NW-SE Fractures Research Articles

Fracture model and structural history of Gunung Keriang, Kedah

Gunung Keriang is a limestone hill in Kedah, northwest Peninsular Malaysia, with well-bedded limestones that gently dip towards the SW and SE, forming N-S trending gentle folds. Fractures are prevalent at both regional and local scales, with three major fracture sets identified: NW-SE, N-S, and NE-SW, all of which are steep to vertically dipping. These fracture sets and their characteristics have been thoroughly analyzed and summarized in this study. The NW-SE fractures have an average length of 137.2 m with a spacing of 92.3 m, the N-S fractures average 120 m in length with 81.3 m spacing, and the NE-SW fractures average 101.6 m in length with 72.7 m spacing. The limestone deposits in Gunung Keriang were formed in a partially unstable shallow marine environment during the Early Permian to Early Triassic period. Subsequently, the Late Triassic collision between the Sibumasu and Indochina terranes led to the formation of N-S trending gentle folds, N-S tension gashes, and potential conjugate fracture sets (NW-SE and NE-SW direction) due to E-W compression. The ensuing uplift exposed the Gunung Keriang limestone and caused extensive dissolution, particularly along fractures.

Fracture Analysis in the Outcrops of the Qara Chauq Anticlines, Zagros Fold and Thrust Belt of Kurdistan Region in Northern Iraq

The Zagros Fold and Thrust belt is one of the world's most prolific petroleum provinces. Most hydrocarbon reserves are stored in naturally fractured reservoirs and such fracture systems can therefore have a significant impact on reservoir performance. Fractures are one of the most important paths for fluid flow in carbonate reservoirs. Fracture data were collected in the outcrops of the Kirkuk Group of Oligocene age around Qara Chauq South and Qara Chauq North anticlines located near the Kirkuk Oil Field. The studied formations outcropping in the Qara Chauq are the main reservoir units in the Kirkuk and Bai Hassan fields. In Kirkuk and surrounding fields, hydrocarbon production comes mainly from primary porosity with assistance from secondary porosity created by dolomitization, karstification, dissolution, vugs and fractures. Fracture attributes collected from outcrops are fracture orientation, density and length. The results show that fractures in the studied reservoir formation are not uniformly distributed due to massive lithologic nature and lack of well bedding. Furthermore, fracture orientations show a clear relationship to the local fold axis in the outcrops. NW-SE fracture set is perpendicular to the NW-SE fold axis. However, some fractures do not show any relation to the local folding. These fractures may have formed in a pre-folding or post folding stage. Other fracture orientations exhibit a symmetrical relation to the maximum horizontal stress direction. The comparative analysis of outcrop data underlines the importance of representative analogue data for reservoir modelling and production strategies.

The Ediacaran Hiyam Formation: A zoom through the diagenetic and structural complexity of the metamorphic Hi2 Member, Saih Hatat Dome, Oman Mountains

This is the first diagenetic study of the metamorphic upper Hiyam Member “Hi2” of the Saih Hatat Dome. Despite metamorphism, texture and paragenesis of the Hi2 Member are so well preserved that it is possible to unravel its diagenetic evolution. We applied lithological and structural field methods, transmission and cathodoluminescence microscopy to establish the paragenetic sequence and vein-forming deformation. Our work reveals a complex diagenetic and structural history, including several alternating dolomitization, calcite precipitation, silicification and fracturing events. Most of the replacive dolomite and silica are linked to early diagenesis under intertidal to sabkha and restricted marine as well as to terrestrial conditions. Evaporation of sea water concentrated Mg2+ and triggered extensive early dolomitization while silica-bearing fluids caused local silicification. Various generations of dolomite and calcite cements pervasively occluded macropores, micropores and veins. Late burial is reflected by pressure solution seams/stylolites, non-ferroan to weakly ferroan saddle-type dolomite cement and non-ferroan blocky and drusy calcite cement, filling veins and macropores. The various generations of calcite cements (e.g., in veins) are considered to have formed during burial or possibly meteoric conditions. The latter potentially resulted from tectonic uplift, while late dolomite cement displays hydrocarbon residues from coeval oil migration. A later minor oil migration event has also been recognized. Initial fracture/fissure formation is most likely related to folding during the Early Cambrian Angudan Orogeny (open NW-SE fractures) and to divergence during the Late Paleozoic Pangean/Neo-Tethys rifting (open NW-SE fractures). Metamorphism impacted the Hi2 Member, resulting in phyllite formation, phyllosilicate crystallization and ductile shearing. Metamorphism occurred during shallow Late Cretaceous subduction. Striking lithological similarities between the Hi2 Member and that of the upper Kharus Formation of the Jabal Akhdar region could indicate their lateral equivalence.

Characteristics and evolution of the Etili silica sinter epithermal deposits, Çanakkale – Turkey: Relation to alkali chloride vs acid-sulfate fluids

The Oligo-Miocene Etili epithermal deposits are a well-preserved fossil geothermal system in the Çanakkale Region and is one of the largest fossil siliceous hot spring deposits of Turkey. Main E-W and NE-SW trending faults systems occur with minor NW-SE fracture systems perpendicular to the main faults. Silica-rich deposits are commonly observed in or on the calc-alkaline tuffs, ashes and pyroclastic rocks that were the products of the magmatism controlled by the extensional tectonic regime.The Etili epithermal system was examined at two representative locations including the Hamamtepe and Muratlar sites. Morphologies of the proximal apron were defined by lithofacies that included silica infiltrate, spring conduits, nodular and finely laminated geyserite, sinter clast breccia, silicified volcanic rocks, and epithermal veins. Microfossils were detected in mat structures developed in the proximal apron. The silica deposits have low abundances of altered mineral assemblages (e.g., kaolinite, halloysite, and alunite), which are otherwise commonly observed in the region. The origin of the Etili Fossil Silica Sinter Region (EFSSR) was constrained by using geochemical and isotopic data. δ18O and δD isotopic values of kaolinites ranged +9.4/+9.6 ‰; to 84/−74 ‰ respectively. δ18O isotopic values from siliceous and silicified samples ranged from 8.3 to 18.4 ‰, which shows two different formation types for the Etili Fossil Silica Sinter Region. We hypothesized hypogene origins for the kaolins and a mixed hypo/supergene origin for siliceous and silicified samples. The calculated model formation temperature from the δ18O values of the silica and siliceous samples is in the range of 63° to 140 °C. δ34S isotopic values of alunite ranged from −19.6 to +16.6 ‰, which also indicated two different sources that include magmatic hydrothermal and meteoric waters affected by bacterial activity. The timing of acid-sulphate alteration can be grouped into three periods by 40Ar/39Ar dating of alunites. These ages are: (A) 32.4 ± 1.2 to 22.6 ± 0.22 Ma in the Muratlar silica site, (B) 12.3 ± 0.3 to 15.2 ± 0.3 Ma in the northern part of the Hamamtepe site and (C) 5 ± 0.18 to 7 ± 0.3 Ma in the southern part of the Hamamtepe silica site. These consistent findings show that the emplacement periods of the Evciler pluton and the ages of alteration deposits are similar to each other. Silica sinters and geyser mounds represent very late stage near-neutral pH alkali chloride geothermal activities. The epithermal deposits in the EFSSR comprises a complex history of three different hydrothermal processes, each of which have different compositional and temporal emplacement periods related to the Evciler pluton.

Sedimentology, geomorphology, structural controls, and detrital zircon ages of the Itiquira River diamond placer deposits, Mato Grosso, western Brazil

The Itiquira River, Mato Grosso state (western Brazil), hosts several diamond placer deposits, mined intermittently over the last century. It runs over volcanic and sedimentary rocks of the Paraná Basin until it discharges in the northern Pantanal Basin. The bedrocks were deposited in marine, continental desertic, alluvial deltaic, and fluvial environments. The meanders of the Itiquira River are controlled by NE-SW, ENE-WSW, NNW-SSE, N–S, and NW-SE fractures and normal faults, developed in response to the evolution of the Paraná Basin and by neotectonics, linked with the development of the Pantanal Basin since the Paleogene. The Itiquira River middle valley, in which the diamondiferous placers are found, is controlled by NE-SW structures inherited from the Neoproterozoic Transbrasiliano Lineament. The landscape comprises dissected plateaus and structure-controlled valleys formed by Cretaceous, Paleogene, and Neogene planation processes. The diamonds occur in the muddy-sandy matrix of the current stream bed and older terraces gravels. In the Itiquira River, the diamond deposits are related to the following traps: point bars, cut-and-fill channels, pockets, and potholes. Sapphire, garnet (including kimberlitic), ilmenite, zircon, rutile, gold, and iron oxides are documented as heavy minerals in the gravels. Detrital zircon dating of grains extracted from the Itiquira River diamond deposits resulted in the ages of 2057, 1184, 873, 645–508, 307–207, and 144-142 Ma. The potential zircon sources are the Goiás Magmatic Arc granitoids, Paraguay Belt metavolcanics and granites, and Serra Geral Formation volcanics. The ages between 307 and 207 Ma are likely to be from an unknown (possibly kimberlitic) source. The Itiquira River tectonic, geomorphological, and sedimentological evolutions suggest potential sources for the diamond placers and paleoplacers.

Hidden but Ubiquitous: The Pre-Rift Continental Mantle in the Red Sea Region

Volcanism in the western part of the Arabian plate resulted in one of the largest alkali basalt provinces in the world, where lava fields with sub-alkaline to alkaline affinity are scattered from Syria and the Dead Sea Transform Zone through western Saudi Arabia to Yemen. After the Afar plume emplacement (∼30 Ma), volcanism took place in Yemen and progressively propagated northward due to Red Sea rifting-related lithospheric thinning (initiated ∼27–25 Ma). Few lava fields were emplaced during the Mesozoic, with the oldest 200 Ma volcanic activity recorded in northern Israel. We report results from volcanic pipes in the Marthoum area, east of Harrat Uwayrid, where over a hundred pipes occupy a stratigraphic level in the early Ordovician Saq sandstones. Most of them are circular or elliptical features marked by craters aligned along NW-SE fractures in the sandstone resulting from phreatomagmatic explosions that occurred when rising magma columns came in contact with the water table in the porous sandstone host. These lavas have Sr-Pb-Nd-Hf isotopic compositions far from the Cenozoic Arabian alkaline volcanism field, being considerably more enriched in Nd-Hf and Pb isotopes than any other Arabian Plate lava ever reported. New K-Ar dating constrains their age from Late Cretaceous to Early Eocene, thus anticipating the Afar plume emplacement and the Red Sea rift. Basalt geochemistry indicates that these volcanic eruptions formed from low-degree partial melting of an enriched lithospheric mantle source triggered by local variations in the asthenosphere-lithosphere boundary. This mantle source has a composition similar to the HIMU-like enriched isotopic component reported in the East African Rift and considered to represent the lowermost lithospheric mantle of the Nubian Shield. The generated melt, mixed in different proportions with melt derived from a depleted asthenosphere, produces the HIMU-like character throughout the Cenozoic Arabian alkaline volcanism. Although apparently hidden, this enriched lithospheric component is therefore ubiquitous and widespread in the cratonic roots of the African and Arabian subcontinental mantle.

Early evidence of pyrometamorphism and a late hydrothermal alteration related to Albian volcanism in the Pernambuco sedimentary basin, northeast Brazil

Pyrometamorphic aureoles and late hydrothermal alterations linked to Albian alkaline volcanism of the Ipojuca Magmatic Suite are described for the first time in the Pernambuco Basin, northeast Brazil. Field features, petrography, scanning electron microscopy (SEM-WDS), reflectance spectroscopy and X-ray diffraction data were used to characterize the mineral assemblage related to these two geological features. The pyrometamorphic aureoles occur when trachybasalts and arcosian sandstones (upper Cabo Formation) are in contact and were classified as buchites, due to the mineral assemblage composed of mullite, spinel (hercynite), tridymite, pyrrhotite and montmorillonite. The sanidinite facies (high temperature and lower pressure) is attributed to the mineral assemblage described above. Regarding the late hydrothermal alteration, two main events occurred in shallow conditions (up to 1 km). The first event is marked by an argillic alteration along NE-SW and NW-SE faults and fractures. The mineral assemblage is composed of kaolinite, quartz and minor magnetite. This alteration is also characterized by a reflectance spectral signature demonstrated by the high crystallinity of kaolinite that could also indicate its hypogene origin, in temperatures ranging from 100 to 250 °C. The second event is characterized by amygdales and veinlets in basalts lava flows that are filled with smectite (e.g montmorillonite), the formation of which is attributed to alkaline hydrothermal fluids with temperatures between 75 and 150 °C. Both events have been associated with the same fluid source. However, the first event occurred at higher temperatures and with acidic fluids, while the second presented lower temperatures and alkaline fluids.

Structural analysis of the Planchón-Peteroa Volcanic Complex: Insights for the geothermal system

The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Transitional Southern Volcanic Zone of the Andean Ridge. Structural control of the main NNE-striking El Fierro fault system (EFFS) over the volcanic activity has been commonly assumed, although a paucity of evidence remains. The aim of this paper is to explore the relationship between the local stress field, the superficial structural setting and the geothermal fluid flow paths related to the volcanic complex. To conduct the structural analysis, this work combines remote sensing determination of lineaments, recognition of fracture patterns, with the inversion of kinematic indicators on outcrop scale faults, to finally evaluate the role of the local stress field over the 2D slip and dilation tendencies of the recognized structures. Mesoscale morphostructural lineaments present three main directions: ~E-W, ~NE-SW, and ~NW-SE. Major lineaments develop inflections, giving rise to left bends between the NW-SE to E-W along the strike, compartmentalized by ~ NNE trending lineaments. Strike-slip fault solutions with an ENE-WSW to NE-SW oriented shortening axis were obtained from fault-slip data analysis. The inversion of fault kinematic indicators constrains a Quaternary to recent strike-slip regime, with a ~ENE-WSW trending σ1, and a subvertical σ2. Under the defined local stress field, ~NE-SW and ~WNW-ESE oriented structures have high slip tendency, while those spanning from NE-SW to E-W are prone to dilate. Our analysis suggests that these transverse structures exert first-order controls on the location of Vergara Pass Hill, and Peñón River and Azufre River Valleys hydrothermal manifestations. It seems that intersection zones with submeridian structures, as EFFS, increase structural damage and facilitate hot fluid migration. Circulation would profit the most from ~ENE-WSW and ~NW-SE striking outcrop-scale faults and fractures associated with the damage zones.

Timing, drivers and impacts of the historic Masiere di Vedana rock avalanche (Belluno Dolomites, NE Italy)

Abstract. The “Masiere di Vedana” rock avalanche, located in the Belluno Dolomites (NE Italy) at the foot of Mt. Peron, is reinterpreted as historic on the base of archeological information and cosmogenic 36Cl exposure dates. The deposit is 9 km2 wide, has a volume of ∼170 Mm3 corresponding to a pre-detachment rock mass of ∼130 Mm3, and has a maximum runout distance of 6 km and an H∕L ratio of ∼0.2. Differential velocities of the rock avalanche moving radially over different topography and path material lead to the formation of specific landforms (tomas and compressional ridges). In the Mt. Peron crown the bedding is subvertical and includes carbonate lithologies from Lower Jurassic (Calcari Grigi Group) to Cretaceous (Maiolica) in age. The stratigraphic sequence is preserved in the deposit with the formations represented in the boulders becoming younger with distance from the source area. In the release area the bedding, the SSE-verging frontal thrust planes, the NW-verging backthrust planes, the NW–SE fracture planes, and the N–S Jurassic fault planes controlled the failure and enhanced the rock mass fragmentation. The present Mt. Peron crown still shows hundreds-of-metres-high rock prisms bounded by backwall trenches. Cosmogenic 36Cl exposure ages, mean 1.90±0.45 ka, indicate failure occurred between 340 BCE and 560 CE. Although abundant Roman remains were found in sites surrounding the rock avalanche deposit, none were found within the deposit, and this is consistent with a late Roman or early Middle Ages failure. Seismic and climatic conditions as landslide predisposing factors are discussed. Over the last few hundred years, earthquakes up to Mw=6.3, including that at 365 CE, have affected the Belluno area. Early in the first millennium, periods of climate worsening with increasing rainfall occurred in the NE Alps. The combination of climate and earthquakes induced progressive long-term damage to the rock until a critical threshold was reached and the Masiere di Vedana rock avalanche occurred.

Connectivity of fractures and groundwater flows analyses into the Western Andean Front by means of a topological approach (Aconcagua Basin, Central Chile)

The misunderstanding of hydrogeological processes together with the oversimplification of aquifer conceptual models result in numerous inaccuracies in the management of groundwater resources. In Central Chile (32–36°S), hydrogeological studies have exclusively focused to alluvial aquifers in valleys (~15% of total area) and mountain-front zones remain considered as no-flux boundary conditions. By a topological approach and an analysis of fractures, the hydrogeological potential of the Western Andean Front along the N–S-oriented Pocuro Fault Zone (PFZ) in the Aconcagua Basin were determined. Perennial springs (23) show evidence of groundwater flows into the fractured Principal Cordillera. Topology allows for quantification of the density of connected fractures within the fault zone and its relationship with groundwater circulation. The study results highlight two areas where the density of fractures and connected nodes (Nc) is high (>2.4 km/km2, 2.5 Nc/km2). Both areas are topologically related to the main springs of the PFZ: Termas de Jahuel (discharge ~14.0 m3/h at 22 °C) and Termas El Corazon (discharge ~7.2 m3/h at 20 °C). Outcrop-scale mapping reveals that groundwater outflows from NW–SE fractures, which is consistent with the preferential orientation of the fracture network (N30–60 W) within the PFZ. The results indicate that oblique basement faults are discrete high-permeability structures conducting groundwater across the Western Andean Front from the Principal Cordillera up to adjacent alluvial aquifers (focused recharge). Therefore, the simplistic hydrogeological view of the Western Andean Front (i.e. impervious limit) is partially erroneous.

Multi-Attribute Analysis Using Coherency and Ant-Tracking Techniques for Fault and Fracture Detection in La Florida Anticline, Llanos Foothills, Colombia

We present techniques to reduce noise and enhance seismic quality, making possible the first multi-attribute analysis of a 3D seismic volume in the Llanos Foothills (La Florida anticline) of Colombia using coherency and ant-tracking techniques for fault and fracture detection. The results could help reduce risk in models of reservoir fracture porosity and permeability. The dominant fracture strike direction in the studied seismic volume (La Florida anticline) is NE–SW (055 ± 20°), parallel to the structural strike of the adjacent Eastern Cordillera Foothills. The application of the ant-tracking technique also reveals the NE-SW fracture set for the reservoir rocks in the La Florida anticline as well as in the non-folded reservoir rocks to the SE. We compared the fracture intensity and orientation in folded rocks with the fracture intensity and orientation in non-folded rocks. Our study showed NE-SW, NW-SE, and E-W fracture orientations in the non-folded seismic volume, suggesting that regional stresses could produce these fracture sets, not just folding processes as previously proposed. The NW-SE and WNW-ESE fracture sets are only found in the Guayabo Formation (11 Ma–Present). A right–lateral strike–slip displacement on the nearby Algeciras fault system in the last 2 m.y. may have generated WNW-ESE and NW-SE Riedel-type shear fractures in the study area.

Neoarchean crustal shear zones and implications of shear indicators in tectonic evolution of Bundelkhand craton, central India

The gneisses and granitoids emplaced along E-W sub-vertical crustal shear zones are represented as important tectonic units in Bundelkhand craton of central India. The tonalite-trondhjemite-granodiorite (TTG) gneisses (3.5-3.2 Ga; oldest unit), and streaky to mafic gneisses structurally deformed in D 1 deformation. The metabasic, felsic, banded iron formation and metasedimentaries of greenstone complex exposed in central part, have characteristics of three sets of folding (F 1 -F 3 ). These gneisses associated with migmatite, amphibolite, quartzite, and schist were evolved in D 2 compressive phase, which are not occurring in northern part of craton. The K-rich Neoarchean granitoids (2.6-2.49 Ga) were intruded as granitic complex (D 3 magmatic phase) and the E-W strike-slip Raksa-Garhmau shear zone reported as important tectonic unit, were evolved in asyn-to post-tectonic D 3 phase. The dolerite dykes (ca. 2.0 Ga) were emplaced along NW-SE fractures in extension setting during D 4 magmatic event. The NE-SW riedel shears occupied by giant quartz veins (reefs) evolved in Paleoproterozoic during D 5 endogenic activity.
 The relationship between macro and microstructural fabrics has been documented within mylonitic foliation, stretching lineation, S-C planes and rotated fabrics, reflect mesoscopic shear indicators, as noted in three types of mylonitic rocks. i) The rotated porphyroclasts of quartz, feldspars and asymmetric pressure shadows showing strong undulose extinction, deformation lamellae, and dynamic recrystallization are characteristic features of protomylonite where altered orthoclase and kinked plagioclase are noticed. ii) Mylonite, a distinct mylonitic foliation represented by parallel orientation of elongated quartz and feldspar with flakes of mica. iii) The ground matrix of recrystallized quartz with few protoliths of quartz and feldspar are observed, important features of ultramylonite. The asymmetric microstructures viz. σa and σb mantled porphyroclasts, othermicrostructures show progressively deformed by crystal plastic (non-coaxial) strain softening under low to moderate temperature conditions. The sinistral top- to- SW sense of shear movement was dominant. The microfractures/ microfaults, kinking and pull apart structures observed in K- feldspars and are indicative of overprinting of brittle deformation on ductile shearing.

Geophysical and Metalogenetic Modelling of the Copper Occurrence in Camaquã Sedimentary Basin, Brazilian Southern

The geophysics application is indicated procedure in mineral exploration activities, by the quickness and possible global reduction of project cost. This work presents the results of the DC resistivity and induced polarization methods joint application, integrated to geological and structural data from a potentially mineralized area with copper sulfides, located in the Northern border of the Camaqua Sedimentary Basin, Brazil Southern. The mineral occurrence is characterized by malachite and azurite impregnation on silicified Neoproterozoic metarenite outcrop of Passo da Promessa Formation (Marica Group). The geophysics acquisition consists in six electrical tomography lines in Schlumberger arrangement with 440 m each, the lines were separated on two groups disposed at orthogonal form where the center area is located the mineral occurrence in surface. The results indicate a low resistivity and high chargeability zone 60 m deep, related to a sulfided zone and surrounded by elevated resistivity, which point silicification areas. The structural analysis has revealed two main fracture systems in the crystalline basement (NE–SW and NW–SE), one in the metarenite (NE-SW) and fold with a N20 axis. The 3D visualization model reveals that the mineralization is oriented in the N125 direction (NW–SE). The NW–SE fracture family is secondary but is present in the occurrence area and coincident with the relaxing direction of the folding event. This context corroborates with the hypothesis of filling NW–SE fractures, result which indicates the relevance of this preferential direction in future mineral research campaigns in the Camaqua Basin.

From Early Contraction to Post-Folding Fluid Evolution in the Frontal Part of the Bóixols Thrust Sheet (Southern Pyrenees) as Revealed by the Texture and Geochemistry of Calcite Cements

Structural, petrological and geochemical (δ13C, δ18O, clumped isotopes, 87Sr/86Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet (Southern Pyrenees). Five fracture events associated with the growth of the thrust-related Bóixols anticline and Coll de Nargó syncline during the Alpine orogeny are distinguished. These fractures were cemented with four generations of calcite cements, revealing that such structures allowed the migration of different marine and meteoric fluids through time. During the early contraction stage, Lower Cretaceous seawater circulated and precipitated calcite cement Cc1, whereas during the main folding stage, the system opened to meteoric waters, which mixed with the connate seawater and precipitated calcite cement Cc2. Afterwards, during the post-folding stages, connate evaporated marine fluids circulated through newly formed NW-SE and NE-SW conjugate fractures and later through strike-slip faults and precipitated calcite cements Cc3 and Cc4. The overall paragenetic sequence reveals the progressive dewatering of Cretaceous marine host sediments during progressive burial, deformation and fold tightening and the input of meteoric waters only during the main folding stage. This study illustrates the changes of fracture systems and the associated fluid-flow regimes during the evolution of fault-associated folds during orogenic growth.

A fracture identification method for low-permeability sandstone based on R/S analysis and the finite difference method: A case study from the Chang 6 reservoir in Huaqing oilfield, Ordos Basin

Low-permeability reservoirs are characterized by poor physical properties, strong heterogeneity and natural fractures. Accurate identification of the fracture distribution is of great significance for the exploration and development of low-permeability reservoirs. Field outcrop, core and imaging log analyses show that stratabound vertical and high-angle structural fractures are the main types of fractures in the Chang 6 formation in the Huaqing oilfield. The fracture orientations include NE-SW, NNE-SSW, NW-SE, and NNW-SSE. The NE-SE-oriented fractures formed in the Himalayan stage, while the NW-SE fractures formed in the Yanshan period, and the other fractures derived from the fracturing in the Yanshan period during the Himalayan tectonic activity. The traditional rescaled range (R/S) analysis method is upgraded by introducing the finite difference (FD) method in this research, and the newly proposed method is called the R/S-FD method. Core data show that the R/S-FD method can accurately recognize vertical fractures and high-angle fractures. By comparing the fracture development section on the imaging log, it is found that fractures discrimination parameter F has a good linear relationship with both the fracture linear density and the fracture surface density. This method is verified by dynamic data (water injection profiles) and static data (image logging), and the results show that the recognition error is eliminated when the lower limit of F is 0.5, resulting in a crack identification accuracy of 76.9%. Combining the R/S and finite difference methods reduces the artificial recognition error of the traditional R/S method, and the recognition process is automated and intelligent. The R/S-FD method can be used in combination with multiple logging curves. A high fracture recognition accuracy could be accomplished by using this proposed method with only conventional logging curves, of great practical significance to some low-permeability oilfields that lack image logging data.

Virtual Structural Analysis of Jokisivu Open Pit Using ‘Structure-from-Motion’ Unmanned Aerial Vehicles (UAV) Photogrammetry: Implications for Structurally-Controlled Gold Deposits in Southwest Finland

Unmanned aerial vehicles (UAVs) are rapidly growing remote sensing platforms for capturing high-resolution images of exposed rock surfaces. We used a DJI Phantom 3 Professional (P3P) quadcopter to capture aerial images that were used to generate a high-resolution three-dimensional (3-D) model of the Jokisivu open-pit gold deposit that is located in southwestern Finland. 158 overlapping oblique and nadir images were taken and processed with Agisoft Photoscan Pro to generate textured 3-D surface models. In addition, 69 overlapping images were taken from the steep faces of the open pit. We assessed the precision of the 3-D model by deploying ground control points (GCPs) and the average errors were found minimal along X (2.0 cm), Y (1.2 cm), and Z (5.0 cm) axes. The steep faces of the open pit were used for virtual structural measurements and kinematic analyses in CloudCompare and ArcGIS to distinguish the orientation of different fracture sets and statistical categorization, respectively. Three distinct fracture sets were observed. The NW-SE and NE-SW striking fractures form a conjugate geometry, whereas the NNW-SSE striking fractures cut the conjugate fracture set. The orientation of conjugate fractures match well with the resource model of the deposit and NW- and NE-trending segments of regional-scale anastomosing shear zones. Based on the conjugate geometry of fracture sets I and II, and the regional pattern of anastomosing shear system lead us to interpret an origin of gold mineralization in two stages. An early N-S or NNW-SSE crustal shortening, corresponding to the regional D4 (ca. 1.83–1.81 Ga) or pre-D4 (ca. 1.87–1.86 Ga) Svecofennian tectonic event(s) that produced anastomosing shear zones. Subsequent E-W directed D5 contraction (ca. 1.79–1.77 Ga) partly reactivated the anastomosing shear zones with the formation of conjugate system, which controlled the migration of fluids and gold mineralization in SW Finland.

Review of the occurrence and structural controls of Baryte resources of Nigeria

Baryte occurrences in Nigeria are spread across the Cretaceous Benue Trough which comprises of carbonaceous shales, limestone, siltstones, sandstones as well as in the northeastern, northwestern and southeastern parts of the Precambrian Basement Complex comprising of metasediments and granitoids. The mineralization is structurally controlled by NW-SE, N-S and NE-SW fractures. The common mode of occurrence for these barytes is the vein and cavity deposits type usually associated with galena, sphalerite, copper sulphide, fluorite, quartz, iron oxide as gangue minerals. Principal areas of baryte occurrences in Nigeria include Nassarawa, Plateau, Taraba, Benue, Adamawa, Cross River, Gombe, Ebonyi, and Zamfara. A large part of the vast baryte resources in Nigeria is still underexploited and further exploration work is needed to boost its exploitation. The inferred resource and proven reserve of baryte is put at over 21,000,000 and about 11,000,000 metric tons respectively. The economic evaluation of these barytes is viable having low (SG = < 3.5) to high (SG = 5.3) grades. The presence of associated minerals produces low quality barytes and as such blending and beneficiation is required to improve its quality.

Geomagnetic evaluation of hydrocarbon prospectivity of the Nigerian sector of the Chad Basin

The interpretation of the geomagnetic data covering the Nigerian Sector of the hydrocarbon elusive Chad Basin has been carried out with the aim of evaluating its hydrocarbon prospectivity. The geomagnetic data was subjected to transformation and enhancement techniques such as reduction to the equator, band-pass filtering, analytic signal, pseudogravity, Source Parameter Imaging (SPI), and Euler deconvolution (ED). The 2-D forward modeling was done using the GM-SYS™ software. The results revealed two subbasins, separated by basement high, where the thickness of sedimentary succession of source rocks, reservoirs, and seals attained about 5 km. Two sets of laterally persistent NE-SW and NW-SE fracture systems capable of forming migratory routes were identified within the study area. Euler solutions show basement fractures that propagate through the sedimentary column at 1000 to 5000 m. Characteristic alternation of positive and negative pseudogravity anomalies exposed basement configuration to be of horst and graben architecture. Constructed models revealed drape anticlines that could act as structural traps in the event of hydrocarbon generation. Analytic signal anomalies indicative of igneous intrusive were mapped within the subbasins. This study concluded that elements that favour hydrocarbon occurrence are present in the Chad Basin and was therefore considered to be of high hydrocarbon prospectivity provided the occurrence and timing of the igneous intrusions had not adversely affected hydrocarbon accumulation.

Insights into the lithosphere to asthenosphere melting transition in northeast Africa: Evidence from the Tertiary volcanism in middle Egypt

Throughout the northeast African and Arabian plates, small-volume basaltic volcanism has erupted sporadically over the last ~35Myr. While magmatic activity associated with the Afar plume and subsequent rifting of the Red Sea, Gulf of Aden and East African rift provide a mechanism for melt generation in those areas, the origin of melt elsewhere in the region has remained enigmatic. We have identified two types of intraplate basalt eruptions from middle Egypt, which we suggest were generated by distinct melting processes: sub-alkaline, hypersthene-normative basalts and basaltic andesites (2.8–4.9wt% total alkalis); and nepheline-normative alkali basalts and trachybasaltic flows (4.9–5.5wt% total alkalis). Estimations of the primary melt compositions suggest about twice as much fractionation in the sub-alkaline basalts (F=32–58%, dominantly clinopyroxene and olivine removal) in comparison to the alkaline basalts (F=18–30%, dominated by clinopyroxene removal). Application of the geochemical model HAMMS1 generates results which suggest the alkaline basalts are likely derived from low degrees of partial melting (F<2%) of a pyroxenite-bearing mantle source at moderate potential temperatures (TP) ~1386–1449°C, and pressures >3.7GPa. These conditions require melting at or below the base of lithospheric mantle. In contrast, the sub-alkaline basalts exhibit negative K-anomalies for all fractionation-corrected melts, suggesting a source with a K-bearing phase (likely amphibole), located within lithospheric mantle, constrained by the stability of amphibole to be <3GPa and 1170°C. We suggest that the enrichment in the lithospheric mantle is best explained by the percolation of fluids/or hydrous melts either from the Late Neo-Proterozoic subduction zone during accretion the Arabian-Nubian Shield, or from an old mantle plume that impinged the base of the lithosphere during the Phanerozoic. Destabilization of these enriched metasomes was likely a function of diffuse stretching associated with the opening of the Red Sea at ca. 30Ma, thermal perturbation from a slightly warmer asthenosphere, and the passage of asthenospheric melts through the lithospheric mantle. The strong correlation between these small-volume lavas and regional structural lineaments (e.g., Baharyia NE-SW Fault), and smaller NW-SE fractures associated with the Red Sea system, suggests that the eruption of lavas in the region is controlled by melt focusing into the lithosphere and favorable stress conditions in the upper crust. Thus, while the potential for melt generation may be present beneath much of north-east Africa, the rarity at which volcanism is discovered at the surface reflects what may be an unusual convergence of circumstances.

Structural pattern of the Saïss basin and Tabular Middle Atlas in northern Morocco: Hydrological implications

The plain of Saïss is a fertile area of great agricultural production with major economic interests. Therefore, the improved knowledge about the water supply is imperative within a context of recurrent droughts and overexploitation of the groundwater. This plain is located in the Meknes-Fes basin and between two deformed domains: the Rif and Middle Atlas. The aquifers are fed by water coming from the Tabular Middle Atlas, for which the pathways are poorly constrained. This study provides new data to determine the water pathways based on a structural map produced from a novel analysis of SPOT images and a digital elevation model. This structural map reveals two fracture sets trending NE-SW and NW-SE. The first set is well known and corresponds to a main trend that controlled the tectonic and stratigraphic evolution of the study area. On the other hand, the NW-SE set was poorly described until now: it is both diffuse and widespread on the Tabular Middle Atlas. A comparison between the regional water flow trend, drainage pattern and structural map shows that the NW-SE fractures control the water flow from the Tabular Middle Atlas to the Saïss plain. A hydrological model is discussed where the water flow is confined onto Liassic carbonates and driven by NW-SE fractures. This study explains how a detailed structural mapping shows hydrology constraints.