La cristalinidad de la illita y las temperaturas de las últimas etapas de deformación en la zona de cizalla extensional de Santa María de La Alameda (Sistema Central, España)

The illite crystallinity index of Kubler (1C) has been studied to establish the conditions of the last deformation stages in the Santa María de la Alameda shear zone. For this study, it has been used mainly the fine grained fraction of the samples (less than 2 mm) which is concentrated along small brittle fractures and zones of protocataclasitic material. The studied rocks give "illite crystallinity index" values between 0.35 D°2q and 0.25 D°2q, pointing to deformation conditions at temperatures which denotes a retrograde metamorphismo zone belonging to the epizone and anquizone. These results indicate a a rétrogradation condition for the late brittle deformation stage of the Santa Maria de alameda fault, in temperatures range between 255 and 200° C