HR: 16:00h
AN: T14B-01    [Abstracts]
TI: Constraints on the Depth of Generation and Emplacement of Magma in the Coast Plutonic Complex, British Columbia, From Magmatic Epidote Textures
AU: * Hamblock, J M
EM: hamblock@montana.edu
AF: Montana State University, Dept. of Earth Sciences, P.O. Box 173480, Bozeman, MT 59717-3480, United States
AU: Andronicos, C L
EM: ca98@cornell.edu
AF: Cornell University, Dept. of Earth and Atmospheric Sciences, Snee Hall, Ithaca, NY 14853-1504, United States
AB: We have examined magmatic epidote-bearing plutons in the Coast Plutonic Complex to understand the depth at which they were generated and emplaced. Mt. Gamsby, located east of the Coast shear zone between Kitimat and Bella Coola, British Columbia, contains a magmatic epidote-bearing tonalite-quartz diorite pluton. This pluton had a crystallization sequence of pyroxene, amphibole, epidote, plagioclase, and biotite. The lack of garnet is consistent with trace element data, which indicate that garnet was not present in the source region and, therefore, that the magma was sourced at pressures less than ca. 1.4 GPa. Epidote inclusions in plagioclase constrain the pressure during early crystallization of the epidote to greater than 1 GPa. P-T estimates from the pluton and surrounding country rock suggest that the magma migrated to shallower levels and was emplaced at depths of ca. 0.8-1.0 GPa. Magmatic epidote also occurs in the Ecstall, Butedale, and Captain Cove plutons west of the Coast shear zone south of Prince Rupert. In the Captain Cove pluton, textures show that plagioclase crystallized before epidote, and pluton crystallization pressures are estimated to be 0.65-0.75 GPa. These data are consistent with experimental work that indicates that the crystallization of plagioclase before epidote occurs at a lower pressure than epidote before plagioclase. The magmatic epidote in the Ecstall and Butedale plutons commonly occurs as large vermicular grains intergrown with quartzofeldspathic minerals. We interpret this texture to indicate late crystallization of epidote, consistent with prior studies. Pressure estimates for the Ecstall pluton are between ca. 0.5 and 0.8 GPa and vary along strike. The pressure of emplacement of the Butedale pluton is not well constrained, but Al-in-hornblende pressures of 0.6 and 0.8 GPa have been obtained from a portion of the pluton. The pressures in the Butedale and Ecstall plutons are lower than pressures at Mt. Gamsby, which shows early crystallization of epidote. Our observations indicate that textures of magmatic epidote, in relationship to other magmatic phases and combined with quantitative P-T estimates, provide a powerful tool for understanding the path followed by magma through the crust.
DE: 3625 Petrography, microstructures, and textures
DE: 3640 Igneous petrology
DE: 3651 Thermobarometry
DE: 8104 Continental margins: convergent
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting