Fault Corridor Research Articles

Building Resilience through Sustainable Tourism: A Case Study of Lembang and Greater Bandung Area

Owing to frequent tectonic activities, the Lembang Fault area in Java Island is highly vulnerable to disasters. Encompassing 51 villages along the fault, this region has witnessed rapid economic growth, transforming it into a sought-after tourist destination. The objective of this research is to map the levels of economic activity in the area and offer recommendations for sustainable economic development. The methodology employed encompasses data collection, in-depth interviews with agencies, business stakeholders, and developers, literature review, and research analysis. The findings of this study indicate that the areas situated along the fault corridor face significant disaster risks while exhibiting substantial economic activity. By utilizing recommendation maps and insights gleaned from interviews, it is determined that the most suitable area for further development lies on the north side of the Lembang Fault corridor. This research strives to provide valuable recommendations for future studies concerning economic sustainability in disaster-prone areas, specifically focusing on the Lembang Fault area. It contributes to enhancing our understanding of economic resilience in vulnerable regions and emphasizes the critical role of sustainable economic development in mitigating disaster risks.

New insights into Upper Cretaceous hydrocarbon traps of platform-basin flanks in the Sahel Eastern Tunisian petroleum province: Inferred optimal hydrocarbon reserves accumulations

The eastern Tunisian margin is considered an Upper Cretaceous and Eocene petroleum province. It has been affected by Mesozoic rifting and Cenozoic compression. Several oil and gas shows and accumulations have been discovered in Upper Cretaceous carbonates within structural anticlinal closures. These anticlinal highs represent inherited rift platform horsts with hiatuses, unconformities and sediment erosion. Seismic sequence stratigraphy and seismic tectonic analyses of Mesozoic and Cenozoic horizons, delineate the control of deep-rooted transtensional and transpressional Flower structure fault corridors, intruded by Upper Triassic salt. Petroleum system modelling and time events chart reconstruction of real and pseudo-wells, indicate that Cretaceous source rocks maturation and hydrocarbon generation began during Late Cretaceous with expulsion occurring from Eocene to Pliocene times. Hence, Upper Cretaceous petroleum system dynamics is intimately linked to basin geodynamics; where hydrocarbon migration pathways could follow the migration, rotation and tilting of platform and basin blocks. The volume of Lower Fahden and Bahloul source rocks expelled hydrocarbons from the basin kitchens, is much greater than that found in the drilled anticlinal axis. These hydrocarbons could have been trapped along the platform-basin border flanks and may not have reached the highest position on the anticlinal crest closure. Such pathways explain the unaccounted-for hydrocarbon volumes. These volumes could be trapped along the faults seal branches, unconformities, pinchouts as well as in the evidenced progradational and reefal system tracts sequences in the flank borders of the platforms. These traps could represent new exploration targets as potential structural and stratigraphic plays.

Analogue modeling of the role of salt in the structuration of thin-skinned pull-apart basins: The case study of El Hamma basin, Central Tunisia

Pull-apart basins are structurally complex features that typically form in between two laterally offset strike-slip zones. The vast majority of analogue experiments on the formation of this type of basins have been conducted using basal discontinuities that transmitted from the bottom up strike-slip motion into the overlying sedimentary cover. Here, we present a series of models whose aim is to demonstrate that pull-apart basins above a viscous layer can be initiated not from the base up, but by the sole effect of lateral forces that allow two blocks to move laterally one past the other. This occurs independently from the basement, from which the brittle cover is fully decoupled by the viscous layer. This work was inspired by a natural example, the El Hamma Basin, located in Central Tunisia West of the city of Gabes and is bounded by two N100-110 trending major fault corridors, the Oum Ali- Fejij corridor in the North, and the Oglet Merteba-Matmata in the South. The area underwent multiple tectonic episodes of both extension and compression from Late Liassic to the Plio-Quaternary times. The region was subjected to regional NE-SW extension during the upper-cretaceous and major NW-SE compression during upper Miocene (Tortonian) and early quaternary (Early Pleistocene). The latter stage resulted in right-lateral strike slip along both corridors with faults forming a pull-apart basin that comprises two lateral mega-grabens separated by a central horst. Although one sub-circular diapir in the area (the El Melah diapir) crops out along the northern wrench zone, whether or not the mobile Triassic series extend farther South of it, beneath the pull-apart basin, is still debated.Through a series of analogue experiments using an innovative technique that generates two narrow, parallel strike-slip zones located within the sedimentary cover, rather than in the basement. Experimental results show remarkably similar geometry and evolution with those of the El Hamma basin. Moreover, from a regional perspective, our results suggest that the pinch out of the Triassic evaporites extends further South than previously thought and underlies at least part of the El Hamma basin.

Petrogenesis and tectonic implication of Neoproterozoic I-Type Granitoids and orthogneisses in the Goa-Mandja area, Central African Fold Belt (Cameroon)

The geological evolution of the Central African Fold Belt (CAFB) remains debated. The granitoids, orthogneisses and granitic veins from the Goa-Mandja area (Adamawa-Yade domain) are considered to constrain this belt. These rocks are consistent with late-D2 regional emplacement and synchronous with the magmatism at ~600 Ma within the CAFB in Cameroon and its extension into northeastern Brazil, as the zircon UPb dating points to 603–598 Ma crystallization ages. Analytical data reveal slightly elevated δ18Ozrn (6.45–7.17‰) and δ18OWR (8.20–8.61‰), moderate to high SiO2 (59.70–77.23 wt%), low MgO (0.07–2.77 wt%), Cr (0.29–55.12 ppm), Ni (0.45–33.6 ppm), V (1.52–116.62 ppm) and Mg# (0.02–0.36) contents, indicating crustal origin. The low to medium 87Sr/86Sri (0.703328–0.722670) and positive to negative εNd(t) (+5.7 to −9.9), coupled with the diversity of Nd model ages (TDM2) support the heterogeneity of crustal protoliths. The high positive εNd(t) (+5.7) of the granitic vein indicates derivation from juvenile Neoproterozoic (Nd-TDM2 at 854 Ma) crustal protolith. TDM2(Nd) and TDM2(Hf) ages of 1188–2120 Ma and 2173–2480 Ma also suggest the involvement of Mesoproterozoic to Paleoproterozoic crustal protoliths.Samples show metaluminous to weakly peraluminous, high-K calc-alkaline to shoshonitic and I-type granitoid features and are similar with crustal rocks in regard to LILE (Rb, K) and LREE enrichments and HFSE (Nb, Ta, Ti) depletions. These combined features indicate slab subduction related setting for the magma generation. Slab subduction may have generated the heat necessary to provoke partial melting at the lower crustal level. Considering their position close to the Tchollire-Banyo Fault corridor, at the transition between the Adamawa-Yade and northern domains, the subduction derived features shown by the Goa-Mandja I-type granitoids could be related to the subduction of an old plate boundary during amalgamation of Gondwana. Therefore, the Goa-Mandja area records dominant magmatic accretion along the northern margin of the Congo craton (active margin) associated with a possible northwestern subduction.

Latest Silurian syntectonic sedimentation and magmatism and Early Devonian orogenic gold mineralization, central Newfoundland Appalachians, Canada: Setting, structure, lithogeochemistry, and high-precision U-Pb geochronology

Abstract The eastern Dunnage Zone of the central Newfoundland Appalachians hosts Paleozoic orogenic gold mineralization along a northeast-trending, crustal-scale fault corridor that extends for more than 200 km. This orogenic gold system is characterized by polyphase, structurally controlled, quartz vein systems that cut Neoproterozoic granitoid rocks and unconformably overlying syntectonic, polymict conglomerate and associated transitional to calc-alkaline bimodal igneous rocks. High-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronology confirms a widespread, latest Silurian magmatic pulse (422–420 Ma) that is attributed to a transient phase of lithospheric extension resulting from asthenospheric and crustal melting related to slab break-off. Syntectonic conglomerate was deposited as a basal unit during extension-related uplift and erosion that lasted until ca. 418 Ma in north-central Newfoundland. Orogenic gold mineralization associated with syntectonic sedimentation and magmatism is hosted within third-order shear vein systems that form offshoots within a triangle zone–like structural corridor between southeast- and northwest-dipping, second-order fault splays and shear zones. The southeast-dipping fault system formed during northwest migration of the Acadian thrust front, whereas the northwest-dipping faults and shear zones are Salinic structures that were reactivated in the Early Devonian. Primary hydrothermal rutile in the orogenic gold-mineralized quartz veins produced ages of ca. 410 Ma. These ages are consistent with quartz vein emplacement and orogenic gold mineralization as a result of hydrothermal fluid-pressure cycling related to far-field compression and thermal perturbations during the Early Devonian Acadian orogenic cycle. The setting and process evolution of the central Newfoundland gold district are remarkably similar to that of world-class orogenic gold systems of the Canadian Shield.

Multiscale Characterisation of Fracture Patterns of a Crystalline Reservoir Analogue

For an accurate multiscale property modelling of fractured crystalline geothermal reservoirs, an enhanced characterisation of the geometrical features and variability of the fracture network properties is an essential prerequisite. Combining regional digital elevation model analysis and local outcrop investigation, the study comprises the characterisation of the fracture pattern of a crystalline reservoir analogue in the Northern Odenwald, with LiDAR and GIS structural interpretation. This approach provides insights into the 3D architecture of the fault and fracture network, its clustering, and its connectivity. Mapped discontinuities show a homogeneous length distribution, which follows a power law with a −2.03 scaling factor. The connectivity of the fracture network is heterogenous, due to a fault control at the hectometric scale. Clustering is marked by long sub-vertical fractures at the outcrop scale, and strongly enhance heterogeneity around weathered fracture and fault corridors. The multi-variable dataset created within this study can be used as input data for accurate discrete fracture networks and fluid-flow modelling of reservoirs of similar type.

A conceptual framework of groundwater flowpath and recharge in Ziban aquifer: south of Algeria

The Zyban aquifers (southern Algeria) are an important source of groundwater and are mainly found in limestone and dolomite from the Senono-Eocene. To be able to assess the effects of overuse of the Zeban groundwater, it is necessary to understand the origin of the recharge and determine its path out of the recharge zones. This study aims to better understand the flow path and replenishment areas using hydrology. For this purpose, 145 water samples were collected and analyzed for the determination of major ions and isotopes (18O, 2H and 3H). The isotope analysis of hydrogen, oxygen and tritium allowed a certain distinction between the origin and the mixture of water. The study area is located in the fault corridor of the South Atlas, a network of migration and folding defects that leads to a complex structure characterized by the subdivision of the formations and the variety of facies. The regional flow pattern is mainly influenced by the topography, and this is through the distribution of supply and flow, which is produced by transport at many depths and levels of distribution (local or regional). The rocky nature and the severe fractures are responsible for the division of the hydrogeological units and play an important role in the dynamics and transport of the groundwater. The hydrodynamic analysis shows the dominance of regional hydrogeology in terms of geological nature and structure. This is supported by a hydrochemical signal showing the distribution and evolution of the elements according to the structural and geological scheme (evolution from calcium bicarbonate facies to calcium sulphate medium facies).

Geophysical study of Hammam Sidi Maamar geothermal site in Central Tunisia for sustainable development

Geophysical methods provide important help to investigate geothermal reservoirs. They permit to delineate deep and near surface structuring and to appreciate fluid circulation. In this study, we performed an integrated geophysical study using regional seismic reflection profiles and local Electrical Resistivity Tomography (ERT) data analyses to identify the relation between faults and specific geothermal pathways around Hammam Sidi Maamar thermal spring site in Hajeb Layoun area (Central Tunisia). The proposed geological model performed from seismic reflection composite sections reveals the geometry in depth series of the Lower Cretaceous from the recharge zone (Jebel Mrhila mountain) to the emergence area of Hammam Sidi Maamar (Jebel Baten Damous mountain) and traces the path of the thermal water, from its recharge area till surfacing, in order to propose a new suitable intake location with higher flow and temperature. The results of seismic and ERT data analysis confirm that the Hammam Sidi Maamar geothermal site is tectonically related to the junction of the NE-SW Baten Damous fault corridor and the NW-SE to E-W northern fault corridor of Hajeb Layoun graben. The water is charged from Lower Cretaceous (Hauterivian to Aptian) outcrop series in Jebel Mrhila Mountain to the West. It flows into the carbonate reservoir below the Hajeb Layoun-Jelma Plain, where the Lower Cretaceous reservoirs are reaching more than 2500 m deep. The reservoir geologic layers show ascent geometry towards Jebel Zaouia Mountain then they sink into the Hajeb Layoun Graben to the East. The thermal water rises to surface thanks to the deep faults that affect the Lower Cretaceous reservoir and the geologic series above. High resolution Electrical Resistivity Tomography panels, we carried out in Hammam Sidi Maamar geothermal site, allowed to locally identify the faulting architecture which controls the flow of hot water. Firstly, filtering and processing of ERT data were performed. 2D ERT modeling, mapping and 3D ERT view interpretation, were also performed to more understand the local tectonic/geothermal flow setting. Finally, to identify the prominent site for lateral and vertical geothermal flow plumes, we propose to drill 50 m–60 m intake well associated with a tectonic junction of the NE-SW Baten Damous fault corridor and the NW-SE to E-W Hajeb Layoun graben fault.

Fracture corridor identification through 3D multifocusing to improve well deliverability, an Algerian tight reservoir case study

It is important to fully understand faulted systems in E&P, whether for a proper understanding of prospects, optimizing well locations or enhancing field development. The identification of fractured zones within a reservoir, usually characterized by sub-seismic faults, is often neglected but can add significant value to a project. This case study focuses on the very prolific Algerian Upper Ordovician tight reservoir target. It discusses a structure at the end of an appraisal well campaign, where an integrated fracture reservoir study has been performed in order to track subtle fault corridors. The use of advanced seismic attributes from 3D multifocusing has proven invaluable when identifying fracture corridors within the reservoir. Results match reasonably well with the fracture orientation and density interpretation from cores, borehole images, and DST interpretations. This approach has proven to be of great value when planning well trajectories and predicting production. In the future, it will be used to locate development wells.

Umicore gains Hazari pre-catalysts

The Jiangnan Orogen, located between the Yangtze and Cathaysia Blocks in southern China, hosts significant gold and antimony resources. Long-standing controversies over the number and precise timing of gold, gold-antimony and antimony mineralization event(s), and the genesis of these deposits, limit the understanding and exploration of this giant gold and antimony system. Together with geological evidence, a critical review of the published geochronological data of these deposits suggest that there were two gold events in the Triassic (~235 Ma) and Early Cretaceous (~142–130 Ma), two gold-antimony events in the Early Devonian (~402 Ma) and Late Triassic-Middle Jurassic (~224–163 Ma: possibly equivalent to the two gold events), and one antimony event in the Early Cretaceous (~130 Ma). There are other possible gold events in the Neoproterozoic or at an even older age, and Ordovician to Early Devonian, which are constrained only by limited geological evidence and a few non-robust isotopic ages. The regional distribution of the gold, gold-antimony and antimony districts, and deposits therein, reveal a first-order control on the mineralization by crustal scale faults which acted as ore-forming fluid pathways connected to deep fluid and metal source areas. Second- and third-order faults that are situated along the jogs of the first-order faults, especially fault corridors defined by NNE-NE-trending second-order faults and third-order NW to E-W-trending discontinuous oblique faults, provided favorable locations for Pre-Cretaceous gold-(antimony) mineralization. In addition, NE-trending open anticlines, linked to deep crustal levels by first-order faults, host significant antimony and minor gold mineralization, and the curvilinear Fanjingshan detachment Fault hosts some gold and antimony deposits. Locally, at deposit to orebody-scales, pre-ore barren quartz veins and magmatic dikes were the loci for mineralization in some gold-antimony deposits. The structural geometry of the pre-Cretaceous gold and gold-antimony deposits suggests an Early Devonian orogenic gold-antimony mineralization event during a transpressional tectonic regime related to coeval intracontinental orogeny between the Yangtze and Cathaysian Blocks. In contrast, Triassic orogenic gold and Triassic-Middle Jurassic orogenic gold-antimony events are interpreted to relate to distal effects of the collision between the North and South China blocks. The structurally-contrasting major Early Cretaceous epizonal antimony mineralization event, together with contemporaneous hydrothermal gold mineralization, is interpreted to have been controlled by normal faults and pre-ore open folds in an extensional tectonic regime related to the distal effects of rollback of the paleo-Pacific Plate after ~135 Ma. For future geoscience-based exploration in the Orogen, documentation and interpretation of critical structural geometries of gold, gold-antimony and antimony deposits is a vital step towards successful target generation.

Lithosphere and shallow asthenosphere rheology from observations of post-earthquake relaxation

In tectonically active regions, post-earthquake motions are generally shaped by a combination of continued fault slippage (afterslip) on a timescale of days to months and viscoelastic relaxation of the lower crust and upper mantle on a timescale of days to years. Transient crustal motions have been observed following numerous magnitude >~7 earthquakes in various tectonic settings: continental rift zones (Basin and Range), continental plate boundary zones (San Andreas fault corridor; Alaska; Turkey), subduction zones (Japan, Chile, Sumatra), ongoing continental collision zones (Arabia; Tibet), and mid-ocean rifting zones (Iceland). When afterslip can be discriminated from viscoelastic relaxation and when temporal coverage of the postseismic measurements is broad (i.e., geodetic surveys of at least several years duration are available), a wide spectrum of relaxation timescales are usually identified. Current temporal resolution and modeling approaches (e.g., Burgers body analog) allow identification of transient (Kelvin) and steady-state (Maxwell) viscosities that are operable in the short-term and long-term, respectively. I compile results from 40 studies of post-earthquake motions, augmented by ten studies of contemporary surface loading or unloading, that illuminate current estimates of transient and steady-state viscosity of the lower crust and/or uppermost mantle. Lower crust viscosity estimates range from ~1018 to 1021 Pa s, with most estimates near the upper end except in areas of overthickened crust. Mantle lithosphere and asthenosphere viscosity estimates are particularly abundant and yield a picture of transient viscosity ranging from ~1016 to 1019 Pa s and steady-state viscosity ranging from ~1018 to 1021 Pa s. To first order, both transient and steady-state viscosities are well correlated with regional heat flow, and steady-state viscosities are comparable with temperature and strain-rate dependent rock viscosities from laboratory-based flow laws.

Contribution of integrated geophysical data in the structural characterization of the El Hamma graben zone (Southern Tunisia): Example of a pull-apart basin along the South Atlasic Fault Corridor

The El Hamma-Gabes Region in southeastern Tunisia belongs to the crustal shear zone of the South Atlasic Fault Corridor, which corresponds to the Meso-Cenozoic North African margin. So far, most geological works on this region are on the stratigraphic order. However, there are few tectonic and structural studies carried on the style and mechanism of structural deformation. The present work analyzes the subsurface structure of the El Hamma grabens area based on gravity and seismic data, calibrated by stratigraphic and tectonic elements. The El Hamma-Gabes Zone is characterized by a horst and graben system associated with N130˚-150° trending parallel extensive/transtensive faults. Two main grabens are recognized: the El Hamma graben in the west and the Chenchou graben in the east. They are separated by the Jebel Hallouga horst. These structures relate to two N100˚-120° trending principal shear corridors (PSC) arranged in right echelon, being the Oum Ali-Fejej Shear corridor towards the northwest and the Matmata-Medenine Shear corridor towards the southeast.Stratigraphic and structural data collected from several outcrops were correlated with the tectonic events and paleostress reconstruction. New data shows that the PSCs marked a dextral transtensive kinematic framework during the N80° directed Upper Cretaceous extension. The extensional movements are the N150˚-180° Paleogene extension and associated transpression during the N130° Neogene shortening. The dextral sliding generated and maintained the opening of the El Hamma-Gabes graben system, creating a “pull-apart” basin that opened in an extensive ramp between the two PSCs. The overall extension of this ramp is estimated to 15% of the initial width.

Corridors of crestal and radial faults linking salt diapirs in the Espírito Santo Basin, SE Brazil

This work uses high-quality 3D seismic data to assess the geometry of fault families around salt diapirs in SE Brazil (Espírito Santo Basin). It aims at evaluating the timings of fault growth, and suggests the generation of corridors for fluid migration linking discrete salt diapirs. Three salt diapirs, one salt ridge, and five fault families were identified based on their geometry and relative locations. Displacement-length (D-x) plots, Throw-depth (T-z) data and structural maps indicate that faults consist of multiple segments that were reactivated by dip-linkage following a preferential NE–SW direction. This style of reactivation and linkage is distinct from other sectors of the Espírito Santo Basin where the preferential mode of reactivation is by upwards vertical propagation. Reactivation of faults above a Mid-Eocene unconformity is also scarce in the study area. Conversely, two halokinetic episodes dated as Cretaceous and Paleogene are interpreted below a Mid-Eocene unconformity. This work is important as it recognises the juxtaposition of permeable strata across faults as marking the generation of fault corridors linking adjacent salt structures. In such a setting, fault modelling shows that fluid will migrate towards the shallower salt structures along the fault corridors first identified in this work.

The Contact uranium prospect, Kiggavik project, Nunavut (Canada): Tectonic history, structural constraints and timing of mineralization

Uranium mineralization in the Kiggavik area, on the eastern border of the Thelon basin (Nunavut, Canada), hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity-related deposits’ structural controls and therefore exploration of these types of deposits in this prospective district. This article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered, basement-hosted prospect in the Kiggavik area, named Contact. The Contact prospect is located along the Andrew Lake Fault (ALF), a major NE-SW fault corridor in the area. This study combines field work, drillcore logging, sampling, and macro- to micro- petro-structural analyses. Key results from this study highlight that the NE-trending ALF, along with the ENE-trending Thelon (TF) and Judge Sissons (JSF) faults, formed early during intracratonic rifting and deposition of the Baker Lake and Wharton groups (ca. 1850–1750 Ma) in response to the Thelon and Trans-Hudsonian orogeny. The ALF was affected by a strong silicification-brecciation event that likely developed at ca. 1750 Ma, and partitioned later deformation and fluid circulation. In the Contact prospect, the ALF was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns, alteration, and mineralization types. Ten fracture stages have been identified at the Contact prospect, f1–f10. The first stage of mineralization, coeval with f5, is related to fluids of unconstrained origin that circulated through E-W faults in the area that locally re-activated quartz veins of the brecciation event at the intersection with the ALF. Mineralization at this stage is polymetallic and associated with weak clay alteration. The second stage of uranium mineralization occurred coeval with transtensional reactivation of the NE-SW trending ALF (f6c) and in relation to circulation of oxidizing basinal brines within the fault zone. Mineralization at this stage is monometallic and associated with illite and sudoite alteration. Later reactivation of the inherited fracture network (f8) led to strong illitization and bleaching of the host rock, with local reworking of the ore body. Finally, reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re-concentration along redox fronts, with strong illitization and bleaching of the host rock. Unlike the classic unconformity-related uranium deposits in the Athabasca Basin where clay alteration halos occur around the ore bodies related to mineralizing processes, in the Contact prospect the strongest clay alteration event (f8) postdates both main stages of mineralization. Along with uranium remobilization, the basement-hosted Contact prospect is likely a relict of what was once a larger deposit.

Shoot first, ask questions later: application of seismic reflection to a greenfields zinc exploration project

As exposed portions of premier Zn belts reach exploration maturity, targets become deeper and more challenging to explore. Explorationists are faced with having limited methods for effective deep exploration. Seismic reflection is one method which can be used effectively to characterise geological targets at depth. Teck has applied seismic reflection at an early stage on several zinc exploration projects, including the greenfields Yalco Zn project. Geophysical methods have been used to assess the structural architecture of the remote Yalco area, located within the highly prospective Emu Fault corridor. 2D Seismic reflection lines have been used in addition to potential field methods and magnetotellurics. The superior resolution of seismic reflection has allowed us to characterise the stratigraphy and map key structures in detail in order to validate a conceptual geological target. The preliminary interpretation of the seismic sections has confirmed favourable depths to host, and resulted in a re-evaluation of target locations. Use of seismic reflection surveys at an early stage has the potential to reduce technical risk and increase the effectiveness of target testing.

Combined effects of blasting and geological structure on rock mass stability—a case study from the Marrakech–Agadir highway, Morocco

The Marrakech–Agadir highway crosses mountainous areas of the Western High Atlas of Morocco with a high risk of slope instability. The use of explosives as an excavation method, especially at kilometric point 33 on the Imintanout–Argana section, has triggered major ruptures. The regional geological setting, together with the lithological and structural characteristics of the rock mass, represent the major factors influencing this operation where the degree of disturbance is estimated as 0.82. The studied slope is located along the trajectory of a submeridian fault corridor remobilised because of blasting during excavation works. This slope reveals instabilities associated with tectonic planes (F1 and F2) and/or bedding (S0) and the presence of argillites and siltstones that coincide with bedding. These unconsolidated layers, inclined in the direction of excavation, act as slide planes. Structurally, the Pk33 slope can be subdivided into three zones depending on the displacement type being recorded and may be a fortiori related to the geomechanical properties of the substrate. The rheological characteristics of zones B and C, highly fractured and with low competence, respectively, explain their relatively different displacement patterns from that of zone A. The maximum instantaneous explosive load used for offloading the upper part of the sliding mass has been estimated in order to increase the safety factor for the instable slope.

North Bullion: Latest gold discovery on the Carlin Trend, Nevada

Gold Standard Ventures Corp. highlighted in their 2014 corporate presentation that “North Bullion and Central Bullion were both gravity- and CSAMT-led discoveries.” The North Bullion gold discovery demonstrates the continued effectiveness of geophysics as applied to gold exploration on the Carlin Trend of northeast Nevada. In combination with geologic understanding and target model development, geophysics provides a cost-effective exploration tool to guide exploration drilling. A sustained, incremental program is critical to realizing the full benefit geophysics brings to the exploration effort. In a program spanning five years, 3587 gravity stations and 51.7 line-km of controlled-source audio magnetotelluric (CSAMT) data have been acquired in a multistage approach. A major structure, called the Bullion Fault Corridor (BFC), hosts two known gold deposits over an 18-km strike length. Gravity, followed up with CSAMT, defines the BFC in detail, as well as hydrothermal alteration products related to the mineralization process. Drill and geologic confirmation is integrated with the geophysics to refine interpretations and adjust ongoing survey design. Application of gravity along the Carlin Trend has been actively used as a structural mapping tool for many years. However, combining the results with CSAMT is a more recent development, particularly along the Carlin Trend.

New ophiolite slivers in the External Rif belt, and tentative restoration of a dual Tethyan suture in the western Maghrebides

AbstractOphiolite slivers have been described recently in the core of the External zones of the Central Rif belt. The present work aims at illustrating new ophiolite slivers further east and discussing the structural position and tectonic emplacement of all these oceanic floor remnants. Their basement consists of gabbros previously dated at 166±3 Ma and their cover includes mafic breccias, micrites and radiolarites. These oceanic slivers are located within the Mesorif nappe stack at the bottom of the Senhadja nappe that roots beneath the Intrarif Ketama unit and was thrust over the more external Mesorif and Prerif units during the Cenozoic inversion of the North African paleomargin. These oceanic crust (OC) slivers belong to the same Mesorif suture zone as the Beni Malek serpentinites and Ait Amrâne metabasites from eastern Rif that also include marbles with ophiolitic clasts and derive from an ocean-continent transition (OCT) domain. After examination of the varied hypotheses that have been suggested to account for the emplacement of these units in the External Rif, we propose that obduction sampled an oceanic corridor opened between the Mesorif and Intrarif domains at the emplacement of the Rif Triassic evaporite basin. The Intrarif block should have been then separated from the African passive margin and connected with the Flysch domain south of the passive margin of the Alboran domain. The pre-collision structure of the Rif transect would involve two hyper-extended passive margins separated by a narrow oceanic transform fault corridor. Therefore the Tethys suture in the western Maghrebides would be split by the Intrarif block and would involve the Flysch zone in the north and the ophiolite bearing Mesorif suture zone in the south.

Magnetic fabrics and Pan-African structural evolution in the Najd Fault corridor in the Eastern Desert of Egypt

In order to assess the Pan-African structural evolution from early orogenic fabrics through Najd wrenching to the latest orogenic collapse/extension, the authors used field work, aided by aerial photographs and satellite images. This work is complemented by the study of the anisotropy of the magnetic susceptibility (AMS, or magnetic fabric). The Pan-African rock associations of the Um Gheig-Kadabora area can be divided into a lower tier composed mainly of amphibolite–migmatite and granitoid gneisses, and an upper tier of ophiolitic rocks, metavolcanics and their related volcaniclastics, and molasse-type Hammamat sediments. Both these units are intruded by late orogenic granitoid plutons and dykes. The lower tier is exposed in a domal structure in the El Sibai area, the upper tier forms a series of weakly to highly deformed thrust units, called Pan-African Nappes here, which are dissected by high strain shear zones. According to their age, these rock units are divided here into early and late-orogenic. The early orogenic rock association is characterized by medium–high metamorphic grades. The late orogenic rock association is characterized by low metamorphic grade. The rocks in the upper tier form a series of low angle thrust sheets, which are bounded by NW-striking high angle shear zones related to the Najd Fault System. The early orogenic rocks show a polyphase structural evolution with early folds, thrusts, and strike-slip shear zones. The late orogenic rocks show a relatively weaker deformation. The latest intrusives studied here are the dykes dissecting the late orogenic Kadabora granite. In the present work magnetic fabric data document the deformational features in detail and assess the role of the Najd Fault System in the deformational evolution. A strong variation in volume susceptibility of various rocks, due to their variations in mineral composition, is observed. Lower values are in the range of 10−6 SI units for late-orogenic alkaline granite and the dykes dissecting it, the highest susceptibilities exceed 7×10−2 SI units in magnetite-bearing serpentinite. Early orogenic rocks are characterized by relatively high anisotropies (P′ up to 1.7) and are deformed in numerous shear zones. Most of these shear zones can be related to the Najd Fault System. In contrast, late orogenic sediments and intrusives show mostly low anisotropies. However, magnetic lineations are still distinctly oriented parallel with the Najd Fault trend. The very latest Pan-African intrusives, the broadly N–S trending dykes crosscutting the Kadabora pluton, imply c. E–W directed extension. Such an extension is consistent with the magnetic fabric in some of the dykes. Therefore, the Kadabora dykes mark the end of Najd wrenching and a late stage of extension in this part of the Eastern Desert of Egypt. The other dykes display mostly primary fabrics, related to magma flow during their intrusion and are thus post-deformational with regard to the Pan-African orogeny.

Pliocene to Quaternary deformation in the Var Basin (Nice, SE France) and its interpretation in terms of “slow-active” faulting

Seismic hazard assessment of active faults in slow orogenic domains is a challenging issue. In this paper we present a multi-disciplinary approach based on a Digital Elevation Model (DEM), 3D-geological modelling, fracture analysis, and strain analysis of pebbles in a Pliocene molasse basin. The basin is cross-cut by "slow-active" faults of the Donaréo and St Blaise-Aspremont fault system. The DEM shows a topographic disturbance emphasized by slope gradients and the drainage system, which is ascribed to the Plio-Quaternary fault trace. Fracturation analysis evidences two fault corridors oriented approximately N150°E and N20°E. Paleo-stress analysis provides orientations similar to those derived from the focal mechanisms of current regional seismicity, with the main stress σ1 oriented N20°E and a (σ2 − σ3)/(σ1 − σ3) ratio of 0.31. The σ2 versus σ3 permutations are in agreement with ongoing strike-slip deformation at least since the early Pliocene. Discontinuous fracturation and comparison with seismic monitoring on regional active fault zones suggest that shallow seismicity may be expressed by low-magnitude (Mw < 4) seismic swarms. Deformation of pebbles occurs mainly by pressure-dissolution processes. Pebble striation orientations show a bimodal distribution, parallel to the two fault strands. Pebble deformation and the paucity of striated surfaces along the main faults suggests rare seismic deformation and long-lasting aseismic creep processes. Geometrical 3D analysis shows the formation and migration of a Plio-Quaternary basin about 500 metres east of the main fault system, together with folding and tilting of the post-Messinian Pliocene molasse. These observations indicate that the fault remained active from the Pliocene to the Quaternary, and possibly up to the present time. However, the estimates of the minimum slip rate on the faults of about 0.02 mm a−1 vertical and 0.03 mm a−1 horizontal are unlikely to produce any significant high-magnitude earthquakes, but rather swarm-like low-magnitude seismicity with long temporal recurrence.