Inversion of the Kechika Trough, Northeastern British Columbia, Canada

Abstract

Summary The Kechika Trough, in the western Rocky Mountains of northern Canada, is a NW-trending fold and thrust belt of Hadrynian through Mississippian strata within the telescoped passive margin of ancestral North America. The Kechika Trough underwent major crustal extension in the Mid-Late Devonian with the deposition of coarse to fine ‘Antler’ type black clastics in an asymmetrical basin consisting of a terraced half-graben system to the west and a roll-over structure to the east. Inversion and contraction of the Kechika Trough occurred during the Jurassic-Cretaceous Columbian-Laramide orogeny. The geometries of the resultant fold and thrust systems were strongly controlled by the half-graben extensional architectures and by the geometries of the synrift sediment packages. Inversion structures include contractionally reactivated extensional faults, rotated and re-utilized extensional faults, and thrust faults pinned by extensional faults as a result of buttressing against rigid sediment wedges. Inversion of the synrift sediments is associated with strongly developed chevron folding, pervasive cleavage development and imbrication by out-of-half-graben thrust faults. These thrust faults may locally climb down stratigraphic section in the direction of transport as a result of cutting through strata tilted by Mid-Late Devonian extensional faults. Major stratigraphic contrasts between adjacent thrust packages have been resolved in terms of lateral facies differences produced by extension, rather than by over-complex thrust geometries. Although syndepositional extensional faults are not preserved in the thrust belt, their position and geometry may be inferred from an analysis of structural, stratigraphic and sedimentological relationships.

Origin of the Nchanga copper–cobalt deposits of the Zambian Copperbelt

“…These veins may have formed in similar circumstances, so appearing to terminate at ore boundaries (which are the lithological contacts of the 'Feldspathic Quartzite') and explaining their highangle intersection with bed-parallel features. basins is often controlled by the pre-existing extensional faults (Cooper & Williams, 1989;McClay et al, 1989). The geometry of such systems is commonly more complicated than simple thrust systems and can vary from small, high-angle thrusts in basins that have undergone small amounts of contraction to large, low-angle thrust systems that override and obliterate the pre-existing extensional fault geometry (McClay & Buchanan, 1992).…”

Structural evolution of the southwestern Daqing Shan, Yinshan belt, Inner Mongolia, China

“…If this is correct, preexisting normal faults essentially controlled the geometry of later contractional structures. The reactivation of extensional faults so that they undergo reverse slip, i.e., the process of inversion (Cooper and Williams, 1989), has been documented in many orogenic belts throughout the world, including the Alps (Butler, 1989), the Canadian Cordillera (McClay et al, 1989), and the Yinshan belt .…”

Positive inversion of extensional footwalls in the southern Serra do Espinhaço, Brazil - insights from sandbox laboratory experiments

“…Only a few studies have described the inversion of a half-graben by the movement of the extensional footwall (e.g. McClay et al 1989, Butler 1989, Hayward and Graham 1989, Knott et al 1995. Their theoretical interpretations present some fea- 'pop-up' structure; and F-combined model. tures that were also produced in our experiments, such as the trapping of the rift fi lls in the hinterland of the inverted basin, the development of a thrust system in the foreland and the introduction of prerift sheets into the synrift sequence.…”

“…Their theoretical interpretations present some fea- 'pop-up' structure; and F-combined model. tures that were also produced in our experiments, such as the trapping of the rift fi lls in the hinterland of the inverted basin, the development of a thrust system in the foreland and the introduction of prerift sheets into the synrift sequence. McClay et al (1989) proposed this architecture for the McCook half-graben of the Kechika Trough, Canada (Fig. 11A), and Butler (1989) for the regional west Alps (Fig.…”

“…Both architectures are in good agreement with our experiment II. In addition, McClay et al (1989), Hayward and Graham (1989) and Knott et al (1995) proposed that, during the progressive evolution of basin inversion, rotation of the normal detachment ramp occurs until complete inversion. The evolution of an " overturned normal fault" can be seen in our physical model II (Fig.…”