After a weekend of sand and sun on the coast last year, hardrockers will welcome a return to the Georgia Blue Ridge this fall. According to Jim Tull who has organized the trip we will concentrate on basement/cover relationships and their implications for late Proterozoic rift architecture around the Fort Mountain area along the Blue Ridge front.  The lower Paleozoic drift facies sequence and younger clastic wedge successor basin sequence will be examined in exposures in the Murphy belt, and accreted Ordovician arc rocks will be examined along the eastern/western Blue Ridge boundary.  Guidebook articles will focus on the Ocoee rift basin evolution, details of Murphy belt stratigraphy and structure, the Pumpkinvine Creek metavolcanic sequence, and recent geochronology studies in the region. 

 In preparation for the trip members may want to read the overview of the western Blue Ridge in Georgia given by Jim Tull and Chris Holm (2005); Structural evolution of a major Appalachian salient-recess junction: Consequences of oblique collisional convergence across a continental margin transform fault; Geological Society of America  Bulletin v. 117, p. 482-499.

The Great Smoky fault marks the location where the sole thrust (decollement) at the base of the Paleozoic section further northwest, descends into Grenville basement and overlying late Proterozoic metasedimentary rocks. The latter, Ocoee Supergroup includes a great thickness of coarse grained clastics deposited in grabens during the rifting of the Iapetus Ocean. It stands in distinct contrast to rocks in the Valley and Ridge province, being both older, and more highly deformed and metamorphosed.  Farther to the southeast these Proterozoic rift stage rocks are overlain by rocks of the Murphy syncline. Although, much debated, most workers agree that these are the metamorphic equivalents of parts of the Paleozoic section in the Valley and Ridge. Although allochthonous, both the Ocoee Supergroup and the Murphy Group of the western Blue Ridge, are part of the original cover sequence deposited on the North American (Laurentian) craton during the opening of Iapetus.  It is not until one crosses the Allatoona fault on the southeast side of the Murphy syncline, that the occurrence of amphibolites of the Pumkinvine Creek Formation, signal the involvement of oceanic crust within the Appalachian thrust stack. Here the stratigraphy is island-arc related and its relationship to Laurentia under current debate.

This year’s field trip will traverse the western Blue Ridge from Grenville basement near Fort Mountain to oceanic crust on Lake Allatoona.  Most of Saturday will be spent around Fort Mountain examining the relationship between Grenville basement and Proterozoic cover. These relationships are best examined along the streams and the trip will include two relatively long hikes up Rock Creek and Holly Creek. A stout walking stick will be helpful for navigating the stream beds. Lunch on Saturday will be at Fort Mountain State Park.  Sunday’s trip will focus on the stratigraphy and structure of the Murphy belt near Canton and on lithologies in the hanging wall of the Allatoona fault in the eastern Blue Ridge. During the lunch stop there will be an opportunity to visit the new Hickory Log Creek dam near Canton.  The trip will end at about 2.00 pm in Canton.

Headquarters for the trip will be the Holiday Inn Express in Canton. The motel is located on Transit Avenue at the intersection of I-575 with Riverstone Parkway (old GA 5) on the north side of town. A special group rate of $69.00/ night is available for participants. Members should make their own reservations by calling 770-479-7300 by the deadline of October 1, 2007.  Please mention your association with GGS when registering.  For members who may wish to camp, sites are available up to October 15 on a first come basis at Victoria Campground on Lake Allatoona about ten miles from Canton 1-877-444-6777 (www.recreation.gov).

Please join us Friday evening beginning at 7.00 pm to pick up registration materials and socialize over a beer. Jim Tull will give an introductory talk and overview of the trip beginning at 8.00 pm.