Title page for ETD etd-08222008-063115

Type of Document Master's Thesis
Author Wood, Keith Yates
URN etd-08222008-063115
Title Petrogenesis and geochemistry of kyanite-bearing pegmatites in the Buncombe Pegmatite District, North Carolina
Degree Master of Science
Department Geology
Advisory Committee
Advisor Name Title
Bodnar, Robert J. Committee Co-Chair
Tracy, Robert J. Committee Co-Chair
Wise, Michael A. Committee Member
  • pegmatite
  • kyanite
  • magmatic
  • biotite
Date of Defense 1996-08-01
Availability unrestricted

Kyanite is generally considered to be a product of metamorphism. This study investigates a set of kyanite-bearing pegmatites that represent a case in which kyanite crystallized directly from melt. The pegmatites intrude spinel orthopyroxene hornblendite in the Buncombe Pegmatite District in the Eastern Blue Ridge of North Carolina. One site was studied in detail and survey studies of two other occurrences were made. The pegmatites contain quartz, large euhedral crystals of plagioclase, biotite, and kyanite, as well as apatite, muscovite, tourmaline, and microscopic primary sillimanite. Potassium feldspar is notably absent. One site, the Thomas Mine, was examined in detail in order to determine the mode of occurrence for these rocks. Excavation revealed pegmatite with two texturally and mineralogically distinct zones. Biotite-rich rocks surrounding the pegmatite indicate strongly potassic alteration of the host hornblendite.

Trace element data obtained for kyanite and biotite from the pegmatite show clear patterns related to chemical fractionation of these components during crystallization. Major element geochemistry of the pegmatite and host ,I rocks are consistent with magmatic intrusion. Reaction of the pegmatite melt with the host rocks led to the formation of large amounts of biotite, and depleted the melt in potassium. The remaining melt became saturated in aluminum silicate and crystallized kyanite and sillimanite. Wallrock assemblages, fluid inclusions in pegmatite quartz, the coexistence of kyanite and sillimanite as primary phases, and geothermobarometry on nearby unaltered rocks all indicate conditions of formation of approximately 600-800 MPa and 625-675°C, near those of peak metamorphism for the region.

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