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Broughton, R. D.
- The Central Himalayan Gneisses in Northern Pakistan
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Authors
Affiliations
1 Department of Geology, University of Leicester, Leicester, LE1 7RH, GB
1 Department of Geology, University of Leicester, Leicester, LE1 7RH, GB
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 31, No 2 (1988), Pagination: 185-196Abstract
The Central Himalayan Gneisses on the northern margin of the Indian plate in the Hazara and Lower Swat areas of N. Pakistan comprise; orthogneisses with minor schists, amphibolites and calc-silicates, overlain unconformably by a cover sequence of graphitic and calcareous schists, marbles and minor amphibolites. These rocks are bounded to the south by a major thrust (equivalent to the Himalayan Main Central Thrust), and to the north by lhe Main Mantle Thrust (Indus Suture). To the south of the MCT there is a thrust slice of basement paragneisses with no relics of cover. The dominant gneissose foliation parallels the main thrusts, and is modified by numerous, large-scale N-S trending open folds.The ortho- and para-gneisses and cover sequence are isofacial, and underwent two phases of metamorphism, prior to 35 Ma. Mineral equilibria indicate conditions for the cover sequence in the range 550-620°C and 8.0-8.9 kb, and for the paragneiss basement at ∼650°C and 6.7-6.8 kb. The two pressure ranges come from different thrust slabs. These data indicate an average cooling rate of ∼17°C my-1, and an average uplift rate of ∼0.8 mm yr-1 over the last 35 My, for the relic cover sequence.