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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
DOI: 10.1306/02071716090
Three-dimensional fault geometries and interactions within experimental models of multiphase extension
Martha Oliver Withjack,1 Alissa A. Henza,2 and Roy W. Schlische3
1Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854; [email protected]
2Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854; present address: Statoil Gulf Services LLC, 2107 City West Blvd, Houston, Texas, 77042; [email protected]
3Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854; [email protected]
ABSTRACT
We use experimental (analog) models to examine the three-dimensional (3-D) fault geometries and interactions that develop during two phases of noncoaxial extension. In the models, a homogeneous layer of wet clay undergoes two phases of extension whose directions differ by 45°. The resulting fault pattern varies significantly with depth. At shallow levels, second-phase
normal faults accommodate most second-
phase
extension. At depth, both second-
phase
normal faults and reactivated, first-
phase
faults with oblique slip accommodate most second-
phase
extension. A variety of interactions occurs between first-
phase
and second-
phase
faults. One interaction involves the upward propagation of second-
phase
faults from tips of reactivated, blind, first-
phase
faults. These hybrid faults have deep segments that strike subperpendicular to the first-
phase
extension direction and shallow segments whose strike varies with depth, becoming increasingly subperpendicular to the second-
phase
extension direction at shallow levels. A second interaction involves the nucleation of second-
phase
normal faults on the surfaces of reactivated, first-
phase
faults. These splay faults propagate upward and laterally from their nucleation sites into the hanging walls of the first-
phase
faults. As they propagate, they commonly encounter and link with different first-
phase
faults. The resulting composite faults have zigzag geometries in both map and cross-sectional views. A third interaction involves either the termination of second-
phase
antithetic normal faults against or near first-
phase
faults or the offset of first-
phase
faults by second-
phase
antithetic normal faults. The 3-D fault patterns and interactions within our models closely resemble those within the Taranaki basin of offshore New Zealand and Milne Point on Alaska’s North Slope.
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