No description available.

The southern margin of the Kochkor Basin in the Kyrgyz Tien Shan is actively shortening. The South Kochkor Fault, a reverse fault that places Paleozoic granite on Neogene sediments, varies in displacement from 0-2 km while the structural relief across the basin margin is 4 km. North of the fault, a 2 km thick panel of steeply-dipping to overturned sediments exhibits flexural shearing. This steep section is bounded by limbs of gently-dipping beds to the north and south. Northward, Neogene section is thrust over late Quaternary deposits in two younger episodes of faulting: the Akchop Hills Fault and the Aigyrdzal Hills Fault. Through 1:25,000 scale mapping I have demonstrated that of structural relief in the area is shared by fault propagation folding and faulting on a steep, reverse fault that shallows into a detachment. A complete geologic map of Kochkor, Kyrgyzstan is included with this thesis as a supplemental file.

No description available.

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 (<1°C/Myr) during the tectonic quiescent period and (2) increased cooling in the late Cenozoic, which occurred diachronously and with variable magnitude in different ranges. This second cooling stage is interpreted to represent increased erosion caused by active deformation, and in many of the sampled mountain ranges, provides the first available constraints on the timing of late Cenozoic deformation. New constraints on the timing of deformation have also been derived from the sedimentary record of intermontane basins. In the intermontane Issyk Kul basin, new magnetostratigraphic data from two sedimentary sections suggests that deposition of the first Cenozoic syn-tectonic sediments commenced at ~26 Ma. Zircon U-Pb provenance data, paleocurrent and conglomerate clast analysis reveals that these sediments were sourced from the Terskey Range to the south of the basin, suggesting that the onset of the late Cenozoic deformation occurred >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 (<1°C/Myr) während einer tektonische Ruhephase und (2) stärkere Abkühlung im späten Känozoikum, die in den verschiedenen Gebirgsketten diachron und mit unterschiedlicher Intensität einsetzt. Diese zweite Abkühlungsphase kann durch einen Anstieg der Erosionsraten durch aktive Deformation interpretiert werden und stellt für viele der untersuchten Gebirgszüge die erste verfügbare Alterabschätzung spätkänozoischer Deformation dar. Neue Deformationsalter wurden weiterhin aus den Sedimenten intermontaner Becken gewonnen. Im intermontanen Issyk Kul Becken lassen neue magnetostratigraphische Daten zweier Sedimentabschnitte vermuten, dass die Ablagerung der ersten syntektonischen Sedimente im Känozoikum um ca. 26 Ma begann. Weiterhin zeigen Zirkon-Provenienzen, Paläoströmungsrichtungen sowie Klastenanalysen konglomeratischer Sedimente, dass diese Sedimente aus der Terskey Range südlich des Beckens stammen, was vermuten lässt, dass der Beginn der spätkänozoischen Deformation in diesem Teil des Gebirgszuges älter als 26 Ma ist. In anderen Bereichen wurden sedimentäre Wachstumsstrukturen zur Identifikation syntektonischer Ablagerung herangezogen, um somit den Zeitpunkt nahe gelegener Deformation zu bestimmen. Zusammengenommen haben meine Beobachtungen und Auswertungen ermöglicht, die räumlichen und zeitlichen Deformationsmuster quer durch das zentral-kirgisischen Tian Shan Gebirge zu erschließen um eine zeitliche Abfolge in der Entstehung und Entwicklung einzelner Gebirgszüge zu entwickeln. Meine Daten lassen vermuten, dass die Deformation in einigen wenigen, weit auseinander liegenden Bergketten im Spätoligozän bis Frühmiozän begann. Typischerweise sind diese frühen Gebirgsketten auf mindestens einer Seite an eine reaktivierte Struktur gebunden. Diese sind die wahrscheinlich schwächsten oder am besten orientierten Strukturen, um die annähernd Nord-Süd gerichtete Einengung im späten Känozoikum aufzunehmen. Darüber hinaus ist es sehr wahrscheinlich, dass die tektonische Gesteinshebung innerhalb der Terskey Range, entlang reaktivierter Störungen vor 26 Ma, eine signifikante Topographiezunahme zur Folge hatte. Dies führte höchstwahrscheinlich zur Ausbildung einer orographischen Barriere und der damit verbundenen Verstärkung der Regenfälle im Becken nördlich des Rückens. Diese Bedingungen konnten mithilfe stabiler Isotopenzusammensetzungen entlang der zwei magnetostratigraphisch datierten Sedimentprofile im Issyk Kul Becken nachgewiesen werden. Während des späten Miozäns (~12‒5 Ma) begann zeitnah die aktive Deformation und Heraushebung mehrerer neuer Gebirgsrücken. Wichtig dabei erscheint, dass der Zeitpunkt dieser spätmiozänen Deformation mit einem Exhumationsschub derer Gebirgszüge zusammenfällt, die schon viel früher (Spätoligozän bis Frühmiozän) mit der Deformation begannen. Aufgrund dieser Beobachtungen habe ich vorgeschlagen, dass es einen generellen Anstieg der Einengungsraten im Tian Shan gegeben haben muss, welcher auf regionale tektonische Veränderungen zurückzuführen ist die große Teile Zentralasiens betrafen. Viele der Gebirgsrücken, die initial im späten Miozän herausgehoben wurden, sind durch unsystematische, tektonische Prozesse der Reaktivierung und Initialisierung von Strukturen (out-of-sequence) entstanden, die zur Teilung vormals großer, zusammenhängender Sedimentbecken führte. Darüber hinaus weisen die meisten intermontanen Becken im zentral-kirgisischen Tian Shan, in etwa zur Zeit der beobachteten, verstärkten Einengung im Spätmiozän, ebenfalls erhöhte Sedimentationsraten und eine signifikante Änderung der Sedimentzusammensetzung. Daher vermute ich, dass die allgemeine Intensität der Deformation im Spätmiozän zunahm, was eine tektonische Absenkung (flexural subsidence) in den intermontane Becken des zentral-kirgisischen Tian Shan Gebirges zur Folge hatte.

La chaîne du Sud Tien-Shan (STS) en Asie Centrale est une des plus grandes chaînes intracontinentales et résulte de la réactivation de structures héritées de son histoire Paléozoïque lors de la formation de la Ceinture Orogénique d’Asie Centrale (CAOB). La compréhension de la tectonique actuelle du STS repose donc sur une bonne connaissance de sa structuration au Paléozoïque qui reste néanmoins largement débattue. La partie kirghize de la chaîne a été moins étudiée que la partie chinoise et cette thèse propose donc une étude détaillée du STS kirghize. En particulier, l’étude des massifs métamorphiques situés le long de la suture du STS permet de contraindre l’histoire de subduction. L’approche utilisée est pluridisciplinaire, basée sur une étude de terrain, puis une analysethermobarométrique utilisant des micro-cartographies chimiques couplées à de la modélisation thermodynamique, et enfin une étude géochronologique.Nous montrons que la faille de Talas-Fergana, faille active de 2000 km de long, est une discontinuité majeure dès le Carbonifère supérieur puisqu’elle délimite deux domaines à l’évolution distincte. A l’ouest, une subduction à vergence nord de l’océan Turkestan a conduit à la formation d’un arc magmatique important. Autour de ca. 301 Ma, la collision entre le Kazakhstan et le craton Alai entraine un épaississement crustal important associé à des nappes. A l’est, une subduction à vergence sud de ce même océan est suggérée par une structure à pendage sud présentant des unités de haute-pression océanique et continentale exhumées au sein d’un paléo-prisme d’accrétion de plus bas degré métamorphique le long de chevauchements à vergence nord et de détachements à vergence sud.La fermeture de l’océan Turkestan est marquée par l’exhumation de l’unité de haute-pression continentale à ca. 320-330 Ma. Au Permien, une première phase de réactivation dans un régime transpressif, est associée à un magmatisme intense. En bordure de la chaîne, ce magmatisme interagit avec un panache mantellique sous le craton du Tarim. Cette phase permienne a conduit d’une part à l’initiation de chevauchements à vergence sud, au sud du STS et d’autre part à la modification de la structure thermique de la lithosphère sous le Tarim.Le modèle d’évolution proposé pour le STS kirghize s’intègre bien dans un modèle d’évolution global de la CAOB. De plus, on voit que la structuration Paléozoïque, de la collision carbonifère à la première phase de réactivation permienne, permet d’expliquer la tectonique actuelle du STS qui est une chaîne à double vergence s’élevant au-dessus de bassin intramontagneux au nord et au-dessus du craton du Tarim au sud qui se comporte comme un bloc rigide / The South Tien-Shan (STS) belt, in Central Asia, is one of the largest intracontinental orogens. It results from the reactivation of Paleozoic structures inherited from the Central Asia Orogenic Belt (CAOB) building. Understanding the current tectonics of STS requires the knowledge of the Paleozoic history which is, however, still debated. As the Kyrgyz part of STS has been less studied than the Chinese one, this thesis aims to provide a detailed study of the Kyrgyz STS. Studying metamorphic ranges along the STS suture allows constraining the subduction history. A pluri-disciplinary approach was used, firstly based on field observations, then on thermobarometric studies combining X-ray micro-mapping and thermodynamic modeling and finally on geochronological studies.Results show that the Talas-Fergana fault, which is a 2000 km long active fault, was an important discontinuity from Upper Carboniferous times as it separated two areas with distinct geodynamic evolutions. To the west, a north-dipping subduction of the Turkestan Ocean led to the development of an important magmatic arc. Around ca. 301 Ma, the collision of Kazakhstan and Alai blocks resulted in crustal thickening and nappe stacking. To the east, a south-dipping subduction is suggested by south dipping structures exhibiting both oceanic and continental high-pressures units exhumed in a lower-grade paleo-accretionnary prism along top-to-the-north thrusts and top-to-the-south detachments. The continental high-pressure unit was exhumed at ca. 320-330 Ma just after the Turkestan Ocean closure. During Permian times, a first reactivation phase was associated to transpressive tectonics and intense magmatism. At the southern boundary of STS, interactions between transpressive tectonics and a mantle plume beneath the Tarim craton are reported. This Permian history led to the initiation of top-to-the-south thrusting to the south of STS and to the modification of thermal state of the lithosphere beneath the Tarim.The geodynamic model proposed for the Kyrgyz STS fits well with proposed models of global CAOB evolution. Moreover, is shows that the Paleozoic structuration, from the Carboniferous collision to the Permian reactivation, explains the current tectonics of STS which is a doubly vergent mountain belt thrusting intramontane basins to the north and the Tarim craton to the south. This latter acts as a rigid block since the Paleozoic

Le Tien Shan est une chaîne de montagne active située à plus de 1000 km de la limite de plaque la plus proche, le front Himalayen. Elle possède une histoire ancienne qui va de la fin du Protérozoïque à la fin du Paléozoïque dans un contexte d’accrétions successives formant la plus grande chaîne d’accrétion du monde, la CAOB. Afin de comprendre comment l’histoire paléozoïque du Tien Shan influence la localisation de la déformation cénozoïque, nous avons dans un premier temps étudié la structuration de la chaîne pour en identifier les principales structures héritées. Nous avons mis en avant le partitionnement de la déformation entre les zones de sutures Sud et Nord au cours de la collision entre le Tarim et le Tien Shan au Carbonifère supérieur. Le front de collision est caractérisé par des chevauchements et des détachements au sein d’unités métamorphiques. Au Nord, se trouve une zone en décrochement caractérisée par une structure en fleur positive. Ensuite, ces résultats sont utilisés comme les conditions initiales de modèles numériques thermo-mécaniques 2D dont le but est de tester l’influence de ces zones héritées sur la localisation de la déformation cénozoïque. Ces modèles montrent que la déformation cénozoïque dans le Tien Shan se localise à la faveur de zones de faiblesses crustales et non mantelliques. De plus, nous avons pu établir que la bordure nord du Tarim avait une rhéologie proche de celle du Tien Shan. Finalement, à l’aide des modèles numériques une étude systématique a permis de mettre en évidence que le couplage entre l’érosion et le réseau de drainage jouait un rôle important dans la répartition et l’âge des roches de basse température exhumées. / The Tien Shan is an active mountain belt located at more than thousand kilometres of the closest plate boundary, the Himalayan front. Its Late Proterozoic to Late Paleozoic history takes place during the CAOB accretion which represents the largest accretionary belt in the world. In order to understand how the Paleozoic tectonics of the Tien Shan influences the Cenozoic strain localization, we aim at identifying the main inherited structures of the belt. We highlighted the strain partitioning between the North and South suture zones during the Tarim-Tien Shan Late Carboniferous collision. The collisional front is characterized by thrusts and detachments in metamorphic units while northward, a strike-slip zone is evidenced by a positive flower structure. Then, these results are used as variable inputs in 2D numerical thermo-mechanical models in order to assess the role of these inherited structures on the Cenozoic strain localization. These models show that the Cenozoic deformation in the Tien Shan is localized in favour of crustal weak zones instead of mantellic ones. Moreover, we are able to show that the northern border of the Tarim has a Tien Shan like rheology. Finally, we performed a systematic numerical modelling analyse in order to show that the coupling between erosion and drainage network plays an important role on low temperature rocks exhumation ages and repartition.

Tian Shan is one of the most important orogenic belts in central Asia. It has been reactivated as a result of the Cenozoic India-Eurasia collision. Dating of the late Cenozoic tectonic deformation of Tian Shan and its piedmonts is important for understanding the mountain building as well as evaluating seismic hazards in the region. This study is focused on the applications of optical dating to the late Quaternary uplift and thrust activity along Manas River, in the northern piedmont of the Tian Shan, China. The sediments on river terraces were dated with optical dating. The elevations were measured with the kinematic global position system (GPS). The results suggest that two phases can be identified according to the significantly different river incision rates. One phase was from ~20 ka to ~4.8 ka, with a much slower incision rate of ~ 2.2 ± 0.6 mm/yr. The other phase was from ~4.8 ka to present, with a faster incision rate of ~ 13.5 ± 0.6 mm/yr. The accelerated incision rate of Manas River was mainly attributed to the tectonic forces, suggesting that the tectonic uplift was significantly intensified since ~4.8 ka in the northern piedmont of Tian Shan. The study region has suffered from multiple thrust activities during the late Quaternary, which led to the intensive deformations of the river terraces. By studying the deformed terraces, I evaluated the timing of the past thrust activities as well as the vertical slip rate of the thrust faults. The results demonstrated that the thrust activity intensified during the late Holocene, as manifested by the more frequent thrust activities and higher vertical slip rates. Both quartz and potassium feldspar can be as dosimeters for optical dating of sediments. However, quartz OSL is sometimes seriously impeded with problems such as very dim signals and insufficient bleaching problems. K-feldspar has attractive advantages over quartz, despite of problem of anomalous fading. K-feldspar was explored in this study, by investigating the relationship between the infrared stimulated luminescence (IRSL) and blue light stimulated luminescence (BLSL) signals. For IRSL and BLSL at 60 °C, it was suggested that most of the IRSL could be bleached by blue light (BL), while the BLSL could only be partially bleached by infrared (IR) stimulation. Besides, the fast and medium components of BLSL were mainly associated with the IRSL. If IR stimulation temperature was raised from 60 to 200 °C, at least two portions of the IRSL signals at 200 °C were observed. One portion could be bleached by BL at 60 °C and the other portion was hardly bleached by BL at 60 °C. Dating of K-feldspar from the various signals provided cross-checking for the reliability of quartz OSL for dating sedimentary samples. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

In the context of changing climate retreat of mountain glaciers occurs at many places on the planet. One of the consequences is emergence or increase of the outburst risk at lakes situated in front of the glacier terminus. Flood caused by the glacial lake outburst often appear suddenly and can threaten settlements in lower parts of a valley. In the Kyrgyz mountains of Tien Shan there are about 350 lakes at risk of outburst, long-term monitored and dangerous locations are presented in this work. The highest attention is paid to Adygine area where several lakes of different genetic type and age can be found. The largest lake of the locality, the Upper Adygine lake, is subjected to more detailed survey aiming to asses its hydrological regime and to confirm or disprove speculation about outburst possibility of this lake. Keywords: glacial lake, hydrological regime, glacier retreat, Tien Shan, Kyrgyzstan

We present a tree-ring based reconstruction of water-year (October–September) streamflow for the Manasi River in the northern Tien Shan mountains in northwestern China. We developed eight Tien Shan spruce (Picea schrenkiana Fisch. et Mey.) chronologies for this purpose, which showed a common climatic signal. The hydroclimatic forcing driving tree growth variability affected streamflow with a three- to four-year lag. The model used to estimate streamflow is based on the average of three chronologies and reflects the autoregressive structure of the streamflow time series. The model explains 51% of variance in the instrumental data and allowed us to reconstruct streamflow for the period 1629–2000. This preliminary reconstruction could serve as a basis for providing a longer context for evaluating the recent (1995–2000) increasing trends in Manasi River streamflow and enables the detection of sustained periods of drought and flood, which are particularly challenging for managing water systems. Several of the reconstructed extended dry (wet) periods of the Manasi River correspond to reconstructed periods of drought (flood) in Central Asia in general and in other Tien Shan mountain locations in particular, suggesting that the analysis of Tien Shan spruce could contribute significantly to the development of regionally explicit streamflow reconstructions.

Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 173-185). Also available for download via the World Wide Web; free to University of Oregon users.