A POSSIBLE NEOACADIAN METAMORPHIC BELT IN THE BLUE RIDGE OF ALABAMA AND GEORGIA: METAMORPHISM OF THE PUMPKINVINE CREEK FORMATION AND THE MAD INDIAN GROUP

The spatial extent of Neoacadian metamorphism is poorly known in the southernmost Appalachians. Large gaps between well-studied areas hinder correlation of metamorphism both along and across strike. We utilize mineral assemblage diagram modeling (MADs) and garnet Sm-Nd geochronology to constrain the P-T-t paths of metamorphism in two along strike units in the Blue Ridge: the Mad Indian group in Alabama (17Ash01) and the Pumpkinvine Creek formation in Georgia (17PumCan01).

Sample 17Ash01 was collected from the Mad Indian Group near Micaville , Alabama and is a garnet-kyanite-biotite-muscovite schist with minor sillimanite and staurolite. The MAD for this sample indicates metamorphism occurred during loading from 6.5 kbar 550°C to 9 kbar 650°C. Garnet growth occurred at 357±3 Ma during the Neoacadian orogeny based on Sm-Nd geochronology. Sample 17PumCan01 was collected from the Pumpkinvine Creek formation near Canton, Georgia, c. 125 km northeast of Micaville. The sample is a coarse-grained garnet-hornblende-kyanite gneiss with minor staurolite. A preliminary MAD indicates c. 150°C of heating and 5 kbar of loading to peak conditions of 610-715°C and 8.5-11 kbar, overlapping with the P-T-t results for the Mad Indian Group.

Recent studies highlight the geochemical and structural similarities between the two units, suggesting both units as part of a c. 460 Ma Laurentian margin and back arc system. No published metamorphic age data exists for the Pumpkinvine Creek formation; however, an unpublished 313 Ma Ar-Ar hornblende cooling age is suggestive of peak metamorphism during the Neoacadian. Additional P-T-t data is needed to confirm the possible extent of Neoacadian metamorphism.