The mountains of the Tien Shan are composed mainly of crystalline and sedimentary rocks of the Paleozoic Era (from 540 to 250 Ma). The inter-montane basins are filled with younger fluvial/lacustrine sediments. Intrusive igneous outcrops can be seen over much of the area in the north and east of the Tien Shan, which underwent folding during an early-Paleozoic orogeny. It has been uplifted and dry since then, so its original sedimentary cover has been almost completely eroded. The southern and western parts of the Tien Shan, however, consist principally of meta-sedimentary rock and, to a lesser extant, of intrusive and extrusive volcanics. These regions experienced folding during the late Paleozoic. A new stage of development began in the middle of the Tertiary Period (~ 25 Ma) and has continued to the present time. The primary evidence for this comes from the presence of foreland sedimentary strata (primarily conglomerates) that have been dated to be from this period (Charreau et al, 2005 - Reference [E1] below). Shallow lakes that formed in many valleys/basins & the arid climate during this time created ideal conditions for vast evaporite deposits. Subsequently, glaciers deposited boulder moraines in the mountains, while gravel and loess strata accumulated in the valleys. The boundaries between inter-montane basins and adjoining ranges are defined by steeply dipping fault zones (Vinnik et al., 2002, Wang et al., 2004 - Reference [B5] below).

It is thought that nearly half of the present-day Indo-Asian convergence is absorbed by deformation roughly 1000-2000 km north of the Himalaya, within the interior ranges of Central Asia (Bullen et al., 2003, Reference [B4] below, and bottom right figure panel above) - namely, the Tien Shan and Altai Ranges. Geodetic studies indicate that the present shortening rate in the Tien Shan is approximately 20-23 km/m.yr. (mm/yr), which is similar to the shortening rate across the main Himalayan Thrust (Avouac, 2003, Reference [A7] below). Rapid shortening in the Tien Shan has created the highest summits outside of the Himalaya. As such, the Tien Shans are make a unique case-study of intracontinental mountain building. The timing of the initial growth of the Tien Shan remains controversial. Magneto-stratigraphic sections and fission track ages in the eastern and southern Tien Shan indicate that erosional exhumation of these ranges began at 20-25 Ma and may have been linked to a switch from extrusion-dominated to crustal thickening- dominated tectonics. Alternatively, initial Tien Shan growth has been estimated at approximately 10 Ma on the basis of extrapolation of the geodetic shortening rate, given that the total Cenozoic shortening across the Tien Shan has been estimated at 200±50 km.

Recent work by Rowley (2006, Reference [A8] below), based on oxygen-isotope-based estimates of the palaeo-altimetry of late Eocene and younger deposits of the Lunpola basin in the centre of the Tibetan Plateau suggest that it was created rapidly, and has remained uplifted for the past 35 million years. If the Traim block can be considered rigid, then it is possible that it could have acted as a stress guide, transferring deformation to its northern margin, to cause the Central Asian ranges to uplift. Either of the above dates for the initiation of deformation at the northern edge of the Tarim Basin is consistent with this progression of deformation from the Himalayan front to the present location of the Tien Shans. But the issue is whether this transfer of stress took approximately 10 Ma (as suggested by magneto-stratigraphic sections & fission track ages) or 25 Ma (as suggested by the extrapolation of geodetic shortening rate).

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