Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic

Abstract

The results of a systematic field mapping campaign at the Haughton impact structure have revealed new information about the tectonic evolution of mid-size complex impact structures. These studies reveal that several structures are generated during the initial compressive outward-directed growth of the transient cavity during the excavation stage of crater formation: (1) sub-vertical radial faults and fractures; (2) sub-horizontal bedding parallel detachment faults; and (3) minor concentric faults and fractures. Uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift. Compressional inward-directed deformation results in the duplication of strata along thrust faults and folds. It is notable that Haughton lacks a central topographic peak or peak ring. The gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults. While the outermost concentric faults dip in toward the crater center, the majority of the innermost faults at Haughton dip away from the center. Complex interactions between an outward-directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted, intensely faulted (sub-) vertical and/or overturned strata at a radial distance from the crater center of ~5.0-6.5 km. Converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures: (1) sub-vertical radial faults and folds; (2) positive flower structures and chaotically brecciated ridges; (3) rollover anticlines in the hanging-walls of major listric faults; and (4) antithetic faults and crestal collapse grabens. Oblique strike-slip (i.e., centripetal) movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage. It is clear that deformation during collapse of the transient cavity walls at Haughton was brittle and localized along discrete fault planes separating kilometer-size blocks.