Intrabasinal Faults Research Articles

Chapter 3. Release of Geothermal Energy: Hot Springs and Tufa-Travertines

Heat and groundwater flow through a rift basin are an integral part of its geodynamics, but predicting what is happening below the surface is often difficult due to a lack of direct information. Field observations on the occurrence, subaerial distribution, temperature and geochemistry of freshwater springs may help to form an idea of groundwater flow through the basin and what it is, or has been, flowing through. Hot springs in the Albertine Rift are common and their occurrence is directly linked to deep-seated main rift bounding faults, or major intra-basinal fault intersections. The majority of Lake Edward and Lake Albert active, or paleo-springs, are also associated with precipitation of localised tufa-travertine limestones. The cooler tufas may contain calcitised plant roots, leaf imprints and freshwater gastropods. Active scavenging of uranium can be demonstrated in the algae and cyanobacteria that inhabit active spring mouths and corresponding tufa-travertines are depleted in radioactive K, U and Th elements. The source for concentrated HCO3- in groundwater at depth, needed to precipitate limestones at the surface, remains problematic. However, REE+Y geochemistry of the tufa-travertines suggest end-member sources of either carbonatites or marine limestones, indicating the possibility of a pre-Neogene rift sequence beneath the Albertine Rift.

Multidisciplinary high resolution Geophysical Imaging of Pantano Ripa Rossa Segment of the Irpinia Fault (Southern Italy)

The Irpinia Fault, also known as the Monte Marzano Fault System, located in the Southern Apennines (Italy), is one of the most seismically active structures in the Mediterranean. It is the source of the 1980, Ms 6.9, multi-segment rupture earthquake that caused significant damage and nearly 3,000 casualties. Paleoseismological surveys indicate that this structure has generated at least four Mw ~ 7 surface-rupturing earthquakes in the past 2 ka. This paper presents a comprehensive, high-resolution geophysical investigation focused on the southernmost fault segment of the Monte Marzano Fault System, i.e., the Pantano-Ripa Rossa Fault, outcropping within the Pantano di San Gregorio Magno intramontane basin. The project, named TEst Site IRpinia fAult (TESIRA), was supported by the University of Napoli Federico II to study the near-surface structure of this intra-basin fault splay that repeatedly ruptured co-seismically in the past thousands of years. Our imaging approach included 2D and 3D electrical and seismic surveys, gravimetry, 3D FullWaver electrical tomography, drone-borne GPR and magnetic surveys, and CO2 soil flux assessment across the surface rupture. This multidisciplinary investigation improved our understanding of the basin shallow structure, providing an image of a rather complex subsurface fault and basin geometry. Seismic data suggest that fault activity at the Pantano segment of MMFS is characterized by a near-surface cumulative displacement greater than previous estimations, calling into question earlier assumptions about the timing of its activation. Despite some challenges with our drone-mounted survey equipment, the integrated dataset provides a comprehensive and reliable image of the subsurface structure. This work demonstrates the utility of developing an integrated approach at high-resolution geophysical imaging and interpretation of fault zones with weak morphological expressions.

Geometry of large normal fault growth and linkage with temporal constraints: a case study on the Lanliao fault in Dongpu Sag, Bohai Bay basin, NE China

The Dongpu Sag exhibits highly representative structural features of the Bohai Bay Basin. By utilizing time depth quantification (TDQ) technology, geological profiles were generated through the processing of seismic data with a velocity model. These profiles were integrated to investigate the linkage geometry and timing of the Lanliao fault, the eastern boundary fault of the Dongpu Sag. Structural analysis revealed at least five original fault segments of the Lanliao fault, each initiating independently during the early growth phase. The development of these isolated fault segments began in the early Eocene, which is concurrent with the deposition of the Es4 member. The southern fault segments were active earlier but became inactive later as the northern segments gained activity during the Es3 member. Transverse anticlines separate the northern and southern faults. By the time of the Es2 member, all segments had linked, forming a continuous boundary fault across the transverse anticlines. As the Dongpu Sag expanded, the depocenter relocated. The southern fault formed a graben, known as the Gegangji subsag, controlling the depocenter during the Es33 and Es32 members. The depocenter of the Es31 member shifted northward swiftly, developing into a half-graben depocenter called the Huzhuangji subsag. In the post-linkage development phase, the activity of the Lanliao fault decreased over time, with displacement becoming more concentrated on the Huanghe fault, an intrabasin fault. The Huanghe fault then dominated basin sedimentation, moving the depocenter to the Mengmangji subsag. This study demonstrates that the fault linkage is a significant event in basin evolution, exerting considerable control over sedimentation and the overall evolution of the basin.

4D fault evolution revealed by footwall exhumation modelling: A natural experiment in the Malawi rift

The evolution of normal fault arrays during rift extension reflects paleo-plate boundary conditions and lithospheric rheology, while controlling seismic hazard and the distribution of basin-hosted resources. Yet, constraining their spatiotemporal development is challenging, particularly where geophysical and subsurface data are absent. Here, we test footwall exhumation modelling using thermochronology as a means of elucidating 4D normal fault array evolution, using the Miocene Central Basin of the Malawi Rift as a natural laboratory. Along-strike trends in exhumational cooling recorded by vertical transects of apatite fission-track and (U–Th)/He data from the basin-bounding Usisya fault scarp reveal a diachronous footwall uplift history that closely reflects 4D trends in hangingwall subsidence recorded by previously published seismic and well data. Initially, pronounced footwall exhumation is restricted to the centres of a series of four isolated normal faults, mirroring the distribution of early syn-rift depocentres. The later onset of footwall exhumation in the intervening areas marks subsequent fault segment propagation and linkage as they formed the through-going Usisya fault system. Elsewhere, cumulative exhumation recorded in the Usisya footwall remains low, coinciding with more significant intra-basinal faulting. This study shows that footwall exhumation modelling constrained by thermochronologic data can reveal the spatiotemporal evolution and strain partitioning within normal fault arrays.

Paleomagnetism of mafic dykes in South Rewa Basin, India: Constraints to extension of Deccan volcanism

The magma source for mafic dykes from South Rewa Basin (SRB) in central India is invariably linked to Rajmahal volcanism (117 Ma) for Damodar, Raniganj-Jharia, and Bengal basin (Permian - Quaternary) to the east, and Deccan volcanism (66 Ma) for Satpura Basin to the west of SRB. However, the magmatic events linked to the SRB are not explicit. To ascertain the dyke association with these volcanic events, we performed a comprehensive paleomagnetic study on the exposed dykes and basalts from Shahdol region in SRB. Rock magnetism indicate that magnetite or titano-magnetite is the main remanence carrier mineral in these dykes. The measured directions produce a mean declination (Dm) of 338° and mean inclination (Im) of - 35° (α95= 8.4°, k = 25.3, N = 13), is close to Deccan normal directions. The calculated Pole position (λp) is at 42.02°N, and (Lp) is at 289.33°E, suggesting that the studied dykes are emplaced simultaneously along with Deccan Traps (36.96°N/78.70°W) and not of Rajmahal Traps (11.37°N/297.58°E). These dykes can be the result of multiple Deccan magma intrusions along the Narmada-Tapti lineament and intra-basinal faults in the SRB of central India.

Three-Dimensional Electrical Structure and Metallogenic Background of the Southeastern Hubei Ore Concentration Area

The Southeastern Hubei Ore Concentration Area (SHOCA) is located in the west section of the Middle and Lower Yangtze River Metallogenic Belt in China, and it is a significant copper and iron mining region in China. Here, 117 pieces of magnetotelluric array data were used to obtain a three-dimensional resistivity model of the SHOCA and to investigate the relationship between the deep electrical features and the genesis of mineral deposits. The model shows that the Qinling-Dabie Orogenic Belt exhibits high-resistivity characteristics, representing Mesozoic granites and high-pressure to ultra-high-pressure metamorphic rocks. There are several low-resistivity anomalies in the upper crust of the SHOCA, which are connected to the widespread low-resistivity anomaly in the middle-lower crust. Near the Yangxin-Changzhou Fault, there is evidence of an electrical gradient zone. The Xiangfan-Guangji Fault, located at the south margin of the Qinling-Dabie Orogenic Belt, also exhibits distinct high- and low-resistivity boundaries at the upper crust. However, the Yangtze Fault and the Tancheng-Lujiang Fault manifest as resistivity gradient zones at the lithospheric scale. These faults are connected the low-resistivity anomaly in the middle to lower crust, possibly serving as upwelling channels of deep thermal fluids, exerting control over shallow diagenesis and mineralization processes. The low-resistivity anomaly in the middle to lower crust of the SHOCA is explained as partial melting resulting from the mixing of crustal and mantle materials. These low-resistivity anomalies play a role as source components in the mineralization system, where mineral-rich hydrothermal fluids migrate upward along intra-basin faults, exerting control over the distribution of shallow mineral deposits.

Inherited extensional faults and bed-parallel slip in Mae Moh Basin, Thailand with implication for basement fabrics

The 3D seismic analysis with structural reconstruction and outcrop study in Mae Moh mine, located in the Central Sub-basin of the Mae Moh Basin, unveil multiple extensional phases and the controls of pre-existing basement fabrics on extensional faults, bed-parallel slip (BPS) and post-rift folding. The coexistence of orthogonal and oblique extensional fault systems characterizes the mine area as a result of regional E-W extension in the Middle Miocene. The dominant NNE-striking normal faults comprise easterly dipping domino-style faults with minor western dipping antithetic faults. Left-stepping en-echelon arrays of NNE-to NNW-striking normal faults at coal levels in the 3D survey follow the deeper early-rift fault that bends along strike from NNE to NW direction. Locations of intra-basin fault bends and offset of basin-bounding faults reflect E-W to ENE-WSW striking basement fabrics that potentially activate during rifting as a transfer zone across the Mae Moh Basin. The focus of rifting migrates eastward with up to 56% extension in the mine. The initial depocenter of early rift phase and the deepest economical coal seams at the center of the post-rift syncline align above the transfer zone. The presence of BPS is observed at outcrop scale, characterized by the offsetting of normal faults or fault zones with antithetic movement. BPS develops during the late rift phase under a NW-SE extension preceding the Late Miocene-Pliocene inversion.

Integrated 3D geological analysis of hydrocarbon maturation and migration in rift basins: Insights from the Niger Chad Basin

This study presents a comprehensive analysis of hydrocarbon maturation and migration in rift basins, with a particular focus on the Niger Chad Basin. The research employs advanced geological techniques, including 3D modelling, to provide essential insights. The use of 3D modelling techniques enhances the reliability of source rock data by accurately predicting vitrinite reflectance (Ro) and temperature values. This validation highlights the crucial importance of robust source rock characterization in hydrocarbon exploration. The role of fault systems in hydrocarbon drainage and accumulation is a prominent finding, with large-scale intra-basinal faults directing basin dynamics effectively. The timing of hydrocarbon generation relative to seal formation emerges as a pivotal factor affecting oil trapping, emphasizing the temporal aspects of petroleum system elements. The Madama Sandstone Formation plays a dual role as a reservoir rock and conduit for oil transmission, underscoring its significance in the hydrocarbon system. Its extensive lateral spread facilitates hydrocarbon drainage, revealing valuable insights into rift basin dynamics. In the future, further research should delve into the intricate interactions within rift basin systems, focusing on fault systems, source rocks, and reservoir rocks. Investigating the influence of lateral lithostratigraphic heterogeneity on hydrocarbon migration pathways is essential. Moreover, applying 3D modelling techniques to diverse rift basins worldwide will broaden our understanding of hydrocarbon maturation and migration, facilitating more precise resource assessments and exploration strategies. This research advances informed decision-making in hydrocarbon exploration and production.

Extensional tectonics, structural architecture modeling and geodynamic evolution in the Cretaceous Tinghir-Errachidia-Boudenib basin (Pre-African Trough, Morocco)

Structural evolution of the Cretaceous Tinghir-Errachidia-Boudenib foreland basin in the south front of the Moroccan High Atlas belt is documented here. Fieldwork, lithostratigraphic and new structural analysis coupled with borehole and geoelectrical data identify two ENE-to NE-trending sub-basins in the large Cretaceous Tinghir-Errachidia-Boudenib (TEB) basin. One named Errachidia sub-basin is situated in the west and the other Boudenib sub-basin is located in the east. They are separated by a major NE-SW trending anticlinal, inherited from a paleohigh structure, where the thickening of the Cretaceous series increases towards the center of the sub-basins and in their northern borders with the central-eastern High Atlas. The Cretaceous series clearly show a considerable thickness variation, angular unconformities and lateral facies change that was related to the syn-sedimentary normal faulting activity. The Albian-Turonian period is characterized by the development of ENE- and NW-trending fault systems. These latter are linked to an extensional tectonics event responsible for half-graben basin geometry associated with significant sedimentary rates. This considerable thickness depocenters geometry is related to normal fault coupled with the intra-basin faults. The intensity of subsidence increases from south to north and from west to east, with a high rate in the Boudenib sub-Basin. The compressive Cenozoic events caused the inversion of these extensional faulting and the folding of the High Atlas area with ENE-trending structures.

A back‐arc transtensional origin for the Nanpanjiang basin in the pre‐Norian Triassic, with implications for the broader intracontinental development of South China

AbstractThe generally accepted foreland interpretation of the Nanpanjiang basin has been regarded as providing support for the hypothesized Indosinian collision between the South China and Indochina blocks, and it has led to the long‐standing view that crustal shortening dominated the Triassic intracontinental development of South China. Here, we examine the stratigraphic architecture, magmatism and gross structural features of the Nanpanjiang basin. Outcrop studies indicate that a north‐stepping axial turbidite system was confined by intrabasinal faults, the active development of which is indicated by mass‐transport complexes. Field mapping combined with U–Pb dating of baddeleyite and zircon reveals that magmatism in the southern part of the basin coincides with a distinct episode of bimodal volcanism from ca. 244 to 242 Ma, and is unrelated to the middle Permian Emeishan plume. Differences in tectonic subsidence between hanging‐wall and footwall blocks, as that has been quantified by the backstripping of composite sections, show that synsedimentary dip slip along intrabasinal faults was of normal sense. Meanwhile, a role for strike‐slip deformation is registered by the left‐lateral offset of middle Permian and Middle Triassic piercing points and the exceptional preservation in outcrop of syndepositional negative flower structures. For these reasons, therefore, the pre‐Norian Triassic Nanpanjiang basin is thought to represent a transtensional back‐arc setting, a result that leads to an unresolved paradox: in adjacent parts of South China to the east, coeval development involves crustal thickening, nonmarine sedimentation and granitic plutonism. A new lateral decoupling model consistent with palaeomagnetic evidence for large‐scale block rotation is tentatively proposed here as a working hypothesis to explain the observed intracontinental evolution of South China during the Triassic assembly of eastern Asia. We propose that such decoupling may relate in part to the configuration of inherited crustal weaknesses.

Seismotectonics and active faulting of Usangu basin, East African rift system, with implications for the rift propagation

Seismicity and focal mechanisms within the NE-SW extending Usangu basin of the Western branch, north to northeast of the Rungwe Volcanic Province (RVP) southern Tanzania were determined from data recorded on temporary SEGMeNT and permanent AfricaArray seismic stations. The aim of the study has been to investigate stress regime and evaluates the role played by the Usangu basin in accommodating the relative movement between the two sub-basins of the Rukwa rift and the Malawi rift. Results show that most of the seismicity (~70%) concentrates along the Usangu border fault. A lesser amount of seismicity (~30%) is found within the basin and in the southwestern end of the basin towards the RVP. These findings suggest that the Usangu border fault, intrabasinal and transfer faults within the basin are associated with the seismic activities. This implies ongoing active deformation within the basin, which is accommodated by slip on the Usangu border fault system and seismicity associated with intrabasinal faults could indicate the temporal strain migration from the border fault. Although it has previously been suggested that the Eastern branch propagates southeasterly towards the coast, however, given the dense and long deployment of seismic station within the study area the possibility of second propagation of the Eastern branch towards the RVP in the Western branch cannot be ruled out. The seismicity therefore indicates that the Western branch could likely link with the Eastern branch via a wide zone of deformation combining the Mamizi-Kilombero-Ruhuhu fault zone and the zone of Mtera-Ruaha-Usangu rift graben, Focal mechanisms along the Usangu border fault and transfer faults within the basin show a combination of normal faulting and strike slip motion indicating extension with sinistral and dextral components of motion, consistent with palaeostress data and the strike slip deformation within the basin through accommodating the relative movement between the southern-most sub-basin of the Rukwa rift and northern-most sub-basin of the Malawi rift.

Structure and formation mechanism of the Pearl River Mouth Basin: Insights from multi-phase strike-slip motions in the Yangjiang Sag, SE China

• The Pearl River Mouth Basin experienced two stages of strike-slip motions along the ENE and WNW directions. • The partial reactivation of the intrabasement faults controlled the evolution of intrabasin faults. • The formation of the basin resulted from the joint effect of oblique Pacific-Eurasian subduction and the Indo-Eurasian collision. The Pearl River Mouth Basin (PRMB) experienced multi-phase rifting and complex tectono-sedimentary evolution during the Cenozoic, and is a topic of many studies regarding the basin-forming mechanism. In the present study, detailed seismic interpretation and tectonic analysis based on the 3D seismic reflection data of the Yangjiang Sag in the northwestern PRMB were carried out, to provide clues to its tectonic evolutionary history. The qualitative-quantitative analysis of fault strikes and migration of depocenter in the Yangjiang Sag indicated the dextral transtensional setting during the Paleocene to Miocene. Meanwhile, the horsetail and en echelon structures on plane view and negative flower structures in cross-section are exhibited, indicating the successive occurrence of strike-slip motions in ENE and WNW directions respectively after initial rifting combined with the structural analysis of Huizhou Sag and Baiyun Sag. In addition, thrust fault systems trending in WNW and ENE were identified in the basement. Their partial and selective reactivation in strike-slip character during the Cenozoic restricted the faults developed in the basin with differential properties. Geometrically, rhombic-shaped sags with cross-basin fault zones were formed, implying the formation of pull-apart structures along with multi-phase strike-slip motions. The pull-apart mechanism could be accounted due to the joint effect of the oblique Pacific-Eurasian subduction and the Indo-Eurasian collision during the Cenozoic.

The development of the eastern Orpheus rift basin, offshore eastern Canada: A case study of the interplay between rift-related faulting and salt deposition and flow

The salt-rich Orpheus rift basin, part of the eastern North American (ENAM) rift system, formed during the Late Triassic to Early Jurassic prior to opening of the Atlantic Ocean. Using a dense grid of 2D seismic-reflection lines, data from nearby wells, and information from adjacent ENAM rift basins, we have established a tectonostratigraphic framework, identified key structural elements, and reconstructed the deformation history for the eastern part of the basin. Our work shows that a series of E-striking, S-dipping faults with normal separation bound the basin on the north. Deformation within the basin is complex with forced folds above deep-seated intrabasin faults, detachment folds, detached thrust faults, and salt diapirs. The synrift evaporite sequence consists of an older massive salt unit that underlies a younger unit with two distinct interfingering facies. Facies A, consisting of salt and interbedded sedimentary rocks (likely shales), developed near the border-fault system and its relay ramps. Facies B, consisting of massive salt with few interbedded sedimentary rocks, developed toward the basin center. The youngest synrift unit accumulated exclusively within minibasins near the northern border-fault system. Based on location, this youngest synrift unit likely consists of coarse-grained and poorly sorted alluvial-fan or talus-slope deposits shed from the footwall. All synrift units are intruded by igneous sheets likely associated with the Central Atlantic Magmatic Province and, thus, are mostly Late Triassic in age (or possibly older). The border-fault system profoundly affected deposition within the eastern Orpheus rift basin by providing pathways for clastic sediment input into the salt-rich basin. These depositional patterns subsequently influenced deformation associated with lateral salt flow during minibasin formation. In regions with interbedded salt, detachment folds and thrust faults developed, whereas salt walls and stocks developed in regions with more massive salt.

Evolution of eastern segment of the Central India Tectonic Zone: an insight from a magnetotelluric study

SUMMARYThe collision process between the South Indian Block (SIB) and North Indian Block (NIB) resulted in the development of the complex crustal nature of the Central India Tectonic Zone (CITZ). The evolutionary past of CITZ covers a long geological time (∼1000 Ma), which corresponds to the assembly and spreading of Columbia and Rodinia supercontinents. Despite several studies in the western and central parts of the CITZ, the location of the suture zone between the SIB and NIB is still under debate. In addition to that, the crustal structure in the eastern segment of CITZ is yet to be resolved. Therefore, for the first time, a dense station coverage magnetotelluric (MT) study is carried out along a 275 km transect in the eastern segment of CITZ from Pandaria to Rewa. The complexity of the Central Indian Shear (CIS) and Tan Shear Zone (TSZ) are reflected as anomalous phases (beyond 90°) in the MT data. A deep crustal resistivity model derived from 2-D and 3-D inversion of the MT data brought out a high-to-moderate conductivity structure (10–100 Ω-m) in the middle of the surface expressions of CIS and TSZ. The conductive structure could be related to a deformation zone formed by tectonic interaction of the CIS and TSZ or multiple tectonic boundaries in the middle of the CIS and TSZ. The conductive structure observed in the southern limit of the CITZ also may indicate the tectonic boundary between the SIB and NIB. The high conductivity in the deformation zone may be explained by the collision-related metallic rich sediments and/or mylonite associated with interconnected fluids. Moderately conductive vertical features delineated from the MT model correlate with the intrabasinal faults which might have acted as the pathways for Deccan volcanism. This study suggests that the CITZ could have been developed under the transition of oceanic subduction to continental collision processes at multiple geological times.

Linking exhumation, paleo-relief, and rift formation to magmatic processes in the western Snake River Plain, Idaho, using apatite (U-Th)/He thermochronology

Abstract The western Snake River Plain (WSRP) in southwest Idaho has been characterized as an intracontinental rift basin but differs markedly in topography and style from other Cordilleran extensional structures and structurally from the down-warped lava plain of the eastern Snake River Plain. To investigate mechanisms driving extension and topographic evolution, we sampled granitoid bedrock from Cretaceous and Eocene-aged plutons from the mountainous flanks of the WSRP to detail their exhumation history with apatite (U-Th)/He (AHe) thermochronometry. AHe cooling dates from seventeen samples range from 7.9 ± 1.4 Ma to 55 ± 10 Ma. Most cooling dates from Cretaceous plutons adjacent to the WSRP are Eocene, while Eocene intrusions from within the Middle Fork Boise River canyon ~35 km NE of the WSRP yield Miocene cooling dates. The AHe dates provide evidence of exhumation of the Idaho batholith during the Eocene, supporting a high relief landscape at that time, followed by decreasing relief. The Miocene AHe dates show rapid cooling along the Middle Fork Boise River that we take to indicate focused river incision due to base level fall in the WSRP. Eocene AHe dates limit magnitudes of exhumation and extension on the flanks of the WSRP during Miocene rift formation. This suggests extension was accommodated by magmatic intrusions and intrabasin faults rather than basin-bounding faults. We favor a model where WSRP extension was related to Columbia River Flood Basalt eruption and enhanced by later eruption of the Bruneau-Jarbidge and Twin Falls volcanic fields, explaining the apparent difference with other Cordilleran extensional structures.

Building tectonic framework of a blind active fault zone using field and ground-penetrating radar data

Blind active faults may lead to earthquake, therefore their identification and characterization constitute an important structural exercise. Such faults can be mapped by high-resolution shallow subsurface geophysical techniques, which offer meter-scale sub-seismic images. The Kachchh Rift Basin (KRB), situated on the western continental edge of the Indian plate, is tectonically active. The KRB is affected by the reactivation of ∼W-striking dip-slip/strike-slip faults. The Kachchh Mainland Fault (KMF) is the largest intra-basinal fault in KRB. The long-term terrain rejuvenation presumably masks the surface expression of the KMF. Shallow subsurface geophysical investigations, assisted by mesoscale structural observations were performed along the western part of the KMF.A ground-penetrating radar (GPR) was used to decipher the sub-seismic position and geometry of KMF. The KMF is inferred to be a near-vertical north-dipping normal fault. GPR data reveal potential colluvial wedges, faulted alluvial and colluvial Quaternary deposits, small-scale horst-graben and off-fault folding, which are not at all apparent in surficial observations and satellite imageries. A sequential evolution of colluvial wedges is explained attributed to KMF reactivation during Cenozoic. The results suggest that the western part of the KMF is tectonically active, and it should not be overlooked despite low seismicity.

Tectonogeomorphic investigation of Kashmir Basin NW Himalaya

ABSTRACT The present study has been carried out in Kashmir Basin (KB), NW Himalaya, to determine the relative tectonic activity using morphotectonic analysis, drainage patterns, lineament analysis and geomorphological field observations. Geomorphic signatures in KB indicate that intrabasinal faults have been quite active during the Quaternary time and have played a dominant role in kinematic and structural evolution of the basin. The manifestation of this activity has been recorded by terrain morphology, uplifted river terraces, warped fluvial surfaces, strath surfaces, fault scarps, offset of Holocene sedimentary successions, braided, and offsetted drainage patterns and recent seismic activity in the region. Presence of active mountain fronts; concave, convex, and concavo-convex hypsometric curves; ambiguous stream gradient index and drainage basin asymmetry, elongated sub-basins clearly manifest tectonic influences in sculpting the basin geometry. The presence of NW-SE to NNE-SSW lineaments that generally strike parallel with the major regional tectonic structures (faults) clearly suggest intense deformation zones produced by ongoing regional tectonism. We propose that the techniques employed, the data obtained and the technical interpretations, are potentially useful and may also be extrapolated to similar tectonically active regions.

Tectonic geomorphology of an active slow-moving, intrabasinal fault: The Galera Fault (Guadix-Baza Basin, central Betic Cordillera, southern Spain)

In this work, we prove the usefulness of morphometric analyses, typically applied to basin-border faults, to define the tectonic geomorphology of a slow-moving, intrabasinal structure: the Galera Fault (Guadix-Baza Basin, southern Spain). The Galera Fault is a 30 km-long, oblique-slip fault with major left-lateral and minor vertical slip components. Through geological and structural analyses, we define for the first time the detailed surface geometry of the fault, which is characterized by features typical of left-lateral strike-slip faults. The morphometric analysis indicates that a combination of slow slip rates and the high erodibility of the juxtaposed basin infill deposits favours a rapid landscape response to fault activity that erases many landscape effects related to active tectonics. This masking is more effective on features generated by strike-slip displacement, leaving only subtle evidence, such as local stream deflections and upstream widening of catchments. In contrast, geomorphic effects related to vertical displacement are better preserved, including the control of the geometry of the main rivers and morphological differences in the drainage network between the two fault blocks. On the upthrown fault block, streams are generally shorter and steeper and have greater valley incision, leading to the development of a badland landscape. Moreover, the vertical deformation of a Middle Pleistocene glacis surface (ca. 90 m) demonstrates the important role of this slow-moving intrabasinal fault in the generation of relief in the Betic Cordillera during recent Quaternary time. Although the impact of this fault on relief building is very low in comparison with oblique-slip, basin-border faults in the mountain range, it has a key control on the Quaternary landscape evolution.

Structural Inheritance Controls Strain Distribution During Early Continental Rifting, Rukwa Rift

Little is known about rift kinematics and strain distribution during the earliest phase of extension due to the deep burial of the pre-rift and earliest rift structures beneath younger, rift-related deposits. Yet, this exact phase of basin development ultimately sets the stage for the location of continental plate divergence and breakup. Here, we investigate the structure and strain distribution in the multiphase Late Paleozoic-Cenozoic magma-poor Rukwa Rift, East Africa during the earliest phase of extension. We utilize aeromagnetic data that image the Precambrian Chisi Shear Zone (CSZ) and bounding terranes, and interpretations of 2-D seismic reflection data to show that, during the earliest rift phase (Permo-Triassic ‘Karoo’): 1) the rift was defined by the Lupa border fault, which exploited colinear basement terrane boundaries, and a prominent intra-basinal fault cluster (329° ± 9.6) that trends parallel to and whose location was controlled by the CSZ (326°); 2) extensional strain in the NW section of the rift was accommodated by both the intra-basinal fault cluster and the border fault, where the intra-basinal faulting account for up to 64% of extension; in the SE where the CSZ is absent, strain is primarily focused on the Lupa Fault. Here, the early-rift strain is thus, not accommodated only by the border fault as suggested by existing magma-poor early-rift models; instead, strain focuses relatively quickly on a large border fault and intra-basinal fault clusters that follow pre-existing intra-basement structures; 3) two styles of early-rift strain localization are evident, in which strain is localized onto a narrow discrete zone of basement weakness in the form of a large rift fault (Style-1 localization), and onto a broader discrete zone of basement weakness in the form of a fault cluster (Style-2 localization). We argue that the CSZ and adjacent terrane boundaries represent zones of mechanical weakness that controlled the first-order strain distribution and rift development during the earliest phase of extension. The established early-rift structure, modulated by structural inheritance, then persisted through the subsequent rift phases. The results of our study, in a juvenile and relatively well-exposed and data-rich rift, are applicable to understanding the structural evolution of deeper, buried ancient rifts.

3‐D Deep Electrical Resistivity Tomography of the Major Basin Related to the 2016 Mw6.5 Central Italy Earthquake Fault

AbstractWe provide the first 3‐D resistivity image of the Pian Grande di Castelluccio basin, the main Quaternary depocenter in the hangingwall of the Mt.Vettore–Mt. Bove normal fault system (VBFS), responsible for the October 30, 2016 Mw6.5 Norcia earthquake (central Italy). The subsurface structure of the basin is poorly known, and its relation with the VBFS remains debated. Using the recent Fullwaver technology, we carried out a high‐resolution 2‐D transect crossing the 2016 coseismic ruptures coupled with an extensive 3‐D survey with the aim of: (a) mapping the subsurface of the basin‐bounding splays of the VBFS and the downdip extent of intrabasin faults; (b) imaging the infill and pre‐Quaternary substratum down to ∼1 km depth. The 2‐D resistivity section highlights under the coseismic ruptures a main dip‐slip fault zone with conjugated splays. The 3‐D resistivity model suggests that the basin consists of two depocenters (∼300 and ∼600 m deep, respectively) filled with silty sands and gravels (resistivity <300 Ωm), bounded and cross‐cut by NNE‐, WNW‐, and NNW‐trending faults with throws of ∼200–400 m. We hypothesize that the NNE‐trending system acted during the early basin development, followed by NNW‐trending and currently active splays of the VBFS that overprint pre‐existing structures and locally control the infill architecture. Moreover, beneath the basin we detect a shallow NW‐dipping blind fault. The latter is likely a hangingwall splay of the adjacent regional Mts. Sibillini Thrust, which may have been partly involved in the rupture process of the Norcia mainshock.