The geology of the Murphy belt in north central Georgia

The Murphy belt of north central Georgia and northwestern North Carolina is a sequence of metasedimentary and metaigneous rocks located within the western Blue Ridge lithotectonic belt of the southern Appalachian Mountains. The Murphy belt is important to regional tectonic models because it contains some of the youngest rocks in the western Blue Ridge. The rocks of the Murphy belt are preserved in the core of a large ({dollar}>{dollar}180 km long), doubly plunging, overturned to the northwest, large wavelength and amplitude, isoclinal syncline. Several folding events have resulted in complex interference patterns. These rocks are at low to medium metamorphic grade. The lower stratigraphy of the Murphy belt documents the rift to drift transition along the ancient Laurentian margin. The Ocoee Supergroup is a rift-fill sequence that marks the opening of the Iapetan (proto-Atlantic) ocean. The Hiwassee River Group is a shelf/carbonate platform sequence that marks the development of a passive continental margin along the edge of the Laurentian continent. The Hiwassee River Group has been correlated to the Lower Cambrian Chilhowee Group of the Appalachian fold and thrust belt. The lower sequence is overlain unconformably by a successor basin sequence, the Mineral Bluff Group, that includes both metasedimentary and metavolcanic units. The pre-Mineral Bluff Group unconformity is a low-angle regional unconformity that truncates units of the Hiwassee River Group and the Ocoee Supergroup. The Mineral Bluff Group rocks document a change in depositional environment from a passive continental margin to an active continental margin. A fossil recovered from the lower Mineral Bluff indicates that these rocks are post-Cambrian or younger. The Mineral Bluff Group has been correlated to rocks of the Siluro-Devonian Talladega Group of Alabama and Georgia. Lithofacies of the Mineral Bluff include: turbidites, olistostromes, conglomerates, sandstones, pelites, and mafic volcanics. These lithofacies indicate that lower Murphy belt units were exposed during Mineral Bluff time and provided detritus for the Mineral Bluff basin. Metavolcanic units within the Mineral Bluff Group show a within-plate geochemical signature. Other intrusive metaigneous rocks of the lower Murphy belt are interpreted to be the feeder system for the stratigraphically higher metavolcanic units.