The Gets nappe, a decollement cover nappe located at the top of the
Prealps, is characterized by the occurrence of ophiolitic rocks. The
metamorphic grade in the Gets nappe was determined using illite
crystallinity and clay mineral assemblages. Samples from the same
locality were analyzed to estimate variations in illite crystallinity
values and in the parageneses of clay minerals, both in sedimentary
elements of a breccia and in the embedding shaly flysch. For samples
from one and the same locality, the range in illite crystallinity data
between breccia elements and the shaly flysch is comparable to the
variation between different shaly beds. Two S-N transects along the Gets
nappe reveal the same metamorphic gradient, with the internal parts of
the nappe being characterized by middle anchizonal metamorphism and the
external parts showing diagenetic conditions. The metamorphic grade is
higher within the Gets nappe than in its hangingwall (i.e. the Breche
and Simme nappes), suggesting that the metamorphism in the Gets unit is
transported. The timing and conditions of thrusting of the Gets Nappe
onto the Br che and the Simme nappes is constrained by stratigraphic and
metamorphic data.