Fault Geometry and Kinematics within the Terror Rift, Antarctica THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By William B. Blocher Graduate Program in Earth Sciences The Ohio State University 2017 Master's Examination Committee: Dr. Terry Wilson, Advisor Dr. Thomas Darrah Dr. Derek Sawyer Copyrighted by William B. Blocher 2017 Abstract The Terror Rift is the youngest expression of the intraplate West Antarctic Rift System that divides the Antarctic continent. Previous studies of the Terror Rift have ascribed a variety of interpretations to its structure, and especially to the regional anticline known as the Lee Arch, which has been explained as a transtensional flower structure, a rollover anticline, and as the result of magmatic inflation. Fault mapping and the documentation of stratal dips in this study have revealed a Terror Rift structure characterized by north-south folds and a complex distribution of faults. Nearly all faults have normal sense dip separation. A continuous zone of west-dipping faults with relatively high-magnitude normal separation are interpreted to be the border fault system defining the eastern margin of Terror Rift. Reconstruction of listric ramp-flat geometry of this border fault system explains intrarift fold and fault patterns well. Zonation of structures indicates that the listric rift detachment faults are segmented along the rift axis. This new model for rift structure indicates orthogonal rift extension in the ENE- WSW direction, with low strains of <10% calculated from bed-length balancing. i Acknowledgments To my advisor, Dr. Terry Wilson, for her inexhaustible knowledge and patience. And to my parents, Richard and Janice, for their unconditional love and support. ii Vita 2007 ..........................................................Whetstone H.S. 2010 ..........................................................Associate of Science, Columbus State 2013 ..........................................................B.S. Geology, Ohio State University 2013 to present ........................................Graduate Teaching Associate, School of Earth Sciences, The Ohio State University Fields of Study Major Field: Earth Sciences iii Table of Contents Abstract ..................................................................................................................... i Acknowledgments .................................................................................................... ii Vita .......................................................................................................................... iii Introduction ............................................................................................................. 1 Background .............................................................................................................. 4 Investigation of Terror Rift Structure .................................................................. 4 Elements of Rift Architecture ............................................................................... 7 Folds in an Extensional or Transtensional Context ............................................ 11 Flower Structures ............................................................................................. 11 Rollover structures .......................................................................................... 13 Problem Statement.................................................................................................. 17 The Orthogonal Model ......................................................................................... 17 The Transtensional Model .................................................................................. 20 Methods .................................................................................................................. 21 Seismic Data........................................................................................................ 21 iv Fault Interpretation ............................................................................................ 23 Fault Correlation Criteria ................................................................................ 25 Dip Analysis ........................................................................................................ 31 Dip Signatures ................................................................................................. 34 Cross-Section Methods ....................................................................................... 36 Bed-length Balancing ...................................................................................... 36 Fault Geometry Construction through Dip Domains ..................................... 37 Results .................................................................................................................... 43 Stratal Dip Patterns ............................................................................................ 43 Map view stratal dip patterns ......................................................................... 43 Stratal dip patterns with depth ....................................................................... 47 Fault Patterns ...................................................................................................... 55 Fault identification, correlation, and mapping ............................................... 55 Fault geometry................................................................................................. 59 Fault motions: sense and separation ............................................................. 61 Fault Profile Reconstruction .............................................................................. 65 Extension Estimates from Balanced Sections .................................................... 75 Interpretive Maps ............................................................................................... 81 Discussion .............................................................................................................. 90 v References .............................................................................................................. 98 Appendix A: Matlab Scripts .............................................................................. 102 Rollover.m ......................................................................................................... 102 Cartesian_intersect.m ...................................................................................... 104 Projectpointtoline.m ......................................................................................... 104 planefit.m .......................................................................................................... 105 fwaz.m ............................................................................................................... 105 haversine.m ....................................................................................................... 105 Appendix B: Plane Fitting ................................................................................. 107 Round Earth Complications ............................................................................. 108 Sensitivity Testing .............................................................................................. 114 vi List of Figures Figure 1. Reconstructed Cretaceous West Antarctic Rift System from Siddoway (2008). Area of this study is in the southwestern Ross Sea. ............................................................ 1 Figure 2. Rift basins of the Ross Sea. TR denotes the Terror Rift, the subject of this study. From Hall et al. (2007) ............................................................................................. 2 Figure 3. An interpretation of Terror Rift structures constructed from the first iteration of seismic interpretation by Cooper et al. (1987) .................................................................... 3 Figure 4. The reflection seismology dataset within the study area comprises data acquired during many different surveys. ........................................................................................... 4 Figure 5. A map from (Salvini et al., 1997) delineating Terror Rift fault patterns and depicting Terror Rift architecture as being the result of an en echelon termination of regional strike-slip faults..................................................................................................... 5 Figure 6. Interpretive maps from Hall et al. (2007) (left) and Salvini et al. (1999) (right) highlighting the different explanations for the same observed architecture, esp. in the proximity of Drygalski Ice Tongue. .................................................................................... 6 Figure 7. Profile geometries of a symmetric (A) and an asymmetric (B) rift (Acocella, 2010). .................................................................................................................................. 7 Figure 8. Offset fault segments becoming linked together as strain progresses (Fossen & Rotevatn, 2016) ................................................................................................................... 8 Figure 9. Different structures that occur at releasing and restraining bends in a translational tectonic system (Cunningham & Mann, 2007). ............................................