Week 14

Question 1

Continental extensional systems =

Answer 1

continental crust undergoes stretching, rifting and fault-controlled differential subsidence

If extension great enough = intracontinental rifts/passive continental margins

Question 2

Where do continental extensional systems mostly occur?

Answer 2

On passive margins/back-arc regions

Question 3

Fault strain envelope

Answer 3

Envelope within which beds are offset
Elastic deformation zone around normal fault

BLIND single normal fault with TIPE LINES

Question 4

Blind fault =

Answer 4

doesn’t show signs on the Earth’s surface

FW 'drags' up
HW 'rollover' down
Footwall uplift (if erosion too slow)

Question 5

Examples of continental extensional systems

Answer 5

Basin and range, death valley

Baikal rift, Siberia

1915 Pleasant Valley earthquake Nevada M~7.2
= 2-3m scarp

N.B. Can have renewed slip on the same scarps

Question 6

What controls the scarp?

Answer 6

ROCK TYPE:

LIMESTONE = high

SCHISTS/UNCONSOLIDATED = low

CRYSTALLINE = open fissure linked to active normal faults at depth
= ‘colluvial wedge’

Question 7

Hard vs soft linkage

Answer 7

Deformation not continuous along strike

Soft = ‘relay ramp’ structures

Question 8

Throw (slip) rate =

Answer 8

throw/time

N.B. inferring slip

Question 9

Non-rotational planar faults

Answer 9

Like Andersonian

Horst-graben-horst

e.g. Rhine graben

Question 10

Problems with non-rotational planar faults

Answer 10

Large scale extensions not accommodated b/c material moved sequentially = energetic issues

Central graben ‘falls in’ i.e. no bedding rotation in model BUT evidence of this

Question 11

Rotational planar faults

Answer 11

Like domino model

Main style of extension in continental crust

Rotates bed and rotates fault

200% extension possible

Secondary faults can form = original ~horizontal
e.g. Gullpaks field, N Sea

Question 12

How can secondary rotational planar faults form?

Answer 12

Blocks above pressing down = energetically unfavourable

Question 13

Debate of extensional detachment

Answer 13

e.g. Corinth rift

Earthquakes cut whole seismogenic layer (>10km) = suggests no active detachment

BUT major earthquakes = steeply dipping and planar while minor are low angle = WITH ACTIVE DETACHMENT

Question 14

Alternative model for extensional detachment

Answer 14

= formed when lower crust flows

• fluid layer in lower crust uplifts and propagates detachment fault
  e. g. Himalayas

Question 15

Possibilities for listric fault gravity-driven deformation zones

Answer 15

1. Unstable sediment piles
2. Weak detachment of thick salt

= mass transport complexes/megaslumps

Question 16

Listric fault gravity-driven deformation zones; unstable sediment piles

Answer 16

Unstable = collapse downhill e.g. landslips

Extension balanced by compression at toe

“Downslope contractional system balances upslope extension”

Question 17

Listric fault gravity-driven deformation zones; thick salt

Answer 17

Weak detachment horizon facilitates collapse

e.g. Gulf of Mexico

Question 18

Uplift rate =

Answer 18

elevation/years

N.B. shells useful because originally at SL

Assumption = sites effectively on fault

Question 19

Marine terraces and uplift

Answer 19

Usually younger over older as SL increases due to high stands and erosion

Uplift = older over younger in low stands UNLESS slip rate too slow = destroyed by highstands

Question 20

Earthquake recurrence interval (yrs)=

Answer 20

slip rate/earthquake event slip rate

Question 21

Extensional detachment =

Answer 21

rotated high angle fault that has stopped moving

Question 22

How do metamorphic core complexes form?

Answer 22

= extreme end member of continental collision

1. Extensional detachment
2. Isostatic exhumation of moho underneath due to crustal thinning
3. Reactivated in brittle manner

Question 23

Moho =

Answer 23

lower angle ductile shear zone at base of seismogenic layer

Question 24

What might indicate the process of metamorphic core complexes?

Answer 24

Minor low angle earthquakes

e.g. Whipple detachment, California

N.B. NO ACTIVE EXAMPLES

Question 25

Rotational non-planar faults

Answer 25

aka listric

Passive fold

Smooth, concave-up form

HW undergoes g-driven deformation to maintain compatibility
- ‘roll over’ anticline

Ductile thinning/distributed shear/antithetic faults fill gap

Question 26

Development of rotational non-planar faults

Answer 26

Can achieve similar ‘duplexes’ etc as with contractional

Gravity driven deformation zones with ramp/flat/ramp

KEY = ductile layer for faults to flatten onto