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AAPG Annual Convention and Exhibition

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Three-Dimensional Evolution of Normal Faults in Two Previous HitPhaseNext Hit Rifting

Abstract

Extensional provinces are known to have experienced multiple phases of rifting. The relative maturity of the initial Previous HitphaseNext Hit of rifting to a subsequent Previous HitphaseNext Hit has been shown through physical analogues to influence the reactivation of existing faults, the orientation and location of new faults, the evolution of the number-length relationship and strain accommodation. These assess the surface geometry and interaction of the structures but cannot determine the three-dimensional interaction of the faults within the media. Understanding the nature of these interactions, may hold the key to determining the underlying controls on fault activity in rifted margins. A three-dimensional discrete element model has been developed to examine the growth, interaction and activity on faults and associated strain accommodation in a two-Previous HitphaseNext Hit rift. The model discretises the crust into an assembly of >2 million spherical elements in a two-layer system that employs brittle and ductile interactions between element pairs, dependent on their initial location within the model and gravitational and isostatic forces. Faults are defined as the breaking of bonds between elements in the upper, brittle crust. The location of elements is known throughout and failure between element pairs is monitored, which in turn is used to define fault location, failure time and throw which is then analysed and interpreted. Results from two-Previous HitphaseNext Hit rifting are presented where the relative maturity of Previous HitphaseNext Hit I (0-10%) to a constant Previous HitphaseNext Hit II (15%) is investigated. The obliquity of Previous HitphaseNext Hit I is held constant to the main (Previous HitphaseNext Hit II) extension throughout. The smallest length of Previous HitphaseNext Hit I extension results in a modification to the location of Previous HitphaseNext Hit II structures. Increased maturity of structures in Previous HitphaseNext Hit I results in localisation and focus of strain accommodation onto early forming structures which become dominant basin-bounding faults; an increased number of faults accommodating the partitioning of the brittle crust and greater displacement of later Previous HitphaseNext Hit faults parallel to the Previous HitphaseTop II extension direction. Fault activity and strain accommodation vary through time, where the complexity of interactions at depth are not readily discernible from surface geometries, and the linkage of along strike antithetic structures within the crust is common.