Search

The Gaoping River-Gaoping Submarine Canyon (GPC) is one of the dispersal river systems in the world. Tens of tons of terrestrial sediments discharge per year at the mouth of the river, where gravity-driven flow can damage the telecommunication cable along the 260-km-long GPC; to the east of the GPC, the continental shelf has been eroded. To understand this geological phenomenon, high-resolution sparker seismic data around the continental shelf as well as parallel and across the GPC were collected. Deep-towed sub-bottom profiler (SBP) data and data from shipboard acoustic Doppler current profiler were also collected. Three major system tracts off southwest Taiwan were identified, based on which the coastline of the last glacial maximum was identified at approximately 138 m below the current sea level. Analysis of the deep-towed SBP profiles suggested sandy sediment overflows through breakages on the east bank of the GPC. A convergence of bottom currents with a speed of up to 1.5 m/s flowing southeastward has eroded the continental shelf intensively, forming the Xiaoliuchiu channel. Although a mud diapir is active to the east of the GPC and forms the Xiaoliuchiu islet, it has been eroded at the Xiaoliuchiu channel. The average erosion rate on the east bank of the GPC was estimated to be approximately 609 cm/ka in the past 8.2 ka; between the GPC and the Xiaoliuchiu islet, the continental shelf is wasted due to severe seabed slumping.

Upper part of sedimentary thickness in the western part of Mediterranean is consist of nontransparent and semitransparent layers with penetration of such named salt domes bodies related to halokinesis process mud and salt diapirism mainly related to the messinian salt crisis fenomena. The data of “Parasound” parametric echo-sounding survey were used for elucidate in details this part of sediment series which was represented before by ordinary seismic methods as single whole transparent layer. The detail descriptions made up for the structure of upper part of sedimentary series in western basin. The position of turbidity-terrigenous marker stratum within the series is determined. The possible age of this stratum is 10–100 thousand of years and corresponds to Vurm glacial epoch. The enormous dimensions of salt diapirs, as they were reflected on the “Parasound” displays, led to the conclusion of modern halokinetic activity on the whole western Mediterranean bottom space.

[Abstract We systematically incorporate burial history, sea floor geometry and tectonic loads from a sequential kinematic restoration model into a 2D evolutionary geomechanical model that simulates the formation of the Sandia salt diapir, Tarfaya basin, NW African Coast. We use a poro‐elastoplastic description for the sediment behaviour and a viscoplastic description for the salt. Sedimentation is coupled with salt flow and regional shortening to determine the sediment porosity and strength and to capture the interaction between salt and sediments. We find that temporal and spatial variation in sedimentation rate is a key control on the kinematic evolution of the salt system. Incorporation of sedimentation rates from the kinematic restoration at a location east of Sandia leads to a final geomechanical model geometry very similar to that observed in seismic reflection data. We also find that changes in the variation of shortening rates can significantly affect the present‐day stress state above salt. Overall, incorporating kinematic restoration data into evolutionary models provides insights into the key parameters that control the evolution of geologic systems. Furthermore, it enables more realistic evolutionary geomechanical models, which, in turn, provide insights into sediment stress and porosity., The present study uses data coming from a sequential kinematic restoration to constrain an evolutionary geomechanical model for the Tarfaya basin. The resulting geomechanical model provides more realistic results that are in accordance with seismic information. Further sensitivity analysis of the evolutionary geomechanical model identifies the sedimentation rates as the key driver for the basin system evolution. ]

This study focuses on seafloor methane seep sites and their distribution in the northwestern part of the German North Sea. Methane seepage is a common phenomenon along marine shelves and known to occur in the North Sea, but proof of their existence was lacking in the study area. Using a ship-based multibeam echosounder we detected a minimum of 166 flares that are indicative for free gas releases from the seafloor in the German “Entenschnabel” area, which are not related to morphologic expressions at the seafloor. However, a group of small depressions was detected lacking water column anomalies but with indications of dissolved fluid release. Spatial analysis revealed that flares were not randomly distributed but show a relation to locations of subsurface salt diapirs. More than 60% of all flares were found in the vicinity of the salt diapir “Berta”. Dissolved methane concentrations of ∼100 nM in bottom waters were ten times the background value in the “Entenschnabel” area (CH4< 10 nM), supporting the finding of enhanced seepage activity in this part of our study area. Furthermore, locations of flares were often related to acoustic blanking and high amplitude reflections in sediment profiler echograms, most prominently observed at location Berta. These hydroacoustic signatures are interpreted to result from increased free gas concentrations in the sediments. Electromagnetic seabed mapping depicts local sediment conductivity anomalies below a flare cluster at Berta, which can be explained by small amounts of free gas in the sediment. In our area of interest, ten abandoned well sites were included in our mapping campaign, but flare observations were spatially not related to these wells. Naturally seeping methane is presumably transported to the seafloor along sub-vertical faults, which have formed concurrently to the updoming salt. Due to the shallow water depths of 30 to 50 m in the study area, flares were observed to reach close to the sea surface and a slight oversaturation of surface waters with methane in the flare-rich northeastern part of the working area indicates that part of the released methane through seepage may contribute to the atmospheric inventory.

We report the structural geometry and facies architecture of a small diapir-related carbonate-dominated basin from the Jurassic rift of the Moroccan High Atlas. The Azag minibasin is a lozenge-shaped depocenter completely enclosed by tectonic boundaries that we interpret as welds after former salt anticlines or salt walls. The exposed ca. 3000 m-thick infill of the Azag minibasin is asymmetric; layers are tilted to the W defining a rollover geometry. Areally-restricted sedimentary discontinuities and wedges of growth strata near the basin margins indicate sedimentation contemporaneous with diapiric rise of a Triassic ductile layer. Facies evolution through the basin reflects local accommodation by salt withdrawal and regional events in the High Atlas rift. The early basin infill in the Sinemurian and Pliensbachian shows thickness variations indicative of low-amplitude halokinetic movements, with reduced exposed thicknesses compared to surrounding areas. The exposed Toarcian and Aalenian deposits are also reduced in thickness compared to areas outside the basin. Subsidence increased dramatically in the Bajocian-early Bathonian (?), the main phase of downbuilding, when over 2600 m of carbonates and shales accumulated at a rate > 0.5 mm/a in the depocentral area of the minibasin governed by W-directed salt expulsion. The stratigraphic units distinguished often show maximum thicknesses and deeper facies in the depocentral area, and rapidly change to shallower facies at the basin margins. The Bajocian carbonate facies assemblage of the minibasin include: reservoir facies as microbialite-coral reefs in the basin margins (formed during periods of strong diapir inflation and bathymetric relief), basin-expansive oolite bars (formed during episodes of subdued relief), and organic-rich, dark lime mudstones and shales that show source-rock characteristics. The Azag basin is a good analog for the exploration of salt-related carbonate plays in rifts and continental margins where source-rock and reservoir can form in a same minibasin., Departament de Geologia, Universitat Autònoma de Barcelona, España, Instituto Geológico y Minero de España, España

Ebeko is one of the most active volcanoes of the Kurile island arc, producing frequent mild Vulcanian explosions with eruption clouds up to 5 km high. The volcano poses a serious threat to the Severo-Kurilsk town with a population of around 2500 inhabitants, located at a distance of only 7 km on a fan of the volcano’s laharic deposits. Here, we report an overview of the activity of the volcano in the 20th–21st centuries and the results of our geological and petrological investigations of the ongoing Vulcanian eruption that started in 2016. We have found that eruptions of Ebeko span a range of mechanisms from purely magmatic to phreatic/hydrothermal. Three of its historical eruptions (the 1934–1935, 1987–1991, and the 2016–ongoing) involved fresh magma, while during the others (1967–1971, 2009–2011) fresh magma was not erupted. Juvenile material of the ongoing eruption represents highly crystalline and highly viscous (more than 108 pa s) low-silica (56–58 wt% SiO2) andesite. Historical data and our observations of the ongoing eruption allowed us to suggest a functional model of the volcano where Vulcanian explosions are caused by shallow intrusions of small diapir-like batches of strongly crystallized and highly viscous andesitic magma ascending into water-saturated, hydrothermally altered rocks composing the volcano summit. We suggest that the diapir’s ascent is governed by their positive buoyancy. Some of the diapirs reach and breach the ground surface producing magmatic eruptions of Ebeko, while the others are stuck at the shallow subsurface level and feed intensive hydrothermal activity as well as phreatic eruptions of the volcano. Positive buoyancy of the diapirs is too weak to allow them to extrude high above the ground surface to form lava domes. Supplementary Information The online version contains supplementary material available at 10.1007/s00445-020-01426-z.

The northern margin of the Organyà basin (Southern Pyrenees) has a complex structure in which syn-rift Lower Cretaceous carbonates flank a wide Keuper evaporite province, featuring the leading edges of the basement-involved thrust sheets of the Pyrenean antiformal stack. Recent studies show that Keuper diapirs and salt walls grew during the Cretaceous extensional episode, conditioning the development of differentiated depocenters and minibasins. The role of salt tectonics during the Pyrenean orogeny has not been addressed in previous structural studies, but present-day cross-sections indicate a Keuper evaporite-bearing vertical thickness of up to 3000 m in the Senterada-Gerri de la Sal area. We infer that salt migration was a determinant mechanism in triggering a gentle northward tilting of the Organyà basin during the Eocene-Oligocene, recorded in the La Pobla de Segur and Gurp syn-tectonic conglomerates in a large north-directed onlap, opposite to the main sedimentary influx direction. Contemporaneously, we interpret that salt migration, promoted by conglomerate differential loading, enabled the sinking and rotation of the unrooted Nogueres thrust units (têtes plongeantes). We use new and published structural data for the Lower Cretaceous margin of the Organyà basin, combined with structural and clast provenance data from the Cenozoic alluvial fan conglomerates of La Pobla and Gurp, to understand the Lutetian to late Oligocene evolution of the northern margin of the Central South-Pyrenean Unit. The tectono-sedimentary evolution of this area and the salt evacuation patterns are closely related to the exhumation history of the stacked Paleozoic thrust sheets of the Pyrenean hinterland to the north. In this study, we correlate the movements over a mobile substratum and the paleogeographic changes of conglomeratic basins at the toe of an exhuming orogenic interior.

Summary High accuracy gravity, used to build a detailed 3D density model of one of the biggest salt diapirs in the Dnieper-Donets basin, evidence the presence of the overturned Middle-Lower Carboniferous flaps. Model is supported by well core data, theoretical geomechanical models, and data from the adjacent hydrocarbon field. Both regional tectonic settings and density anomalies in the inverted 3D density model suggest a high probability of big to huge hydrocarbon accumulations to be associated with an identified overturned flaps.

The Yinggehai Basin is a typical high temperature and high pressure (HTHP) gas-bearing basin. The pressure coefficient exceeds 2.2 in deeply-buried Miocene reservoirs in the Ledong Slope, a nondiapir zone in the Yinggehai Basin. Determining the overpressure mechanisms and predicting the pore pressure are key issues for natural gas exploration and development in the Ledong Slope. In this paper, overpressure mechanisms were investigated according to the analysis of vertical effective stress-logging responses and geological evaluations, and the pore pressure was predicted using the Bowers method. The loading-unloading crossplots indicated that the overpressure that existed in reservoirs mainly consists of two types: neighbor-source and allo-source overpressure. The neighbor-source overpressure is mainly caused by the pressure transmission from the adjacent mudstone to the reservoir, with a pressure coefficient less than 1.5 ~ 1.6. The high-magnitude overpressure points with pressure coefficients greater than 1.6 show a typical unloading response, indicating elevated sandstone pressures rather than in situ mudstone pressures, which are most likely to be generated by overpressure vertical transfer. The high-magnitude overpressure fluid generated by the high mature ultradeep buried N1s source rock migrated to the shallower reservoirs via hidden faults/microfractures, which led to the vertical transfer of overpressure. Vertically transferred overpressure was generated at 1.5 ~0.2 Ma, which is beneficial for the preservation of overpressure in lenticular sandbodies. The estimated pore pressure by the Bowers method is in good agreement with the measured pressure and provides a meaningful reference for predrilling pressure prediction in nondiapir or diapir zones in the Yinggehai Basin.

Salt diapirs/bodies are remarkable structures often presenting a rich internal structure, with features like isoclinal folds, sheath folds, curtain folds, boudinage, etc. Salt structures are themselves valuable as a resource but are also often associated with significant hydrocarbon accumulations, as well as valuable as storage sites. While significant progress has been made to imagine the external geometry of salt bodies, especially using 3D seismic, the complex internal structure of the salt diapirs is less known. Such structures can mainly be investigated using salt mines, outcrops, physical models and rarely seismic for larger structures. There are just a few places in the world where salt mines or outcrops can be studied, and Romania is such an example. The Romanian Carpathians and the Transylvanian Basin offer access to multiple salt mines (and outcrops) which are easily accessible especially because most of the salt mines have been converted into public treatment facilities. The walls of the galleries have been cleaned, polished and well lighted, offering unique 3D exposures which can be used to observe and map in detail the deformation of these salt domes. In this field-trip guide, we propose a route with five stops, visiting four salt mines and one important location from the link between salt tectonics and hydrocarbons. Each of the chosen locations is unique as it records a different regional kinematic evolution and offers the opportunity to compare and contrast the specific internal structures.

Salt lithologies are mechanically weaker than other sedimentary rocks. Salt horizons usually act as decollements and precursor salt bodies preferentially deform early during contraction, concentrate deformation, and impact the structural style and kinematics during mountain building. Focusing on shortened isolated-diapir provinces, our analog modeling program investigates the influence of two salt walls on folding and thrusting. High resolution topographic scans and particle image analysis show that the presence of precursor diapirs impacts the layer parallel shortening patterns and presumably the stress field at the onset of contraction. Shortening concentrates on diapirs, leading to roof arching, crestal extension and salt extrusion. This sequence of events occurs earlier on thinner salt-sediment sequences including diapirs having well-developed pedestals, particularly when proximal to the deformation front. Folds and thrusts nucleate at salt walls if they feature a well-developed pedestal. Further shortening results in secondary welding as evidenced by the collapse of uplifted roof domes, cessation of indentation and reverse faulting nucleated at the secondary welds. Meanwhile, and depending upon the processes occurring on the diapir closer to the backstop, the deformation of the distal salt wall is discontinuous. Our modeling results are compared with experimental works and natural examples from the Fars (Zagros Mountains).

International audience; Orogens are traditionally classified according to their tectonic style. Paleoproterozoic tectonics is referred to as “ancient-style tectonics” while Proterozoic tectonics is referred to as “modern-style tectonics”. Ancient-style tectonics is characterised by distributed vertical structures and low topography gradients, often associated with diapirism and partial melting. In contrast, modern-style tectonics involve prominent strain localisation and the formation of thrusts, nappes and high topographic gradients. However, the parameters controlling the transition from ancient to modern-style tectonics are poorly understood. To quantify this transition, a combination of 1D and 2D high resolution lithospheric-scale thermo-mechanical models was conducted. The parameters controlling the strength of the lithosphere (i.e., Moho temperature, strain rate, crustal rheology, crustal radiogenic heat production and role of shear heating) were investigated in detail. Our results show that tectonic style is controlled by the maximum of crustal strength (shear stress). Modern-style tectonics is observed to occur when the maximum of crustal strength is greater than 300 MPa. At the opposite, a maximum crustal strength lower than 300 MPa leads to ancient style tectonic structures. Therefore, crustal rheology, temperature and background strain rate significantly influence the transition from ancient to modern-style tectonics. Shear heating remains a key factor in promoting strain localisation in modern-style tectonics. Crustal radiogenic heat production has a moderate influence by increasing/decreasing the tendency for faulting within the crust. This crustal strength criterion also provides an excellent fit for a second potential proxy: a localisation criterion of ca. 225°C. These two proposed proxies can be used interchangeably to predict the transition from ancient to modern-style tectonics.

Summary Reprocessing and integrated interpretation of vintage and newly available data provided new insight into structural framework of thrust belt in the northeastern part of the Timan Pechora basin. It showed that structural evolution of the fold and thrust belt was influenced by the multiphase development of salt diapirs which finally were squeezed during pulses of the orogenic shortening. This was accompanied with expulsion of salt and the development of divergent thrusting. The improved seismic imaging has allowed for more accurate definition of the structure and stratigraphy below thrust sheets including salt sole in frontal zone of the fold and thrust belt. The updated interpretation shows new exiting opportunities for petroleum exploration provided by subsalt traps.

The external Alps record a whole Wilson cycle that began at early Mesozoïc times by an extensional phase leading to the deposition of thick marine deposits upon an upper Triassic basement including a thick salt layer. Several diapiric structures (e.g. Astoin, the Barre de Chine ; Célini et al., 2020) are the witnesses of this important salt activity during deposition and the subsequent deformation through the Lower Jurassic. Otherwise, Triassic salt allowed thrusting on several decollement levels and emplacement of major thrusted units, such as the “Nappe de Digne” or the Authon thrust sheet, during the alpine phase s.s, initiated at the Oligocene-Miocene boundary. Between these two periods, the external Alps story is more uncertain and none salt activity has been clearly demonstrated except westwards in the Vocontian basin. In the whole South-East basin, only few clues, as bipyramidal quartz found in Priabonian deposits in the western Baronnies suggest a potential salt activity at surface during the Paleogene. However, in the St-Geniez areas, some Oligocene sediments, located at the vicinity of salt structures suggest a potential diapiric growth during this period. Indeed, some stratigraphic gypsum beds are found in an Oligocene lacustrine series, directly thrusted by the Authon thrust sheet. None evaporite environments are described in the whole region at Oligocene times, which suggest a possible recycling of Triassic evaporites.In order to determine if theses deposits are related to a Paleogene salt activity, a multi-analytical approach was used. First, a field study allowed characterizing the facies and the sedimentary filling and defining the stress regime during the deposit, by kinematic inversion on fractures which indicates a constant N-S compression during the Oligocene. The presence of halophilic fauna at the base of the lacustrine series of the St-Geniez area attests for saline influences during deposit. Moreover, 4km to the SW, a wedge in the conglomerates of the alpine continental molasse (so called red molasse) resting directly on Sorine’s Triassic diapir was put forward. Cargneules and dolomites from the Triassic constitute an important part of the reworked material. These observations indicate that the Sorine's diapir was active during the deposition of the Oligocene series. Then, a precise chemostratigraphic framework was determined by use of δ13C and δ18O isotopic data on the lacustrine limestones. 87Sr/86Sr isotopic ratio on gypsum beds of the lacustrine series aimed at determining their ages and a possible Triassic evaporite sourcing. Our results gave an age ranging from 6 to 23 Ma, which does not correspond with the Oligocene age of the overlying and underlying sediments. Moreover, the large variation in isotope ratios suggests that this gypsum did not come from primary precipitation but from leaching of a pre-existing evaporite source. In conclusion, field observations, together with geochemical analyses, made it possible to highlight the relationships between tectonics, salt tectonics and sedimentation and also to reconstruct the paleogeography of the region at the end of the Paleogene. ReferencesCélini, N., Callot, J.P., Ringenbach, J.C., Graham, R. (2020,). Jurassic salt tectonics in the SW sub-Alpine fold and thrust belt. Tectonics

This paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.

Summary Several authors have identified salt karst as a geohazard onshore and offshore. I study how the expression of different salt karst features can be interpreted to assess geohazards related to salt tectonics. In the Green Canyon area of the USA Gulf of Mexico, three different mechanisms generating salt karst are identified for breaking the caprock, providing access for low-salt-saturation seawater dissolving the salt and causing collapse of the caprock. Active diapirism exciting extensional stress on the caprock, collision of salt diapirs with gravity gliding of salt canopy exciting compressional stress on the caprock, and differential gravity gliding of different sections of the salt canopy resulted in shear stress of the caprock. These three mechanisms have been identified as the primary sources for offshore salt karsting. Erosion by strong deep-water currents, which has previously been considered a significant cause of salt karsting, appears to be a secondary process contributing to the overall efficiency of the salt dissolution. This approach allows mapping geohazards such as unstable caprock as well as delineating lineaments that are interpreted as strike-slip faults in the seafloor and that cannot be detected otherwise because strike-slip faults do not show any vertical offset of the seismically detectable strata.

The origin and evolution of sedimentary basin could be a clue for oil-gas deposits forecasting. For simulation of the basin evolution and pressure and heat flow density distribution the thermo mechanical model of a multilayer, highly viscous fluid was used. Data on vitrinite reflectance were used as a geothermometer for paleothermal reconstruction of the sedimentary basin. Thermo mechanical modeling together with field investigations and wells data gives the possibility to research the geothermal field changing during the sedimentary basin evolution. All geological, geophysical and petrological data were used for sedimentary basins evolution modeling. It is possible to evaluate the lithosphere thickness and the mantle diapir upwelling by original gravity-geothermal model. The model is investigated on the example of the Pre-Caspian Depression.

The excursion for each day is shown in Fig. 3.1. Excursion 1 consists of a visit to El Papalote diapir in La Popa basin and return via Potrero Chico near Hidalgo to compare diapiric and detachment structures. Excursion 2 is a tour of La Popa weld to observe the structural and stratigraphic variability of that feature. Both excursions, especially Excursion 2, contain ambitious itineraries polished during many trips by the authors; a newcomer to these itineraries might consider allotting additional time to visit all of the stops described here.

The classical concept of collisional orogens suggests that mountain belts form as a crustal wedge between the downgoing and overriding plates. However, this orogenic style is not compatible with the presence of (ultra-)high pressure crustal and mantle rocks far from the plate interface in the Bohemian Massif of Central Europe. Here we use a comparison between geological observations and thermo-mechanical numerical models to explain their formation. We suggest that continental crust was first deeply subducted, then flowed laterally underneath the lithosphere and eventually rose in the form of large partially molten trans-lithospheric diapirs. We further show that trans-lithospheric diapirism produces a specific rock association of (ultra-)high pressure crustal and mantle rocks and ultra-potassic magmas that alternates with the less metamorphosed rocks of the upper plate. Similar rock associations have been described in other convergent zones, both modern and ancient. We speculate that trans-lithospheric diapirism could be a common process., Communications Earth & Environment, 2 (1), ISSN:2662-4435

Ustyansky perspective area is characterized by the combination of all favorable regional and local search prerequisites (morphological, tectonic, geological-stratigraphic, geophysical, morphometric, mineralogical) and search features, which may be due to the introduction of mantle diapir (plume) and may be accompanied by diamondiferous kimberlite magmatism. The content of the diamond indicator minerals with not distant moving: first of all, pyrope, less than picroilmenite, chrome spinel, olivine, and chrome-diopside in the alluvium of the region is 3–5 times higher than in the Zimny Bereg diamond-bearing region, and the share of G10 group diamond paragenesis pyrope is about 10%. Nine diamond crystals were found in panned samples of minimal volume from alluvial and quaternary sediments, of which six crystals (large octahedrons and dodecahedroids up to 3.8 mm in size and weighing up to 52 mg) were found in the predicted kimberlite field “Severnoye”. In terms of morphological features and physical properties, all diamonds of the Ustyansky region occupy a completely isolated position and have virtually no analogues among the diamonds of the known deposits of Arkhangelsk, Finland, the Urals and Timan. This may indicate that the crystals are coming from a new, not yet known kimberlite source (or sources). This potential new root kimberlite source may have an increased diamondiferous capacity, high quality and size of diamonds. The discovery of this new kimberlite source will be the final confirmation of the predicted isolation of the Ustyansky Region as an area of plume activity. Signs of a possible similarity between the Arkhangelsk diamondiferous province and the Yakutian diamondiferous province in terms of kimberlite location patterns and morphological features of diamond crystals confirm the high prospects for diamondiferous activities in the central regions of European Russia as a whole, and, above all, in the Ustyansky promising region with the predicted kimberlite field “Severnoye”.

Understanding triggers and evolution of post-depositional sediment intrusion is of major importance to decrease the risk associated with hazards to infrastructure and environment from events such as submarine landslides and fluid escape. Whereas deep-sourced intrusions (>1km) are widely documented, early burial examples are poorly recognized and have been described only in large deltas. Their formation had not yet been documented in deformed foredeeps. Here, we show an exceptionally well-exposed, early burial mud diapir in the Northern Apennines fold and thrust belt. Disequilibrium compaction and tectonic basin tilt led to lateral pressure migration within shallow (

[Abstract Reprocessed, regional, 2D seismic reflection profiles, 3D seismic volumes and well data (exploration and shallow boreholes), combined with 2D structural restorations and 1D backstripping were used to study the post‐salt evolution of the Nordkapp Basin in Barents Sea. The post‐salt evolution took place above a pre‐salt basement and basin configuration affected by multiple rift events that influenced the depositional facies and thickness of Pennsylvanian‐lower Permian‐layered evaporite sequence. Initially, regional mid‐late Permian extension reactivated pre‐salt Carboniferous faults, caused minor normal faulting in the Permian strata and triggered slight salt mobilization towards structural highs. The main phase of salt mobilization occurred during earliest Triassic when thick and rapidly prograding sediments entered from the east into the Nordkapp Basin. In the early‐mid‐Triassic, the change in the direction of progradation and sediment entry‐points shifted to the NW led to rotation of the earlier‐formed mini‐basins and shift of dominant salt evacuation direction to the south. The prograding sediment influx direction, sediment transport velocity and thickness influenced the dynamics of the early to late passive diapirism, salt expulsion and depletion along the strike of the basin. The basin topography resulting from salt highs and mini‐basin lows strongly affected the Triassic progradational fairways and determined the distinct sediment routing patterns. Minor rejuvenation of the salt structures and rotation of the mini‐basins took place at the Triassic–Jurassic transition, due to far‐field stresses caused by the evolving Novaya Zemlya fold‐and‐thrust belt to the east. This rejuvenation influenced the sediment dispersal routings and caused formation of dwarf secondary mini‐basins. The second and main rejuvenation phase took place during likely early‐mid‐Eocene when propagated far‐field stresses from the transpressional Eurekan/Spitsbergen orogeny to the NW inverted pre‐salt normal faults, reactivated the structural highs and rejuvenated the salt structures. The studied processes and study outcomes can be applicable to other evaporite‐dominated basins worldwide., Sequential structural restoration of an interpreted and depth‐converted section showing the supra‐salt evolution of the NENB segment in the Nordkapp Basin. The detailed temporal evolution shows the interplay between the base‐salt relief, laterally‐varying syn‐ to early post‐rift LES and prograding sediments. The models shows the salt flow direction (within and out of the plain or three‐dimensions), was influenced by the far‐field stresses during the Triassic‐Jurassic transition and early‐middle Eocene, and by the rotation of the mini‐basins. ]

The formation of mud volcanoes/mud diapirs is directly related to oil and gas accumulation and gas-hydrate mineralization. Their eruptive activities easily cause engineering accidents and may increase the greenhouse effect by the eruption of methane gas. Many scholars have performed much research on the developmental characteristics, geochemistry, and carbon emissions of mud diapirs/mud volcanoes, but the formation mechanism of mud diapirs/mud volcanoes is still controversial. Mud diapirs and mud volcanoes are especially developed in the northern South China Sea and are accompanied by abundant oil, gas, and gas-hydrate resources. Based on the mud volcanoes/mud diapirs in the northern South China Sea, the physical simulation experiments of mud diapir/mud volcano formation and evolution under different fluid pressures and tectonic environments have been performed by loading a fluid-input system in traditional sandbox simulation equipment. The genetic mechanism of mud diapirs/mud volcanoes is revealed, and a fluid-leakage model of mud diapirs/mud volcanoes under different geological conditions is established. We believe that in an overpressured environment, the greater the thickness of the overlying strata is, the greater the pressure or power required for the upward migration of muddy fluid to penetrate the overlying strata. Tectonic activity promotes the development of mud volcanos/mud diapirs. To a certain extent, the more intense the tectonic activity is, the more significant the effect of promoting the development of mud volcanoes/mud diapirs and the larger the mud diapirs/mud volcanoes become.

The Sinu fold belt, located in northwestern Colombia, is the southwesternmost part of the South Caribbean Deformed Belt, which has been interpreted as an accretionary wedge resulting from the subduction of the Caribbean Plate under the South American Plate. The geological interpretation of 2D seismic surveys and bathymetric maps, with the aid of a few exploration wells, has been the basis to construct a structural map and several geological sections to illustrate the offshore part of the Sinu Fold Belt and the portion of the Colombian Basin adjacent to the belt. Their analysis has allowed us to characterize different structural styles (thrusts and related folds in the outer part of the belt, and normal faults and shale diapirs in the inner one), the timing of the structures, as well as the kinematic evolution from a Cretaceous-Paleocene extensional event responsible for the Colombian Basin structure to the Pliocene-Quaternary contractional event which caused the Sinu Fold Belt.

The Alps are the result of the opening of the Alpine Tethyan oceanic domain during the Mesozoic and its closure during the Cenozoic. The Digne Nappe constitutes the thrust front of the southwestern branch of the Alpine arc, emplaced during Mio-Pliocene times, and uses Upper Triassic (Keuper) evaporites as a décollement level. These evaporites are also known to be involved in salt tectonics since the early Mesozoic in several locations of the Southeast of France. The aim of this work is to identify and characterise the role of the evaporites in the evolution of the Southwestern French Alps, where the evaporites were deposited prior to the Tethyan Liassic rifting which marked the beginning of the Alpine cycle. The study area is located between Remollon to the North and Digne-les-Bains to the South as this zone presents many outcrops of Liassic rocks allowing to study the impact of pre-rift salt. Field works revealed new salt structures and allowed to improve the knowledge of already known ones as the “Astoin diapiric complex” recognised since the 1930’s. This structure, active since the Liassic, developed an allochtonous advancing salt sheet in passive margin setting during Apto-Albian times. At the scale of the Digne Nappe, salt structures highlight a coeval initiation of diapirism during the Liassic triggered either by the Tethyan rifting or by downbuilding. Passive diapirism carried on during the post-rift stage controlled by downbuilding, and a few structures were still active during the Cenozoic orogeny. The latest step of diapirism was recorded during the Mio-Pliocene with the development of the Vélodrome. It is a secondary minibasin developed above an aerial salt glacier emplaced by source-fed thrust mechanism during the emplacement of the Authon – Valavoire thrust sheet, forming thus a salt front. Salt structures created an important structural inheritance forming discontinuities and weak zones in the sedimentary pile. They accommodated a part of the Alpine shortening through squeezing, preserving thus the surrounding depocenters from deformation.; Les Alpes résultent de l’ouverture du domaine océanique téthysien durant le Mésozoïque, et de sa fermeture lors du Cénozoïque. La Nappe de Digne constitue le front de chevauchement dans la partie sud-ouest de l’arc alpin. Elle s’est majoritairement mise en place durant le Mio-Pliocène utilisant les évaporites du Trias Supérieur (le Keuper) comme niveau de décollement. Ces évaporites sont également connues dans le Sud-Est de la France pour avoir formé des structures diapiriques, et ce dès le Mésozoïque inférieur. Le but de ce travail est d’identifier et caractériser le rôle des évaporites dans l’évolution des Alpes Occidentales Méridionales. Les évaporites s’y sont déposées avant le début du cycle alpin qui débute avec le rifting téthysien lors du Lias. La zone d’étude est localisée entre Remollon et Digne-les-Bains car elle présente de nombreux affleurements de Lias, permettant d’étudier l’impact des évaporites anté-rift. L’analyse de terrain a permis d’identifier de nouvelles structures salifères comme d’approfondir les connaissances sur celles déjà reconnues telles que le « complexe diapirique d’Astoin », identifié dès les années 1930. Ce complexe, actif dès le Lias, développe une nappe de sel allochtone en contexte de marge passive durant l’Apto-Albien. Á l’échelle de la Nappe de Digne, les structures salifères présentent une initiation liasique synchrone, soit sous l’impulsion du rifting téthysien, soit par le seul contrôle de la charge sédimentaire. Le diapirisme s’est poursuivi passivement durant le stade post-rift, entretenu par la charge sédimentaire, et quelques structures sont encore actives durant la compression cénozoïque. La dernière étape d’activité salifère recensée est datée du Mio-Pliocène, avec la mise en place du Vélodrome. Ce dernier constitue un minibassin secondaire déposé sur un glacier de sel, mis en place par transport des évaporites avec le toit du chevauchement de l’écaille d’Authon – Valavoire, formant ainsi un front salifère. Les structures salifères ont induit un important héritage structural, créant des zones de faiblesses et des discontinuités dans la pile sédimentaire. Elles ont accommodé une partie du raccourcissement alpin en étant resserrées, préservant ainsi les dépôtcentres adjacents de la déformation.

The termination of a deep-sea turbiditic channel represents the ultimate sink of terrigenous sediment in the oceans or lakes. Such environment is characterized by rapid slope decrease and by loss of confinement of turbidity currents. It results in the deposition of Channel-Mouth-Lobes that can be separated from the channel mouth by an erosional (scoured) or by-pass dominated Channel-Lobe Transition Zone. Several factors can control the occurrence, extent and morphologic expression of the area such as the slope break angle, the upslope and downslope angle and the mud/sand ratio in flows. Disentangling these factors remains challenging due to the scarcity of outcrops and to the usual faint morphologies and low thickness of deposits. With bathymetric and seismic data we calculated the morphometric parameters of 8 channel-levees and their Channel-Mouth Lobes from the deepest area of the Rhone fan, a mud-sand rich system, and among which the youngest one (called neofan) was deposited at the end of the Last Glacial Maximum between 21.5 and 18.3 ka cal. BP. Emplacement and shape (finger-shaped or pear-shaped bulges) of Channel-Mouth Lobes is controlled by the seabed morphology (adjacent channel-levees and salt diapirs). A less prominent morphology of the neofan is attributed to premature quiescence related to the post sea-level rise sediment starvation. We show that the occurrence and expression of a Channel-Lobe Transition Zone is controlled by the gradient upstream of the channel mouth slope break. The extended Channel-Lobe Transition Zone and detached lobe of the neofan are attributed to the high upslope gradient (0.26°) while the less detached or attached lobes of other channel-levees is attributed to lower upslope gradient (0.13°). We show that scouring and scours concatenation into flutes at the Channel-Lobe Transition Zone is a major driver for the inception of channels and further confinement of turbidity current. For the first time we show that concatenation of scours in shingled disposition developed an incipient channel sinuosity at this very early stage of channel development. The channel-levee can extend downslope nearly instantaneously by tens of kilometers when isolated nascent channels connect to the channel mouth.

In general, offshore geohazards consist of variety in geological features that contribute potential risks to human health, safety and the environment due to consequences of long or short period of geological processes. A geohazard can be defined as a geological state that may lead to widespread damage or risk. Geohazards are geological and environmental factors and involve long-term or short- term geological processes. Geohazards may have relatively small features, but they can also spread out to huge dimension so as to affect local and regional socio-economy to a large extent (Wikipedia, 2019). From the viewpoint of the oil and gas industry, geohazards mean either geological processes or factors to cause such processes that may provoke damage to the industry to risk human health, safety and the environment no matter where they are caused. Geohazards could also risk the suspension of the oil and gas production for a certain period of time. There are many type of geohazards related to offshore oil and gas developments such as "mud diapirs and volcanoes", "fault ruptures", "shallow gas", "seabed gas hydrates", "debris flow run out", "unstable slopes", "landslides", "pockmarks", "liquefaction", "turbidity current and rock outcrops" and "Methane-Derived Authigenic Carbonate (MDAC)". The geohazards can occur in the form of combination between various types of geohazards. It may cause huge damage and complicated problem to be solved. Each geohazards type has different problems solving due to different period of occurrence in geological processes. Generally, this paper will explain about the identification of gas cloud by applying several seismic attributes on specific parameter.

To suggest the impacts of diapir evolutions on the ore deposits genesis, combined mineralogical, Raman spectrometry and C-, O- and H- isotopes studies of fluid inclusions trapped by their minerals were studied. In diapir zone, the evolution of hydrothermal fluids has been distinguished: The last halokinetic stage occurred during the dominant compressive and transpressive pyrenean and Alpine collision period. The similarities observed between geochemistry characteristics of type III and ore-bearing fluids of some peridiapiric mineralizations implying that only the last hydrothermal events had contributed to the genesis of ore deposits in the diapir zone.

An article ( Zafar et al., 2020 , 372–373, 105,691) recently published in Lithos proposes new petrogenetic interpretations regarding the Chilas Complex (CC) gabbros, and collisional history of the Kohistan Island Arc (KIA). Geochemical modeling based on bulk analysis of a single rock type has led the authors to argue against the previously proposed interpretations about the (1) genesis of CC through diapirism or rift-related magmatism and (2) timing of the collision of the Indian continental plate with KIA. The authors have postulated that the CC gabbroic rocks originated as a result of the northward subduction of the Indian plate beneath the Eurasian plate at ca. 85 Ma; mature arc-type magmatism in the Neo-Tethys Ocean. The irrefutable evidence for the existence of the thousands of km thick Kohistan-Ladakh Island Arc (KLA) system and the Neo-Tethys Ocean between the Indian and Eurasian plates preclude the possibility for such subduction and direct collision in the northern territory of Pakistan. Furthermore, the geochemical signatures do not offer unequivocal evidence for arc-continent collisional setting; instead petrogenetic modeling based on a re-evaluation of Zafar et al. (2020) data favors a back-arc basin (BAB) origin for the CC gabbros and thus endorses the previously proposed BAB tectonic setting for CC. Hence a thorough investigation of the data acquired and rationality of the interpretation by Zafar et al. (2020) is warranted since it contradicts the previously proposed and generally accepted concepts regarding the genesis of CC and collision of KIA with the Indian and Eurasian plates.

Most landscapes of Iran are under the influence of structural and intrusive processes. One of these landforms is salt diapirs distributed in vast areas and has unique diversity. In fact, one of the unique and spectacular landforms of Iran is salt diapirs or salt domes. These landforms can be classified based on geographical distribution, ages, and other characteristics. All kinds of karstic features such as sink hole, cave, karen and others can be seen in the salt domes. Another spectacular feature in desert areas of Iran is meteorites which can be observed in desert area because of dryness and conserved situation. In recent years, several numbers of meteorites are explored, specifically in desert areas, and registered in the Meteoritical Bulletin of international society for meteorites and planetary science.

Romania has a long history of hydrocarbon production and tens of thousands of boreholes have penetrated Miocene strata. Many well cores or cuttings have been either lost or damaged, but lab reports containing valuable petrographic, paleontological and structural data are still available. Most of the knowledge of the subsurface relies on old descriptions and interpretations used by the oil industry. These data have not been recently updated, while research results from the last decade suggest potential changes in stratigraphy, especially for the lower to middle Miocene succession. In order to update, calibrate, and reduce uncertainties regarding the subsurface stratigraphic record, we have reviewed the lab reports and used equivalent field samples for an updated interpretation of the lower to middle Miocene succession. Core and cutting descriptions from boreholes covering an area of ~10,000 km2 in the Diapir Fold Zone of the Eastern Carpathians have been selected and biostratigraphically re-evaluated based on microfossils and calcareous nannofossils. In many cases, highly uncertain ages were previously interpreted as Oligocene and early Miocene. Our recent data suggest that most of the lower Miocene is either difficult to determine or has been reinterpreted as middle Miocene (e.g., Cornu and Doftana formations). This significant change in ages requires an updated model for the timing of regional structural evolution and may open new exploration opportunities in this highly mature hydrocarbon area. This study demonstrates the need for a new complete and reliable stratigraphic framework for the whole Miocene stratigraphic record of the Eastern Carpathians.

The base of the gas hydrate stability zone (GHSZ) is a critical interface, providing a first-order estimate of gas hydrate distribution. Sensitivity to thermobaric conditions makes its prediction challenging, particularly in the regions with dynamic pressure–temperature regime. In Green Canyon Block 955 (GC 955) in the northern Gulf of Mexico, the seismically inferred base of the GHSZ is 450 m (1476 ft) below the seafloor, which is 400 m (1312 ft) shallower than predicted by gas hydrate stability modeling using standard temperature and pressure gradient assumptions and an assumption of structure I (99.9% methane gas) gas hydrate. We use three-dimensional seismic log data and heat-flow modeling to explain the factor of the salt diapir on the observed thinning of the GHSZ. We also test the alternative hypothesis that the GHSZ base is actually consistent with the theoretical depth. The heat-flow model indicates a salt-induced temperature anomaly, reaching 8°C at the reservoir level, which is sufficient to explain the position of the base of the GHSZ. Our analyses show that overpressure does develop at GC 955, but only within an approximately 500-m (∼1640-ft)-thick sediment section above the salt top, which does not currently affect the pressure field in the GHSZ (∼1000 m [∼328 ft] above salt). Our study confirms that a salt diapir can produce a strong localized perturbation of the temperature and pressure regime and thus on the stability of gas hydrates. Based on our results, we propose a generalized evolution mechanism for similar reservoirs, driven by salt-controlled gas hydrate formation and dissociation elsewhere in the world.

It is conventionally believed that magma generation beneath the volcanic arc is triggered by the infiltration of fluids or melts derived from the subducted slab. However, recently geochemical analyses argue the arc magma may be formed by mélange diapirs that are physically mixed by sediment, altered oceanic crust, fluids, and mantle above the subducted slab. Further numerical modeling predicts that the mantle wedge diapirs have significant seismic velocity anomalies, even though these have not been observed yet. Here we show that unambiguously later P-waves scattered from some obstacles in the mantle wedge are well recorded at a dense seismic array (Formosa Array) in northern Taiwan. It is the first detection of seismic scattering obstacles in the mantle wedge. Although the exact shape and size of the scattered obstacles are not well constrained by the arrival-times of the later P-waves, the first order approximation of several spheres with radius of ~ 1 km provides a plausible interpretation. Since these obstacles were located just beneath the magma reservoirs around depths between 60 and 95 km, we conclude they may be mantle wedge diapirs that are likely associated with magma generation beneath active volcanoes.

Arzacq and Tartas were two Cretaceous basins developing in the Bay of Biscay as secondary depocentres in the larger Aquitaine Basin. They belong to an Albian rift system, where recent studies have stressed the role of simple-shear thinning on the genesis of regional asymmetric basins. However, the two basins differ from recent models in having a pseudo-symmetric morphology. Here, we address the Early Cretaceous tectono-sedimentary evolution of the Arzacq and Tartas rift basins and the lithospheric processes associated with their genesis. These basins did not suffer major brittle deformation during rifting stage, but nevertheless record a major change in their configuration between the Aptian and the Albian. The Arzacq Basin shifted from a symmetric to a slightly asymmetric configuration. This change was controlled by gravity sliding of the pre-rift sedimentary cover in the eastern Arzacq Basin moving its depocenter south, and by salt diapirism in the western Arzacq Basin moving its depocenter north. Several inherited Paleozoic structures were reactivated as transfer zones and appear to be responsible for this depocenter shift, the emplacement of salt diapirs, at same time regionally limiting gravity sliding. The Tartas Basin maintained a symmetric regime throughout the Early Cretaceous, except along the Barlanes transfer zone where the Lussagnet salt diapir originated. Two drivers of subsidence are thus envisaged in the Arzacq Basin: a Neocomian-Aptian crustal thinning stage, followed by reactivation of Paleozoic faults in Albian time accompanied by salt diapirism and gravity cover sliding. The Mauleon North Pyrenean Basin and its north adjacent Tartas and Arzacq basins thus formed part of a series of rift basins that progressed in maturity southward, from a simple sag basin (Tartas) to a slightly asymmetric basin (aborted detachment, Arzacq) to a hyperthinned basin (Mauleon). Our results offer new insights on the role of: (1) structural inheritance in partitioning extensional strain, (2) transfer zones as able to influence the sedimentary record of basins during crustal thinning, and (3) pre-rift salt decollements as able to separate the structural styles of sub- and supra-salt successions.

The onshore Lusitanian Basin is dominated by two large diapiric salt walls which extend for up to 100 km. Seismic sections indicate that stratal onlap onto an intervening salt pillow initiated in Early Jurassic times. Well-exposed diapir flanks reveal three types of halokinetic-related unconformities (hook, low-angle wedge and high-angle flap-onlap – a new term) of Kimmeridgian to Turonian age, indicating that diapirism was active throughout this period. Stratal dip-fanning and wedge-thinning is predominantly caused by original sedimentary depositional processes with multiple low-angle unconformities (1°–5° pinchout angles) in both carbonate- and clastic-dominated sequences. No significant sedimentary slumping was observed in the clastic-dominated strata but important slumping of flank material is present in the carbonate-dominated sequences. Two tar accumulations are derived from oil trapped in sandstones on the flanks of the Sao Pedro de Moel and Santa Cruz salt diapirs. These are interpreted to be exhumed, but now biodegraded, oilfields. To our knowledge, these are the only exposed examples of salt-flank hydrocarbon accumulations that have been documented in the literature.

The composition of the Earth's core and mantle is set by the chemical equilibrium between metals and silicates during core/mantle segregation. The metallic core separated from the mantle by gravitational descent in the form of diapirs in a magma ocean, and therefore the dynamics of the diapir's downward movement has an influence on the chemical equilibrium. In this study, we characterize the descent of metallic droplets into a molten silicate using numerical models. By varying the silicate and metal viscosities (between 0.1 and 1000 Pa·s for each phase) as well as the partition coefficient between metal and silicate (Dmet/sil, varying between 1 and 1000), we obtained quantifying parametrizing equations for the degree of equilibrium between molten metal and molten silicate, in a regime characterized by low We (We < 10) and low Re (10−3 < Re

The Coastal Fars sub-basin located in the Zagros Fold-Thrust Belt contains giant hydrocarbon fields. The existence of hydrocarbon micro-seepage on the surface can be an important indicator for the presence of oil and gas in subsurface formations. So the leakage of hydrocarbon micro-seepage to the surface leads to the alteration of some of the rocks and minerals and causes numerous effects on the surface. Therefore, by detecting these alterations, hydrocarbon seeps in the surface can be recognized. This study aims to investigate the hydrocarbon micro-seepage and its relationship with the structures of the western part of the Coastal Fars sub-basin. For this purpose, the Advanced Spaceborne Thermal Emission and Reflection Radiometer satellite images and remote sensing techniques, such as the band ratio method and the band ratio composite were used as effective tools for detecting alterations due to hydrocarbon micro-seepage. The comparison of the obtained results with surface and subsurface data indicates that there is a close relationship between the amount of hydrocarbons available in the reservoirs and the frequency of micro-seepages at the surface. Also, important structures of the region, such as Dashti strike-slip fault and salt diapirs, have affected the distribution of hydrocarbon micro-seepage and hydrocarbon reservoirs. Among these structures, the Darang buried salt diapir has played a destructive role and caused the evacuation of the reservoir, while Dashti emergent salt diapir has a positive impact on hydrocarbon accumulation.

We present a new seismic reflection dataset and use it to characterize fossil mud volcanoes in the southwestern Songliao graben basin in northeastern China. The results reveal a link between mud volcanism and slab rollback along the eastern Asian margin. This study focuses on the upper 3 km of the Lujiapu sub-basin, which lies in the southwestern Songliao basin. The base of the sequence consists of Lower Cretaceous siliciclastic deposits that are penetrated by mud volcano fluidization pipes. These deposits are overlain by Upper Cretaceous strata that have been deformed by the mud volcanoes. The sequence is capped by undeformed Neogene–Quaternary sediments. These observations constrain the timing of mud volcanism to the Santonian–Campanian (~87–72 Ma). During Late Cretaceous diapirism, normal faulting at the tops of the mud volcanoes formed horsts and grabens. Surface anticlines and inversion structures near the mud volcano source layer indicate that basin inversion occurred during deposition of the Sifangtai and Mingshui formations (Campanian). Similar structures are also identified in the central Songliao basin. Thus, we propose that slab flattening to deepening during paleo-Pacific Plate subduction led to basin inversion. This process triggered the migration of high-pressure fluids and brecciated plastic rocks along pre-existing normal faults, which in turn produced the mud volcano system.

The Barreme Basin and the Gevaudan diapir - an example of the interplay between compressional tectonics and salt diapirism Adam Csicsek and Rod GrahamImperial College London Our understanding of the role of salt diapirism in determining the finite geometry of fold and thrust belts has grown apace in the last few years, but the interplay between the two remains a significant problem for structural interpretation. The Gevaudan diapir in the fold and thrust belt of the sub-Alpine chain of Haute Provence is well known and has been documented by numerous eminent alpine structural geologists. Graciansky, Dardot, Mascle, Gidon and Lickorish and Ford have all described and illustrated the geometry and evolution of the structure, and Lickorish and Ford’s interpretation is figured as an example of diapirism in a compressional setting by Jackson and Hudec in their text on salt tectonics. We review these various interpretations and present another.The differences between the various interpretations say much about the complex interplay of salt diapirism and thin-skinned thrusting and have profound implications for the way we interpret the tectonic and sedimentary evolution of the Barreme basin which lies adjacent to the diapirThe Barreme basin is a thrust-top fragment of the Provencal foreland basin and has been described in detail from both sedimentological (e.g. Evans and Elliott, 1999) and structural (e.g. Antoni and Meckel, 1997) points of view. Here we make the case that it is also a salt related minibasin - a secondary minibasin developed on a now welded allochthonous Middle Cretaceous salt canopy. We believe that within the basin it is possible to interpret successive depocentres which may record progressive salt withdrawal. We argue that though thrust loading must be the fundamental driving mechanism responsible for salt movement late in the tectonic history of the region, thrusting has not done much more than modify existing salt related geometry.

Cold seeps occur where fluids, such as hydrocarbons, migrate from depth and escape at the seabed. They are relatively common features in petroleum basins around the world. Cold seeps often host unique biological communities and are a potential geological hazard as they can indicate excess pore fluid pressures in shallow sediments. In addition, they can provide critical information about fluid migration pathways and fluid source. This study presents the detailed geomorphology and seismic stratigraphy of recently discovered cold seeps in 2700 metres water depth offshore Nova Scotia, Canada. Petroleum industry 3D seismic reflection data, high-resolution single channel G.I. gun and sparker seismic reflection data, Autonomous Underwater Vehicle (AUV) sidescan, swath bathymetry, and sub-bottom profiler data were used to investigate the geomorphology of the cold seep and surrounding seabed. Piston core samples and seabed photography were also acquired in the study area.The geomorphology in the study area is dominated by the seafloor expression of a salt diapir (L. Triassic to E. Jurassic). Despite being buried by ~1700 m of Cretaceous to Holocene sediment, the diapir forms an oblong mound, 10 km long by 5 km wide that rises 200 m above the surrounding seabed. Two major orthogonal faults are apparent on the seabed that cut the mound along its major and minor axes. Several crestal faults are imaged in the 3D seismic data but do not have a seabed expression. AUV data acquired over the crest of the diapir reveal a 500 m by 200 m fissure on the western flank of the diapir. The fissure is composed of a blocky central zone along its axis, and radiating “cracks” that show backscatter variation, possibly indicating recent fluid expulsion. Integration of the AUV data with the 3D seismic data show that the fissure is fed by a vertical chimney that intersects a bottom simulating reflection above the diapir. Remarkably, the chimney does not appear to be related to any of the sub-vertical crestal faults. Another seep occurs on the eastern flank of the diapir crest and, in contrast, coincides with a crestal fault. There is also evidence for mass wasting down-dip from the fault. Core samples recovered from the second seep contained gas hydrate. In both cases, the cold seeps present as very subtle features on the 3D seismic reflection data and are only positively identified in the AUV datasets. This study shows that conventional surface-acquired acoustic data are potentially insufficient for detecting cold seep morphologies in deep-water settings.

We present the first high resolution seismic images illuminating the hitherto-elusive crustal architecture beneath the Eastern Ghats Mobile Belt (EGMB) using teleseismic receiver functions. Data were collected using 27 broadband seismic stations operated in a continuous mode covering two distinct seismic profiles (~550 km long) during 2015–2018. Several interesting observations and inferences are made through analysis of the receiver functions such as (a) a very thick crust (>40 km) with oppositely dipping Moho beneath the EGMB and Archean Bastar Craton, (b) EGMB formed from amalgamation of different crustal domains thrust over one another possibly during the Pan-African orogeny, (c) the Archean Bastar Craton crust extends (~75 km) eastward beneath the EGMB, from its surficial geological boundary, (d) there is a sharp contrast in the crustal structure (with ~20 km Moho offset) at the contact between the Rengali Province and Singhbhum Craton which does not support southward growth of the Singhbhum Craton through accretion, (e) anorthosite complexes may possibly be created by rising diapirs channeled through the weak zones in the crust, from the magma chambers developed by melting of frontal portion of the underthrusting lower crust. We report a significant change in the crustal architecture just east of the most elevated topography observed along the profile covering the Bastar Craton and the EGMB. It requires further careful petrological investigations to ascertain the relationship of high elevation and its linkages with the deep crust, forming a separate domain. Our results do not support or discard a Grenvillian age (~1 Ga) docking of the EGMB with Proto-India, though it is preferred to explain the present day crustal features with intense Pan-African (0.5–0.6 Ga) reorganization.

In the easternmost part of the European Variscan collisional belt, the Bohemian Massif, strongly metamorphosed felsic rocks crop out at several locations in a current distance of up to several hundreds of kilometers from the supposed contact of the subducting and overriding plates. These rocks were interpreted to originate from the subducting plate (now the Saxothuringian domain), which means that the orogenic root (the Moldanubian domain) consists of rocks that originate from both upper and lower plate. More specifically, the root domain is composed of (U)HP granulites and orthogneiss, garnet peridotites, eclogites and ultra-potassic plutons that alternate with the less metamorphosed rocks of the upper plate.Such a process of subduction and emplacement of the subducted crust into the upper plate is called relamination. In order to better constrain the dynamics of relamination, we set up a numerical thermal-mechanical model and compare the modeling results with the data from the Bohemian Massif. The model simulates oceanic and continental subduction and takes into account non-linear visco-plastic rheology, percolation of fluids, melting and melt extraction. For different parameter values, the models show different styles of behavior, namely (i) exhumation of the subducted crust along the plate interface, and (ii) flow of the subducted crust beneath the upper plate and then incorporation into its crust (i.e. relamination).In the former case, the material records heterogeneous peak metamorphism sampling the conditions along the subduction zone, and cooling during decompression. Similar features are typical for the metamorphic complex in the Saxothuringian domain of the Bohemian Massif.In the latter case, the typical feature is the development of diapirs that grow from the subducted continental crust, pierce the overlying lithosphere and intrude into the middle crust of the upper plate. We show that growth of such trans-lithospheric diapirs results in a similar rock assemblage as observed in the orogenic root in the Bohemian Massif. The pressure-temperature-time paths obtained in the modeled diapirs mimic those of the Moldanubian granulites. The flow of crustal material through the mantle wedge results into mixing, hydration of the mantle and melting of both materials. Emplacement of the resulting melt into crust can explain formation of the Moldanubian ultra-potassic plutons.