Pattern Of Uplift Research Articles

Dynamic Divide Migration as a Response to Asymmetric Uplift: An Example from the Zhongtiao Shan, North China

Previous numerical–analytical approaches have suggested that the main range divide prefers to migrate towards the high uplift flank in the asymmetric tectonic uplift pattern. However, natural examples recording these processes and further verifying the numerical simulations results, are still lacking. In this study, the landscape features, and the probable drainage evolution history of the Zhongtiao Shan, a roughly west-east trending, half-horst block on the southernmost tip of the Shanxi Graben System, were investigated through the geomorphic analyses (i.e., slope and steepness distributions, and the Gilbert and χ metrics). The topographic slope and steepness results indicate that the Zhongtiao Shan, controlled by the north Zhongtiao Shan normal fault, experiences asymmetric uplift and erosion patterns, with higher uplift and erosion on the north range. In addition, the Gilbert and χ metrics suggest that the western part of the main divide is currently stable, while the eastern divide is moving southward. According to the drainage divide stability criteria, we suggest that the uplift and erosion, on the fault side, balance each other well on the western part of the range, while on the eastern part, the uplift is outpaced by the erosion. In addition, a dynamic divide migration model in the asymmetric uplift condition is proposed, indicating that the interaction between uplift and erosion controls the migration and/or stability of the main divide. Deducing through this dynamic model, we suggested that the eastern segment of the north Zhongtiaoshan Fault must have experienced higher activities in the geological history, and the western fault may remain its activity along with the mountain relief generation. This gives a case that specific information on asymmetric neotectonic history and landscape evolution in an orogenic mountain can be uncovered by the proposed dynamic model.

Active Deformation and Relief Evolution in the Western Lurestan Region of the Zagros Mountain Belt: New Insights From Tectonic Geomorphology Analysis and Finite Element Modeling

AbstractTo unravel how and where coseismic and interseismic deformation impacts the spatial and temporal patterns of rock uplift of the Lurestan sector of the Zagros Mountains, we performed an investigation of the large‐scale features of topography and river network coupled with 2‐D finite element modeling. Geomorphological analysis and constraints from parameters such as elevation, local relief, normalized channel steepness index (ksn), river longitudinal profiles, and transformed river profiles (chi plots) were used to unravel the time‐space distribution of vertical motions. Whereas the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphology. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. The outputs illustrate how coseismic slip controls localized uplift of a prominent topographic feature—the Mountain Front Flexure—located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located farther to the NE, in the interior of the orogen.

Towards stratigraphic-thermo-mechanical numerical modelling: Integrated analysis of asymmetric extensional basins

Abstract Subsidence and uplift patterns and thermal history of sedimentary basins are controlled by tectonics, mantle dynamics and surface processes, such as erosion, sediment transport and deposition and their links to climatic variations. We use combined thermo-mechanical and stratigraphic numerical modelling techniques to quantify the links between tectonic and surface processes. We aim to assess the thermal evolution and subsidence rates of asymmetric extensional basins during the syn- and post-rift times by simulating different erosion and sedimentation rates. We analyse the 3D sedimentary architecture and facies distribution of the depocenters. Model results are validated by observations in the Pannonian Basin of Central Europe. Extensional reactivation of inherited suture zones creates asymmetric basin systems controlled by large-scale detachments or low-angle normal faults, where crustal and lithospheric mantle thinning are often rheologically decoupled. Subsidence rates and basement heat flow in the depocenters show large variabilities during asymmetric extension and post-rift evolution controlled by their initial position from the suture zone and migration of deformation. Transient heat flow anomalies mirror crustal exhumation of footwalls, sediment blanketing and erosion effects in the basins. Enhanced erosion and sedimentation facilitate lower crustal deformation and elastic flexure of the weak, extended lithosphere leading to accentuated differential uplift and subsidence during the syn- and post-rift basin evolution. Tectonics, climate and autogenic processes control transgressive-regressive cycles at different timescales together with the overall sedimentary facies distribution. In our models assuming wet climate the high subsidence rate often outpaces moments of eustatic water-level fall preventing relative base-level fall and enhances the effects of autogenic processes, such as lobe switching processes.

The contemporary strain rate field in Uruguay and surrounding region – vertical velocities

This study supplements analyses of the horizontal strain rate fields in the region in and around Uruguay presented in Baxter and Smith (2020). Whilst the original study did not consider the vertical component, because of high levels of noise and discontinuities in the raw data, these effects have been minimized and appropriate analyses are presented with consideration of the uncertainties. The results show that, similarly to the horizontal strain rate field, the vertical velocity field in the region appears to have been influenced by two subduction earthquakes that occurred in Chile. The patterns of uplift and subsidence revealed by these analyses suggest influences from the underlying structure of the Rio de la Plata estuary, and perhaps the Mesopotamian region in Argentina, that may relate to enhanced seismicity in these specific areas.

Emerged Coral Reefs Record Holocene Low‐Angle Normal Fault Earthquakes

AbstractLow‐angle normal faults (LANFs; dip <30°) accommodate kilometers of crustal extension, yet it remains unclear whether these faults can host large earthquakes or if they predominantly creep aseismically. Most active LANFs typically slip at rates of <3 mm/year. Here, we report U‐Th ages from a series of distinct levels of formerly shallow‐living corals killed by uplift‐induced emergence of the footwall of one of the world's fastest‐slipping LANFs, the Mai'iu fault in Papua New Guinea, which slips at rates of 8–12 mm/year. Coral ages and coastal morphology indicate punctuated episodic uplift events consistent with seismic slip on the Mai'iu fault. Maximum episodic uplift increments of 0.5–1.8 m imply earthquakes of Mw > 7. We present the first coral paleoseismological record of normal fault earthquakes, which constrain the timing and surface uplift patterns of multiple LANF seismic cycles and confirm that LANFs can slip in large (Mw > 7) earthquakes.

Quaternary deformation and uplift of coral reef terraces produced by oblique subduction and underthrusting of the Bahama Platform below the northern Hispaniola forearc

Active tectonics linked to the rise of the Hispaniola forearc explain the morphological characteristics, spatial distribution and U-Th geochronological ages of the uplifted coral reef terraces of the La Isabela Formation in both the eastern Cordillera Septentrional and the Samaná Peninsula of northeastern Dominican Republic. Depositional coral reef terraces of MIS 5e (TII), 7e (TIII) and 9 (TIV) stages occur respectively at maximum heights of about 25 m, 80 m and 120 m above the current sea level. The development of heterogeneous brittle deformation structures in the coral limestone at all scales document active tectonics and include small faults, shear fractures, extensional joints and calcite veins. Their geometric and kinematic characteristics, as well as the stress tensors calculated from fault-slip and fracture orientation data, are all compatible with ENE to NE-trending regional shortening, and indicate that a left-lateral transpressive regime is deforming the forearc during the Quaternary.Along the northern Hispaniola coastline, the tectonic uplift mimics the distribution of the bathymetric features on the subducting Bahamas Platform, outboard the Hispaniola-Puerto Rico Trench. The highest calculated uplift rates in the eastern Cordillera Septentrional and Samaná Peninsula correspond to the collision zone of the Silver Spur and Navidad Bank (≥0.4 m/ka), respectively. Uplift rates decrease towards the west (≤0.2 m/ka), where the oblique collision of carbonate ridges and related forearc deformation would not have been recorded since at least the Early Pleistocene. Oblique subduction and underthrusting of the Bahamas Platform followed by basal erosion at the subduction channel explain the observed time-transgressive pattern of uplift and subsidence in the northern Hispaniola forearc and the change from accretionary to erosive processes in the convergent margin.

Geodynamic Modeling of Edge-Delamination Driven by Subduction-Transform Edge Propagator Faults: The Westernmost Mediterranean Margin (Central Betic Orogen) Case Study

Lithospheric tearing at slab edges is common in scenarios where retreating slabs face continental margins. Such tearing is often accommodated via subvertical STEP (SubductionTransform Edge Propagator) faults that cut across the entire lithosphere and can result in sharp lateral thermal and rheological variations across the juxtaposed lithospheres. This setting favors the occurrence of continental delamination, i.e., the detachment between the crust and the lithospheric mantle. In order to evaluate this hypothesis, we have chosen a wellstudied natural example recently imaged with unprecedented seismic resolution: the STEP fault under the central Betic orogen, at the northern edge of the Gibraltar Arc subduction system (westernmost Mediterranean Sea). The Gibraltar Arc subduction is the result of the fast westward roll-back of the Alboran slab and it is in its last evolutionary stage, where the oceanic lithosphere has been fully consumed and the continental lithosphere attached to it collides with the overriding plate. In this study we investigate by means of thermo-mechanical modeling the conditions for, and consequences of, delamination post-dating slab tearing in the central Betics. We consider a setup based on a STEP fault separating the orogenic Betic lithosphere and the adjacent thinned lithosphere of the overriding Alboran domain. Our model analysis indicates that delamination is very sensitive to the initial thermal and rheological conditions, transitioning from a stable to a very unstable and rapidly evolving regime. We find two clearly differentiated regimes according to the time at which the process becomes unstable: fast and slow delamination. Although the final state reached in both the fast and slow regimes is similar, the dynamic surface topography evolution is dramatically different. We suggest that given a weak enough Iberian lower crust the delaminating lithospheric mantle peels off the crust and adopts a geometry consistent with the imaged southward dipping Iberian lithosphere in the central Betics. The lack of spatial correspondence between the highest topography and the thickest crust, as well as the observed pattern of uplift/ subsidence are properly reproduced by a model where relatively fast delamination (Reference Model) develops after slab tearing.

Deformation patterns and potential active movements of the Fansipan mountain range, northern Vietnam

Located in northern Vietnam, the Fansipan mountain range is the highest topography in the Indochina area. Until recently, there has been limited research regarding the tectonic deformation of the Fansipan mountain range and whether there are notable surface ruptures or active faults in the area. This study provides the first insight into the deformation patterns and potential active movements of the Fansipan mountain range, and may improve our understanding of the overall tectonic activities in northern Vietnam. Our observations from ASTER 30-m DEM show a symmetrical mountain form in the north and an asymmetrical form in the south. The analysis of river profiles indicates similar patterns on both sides in the north and different patterns in the south with short and steep rivers on the SW side and long and gentle rivers on the NE side. The results of the normalized steepness index (ksn) also show higher values on the SW side of the south part than the values from the other sides. These results suggest a spatial variation in rock uplift patterns of the Fansipan mountain range. Notably, the mountain front of the SW side of the southern Fansipan mountain range is associated with the Phong Tho-Nam Pia normal fault, suggesting that the normal faulting activity likely played an important role in tectonic uplift of this high mountain range. Our investigation of the stress field using fault kinematics indicates that the Fansipan mountain range and its surrounding areas are undergoing an inhomogeneous mixture of strike-slip and normal faulting. It is proposed that the strike-slip and normal motions alternated because of a permutation of σ1/σ2 under the same extensional stress regime of approximately NE–SW σ3. This kinematic pattern may effectively control the recent tectonic movements in northern Vietnam.

Quaternary Rock Uplift Rates and Their Implications for the Western Flank of the North Anatolian Fault Restraining Bend; Inferences From Fluvial Terrace Ages

AbstractIn the western flank of the North Anatolian Fault restraining bend (i.e., Central Pontides), the Filyos River incises through the uplifting Karabük Range, creating the ~1.7‐km‐deep Filyos River Gorge on the hanging wall of the reverse Karabük Fault. Seven fluvial strath terrace levels are preserved in this gorge. optically stimulated luminescence ages from quartz‐rich sediments of five terrace levels reveal an average long‐term rock uplift rate of 0.45 ± 0.02 mm yr−1 with an unsteady pattern of uplift during the last 542 ± 24 kyr. Uplift rates of 1.52 ± 0.6 and 0.74 ± 0.3 mm yr−1 occurred before 366 ± 19 kyr, followed by lower rates of ~0.1 and 0.31 mm yr−1 through present. These later uplift rates may reflect relatively slower tectonic rates since ~366 kyr, with closer similarity to regional uplift rates of ~0.3 mm yr−1 yielded from the eastern flank of the Central Pontides. The Karabük Range fluvial terraces are near the North Anatolian Fault, meaning pre‐ ~366 kyr uplift rates may be a glimpse of the highest Central Pontides Quaternary rock uplift rates on uplifting hanging wall blocks activated by the restraining bend. When we consider offshore seismic reflection data, the focal mechanism solution of the Bartın Earthquake, onshore structural data, and regional tectonic geomorphology, the western flank of the Central Anatolian Plateau's northern margin is propagating northward as a growing orogenic wedge with a positive flower‐structure geometry.

Implications of glacial isostatic adjustment on petroleum reservoirs in the Grand banks of Newfoundland

Glacial Isostatic Adjustment (GIA), or postglacial rebound refers to the crustal response to glacial loading and unloading processes. In this investigation, we run numerical simulations using different rheological parameters and ice loading histories to obtain models of the glacial isostatic response for the Grand Banks of Newfoundland. The objective is to assess in general the potential impact of GIA on hydrocarbon reservoirs and trapping structures in terms of tilting, deformation, fault activity or geochemical implications on the trapped fluids. Comparisons may be drawn to related studies, including analogous impacts on reservoirs in the Barents Sea, as well as validation of GIA model predictions of vertical crustal motion using GNSS stations, levelling networks and relative sea level (RSL) observations at numerous sites across eastern Canada. By running a series of GIA models, a range of vertical motion rates are output through time to determine displacement amounts, and calculations are performed on these outputs to disseminate other valuable data attributes such as the displacement gradient and differences in time and space. In general, the vertical motion rate is seen to change drastically over time for certain points, as the lag in response of regions near the ice periphery leads to a distinct pattern of uplift and subsidence. The Grand Banks generally experienced between 57 m of subsidence to 34 m of uplift since the last glacial maximum, depending on the specific location and the GIA model parameters. At the reservoir scale, model results along a 10 km baseline show up to −1.0–1.5 m of differential vertical displacement, which could have led to reservoir tilting or even hydrocarbon migration. As a result of this study, it is clear that there are implications of GIA on hydrocarbon reservoirs since the Last Glacial Maximum, and these effects are ongoing.

Development of an incipient Paleogene topography between the present‐day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina

AbstractThe structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north‐western Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the present‐day transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present‐day plateau correspond to an approximately north‐south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts.

Application of Time-Series Sentinel-1A for Land Deformation in Central Aceh, Indonesia

Several decorrelation phenomena of Interferometric Synthetic Aperture Radar (InSAR) have led researchers to develop various multitemporal InSAR (MT-InSAR) techniques with the application of time series/stack of images. In this study, we present the land surface movement monitoring using MT-InSAR techniques in the Central of Aceh-Indonesia, and focus on the temporal and spatial pattern of uplift and subsidence by using multi InSAR methods such as Quasi-Persistent Scatterer (Q-PS) and Small Baseline Subset (SBAS). A total of 18 scenes of Sentinel-1A(S-1A) and 14 scenes of ALOS PALSAR-1(PALSAR-1) images were acquired between 2018 and 2019, as well as 2007 and 2010, where then the multitemporal methods and techniques were applied sequentially to a set of those data. The results showed that the either the S-1A and PALSAR-1 velocity subsidence at Nunang and Musara Alun villages were range from 2.4 to 5.7 and 0.6 to 2.3 mm/year, respectively which corresponded to the results obtained by other research publication. The deformation in Central Aceh needs continuous monitoring using InSAR as the place is a landslide prone area because of the nature of the terrain.

Quantitative assessment of ground deformation risks, controlling factors and movement trends for onshore petroleum and gas industry using satellite Radar remote sensing and spatial statistics

ABSTRACT A number of productive oil and gas fields are located in the Absheron Peninsula of Azerbaijan. The primary goal of the presented study was to quantitatively assess the ground deformation (subsidence and uplift) rates of oil and gas fields, determine natural and man-made influencing factors and predict deformation trends. Persistent Scatterer Interferometric Synthetic Aperture Radar technique was used for the present studies to detect ground deformation rates and velocities in the Absheron oil and gas fields. The existence of ground deformation processes was observed for the period of 2015–2017 with three hotspots of highest subsidence rates and three hotspots of highest uplift rates in oil and gas fields. The determined maximum displacement rates of subsidence and uplift processes were −26 mm/y and +23 mm/y, respectively. However spatial density analysis of deformation velocity presented the natural patterns of uplift and subsidence tectonic processes. This allowed to determine that two oil and gas fields hold a higher probability of being affected by man-made oil and gas exploration activities, whereas the one oil field is affected by both natural and man-made processes. Geographically Weighted Regression analysis revealed that well concentration and elevation factors provided 32% of explanation to subsidence processes.

Coseismic Uplift of the 1999 Mw7.6 Chi‐Chi Earthquake and Implication to Topographic Change in Frontal Mountain Belts

AbstractLarge dip‐slip earthquakes have a major contribution to mountain building while earthquake‐induced landslides lower mountains simultaneously. The amount of the coseismic uplift and landslides may dominate long‐term mountain evolution. However, how earthquakes contribute to mountain evolution through coseismic uplift and landslides is less constrained in real cases. We present the regional coseismic uplift of the 1999 Mw7.6 Chi‐Chi earthquake by using synthetic aperture radar (SAR) images and GPS. The coseismic uplift pattern is consistent with field observations showing increasing movement to the north with ~8 m of uplift toward the northern end. We estimated uplifted rock volume of 2.60 ± 1.09 km3, which is five times greater than the coseismic landslide volume. Intense erosion of the Taiwan orogen may erode elevated rocks rapidly, but the uplift and landslide distributions do not match and correlate more inversely, suggesting the frontal orogenic topography should be increased rather than annulled over earthquake cycles.

Tectonic geomorphology and Plio-Quaternary structural evolution of the Tuzgölü fault zone, Turkey: Implications for deformation in the interior of the Central Anatolian Plateau

AbstractSituated 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.

Effect on Subduction of Deeply Buried Seamounts Offshore of Kodiak Island

AbstractSeamounts are ubiquitous on the oceanic plate; those situated near convergent margins will eventually undergo subduction. Using six prestack depth migrated MCS profiles transecting the Aleutian Trench, we investigate deeply buried seamounts offshore Kodiak Island, within 145–155°W and 55–58°N. A distinct sedimentary horizon exists in all six seismic profiles, at or above the average height of seamounts, which appears to be the preferred structural detachment zone. Where drilled, this horizon contains gravel‐sized debris interpreted to be ice rafted and marks the onset of intensification of Northern Hemisphere glaciation at ~2.7 Ma. Beneath this horizon, sediments prior to the Surveyor Fan development were deposited, all or the majority of these sediments will eventually be subducted. Despite the subducted seamounts being deeply buried, these features cause enhanced surface slope of the accretionary prism. Our observations lead us to propose a model for the stages of subduction for deeply buried seamounts. These stages include the following: (1) Prior to subduction, the protothrust zone undergoes enhanced shortening, (2) frontal thrust steepening and enhanced backthrusting occurs during subduction with a potential décollement step down seaward and a steeping outward of the deformation front to the limit of the protothrust zone, and (3) further subduction results in a pattern of uplift farther into the wedge resulting in enhanced out‐of‐sequence thrusting and persistence of the more seaward deformation front position. This pattern is distinct from the dominance of embayments and effective removal of prism material during seamount subduction described along margins with less deeply buried edifices.

Uplift of the Transdanubian Range, Pannonian Basin: How fast and why?

Abstract The cumulative incision rates of ~50–70 m/Ma integrating over the last ~3 Ma have been derived from published terrace-chronological data of the Danube river in the Western Pannonian Basin. An apparent acceleration of uplift rates was observed for shorter timescales culminating at ~200 m/Ma over the last ~140 ka. An examination of the change of the incision rates through time revealed that the incision rate was fairly constant at ~50 m/Ma from ~3 Ma to ~140 ka, and the faster rates are valid only for the last ~140 ka. These findings suggest that the long-term uplift rate of the northwestern limb of the Transdanubian Range is ~50 m/Ma, and the apparent acceleration of river incision during the Late Pleistocene is considered as the result of faster, most probably climate-driven incision during the last glacial cycle, outpacing the long-term uplift rate. The observed upper crustal neotectonic faults are not sufficient to accommodate the deformation necessary for the reported Pliocene to Quaternary vertical motion. The geodynamic model for the explanation of the magnitude and pattern of surface uplift in the western Pannonian Basin involves a complex interplay between (1) deep lithosphere-asthenosphere dynamics, (2) structural inversion governed by the northward drift of Adria, (3) inherited geological structures and (4) climate driven surface processes (denudation and sediment loading).

Prominent thermal anomalies in the mantle transition zone beneath the Transantarctic Mountains

Abstract The Transantarctic Mountains (TAMs), Antarctica, exhibit anomalous uplift and volcanism and have been associated with regions of thermally perturbed upper mantle that may or may not be connected to lower mantle processes. To determine if the anomalous upper mantle beneath the TAMs connects to the lower mantle, we interrogate the mantle transition zone (MTZ) structure under the TAMs and adjacent parts of East Antarctica using 12,500+ detections of P-to-S conversions from the 410 and 660 km discontinuities. Our results show distinct zones of thinner-than-global-average MTZ (∼205–225 km, ∼10%–18% thinner) beneath the central TAMs and southern Victoria Land, revealing throughgoing convective thermal anomalies (i.e., mantle plumes) that connect prominent upper and lower mantle low-velocity regions. This suggests that the thermally perturbed upper mantle beneath the TAMs and Ross Island may have a lower mantle origin, which could influence patterns of volcanism and TAMs uplift.

Development and growth of basement-involved structural wedges in the northwestern Qaidam Basin, China

Structural wedges contain two connected fault segments, a fore thrust and back thrust, that bound a triangular- or wedge-shaped fault block. Coeval displacements on both faults drive the wedge into surrounding rock, causing distinctive patterns of uplift and folding. We identified a series of thick-skinned structural wedges in northwestern Qaidam Basin, China, where syntectonic strata record deformation timing and kinematics. The Qaidam Basin is located at the northern margin of the Tibetan Plateau and contains more than 100 large anticlinal structures, many of which exhibit characteristics of structural wedges. We interpreted and modeled these structures using seismic reflection data, well logs, surface geological exposures, remote sensing images, and digital elevation data. These wedge structures are distinguished by having elevated and deformed strata in the footwalls of the back thrusts and synclinal folds that extend upward from the wedge tips. With the constraints of fold shape, growth strata, structural relief, and shallow fault geometry, we developed a series of forward models that describe the geometry and kinematic evolution of these wedge structures. The analysis suggests that some of the wedge structures reactivate preexisting normal faults. Our results provide a better understanding of how to identify thick-skinned wedge systems and model their geometry and kinematic evolution, which has implications for studying the tectonic history of the basin. Understanding the geometry and kinematics of the wedge structures is also crucial for petroleum exploration because both hanging-wall and footwall traps constitute an important component of current exploration targets.

Assessment of relative active tectonics in Edea – Eseka region (SW Cameroon, Central Africa)

The Edea-Eseka region (EER), a portion of West African Margin located in SW Cameroon between 3°30′—4°00′ N and 10°00′—10°55′ E and submitted to equatorial climate since early Miocene is used here as a proxy for climatic conditions. Geomorphological analysis based on morphometric parameters computed from DEM (30 m) combined with geological maps and field observations were used to constrain geomorphic evolution and landscape adjustment to tectonic processes in this humid zone. Three types of geomorphic indices reflecting specially patterns of differential uplift, those efficient in detecting tilting, and those revealing interactions between erosion and tectonics.-The obtained results show that lithological boundaries and base level controls on landscape are very limited. Tectonic processes, peculiarly uplift induced by faults or tilting at local scale and by mantle dynamics at large scale coupled with climate condition, represent the main factors that drove the geomorphic evolution of this area discriminating three main morphotectonic provinces different by their geomorphic characteristics, uplift and degree of incision. There are, from West to East: (1) the coastal province (CP), deeply incised and built on Douala-Kribi/Campo basin (<65 Ma) set up during the South Atlantic opening, recorded the very low uplift rate; (2) the intermediate province (IP), developed on Nyong (2400–1800 Ma) and Oubanguide (650–540 Ma) crystallophyllian complexes and marked by high differential erosion, includes middle to high residual reliefs; and (3) the upper province (UP), developed like the pervious on Nyong and Oubanguide crystallophyllian complexes is characterized exclusively by continental high reliefs, representing high post-Cambrian continental uplifts.-Several geomorphic indices used to evaluate tectonic activities and their average the index of relative active tectonics (IAT) show that tectonic activity differs from one province to another and within each province. Generally, it increases from coast (coastal province) to hinterland (UP). EER are represented by classes 2 and 3 of IAT indicating moderate to high active tectonics. Class 1 revealing the highest tectonic activity, occurs exclusively in the UP. Class 2 corresponding to high tectonic activity happens largely in the south of the IP along the Nyong Fault and the UP where relief are particularly high. Class 3 indicates the moderate relative tectonic in the IP. Class 4 mainly takes place in tectonically low to inactive Douala-Kribi/Campo basin, except along the South part of Sanaga Fault.The development and the evolution of Edea-Eseka region landscape is then acted by a dominant high-uplift rate in SW Cameroon. This tectonic activity apparently incompatible with the passive margin context is however realistic in this area, on one hand justified by the numerous reactivations over time of faults crossing the region that generate earthquakes in some places and on the other hand, by the activity of the Cameroon Volcanic Line, and particularly that of the Mount Cameroon located near the study area. It appears at the end that, due to mantle dynamics, the EER has been rejuvenated under the tectonics and climate forcings, returning to a transient stage of its geomorphic evolution.