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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). GEOLOGICAL INSTITUTE. ZURICH. Gerold Zeilinger, Jean- Pierre Burg, Nawaz Chaudhry, Hamid Dawood & Shahid Hussain. Outline. Overview Field examples Data Method Results Interpretation.

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

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  1. Fault systems and Paleo-stress tensors in the Indus Suture Zone (NW Pakistan) GEOLOGICAL INSTITUTE ZURICH Gerold Zeilinger, Jean- Pierre Burg, Nawaz Chaudhry, Hamid Dawood & Shahid Hussain

  2. Outline • Overview • Field examples • Data • Method • Results • Interpretation

  3. Overview • 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.

  4. Overview Map

  5. Example 1 305/36 E W

  6. Example 2 E W

  7. Superposed Striations 274/17 011/03 290/18 S N

  8. 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.

  9. Example of raw data NE - Continuation is not shown here

  10. Data processing

  11. Example of processed data NE - Continuation is not shown here

  12. Data processing

  13. 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).

  14. Relative timing

  15. …and thanks to our Pakistani guides

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