Abstract
Evolution of contractional structures in northern Idaho; Part 2, Structural analysis
Abstracts with programs - Geological Society of America, Vol.32(5), p.33
Geological Society of America, Rocky Mountain Section, 52nd annual meeting
03/2000
Abstract
Preliminary structural analysis along a transect within metamorphic rocks at the northwestern margin of the Idaho batholith suggests that both low grade and high grade metamorphic rocks share similar regional deformational histories. D1 fabrics are represented by composite foliations. Compositional layering in low-grade metaclastic rocks of the Belt Supergroup northeast of Potlatch is cut by two foliations (S1a/b) that subparallel low angle shear zones. With increasing metamorphic grade to the northeast, S1a/b are penetrative foliations defined by metamorphic mineral growth and axial planar to isoclinal folds defined by compositional layering. Within the highest grade rocks in Marble Creek S1b is axial planar to isoclines defined by S1a and cut by two additional late to post-metamorphic foliations (S1c/d). S1a foliation observed in low-grade rocks in Wallace is axial planar to folds defined by compositional layering. Variation in D1 fabrics across the transect is inferred to record a strain gradient from shallow crustal levels in the Potlatch and Wallace areas to deeper crustal levels in the Marble Creek area within a contractional system. D1 fabrics are everywhere cut by steeply dipping, northeast-striking (N20-50 degrees E) crenulation cleavage of D2 and steeply dipping, northwest-striking (N20-50 degrees W) crenulation cleavage of D3. The consistency of D1 to D3 deformational fabrics and lack of structures related to regional extension suggest that all fabrics in this transect region are related to Cretaceous-early Tertiary contraction. On the basis of relative timing and the spatial orientation of structures, we propose that the fabrics record the progressive evolution of a northwest striking lateral ramp within the northern Rocky Mountain thrust belt. In this model, motion across the lateral ramp is recorded by the northwest-striking D3 fabrics and displacement up the ramp accounts for exhumation of the high-grade metamorphic rocks of Marble Creek within a regime that is kinematically compatible with fabrics observed in the low-grade rocks. This model also accounts for the south to north variation from northwest trending to north-trending folds observed across the Coeur d'Alene district.
Details
- Title: Subtitle
- Evolution of contractional structures in northern Idaho; Part 2, Structural analysis
- Creators
- William C McClelland - University of IdahoJ. S Oldow
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.32(5), p.33
- Conference
- Geological Society of America, Rocky Mountain Section, 52nd annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, Rocky Mountain Section, 52nd annual meeting
- Language
- English
- Date published
- 03/2000
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240900502771
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