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Transform tectonics

Transform tectonics. Part I- Modern systems GEOS 425/525. Outline. Modern and young systems (TODAY) Ancient systems (THURSDAY) Strike slip faults vs transforms Mechanics and tectonics Determining slip. transform boundaries (continental) and strike-slip tectonics.

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Transform tectonics

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  1. Transform tectonics Part I- Modern systems GEOS 425/525

  2. Outline • Modern and young systems (TODAY) • Ancient systems (THURSDAY) • Strike slip faults vs transforms • Mechanics and tectonics • Determining slip

  3. transform boundaries (continental) and strike-slip tectonics we have examined transform faults in oceanic crust… …transform faults also occur in continental crust…. continental transforms tend to be more complex than oceanic and occur over broader area San Andreas right from: http://www.gps.caltech.edu/~sieh/research

  4. let us look at some characteristics of strike-slip faults… • may or may not be plate boundary features • do not necessarily terminate at plate boundary • die out along their lengths initiate at point and grow along their length …displacement greatest near center of trace and goes to zero at the ends from: van der Pluijm and Marshak, 1997

  5. tectonic settings of strike-slip faults • oblique convergent margins • fold-thrust belts • rifts • oceanic transforms and fracture zones • continental transforms from: van der Pluijm and Marshak, 1997

  6. strike-slip faults accommodate along strike variations of dip-slip faults fold-thrust belts So called lateral ramps rifts Garlock fault (California) ~ 250 km transfer fault; extension greater north of fault than to south; San Andreas moved west, creating restraining bend and Transverse Ranges from: van der Pluijm and Marshak, 1997

  7. In addition, all segmented slabs in subduction zones require strike slip ramps; Strike slip faults also accommodate lateral extrusion

  8. move to east along collision belt to Himalayas …large strike-slip faults develop in response to India indentor… extrusion/indentor tectonics plasticine model Molnar and Tapponier, 1975’ Tapponier et al., 1982; 1986

  9. matches pattern of faults in eastern Asia • sinistral Red River fault (Kashmir east) • extrusion of SE Asia • 2nd block extrusion (China) • Altyn Tagh Fault • more extrusion of SE Asia and rotation • Andaman Sea opening • major faults to east originate in NW corner of indentor • NW trending faults exist • Tibetan zone minor faulting predict another block forms and deformation line through Baikal? from: Moores and Twiss, 1995

  10. Altyn Tagh fault, China

  11. strike-slip faults also may have components of shortening or extension across them (...not perfectly strike-slip) if movement along strike-slip fault results in some compression across it: transpression if movement along strike-slip fault results in some tension across it: transtension transpression transform boundary not perfectly parallel to relative plate motion (doesn’t form small circle about Euler pole) transtension

  12. bends (or steps) cause abrupt changes in strike of fault… ….if the bend moves the fault plane to the left, it is a left step ….if the bend moves the fault plane to the right, it is a right step map view right step left step steps along strike-slip faults result in either extension or contraction along the step fault segment from: http://www.naturalfractures.com

  13. pull-apart (Salton Sea) no surface volcanic rocks - large positive gravity anomaly extensive geothermal activity metal-rich brines about 3 km deep (Quaternary sediments). from: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.ppt

  14. bimodal volcanism basalt-rhyolite on margins marginal fault zones normal fault zones en echelon sediments young to centre fanglomerates some characteristics of pull-apart basins: from: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.ppt

  15. Owens Valley, CA

  16. http://www.johnmartin.com/eqsafs/safig_3_3c.htm http://pollux.geog.ucsb.edu/~joel/g148_f98/scal/shaded_relief.jpg opposite of pull-apart basins occurs at restraining bends … "transverse ranges" rapid uplift erosion basin fill L. A. basin is 15 km deep from: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.ppt

  17. what types of structures form in bends? experimental modeling of restraining bend: …note uplift and development of faults… from: http://www.searchanddiscovery.com/documents/mcclay02

  18. pattern of faults in bends called: flower structures restraining bend restraining bends: thrusts (positive flower structure) releasing bends: normal faults (negative flower structure) 3D map from: http://www.searchanddiscovery.com/documents/mcclay02

  19. …let us return to transform boundaries… • transform faults best known in mid-ocean ridges • …many examples in arcs: • west Aleutians • Hunter transform (Fiji) • Alpine Fault (New Zealand) • North Caribbean • North and South Sandwich • …some transform faults that come on land: • San Andreas fault system • Anatolian faults • Dead Sea fault zone • several in S and SE Asia

  20. continental transform boundary • distributed shear • subparallel faults San Andreas one of many faults from: van der Pluijm and Marshak, 1997

  21. San Andreas joins two ridges • Gulf of California • Juan de Fuca remember subduction of Farallon from: http://pubs.usgs.gov/publications/text/understanding.html from: http://www.geol.ucsb.edu/Outreach/Download/RegistrationAtwater.html

  22. short segment along San Andreas (~3 km) offset channels; sag pond; linear ridges

  23. New Zealand (trench-transform-trench) Alpine fault joins trenches left from: http://people.colgate.edu/smichel/geol305/New%20Zealand%20Fault%20System/characteristics.htm right from: http://www.otago.ac.nz/geology/features/earthquake/earthquakes.htm

  24. why is New Zealand there? … transform is transpressive in area of atypical oceanic crust (submarine plateau) uplift along Alpine Fault is ongoing …0.1 to 0.5 mm/a (= 100-500 m/Ma) strike-slip component motion is >27 mm/a …(= 27 km/Ma) amphibolite facies rocks abut against gravels …uplift >15 km in 20 Ma high erosion rates keep elevation < 5000 m from: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.ppt

  25. Dead Sea transform joins Red Sea Rift to Anatolian system from: http://maps.unomaha.edu/maher/plate/ week9/Deadsea.html#anchor1337963 from: Reilinger et al. 2000, GSA Today

  26. Anatolian system: collision of Arabian peninsula with Eurasia from: http://www.scotese.com/earth.htm

  27. from: http://www.scotese.com/earth.htm

  28. from: http://www.scotese.com/earth.htm

  29. ten M > 6.7 km earthquakes from 1939-1992 very similar to San Andreas (slip rates; straightness; length)

  30. models for transform boundaries (Pacific-NOAM) blue arrows are paleomag directions from: Moores, 1990, Shaping the Earth, Scientific American

  31. progressive slip on strike-slip faults may result in rotation of crustal blocks about a vertical axis mechanisms of block rotation…measure through paleomag middle: large pieces slip on parallel strike-slip faults (bookshelf faulting) right: small pieces may rotate like “ball-bearings” ball-bearing tectonics: advocated for some of western US …rotation of terranes from: van der Pluijm and Marshak, 1997

  32. rotations (blue arrows) relative to north 60 million years from: Moores, 1990, Shaping the Earth, Scientific American

  33. changing locations of faults from: Moores, 1990, Shaping the Earth, Scientific American

  34. oblique convergent margins relative motion between two plates can be partitioned into components of dip-slip perpendicular to and strike-slip parallel to convergent margin strike-slip faults in • accretionary wedge • volcanic arc and • backarc can cut these elements of convergent margin pieces may be missing or duplicated along a given margin from: van der Pluijm and Marshak, 1997

  35. partitioning also accompanies collision oblique convergence collision terrane dismemberment from: van der Pluijm and Marshak, 1997

  36. Lessons from modern systems • Strike slip faults with large displacement may or may not be transform boundaries; • We know relatively little about the behavior of these faults at depth and where do they root; • Present day plate tectonics suggest that lateral assembly could be significant in shaping continents; • Rotations associated with strike slip crunch; • Magmatism not a player.

  37. Ancient systems • Difficult to interpret unless major transcontinental truncations; • Not clear how the San Andreas type fault looks at 20 km; • The subcretion vs translation controversy; • Can we track translation with no uplift markers?

  38. Other example: Mojave Sonora megashear

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