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Modeling of Pull-Apart Basins1
Tim Dooley and Ken McClay2
Scaled sandbox models have successfully
simulated the geometries and progressive evolution of pull-apart basins
developed in a weak sedimentary cover above right-stepping (releasing)
dextral strike-slip fault systems in rigid basement. Synkinematic basin
infill was added progressively as the models were deformed. Vertical and
horizontal sectioning of the completed models has allowed the full three-dimensional
architecture of the pull-apart system to be analyzed. We present three
representative end-member experiments: 30° underlapping releasing sidestep,
90° sharp nonoverlapping releasing sidestep, and 150° overlapping
releasing sidestep. The pull-apart basin geometries are typically sigmoidal
to rhombic grabens, the geometries of which are dependent upon the architecture
of the underlying basement fault systems. Underlapping releasing sidestepping
faults (offset angles of 30-75°) typically form elongate rhomboidal
grabens; 90° releasing offset sidesteps produce shorter, squat, rhomboid
pull-apart basins; and overlapping releasing sidesteps (115-150°) produce
box-like grabens with highly kinked basin sidewalls. The pull-apart basins
are bounded by terraced oblique-slip extensional sidewall fault systems
that link the laterally offset principal displacement zones (PDZ) of the
main dextral strike-slip faults. The sidewall faults show changes in kinematics
from dominantly dip-slip extension in
1997. The American Association of Petroleum Geologists. All rights reserved.
received June 24, 1996; revised manuscript received November 20, 1996;
final acceptance June 10, 1997.
Dynamics Project, Geology Department, Royal Holloway, University of London,
Egham, Surrey TW20 OEX, United Kingdom.
by the Fault Dynamics Project [sponsored by ARCO British Limited, PETROBRAS
U.K. Ltd., BP Exploration, Conoco (U.K.) Limited, Mobil North Sea Limited,
and Sun Oil Britain]. We also acknowledge additional funding from Sun Oil
Britain. Landsat Thematic Mapper data courtesy of RTZ Mining and Exploration
Limited, South American Division. Jurrian Reijs is thanked for field data
relating to the Salina del Fraile pull-apart basin. Chris Elders is thanked
for reviewing earlier versions of this manuscript, and J. Crowell, C. Morley,
and K. Biddle are thanked for constructive reviews of the manuscript. The
contents of this paper have been
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