Uplift Mechanism Research Articles

Test and analysis on a novel self-restoring uplift column

A novel self-restoring uplift column was proposed to allow uplift of exterior column bases of core-outrigger structures, which may make upper structure rock and hence mitigate seismic damage. The self-restoring uplift column consists of two steel sub-columns, a steel shear panel and several post-tensioned strands. Besides uplift mechanism, energy dissipating and self-restoring mechanisms were involved to dissipate energy and reduce structural residual drift, respectively. Low cycle test of four one-seventh scaled specimens were conducted and then simulated by finite element analysis. Self-restoring capability and satisfactory energy dissipating ability were observed in experimental results. The calibrated finite element models were then used to explore key design issues of the self-restoring uplift column. It was indicated that the elastic state of post-tensioned strands and sufficient restoring force were the two main factors influencing the restoring behavior most. A simplified model for axial behavior of the self-restoring uplift column was developed to simplify the design of the self-restoring uplift column. Finally, key design requirements about gap opening, shear panel, and self-centering capability were discussed.

Geomorphic origin of Merritt Island-Cape Canaveral, Florida, USA: A paleodelta of the reversed St. Johns River?

The Merritt Island-Cape Canaveral (MICCSC) sedimentary complex consists of a series of adjacent, non-conformable, beach ridge sets that suggest a multi-phase constructional history, but the feature's geomorphic and sedimentary origins are not well-understood. In spite of its notable sedimentary volume (surface area = 1200 km2), the MICCSC lacks a clear sediment source, or supply mechanism, to explain its presence today. Previously published U/Th, radiocarbon and OSL dates indicate that beach ridge deposition was active during MIS 5 (130–80 ka) on Merritt Island, but has occurred over a shorter, younger time interval on Cape Canaveral proper (6 ka to present). In this paper, it is proposed that the MICCSC is an abandoned paleodelta whose fluvial source provided a sediment supply sufficient for coastal progradation. Although the MICCSC, today, does not receive an appreciable sediment supply, the nearly 23,000 km2 drainage basin of the St. Johns River may well have provided such a sediment supply during MIS 5 times. This low-gradient fluvial system currently empties to the Atlantic Ocean some 200 km north of the MICCSC (near Jacksonville, Florida) but may have flowed southward during the time of MICCSC sedimentary construction, then experienced flow reversal since MIS 5 times. Three possible uplift mechanisms are proposed to explain the northward down-tilting that may have reversed the flow direction of the St. Johns, abandoning deltaic construction of the MICCSC: (1) karst-driven, flexural isostatic uplift in response to carbonate rock dissolution in central Florida, (2) glacio-hydro-isostatic tilting/back-tilting cycles during loading and unloading of the Laurentide ice sheet during the Pleistocene, and (3) mantle convection-driven dynamic topography operating within southeastern North America since the Pliocene. This example testifies to the sensitivity of low-gradient, low-relief landscapes to various sources of uplift, be they isostatic or otherwise.

Postseismic deformation associated with the 2015 Mw 7.8 Gorkha earthquake, Nepal: Investigating ongoing afterslip and constraining crustal rheology

The 2015 Mw 7.8 Gorkha earthquake has not only imposed effective constraints on the geometrical structures, friction behaviours and seismogenic patterns of the Nepal Himalaya thrustsystems but has also provided valuable insights into the uplift mechanism and lithosphere rheology of the Tibetan Plateau. Here, ∼1.6-year GPS observations are used to reveal the postseismic deformation characteristics following the Gorkha earthquake, investigate the ongoing aseismic afterslip on the Main Himalayan Thrust (MHT) fault and constrain the crustal rheology of the Southern Tibetan Plateau. First, afterslip is considered to be solely responsible for the postseismic deformation (afterslip-only model). The results show that afterslip is anticorrelated with peak coseismic slip areas. One high-afterslip-concentration area, with a peak of ∼24 cm, is distributed downdip of the coseismic rupture, as well as in two other regions: one partially overlapping the mainshock rupture, and the other next to the Mw 7.3 aftershock area. Second, the GPS postseismic observations are inverted to jointly investigate afterslip and viscoelastic deformation (multiple-mechanism model). The afterslip inversion results of the above two models are highly consistent, indicating the dominant contribution of afterslip to surface deformation during the ∼1.6-year postseismic period. Considering the interseismic fault coupling and historical seismicity, no appreciable fault slip associated with the Gorkha earthquake is found to occur both updip and west of the mainshock rupture areas. This reveals that the Gorkha earthquake only unzipped the lower edge of the locked portion of the MHT, leaving the shallow portion and western segment of the seismogenic zone still locked and the Nepal region under high seismic risk. The viscoelastic mechanism contributes minorly to surface deformation during the ∼1.6-year postseismic period. The middle-lower crust is assumed to comprise Maxwell material beneath an elastic ∼25-km-thick upper crust and the optimal viscosity is conservatively estimated to be 1.6 × 1019 Pa s beneath the Southern Tibetan Plateau, which should be robustly constrained with more long-term observations, more effective spatial constraints, and more detailed crustal models.

Mass-deformed M2 branes in Stenzel space

We obtain finite-temperature M2 black branes in 11-dimensional supergravity, in a G4-flux background whose self-dual part approaches a solution of Cvetič, Gibbons, Lü, and Pope, based upon Stenzel’s family of Ricci-flat Kähler deformed cones. Our solutions are asymptotically AdS4 times a 7-dimensional Stiefel manifold V5,2, and the branes are "smeared" to retain SO(5) symmetry in the internal space. The solutions represent a mass deformation of the corresponding dual CFT3, whose full description is at this time only partially-understood. We investigate the possibility of a confinement/de-confinement phase transition analogous to the AdS5 × S5 case, and a possible Gregory-Laflamme type instability which could lead to polarised brane solutions which break SO(5). We discuss possible consequences for AdS/CFT and the KKLT cosmological uplift mechanism.

Outlining tectonic inheritance and construction of the Min Shan region, eastern Tibet, using crustal geometry

The ongoing collision between India and Eurasia has created the Tibetan Plateau, which features high elevations and large crustal thicknesses. The easternmost portion of the plateau has long been a key region for studying the uplift mechanism of the Tibetan Plateau, especially after the 2008 Ms. 7.9 Wenchuan earthquake. However, previous studies have assumed that easternmost Tibet is tectonically homogeneous, and the tectonic significance of the Min Shan has been overshadowed by that of its more conspicuous neighbour, the Longmen Shan region. Here, we describe the crustal geometry of the Min Shan region using two newly obtained deep seismic reflection profiles. In this study, we identify an upper-lower crust mechanical decoupling within the Min Shan region; the Min Shan region is tectonically delineated by an inherited boundary fault zone, the Huya fault zone, which was responsible for triggering the 2017 Jiuzhaigou M 7.0 earthquake. Together with the gravity dataset and previous studies in this area, the outlined crustal geometry indicated that crustal-scale shortening at the eastern plateau margin is a primary mechanism driving uplift, although extensive uplift might have occurred due to the decoupled shortening between the upper and lower crust.

First report of (U\u2013Th)/He thermochronometric data across Northeast Japan Arc: implications for the long-term inelastic deformation

(U–Th)/He thermochronometric analyses were performed across the southern part of the Northeast Japan Arc for reconstructing the long-term uplift and denudation history in the region. Apatite (U–Th–Sm)/He ages ranged from 64.3 to 1.5 Ma, while zircon (U–Th)/He ages ranged between 39.6 and 11.0 Ma. Apatite (U–Th–Sm)/He ages showed obvious contrast among the morphostructural provinces; older ages of 64.3–49.6 Ma were obtained in the Abukuma Mountains on the fore-arc side, whereas younger ages of 11.4–1.5 Ma were determined in the Ou Backbone Range (OBR) along the volcanic front and the Asahi Mountains on the back-arc side. The age contrasts are basically interpreted to reflect the differences in the uplift and the denudation histories of the provinces considering the thermal effects of magmatism and timing of the known uplift episodes. Denudation rates were calculated to be <0.1 mm/year in the Abukuma Mountains, ~0.1 to 1 mm/year in the Ou Backbone Range, and ~0.1 to 0.3 mm/year in the Asahi Mountains. The denudation rates tend to increase from the mountain base to the ridges in the OBR (and the Asahi Mountains). This relationship shows a contrast with the previous findings in fault-block mountains in the Southwest (SW) Japan Arc, where the highest denudation rates were estimated near fault(s) along the base(s). This observation might reflect a difference in mountain uplift mechanisms between the NE and the SW Japan Arcs and imply that thermochronometric approaches are useful for constraining uplift and denudation histories at the scale of an island arc, as well as continental orogens. However, careful discussion of magmatic thermal effects is required.Graphical abstract(U–Th)/He ages across NE Japan Arc, indicating different uplift/denudation histories among the morphostructural provinces.

Lithospheric foundering and underthrusting imaged beneath Tibet

Long-standing debates exist over the timing and mechanism of uplift of the Tibetan Plateau and, more specifically, over the connection between lithospheric evolution and surface expressions of plateau uplift and volcanism. Here we show a T-shaped high wave speed structure in our new tomographic model beneath South-Central Tibet, interpreted as an upper-mantle remnant from earlier lithospheric foundering. Its spatial correlation with ultrapotassic and adakitic magmatism supports the hypothesis of convective removal of thickened Tibetan lithosphere causing major uplift of Southern Tibet during the Oligocene. Lithospheric foundering induces an asthenospheric drag force, which drives continued underthrusting of the Indian continental lithosphere and shortening and thickening of the Northern Tibetan lithosphere. Surface uplift of Northern Tibet is subject to more recent asthenospheric upwelling and thermal erosion of thickened lithosphere, which is spatially consistent with recent potassic volcanism and an imaged narrow low wave speed zone in the uppermost mantle.

Three-dimensional structural model of the Qaidam basin: Implications for crustal shortening and growth of the northeast Tibet

AbstractThe Qaidam basin, bounded by the Altyn Tagh fault in the north, is located in the northeast of the Tibet plateau, and it has important implications for understanding the history and mechanism of Tibetan plateau formation during the Cenozoic Indo-Eurasia collision. In this study, we constructed the main geological structures and surfaces in three dimensions through the interpolation of regularly spaced 2D seismic sections, constrained by wells data and surface geology of the Qaidam basin in northeast Tibet. Meanwhile the Cenozoic tectonic history of the Qaidam basin was reconstructed and the uplift mechanism of the Tibetan plateau was discussed. This study presents the subsurface data in conjunction with observations and analysis of the stratigraphic and sedimentary evolution. The Cenozoic deformation history of the Qaidam basin shows geologic synchroneity with uplifting history of the Tibet Plateau. It is therefore proposed that the deformation and uplifting in the south and north edges of the Tibet Plateau was almost synchronous. The total shortening and shortening rate during Cenozoic reached 25.5 km and 11.2% respectively across the Qaidam basin, indicating that the loss of the left-lateral strike slip rates of the Altyn Tagh fault has been structurally transformed into local crustal thickening across NW-trending folds and thrust faults. Meanwhile there is an about 11° vertical component along the strike-slip Altyn Tagh fault, the block oblique slip shows one more growth mechanism of the northeast Tibet.

The role of lower-crustal hydration in the tectonic evolution of the Colorado Plateau

Geologists have long debated the timing and mechanism for uplift of the Colorado Plateau with numerous hypotheses proposed to explain each. We use surface wave tomography to examine the lithospheric structure of the Colorado Plateau and surrounding regions and combine these data with thermodynamic modeling to better constrain lower crustal composition, water content, and density. Our results show that about 15% (~290m) of the modern plateau elevation can be supported isostatically by hydration of the lower crust, which reduces the overall density of the lithosphere. Hydration of the Colorado Plateau lithosphere likely occurred due to dewatering of the Farallon slab during flat-slab subduction. Subsequent warming and extension have likely further reduced the density of the crust along the plateau margins by as much as 110kg/m3. This is likely a result of extension encroaching into the plateau and small-scale convection occurring within the mantle surrounding the plateau, and may help explain the high topography on the margins of the plateau.

Constraining the timing of the India-Asia continental collision by the sedimentary record

Placing precise constraints on the timing of the India-Asia continental collision is essential to understand the successive geological and geomorphological evolution of the orogenic belt as well as the uplift mechanism of the Tibetan Plateau and their effects on climate, environment and life. Based on the extensive study of the sedimentary record on both sides of the Yarlung-Zangbo suture zone in Tibet, we review here the present state of knowledge on the timing of collision onset, discuss its possible diachroneity along strike, and reconstruct the early structural and topographic evolution of the Himalayan collided range. We define continent-continent collision as the moment when the oceanic crust is completely consumed at one point where the two continental margins come into contact. We use two methods to constrain the timing of collision onset: (1) dating the provenance change from Indian to Asian recorded by deep-water turbidites near the suture zone, and (2) dating the age of unconformities on both sides of the suture zone. The first method allowed us to constrain precisely collision onset as middle Palaeocene (59±1 Ma). Marine sedimentation persisted in the collisional zone for another 20–25 Ma locally in southern Tibet, and molassic-type deposition in the Indian foreland basin did not begin until another 10–15 Ma later. Available sedimentary evidence failed to firmly document any significant diachroneity of collision onset from the central Himalaya to the western Himalaya and Pakistan so far. Based on the Cenozoic stratigraphic record of the Tibetan Himalaya, four distinct stages can be identified in the early evolution of the Himalayan orogen: (1) middle Palaeocene-early Eocene earliest Eohimalayan stage (from 59 to 52 Ma): collision onset and filling of the deep-water trough along the suture zone while carbonate platform sedimentation persisted on the inner Indian margin; (2) early-middle Eocene early Eohimalayan stage (from 52 to 41 or 35 Ma): filling of intervening seaways and cessation of marine sedimentation; (3) late Eocene-Oligocene late Eohimalayan stage (from 41 to 25 Ma): huge gap in the sedimentary record both in the collision zone and in the Indian foreland; and (4) late Oligocene-early Miocene early Neohimalayan stage (from 26 to 17 Ma): rapid Himalayan growth and onset of molasse-type sedimentation in the Indian foreland basin.

Eocene adakitic porphyries in the central‐northern Qiangtang Block, central Tibet: Partial melting of thickened lower crust and implications for initial surface uplifting of the plateau

AbstractThe time and mechanism of crustal thickening and initial surface uplift of the Tibetan Plateau remain highly controversial. Here we report on zircon U‐Pb age, and mineral, element, and Sr‐Nd isotope composition data for Eocene adakitic porphyries in the Laorite Co area of central‐northern Qiangtang Block, central Tibet. Laser ablation‐inductively coupled plasma‐mass spectrometry zircon U‐Pb age dating shows that the porphyries were generated at 42–41 Ma. All samples display adakitic geochemical characteristics, such as high SiO2 and Al2O3, and low Y and Yb contents, and high Sr/Y and La/Yb ratios with positive Sr and negligible Eu anomalies and Nb‐Ta depletion. They also have low magnesium number (Mg #) (16–45) and high K2O (4.0–4.6 wt %) values, as well as high (87Sr/86Sr)i (0.7076–0.7080) and low εNd(t) (−5.9 to −4.4) values. These adakitic rocks were most probably generated by partial melting of thickened lower crust in the stability field of garnet, amphibole, and rutile but with relatively minor plagioclase. Moreover, such a crustal thickening process beneath this block likely occurred no later than the middle Eocene and was most probably caused by the southward subduction of the Songpan‐Ganzi Block in the early Cenozoic. In addition, the occurrences of exposed adakitic porphyries unambiguously indicate that exhumation process occurred after their formation. Thus, these ~42 Ma adakitic porphyries indicate the occurrence of significant exhumation since 42 Ma. Integrated with the thermochronological and paleoelevation data, we suggest that the initial surface uplift of the Qiangtang Block, triggered by crustal thickening, was underway by the middle Eocene (~42 Ma).

Raising the Gangdese Mountains in southern Tibet

AbstractThe surface uplift of mountain belts is in large part controlled by the effects of crustal thickening and mantle dynamic processes (e.g., lithospheric delamination or slab breakoff). Understanding the history and driving mechanism of uplift of the southern Tibetan Plateau requires accurate knowledge on crustal thickening over time. Here we determine spatial and temporal variations in crustal thickness using whole‐rock La/Yb ratios of intermediate intrusive rocks from the Gangdese arc. Our results show that the crust was likely of normal thickness prior to approximately 70 Ma (~37 km) but began to thicken locally at approximately 70–60 Ma. The crust reached (58–50) ± 10 km at 55–45 Ma extending over 400 km along the strike of the arc. This thickening was likely due to magmatic underplating as a consequence of rollback and then breakoff of the subducting Neo‐Tethyan slab. The crust attained a thickness of 68 ± 12 km at approximately 20–10 Ma, as a consequence of underthrusting of India and associated thrust faulting. The Gangdese Mountains in southern Tibet broadly attained an elevation of &gt;4000 m at approximately 55–45 Ma as a result of isostatic surface uplift driven by crustal thickening and slab breakoff and reached their present‐day elevation by 20–10 Ma. Our paleoelevation estimates are consistent not only with the C–O isotope‐based paleoaltimetry but also with the carbonate‐clumped isotope paleothermometer, exemplifying the promise of reconstructing paleoelevation in time and space for ancient orogens through a combination of magmatic composition and Airy isostatic compensation.

Cenozoic incision history of the Little Colorado River: Its role in carving Grand Canyon and onset of rapid incision in the past ca. 2 Ma in the Colorado River System

This paper documents a multi-stage incision and denudation history for the Little Colorado River (LCR) region of the southwestern Colorado Plateau over the past 70 Ma. The first two pulses of denudation are documented by thermochronologic data. Differential Laramide cooling of samples on the ­Mogollon Rim suggests carving of 70–30 Ma paleotopography by N- and E-flowing rivers whose pathways were partly controlled by strike valleys at the base of retreating Cretaceous cliffs. A second pulse of denudation is documented by apatite (U-Th)/He dates and thermal history models that indicate a broad LCR paleovalley was incised 25–15 Ma by an LCR paleoriver that flowed northwest and carved an East Kaibab paleovalley across the ­Kaibab uplift. Lacustrine strata of the lower Bidahochi Formation were deposited 16–14 Ma in the LCR paleovalley in a closed basin playa or marsh with a valley center near the modern LCR. There is a hiatus in the depositional record in the LCR valley from 12 to 8 Ma followed by aggradation of the 8–6 Ma fluvial upper Bidahochi Formation. Interlayered 8–6 Ma maar basalts that interacted with groundwater mark local base level for upper Bidahochi fluvial deposits; this was also a time of increased groundwater flow to Hualapai Limestone at the western edge of the Colorado Plateau. The paleo–base level in the central LCR valley remained stable (∼1900 m modern elevation) from 16 to 6 Ma. The third pulse of regional incision and denudation, most recent and ongoing, started after integration of the Colorado River (CR) through Grand Canyon. Thermochronology from Marble Canyon indicates that early CR integration took place across the Vermillion Cliffs at Lees Ferry after 6 Ma. The elevation of the paleoconfluence between the LCR and CR at 5–6 Ma is poorly constrained, but earliest CR integration is hypothesized to have reoccupied the East Kaibab paleocanyon. In the upper LCR drainage, topographically inverted basalt ­mesas have elevations and K-Ar dates indicating a transition from aggradation to incision ca. 6 Ma followed by semi-steady incision of 20–40 m/Ma. In the lower LCR, incision accelerated to 120–170 m/Ma after 2 Ma as indicated by 40 Ar/ 39 Ar dating of basalt, ash-fall, and detrital sanidine. A 1.993 ± 0.002 Ma sanidine age for a tuff in the White Mesa alluvium provides a breakthrough for LCR and CR incision studies. Post–2 Ma differential incision magnitudes (and rates) in the lower LCR and at the LCR-CR confluence were 280–320 m (140–160 m/Ma), about three times greater than the 40–80 m (20–40 m/Ma) in the LCR headwaters. The proposed mechanisms driving overall post–6 Ma differential incision of the LCR involve headwater uplift associated with the Hopi Buttes and Springer­ville volcanic fields plus base-level fall caused by CR integration to the Gulf of California. A proposed mechanism to explain the accelerated post–2 Ma differential incision in the central and lower LCR valley, but not in the head­waters, involves mantle-driven epeirogenic uplift due to NE-migrating vol­canism associated with the San Francisco volcanic field. Tectonically driven differential surface uplift mechanisms were likely amplified by changes toward more erosive climate at ca. 6 Ma and ca. 2 Ma.

Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited

The growth and decay of ocean-island volcanoes are intrinsically linked to vertical movements. While the causes for subsidence are better understood, uplift mechanisms remain enigmatic. Santa Maria Island in the Azores Archipelago is an ocean-island volcano resting on top of young lithosphere, barely 480 km away from the Mid-Atlantic Ridge. Like most other Azorean islands, Santa Maria should be experiencing subsidence. Yet, several features indicate an uplift trend instead. In this paper, we reconstruct the evolutionary history of Santa Maria with respect to the timing and magnitude of its vertical movements, using detailed field work and 40Ar/39Ar geochronology. Our investigations revealed a complex evolutionary history spanning ∼6 m.y., with subsidence up to ca. 3.5 Ma followed by uplift extending to the present day. The fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms. Localized uplift in response to the tectonic regime affecting the southeastern tip of the Azores Plateau is unlikely, since the area is under transtension. Our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions, suggesting that intrusive processes play a significant role even on islands standing on young lithosphere, such as in the Azores.

Constraints on the uplift mechanism of northern Tibet

Enhanced latest Oligocene to present uplift of northern Tibet is manifest in a variety of geological records. However, the main controversy is how the crust came to be thickened. Theories seeking to explain the growth of northern Tibet include removal of the mantle lithosphere beneath Tibet and the cessation of fast motion on major strike-slip faults. To address this issue, we conducted a detailed paleomagnetic study in the central Kumkol basin, south of the Altyn Tagh fault (ATF). Combined with our previous study from the Janggalsay area, north of the ATF, magnetic declination data suggest fast strike-slip motion for the left-lateral ATF between 22 and 15 Ma. However, the fast motion along the ATF terminated between 15 and <6.3 Ma. This change was accompanied by widespread and simultaneous uplift of northern Tibet at ∼15 Ma. Our results argue in support of a Mid-Miocene transition in tectonic regime from extrusion to distributed shortening in northern Tibet and emphasize the role of the ATF in governing widespread and simultaneous uplift of northern Tibet.

Seismic evidence of the rebound of the Adria foreland and the current geodynamics of the Central and Southern Apennines (Italy)

The sedimentary wedge of the Apennines foredeep in the Central Adriatic Sea provides evidence of westward tilting of the foreland during the Lower Pliocene. The wedge was covered by an Upper Pliocene-Lower Pleistocene sequence of parallel and horizontal strata that onlapped onto the pre-wedge sediments. The Southern Apennines contain younger foredeep growth strata because the chain front migrated until the Lower Pleistocene.Seismic profiles from the Central and Southern Apennines foredeep show a regional, apparently contrasting eastward-dipping set of post-growth parallel layers that are covered by a Middle/Upper Pleistocene Prograding Sedimentary Wedge (PSW), which is particularly thick in the Central Adriatic basin.In accordance with the “Law of Original Horizontality” and by excluding possible exceptions to this law (inclined depositions in several specific frameworks), the observed geometric setting can be explained as an effect of post-deposition inversion of the previous orogen-ward tilting. We infer that the driving mechanism of uplift was the regional isostatic rebound of the Adria foreland, which started in the Middle Pleistocene and is still active as indicated by the current uplift of Adria and by the passively raised chain. Under the same conditions, the greater the tilting of the foredeep during the chain migration, the greater the degree of isostatic rebound. The rheology of the foreland and sedimentary loading are also key elements of these crustal-scale vertical movements. Furthermore, normal faults and greater foredeep uplift of the foreland can play local roles in short-wavelength deformations.The current axis of the chain, which was affected by imbrication of the Apennine and Apulia units, is now subject to higher rates of rebound and erosion. We infer that inversion of some of the previous faults that originated the buried western margin of the Apulia carbonate platform (AP) triggered the extensional seismicity that is recorded along the chain.The rapid uplift of the foreland and of the overlying thrust belt since the Middle Pleistocene caused a change in the drainage network on the Adriatic side of the chain from a longitudinal pattern to a transverse pattern. In addition, erosion of the uplifted units contributed to the high rate of deposition of the PSW in the Adriatic foreland basin.The regional rebound process that is proposed in this work implies a primary role of the AP buoyancy and rejects the hypothesis of its current passive sinking, which is often regarded as the primary source of Apennines tectonics.

Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains

The Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth, and while a variety of uplift mechanisms have been proposed, the origin of the TAMs is still a matter of great debate. Most previous seismic investigations of the TAMs have focused on a central portion of the mountain range, near Ross Island, providing little along-strike constraint on the upper mantle structure, which is needed to better assess competing uplift models. Using data recorded by the recently deployed Transantarctic Mountains Northern Network, as well as data from the Transantarctic Mountains Seismic Experiment and from five stations operated by the Korea Polar Research Institute, we investigate the upper mantle structure beneath a previously unexplored portion of the mountain range. Rayleigh wave phase velocities are calculated using a two-plane wave approximation and are inverted for shear wave velocity structure. Our model shows a low velocity zone (LVZ; ∼4.24 km s−1) at ∼160 km depth offshore and adjacent to Mt. Melbourne. This LVZ extends inland and vertically upwards, with more lateral coverage above ∼100 km depth beneath the northern TAMs and Victoria Land. A prominent LVZ (∼4.16–4.24 km s−1) also exists at ∼150 km depth beneath Ross Island, which agrees with previous results in the TAMs near the McMurdo Dry Valleys, and relatively slow velocities (∼4.24–4.32 km s−1) along the Terror Rift connect the low velocity anomalies. We propose that the LVZs reflect rift-related decompression melting and provide thermally buoyant support for the TAMs uplift, consistent with proposed flexural models. We also suggest that heating, and hence uplift, along the mountain front is not uniform and that the shallower LVZ beneath northern Victoria Land provides greater thermal support, leading to higher bedrock topography in the northern TAMs. Young (0–15 Ma) volcanic rocks associated with the Hallett and the Erebus Volcanic Provinces are situated directly above the imaged LVZs, suggesting that these anomalies are also the source of Cenozoic volcanic rocks throughout the study area.

Uplift mechanism of open-cut tunnel in liquefied ground and simplified method to evaluate the stability against uplifting

The liquefaction of sandy soil during earthquakes causes the uplift of relatively light structures such as open-cut railway tunnels. The potential for the uplift of underground structures is usually evaluated by the factor of safety against uplift (Fs), which only considers the force equilibrium of the structures in the vertical direction. However, design procedures which employ the factor of safety to evaluate uplift may be too conservative for assessing the uplift behavior of underground structures. It is necessary to establish a new method to directly predict the residual displacement or to predict whether or not the uplift behavior will have a negative influence on the serviceability of underground structures. In this study, therefore, a series of shaking table tests was performed using the open-cut tunnel model, and the relationship among the uplift behavior of the tunnel, the degree of liquefaction, the external forces acting on the tunnel and the deformation of the liquefied ground was investigated through precise measurements. The experiment revealed that critical uplift behavior does not occur when the level and the area of liquefaction are limited to a restricted range even if the factor of safety against uplift falls to less than 1.0. After the wide area around the tunnel reached complete liquefaction, the uplift behavior of the tunnel increased rapidly. Based on these test results, the detailed mechanism of the uplift behavior and the applicability of the factor of safety were examined. In addition, a new method was suggested to evaluate the stability level of open-cut tunnels against uplift.

Ice cap melting and low‐viscosity crustal root explain the narrow geodetic uplift of the Western Alps

AbstractMore than 10 years of geodetic measurements demonstrate an uplift rate of 1–3 mm/yr of the high topography region of the Western Alps. By contrast, no significant horizontal motion has been detected. Two uplift mechanisms have been proposed: (1) the isostatic response to denudation responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting which predicts a broader uplifting region than the one evidenced by geodetic observations. Using a numerical model to fit the geodetic data, we show that a crustal viscosity contrast between the foreland and the central part of the Alps, the latter being weaker with a viscosity of 1021 Pa s, is needed. The vertical rates are enhanced if the strong uppermost mantle beneath the Moho is interrupted across the Alps, therefore allowing a weak vertical rheological anomaly over the entire lithosphere.

Movement vectors and deformation mechanisms in kinematic restorations: A case study from the Colombian Eastern Cordillera

We have developed a new method to assess the movement of particles in different steps of a well-calibrated sequential kinematic restoration. Calibration included correct assessment of amounts of overburden, sedimentation, erosion, and thermal behavior through time. Our method allowed a better understanding of the mechanisms of deformation and uplift in different geologic provinces. In our pilot case study in the Colombian Eastern Cordillera, we have used movement vectors in balanced cross sections to document an initial phase of dominant vertical uplift and a final phase of dominant tangential horizontal shortening. Our findings challenged the common assumptions related to folding and deformation mechanisms in fold-and-thrust belts used for cross-section balancing and palinspastic reconstructions. Thus, we found that the movement vectors in cross sections can be used to test and validate a complete procedure to obtain calibrated sequential kinematic restorations and represent a powerful tool to better understand deformation mechanisms in different settings.