| In southern Cleburne County, Alabama, the Coosa block is thrust over the Talladega block along the Hollins Line thrust fault. The Talladega block is composed of low grade metamorphic rocks, and contains evidence for four structural events. The units in the Talladega block indicate a continental origin for the depositional environment. Within the Talladega block, geochemical analyses indicate that the Hillabee Chlorite Schist, known as the Hillabee Greenstone, is associated with island arc volcanic activity and may represent distal lava flows. The Coosa block is composed of a high-grade metasedimentary sequence and amphibolite, and also shows evidence of four structural events. The Poe Bridge Mountain amphibolite of the Coosa block has an unrelated origin to the Hillabee Greenstone. Origin of the Talladega block units is related to subduction associated with an island arc-continental fragment collision of sedimentary-volcanic rock. During this collision, F1 -folds were formed which are found both in the Talladega and Coosa blocks. Continued collision of North America and Africa possibly created the F 2-F3 folds, the Hollins Line fault, and subsequently the F4 folds found in both blocks. |
