GLG310 Structural Geology

24 February 2016GLG310 Structural Geology Description of faults NormalThrust/reverseStrike-slip Horizontal stretch >1<1>1 in one direction and < 1 in another Crustal thickness ThinThickenNo change Regional elevation Usually lowerUsually higherNo 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 IssuesDetachments, Listric, rotation, rifted margins Layered rocks, reverse versus thrust Transforms, bends and stepovers

Normal faults Put younger over older Often in “rifts” Normal faults in Iran (

Global Spreading Ridges from

24 February 2016GLG310 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

horst graben 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”

Experimental development of a normal fault system

1983 M7.3 Borah Peak Earthquake Classic study by Stein and Barrientos

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

Normal arrays, their displacement profiles, and relays

24 February 2016GLG310 Structural Geology

Burbank and Anderson

Sedimentary fills Rift basin architecture Sedimentary 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 3 Withjack and Schlische, 2002 Faunal Evolution ? J. Gurche DiMaggio

26 October 2004GLG310 Structural Geology Normal faults

Rotating faults become less well oriented and a second set forms

Normal fault geometries

24 February 2016GLG310 Structural Geology Idealized diagram of a metamorphic core complex or detachment system --these are common in Arizona

26 October 2004GLG310 Structural Geology Development of extensional systems Normal faults

26 October 2004GLG310 Structural Geology Inversion tectonics and fault reactivation

24 February 2016GLG310 Structural Geology Description of faults NormalThrust/reverseStrike-slip Horizontal stretch >1<1>1 in one direction and < 1 in another Crustal thickness ThinThickenNo change Regional elevation Usually lowerUsually higherNo 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 IssuesDetachments, Listric, rotation, rifted margins Layered rocks, reverse versus thrust Transforms, bends and stepovers

24 February 2016GLG310 Structural Geology Description of faults NormalThrust/reverseStrike-slip Horizontal stretch >1<1>1 in one direction and < 1 in another Crustal thickness ThinThickenNo change Regional elevation Usually lowerUsually higherNo 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 IssuesDetachments, Listric, rotation, rifted margins Layered rocks, reverse versus thrust Transforms, bends and stepovers