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Normal faults Put younger over older Often in “rifts” Normal faults in Iran (http://www.imaggeo.net/view/807)
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GLG310 Structural Geology
May 6, 2023 GLG310 Structural Geology
Description of faults
Normal Thrust/reverse Strike-slipHorizontal stretch
>1 <1 >1 in one direction and < 1 in another
Crustal thickness
Thin Thicken No change
Regional elevation
Usually lower Usually higher No change
Regional character
Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults
Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults
Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems
Issues Detachments, Listric, rotation, rifted margins
Layered rocks, reverse versus thrust
Transforms, bends and stepovers
Normal faults
http://www.tectonics.caltech.edu/taiwan/regional.htm
• Put younger over older
• Often in “rifts”
Normal faults in Iran (http://www.imaggeo.net/view/807)
Global Spreading Ridges from http://topex.ucsd.edu/marine_topo/globe.html
May 6, 2023 GLG310 Structural Geology
Comparative “riftology”
East African Rift
Gulf of California
Eastern North America
T. Rooney
Significant variation in fault array geometry along the system
Development of extensional systems
Clay cake on a rubber sheet: analogy for brittle upper crust (clay) over ductile and uniformly extending lower crust
horstgraben
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”
http://archives.datapages.com/data/bulletns/2009/04apr/BLTN08117/BLTN08117.HTM
Experimental development of a normal fault system
1983 M7.3 Borah Peak Earthquake
Classic study by Stein and Barrientos
Borah Peak earthquakeDisplacements 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
Normal arrays, their displacement profiles, and relays
May 6, 2023 GLG310 Structural Geology
Burbank and Anderson
Burbank and Anderson
Sedimentaryfills
Rift basin architecture
Sedimentary Rift BasinsSedimentary Rift Basins
What are rift basins and why are they important?
Depositional environments
Process
- elongate crustal depressions- variety of tectonic settings- economically important
Project Focus: Inverse problem – extract process from structure
and fills
3Withjack and Schlische, 2002
Faunal Evolution
?J. Gurche
DiMaggio
26 October 2004 GLG310 Structural Geology
Normal faults
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
Normal fault geometries
May 6, 2023 GLG310 Structural Geology
Idealized diagram of a metamorphic core complex or detachment system--these are common in Arizona
26 October 2004 GLG310 Structural Geology
Development of extensional systems
Normal faults
26 October 2004 GLG310 Structural Geology
Inversion tectonics and fault reactivation
May 6, 2023 GLG310 Structural Geology
Description of faults
Normal Thrust/reverse Strike-slipHorizontal stretch
>1 <1 >1 in one direction and < 1 in another
Crustal thickness
Thin Thicken No change
Regional elevation
Usually lower Usually higher No change
Regional character
Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults
Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults
Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems
Issues Detachments, Listric, rotation, rifted margins
Layered rocks, reverse versus thrust
Transforms, bends and stepovers
May 6, 2023 GLG310 Structural Geology
Description of faults
Normal Thrust/reverse Strike-slipHorizontal stretch
>1 <1 >1 in one direction and < 1 in another
Crustal thickness
Thin Thicken No change
Regional elevation
Usually lower Usually higher No change
Regional character
Rifting, Mid Ocean ridges, gravitational collapse, local accommodation along strike-slip faults
Subduction zones/accretionary prisms, continent/continent collision, back arc fold thrust belts, local accommodation along strike-slip faults
Transforms, oblique convergence (i.e., Sumatra), continental collision, Transfers in other fault systems
Issues Detachments, Listric, rotation, rifted margins
Layered rocks, reverse versus thrust
Transforms, bends and stepovers
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