1. An introduction to various styles of extension found throughout the lithosphere See instructor notes below for each slide!

2. Outline Normal faulting Transtensional faulting Variations across the entire lithosphere The variety of rifted margins 3. Outline Normal faulting Transtensional faulting Variations across the entire lithosphere The variety of rifted margins 4. Based on experiments and an activity developed by Robert Burger, Smith College The evolution of normal faults: how the crust responds to extension 5. Here are a few figures of a normal fault typically found in an intro textbook http://geomaps.wr.usgs.gov/archive/socal/geology/inland_empire/images/guataemala.jpg http://geomaps.wr.usgs.gov/parks /deform/ Great images to introduce fault components and their terms!! 6. But what is missing?? How does a fault behave through time? Does it always have the same geometry? Is there always just one fault? If not, how does a set of faults form and interact? How does the earths surface respond during faulting? How does it change? What new rocks form in the process? How do they form? How are they affected by the faulting?? 7. How do we get from this to this? 8. Lets take a look!! Watch the following movie of a sandbox experiment Layers represent strata in the earth The experiment uses the apparatus below: layers of sand are filled in and the walls are pulled apart (in the photo below you see an example of compression, not extension) 9. Extension in a Sandbox 10. Watch the movie a second time What did you notice?? What can you say about these questions?? How does a fault behave through time? Does it always have the same geometry? Is there always just one fault? If not, how does a set of faults form and interact? How does the earths surface respond during faulting? How does it change? What new rocks form in the process? How do they form? How are they affected by the faulting?? 11. 20 and 40 seconds into the movie 12. 60 and 80 seconds into the movie 13. 100 and 112 seconds into the movie 14. NOT ALL FAULTS ARE STRAIGHT Listric Faults 15. Watch a second movie: same experiment, same questions, different fault geometry How does a fault behave through time? Does it always have the same geometry? Is there always just one fault? If not, how does a set of faults form and interact? How does the earths surface respond during faulting? How does it change? What new rocks form in the process? How do they form? How are they affected by the faulting?? 16. Listric faults 17. What did you see? How does a fault behave through time? Does it always have the same geometry? Is there always just one fault? If not, how does a set of faults form and interact? How does the earths surface respond during faulting? How does it change? What new rocks form in the process? How do they form? How are they affected by the faulting?? 18. What else did you see? 19. What new rocks form in the process? How do they form? How are they affected by the faulting?? 20. Observations: Summary Faults may form at one angle and the angle changes through time (dip becomes shallower) More than one fault forms Different sizes and amount of offset May dip in two directions Faults are active for a time, become inactive, new faults form New sediment is deposited in the lows created The new layers become tilted by the ongoing faulting New layers may vary in thickness This is evidence of growth faulting 21. Examples from the Loreto Basin, Gulf of California Evidence of growth faulting: - new sedimentary layers are thicker where more accommodation space is created next to the fault - fanning of dips: youngest layers are less tilted than older layers 22. Multiple faults seen in cross-section from earlier map More than one fault forms!! 23. A geologic map of faults doesnt reveal the evolution (the growth and activity) of an entire set faults 24. How do we determine that evolution in the real world? And get beyond the sandbox? Detailed mapping combined with Structural analysis Basin analysis Detailed stratigraphic analysis Dating Basin reconstruction Work done by MARGINS and GeoPRISMS teams of researchers from a variety of disciplines aims to unravel the extension step by step and understand how continental lithosphere ruptures! 25. Outline Normal faulting Transtensional faulting Variations across the entire lithosphere The variety of rifted margins 26. How does the crust respond to transtension: oblique, normal and strike-slip faults Lets start by reviewing typical strike-slip features 27. Here are a few figures of a strike-slip fault typically found in an intro textbook Great images to introduce fault terms!! http://geomaps.wr.usgs.gov/parks/deform/strikeslip.gif Right-lateral strike-slip fault Left-lateral strike-slip fault Oblique-slip fault http://geomaps.wr.usgs.go v/parks/deform/7faults.ht ml 28. Strike-slip faults can produce a range of structures! But its only a start! 29. Wilcox et. al. (1973) predictive model 30. Bends and step-overs of strike-slips faults create a variety of features 31. Pull-apart basin 32. Transpression and Transtension: Variations on the pure strike-slip features 33. Outline Normal faulting Transtensional faulting Variations across the entire lithosphere The variety of rifted margins 34. Continental Rifts: display a variety of geometries and features Narrow versus wide Symmetric versus asymmetric Core complexes Some rifts have them, some dont Varying styles and processes 35. Core Complexes Different styles of deformation 36. Outline Normal faulting Transtensional faulting Variations across the entire lithosphere The variety of rifted margins 37. Rifted Margins: not all the same!! Old end members: Volcanic (magma- rich) versus amagmatic (magma-poor) New kid on the block: heavily- sedimented 38. Newer studies show different types of rifted margins, each with a unique Oceanic-Continental Transition (OCT) O.C.T. Typical intro text book figure of a rifted margin But wait! Theres more!! 39. Previously recognized end members: Magma-rich and Magma poor 40. 1. Non-Volcanic Margins (Hyper- Extended): Thin, magma-starved crust Mantle exhumed to near surfaceBoillot & Froitzheim (2001) O.C.T. 2. Volcanic Rifted Margins: Thick mafic crust constructed by robust syn-rift magmatism. Geoffroy (2005) C.R. Geoscience O.C.T. Schematic diagrams of these end Members 41. MARGINS work plus work in other places has led to the recognition of heavily-sedimented margins that produce a new type of continental crust 42. 3. Non-Oceanic New Crust: Geometry similar to that of volcanic margins, but crust is not volcanic (at some margins). Intermediate seismic velocities, crust is syn- rift sediments, with mafic magmatic intrusions. Where does all the sediment come from? Need large non-local input (= big river). Nova Scotia margin (Funck et al., 2004) O.C.T. New end memberhybrid crust 43. Iberia- Newfoundland: Magma-Poor, hyper-extended NW Europe-East Greenland, NW Australia: Magma- Dominated N. Gulf of California: Non-Oceanic New Crust Sawyer et al., 2007, Scientific Drilling, No.5 Examples of the three end members 44. References (websites used are noted on individual slides) Boillot, G. and Froitzheim, N., 2001, Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions, Geological Society, London, Special Publications 2001, v. 187, p. 9-30. Brune, Sascha , Anton A. Popov, and Stephan V. Sobolev, 2012, Modeling suggests that oblique extension facilitates riftingand continental break-up, JOURNAL OF GEOPHYSICAL RESEARCH, v. 117, B08402, doi:10.1029/2011JB008860, 2012 Dorsey, Rebecca J., and Umhoefer, Paul J., 2000, Tectonic and eustatic controls on sequence stratigraphy of the Pliocene Loreto basin, Baja California Sur, Mexico: Geological Society of America Bulletin, v. 112, no. 2, p. 177-199 Funck, T., Jackson, H.R., Louden, K.E., Dehler, S.A., and Wu, Y., 2004, Crustal structure of the northern Nova Scotia rifted continental margin (eastern Canada: Journal of Geophysical Research, v. 109, B09102, doi:10.1029/2004JB003008 Geoffroy, Laurent, 2005, Volcanic passive margins: C. R. Geoscience 337 (16): 13951408 Sanderson, D.J., and Marchini, W.R.D., 1894, Transpression: Journal of Structural Geology, v. 6, n. 5, p. 449- 458. Sawyer, D.S., Coffin, M.F., Reston, T.J., Stock, J.M., and Hopper, J.R., 2007, COBBOOM: The Continental Breakup and Birth of Oceans Mission. Scientific Drilling, No. 5, September, p. 13-25. Whitney, D. and Tessier, C., 2013, Whitney, D.L., Teyssier, C., Rey, P.F., Buck, W.R., 2013, Continental and oceanic core complexe: Geological Society of America Bulletin, 26 p., doi:10.1130/B30754.1. Wilcox, R.E., Harding, T.P., Seely, D.R., 1973. Basic wrench tectonics: Association of Petroleum Geologists Bulletin, v. 57, no. 1, p. 74-96.