Structural evolution of connecting splay duplexes and their implications for critical taper: an example based on geometry and kinematics of the Canyon Range culmination, Sevier Belt, Central Utah

Abstract

Critical taper in an evolving orogenic wedge can be maintained by structural thickening in the back of the wedge. This is often achieved by folding and uplift of pre-existing large, internal thrust sheets by the continued growth and/or reactivation of duplexes in the hinterland. The growth of a blind imbricate complex off a lower thrust provides another mechanism for folding a higher thrust. Individual splays in a blind imbricate complex may have fault propagation folds and/or fault bend folds associated with them. If the splays reach the overlying thrust, they serve as connecting splays between the lower thrust (floor) and the upper thrust (roof), thereby forming a connecting splay duplex (CSD). This type of duplex geometry requires periodic reactivation of the pre-existing roof thrust. The Canyon Range thrust in central Utah is an internal thrust that is folded into an overturned antiform-synform pair and overrides its own synorogenic conglomerates. The same conglomerates are infolded into the core of the synform and preserve critical timing information regarding the history of folding and thrust reactivation. The folding is caused by the development of a footwall antiformal stack in the core of the Canyon Range antiformal culmination; the geometry and timing relationships suggest that the structure grew as a CSD. Regional timing relationships suggest that the growth of the CSD and reactivation of the thrust took place during the later part of the evolution of the orogenic wedge, and may have helped the wedge maintain critical taper during thrusting in the external fold-and-thrust belt.