Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden
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Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden. / Holm-Alwmark, Sanna; Erickson, Timmons M.; Cavosie, Aaron J.
I: Geology, Bind 50, Nr. 3, 10.02.2022, s. 377-382.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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TY - JOUR
T1 - Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden
AU - Holm-Alwmark, Sanna
AU - Erickson, Timmons M.
AU - Cavosie, Aaron J.
PY - 2022/2/10
Y1 - 2022/2/10
N2 - 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 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.
AB - 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 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.
KW - DEFORMATION
KW - ZIRCON
KW - MICROSTRUCTURES
KW - MAGNETIZATION
KW - VREDEFORT
KW - BAROMETRY
KW - FEATURES
KW - SAMPLES
KW - QUARTZ
KW - ROCKS
U2 - 10.1130/G49498.1
DO - 10.1130/G49498.1
M3 - Journal article
VL - 50
SP - 377
EP - 382
JO - Geology
JF - Geology
SN - 0091-7613
IS - 3
ER -
ID: 291808161