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GEOL 360 Fault related folds: Geometry & kinematics

GEOL 360 Fault related folds: Geometry & kinematics. Outline. Fault Related Folds (Fault Propagation, Fault Bend, Buckle) Pre-Tectonic, Syn-Tectonic, and Post-Tectonic Deposition Exercise. Fault Bend Folds. Fault Propagation Folds Includes Trishear Folds. Decollement Buckle Folds.

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GEOL 360 Fault related folds: Geometry & kinematics

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  1. GEOL 360 Fault related folds: Geometry & kinematics

  2. Outline • Fault Related Folds (Fault Propagation, Fault Bend, Buckle) • Pre-Tectonic, Syn-Tectonic, and Post-Tectonic Deposition • Exercise

  3. Fault Bend Folds Fault Propagation Folds Includes Trishear Folds Decollement Buckle Folds

  4. Growth Strata on Buckle Folds: Both limbs exhibit progressive limb rotation Common above salt layers

  5. Decollement Bucking Examples Bavarian Alps (Jura) Chuhuangkeng Anticline Taiwan

  6. Outcrop scale buckle fold, Spanish Pyrennees

  7. Halfway River, Northern Canadian Rocky Mountains

  8. Fault Bend Folds • Flat-ramp-flat geometry for fault surface • Fault surface exists across entire cross-section • Fold develops above ramp where limb angles related to fault dip

  9. Shear in hangingwall can affect limb width and fold geometry

  10. Fault-Propagation Folds Fault tip propagates thru cross-section Fold develops above ramp with uniform forelimb angles Original FPP has forelimb with same dip, trishear dips flatten upwards (trishear = reality)

  11. Downtown Osaka Now lets move to Japan… Kuwana Anticline Uemachi Upland/Fold

  12. Osaka Bay Osaka Bay Flexure

  13. Dip profile of forelimb of Osaka Bay TrishearFPF/blind thrust Most of reflectors are growth strata 1.5-2.0 km of sediment fill in the last 1800 ka Note homogeneous shear in forelimb

  14. Dip profile of forelimb of Osaka Bay FPF/blind thrust Most of reflectors are growth strata 1.5-2.0 km of sediment fill in the last 1800 ka Note homogeneous shear in forelimb

  15. Dip profile of forelimb of Osaka Bay FPF/blind thrust Best fit trishear solution yields: steep (74 deg) thrust, 12km upward propagation (Fault tip from 15->3km) 10 deg apical angle

  16. Fault Propagation Fold (Trishear) movie

  17. Fault Bend folding: Pregrowth strata Bends in fault produce bending in hangingwall, marked by active axial surfaces

  18. Fault Bend folding: Pregrowth strata Fault Bend folding: Limbs widen self similarly Growth triangle records progressively more slip with time Inactive axial surfaces once at axial surfaces, now translated above thrust

  19. Fault Bend folding: Limbs widen self similarly Growth triangle records progressively less slip

  20. Post tectonic deposition caps growth triangles Post tectonic

  21. Exercise West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 What is the age of initiation of faulting?

  22. Exercise West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 What is the age of initiation of faulting? 13 Ma

  23. Exercise West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 What is the age of termination of faulting?

  24. Exercise West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 What is the age of termination of faulting? 6 Ma

  25. Exercise West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 4km 5km 6km What is the slip rate on the thrust?

  26. West East 0 2 Ma 4 Ma 6 Ma post-tectonic 8 Ma 100 10 Ma Depth (m) 12 Ma 200 14 Ma 16 Ma 18 Ma 20 Ma 400 2km 4km 6km What is the slip rate on the thrust?

  27. West East 0 2 Ma 4 Ma post-tectonic 6 Ma 8 Ma 100 10 Ma 12 Ma Depth (m) 200 14 Ma 16 Ma 18 Ma 20 Ma 400 2km 4km 6km What is the slip rate on the thrust? 1 mm/yr

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