Abstract/Details

Tectonic and petrogenetic evolution of sub-horizontal granulite-grade fabric in lower continental crust: Constraints on lower crustal flow from the western Canadian Shield


2008 2008

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Abstract (summary)

Ductile, weak flow of continental lower crust is inferred for a number of orogenic systems, including the Andes and the Himalayan-Tibetan system. Sub-horizontal, high-temperature fabrics in rare exposures of exhumed lower continental crust provide important directly observable constraints on the physical mechanisms of lower crustal flow. This study uses m- to tens-of-km-scale examples of sub-horizontal granulite grade fabric in a large exposure of exhumed lower continental crust to constrain the conditions and timing of lower crustal flow. High-resolution electron microprobe monazite geochronology and trace element analysis in oriented tectonites reveals a protracted record of Neoarchean (ca. 2.63-2.53 Ga) garnet growth and sub-horizontal fabric development in migmatitic felsic granulites during lower crustal flow and subsequent cooling. Penetrative, sub-horizontal gneissic fabrics were over-printed by discrete steeply-dipping shear zones and upright folds. In situ dating of shear zones constrains the timing of sub-horizontal shortening and dextral shear strain to ca. 1.92-1.8 Ga. The results demonstrate the dynamic and evolving strength of continental lower crust. In this particular case, flow of relatively weak lower crust during production of sub-horizontal fabrics in the Neoarchean was followed by a period of near-isobaric cooling and strengthening. Subsequent Paleoproterozoic deformation events produced steep fabrics, outcrop- to crustal-scale steeply-dipping shear zones, and local reactivation of early sub-horizontal fabrics—a record of strain partitioning and strain hardening in an isobarically-cooled anisotropic medium.

Indexing (details)


Subject
Geology
Classification
0372: Geology
Identifier / keyword
Earth sciences; Continental crust; Geochronology; Granulite facies; Lower crustal flow; Monazite; Rheology; Shear zone; Tectonics
Title
Tectonic and petrogenetic evolution of sub-horizontal granulite-grade fabric in lower continental crust: Constraints on lower crustal flow from the western Canadian Shield
Author
Dumond, Gregory
Number of pages
206
Publication year
2008
Degree date
2008
School code
0118
Source
DAI-B 69/12, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549916017
Advisor
Williams, Michael L.
Committee member
Bowring, Samuel A.; Jercinovic, Michael J.; Seaman, Sheila J.; Winter, H. H.
University/institution
University of Massachusetts Amherst
Department
Geosciences
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3337014
ProQuest document ID
304570130
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304570130
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