Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena
Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.
- Research Organization:
- Texas A & M Univ., College Station, TX (United States)
- OSTI ID:
- 5549431
- Journal Information:
- Geology; (United States), Vol. 14:5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CRETACEOUS PERIOD
BOUNDARY CONDITIONS
INDONESIA
VOLCANIC ROCKS
TERTIARY PERIOD
DEFORMATION
ANIMALS
BIOLOGICAL EXTINCTION
GEOLOGIC HISTORY
MICROSTRUCTURE
PLANTS
STRESS ANALYSIS
STRESSES
TEXTURE
VOLCANOES
ASIA
CENOZOIC ERA
CRYSTAL STRUCTURE
DEVELOPING COUNTRIES
GEOLOGIC AGES
IGNEOUS ROCKS
ISLANDS
MESOZOIC ERA
ROCKS
580202* - Geophysics- Volcanology- (1980-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)