Abstract
Evidence of Grenville-age deformation and metamorphism in Belt Supergroup metapelites of northern Idaho
Abstracts with programs - Geological Society of America, Vol.41(7), p.181
Geological Society of America, 2009 annual meeting
10/2009
Abstract
Metapelites of the Belt Supergroup in northern Idaho preserve a complex polyphase deformational and metamorphic history that in earlier studies was attributed to Cretaceous tectonism due to the close proximity of the Cretaceous Idaho Batholith. Recent Lu-Hf geochronology of garnet-bearing metamorphic rocks, however, indicates a much older (Proterozoic) metamorphism. These ages include recent results from this study of 1084 + or - 21 Ma and 1207 + or - 48 Ma for pelitic schists near Middle Sister Peak and Junction Peak, respectively, and ages from previous studies ranging from 1006 + or - 5 Ma to 1149 + or - 4 Ma for metamorphic rocks in the Clearwater Complex and the Clarkia area (Zirakparvar et al., in review). Garnets in samples proximal to the batholith occasionally have Cretaceous overgrowths and, therefore, the timing relations of metamorphism and deformation needs to be reevaluated for the Belt Supergroup. Microstructural analysis of garnet-fabric relationships combined with Lu-Hf garnet geochronology allows correlation of relative and absolute timing estimates for multiple deformational events. As many as 4 fabrics are observed in areas of exclusively >1.0 Ga garnet growth: 1) S (sub 1) compositional layering, possibly after original bedding, 2) the preferred orientation of elongate quartz, S (sub 2) , preserved as an interior fabric within garnet, 3) S (sub 3) defined by the preferred orientation of planar matrix minerals which shares a syn-tectonic (syn-kinematic) relationship with garnet growth, and 4) a poorly developed crenulation cleavage, S (sub 4) , which deforms S (sub 3) and post-dates garnet growth. Previous studies in northern Idaho linked regional metamorphism and deformation to Cretaceous tectonism because of the Belt meta-sediment's close proximity to the Cretaceous Idaho Batholith. The presence of regional 1.1 Ga tectonites in northern Idaho contradicts previous assumptions that western Laurentia was a tectonically passive margin during the construction of Rodinia.
Details
- Title: Subtitle
- Evidence of Grenville-age deformation and metamorphism in Belt Supergroup metapelites of northern Idaho
- Creators
- Timothy O Nesheim - Washington State UniversityJane A GilottiWilliam C McClellandHelen M LangJeffrey D VervoortAshley M TefftC. T Foster
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.41(7), p.181
- Conference
- Geological Society of America, 2009 annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2009 annual meeting
- Language
- English
- Date published
- 10/2009
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240906802771
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