The Science Seminar Series: October 28, 2010
When Georgia Had Volcanoes: The Earliest Phases of Appalachian Mountain Building
Dr. Clint Barineau
Department of Earth and Space Sciences
Columbus State University
Student Union Theater
Time: 4:00 -5:00pm
On a geologically active planet such as Earth, changes in the physical character of continents and oceans are the norm. Although the Georgia of today, like much of the east coast of North America, consists of a deeply eroded and topographically low mountain chain (Appalachians) flanked on the east-southeast by flat lying sedimentary rocks (Atlantic and Gulf Coastal Plains), Georgia's geologic past was far more tectonically active. The Georgia of 480 million years ago was home to active volcanoes associated with a convergent plate margin, not dissimilar to portions of the west coast of North America and much of the Pacific Rim. Geologists have recognized for the better part of a century that many rocks within the Piedmont and Blue Ridge physiographic provinces were magmatic-volcanic in origin. However, in recent decades the geologic relationship between these rocks and the continent of North America has come into question. Researchers from the New England and Canadian segment of the Appalachians have long suggested that North America was subducted beneath one or more volcanic island arcs during the Ordovician, resulting in the accretion of volcanic terranes to the ancient North American margin. However, research from the Appalachians of Alabama, Georgia, and North Carolina suggests that a very different tectonic setting is needed to account for the geologic history and geometry of lithotectonic terranes in this region. Contrasts between the northern and southern ends of the Appalachian Mountains suggests that a major transform plate boundary must have accommodated subduction zones of opposite polarity during the Ordovician – not unlike modern day New Zealand and Taiwan – implying that the earliest phases of Appalachian mountain building (orogeny) involved the development of volcanoes directly on the ancient North American plate.