STRUCTURAL EVOLUTION OF THE MULBERRY RECESS EASTERN BLUERIDGE-TALLADEGA: NORTHWEST GEORGIA APPALACHIANS

Abstract

The Mulberry Rock recess exposes four different lithotectonic metamorphic units; these lithotec-tonic units were metamorphosed before the thrusting that occurred due to the Alleghanian orogeny.The lithotectonic units were divided into 1. allochthonous assemblages consist of two stratigraphicsequences: 1. the Talladega slate belt and 2. the Hillabee Greenstone and 2. parautochthonousassemblages consist of three units: 1. the Wedowee Formation (New Georgia Group, the north-eastern extension in Georgia) 2. the Emucfaw Group, and 3. the Dahlonega Gold Belt. Theallochthonous assemblages were deposited in extensional basins formed along the eastern Lauren-tian plate’s outermost passive margin. In contrast, the parautochthonous assemblages consist ofpredominantly deep-water immature metasedimentary units beside bimodal volcanic rocks formedin a supra subduction system built on adjacent late Neoproterozoic early Paleozoic rocks of thepassive Laurentian margin at the trailing edge of the Iapetus ocean, specifically in a continentalmargin back-arc setting.The Hillabee Greenstone metavolcanic unit shows a bimodal volcanic suite comprising of twodistinct lithologies: one composed of metadacite that was crystallized at 470±3 Ma and theother composed of metabasalt formed in an island arc basalt environment for the felsic unit. ThePumpkinvine Creek Formation rocks samples are characterized as metavolcanic (basalt) formed in atholeiitic environment and metafelsic (rhyolite and/or dacite) formed in a calc-alkaline environment.The Mulberry Rock Gneiss was formed by anatectic melting of older Grenville-aged rocks. TheWedowee-Emuckfaw-Dahlonega basin comprises two units metabasaltic rocks and metasedimentaryrocks formed in a supra subduction zone environment.Stereographic analysis of the orientational data inside and outside the Mulberry Rock recessshows that all units generally strike northeast and dip northwest. Isoclinal antiformal and synformalregional folds are the dominant structures in the mapping area. Cross-sections across the MulberryRock recess were drawn to scale and show no vertical exaggeration. The cross-sections show thatthe overthrust sheets vary in thickness and dip gently in all directions around the Mulberry Rockrecess and reveal that the Mulberry rock antiform is an upright open fold that broadly arches theoverriding thrust sheets. Moreover, the cross-sections also show that the Allatoona fault follows thegeometry of an out-of-sequence thrust fault. Furthermore, the Mulberry Rock Gneiss’s structuralxi position might suggest that it was a laccolith-size intrusion reduced in size by faulting. The cross-sections reveal that the Allatoona fault cuts down section in its footwall and became the base of thePumpkinvine Creek and Canton Formations thrust sheet on top of the Talladega slate belt thrustsheets in the western part of the recess.Many tectonic settings could collaborate in the buried basement to generate differential move-ment and uplift the antiform. The fact that the Mulberry Rock antiform is doubly plunging is oneevidence of cross folding events.