Structural Geological Mapping Research Articles

Crustal structure of the Indus–Tsangpo suture zone and its ophiolites in southern Tibet

The >2000-km-long Indus–Tsangpo suture zone (ITSZ) in southern Tibet contains remnants of Neotethyan oceanic lithosphere, ophiolitic mélanges, flysch units and continental rocks, and has been interpreted as the boundary between the India and Eurasia plates. We have used field-based structural analyses and geological mapping in five key ophiolite massifs (Luobusa, Zedang, Xigaze, Jiding and Dongbo) and petrofabric studies of core samples recovered through the Luobusa Scientific Drilling Project to document the structural architecture and the deformation history of the ITSZ. The structural and kinematic analyses of the suture zone units indicate the occurrence of superposed deformation fabrics, which developed first during the ophiolite emplacement and then during the subsequent India–Asia continental collision. The suprasubduction zone ophiolites were emplaced southward onto the northern margin of the proto-Indian plate in the late Cretaceous. The continental collision between the ophiolite-laden proto-Indian margin and the Lhasa terrane of the Eurasian plate in the early Paleogene resulted in backthrusting and inversion of the structural order of the ITSZ. The ophiolite massifs, ophiolitic mélanges and flysch units were thrust northward as nappe sheets over the Eocene and younger forearc basin strata. The ITSZ shows, therefore, a complex structural anatomy characterized by both south and north-directed thrust faults, and ductile and brittle deformation fabrics.

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.

Structural map of Variscan northern Sardinia (Italy)

In this paper, we present a geological structural map (1:100,000 scale, ∼2300 km2 surface area) of the Variscan basement of northern Sardinia. The map integrates field structural analysis, extensive gamma-ray spectrometry, and high-resolution ELA-ICP-MS U/Th-Pb zircon and monazite dating. A set of 10 samples of granitic rocks collected from different plutons were characterized for their crystallization age. This provided an accurate timing of magmatic events related to the development of the Corsica-Sardinia Batholith. The structural map, complemented with geochronological results represents a benchmark for future studies on Variscan geodynamics.

Semi-automatic mapping of geological Structures using UAV-based photogrammetric data: An image analysis approach

Recent advances in data acquisition technologies, such as Unmanned Aerial Vehicles (UAVs), have led to a growing interest in capturing high-resolution rock surface images. However, due to the large volumes of data that can be captured in a short flight, efficient analysis of this data brings new challenges, especially the time it takes to digitise maps and extract orientation data.We outline a semi-automated method that allows efficient mapping of geological faults using photogrammetric data of rock surfaces, which was generated from aerial photographs collected by a UAV. Our method harnesses advanced automated image analysis techniques and human data interaction to rapidly map structures and then calculate their dip and dip directions. Geological structures (faults, joints and fractures) are first detected from the primary photographic dataset and the equivalent three dimensional (3D) structures are then identified within a 3D surface model generated by structure from motion (SfM). From this information the location, dip and dip direction of the geological structures are calculated.A structure map generated by our semi-automated method obtained a recall rate of 79.8% when compared against a fault map produced using expert manual digitising and interpretation methods. The semi-automated structure map was produced in 10min whereas the manual method took approximately 7h. In addition, the dip and dip direction calculation, using our automated method, shows a mean±standard error of 1.9°±2.2° and 4.4°±2.6° respectively with field measurements. This shows the potential of using our semi-automated method for accurate and efficient mapping of geological structures, particularly from remote, inaccessible or hazardous sites.

Ground penetrating radar and structural geological mapping investigation of karst and tectonic features in flyschoid rocks as geological hazard for exploitation

We evaluated the use of ground penetrating radar (GPR) in detecting karst cavities and discontinuities that could form potential landslide surfaces in flyschoid rocks of the Rodež open pit mine in Anhovo (W Slovenia). We recorded 21 GPR profiles in three consecutive benches with the unshielded 50MHz rough terrain antenna (RTA) system, and correlated them with the results of detailed structural and lithological mapping of the area. We located several karst cavities and confirmed the presence of discontinuities with the interpretation of GPR profiles alone. However, their correlation with geological and structural data gave a more precise insight into the structural setting of the studied area. The different discontinuity families specified in the Rodež open pit mine are mainly the result of the strike-slip tectonics and gradual anisotropic lithology. The complexity of the intersections of structural discontinuities and the mechanical properties of rocks contribute to the formation of sliding surfaces and the developing of karst features. Cavities and phreatic channels develop in the vadose zone in calcarenites and result from complex structural deformation and karstification factors at the open joints or larger structural fractures.

Pull-apart formation mechanism of Cenozoic basins in the Tien Shan and their transpressional evolution: Structural and experimental evidence

The geodynamic settings of the evolution of Cenozoic basins in the North and Middle Tien Shan and their Paleozoic framework have been estimated from a kinematic analysis and detailed structural geological mapping of key sites. Two stages of their development in different geomechanical settings are distinguished. It is suggested that in the late Oligocene, Miocene, and early Pliocene, the pull-apart basins developed under the setting of simple left-lateral shear or transtension. Presumably in the late Pliocene and Quaternary, this setting gave way to right-lateral transpression; extension in the basins was changed by compression with the formation of local fold-thrust structural elements. The reconstruction of geomechanical sections was tested by analog tectonophysical simulation. The natural and experimental structural assemblies and patterns reveal satisfactory convergence.

A Geological Structure Mapping Tool using Photogrammetric Data

Accurate and efficient identification and mapping of geological structures has broad application across the minerals industry. Recent advances in data acquisition technologies using Unmanned Aerial Vehicles (UAV), have led to a growing interest in capturing high-resolution rock surface images and analysing those datasets remotely. However due to the large volumes of data that can be captured in a short flight, efficient analyses of these data brings new challenges. We propose a semi-automated method that allows efficient mapping of geological structures using photogrammetry of rock surface data collected by UAV. Our method harnesses advanced automated image analysis techniques and human data interactions to identify structures and calculate dip and dip angles of structures. Geological features were detected in two dimensional (2D) images and the corresponding three dimensional (3D) features were automatically identified from 3D surface models. The location, dip and dip angle of geological features were then calculated. A feature map generated by our semi-automated method correlates well with a fault map resulting from visual interpretation by an expert. Some advantages of our semi-automatic method include the following: Firstly; it generates results in few minutes whilst manual interpretation took around an hour, thus contributing significantly in time saving. Secondly; unlike manual interpretation, our software technology provides objective and consistent results that can be reproduced.

Aeromagnetic data analysis using the 2D directional continuous wavelet transform (DCWT)

In this paper, we have analyzed the geomagnetic anomaly field reduced to the pole by the 2D directional continuous wavelet transform (DCWT). The objective is to identify geological contacts. The proposed idea has been applied firstly at a synthetic model, the obtained results showed the robustness of the proposed technique, after that the synthetic data has been noised; analysis shows that contacts identified by DCWT are affected by noise. To resolve this problem, we have proposed an algorithm to reduce the noise effect in the contacts model. Application on the real geomagnetic data of In Ouzzal area located in the West of Hoggar (Algeria) shows clearly the robustness of the proposed method. Comparison with the analytic signal solutions exhibits a difference between the two models of contacts. Our method gives results that are accurate with the structural geological map.

Three-dimensional seismic attenuation tomography of Egypt

The main purpose of the paper is assessing the three-dimensional (3-D) seismic tomography beneath Egyptto reveal the laws of the tectonic activity, dynamic features of the crust and the upper mantle as well as the thermal structure. Thecoda wave attenuation (Q-1c ) was obtained using the single scattering theory for the central frequencies of interest laid between 1 and 24 Hz. A regionalization of the estimated Q-1c values was performed by means of a generalized inversion technique.The obtained spatial distribution of 3-D attenuation results revealshigh contrasts between East and West Egypt. A remarkable contrast in the attenuation levels was compared with the tectonic structures, geothermal gradient and heat flow features. The highest attenuations are concentrated in the east and north western offshore regionsat central frequency 1.5 Hzthat draw a good matching with the seismic andthermal features of Egypt. Smaller attenuation levels were detected with young sediments of the Nile Valley from South to the northern triangle of Nile Delta basin except seismic active areas. Low or normal attenuation was detected at western desert where there is a stable and simple shelf. We can conclude that the extended highest attenuation joins to the strong seismic sources and geothermal structures at lower frequency and the centralized high attenuation takes place at moderate seismic sources at a higher frequency. The 3D attenuation maps can draw not only tectonic and geothermal structures but also the general geologic structure map.

Optimization of nonlinear geological structure mapping using hybrid neuro-genetic techniques

A fairly reasonable result was obtained for nonlinear engineering problems using the optimization techniques such as neural network, genetic algorithms, and fuzzy logic independently in the past. Increasingly, hybrid techniques are being used to solve the nonlinear problems to obtain a better output. This paper discusses the use of neuro-genetic hybrid technique to optimize the geological structure mapping which is known as seismic survey. It involves minimization of objective function subject to the requirement of geophysical and operational constraints. In this work, the optimization was initially performed using genetic programming, and followed by hybrid neuro-genetic programming approaches. Comparative studies and analysis were then carried out on the optimized results. The results indicate that the hybrid neuro-genetic hybrid technique produced better results compared to the stand-alone genetic programming method.

Karstic uvala revisited: Toward a redefinition of the term

Uvalas are a particular type of karst closed depression. While other types of closed depression – dolines and poljes – are regularly listed and relatively well defined in overviews of karst surface morphology, uvalas are either excluded or their vague identification is stressed. The leading idea of this paper is to obtain a clearer meaning of the term uvala and prevent its abandonment from karstology and general geomorphology. Within the study, 43 examples of uvalas have been selected. The studied uvalas are located in the Dinaric karst and karst of the Carpatho–Balkanides. All the case examples have been digitally processed in the same way. Creation of high-resolution digital elevation models enabled quantification of morphometric parameters, generation of inclination maps and cross-sections, as well as application of statistical analyses. Formation of the geographical information system of the studied uvalas was done using raster-based and vector-based GIS software packages. In 12 studied uvalas, detailed structural–geological mapping has been carried out, which revealed dominant development of uvalas along regional scale tectonically broken zones. A revised definition of the term uvala is suggested, leaving the opportunity for further discussion.

The SHAllow RADar (SHARAD) Onboard the NASA MRO Mission

This paper describes the mission concepts, design, and achievements of the Italian Space Agency (ASI)-provided Mars SHAllow RADar (SHARAD) sounder high-frequency (HF) sounding radar, used onboard the National Aeronautics and Space Administration (NASA) Mars Reconnaissance Orbiter (MRO) Spacecraft. Its goals are the detection of liquid or solid water below the surface, and the mapping of subsurface geologic structures. Following a brief overview of the MRO mission and of its main science objectives, the paper introduces the basic principles of operation of the radar sounder, and addresses the major design issues faced by such a system. The greatest challenges faced in the design are the control of the interference from off-nadir echoes and the need for a high signal fidelity over a very large fractional bandwidth. The core of the paper is devoted to describing how the above problems have been tackled in the design of the SHARAD instrument, and the main characteristics of its architecture. The two key features of the instrument system design are 1) generation of the transmitted signal directly at the transmitted frequency; and 2) sampling performed directly at the radio frequency (by means of a subsampling technique). The careful design of these features, intended to keep the analog signal path very simple, minimizes distortions and stability problems. An overview of the calibration approach of both the system impulse response and the antenna gain at nadir versus solar array position, an assessment of the in-flight performance of the instrument, and a short summary of the achieved science results are also provided.

The Texel-Schneeberg boundary in the Pfossen valley (Merano, NE Italy): geological-structural map and explanatory notes

The Schneeberg Complex (Merano, NE Italy) was traditionally distinguished from the surrounding Austroalpine basement on the base of its peculiar lithological association made of garnet-rich metapelites, calc-schists, paragonite amphibolites and garnet-amphibole schists, locally with megablasts of garnet and amphibole. As the Schneeberg Complex is considered to be a monometamorphic unit with Alpine metamorphism only, its southern boundary with the polymetemorphic Texel Complex is a key-element in deciphering the tectono-metamorphic evolution of the Austroalpine basement in the western sector of the Eastern Alps. On the base of the field structural analyses the two units display a common structural evolution at least from the Alpine amphibolite facies event (D2 in our reconstruction). In the upper Pfossen valley the marbles, amphibolites and garnet mica schists succession forming the external part of the Schneeberg Complex are folded together with the Texel metapelites in tight structures with step axes, known as «Schlingen» folds. These peculiar structures are due to the D2-D3 folds interference pattern. The results of the structural analysis in the study area are almost coherent with recent interpretations that propose the entire Schneeberg Complex to represent a greenschist facies crustal scale shear zone (SNFZ, Schneeberg Normal Fault Zone) along which the Texel Complex, containing rocks with eclogitic relics of Alpine age, have been exhumed with a SE direction, starting from the late Cretaceous times

Structural Geology of the Škocjan Caves

The Skocjan Caves are developed inside 300 m thick column of Cretaceous and Paleocene limestones. Most of the underground Reka River flows within the 130 m thick Lipica Formation (K2 4-5). Data from field structural geological mapping (1:500) performed in 1991-1992 (Hankejev Kanal) and in 1997- 2007 (Tiha and Sumeca Jama) are analysed and presented on a new structural geological map. The Reka River follows bedding- plane strike and dip direction in Sumeca Jama and Hankejev Kanal. From the western part of Hankejev Kanal to the ponor in Martelova Dvorana the Reka River flows perpendicular to strike direction of bedding-planes with dip direction of the bedding contrary to river flow. Bedding planes with interbedded slips were especially favourable for the development of initial passages. The bend of the Reka River in Hankejev Kanal is developed at the intersection of multiple fault zones. Cross- Dinaric oriented faults in Podorna Dvorana and at northern edge of Martelova Dvorana can potentially be neotectonically active.

Aeromagnetic mapping of Precambrian geological structures that controlled the 1968 Meckering earthquake ( Ms 6.8): Implications for intraplate seismicity in Western Australia

Occurring in the southwest of Western Australia, the 1968 Meckering earthquake ( M S 6.8) resulted in the formation of an extensive surface rupture complex comprising faults with a range of orientations and reverse and dextral lateral offsets. Modeling of the seismological characteristics of the source showed that reverse failure occurred on a north–south striking, east-dipping surface, but how this is related to the local Precambrian bedrock geology is not clear. Interpretation of new aeromagnetic data has allowed concealed bedrock lithology and structure to be mapped in previously unachievable detail. These data show that the surface faulting correlates closely with linear magnetic anomalies, interpreted as dykes/faults and lithological contacts. The complicated pattern of surface faulting contrasts with the more simple seismological fault model, but can be explained in terms of the reactivation of northeasterly (dykes and faults) and northwesterly (stratigraphic) trending features in a stress regime with an east–west oriented maximum principal stress. Space problems created where these two trends converge led to the creation/reactivation of a linking north–south trending thrust fault which accommodated the greatest displacements recorded for the 1968 event. The district scale distribution of epicentres in the 3 years encompassing the Meckering event shows the same northeasterly and northwesterly trends as seen in the aeromagnetic data. The implied basement features controlling the seismicity will be prone to strike–slip failure in the regional, east–west oriented stress field. It is speculated that smaller events in the Meckering area will tend to be strike–slip and these account for most of the strain. Larger events, all known examples of which involve predominantly thrusting, are caused by stress build up where strike–slip faults with the two orthogonal trends intersect. This hypothesis provides an explanation for the lack of topography in the region, which is incompatible with the high level of seismic activity and a predominance of thrust faulting.

Rock bridge slice element method in slope stability analysis based on multi-scale geological structure mapping

The searching method of failure surface which consists of complex geological structures in high and steep rock slopes was studied. Based on computer simulation technology and Monte-Carlo method, three dimensional multi-scale geological structures such as engineering scale and statistical scale structures of the slope were simulated. The searching method of failure route which consists of joints and rock bridges was determined via simulation annealing method by considering the shear strength of joints or rock bridges in one supposed route. When shear strengths of all the supposed routes were computed, the least shear strength route was considered failure route. Then, the inclined slice of joint slices and rock bridge slices were separated according to the position of joints and rock bridges. For the rock bridge slices, by distinguishing the failure model, the force direction to the next slice was defined. Finally, the limit equilibrium equations for every slice were established, and the slope stability factor was obtained. One practical example indicates that the discussed method is more closely to the real condition.

Structural, tectonic and glaciological controls on the evolution of fjord landscapes

The fjord landscape of South America, stretching ~ 1500 km between Golfo Corcovado (~ 43°S) and Tierra del Fuego (~ 56°S), is the largest continuous fjord landscape on Earth. This paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models. First-order geological structures are represented by strike-slip faults forming lineaments up to hundreds of kilometres long. The strike-slip faulting has been active since Late Cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to ~ 10 km long. A detailed analysis of these second-order lineaments from digital image data was carried out in three sectors. In Sector 1, located northwest of the North Patagonian Icefield, there are three distinct mean orientations, characterized by a main nearly orogen-parallel orientation (az. ~ 145°) and two orogen-oblique secondary orientations (az. ~ 20° and az. ~ 65°). In Sector 2, located west of the South Patagonian Icefield, there are also three separate mean orientations, with most of the lineaments concentrated between azimuths 0° and 80° (mean at ~ 36°); and two other orogen-oblique means at azimuth ~ 122° and ~ 163°. In Sector 3, around the Cordillera Darwin, there is a single main orogen-parallel mean at ~ 100–115°. In all three sectors, mapped fjord orientations bear a striking similarity to the structural data, with fjords orientated preferentially in the same direction as structural lineaments. We infer that successive glaciations followed the same ice-discharge routes, widening and deepening pre-existing geological structures at the expense of the surrounding terrain to create the fjord landscape. This study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological.

Cenozoic structural and metamorphic evolution and geological map and sections of the NW Indian Himalaya

No abstract

Visual interpretation of ASTER satellite data, Part 1: Geologic mapping in the Cradle of Humankind World Heritage Site

Since the first earth observing satellite was launched in 1972, remote sensing has become a powerful tool in the arsenal of geoscientists. This satellite became known as Landsat 1 and carried the Multispectral Scanner (MSS) delivering imagery at a spatial resolution of 80, and spectral resolution from blue to near infrared. Ongoing satellite and sensor development to the end of the century produced the Landsat Thematic Mapper (TM) with improved spatial and spectral resolution, as well as the SPOT series of satellites delivering the highest spatial but limited spectral resolution. These developments culminated in the SPOT 4 (1998) and Landsat Enhanced Thematic Mapper (1999) sensors. While Landsat ETM in particular provided much improved spatial and spectral resolutions, on the basis of which a large amount of geoscientific remote sensing was conducted world wide, the data did not provide adequate spectral and spatial sensitivity to be optimally effective for geological mapping at the local scale. On 18 December 1999 the Terra platform was launched, carrying five remote sensing instruments, including ASTER (Advanced Space borne Thermal Emission and Reflection Radiometer). ASTER consists of three separate instrument subsystems, each operating in a different spectral region, and using separate optical systems. These are the Visible and Very Near Infrared (VNIR) subsystem with a 15m-spatial resolution, the Short Wave Infrared (SWIR) subsystem with a 30m-spatial resolution and the Thermal Infrared (TIR) subsystem with a 90m-spatial resolution. ASTER effectively offers an improvement on Landsat MSS, Landsat TM, Landsat ETM+ and SPOT spectral and spatial resolutions. Given the paucity of published research on geological remote sensing at the local scale in South Africa, and particularly on the use of ASTER for geological mapping in South Africa, it is imperative that the value of ASTER be investigated. This article reports on the improved detail and scale achieved in the mapping of litho-stratigraphy, geological structures and mining-related features by the visual interpretation of processed ASTER images. ASTER imagery obtained from the EOS website was subjected to a range of image enhancement and analysis techniques including colour composites, band ratios, normalised difference indices, regression and decorrelation, in order to obtain optimal visual interpretability. Eight images thus obtained could be used for visual analysis, and it became evident that litho-stratigraphy, faults, fracture zones and elements of the regional seam system, as well as remnants of mining activities, were readily identifiable. Some of these were in accordance with the most recent and accurate geological map of the area, but many of them had apparently not been mapped. These features were annotated and were verified by field checks. In all cases the accuracy of detection and location from satellite imagery was confirmed on the ground. The improved detail and accuracy obtained by visual interpretation of processed ASTER satellite data for mapping a section of the Cradle of Humankind World Heritage Site demonstrated the potential value of this data for a variety of other geoscience applications. It appears that the improved accuracy can be ascribed jointly to the higher spatial and spectral resolution provided by ASTER data.

Ground Stability Analysis on the Limestone Region

ABSTRACT A Natural cavities were found at shallow depth during construction of a huge bridge in Moon-Kyung, Korea. The distribution patterns of cavities in the Moon-Kyung limestone were investigated carefully with a supplementary field job such as a structural geological survey, a geophysical survey, and a rock mechanical test in laboratory or field. A structural geological mapping produced a detail geological map on this area. It suggested that there were three faults in this area, and these faults had an influence on the natural cavities. Among many kinds of geophysical surveys, an electrical resistivity prospecting was applied firstly on the specific area that was selected by results from the geological survey. Many evidences for cavities were disclosed from this geophysical data. Therefore, a seismic tomography was tested on the target area, which was focused by results from the electrical resistivity prospecting and was believed to have several large cavities. A distinct element numerical simulation using the UDEC was followed on the target area after completing all of field surveys. Data from field tests were directly dumped or extrapolated to numerical simulations as input data. It was verified from numerical analysis that several natural cavities underneath the foundation of the bridge should be reinforced. Based on the project result, finally, most of foundations for the bridge were re-examined and the cement grouting reinforcement was constructed on several foundations among them.