Petrography and Mineral Chemistry of Pelites

This chapter describes the petrography and mineral chemistry of an exceptionally well-developed sequence of prograde mineral zones in pelitic and semipelitic rocks in the Ballachulish aureole. Two schematic petrogenetic grids are derived: the first is for mineral assemblages below the onset of partial melting, which define the mapped isograds in Maps 1 and 2 and Figure. 8.1; and the second is for high-grade mineral assemblages which occur sporadically within the zone of partial melting (Harte et al., Chap. 9, this Vol.) and within pelitic screens within the igneous complex. The two grids, when linked, provide a continuous petrogenetic grid from the lowest to highest grade in the aureole. In Pattison (Chap. 16, this Vol.) the continuous grid is calibrated in P-T space.