Petrology of the Dark Ridge Dunite, North Carolina.
The ultramafic bodies of the Appalachian mountain range have been of interest to geologists for years. Studies of these bodies give us a better understanding of the formation and metamorphic history of the Appalachians. This project focuses on the Dark Ridge dunite in Jackson County, North Carolina. Our objectives were to determine the mineralogy, conditions of metamorphism, and formative history of the body. Samples were collected at approximate 100 foot intervals along a westward traverse, starting from near the center of the body; an additional sample was taken at the northern edge of the exposed body. Polished thin sections were made from the samples and studied with a petrographic microscope. Mineral abundances were determined by point count and mineral compositions by electron microprobe. From our studies, we determined that the most common assemblage at Dark Ridge is olivine + talc + tremolite + chlorite + chromite, which indicates metamorphism in the amphibolite facies. The samples suggest higher temperature assemblages once existed, possibly granulite facies. Abundant serpentine (antigorite, replacing olivine and chlorite) reflects hydration of the metadunites during retrograde metamorphism. Mineral assemblages at Dark Ridge therefore preserve a record of a range of metamorphic conditions. Olivine % Fo is highest in the interior of the body and decreases outward, in response to increased hydration of the rocks. Chromite are Cr-rich due to the formation of surrounding chlorite crystals. Thus, olivine and chromite compositions are the result of metamorphic recrystallization.
Lauren Bissey, Chris Hepler, Valerie Martin, Matt Poole, Richard Warner Department of Geological Sciences Clemson University
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|Author:||Bissey, Lauren; Hepler, Chris; Martin, Valerie; Poole, Matt; Warner, Richard|
|Publication:||Bulletin of the South Carolina Academy of Science|
|Article Type:||Brief Article|
|Date:||Jan 1, 2001|
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