Scale of pluton/wall rock interaction near May Lake, Yosemite National Park, California, USA

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.