Discussion
Thrusting and folding of sediments in the Himalaya appears to have caused a crustal shortening of the order of :
Answer: C
The answer given is a shortening of the order of 1,000 km.
India and Asia have converged by roughly 2,500 km since the collision. Plate-reconstruction estimates, such as that of Dewey, Cande and Pitman (1989), credit about 1,000 km of this to the thrusting and folding of the sediments of the old Indian margin together with deformation of Tibetan crust; the rest is attributed to other processes such as subduction of Indian crust and lateral extrusion of blocks.
10,000 km is several times the whole convergence, and 2,400 km is about the whole convergence rather than the part taken by thrusts and folds. A shortening of 500 m would be a trivial fraction of a single fault's displacement, so it cannot describe a mountain belt.
Note that this is a figure from plate reconstructions. Shortening measured by balancing cross-sections is smaller, commonly a few hundred kilometres, so the size of the number is debated; among the options only 1,000 km fits the textbook statement.
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