Top Of Basement Research Articles

Multiple Upward Residual Gravity and Magnetic Maps to Estimate the Deep Crustal Layers and Moho Discontinuity in Eastern Iraq

The upward continuation technique was applied to the gravity and magnetic data to obtain the residual anomalies maps in eastern Iraq. A new processing method is introduced to calculate the crustal layers depending on the relation between the total range of the residual anomalies of gravity, magnetic data and the upward continuation, with multi-elevations. The significant relationship shows slope variations, which may reflect the maximum contrast in the physical properties (density and/or susceptibility) and the intersection point representing the depth of layer contacts. This method was applied to the eastern central part of Iraq, adjacent to the Iranian borders. It is found that the average depth range to the Jurassic formations, top basement rocks, transition layer (Curie point), and Moho discontinuity are 3.1- 4.8 km, 8-12.9 km, 20.9-22.4 km and 43.6 km, respectively. The Sedimentary cover in the study area ranges from 8 to 13 km. The maximum depth to the Moho discontinuity obtained by gravity data in the study area is 43.6 km. The radially average power spectrum technique was applied in the study area to calculate the gravity depth and magnetic sources' depth. Three depth levels of sources from gravity and magnetic data were obtained. These depths are shallow sources, average basement rock and deep sources (Moho) at 3km, 13.2-12.1 km, and 32.2-34km, respectively. The obtained results concerning the main layers in the crust were compared between the two methods, and the new method shows more reliable results. The detected depth levels refer to top Jurassic, basement rocks, and Moho discontinuity. The new method is believed to be used to detect the crustal layers depth with good results.

Kureika–Tunguska Composite Tectono-Sedimentary Element, northern East Siberia

The Kureika–Tunguska Composite Tectono-Sedimentary Element (KT CTSE) is located in East Siberia. Geologically, it is confined to the homonymic basin in the northwestern part of the Siberian Craton. The basement of the basin is composed of Archean–Early Proterozoic metamorphic rocks. The sedimentary cover is composed of Mesoproterozoic, Neoproterosoic and Early Paleozoic predominantly carbonate rocks capped with a succession of Pennsylvanian–Permian coal-bearing sediments overlain by thick section of Early Triassic tuffs and lavas. The entire sedimentary cover, especially its upper part, is saturated with mafic intrusive bodies. The maximum depth to the top basement can exceed 10 km. The KT CTSE is characterized by a very low degree of exploration. The rather scarce prospecting work carried out on oil and gas in the CTSE has not yet yielded positive results. However, indirect data such as, for example, numerous bitumen fields and evidence of the source rocks are promising for potential discoveries including large hydrocarbon accumulations.

Late Palaeozoic structural evolution of the Patch Bank Ridge and Utsira High, northern North Sea

AbstractThis study focuses on the Late Palaeozoic development of the area east of Utsira High in the North Sea, where the stratigraphic section below the late Permian Rotliegend Group is undrilled. We use regional 3D seismic data to study structuring, sediment distribution and geomorphology across the Patch Bank Ridge and Utsira High in the North Sea. The results show that the Stord Basin and the bounding Utsira East fault initially developed during the Late Palaeozoic extension, probably during the Devonian, and that the Utsira Shear Zone controlled the location of Late Palaeozoic depocentres. The Patch Bank Ridge is an uplifted part of the Stord Basin where we identify Late Palaeozoic growth strata along the southern and northern flanks, indicating a similar timing of the structural evolution in this area. Two key wells, in the Sele High and Ling Depression, are used to relate a Late Palaeozoic isopach map with regional structuring, surface tilt and basement morphology to the enigmatic parts of the Late Palaeozoic basin system. Our results supplement regional models for the Late Palaeozoic basin development, we suggest that the deeply eroded Devonian half‐grabens preserved on the Utsira High formed parts of an extensive basin system that show stratigraphic expansion towards their bounding faults. The Top Basement surface at these highs offers several distinct geomorphologies that evolved during three periods of exposure, expressed as (i) a tilted and rugose landscape, (ii) distinct drainage networks and (iii) peneplain surfaces. Cover sediments place these landscapes to the (i) Devonian, (ii) Carboniferous/Permian/Triassic and (iii) Late Triassic periods.

Unraveling the link between magma and deformation during slow seafloor spreading

Detachment faulting related to oceanic core complexes (OCCs) has been suggested to be a manifestation of slow seafloor spreading. Although numerical models suggest OCCs form under low magma supply, the specific interaction between magmatism and tectonic faulting remains elusive. This paper examines seismic observations detailing the spatiotemporal interactions between magmatism, high-angle faulting, and detachment faulting at a slow-spreading mid-ocean ridge in the West Philippine Basin. We identified a magma-rich spreading phase, indicated by a magmatic top basement and oceanic crust with shallow-penetrating high-angle normal faults. An axial valley reveals an along-strike transition from magmatically-dominated to highly tectonized oceanic crust over a distance of 70 km. Two older OCCs with concave-down fault geometries and a younger OCC with steep-dipping faulting suggest sequential detachments with the same polarity. Our findings suggest: (1) slow seafloor spreading alternates between high-angle faulting with a relatively high magma supply and detachment faulting with a limited magma supply; (2) sequential development of younger detachments in the footwall of its predecessor leads to an asymmetric split in the newly accreted crust; and (3) the life cycle of OCC ends with high-angle faults that overprint the detachment and act as magma pathways, sealing the OCC. Our study captures the dynamic interaction between high-angle and detachment faults and their concurrent and subsequent relationship to magmatic systems. This reveals that strain distribution along strike is critical to OCC formation, thus enriching our understanding beyond conventional considerations such as spreading rates and melt budgets at mid-ocean ridges.

Intra-oceanic emplacement of the Comoros Archipelago through inherited fracture zones

We shed light on the nature and structure of the crust surrounding the Comoros Archipelago, western Indian Ocean, offering insights into the region's geological history and volcanic island formation. Our comprehensive study encompasses the acquisition of new, deeply penetrating seismic data from the SISMAORE cruise (refraction and reflection seismic), and the subsequent analysis of the characteristics and structure of the crust surrounding the Comoros Archipelago. Both the reflection seismic imaging and the velocity structure using ocean bottom seismometers indicate that the crust of the Comoros Basin exhibits oceanic characteristics, thus resolving previous controversies about its nature. The thickness of the oceanic crust ranges from 5.8 to 6.6 km in the north of the archipelago to 6–7.2 km within the Comoros Basin. The estimated roughness of the top basement in the Comoros Basin ranges from 110 to 200 m values typical of intermediate to slow spreading ridges, such as the extinct spreading centre in the West Somali Basin.The unloaded basement depth of the Comoros Basin closely matches the expected water-loaded subsidence for a Cretaceous or Jurassic oceanic lithosphere. In contrast, the West Somali Basin to the north of the Comoros Archipelago has shallower basement depths, potentially linked to recent volcanic activity along the archipelago.We propose that the pre-existing oceanic fracture zones in the West Somali Basin underwent reactivation, first during the Turonian period and later during the Late Eocene. These reactivated fracture zones may have acted as preferred pathways for the emplacement of the volcanic islands of the Comoros Archipelago. The EW trend of the archipelago appears to follow a marked change in the direction of these reactivated fracture zones, suggesting that the associated lithospheric weakening likely played a critical role in facilitating the formation of the Comoros Archipelago.

Gravimetric inversion applied to the study of the basement relief of the Recôncavo-Tucano-Jatobá Rift System in Northeast Brazil

This article presents results from the implementation of an inverse modeling algorithm that considers the Bouguer anomaly signal to estimate and gain a better understanding of the boundary between the sedimentary package and the basement of the sub-basins within the Recôncavo-Tucano-Jatobá rift system. The algorithm for modeling the basement relief is considered a medium constituted by a set of discrete two-dimensional prisms with fixed density contrasts between sediment and basement and variable depth. Initially, it was applied to synthetic models, resulting in depth variation curves of the basement top that fit well with the true model. Subsequently, this methodology was applied to satellite gravity data obtained from the high-resolution Earth gravity field model called SGG-UGM-2. The results of this application were compared with the depth of the Moho interface estimated beneath the studied units and obtained through the Parker-Oldenburg methodology. The information produced here allowed the interpretation of the gravity anomaly over the depositional space of the studied basins and the geometry of their basement. Together with the knowledge of their stratigraphy, this interpretation may be analyzed to characterize the region's reservoirs. By interpreting the basement relief in conjunction with the Moho topography, this study portrays the geotectonic evolution of the aulacogen and its association with estimating the depocenters of the Recôncavo, Tucano, and Jatobá sub-basins.

Along-strike break-up variations of the continent–ocean transition zone in the northern South China Sea

We analyse how the potential field and deep structures of the continent–ocean transition (COT) zone in the northern South China Sea vary along-strike with the aim of understanding the break-up styles and synrift magmatism in this region. The high free-air gravity anomaly and the accompanying basement structures are evidence of significant mantle upwelling and serpentinization in the northeastern COT zone. The top-basement of the COT is uplifted and rough, but gradually retrogrades into a relatively flat and low relief towards the mid-northern margin, where the reduced gravity anomaly reflects subdued mantle upwelling, but perhaps stronger synrift magmatism. On the northwestern margin, the low gravity anomaly suggests fairly limited mantle upwelling, but more synrift magmatic intrusions in the crust; the top-basement of the COT zone is smooth and slightly deepened. The width of the COT zone is mostly <30 km and the oldest legible magnetic anomaly (C11r) within the zone is related to the final continental break-up. The seaward limit of the COT should be relocated further south beyond anomaly C11r, pointing to a very narrow zone of true oceanic lithosphere in the NW Sub-basin. The coexistence of mantle upwelling/serpentinization, magmatic underplating and volcanism on top of the COT during continental break-up characterizes a typical intermediate rifted margin, although there are significant along-strike variations. Thematic collection: This article is part of the Emerging knowledge on the tectonics of the South China Sea collection available at: https://www.lyellcollection.org/topic/collections/south-china-sea

3D Crustal Architecture and Along‐Strike Variation in the Mid‐Northern South China Sea Rifted Margin

AbstractRifted margins often show apparent along‐strike variations at the continent‐ocean transition (COT) region, typically occurring gradually over hundreds‐to‐thousands of km between the “magma‐rich” and “magma‐poor” endmembers. In contrast, comparatively smaller‐scale lateral variabilities of rifting structure and faulting style in hyper‐thinned continental crust are not yet well described. The South China Sea (SCS) was recently defined as the archetype of a new “intermediate‐type” margin with neither excess magmatism nor mantle exhumation. However, along‐strike crustal variations along this new type of margin are still little explored. Based on previously unpublished 2D grid of seismic reflection lines and overlapping 3D seismic volumes, we have investigated the crustal structure, faulting style, and the lower crustal reflectivity along ∼400 km of the mid‐northern SCS margin. Our new maps of crystalline‐crust thickness and top basement show that the SCS extension developed in two segments with contrasting tectonic styles separated by a narrow boundary. The eastern domain, resembling a wide‐rift model, displays low‐angle detachment faults and high‐velocity lower crust mainly associated with syn‐rift magmatism indicating weak crustal rheology. The neighboring western domain, resembling a narrow rift model, displays steep crustal‐scale faults indicating comparatively strong rheology. The change from wide to narrow rift—or weak to strong rheology—occurs abruptly, which appears at odds with the current conventional wisdom of mostly gradual transitions over a long distance between rift models. We speculate that the inherited heterogeneity in mantle composition and 3D melt focusing effect may drive this abrupt along‐strike variability in the mid‐northern SCS.

Linking rifted margin crustal shape with the timing and volume of magmatism

AbstractDetermining the volume and timing of magmatism during rifting and breakup is challenging due to the similar density and seismic velocity of inherited continental crust, magmatic additions and serpentinized mantle; and the difficulty of dating magmatic additions. Here rules of thumb to estimate these are proposed based on the characteristics of the top basement and Moho on seismically imaged margins. A simple kinematic model is used to generate first‐order crustal shapes of margins as a function of magma volume and timing of emplacement, which are successfully compared to a representative number of rifted margins. It appears that ‘magma‐rich margins’ require melt emplacement in advance of crustal thinning but not necessarily enhanced melt volume, while margins with exhumed mantle require a delay in melt emplacement but not necessarily a low magmatic volume. An alternative classification for the magma‐poor/magma‐rich dichotomy is proposed to better represent the crustal shape variability of rifted margins.

Changes in Thermal Conductivity of the Rocks of the West Siberian Basin Lithosphere in the Vicinity of the Tumenskaya SG-6 Well

Numerical reconstructions of the thermal regime of the lithosphere of the West Siberian basin in the Koltogor-Urengoi graben in the vicinity of the Tyumenskaya SG-6 superdeep well are used to analyze the depth distribution of thermal conductivity of basin rocks. Five depth intervals which differ in the character of changes in thermal conductivity of rocks are distinguished: the permafrost zone, the sedimentary section below this zone, the zone of anomalous rock weakening, the consolidated crust, and the mantle. The algorithms for calculating the thermal conductivity are considered and the main factors affecting its change with depth are determined for each of the five intervals. A sharp decrease in the thermal conductivity of rocks in the bottom part of the sedimentary cover and in the basement top in the vicinity of the SG-6 well is associated with rock weakening due to tectonic fracturing and hydrothermal erosion. The analysis suggests that the stationarity conditions of the process are not observed in optical scanning thermal conductivity measurements and, therefore, this method may overestimate the true thermal conductivity of rocks.

Footwall geomorphology during necking domain evolution: A new model for the Frøya High, mid‐Norwegian rifted margin

AbstractObservations and modelling results from highly extended regions indicate that detachment fault systems recording displacements of 10 km or more become associated with footwall uplift and back‐rotation. This is commonly explained by the rolling hinge model, which predicts detachment fault back‐rotation and severe dip reduction (<20°) controlled by the amount of extension. Although detachment faults within necking domains at rifted margins often record displacements in orders consistent with those for the rolling hinge model, it is rarely invoked to explain the associated footwall configurations. Our study area encircles the necking domain of the mid‐Norwegian rifted margin, where the Middle Jurassic–Early Cretaceous Klakk Fault Complex (KFC) directly separates the Frøya High from the Rås Basin. The Frøya High represents the eroded footwall of the KFC detachment fault system which records displacements of 20–40 km. Seismic mapping and well correlation across the Frøya High reveal how three erosional unconformities correspond to three laterally extensive top basement segments which follow the strike of the sinuous KFC. The segments differ in terms of dip, basement geomorphology and the composition and age of the sediments that rest unconformably on the top of basement. We attribute the associated cross‐cutting basement unconformities across the Frøya High to footwall uplift and back‐rotation during fluctuating relative sea‐level and repeated subaerial exposure during Middle Jurassic–Early Cretaceous times. We herein introduce a revised tectono‐sedimentary model for the evolution of the Frøya High, with significant implications for sediment (re‐)routing across the high during rifting. The model indicates that spatio‐temporal sediment distribution was ultimately controlled by the process of necking and evolution of the KFC. Our findings indicate a rolling hinge‐type evolution for the KFC and further suggest that the associated mechanisms may be more common in the necking domains of rifted margins than previously assumed.

Proterozoic fold and thrust belt imaged on reflection seismic in Arabian plate basement

Major structures are imaged on 2D reflection seismic data within the Precambrian basement of the western Rub’ Al-Khali of Saudi Arabia for the first time. In this area the base-Cambrian Angudan Unconformity that defines top basement is at a depth of 1–2 km with a gentle easterly dip. Large antiformal structures are clear on 2D reflection seismic within the basement. The antiforms are separated by zones that are interpreted as low-angle faults. No basal detachment is seen and the faults pass below the base of reflection seismic at a depth of approximately 12 km. Individual folds have dimensions in the order of 20 km wavelength and 2 km amplitude and occur between 3 and 10 km depth. The structural style is interpreted as compressional by comparison with thrust systems and accretionary prisms elsewhere. Regional studies indicate that basement is comprised of a series of north-south trending oceanic Proterozoic terranes that were brought together in the Ediacaran East African Orogeny. Based on current regional tectonic maps the newly-imaged fold belt is on the east margin of the Khida-Abas terrane. Depth conversion shows the thrusts dip at approximately 10° north in the line of section. A novel combination of cross-section to structural trend obliquity estimates combined with matched filtering of potential field data indicate the fold and thrust belt trends 015°-195° with ESE vergence. This compressional belt may be some internal structure of the Khida-Abas terrane, or may be a non-outcropping accretionary prism on the margin of that terrane, or may even represent a set of amalgamated microterranes that do not outcrop along trend. Either way, these observations represent a major, previously undescribed element of this sector of the East African Orogen.

The Iglesia basin (San Juan, Argentina), seismic interpretation, geometry basin, and implications for geothermal systems

The Iglesia basin, in the San Juan Province, is the northern part of a Cenozoic piggy-back basin (the Iglesia-Calingasta-Uspallata basin), located above of the active flat-slab subduction zone of western Argentina. This basin is located between two mountain ranges, the Cordillera Frontal to the west and the Precordillera to the east, affected by thin and thick skinned tectonics, respectively. It is elongated in a north-south direction (70 km) and has a maximum width of 35 km. We have analyzed 17 seismic reflection lines corresponding to more than 500 km of interpreted sections. A strong reflection at 0.5-2 s is interpreted as indicative of shales and sandstones in the upper part of the Agua Negra Formation (Carboniferous); this represents a seismic basement for the Iglesia basin clearly separating stratified (shallower) from chaotic (deeper) reflectors. Several high angle faults have been recognized in the interpreted seismic lines affecting the Neogene fill and even the basement; some of them correlate with structures observed at the surface such us El Tigre Fault System. A 3D model shows the seismic top of basement smoothly deepening down to 3,650 m beneath the Pismanta area. The basement continues upward to the east with a steeper slope clearly defining an asymmetrical shape for the basin. Moreover, there are three depocenters of similar maximum depths around the geothermal hot spring of the Pismanta center. Some of the interpreted faults may be helping in the outflow process of meteoric water heated by a normal geothermal gradient. Considering earthquake data framework, our observations correlate with transpressive deformation likely associated with El Tigre Fault System, which affects Neogene and Pleistocene strata of the Iglesia Group.

Mapping of subsurface geological structures and depth to the top of magnetic basement in Bornu Basin and its environs, NE Nigeria, for possible hydrocarbon presence

Mapping of subsurface geological structures and depth to the top of magnetic basement in Bornu Basin and its environs, NE Nigeria, for possible hydrocarbon presence

The Role of Crustal Accretion Variations in Determining Slab Hydration at an Atlantic Subduction Zone

AbstractWe present a 2D P‐wave velocity model from the outer rise region of the Lesser Antilles island arc, the first wide‐angle seismic study of outer rise processes at an Atlantic subduction zone. The survey consists of 46 OBS receivers over a 174 km profile with velocities resolved to 15 km below top basement. The final velocity model, produced through tomographic inversion, shows a clear decrease in the velocity of the lower crust and upper mantle of the incoming plate as it approaches the trench. We attribute this drop to outer rise bend‐related hydration, similar to Pacific cases, but superimposed on spatial variations in hydration generated at the slow‐spreading ridge axis. In thin, tectonically controlled crust formed under magma‐poor spreading conditions the superposition of these sources of hydration results in compressional velocities as low as 6.5 km s−1 beneath the PmP reflector. In contrast, segments of crust interpreted as having formed under magma‐rich conditions show velocity reductions and inferred hydrous alteration more like that observed in the Pacific. Hence, variations in the style of crustal accretion, which is observed on 50–100 km length scales both along and across isochrons, is a primary control over the distribution of water within the slab at Atlantic subduction systems. This heterogeneous pattern of water storage within the slab is likely further complicated by along strike variations in outer rise bending, subducting fracture zones and deformation at segment ends and may have important implications for our understanding of long‐term patterns of hazard at Atlantic subduction systems.

Structural and petrological characteristics of a Jurassic detachment fault from the Mont-Blanc massif (Col du Bonhomme area, France)

Necking zones, located between the proximal and distal domains of passive margins, are characterized by important crustal thinning and the occurrence of extensional detachment faults. Here we provide a petrographic, microstructural and geochemical study of an extensional detachment fault discovered in the Mont-Blanc massif, which was located in the necking zone of the European margin during Early Jurassic rifting. The footwall of the fault consists of basement gneisses, while its hanging wall presents pre-to syn-rift deposits. A careful observation of the basement/cover contact also reveals the presence of a strain gradient affecting the Variscan gneisses, which are progressively deformed to cataclasite and to black gouges at the top basement, and sealed by undeformed Jurassic syn-rift sandstones, the Grès Singuliers, which rework fault rock pebbles. Microscale observations also indicate fluid-assisted deformation, characterized by the total breakdown of feldspars and the coeval formation of white mica, leading to strain softening along the fault plane. The overall observations point toward a rift-related detachment fault responsible for the exhumation of the internal Mont-Blanc basement, an interpretation which challenges previous models of crustal exhumation in the External massifs of the Alps. Finally, the preservation of an undeformed syn-rift sedimentary cover sealing a tectonized top basement makes this area a fossil analogue for detachment faults in necking domains. It demonstrates that preservation of pre-Alpine, rift related structures is possible even in highly deformed areas, and emphasizes the role played by pre-Alpine inheritance on the building of the Alpine Mountain belt.

Basement structure investigation using 3-D forward modeling and inversion of geomagnetic data of the Zeit basin area, Gulf of Suez, Egypt

The Zeit basin is located on the western coast of the Gulf of Suez. It is a major, elongated half-graben structure with faults dipping steeply to the southwest. The Zeit basin contains the thickest Miocene sediments and evaporites in the Gulf of Suez. Many exploration activities have been conducted in and around the study area due to the known presence of hydrocarbon resources. In petroleum exploration, the estimation of basement depth (or sedimentary thickness) is a primary exploration risk parameter, in particular, for estimation of heat flow. The magnetic method is one of the few methods that can be used to study the basement structure and estimate the top basement depth. In this paper, the top basement geometry, distribution of the magnetic susceptibility and the basement depth of the Zeit basin were investigated using 3-D forward magnetic modeling and the 3-D inversion of geo-magnetic data. The 3-D forward modeling of the aeromagnetic field data from the Zeit basin area revealed a NW-SE trending half-graben structure, consistent with the known geology of the study area. Magnetic susceptibility cutoff 0.005 SI was applied to show the subsurface relationships among the basement sedimentary units. The calculated depth of the Zeit basin is around 4–5 km. The magnetic field data, calculated using the Gauss Legendre quadrature method, generally agree with the measured data as well as data calculated using the inversion process. The depth and magnetization intensity values used in the 3-D forward modeling, as well as petroleum borehole data, provide a structural basis for the 3-D inversion process.

The North-East Atlantic Mid-Norwegian rifted margin: Insights from the deep imaging Geoex MCG RDI19 dataset

The Norwegian Continental Shelf is one of the world's most used laboratories to study rifting processes and rifted margin architecture. Available datasets are dense, various and of good quality. However, since the full basement is rarely imaged, major questions remain unanswered regarding the structural details and nature of rocks at depth. The Geoex MCG Regional Deep Imaging 2019 (RDI19) dataset presents - for the first time - a series of regional long-offset seismic reflection profiles, of high resolution and deep imaging (16 s-twtt). The dataset offers an unprecedented imaging of the entire margin architecture including deep basement units, Moho and upper mantle - from the proximal margin to the outer margin.This contribution introduces the dataset and proposes an interpretation accompanied by gravity modelling experiments. Focus is set on the identification and seismic facies characteristics of the top basement and Moho core envelopes to discuss the dip and lateral variability of the various basement/crustal units. Basic gravity models are used to develop a discussion on the possible nature of the acoustic basement in the distal margin (crust, magma, mantle, combinations). Based on the observations and interpretation, an updated map of the Møre and Vøring margin structural domains is proposed and discussed.

The tectono-stratigraphic and magmatic evolution of conjugate rifted margins: Insights from the NW South China Sea

This study is based on a careful analysis of high-quality reflection seismic sections located at the tip of the NW South China Sea V-shaped rift basin. Using the CGN-1 section, a seismic line imaging the complete sedimentary and magmatic architecture of conjugate rifted margins, we: (1) provide a detailed description of the crustal architecture; (2) define extensional domains, which we relate to specific deformation phases; and (3) determine the tectono-stratigraphic evolution linked to rifting. Based on these, we propose a kinematic restoration and quantify the amounts of extension and associated strain rates. We discuss the link between the kinematic evolution and the sedimentary and magmatic record and illustrate it in a Wheeler Diagram. Relying on the identification and characterization of distinct stratal patterns and crustal architectures, we propose qualitative and quantitative criteria to interpret two critical rift events that are necking and hyperextension. These two events are linked to the individualization and subsequent dismembering of a so-called keystone, here referred to as H-block. It is the first time such an approach is used to decipher the tectono-stratigraphic evolution of a complete syn-rift mega-sequence across present-day conjugate rifted margins. This study differs from previous interpretations of correlative surfaces in the distinction between: (1) different types of top basement; and (2) syn- and post-tectonic packages within the syn-rift record. It leads to new interpretations of the tectono-stratigraphic evolution of the NW South China Sea and has the potential to be used as a new approach to analyze, quantify and correlate events recorded in seismic sections across rifted margins.

3D constrained inversion of gravity and magnetic data to image basement and plutonic bodies: A case study from Dood Arale Basin, eastern Somaliland

We have developed 3D inversion models derived from airborne gravity and magnetic data, which are constrained by seismic and well data, in eastern Somaliland. The density model reveals a northwest–southeast-trending basin, 125 km long and 25 km wide and called the Dood Arale Basin. The basin comprises two subbasins separated by a basement high and is infilled by up to 2500–3200 m of sediments. Smaller and shallower subbasins are also identified to the west of Lafaweyne and northeast of Dararweyne. The density model shows that the top basement in the platform areas is at approximately 1500–1700 m in depth and shallows to approximately 300 m at the Bur Anod, Hagraajin, and Hagrin Ranges and northwest of Eil Afwein. The basement depths in these areas are more uncertain and could be deeper because they occur in areas of high gravity anomalies caused by a combination of near-surface high-density sediments and high-density plutonic bodies within the basement. The susceptibility model indicates that the basement consists of very weakly magnetized metasediments of the Inda Ad Complex intruded by three northeast–southwest-trending magnetic bodies with upper surfaces at depths of approximately 300–3000 m. These magnetic bodies are interpreted as plutonic complexes of similar age and composition to the Lower Cretaceous syenite intrusions outcropping at Gorei in the Shilah Madu Range. Seismic reflection profiles image the sedimentary sequences, but they do not clearly map the top basement or detect any of the plutonic bodies. The plutonic bodies could have controlled the location of the basin’s border faults and contributed to the high geothermal gradient recorded at the Faro Hills-1 well. The Upper Cretaceous Gumburo and Jesomma Formations in the basin could potentially have reached maturation close to and above the plutonic bodies within the center of the basin.