Uplift Zone Research Articles

Geomorphic mapping and investigation of the uplifted piedmont zone between Haridwar and Kotdwar, Indo-Gangetic Plain, India

Active tectonics plays a crucial role in the landscape evolution at the decadal to thousand to million-year time scale. Datasets to examine landscape changes at a decadal scale are rare in the Indo-Gangetic Plain (IGP), which is one of the most dynamic areas in the Himalayan orogenic front. In this paper, we report decadal-scale landscape changes, which occurred in the last 40 years in the piedmont zone of the Haridwar – Kotdwar region due to an active blind fault in the IGP. The identification of tectono-morphic features in IGP is difficult to comprehend due to the combined effect of climatically induced sediment supply and tectonically driven subsurface deformation of alluvium sediments in the piedmont zone. We used various satellite imageries and aerial photographs available from 1970, to detect and map the changes in the flow pattern of rivers in the study area, which resulted due to gradient change. Using optical satellite imagery, geomorphic indices, and field investigation, we mapped various morpho-tectonic features in the piedmont zone. Due to uplift caused by upwarping, a topographic high of ~40 ​m is observed in the Malin Fan, which has led to the migration of the subparallel rivers emerging from the Sub-Himalaya. We report an eastward shift of ~8 ​km in a period of ~40 years by the Malin River; the Khoh River also migrated towards the east and the Sigadi Sot River migrated towards the west abandoning its paleo courses. We propose that the neotectonic deformation by the subsurface Najibabad Fault (NF) has caused an upwarp of the Malin alluvial fan in the western Ganga Plain. The Gradient Length Index (GLA) anomalies calculated for the major rivers in the study area also show a series of negative anomalies, which is in agreement with an upliftment zone in the IGP. Remote sensing and morphometric analysis identified the potential uplift zone ~5 ​km north of NF in the piedmont zone, which is supported by field studies. It is concluded that the slip along NF will be essential to understand the evolution of the piedmont zone, which is actively deforming and can be a potential seismic hazard zone in the future.

Comparison of Seismicity and Average Focal Mechanisms of Javakheti Highland Earthquakes with Regional Gravitational-Field Anomalies

This article provides a comparative analysis of the anomalies in the values of the regional gravity field with the spatial distribution of the earthquake epicenters in the Javakheti Highland. It is shown that the epicenters of earthquakes with magnitudes M ≥ 4 are confined to the gradient zones, where significant relative minima and maxima of the anomalies of the gravitational field in the Bouguer reduction are observed. The average mechanisms of earthquakes in individual seismogenic blocks of the region were obtained for the observation period from 1971 to 2015, which indicate that normal faulting is the dominant type of movements in the earthquake foci. The result is explained by the processes occurring in the subcrustal layer and leading to the decompaction of matter in the uplift zones, which is one of the main factors in the occurrence of negative gravity anomalies in the area under consideration.

Metallogeny of the Jinyu Graphite Deposit, Sichuan Province

Graphite deposit is important ore in Huili County, Sichuan Province. It is located in the middle part of the Kangdian axis and the middle part of the Kangdian basement fault uplift zone. The graphite deposit is located in the strata of the Dayingshan Formation of the Lower Proterozoic Hekou Group. The deposit belongs to sedimentary metamorphic graphite deposit formed under the dual factors of regional and thermal contact metamorphism. The ore body is strictly controlled by horizons. Graphite is composed of migmatized graphite quartz schist ore and migmatized graphite schist ore. The former is of the main type and the latter to the second type. Through comparative analysis of metallogenic geological and geophysical characteristics, it is considered that the gold rain graphite deposit is influenced by strata, structure, magmatic rocks, metamorphism, migmatization and other factors.

Tectonic evolution in the Early to Middle Pleistocene off the east coast of the Boso Peninsula, Japan

Abstract The Kanto Basin developed, starting c. 3 Ma, influenced by the subduction of the Philippine Sea plate and the Pacific plate. Sediments in this basin have influenced the geomorphology of the Kanto region. In the Boso Peninsula, located at the eastern edge of the Kanto Basin, uplift continues in what is called the Kashima–Boso uplift zone. Although the development of this uplift after the Late Pleistocene is well understood, there are few data from the Early to Middle Pleistocene. In this study, we investigated the offshore shelf area east of the Boso Peninsula using a high-resolution seismic reflection survey, and report new information on the geological structure and uplift processes in the area from the Early to Middle Pleistocene. We identified the Kujukuri-oki anticline and the Kujukuri-oki normal fault zone. The Kujukuri-oki anticline, more than 47 km long, is north–south striking and deforms the Kujukuri-oki Group. There are numerous normal faults with displacements of less than tens of metres spread widely in the survey area (Kujukuri-oki normal fault zone). These findings reveal that the Kujukuri-oki anticline uplifted during the end of the Early Pleistocene and attenuated during the Middle Pleistocene. This anticline comprised the axis of the Kashima–Boso uplift zone at the Boso Peninsula from the Early to Middle Pleistocene and the Boso Peninsula is located at the western limb of this anticline.

Crustal structure beneath the volcanic field in the Tihamat Plains, Saudi Arabia: An integrated model constrained by gravity modelling and receiver function results

• Structure of rift-related volcanic rocks in Tihamat Plains is constrained by gravity and receiver function results. • Two-layered-crustal-structure is envisaged in the Tihamat Plains, Saudi Arabia. • Moho uplift and magma underplating in the lower crust are visualized. The Tertiary Tihamat-Asir-Volcanic-Zone (TAVZ) in the Tihamat Plains (TP) at the Arabian Shield margin north of the southern Red Sea is largely obscured by Quaternary alluvium and salt deposits, but partly exposed. We integrate available gravity data in the TP which is represented by three semi-circular Bouguer Anomaly (B.A.) highs with peak values of 30 mgal, situated at distances of ~ 50 km. This feature suggests prevailing anomalous crustal masses under the TP and were investigated using: (i) Digital Elevation Model (DEM); (ii) radially averaged spectral estimates on the causative source body depths within the crust; (iii) tilt-angle derivatives with horizontal derivatives of the tilt-angle values; and (iv) a theta map to define the edge of the continental crust in offshore Jizan. 2D gravity models for two traverses, the Mansiyah-Baysh Traverse (MBT) and Suq-Al-Ahad Traverse (SAAT), were constructed across the TAVZ, constrained by Receiver Function (REF) results from ten broadband seismic stations. Additional constraints for gravity interpretation come from the physical properties derived from REF results for the upper and lower crust. Our integrated crustal model infers a zone of Moho uplift approximately ~ 40 km wide, with vertical relief of 10–12 km at depths of ~ 37–45 km, where the average density of the crust is appreciably higher. Gravity models indicate a large volcanic field beneath the TP extending along the coast of the Red Sea. We find that crustal modification is an outcome of crust–mantle interaction owing to an elevated thermal regime under the TP.

Late Holocene uplift of a coastal terrace near the Akatore Fault, southern New Zealand

ABSTRACT Late Holocene earthquake activity on the reverse Akatore Fault of southeastern South Island has caused uplift along >20 km of nearby coastline, with the last major earthquake event c. 800 years ago. Fault-related uplift has exposed a prominent rocky and sandy terrace along the coastline. We used a combination of approaches including land-based observations, LIDAR remote sensing, and radiocarbon dating of shell deposits, to reveal the extent and nature of past uplift in the region. Cumulative uplift of this terrace varies laterally from <1 m at the northern and southern ends to possibly exceed 5 m in the central portion. The coastal terrace lies below a steep fossil sea cliff. Caves at the base of this cliff contain shells with radiocarbon ages <500 years old, implying persistence of large wave incursion right across the terrace after uplift. A major uplift event of ∼2 m along the whole 20 km of shoreline caused extirpation of some intertidal kelps that now have genetically distinct lineages in the uplift zone.

A novel geomatics method for assessing the Haughton impact structure

AbstractTerrestrial impact structures are typically modified by erosion, burial, and tectonic deformation. Their systematic morphologies are typically reconstructed through a combination of geological and topographic mapping, satellite imagery, and geophysical surveys. This study applies a novel geomatics approach to assessment of the morphology of the extensively studied Haughton impact structure (HIS), Devon Island, Nunavut, in order to test its potential to improve the accuracy and quality of future impact structure reconstruction. This new methodology integrates HIS lithological data, in the form of digitized geologic mapping, with a digital elevation model, within diametrically opposed, wedge‐shaped couplets, and plots these data as pseudo cross sections that capitalize on the radial symmetry of the impact structure. The pseudo cross sections provide an accurate reconstruction of the near‐surface stratigraphic sequences and terraces in the faulted annulus of the modified crater rim. The resultant pseudo cross sections support current interpretations regarding the 10–12 km diameter of the transient cavity, and successfully reproduce the visible outer ring and intermediate uplifted zone within the central basin. Observed positions of vertical offsets suggest that the extent of impact deformation extends beyond the current estimates of the apparent crater rim to radial distances of between 14 and 15 km. Finally, the new geomatics approach provides an improved determination of the spatial, stratigraphic, and temporal relationships among the Haughton Formation lake sediments, allochthonous crater‐fill impactites, and uplifted target rocks, and indicates that there was a not‐insignificant time gap between the formation of the impact structure and the deposition of the sediments.

Dating the Acraman asteroid impact, South Australia: the case for deep drilling the ‘hot shock’ zone of the central uplift

The deeply eroded Acraman structure in the Mesoproterozoic Gawler Range Volcanics, Gawler Craton, South Australia, ranks among the world’s largest known impact structures, with a transient crater ∼40 km in diameter and a ∼90 km-diameter collapse crater. An impact age of ca 590 Ma is suggested by Rb–Sr shale dating of Ediacaran strata hosting a related ejecta band of volcanic fragments in the Adelaide Rift Complex and Officer Basin, and ca 580 Ma by chemostratigraphy. Ascertaining an accurate and precise impact age would greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. However, numerous attempts to date the impact, using material from exposures at Acraman and the ejecta band, have been unsuccessful. U–Pb dating of zircons from shattered dacite basement, melt rock and ejecta by three laboratories gave ages related to the 1592 Ma Yardea Dacite. K/Ar and 40Ar/39Ar dating of end-member K-feldspar in melt rock by two laboratories provided early Paleozoic ages, indicating later fluid movement. Although 80% of terrestrial impact structures ≥40 km in diameter have been drilled, Acraman has not. Deep drilling of the ‘hot shock’ zone of the unexposed central uplift is required to obtain zircons with U–Pb ratios that were likely reset by the impact. High-resolution aeromagnetic data for Acraman reveal an elliptical magnetic low measuring 19.5 × 18.3 km, with NNE–SSW-trending major axis and a high-amplitude dipolar anomaly of the central uplift that is offset to the SSW. The magnetic signature suggests oblique impact from the SSW. The source of the dipolar magnetic anomaly, centred ∼1 km below the Lake Acraman salina and with a remanence direction concordant with that of the melt rock, marks the ‘hot shock’ zone and a potential target for drilling. The scientific rewards of such drilling could be substantial. KEY POINTS Acraman in the Mesoproterozoic Gawler Range Volcanics, South Australia, is one of the world’s largest known impact structures, with a related ejecta band of volcanic fragments hosted by Ediacaran (ca 590–580 Ma) strata in the Adelaide Rift Complex and Officer Basin at unfolded distances from 250 km up to 550 km from the impact site. Numerous attempts at U–Pb dating of zircons from shattered volcanic basement and melt rock at Acraman, and zircons from the ejecta, gave un-reset basement ages, and K/Ar and 40Ar/39Ar dating of melt rock gave early Paleozoic ages related to later fluid movement. An accurate and precise age for the impact would provide a reliable age for the ejecta-hosting Ediacaran strata and greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. Deep drilling of the ‘hot shock’ zone of Acraman’s central uplift, inferred to be the source of a high-amplitude dipolar aeromagnetic anomaly centred ∼1 km below the Lake Acraman salina, is required to obtain zircons with U–Pb ratios most likely to have been reset by the impact.

Characteristics of the central uplift zone in Qiangtang Basin and its tectonic implications:Evidences from airborne gravity and magnetic data

Academia still has different opinions on whether there is a consecutive central uplift belt in the Qiangtang Basin.The latest high-precision airborne gravity and aeromagnetic data provided in this article verify the existence of the central uplift belt,which is controlled by two faults,traversing the Qiangtang Basin from east to west.A set of near-north-south left-lateral slip fault systems divide this uplift belt into several parts.The uplift belt,gradually converged from west to east,has obviously different characteristics between the east and west sides of Shuanghu County.The west section shows large-scale uplift of the basement,and the bedrock depth is generally within 3~5 km,which is much shallower than those in the North and South Qiangtang depression with the basement depth of 7~15 km.However,the uplift amplitude of the eastern segment decreases significantly,mainly manifested as a low base uplift.In addition,the central uplift belt shows obvious“multi-segments”and“step-like”decreasing trend from west to east,controlled by near-north-south faults.The basement depth of the Shuanghu-Yaqu section is between 5 and 7 km,and that of the Yaqu-Gonney section is between 7 and 9km.According to the structural stratification comparison,it is reveraled that the North Qiangtang Block has a smaller uplift amplitude and better stability than the South Qiangtang Block.The differences in geophysical properties of the basement between the North and South Qiangtang depression indicate that there is not an unified Precambrian metamorphic basement in the Qiangtang Basin,and the formation of the central uplift zone may be related to the melange zone formed during the closure of the Paleo-Tethys Ocean.

Structural Controls on Slope Failure Within the Western Santa Barbara Channel Based on 2‐D and 3‐D Seismic Imaging

AbstractThe Santa Barbara Channel, offshore California, contains several submarine landslides and ample evidence for incipient failure. This region hosts active thrust and reverse faults that accommodate several mm/yr of convergence, yet the relationships between tectonic deformation and slope failure remain unclear. We present 3‐D and 2‐D multichannel seismic reflection (MCS) data sets, multibeam bathymetry, and chronostratigraphic constraints to investigate the controls on slope failure. Splay faulting along the North Channel Deformation Trend (NCDT) coincides with a distinct zone of compressional uplift and onlapping of steeply dipping Quaternary strata. The NCDT is spatially correlated with seafloor fissures, and 3‐D seismic analyses reveal an intricate system of en echelon reverse faults that offset sediments younger than ~25 ka. Localized uplift zones are located between faults, one of which underlies the Gaviota landslide headscarp. We observe a direct relationship between slope failure and along‐strike variations in the tectonostratigraphic framework. Based on geophysical properties at Ocean Drilling Program (ODP) Site 893, we predict a trend in compaction and porosity reduction in the basin that drives pore fluids up‐dip, toward the zone of onlap above the NCDT, thus reducing slope stability. This interplay between tectonic, sedimentary, and fluid‐flow processes along the NCDT has created a confluence of preconditioning factors, with Gaviota and Goleta landslides being distinguished from the surrounding slopes by their position above the NCDT. The distribution of seafloor fissures suggests sections of the slope remain unstable and are prone to future landsliding. These results provide insights into the processes and 3‐D feedbacks that lead to slope instability along other convergent margins.

Crustal control on basement uplift beneath the Ghawar Anticline, Saudi Arabia—gravity modeling with receiver function constraints

The Ghawar Anticline (GA) belongs to super-giant Rayn Anticlines in Eastern Saudi Arabia (ESA). The origin of GA is ascribed to basement-uplift, although, its evolution remains obscure due to inadequate knowledge on configuration of deeper crust and role of crust in producing the basement uplift. The nature of deeper crust is comprehended by an integrated crustal model utilizing DEM, Bouguer anomaly (BA) map, and high-pass-filtered residual BA map by using Laplacian operator, tilt derivative, theta maps, and Euler 3D convolution map on BA data. These maps prove helpful in delineating the structural outline of GA and its edge detection of the uplifted basement against the adjoining sub-basins. 2D gravity inversion for a traverse represents a model on subsurface mass anomalies extending from basement to Moho depth, for which, constraints are utilized based on the nature of seismogenic crust in ESA and available results of receiver function for four seismic stations. A 3-layer source on mass anomalies with depths of 3–5, 22.5, and 40 km is inferred. Poisson’ ratio based on Vp/Vs values is high: 0.41–0.42 on its limbs to 0.44 at its median part, where the receiver function data reveals a zone of mantle uplift. Main results derived from Integrated Gravity Model underlying the traverse are as follows: (i) Moho is uplifted by ~ 9 km below GA, for a 220-km width, (ii) the zone of basement uplift in the top crust is ~ 4.5 km over a distance of ~ 75 km, where deep-penetrative faults assist the basement uplift, and (iii) a higher thermal regime probably influenced the crustal configuration below GA.

Structural deformation characteristics and shale gas preservation conditions in the Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin

The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China, where shale deformation and reformation are intense and the factors controlling sweet spots are complex, so the preservation conditions have an important impact on the enrichment of shale gas. In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling, this paper carried out a geological survey on field outcrops. Then, based on drilling, mud logging and physical property test data, the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed, and the development characteristics of formation joints and fractures, the sealing capacity of shale surrounding rock and the distribution characteristics of gas reservoirs were studied. Finally, the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed. And the following research results were obtained. First, in the Zhaotong National Shale Gas Demonstration Area, three structural deformation patterns are developed from south to north, including trough type, equal amplitude type and baffle type, which are distributed in three major deformation zones, respectively, i.e., the shear deformation zone of Central Guizhou Uplift, the compression–torsion deformation zone of northern Yunnan–Guizhou Depression and the compression deformation zone of Southern Sichuan Depression. Second, three types of joints and fractures whose relationships with the direction of strata are high angle, middle–low angle and bedding intersection are developed in the Wufeng–Longmaxi formations and its overlying strata, and their occurrence characteristics are basically consistent with those of the three major deformation zones. Third, the shale of Wufeng–Longmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of source–reservoir integration and self-sealing hydrocarbon accumulation. And combined with the sealing ability of the overburden strata and the roof and floor, its preservation conditions are overall better. Fourth, from the perspective of shale gas component, this area can be divided into three belts, i.e., methane, methane + nitrogen mixture and nitrogen from north to south. And the preservation conditions of shale gas are generally better in the north and worse in the south. In conclusion, the shale in the central–northern part of Zhaotong National Shale Gas Demonstration Area (compression deformation area and its southern margin) is the most favorable area because of its large shale thickness, weak reformation and deformation, bedding development of joints and fractures, good sealing performance and excellent preservation conditions. The compression–torsion deformation zone of northern Yunnan–Guizhou Depression in the central part is moderate in preservation conditions, and it is the relatively favorable area. The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions, and it is a prospective area.

Measurement of coarse aggregates movement characteristics within asphalt mixture using digital image processing methods

The movement of aggregates plays an important role in the permanent deformation of asphalt mixture. To provide a reference for the design of asphalt mixture, this study conducted in-depth analyses of the mechanisms involved in coarse aggregate movement and rutting subjected to load by using digital image processing (DIP) technique. The movement characteristics of coarse aggregates within different asphalt mixtures were investigated from a mesoscopic perspective, and correlations between meso-parameters of coarse aggregates movement and rut depth (RD) were analyzed. Finally, a meso-structural model of coarse aggregate movement was proposed. The results indicated that the anti-rutting performance of asphalt mixture is closely related to the meso-movement parameters of coarse aggregates. The movement regions of coarse aggregates subjected to load can be divided into a compacted flow zone, uplifted zone, and a disturbed zone, depending on the movement characteristics of coarse aggregates. There is an obvious linear correlation between the RD and the movement parameters of coarse aggregates in the compacted flow and uplifted zones. Material design measures of asphalt mixture can effectively improve the rutting resistance include using materials that have a coarse gradation and asphalt with high cohesion.

Induced Polarization as a Proxy for CO2-Rich Groundwater Detection—Evidences from the Ardennes, South-East of Belgium

CO 2 -rich mineral groundwaters are of great economic and touristic interest but their origin and circulation paths in the underground are often poorly understood. A deeper understanding of the system plumbery and the development of non—to minimally—invasive near-surface geophysical methods for the prospection of potential productive areas is therefore of great interest to manage future supply. The objective of this contribution is to assess the ability of the time-domain induced polarization (TDIP) method, combined with the electrical resistivity tomography (ERT) method, to make the distinction between CO 2 -rich groundwater from non-gaseous groundwater. Three combined ERT/TDIP tomographies were performed above known uplift zones in the south-east of Belgium where thousands of CO 2 -rich groundwater springs exist. On all profiles, important contrasts in both electrical resistivity and chargeability distributions were observed in the vicinity of the upflow zone, also reflected in the normalized chargeability sections computed from the measured data. Low resistivity vertical anomalies extending in depth were interpreted as a saturated fracture network enabling the upflow of deep groundwater to the surface. High chargeability anomalies appearing directly close to the CO 2 -rich groundwater springs were inferred to metallic oxides and hydroxides precipitation in the upper part of the aquifer, linked to pressure decrease and changing redox conditions in the up-flowing groundwater approaching the land surface. The combined interpretation of electrical resistivity and induced polarization datasets provides a very promising method for a robust prospection of CO 2 -rich groundwater.

New hypothesis to explain Quaternary forearc deformation and the variety of plate boundary earthquakes along the Suruga\u2013Nankai Trough by oblique subduction of undulations on the Philippine Sea Plate

Plate-boundary earthquakes of magnitude 8 or greater along the Suruga–Nankai Trough subduction zone have repeated at intervals of 90–150 years, but with widely varying magnitudes and rupture areas. We propose, based on geologic data on crustal movements of the forearc wedge, that these earthquake variations are controlled by two separate locked zones in the deeper part of the plate boundary. Long-wavelength topographic undulations, composed of alternating zones of uplift and subsidence along the forearc wedge, are associated with 2000 to 3000 m of vertical relief that has accumulated during Quaternary time. We suggest that this crustal deformation in the forearc wedge is caused not by stress loading and release during earthquake cycles, but rather by vertical displacements of the plate boundary caused by the westward movement of undulations in the obliquely subducting slab of the Philippine Sea Plate as it subducts beneath Southwest Japan. Dating of emergent marine shell fossil assemblages shows that the Kii Mountains, an uplift zone at the midpoint of the trough, has undergone uplift events at intervals of 400–600 year, and the latest event of those occurred when the 1707 Hoei earthquake ruptured the entire plate boundary along the trough. We infer that the plate boundary under the Kii Mountains is a locked zone and that slips of this zone, which accompanied ruptures of the entire plate boundary, caused uplift of the mountains by decreasing the plate boundary depth. A similar locked zone is inferred under the uplift zone of the Akaishi Mountains, along the eastern margin of the trough, and the 1854 Ansei earthquake pair was presumably caused by the slip of this zone. During the two 1854 events, the locked zone under the Kii Mountains presumably restricted the rupture propagation to the eastern half of the trough, then a rupture of the western half of the trough followed within 32 h. These locked zones are inferred to slip independently every few hundred years and determine the major patterns of characteristic ruptures along the Suruga–Nankai Trough.

Research and Field Application of ultra-high temperature and high pressure gas wells test in the northern slope of Tazhong

The Shunnan block located on the northern slope of Kathake uplift on the footwall of the Tazhong No. 1 fault zone in the central uplift zone of the Tarim Basin is featured by ultra-large burial depth, which results in the formation pressure of higher than 140 MPa, the formation temperature of higher than 200°C, the serious leakage of large density mud and the extremely-high difficulty in test. Through continuous innovation and exploration of processes and technologies, and continuous summing up of experiences, a complete set of test technologies for the three ultra-wells in the Shunnan block have been formed and successfully applied in the test of well NS7 that has the most adverse working conditions, which provides a certain reference significance for the test of similar three ultra-wells.

Coupling relationship between sedimentary basin and Moho morphology in the South Yellow Sea, East China

The development of the sedimentary basin in the South Yellow Sea that lies between the Chinese mainland and the Korean Peninsula well documents the tectonic evolution of eastern China. However, the Moho morphology and its relationship with the basin in this area remain poorly understood. Here we used high‐resolution 2D seismic lines and well data to map the geometry, structure, and distribution of the sedimentary basin in the South Yellow Sea. Our results suggest that the South Yellow Sea Basin can be divided into two distinct depressions and three uplifts. The depressions consist of eight depositional sags that are largely controlled by ENE‐, EW‐, and WNW‐striking normal faults. The basin depth reaches 9,500 m in the depressions, but is only &lt;2000 m in the uplift zones. Calculated using a gravity stripping method, the Moho depth varies between 27.4 and 31.5 km. The basin is isostatically compensated and the Moho morphology approximately mirrors that of the basin basement. The Moho lows correspond to the uplift zones and Moho highs correspond to the depression zones, with exception of a sag in the Northern Depression. This exception is caused by the presence of a geological body of high velocity and high density beneath the sag. This body is likely to represent high‐pressure metamorphic rock that initially formed during the collision between the Sino‐Korean and Yangtze cratons and are currently overlain by the sedimentary basin. Based on the stretching factors and strain rates of the South Yellow Sea Basin, we propose that development of the basin was primarily driven by the subduction and retreat of the Pacific Plate since the Late Cretaceous, combined by far‐field effects from the convergence between the Indian and Eurasian plates during the Cenozoic.

Geological Controls on High Production of Tight Sandstone Gas in Linxing Block, Eastern Ordos Basin, China

AbstractTight sandstone gas in the Linxing Block, eastern Ordos Basin, has been successfully exploited. The high performance is mainly a result of the special geological conditions. The key geological controls for high production have been discussed on the basis of seismic data, field observation, sample features, mercury porosimetry, mechanical properties, and basin modeling. Firstly, the coal measures have good gas generation potential, not only because of the existence of coalbeds and organic‐rich shales, but also because coal laminae and microbial mats in the shales significantly increase their total organic carbon (TOC) contents. Secondly, except for the uplifted zone of the Zijinshan complex and the eastern fault zone, rare large faults develop in the Carboniferous–Permian sequence, ensuing the sealing capacity of cap rock. Small fractures generally concentrated in the sandstones rather than the mudstones. Thirdly, gas accumulation in the Linxing Block was controlled by the tectonic, burial and thermal histories. Gas accumulation in the Linxing Block started in the Late Triassic, followed by three short pauses of thermal maturation caused by relatively small uplifts; the maximum hydrocarbon generation period is the Early Cetaceous as a combined result of regional and magmatic thermal metamorphisms. Field profiles show abundant fractures in sandstone beds but rare fractures in mudstone beds. Mechanical properties, determined by lithostratigraphy, confine the fractures in the sandstones, increasing the permeability of sandstone reservoirs and retaining the sealing capacity of the mudstone cap rocks. The modern ground stress conditions favor the opening of predominant natural fractures in the NNW–SSE and N–S directions. These conclusions are useful for exploring the potential tight sandstone gas field.

Evolution of the Ecuador offshore nonaccretionary-type forearc basin and margin segmentation

Forearc basins have developed along accretionary and nonaccretionary convergent margins. Here, we investigate the evolution of an offshore nonaccretionary-type forearc basin that has developed along the Ecuadorian convergent margin. We used 2D-Multichannel Seismic Reflection profiles to recognize five seismic units overlying the acoustic basement. The units were dated by correlation with wells and regional stratigraphy. They recorded the structural evolution of the margin into North, Central-North and Central-South margin segments identified from Gravity Free Air Anomalies. Intersegment transition zones accommodated deformation related to the margin segmentation, contributing to the development of shelf forearc depocenters. An offshore forearc basin (subunit L1a) developed on accreted oceanic terranes during the middle-to-late Eocene. The basin was affected by normal faulting during the Oligocene to early-middle Miocene (subunit L1b). This extension stage initiated during the rifting and oblique subduction of the Farallon plate beneath the Ecuador margin. The basin underwent an early-middle Miocene uplift outlined by unconformity U1 potentially associated with the subduction of the young Nazca plate, in a less oblique plate convergence environment. During the early-Pliocene, the Central-South margin segment individualized by uplift during the formation of unconformity U2. The Manta anticline, which developed in the intersegment transition zone, accommodated the segmentation. This event is associated with the arrival of the Carnegie ridge in the subduction. The North segment individualized by uplift during the Pliocene early-Pleistocene formation of the Pedernales structural high, which may coincide with a reactivation of the Canandé fault. Synchronously, unit L3 sediment recorded the subsidence of the Central-North segment, and strike-slip tectonics in the area of the Jama-Bahía depocenter. A mosaic of middle-to-late Pleistocene unit L5 depocenters that alternate with uplifted zones along the shelf likely recorded the subduction of the topographically irregular Carnegie ridge. The study provides a remarkable example of the evolution of a non-accretionary-type forearc basin.

Geomorphic indices and longitudinal profile of the Daba Shan, northeastern Sichuan Basin: Evidence for the late Cenozoic eastward growth of the Tibetan Plateau

The Daba Shan Orocline is located in the northeastern Sichuan Basin, and has undergone foreland propagation and distinct surface uplift owing to the eastward expansion of the Tibetan Plateau since the late Cenozoic. In order to describe and quantify the earth surface processes respond to deep geological mechanisms, and to detect the kind of tectonic deformation in the Daba Shan area during the late Cenozoic, various geomorphic indices were analyzed for study area. The obtained results are: (1) The northeast of the Hanzhong Basin, the Hannan-Micang Massifs, along the Chengkou-Fangxian fault, and the Shennongjia Massif exhibit intense tectonic activity. (2) The spatial patterns of the channel steepness indices indicate that the western segment of the northern Daba Shan (Fenghuang Shan and Paotaizi region) have higher uplift rates than the eastern. (3) The longitudinal profile analysis revealed that the landscape evolution of the Shennongjia Massif is in a transient state, with an uplift amplitude of 1700–1900 m since the end of the Paleogene (25 Ma), and an average uplift rate of 0.072 ± 0.004 mm/a. The paleochannel reconstruction indicate an incision of ~900–1000 m since the late Neogene (3.0–3.4 Ma), with the average uplift rate being 0.3 ± 0.03 mm/a. (4) Three tectonic deformation zones can be distinguished in the Daba Shan (from west to east), the shortening deformation, strike-slip deformation, and vertical uplift zones. These observations suggest that the eastward growth of the Tibetan Plateau has affected the Daba Shan area and shaped the modern landscape.