The western outer granodiorite of the Tuolumne Intrusive Suite intruded a variety of metasedimentary wall rocks at 93.1 ± 0.1 Ma. The May Lake metamorphic screen (4500 x 550 m) is a remnant of the chemically diverse metasedimentary host rocks. Their chemical contrast with the invading pluton provides an excellent location to study pluton/wall rock interactions. Outside the screen, visible wall-rock xenoliths (mostly pelitic quartzite) are predominantly located in an elongate horizon surrounded by a hybridized fine-grained granodiorite. Initial Sr and Nd isotopic ratios of the hybridized granodiorite indicate incorporation of crustal material. Major- and trace-element geochemical data indicate contamination of the granodiorite with pelitic metasedimentary rocks occurred in two modes, selective assimilation of 1) a high-K partial-melt derived from pelitic quartzite, and 2) a low-K partial-melt derived from pelitic quartzite. However, there is little evidence for contamination of granodiorite beyond the immediate vicinity of wall rock inclusions
