| The Tien Shan is the pre-eminent mountain range of Central Asia, and an active intracontinental orogeny, located over 1000 kilometers from the tectonic boundary where India is colliding with and intruding into Asia. Explanations for this far-field manifestation claim the Tien Shan consists of reactivated basement, more prone to deformation than the older, stronger cratonic blocks north and south of it. This study supports that scenario, demonstrating that pre-existing structures played an important and pervasive, although not exclusive, role in localizing and orienting the ongoing orogeny.; Paleozoic through mid-Mesozoic assembly of terranes to create Central Asia left basement rocks multiply folded and faulted. Late Mesozoic quiescence and planation created an erosion surface or peneplane, originally horizontal, throughout much of Central Asia. This surface provides a stratigraphic marker separating poly-deformed pre-Cenozoic strata from less deformed Tertiary beds manifesting only Cenozoic strain, allowing the unambiguous temporal distinction of deformational events.; The Central Tien Shan Terrane in Kyrgyzstan consists of two basement-cored mountain ranges and intervening river valleys. Both ranges contain specific inherited structures used by the current orogeny. Within the Baybiche-Too Range, restoration of the faulted erosion surface to its originally continuous geometry leaves different lithologies with different dips juxtaposed across some faults. These faults, which include the range-front fault and the intramontane basin-forming fault, must be reactivated. The northern margin of Karatal Basin within the Molda-Too Range is formed by a sub-vertical east-west trending fault within sub-vertical east-west trending limestone bedding, suggesting that this fault followed bedding as a plane of weakness.; In addition to these examples of specific inherited structures involved in ongoing deformation, there is evidence for a more cryptic regional strength anisotropy. Folds in Paleozoic rocks across the Molda-Too Range can be restored to their pre-orogenic orientations using the erosion surface as a reference. The predominantly NE-SW to WNW-ESE range of fold axis trends closely corresponds to the current north-south direction of maximum shortening determined from GPS, terrace deformation, Cenozoic fold axes and fault surfaces. This suggests that the combination of bedding and small-scale faulting that constitutes pre-existent folding also contributes to controlling the active orogeny. |
