Abstract
Interlayering, slip, and cleavage phenomena have been observed using high-resolution transmission electron microscopy in tectonically deformed biotite. The unit mica layers and the positions of the interlayer cations can be imaged with this technique. From the observations, we conclude first that slip and cleavage occur in the interlayer level of the structure. The biotite shows partial interlayers of brucite-like sheets, which form, with the adjacent talc-like layers of the mica, single chlorite layers interstratified in the mica structure. From structural and physical considerations, brucite interlayering is interpreted here as a “brucitization” of an interlayer level of the mica where partial slip or cleavage has previously occurred. It is an example of a chemical process at the atomic scale (local chloritization of the mica) favored by deformation microstructures.
