Evidence for synchronous thrusting in the northern Sawtooth Range, Montana
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5421247
- Univ. of Washington, Seattle, WA (United States). Dept. of Geological Sciences
The critical-taper wedge model of the thrust belt development requires synchronous and so-called out-of-sequence movement on thrust faults to be common. Analysis of new field data reveals a positive test of recently proposed geometric/kinematic model of synchronous thrusting. The northern Sawtooth Range in northwestern Montana presents an intriguing pattern on regional maps: thrust faults terminate in the core of a large northwest-trending and -plunging anticline; the anticline folds an overlying detachment and supports on its forelimb a slack of closely spaced and variably folded thrust imbricates. The plunging nature of mapped structures and excellent exposures permit them to observe different structural levels and to incorporate the three-dimensional observations into cross-sections is parallel to the mean transport direction. Transport direction was determined using kinematic analysis of mesoscopic asymmetric folds and composite Riedel structures along the faults. Despite an apparently uninterpretable tangle of Cretaceous imbricates in map view, down-plunge projections, such as the example below, reveal strikingly planar imbricates which break off the top of both regional and subsidiary culminations. Retrodeformation of the cross-sections is compatible with simultaneous movement on two or more faults. The results are in accord with predictions of the proposed synchronous thrust model.
- OSTI ID:
- 5421247
- 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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