Petrophysical, mineralogical and chemical consequences of shock metamorphism of granitic rocks at the Kärdla crater, Estonia

Migmatite-rorming microdine-plagiodase granites occur 8l> neosorue wilhin a complex of mctamnrphic rocks of the basement. 11te granites have quile a stable mean chemical and mineralogical composition suitable for comparative studies. The SOO m deep crater formed in a 5hallow (20 m) marine environment in the about 100 m thick sedimcntary cover and underlying Precambrian crystalline basement. The trcnds of cha~s in chemistry (including systematic changes of K20INazO ratio), mineralogy, Ouid inclusion characteristics, and different petrophysical parameters of granites principally conform to each otber, demonstrating the gelleral compkx reWQrking of the whok composition of the impacted crater bottonl roeks and ai, rail breccias without any remarkable mclting of them. Mineralogical studies (including X-ray difractometry) have shown decomposition of plagioclase explaining the decrease of NazO con~ent and formation of micas and clay minerals as an evidence of pO!\~iblc K20 input.