PETROLOGIC ANALYSIS AND REMAPPING OF THE TODD ULTRAMAFIC BODY IN THE EASTERN BLUE RIDGE MOUNTAINS, NC

The eastern Blue Ridge Mountains of North Carolina contain a record of metamorphism that spans several orogenies and protoliths. The Ashe Metamorphic Suite (AMS), which comprises much of this region, consists mostly of metabasalt, metasediment, and ultramafic rocks that have been altered by multiple metamorphic events. Our focus within the AMS is the ultramafic bodies, specifically a large body mapped near Todd, NC. Understanding the emplacement, deformation, and metamorphism of these ultramafic bodies could change our understanding of the orogenies of Eastern North America. This is part of ongoing mapping and petrologic research on ultramafic rocks of the Blue Ridge. New mapping indicates that the Todd body consists of several lenses rather than one contiguous unit; rock units of a different protolith outcrop within the previously mapped boundaries of the Todd body. These lenses are mineralogically distinct, as only the central lens contains olivine. We present an updated map of this region produced in ArcGIS.

Petrographic analysis of 10 ultramafic samples indicates different mineral assemblages, and therefore differing metamorphic conditions recorded in the ultramafic rocks. All samples contain chlorite and tremolite. Olivine is only present in samples from the center of the body, which also contain chlorite, tremolite, and talc, recording a temperature range of ~500-650°C. Anthophyllite, chlorite, tremolite, and enstatite records the peak metamorphic grade of the body, a temperature range of ~650-750°C. These samples are from the central and northern section of the body. The presence of these two metamorphic grades could provide further evidence of multiple orogenic events.