Cracking a Geologic Cold Case: A 500-470 Million Year Old Missing Volcanic Arc in Central-Eastern Alabama
Primary Faculty Mentor’s Name
Dr. Clinton I. Barineau
Proposal Track
Student
Session Format
Poster
Abstract
The geologic history of the Appalachians begins over 480 million years ago with the earliest phases of mountain building during the Taconic orogeny. Geologists working in the northern Appalachians of Canada and the New England states over four decades ago recognized evidence for a collision between the North American continent and a volcanic arc complex which formed in the ancient Iapetus Ocean during the earliest parts of the Ordovician Period. During this arc-continent collision, rocks of the Taconic volcanic arc were emplaced along faults above rocks of the ancient North American continental margin, pushing up “Taconic Highlands” in the process – similar to modern uplift of the island of Taiwan where subduction of the southeastern Asian continent beneath oceanic crust of the Pacific Ocean is ongoing. Although geologists in the southern Appalachians recognize similar tectonic activity during the Ordovician, the evidence for an arc-continent collision in the Appalachians of Alabama, Georgia and North Carolina has been problematic. In fact, one key difference between the two ends of the mountain belt is the paucity of geologic features typical of an arc-continent collision in the southern Appalachians – including the absence of the Taconic volcanic arc. Instead, the geology of the southern Appalachians is more typical of a “Sea of Japan-type” orogen. Over the last few decades, geological work in the southern Appalachians has established that the eastern Blue Ridge in Alabama, comprised of the Ashland-Wedowee-Emuckfaw belt, represents a back-arc basin which formed on the Iapetus margin of the Laurentian plate. This would, therefore, suggest that the Taconic arc should be found farther southeast of these back-arc sequences, unlike in the northern Appalachians, where rocks of the arc and North American continent are separated only by rocks of an accretionary prism. Up until recently, there has been little definitive evidence to support a specific location for the Taconic arc. One candidate for the “missing” Taconic arc, however, is the Dadeville Complex of central-eastern Alabama. Geochemical analysis of these rocks, including major- and trace element analyses, suggest units of the Dadeville Complex are similar in character to modern volcanic arcs. In addition, radiometric dating of zircon obtained from the Dadeville Complex has yielded Ordovician ages, consistent with formation of this arc in the time frame spanned by the Taconic orogeny.
Keywords
Geology; southern Appalachians; back-arc; volcanic arc; Taconic; geochemistry
Location
Concourse and Atrium
Presentation Year
2015
Start Date
11-7-2015 10:10 AM
End Date
11-7-2015 11:20 AM
Publication Type and Release Option
Presentation (Open Access)
Recommended Citation
Perry, Patsy J., "Cracking a Geologic Cold Case: A 500-470 Million Year Old Missing Volcanic Arc in Central-Eastern Alabama" (2015). Georgia Undergraduate Research Conference (2014-2015). 33.
https://digitalcommons.georgiasouthern.edu/gurc/2015/2015/33
Cracking a Geologic Cold Case: A 500-470 Million Year Old Missing Volcanic Arc in Central-Eastern Alabama
Concourse and Atrium
The geologic history of the Appalachians begins over 480 million years ago with the earliest phases of mountain building during the Taconic orogeny. Geologists working in the northern Appalachians of Canada and the New England states over four decades ago recognized evidence for a collision between the North American continent and a volcanic arc complex which formed in the ancient Iapetus Ocean during the earliest parts of the Ordovician Period. During this arc-continent collision, rocks of the Taconic volcanic arc were emplaced along faults above rocks of the ancient North American continental margin, pushing up “Taconic Highlands” in the process – similar to modern uplift of the island of Taiwan where subduction of the southeastern Asian continent beneath oceanic crust of the Pacific Ocean is ongoing. Although geologists in the southern Appalachians recognize similar tectonic activity during the Ordovician, the evidence for an arc-continent collision in the Appalachians of Alabama, Georgia and North Carolina has been problematic. In fact, one key difference between the two ends of the mountain belt is the paucity of geologic features typical of an arc-continent collision in the southern Appalachians – including the absence of the Taconic volcanic arc. Instead, the geology of the southern Appalachians is more typical of a “Sea of Japan-type” orogen. Over the last few decades, geological work in the southern Appalachians has established that the eastern Blue Ridge in Alabama, comprised of the Ashland-Wedowee-Emuckfaw belt, represents a back-arc basin which formed on the Iapetus margin of the Laurentian plate. This would, therefore, suggest that the Taconic arc should be found farther southeast of these back-arc sequences, unlike in the northern Appalachians, where rocks of the arc and North American continent are separated only by rocks of an accretionary prism. Up until recently, there has been little definitive evidence to support a specific location for the Taconic arc. One candidate for the “missing” Taconic arc, however, is the Dadeville Complex of central-eastern Alabama. Geochemical analysis of these rocks, including major- and trace element analyses, suggest units of the Dadeville Complex are similar in character to modern volcanic arcs. In addition, radiometric dating of zircon obtained from the Dadeville Complex has yielded Ordovician ages, consistent with formation of this arc in the time frame spanned by the Taconic orogeny.
