Premium
P–T–t estimation of deformation in low‐grade quartz‐feldspar‐bearing rocks using thermodynamic modelling and 40 Ar/ 39 Ar dating techniques: example of the Plan‐de‐Phasy shear zone unit (Briançonnais Zone, Western Alps)
Author(s) -
Lanari Pierre,
Rolland Yann,
Schwartz Stéphane,
Vidal Olivier,
Guillot Stéphane,
Tricart Pierre,
Dumont Thierry
Publication year - 2014
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12079
Subject(s) - geology , subduction , phengite , massif , quartz , shear zone , coesite , geochemistry , seismology , paleontology , tectonics , eclogite
Pressure–Temperature–time ( P–T – t ) estimates of the syn‐kinematic strain at the peak‐pressure conditions reached during shallow underthrusting of the Briançonnais Zone in the Alpine subduction zone was made by thermodynamic modelling and 40 Ar/ 39 Ar dating in the Plan‐de‐Phasy unit (SE of the Pelvoux Massif, Western Alps). The dated phengite minerals crystallized syn‐kinematically in a shear zone indicating top‐to‐the‐N motion. By combining X‐ray mapping with multi‐equilibrium calculations, we estimate the phengite crystallization conditions at 270 ± 50 °C and 8.1 ± 2 kbar at an age of 45.9 ± 1.1 Ma. Combining this P–T – t estimate with data from the literature allows us to constrain the timing and geometry of Alpine continental subduction. We propose that the Briançonnais units were scalped on top of the slab during ongoing continental subduction and exhumed continuously until collision.