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Transform tectonicsOutlinePowerPoint PresentationSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Lessons from modern systemsAncient systemsSlide 43Slide 44Slide 45Transform tectonicsPart I- Modern systemsGEOS 425/525OutlineModern and young systems (TODAY)Ancient systems (THURSDAY)Strike slip faults vs transformsMechanics and tectonicsDetermining sliptransform boundaries (continental) and strike-slip tectonicswe 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 arearight from: http://www.gps.caltech.edu/~sieh/researchSan Andreaslet 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 lengthsinitiate at point and grow along their length…displacement greatest near center of traceand goes to zero at the endsfrom: van der Pluijm and Marshak, 1997tectonic settings of strike-slip faults• oblique convergent margins• fold-thrust belts• rifts• oceanic transforms and fracture zones• continental transformsfrom: van der Pluijm and Marshak, 1997fold-thrust beltsriftsstrike-slip faults accommodate along strike variations of dip-slip faultsSo called lateral rampsGarlock fault (California) ~ 250 km transfer fault;extension greater north of fault than to south;San Andreas moved west, creating restraining bend and Transverse Rangesfrom: van der Pluijm and Marshak, 1997In addition, all segmented slabs in subduction zones require strike slip ramps;Strike slip faults also accommodate lateral extrusionmove to east along collision belt to Himalayas…large strike-slip faults develop in response to India indentor…Molnar and Tapponier, 1975’Tapponier et al., 1982; 1986plasticine modelextrusion/indentor tectonicsmatches 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 faultingpredict another block forms anddeformation line through Baikal?from: Moores and Twiss, 1995Altyn Tagh fault, Chinaif movement along strike-slip fault results in some compressionacross it: transpressionif movement along strike-slip fault results in some tensionacross it: transtensiontranspressiontranstensionstrike-slip faults also may have components ofshortening or extension across them (...not perfectly strike-slip)transform boundarynot perfectly parallel torelative plate motion(doesn’t form small circleabout Euler pole)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 stepright step left stepsteps along strike-slip faults result in either extension or contraction along the step fault segment map view from: http://www.naturalfractures.comno surface volcanic rocks - large positive gravity anomalyextensive geothermal activitymetal-rich brinesabout 3 km deep (Quaternary sediments).pull-apart (Salton Sea)from: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.pptsome characteristics of pull-apart basins:marginalfault zonesnormalfault zonesen echelonsedimentsyoung to centrefanglomeratesbimodal volcanismbasalt-rhyoliteon marginsfrom: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.pptOwens Valley, CAQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.opposite of pull-apart basins occurs at restraining bends … "transverse ranges"http://www.johnmartin.com/eqsafs/safig_3_3c.htmhttp://pollux.geog.ucsb.edu/~joel/g148_f98/scal/shaded_relief.jpgrapid uplifterosionbasin fillL. A. basin is 15 km deepfrom: ace.acadiau.ca/SCIENCE/GEOL/rraeside/backup/work/Courses%203-5/3613/lecture%2010.pptwhat types of structures form in bends?experimental modeling of restraining bend:…note uplift and development of faults…from: http://www.searchanddiscovery.com/documents/mcclay02pattern of faults in bends called: flower structuresrestraining bends: thrusts (positive flower structure)releasing bends: normal faults (negative flower structure)restraining bendmap3Dfrom: http://www.searchanddiscovery.com/documents/mcclay02transform 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…let us return to transform boundaries…continental transformboundary• distributed shear• subparallel faultsSan Andreas one of many faultsfrom: van der Pluijm and Marshak, 1997from: http://pubs.usgs.gov/publications/text/understanding.htmlSan Andreas joins two ridges • Gulf of California • Juan de Fucaremember subduction of FarallonQuickTime™ and aAnimation decompressorare needed to see this picture.from: http://www.geol.ucsb.edu/Outreach/Download/RegistrationAtwater.htmlshort segment along San Andreas (~3 km)offset channels; sag pond; linear ridgesleft from: http://people.colgate.edu/smichel/geol305/New%20Zealand%20Fault%20System/characteristics.htmright from: http://www.otago.ac.nz/geology/features/earthquake/earthquakes.htmNew Zealand (trench-transform-trench)Alpine faultjoinstrencheswhy 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 Mahigh erosion rates keep elevation < 5000 mfrom:


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UA GEOS 425 - Transform tectonics

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