scholarly journals Shock deformation in zircon grains from the Mien impact structure, Sweden

2021 ◽  
Vol 56 (2) ◽  
pp. 362-378
Author(s):  
Josefin Martell ◽  
Carl Alwmark ◽  
Sanna Holm‐Alwmark ◽  
Paula Lindgren
Keyword(s):  
Impact Structure ◽  
Shock Deformation

Shock deformation microstructures in xenotime from the Spider impact structure, Western Australia

2021 ◽  
Author(s):  
Morgan A. Cox ◽  
Aaron J. Cavosie ◽  
Michael Poelchau ◽  
Thomas Kenkmann ◽  
Phil A. Bland ◽  
...  
Keyword(s):  
Western Australia ◽  
Impact Structure ◽  
High Angle ◽  
Deformation Bands ◽  
Stress Regime ◽  
Shock Deformation ◽  
Deformation Twins ◽  
Formation Conditions ◽  
Shatter Cones ◽  
Micro Structures

ABSTRACT The rare earth element–bearing phosphate xenotime (YPO4) is isostructural with zircon, and therefore it has been predicted that xenotime forms similar shock deformation microstructures. However, systematic characterization of the range of micro structures that form in xenotime has not been conducted previously. Here, we report a study of 25 xenotime grains from 10 shatter cones in silicified sandstone from the Spider impact structure in Western Australia. We used electron backscatter diffrac tion (EBSD) in order to characterize deformation and microstructures within xenotime. The studied grains preserve multiple sets of planar fractures, lamellar {112} deformation twins, high-angle planar deformation bands (PDBs), partially recrystallized domains, and pre-impact polycrystalline grains. Pressure estimates from micro structures in coexisting minerals (quartz and zircon) allow some broad empirical constraints on formation conditions of ~10–20 GPa to be placed on the observed microstructures in xenotime; at present, more precise formation conditions are unavailable due to the absence of experimental constraints. Results from this study indicate that the most promising microstructures in xenotime for recording shock deformation are lamellar {112} twins, polycrystalline grains, and high-angle PDBs. The {112} deformation twins in xenotime are likely to be a diagnostic shock indicator, but they may require a different stress regime than that of {112} twinning in zircon. Likewise, polycrystalline grains are suggestive of impact-induced thermal recrystallization; however, in contrast to zircon, the impact-generated polycrystalline xenotime grains here appear to have formed in the solid state, and, in some cases, they may be difficult to distinguish from diagenetic xenotime with broadly similar textures.

scholarly journals Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden

Geology ◽  
2021 ◽  
Author(s):  
Sanna Holm-Alwmark ◽  
Timmons M. Erickson ◽  
Aaron J. Cavosie
Keyword(s):  
Electron Backscatter Diffraction ◽  
Crystallographic Analysis ◽  
Hypervelocity Impact ◽  
Accessory Mineral ◽  
Shear Direction ◽  
Impact Structure ◽  
Shock Deformation ◽  
Deformation Features ◽  
Backscatter Diffraction ◽  
Impact Events

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.

Asymmetric shock deformation at the Spider impact structure, Western Australia

2021 ◽  
Author(s):  
Morgan A. Cox ◽  
Aaron J. Cavosie ◽  
Michael H. Poelchau ◽  
Thomas Kenkmann ◽  
Katarina Miljković ◽  
...  
Keyword(s):  
Western Australia ◽  
Impact Structure ◽  
Shock Deformation ◽  
Asymmetric Shock

Effect of Shock Loading on the Microstructure of Uniloy 326

1974 ◽  
Vol 32 ◽  
pp. 504-505
Author(s):  
K. P. Staudhammer ◽  
L. E. Murr
Keyword(s):  
Grain Size ◽  
Shock Loading ◽  
Current Investigation ◽  
Two Phase ◽  
05 C ◽  
Shock Deformation ◽  
Heat Treated

The effect of shock loading on a variety of steels has been reviewed recently by Leslie. It is generally observed that significant changes in microstructure and microhardness are produced by explosive shock deformation. While the effect of shock loading on austenitic, ferritic, martensitic, and pearlitic structures has been investigated, there have been no systematic studies of the shock-loading of microduplex structures.In the current investigation, the shock-loading response of millrolled and heat-treated Uniloy 326 (thickness 60 mil) having a residual grain size of 1 to 2μ before shock loading was studied. Uniloy 326 is a two phase (microduplex) alloy consisting of 30% austenite (γ) in a ferrite (α) matrix; with the composition.3% Ti, 1% Mn, .6% Si,.05% C, 6% Ni, 26% Cr, balance Fe.

Sign in / Sign up

Export Citation Format

Share Document