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TitleMineralogy and petrology of melt rocks from the Popigai impact structure, Siberia
AuthorWhitehead, J; Grieve, R A F; Spray, J G
SourceMeteoritics and Planetary Science vol. 37, no. 5, 2002 p. 623-647, Open
Access logo Open Access
Alt SeriesGeological Survey of Canada, Contribution Series 2001099
Mediapaper; on-line; digital
File formatpdf
AreaSiberia; Popigai River; Russian Federation
Lat/Long WENS 109.0000 113.0000 72.5000 71.5000
Subjectsmineralogy; igneous and metamorphic petrology; extraterrestrial geology; geochemistry; craters; meteorite craters; structural analyses; structural features; Eocene; crystallization; electron microscopy; metamorphism, shock; trace element geochemistry; major element geochemistry; geochemical analyses; radiometric dating; Archean; Popigai Impact Structure; Cenozoic; Precambrian; Proterozoic
Illustrationslocation maps; geological sketch maps; profiles; tables; photomicrographs; ternary diagrams; box plots; images; plots; graphs; charts
Released2002 05 01
AbstractThe late Eocene Popigai impact structure of Siberia comprises an approximately 0.5-1.5 km thick, ~ 100 km diameter sequence of clast-rich and clast-poor andesitic to rhyolitic impact melt rocks and impact breccias, underlain by Archean to Proterozoic crystalline basement and Proterozoic to Phanerozoic sedimentary rocks. The fine-grained to cryptocrystalline texture of the more melt-rich rocks, despite their occurrence in bodies locally in excess of 800 m thick and 28 km long, suggests that the melt crystallized in response to (1) cooling by the clast load, and/or; (2) rapid nucleation on finely brecciated clasts, which have since been assimilated and/or; (3) crystallization enhanced by the relatively low water contents of the melts. Rapid crystallisation of the melt is indicated by the lack of zoning in minerals, the presence of glass, the lack of strain recovery features in clasts and the lack of evidence for fractionation in the major and trace elements, including the rare earth elements. Optical and analytical electron microscopy reveal that the previously reported division of the melt rocks into high- and low-temperature variants based on hand sample appearance, or glass content, is not warranted.
Clasts within the melt-rich rocks exhibit a wide range of shock metamorphic features, though they are not distributed in the impact melts in a systematic manner. This indicates that the melt-rich rocks were well mixed during their formation, thus juxtaposing unshocked with shocked material. Injection of mesostasis melt into partially melted checkerboard plagioclase and orthopyroxene clasts also occurred during this mixing stage.

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