PETROLOGY AND GEOCHEMISTRY OF IRON RICH GARNET CHLORITE SCHIST IN ASHE METAMORPHIC SUITE

Ultramafic pods are common along the southern Blue Ridge belt of western North Carolina. Previous work in the Ashe Metamorphic Suite in northwestern North Carolina indicates an ophiolite origin for these ultramafic bodies, but questions remain about the mechanism of emplacement and metamorphic history [1; 2]. One of these metaultramafic bodies is exposed in Todd, North Carolina as a retrograde chlorite-tremolite schist that is next to an iron-rich garnet-chlorite-magnetite schist. The mineralogy of the metaultramafic body cannot confirm the current metamorphic temperature and pressure estimates of 600-650°C and 7.5 kbar [3] thus the surrounding garnet-chlorite-magnetite schist was studied. Samples of the iron rich schist were analyzed using scanning electron microscropy and X-ray diffraction and contain garnet, chlorite, magnetite, ilmenite, hercynite, corundum, biotite, and possibly sillimanite. Magnetite and ilmenite contain exsolution textures as do magnetite, corundum, and hercynite. The garnet can be classified as almandine with rims that range from Gr_0-0.1Pyp_0.1-0.2Alm_0.7-0.9 and cores that range from Gr_0.2-0.4Pyp_0-0.1Alm_0.5-0.7. The chlorite can be classified as aluminum rich clinochlore with a composition of Cham_0.3Clin_0.6. Previous research concluded the temperature ranges were between 600-650°C using garnet-biotite and garnet-hornblende geothermometry. Garnet-chlorite thermometry will be used to refine previous temperature data and provide a baseline for future studies.

1. Abbott and Raymond (1984) American Journal of Science, 284(4-5): 350-375.

2. Scotford and Williams (1983) American Mineralogist, 68(1-2): 78-94.

3. McSween et al. (1989) Geology, 17(12): 1140-1143.