NW-SE Lineaments Research Articles

Aeromagnetic geophysical data 3D inversion: Revealing internal and external structures of Morro São João Alkaline Complex, Southeast Brazil

This study investigates the internal and external structures of the Morro São João Alkaline Complex, located in Southeast Brazil, using high-resolution aeromagnetic geophysical data. The primary objective is to delineate the architecture of the underlying magma chamber system. The geophysical investigation primarily employs aeromagnetic data processing techniques, unveiling subsurface structures and shedding light on the magmatic evolution of the region. Aeromagnetic data from the Rio de Janeiro Aerogeophysics Project were processed and interpreted to identify significant magnetic anomalies and structural features. The results reveal five distinct magnetic domains correlating with various lithologies, including Monzogranite and Amphibolite Paragneiss. The observed NW-SE and NE-SW magnetic lineaments are crucial indicators of the region’s structural complexities, reflecting tectonic influences and highlighting the significance of regional geological context in deciphering magnetic anomalies. The geophysical anomaly associated with Morro São João, characterized by its rounded shape and eccentricity, aligns with the documented lithological variations. Numerical inversion techniques were employed to create a detailed three-dimensional model of the magmatic system. The main geophysical result is the 3D inversion model, which unveils a magmatic chamber approximately 4 km beneath the surface. This model reveals the subsurface architecture and conduits from the chamber, providing a dynamic perspective on the processes shaping the hill’s morphology. The integration of regional magnetic lineaments, lithological variations, and the 3D inversion model elevates our comprehension of the geophysical intricacies of the Morro São João Alkaline Complex.

Digital topographic analysis and lineament interpretation south of the Lena Delta, North Siberia: Landscape expression of its tectonic activity

This study applies semi-automated techniques to analyze the landforms, morphostructure, and geology of the Kharaulakh and Chekanovsky sectors, south of the Lena Delta, northern Siberia. High-resolution data, including TanDEM-X 30 m spatial resolution Digital Elevation Models (DEM), 2 m spatial resolution ArcticDEM Digital Surface Models (DSM), and Sentinel-2 satellite imagery, serve as the basis for the analysis. Digital terrain classification and identification of tectonic lineaments are performed using the Benthic Terrain Modeler (BTM) and Linear Extraction (LINE) algorithm, respectively. Additionally, a hypsometric analysis is conducted to assess areas of potential neotectonic activity. 873 lineaments are identified, primarily in NE-SW and E-W orientations. NW-SE lineaments perpendicular to the lithological and fold belt strikes in the Kharaulakh Ridge suggest inheritance from original depositional settings or later compressional tectonics, now appearing as valleys and weak zones facilitating erosion and river incision. Longer N-S or NNW-SSE lineaments in the Kharaulakh Sector are associated with thrust sheets of the Verkhoyansk fold-and-thrust belt and Cenozoic graben structures linked to the formation of the Laptev Sea Rift System and ongoing regional deformation. The Chekanovsky Sector, marked by epiplatform blocks and hills, presents a dissected plateau with steep valleys. Here, high hypsometric integral values are attributed to compression and uplift near the southwestern boundary of the Laptev Sea Microplate.

Potential field survey of subsurface structures of the NW segment of the Zagros Fold‐Thrust Belt, Kurdistan Region

AbstractThis study reports results of gravity and magnetic surveys conducted for the first time in the western segment of the Zagros Fold‐and‐Thrust Belt in the Kurdistan Region. This study attempts to delineate deep structures in an area, which has not been surveyed before. CG‐5 Autograv gravimeter and G‐857 portable proton‐precession magnetometer were used to acquire gravity and magnetic data from 750 stations along over eleven traverses across and parallel to the Zagros trend (NW–SE). Six of these traverses are parallel to the Zagros trend, whereas the others are perpendicular to the trend of the other traverses and can be tied where they intersect. The total length of the traverses is about 1000 km. Tilt Angle of horizontal gradient method is used to detect regional gravity and magnetic lineaments. The mapped lineaments from regional gravity and magnetic surveys are divided into two categories: the NE–SW lineaments, which represent transversal faults in the study area, and the NW–SE lineaments, which represent the Zagros Thrust Faults, some of which may be linked to the inverted basement normal faults of Arabian passive margin (the NW–SE Najd Fault system). The results show that there is a relationship between the regional gravity and magnetic lineaments outlining the same deep geological features. The data presented here confirm the presence of regional longitudinal and transversal lineaments documented in other studies (e.g. Anah‐Qalat Dizeh Fault, Surdash‐Tikrit Fault, Sirwan Fault, Khanaqin Fault, Zagros Mountain Front Fault, Baranan Back Thrust Fault and High Zagros Reverse Fault) and outlines new lineaments not mapped before. Most of the detected regional lineaments in the current study coincide with the previously confirmed lineaments, which have played a significant role in the tectonic evolution of the Zagros Fold‐and‐Thrust Belt. As such, this study contributes to a better understanding of the subsurface structure of the Kurdistan segment of the Zagros Fold‐and‐Thrust Belt and probably the rest of the belt.

A GIS-based modified frequency ratio model for gold potential mapping in Kelantan Malaysia

Mineral system factors control the distributions of orogenic gold deposits in our immediate geological environment. The spatial knowledge of the relationship between the mineral factors and the gold deposits are crucial to locating these deposits in the environment. However, there is a current challenge in understanding the spatial correlation between ore genesis factors and orogenic deposits. Our paper analysed the spatial relationship between ore controlling factors and orogenic gold deposits in the Gua Musang area Kelantan, Malaysia. The procedure applied a modified frequency ratio model (MFR) to generate the gold potential map of the study area. The model relied on the spatial distribution of known gold deposits to predict new ones. Eight (8) known gold deposits and five (5) selected factors were used in the analysis. These factors include NE-SW lineaments, NW-SE lineament, host rock, heat source, alteration of iron and clay. The new findings show the factor with the highest predicting rate (Lineaments NE-SW) as the major gold deposits distribution factors within the study area. The created map highlight both known and new deposit locations. The area under curved (AUC) statistical graphs were used for the accuracy test. The results show 92.50% accuracy; thus, the approach is adaptable for gold mapping in Malaysia.

Carbonate-rock aquifers in arid environments (central Tunisia, Western Mediterranean province): gravity and time domain electromagnetic methods investigations

Gravity and time domain electromagnetic (TDEM) methods were used in this study to investigate the subsurface hydrogeology of the carbonate-rock aquifer in arid environments (central Tunisia, Western Mediterranean province). The El Houdh basin can be considered an appropriate case for evaluating the vulnerability of groundwater resources under present-day climate change. The identification of structural context and the discontinuities affecting the Eocene or Campanian to Maastrichtian carbonates is an important key to recognize water recharge and discharge pathways and to develop effective and long-term groundwater exploration strategies. First, we have produced an available residual gravity field using a specific Gaussian filter. Then, we generated derivative maps, Euler deconvolution solutions map and a 3D gravity model to delineate different anomalies and to estimate the depth-to-basement parameter and the subsurface density contrasts. Positive and negative anomalies mapping and 3D gravity modelling showed that the El Houdh basin is associated with an asymmetric ‘perched syncline’ with a segmentation into NE–SW sub-basins (local negative residual anomalies) separated by NW–SE lineaments. The TDEM survey was calibrated using boreholes to image the karst saturated and unsaturated zone and to deduce the epikarst and endokarst relationship. Finally, the proposed method provides a fast and valuable approach for better management of hydrogeological exploitation. Thematic collection: This article is part of the Climate change and resilience in Engineering Geology and Hydrogeology collection available at: https://www.lyellcollection.org/cc/climate-change-and-resilience-in-engineering-geology-and-hydrogeology

The Relationship between Lineament Patterns and Mass Movements in the Municipality of Vitória (Espírito Santo, Southeast Brazil)

The main objective of this research is to analyze and relate lineament patterns to the occurrence of mass movements in the municipality of Vitória (Espírito Santo, Brazil). The methodology used consists of cabinet and field analyses. In a cabinet, Lineament Maps were made from the manual extraction technique, using ArcGIS 10.5 tools, on a Digital Elevation Model (DEM) with different artificial lighting (scale 1:110000) and Digital Orthophotos (scale 1:25000) and orientation rosettes generated. In the field, the geological structures were identified and analyzed from the lineaments identified in the cabinet, and their orientations were measured (Brunton compass). These data were integrated and analyzed from the Municipal Civil Defense mass movements records, referring to the period between 2006 and 2020. It was possible to verify the orientation patterns of dominant geological structures in the area (NNW-SSE and NW-SE, followed by NE-SW), including all measured fractures. At the regional scale, more mass movements occurred near NNW-SSE, NW-SE, and NE-SW orientation lineaments. At the local scale, these processes occurred more frequently in the vicinity of NNW-SSE, NNE-SSW, and NE-SW orientation lineaments. Data analysis demonstrates the important relationship between lineaments and occurrences of mass movements with regional geological structures and neotectonic events of the Espírito Santo in altered rocks of the Precambrian basement and Cenozoic deposits. The data revealed an association between the density of geological structures and the occurrence of mass movements since the increase in density is directly proportional to these processes, except for the Very High -density class, which presented little area representation.

Fractal analysis of lineaments using CryoSat-2 and Jason-1 satellite-derived gravity data: Evidence of a uniform tectonic activity over the middle part of the Central Indian Ridge

The availability of high-accuracy altimetry and satellite gravity data leads to the development of high-resolution global gravity model data. It helps in understanding the structure and evolution of remote oceanic regions. The present study utilizes fractal analysis of structural patterns identified from the Sandwell (2014) gravity data to understand the geological implication over the Central Indian Ridge (CNIR). The normalized standard deviation (NSTD) edge detection technique has been used to identify different possible lineaments/structural patterns. Generally, the Northern, Middle, and Southern blocks of CNIR are characterized by ENE-WSW, NE-SW, NNE-SSW, and NW-SE lineaments. However, the Southern block is additionally characterized by few E-W-oriented lineaments. The lineament density map indicates Southern block exhibit a maximum lineament concentration than other two blocks. The fractal dimensions of lineaments in the Northern, Middle, and Southern blocks are in the order of 1.64, 1.627, and 1.666, respectively. The high fractal dimension and lineament density values of the Southern block indicate a concentrated distribution of lineaments. The low fractal dimension and lineament density values over the Middle block indicate a greater degree of uniformity in the lineament distribution than the other two blocks, representing a relatively stable tectonic setup over the Middle block. The high multifractal width of the Southern block is characterized by variable spreading rates and frequent ridge jumps. The multifractal studies demonstrate the presence of medium-small scale lineaments over the CNIR. The large numbers of small and discontinuous lineaments over the CNIR indicate strong but less frequent tectonic activity along the ridge axis.

Influence of geological discontinuities on the groundwater flow of the Serra Geral Fractured Aquifer System

Groundwater circulation in fractured aquifer systems is a topic of worldwide interest as they are heterogeneous and peculiar environments. In Brazil, little is known about the groundwater flow within fractured rocks. This knowledge gap motivated the investigation of (1) the statistical variance of the exploited discharges and their relationship with the directions of geological lineaments, (2) the analyzes of the relationship between of the groundwater flow with the different characteristics of the discontinuities and (3) the correlation between the acting stresses with the fracturing geometries that present groundwater flow. To reach these objectives, this paper is circumscribed within the following methods: frequency graphs, normality assumptions test, non-parametric homogeneity tests, multiple correspondence analysis, scanline profiles, and in situ stress analysis. This study was carried out in the Serra Geral Fractured Aquifer System, in Caxias do Sul, Rio Grande do Sul, Brazil. The results showed that most the exploited water wells are associated with the NW-SE and NE-SW lineament directions. There was a predominance of four sets of subvertical fractures (S1, S2, S3, and S4) and one sub-horizontal (S5). Sets of fractures S3, S4, and S5 showed the greatest persistence of fractures and presence of exudation. The tension axes σ1 and σ3 were identified in the (310°; 113°–141°) and (218°; 020°–051°) directions, respectively. The groundwater circulation in sets of fractures S3 and S4 is related to tensions σ1 and σ3 and the most exploited lineament directions NW-SE and NE-SW, while S5 is correlated to tension σ2 and behaves as a facilitator of the groundwater circulation in the underground flow network.

Structural signatures of the Amazonian Craton in eastern Colombia from gravity and magnetometry data interpretation

Geophysical interpretation of potential field data plays an important role in the integration of geological data. Estimation of density and magnetic susceptibility variations within the upper crust helps evaluating the continuity of geological structures in the field. In the present study we use gravity and magnetic data in NW Amazonian Craton in Colombia. Total horizontal gradient of the reduction to magnetic pole were used to delineate magnetic lineaments and domains showing four zones, each with its own features. Multiscale edge detection (worming) of the data help delineate upper crustal structures that we interpret as tectonic boundaries that correlate with the four zones identified. 3D density and magnetic susceptibility inversion showed high density and/or high magnetic susceptibility sources correlated with these crustal structures. Zone (1) is located south of the Guaviare River, with predominant NW-SE and NE-SW magnetic lineaments; zone (2), located from south of the Guaviare River to the north, present nearly E-W magnetic lineaments and a deep E-W edge interpreted as a possible shear zone parallel to Guaviare, Orinoco and Ventuari rivers; zone (3) from south of the Vichada River to the north, with NE-SW and NW-SE lineaments; N-S zone (4) cuts the zones (2) and (3), characterized by high density/magnetic susceptibility source bounded by N-S deep edges. A more complete tectonic evolution interpretation requires further work, but we speculate that the zone (4) could indicate an aborted rift/collision suture and that the zone (2) is indicative of a younger deformation event. Shear direction at (2) is not clear: geological maps show NEE-SWW right-lateral faulting, but geophysical anomalies suggest left-lateral displacement, highlighted by left dislocation of the Orinoco River. We also speculate that a N-S edge located at the SE of the area can be related with the Atabapo Belt and the limit of Ventuari-Tapajós and Rionegro geochronological provinces.

MAPPING TECTONIC LINEAMENTS IN THE PRE-CAMBRIAN TERRAIN OF THE ZURU SCHIST BELT, NORTHWESTERN NIGERIA.

Tectonic lineaments within Danko area of Zuru Schist Belt have been generated and analyzed. Digital Elevation Model (DEM) data obtained from United States Geological Survey (USGS) (www.earthexplorer.com) was used for the extraction process. Lineaments extracted were analyzed for their numbers, density, intersection density, relative abundance and spatial distribution using ArcGIS software. The orientation of lineaments was analyzed using Rockware software. Two hundred and eleven (211) lineaments were extracted out of which, 74.4% had a N-S orientation suggesting a wide spread of Pan-African deformation effect while E-W lineaments were less dominant with about 3.971% and may be as a result of not been reoriented north or south away from their original direction. Lineament density is high in the northern and southeastern parts suggesting intense deformation and low in the eastern and southwestern parts of the study area. Lineament intersection reflect multiple deformation events which deformed the region through geologic time. A close relationship between the NE-SW and NW-SE lineaments as revealed by a dendrogram chart suggest that they are conjugate pair with one been dextral and the other sinistral, thus supporting similar deductions about the conjugate mature of the lineaments in northwestern Nigeria.

Recent faulting along Gorontalo fault based on seismicity data analysis and lineament mapping

We focused our study to characterize the geometry and activity of Gorontalo fault. We analysed reviewed the ISC seismic catalogue and the BMKG relocated earthquake events available for the time period of 1960 to 2021, located along the expected location of this fault. In addition, we analysed continuous record from local seismic observatory available for the same period. Further, we mapped the lineaments using 8.3-m resolution DEMNAS data. Tens on shallow earthquakes occurred in the vicinity of this fault with a range magnitude of M 2 to 3. Our lineament analysis however does not reveal distinctive pattern that may indicate the fault manifestation at the surface. The NW-SE trending lineaments are coincidence with the mapped trace of Gorontalo Fault. The weak surface manifestation of the fault scarp may be related to the tropical climatic condition of the area which may obliterate the faulting topography. However, we observed alignment of the seismicity distribution with the mapped NW-SE lineament, indicating that the lineament is likely representing active fault and these earthquakes are associated with faulting along this fault. Our study provide indication that the Gorontalo Fault is active and further study is necessary to investigate subsurface geometry and mitigate its seismic hazards.

Geological Signatures of Tectonic Instability along the North Cambay Basin during the Late Holocene Period, North Gujarat, India

Abstract In the present study, the tectono-geomorphic attributes of the northern part of the Cambay basin, Western India, which has recently witnessed a surge in seismic activity has been investigated. The anomalies in the drainage network (morphometry) along with the sedimentological character of the drainages with OSL chronology was used to unravel the abrupt aggradation and incision processes during the late Holocene period. The analysis reveals two major lineaments i.e. NE-SW, which are related to the transfer faults and NW-SE lineaments, related to the listric/normal faults prevalent in the northern Cambay region. The NW-SE trend exhibited the first order streams, which hints the ongoing tectonic activity along the buried structural elements/faults. The valley fill sediments were incised during the late Holocene period i.e. < 3 ka, which is ascribed to the tectonic activity along the buried structure/faults in the Tharad-Sanchor block of the north Cambay basin. The present study is the first attempt to characterize the tectonic activity along the Tharad-Sanchor block of the north Cambay basin using geomorphometry and optical dating.

An integrated lineament extraction from satellite imagery and gravity anomaly maps for groundwater exploration in the Gongola Basin

Structural trends in the earth's crust can be detected in the form of lineaments and may be useful in several environmental applications such as mineral exploration and hydrogeology. In this study, structural lineaments in the western sector of the Gongola Basin of northern Nigeria were mapped using two approaches - the analysis of gravity data and the processing of Landsat 8 imagery. In the analysis of gravity data, a convolution was done between the fourier kernel obtained from the second horizontal derivative of the truncated horizontal plate and the gravity anomaly. The lineaments were extracted as the sharp gradients in the second horizontal derivative map. The NE-SW and E-W trending lineaments were interpreted as fault (strike-slip wrench) systems. In the second approach, a 5 × 5 directional filter was applied to the Landsat imagery in the N–S, NE-SW, E-W and NW-SE directions. Next, edge detection, thresholding and curve detection were done to extract the lineaments. It was observed that the NW-SE and NE-SW lineaments correlated more with the lineaments/faults in the gravity maps. Comparison of rose diagrams of lineaments as obtained from the remote sensing method shows a high correlation with the major linear structures in the study area. High correlation exists between lineaments delineated from remote sensing and gravity data. Results from the lineament analysis show that groundwater potential is high in the areas with high lineament density. Settlements such as Mallurin Tudu Yautare, Wuro Bundu, Kunde and Tauya which are located in the northern part of the basin have high groundwater potential due to the high lineament density observed from the gravity and the remote sensing methods. Lafiya and Jimbom communities located in the south eastern part of the basin also have high lineament density which signifies good groundwater potential. These results have demonstrated the advantage of remote sensing for detecting lineaments in support of groundwater mapping. This good correlation between lineaments mapped from both methods strengthens existing studies on the structural manifestation of the Gongola Basin. This can serve as a reconnaissance approach to aid more precise geophysical observations.

Variability of orographic architecture of Indo-Burmese Ranges (NE India): constraints from morphotectonic and lineament analysis

Activeness of the tectonic and related sub-surface processes control the surface features that lead to variations in topography and lithostratigraphy. To understand the role of active tectonics in shaping the topography, morphotectonic and lineament studies are important. In this study, geological categorization has helped understand the orogenic evolution of the Indo-Burmese Range (IBR), NE India. This is an arcuate hill range that shows many unique topographic characteristics that incited to categorise the entire IBR into different tectonically active domains: Northern (Changlang district of Arunachal Pradesh); Naga Hills; Cachar and Manipur; and Southern (Mizoram). The Northern and Southern domains are more active than the others. Lineament analysis also indicates the presence of active features in the region with NW–SE, NE–SW, ESE–WNW trends are being common. The Northern and Naga Hills domains have mostly E–W younger lineaments whereas the Cachar and Manipur domains rather show N–S younger trends. The Southern Mizoram domain shows a dominance of older N–S lineaments with younger NW–SE lineaments. These variations result from differential stress conditions, i.e. Indian Plate movement and westward stress from the Burma Plate. This study shows how overall variations in tectonic settings can be related to the orogenic evolution.

Fracture network analysis of Yacoraite Formation in the Tres Cruces sub-basin, northwestern Argentina

The Tres Cruces sub-basin, located in Jujuy province, northwestern Argentina, is characterized by intense N-S folding and faulting. These structures were formed as a result of the Cenozoic shortening that produced the tectonic inversion of the Salta Rift Basin normal faults. Some of the main folds and faults show abrupt trend variations, controlled by NW-SE transverse lineaments. We performed a fracture network analysis over the Maastrichtian-Danian limestones of the Yacoraite Formation, at three folds located in the central sector of the sub-basin. A total of 832 planar fractures were measured in different structural domains. Five main fracture sets were identified, trending NW-SE, NE-SW, ENE-WSW, WNW-ESE and N-S to NNW-SSE. Their relative chronology was established based on the observed abutting relationships. The analysis performed suggests that NW-SE, NE-SW and ENE-WSW trending sets are regionally represented and were formed before the initial stages of folding. Set ENE-WSW is sub-parallel to the convergence direction acting during the Neogene. The other two sets are associated with local perturbations of the far-field signal control by the oblique NW-SE lineaments. The origin of the WNW-ESE set remains unclear; its distribution is locally restricted to the San Bernardo domain. Finally, the N-S to NNW-SSE set shows a synfolding origin generated when the surveyed folds were growing. We then place the various identified fracture sets into a single stress field setting, perturbed by the leading NW-SE transverse lineaments that dominate this region.

Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal)

Volcanic oceanic islands are the emerged portions of large volcanoes that rise abruptly from the ocean floor. Although the geological record of these islands provide some insights into the evolution of their entire volcanic edifices, for a complete picture, it is essential to study the islands' submarine pedestals and surrounding settings. In this study we document the submarine morphology of the Selvagens Islands (Madeira Archipelago, Portugal) and relate it with their subaerial evolution, in order to gain a more complete insight on the evolutionary history of these islands. To this purpose, we employed bathymetric surfaces, backscatter mosaics and subbottom profiler data integrated with geological observations of the subaerial part of the islands. Our study reveals the presence of a complex submarine morphology composed mainly of two deeply eroded central volcanoes – the edifices of Selvagem Grande and Selvagem Pequena – and a less eroded saddle-like ridge related to a fissural volcanic system located between them. Other secondary landforms generated by volcanism, erosion, gravitational collapses, and possible faulting activity, are also present. Whilst the building of the two central volcanoes relates to the older volcanic stages of both islands, the fissural system, with a general NE-SW trend, is probably contemporaneous of the younger volcanic stages of Selvagem Grande. The shelf of Selvagem Grande also features the eroded remains of numerous relatively young volcanic cones, seemingly forming several NW-SE and NE-SW lineaments, the same direction observed onshore for the younger volcanic stage of this edifice. The shelves' break of both Selvagens was affected by multiple landslide scars and channel headwalls. The channels constitute a large drainage network that fans out in a radial pattern along the flanks of both central edifices. In the deeper parts of this submarine drainage, large sediment wave fields are observed in some locations with wavelengths of 300–1,900 m and 2–45 m in height; these tend to form cyclic steps that change gradually downslope to antidunes, and their origin is attributed to sediment density flows that suffer hydraulic jumps when their channel confinement ends and the slope gradient decreases from ~7° to ~2.5°. Several scour features are also found at 3,300–4,000 m water depth, being 3–20 km in width, 10–20 km in length, rectangular or U-shaped in cross-section and 40–100 m deep. They occur around the base of the submarine edifices, where seafloor gradients change to 3.0°–0.5°. Their origin is also related to hydraulic jumps of unconfined sediment density flows, which are able to erode the seafloor and create these features. These morphologies are a testimony to how volcanic, erosional and depositional processes conjugate to shape the flanks of a very long-lived volcanic island system, one of the oldest in the North Atlantic Ocean.

Application of Radar Imagery to Tectonic, Structural and Geological Studies in Afikpo Basin, Southeastern Benue Trough, Nigeria

Radar imagery was used to identify geological features and the production of geological maps of the Afikpo basin. The essence of this study was to delineate significant geological and geomorphological features that have not been imaged by the traditional ground field mapping. The application of Radar imagery technique will be relevant to the discovery of subsurface structures that will aid the accumulation or concentration of certain economic minerals or natural resources. It will enhance the identification of significant geological information such as lineaments, geologic structures, drainages, etc, that will serve as a guide to the actual ground field work investigation. Results from radar imageries revealed drainage pattern, major geomorphological units, mega lithostratigraphic units, lineaments and structures. The geology of Afikpo basin consist of Cretaceous, Tertiary and Quaternary rocks are recognizable; the highly deformed Cretaceous rocks are characterized by regional lineaments. Some of the rivers are aligned along the regional lineaments. The NW-SE and NE-SW lineaments truncate one another, suggesting different ages for the lineament groups. A few sinistral tensional movements occur in the eastern sector of the basin. The major folds in the Afikpo basin have NE-SW and NW-SE trends, and occur as anticlines and synclines. The basement structuring and basin framework suggest a tectonic setting in the southeastern Benue Trough resulting from the Early Cretaceous opening of the South Atlantic Ocean and interpolate movement in Africa. From the evidence currently available we may conclude that the post Santonian Afikpo basin falls within the transtenstional basin categories associated with transform faults. The regional tectonics interpreted from the radar imageries are likely hydrocarbon related structural features.

Episodes of dormancy and eruption of the Late Pleistocene Ciomadul volcanic complex (Eastern Carpathians, Romania) constrained by zircon geochronology

Ciomadul is the youngest volcanic system in the Carpathian-Pannonian Region recording eruptive activity from ca. 1 Ma to 30 ka. Based on combined zircon U-Th and (U-Th)/He geochronology, Ciomadul volcanism is divided into two main eruptive periods: Old Ciomadul (1 Ma – 300 ka; OCEP) and Young Ciomadul Eruptive Period (160–30 ka; YCEP). OCEP activity comprises Eruptive Epochs 1–3, whereas new ages for eight lava domes and four pyroclastic units belonging to the YCEP lead to its further subdivision into two eruptive epochs: Eruptive Epochs 4 and 5. The extrusion of most of the lava domes occurred between 160 and 90 ka (Eruptive Epoch 4) during three eruptive episodes at ca. 155 ka, 135 ka and 95 ka (Eruptive Episodes 4/1, 4/2 and 4/3, respectively) along a NE-SW lineament, which is perpendicular to the regional NW-SE trend of the Călimani-Gurghiu-Harghita volcanic chain. Eruptive Epoch 5 occurred after a ca. 40 kyr of quiescence at ca. 55–30 ka, and is mainly characterized by explosive eruptions with a minor lava dome building activity. All of the dated pyroclastic outcrops, together with the lava dome of Piscul Pietros, belong to the older Eruptive Episode 5/1, with an eruption age of 55–45 ka. The eruption centers of Eruptive Epoch 5 are located at the junction of the conjugated NW-SE and NE-SW lineaments defined by the older eruptive centers. The whole-rock geochemistry of all studied samples is fairly homogeneous (SiO2 = 63–69 wt%, K2O = 3–4 wt%). It also overlaps with the composition of the lava domes of the Old Ciomadul Eruptive Period, implying a monotonous geochemical characteristic for the past 1 Myr. The eruption rates for the Ciomadul volcanism were determined based on the erupted lava dome volume calculations, supplemented with the eruption ages. The activity peaked during the Eruptive Epoch 4 (160–90 ka), having an eruption rate of 0.1 km3/kyr. In comparison, these values are 0.05 km3/kyr for the YCEP (160–30 ka) and 0.01 km3/kyr for the overall Ciomadul volcanism (1 Ma–30 ka). Based on the geochemical characteristics, the quiescence periods and the lifetime of the complex, as well as the relatively small amount of erupted material, this volcanic system can be placed in a subduction-related post-collisional geodynamic setting, which shows strong chemical similarities to continental arc volcanism. The commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption. Instead, comprehensive geochronology, coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields, where the last eruptions occurred several 10's of thousand years ago and therefore they are not considered as potentially active.

The Campo de Calatrava Volcanic Field (central Spain): Fluid geochemistry in a CO2-rich area

The Campo de Calatrava Volcanic Field (CCVF) located in central-southern Spain (along with Selva-Emporda in Catalonia, NE Spain) is regarded as one of the most important CO2 emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and CO2-rich gas discharges from the CCVF. Locally, these CO2-rich fluid emissions represent the remnants of the past volcanic activity that affected this area from the late Miocene through the Quaternary, with the most recent events occurring in the Holocene. The locations of discharging fluids and previous volcanic centers appear to be aligned along well-defined NW-SE and NNW-SSE lineaments, with subordinate trends in the ENE-WSW direction. The chemical and isotopic composition of the thermal waters suggests a meteoric origin, dominated by three distinct geochemical facies: 1) HCO3-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO2-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO4(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalón) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO3-Na type waters, hosted in deep geopressurized CO2-rich reservoirs within the Ordovician basement rocks.The 87Sr/86Sr isotopic compositions (ranging between 0.70415 and 0.71623) and δ34S-SO4 values (+10.7 to +18.3‰ vs. CDT) of CO2-rich fluids are consistent with interactions between water and either the Paleozoic basement, Triassic evaporites, Quaternary volcanic rocks, or a combination thereof. Dissolution of a CO2-rich gas phase into the aquifer produces low pH values (down to 5.4) and enhances water-rock interactions causing relatively high salinity (Total Ionic Salinity: up to ∼185 meq/L). Carbon dioxide is by far the most abundant gas constituent (up to 992 mmol/mol) and is dominated by mantle-derived sources as indicated by the combination of relatively high helium isotopic ratios (up to 2.7 R/Ra), high isotopic ratios of carbon in CO2 (ranging between −6.8 and −3.2‰ V-PDB), and the carbon isotopic signature of TDIC (from −6.8 to +2.2‰ vs. VPDB).In the last two decades, numerous (CO2-rich) gas blowouts have occurred in the area during well drillings, suggesting the presence of a geopressurized gas reservoir at relatively shallow depth.

Structural pattern recognition applied on bathymetric data from the Eratosthenes Seamount (Eastern Mediterranean, Levantine Basin)

The scope of the present work is to apply tested techniques of pattern recognition on bathymetric data from the Eratosthenes Seamount to (a) detect topographic highs and linear-curvilinear lineaments present on the seabed, (b) evaluate the morphostucture of the seamount and its relation with the degree of deformation the region has suffered, and (c) to check if shallow salt movements are associated with specific patterns on bathymetric data. Our scope is implemented by applying a two-step procedure on bathymetric data. Initially, the topographic highs in the study area are detected and their geomorphologic attributes (orientation, average slope, eccentricity, and shape complexity) associated with the degree of seabed deformation are computed. Then, quantitative attributes (slope, aspect, and their derivatives) are combined to automatically detect seabed morphologic structures (lineaments, highs, or depressions), which are potentially related to the presence of geological faults or triggered by other subsurface processes. Based on the analysis in this work, two major segments (the northern and the southern) are identified on the Eratosthenes Seamount and related to E–W trending oblique faults. These two segments are highly deformed according to the quantitative estimation of the geomorphologic attributes. Furthermore, ENE–WSW to NE–SW and WNW–ESE to NW–SE lineaments are identified and limit this prominent topographic high. Smaller topographic highs accompanied by topographic depressions, north and southwest of the Eratosthenes Seamount are also detected, showing medium to strong deformation and reflecting a similar geodynamic activity in this area. As a corollary, a comparison of the bathymetric patterns shows that the present seabed morphology north of the Eratosthenes Seamount relates to shallow salt movements, which create a chaotic pattern. This pattern is expressed by short and curved normal faults, shear zones, possible small-scale reverse faults, massive extrusion of salt bodies (possibly allochthonous), and Pliocene–Quaternary minibasins or peripheral sinks.