Datowanie apatytów z żył kwarcowo-chlorytowo-apatytowych w fyllitach z Podmąchocic (Góry Świętokrzyskie)
Abstract
Dating of apatites from the quartz-chlorite-apatite veins in phyllites from Podmąchocice (Holy Cross Mountains).
A b s t r a c t. Metamorphic rocks of greenstone facies (phyllites) have been discovered quite recently in the Łysogóry region of the Holy Cross Mountains. The following minerals predominate in the mineral composition of these rocks: bright mica (sericite), quartz, chlorites, rutile, pyrophyllite, xenotime, pyrite, tourmaline, apatite and monacite, while chalcopyrite, sphalerite and galena are also present in mineral veins. The phyllites from Podmąchocice are intensely tectonically deformed, while their metamorphism displays a syndeformation character. The age of the tectonic-metamorphic processes has been initially estimated based on their relation to the silicification process. The phyllites are cut by numerous hydrothermal mineral veins, including quartz-chlorite-apatite ones. These veins occur as small post-tectonic and syntaxial forms, a few centimetres long and up to 1 cm thick. In the central parts of the veins, apatite forms colourless crystals, up to 1 mm long and up to 0.1 mm thick. The age of the apatites was determined by means of the laser ablation system combined with the mass spectrometer. The results of isotopic measurements were reduced using the “Vizual Age” reduction program. The U-Pb age has been estimated to ~389 ± 18 Ma (upper intercept) that points to the maximum Devonian age (Eifelian/Givetian) of formation of the quartz apatite veins. This is the first dating that points to hydrothermal activity of this age in the study area. As the veins cut discordantly the metamorphic rocks, the metamorphism itself may be older than the apatite age.
A b s t r a c t. Metamorphic rocks of greenstone facies (phyllites) have been discovered quite recently in the Łysogóry region of the Holy Cross Mountains. The following minerals predominate in the mineral composition of these rocks: bright mica (sericite), quartz, chlorites, rutile, pyrophyllite, xenotime, pyrite, tourmaline, apatite and monacite, while chalcopyrite, sphalerite and galena are also present in mineral veins. The phyllites from Podmąchocice are intensely tectonically deformed, while their metamorphism displays a syndeformation character. The age of the tectonic-metamorphic processes has been initially estimated based on their relation to the silicification process. The phyllites are cut by numerous hydrothermal mineral veins, including quartz-chlorite-apatite ones. These veins occur as small post-tectonic and syntaxial forms, a few centimetres long and up to 1 cm thick. In the central parts of the veins, apatite forms colourless crystals, up to 1 mm long and up to 0.1 mm thick. The age of the apatites was determined by means of the laser ablation system combined with the mass spectrometer. The results of isotopic measurements were reduced using the “Vizual Age” reduction program. The U-Pb age has been estimated to ~389 ± 18 Ma (upper intercept) that points to the maximum Devonian age (Eifelian/Givetian) of formation of the quartz apatite veins. This is the first dating that points to hydrothermal activity of this age in the study area. As the veins cut discordantly the metamorphic rocks, the metamorphism itself may be older than the apatite age.