We have determined slip rates on the most active reverse faults, reconstructed an extensive preorogenic erosion surface, constructed local and regional cross sections, and dated syntectonic Tertiary sedimentary rock with magnetostratigraphy along a north-south transect that spans the Kyrgyz portion of the Tien Shan. The cumulative Late Quaternary shortening rate along this transect is 10 mm/yr, divided into five major fault zones, with the most active in the interior of the range. Using geometrical models developed in other regions of basement-involved deformation, we calculate 35–80 km of shortening during the Late Cenozoic. Apparently simultaneous onset of significant basin formation in at least three major basins around 12 Ma is interpreted to mark the onset of the current orogeny. Given the current shortening rate of about 10 mm/yr, measured across active faults and by GPS, we infer that the rate has increased with time. While we propose an acceleration of shortening, our studies indicate that it has always been of similar style, dominated by north-south shortening across east-west basement-involved reverse faults with deformation localized in live zones that border the largest and deepest Tertiary basins, show the greatest structural relief, and contain the currently most active faults.

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