40 Ar/39 Ar AGES OF MUSCOVITE FROM THE WESTERN BLUE RIDGE AND TALLADEGA BELT, GEORGIA AND NORTH CAROLINA Except where reference is made to the work of others, the work described in this thesis is my own or was done in collaboration with my advisory committee. This thesis does not include proprietary or classified information. _________________________________________ Wayne M. McDonald Certificate of Approval: ________________________________ ________________________________ Luke J. Marzen Willis E. Hames, Chair Associate Professor Professor Geology and Geography Geology and Geography ________________________ ________________________ Mark G. Steltenpohl George T. Flowers Professor Interim Dean Geology and Geography Graduate School 40 Ar/39 Ar AGES OF MUSCOVITE FROM THE WESTERN BLUE RIDGE AND TALLADEGA BELT, GEORGIA AND NORTH CAROLINA Wayne M. McDonald A thesis Submitted to the graduate faculty of Auburn University in partial fulfillment of the Requirements for the Degree of Master of Science Auburn, Alabama May 10, 2008 40 Ar/39 Ar AGES OF MUSCOVITE FROM THE WESTERN BLUE RIDGE AND TALLADEGA BELT, GEORGIA AND NORTH CAROLINA Wayne M. McDonald Permission is granted to Auburn University to make copies of this thesis at its discretion, upon request of individuals or institutions and at their expense. The author reserves all publication rights. ________________________ Signature of Author ________________________ Date of Graduation iii VITAE Wayne M. McDonald, son of Dr. William J. McDonald and Virginia M. Leritz, was born January 25, 1974, in West Palm Beach, Florida. He graduated from Cardinal Newman High School in 1992. Subsequently, he attended Auburn University, Alabama, and graduated in December, 1998 with a Bachelor of Science degree in Geology. He worked as an environmental consultant for a few years and then entered Graduate School, Auburn University, in August, 2003. iv THESIS ABSTRACT 40 Ar/39 Ar AGES OF MUSCOVITE FROM THE WESTERN BLUE RIDGE AND TALLADEGA BELT, GEORGIA AND NORTH CAROLINA Wayne M. McDonald Masters of Science, May 10, 2008 (B.S., Auburn University, 1998) 114 Typed Pages Directed by Willis E. Hames Radiometric age constraints regarding the timing of metamorphism in the western Blue Ridge province of the southern Appalachians have been too limited or uncertain to enable broader correlation and understanding of Taconian, Acadian, and Alleghanian events in the region between western North Carolina and Alabama. Moreover, various fossil, stratigraphic and radiometric data for the timing of metamorphism in the Talladega belt of Alabama are difficult to reconcile with radiometric ages of comparable tectonic units in the western Blue Ridge of North Carolina. New 40 Ar/ 39 Ar radiometric data for single-muscovite crystals have been collected, utilizing the Auburn Noble Isotope Mass Analysis Laboratory (ANIMAL), to help constrain the timing of metamorphism in the western Blue Ridge of Georgia and North Carolina. The mean ages of muscovite in v phyllites collected from the Cartersville transverse zone record crystallization and cooling in the interval from 321.4±0.3 - 335.5±0.8 Ma (corresponding to Serpukhovian and Visean stages of the Mississippian). The mean ages of muscovite in three phyllites from a sampling transect along U.S. Hwy. 64 (between Murphy, North Carolina and Ducktown, Tennessee) are similar to those of the Cartersville transverse zone. However, the age distributions of single-crystal muscovite in six other schists and phyllites from this Murphy-Ducktown transect are complex, with ages ranging up to ca. 465 Ma. The mean ages of muscovite in metasiltstones and phyllites collected within or near the Great Smoky fault (between the Murphy-Ducktown transect and the Cartersville transverse zone) also tend to be Visean. However, several samples from this tectonic setting also yield very complex age distributions. The complex age distributions determined in this study seem mainly due to effects of polymetamorphism in some rocks, but are also influenced by the presence of relict-detrital muscovite and incorporation of unsupported- extraneous (‘excess’) 40 Ar in some samples. The single-crystal 40 Ar/ 39 Ar ages determined in this study are interpreted to indicate that Mississippian tectonic events dominated metamorphic and structural evolution in the Talladega belt and in the Mineral Bluff Group of the western Blue Ridge. For Ocoee Supergroup rocks, in the western Blue Ridge, the muscovite in phyllites and schists record a history of pre-Carboniferous (Acadian or Taconian) events partially overprinted by Mississippian deformation. The Mississippian ages are interpreted to represent Alleghanian events recorded in the muscovite of Talladega belt-western Blue Ridge rocks that pre-date final emplacement of the Blue Ridge thrust sheet, as the youngest deformed strata of the Valley and Ridge (Pottsville Formation; 316-303 Ma) indicates Pennsylvanian deposition. This combined vi with Tournaisian fossil control ( Periastron plant fossil; 360-350 Ma) indicates Alleghanian metamorphism and deformation in the Talladega belt-western Blue Ridge is constrained to ~ 360-300 Ma, older and longer in duration than the classic view of the Alleghanian as Pennsylvanian to Permian. vii ACKNOWLEDGEMENTS The National Science Foundation funded this study and provided financial assistance to the author for one year. Special thanks to Dr. Willis Hames for the opportunity to work on this study and his effort to see it through. Thanks are also due to committee members Dr. Luke Marzen, for assistance with the GIS, and Dr. Mark Steltenpohl, for help with understanding structural aspects of this study. Also worth noting are Dr. Ashraf Uddin and Dr. Charles Savrda for their moral support and general guidance, John Simms for his almost daily assistance with various things, and Dr. Mehmet Billor for many helpful discussions. Thanks are mostly due to family members William and Virginia whose financial support made working on this study a possibility. viii Style manual or journal used: Geology Computer software used: Adobe® EasySVG, Adobe® Photoshop®, ESRI® ARCGIS® 9.1, Microsoft® Excel® 2003, Microsoft® FrontPage® 2003, Microsoft® Word® 2003, Microsoft® PowerPoint® 2003 ix TABLE OF CONTENTS LIST OF FIGURES .......................................................................................................... xii LIST OF TABLES.......................................................................................................... xvii INTRODUCTION ...............................................................................................................1 GEOLOGIC SETTING OF THE SOUTHERN BLUE RIDGE PROVINCE.....................4 REGIONAL GEOLOGY.........................................................................................4 TACONIAN OROGENY ........................................................................................8 ACADIAN OROGENY...........................................................................................8 ALLEGHANIAN OROGENY ................................................................................9 TIMING OF EVENTS.......................................................................................................10 STRATIGRAPHIC CONSTRAINTS ...................................................................10 RADIOMETRIC CONSTRAINTS .......................................................................11 GIS DATABASE...............................................................................................................16 DESCRIPTION OF TECTONIC UNITS STUDIED........................................................19 SAMPLE PETROGRAPHY..............................................................................................24 CARTERSVILLE TRANVERSE ZONE..............................................................25 GREAT SMOKY FAULT.....................................................................................30 DUCKTOWN ANTICLINORIUM.......................................................................32 MURPHY SYNCLINORIUM...............................................................................34 40 Ar/ 39 Ar ANALYSIS........................................................................................................37 x BASIS OF THE METHOD ...................................................................................37 40 Ar/ 39 Ar DATING TECHNIQUES ......................................................................38 ANALYTICAL METHODS .............................................................................................42 ANALYTICAL RESULTS ...............................................................................................46 CARTERSVILLE TRANSVERSE ZONE............................................................48 GREAT SMOKY FAULT.....................................................................................54 DUCKTOWN-MURPHY TRANSECT ................................................................60 INTERPRETATION OF RESULTS .................................................................................65 DISCUSSION....................................................................................................................73 CONCLUSIONS................................................................................................................77 REFERENCES ..................................................................................................................79 APPENDICES ...................................................................................................................86