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Petrography of impact glasses and melt breccias from the El'gygytgyn impact structure, Russia
Author(s) -
Pittarello Lidia,
Koeberl Christian
Publication year - 2013
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12048
Subject(s) - impact crater , petrography , geology , breccia , impact structure , geochemistry , ejecta , melt inclusions , volcano , shock metamorphism , rhyolite , pyroclastic rock , basalt , inclusion (mineral) , volcanic rock , mineralogy , astrobiology , physics , quantum mechanics , supernova
The El'gygytgyn impact structure, 18 km in diameter and 3.6 Ma old, in Arctic Siberia, Russia, is the only impact structure on Earth mostly excavated in acidic volcanic rocks. The Late Cretaceous volcanic target includes lavas, tuffs, and ignimbrites of rhyolitic, dacitic, and andesitic composition, and local occurrence of basalt. Although the ejecta blanket around the crater is nearly completely eroded, bomb‐shaped impact glasses, redeposited after the impact event, occur in lacustrine terraces within the crater. Here we present detailed petrographic descriptions of newly collected impact glass‐bearing samples. The observed features contribute to constrain the formation of the melt and its cooling history within the framework of the impact process. The collected samples can be grouped into two types, characterized by specific features: (1) “pure” glasses, containing very few clasts or new crystals and which were likely formed during the early stages of cratering and (2) a second type, which represents composite samples with impact melt breccia lenses embedded in silicate glass. These mixed samples probably resulted from inclusion of unmelted impact debris during ejection and deposition. After deposition the glassy portions continued to deform, whereas the impact melt breccia inclusions that probably had already cooled down behaved as rigid bodies in the flow.