Monazite as a monitor of shear strain in orogenic crust

The Ramsay-Graham heterogeneous simple shear zone model revolutionized our understanding of finite strain variation in orogenic belts. Many deeply exhumed (>20 km depths) shear zones in orogenic continental crust are a consequence of sub-simple shear strain accumulation during contraction and dis...

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Bibliographic Details
Published in:Journal of structural geology 2022-08, Vol.161, p.104672, Article 104672
Main Authors: Dumond, Gregory, Mahan, Kevin H., Goncalves, Philippe, Williams, Michael L., Jercinovic, Michael J.
Format: Article
Language:English
Subjects:
Continental crust
Dissolution precipitation creep
EBSD
Monazite
Mylonite
Shear zone
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Summary:The Ramsay-Graham heterogeneous simple shear zone model revolutionized our understanding of finite strain variation in orogenic belts. Many deeply exhumed (>20 km depths) shear zones in orogenic continental crust are a consequence of sub-simple shear strain accumulation during contraction and displacement at high temperature. Here we explore the micro-scale record of this process using syn-kinematic monazite in two shear zones in a >20,000 km2 terrane of exhumed lower continental crust. Field observations combined with high-spatial resolution X-ray mapping, Th–U-Pb electron microprobe petrochronology, and electron backscatter diffraction analysis demonstrate that monazite grains can provide an important textural and temporal record of shear strain in mylonite and ultramylonite gneisses. Monazite grains exhibit aspect ratios of 1.7–4.6 parallel to the stretching lineation and parallel or oblique (
ISSN:0191-8141
1873-1201
DOI:10.1016/j.jsg.2022.104672