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Fluid inclusions in microstructures of shocked quartz from the Keurusselkä impact site, Central Finland
Author(s) -
Poutiainen Matti,
Heikkilä Pasi
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.12128
Subject(s) - geology , quartz , geochemistry , hydrothermal circulation , chlorite , mineralogy , inclusion (mineral) , metamorphic rock , seismology , paleontology
Granitoid rock samples from the assumed center of the Keurusselkä impact site were subjected to a systematic study of fluid‐inclusion compositions and densities in various microstructures of the shocked quartz. The results are consistent with the following impact‐induced model of formation. After cessation of all major regional tectonic activity and advanced erosional uplift of the Fennoscandian shield, a meteorite impact (approximately 1.1 Ga) caused the formation of planar fractures ( PF s) and planar deformation features ( PDF s) and the migration of shock‐liberated metamorphic fluid (CO 2 ± H 2 O) to the glass in the PDF s. Postimpact annealing of the PDF s led to the formation of CO 2 (±H 2 O) fluid‐inclusion decorated PDF s. The scarce fluid‐inclusion implosion textures ( IP s) suggest a shock pressure of 7.6–10 GPa. The postimpact pressure release and associated heating initiated hydrothermal activity that caused re‐opening of some PF s and their partial filling by moderate‐salinity/high temperature (>200 °C) H 2 O (+ chlorite + quartz) and moderate‐density CO 2 . The youngest postimpact endogenic sub‐ and nonplanar microfractures ( MF s) are characterized by low‐density CO 2 and low‐salinity/low‐temperature (<200 °C) H 2 O.