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The evolution and course of Himalayan rivers when exiting the orogen is controlled by the interplay between tectonics, climate, and associated sediment flux. We investigate these interactions by studying a Late Pleistocene deflection of the Sutlej River at the southern margin of the western Himalayan. This part of the Himalaya is also referred to as Kangra Recess. Late Quaternary faulting and folding along the Main Frontal Thrust and related back thrusts has created anticlinal structures in the south and piggyback basins in the north. Combined field observations and chronological constraints have shown that the anticline evolved as multiple fault segments, which grew through lateral propagation and led to the permanent deflection of the Sutlej River by ~ 50 km to the southeast. In this work, we present new luminescence and cosmogenic nuclide chronologies combined with previously published data to better identify the sedimentation history. Most importantly, we focus on the cause and final timing of the permanent river deflection. We show evidence for widespread aggradation and sediment deposition by the Sutlej River megafan and its tributaries starting before 47 ka and continuing until ~ 26 ka. Our 10Be and 26Al results in combination with available OSL data document the last widespread throughflow of the Sutlej at ~ 30-25 ka. We argue that a combination of climate and tectonic factors, especially the variability of monsoonal strength, led to major changes in sediment supply at short time scales and therefore affected the course of the Sutlej River system.

The Himalaya is the highest and steepest mountain range on Earth and forms today efficient north-south barrier for moisture-bearing winds. 1D-thermokinematic modeling of new zircon (U-Th)/He bedrock-cooling ages and >100 previously published mica 40Ar/39Ar, zircon and apatite fission track ages from the Sutlej Valley document a consistent rapid decrease in exhumation rates that initiated at ~17-15 Ma across the entire Greater and Tethyan Himalaya and the north-Himalayan Leo Pargil dome. We observe a rapid decrease from >1 km/Myr to

The Pamir orogen forms the northwest prolongation of the Tibetan plateau. The most important surficial structure bounding the northern and northwestern margin is the Main Pamir Thrust (MPT); however, despite the importance of the structure, surprisingly little is known about the displacement history of the fault. Together with the younger, foreland-oriented Pamir Frontal thrust system (PFT), displacement estimates range from 50 to over 300 km. The larger estimates are based on the estimated Cenozoic northward indentation of the Pamir with respect to Tibet as well as the length of the intracontinental Pamir seismic zone. However, recent work suggests that some of the indentation predates the Cenozoic or is related to an original Paleozoic embayed paleogeography and other studies have suggested that the seismic zone is not related to intracontinental subduction. Shortening estimates in the hanging walls of the MPT and PFT suggest more modest amounts: between 30 and 75 km in the north, with higher values for SE-NW shortening in the Tadjik depression.Constraining the onset of deformation has proven challenging. Most publications suggest a late Oligo-early Miocene onset age. Cenozoic stratigraphic sequences are unfossiliferous and poorly dated. We have attempted to resolve this question by collecting samples for thermochronologic analysis from many locations along the arcuate margin. In general, zircon (U-Th-Sm)/He (ZHe) samples yield ages between ~60 and 17 Ma. Many are likely to be partially reset. Ages are slightly older in the east, which could reflect an overall westward increase in exhumation. The relatively small amount of exhumation in the north supports our structural interpretation that the MPT there has a low dip angle and might not have produced pronounced topography. Apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) are often much younger; often between

We present new Late Pleistocene-Holocene shortening rates across the frontal fold-and-thrust belt, namely as, the Sub-Himalaya (SH) from the far-western Himalayan sector of Jammu. OSL-dated offset/ folded fluvial strath terraces suggest that the intraplate convergence is partitioned among several active structures in the SH. Estimated cumulative Late Pleistocene- Holocene shortening rate in the SH is ~9.5±1.3 mm/yr, which is ~70–75% of the measured geodetic convergence rates. Our study invokes the existence of a ~350–400 km-long out-of-sequence fault-boundary within the SH which accommodates ~5.3±2.3 mm/yr shortening since Late Pleistocene-Holocene. Our study also highlights that ongoing crustal shortening is not accommodated only at the toe of the Himalayan wedge.

The Pamir forms the northwestern tail of the Tibetan plateau and is a first-order tectonic feature of the Cenozoic Indo-Eurasian collision. The nature of the topographic uplift and orogenic growth of the entire northwestern margin of the Pamir is poorly constrained; however, this history can provide important constraints that are required to test geodynamic models of the tectonic evolution of the Pamir. Here we focus on the uplift history of the western and northwestern unglaciated margin of the Northern Pamir, the Darvaz and the Peter-the-First Ranges. These three ranges were formed by three major fault systems: the Main Pamir Thrust (MPT), the Darvaz and the Vakhsh fault zones (DFZ, VFZ). To assess the impact of tectonic uplift on the geomorphic evolution, we analyzed geomorphic characteristics of the topography, the longitudinal river profiles and the relief. To better constrain the regional crustal cooling history and uplift, we obtained thermochronologic cooling ages from the three regions.We present 19 new zircon (U-Th-Sm)/He (ZHe) ages, 7 apatite fission track (AFT) ages, and 4 apatite (U-Th-Sm)/He (AHe) ages, ranging between >200 and 4 Ma, 14 and 4 Ma, and 15 and 3 Ma, respectively. The three units are characterized by unique Neogene cooling pathways, suggesting that they exhumed independently.We discovered extensive low-relief landscapes with Neogene sedimentary cover uplifted ~2 km in elevation above the present-day regional base level. Our analysis indicates that the Panj and Vakhsh rivers form the regional base levels for the river network draining the entire northern and western margin of the Pamir. In the hanging wall of DFZ, the Paleozoic bedrock is characterized by significant relief (>1 km), the Neogene cover onlaps directly onto this Paleozoic bedrock. The tributary rivers crossing these landscapes are characterized by gentle, concave upstream longitudinal profiles at high elevation. These are interrupted by major knickpoint zones and steep downstream segments draining towards the deeply incised Panj and Vakhsh rivers. This indicates that the Darvaz Fault hanging wall had been uplifted and eroded prior to deposition of upper Neogene sediments, suggesting that the DFZ has a prolonged Neogene slip history. In contrast to the northeastern Pamir, here, the MPT-hanging-wall is characterized by reset late Oligocene-Early Miocene ZHe cooling ages ranging between 26 and 17 Ma. AFT and AHe-ages between 15 and 13 Ma suggest that exhumation suddenly terminated during the middle Miocene. In contrast, Jurassic sandstones exposed near the DFZ yield mostly un-reset Triassic-Jurassic ZHe ages (~250-170 Ma), a reset AFT age of ~5 Ma and a 2.5 Ma AHe age. Within the Peter-the-1st-Range, we obtained fully reset ~ 5 Ma ZHe ages, and ~4 Ma AFT ages. The rapid cooling trends since at least ~5 Ma suggest that deformation and a significant portion of crustal shortening propagated into the Tadjik foreland basin, causing enhanced uplift and erosion of the hanging wall of the VFZ and related faults. This deformation triggered ~2 km uplift of the entire northwest Pamir, recorded in uplifted paleo-landscapes and dissected tributaries of the Panj and Vakhsh rivers.

The intensity of the Asian summer-monsoon circulation varies over decadal to millennial timescales and impacts surface processes, terrestrial environments, and marine sediment records. The duration and magnitude of this climatic forcing on erosion processes varies, depending on duration and intensity of the climatic events, as well as on the tectonic and geomorphologic preconditioning of the landscape. In this study, we focus on a region in the transition zone between continuous and episodic monsoon impacts: the Spiti River, the largest tributary (12x103 km2 ) to the Sutlej River in the western Himalaya. The river valley is located in the northern lee of the Himalayan orographic barrier in a presently arid environment. The Spiti Valley has received significant precipitation during intensified monsoon periods during the late Pleistocene and Holocene and thus constitutes an ideal location to evaluate effects of episodic moisture transport into an arid, high-relief mountainous region.Here we present 21 new surface-exposure ages of fluvial-fill terraces combined with previously published data to quantify temporal patterns in river incision and erosion rates. Our data include catchment-wide erosion rates and in-situ cosmogenic nuclide ages derived from 10Be, 26Al, and 21Ne and document that terrace formation (i.e., terrace abandonment) occurred during intensified monsoon phases at ∼100 ka, ∼65 ka, ∼43 ka, and ∼12 ka, although dating uncertainties prevent the calculation of exact correlation between monsoonal strength and terrace formation. We show that incision into Late Pleistocene valley fills that integrate over several cut-and-fill cycles at 105 y are comparable to exhumation rates determined from thermochronology studies averaging over 10^6 y in that area. We argue that the limiting factor for sediment removal and river incision on shorter, millennial timescales is due to large bedrock landslides that impounded the river network and formed transient sedimentary basins lasting for 103 -104 years. We suggest a feedback process between sediment removal and landsliding, where large landsliding predominantly occurs when the transiently-stored valley fills have been carved out, leading to exposed valley bottoms, bedrock erosion, lateral scouring of rivers, and ultimately to the over-steepening of hillslopes. We suggest that Late Quaternary climatic variability is the main forcing factor in filling and evacuating transiently stored sediments in high mountain ranges and thus plays a direct role in controlling bedrock incision.

A lateral continuity between belts of mafic and ultramafic Paleozoic rocks found in the West Kunlun of Northern Tibet and comparable rocks, known from an outcrop in the Chinese North Pamir, has long been proposed. This led to the concept of an originally generally straight, E–W trending Oytag–Kudi suture zone. In turn, this paleogeographic model formed a key constraint for the hypothesis, that the Pamir has indented 300 km northward with respect to Tibet during the Cenozoic. We show, that the arc volcanic rocks found in the North Pamir are distinguishable from the units known from the West Kunlun.The North Pamir is dominated by Paleozoic arc volcanic rocks. We present new geochemical and geochronological data to give a holistic view of an early to mid-Carboniferous arc complex. This belt was previously identified as an intraoceanic arc in the northeastern North Pamir. Our data yields evidence for a gradual lateral change towards the west into a Cordilleran-style arc in the Tajik North Pamir. Large leucocratic granitoid intrusions are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveal a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago.The West Kunlun experienced two major intrusive phases, connected with arc-volcanic activity — a first phase during Proto-Tethys closure in Ordovician and Silurian times and a second phase connected to the Triassic Paleo-Tethys closure. The Carboniferous arc-volcanic phase in the North Pamir clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.

The Himalaya is the highest and steepest mountain range on Earth and an efficient north-south barrier for moisture-bearing winds. The close coupling of changes in topography, erosion rates, and uplift has previously been interpreted as an expression of a climatic control on tectonic deformation. Here, we present 17 new zircon U/Th-He (ZHe) bedrock-cooling ages from the Sutlej Valley that – together with >100 previously published mica 40Ar/39Ar, zircon and apatite fission track ages – allow us to constrain the crustal cooling and exhumation history over the last ~20 Myr. Using 1D-thermal modeling, we observe a rapid decrease in exhumation rates from >1 km/Myr to

Tectonics and regional monsoon strength control weathering and erosion regimes of the watersheds feeding into the Bay of Bengal, which are important contributors to global climate evolution via carbon cycle feedbacks. The detailed mechanisms controlling the input of terrigenous clay to the Bay of Bengal on tectonic to orbital timescales are, however, not yet well understood. We produced orbital‐scale resolution geochemical records for International Ocean Discovery Program Site U1443 (southern Bay of Bengal) across five key climatic intervals of the middle to late Miocene (15.8–9.5 Ma). Our new radiogenic Sr, Nd, and Pb isotope time series of clays transported to the Ninetyeast Ridge suggest that the individual contributions from different erosional sources overall remained remarkably consistent during the Miocene despite major tectonic reorganizations in the Himalayas. On orbital timescales, however, high‐resolution data from the five investigated intervals show marked fluctuations of all three isotope systems. Interestingly, the variability was much higher within the Miocene Climatic Optimum (around 16–15 Ma) and across the major global cooling (~13.9–13.8 Ma) until ~13.5 Ma, than during younger time intervals. This change is attributed to a major restriction on the supply of High Himalayan erosion products due to migration of the peak precipitation area toward the frontal domains of the Himalayas and the Indo‐Burman Ranges. The transient excursions of the radiogenic isotope signals on orbital timescales most likely reflect climatically driven shifts in monsoon strength., Key Points: A consistent mix of clay sources contributed to the Bay of Bengal throughout the middle to late Miocene A marked change in detrital Sr, Nd, and Pb isotope variability at 13.5 Ma was related to Miocene global cooling Transient orbital‐scale fluctuations in clay source most likely reflect changes in monsoon intensity, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

In this study, we investigate the age and geochemical variability of volcanic arc rocks found in the Chinese, Kyrgyz, and Tajik North Pamir in Central Asia. New geochemical and geochronological data together with compiled data from the literature give a holistic view of an early to mid-Carboniferous intraoceanic arc preserved in the northeastern Pamir. This North Pamir volcanic arc complex involves continental slivers in its western reaches and transforms into a Cordilleran-style collision zone with arc-magmatic rocks. These are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. We discuss whether a sliver of Carboniferous subduction-related basalts and intruded tonalites close to the Chinese town of Mazar was part of the same arc. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveals a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago. This clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of the Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.

The Kishtwar Window (KW) of the NW Himalaya exposes the northwestern termination of the orogen-parallel anticlinal stack of thrust nappes, termed as the Lesser Himalayan Duplex and its evolution portrays rapid exhumation at least over the last 2–3 Myr. However, speculations remain if it still actively deforming. Here we combine morphometric analyses with structural and field evidences to describe the spatial pattern of internal deformation of the duplex. We suggest that the variations in the geometry of the basal décollement, the Main Himalayan Thrust (MHT) and internal faulting within the duplex define the observed neotectonic deformation. We recognize two significant steep stream segments/ knickzones, one in center of the window, and a second one along its western margin, which we relate to fault-ramps emerging from the MHT. The larger of the knickzones, in the core of the window, show an increase in the angle of foliations towards downstream. Highly-fractured and folded rocks at the base of the steep stream segment, suggest internal deformation of the duplex, possibly linked to surface-breaking thrust fault-ramp at the core of the duplex. The second steepened knickzone coincides with the western margin of the window and is identified by a narrow channel through a comparatively weaker bedrock gorge. Summarizing our findings, we favor a structural and active tectonic control on the growth of the duplex even over geomorphic timescales. Corroborating with previous studies, we suggest that the differential uplift and growth of the duplex is linked to several flat-ramp structures along the MHT.

Rutile is frequently found in metamorphic and less commonly in igneous rocks, as well as sediments derived from the former rock types. It may contain enough U (typically up to ~100ppm) to be dated by U/Pb geochronology. In detrital studies, rutile U/Pb ages supplement zircon U/Pb data, as zircon age peaks often reflect magmatic activity, while rutile U/Pb age peaks can be connected to metamorphic events. Using Zr-in-rutile thermometry, one could also estimate metamorphic facies of the terrane, from which detrital rutile grains are derived. Zircon U/Pb dating provides usually a crystallization age, while rutile gives cooling ages that are dependent on the size of the diffusion domain and its cooling rate. The closure temperature has been estimated at ca. 600°C. A major challenge of rutile U/Pb geochronology is the variable amount of common Pb present and most rutile dating requires the correction for common Pb. A widely used method is the Stacey & Kramers approach, which estimates a formation age for a group of rutile grains and assigns them an age-dependent initial Pb isotope composition from the terrestrial Pb evolution curve (Stacey and Kramers, 1975). We present detrital rutile U/Pb data measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) from Mesozoic and Cenozoic units in the North Pamir in Central Asia. The laser ablation system obtains a time resolved signal of all required isotopes. Using data reduction schemes in Iolite (Paton et al., 2011) and VizualAge (Petrus and Kamber, 2012), the signal is routinely integrated to a single spot age for each ablation pit. Following a similar approach for apatite (Stockli et al., 2017), we subdivided the signal of each single spot into several time-slices and obtained data that crosses diffusion domains or compositional zones within a single rutile grain. Time slices in most cases are aligned along a Discordia in the Tera-Wasserburg diagram, enabling us to calculate a lower intercept age and initial 207Pb/206Pb ratio. We also discuss similarities and differences between these internally corrected ages and the Stacey & Kramers approach-corrected ages. Paton, C., Hellstrom, J., Paul, B., Woodhead, J., Hergt, J., 2011. Iolite: Freeware for the visualisation and processing of mass spectrometric data. Journal of Analytical Atomic Spectrometry 26 (12), 2508–2518.Petrus, J.A., Kamber, B.S., 2012. VizualAge: A Novel Approach to Laser Ablation ICP-MS U-Pb Geochronology Data Reduction. Geostandards and Geoanalytical Research 36 (3), 247–270.Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26 (2), 207–221.Stockli, D.F., Boyd, P., Galster, F., 2017. Intra-grain common Pb correction in apatite by LA-ICP-MS depth profiling and implications for detrital apatite U-Pb dating. EGU General Assembly Abstract Volume.

The Himalaya is the highest and steepest mountain range on Earth and an efficient north-south barrier for moisture-bearing winds. The close coupling of changes in topography, erosion rates, and uplift has previously been interpreted as an expression of a climatic control on tectonic deformation. Here, we present 17 new zircon U/Th-He (ZHe) bedrock-cooling ages from the Sutlej Valley that – together with >100 previously published mica 40Ar/39Ar, zircon and apatite fission track ages – allow us to constrain the crustal cooling and exhumation history over the last ~20 Myr. Using 1D-thermal modeling, we observe a rapid decrease in exhumation rates from >1 km/Myr to

The location and magnitude of Himalayan tectonic activity has been debated for decades, and several aspects remain unknown. For instance, the spatial distribution of crustal shortening that ultimately sustains Himalayan topography and the activity of major fault zones remain unknown at Ma timescales. In this study, we address the spatial deformation pattern in the data-scarce western Himalaya. We calculated catchment averaged, normalized river-steepness indices of non-glaciated drainage basins with tributary catchment areas between 5 and 200 km(2) (n = 2138). We analyzed the spatial distribution of the relative change of river steepness both along and across strike to gain information about the regional distribution of differential uplift pattern and relate this to the activity of distinctive fault segments. For our study area, we observe a positive correlation of averaged k(sn) values with long-term exhumation rates derived from previously published thermochronologic datasets combined with thermal modeling as well as with millennial timescale denudation rates based on cosmogenic nuclide dating. Our results indicate three tectono-geomorphic segments with distinctive landscape morphology, structural architecture, and fault geometry along the western Himalaya: Garhwal-Sutlej, Chamba, and Kashmir Himalaya (from east to west). Moreover, our data recognize distinctive fault segments showing varying thrust activity along strike of the Main Frontal Thrust, the Main Boundary Thrust, and in the vicinity of the steep topographic transition between the Lesser and Greater Himalaya. In this region, we relate out-of-sequence deformation along major basement thrust ramps, such as the Munsiari Thrust with deformation along a mid-crustal ramp along the basal decollement. We suggest that during the Quaternary, all major fault zones in the Western Himalaya experienced out-of-sequence faulting and have accommodated some portion of crustal shortening.

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 (

The southernmost thrust of the Himalayan orogenic wedge that separates the foreland from the orogen, the Main Frontal Thrust (MFT), is thought to accommodate most of the ongoing crustal shortening in the Sub-Himalaya. Steepened longitudinal river-profile segments, terrace offsets, and back-tilted fluvial terraces within the Kangra re-entrant of the NW Sub-Himalaya suggest Holocene activity of the Jwalamukhi Thrust (JMT) and other thrust faults that may be associated with strain partitioning along the toe of the Himalayan wedge. To assess the shortening accommodated by the JMT, we combine morphometric terrain analyses with in-situ 10Be-based surface exposure dating of the deformed terraces. Incision into upper Pleistocene sediments within the Kangra Basin created two late Pleistocene terrace levels (T1 and T2). Subsequent early Holocene aggradation shortly before ~10 ka was followed by episodic re-incision, which created four cut-and-fill terrace levels, the oldest of which (T3) was formed at 10.1 ± 0.9 ka. A vertical offset of 44 ± 5 m of terrace T3 across the JMT indicates a shortening rate of 5.6 ± 0.8 to 7.5 ± 1.1 mm.a-1 over the last ~10 ka. This result suggests that thrusting along the JMT accommodates 40-60% of the total Sub-Himalayan shortening in the Kangra re-entrant over the Holocene. We speculate that this out-of-sequence shortening may have been triggered or at least enhanced by late Pleistocene and Holocene erosion of sediments from the Kangra Basin.

The potential link between erosion rates at the Earth’s surface and changes in global climate has intrigued geoscientists for decades1,2 because such a coupling has implications for the influence of silicate weathering3,4 and organic-carbon burial5 on climate and for the role of Quaternary glaciations in landscape evolution1,6. A global increase in late-Cenozoic erosion rates in response to a cooling, more variable climate has been proposed on the basis of worldwide sedimentation rates7. Other studies have indicated, however, that global erosion rates may have remained steady, suggesting that the reported increases in sediment-accumulation rates are due to preservation biases, depositional hiatuses and varying measurement intervals8–10. More recently, a global compilation of thermochronology data has been used to infer a nearly twofold increase in the erosion rate in mountainous landscapes over late-Cenozoic times6. It has been contended that this result is free of the biases that affect sedimentary records11, although others have argued that it contains biases related to how thermochronological data are averaged12 and to erosion hiatuses in glaciated landscapes13. Here we investigate the 30 locations with reported accelerated erosion during the late Cenozoic6. Our analysis shows that in 23 of these locations, the reported increases are a result of a spatial correlation bias—that is, combining data with disparate exhumation histories, thereby converting spatial erosion-rate variations into temporal increases. In four locations, the increases can be explained by changes in tectonic boundary conditions. In three cases, climatically induced accelerations are recorded, driven by localized glacial valley incision. Our findings suggest that thermochronology data currently have insufficient resolution to assess whether late-Cenozoic climate change affected erosion rates on a global scale. We suggest that a synthesis of local findings that include location-specific information may help to further investigate drivers of global erosion rates. Reported acceleration of erosion in mountainous landscapes during the late Cenozoic is the result of combining thermochronology data with disparate exhumation histories, thereby converting spatial variations in erosion rates into temporal increases.

Despite remarkable tectonostratigraphic similarities along the Himalayan arc, pronounced topographic and exhumational variability exists in different morphotectonic segments. The processes responsible for this segmentation are debated. Of particular interest is a 30- to 40-km-wide orogen-parallel belt of rapid exhumation that extends from central Nepal to the western Himalaya and its possible linkage to a midcrustal ramp in the basal decollement, and the related growth of Lesser Himalayan duplex structures. Here we present 26 new apatite fission track cooling ages from the Beas-Lahul region, at the transition from the Central to the Western Himalaya (77 degrees-78 degrees E) to investigate segmentation in the Himalayan arc from a thermochronologic perspective. Together with previously published data from this part of the orogen, we document significant lateral changes in exhumation between the Dhauladar Range to the west, the Beas-Lahul region, and the Sutlej area to the east of the study area. In contrast to the Himalayan front farther east, exhumation in the far western sectors is focused at the frontal parts of the mountain range and associated with the hanging wall of the Main Boundary Thrust fault ramp. Our results allow us to spatially correlate the termination of the rapid exhumation belt with a midcrustal ramp to the west. We suggest that a plunging anticline at the northwestern edge of the Larji-Kullu-Rampur window represents the termination of the Central Himalayan segment, which is related to the evolution of the Lesser Himalayan duplex. Key Points

[1] The northward motion of the Pamir indenter with respect to Eurasia has resulted in coeval thrusting, strike-slip faulting, and normal faulting. The eastern Pamir is currently deformed by east-west oriented extension, accompanied by uplift and exhumation of the Kongur Shan (7719 m) and Muztagh Ata (7546 m) gneiss domes. Both domes are an integral part of the footwall of the Kongur Shan extensional fault system (KES), a 250 km long, north-south oriented graben. Why active normal faulting within the Pamir is primarily localized along the KES and not distributed more widely throughout the orogen has remained unclear. In addition, relatively little is known about how deformation has evolved throughout the Cenozoic, despite refined estimates on present-day crustal deformation rates and microseismicity, which indicate where crustal deformation is presently being accommodated. To better constrain the spatiotemporal evolution of faulting along the KES, we present 39 new apatite fission track, zircon U-Th-Sm/He, and 40Ar/39Ar cooling ages from a series of footwall transects along the KES graben shoulder. Combining these data with present-day topographic relief, 1-D thermokinematic and exhumational modeling documents successive stages, rather than synchronous deformation and gneiss dome exhumation. While the exhumation of the Kongur Shan commenced during the late Miocene, extensional processes in the Muztagh Ata massif began earlier and have slowed down since the late Miocene. We present a new model of synorogenic extension suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting Alai slab localize extensional upper plate deformation along the KES and decouple crustal motion between the central/western Pamir and eastern Pamir/Tarim basin.

Competing hypotheses suggest that Himalayan topography is sustained and the plate convergence is accommodated either solely along the basal decollement, the Main Himalayan thrust (MHT), or more broadly, across multiple thrust faults. In the past, structural, geomorphic, and geodetic data of the Nepalese Himalaya have been used to constrain the geometry of the MHT and its shallow frontal thrust fault, known as Main Frontal thrust (MFT). The MHT flattens at depth and connects to a hinterland mid-crustal, steeper thrust ramp, located similar to 100 km north of the deformation front. There, the present-day convergence across the Himalaya is mostly accommodated by slip along the MFT. Despite a general agreement that in Nepal most of the shortening is accommodated along the MHT, some researchers have suggested the occurrence of persistent out-of-sequence shortening on interior faults near the Main Central thrust (MCT). Along the northwest Himalaya, in contrast, some of these characteristics of central Nepal are missing, suggesting along-strike variation of wedge deformation and MHT fault geometry. Here we present new field observations and seven zircon (U-Th)/He (ZHe) cooling ages combined with existing low-temperature data sets. In agreement with our previous findings, we suggest that the transect of cooling age patterns across the frontal Dhauladhar Range reveals that the Main Boundary thrust (MBT) is a primary fault, which has uplifted and sustained this spectacular mountain front since at least the late Miocene. Our results suggest that the MBT forms an similar to 40-km-long fault ramp before it soles into the MHT, and motion along it has exhumed rocks from depth of similar to 8-10 km. New three-dimensional thermokinematic modeling (using Pecube finite-element code) reveals that the observed ZHe and apatite fission track cooling ages can only be explained by sustained mean MBT slip rates between similar to 2.6 and 3.5 mm a(-1) since at least 8 Ma, which corresponds to a horizontal shortening rate of similar to 1.7-2.4 mm a(-1). We propose that the MBT is active today, despite a lack of definitive field or seismogenic evidence, and continues to accommodate crustal shorting by out-of-sequence faulting. Assuming that present-day geodetic shorting rates (similar to 14 +/- 2 mm a(-1)) across the northwest Himalaya have been sustained over geologic time scales, this implies that the MBT accommodated similar to 15% of the total Himalayan convergence since its onset. Furthermore, our modeling results imply that the MHT is missing a hinterland mid-crustal ramp further north.

Explaining the presence of normal faults in overall compressive settings is a challenging problem in understanding the tectonics of active mountain belts. The Himalayan-Tibetan orogenic system is an excellent setting to approach this problem because it preserves one of the most dramatic records of long-term, contemporaneous shortening and extension. Over the past decades, several studies have described extensional features, not only in the Tibetan Plateau, but also in the Himalaya. For a long time, the favored model explained the function of the Southern Tibetan detachment system, a major fault zone in the Himalaya, as a decoupling horizon between the regime of crustal shortening forming the Himalayan wedge to the south and the extensional regime of the Tibetan Plateau to the north. However, in recent years, increasing evidence has shown that N-S-trending normal faults in the Central Himalaya crosscut not only the Southern Tibetan detachment system, but also the Main Central thrust. Here, we present new structural data and geologic evidence collected within the NW Indian Himalaya and combine them with previously published seismicity data sets in order to document pervasive E-W extension accommodated along N-S-trending faults extending as far south as the footwall of the Main Central thrust. We conducted a kinematic analysis of fault striations on brittle faults, documented and mapped fault scarps in Quaternary sedimentary deposits using satellite imagery, and made field observations in the Greater Sutlej region (Spiti, Lahul, Kinnaur) and the Garhwal Himalaya. Studies of extensional features within the regionally NW- SE-trending NW Indian Himalaya provide the advantage that arc-parallel and E-W extension can be separated, in contrast to the Central Himalaya. Therefore, our observations of E-W extension in the Indian NW Himalaya are well suited to test the applicability of current tectonic models for the whole Himalaya. We favor the interpretation of E-W extension in the NW Indian Himalaya as a propagation of extension driven by collapse of the Tibetan Plateau.

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives. New surface-exposure dating of six terrace levels with in-situ cosmogenic 10Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4 ± 3.2 ka and 43.0 ± 2.7 ka (1σ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6 ± 1.2 ka and 15.3 ± 0.9 ka , while terraces sculpted into the upper Pleistocene–Holocene fan (AF2) provide ages of 9.3 ± 0.4 ka (T3), 7.1 ± 0.4 ka (T4), 5.2 ± 0.4 ka (T5) and 3.6 ± 0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision.

Despite a large number of dated glacial landforms in the Himalaya, the ice extent during the global Last Glacial Maximum (LGM) from 19 to 23 ka is only known to first order. New cosmogenic Be-10 exposure ages from well-preserved glacially polished surfaces, combined with published data, and an improved production rate scaling model allow reconstruction of the LGM ice extent and subsequent deglaciation in the Chandra Valley of NW India. We show that a >1000 m thick valley glacier retreated >150 km within a few thousand years after the onset of LGM deglaciation. By comparing the recession of the Chandra Valley Glacier and other Himalayan glaciers with those of Northern and Southern Hemisphere glaciers, we demonstrate that post-LGM deglaciation was similar and nearly finished prior to the Bolling/Allerod interstadial. Our study supports the view that many Himalayan glaciers advanced during the LGM, likely in response to global variations in temperature.

Whether variations in the spatial distribution of erosion influence the location, style, and magnitude of deformation within the Himalayan orogen is a matter of debate. We report new 40Ar/39Ar white mica and apatite fission-track (AFT) ages that measure the vertical component of exhumation rates along an ∼120-km-wide NE-SW transect spanning the greater Sutlej region of northwest India. The 40Ar/39Ar data indicate that first the High Himalayan Crystalline units cooled below their closing temperature during the early to middle Miocene. Subsequently, Lesser Himalayan Crystalline nappes cooled rapidly, indicating southward propagation of the orogen during late Miocene to Pliocene time. The AFT data, in contrast, imply synchronous exhumation of a NE-SW–oriented ∼80 × 40 km region spanning both crystalline nappes during the Pliocene–Quaternary. The locus of pronounced exhumation defined by the AFT data correlates with a region of high precipitation, discharge, and sediment flux rates during the Holocene. This correlation suggests that although tectonic processes exerted the dominant control on the denudation pattern before and until the middle Miocene; erosion may have been the most important factor since the Pliocene.

The Cretaceous eo-Alpine collisional event in the European Eastern Alps is generally accepted to induce W–NW-directed thrusting both in basement and in sedimentary cover units. This study presents the first evidence of eo-Alpine W–NW directed normal kinematics along the Schneeberg Normal Fault Zone, which separates eo-Alpine high-pressure rocks in a footwall position from pre-Alpine basement rocks in a hanging wall position. New Garnet Sm–Nd data indicate that exhumation of the high-pressure rocks along the normal fault zone started around 95 Ma ago and continued up to low greenschist/brittle conditions at 76 Ma, as indicated by a Rb–Sr age from a low temperature mylonite. The occurrence of pre-Alpine basement rocks both in the hanging wall and the footwall of eo-Alpine high-pressure rocks suggests exhumation by extrusion processes. Despite the displacement or removal of parts of the lower portion of the high-pressure unit by Tertiary strike-slip faults, eo-Alpine top-to-ESE thrusting, as expected for the structurally lower part of an extruding wedge, was found at and below the base of the eo-Alpine high-pressure rocks. A Rb–Sr age of 77 Ma from a greenschist facies mylonite in this thrust shear zone shows the contemporaneity of deformation at the base and the top of the wedge. The tectonic transport direction within the extruding wedge was E–SE, opposite to the W–NW direction so far reported for the eo-Alpine event in the Eastern Alps. The contemporaneity of opposite tectonic transport directions during continental subduction may be explained by a double-vergent wedge model with a narrow zone of ductile flow, where the high-pressure rocks were exhumed.

The interplay between topography and Indian summer monsoon circulation profoundly controls precipitation distribution, sediment transport, and river discharge along the Southern Himalayan Mountain Front (SHF). The Higher Himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north. During the Indian summer monsoon, vortices transport moisture from the Bay of Bengal, swirl along the SHF to the northwest, and cause heavy rainfall when colliding with the mountain front. In the eastern and central parts of the Himalaya, precipitation measurements derived from passive microwave analysis (SSM/I) show a strong gradient, with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen. The end of the monsoonal conveyer belt is near the Sutlej Valley in the NW Himalaya, where precipitation is lower and rainfall maxima move to lower elevations. This region thus comprises a climatic transition zone that is very sensitive to changes in Indian summer monsoon strength. To constrain magnitude, temporal, and spatial distribution of precipitation, we analyzed high-resolution passive microwave data from the last decade and identified an abnormal monsoon year (AMY) in 2002. During the 2002 AMY, violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest Himalaya at elevations in excess of 3 km asl. While precipitation in these regions was significantly increased and triggered extensive erosional processes (i.e., debris flows) on sparsely vegetated, steep hillslopes, mean rainfall along the low to medium elevations was not significantly greater in magnitude. This shift may thus play an important role in the overall sediment flux toward the Himalayan foreland. Using extended precipitation and sediment flux records for the last century, we show that these events have a decadal recurrence interval during the present-day monsoon circulation. Hence, episodically occurring AMYs control geomorphic processes primarily in the high-elevation arid sectors of the orogen, while annual recurring monsoonal rainfall distribution dominates erosion in the low- to medium-elevation parts along the SHF.

Along the Southern Himalayan Front (SHF), areas with concentrated precipitation coincide with rapid exhumation, as indicated by young mineral cooling ages. Twenty new, young ( 80% of the annual precipitation. AFT cooling ages reveal a coincidence between rapid erosion and exhumation that is focused in a ∼50–70-km-wide sector of the Himalaya, rather than encompassing the entire orogen. Assuming simplified constant exhumation rates, the rocks of two age vs. elevation transects were exhumed at ∼1.4±0.2 and ∼1.1±0.4 mm/a with an average cooling rate of ∼40–50 °C/Ma during Pliocene–Quarternary time. Following other recently published hypotheses regarding the relation between tectonics and climate in the Himalaya, we suggest that this concentrated loss of material was accommodated by motion along a back-stepping thrust to the south and a normal fault zone to the north as part of an extruding wedge. Climatically controlled erosional processes focus on this wedge and suggest that climatically controlled surface processes determine tectonic deformation in the internal part of the Himalaya.

In the last decade growing interest has emerged in quantifying the spatial and temporal variations in mountain building. Until recently, insufficient data have been available to attempt such a task at the scale of large orogens such as the Himalaya. The Himalaya accommodates ongoing convergence between India and Eurasia and is a focal point for studying orogen evolution and hypothesized interactions between tectonics and climate. Here we integrate 1126 published bedrock mineral cooling ages with a transient 1D Monte-Carlo thermal-kinematic erosion model to quantify the denudation histories along similar to 2700 km of the Himalaya. The model free parameter is a temporally variable denudation rate from 50 Ma to present. Thermophysical material properties and boundary conditions were tuned to individual study areas. Monte-Carlo simulations were conducted to identify the range of denudation histories that can reproduce the observed cooling ages. Results indicate large temporal and spatial variations in denudation and these are resolvable across different tectonic units of the Himalaya. More specifically, across > 1000 km of the southern Greater Himalaya denudation rates were highest (similar to 1.5-3 mm/yr) between similar to 10 and 2 Ma and lower (0.5-2.6 mm/yr) over the last 2 My. These differences are best determined in the NW-Himalaya. In contrast to this, across the similar to 2500 km length of the northern Greater Himalaya denudation rates vary over length scales of similar to 300-1700 km. Slower denudation (

The Himalaya–Karakoram–Tibet orogen, a product of India–Eurasia collision *55 Ma back, continues to attract global attention for its many geoscientific uniqueness. This orogen is the most exciting ‘natural laboratory’ to study continental dynamics and its evolution. During past few decades, phenomenal progresses have been made in uplift and extrusion models, dynamic metamorphism, magmatism, climate–tectonics interaction, etc. This thematic volume on the geosciences of the Himalaya–Karakoram– Tibet consists of eighteen papers and two Geosites. In the first paper, Kirby and Harkins correlated variation in slip rate along the Kunlun fault with topography of the Anyemaqen Shan Mountain at the eastern Tibetan plateau. Their work indicates that fault terminations might be associated with crustal thickening of the plateau and demonstrate that the upper crustal deformation of the Tibetan plateau to be pervasive and dispersed throughout the crustal blocks rather than localized along narrow fault zones. Robinson and Pearson compiled an orogen-wide correlation of footwall and hanging wall units of the Ramgarh and Munsiari thrust sheets. They considered the Ramgarh–Munsiari thrust sheet as a single ‘major orogenscale fault’ system. They hypothesized that the extensional shear within the South Tibetan Detachment was triggered possibly by ‘slip transfer’ from the Main Central Thrust into the Ramgarh–Munsiari Thrust during the Miocene. Thakur reviewed the tectonics of the Siwalik range of the Himalaya. He concluded in-sequence deformation and critical taper mechanism acted in this terrain. Presuming the crustal channel flow model to be correct, Mukherjee estimated a viscosity of 10–10 Pa s, and a Prandtl number of 10–10 for the Greater Himalayan Crystallines. Moharana et al., described the Munsiari Thrust from Kumaun Himalaya to consist of a core and a damage zone and described their structural geology in detail. Mukherjee described a ‘basal detachment’ of extensional ductile shear from the base of the Greater Himalayan Crystallines at Bhagirathi section of the Indian Himalaya and explained it in terms of a shifting crustal channel flow. Ubiquitous backthrusts within this terrain were another new finding and were explained by southward subduction of Eurasian plate below the Indian plate. Based on balanced crosssection studies, Khanal and Robinson estimated slip along major Himalayan faults from the Budhi-Gandhaki river section of central Nepal. Sen and Collins inferred dextral transpression and changing angle of convergence of the formation of the Ladakh magmatic arc. They also reported Late Eocene S-type granite magmatism in its central part. Mathew et al. discuss the tectonothermal evolution of the Arunachal Himalaya. They obtained isothermal decompression for the Greater Himalayan Sequence and isobaric cooling from the Main Central Thrust region. Jayangondaperumal et al. reevaluated co-seismic slip of the Himalayan Frontal Thrust. The estimated shortening around the Himalayan Frontal Thrust would lead a bigger earthquake in the western part of Indian Himalaya. Shah presented a geomorphologic study from Kashmir Basin in India, identified faults from remote sensing studies, and predicted a future earthquake of Mw 7.6. Srivastava et al. S. Mukherjee (&) Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India e-mail: soumyajitm@gmail.com

The northern part of the Pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent–continent collision. Such zones are the least understood type of plate boundaries because modern examples are few and of limited access, and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes. In the Pamir, it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate-bounding Main Pamir Thrust (MPT), which forms the principal northern mountain and deformation front of the Pamir. However, the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the MPT experienced relatively minor amounts of late Cenozoic exhumation. The Pamir orogen as a whole is an integral part of the overriding plate in a subduction system, while the remnant basin to the north constitutes the downgoing plate, with the bulk of the convergence accommodated by underthrusting. Herein, we demonstrate that the observed deformation of the upper and lower plates within the Pamir–Alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback, subduction erosion, subduction accretion, and marginal slab-tear faults. We suggest that the curvature of the North Pamir is genetically linked to the short width and rollback of the south-dipping Alai slab; northward motion (indentation) of the Pamir is accommodated by crustal processes related to this rollback. The onset of south-dipping subduction is tentatively linked to intense Pamir contraction following break-off of the north-dipping Indian slab beneath the Karakoram.

[1] Synorogenic extension has been recognized as an integral structural constituent of mountain belts and high-elevation plateaus during their evolution. In the Himalaya, both orogen-parallel and orogen-normal extension has been recognized. However, the underlying driving forces for extension and their timing are still a matter of debate. Here we present new fault kinematic data based on systematic measurements of hundreds of outcrop-scale brittle fault planes in the NW Indian Himalaya. This new data set, as well as field observations including crosscutting relationships, mineral fibers on fault planes, and correlations with deformation structures in lake sediments, allows us to distinguish different deformation styles. The overall strain pattern derived from our data reflects the large regional contractional deformation pattern very well but also reveals significant extensional deformation in a region, which is dominated by shortening. In total, we were able to identify six deformation styles, most of which are temporally and spatially linked, representing protracted shortening. Our observations also furnish the basis for a detailed overview of the younger deformation history in the NW Himalaya, which has been characterized by extension overprinting previously generated structures related to shortening. The four dominant deformation styles are (1) shortening parallel to the regional convergence direction; (2) arc-normal extension; (3) arc-parallel extension; and finally, (4) E–W extension. This is the first data set where a succession of both arc-normal and E–W extension has been documented in the Himalaya. Importantly, our observations help differentiate E–W extension triggered by processes within the Tibetan Plateau from arc-parallel and arc-normal extension originating from the curvature of the Himalayan orogen.

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.

In the Himalaya of Chamba, NW India, a major orographic barrier in front of the Greater Himalayan Range extracts a high proportion of the monsoonal rainfall along its southern slopes and effectively shields the orogen interior from moisture-bearing winds. Along a similar to 100-km-long orogen perpendicular transect, 28 new apatite fission track (AFT) and 30 new zircon (U-Th)/He (ZHe) cooling ages reveal marked variations in age distributions and long-term exhumation rates between the humid frontal range and the semi-arid orogen interior. On the southern topographic front, very young, elevation-invariant AFT ages of

Erosional exhumation and topography in mountain belts are temporally and spatially variable over million year timescales because of changes in both the location of deformation and climate. We investigate spatiotemporal variations in exhumation across a 150 x 250 km compartment of the NW Himalaya, India. Twenty-four new and 241 previously published apatite and zircon fission track and white mica Ar-40/Ar-39 ages are integrated with a 1-D numerical model to quantify rates and timing of exhumation alongstrike of several major structures in the Lesser, High, and Tethyan Himalaya. Analysis of thermochronometer data suggests major temporal variations in exhumation occurred in the early middle Miocene and at the Plio-Pleistocene transition. (1) Most notably, exhumation rates for the northern High Himalayan compartments were high (2-3 mm a(-1)) between similar to 23-19 and similar to 3-0 Ma and low (0.5-0.7 mm a(-1)) in between similar to 19-3 Ma. (2) Along the southern High Himalayan slopes, however, high exhumation rates of 1-2 mm a(-1) existed since 11 Ma. (3) Our thermochronology data sets are poorly correlated with present-day rainfall, local relief, and specific stream power which may likely result from (1) a lack of sensitivity of changes in crustal cooling to spatial variations in erosion at high exhumation rates (>similar to 1 mm a(-1)), (2) spatiotemporal variation in erosion not mimicking the present-day topographic or climatic conditions, or (3) the thermochronometer samples in this region having cooled under topography that only weakly resembled the modern-day topography.

Metamorphic dome complexes occur within the internal structures of the northern Himalaya and southern Tibet. Their origin, deformation, and fault displacement patterns are poorly constrained. We report new fi eld mapping, structural data, and cooling ages from the western fl ank of the Leo Pargil dome in the northwestern Himalaya in an attempt to characterize its post‐middle Miocene structural development. The western fl ank of the dome is characterized by shallow, west-dipping pervasive foliation and WNW-ESE mineral lineation. Shear-sense indicators demonstrate that it is affected by east-west normal faulting that facilitated exhumation of highgrade metamorphic rocks in a contractional setting. Sustained top-to-northwest normal faulting during exhumation is observed in a progressive transition from ductile to brittle deformation. Garnet and kyanite indicate that the Leo Pargil dome was exhumed from the mid-crust. 40 Ar/ 39 Ar mica and apatite fi ssion track (AFT) ages constrain cooling and exhumation pathways from 350 to 60 °C and suggest that the dome cooled in three stages since the middle Miocene. 40 Ar/ 39 Ar white mica ages of 16‐14 Ma suggest a fi rst phase of rapid cooling and provide minimum estimates for the onset of dome exhumation. AFT ages between 10 and 8 Ma suggest that ductile fault displacement had ceased by then, and AFT track-length data from high-elevation samples indicate that the rate of cooling had decreased signifi cantly. We interpret this to indicate decreased fault displacement along the Leo Pargil shear zone and possibly a transition to the Kaurik-Chango normal fault system between 10 and 6 Ma. AFT ages from lower elevations indicate accelerated cooling since the Pliocene that cannot be related to pure fault displacement, and therefore may refl ect more pronounced regionally distributed and erosion-driven exhumation.

Aluminum-26 and beryllium-10 surface exposure dating on cut-and-fill river-terrace surfaces from the lower Sutlej Valley (northwest Himalaya) documents the close link between Indian Summer Monsoon (ISM) oscillations and intervals of enhanced fluvial incision. During the early Holocene ISM optimum, precipitation was enhanced and reached far into the internal parts of the orogen. The amplified sediment flux from these usually dry but glaciated areas caused alluviation of downstream valleys up to 120 m above present grade at ca. 9.9 k.y. B.P. Terrace formation (i.e., incision) in the coarse deposits occurred during century-long weak ISM phases that resulted in reduced moisture availability and most likely in lower sediment flux. Here, we suggest that the lower sediment flux during weak ISM phases allowed rivers to incise episodically into the alluvial fill.

The intensity of the Asian summer-monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes, terrestrial environments, and marine sedi- ment records. However, the mechanisms of long-lived (2-5 k.y.) intensified monsoon phases, the related changes in precipitation distribution, and their effect on landscape evolution and sedimen- tation rates are not yet well understood. The arid high-elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal (i.e., strength- ened) monsoon seasons. Analogous to present-day rainfall anom- alies, enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure. We as- sociate landslide triggering during intensified monsoon phases with enhanced precipitation, discharge, and sediment flux leading to an increase in pore-water pressure, lateral scouring of rivers, and ov- ersteepening of hillslopes, eventually resulting in failure of slopes and exceptionally large mass movements. Here we use lacustrine deposits related to spatially and temporally clustered large land- slides (.0.5 km 3 ) in the Sutlej Valley region of the northwest Him- alaya to calculate sedimentation rates and to infer rainfall patterns during late Pleistocene (29-24 ka) and Holocene (10-4 ka) inten- sified monsoon phases. Compared to present-day sediment-flux measurements, a fivefold increase in sediment-transport rates re- corded by sediments in landslide-dammed lakes characterized these episodes of high climatic variability. These changes thus em- phasize the pronounced imprint of millennial-scale climate change on surface processes and landscape evolution.

[1] The Pamir indentor of the northwestern Himalayan syntaxis is a first-order feature demonstrating partly the northward extent of deformation due to the Cenozoic Indo-Eurasia collision. The Alai Valley of Kyrgyzstan at the northern end of the indentor is a strategically positioned, E-W trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone. To quantify the convergence accommodated across the Alai Valley during the Late Cenozoic, we collected structural and stratigraphic field data, reviewed existing Soviet literature, and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin. Our study suggests that the development, progressive closure, and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events: (1) Distributed north-south contraction took place during the late Oligocene–early Miocene, accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface; and (2) N-S shortening resumed in the mid-Miocene and continues today. During this second episode the thrust front migrated southward, localized along the Trans Alai ranges, and failed to reactivate earlier Neogene structures. Horizontal shortening of about 35% across the Alai Valley implies relatively low strain rates and displacement rates of about 4.18–4.69 × 10−16 s−1 and 0.66–0.78 mm yr−1, respectively, for the last 25 Myr. Our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the Asian continent as early as the late Oligocene.