GLG310 Structural Geology Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology 1
Normal faults Put younger over older Often in rifts Normal faults in Iran (http://www.imaggeo.net/view/807) http://www.tectonics.caltech.edu/taiwan/regional.htm Global Spreading Ridges from http://topex.ucsd.edu/marine_topo/globe.html 2
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Comparative riftology East African Rift Gulf of California Eastern North America 4
Significant variation in fault array geometry along the system T. Rooney Development of extensional systems 5
Clay cake on a rubber sheet: analogy for brittle upper crust (clay) over ductile and uniformly extending lower crust graben horst Upper part of system has steep, Andersonian dips, but lower portion has a detachment (salt horizon or other ductile level) into which the faults root The down dip curving or shallowing of dip is listric 6
Experimental development of a normal fault system http://archives.datapages.com/data/bulletns/2009/04apr/bltn08117/bltn08117.htm 1983 M7.3 Borah Peak Earthquake Classic study by Stein and Barrientos 7
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Borah Peak earthquake Displacements and long term offset Top map showings discontinuous rupture trace and several zones of complex faulting, such as near Arentson Gulch, West Spring, and Elkhorn Creek. Displacement along strike shows greatest vertical offset near Rock Creek (where the highest peak is also found in the footwall), overlapping offsets where decreasing displacement on one fault is compensated for by increasing displacement on another fault (Arentson Gulch to West Splay Junction), and a broadly bow-shaped displacement pattern (dashed line) along this succession of fault traces that is similar to the pattern seen on individual normal. Double arrows depict orientation of striae on the fault plane and indicate oblique dip-slip on this fault. The location of the levelling line survey runs approximately perpendicular to the rupture trace. Modified after Crone and Machette (1984). --Burbank and Anderson 10
Normal arrays, their displacement profiles, and relays 4 November 2013 GLG310 Structural Geology 11
Burbank and Anderson Burbank and Anderson 12
Sedimentary Rift Basins What are rift basins and why are they important? - elongate crustal depressions - variety of tectonic settings - economically important Faunal Evolution Project Focus: Inverse problem extract process from structure and fills Sedimentary fills J. Gurche Depositional environments? Rift basin architecture Process Withjack and Schlische, 2002 DiMaggio 3 Normal faults 26 October 2004 GLG310 Structural Geology 13
Rotating faults become less well oriented and a second set forms Rotating faults become less well oriented and a second set forms http://blog.summitkwan.com/?p=182 14
Normal fault geometries Idealized diagram of a metamorphic core complex or detachment system --these are common in Arizona 4 November 2013 GLG310 Structural Geology 15
Normal faults Development of extensional systems 26 October 2004 GLG310 Structural Geology Inversion tectonics and fault reactivation 26 October 2004 GLG310 Structural Geology 16
Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology Description of faults Horizontal stretch Crustal thickness Regional elevation Regional character Issues Normal Thrust/reverse Strike-slip >1 <1 >1 in one direction and < 1 in another Thin Thicken No change Usually lower Usually higher No change Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults Detachments, Listric, rotation, rifted margins Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults Layered rocks, reverse versus thrust Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems Transforms, bends and stepovers 4 November 2013 GLG310 Structural Geology 17