scholarly journals Variations in shock deformation at the Slate Islands Impact Structure, Lake Superior, Canada

1977 ◽  
Vol 61 (1) ◽  
pp. 107-107 ◽  
Author(s):  
R. A. F. Grieve ◽  
P. B. Robertson
Keyword(s):  
Lake Superior ◽  
Impact Structure ◽  
Shock Deformation

Variations in shock deformation at the Slate Islands impact structure, Lake Superior, Canada

1976 ◽  
Vol 58 (1) ◽  
pp. 37-49 ◽  
Author(s):  
Richard A. F. Grieve ◽  
P. Blyth Robertson
Keyword(s):  
Lake Superior ◽  
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.

Slate Islands, Lake Superior, Canada: A mid-size, complex impact structure

1999 ◽  
Author(s):  
Burkhard O. Dressler ◽  
Virgil L. Sharpton ◽  
P. Copeland
Keyword(s):  
Lake Superior ◽  
Impact Structure

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

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

Micro-Shock Deformation adjacent to the Surface of Shatter Cones from the Beaverhead Impact Structure, Montana

1996 ◽  
Vol 104 (2) ◽  
pp. 233-238 ◽  
Author(s):  
R. B. Hargraves ◽  
J. C. White
Keyword(s):  
Impact Structure ◽  
Shock Deformation ◽  
Shatter Cones

THERMOCHRONOLOGICAL INSIGHTS ON THE TIMING OF THE SLATE ISLANDS IMPACT STRUCTURE, LAKE SUPERIOR, CANADA

2018 ◽  
Author(s):  
Andrew F. Parisi ◽  
◽  
Elizabeth J. Catlos ◽  
Michael Brookfield ◽  
Daniel P. Miggins
Keyword(s):  
Lake Superior ◽  
Impact Structure

The Slate Islands: a probable complex meteorite impact structure in Lake Superior

1976 ◽  
Vol 13 (9) ◽  
pp. 1301-1309 ◽  
Author(s):  
H. C. Halls ◽  
R. A. F. Grieve
Keyword(s):  
Country Rock ◽  
Lake Superior ◽  
Impact Structure ◽  
Early Paleozoic ◽  
Meteorite Impact ◽  
Erosion Level ◽  
Igneous Activity ◽  
Shatter Cones ◽  
Host Rocks ◽  
Sedimentary Unit

Shock metamorphic effects in samples from the Slate Islands, Lake Superior (48°40' N, 87°00' W) suggest that the islands are part of a meteorite impact structure. The islands form the central uplift of a complex crater and are ringed by a submerged trough and annular ridge with a diameter of 30 km. Precambrian bedrock units are locally brecciated and cut by allochthonous breccia dikes. These dikes contain clasts of identifiable country rock and also fragments of a sedimentary unit, possibly Upper Keweenawan in age, which is no longer present in outcrop. The orienta tions of shatter-cones present in the breccia host-rocks indicate the interior of the islands as the approximate shock centre. Microscopic planar features, equivalent to those described from other impact sites, occur in quartz and plagioclase and the level of shock deformation increases towards the interior of the islands. The shock event postdates Keweenawan igneous activity (about 1.1 b.y. old) and, on the basis of the erosion level, may be early Paleozoic in age.

scholarly journals Exceptional preservation of reidite in the Rochechouart impact structure, France: New insights into shock deformation and phase transition of zircon

2021 ◽  
Author(s):  
Anders Plan ◽  
Gavin G. Kenny ◽  
Timmons M. Erickson ◽  
Paula Lindgren ◽  
Carl Alwmark ◽  
...  
Keyword(s):  
Phase Transition ◽  
Impact Structure ◽  
Exceptional Preservation ◽  
Shock Deformation
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