Field trip to explore Brevard Zone in Metro Atlanta
June 1 @ 10:00 am - 2:00 pm
The Brevard Zone is a classic mylonite zone extending from Alabama nearly to Virginia. Within it are deformed rocks of many different mineral compositions. Register at this link for the June 1 AGS trip examining contrasting rock types at 4 outcrops, to my knowledge never before visited by any geological society field trip.
Time: 10-AM to about 2 PM, Sunday, June 1
Where to meet: Blue Heron Nature Preserve, 4055 Roswell Rd NE, Atlanta, GA 30342
What to bring: sack lunch, outdoor wear, sunscreen, hammers and eye protection.
Please register at this link by completing a waiver.
As soon as everyone has checked in at Blue Heron, we will drive in fewer cars 1 mile to a smaller lot in Chastain Park off Lake Forrest Drive. There we look at two exposures of a quartz-feldspar-rich rock. The exposure across the road from the park shows prominent feldspar porphyroclasts. Returning to Blue Heron, we will examine a decent outcrop of the ordinarily poorly exposed “button schist” lithology traced for more than a hundred miles along the zone.
After a lunch break, we’ll drive 6 miles to the Perimeter Center Parkway bridge over I-285, which overlooks a gigantic new cut in Long Island Gneiss, a unit that persists from here well into Alabama. Although we view the big cut through a fence, there are a couple of hundred feet of road cut along the street to see this uniform rock type interrupted by a few granitic dikes.
The final stop, 14 miles east, is the pair of nearly 1000-foot-long road cuts accessible along the sidewalks that line Pleasant Hill Road in Duluth. This site features on p. 298 of Roadside Geology of Georgia. It lies within a unit that Higgins et al. (2003) mapped as “button schist and sheared amphibolite” (POms). Our thin sections confirm the presence of hornblende in this outcrop.
As mentioned in previous newsletters, you can find photomicrographs from three of the stops in the AGS Fieldtrips Folder on Google Drive. They are in the 2025PhotomicrographsForTrips.pdf file. Feel free to add comments and questions there. By field trip time, we should also have thin sections from the Perimeter Center Parkway stop.