Geological Structural Analysis Research Articles

Role of Basement Structural Inheritance and Strike-Slip Fault Dynamics in the Formation of the Pataz Gold Vein System, Eastern Andean Cordillera, Northern Peru

Abstract New regional- to vein-scale geologic mapping and structural analysis of the Carboniferous Pataz gold vein system (~10 Moz Au) reveal critical insights into the structural control on gold mineralization along the Eastern Andean Cordillera of northern Peru. The Pataz basement comprises continental volcanic arc and marginal to marine sedimentary rocks, which experienced intensive D2 deformation associated with Late Famatinian northeast to southwest compressive fold-and-thrust belt development. The D2 event produced an E-NE–dipping structural grain, including (1) tilted and F2 folded S1 foliations, (2) local F2 axial planar S2 foliations, and (3) subparallel D2 thrust faults. Intrusions, constituting the ca. 342 to 332 Ma (Mississippian) Pataz batholith, were emplaced along strike of the prominent Río Marañón fault and inherited the D2 basement structures, as evident in the orientation of suprasolidus magmatic flow zones and intrusive contacts within the batholith. Progressive horst-and-graben development affecting the volcanic carapace of the Pataz batholith records late syn- to postmagmatic uplift and transition into a NW-SE–extensional regime. We show that the E-NE–dipping, batholith-hosted gold vein system formed through synchronous activation of two geometric fault-fill vein types, following (1) the moderately E-NE–dipping D2 basement-inherited competency contrasts within the batholith and (2) shallow NE-dipping Andersonian footwall thrusts, during NE-directed shortening (D3a). Both geometric vein types display an early paragenetic stage (I) of quartz-pyrite, progressing texturally from hydraulic breccia into crack-seal laminated shear veins. A second (II), undeformed quartz-pyrite-sphalerite-galena paragenetic stage is observed to fill previously established dilational sites adjacent to newly formed D3b normal faults, which likely formed during regional NW-SE–extensional horst-graben development. Kinematics and relative timing indicate that, upon batholith solidification, D3a transpressional dextral strike-slip ruptures along the Río Marañón fault superimposed a lower-order Riedel-type fault system. Fluid-assisted fault activation preferentially impinged on the D2 basement-inherited competency contrasts within the batholith. Subsequent transition into a transtensional regime led to the D3b normal faulting, providing a feeder system for stage II fluid influx. The tectonic switch may be explained either by increasing tensile strain accommodation upon progressive strike-slip movement within a regional dilational jog or by larger-scale crustal relaxation of the late Gondwana margin upon final Pangea assembly. Our new structural model for the Pataz vein system evolution highlights the importance of basement structural inheritance in controlling the localization of gold mineralization along polycyclic supercontinent margins. We provide valuable insights for exploration targeting of complex vein arrays within rheologically heterogeneous host rocks.

Quantitative Analysis and Evaluation of Coal Mine Geological Structures Based on Fractal Theory

With the increasing depth of coal mining, the quantitative evaluation of the degree of geological structure development is becoming increasingly important for the control of mine water hazards in coal mining areas. Understanding the complexity of geological structure development can improve the safety and efficiency of coal production. At present, various evaluation indicators of the geological structure development cannot fully reflect the complexity of faults and folds, and the evaluation process is usually affected by subjective human factors. In this paper, the fractal dimension from fractal theory is used as the evaluation indicator to quantitatively analyze and evaluate the complexity of fault and fold structure in the mining area. To verify the evaluation results, the mathematical geology method is applied in an analysis of the trend surface of fault and fold networks. The results indicate that the fractal dimension can be applied for the quantitative analysis and evaluation of the complexity of fault and fold networks. In addition, the outcome of this work provides new insights into how to characterize the fault and fold structures of coal mining areas in northern China, and has some important implications to ensure the coal production safety.

The contribution of remotely sensed data to the stress state evaluation in underground marble quarries

An in-depth knowledge of the geostructural characteristics of the territory is fundamental for optimizing the design of artificial structures. Feasibility, costs, duration, and issues of the works are strictly correlated with the geological, geomechanical, and in situ stress features of the area. Remotely sensed data represent a source of information for detecting tectonic structures that can be complementary to traditional surveys, with the advantage of being cheaper, of covering large areas and of reducing time for surveying. The study of the regional tectonic setting together with local structural features is fundamental to define the far-field tectonic stress and for correctly modeling the induced stress during excavation activities and monitoring stress variations. A multiscale and multidisciplinary approach was set up and applied to an area in the Alpi Apuane marble district (Tuscany, Italy). Visually and semi-automatically detected geological structures were analyzed and correlated to data from in-situ measurements in four underground marble quarries, to define the far-field stress state. This study is also an attempt to bridge the gap between structural geology analysis and remotely sensed data for far-field stress definition, correlating on-field kinematic observations and in situ stress measurements.

ГЕОДИНАМІКА

Purpose. The purpose of the paper is the reconstruction of the geodynamic development of the shear dislocation zone (shear stress fields) of the Krasnoarmiiska monocline (KM) of Donbas (Eastern Ukraine) and determining the relationships of their impact on the emergence of gas-dynamic phenomena (GDP) in coal sediments. Methodology. Methods of digital geological cartography, mining-geometric simulation, geological-structural analysis, and structural-geomorphological reconstruction are used for the analysis of structural-geological information. A complex of methods for statistical processing of data on the tectonic disturbance is used – estimation of the frequency of azimuth orientations by the roses-diagram method. Techniques of morphotectonic analysis of the coal bed (a mathematical technique for identifying the gradient structures) are applied. Results. A tectonic model of formation of pull-aparts in the mode of transtension on the territory of KM (on the example of “Dobropilska” mine) is proposed, which results in manifestations of GDP (in particular “wet blowers”) in the form of a small kettle of subsidence in zones of en echelon overlapping of shears. The latter ones are formed under the action of the shear field of tectonic stresses (the axis of space shortening is (σ1) due to the horizontal shear is oriented in azimuth 160-170° (340-350°), the axis of elongation is (σ3) – 70-80° (250-260°). At this, the combination of fringing Y and T faultings in the conditions of transtension, most likely, provides gas permeability and water permeability of the zone. Structure-kinematic relationships of formation and development of shear dislocations of KM at Donbas are researched. Originality. The structural-kinematic relationships in the formation and development of shear dislocations of the Krasnoarmiiskyi district of Donbas and their impact on the formation of GDP zones were studied firstly. They based on the developed digital model of the actual tectonic disturbance of the rock massif on the example of the mining allotments group of KM. It is established for the first time: a) subparallel disjunctives of the NE orientation (15-30°), regardless of morphology, are as the boundaries of parallelogram-like blocks, forming either scaly packets or packets of fault scarps (depending on the morphology of the faultings), limited in the strike by the fault planes of N-NE and SW fall; in the case of scaly packets in the orientation of the fall of the fault plane it is dominated by the E-SE direction, the faultings limiting the fault scarps are characterized by the opposite WN direction of the fall; b) faultings of SE orientation are morphologically represented by shear-thrusts, and with depth change not only the angle of incidence from 35° to 85°, but also the azimuth of strike (from 20-25° to 50°), forming a fanlike feathering of the main faulting in the plan; c) faultings of different morphology are represented not by a single fault plane, but by a series of disturbances on all stratigraphic horizons, which form a zone of faulting formation – a vertical "tectonic strip"; d) in the SE part of the mine "Pioner" a duplex of compression (transpression mode) was found, it is expressed by a folded system (F), up to 287 m wide and fragments of sloping, changing the strike of the Novoiverskyi thrusts; e) the zone of tension duplexes located in the chain, which have a characteristic broken-step configuration at the "Dobropilska" mine, to which “wet blowers” are connected with, develops due to local strike (transtension); f) paragenesis of deformations in the study area corresponds to the shear field of tectonic stresses with north-northwest direction of compression and east-northeast tension, in which fault-shear displacement occurs along with the disjunctive breaks. Practical significance. The established relationships of the impact of shear tectonics on the formation of GDP in coal beds are important both by clarifying the mechanism of tectonogenesis and the nature of pull-aparts formation (en echelon zones of tension), and by the possibility of using additional prognostic criteria for searching for accumulations of free methane and its sudden manifestations (GDP) in coal beds. The application of knowledge of these relationships at mining enterprises will allow reducing the costs for the struggle against dangerous GDP manifestations and predicting them reliably.

77Namibian Journal forResearch, Science andTechnologyVol 2, December2020NJRST 2 (2020): 77-89 Geological Mapping and Major Elements Characterization of the Tschaukaib Granitic Suite, South West Namibia

ABSTRACTOngoing studies in the Namaqua Sector, situated in the Namaqua-Natal Metamorphic Province (NNMP), have been vital in understanding the geological activities that occurred during the Rodinia supercontinent assembly. These geological activities are usually key to discovering new mineral raw materials. The Tschaukaib Granitic Suite, which is believed to be part of the Gordonia Thrust Stack (GTS) of the Kakamas Domain, crops out within Tschaukaib Mountains and was characterized in this study on the basis of surface mapping, petrographic and major element geochemistry. Three types of granites were identified, namely: granodiorite, quartz monzonite and granite with SiO2 content ranging from 64.9 wt % to 69.8 wt %. Whole rock geochemistry further shows that they are calc-alkaline, alkali-calcic, ferroan, peraluminous (Al2O3 > K2O + Na2O + CaO) and have >1 % Cross, Iddings, Pirsson and Washington (CIPW) corundum. The geochemical characteristics indicates that the granitoids were emplaced during the continental collision and are formed from partial melting of recycled crustal material which took place during the Rodinia supercontinent. The geochemistry shows a conspicuous fractional crystallization signature. Geological mapping and structural analysis of the Tschaukaib Granitic Suite area shows a NW-SE and E-W trending regional foliation in the Tschaukaib Augen Gneiss (quartz monzonite) which corresponds to the main D2 Namaqua metamorphic event. Several shear zones were mapped and are consistent to the Pofadder Shear Zone which runs in the NW-SE and E-W directions, parallel to the study area. Petrographic analysis of the granitoids has identified mineral assemblages which shows that the granitoids have undergone high strain and alterations, however, it is not clear which Namaqua deformation episode brought about these features.

A geological and biostratigraphic study of the Paleozoic of the Malaguide Complex in the Cogollos Vega Zone (Granada) using conodonts

A detailed geological characterization of the Malaguide Complex in the Cogollos Vega Zone has been made by integrating geological mapping, lithostratigraphy and structural analysis with conodont studies. The Falcoña Formation constitutes an important guide-horizon to correlate different stratigraphic sections and to distinguish pre-Falcoña and post-Falcoña successions with slightly different facies and different ages: the first one is Devonian (Emsian, Frasnian and Famennian) and the second one Carboniferous (upper Visean-lower Serpukhovian). The Alpine structure of the area is determined by the presence of backthrusts associated with south-vergent folds that repeat the general stratigraphy and divide the Malaguide Complex into three tectonic units. These structures are systematically cut by (mainly NW-SE oriented) normal and dextral strike-slip faults. Preliminary Colour Alteration Index (CAI) and micro-textural studies of conodontal elements have revealed interesting differences between the tectonic units present in the area, which should be the subject of a more detailed study.

Comparison between Rafidhiya and Shuaiba Domes within the properties of Mishrif Formation in Zubair Field; the implication of structural Geology and petrophysical analyses

The current study combined both concepts of structural geology and petrophysical to understand the structural feature of Mishrif Formation and its implication on the petrophysical characterization of the formation in Shuaiba and Rafidhiya Domes (or culminations) in Zubair Field. Shuaiba and Rafidhiya are adjacent domes and these domes belong to the same Field but the domes separated by saddle may related to Basra – Zubair basement fault.
 The domes have different petrophysical properties of Mishrif Formation; consequently, influenced in water and oil saturation. Therefore, the study tries to understand the structural and petrophysical position of Mishrif Formation of the domes. The structural analysis included geometric and genetic analysis, whereas petrophysical analysis used open hole logs interpretation to determine the petrophysical characteristics (especially the distribution of porosity, permeability, and water saturation.
 It was concluded that may a variation in porosity and permeability of Mishrif Formation for Shuaiba and Rafidhiya domes because each dome was formed by a different folding mechanism effected on the petrophysical properties. The structural geology analysis detects that may be Shuaiba dome formed by bending fold mechanism (vertical force of salt structure), while Rafidhiya dome by buckling fold mechanism (parallel force of collision of Arabian and Eurasian plate). These mechanisms may directly be affected in permeability distribution, and consequently on oil and water saturation of Mishrif Formation. Thus, Shuaiba Dome has thinning in hinge area and extensional force leads to create fractures and karst phenomena, and as a result, high permeability in upper Mishrif. On the contrary, Rafidhiya Dome has a thickening feature and there is no indication of karst phenomena and low permeability. Therefore, the Mishrif of Shuaiba dome permeable and oil-saturated, while, it flooded with water in Rafidhiya Dome. The disconnection in reservoir pressure confirmed by difference in initial reservoir pressure of Mishrif Formation of Shuaiba Dome and recent reservoir pressure of Mishrif Formation of Rafidhiya Dome

Statistical Simplification and Discrete Element Analysis of Seepage Model for Complex Fracture Network of Dam Foundation Rock Mass

In this paper, a model of seepage in a fracture network is analyzed by taking the rock mass of the dam foundation of Datengxia Hydropower Station, the No. 1 Project of the Ministry of Water Resources, as an example. Complex discontinuity systems are present in the rock mass of the Datengxia Hydropower Station dam foundation, and faults, soft interlayers, and structural fracture systems intersect with one another. A multi scalar structural analytical scheme that combines the deterministic analysis of large scale geological structures (i.e., faults and weak interlayers) with the statistical simulation of random discontinuities (i.e., structural fractures) is proposed in this paper to reduce the difficulty and uncertainty of the analysis of rock masses with complex structures. In particular, a chain analytical method from dominant group definition to statistical parameters (i.e., spacing and occurrence) is formed for the structural fracture system. In this way, the analysis of rock masses with complex structures is simplified to a regular and feasible scientific problem that could be solved by rock mass simulation. We then establish a seepage model of the rock mass in dam section 29# in UDEC by adopting the above structural simplification scheme. The quantitative analysis of seepage in complex structured rock masses under normal water storage and dynamic conditions is then realized. Results show that the statistical simplification of the rock mass structure and discrete element simulation can efficiently solve the seepage analysis of complex rock masses. The negative influence of pore pressure caused by seepage on the rock mass, especially under dynamic conditions, should be emphasized for safety assurance in the stability analysis of dam foundations.

A New Understanding on the Emplacement of Ophiolitic Mélanges and Its Tectonic Significance: Insights from the Structural Analysis of the Remnant Oceanic Basin‐Type Ophiolitic Mélanges

AbstractOphiolites represent on‐land fragments of paleo‐oceanic crust and have been recognized as one of the key markers of suture zones. Here, we provide new insights into the emplacement of ophiolitic mélanges based on detailed geological mapping and structural analysis in the West Junggar and Songpan‐Ganzi‐Bayan Har orogens (Fig.1 and Fig.2). The results show that some ophiolitic mélange belts cannot be regarded as suture zones. The distribution of these ophiolitic mélange belts are usually associated with the structural processes during the closure of remnant oceanic basins. After the remnant‐oceanic basin is filled with thick clastic deposit, the oceanic lithosphere material as the base of the remnant basin can be injected into the overlying sedimentary strata through various faultings under the regional compressive stress, forming the remnant oceanic basin‐type ophiolitic mélange system with dispersive distribution characteristics. Combining with previous researches, the emplacement mechanism of ophiolitic mélanges can be divided into four categories: subduction type which oceanic lithosphere subducted beneath active continental margin, obduction type which oceanic lithosphere obducted over passive continental margin, collision type between two continental lithospheres, and closure type of remnant‐oceanic basin (Fig.3). These different types of ophiolitic mélange belts will be superimposed and even re‐emplacement by the tectonic processes of post‐plate convergence, complicating their distribution. Therefore, identifying the emplacement mechanism type of ophiolitic mélange belts formed in different tectonic processes and backgrounds is of importance for understanding the process of ocean‐continental transition and the evolution of orogenic belts.

Structural control and genesis of gold deposits in the Liaodong Peninsula, northeastern North China Craton

Two distinct styles of gold mineralization occurred in the Liaodong Peninsula, in the northeastern North China Craton. One formed an altered rock-type gold deposit in the west, and the other formed a quartz vein-type deposit in the east. Geological investigations and structural analysis show that these deposits may have originated from two distinct tectono-magmatic hydrothermal systems. The former is an E–W-trending contractional–extensional structural system formed in the Late Triassic, which includes the deposits in Baiyun, Jianshangou, and Maoling. The latter is related to high-angle strike-slip faults formed in the Early Cretaceous, and includes the Wulong gold deposit. Stress-induced tectonic analyses show that the principal stress in the western district was nearly N–S-oriented contractional stress initially, which subsequently changed to extensional stress; this might have been the result of the collision and subsequent extension of the Siberia Craton, North China Craton, and Yangzi Craton in the Late Triassic. The principal stress in the eastern district was nearly NW–SE-oriented contractional and sinistral shear stress initially, which subsequently changed to extensional stress, which may be the result of regional extension associated with the westward subduction of the Paleo-Pacific Plate in the Early Cretaceous.The structural control of the gold mineralization is manifested at all scales from regional to mines to orebodies; that is, the grading of the ores was controlled by different generations or orders of deformation. Gold ores were mainly formed under brittle or brittle-shear deformation conditions; in particular with extensive ore-bearing catalasite flows; which were generated by both the brittle or brittle-shear failure along major fault systems and related Late Triassic and Early Cretaceous magmatic hydrothermal activity. This genetic origin for gold mineralization and ore-bearing catalasite flows may provide support for the mechanism of flash vaporization in mineralization processes that form mesothermal gold systems.

Lineament Analysis and Inference of Geological Structures in Bansara-Boki Area, Southeastern Nigeria

The purpose of this study is to extract lineaments from satellite images in order to contribute to the understanding of the structural geology of parts of Boki and its environs. Shuttle Radar Topographic Mission (SRTM) and Landsat 7 ETM images of path 187 and row 056 were used for the analysis which is processed for automated extraction, validated through ground-truthing of planar and linear geological features displaying altitude of about 233 for Bansara sheet 304. Lineament extraction processing was done using PCI Geomatica version 2016 for Landsat imagery and ArcGIS 10.5 used to generate Digital Elevation Model (DEM) and Slope Map for SRTM imagery. Statistically a total of 3191 count of highly dense lineament were generated ranging between 0.86 to 4.33 km in length with the mean of 1.22 and a standard deviation of 0.83 intersecting at low percentage of 3-6%. The DEM display a range of 1335 to -1335 m sloping in the range of 0-2.81 and 61.224-89.725 m for topographic analysis. The lineament extracted were trending majorly in NW/SE and other minor ones in NE/SW directions some which were agreement with the altitude of the ground-truth data. The variation is possibly as a result of influence from regional process such as deformation, metamorphism, magmatism and method of data acquisition and analysis. Lineament analysis are profound index parameters for engineering of dams, economic mineral and water resources exploration, exploitation, planning and development. It is also useful in geohazard studies and its mitigation as the areas are prone to rockfalls, rockslides, landslides, mudslides and flooding due to high rainfall and human activities at the foot of the highlands.

Hydrogeochemical model of Ciseeng geothermal field, Bogor, West Java

Ciseeng geothermal field is located Northwest of West Java 40 km from Jakarta. Three surface manifestations are in Tirta Sayaga, Panjang Mountain, and Peyek Mountain. This study aims to build a hydrogeochemical model based on water analysis. The secondary regional geological data are retrieved to complete geological information of Ciseeng. The research method is divided into several stages: introduction includes the literature study, data collection includes the measurement of temperature and pH in several surface manifestations, rock sampling and structural geology analysis in Ciseeng. The type of manifestation that can be found in Ciseeng is a warm pool with chloride fluid type. Extensive travertine deposits were found in all three locations. The fluid temperature of three surface manifestations is about 30-38 °C with pH 6. According to the measurement of Na-K-Ca geothermometer, the reservoir temperature in Ciseeng geothermal field is 180 °C. The three manifestations of Ciseeng geothermal field are classified as mature water based on a ternary plot diagram. The isotopic analysis shows shifting in O18 indicating hydrothermal process due to magmatic activities in the subsurface. It is predicted that Ciseeng geothermal field is part of Salak/Pangrango Mountain geothermal system. The presence of surface manifestation confirms that geological structure trending from North to South, play a significant role to circulate the heated fluid in the subsurface and subsequently to the surface. The result is a geothermal conceptual model of Ciseeng field that shows the fluid origin and movement in the subsurface.

Structural setting of a transpressive shear zone: insights from geological mapping, quartz petrofabric and kinematic vorticity analysis in NE Sardinia (Italy)

AbstractThe Posada–Asinara Line is a crustal-scale transpressive shear zone affecting the Variscan basement in northern Sardinia during Late Carboniferous time. We investigated a structural transect of the Posada–Asinara Line (Baronie) with the aid of geological mapping and structural analysis. N-verging F2 isoclinal folds with associated mylonitic foliation (S2) are the main deformation features developed during the Posada–Asinara Line activity (D2). The mineral assemblages and microstructures suggest that the Posada–Asinara Line was affected by a retrograde metamorphic path. This is also confirmed by quartz microstructures, where subgrain rotation recrystallization superimposes on grain boundary migration recrystallization. Crystallographic preferred orientation data, obtained using electron backscatter diffraction, allowed analysis of quartz slip systems and estimation of the deformation temperature, vorticity of flow and rheological parameters (flow stress and strain rate) during the Posada–Asinara Line activity. Quartz deformation temperatures of 400 ± 50 °C have been estimated along a transect perpendicular to the Posada–Asinara Line, in agreement with the syn-kinematic post-metamorphic peak mineral assemblages and the late microstructures of quartz. The D2 phase can be subdivided in two events: an early D2early phase, related to the metamorphic peak and low kinematic vorticity (pure shear dominated), and a late D2late phase characterized by a lower metamorphic grade and an increased kinematic vorticity (simple shear dominated). Palaeopiezometry and strain rate estimates associated with the D2late deformation event showed an intensity gradient increasing towards the core of the shear zone. The D2early deformation developed under peak temperature conditions, while the D2late event was active at shallower structural levels.

THE EFFECT OF WEST QURNA OILFIELD ON THE PART OF EUPHRATES RIVER, NORTHERN BASRA GOVERNORATE, IRAQ: GEOMORPHIC AND STRUCTURAL GEOLOGY INTEGRATED ANALYSIS

AbstractThe study utilized geomorphic and structural geology analysis integrated analysis to understand the effect of West Qurna Oil Field (or West Qurna Structure) on the part of Euphrates river route, whether it’s related to neotectonic activity or it’s a natural phenomenon. The Euphrates River Drainage Basin is located in the northern part of the Basra governorate in the south of the Mesopotamian Basin. The channel of the river is mostly straight and characterized by large loops. The channel sinuosity of this river system is analyzed in order to draw conclusions on the neotectonic activity of the region. The original status of the river thalweg was digitized from recent satellite images using the new Landsat 8 Scenes. Sinuosities at different sample section lengths were computed in a GIS software environment ArcGIS 10, providing so-called ‘sinuosity spectra’ for each point of the analyzed using a moving-window method and different window sizes channels. High sinuosity sections were correlated to geological subsurface structures of West Qurna Oil Field identified, indicating their neotectonic activity. A structural analysis (geometric and genetic analyses) performed to identify its type, origin and to find its relevance to main regional tectonic events. The geometric analysis detect that the bending fold mechanism (vertical force) could responsible about form West Qurna oil. Thus, thinning feature associated with West Qurna Oil Field. This mechanism could be connected with growth of salt structure of Hormuz Salt below it as confirmed by negative residual anomaly associated with West Qurna Oil Field.

Geodynamical evolution of the Misis structural high, Ceyhan (Adana)/Turkey

An elongate mountain range known as the “Misis Structural High” located ca. 40 km southeast of Adana city in Turkey, evidences vast tectonic processes in Neogene time. This lineation represents the former border of the Tauride and Eastern Mediterranean basins and extends from Northern Cyprus to the Engizek Mountains by passing through the Misis (Yakapınar) and northerly Andırın regions. Located about 80 km west of the triple junction of the Arabian, Anatolian and African plates, this region is one of the key tectonic lineaments studied for understanding the geologic development of southeast Anatolia. To reveal the geodynamical evolution of the Misis Structural High, we analysed measurements of fault planes including movement vectors (striae), obtained mainly from the highly deformed Misis Complex. The complex is thought to have formed in a basin by the destabilisation of the northerly Tauride margin related to slab pull-back in the Paleogene. Following generation of the Misis Complex by continental collision in the region, units were compressed, thrust over each other and began to rise as an elongate mountain range. Detailed geological fieldwork, mapping and structural analysis of fault planes in the region indicate that the Misis Structural High was uplifted by the effects of a regional transpressional tectonic regime from the NNE-SSE direction which is forming a positive flower structure.

Confidence-Constrained Support Vector Regression for Geological Surface Uncertainty Modeling

Reconstruction of complex geological surface is widely used in oil and gas exploration, geological modeling, geological structure analysis, and other fields. It is an important basis for data visualization and visual analysis in these fields. The complexity of geological structures, the inaccuracy and sparsity of seismic interpretation data, and the lack of tectonic morphological information can lead to uncertainty in geological surface reconstruction. The existing geological surface uncertainty characterization and uncertain reconstruction methods have a shortcoming in balancing the interpolation error of high-confidence samples and model structure risk. Based on support vector regression (SVR), a method with confidence constraints for uncertainty characterization and the modeling of geological surfaces is proposed in this article. The proposed method minimizes the structural risk by adding a regularization term representing the model complexity, integrates high-confidence samples, such as drilling data, based on confidence constraints, and utilizes well path points by assigning appropriate inequality constraints to the corresponding prediction points. The results based on a real-world fault data set show that the uncertainty envelopes and fault realizations generated by the proposed method are constrained by well observations and well paths, effectively reducing the uncertainty.

Laramide Uplift near the Ray and Resolution Porphyry Copper Deposits, Southeastern Arizona: Insights into Regional Shortening Style, Magnitude of Uplift, and Implications for Exploration

AbstractThis study integrates new geologic mapping and structural analysis with previous work near Walnut Canyon and Telegraph Canyon to address the style and magnitude of shortening and the relationship between contractional structures and porphyry preservation and localization between the Ray and Resolution porphyry copper deposits. Cenozoic extensional structures were superimposed on earlier contractional structures formed during the Laramide orogeny, which dates from ~80 to 50 Ma. This superposition requires that Cenozoic normal faults be restored prior to analysis of Laramide contractional structures and their relationship to nearby porphyry copper deposits. Five distinct sets of normal faults within the study area progressively tilted the region 65° east. The amount of extension was 10.3 km or 276%. Using key constraints such as offset strata, cutoff angles between faults and various units, and Laramide fault geometries, the study area was structurally reconstructed and verified using 2-D kinematic modeling of reverse fault offset and related folding. Total shortening is 7.2 km or 98%. Laramide reverse faults are interpreted as thick-skinned basement-cored uplifts, because they restore to moderate angles, have related fault-propagation folds, and involve significant crystalline basement rock. The Telegraph Canyon reverse fault has at least 5.3 km of offset, and the Walnut Canyon reverse fault has 3.2 km. The preferred estimate of the total vertical uplift for the fault system is 5.2 km but could be several kilometers greater. The restored strike direction of these faults combined with mid-Cenozoic erosion surfaces throughout the region suggests that this fault system may be responsible for the Laramide uplift of the Tortilla Mountains and Black Hills. In addition, most major porphyry centers appear to have been intruded into the footwall of this large uplift, with local examples including Ray and Resolution, suggesting that topography generated from this uplift may have been critical to preservation of these ore systems. Though definitive crosscutting relationships do not exist in the immediate map area, geologic relationships in a broader area suggest that shortening here began after 74 Ma and, in the Ray area, had ended by ~69 Ma and that porphyry formation postdated reverse faulting by as much as 5 m.y. to as little as <1 m.y.

谢桥矿11518工作面围岩地质构造分析

谢桥矿11518工作面围岩地质构造分析

A safer future with clues from earthquakes past

Understanding the short- and long-term mechanical behaviour of the lower crust is of fundamental importance when trying to understand the earthquake cycle and related hazard along active fault zones. In some regions some 20% of intracontinental earthquakes of magnitude > 5 nucleates in the lower crust at depth of 30-40 km. For example, a significant proportion of seismicity in the Himalaya, as well as aftershocks associated with the destructive 2001 Bhuj earthquake in India, nucleated in the granulitic lower crust of the Indian shield. Earthquakes in the continental interiors are often devastating and, over the past century, have killed significantly more people than earthquakes that occurred at plate boundaries. Thus, a thorough understanding of the earthquake cycle in intracontinental settings is essential. This requires knowledge of the mechanical behaviour and of the strength (by which Earth scientists commonly mean the maximum stress that rocks can sustain before deforming) of the lower crust. The most common conceptual model of the strength of the continental crust predicts a strong, seismogenic brittle upper crust (where the base of the seismogenic layer is typically considered to be at depth of 10-15 km), and a weak, viscous, aseismic lower crust. This model has been recently questioned by the finding that the lower crust can be seismic and, therefore, mechanically strong. The question arises, how thick is the seismogenic layer in the crust? Answering this question is crucial to determine the potential hazard caused by large earthquakes, which are also generally the deepest.<br/> Our limited knowledge of the mechanical behaviour of the lower crust is largely due to the lower crust itself being poorly accessible for direct geological observations, so that most of our knowledge derives from indirect geophysical measurements (like the distribution of earthquakes). There are only a few well-exposed large sections of exhumed continental lower crust in the world. One of these is located in the Lofoten islands (northern Norway), which were exhumed from their original deep crustal position during the opening of the North Atlantic Ocean.<br/> We propose an integrated, multi-disciplinary study of a network of brittle-viscous shear zones (i.e. zones of localized intense deformation of geological materials) from Lofoten, which records episodic rapid slip events (earthquakes) alternating with long-lasting aseismic creep. The study will link structural geology (analysis of geological faults and shear zones), petrology (analysis of the composition and textures of rocks), geochemistry (detailed chemical characterization of rocks and minerals) and experimental rock deformation (to reproduce in the lab under controlled conditions the deformation processes operative in the deep Earth's crust). This integrated dataset will provide a novel, clear picture of the mechanical behaviour of the continental lower crust during the earthquake cycle. Our direct geological and experimental observations will be tested against geophysical observations of currently active seismic deformation. The cumulative results of the projects will shed light on the currently poorly constrained mechanical behaviour of the lower crust during the earthquake cycle, and therefore on the sequence of inter-seismic slip (the period of slow accumulation of elastic deformation along a fault), co-seismic slip (the sudden rupture along a fault that is the earthquake) and post-seismic slip (the immediate period after an earthquake when the crust and the fault adjust to the modified state of crustal stress caused by an earthquake). This will greatly extend and complement existing efforts by the scientific community to understand and interpret the mechanical behaviour of rocks during the earthquake cycle recorded in the lower crust and the related hazard, and will provide key input for numerical models of continental dynamics.

Geology of the Susa Shear Zone (Susa Valley, Western Alps)

ABSTRACT The 1:10,000 scale geological map of the Susa Shear Zone (SSZ) in the inner sector of the Western Alps, aims to describe the geological setting and tectonic evolution of a first-order Alpine shear zone, which drove exhumation and juxtaposition of different oceanic and continental margin units (i.e. the blueschist-facies External Piedmont Zone in its hanging wall and the eclogite-facies Internal Piedmont Zone and Dora Maira Massif in its footwall). The SSZ corresponds to a tectonic mélange showing a block-in-matrix structure, wherein mylonitic calcschists embed blocks of different rock units. Geological mapping and structural analysis investigated overprinting relationships among shear planes and structures related to different deformation phases: they show that the SSZ evolved through two tectonic events, during which apparent reverse top-to-E shear planes were superposed by extensional top-to-W ones.