@phdthesis{Kooten2023, author = {Kooten, Willemijn Sarah Maria Theresia van}, title = {Structural inheritance of the Salta Rift basin and its control on exhumation patterns of the Eastern Cordillera between 23 and 24°S}, doi = {10.25932/publishup-61798}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617983}, school = {Universit{\"a}t Potsdam}, pages = {XIX, 188}, year = {2023}, abstract = {The deformation style of mountain belts is greatly influenced by the upper plate architecture created during preceding deformation phases. The Mesozoic Salta Rift extensional phase has created a dominant structural and lithological framework that controls Cenozoic deformation and exhumation patterns in the Central Andes. Studying the nature of these pre-existing anisotropies is a key to understanding the spatiotemporal distribution of exhumation and its controlling factors. The Eastern Cordillera in particular, has a structural grain that is in part controlled by Salta Rift structures and their orientation relative to Andean shortening. As a result, there are areas in which Andean deformation prevails and areas where the influence of the Salta Rift is the main control on deformation patterns. Between 23 and 24°S, lithological and structural heterogeneities imposed by the Lomas de Olmedo sub-basin (Salta Rift basin) affect the development of the Eastern Cordillera fold-and-thrust belt. The inverted northern margin of the sub-basin now forms the southern boundary of the intermontane Cianzo basin. The former western margin of the sub-basin is located at the confluence of the Subandean Zone, the Santa Barbara System and the Eastern Cordillera. Here, the Salta Rift basin architecture is responsible for the distribution of these morphotectonic provinces. In this study we use a multi-method approach consisting of low-temperature (U-Th-Sm)/He and apatite fission track thermochronology, detrital geochronology, structural and sedimentological analyses to investigate the Mesozoic structural inheritance of the Lomas de Olmedo sub-basin and Cenozoic exhumation patterns. Characterization of the extension-related Tacur{\´u} Group as an intermediate succession between Paleozoic basement and the syn-rift infill of the Lomas de Olmedo sub-basin reveals a Jurassic maximum depositional age. Zircon (U-Th-Sm)/He cooling ages record a pre-Cretaceous onset of exhumation for the rift shoulders in the northern part of the sub-basin, whereas the western shoulder shows a more recent onset (140-115 Ma). Variations in the sedimentary thickness of syn- and post-rift strata document the evolution of accommodation space in the sub-basin. While the thickness of syn-rift strata increases rapidly toward the northern basin margin, the post-rift strata thickness decreases toward the margin and forms a condensed section on the rift shoulder. Inversion of Salta Rift structures commenced between the late Oligocene and Miocene (24-15 Ma) in the ranges surrounding the Cianzo basin. The eastern and western limbs of the Cianzo syncline, located in the hanging wall of the basin-bounding Hornocal fault, show diachronous exhumation. At the same time, western fault blocks of Tilcara Range, south of the Cianzo basin, began exhuming in the late Oligocene to early Miocene (26-16 Ma). Eastward propagation to the frontal thrust and to the Paleozoic strata east of the Tilcara Range occurred in the middle Miocene (22-10 Ma) and the late Miocene-early Pliocene (10-4 Ma), respectively.}, language = {en} } @article{StuebnerGrujicDunkletal.2017, author = {St{\"u}bner, Konstanze and Grujic, Djordje and Dunkl, Istvan and Thiede, Rasmus Christoph and Eugster, Patricia}, title = {Pliocene episodic exhumation and the significance of the Munsiari thrust in the northwestern Himalaya}, series = {Earth \& planetary science letters}, volume = {481}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2017.10.036}, pages = {273 -- 283}, year = {2017}, abstract = {The Himalayan thrust belt comprises three in-sequence foreland-propagating orogen-scale faults, the Main Central thrust, the Main Boundary thrust, and the Main Frontal thrust. Recently, the Munsiari-Ramgarh-Shumar thrust system has been recognized as an additional, potentially orogen-scale shear zone in the proximal footwall of the Main Central thrust. The timing of the Munsiari, Ramgarh, and Shumar thrusts and their role in Himalayan tectonics are disputed. We present 31 new zircon (U-Th)/He ages from a profile across the central Himachal Himalaya in the Beas River area. Within a ∼40 km wide belt northeast of the Kullu-Larji-Rampur window, ages ranging from to constrain a distinct episode of rapid Pliocene to Present exhumation; north and south of this belt, zircon (U-Th)/He ages are older ( to ). We attribute the Pliocene rapid exhumation episode to basal accretion to the Himalayan thrust belt and duplex formation in the Lesser Himalayan sequence including initiation of the Munsiari thrust. Pecube thermokinematic modelling suggests exhumation rates of ∼2-3 mm/yr from 4-7 to 0 Ma above the duplex contrasting with lower (<0.3 mm/yr) middle-late Miocene exhumation rates. The Munsiari thrust terminates laterally in central Himachal Pradesh. In the NW Indian Himalaya, the Main Central thrust zone comprises the sheared basal sections of the Greater Himalayan sequence and the mylonitic 'Bajaura nappe' of Lesser Himalayan affinity. We correlate the Bajaura unit with the Ramgarh thrust sheet in Nepal based on similar lithologies and the middle Miocene age of deformation. The Munsiari thrust in the central Himachal Himalaya is several Myr younger than deformation in the Bajaura and Ramgarh thrust sheets. Our results illustrate the complex and segmented nature of the Munsiari-Ramgarh-Shumar thrust system.}, language = {en} } @article{GeorgievaGallagherSobczyketal.2019, author = {Georgieva, Viktoria and Gallagher, Kerry and Sobczyk, Artur and Sobel, Edward and Schildgen, Taylor F. and Ehlers, Todd and Strecker, Manfred}, title = {Effects of slab-window, alkaline volcanism, and glaciation on thermochronometer cooling histories, Patagonian Andes}, series = {Earth \& planetary science letters}, volume = {511}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2019.01.030}, pages = {164 -- 176}, year = {2019}, abstract = {Southern Patagonia is a prime example of ongoing oceanic ridge collision and slab-window formation sustained over several million years. The impact of these phenomena on the thermal structure and exhumation of the crust have been mainly assessed with low-temperature thermochronology of bedrock samples. Here, we infer thermal histories from new and existing thermochronological data from the region of most recent ridge collision. In particular, we evaluate the potential far-reaching thermal effects of the evolving slab window, which have previously been considered responsible for patterns of late Miocene reheating associated with back-arc alkaline volcanism. Our model results define protracted cooling since similar to 15 Ma and stepwise exhumation since the late Miocene. The pattern of stepwise exhumation closely matches the onset of Patagonian glaciation at 7 Ma and the successive pulse of glacial incision coeval with neotectonic activity since 3-4 Ma that are also documented by independent geological and geomorphological evidence in the region. Importantly, our findings challenge the recently suggested lack of glacial erosion and incision since 5 Ma in this region. Furthermore, in contrast to previous modelling studies, we find that the available data do not evidence a previously proposed northward-propagating heating event associated with alkaline volcanism. We hypothesize that the anomalous alkaline volcanism in the Patagonian back-arc might be related to trench-orthogonal tears aligned with transform faults in the subducting plate. The substantial differences from the previous modelling procedure on some of the same samples is demonstrated to result from an important lack of convergence in model runs. (C) 2019 Elsevier B.V. All rights reserved.}, language = {en} } @article{HansmanRingThomsonetal.2017, author = {Hansman, Reuben J. and Ring, Uwe and Thomson, Stuart N. and den Brok, Bas and Stuebner, Konstanze}, title = {Late Eocene Uplift of the Al Hajar Mountains, Oman, Supported by Stratigraphy and Low-Temperature Thermochronology}, series = {Tectonics}, volume = {36}, journal = {Tectonics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0278-7407}, doi = {10.1002/2017TC004672}, pages = {3081 -- 3109}, year = {2017}, abstract = {Uplift of the Al Hajar Mountains in Oman has been related to either Late Cretaceous ophiolite obduction or the Neogene Zagros collision. To test these hypotheses, the cooling of the central Al Hajar Mountains is constrained by 10 apatite (U-Th)/He (AHe), 15 fission track (AFT), and four zircon (U-Th)/He (ZHe) sample ages. These data show differential cooling between the two major structural culminations of the mountains. In the 3km high Jabal Akhdar culmination AHe single-grain ages range between 392 Ma and 101 Ma (2 sigma errors), AFT ages range from 518 Ma to 324 Ma, and ZHe single-grain ages range from 62 +/- 3Ma to 39 +/- 2 Ma. In the 2 km high Saih Hatat culmination AHe ages range from 26 +/- 4 to 12 +/- 4 Ma, AFT ages from 73 +/- 19Ma to 57 +/- 8 Ma, and ZHe single-grain ages from 81 +/- 4 Ma to 58 +/- 3 Ma. Thermal modeling demonstrates that cooling associated with uplift and erosion initiated at 40 Ma, indicating that uplift occurred 30 Myr after ophiolite obduction and at least 10 Myr before the Zagros collision. Therefore, this uplift cannot be related to either event. We propose that crustal thickening supporting the topography of the Al Hajar Mountains was caused by a slowdown of Makran subduction and that north Oman took up the residual fraction of N-S convergence between Arabia and Eurasia.}, language = {en} } @article{NouryBernetSchildgenetal.2016, author = {Noury, M. and Bernet, M. and Schildgen, Taylor F. and Simon-Labric, T. and Philippon, M. and Sempere, T.}, title = {Crustal-scale block tilting during Andean trench-parallel extension: Structural and geo-thermochronological insights}, series = {Tectonics}, volume = {35}, journal = {Tectonics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0278-7407}, doi = {10.1002/2016TC004231}, pages = {2052 -- 2069}, year = {2016}, abstract = {Despite a long history of plate convergence at the western margin of the South American plate that has been ongoing since at least the Early Paleozoic, the southern Peruvian fore-arc displays little to no evidence of shortening. In the light of this observation, we assess the deformation history of the southern Peruvian fore-arc and its geodynamic implications. To accomplish this, we present a new structural and geo-thermochronological data set (zircon U-Pb, mica Ar-40/Ar-39, apatite and zircon fission-track and zircon (U-Th)/He analyses) for samples collected along a 400km long transect parallel to the trench. Our results show that the Mesoproterozoic gneissic basement was mainly at temperatures 350 degrees C since the Neoproterozoic and was later intruded by Jurassic volcanic arc plutons. Along the coast, a peculiar apatite fission-track age pattern, coupled with field observations and a synthesis of available geological maps, allows us to identify crustal-scale tilted blocks that span the coastal Peruvian fore-arc. These blocks, bounded by normal faults that are orthogonal to the trench, suggest post-60Ma trench-parallel extension that potentially accommodated oroclinal bending in this region. Block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore-arc basin. Our data set allows us to estimate the cumulative slip on these faults to be less than 2km and questions the large amount of trench-parallel extension suggested to have accommodated this bending.}, language = {en} } @phdthesis{Eugster2018, author = {Eugster, Patricia}, title = {Landscape evolution in the western Indian Himalaya since the Miocene}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-420329}, school = {Universit{\"a}t Potsdam}, pages = {XXI, 208}, year = {2018}, abstract = {The Himalayan arc stretches >2500 km from east to west at the southern edge of the Tibetan Plateau, representing one of the most important Cenozoic continent-continent collisional orogens. Internal deformation processes and climatic factors, which drive weathering, denudation, and transport, influence the growth and erosion of the orogen. During glacial times wet-based glaciers sculpted the mountain range and left overdeepend and U-shaped valleys, which were backfilled during interglacial times with paraglacial sediments over several cycles. These sediments partially still remain within the valleys because of insufficient evacuation capabilities into the foreland. Climatic processes overlay long-term tectonic processes responsible for uplift and exhumation caused by convergence. Possible processes accommodating convergence within the orogenic wedge along the main Himalayan faults, which divide the range into four major lithologic units, are debated. In this context, the identification of processes shaping the Earth's surface on short- and on long-term are crucial to understand the growth of the orogen and implications for landscape development in various sectors along the arc. This thesis focuses on both surface and tectonic processes that shape the landscape in the western Indian Himalaya since late Miocene. In my first study, I dated well-preserved glacially polished bedrock on high-elevated ridges and valley walls in the upper of the Chandra Valley the by means of 10Be terrestrial cosmogenic radionuclides (TCN). I used these ages and mapped glacial features to reconstruct the extent and timing of Pleistocene glaciation at the southern front of the Himalaya. I was able to reconstruct an extensive valley glacier of ~200 km length and >1000 m thickness. Deglaciation of the Chandra Valley glacier started subsequently to insolation increase on the Northern Hemisphere and thus responded to temperature increase. I showed that the timing this deglaciation onset was coeval with retreat of further midlatitude glaciers on the Northern and Southern Hemispheres. These comparisons also showed that the post-LGM deglaciation very rapid, occurred within a few thousand years, and was nearly finished prior to the B{\o}lling/Aller{\o}d interstadial. A second study (co-authorship) investigates how glacial advances and retreats in high mountain environments impact the landscape. By 10Be TCN dating and geomorphic mapping, we obtained maximal length and height of the Siachen Glacier within the Nubra Valley. Today the Shyok and Nubra confluence is backfilled with sedimentary deposits, which are attributed to the valley blocking of the Siachen Glacier 900 m above the present day river level. A glacial dam of the Siachen Glacier blocked the Shyok River and lead to the evolution of a more than 20 km long lake. Fluvial and lacustrine deposits in the valley document alternating draining and filling cycles of the lake dammed by the Siachen Glacier. In this study, we can show that glacial incision was outpacing fluvial incision. In the third study, which spans the million-year timescale, I focus on exhumation and erosion within the Chandra and Beas valleys. In this study the position and discussed possible reasons of rapidly exhuming rocks, several 100-km away from one of the main Himalayan faults (MFT) using Apatite Fission Track (AFT) thermochronometry. The newly gained AFT ages indicate rapid exhumation and confirm earlier studies in the Chandra Valley. I assume that the rapid exhumation is most likely related to uplift over subsurface structures. I tested this hypothesis by combining further low-temperature thermochronometers from areas east and west of my study area. By comparing two transects, each parallel to the Beas/Chandra Valley transect, I demonstrate similarities in the exhumation pattern to transects across the Sutlej region, and strong dissimilarities in the transect crossing the Dhauladar Range. I conclude that the belt of rapid exhumation terminates at the western end of the Kullu-Rampur window. Therewith, I corroborate earlier studies suggesting changes in exhumation behavior in the western Himalaya. Furthermore, I discussed several causes responsible for the pronounced change in exhumation patterns along strike: 1) the role of inherited pre-collisional features such as the Proterozoic sedimentary cover of the Indian basement, former ridges and geological structures, and 2) the variability of convergence rates along the Himalayan arc due to an increased oblique component towards the syntaxis. The combination of field observations (geological and geomorphological mapping) and methods to constrain short- and long-term processes (10Be, AFT) help to understand the role of the individual contributors to exhumation and erosion in the western Indian Himalaya. With the results of this thesis, I emphasize the importance of glacial and tectonic processes in shaping the landscape by driving exhumation and erosion in the studied areas.}, language = {en} } @phdthesis{Bande2016, author = {Bande, Alejandro}, title = {The tectonic evolution of the western Tien Shan}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-398933}, school = {Universit{\"a}t Potsdam}, pages = {xiv, 119}, year = {2016}, abstract = {Intracontinental deformation usually is a result of tectonic forces associated with distant plate collisions. In general, the evolution of mountain ranges and basins in this environment is strongly controlled by the distribution and geometries of preexisting structures. Thus, predictive models usually fail in forecasting the deformation evolution in these kinds of settings. Detailed information on each range and basin-fill is vital to comprehend the evolution of intracontinental mountain belts and basins. In this dissertation, I have investigated the complex Cenozoic tectonic evolution of the western Tien Shan in Central Asia, which is one of the most active intracontinental ranges in the world. The work presented here combines a broad array of datasets, including thermo- and geochronology, paleoenvironmental interpretations, sediment provenance and subsurface interpretations in order to track changes in tectonic deformation. Most of the identified changes are connected and can be related to regional-scale processes that governed the evolution of the western Tien Shan. The NW-SE trending Talas-Fergana fault (TFF) separates the western from the central Tien Shan and constitutes a world-class example of the influence of preexisting anisotropies on the subsequent structural development of a contractile orogen. While to the east most of ranges and basins have a sub-parallel E-W trend, the triangular-shaped Fergana basin forms a substantial feature in the western Tien Shan morphology with ranges on all three sides. In this thesis, I present 55 new thermochronologic ages (apatite fission track and zircon (U-Th)/He)) used to constrain exhumation histories of several mountain ranges in the western Tien Shan. At the same time, I analyzed the Fergana basin-fill looking for progressive changes in sedimentary paleoenvironments, source areas and stratal geometrical configurations in the subsurface and outcrops. The data presented in this thesis suggests that low cooling rates (<1°C Myr-1), calm depositional environments, and low depositional rates (<10 m Myr-1) were widely distributed across the western Tien Shan, describing a quiescent tectonic period throughout the Paleogene. Increased cooling rates in the late Cenozoic occurred diachronously and with variable magnitudes in different ranges. This rapid cooling stage is interpreted to represent increased erosion caused by active deformation and constrains the onset of Cenozoic deformation in the western Tien Shan. Time-temperature histories derived from the northwestern Tien Shan samples show an increase in cooling rates by ~25 Ma. This event is correlated with a synchronous pulse iv in the South Tien Shan. I suggest that strike-slip motion along the TFF commenced at the Oligo-Miocene boundary, facilitating CCW rotation of the Fergana basin and enabling exhumation of the linked horsetail splays. Higher depositional rates (~150 m Myr-1) in the Oligo-Miocene section (Massaget Fm.) of the Fergana basin suggest synchronous deformation in the surrounding ranges. The central Alai Range also experienced rapid cooling around this time, suggesting that the onset of intramontane basin fragmentation and isolation is coeval. These results point to deformation starting simultaneously in the late Oligocene - early Miocene in geographically distant mountain ranges. I suggest that these early uplifts are controlled by reactivated structures (like the TFF), which are probably the frictionally weakest and most-suitably oriented for accommodating and transferring N-S horizontal shortening along the western Tien Shan. Afterwards, in the late Miocene (~10 Ma), a period of renewed rapid cooling affected the Tien Shan and most mountain ranges and inherited structures started to actively deform. This episode is widely distributed and an increase in exhumation is interpreted in most of the sampled ranges. Moreover, the Pliocene section in the basin subsurface shows the higher depositional rates (>180 m Myr-1) and higher energy facies. The deformation and exhumation increase further contributed to intramontane basin partitioning. Overall, the interpretation is that the Tien Shan and much of Central Asia suffered a global increase in the rate of horizontal crustal shortening. Previously, stress transfer along the rigid Tarim block or Pamir indentation has been proposed to account for Himalayan hinterland deformation. However, the extent of the episode requires a different and broader geodynamic driver.}, language = {en} } @phdthesis{Georgieva2016, author = {Georgieva, Viktoria}, title = {Neotectonics \& Cooling History of the Southern Patagonian Andes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104185}, school = {Universit{\"a}t Potsdam}, pages = {xviii, 200 Seiten}, year = {2016}, abstract = {The collision of bathymetric anomalies, such as oceanic spreading centers, at convergent plate margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Southern Patagonian Andes of South America are a prime example for sustained oceanic ridge collision and the successive formation and widening of an extensive asthenospheric slab window since the Middle Miocene. Several of the predicted upper-plate geologic manifestations of such deep-seated geodynamic processes have been studied in this region, but many topics remain highly debated. One of the main controversial topics is the interpretation of the regional low-temperature thermochronology exhumational record and its relationship with tectonic and/or climate-driven processes, ultimately manifested and recorded in the landscape evolution of the Patagonian Andes. The prominent along-strike variance in the topographic characteristics of the Andes, combined with coupled trends in low-temperature thermochronometer cooling ages have been interpreted in very contrasting ways, considering either purely climatic (i.e. glacial erosion) or geodynamic (slab-window related) controlling factors. This thesis focuses on two main aspects of these controversial topics. First, based on field observations and bedrock low-temperature thermochronology data, the thesis addresses an existing research gap with respect to the neotectonic activity of the upper plate in response to ridge collision - a mechanism that has been shown to affect the upper plate topography and exhumational patterns in similar tectonic settings. Secondly, the qualitative interpretation of my new and existing thermochronological data from this region is extended by inverse thermal modelling to define thermal histories recorded in the data and evaluate the relative importance of surface vs. geodynamic factors and their possible relationship with the regional cooling record. My research is centered on the Northern Patagonian Icefield (NPI) region of the Southern Patagonian Andes. This site is located inboard of the present-day location of the Chile Triple Junction - the juncture between the colliding Chile Rise spreading center and the Nazca and Antarctic Plates along the South American convergent margin. As such this study area represents the region of most recent oceanic-ridge collision and associated slab window formation. Importantly, this location also coincides with the abrupt rise in summit elevations and relief characteristics in the Southern Patagonian Andes. Field observations, based on geological, structural and geomorphic mapping, are combined with bedrock apatite (U-Th)/He and apatite fission track (AHe and AFT) cooling ages sampled along elevation transects across the orogen. This new data reveals the existence of hitherto unrecognized neotectonic deformation along the flanks of the range capped by the NPI. This deformation is associated with the closely spaced oblique collision of successive oceanic-ridge segments in this region over the past 6 Ma. I interpret that this has caused a crustal-scale partitioning of deformation and the decoupling, margin-parallel migration, and localized uplift of a large crustal sliver (the NPI block) along the subduction margin. The location of this uplift coincides with a major increase of summit elevations and relief at the northern edge of the NPI massif. This mechanism is compatible with possible extensional processes along the topographically subdued trailing edge of the NPI block as documented by very recent and possibly still active normal faulting. Taken together, these findings suggest a major structural control on short-wavelength variations in topography in the Southern Patagonian Andes - the region affected by ridge collision and slab window formation. The second research topic addressed here focuses on using my new and existing bedrock low-temperature cooling ages in forward and inverse thermal modeling. The data was implemented in the HeFTy and QTQt modeling platforms to constrain the late Cenozoic thermal history of the Southern Patagonian Andes in the region of the most recent upper-plate sectors of ridge collision. The data set combines AHe and AFT data from three elevation transects in the region of the Northern Patagonian Icefield. Previous similar studies claimed far-reaching thermal effects of the approaching ridge collision and slab window to affect patterns of Late Miocene reheating in the modelled thermal histories. In contrast, my results show that the currently available data can be explained with a simpler thermal history than previously proposed. Accordingly, a reheating event is not needed to reproduce the observations. Instead, the analyzed ensemble of modelled thermal histories defines a Late Miocene protracted cooling and Pliocene-to-recent stepwise exhumation. These findings agree with the geological record of this region. Specifically, this record indicates an Early Miocene phase of active mountain building associated with surface uplift and an active fold-and-thrust belt, followed by a period of stagnating deformation, peneplanation, and lack of synorogenic deposition in the Patagonian foreland. The subsequent period of stepwise exhumation likely resulted from a combination of pulsed glacial erosion and coeval neotectonic activity. The differences between the present and previously published interpretation of the cooling record can be reconciled with important inconsistencies of previously used model setup. These include mainly the insufficient convergence of the models and improper assumptions regarding the geothermal conditions in the region. This analysis puts a methodological emphasis on the prime importance of the model setup and the need for its thorough examination to evaluate the robustness of the final outcome.}, language = {en} } @misc{MacaulaySobelMikolaichuketal.2014, author = {Macaulay, Euan A. and Sobel, Edward and Mikolaichuk, Alexander and Kohn, Barry and Stuart, Finlay M.}, title = {Cenozoic deformation and exhumation history of the Central Kyrgyz Tien Shan}, series = {Tectonics}, volume = {33}, journal = {Tectonics}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0278-7407}, doi = {10.1002/2013TC003376}, pages = {135 -- 165}, year = {2014}, abstract = {New low-temperature thermochronological data from 80 samples in eastern Kyrgyzstan are combined with previously published data from 61 samples to constrain exhumation in a number of mountain ranges in the Central Kyrgyz Tien Shan. All sampled ranges are found to have a broadly consistent Cenozoic exhumation history, characterized by initially low cooling rates (<1 degrees C/Myr) followed by a series of increases in exhumation that occurred diachronously across the region in the late Cenozoic that are interpreted to record the onset of deformation in different mountain ranges. Combined with geological estimates for the onset of proximal deformation, our data suggest that the Central Kyrgyz Tien Shan started deforming in the late Oligocene-early Miocene, leading to the development of several, widely spaced mountain ranges separated by large intermontane basins. Subsequently, more ranges have been constructed in response to significant shortening increases across the Central Kyrgyz Tien Shan, notably in the late Miocene. The order of range construction is interpreted to reflect variations in the susceptibility of inherited structures to reactivation. Reactivated structures are also shown to have significance along strike variations in fault vergence and displacement, which have influenced the development and growth of individual mountain ranges. Moreover, the timing of deformation allows the former extent of many intermontane basins that have since been partitioned to be inferred; this can be linked to the highly time-transgressive onset of late Cenozoic coarse clastic sedimentation.}, language = {en} } @article{SobelSchoenbohmChenetal.2011, author = {Sobel, Edward and Schoenbohm, Lindsay M. and Chen, Jie and Thiede, Rasmus Christoph and Stockli, Daniel F. and Sudo, Masafumi and Strecker, Manfred}, title = {Late Miocene-Pliocene deceleration of dextral slip between Pamir and Tarim: Implications for Pamir orogenesis}, series = {EARTH AND PLANETARY SCIENCE LETTERS}, volume = {304}, journal = {EARTH AND PLANETARY SCIENCE LETTERS}, number = {3-4}, publisher = {ELSEVIER SCIENCE BV}, address = {AMSTERDAM}, issn = {0012-821X}, doi = {10.1016/j.epsl.2011.02.012}, pages = {369 -- 378}, year = {2011}, abstract = {The timing of the late Cenozoic collision between the Pamir salient and the Tien Shan as well as changes in the relative motion between the Pamir and Tarim are poorly constrained. The northern margin of the Pamir salient indented northward by similar to 300 km during the late Cenozoic, accommodated by south-dipping intracontinental subduction along the Main Pamir Thrust (MPT) coupled to strike-slip faults on the eastern flank of the orogen and both strike-slip and thrust faults on the western margin. The Kashgar-Yecheng transfer system (KYTS) is the main dextral slip shear zone separating Tarim from the Eastern Pamir, with an estimated cumulative offset of similar to 280 km at an average late Cenozoic dextral slip rate of 11-15 mm/a (Cowgill, 2010). In order to better constrain the slip history of the KYTS, we collected thermochronologic samples along the eastward-flowing, deeply incised, antecedent Tashkorgan-Yarkand River, which crosses the fault system on the eastern flank of the orogen. We present 29 new biotite (40)Ar/(39)Ar ages, apatite and zircon (U-Th-Sm)/He ages, and apatite fission track (AFT) analysis, combined with published muscovite and biotite (40)Ar/(39)Ar and AFT data, to create a unique thermochronologic dataset in this poorly studied and remote region. We constrain the timing of four major N-trending faults: the latter three are strands of the KYTS. The westernmost, the Kuke fault, experienced significant dip-slip, west-side-up displacement between > 12 and 6 Ma. To the east, within the KYTS, our new thermochronologic data and geomorphic observations suggest that the Kumtag and Kusilaf dextral slip faults have been inactive since at least 3-5 Ma. Long-term incision rates across the Aertashi dextral slip fault, the easternmost strand of the KYTS, are compatible with slow horizontal slip rates of 1.7-5.3 mm/a over the past 3 to 5 Ma. In summary, these data show that the slip rate of the KYTS decreased substantially during the late Miocene or Pliocene. Furthermore, Miocene-present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of Tarim rather than a significant decrease of the northward velocity of the Pamir. (C) 2011 Elsevier B.V. All rights reserved.}, language = {en} }