Fault systems and Paleo-stress tensors in the Indus Suture Zone (NW Pakistan)

Gerold Zeilinger, Jean- Pierre Burg,

Nawaz Chaudhry, Hamid Dawood &

Shahid Hussain

Outline

• Overview

• Field examples

• Data

• Method

• Results

• Interpretation

• Analysis of fault-striations to document the dynamics

of the Indus Suture Zone during hypercollision.

– The area straddles the Main Mantle Thrust and comprises

three main units.

• The Indian unit: granodiorite and intensely foliated and folded

gneisses.

• The lower Kohistan unit: ultramafic and mafic rocks.

• The Chilas Complex: gabbro-norite and diorites.

Overview

Overview Map

Example 1

W E

305/36

Example 2

EW

Superposed Striations

SN

290/18

274/17

011/03

Method

• chronological sequence– field relationships between fault and striation sets.

• regional stress tensor – 250 measurements processed as one single data set. The 4 best tensors

have the highest number of < 30° misfit angles, and close to 0°.

• faults fitting the regional stress tensors – data from each site separated from smallest misfit angle of each

fault/striation pair for the 4 reference regional tensors.

• local deviations from the regional stress tensors– local stress tensor orientation from new random tensor search procedure

on separated data sets.

Example of raw dataNE - Continuationis not shown here

Data processing

Example of processed dataNE - Continuationis not shown here

Data processing

Interpretation

• Population 1: Higher temperature faults (the oldest ones). SSE-NNW

compression fits the Himalayan convergence.

• Population 2: E-W compression - Formation of the Nanga Parbat

crustal antiform.

• Population 3: Extension shortly afterwards. Collapse in the hanging

walls of the Nanga Parbat crustal antiform?

• Population 4: Compression fitting the present stress field (Patan

earthquake, December 1974).

Relative timing

…and thanks to our Pakistani guides