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