Record details

Title
    Shock metamorphism of some minerals: Basic introduction and microstructural observations
Statement of responsibility
    Falko Langenhorst
Author
    Langenhorst, Falko
Language
    anglicky
Source title - serial
    Věstník Českého geologického ústavu (Bulletin of the Czech Geological Survey)
Vol./nr.
    Roč. 77, č. 4
Pages
    s. 265-282
Year
    2002
Notes
    8 obr., 5 fot., 1 tab., 4 s. bibl.
    il.
    Zkr. název ser.: Věst. Čes. geol. Úst. (Bull. Czech geol. Surv.)
Subject group
    jevy šokové
    krystalová struktura
    Měsíc
    metamorfóza šoková
    minerály
    planeta Země
    studie experimentální
Geographical name
    Země
Keyword
    Basic
    Introduction
    Metamorphism
    Microstructural
    Minerals
    Observations
    Shock
Abstract (in english)
   Minerals show a unique behaviour when subjected to shock waves. The ultradynamic loading to high pressures and temperatures causes deformation, transformation and decomposition phenomena in minerals that are unequivocal indicators of impact events. This paper introduces into the basics of shock compression, required to understand the formation and experimental calibration of these shock effects in minerals, and particularly focuses on the recent advances in the field of shock metamorphism achieved by the application of transmission electron microscopy (TEM). TEM studies underline that the way minerals respond to shock compression largely depends on their crystal structures and chemical compositions, as is illustrated here on the basis of four minerals: quartz, olivine, graphite and calcite.
   The crystal structure of a mineral exerts an important control on the shock-induced deformation phenomena, comprising one- to two-dimensional lattice defects, such as dislocations, mechanical twins, planar fractures, and amorphous planar deformation lamellae. For example, dislocations cannot be activated in quartz due to the strong covalent bonding, whereas the island silicate olivine easily deforms by dislocation glide. Transformation phenomena include phase transitions to (diaplectic) glass and/or high-pressure polymorphs. TEM studies reveal that high-pressure polymorphs such as coesite, stishovite and ringwoodite are liquidus phases, which form upon decompression by crystallization from high-pressure melts. The graphite-to-diamond transition is however a rare example for a solid-state transformation, taking place by a martensitic shear mechanism.
   Shock-induced decomposition reactions are typical of volatile-bearing minerals and liberate toxic gases that, in case of large impacts, may affect Earth's climate. Shock experiments show that degassing of calcite does not take place under high pressure but can massively occur after decompression if the post-shock temperature is sufficiently high. A recombination reaction happens however if CaO and CCh are not physically separated
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    28. 3. 2008
Import date
    8. 8. 2012