Geometry and sequential evolution of thrust systems in the thrust belt of northwest Montana: Support for the critical-wedge model
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5291601
- Univ. of Washington, Seattle, WA (United States). Dept. of Geological Sciences
Cross sections of the northwest Montana thrust belt, constructed principally from published geologic maps and a number of cross-strike traverses, provide constraints on the geometry and sequential evolution of thrust systems, which in turn are compatible with the critical-wedge model of thrust-belt mechanics. Sequential restorations of Sawtooth Range thrust systems, in map and cross section, indicate that earlier formed thrusts to the west remained active during the eastern advance of the thrust front. Three-dimensional balancing arguments likewise suggest that the Lewis thrust, to the north and west, continued to move during the development of the Sawtooth Range. Continuous or periodically reactivated motion on the Lewis was responsible for the maintenance of critical taper in the northern and western Sawtooth Range, the footwall Paleozoic were strengthened by the overlying sheet and experienced little internal imbrication. However, where the thrust front advanced in front of the leading edge of the Lewis, the thinly-tapered Paleozoic package was imbricated to from the characteristic sawtooth-shaped ranges of the Montana thrust belt. Thus, critical taper in the Sawtooths was maintained by duplexing of Paleozoic rocks and back-rotation accompanying piggy-back thrusting. Additional duplexes of Paleozoic rocks in the footwall of the Lewis may have developed late in the orogeny to compensate for erosion of the overlying Lewis sheet. Continuing motion on the Lewis, as it was folded over footwall duplexes, produced out-of-sequence imbricates within the Lewis sheet.
- OSTI ID:
- 5291601
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
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