Record details

Title
    The recognition of terrestrial impact structures
Statement of responsibility
    Ann M. Therriault, Richard A. F. Grieve, Mark Pilkington
Author
    Grieve, Richard A. F.
    Pilkington, Mark
    Therriault, Ann M.
Language
    anglicky
Source title - serial
    Věstník Českého geologického ústavu (Bulletin of the Czech Geological Survey)
Vol./nr.
    Roč. 77, č. 4
Pages
    s. 253-263
Year
    2002
Notes
    2 obr., 8 fot., 3 s. bibl.
    il.
    Zkr. název ser.: Věst. Čes. geol. Úst. (Bull. Czech geol. Surv.)
Subject group
    anomálie geofyzikální
    impaktní struktura
    jevy šokové
    metamorfóza šoková
    planeta Země
    sklo přírodní
    tavení
Geographical name
    Svět
    Země
Keyword
    Impact
    Recognition
    Structures
    Terrestrial
Abstract (in english)
   The Earth is the most endogenically active of the terrestrial planets and, thus, has retained the poorest sample of impacts that have occurred throughout geological time. The current known sample consists of approximately 160 impact structures or crater fields. Approximately 30 per cent of known impact structures are buried and were initially detected as geophysical anomalies and subsequently drilled to provide geologic samples. The recognition of terrestrial impact structures may, or may not, come from the discovery of an anomalous quasi-circular topographic, geologic or geophysical feature. In the geologically active terrestrial environment, anomalous quasi-circular features, however, do not automatically equate with an impact origin. Specific samples must be acquired and the occurrence of shock metamorphism, or, in the case of small craters, meteoritic fragments, must be demonstrated before an impact origin can be confirmed.
   Shock metamorphism is defined by a progressive destruction of the original rock and mineral structure with increasing shock pressure. Peak shock pressures and temperatures produced by an impact event may reach several hundreds of gigaPascals and several thousand degrees Kelvin, which are far outside the range of endogenic metamorphism. In addition, the application of shock-wave pressures is both sudden and brief. Shock metamorphic effects result from high strain rates, well above the rates of normal tectonic processes. The well-characterized and documented shock effects in quartz are unequivocal indicators and are the most frequently used indicator for terrestrial impact structures and lithologies
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    28. 3. 2008
Import date
    8. 8. 2012