Finite strain has no influence on the illite crystallinity of tectonized Eocene limestone breccias of the Morcles nappe, Swiss Alps

The relationship between illite crystallinity (IC) and finite strain as wel l as lattice strain and crystallite size of illite is examined in a series of 27 deformed breccia samples from the inverted limb of the Morcles nappe. The IC is determined independently for limestone components and a red/gree n clay-silt matrix. The finite strain varies widely (D = 0.8-2.5). The IC v alues vary from diagenetic to epizonal, but no correlation with finite stra in could be established. The spread of IC values is explained by heterogene ities within the protolith which have not been homogenized/obliterated by t he anchizonal to epizonal metamorphic overprint. While limestone pebbles di splay IC values in agreement with the regional metamorphic conditions, the clay-silt matrix has anomalously high IC values, even after deconvolution o f the 10 K peak to correct for the presence of paragonite/muscovite. No cor relation could be established between finite strain, lattice strain and/or crystallite size of illite.