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Lecture 5. Rifting, Continental break-up, Transform faults

Lecture 5. Rifting, Continental break-up, Transform faults. How to break continent? Continental transform faults Dead Sea transform Dead Sea pull-apart basin. Continental break-up. Continental break-up. Continental break-up. Continental break-up. Continental break-up.

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Lecture 5. Rifting, Continental break-up, Transform faults

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  1. Lecture 5. Rifting, Continental break-up, Transform faults • How to break continent? • Continental transform faults • Dead Sea transform • Dead Sea pull-apart basin

  2. Continental break-up

  3. Continental break-up

  4. Continental break-up

  5. Continental break-up

  6. Continental break-up

  7. How to break continent? Cold lithosphere is too strong Buck (2006)

  8. Effect of magma-filled dikes Buck (2006)

  9. Effect of magma-filled dikes Not enough if lithosphere is thicker than 75 km. Buck (2006)

  10. Effect of magma-filled dikes and lithospheric erosion It works if lithosphere is first thinned to about 75 km

  11. Effect of oblique rifting

  12. Effect of oblique rifting (more during visit to Section from Sasha Brune)

  13. Lithospheric thinning above mantle plume Sobolev et al. 2011

  14. Conclusion To break a continent are required: (1) extensional deviatoric stresses (internal, from ridge push or slubduction zones roll-back) and (2) lithospheric weakening Large Igneous Provinces are optimal for lithospheric weakening, as they may both thin lithosphere and generate magma-filled dikes. Intensive strike-slip deformation is also helpful

  15. Continental transform faults (case Dead Sea Transform)

  16. Continental Transform Faults San Andreas Fault Dead Sea Fault

  17. With the surface heat flow 50-60 mW/m2, the DST is the coldest continental transform boundary Regional setting

  18. Regional setting Very low heat flow 50 mW/m2

  19. Lithospheric thickness and magmatism Magmatism at 30-0 Ma

  20. Lithosphere-asthenosphere boundary (LAB) from seismic data Chang and Van der Lee, EPSL, 2011 Chang et al, GRL, 2011 Mohsen et al., Geophys. J. Int. 2006 LAB depth 70-80 km Inconsistent with the heat flow of 50-60 mW/m2

  21. Present day lithospheric thickness Hansen et al., EPSL 2007 LAB depth 70-80 km Inconsistent with the heat flow of 60 mW/m2 or less! Mohsen et al., Geophys. J. Int. 2006

  22. Conclusion Lithosphere around DST was thinned in the past and related high heat flow had not enough time to reach the surface

  23. Model setup Flat Earth approximation

  24. Modeling technique LAPEX 3D combining FE and FD (Petrunin and Sobolev, Geology, 2006, PEPI, 2008) Simplified 3D concept.

  25. Initial lithospheric structure: Moho map LAB map Heat flow

  26. Modeling results: role of the thermal erosion of the lithosphere

  27. Model setup Flat Earth approximation

  28. Modeling results: role of the thermal erosion of the lithosphere Applied force is 1.6e13N/m erosion at 10 Myr no erosion Initial stage: 5-7 km net slip

  29. Modeling results: role of the thermal erosion of the lithosphere Fault initiation, 15-20 km net slip Thermal erosion of the lithosphere erosion at 10 Myr no erosion

  30. Modeling results: role of the thermal erosion of the lithosphere erosion at 10 Myr no erosion Fault development, 35-40 km net slip

  31. Modeling results: role of the thermal erosion of the lithosphere erosion at 10 Myr no erosion Present day, 107 km net slip

  32. Possible scenario Plumes at 25-35 Ma Lithospheric erosion 20-30 Ma Localization of the DST 15-17 Ma Lithospheric erosion has triggered the DST Chang and Van der Lee, EPSL, 2011

  33. San Andreas Fault System

  34. San Andreas Fault System Hayward & Calaveras Faults Salinian Block Bay Area Block Big Bend USGS Professional Paper 1515

  35. Tectonic Evolution of SAFS Time N S (animation by T. Atwater)

  36. Questions addressed Why the locus of deformation in SAFS migrates landwards with time? How differently would evolve SAFS with “strong” and “weak” major faults?

  37. Why the locus of deformation in SAFS migrates landwards with time?

  38. Y Extended 2D Model Setup (South view)

  39. W E • Eastward migration of maximum temperature and minimum lithospheric strength (Furlong, 1984,1993, Furlong et al., 1989)

  40. N 3.5 cm/yr 4 cm/yr 3.5 cm/yr Model Setup( view from the North ) Mendocino Triple Junction North American Plate 140-250 km 80 km Slab window Gorda Plate

  41. Physical background Balance equations Deformation mechanisms Mohr-Coulomb Popov and Sobolev (2008)

  42. Numerical background Discretization by Finite Element Method Arbitrary Lagrangian-Eulerian kinematical formulation Fast implicit time stepping + Newton-Raphson solver Remapping of entire fields by Particle-In-Cell technique Popov and Sobolev ( 2008)

  43. “Strong faults” model: the friction coefficient decreases only slightly (from 0.6 to 0.3) with increasing plastic strain “Weak faults” model: thefriction coefficient decreases drastically (from 0.6 to 0.07) with increasing plastic strain “Strong” and “weak” faults models

  44. 3D Model Setup (12-15 MA) NW Salinian Block Great Valley Block Great Valley Block Gorda Plate Pacific Plate 1100 km Salinian Block North American Plate Monterrey Microplate Monterrey Microplate SE 250km

  45. Qualitative comparison of basic fault features Fault Map Hayward Calaveras San Andreas Bay Area Big Bend Salinian Modeling Results (present day) Calaveras Hayward San Andreas Bay Area Big Bend Salinian

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