Krantz, Robert W.¹, Mary K. Johns², Erik Lundin³ 
(1) ConocoPhillips, Houston, TX 
(2) ExxonMobil, Houston, TX
(3) NGU (Norwegian Geological Survey), Norway

ABSTRACT: Oblique Inversion Structures and 3D Processes: Results from Analog Models

Inversion structures are common in many important producing basins. Inversion structures result from compressional deformation and uplift of existing extensional features. Inversion commonly induces variable degrees of fault reactivation and slip reversal, making for complex tectonic evolution and challenging interpretation. 
Many classic investigations of inversion focus on 2D cross section geometries, and assume or imply that the compression during the inversion phase parallels the extension of the initial phase. Our investigation considers the more general case, where compression and shortening are oblique to earlier extension. Each model, scaled for normal gravity and mechanical properties by using sand and silicone putty, included an extension phase that produced normal faults, subsidence, and growth sediments. During the inversion phase, we varied the compression direction from parallel to extension to oblique to strike-slip. By using a CT scanner to record internal geometries, we documented the complete 3D evolution of each inversion system. 
The model results suggest that both the structural styles and the degree of fault reactivation are strongly dependent on the component of oblique displacement. Less oblique systems produced new, low angle thrusts. More oblique systems induced nearly complete fault reactivation and slip reversal. 3D geometries and kinematics also vary: less oblique systems include more cylindrical structures, whereas more oblique systems develop en-echelon map patterns and significant slip partitioning. 
Since we expect oblique inversion to be the more general case in nature, these model results can aid subsurface interpretation with implications for 3D geometries, fault timing, and kinematic-dynamic evolution of sub-seismic structures.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.