Sanna Alwmark
Biträdande universitetslektor
Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden
Författare
Summary, in English
Little is known about the microstructural behavior of magnetite during hypervelocity impact events, even though it is a widespread accessory mineral and an important magnetic carrier in terrestrial and extraterrestrial rocks. We report systematic electron backscatter diffraction crystallographic analysis of shock features in magnetite from a transect across the 52-km-diameter ca. 380 Ma Siljan impact structure in Sweden. Magnetite grains in granitoid samples contain brittle fracturing, crystal-plasticity, and lamellar twins. Deformation twins along {111} with shear direction of <112> are consistent with spinel-law twins. Inferred bulk shock pressures for the investigated samples, as constrained by planar deformation features (PDFs) in quartz and shock twins in zircon, range from 0 to 20 GPa; onset of shock-induced twinning in magnetite is observed at >5 GPa. These results highlight the utility of magnetite to record shock deformation in rocks that experience shock pressures >5 GPa, which may be useful in quartz-poor samples. Despite significant hydrothermal alteration and the variable transformation of host magnetite to hematite, shock effects are preserved, which demonstrates that magnetite is a reliable mineral for preserving shock deformation over geologic time.
Avdelning/ar
- Berggrundsgeologi
Publiceringsår
2022
Språk
Engelska
Sidor
377-382
Publikation/Tidskrift/Serie
Geology
Volym
50
Issue
3
Dokumenttyp
Artikel i tidskrift
Förlag
Geological Society of America
Ämne
- Geology
Aktiv
Published
ISBN/ISSN/Övrigt
- ISSN: 0091-7613