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Abstract

AAPG Bulletin, V. 86, No. 6 (June 2002), P. 935-960.

Copyright ©2002. The American Association of Petroleum Geologists. All rights reserved.

4-D evolution of rift systems: Insights from scaled physical models

K. R. McClay,1 T. Dooley,2 P. Whitehouse,3 M. Mills4

1Fault Dynamics Research Group, Geology Department, Royal Holloway University of London, Egham, Surrey, TW20 0EX, United Kingdom; email: [email protected]
2Fault Dynamics Research Group, Geology Department, Royal Holloway University of London, Egham, Surrey, TW20 OEX, United Kingdom; email: [email protected]
3Fault Dynamics Research Group, Geology Department, Royal Holloway University of London, Egham, Surrey, TW20 OEX, United Kingdom; email: [email protected]
4Fault Dynamics Research Group, Geology Department, Royal Holloway University of London, Egham, Surrey, TW20 OEX, United Kingdom

AUTHORS

Ken McClay graduated with a B.Sc. (honors) degree from Adelaide University, Australia. He subsequently undertook an M.Sc. degree in structural geology and rock mechanics at Imperial College, London University, where in 1978 he also obtained a Ph.D. in structural geology. He was awarded a D.Sc. by Adelaide University, Australia, in 2000. He is BP Professor of Structural Geology and director of the Fault Dynamics Research Group at Royal Holloway University of London. His research involves the study of extensional thrust, strike-slip, and inversion terranes and their applications to hydrocarbon exploration. He publishes widely, consults, and offers short courses to industry.

Tim Dooley, a native of Waterford, Ireland, graduated with a B.A. (honors) degree (Mod.) from Trinity College Dublin, Ireland, in 1988. Subsequently, he undertook a Ph.D. in structural geology at Royal Holloway University of London. Since 1994 Tim has been a postdoctoral research assistant with the Fault Dynamics Research Group in the structural modeling laboratories at Royal Holloway. His current research interests include analog modeling of extensional, strike-slip, salt and shale, and compressional tectonics, as well as developing graphic and interactive techniques for the presentation of these data to students and industry.

Paul Whitehouse graduated from the University of Birmingham in 1996 with a B.Sc. degree in geology. In 1998, he completed an M.Sc. degree in basin evolution and dynamics at Royal Holloway University of London before joining the Fault Dynamics Research Group as a postgraduate research assistant. His recent research topics include analog modeling of three-dimensional extensional fault systems and analog modeling of doubly vergent thrust wedges. His current work concentrates on fault and fracture systems in extensional tectonic settings, incorporating analog modeling and field studies in the Gulf of Suez, Egypt.

Michelle Mills graduated from the University of Edinburgh in 1997 with a B.Sc. degree in geology, having spent her third year at the University of California, Santa Cruz. She spent a year as a voluntary worker before completing her M.Sc. degree in tectonics at Royal Holloway College in 1999. She currently works at Heriot-Watt University evaluating computer-aided learning software for engineering.

ACKNOWLEDGMENTS

This research was supported by the Natural Environment Research Council (NERC) ROPA Grant GR3/R9529. Additional support came from the Fault Dynamics Project (sponsored by ARCO British Limited, Petrobras U.K. Ltd., BP Exploration, Conoco [United Kingdom] Limited, Mobil North Sea Limited, and Sun Oil Britain). McClay also gratefully acknowledges support from BP Exploration. Howard Moore and Mike Creager constructed the deformation apparatus. This article is Fault Dynamics Publication 101.

ABSTRACT

The four dimensional (4-D) evolution of brittle fault systems in orthogonal, oblique, and offset rift systems has been simulated by scaled sandbox models using dry, cohesionless, fine-grained quartz sand. Extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model. The results of these analog model studies are compared with natural examples of rift fault systems.

Rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction. Segmentation of the rift margin increases with increase in obliquity of the rift axis, resulting in a consequent increase in displacement on intrarift fault systems. Offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone.

Along-strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones. High-relief, extension-parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems. Changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults. The second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low-relief oblique-slip zone or grabens. These typically are found in highly oblique rift systems (<45 degrees) and above right steps in offset rift models.

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