(From a poster displayed at the Himalayan Workshop, Flagstaff, Arizona, April 1996)
Metamorphic profiles across the High Himalaya in western Zanskar, India
D.J. Waters, M.P. Searle, M.W. Dransfield, D.C. Rex and B Stephenson
We present thermobarometric and geochronological data along two profiles which cross the central part of the High Himalayan Slab. One of these passes from the Main Central thrust in the Kishtwar window (at the base) through the high-grade core of the slab to the Zanskar Shear Zone, a normal fault which has cut out much of the section at the top of the slab. The second crosses a region along the Suru Valley where higher structural levels of the slab are better preserved. Earlier, higher-pressure assemblages (P = 9 - 11 kbar) are preserved at high structural levels in the Suru Valley and in the telescoped metamorphic sequence above the Main Central thrust. Elsewhere, a later foliation developed around domal structures and largely obliterated these early assemblages. The record of P and T along the traverses is polychronic, but the timing is not easily constrained by the geochronological data because of the presence of excess argon, particularly at deeper structural levels.
The patterns are consistent with
- A post-collisional Barrovian metamorphism with typical conditions 600 - 650°C, 10 kbar, largely pre-dating movement on the Main Central thrust.
- The rise of domal structures in the centre of the slab, associated with higher grade but lower pressure assemblages, probably coeval with movements on the Main Central thrust and Zanskar normal fault. Metamorphism peaked in the Suru Dome at 650 - 680°C, 7 - 8 kbar, and in the more extensively-developed high-grade domes at 700 - 750°C, 5 kbar, before cooling associated with exhumation froze in the mineral assemblages.
- Continued rapid exhumation of the slab, with cooling through 400 - 300°C ca. 15 - 18 Ma ago.
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Created 19 September 1996