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Intra-continental mountain belts typically form as a result of tectonic forces associated with distant plate collisions. In general, each mountain belt has a distinctive morphology and orogenic evolution that is highly dependent on the unique distribution and geometries of inherited structures and other crustal weaknesses. In this thesis, I have investigated the complex and irregular Cenozoic orogenic evolution of the Central Kyrgyz Tien Shan in Central Asia, which is presently one of the most active intra-continental mountain belts in the world. This work involved combining a broad array of datasets, including thermochronologic, magnetostratigraphic, sediment provenance and stable isotope data, to identify and date various changes in tectonic deformation, climate and surface processes. Many of these changes are linked and can ultimately be related to regional-scale processes that altered the orogenic evolution of the Central Kyrgyz Tien Shan. The Central Kyrgyz Tien Shan contains a sub-parallel series of structures that were reactivated in the late Cenozoic in response to the tectonic forces associated with the distant India-Eurasia collision. Over time, slip on the various reactivated structures created the succession of mountain ranges and intermontane basins which characterises the modern morphology of the region. In this thesis, new quantitative constraints on the exhumation histories of several mountain ranges have been obtained by using low temperature thermochronological data from 95 samples (zircon (U-Th)/He, apatite fission track and (U-Th)/He). Time-temperature histories derived by modelling the thermochronologic data of individual samples identify at least two stages of Cenozoic cooling in most of the region’s mountain ranges: (1) initially low cooling rates (26 Ma in that particular range. Elsewhere, growth strata relationships are used to identify syn-tecotnic deposition and constrain the timing of nearby deformation. Collectively, these new constraints obtained from thermochronologic and sedimentary data have allowed me to infer the spatiotemporal distribution of deformation in a transect through the Central Kyrgyz Tien Shan, and determine the order in which mountain ranges started deforming. These data suggest that deformation began in a few widely-spaced mountain ranges in the late Oligocene and early Miocene. Typically, these earlier mountain ranges are bounded on at least one side by a reactivated structure, which probably corresponds to the frictionally weakest and most suitably orientated inherited structures for accommodating the roughly north-south directed horizontal crustal shortening of the late Cenozoic. Moreover, tectonically-induced rock uplift in the Terskey Range, following the reactivation of the bounding structure before 26 Ma, likely caused significant surface uplift across the range, which in turn lead to enhanced orographic precipitation. These wetter conditions have been inferred from stable isotope data collected in the two magnetostratigraphically-dated sections in the Issyk Kul basin. Subsequently, in the late Miocene (~12‒5 Ma), more mountain ranges and inherited structures appear to have started actively deforming. Importantly, the onset of deformation at these locations in the late Miocene coincides with an increase in exhumation of ranges that had started deforming earlier in the late Oligocene‒early Miocene. Based on this observation, I have suggested that there must have been an overall increase in the rate of horizontal crustal shortening across the Central Kyrgyz Tien Shan, which likely relates to regional tectonic changes that affected much of Central Asia. Many of the mountain ranges that started deforming in the late Miocene were associated with out-of-sequence tectonic reactivation and initiation, which lead to the partitioning of larger intermontane basins. Moreover, within most of the intermontane basins in the Central Kyrgyz Tien Shan, this inferred late Miocene increase in horizontal crustal shortening occurs roughly at the same time as an increase in sedimentation rates and a significant change sediment composition. Therefore, I have suggested that the overall magnitude of deformational processes increased in the late Miocene, promoting more flexural subsidence in the intermontane basins of the Central Kyrgyz Tien Shan. Intrakontinentale Gebirge sind typischerweise das Ergebnis tektonischer Kräfte, die auf entfernte Plattenkollisionen beruhen. Im Allgemeinen hat jedes Gebirge sein charakteristisches morphologisches Erscheinungsbild und seine eigene und einzigartige Entstehungsgeschichte, die zum Großteil von der Verteilung und der Geometrie vorgeprägter Strukturen und anderer Schwächzonen innerhalb der Erdkruste abhängt. In der vorliegenden Arbeit habe ich die komplexe känozoische Gebirgsbildung des zentral-kirgisischen Tian Shan Gebirges, eines der weltweit aktivsten intrakontinentalen Gebirge, untersucht. Diese Arbeit kombiniert verschiedenste Datensätze, darunter thermochronologische und magnetostratigraphische Daten, Sedimentprovenienzen und stabile Isotopenzusammensetzungen, um Änderungen der tektonischen Deformationsprozesse sowie Klima- und Oberflächenveränderungen zu erkennen und gegebenenfalls zu datieren. Viele dieser Veränderungen sind eng miteinander verknüpft und können letztendlich auf regionale Prozesse zurückgeführt werden, die die Entwicklung des zentral-kirgisischen Tian Shan beeinflussen. Das Tian Shan Gebirge besteht aus einer subparallelen Folge einzelner Gebirgsrücken und deren Strukturen, welche im späten Känozoikum als Reaktion auf die entfernt stattfindende Indo-Eurasische Kollision reaktiviert wurden. Im Laufe der Zeit haben Deformation und Versatz entlang dieser reaktivierten Strukturen eine Abfolge von individuellen Gebirgszügen und dazwischen liegenden Sedimentbecken geschaffen deren Morphologie prägend für die heutige Region ist. In dieser Arbeit wurden neue quantitative Altersbestimmungen zur Exhumationsgeschichte mehrerer Gebirgszüge durch thermochronologische Auswertungen an 95 Gesteinsproben durchgeführt (ZHe, AFT und AHe). Die aus Modellierungen einzelner thermochronologischer Datensätze gewonnenen Temperaturgeschichten lassen für die meisten untersuchten Gebirgszüge mindestens zwei Abschnitte känozoischer Abkühlung erkennen: (1) anfänglich niedrige Abkühlungsraten ( |
