Formula omitted] variations and fluid circulation in a deep shear zone: The case of the Alpine ultramylonites from the Aar massif (Central Alps, Switzerland)

Abstract

Alpine deformation in the shear zones from the Aar granite was accompanied by mobility of some major and trace elements. With increasing strain intensity, the variation of some elements (Mg, Ca) suggests that the deformed zone was an open system with respect to fluids while the variation of other elements (Na, K, Sr, Rb) is more consistent with a closed-system model. 18 O 16 O ratios of representative samples of shear zones in sizes of hundreds of meters and meters are significantly higher in mylonitic and ultramylonitic rocks. Such isotopic variations are not readily compatible with a model of closed-system redistribution of the elements in the deformed section and suggest that the shear zones, especially the largest one, were open to an external fluid supply likely occurring in the course of the deformation process.