HR: 1400h
AN: V53B-09    [Abstracts]
TI: Scale of Pluton/Wall Rock Interaction in the Tuolumne Intrusive Suite, Yosemite National Park, California
AU: * Mills, R D
EM: rdmills@email.unc.edu
AF: University of North Carolina, Department of Geological Sciences, Chapel Hill, NC 27599- 3315, United States
AU: Glazner, A F
EM: afg@unc.edu
AF: University of North Carolina, Department of Geological Sciences, Chapel Hill, NC 27599- 3315, United States
AU: Coleman, D S
EM: dcoleman@email.unc.edu
AF: University of North Carolina, Department of Geological Sciences, Chapel Hill, NC 27599- 3315, United States
AB: The western outer unit of the concentrically zoned Tuolumne Intrusive Suite (tonalite of Glen Aulin, Kga) intruded a variety of metasedimentary wall rock units at approximately 93.5 Ma. The May Lake interpluton screen (4500 m x 550 m) is a remnant of the host rocks that includes marble, calc-silicate, quartzite, and pelitic quartzite units that are all in contact with the tonalite. The chemical and physical diversity of the rocks in the screen and their contrast with the invading pluton provide an excellent location to study pluton/wall rock interactions using chemical techniques. Chemical analyses show that contamination of the tonalite is localized within 1-2 meters of wall rock material. Outside the screen, visible wall rock material is predominantly located in an elongate zone of xenoliths (chiefly pelitic quartzite) surrounded by a hybridized fine-grained tonalite that is subparallel to the screen contact and extends from an interbedded quartzite and pelitic quartzite section of the screen into the pluton. Whole-rock geochemistry of tonalite samples near the screen contact and across the hybridized zone suggests localized contamination of various levels. Hybridized tonalite ⁸⁷Sr/⁸⁶Sr (i) values range from 0.7061 to 0.7141 and εNd(t) from -3.5 to -10.5, significantly different from typical Kga (⁸⁷Sr/⁸⁶Sr (i) = 0.7057- 0.7059 and εNd(t) ~ -3.3 ). Mixing models using the various metasedimentary wall rocks and normal tonalite as end-members show calc-silicate/tonalite and marble/tonalite mixing trends are not consistent with any of the hybridized samples. Contamination of the tonalite with quartz-rich and pelitic metasedimentary rocks occurs in two modes including, 1) bulk assimilation of quartzite and pelitic quartzite (occurring in about half of the contaminated samples), and 2) selective assimilation of partial melts of pelitic quartzite. For selective assimilation, partially melting fertile metasedimentary rocks, such as pelitic quartzite, can produce liquids similar to minimum melt granite and mixing models using experimental minimum melt compositions as the contaminant fit the remaining hybridized samples. We conclude that there are 2 distinct modes of contamination, but there is little evidence for contamination of tonalite beyond the immediate vicinity of wall rock inclusions and therefore assimilation is not a significant space creating mechanism for the Tuolumne Intrusive Suite.
DE: 1037 Magma genesis and partial melting (3619)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 3690 Field relationships (1090, 8486)
DE: 8035 Pluton emplacement
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly