The evolution of fine-grained pelitic rocks from early diagenesis through low grade metamorphism is being studied with an emphasis on techniques of scanning and scanning transmission electron microscopy (SEM/STEM). The textures, compositions and structures of minerals from sequences of samples representing the ranges of a variety of processes are each being characterized in order to distinguish the changes that characterize the processes. Specific projects include: (a) characterization of the smectite to illite transformation. (b) evolution of the composition, defect- state and crystal dimensions of illite, in part to determine the origins of changes in illite "crystallinity." (c) evolution of changes in chlorite leading to changes in chlorite crystallinity. (d) prograde hydrothermal alteration of MORB with emphasis on the evolution of mixed-layer relations of trioctahedral phyllosilicates. (e) prograde evolution of trioctahedral mixed- layer phyllosilicates in pelites. (f) evolution of Na/K dioctahedral micas. (g) contact metamorphism of pelites. (h) formation of homogenized shales with chlorite/mica "stacks." (i) relation between XRD patterns and mixed-layer clay sequences. The research addresses the fundamental question as to how fine-grained sediments become metamorphic rocks.
