A technique combining 40Ar/39Ar step-heating analyses, in situ UV laserprobe dating and electron microprobe chemical characterization has been developed to unravel the relationships between microstructures, metamorphism and K/Ar systematics. This technique has been applied to white micas of a discrete shear zone in the Roffna metarhyolite in the Suretta nappe (SE Switzerland). Neoformed phengites from the Roffna metarhyolite crystallised in shear zones during Tertiary Alpine deformation under blueschist- and greenschist-facies conditions. In situ 40Ar/39Ar UV laser dating of white micas defining the schistosity and C-planes yield systematically younger isotopic dates in the C-planes, which are also correlated with decreasing celadonite content (i.e., Si/Al ratio). These results suggest that the timing of the high-pressure deformation event is preserved in the schistosity; high-Si micas appear to have lost no Ar. Later deformation was localised preferentially in C-planes giving younger 40Ar/39Ar dates probably related to a later period of phengite growth. The age sequence is broadly consistent with the textural constraints and geological field relations. © 2002 Elsevier Science B.V. All rights reserved.

Challandes, N., Marquer, D., Villa, I. (2003). A combined 40Ar/39Ar step-heating and UV laserprobe analysis of C-S microstructures in an Alpine shear zone. CHEMICAL GEOLOGY, 197(1), 3-19.

A combined 40Ar/39Ar step-heating and UV laserprobe analysis of C-S microstructures in an Alpine shear zone

VILLA, IGOR MARIA
2003

Abstract

A technique combining 40Ar/39Ar step-heating analyses, in situ UV laserprobe dating and electron microprobe chemical characterization has been developed to unravel the relationships between microstructures, metamorphism and K/Ar systematics. This technique has been applied to white micas of a discrete shear zone in the Roffna metarhyolite in the Suretta nappe (SE Switzerland). Neoformed phengites from the Roffna metarhyolite crystallised in shear zones during Tertiary Alpine deformation under blueschist- and greenschist-facies conditions. In situ 40Ar/39Ar UV laser dating of white micas defining the schistosity and C-planes yield systematically younger isotopic dates in the C-planes, which are also correlated with decreasing celadonite content (i.e., Si/Al ratio). These results suggest that the timing of the high-pressure deformation event is preserved in the schistosity; high-Si micas appear to have lost no Ar. Later deformation was localised preferentially in C-planes giving younger 40Ar/39Ar dates probably related to a later period of phengite growth. The age sequence is broadly consistent with the textural constraints and geological field relations. © 2002 Elsevier Science B.V. All rights reserved.
Articolo in rivista - Articolo scientifico
geochronology, 40Ar/39Ar dating, UV laser microprobe, C-S microstructures, shear zone
English
2003
197
1
3
19
none
Challandes, N., Marquer, D., Villa, I. (2003). A combined 40Ar/39Ar step-heating and UV laserprobe analysis of C-S microstructures in an Alpine shear zone. CHEMICAL GEOLOGY, 197(1), 3-19.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/3759
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