Characterization of the samples by SEM indicates the presence of two white mica populations, a coarser grained, deformed, detrital mica that probably corresponds to the 2M 1 phengite and a finer grained neoformed 1M mica. 200–300 Ma), a significant Eoalpine component (64–80 Ma) forming 40Ar/ 39Ar age plateaus, and a very minor Tertiary component (ca. High precision 40Ar/ 39Ar age spectra from different size fractions of these micas record three distinct components, a small Hercynian component (ca. The K/Ar and Rb/Sr ages are generally younger in the smaller size fractions, which also containless 2M 1 phengite. This variation is correlated with two parameters, the size of the mineral fraction, and the proportion of 2M 1 (more phengitic) to 1M (more muscovitic) polytype in the sample. Analyses of white mica separates of varying size fractions from the mylonitic rocks by K/Ar and Rb/Sr techniques yield ages between 57 and 103 Ma. Stable isotope measurements of the coexisting calcite (δ 18O SMOW=24.5) and quartz (δ 18O SMOW=28.4) from the mylonite indicate relatively low temperatures (<300☌) during mylonitization. At the base of the klippe is a 10–50 m thick, ductilely deformed marble mylonite containing deformed authigenic quartz segregations. The klippe consists mainly of Mesozoic to early Tertiary carbonate rocks metamorphosed from anchizonal to epizonal conditions. A combined 40Ar/ 39Ar, K/Ar, Rb/Sr and stable isotope study has been made of white micas from the Gummfluh klippe (Briançonnais domain of the Préalpes), Switzerland.
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