Zones of mylonites are a prominent feature of rocks that occur at the Grenville Front in central Ontario. They represent periods of northwest-directed thrusting during the Mesoproterozoic, the latest period due to the Grenville Orogeny at ∼1.0 Ga. We describe the strain and folding of a 300 m wide zone of mylonites southeast of Coniston, Ontario that occur in the foreland to the Grenville Province. They are greenschist facies quartz mylonites and quartz feldspar mylonites formed in the upper crust from sandstones and granites in the Southern Province. They are bounded to the north and south by the Murray Fault and Grenville Front Boundary Fault, respectively, steeply dipping reverse faults, which are post-mylonitization in age. The latter fault marks the southern boundary of the foreland mylonites with zones of mylonite in high grade, lower crustal schists, and gneisses of the Grenville Province. The Murray Fault marks their northwestern boundary against a middle Proterozoic metamorphic terrane. Shape fabric measurements of quartz indicate that strain intensity is random across the mylonite zone. Open angle quartz c-axis fabrics, the dominance of subgrain rotation recrystallization of quartz, and the metamorphic paragenesis quartz–muscovite–chlorite indicate that the mylonites formed at low greenschist facies temperature (350–430 °C). The measured variation in strain is attributed to variations in strain rate and water weakening. The mylonites are folded; hinge lines and axial planar stretching lineations plunge southeast perpendicular to the Grenville Front. The mylonites are similar to those that occur in the foreland of the Moine Thrust (northwest Scotland) and the Munsiari Thrust (northwest India).
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Research Article|
February 19, 2025
Structural analysis of an area of ductile deformation between the Murray Fault and the Grenville Front Boundary Fault near Coniston, Ontario
D.H. Rousell;
D.H. Rousell
(Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing)
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 Canada
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R.S. James;
(Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing)
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 CanadaCorresponding author: R.S. James (email: [email protected])
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T.M. Roth
T.M. Roth
(Data curation, Project administration, Software, Visualization)
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 Canada
Search for other works by this author on:
D.H. Rousell
Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 Canada
R.S. James
Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 Canada
T.M. Roth
Data curation, Project administration, Software, Visualization
a
Harquail School of Earth Sciences, Laurentian University
, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6 CanadaCorresponding author: R.S. James (email: [email protected])
Publisher: Canadian Science Publishing
Received:
16 Jan 2023
Accepted:
01 Nov 2024
First Online:
05 Mar 2025
Online ISSN: 1480-3313
Print ISSN: 0008-4077
Funding
- Funder(s):Laurentian University Research Fund for Retired Members
- Funder(s):Geological Survey of Canada
The Authors
Permission for reuse (free in most cases) can be obtained from copyright.com.
Canadian Journal of Earth Sciences (2025) 62 (3): 549–568.
Article history
Received:
16 Jan 2023
Accepted:
01 Nov 2024
First Online:
05 Mar 2025
Citation
D.H. Rousell, R.S. James, T.M. Roth; Structural analysis of an area of ductile deformation between the Murray Fault and the Grenville Front Boundary Fault near Coniston, Ontario. Canadian Journal of Earth Sciences 2025;; 62 (3): 549–568. doi: https://doi.org/10.1139/cjes-2023-0010
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