Week 17

Question 1

Impact of transpression and transtension

Answer 1

Diverting from simple shear

Question 2

Transpression

Answer 2

Contraction and S-S

Strain partition into:

1) inline folds
2) en echelon folds

For overall movement

Structures have lower angles to PDZ than in transtension

Question 3

Strike slip shuffle =

Answer 3

At subduction zone
= moves plate 100s-1000s km

“Terrane tectonics”

Question 4

Transtension

Answer 4

Extension and S-S

Strain partition into:

1. Wrench dominated domains (WDD)
2. Extension dominated domains (pure shear) (EDD)

= EXTENSIONAL S-S ZONE WITH SHORTENING STRUCTURES!!!

Question 5

WDD structures

Answer 5

Shortening

• folds
• stylolites
• reverse faults

Question 6

EDD structures

Answer 6

Extension

= conjugate Andersonian normal faults

Question 7

When does TP and TT occur?

Answer 7

When a pre-existing structure is reactivated under oblique convergence or divergence

Question 8

How to recognise TP and TT in cross section?

Answer 8

Look for additional S-S components

Question 9

Examples of transtension

Answer 9

Northumberland basin

Liache basin

Bohai basin, NE China

Question 10

Vertical and horizontal partitioning

Answer 10

Depends on lithology and T i.e. RHEOLOGY

e. g. Central California
- pervasive steep shear zone in mantle lithosphere linked via mid-lower crustal attachment zone = translation of upper crustal blocks
- requires mantle lithosphere to have strength i.e. jelly sandwich
- analogy = car clutch
- “attachment zone” = sub-horizontal shear zone because there to maintain kinetic compatibility

Question 11

Where is there often a zone of distributed S-S/diffuse zone in strain partitioning?

Answer 11

Due to ‘dragging’

Question 12

Perfect partitioning

Answer 12

Splits at 90’
Equal amount of shortening (x)

Use pythagoras to find total convergence