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Frost cracking is a dominant mechanical weathering phenomenon facilitating the breakdown of bedrock in periglacial regions. Despite recent advances in understanding frost cracking processes, few studies have addressed how global climate change over the late Cenozoic may have impacted spatial variations in frost cracking intensity. In this study, we estimate global changes in frost cracking intensity (FCI) by segregation ice growth. Existing process-based models of FCI are applied in combination with soil thickness data from the Harmonized World Soil Database. Temporal and spatial variations in FCI are predicted using surface temperature changes obtained from ECHAM5 general circulation model simulations conducted for four different paleoclimate time slices. Time slices considered include pre-industrial (∼ 1850 CE, PI), mid-Holocene (∼ 6 ka, MH), Last Glacial Maximum (∼ 21 ka, LGM), and Pliocene (∼ 3 Ma, PLIO) times. Results indicate for all paleoclimate time slices that frost cracking was most prevalent (relative to PI times) in the middle- to high-latitude regions, as well as high-elevation lower-latitude areas such the Himalayas, Tibet, the European Alps, the Japanese Alps, the US Rocky Mountains, and the Andes Mountains. The smallest deviations in frost cracking (relative to PI conditions) were observed in the MH simulation, which yielded slightly higher FCI values in most of the areas. In contrast, larger deviations were observed in the simulations of the colder climate (LGM) and warmer climate (PLIO). Our results indicate that the impact of climate change on frost cracking was most severe during the PI–LGM period due to higher differences in temperatures and glaciation at higher latitudes. The PLIO results indicate low FCI in the Andes and higher values of FCI in Greenland and Canada due to the diminished extent of glaciation in the warmer PLIO climate.

The hydroclimate of the Tibetan Plateau (TP) and Central Asia (CA) plays a crucial role in sustaining surface water reservoirs and thus water resources in the respective regions. In this study, we investigate the changes in Asian hydroclimate and its driving forces during specific time intervals in the last 3 Ma. We conduct high-resolution (∼0.75° per grid cell) general circulation model ECHAM-5 experiments with boundary conditions for the mid-Pliocene (∼3 Ma), the Last Glacial Maximum (LGM; ∼21 ka), the mid-Holocene (∼6 ka), and the pre-industrial. Results suggest that seasonally relatively high precipitation rates (>1 mm day−1) were longer in the mid-Pliocene and shorter in the LGM, relative to the pre-industrial. We calculate different monsoon indices to detect changes in the intensity, strength and duration of the East Asian summer monsoon (EASM), South Asian summer monsoon (SASM), and the Indian summer monsoon (ISM), and construct climatologies of mid-latitude high-level westerly jet (WJ) stream occurrences based on the ECHAM5 wind fields. Our results suggest that in warm periods (e.g., mid-Pliocene or interglacial), the WJ migrates northward earlier in the year (April) and reaches higher latitudes than in the pre-industrial, resulting in a wetter TP and CA. During cooler periods (e.g., LGM or glacial), the WJ migrates northward later in the year (June) and remains over lower latitudes, resulting in a drier TP and CA. Increased/decreased local precipitation in TP and CA for the mid-Pliocene/LGM experiments correlates strongly with (a) intensity, strength and duration of the EASM, SASM, and the ISM and (b) WJ latitudinal position.

The propagation of slab break-off (slab tearing) is usually attributed to laterally variable plate convergence systems with a spatial transition between simultaneous oceanic subduction and continental collision. To study the process of slab tearing in a non-collisional geodynamic context, here we use a 3D thermo-mechanical numerical approach to model the oblique subduction of a homogeneous oceanic plate. We investigate the effects of the following parameters: (1) subduction obliquity angle, (2) age of oceanic slab, and (3) partitioning of boundary velocities (i.e., the ratio between the subduction component and the advance of the overriding plate in the total convergence). In our simulations, the retreat of the subduction zone leads to a thinning of the fore-arc and back-arc lithosphere, which are decoupled from the subducting slab by the rise of the hot asthenosphere from the underlying mantle wedge. As a consequence of the initial obliquity of the active plate margin, slab roll-back velocities are subject to progressive along-trench variations. Consistent with the gradual rotation of the trench, the front of the decoupling between the overriding and downgoing plates (together with predicted magmatic activity and topographic uplift) migrates in a horizontal direction. In the experiments with low angles of subduction obliquity (< 15°), relatively old subducting plates (> 50 Ma), and in the absence of the subduction component in the overall shortening, slab detachment either develops simultaneously along the entire length of the subduction zone or does not occur at all. In contrast, with higher subduction obliquity (≥ 15°), younger slabs (≤ 50 Ma) and in the presence of a boundary push on the oceanic side, the initial slab break-off is followed by the gradual growth of the “tear” window in the direction opposite to the migration path of the previously established plates decoupling. The sharp contrast in trench retreat rates between subduction zone segments affected and unaffected by slab detachment results in the arcuate shape of the trench. Furthermore, the direction of slab tearing may change from horizontal to vertical, eventually leading to the formation of a transform fault on the subducting plate. Our results show striking similarities with several features – such as trench curvature, subduction zone segmentation, magmatic production, lithospheric stress/deformation fields, and associated topographic changes – observed in many subduction zones (e.g., Marianas, New Hebrides, Mexico, Calabrian).

Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes beneath ice streams, ice rheology and ice-shelf buttressing. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between localized, temporally well-resolved GNSS and area-wide but sparse satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. On the freely floating ice shelves, we find velocity peaks both during high- and low-tide suggesting that ice-shelf buttressing varies temporally as a function of flexural bending from tidal displacement. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream and ice-shelf mechanics.

The Qaidam Basin (QB) in the northeastern Tibetan Plateau held a megalake system during the Pliocene. Today, the lower elevations in the basin are hyperarid. To understand to what extent the climate plays a role in the maintenance of the megalake system during the Pliocene, we applied the Weather Research and Forecasting model for dynamical downscaling of ECHAM5 global climate simulations for the present day and the mid���Pliocene. When imposing the mid���Pliocene climate on the QB with its modern land surface settings, the annual water balance (��S), that is, the change in terrestrial water storage within the QB, increases. This positive imbalance of ��S induced solely by the changes in the large���scale climate state would lead to a readjustment of lake extent, until a new equilibrium state is reached, where loss due to evaporation over lake areas compensates for the input by runoff and precipitation. Atmospheric water transport (AWT) analysis at each border of the QB reveals that this imbalance of ��S is caused by stronger moisture influx across the western border in winter, spring, and autumn and weaker moisture out���flux across the eastern border in summer. These changes in AWT are associated with the strengthening of the midlatitude westerlies in all seasons, except for summer, and the intensification of the East Asian Summer Monsoon. Given that the mid���Pliocene climate is an analog to the projected warm climate of the near future, our study contributes to a better understanding of climate change impacts in central Asia., Key Points: ECHAM5 global climate simulations for the present day and the mid���Pliocene were dynamically downscaled over the Qaidam Basin (QB). Results show a positive imbalance in water balance when the mid���Pliocene climate is imposed on the QB with its modern surface settings. This imbalance in water balance is closely associated with changes in the midlatitude westerlies and in the East Asian Summer Monsoon., Bundesministerium f��r Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347, Technische Universit��t Berlin

Catchment erosion and sedimentation are influenced by variations in the rates of rock uplift (tectonics) and periodic fluctuations in climate and vegetation cover. This study focuses on quantifying the effects of changing climate and vegetation on erosion and sedimentation over distinct climate–vegetation settings by applying the Landlab–SPACE landscape evolution model. As catchment evolution is subjected to tectonic and climate forcings at millennial to million-year timescales, the simulations are performed for different tectonic scenarios and periodicities in climate–vegetation change. We present a series of generalized experiments that explore the sensitivity of catchment hillslope and fluvial erosion as well as sedimentation for different rock uplift rates (0.05, 0.1, 0.2 mm a−1) and Milankovitch climate periodicities (23, 41, and 100 kyr). Model inputs were parameterized for two different climate and vegetation conditions at two sites in the Chilean Coastal Cordillera at ∼26∘ S (arid and sparsely vegetated) and ∼33∘ S (Mediterranean). For each setting, steady-state topographies were produced for each uplift rate before introducing periodic variations in precipitation and vegetation cover. Following this, the sensitivity of these landscapes was analyzed for 3 Myr in a transient state. Results suggest that regardless of the uplift rate, transients in precipitation and vegetation cover resulted in transients in erosion rates in the direction of change in precipitation and vegetation. The transients in sedimentation were observed to be in the opposite direction of change in the precipitation and vegetation cover, with phase lags of ∼1.5–2.5 kyr. These phase lags can be attributed to the changes in plant functional type (PFT) distribution induced by the changes in climate and the regolith production rate. These effects are most pronounced over longer-period changes (100 kyr) and higher rock uplift rates (0.2 mm yr−1). This holds true for both the vegetation and climate settings considered. Furthermore, transient changes in catchment erosion due to varying vegetation and precipitation were between ∼35 % and 110 % of the background (rock uplift) rate and would be measurable with commonly used techniques (e.g., sediment flux histories, cosmogenic nuclides). Taken together, we find that vegetation-dependent erosion and sedimentation are influenced by Milankovitch timescale changes in climate but that these transient changes are superimposed upon tectonically driven rates of rock uplift.

Many convergent orogens, such as the eastern European Alps, display an asymmetric doubly vergent wedge geometry. In doubly vergent orogens, deepest exhumation occurs above the retro‐wedge. Deep‐seismic interpretations depict the European plate dipping beneath the Adriatic, suggesting the pro‐wedge location on the north side of the orogen. Our new thermochronometer data across the Eastern Alps confirm distinct shifts in the locus of exhumation associated with orogen‐scale structural reorganizations. Most importantly, we find a general Mid‐Miocene shift in exhumation (in the Tauern Window and the Southern Alps) and focus of modern seismicity across the Southern Alps. Taken together, these observations suggest a subduction polarity reversal at least since the Mid‐Miocene such that the present‐day pro‐wedge is located on the south side of the Alps. We propose a transient tectonic state of a slow‐and‐ongoing slab reversal coeval with motion along the Tauern Ramp, consistent with a present‐day northward migration of drainage divides., Plain Language Summary: When tectonic plates collide, they bend downwards and form two lithospheric wedges dipping in opposite directions, such as in the Eastern Alps. We present new crustal cooling data along a transect in the Eastern Alps confirming that surface rocks across the central Tauern Window originated from the deepest structural levels along the transect. South of the Tauern Window rocks were exhumed from higher depths compared to those north of it and were exhumed more recently, while seismic activity is also focused across the Southern Alps. These observations suggest a subduction polarity reversal because they are inconsistent with the original southern and northern locations of overriding and subducting plates, respectively, >15 million years ago. This interpretation is contrary to lithosphere‐scale tomography that shows no change in subduction polarity. Therefore, we propose a transient tectonic state, that is, a slow‐and‐ongoing subduction polarity reversal that initiated when Tauern Window rocks began their steep ascent to the surface along a deep‐seated fault known as the Tauern Ramp. This study bridges observations in the mantle, crust and on the surface over geologic time., Key Points: Thermochronologic data in the Eastern Alps is consistent with a transient tectonic state toward complete slab reversal. The pro‐wedge has switched from north to south of the Periadriatic Fault along TRANSALP. Mid‐Miocene motion along the Tauern Ramp is the consequence of slab‐reversal., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Ice shelves around Antarctica can provide back stress for outlet glaciers and control ice sheet mass loss. They often contain narrow bands of thin ice termed ice shelf channels. Ice shelf channel morphology can be interpreted through surface depressions and exhibits junctions and deflections from flowlines. Using ice flow modeling and radar, we investigate ice shelf channels in the Roi Baudouin Ice Shelf. These are aligned obliquely to the prevailing easterly winds. In the shallow radar stratigraphy, syncline and anticline stacks occur beneath the upwind and downwind side, respectively. The structures are horizontally and vertically coherent, except near an ice shelf channel junction where patterns change structurally with depth. Deeper layers truncate near basal incisions. Using ice flow modeling, we show that the stratigraphy is ∼9 times more sensitive to atmospheric variability than to oceanic variability. This is due to the continual adjustment toward flotation. We propose that syncline‐anticline pairs in the shallow stratigraphy are caused by preferential snow deposition on the windward side and wind erosion at the downwind side. This drives downwind deflection of ice shelf channels of several meters per year. The depth variable structures indicate formation of an ice shelf channel junction by basal melting. We conclude that many ice shelf channels are seeded at the grounding line. Their morphology farther seaward is shaped on different length scales by ice dynamics, the ocean, and the atmosphere. These processes act on finer (subkilometer) scales than are captured by most ice, atmosphere, and ocean models, yet the dynamics of ice shelf channels may have broader implications for ice shelf stability., Plain Language Summary Ice flows from Antarctica's interior toward the coast. At the contact point between ice and ocean, the ice becomes afloat and forms fast‐flowing ice shelves. Snowfall continuously accumulates at the ice shelf surface, and at the ice shelf bottom the relatively warm ocean water can melt ice from below. Ice shelves sometimes exhibit a network of surface depressions resembling a river network. At the base, the depressions are accompanied by large incisions termed ice shelf channels. Using radar as a tool for echolocation, we investigate how the shape of this network is formed. We find that snow preferentially collects in the upwind side of the surface depressions. This makes ice shelf channels move to the downwind side. We also find that ice shelf channels can form junctions through localized ocean melting. This is important because it helps us to better understand how the Antarctic ice sheet interacts with the surrounding ocean., Key Points The radar stratigraphy in ice shelves is 9 times more sensitive to variability in snow deposition than to variability in basal melting Some ice shelf channels at Roi Baudouin Ice Shelf deflect from flowlines; the radar stratigraphy reflects related processes Variable snow deposition causes slow deflection, and basal melting can form ice shelf channel junctions far from the grounding line, InBev Baillet Latour Antarctica Fellowship, Belgian Science Policy Office http://dx.doi.org/10.13039/501100002749, DFG Emmy Noether, Academy of Finland http://dx.doi.org/10.13039/501100002341, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, “Antarctic Research with comparative investigations in Arctic ice areas”, Academy of Finnland, Belgium Science Policy Office

In this study, we combine geophysical observations from Ground Penetrating Radar (GPR) with soil physical, and geochemical properties from pedons excavated in four study areas spanning 1,300 km of the climate and ecological gradient in the Chilean Coastal Cordillera. Our aims are to: (1) relate GPR observations to depth varying soil physical and weathering-related chemical properties in adjacent pedons, and (2) evaluate the lateral extent to which these properties can be extrapolated along a hillslope using GPR observations. Physical observations considered include soil bulk density and grain size distribution whereas chemical observations are based on major and trace element analysis. Results indicate that visually-determined soil thickness and the transition from the soil B to C horizons generally correlate with maximums in the 500 and 1000 MHz GPR envelope profiles. To a lesser degree, these maximums in the GPR envelope profiles agree with maximums in weathering related indices such as the Chemical Index of Alteration (CIA) and the chemical index of mass transfer (τ) for Na. Finally, we find that up-scaling from the pedon to hillslope scale is possible with geophysical methods for certain pedon properties available. Taken together, these findings suggest that the GPR profiles along hillslopes can be used to infer lateral thickness variations in soil horizons, and to some degree the physical and chemical variations with depth.

The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica., Plain Language Summary: Antarctica is surrounded by floating ice shelves, which play a crucial role in regulating the flow of ice from the continent into the oceans. The ice shelves are susceptible to melting from warm ocean waters beneath them. In order to better understand the melting, knowledge of the shape and depth of the ocean cavity beneath ice shelves is crucial. In this study, we present new measurements of the sea floor depth beneath Ekström Ice Shelf in East Antarctica. The measurements reveal a much deeper sea floor than previously known. We discuss the implications of this for access of warm ocean waters, which can melt the base of the ice shelf and discuss how the observed sea floor features were formed by historical ice flow regimes. Although Ekström Ice Shelf is relatively small, the geometry described here is thought to be representative of the topography beneath many ice shelves in this region, which together regulate the ice loss from a substantial area of East Antarctica., Key Points: Vibroseis seismic surveys used to map the ice shelf cavity beneath Ekström Ice Shelf in Antarctica. Deep trough with transverse sills and overdeepenings provide evidence of past ice streaming and retreat. Two ocean circulation regimes inferred in the shallow and deep parts of the cavity., Belgian Science Policy Contract, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, DFG Cost S2S project, RD http://dx.doi.org/10.13039/100009936

Careful study of the processes transporting sediment across Earth's surface is critical for robust interpretation of the sedimentary record. Here we consider the specific influence of cyclic glaciation on the export of sediment from mountain landscapes to ocean basins. Using detrital apatite fission-track tracer thermochronology, we present new observations of sediment provenance from six large river systems draining the eastern flank of the Southern Alps, New Zealand. Detrital cooling ages in all six rivers reflect erosion of partially-reset and fully-unreset bedrock exposed in lower catchment areas and indicate that sediment is not currently contributed in proportion to long-term ( > 10 6 yr ) erosion patterns. Instead, detrital cooling ages are better explained by either localized erosion along the eastern mountain front or intermontane sediment storage. Of these two alternatives, only intermontane sediment storage is further consistent with suspended sediment flux measurements in eastern rivers. Our observations are consistent with prior interpretations of Holocene sediment retention, and contrast with tracer thermochronology from continental margin deposits indicating sediment was rapidly exported to the continental shelf during the late Pleistocene. Collectively, this evidence argues for a reactive sediment routing system east of the main drainage divide that responds to cyclic glaciation by retaining sediment onshore following deglaciation and evacuating sediment reservoirs offshore during the subsequent glacial advance. Our research demonstrates the importance of intermontane sediment storage on the transmission of high-frequency ( ∼ 10 4 – 5 yr ) climate signals to offshore sedimentary archives while highlighting a novel approach to detailing sediment provenance in tectonically active mountain ranges.

The Earth surface is modulated by interactions among tectonics, climate, and biota. The influence of each of these factors on hillslope denudation rates is difficult to disentangle. The Chilean Coastal Cordillera offers a strong climate and vegetation gradient from arid and unvegetated in the North to humid and vegetated in the South. A similar (convergent) plate tectonic boundary lies to the West of the Coastal Cordillera. We present eight depth profiles analyzed for in situ-produced cosmogenic 10Be in four study areas. These profiles reveal denudation rates of soil-mantled hillslopes and the depth of mobile layers. Depth profiles were investigated from both S- and N-facing mid-slope positions. Results indicate the depth of the mobile layers in the four study areas increase from N to S in latitude. When mixing is present in the mobile layers they are completely mixed. In the S- and N-facing hillslopes of each study area, mid-slope positions do not show a systematic change in depth of the mobile layers nor in denudation rates based on cosmogenic depth profiles. From N to S in latitude, modelled denudation rates of hillslopes increase from ∼0.46 to ∼5.65 cm/kyr and then decrease to ∼3.22 cm/kyr in the southernmost, highest vegetation cover, study area. Calculated turnover times of soils decrease from ∼30 to ∼11 kyr and then increase to ∼22 kyr. In this work, the increasing denudation rates are attributed to increasing mean annual precipitation from N to S. However, despite the ongoing increase in precipitation from N to S, the denudation rate in the southernmost location does not continue to increase due to the protective nature of increasing vegetation cover. This indicates a vegetation induced non-linear relationship with denudation rates.

Rocks vary significantly in strength and erodibility. Here we evaluate if rock erodibility variations should be considered when interpreting thermochronologic datasets. We do this by applying 1D thermo–kinematic numerical models that exhume two lithologies of contrasting erodibility. For thick layers (>2 km), soft over hard layering causes earlier cooling and therefore older thermochronologic dates than no layering, with the opposite true for hard over soft layering. In some circumstances, even 2–10x erodibility contrasts substantially influence the results, and a 10x erodibility contrast can be nearly as important as contrasts several orders of magnitude greater. Thinner alternating layers (

Landscape evolution is a product of the forces that drive geomorphic processes (e.g., tectonics and climate) and the resistance to those processes. The underlying lithology and structural setting in many landscapes set the resistance to erosion. This study uses a modified version of the Channel-Hillslope Integrated Landscape Development (CHILD) landscape evolution model to determine the effect of a spatially and temporally changing erodibility in a terrain with a complex base level history. Specifically, our focus is to quantify how the effects of variable lithology influence transient base level signals. We set up a series of numerical landscape evolution models with increasing levels of complexity based on the lithologic variability and base level history of the Jura Mountains of northern Switzerland. The models are consistent with lithology (and therewith erodibility) playing an important role in the transient evolution of the landscape. The results show that the erosion rate history at a location depends on the rock uplift and base level history, the range of erodibilities of the different lithologies, and the history of the surface geology downstream from the analyzed location. Near the model boundary, the history of erosion is dominated by the base level history. The transient wave of incision, however, is quite variable in the different model runs and depends on the geometric structure of lithology used. It is thus important to constrain the spatiotemporal erodibility patterns downstream of any given point of interest to understand the evolution of a landscape subject to variable base level in a quantitative framework.

Quantifying mountain building processes in convergent orogens requires determination of the timing and rate of deformation in the overriding plate. In the central Andes, large discrepancies in both timing and rate of deformation prevent evaluating the shortening history in light of internal or external forcing factors. Geologic map patterns, age and location of reset thermochronometer systems, and synorogenic sediment distribution are all a function of the geometry, kinematics, and rate of deformation in a fold-thrust-belt-foreland basin (FTB-FB) system. To determine the timing and rate of deformation in the northern Bolivian Andes, we link thermokinematic modeling to a sequentially forward modeled, balanced cross section isostatically accounting for thrust loads and erosion. Displacement vectors, in 10 km increments, are assigned variable ages to create velocity fields in a thermokinematic model for predicting thermochronometer ages. We match both the pattern of predicted cooling ages with the across strike pattern of measured zircon fission track, apatite fission track, and apatite (U-Th)/He cooling ages as well as the modeled age of FB formations to published sedimentary sections. Results indicate that northern Bolivian FTB deformation started at 50 Ma and may have begun as early as 55 Ma. Acceptable rates of shortening permit either a constant rate of shortening (~4–5 mm/yr) or varying shortening rates with faster rates (7–10 mm/yr) at 45–50 Ma and 12–8 Ma, significantly slower rates (2–4 mm/yr) from 35 to 15 Ma and indicate the northern Bolivian Subandes started deforming between 19 and 14 Ma.

The Talesh Mountains at the NW margin of the Iranian Plateau curve around the southwestern corner of the south Caspian Block and developed in response to the collision of the Arabian-Eurasian plates. The timing, rates, and regional changes in late Cenozoic deformation of the Talesh Mountains are not fully understood. In this study, we integrate 23 new apatite and zircon bedrock U-Th/He ages and structurally restored geologic cross-sections with previously published detrital apatite fission track data to reconstruct the deformation history of the Talesh Mountains. Our results reveal that slow rock exhumation initiated during the late Oligocene (~27–23 Ma) and then accelerated in the middle Miocene (~12 Ma). These events resulted in the present day high elevation and curved geometry of the Mountains. The spatial and temporal distribution of cooling ages suggest that the Oligocene bending of the Talash Mountains was earlier than in the eastern Alborz, Kopeh- Dagh, and central Alborz Mountains that initiated during the late Cenozoic. Late Oligocene and middle Miocene deformation episodes recorded in the Talesh Mountains can be related to the collisional phases of the Arabian and Eurasian plates. The lower rate of exhumation recorded in the Talesh Mountains occurred during the initial soft collision of the Arabia – Eurasia plates in the late Oligocene. The accelerated exhumation that occurred during final collision since the middle Miocene resulted from collision of the harder continental margin.

Glacial chronologies provide insight into the evolution of paleo-landscapes, paleoclimate, topography, and the erosion processes that shape mountain ranges. In the Pamir of Central Asia, glacial morphologies and deposits indicate extensive past glaciations, whose timing and extent remain poorly constrained. Geomorphic data and 15 new 10Be exposure ages from moraine boulders and roches moutonnees in the southwestern Pamir document multiple Pleistocene glacial stages. The oldest exposure ages, 113 ± 10 ka , underestimate the age of the earliest preserved glacial advance and imply that the modern relief of the southwestern Pamir (peaks at ∼5000–6000 m a.s.l.; valleys at ∼2000–3000 m a.s.l.) already existed in the late Middle Pleistocene. Younger exposure ages (∼40–80 ka, ∼30 ka) complement the existing Central Asian glacial chronology and reflect successively less extensive Late Pleistocene glaciations. The topography of the Pamir and the glacial chronologies suggest that, in the Middle Pleistocene, an ice cap or ice field occupied the eastern Pamir high-altitude plateau, whereas westward flowing valley glaciers incised the southwestern Pamir. Since the Late Pleistocene deglaciation, the rivers of the southwestern Pamir adjusted to the glacially shaped landscape. Localized rapid fluvial incision and drainage network reorganization reflect the transient nature of the deglaciated landscape.

Modern climate in the Andes is characterized by strong N–S decreasing trends in precipitation rates. Here we use stratigraphic records to show that this pattern has been established since as early as 12–11 Ma, at least on the western Andean margin of Northern Chile. The stratigraphic architecture on the western Andean margin documents a transition between 19°–20°S latitude where matrix-supported debris flow deposits shift to fluvial conglomerates between 12–11 Ma. The deposition of fluvial sediments has been maintained to the present north of 19°–20°S, while the occurrence of post 11 Ma aeolian sand, matrix-supported breccias with conglomerate interbeds south of these latitudes implies ongoing sedimentation with less water and thus under drier conditions. We relate these changes to the tectonic development of the Andes. Existing palaeoclimate models suggest that an elevated plateau deflects the Andean jet towards the south, thereby focusing moisture from the equatorial Atlantic to the northeastern flanks of the Altiplano. In addition, the formation of the eastern Andean foothills most likely intercepted moisture transport, and shifted it farther to the east, thereby keeping the western Andean margin dry south of 19°–20°S latitudes. The sedimentological data support a strong linkage between orographic precipitation and stratigraphy whereby central Andean deformation controls the distribution of available moisture on the western flank through a combination of orographic precipitation and deflection of air masses.

Many stable isotope paleoaltimetry studies have focused on paleoelevation reconstructions of orogenic plateaus such as the Tibetan or Andean Plateaus. We address the opportunities and challenges of applying stable isotope paleoaltimetry to “smaller” orogens. We do this using a high‐resolution isotope tracking general circulation model (ECHAM5‐wiso) and explore the precipitation δ18O (δ18Op) signal of Cenozoic paleoclimate and topographic change in the European Alps. Results predict a maximum δ18Op change of 4–5‰ (relative to present day) during topographic development of the Alps. This signal of topographic change has the same magnitude as changes in δ18Op values resulting from Pliocene and Last Glacial Maximum global climatic change. Despite the similar magnitude of the isotopic signals resulting from topographic and paleoclimate changes, their spatial patterns across central Europe differ. Our results suggest that an integration of paleoclimate modeling, multiproxy approaches, and low‐elevation reference proxy records distal from an orogen improve topographic reconstructions., Plain Language Summary: Here we use a climate model with water isotopes implemented to explore the maximum precipitation isotopic signal of Cenozoic topographic and paleoclimate change in the European Alps. Our results show that the impact of topography change has the same magnitude as changes in the isotopic composition of local precipitation resulting from Pliocene and Last Glacial Maximum global climatic change., Key Points: High‐resolution isotope tracking general circulation model (ECHAM5‐wiso) is used to explore changes in past oxygen isotope ratios in precipitation in the Alps. Model‐simulated isotopic signals of topographic change and difference between glacials and interglacials show the same magnitude. Low‐elevation proxy records improve reconstructions of paleotopography by reducing long‐term climate change bias., German Research Foundation (DFG) http://dx.doi.org/10.13039/501100001659

This study investigates the influence of the 3-D geometry of a down-going plate, the rheological structure of the upper plate, and the migration of the overriding plate toward the trench in relation to the overall subduction velocity on the exhumation pattern in orogen syntaxes. Using a thermomechanical numerical code (DOUAR), we analyze the strain localization, rock uplift, and exhumation response of a rheologically stratified continental lithosphere to subduction of a convex-upward-shaped indenter. The models consider three thermorheological lithospheric profiles that determine the degree of mechanical coupling between the upper crust and lithospheric mantle. These models include a strong, cratonic lithosphere; a weaker, younger (and hotter) continental plate; and an intermediate case. The strongly coupled case predicts a localization of high rock uplift rates along narrow linear bands crossing the entire model domain parallel to the trench. In contrast, in a weakly coupled lithosphere, rock uplift is concentrated within a curved ellipse region of anomalously high exhumation rates located above the indenter apex. The aspect ratio of the localized area of rapid rock uplift is controlled by the initial width of the rigid indenter and the relationship between boundary velocities. In particular, the combination of little or no upper plate migration with a narrow indenter causes a nearly circular region (similar to 100-km diameter) of rapid exhumation that resembles the pattern of thermochronometer ages observed in orogen syntaxes such as the Southeast Alaska and the Olympic Mountains of the Cascadia subduction zone (western USA).

Separation of microcontinents is explained by a ridge jump toward the passive margin as a possible consequence of plume-induced rheological weakening, ultimately leading to breakup followed by accretion of the oceanic crust along a new spreading center. In contrast to such a purely extensional case, the separation of continental microblocks from the main body of the African plate during its continuous northward motion and subduction under Eurasia is still poorly understood. Our numerical experiments show the thermal and buoyancy effects of mantle plume impingement on the bottom of the continental part of a subducting plate are sufficient to induce separation of an isolated microcontinental block from the main subducting continent, even during induced plate motion necessary for uninterrupted oceanic and continental subduction. Subsequent continental accretion occurs by decoupling upper-crustal nappes from the newly formed subducting microcontinent, which is in agreement with the Late Cretaceous-Eocene evolution of the eastern Mediterranean.

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.

Highlights • The South Tibetan detachment system played a major role in Himalayan evolution. • Near Mt Everest, the detachment system accommodated large displacements under both brittle and ductile conditions. • Rapid cooling of footwall rocks reflected tectonic denudation by brittle slip from ca. 15.6 to at least 13.0 Ma. • Thermal–kinematic modeling suggests displacement on the detachment to be at least 61 km. Abstract North-dipping, low-angle normal faults of the South Tibetan detachment system (STDS) are tectonically important features of the Himalayan–Tibetan orogenic system. The STDS is best exposed in the N–S-trending Rongbuk Valley in southern Tibet, where the primary strand of the system – the Qomolangma detachment – can be traced down dip from the summit of Everest for a distance of over 30 km. The metamorphic discontinuity across this detachment implies a large net displacement, with previous studies suggesting >200 km of slip. Here we refine those estimates through thermal–kinematic modeling of new (U–Th)/He and 40Ar/39Ar data from deformed footwall leucogranites. While previous studies focused on the early ductile history of deformation along the detachment, our data provide new insights regarding the brittle–ductile to brittle slip history. Thermal modeling results generated with the program QTQt indicate rapid, monotonic cooling from muscovite 40Ar/39Ar closure (ca. 15.4–14.4 Ma at ca. 490 °C) to zircon (U–Th)/He closure (ca. 14.3–11.0 Ma at ca. 200 °C), followed by slower cooling to apatite (U–Th)/He closure at ca. 9–8 Ma (at ca. 70 °C). Although previous work has suggested that ductile slip on the detachment lasted only until ca. 15.6 Ma, thermal–kinematic modeling of our new data suggests that rapid (ca. 3–4 km/Ma) tectonic exhumation by brittle–ductile to brittle fault slip continued to at least ca. 13.0 Ma. Much lower modeled exhumation rates (≤0.5 km/Ma) after ca. 13 Ma are interpreted to reflect erosional denudation rather than tectonic exhumation. Projection of fault-related exhumation rates backward through time suggests total slip of ca. 61 to 289 km on the Qomolangma detachment, with slightly more than a third of that slip occurring under brittle–ductile to brittle conditions.

This study presents the first comprehensive dataset of low-temperature thermochronology from 43 bedrock samples collected north of the active Yakutat–North American plate boundary. Our apatite and zircon (U–Th)/He and fission-track data reveal the cooling history of the inboard Wrangellia Composite Terrane that is dominated by rapid cooling after Late Jurassic to Early Cretaceous arc magmatism followed by very little cooling and exhumation until today. Deformation resulting in rock exhumation due to the collision of the Yakutat microplate is spatially very limited (20–30 km) and is concentrated mainly in the Chugach–Prince William Terrane and rocks near the Border Ranges Fault. Focused exhumation from greater depths of ca. 10 km with very high rates (>5 km/Myr) is localized at the syntaxis region, starting ca. 10 Ma and shifted south through time. The rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion, which started already before glaciation of the area. The shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate, which is changing on local and global scales since the Late Miocene.

Plate tectonics drives mountain building in general, but the space-time pattern and style of deformation is influenced by how climate, geodynamics, and basement structure modify the orogenic wedge. Growth of the Subandean thrust belt, which lies at the boundary between the arid, high-elevation Central Andean Plateau and its humid, low-elevation eastern foreland, figures prominently into debates of orogenic wedge evolution. We integrate new apatite and zircon (U–Th)/He thermochronometer data with previously published apatite fission-track data from samples collected along four Subandean structural cross-sections in Bolivia between 15° and 20°S. We interpret cooling ages vs. structural depth to indicate the onset of Subandean exhumation and signify the forward propagation of deformation. We find that Subandean growth is diachronous south ( 11 ± 3 Ma ) vs. north ( 6 ± 2 Ma ) of the Bolivian orocline and that Subandean exhumation magnitudes vary by more than a factor of two. Similar north–south contrasts are present in foreland deposition, hinterland erosion, and paleoclimate; these observations both corroborate diachronous orogenic growth and illuminate potential propagation mechanisms. Of particular interest is an abrupt shift to cooler, more arid conditions in the Altiplano hinterland that is diachronous in southern Bolivia (16–13 Ma) vs. northern Bolivia (10–7 Ma) and precedes the timing of Subandean propagation in each region. Others have interpreted the paleoclimate shift to reflect either rapid surface uplift due to lithosphere removal or an abrupt change in climate dynamics once orographic threshold elevations were exceeded. These mechanisms are not mutually exclusive and both would drive forward propagation of the orogenic wedge by augmenting the hinterland backstop, either through surface uplift or spatially variable erosion. In summary, we suggest that diachronous Subandean exhumation was driven by piecemeal hinterland uplift, orography, and the outward propagation of deformation.

Age constraints of late Cenozoic fluvial terraces are important for addressing surface process questions related to the incision rates of rivers, or tectonic and climate controls on denudation and sedimentation. Unfortunately, absolute age constraints of fluvial terraces are not always possible, and many previous studies have often dated terraces with relative age constraints that do not allow for robust interpretations of incision rates and timing of terrace formation. However, in situ-produced cosmogenic nuclides allow absolute age determination, and hence incision rates, of fluvial deposits back to 5 Ma. Here we present, cosmogenic depth profile dating and isochron burial dating of four different river systems in Europe spanning 12° of latitude. We do this to determine river incision rates and spatial variations in the timing of terrace formation. Isochron burial age constraints of four selected terraces from the Vltava river (Czech Republic) range between 1.00 ± 0.21 to 1.99 ± 0.45 Ma . An isochron burial age derived for the Allier river (Central France) is 2.00 ± 0.17 Ma . Five terrace levels from the Esla river (NW Spain) were dated between 0.08 + 0.04 / − 0.01 Ma and 0.59 + 0.13 / − 0.20 Ma with depth profile dating. The latter age agrees with an isochron burial age of 0.52 ± 0.20 Ma . Two terrace levels from the Guadalquivir river (SW Spain) were dated by depth profile dating to 0.09 + 0.03 / − 0.02 Ma and 0.09 + 0.04 / − 0.03 Ma . The one terrace level from the Guadalquivir river dated by isochron burial dating resulted in an age of 1.79 ± 0.18 Ma . Results indicate that the cosmogenic nuclide-based ages are generally older than ages derived from previous relative age constraints leading to a factor 2–3 lower incision rates than previous work. Furthermore, the timing of terrace formation over this latitudinal range is somewhat obscured by uncertainties associated with dating older terraces and not clearly synchronous with global climate variations.

Quantifying controls on glacial erosion over geologic timescales is central to understanding the role of Cenozoic climate change on the development of modern mountain belts, yet the mechanisms that produce the distinct relief and topography visible in glaciated regions remain poorly constrained. We test the hypothesis that commonly assumed glacial sliding parameterizations control denudation rates over geologic timescales. We do this by modeling glacier dynamics over a glacial–interglacial cycle and compare with a dense dataset of (U–Th)/He thermochronometer derived denudation rates from the southern Coast Mountains, BC. Results indicate zones of rapid Quaternary erosion correspond to locations where the model predicts the highest averaged sliding velocities. The results are consistent with the hypothesis that sliding influences the rate of glacial erosion. Regression between sliding predicted by the model and erosion rates shows a statistically significant correlation ( r 2 = 0.6 ). The coefficient of the regression ( 10 − 5 ) is smaller than previous estimates based on data from much shorter timescales. The model results also reveal that for a specific location, active subglacial sliding, and hence erosion, occurs for only ∼10–20% of a glacial–interglacial cycle, suggesting high temporal variations in erosion rates. This intermittency of erosion requires instantaneous erosion rates to be greater than long term averages, explaining how timescale averaging can impact estimates of glacial erosion rates.

Variations in oxygen isotope compositions (δ18O) provide insight into modern climate and past changes in climate and topography. In addition, in regions such as Tibet, geologic archives of isotope ratios record climate change driven by plateau uplift and therefore also provide information about the surface uplift history. A good understanding of modern-day controls on δ18O is crucial for interpreting geologic δ18O in this context. We use the ECHAM5-wiso global atmospheric general circulation model to calculate δ18O in precipitation (δ18Op) for the present-day climate. In the region of the Tibetan Plateau, spatial variations of monthly means of δ18Op are statistically related to spatial variations of 2 m air temperature and precipitation rate, as well as to topography. The size and location of investigated regions are varied in our study to capture regional differences in these relationships and the processes governing the modern δ18Op. In addition to correlation analyses, a cross-validated stepwise multiple regression is carried out using δ18Op as the predictand, and topography and atmospheric variables (temperature and precipitation amount) as predictors. The 2 m air temperature and topography yield the highest spatial correlation coefficients of >0.9 and 90% of the δ18Op spatial variance in the same regions. The 2 m air temperature is the dominant predictor and contributes 93.6% to the total explained spatial variance on average. The results demonstrate that most of the δ18Op pattern on and around the Tibetan Plateau can be explained by variation in 2 m air temperature and altitude. Correlation of the dependent predictors indicate that in low-altitude regions where topography does not determine temperature variability, the high correlation of temperature and δ18Op may partially be explained by variations in precipitation rates.

The subduction of bathymetric anomalies at convergent margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Northern Patagonian Icefield (NPI) is located east of the Chile Triple Junction at similar to 47 degrees S, where the Chile Rise spreading center collides with South America. This region is characterized by an abrupt increase in summit elevations and relief that has been controversially debated in the context of geodynamic versus glacial erosion effects on topography. Here we present geomorphic, thermochronological, and structural data that document neotectonic activity along hitherto unrecognized faults along the flanks of the NPI. New apatite (U-Th)/He bedrock cooling ages suggest faulting since 2-3 Ma. We infer the northward translation of an similar to 140 km long fore-arc sliver-the NPI block-results from enhanced partitioning of oblique plate convergence due to the closely spaced collision of three successive segments of the Chile Rise. In this model, greater uplift occurs in the hanging wall of the Exploradores thrust at the northern leading edge of the NPI block, whereas the Cachet and Liquine-Ofqui dextral faults decouple the NPI block along its eastern and western flanks, respectively. Localized extension possibly occurs at its southern trailing edge along normal faults associated with margin-parallel extension, tectonic subsidence, and lower elevations along the Andean crest line. Our neotectonic model provides a novel explanation for the abrupt topographic variations inland of the Chile Triple Junction and emphasizes the fundamental effects of local tectonics on exhumation and topographic patterns in this glaciated landscape.

Numerical modeling coupling erosion with crustal deformation predicts that development of an orographic rain shadow may explain the asymmetric exhumation of convergent plate boundary orogens. This prediction is consistent with observations from the Southern Alps of New Zealand, where bedrock thermochronology indicates crustal exhumation has been concentrated along the wet, windward side of the mountains. While the spatial correspondence of exhumation and precipitation patterns is compelling, a robust evaluation of the link between orographic and orogenic processes further requires a temporal comparison between exhumation history, plate reconstructions and paleoclimatic records. We present a detailed exhumation history of the Southern Alps from detrital apatite and zircon fission-track thermochronology of the Waiho-1 borehole, a 3.6 km-thick sequence of proximal foreland basin sediments. Inverse thermal modeling of a 2062-grain dataset predicts two periods of rapid exhumation in the Early and Late Miocene. Rapid exhumation in the Early Miocene was synchronous with the development of transpression along the Alpine Fault and a ca. 20–22 Ma pulse of exhumation may reflect cooling during inversion of preexisting extensional basins. Rapid exhumation in the Late Miocene was not synchronous with a discrete change in plate convergence but increased exhumation rates after 7.4 Ma may instead reflect localization of plate boundary deformation along the Alpine Fault as orographic precipitation concentrated exhumation in the Alpine Fault hanging wall. We propose that, similar to prior interpretations from bedrock thermochronology, detrital thermochronology of the Southern Alps foreland basin is consistent with numerical model predictions linking asymmetric exhumation of the orogen to the growth of an orographic rain shadow.

Recent work has highlighted a strong, worldwide, alpine glacial impact on orogen erosion rates over the last 2 Ma. While it may be assumed that glaciers increased erosion rates when active, the degree to which past glaciations influence Holocene erosion rates through the adjustment of topography is not known. In this study, we investigate the influence of long-term tectonic and post-glacial topographic controls on erosion in a glaciated orogen: the Olympic Mountains, USA. We present 14 new 10Be and 26Al analyses which constrain Holocene erosion rates across the Olympic Mountains. Basin-averaged erosion rates scale with basin-averaged values of 5 km local relief, channel steepness, and hillslope angle throughout the range, similar to observations from non-glaciated orogens. These erosion rates are not related to mean annual precipitation or the marked change in Pleistocene alpine glacier size across the range, implying that glacier modification of topography and modern precipitation parameters do not exert strong controls on these rates. Rather, we find that despite spatial variations in glacial modification of topography, patterns of recent erosion are similar to those from estimates of long-term tectonic rock uplift. This is consistent with a tectonic model where erosion and rock uplift patterns are controlled by the deformation of the Cascadia subduction zone.

The Olympic Mountains of Washington state (USA) represent the aerially exposed accretionary wedge of the Cascadia Subduction Zone and are thought to be in flux steady state, whereby the mass outflux (denudation) and influx (tectonic accretion) into the mountain range are balanced. We use a multi-method approach to investigate how temporal variations in the influx and outflux could affect previous interpretations of flux steady state. This includes the analysis of published and new thermochronometric ages for (U–Th) ∕ He dating of apatite and zircon (AHe and ZHe, respectively), fission-track dating of apatite and zircon (AFT and ZFT, respectively), 1-D thermo-kinematic modeling of thermochronometric data, and independent estimates of outflux and influx. In total, we present 61 new AHe, ZHe, AFT, and ZFT thermochronometric ages from 21 new samples. AHe ages are generally young ( 2 to −1 around 5–7 Ma. With the onset of Plio–Pleistocene glaciation, exhumation rates increased to values > 1 km Myr−1. This demonstrates that the material outflux varies through time, requiring a commensurate variation in influx to maintain flux steady state. Evaluation of the offshore and onshore sediment record shows that the material influx is also variable through time and that the amount of accreted sediment in the wedge is spatially variable. This qualitatively suggests that significant perturbations of steady state occur on shorter timescales (105–106 years), like those created by Plio–Pleistocene glaciation. Our quantitative assessment of influx and outflux indicates that the Olympic Mountains could be in flux steady state on long timescales (107 years).

Upper crustal extensional structures range from steep normal faults to shallow-dipping detachments. The relationship between extension and formation of synkinematic hanging wall basins including their relative timing is not well understood. The South Rhodope core complex, Southern Balkans, has experienced extension for >40 Ma leading to a number of extensional structures and Cenozoic sedimentary basins. We present new bedrock and basin detrital zircon and apatite (U-Th-Sm)/He ages from the Pirin and Rila Mountains and the Sandanski basin. Results identify three episodes of Cenozoic extension in SW Bulgaria accommodated by (1) the Eocene/Oligocene Mesta detachment; (2) the early to middle Miocene Gorno Spanchevo fault (circa 18–15 Ma), which is the northern prolongation of the Strymon low-angle detachment; and (3) the late Miocene West Pirin fault (≤10 Ma). Detachment faulting on the Strymon fault accommodated tens of kilometers of ENE-WSW extension and created ~1500 m topographic relief, but because the resulting hillslopes were gentle (≤10°), extension did not lead to enhanced footwall erosion or formation of a hanging wall basin. In contrast, the West Pirin normal fault resulted in mostly vertical motion of its footwall causing steep topography, rapid erosion, and formation of the synrift Sandanski basin. Digital topographic analysis of river channel profiles identifies the latest episodes of deformation including westward tilting of the Sandanski and Strymon basins and Quaternary N-S extension. This study demonstrates that basin formation in the South Rhodope core complex is related to normal faulting postdating the main episode of crustal stretching by detachment faulting.

Central Andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude (>2 km) Miocene-to-modern surface uplift. However, the isotopic relationships between precipitation, surface waters, and soil waters upon which these reconstructions are based remain poorly constrained for both past, and in many cases, modern conditions. We quantify the relationships between central Andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples (δ18O and δD) collected between April 2009 and October 2012. The isotopic compositions of stream waters match precipitation along the eastern flank. In contrast, Altiplano surface waters possess a lower δD–δ18O slope (4.59 vs ∼8 for meteoric waters) not observed in precipitation, which signals heavy isotope evaporative enrichment in surface waters. Paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout Andean uplift, and that conditions may have been more evaporative when the Andes were lower. Thus, more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central Andean plateau proxy materials likely overstate Miocene-to-present surface uplift. We propose Altiplano paleoelevations of 1–2 km at 24.5 Ma, 1.5–2.9 km by 11.45 Ma, and modern elevations by ∼6 Ma based on the lightest isotopic compositions observed in Altiplano proxy materials, which are least likely to be influenced by evaporation. These constraints limit total late-Miocene-to-modern uplift to

Steep U-shaped valleys produced by glaciation are commonly eroded by rockfall. In this study we investigate modern and long-term (power law predicted) rates of rock wall retreat in a deglaciated valley. Our emphasis is on the 5.2 km2 calcareous cliffs covering in the Lauterbrunnen Valley, Switzerland. Terrestrial laser scans were collected during nine field campaigns over 18 months to provide a continuous coverage of most of the valley walls. Results indicate a total of 122 rockfalls with volumes ranging between 0.06 ± 0.01 and 119.34 ± 1.07 m3. Different size groups of rockfall events were correlated with environmental factors (e.g., freeze-thaw cycles/temperature, precipitation, and seismicity) using a linear regression with variable lag times of 0–6 months. The highest correlation factor (r = 0.6, P = 0.08, 90% significance level) is observed for freeze-thaw cycles and rockfall events smaller than 1 m3 with a 2 month delay between temperature extremes and rockfall. Frequency-magnitude relationships for rockfall events were calculated to predict less frequent larger rockfall events that did not occur during the observation period. A Monte Carlo analysis was applied to the frequency-magnitude relationship to evaluate the sensitivity of results to their stochastic nature. An average power law exponent of 1.71 ± 0.09 was calculated using linear regression. The calculated exponents are similar to other studies in calcareous rock settings conducted over different observation durations. Finally, we determine an average total eroded volume of 2.0−0.01+0.6⋅103 m3/yr and a corresponding long-term (power law predicted) cliff retreat rate of 0.39−0.02±0.12mm/yr.

Advancements in thermochronology and numerical modeling offer the potential to associate the age of thermochronometric samples to both exhumational and deformational processes. However, understanding how these components are related in compressional systems requires linking the geometry and magnitude of fault slip to the distribution and amount of erosion. To address this, we apply a 2-D thermokinematic model to a forward modeled balanced cross section to quantify the cooling history in fold-thrust belt settings. The restored cross section provides a kinematic path of rocks and structures necessary to reproduce the surface geology. By assigning ages to displacement amounts, we produced a range of potential velocity vectors used to calculate heat transport, erosion, and rock cooling. We test the predicted ages against a suite of previously published thermochronometric data from the Bhutan Himalaya to explore the utility of the data to constrain the timing, rate, and geometry of fault motion as well as variations in the exhumation rate. We evaluate the cooling history associated with a constant rate of shortening of 18 mm/yr, rates that are 2.0, 1.5, 0.75, and 0.5 times the constant rate, and rates that vary with time to determine which kinematic history best matches the measured cooling ages. The combination of relatively old apatite fission track and zircon (U-Th)/He measured ages and younger (15–9 Ma) 40Ar/39Ar ages from white mica is best matched with faster rates (relative to constant rates) between 11.5 and 8 Ma and slower than constant rates from 17 to 11.5 Ma and 8 Ma to present.

The observed geomorphology and calculated thermal histories of the Bhutan Himalaya provide an excellent platform to test ideas regarding the influence of tectonics and climate on the evolution of a convergentmountain range. However, little consensus has been reached regarding the late Cenozoic history of the Bhutan Himalaya. Some researchers have argued that observed geologic relationships show slowing deformation rates, such that the range is decaying from a geomorphic perspective, while others see the range as growing and steepening. We suggest that a better understanding is possible through the integrated interpretation of geomorphic and thermochronometric data from the comparison of predictions from models of landscape evolution and thermal-kinematic models of orogenic systems. New thermochronometric data throughout Bhutan aremost consistent with a significant decrease in erosion rates, from2 to 3 km/Ma down to 0.1–0.3 km/Ma, around 6–4Ma. We interpret this pattern as a decrease in rock uplift rates due to the activation of contractional structures of the Shillong Plateau, an uplifted region approximately 100 km south of Bhutan. However, low-relief, fluvial landscapes throughout the Bhutanese hinterland record a late pulse of surface uplift likely due to a recent increase in rock uplift rates. Constraints from our youngest thermochronometers suggest that this increase in rock uplift and surface uplift occurred within the last 1.75Ma. These results imply that the dynamics of the Bhutan Himalaya and Shillong Plateau have been linked during the late Cenozoic, with structural elements of both regions active in variable ways and times over that interval.

Understanding the spatial distribution of glacial catchment erosion during glaciation has previously proven difficult due to limited access to the glacier bed. Recent advances in detrital thermochronology provide a new technique to quantify the source elevation of sediment. This approach utilizes the tendency of thermochronometer cooling ages to increase with elevation and provides a sediment tracer for the elevation of erosion. We apply this technique to the Tiedeman Glacier in the heavily glaciated Mount Waddington region, British Columbia. A total of 106 detrital apatite (U-Th)/He (AHe) and 100 apatite fission track (AFT) single-grain ages was presented from the modern outwash of the Tiedemann Glacier with catchment elevations between 530 and 3960 m. These data are combined with nine AHe and nine AFT bedrock ages collected from a ~2400 m vertical transect to test the hypotheses that erosion is uniformly or nonuniformly distributed in the catchment. A Monte Carlo sampling model and Kuiper statistical test are used to quantify the elevation range where outwash sediment is sourced. Model results from the AHe data suggest nearly uniform erosion in the catchment, with a preference for sediment being sourced from ~2900 to 2700 m elevation. Ages indicated that the largest source of sediment is near the present-day ELA. These results demonstrate the utility of AHe detrital thermochronology (and to a lesser degree AFT data) to quantify the distribution of erosion by individual geomorphic processes, as well as some of the limitations of the technique.

Understanding the patterns of rainfall isotopic composition in the central Andes is hindered by sparse observations. Despite limited observational data, stable isotope tracers have been commonly used to constrain modern-to-ancient Andean atmospheric processes, as well as to reconstruct paleoclimate and paleoaltimetry histories. Here, we present isotopic compositions of precipitation (δ18Op and δDp) from 11 micrometeorological stations located throughout the Bolivian Altiplano and along its eastern flank at ~21.5°S. We collected and isotopically analyzed 293 monthly bulk precipitation samples (August 2008 to April 2013). δ18Op values ranged from −28.0‰ to 9.6‰, with prominent seasonal cycles expressed at all stations. We observed a strong relationship between the δ18Op and elevation, though it varies widely in time and space. Constraints on air sourcing estimated from atmospheric back trajectory calculations indicate that continental-scale climate dynamics control the interannual variability in δ18Op, with upwind precipitation anomalies having the largest effect. The impact of precipitation anomalies in distant air source regions to the central Andes is in turn modulated by the Bolivian High. The importance of the Bolivian High is most clearly observed on the southern Bolivian Altiplano. However, monthly variability among Altiplano stations can exceed 10‰ in δ18Op on the plateau and cannot be explained by elevation or source variability, indicating a nontrivial role for local scale effects on short timescales. The strong influence of atmospheric circulation on central Andean δ18Op requires that paleoclimate and paleoaltimetry studies consider the role of South American atmospheric paleocirculation in their interpretation of stable isotopic values as proxies.