Illite and chlorite "crystallinity" and phyllosilicate parageneses have been employed to characterize very-low grade metamorphism in tectonic units of Trebbia Valley (Mt. Gottero Unit and Helminthoid Flysch Unit). Illite "crystallinity" values (Kübler index) indicate anchizone conditions for Mt. Gottero Unit (x = 0.35° as Δ2θ) and late diagenesis conditions for Helminthoid Flysch Unit (x = 0.46° as Δ2θ). Chlorite "crystallinity" index has a mean value of 0.22° Δ2θ) in the Mt. Gottero Unit and a mean value of 0.30° (Δ2θ) in the Helminthoid Flysch Unit. Illite + chlorite paragenesis characterizes samples from Mt. Gottero Unit, while illite + chlorite ± kaolinite ± randomly interstratified illite/smectite ± randomly interstratified chlorite/smectite is the paragenesis of Helminthoid Flysch Unit. Phyllosilicate parageneses are in good agreement with the metamorphic grade assigned through illite and chlorite "crystallinity" measurements. The different metamorphic grade found in the Mt. Gottero Unit and in the Helminthoid Flysch Unit fit very well with their tectonic setting and allows to locate with a good precision the tectonic contact between them in the examined area.
"Cristallinità " di illite e clorite nelle Unità Liguri dell'Alta Val Trebbia (Appennino Settentrionale)
MOLLI, GIANCARLO;PANDOLFI, LUCA;TAMPONI, MARCO
1993-01-01
Abstract
Illite and chlorite "crystallinity" and phyllosilicate parageneses have been employed to characterize very-low grade metamorphism in tectonic units of Trebbia Valley (Mt. Gottero Unit and Helminthoid Flysch Unit). Illite "crystallinity" values (Kübler index) indicate anchizone conditions for Mt. Gottero Unit (x = 0.35° as Δ2θ) and late diagenesis conditions for Helminthoid Flysch Unit (x = 0.46° as Δ2θ). Chlorite "crystallinity" index has a mean value of 0.22° Δ2θ) in the Mt. Gottero Unit and a mean value of 0.30° (Δ2θ) in the Helminthoid Flysch Unit. Illite + chlorite paragenesis characterizes samples from Mt. Gottero Unit, while illite + chlorite ± kaolinite ± randomly interstratified illite/smectite ± randomly interstratified chlorite/smectite is the paragenesis of Helminthoid Flysch Unit. Phyllosilicate parageneses are in good agreement with the metamorphic grade assigned through illite and chlorite "crystallinity" measurements. The different metamorphic grade found in the Mt. Gottero Unit and in the Helminthoid Flysch Unit fit very well with their tectonic setting and allows to locate with a good precision the tectonic contact between them in the examined area.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
