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1 year ago in Stellar Kinematics , StructuralGeology By Coren
In structural mapping, how do we distinguish between a fold hinge that’s stationary versus one that has moved during deformation?
I'm mapping a complex fold-thrust belt, and my stereonet analyses show conflicting hinge line orientations for the same fold in different layers. My advisor mentioned the concept of hinge migration, but the literature is somewhat abstract. What are the definitive field relationships or strain markers I should look for to confidently diagnose a migrating hinge?
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By Nisha Ali Answered 1 year ago
From my experience mapping in orogenic belts, the diagnosis comes down to a mismatch between geometry and finite strain. For a fixed hinge, the hinge line is perpendicular to the axial plane trace in all layers, and stretching lineations will fan around it symmetrically. A migrating hinge often leaves a trail: you'll see curved hinge lines in profile, non-cylindrical fold shapes, and a strongly asymmetric pattern of stretching lineations and shear sense indicators around the fold. I've often used detailed serial cross-sections to track these changes in hinge position layer by layer.
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