Author: Benjamin Lee Davis

Publisher:

Published: 2021

Total Pages: 0

ISBN-13:

Taconic orogenesis along the eastern Laurentian margin was a dynamic tectonic event during the Ordovician that has been difficult to reconcile until as of late. The record of the Taconic orogeny is complex, and each section of the Appalachians has different geologic attributes that are unique to that specific section. In the northern and central Appalachians, the record of Taconic orogenesis is well preserved and understood, but in the southern Appalachians there are discrepancies in subduction style that suggest a different manor of tectonic evolution occurred. The probable model for the southern Appalachians suggests a B-type subduction system, where the Dadeville complex represents a marginal volcanic arc, due to a subduction polarity reversal north of the Virginia promontory, relative to the northern Appalachians during the Taconic orogeny, causing Laurentian continental lithosphere to override subducting Iapetan oceanic lithosphere. This model depicts the fringing Dadeville complex arc and associated Wedowee-Emuckfaw-Dahlonega back-arc basin originating on distended Laurentian crust, fueled by extensional rather than convergent tectonics.The Dadeville complex is a large klippe located in the Alabama and Georgia Inner Piedmont of the southern Appalachian orogen lying immediately above rocks of the eastern Blue Ridge, Brevard Zone, and Opelika Group in the core of the Tallassee/Newnan-Tucker synform. The Dadeville complex consists of an array of metaigneous, metaplutonic, and metasedimentary rocks including the Ropes Creek Amphibolite, a bimodal metabasalt/metatuff, metadacite at the base, overlain by the Agricola Schist, a metaturbidite consisting of metapelite, metagreywacke, and minor metabasalt. The Chattasofka Creek Gneiss (granite) is intrusive into the Agricola Schist, Ropes Creek Amphibolite, and a mafic-ultramafic suite. The Camp Hill Gneiss (tonalite) is intrusive into the Ropes Creek Amphibolite. Also intrusive into the Agricola Schist is a mafic-ultramafic suite consisting of the Doss Mountain and Slaughters Gabbro units. There are a multitude of mafic-ultramafic suites and felsic plutonic rocks in the Dadeville complex that span from Camp Hill, Alabama to southeast Atlanta, Georgia that have been identified over the course of this research. Distinctive major and trace element geochemical signatures of the felsic intrusives, Ropes Creek Amphibolite, and various mafic-ultramafic suites all suggest formation within a volcanic arc environment. U/Pb dating of detrital zircons in the Agricola Schist, and equivalent metasedimentary rocks, as well as igneous zircons in the Chattasofka Creek Gneiss, Camp Hill Gneiss, and Ropes Creek Amphibolite yield Middle Ordovician ages, with the Agricola Schist also containing a subordinate fraction of Grenville and Granite-Rhyolite Province ages. Additionally, the Camp Hill Gneiss, Chattasofka Creek Gneiss, and Doss Mountain and Slaughters Gabbro suites all exhibit negative initial epsilon Nd (ENdi) values indicative of a continental origin. These relationships suggest that the Dadeville Complex volcanic arc, and the associated Wedowee-Emuckfaw-Dahlonega back-arc basin, resulted from a B-type suprasubduction system where Iapetan oceanic lithosphere subducted beneath a distended Laurentian continental plate, and that there could be other Taconic arc fragments in the southern Appalachians, akin to or apart of the Dadeville complex, that have yet to be identified.