32 Gondwana vs. Laurentia: Terrane Accretion and Crustal Growth in the Southeastern United States

Friday, 29 March 2019
8:15 AM - 12:00 PM
Colonial Ballroom

THE WEDOWEE-EMUCKFAW-DAHLONEGA BASIN AND DADEVILLE COMPLEX: IMPLICATIONS FOR THE BREVARD ZONE OF ALABAMA AND GEORGIA

Paper number: 32-9
Program: Theme Sessions
Time: 10:35 AM – 10:55 AM

Authors

Abstract

Recent advances in our understanding of the southern Appalachian orogen have resulted in recognition of a paired Ordovician arc-backarc system in the eastern Blue Ridge (EBR) and western Inner Piedmont (WIP) of Alabama (AL) and Georgia (GA). The structural juxtaposition of these arc-backarc terranes provide valuable insight into the kinematics of the Brevard fault zone (BFZ) in AL and GA. Rocks of the AL-GA EBR composite terrane, northwest of the BFZ, lie within the Ashland-Wedowee-Emuckfaw belt (AWEB) in the hanging wall of the Hollins Line fault system, but also include rocks of the Tallulah Falls Formation in the hanging wall of the Chattahoochee fault (western Tugaloo terrane). Stratigraphy of the AWEB includes Ordovician back-arc rocks of the Wedowee-Emuckfaw-Dahlonega basin (WEDB). Southeast of the BFZ, rocks of the WIP include the arc-affinity Dadeville Complex (DC) and back-arc affinity Opelika Complex (OC). Rocks of the DC lie in a synformal klippe structurally above those of the OC, which include the Loachapoka and Auburn Formations. OC strata wrap around the hinge of the northeasterly-plunging Tallassee synform (i.e. beneath the DC klippe), and are interpreted as stratigraphic equivalents of WEDB rocks in the EBR. Interestingly, the BFZ, including the internal stratigraphy of the Jacksons Gap Group between the Abanda and Katy Creek faults, lies between the DC and EBR. Rocks of the extensive WEDB, therefore, lie partially in the EBR and partially in the WIP of AL and GA, but are structurally overlain by the similarly-aged DC arc terrane that originated outboard of the WEDB on the Ordovician seaward margin of the Laurentian plate. Emplacement of the DC directly above the WEDB along nearly the entire strike-length of both suggests a significant orthogonal (NW-SE) displacement component associated with Alleghanian thrust faulting along the BFZ in AL and GA. In contrast, structural analysis farther to the northeast (e.g. North Carolina) has led some workers to suggest predominantly strike-slip kinematics that displaced the WIP 100 km or more from northeast to southwest along the BFZ. Although the kinematics of the BFZ in AL and GA are complex, reconciling the significant strike-slip displacement interpreted for the BFZ in North Carolina with the absence of similar displacement in AL and GA is challenging.

Geological Society of America Abstracts with Programs. Vol. 51, No. 3

doi: 10.1130/abs/2019SE-327841

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.