressures to samples based on PDFs in quartz is necessary to allow comparison of data sets. This method needs to take into account not only the average number of PDF sets/grain but also the number of high Miller-Bravais index planes, both of which are important factors according to our study. Finally, we present a suggestion for such a method (which is valid for nonporous quartz-bearing rock types), which consists of assigning quartz grains into types (A-E) based on the PDF orientation pattern, and then calculation of a mean shock pressure for each sample.
Avdelning/ar
- Berggrundsgeologi
Publiceringsår
2018-01
Språk
Engelska
Sidor
110-130
Publikation/Tidskrift/Serie
Meteoritics and Planetary Science
Volym
53
Issue
1
Dokumenttyp
Artikel i tidskrift
Förlag
Wiley-Blackwell
Ämne
- Geology
Aktiv
Published
ISBN/ISSN/Övrigt
- ISSN: 1086-9379