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The Himalaya is known for dramatically rugged landscapes including the highest mountains in the world. However, there is a limited understanding of the timing of attainment of high elevation and relief formation, especially in the Nepalese Himalaya. Anomalous high-elevation low-relief (HELR) surfaces, which exhibit geomorphic antiquity and are possibly remnants of formerly widespread high-elevation paleosurfaces, provide a unique opportunity to assess the attainment of regional high elevation in the Himalaya. The Bhumichula plateau is one such HELR surface (4300−4800 m) in the western Nepalese Himalayan fold-thrust belt. The Bhumichula plateau is situated in the Dadeldhura klippe (also called the Karnali klippe), an outlier of Greater Himalayan Sequence high-grade metasedimentary/igneous rocks surrounded by structurally underlying Lesser Himalayan Sequence low-grade metasedimentary rocks. We assess the origin of the Bhumichula plateau by combining regional geological relationships and zircon and apatite (U-Th-Sm)/He and apatite fission track thermochronologic ages. The HELR surface truncates pervasive west-southwestward dipping foliations, indicating that it post-dates tilting of rocks in the hanging wall of the Main Central thrust above the Lesser Himalayan duplex. This suggests that the surface originated at high elevation by erosional beveling of thickened, uplifted crust. Exhumation through the ∼180−60 °C thermal window occurred during middle Miocene for samples on the plateau and between middle and late Miocene for rocks along the Tila River, which bounds the north flank of the Bhumichula plateau. Cooling ages along the Tila River are consistent with erosional exhumation generated by early Miocene emplacement of the Main Central (Dadeldhura) thrust sheet, middle Miocene Ramgarh thrust emplacement, and late Miocene growth of the Lesser Himalayan duplex. The most recent middle-late Miocene exhumation took place as the Tila River and its northward flowing tributaries incised upstream, such that the Bhumichula plateau is a remnant of a more extensive HELR paleolandscape. Alpine glaciation lowered relief on the Bhumichula surface, and surface preservation may owe to its relatively durable lithology, gentle structural relief, and elevation range that is above the rainier Lesser Himalaya.

In this integrative, team-based capstone project, students in an upper year Tectonics course built a planet of their own design from the basic concepts of plate tectonics. They created a tectonic m...

Situated within the interior of the Central Anatolian Plateau (Turkey), the 200-km-long Tuzgölü extensional fault zone offers first-order constraints on the timing and pattern of regional deformation and uplift. In this study, we analyze the morphometrics of catchments along the Tuzgölü range-front fault and the parallel, basinward Hamzalı fault using a variety of measured morphometric indicators coupled with regional geomorphic observations and longitudinal profile analysis. In addition, we use field and remote mapping to constrain the geometry of two key marker beds, the Pliocene Kızılkaya ignimbrite and Kışladaǧ limestone, in order to investigate deformation in the footwall of the Tuzgölü fault zone. The marker beds form a broad arch along the footwall of the fault, with greatest cumulative displacement along the central part of the fault zone, suggesting early Pliocene extensional reactivation of the Tuzgölü fault with a typical fault-displacement profile. However, a change in deformation pattern is marked by transient knickpoints along river channels; morphometric indicators sensitive to shorter (1−3 Ma) time scales, including river steepness, basin elongation, and mountain front sinuosity, indicate an overall southeastward increase in footwall uplift rate of the Tuzgölü fault zone, which could reflect block rotation or interaction with the Hasan Dag volcano. Basin asymmetry and basin-fault azimuth measurements indicate north-northwest tilting of footwall catchments, which may be linked to regional tilting across the Central Anatolian Plateau interior. Varying patterns of spatial and temporal deformation along the length of the Tuzgölü fault zone are likely due to the interference of crustal- and lithospheric-scale processes, such as rotation of crustal blocks, extrusion of the Anatolian microplate, crustal heating, gravitational collapse associated with plateau uplift, and mantle-driven vertical displacements.

The most striking structural features in the interior of the Shan Plateau, southeast of the eastern Himalayan syntaxis, are a series of NE-trending faults that exhibit sinistral movement and an arcuate geometry. Their origin and tectonic evolution remain poorly understood. Furthermore, a switch in slip sense is recorded along many of these faults, but the timing of kinematic reversal is still unclear, hindering an understanding of the causal geodynamic mechanisms. We conducted an integrative study of apatite and zircon (U-Th)/He thermochronology, 40Ar/39Ar geochronology, and structural and geomorphic analysis to decipher the evolution of two major NE-trending faults: the Nantinghe and Dayingjiang faults. At least three deformation stages are identified within the Nantinghe fault zone, including top-to-the-SE/ESE thrusting, dextral ductile strike-slip shearing, and sinistral movement. Zircon and apatite (U-Th)/He data, collected from the northeastern terminus of the Nantinghe fault, reveal rapid cooling in the early Miocene. Combined with the 40Ar/39Ar data from sinistrally sheared mylonite, left-lateral movement on the Nantinghe fault is inferred to have initiated as early as ca. 20 Ma. The Dayingjiang fault reactivated as a sinistral brittle fault along the dextral Yingjiang shear zone. A two-stage thermal history is identified along the shear zone, with prominent cooling during dextral ductile shearing in the early- to mid-Miocene followed by a lower-magnitude cooling episode at ca. 11 Ma caused by sinistral transtension along the Dayingjiang fault. The evolution of the Nantinghe and Dayingjiang faults suggests that the NE-trending fault system in the Shan Plateau may have developed along preexisting structures and underwent diachronous slip-sense inversion in the late Cenozoic. The northward advance of the eastern Himalayan syntaxis caused a major change in both the regional stress field and fault geometries in the eastern India-Eurasia oblique convergence zone, contributing to the inversion of fault kinematics.

The Cona-Oiga rift (COR) is the easternmost member of a series of ∼N-S trending Cenozoic rifts in the southern Tibetan Plateau. The Yarlung River flows from west to east, across the COR and exhibits diverse river morphology along strike. We analyze tributary fluvial longitudinal profiles in the Yarlung drainage and the published strain rate field on both sides of the rift in order to gain knowledge about its development and crustal deformation patterns within the plateau interior. Tributaries on the western side of the rift have relatively low normalized steepness index (ksn). Concave curves in χ-elevation plots and cross-divide contrasts in χ, mean relief, and mean gradient, indicate ongoing river reorganization in this region. In contrast, high topographic relief and steep stream channels developed on the eastern side. In addition, spatial variations in negative dilatational strain rates indicate diverse crustal shortening and regional uplift across the COR. We suggest that the Cona-Oiga rift plays an important role in accommodating deformation associated with the continuing indentation of the eastern Himalayan syntaxis. Tectonic forcing might be the dominant factor controlling landscape evolution across the COR.

We present field and analytical results from the Tashkurgan and Waqia valleys in the southeastern Pamir that shed new light on the tectonic evolution and terrane architecture of the region. Field mapping of metasedimentary and igneous units along the Tashkurgan and Waqia valleys in the Southeast Pamir, integrated with metamorphic petrology, garnet-biotite thermometry, and zircon U/Pb isotopic analysis, help identify major structures and terrane boundaries in the region, as well as compare structural units across the Miocene Muztaghata gneiss dome. South of the Muztaghata dome, the gently northwest-plunging synformal Torbashi thrust klippe juxtaposes amphibolite facies Triassic Karakul-Mazar terrane schist and gneiss structurally above (1) greenschist facies Triassic Karakul-Mazar terrane metasedimentary rock in the north, and (2) lower-amphibolite facies schist in the south that are interpreted to be Gondwanan-derived crust (Central or South Pamir terrane). Farther south, the Rouluke thrust fault imbricates the Gondwanan crust, placing early Paleozoic schists over Permian marble and slate. Exposure of the Torbashi thrust sheet terminates in the southeast, and with it the surface exposure of the Triassic Karakul-Mazar terrane, leaving the Paleozoic Kunlun terrane juxtaposed directly against Gondwanan terrane crust. Based on lithologic and isotopic similarities of units north and south of the Muztaghata gneiss dome, we document the existence of a regionally extensive thrust nappe that stretched across the northern and eastern Pamir, prior to being cut by Miocene exhumation of the Muztaghata dome. The thrust nappe links the Torbashi thrust in the southeast Pamir with the Tanymas thrust in the northern Pamir, and documents regionally extensive exposure of lithologically continuous units across the northeast Pamir. While timing of emplacement of the Torbashi thrust klippe and displacement on the Rouluke fault to the south is not well constrained, we interpret shortening to be Cretaceous in age based on previously published cooling ages. However, a component of Cenozoic shortening cannot be ruled out. A key observation from our mapping results is that the surface exposures of the Karakul–Mazar–Songpan Ganzi terrane are not continuous between western Tibet and the Pamir, which indicates tectonic and/or erosional removal, likely sometime in the Mesozoic. Furthermore, our documentation of the Jinsha suture in the southeast Pamir on the eastern side of the Karakoram fault shows deflections of terranes across the Himalayan-Tibetan orogen were not primarily accommodated along discrete, large displacement faults (>400 km) faults. Instead, oroclinal bending of the northern Pamir, and dextral shear along the Pamir margins, may be largely responsible for the northward deflection of terranes.

Most of the permanent deformation in the Pampean Flat slab segment of the central Andes is taken up at the Andean Orogenic Front in Argentina, a narrow zone between the Eastern Precordillera and Sierras Pampeanas that comprises one of the world's most seismically active thrust zones. Active faults and folds in the region have been extensively mapped but still largely lack information on style and rates of deformation, which is essential for understanding the distribution of regional strain and estimating the seismic potential of individual faults. Structural, geomorphic, and 36Cl cosmogenic radionuclide surface exposure age methods are used to focus on key sites along the 30-km-long La Rinconada Fault Zone in this region of west-central Argentina, which is ~15 km away from the highly populated (~500,000) city of San Juan, to define a late Quaternary average shortening rate of 0.41 ± 0.01 mm/year. This slip rate is the same order of magnitude, but slightly lower than nearby similar east dipping Eastern Precordillera faults including the La Laja and Las Tapias Faults. Relatively low slip rates are interpreted as being a consequence of distributed deformation between the latitude of the La Rinconada Fault Zone (31 and 32°S), as compared to between latitudes 32 to 33°S where deformation appears to be focused on fewer structures, including the Las Peñas and La Cal Thrust Faults. The La Rinconada Fault Zone is capable of generating earthquakes of Mw 6.6–7.2, but further investigations are required to determine timing and recurrence intervals of discrete events. Fil: Rimando, Jeremy. University of Toronto; Canadá Fil: Schoenbohm, Lindsay. University of Toronto; Canadá Fil: Costa, Carlos Horacio. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina Fil: Owen, Lewis. University of Cincinnati; Estados Unidos Fil: Cesta, Jason M.. University of Cincinnati; Estados Unidos Fil: Richard, Andrés David. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina Fil: Gardini, Carlos Enrique. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina

Continental-scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the Ailaoshan-Red River shear zone (ASRRSZ) in the SE Tibetan Plateau. This study presents 13 apatite (U-Th)/He, 11 zircon (U-Th)/He, and three apatite fission track dates, together with thermal modeling in the Ailaoshan and Xuelongshan segments (ALSZ and XLSZ) of the shear zone to investigate its Cenozoic exhumation history and mechanism, which are critical for understanding its tectonic and landscape evolution. Our results, combined with published chronologic data, reveal that shear zone rocks along the ALSZ experienced prominent and rapid cooling from high temperature (>500°C) to 120–60°C at a rate of 75–100°C/Myr during 29–17 Ma with northwestward younging onset. A second, lower magnitude accelerated cooling occurred at 14–10 Ma along the ALSZ at a rate of 20–30°C/Myr, with a later initiation on the XLSZ at ~5 Ma and continuing to present with a cooling rate of ~20°C/Myr. Thermal modeling reveals a single rapid cooling phase with a rate of 17–14°C/Myr in the Eocene to early Oligocene for samples outside the shear zones. These three fast cooling episodes are directly related to deformation stages including crustal shortening across the SE plateau, sinistral ductile shearing along the ASRRSZ, and dextral faulting with a dip-slip component on the Red River and Weixi-Qiaohou faults along the shear zone flanks. Furthermore, the northward migration of kinematic reversal and associated cooling along strike since the mid-late Miocene likely reflects the northward advance of the eastern Himalayan syntaxis.

Wind erosion is integral to the evolution of arid landscapes on Earth and Mars, but the nature of long-term wind erosion of bedrock is poorly understood. Here we describe the Salina del Fraile (SdF...

Three continent-scale shear zones are arguably the most outstanding structural features in the southeastern Tibetan Plateau, and therefore, their tectonic and landscape evolution have significant implications for understanding the history and mechanisms of intracontinental mountain building and plateau growth. This study presents low-temperature thermochronology from the Gaoligong and Chongshan shear zones (GLSZ and CSSZ) and quantitative analyses of fluvial longitudinal profiles of tributaries in the Salween drainage, which lies between the shear zones. Apatite and zircon (U-Th)/He data reveal a two-stage exhumation history for both shear zones: rapid and prominent cooling in the middle Miocene followed by a second, lower magnitude cooling event in the late Miocene to early Pliocene. Ductile transpressional shearing is inferred to have caused the first cooling, continuing until ~11 Ma. The northward migration of the tectonic events along the Mogok metamorphic belt and GLSZ and synchronous dextral displacement along the Jiali fault indicate the dominant role of the north advancing eastern Himalayan syntaxis on the surrounding structures. Increased river incision is identified in the middle Salween drainage, leading to two-segment river profiles and further exhumation along the GLSZ and CSSZ. The tributary transient response could result from temporal changes in uplift or adjustments of the trunk channel to climatic change. Furthermore, glaciers play an important role in shaping the landscape of the upper reaches of catchments in the northern segment of the shear zones. Different drivers for the two exhumation events may reflect distinct stages of plateau growth characterized by different crustal deformation patterns.

Quaternary valley fills and landforms in the Waqia valley of the Chinese Pamir were examined using geomorphic mapping, geomorphic and sedimentological analysis of landforms and sediments, and cosmogenic 10Be surface exposure dating. Six sets of moraines (M-1 to M-6) are identified and date to the penultimate or an older glacial cycle (M-1), penultimate glacial cycle (M-2), early last glacial and probably Marine Oxygen Isotope Stage (MIS) 4 (M-3), MIS 2 (M-4), Late Glacial (M-5), and early Holocene (M-6). Younger moraines are also present, but these were not examined in detail. Alluvial fans and outwash/river terraces are present throughout the valley. Four surfaces on alluvial fans and river terraces were dated to ~ 580 ka (T-1), ~ 120 ka (T-2), ~ 100 ka (T-3), and ~ 70 ka (T-4). Large landslide and lacustrine deposits are common within the valley fills and represent periods of major slope instability and possible damming of drainages. Glacial processes dominate the western side of the valley; landsliding is the leading process on its eastern side. Defining the nature and timing of landform formation in this valley highlights the punctuated nature of landform evolution in the Himalaya and Tibet and provides a framework for considering the abundant valley fill successions elsewhere in the orogen.

Unraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles, 10Be‐derived catchment mean modern and paleo‐erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquí River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base‐level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo‐erosion rates, ranging from 56 +43/‐19 to 105 +60/‐33 mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic 10Be. However, punctuated abandonment of pediment and strath terraces at 43.6 +15.0/‐11.6, 91.2 +54.2/‐22.2, and 151 +92.7/‐34.1 ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long‐term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional‐scale studies which find precipitation to exert the dominant control.

Forebergs are landforms characterized by low, elongated ridges or hills rising above the surrounding alluvial fans or floodplains, and are typically formed by folding associated with thrust faulting. Forebergs in the Gobi-Altay range, south-central Mongolia, have developed in the forelands of mountains transpressionally uplifted in restraining bends along the E–W-trending sinistral strike-slip Bogd fault. Along the easternmost part of the Bogd fault, six forebergs have formed in the foreland of the Artz Bogd restraining-bend. We surveyed one of these forebergs to ascertain the fault geometry associated with its formation and understand how it has developed over time. This foreberg is ~6 km long and ~1 km wide and rises about 40 m above the low-lying floodplain. We also constrained its evolution using cosmogenic 10Be denudation rates measured from individual catchments along the foreberg, and morphometric analyses using a high-resolution DEM generated from images captured by an unmanned aerial vehicle. We suggest that the foreberg evolved via fault-propagation folding, developing an asymmetric across-foreberg topographic profile. This asymmetry results in differences in 10Be catchment-wide denudation rates and geomorphic metrics between its northern and southern slopes, causing migration of the drainage divide of the growing foreberg to adjust to the tectonic regime. By analyzing the along-foreberg variation in denudation rates and geomorphic metrics, we infer that the foreberg formed via lateral growth and linking of four discrete segments. Our study illuminates the formation of a unique landform and sheds light on how a structure enlarges both vertically and laterally during the early stage of thrust-related fold developments.

We present a multidisciplinary study that constrains the development history of the southern part of the Central Andean Plateau, a prototypical noncollisional orogenic system. In the Antofagasta de la Sierra region of NW Argentina, data from sedimentary geology, sandstone modal composition, detrital zircon U-Pb geochronology, and apatite fission-track and (U-Th-Sm)/He thermochronology indicate that sediments accumulated in the late Eocene to early Oligocene, with a maximum depositional age of ca. 39–38 Ma provided by the youngest detrital zircon U-Pb dates. Provenance data, including paleocurrent indicators, sandstone modal composition, and detrital zircon U-Pb ages, point to prevailing western sources, including the Sierra de Quebrada Honda (a proximal source), the Ordovician to Late Cambrian Famatinian magmatic arc in western Argentina and Chile (a distal source), and the Permian–Triassic plutonic and volcanic rocks in coastal Chile (a distal source). Along the western basin margin, these strata were deformed by a basement-involved thrust fault that was active at ca. 25–20 Ma, as constrained by apatite fission-track and (U-Th-Sm)/He data. Analysis of new and existing U-Pb geochronologic data from both detrital and basement samples across the Puna suggests that the Sierra Laguna Blanca, a major mountain range in the southern Puna, remained buried during the late Eocene to early Oligocene. Our multidisciplinary data indicate that the southern Central Andean Plateau may have hosted a regional basin primarily formed by lithospheric flexure during the late Eocene to early Oligocene. Furthermore, this study refines the history of basin compartmentalization and exhumation of the major mountain ranges in the southern Puna, revealing propagation of deformation from the west to east, starting as early as the late Eocene and continuing to the mid-late Miocene.

The Puna Plateau, adjacent Eastern Cordillera and the Sierras Pampeanas of the central Andes are largely characterized by thick-skinned, basement-involved deformation. The Puna Plateau hosts ∼N–S trending bedrock ranges bounded by deep-seated reverse faults and sedimentary basins. We contribute to the understanding of thick-skinned dynamics in the Puna Plateau by constraining regional kinematics of the poorly understood southern Puna Plateau through a multidisciplinary approach. On the southeastern plateau, sandstone modal composition and detrital zircon U–Pb and apatite fission-track data from Cenozoic strata indicate basin accumulation during the late Eocene to early Oligocene (∼38–28 Ma). Provenance analysis reveals the existence of a regional-scale basin covering the southern Puna Plateau during late Eocene to early Oligocene time (∼38–28 Ma) that was sourced from both the western plateau and the eastern plateau margin and had a depocenter located to the west. Petrographic and detrital zircon U–Pb data reveal erosion of proximal western and eastern sources after ∼12 Ma, in mid-late Miocene time. This indicates that the regional basin was compartmentalized into small-scale depocenters by the growth of basement-cored ranges continuing into the late Miocene (∼12–8 Ma). We suggest that the Cenozoic history of the southern Puna Plateau records the formation of a regional basin that was possibly driven by lithospheric flexure during the late Eocene to early Oligocene, before the growth of distributed basement-cored ranges starting as early as the late Oligocene.

The landscape of Western Nepal has been dramatically shaped by tectonics and by both glacial and fluvial erosion. Here we investigate the modern geomorphic and glacial features of the Dolpo basin in northern mid-western Nepal. We analyze attributes such as glacier size, slope, aspect and toe, head and peak elevation for 446 glaciers within and around the basin, determining their relationship with basin features such as lithology, slope and precipitation. Glaciers reflect lithology and precipitation, but glacier size is strongly correlated with base-level and slope. Our data suggest that low-slope glaciers with high base-level, i.e., those that flow onto the Tibetan plateau, are forced to grow large because they exist at or above the equilibrium-line altitude. Glaciers within the basin, particularly in the western part, can become dismembered on steep slopes, an effect only partly offset by precipitation. The spatial variability in regional slope and presence of a wind gap along the northern basin border suggest recent capture of the Dolpo basin. A plateau-like morphology would have thus once extended at least 45 km southward. The southward opening of the basin allowed precipitation to enter, forming glaciers along the western end of the northern basin border. Larger glaciers (resulting from high base-level) pushed the ridge southward over time through headward erosion. Our study suggests dramatic landscape reorganization in western Nepal, consistent with other recent studies suggesting a more extensive proto-Tibet.

The Pampean flat slab segment of the Central Andes in Argentina is a broad, active deformation zone subject to both plate boundary-related and intraplate deformation. To the west, plate boundary-related deformation is dominated by thin-skinned fold-and-thrusts of the Precordillera, while to the east, intraplate deformation involves thick-skinned reverse faults of the Sierras Pampeanas. GPS data and absolute dating of displaced geomorphic features suggest that most of the active permanent deformation occurs between these two regions at the Andean orogenic front and that there is a west-to-east trend of decreasing shortening rates. However, GPS stations and sites with geomorphic slip rate measurements are currently too sparse and cover too short a time period to make reliable inferences about the longer-term distribution and relative rates of deformation. Mountain range-scale geomorphic indices, on the other hand, reflect tectonic activity since at least the Pleistocene. In this study, we measured geomorphic indices (hypsometric integral and curves, basin elongation ratio, basin volume-to-area-ratio, valley floor width-to-height ratio, mountain front sinuosity, and normalized steepness indices of rivers) from 10 different N-S striking, range-bounding faults that span both the Precordillera and Sierras Pampeanas regions from west to east. We use these data to assess the regional relative tectonic activity of major Quaternary deformation features in the Pampean segment of the Central Andes. Even when variations in climate and geology are considered, mean values for each geomorphic index suggests uplift rates for the 10 mountain-range bounding faults display local trends that are closely associated with the structural style and tectonic evolution of these structures. Although vertical uplift rates vary little, horizontal shortening rates are higher for the Precordillera fold-and-thrusts in the west than the thick-skinned reverse faults of the Sierras Pampeanas in the east, due to shallower fault dips for Precordilleran structures. The similarity with decadal slip rate gradients from GPS studies could possibly indicate that the stress-field has been constant since at least the Pleistocene, but further slip rate studies over broader time intervals in the late Quaternary are necessary to confirm this. Variations observed in relative uplift rates along each fault point to sites that warrant further detailed study of slip rates and evaluation of associated seismic hazards.

As the kinematics of active faults that bound the Anatolian plate are well studied, it is now essential to improve our understanding of the style and rates of intraplate deformation to constrain regional strain partitioning and improve seismic risk assessments. One of these internal structures, the Central Anatolian fault zone (CAFZ), was originally defined as a regionally significant left-lateral “tectonic escape” structure, stretching for 700 km in a NE direction across the Anatolian plate. We provide new structural, geomorphic, and geochronologic data for several key segments within the central part of the CAFZ that suggest that the sinistral motion has been overstated. The Ecemis fault, the southernmost part of the CAFZ, has a late-Quaternary minimum slip rate of 1.1 ± 0.4 mm a−1, slower than originally proposed. Farther north, the Erciyes fault has fed a linear array of monogenetic vents of the Erciyes stratovolcano and 40Ar/39Ar dating shows a syneruptive stress field of ESE-WNW extension from 580 ± 130 ka to 210 ± 180 ka. In the Erciyes basin, and central part of the CAFZ, we mapped and recharacterized the Erkilet and Gesi faults as predominantly extensional. These long-term geological rates support recent GPS observations that reveal ESE-WNW extension, which we propose as the driver of faulting since 2.73 ± 0.08 Ma. The slip rates and kinematics derived in this study are not typical of an “escape tectonic” structure. The CAFZ is a transtensional fault system that reactivates paleotectonic structures and accommodates E-W extension associated with the westward movement of Anatolia.

The origin and evolution of the central Andes, a noncollisional orogenic system, have been hypothesized to evolve as a result of several dynamic processes, including formation of an eastward-propagating orogenic wedge, segmentation into rhomb-shaped basins as a result of N-S gradients in crustal shortening, reactivation of inherited deep structures, and lithospheric foundering. How these proposed processes dominate the orogen spatially and temporally is uncertain; however, constraining the timing of upper-crustal deformation is critical for investigating these models. We document the formation and deformation of the Pasto Ventura basin (NW Argentina) in the southern Puna Plateau. Through field mapping, deformation analysis, secondary ion mass spectrometry U-Pb dating of zircon from interbedded volcanic ashes, and Ar/Ar geochronology of volcanics, we show that major basin formation started ca. 11.7-10.5 Ma and continued until at least ca. 7.8 Ma. The basin underwent syndepositional faulting and folding from ca. 10 to 8 Ma. Contractional deformation in the Pasto Ventura basin ended between ca. 7.3 and 4 Ma, based on the onset of regional horizontal extension. Data from the Pasto Ventura region allow us to bridge existing data and complete a regional compilation of upper-crustal deformation for the Puna Plateau. Our analysis shows that late Miocene formation and deformation of the Pasto Ventura basin represent an important out-of-sequence contractional event in the southern Puna Plateau. While a number of geodynamic processes likely shape the evolution of the southern Puna, multidisciplinary data sets, including deformation in the Pasto Ventura basin studied here, highlight the role of the formation and detachment of a late Miocene lithospheric drip in causing the upper-crustal deformation on the southern Puna Plateau since the mid-late Miocene.

Models that treat long-term evolution of the Tibetan orogen in terms of interactions between rigid blocks require the right-slip Karakoram fault that bounds the western margin of the Tibetan plateau to be a long-lived, stable, high slip-rate feature. While the southern portion of the fault clearly remains active, recent work has proposed that the northern half of the Karakoram fault is currently inactive. New field observations and geochronologic results from the northern end of the Karakoram fault system confirm this interpretation and provide the first quantitative data on the minimum age for the termination of slip. In the southeast Pamir, gravel that yields a U-series age of 198 ± 5 ka on secondary carbonate caps a non-deformed strath terrace that extends across the main strand of the Karakoram fault. The secondary Achiehkopai fault strand is overlain by undisturbed Hangdi glacial stage ( 24 ± 6 ka ) deposits and Dabudar glacial stage (penultimate glacial cycle, ∼ 150 ka , or older) deposits, which lack observable lateral displacement or deformation. Together, these observations show that the northern portion of the Karakoram fault system has not accommodated any detectable strike-slip deformation since at least 24 ± 6 ka , and most likely since ∼ 200 ka or more. These results show that the Karakoram fault system no longer forms a continuous discrete kinematic boundary at the western margin of the Tibetan Plateau. This suggests that even long ( > 500 km ) strike-slip faults within orogenic belts are inherently unstable features, consistent with models of continental collision zones involving relatively weak crust and distributed deformation.

This study contributes to the uplift history of the Andes, which has received increasing attention in recent years because of its implications for geodynamic models and climate feedbacks. Shortening resulting in crustal thickening and removal of gravitationally unstable mantle lithosphere has been proposed to control deformation and uplift of Cordillera-type orogenic systems such as the Puna Plateau of the central Andes and its eastern margin, the Eastern Cordillera. We present new clumped isotope (Δ47), δ18O, and δ2Η data from carbonate nodules, marlstone, spring deposits, and volcanic ashes from the Puna Plateau and Eastern Cordillera of NW Argentina. When combined with other geological evidence, our data indicate that the Puna Plateau was near its present elevation since at least ~10 Ma, whereas the Eastern Cordillera rose ~1.5 km between ~14 and ~7 Ma. This history of uplift correlates with active shortening in the Eastern Cordillera and with incorporation of a regional foreland into the propagating orogenic wedge. Our study suggests that the elevation of the Puna Plateau changed little during the Miocene-Pliocene, whereas the margin experienced significant uplift associated with active deformation and crustal thickening.

Uplift of the Central Andes is largely thought to have occurred during the past 10 m.y. based on paleoaltimetry studies from the Altiplano of Bolivia. However, the spatio-temporal uplift history may not be uniform across the Central Andes. We present new stable isotopic results from the Salar de Antofalla, Salina del Fraile, and Arizaro Basin on the Puna Plateau (24°–26°S) of northwestern Argentina. Samples of volcanic glass give δD paleowater values and modeled paleoelevations that indicate an elevated (∼4 km) Puna Plateau since ca. 36 Ma with limited (

Differential exhumation in the Puna Plateau and Eastern Cordillera of NW Argentina is controlled by inherited paleostructures and resulting paleotopography related to the Cretaceous Salta Rift paleomargins. The Ceno zoic deformation front related to the development of the Andean retro-arc orogenic system is generally associated with >4 km of exhumation, which is recorded by Cenozoic apatite fi ssion-track (AFT) and (U-Th-[Sm])/He ages (He ages) in the Eastern Cordillera of NW Argentina. New AFT ages from the top of the Nevado de Cachi document Oligocene (ca. 28 Ma) cooling, which, combined with existing data, indicates exhumation of this range between ca. 28 Ma and ca. 14 Ma. However, some of the highest ranges in the Eastern Cordillera preserve Cretaceous ages indicative of limited Cenozoic exhumation. Samples collected from an similar to 3-km-elevation transect along the northern part of the Sierra de Quilmes paleorift fl ank (Laguna Brava) show AFT ages between ca. 80 and ca. 50 Ma and He ages between ca. 45 and ca. 10 Ma. Another set of samples from an similar to 1-km-elevation transect farther to the southwest (La Quebrada) shows Cretaceous AFT ages between ca. 116 Ma and ca. 76 Ma, and mainly Cretaceous He ages, in agreement with AFT data. Analysis of existing AFT and He ages from the area once occupied by the Salta Rift reveals a pattern characterized by Cretaceous ages along paleorift highs and Cenozoic ages within paleorift hanging-wall basins and later foreland basin depocenters. This pattern is interrupted by the Sierras Pampeanas at similar to 28 degrees S, which record mid-Cenozoic ages. Our data are consistent with a complex inherited pattern of pre-Andean paleostructures, likely associated with paleotopography, which was beveled by the Cenozoic regional foreland basin and reactivated during the late Neogene (ca.

Convective removal of continental lithospheric roots has been postulated to be the primary mechanism of recycling lithospheric mass into the asthenosphere under large plateaux such as the Altiplano-Puna in the central Andes. Convective instabilities are especially likely to develop where there is extensive intermediate arc-like magmatism in the upper plate, as the residual masses complementing these magmatic products are typically denser than the underlying mantle. Mafic volcanic rocks erupted on the central Andean Altiplano-Puna plateau during the past 25 m.y. contain evidence of this process. Here we use equilibration temperatures, age data, and geochemical constraints—primarily based on transition metals—to show that the most important source materials by mass for this mantle-derived magmatism are pyroxenites from the lower parts of the lithosphere, with only minor contributions from mantle peridotite. Pyroxenites are denser than typical upper mantle whether they are garnet bearing or not, and are therefore likely to contribute to destabilizing parts of the continental lithosphere. The pattern of melting is consistent with the process of foundering/dripping of small-scale (

[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.

[1] Recent normal and strike-slip faulting on the Puna Plateau of NW Argentina has been linked to lithospheric foundering, gravitational spreading, plate boundary forces and a decrease in crustal shortening from north to south. However, the timing, kinematics and rate of extension remain poorly constrained. We focus on the Pasto Ventura region (NW Argentina) located on the southern Puna Plateau and recent deformation (

International audience; The tectonic and topographic history of the Himalaya-Tibet orogenic system remains controversial, with several competing models that predict different exhumation histories. Here, we present new low-temperature thermochronological data from the Mount Everest region, which, combined with thermal-kinematic landscape evolution modeling, indicate asymmetric exhumation of Mount Everest consistent with a scenario in which the southern edge of the Tibetan Plateau was located >100 km farther south during the mid-Miocene. Northward plateau retreat was caused by erosional incision during the Pliocene. Our results suggest that the South Tibetan Detachment was a localized structure and that no coupling between precipitation and erosion is required for Miocene exhumation of Greater Himalayan Sequence rocks on Mount Everest.

The Quaternary glacial history of Tashkurgan valley, in the transition between the Pamir and Karakoram, in Xinjiang Province, China was examined using remote sensing, field mapping, geomorphic analysis of landforms and sediments, and 10Be terrestrial cosmogenic nuclide dating. Moraines were assigned to four glacial stages: 1) the Dabudaer glacial stage that dates to the penultimate glacial cycle and/or earlier, and may represent one or more glaciations; 2) the Tashkurgan glacial stage that dates to early last glacial, most likely Marine Oxygen Isotope Stage (MIS) 4; 3) the Hangdi glacial stage that dates to MIS 2, possibly early MIS 2; and 4) the Kuzigun glacial stage that dates to the MIS 2, possibly the global Last Glacial Maximum, and is younger than the Hangdi glacial stage. Younger moraines and rock glaciers are present at the heads of tributary valleys; but these were inaccessible because they are located close to politically sensitive borders with Pakistan, Afghanistan and Tajikistan. Glaciers during the Dabudaer glacial stage advanced into the central part of the Tashkurgan valley. During the Tashkurgan glacial stages, glaciers advanced several kilometers beyond the mouths of the tributary valleys into the Tashkurgan valley. Glaciers during the Hangdi and Kuzigun glacial stages advanced just beyond the mouths of the tributary valleys. Glaciation in this part of the Himalayan–Tibetan orogen is likely strongly controlled by northern hemisphere climate oscillations, although a monsoonal influence on glaciation cannot be ruled out entirely.

The Pamir salient is the western expression of mountain growth related to Indo-Eurasian convergence. Though a rough framework has emerged describing the tectonic evolution of the Pamir, detailed knowledge of the spatial and temporal evolution of Cenozoic deformation is necessary to determine how strain progressed through the orogenic belt. Here we present new stratigraphic, zircon provenance, and stable isotope data from Jurassic to Miocene strata along the Pamir’s northeastern margin near the town of Oytag (Wuyitake) in the Tarim Basin (west China). Prominent ∼40 Ma peaks in Oligocene to early Miocene detrital zircon grains record the erosion of an Eocene belt of shoshonitic rocks in the central to southeastern Pamir. This is roughly coincident with an ∼4‰ shift in the oxygen isotopic composition (δ18O) of carbonates during the Eocene and/or Oligocene (from an average of −8.7‰ to −12.6‰), suggesting a reorganization of atmospheric circulation during that time. This could have been caused by uplift of Tarim Basin-bounding ranges and/or retreat of the Paratethys Sea. A subsequent change from Eocene to Jurassic aged detrital zircon grains in the early to middle Miocene indicates provenance shifted from source rocks in the central and/or SE Pamir to the hanging wall of the Main Pamir Thrust (MPT), coincident with prograding facies at that time. This suggests deformation progressed outward toward the northeast margin of the Pamir plateau in the early to middle Miocene. Our results corroborate outward advancement of Himalayan deformation, affecting all margins of the Tarim Basin by the middle Miocene.

This study evaluates the effect of climate on facies, grain size, and sedimentation rates using sedimentology, geochronology, and stable isotope geochemistry for Miocene–Pliocene deposits in the Angastaco basin (Eastern Cordillera, northwest Argentina). U-Pb zircon data from ash layers constrain the transition between the finer grained fluvial-lacustrine Palo Pintado Formation and the coarser grained fluvial-alluvial San Felipe Formation to ca. 5.2 Ma and the first deposition of sediment derived from the present-day orographic barrier to ca. 4 Ma. δ 13 C values from pedogenic carbonate nodules range from −15.4‰ to −10.2‰ for the Palo Pintado Formation and from −9.5‰ to −8.2‰ for the San Felipe Formation; this can be best explained by increased, sustained aridity since ca. 5 Ma. The δ 18 O values range from −9.6‰ to −5.9‰ for the Palo Pintado Formation and from −6.1‰ to −5.2‰ for the San Felipe Formation, corroborating this interpretation. The shift toward more arid conditions correlates with a significant increase in grain size but no significant change in sedimentation rate. Because aridity precedes the development of an orographic effect, we interpret the grain size increase in the Angastaco basin since ca. 5 Ma to be a response of the sedimentary system to aridification resulting from regional climate change.

Lithospheric foundering has drawn increasing attention as an important contributor to continental plateau formation, especially as a driver for increased elevation, extension, and mafic magmatism. This contribution focuses on the mafic magmatism that led to the creation of monogenetic volcanoes throughout the Puna Plateau of NW Argentina. Lavas from these volcanoes provide a means to evaluate the recent petrotectonic development of the plateau and, in combination with basement intrusive rocks, determine the isotopic composition and long-term evolution of the lithosphere beneath the central Andean back-arc domain. Mafic samples have trace-element concentrations and isotopic values typical of an enriched magma source region. We propose that the mafic magmas originated from an aged, metasomatized subcontinental lithospheric mantle. The lavas have isotopic values nearly identical to those of Early Ordovician Famatinian gabbro and granodiorite. We suggest the most primitive Puna lavas and Famatinian magmas originated from the same subcontinental lithospheric mantle. This implies that at least a thin portion of the subcontinental lithospheric mantle has remained intact beneath NW Argentina for the past ~485 Ma. A comparison to coastal Jurassic igneous rocks and mantle xenoliths from the nearby Salta rift system suggests that the sub-continental lithospheric mantle is chemically decoupled from the depleted mantle to the west and east. This has been the case for hundreds of millions of years despite long-term tectonomagmatic activity along the proto-Andean and Andean margin and within the continental interior. Our data almost certainly rule out large delaminating bodies, suggesting instead partial or piecemeal removal of the lithosphere beneath the Puna Plateau.

ARTICLE I NFO Muztag Ata and Kongur Shan massifs represent a significant area of anomalously high topography at the northwestern end of the Tibetan Plateau, rising to N7500 m above sea-level (asl) from the plateau that has an average elevation of ~3500 m asl. These massifs provide an excellent opportunity to test geomorphic concepts, such as the glacial buzz-saw model. Using remote sensing, digital elevation modeling, field mapping and terrestrial cosmogenic nuclide (TCN) methods, the massifs were examined to determine the relative importance of tectonics and geomorphic processes in shaping the regional landscape and to provide a framework for testing geomorphic models. The gneiss domes that underlie the peaks are the result of exhumation along the Kongur detachment fault that has unroofed the massifs at a rate of between 4-6 km/ Ma over the last few million years. This has resulted in rapid uplift and active seismicity, which is exemplified by the numerous fresh fault scarps throughout the region and large historic earthquakes. The geomorphic system is dominated by glaciation and the region contains extensive successions of moraines and paraglacial landforms, including fans, terraces and landslides. Glaciers have oscillated considerably throughout the latter part of the Quaternary, and three major glacier stages are recognized (Karasu (oldest), Olimde and Subaxh (youngest) glacial stage) that include at least 10 smaller glacial advance. The style of glaciation has changed over time from expanded ice caps to piedmont glaciers to valley and cirque glaciers. This possibly reflects a change in climate and/or topographic constraints as the massifs grew and became incised. The topography and glaciers in the region vary across the massifs divided by a broadly N-S trending high ridge and watershed. The western portion, situated upwind (the stoss slopes) of the mid-latitude westerlies, that bring moisture to the region, has gentle high topography and small valley glaciers. In contrast, on the eastern leeward slopes, gradients are higher and long debris-covered valley glaciers are present. The hypsometry of the region indicate two peaks in the distribution frequency of elevation (3600-4100 m and 4400-4800 m asl). These two elevation zones are consistent in space with the former equilibrium-line altitudes during the Olimde and Subaxh glacial stages and suggest that glacial erosion (most effective at the ELA) has helped control topography. This observation supports the glacial buzz-saw hypothesis, which argues that glaciers determine hypsometry by means of rapid surface erosion. Based on TCN methods, basin-wide rates of erosion range from ~0.1 to 1.4 km/Ma and are five to ten times lower than the unroofing rate of both massifs. The discrepancy over different time scales suggests that initial unroofing was produced by abrupt tectonic uplift and that the unroofing of the massifs has continued at a slower pace during the Late Quaternary.

The thick-skinned Sierras Pampeanas morphotectonic domain of western and northwestern Argentina (27°S–33°S) is characterized by reverse-fault–bounded basement blocks that delimit internally deformed, Neogene sedimentary basins. Foreland-basin evolution in this part of the Andes is still not very well understood. For example, challenging questions exist as to how thick-skinned deformation develops, if there are distinct spatiotemporal trends in deformation and exhumation, how such deformation styles influence sedimentation patterns, and whether or not broken foreland basins are related to regional plate-tectonic processes, such as flat-slab subduction. The Fiambala basin of the northwestern Sierras Pampeanas is the largest of several intermontane basins in the transition to the southern margin of the Puna Plateau. This basin preserves a thick continental Neogene sequence that provides information on the dynamics of thick-skinned deformation and resulting sedimentation. The Fiambala basin contains ~4 km of fluvial-alluvial sedimentary rocks that comprise the Tamberia, Guanchin, and Punaschotter Formations. U-Pb geochronology of ashes intercalated within the Fiambala stratigraphic sequence demonstrates that these sedimentary rocks are late Miocene to Pliocene (8.2 ± 0.3 Ma to 3.05 ± 0.4 Ma) in age. Sedimentology and provenance data indicate that the source of the Tamberia Formation was located to the west of the modern western basin-bounding range. The Guanchin and Punaschotter Formations record input from local sources, including the modern basin-bounding range to the west and the southern Puna Plateau to the north, suggesting reorganization of the catchment area at ca. 5.5 Ma. The coarsening-upward trends recorded by the fluvial Tamberia and Guanchin Formations indicate enhanced tectonics and relief during sedimentation. The Punaschot-ter conglomerates record alluvial-fan sedimentation and local sources. Fault kinematic data document a contractional regime, characterized by E-W and NE-SW shortening, active throughout the middle-late Miocene and Pliocene. Furthermore, a comparison between the Fiambala basin and similar sedimentary basins in the Sierras Pampeanas (e.g., Bermejo foreland basin) and the Eastern Cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland-basin system (thin-skinned) for much of its early history. Our data suggest coeval intrabasin deformation along strike from the Bermejo region northward to the Eastern Cordillera. The coeval change at ca. 6 Ma from a regional to more compartmentalized (thick-skinned) tectono-sedimentary environment in the regions adjacent to the Eastern Cordillera, the southern Puna margin, and other sectors within the Sierras Pampeanas domain may thus reflect a regional tectonic process related to flat subduction. Our data, combined with existing sedimentological and petrological evidence, imply that the passage from steep to flat subduction occurred synchronously from ~30°S to ~26°S.