Normal Faults Research Articles

Characterization and Evolution of Seismic Sequences in the Normal Fault Environment of the Southern Apennines

AbstractThe use of seismic catalogs enhanced through advanced detection techniques improves the understanding of earthquake processes by illuminating the geometry and mechanics of fault systems. In this study, we performed accurate hypocentral locations, source parameters estimation and stress release modeling from catalogs of microseismic sequences nucleating in the complex normal fault system of the Southern Apennines (Italy). The application of advanced location techniques resulted in the relocation of ∼30% of the earthquakes in the enhanced catalogs, with hypocenters clearly identifying local patches on kilometer‐scale structures that feature consistent orientation with the main faults of the area. When mapping the stress change on the fault plane, the inter‐event distance compared to the size of the events suggests that the dominant triggering mechanism within the sequences is static stress transfer. The distribution of events is not isotropic but dominantly aligned along the dip direction. These slip‐dominated lineations could be associated with striations related to fault roughness and could map the boundary between locked and creeping domains in Apulian platform and basement.

Geochemical, Mineralogical, and Fluid Processes in the Brittle‐Plastic Transition of Continental Crust

AbstractThe brittle‐plastic transition (BPT), the strongest part of the crust, is critical to continental geodynamics but is poorly understood relative to simpler crust above and below. It is typically represented as a depth transition from brittle/frictional to plastic/viscous deformation controlled by temperature and pressure. Footwalls of low‐angle normal faults (LANFs) exhumed through the BPT provide rock records that challenge this view. Three well‐studied LANF footwalls are reviewed. All record geochemical, mineralogical and fluid‐related controls on embrittlement, not just monotonic P‐T decrease. Two quartz‐rich examples record embrittlement at unexpectedly high T (≥450–500°C) that was modulated by wetting characteristics of fluids. One had an inverted BPT: brittle fracture beneath contemporaneous mylonites. In another study, a brittle LANF grew from plastic mylonites due to mineralogic changes that strengthened parts, causing initial frictional slip and cataclasis on weak planes that ultimately linked. In all, geologically abrupt small‐scale processes controlled behavior at kilometer scales. Similar processes likely affect other tectonic settings and seismic cycles. Such processes offer fertile research opportunities in continental geodynamics; they will be increasingly tractable as computational abilities improve. Adaptive, multi‐scale approaches including the effects of fluid‐rock geochemistry and mineralogical changes on rock strength and deformation are needed. Thoughtful modeling approaches may yield key insights into the positive and negative feedbacks that are likely. Discontinuous deformation is probably needed explicitly along with exploration of initial and boundary conditions.

Deformation Mechanisms During the Syn‐Orogenic Extrusion of the High‐Pressure Phyllites‐Quartzites Unit in the Central and Northern Peloponnese, Greece

AbstractThe High‐Pressure Phyllites‐Quartzites (PQ) unit of the External Hellenides is exposed in tectonic windows in the central and northern Peloponnese (Greece). Understanding the deformation history of this unit is essential to interpreting the Oligo‐Miocene evolution of the External Hellenides belt and its associated exhumation events. This study integrates new field observations and microtectonic analyses with previous studies to offer a comprehensive deformation model of the PQ unit since the Late Oligocene. The first deformation phase (D1), captures the progressive incorporation of the PQ into an orogenic wedge. This phase is largely overprinted and only preserved as relict features. The second phase (D2) displays coeval top‐to‐the‐ENE and top‐to‐the‐WSW localized ductile shear. A transition is observed from top‐to‐the‐ENE non‐coaxial deformation at the upper parts of the nappe to intense isoclinal folding (refolding S1) at the lower structural levels. We associate D2 with the ductile syn‐orogenic exhumation of the PQ within an extrusion wedge, accompanied by greenschist‐facies retrogression. In the third phase (D3), semi‐brittle to brittle extensional fault planes cut through the previous ductile structures. D3 faults exhibit extensional kinematics in all directions on the flanks of exhumation domes. This phase correlates with a late‐orogenic doming event, marking the final exhumation stage of the PQ unit in the upper crust. The exhumation of high‐pressure units results from the interplay between ductile syn‐orogenic extrusion and continuous underplating within the subduction zone. This underplating maintains vertical movements and uplift of the units, initiating a 3D upper‐crustal extensional collapse along low‐angle normal faults.

Mineralization of sulfide mound at Wocan-1 hydrothermal field based on geological mapping, mineralogy and sulfur isotope studies, Carlsberg Ridge, Northwest Indian Ocean

The Wocan-1 hydrothermal field is distinct on the occurrence of an active sulfide mound, discovered on an axial volcanic ridge of the slow-spreading Carlsberg Ridge. The size of the mound is comparable to TAG active mound located in off-axis of Mid-Atlantic Ridge. In order to understand its formation and controlling factors, we did field geological mapping, mineralogical and geochemical analysis on the hydrothermal precipitates. Our results show the sulfide mound is ∼ 260 m in diameter and ∼ 50 m in height. The southern area of the mound is enriched in high-temperature Cu-rich sulfides, while the northern area is characterized by moderate-temperature Fe-rich sulfides and a talus of pyrite-anhydrite breccias and sands extending for > 200 m. The pyrite here exhibits recrystallization textures characterized by heavier δ34S compositions when compared to that in the southern area. It is considered that the normal faults extending into the northern area of the mound and the associated mass wasting facilitated the infiltration of seawater, which is responsible for the regional difference in mineralization of the mound. This study contributes to the understanding of the formation and controls of large sulfide mounds on the AVRs at the slow-spreading ridges.

Tectonic Inversion and Deformation Differences in the Transition from Ionian Basin to Apulian Platform: The Example from Ionian Islands, Greece

The studied areas (the Ionian Islands: Paxoi, Lefkas, Kefalonia, and Zakynthos), are situated at the western ends of the Ionian Basin in contact with the Apulian Platform and named as Apulian Platform Margins. The proposed model is based on fieldwork, previously published data, and balanced geologic cross-sections. Late Jurassic to Early Eocene NNW–SSE extension, followed by Middle Eocene to Middle Miocene (NNW–SSE compression, characterizes the Ionian basin). The space availability, the distance of the Ionian Thrust from the Kefalonia transform fault and the altitude between the Apulian Platform and the Ionian Basin that was produced during the extensional regime were the main factors for the produced structures due to inversion tectonics. In Zakynthos Island, the space availability (far from the Kefalonia Transform Fault), and the reactivation of normal bounding faults formed an open geometry anticline (Vrachionas anticline) and a foreland basin (Kalamaki thrust foreland basin). In Kefalonia Island, the space from the Kefalonia Transform Fault was limited, and the tectonic inversion formed anticline geometries (Aenos Mountain), nappes (within the Aenos Mountain) and small foreland basins (Argostoli gulf), all within the margins. In Lefkas Island, the lack of space, very close to the Kefalonia Transform Fault, led to the movement of the Ionian Basin over the margins, attempting to overthrust the Apulian Platform. Because the obstacle between the basin and the platform was very large, the moving part of the Ionian Basin strongly deformed producing nappes and anticlines in the external part of the Ionian Basin, and a very narrow foreland basin (Ionian Thrust foreland basin).

The Tectonic Framework of Parecis Basin: Insights from a Multiphysics Interpretation Workflow

The Parecis Basin, one of Brazil’s most extensive intracratonic basins, holds significant potential for hydrocarbon exploration. Despite its vast size, Parecis has yet to be extensively explored, with only five wildcat wells drilled. So far, no commercial discoveries have been announced. Regional studies have suggested Paleozoic sedimentation, while recent analyses have revealed a Neoproterozoic infill. Its tectonic model is still a matter of debate, and to date, no detailed structural map for the whole basin has been published. The present work proposes a new detailed structural map of the Parecis Basin based on a four-step interpretation workflow integrating seismic and gravimetric data. The first step includes converting the public 2D seismic lines to the depth domain. The second step is estimating the residual Bouguer anomaly, where the computed residual anomalies should relate to the basin’s tectonic features. The third step comprises the 2D forward modeling of the gravimetric anomalies using the 2D seismic interpretation as a constraint. The final step compiled all the interpreted features into our new structural map. This map reveals the top of the basement, forming a complex framework of horsts and grabens. Normal faults define the main structural style in the basin. Further, we could recognize thick, high-density bodies embedded in the crystalline basement. These bodies consist of Orosian–Calimian (1.8–1.6 Ga) mafic and ultramafic rocks, which may be a potential source for hydrogen exploration in the basin. Subsequent geophysical and geochemical surveys will assess the hydrogen potential in the area.

3D Structure of Low‐Angle Normal Faults and Tectono‐Sedimentary Processes of Nascent Continental Core‐Complexes in the SE South China Sea

AbstractThis contribution explores the formation and evolution of hyper‐extended basins, associated with the early stage of core complex formation, controlled by low‐angle normal faults active at <30°. Based on a high‐resolution industrial 3D seismic reflection survey along the southern margin of the South China Sea (SCS) (Dangerous Grounds), we mapped and analyzed the 3D geometry of low‐angle normal fault systems and the related stratigraphy. Two main hyper‐extended basins were documented, filled by up to 6 km of sediments including pre‐ to post‐rift sequences. The observed normal faults on depth migrated seismic sections show an average dip angle of <30° and appear planar, characterized by continuous reflections with no clear steepening at depth and sole‐out on distinct decollement levels. Detailed fault surface mapping reveals the occurrence of km‐scale corrugations together with large wavelength undulation. The formation of these hyper‐extended basins is associated with polyphased syn‐rift infill during the development of the low‐angle normal faults. The first syn‐rift sequence appears as chaotic and discontinuous packages that has been dismembered and fragmented during the activity of low‐angle normal faults. The second syn‐rift package shows unexpected sedimentary wedges developing successively toward the footwall and the hangingwall. This geometry results from the interplay between the main low‐angle normal fault and antithetic faults defining a so‐called extensional fishtail. The deep structure of these basins shows nascent domes with limited evidence of magmatism. Eventually, these basins likely capture the earliest stage of core complex development in the proximal margin of the southern SCS.

Localization of Deformation on Faults Driven by Fluids During the L’Aquila 2009 Earthquake

AbstractCoseismic rupture and aftershock development on a fault plane are complex and heterogeneous processes. The Mw 6.1 L’Aquila 2009 normal faulting earthquake is a perfect case to explore how fault geometry and rheology influence the rupture process and aftershocks distribution. In this study, we use for the first time a dense set of earthquake data to obtain enhanced images of the causative normal fault structure to the kilometer scale. The hypocenter of the emergent onset of the mainshock took place within a low Vp/Vs volume, while the large coseismic slip occurred a few kilometers above, as the rupture propagated through a high Vp and high Vp/Vs fluid‐filled rock volume. The increase of Vp/Vs in the fault hanging wall during the sequence suggests a strong dehydration in the earthquake asperity, with an upward fluid pressure migration along the fault toward the host rock volume. We propose that the localization of deformation on the fault plane is favored by high fluid pressure, while the spreading of aftershocks on a wide volume around the fault is driven by the depletion of fluids from the slipped portion of the fault plane and migration to small segments within the fault host rocks.

Structural assessment and petrophysical evaluation of the pre-Cenomanian Nubian sandstone in the October Oil Field, central Gulf of Suez, Egypt

The low quality of the seismic resolution of the studied Cambrian Pre-Cenomanian formations, which rest directly on the basement in the October Field in the Gulf of Suez, requires study, and the structure pattern controlling these formations is uncertain. The poor quality of the seismic data resolution in the Gulf of Suez is due to the presence of thick sequences of evaporites represented by the South Gharib and Zeit formations. Therefore, the current study used seismic reflection data integrated with well-log data to define the structural-stratigraphic setting of the pre-Cretaceous Nubian reservoir sequence. The study aims at locating and delineating zones having excellent reservoir potential within the Nubian sequence horizons (Nubian Transition, main Nubian, Nubian marker-1, and Nubia marker-2, referred to as NT, MN, M1 and M2, respectively) through the integration of the 3D static modelling and the petrophysical parameters deduced from the well-log data processing. A detailed petrophysical analysis, based on the wireline logs of some wells, was performed to determine the lithological units using two types of cross plots (Neutron-Density and M-N plots), and the different petrophysical parameters that characterize the various Nubian horizons were also computed. 3D modelling was used to visualise the lateral and vertical changes of the reservoir characteristics. The seismic mapping reveals that the Nubian structure is controlled by an NW-SE trending (Clysmic trend) of an NE-plunging asymmetrical anticlinal feature unconformably resting on a basement horst. The main structure is affected by two major normal faults, which trend NW, andis cut by two smaller sub-parallel faults that disturb the core of the structure, which is unaffected by the easterly oriented faults of the Aqaba trend. The petrophysical analyses indicate that the Nubian sandstones have intervals of good reservoir quality, with a total net-pay thickness of about 500 m, net sand ratios (60–90 %), effective porosity (10–25 %), and hydrocarbon saturation (85%), which may encourage further drilling, especially in the southeast portion. The result of this study can be extended to the other Nubia sandstones resting on the basement complex in the Gulf of Suez.

Seismicity and Tectonics of the Republic of Kosovo

Abstract Kosovo is distinguished by a particularly high degree of seismic activity as a result of its location in the alpine-Mediterranean seismic area. The thickness of the seismic zone in the Earth’s crust is a crucial element in seismotectonics, as it affects the design of fault systems, relative fault activity, earthquake size and distribution within a fault system, and the long-term accumulation of tectonic deformation. Kosovo’s large depressions and high relief make it challenging geomorphologically. The country of Kosovo is divided into numerous chunks along the fault lines because of the inclinations of these prevalent motions. Normal faults, along which differentiations on the order of 2000 m occurred during the neotectonics period, identify the contacts between these blocks. Understanding Kosovo’s seismotectonic characteristics requires an exact analysis of hypocenter parameters when historical earthquakes that have struck the country are reassessed for magnitude. This study deals with the seismicity and tectonics of the territorial space of the Republic of Kosovo.

Satellite land surface temperature for mapping the structurally controlled geothermal anomalies in the Cretaceous rift, South Egypt

ABSTRACT Exploration of new geothermal systems often requires regional-scale investigation. Satellite Land Surface Temperature (LST) products are essential in geothermal anomaly identification and mapping. In this study, seven thermal anomalies covering Egypt were observed using the Sentinel-3 LST images acquired in 2019 and confirmed using the 2020 LST images. In addition, the LST analysis reveals three new anomalies covering the southern part of Egypt (Kalabsha, Natash, and Wadi Allaqi), which are structurally controlled. Nuqra-Kharit-Natash is a good site for geothermal energy owing to the following reasons: 1) the high geothermal gradient beneath the Wadi Natash region (heat flow ~100 mW/m2); 2) the presence of many geothermal anomalies retrieved from the analyses of the Landsat-8 acquired in August 2018; 3) existence of surface geothermal manifestation at the western boundary of the basin includes warm springs and the tufa deposits. Intricate structural patterns, including NW-oriented normal faults, ENE-to-WNW-oriented right-lateral faults, and NNE-oriented sinistral strike-slip faults, characterise Wadi Natash. Wadi Natash LST anomaly shows a solid relation to fault trends. High values of LST are arranged along NW and NNE faults and recorded the peak at the intersection of two fault trends. Recent seismic activity along the NNE fault system enhances the permeability along this trend and its intersection with the NW-oriented fault.

Numerical investigation on the deformation of railway embankment under normal faulting

Active faults in the earthquake region are consistently regarded as a potential geological hazard to the construction and operation of railway engineering. However, the effects of normal faulting on railway embankments have not been investigated thoroughly. For bridging this knowledge gap, three-dimensional finite element analysis considering the influence of faulting offset, the soil layer’s thickness, the fault dip angle and the embankment cross-fault angle are conducted to clarify the normal faulting effects on the railway embankment. Emphasis is given to the stress and strain characteristic in the fault rupture outcropping regions on the embankment, the deformation of the embankment centerline for design purposes, and the determination of the affected zones for railway embankment preservation. The analysis shows that the normal fault rupture outcropping regions on railway embankment are tensile yield in most cases. The existence of the soil layer and its thickening would widen the affected zones and the regions where the fault ruptures outcrops. The fault dip angle and the cross-fault angle of the embankment have a complex effect on the behaviors of the crossing embankment. The depth of the subsidence zone of the embankment would increase with the decrease of the fault dip angle and the large fault dip angle would change the primary fault rupture to be a compressive one directly above the fault line. If the embankment crosses the fault line obliquely, the curvature radius of the centerline would hardly meet the design code.

Eurasian Arctic Rifted Margin Composite Tectono-Sedimentary Element

The Eurasian Arctic Rifted Margin (EARM) spans a poorly studied transition region between the Eurasian continental shelf and the deep-water Nansen Basin. It is a conjugate margin to the Lomonosov Ridge, as both domains were united before the opening of the oceanic Eurasia Basin. The EARM is considered as a Composite Tectono-Sedimentary Element (CTSE) consisting of two individual tectono-sedimentary elements (TSEs): (1) an undefined group of poorly known pre-rift Mesozoic and Paleozoic sedimentary successions; and (2) Late Cretaceous–Paleocene synrift strata. The latter are bounded by a c. 56 Ma break-up unconformity and are overlain by the Eurasia Basin prograded margin TSE, which is not included in EARM. In the absence of drilled wells, we utilize multichannel seismic reflection (MCS) data for seismic stratigraphic correlations with nearby, better-explored, areas. The EARM CTSE is subdivided into three along-strike segments (from west to east): Svalbard–Barents Sea, the North Kara Sea and the Taimyr–Laptev Sea. Across-strike, the EARM CTSE is composed of a proximal zone of stretched crust characterized by normal faulting and a relatively narrow distal transition zone that may contain unroofed serpentinized mantle. The lack of drilled wells makes it challenging to evaluate the petroleum potential of the CTSE, although some indications of a working petroleum system presence exist.

Reactivated Seismogenic Faults and Earthquake Source Mechanisms in the Snyder Area of Texas

Abstract Stretching across New Mexico and Texas of the United States, the greater Permian basin is composed of two subunits—the Delaware and the Midland basins. Induced seismicity in the greater Permian basin has significantly increased since 2008, which has revealed previously unmapped seismogenic structures in several geographic regions. Among them, the Snyder area of northwest Texas has a long history of oil and gas activities, resulting in a higher rate of induced seismicity. In this study, we investigated these previously unknown seismogenic structures using three main approaches: (1) relocated and delineated seismicity, (2) performed waveform moment tensor inversion to determine earthquake source mechanisms, as well as (3) conducted stress inversion to assess the stress state. The results show that the overall depth range of seismicity is 0–5.5 km and concentrated in a range of 2–3 km below mean sea level, in the top portion of the crystalline basement. As we have determined 297 source mechanisms, their collective pattern presents a mix of strike-slip and normal faulting, suggesting an extensional strain field at the edge of the Midland basin. We have identified nine significant seismogenic episodes by distinctive increases of seismic moment release in 2017–March 2024. The results also demonstrate a temporal variation of b-value spanning across the seismogenic episodes, associated with the progression of fault reactivation initiated by fluid injection.

Fault system dynamics of the Kashmir, NW Himalaya, India using continuous GPS observations and geomorphic evidences

We collected data from the continuous Global Positioning System (cGPS) sites across the Kashmir Valley, situated at latitude 34◦N, spanning from 2008 to 2021. Inter-site velocities define a region of approximately 15,000 km2 with broadly distributed strain accumulation at −7.22×10−8 nano strain/year (compression component) and the maximum shear strain γmax of 1.9051×10−7 nano strain/year. The estimated site velocity in the ITRF14 ranges between 30.5±1–42.85±3 mm/yr. It was observed that the average deformation rate of the GPS sites in the Kashmir region ranges between 2.86±1–15.47±3 mm/yr relative to the India fixed reference frame, suggesting a predominant N-S directed compressional tectonic regime. The focal mechanism solutions of the earthquakes in and around the Kashmir Valley suggest dominant thrust faulting followed by normal faulting. Analysis of the vertical component of the GPS time series shows that the northwest segment of the valley subsides at the rate of −1.71± 0.70 mm/yr, while the southeast segment uplifts at the rate of 5.4 ± 0.5 mm/yr. In addition to vertical component, we observed differential movement of the sites relative to IISC site on the northwest and southeast segments. The rate of baseline change of the GPS sites indicates 7.30 ± 0.75 mm/yr extension in SE-NW direction and −5.32 ± 0.75 mm/yr NE-SW compression across and along the Kashmir Valley. Geodetic observations reveal a transition that aligns with the Magam lineament/fault previously identified by Ganju and Khar (1984) using gravity and magnetic data. The observation was supported by the field investigations and remote sensing techniques, confirming the existence of Magam Fault. During the field investigations, various geomorphic expressions of fault were observed, including fault ruptures, fault scarps, offset ridges, deflected drainages/rivers, linear alignment of springs, linear drainage lines, triangular facets and offset Recent sedimentary deposits (Karewas) were observed. The field evidence suggests exposure of normal faults at Kondabal, Nasrullapora, Biru and Radbugh. These exposed extensional structures, trends in NE-SW direction and dip in NW direction with varying offset and dip amount. GPS observations supplemented by geomorphic evidences infer the presence of normal fault ̴ 80 Km extending from northeast to southwest.

Mechanism of Ivughli salt dome exhumation, northwestern Iran

ABSTRACT The Ivughli salt dome, located in the West Azerbaijan province of Iran, is sourced in the Miocene Upper Red Formation, which includes salt and gypsum layers, red marl, and sandstone. The salt diapirs of West Azerbaijan are located along the North Tabriz Fault. Faults related to fractures around the Ivughli salt dome have displaced the folded layers and have caused subsidence in some parts of the salt dome. Based on the results of interferometry data, there are smaller and bigger elevation/subsidency rates with a total average of 4 mm for the whole body of the dome. The east of the dome shows high elevation and this may be due to the effect of a hidden fault that branches off the North Tabriz Fault. As well as the role of normal faults in the lower elevation of the western parts of the dome, there may have been subsidence related to surface washing and driven by erosion and agriculture in the region. Regarding the emplacement and shape of the Ivughli salt dome, it is young diapirism and currently acctive. In general, tectonic activity is still causing the rise of the Ivughli salt dome at a rate of movement that is not uniform across its structure.

A Failed Rift in the Eastern Adventure Plateau (Sicilian Channel, Central Mediterranean)

Widespread volcanism has been known in the Sicilian Channel for a long time, even if some submarine volcanoes have only recently been discovered. Most of this volcanism formed along the NNE-trending transfer zone known as the Capo Granitola–Sciacca Fault Zone, while others, such as the islands of Pantelleria and Linosa, are associated with the continental rift zone that has developed since the early Pliocene in the central part of the Sicilian Channel through the formation of three deep tectonic troughs (Pantelleria, Linosa and Malta). However, the origin of a group of five volcanoes (here called “Tetide volcanic cluster”) that form a NW-SE alignment on the eastern edge of the Adventure Plateau is not yet known. In this work, we hypothesize that this volcanic alignment may represent the remnants of a failed rift attempt that was unable to generate another tectonic trough in the Sicilian Channel. Based on seismic sections and gravimetric data, three phases in the formation of this volcanic alignment can be identified: (i) a major magmatic intrusion in the early Pliocene associated with a NW-SE normal fault that formed during the opening of the Pantelleria graben, leading to the uplift and deformation of the host sedimentary rocks; (ii) a late Pliocene-Quaternary tectono-magmatic quiescent phase; and (iii) a renewed magma intrusion through fissures or cracks that led to the formation of the volcanoes in the late Quaternary. This process was not able to cause significant extension and only limited volcanism, which is why the “Tetide volcanic cluster“ is interpreted as the morphological expression of a failed rift.

Reprocessing and interpretation of legacy seismic data using machine learning from the Granada Basin, Spain

The Granada Basin (Spain) is a Neogene sedimentary depression with irregular geomorphology and deep depocenters. It is located in the most seismically hazardous part of the Iberian Peninsula with an historically experienced extremely destructive earthquakes, followed by periods of low to moderate seismicity. In 1980s the Chevron Oil Company collected a set of 30 deep seismic reflection sections in this Basin of which only the results on paper are kept. Due to the fact that many of these seismic profiles are currently located in urban areas and the economic cost of carrying out a similar exploration, it was decided to recover these old data and apply a post-stack treatment to improve their quality. The purpose of this study is to show the applied reprocessing flow and, with the new sections, to present a spatial model of the basin. The first stage of recovery and enhacement of seismic sections has consisted in three phases: first, high-resolution scanning of paper copies to TIFF images followed by the transformation of TIFF images to SEG-Y format; second, poststack processing workflow to increasing resolution and lateral coherence of these seismic lines; and third, it has been used a machine learning algorithm, among others, increasing the spatial resolution, signal-to-noise ratio, and coherence of the seismic signals. In addition, basement horizons, as well as three sedimentary sequences, were identified in all seismic sections and interpolated to create a three-dimensional basement model composed by normal faults, horst and grabens related to the seismotectonic behavior of the basin. As an overall assessment, this work is an example of the usefulness of ‘recycling’ legacy seismic data, which nowadays are usually in archived boxes, but at the time required a great economic and acquisition effort.

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.

Geochemistry and fluid inclusion study of the Jbel Tirremi fluorite-baryte deposit, Morocco: New insights into the genetic model in relation to Mesozoic tectonics

The highly fractured Jurassic carbonates at Jbel Tirremi in northeastern Morocco host fluorite-baryte deposit. The mineralization occurs both as stratabound in marl-limestone contact and as fault-hosted veins (N-S- and NNW-SSE). The mineral paragenesis consists of two fluorite and baryte generations and calcite with subordinate amounts of quartz, dolomite, traces of sulfides (chalcopyrite, pyrite, galena), and oxidized minerals. Fluid inclusion data reveal that hot moderately saline fluids derived from the Paleozoic basement mixed with Triassic brines and cooler, meteoric waters. The REY inventory, C-O-S-Pb-Sr-Nd isotope, and crush-leach data point to the Paleozoic basement as the primary source of metals with a contribution from the Triassic red beds. The refined ore genetic model developed in this study from our new geological and geochemical data includes the downward movement of Triassic-Jurassic evaporated seawaters along normal faults, followed by the leaching of metals from Paleozoic and Triassic rocks, and the subsequent upward flow of these metalliferous fluids. During the Late Cretaceous-Paleocene basin inversion, the deep-seated ore-forming fluids migrated upward, which eventually mixed with Triassic brines and cooler meteoric waters. This fluid mixing caused the precipitation of multiple generations of fluorite and baryte.