Baum, Mark S.1, Jennifer A. Elder Brady1, Roy W. Schlische1,
Martha Oliver Withjack1
(1) Rutgers University, Piscataway, NJ
ABSTRACT: Oblique Shortening Following Oblique Extension: An Experimental Study of Their Relative Influence on the Geometry of Inversion Structures
Inversion structures result from two phases of deformation: an extensional phase and an ensuing shortening phase. We conducted a series of scaled experimental models in which we independently varied the obliquity for both stages of deformation. In our models, a layer of wet clay covered two overlapping metal plates: one fixed and one mobile. The edge of the fixed plate represents a preexisting zone of weakness. The angles between the displacement direction of the mobile plate and the edge of the fixed plate for the extensional phase and the shortening phase are and , respectively.
Our work shows that the degree of obliquity during both tectonic episodes influences the final deformation pattern. Obliquity during the extensional phase produces a fault zone that parallels the preexisting zone of weakness, with secondary normal faults subperpendicular to the displacement direction. All major through-going faults reactivate during inversion. Secondary normal faults striking obliquely to the major fault zone show varying degrees of reactivation, depending on their orientation relative to . For any initial , deformation patterns are similar for all >45°: new large-scale folds and thrust faults form subparallel to the preexisting zone of weakness. For all <30°, no new large-scale folds and few new thrust faults form. Instead, strike-slip faults develop subparallel to the preexisting zone of weakness. We conclude that the inversion deformation pattern is more sensitive to variations in than to variations in . The modeling results resemble deformation patterns in inverted rift basins of eastern North America.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.