Salt diapir Research Papers - Academia.edu (original) (raw)

We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show highreflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (, 1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data. We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km 2) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as 'chimney' features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. Published by Elsevier Science Ltd.

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- Geology, Geophysics, Gas Hydrate, Salt diapir

One of the main salt basins in South Arabia is located in the southern part of Yemen, along the edges of Ramlat as-Sabʿatayn. This basin, some 600 km long and 100 km wide, shows diapiric walls orientated northwest-southeast, from the Indian Ocean to the Jawf. The salt-mines follow a long line west of Ḥaḍramawt cliffs (Jawl) and north of Jabal al-Nisiyīn. Salt-mines are sometimes located at the tail of main wādīs, such as Wādīs ʿIrmā/ʿAṭf, Jirdān, Ḥammām and Bayḥān. Salt was probably a small-scale production, feeding a local and regional trade in antiquity.
In Northern Tihâma, salt mines around as-Salîf were known to exist in the medieval period.
In the Afar depression on the western side of the Red Sea, salt traded to Highlands.

The emergent salt domes of the United Arab Emirates (UAE) have been investigated in detail and examples from central Oman have been studied for comparison. The salt domes contain exotic clasts of igneous, sedimentary and low-grade metamorphic rocks of the Arabian basement that have been brought to the surface from depths of over 8 km. The clasts thus provide an opportunity to examine the lithology, geochemical composition and age of the "basement" underlying this part of eastern Arabia, where no other outcrops are available for direct study. Five volcanic rocks give consistent latest Ediacaran U-Pb zircon crystallisation dates of ca. 560-545 Ma, with Neoproterozoic, Palaeoproterozoic and Neoarchaean ages of inherited zircons. These rocks, although strongly altered, preserve geochemical characteristics compatible with formation in a within-plate, extensional setting along the northern edge of Gondwana, adjacent to Prototethys. U-Pb analyses of detrital zircons in sedimentary and low-grade metamorphic rocks indicate deposition younger than ca. 597 Ma in UAE and <734 Ma in Oman. The two UAE sedimentary rocks may correlate with the Shuram and Khufai Formations of the Nafun Group (Huqf Supergroup) in Oman. Like the volcanic rocks, the two sedimentary samples from the UAE show derivation from the erosion of Neo-, Palaeoproterozoic and Neoarchaean sources. These sources could be from the Arabian basement itself or from other basement blocks such as those embedded in present-day Iran and Afghanistan, the precise whereabouts of which in Neoproterozoic times remains somewhat uncertain. The zircon age spectra of samples from the UAE show Neoproterozoic age peak characteristics of sources from both the western and eastern Arabian basement blocks, indicating that the two segments were juxtaposed by about 597 Ma, the maximum age of their deposition.

- by Bob Thomas
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- Earth Sciences, Geochronology, Sedimentary provenance, Salt diapir

Damien Closson, Abou Karaki N., Nada Milisavljević, Frédéric Hallot, and Marc Acheroy, 2011, Salt Tectonics of the Lisan Diapir Revealed by Synthetic Aperture Radar Images, in Tectonics, Damien Closson(Editor), Publisher: InTech,... more

- by Najib ABOU KARAKI and +2
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- Tectonics, Jordan, Subsidence, Salt diapir

Formation of salt diapirs has been described to be due to upbuilding (i.e. Rayleigh-Taylor like instability of salt diapirs piercing through a denser sedimentary overburden) or syndepositional down-building process (i.e. the top of the salt diapir remains at the surface all the time). Here we systematically analyse this second end-member mechanism by numerical modelling. Four parameters are varied: sedimentation rate vsed, salt viscosity ηsalt, amplitude δ of the initial perturbation of the sedimentation layer and the wavenumber k of this perturbation. The shape of the resulting salt diapirs strongly depends on these parameters. Small diapirs with subvertical side walls are found for small values of vsed and ηsalt or large values of δ, whereas taller diapirs with pronounced narrow stems build for larges values of vsed and ηsalt or small values of δ. Two domains are identified in the four-parameter space, which separates successful down-building models from non-successful models. By applying a simple channel flow law, the domain boundary can be described by the non-dimensional law ?, where ? is the sediment density scaled by the density contrast Δρ between sediment and salt, the wavelength is scaled by the salt layer thickness hsalt, and velocity is scaled by ηsalt/(?Δρg), where ηsalt is the salt viscosity and g is the gravitational acceleration. From the numerical models, the constants C1 and C2 are determined as 0.0283 and 0.1171, respectively.

- by Hemin Koyi
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- Geology, Geophysics, Mechanics, Theory

The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguía diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.

- by Geologica Acta and +1
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- Earth Sciences, Geochemistry, Hydrogeology, Mineralogy

Despite numerous studies examining salt tectonics, relatively little is known regarding the internal movements of salt units that build diapirs such as the Mount Sedom salt wall. In this study we focus on the recent deformation processes of southern Mount Sedom. We choose a fossilized dissolution surface known as the "salt mirror" of Mount Sedom as a structural datum, in order to understand and resolve the deformation processes during the last 14 ka. Surveying the salt mirror surface from outcrops and natural dissolution "chimney" caves, sets constraints for the structural map. Our results indicate that the salt wall rises as a telescopic antenna, with the internal salt units sliding across each other along bedding-plane slip faults, influenced by the subsiding Dead Sea basin. The flow of the rising salt forms an elongated ridge, distinctly asymmetric across its short dimension. The uplift rate of the Southern part of Mount Sedom throughout the last 14 ka is at least 11 mm/yr. This result is somewhat higher but in a fair agreement with the results of previous studies that assessed the rates in a variety of methods. The telescopic behavior of the salt wall represents a mode of internal deformation that might be applicable to other salt diapirs worldwide.

- by Amos Frumkin
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- Salt diapir, Dead Sea Fault, Salt Dissolution

In diapir flanks, unconformity-bounded sedimentary packages associated with gravity-driven deposits, controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences. The Bakio Breccias Formation (Basque Country, Spain) corresponds to redeposited carbonate deposit that developed in response to the Bakio diapir growth during the Middle Albian. These deposits provide on of the rare documented example of carbonate dominated halokinetic sequences. The Bakio Breccias Formation consists of an alternation of clast- and matrix-supported breccias, calcirudite, calcarenite and marl, deposited along the flanks of the diapir. The description and the analysis of the Bakio Breccias Formation lead to a new model for carbonate-dominated halokinetic sequences. These sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs, while sediments are preferentially deposited in the mini-basins adjacent of the diapirs, in siliciclastic settings. During transgressive system tract, carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs, forming thick and resistant roof, which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities (wedge halokinetic sequences). During late highstand system tract deposition (and lowstand system tract if present), platform progradation results in high sediment accumulation in the adjacent depocenters, loading the autochthonous salt layer and promote diapir growth and creation of topographic relief. In addition, if the diapir roof reaches emersion, karstification of the carbonate platform top may also favour roof destruction and diapir growth. Depending on the thickness of the roof developed previously and the amplitude of the sea level fall, the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities (hook halokinetic sequences). Furthermore, gravity-driven deposits are assumed to be more common in carbonate-dominated halokinetic sequences, compared to their siliciclastic counterparts, since carbonate platform aggradation creates steep slopes on the diapir margins, leading to the partial collapse of the margin, even when limited diapir growth occurs. The carbonate-dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution, seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed.

- by yohann poprawski
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- Salt diapir, Carbonates, Halokinesis, Mass Transport Deposits

Based on old detailed mining maps and own observations in the Hallstatt salt mine, we reinterpret the structure of the Hallstatt evaporite body of the Upper Permian to Lower Triassic Haselgebirge Fm. within the Northern Calcareous Alps (NCA). The Haselgebirge Fm. represents a rocksalt mylonite with abundant lenses of sulphates, mudstones and limestones. In comparison to published results of analogue modeling we interpret the present shape of the Hallstatt body as a WNW-ESE elongated compressive teardrop-like diapir. This is overprinted by NNE-SSW shortening and dominantly sinistral shearing along a W-trending shear zone. The internal structure shows steeply dipping rock units and foliation. Earlier dextral ductile shear fabrics of likely late Early Cretaceous age are preserved in sulphate rocks and are subsequently overprinted by mylonitic fabrics in rocksalt and cataclastic fabrics in other rocks. The low strength of halite results in recent subvertical shortening and a strain rate of 8 x 10-10 [s-1 ] is deduced from deformed subhorizontal boreholes. This value is similar to such strain rates (10-10 to 10-9 s-1) estimated by the halite grain size distribution from other salt mines in the NCA and thus indicative of sub-recent formation of the halite microfabrics. 1. Introduction Within mountain belts, evaporite bodies tend to develop complex shapes because of the superposition of several sequential deformation events. Evaporites of mountain belts are usually deposited in the rift stage of passive continental margins at the transition from initial terrestrial to subsequent shallow marine conditions. This predates the plate-tectonic drift stage at ocean margins. Because of the early deposition and the low strength of halite, many evaporite layers are deformed by raft tectonics during the drift stage (e.g., Butler and Paton,

- by Anja Schorn
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- Geology, Structural Geology, Salt diapir, Shear Zone

Very-high-resolution (VHR) seismic and magnetic investigations were carried out over a chemical munition dumpsite in the Bornholm Basin, southwestern Baltic Sea. The main goal of the investigations was to image the shallow internal structure of the dumpsite and to map the lateral and vertical distribution of the dumped war material. The shallow geology was imaged in great detail on the seismic data. Seven seismicstratigraphic units were identified, related to different stages in the Holocene and late-glacial history. A large number of diapir-like features were observed that most likely represent fluid expulsion phenomena. Four shipwrecks were identified in the dumpsite area. The wrecks have partly sunk into the soft upper sediments, their height above the sea floor reaching no more than 2 m. Seismic and magnetic data indicate the presence of a large number of buried objects. In most cases there is a good correlation between the seismic and magnetic data sets. The objects are generally buried no deeper than 1 to 2 m. Their size varies between 1.5 and 5 m, occasionally up to 10 m. Shallow pits in the sea bed are likely due to the impact of dumping. The data confirm the wide variety of dumped war material ranging from bombs and shells to encasements and containers. The distribution of the buried objects seems rather heterogeneous, with locally high object concentrations surrounded by areas of lower object density. The results of this case study demonstrate the benefit of complementary, concurrent geophysical investigations for munition dumpsite research. Finally this will yield a better assessment of the current status of the dumpsite and the possible ecological risks related to the dumped war material.

- by Tine Missiaen
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- Geophysics, Case Studies, Density, Concentration

The Triassic rocks of the Debadib-Ben Gasseur area (northwestern Tunisia): diapir with overhangs spreading downslope in the Albian Sea and deformed during the Tertiary compressional deformations. The Triassic outcrops of the Debadib-Ben Gasseur area, located in the Kef area (northwestern Tunisia) have recently been interpreted as submarine 'salt glaciers' interbedded within the Albian deposits (J.-M. Vila et al., C. R. Acad. Sci. Paris, Ser. II 318 (1994) 1661-1667). New cartographic, drills and gravimetric data recognised evidence for an Albian diapiric stage for the Triassic rocks. The Triassic rocks as pulling out of the sedimentary cover could spread laterally as small size 'salt glaciers' before they have been deformed during the Tertiary compressional deformations. To cite this article: M.

- by Chokri Jallouli
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- Cartography, Geology, Salt diapir, Cretaceous

Chalk is exposed in the Heidestrasse quarry at Lägerdorf, at the top of the NE-SW trending Krempe salt ridge. Structural data indicate the presence of two joint sets, striking almost parallel and perpendicular to the salt ridge, respectively, and of a set of conjugate extensional faults and fault zones striking NW-SE, i.e. almost perpendicular to the salt ridge. Within the overall NW-SE trend of joints and faults, strike variations occur from the massive chalk exposed in the lower half of the quarry, to the overlying layered chalk. A large variability characterizes the normalized spacing of both joint sets, which does not show any clear trend with layer dip. In situ measurements indicate that the cross-sectional permeability of tight joints increases 1e2 orders of magnitude with respect to the undeformed chalk. We propose that joint and fault azimuthal variability resulted from changes through time of the stress ellipsoid at the top of the salt ridge, while joint spacing variability is associated with the weak mechanical influence of bedding in chalk. Azimuthal variability improves fracture connectivity and, hence, permeability and fluid flow.

- by Fabrizio Storti
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- Geology, Geophysics, Structural Geology, Stress field

Spring waters, with a high salt content (390 g/l) and a strong pungent odor, were collected from the flanks of the Mt Scdom diapir near the Dead Sea and analyzed for low molecular weight (LMW) mono-and di-carboxylic acids, lipid class compounds and dissolved organic carbon. Concentrations of LMW carboxylic acids were found to be very high (C~9 monoacids: 305 mgC/l, C2-C9 diacids: 27 mgC/l). The dominant species is acetic acid (220 mgC/l) followed by propanoic (49 mgC/1), succinic (18 mgC/l) and methylpropanoic acid (11 mgC/l). These organic acids comprised major portions of dissolved organic carbon (DOC: 480 mgC/l) of the hypersaline brine: monoacids contribute 64% of IX)C and diacids 5.4%. Volatile organic acids such as acetic, propanoic, butyric and valeric acids were found to be the source for the pungent smell of the spring water. These organic acids were most likely produced in a deeply buried block of the Upper Cretaceous bituminous chalks in the Dead Sea Rift Valley by thermal alteration of the organic matter and were transported upward to the surface together with connate brines along the margins of the diapir. The monoacid/diacid proportions in the brine water and the predominance of oxalate in the precipitates from the brines suggested a selective removal of dicarboxylic acids by forming organic salt precipitates such as calcium oxalate during upward transport of the brines to the surface.

- by Arie Nissenbaum
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- Earth Sciences, Organic Geochemistry, Israel, Middle East

Mass-wasting on the Brazilian margin during the Mid-Eocene/Oligocene resulted in the accumulation of recurrent Mass Transport Deposits (MTDs) offshore Espírito Santo, SE Brazil. In this paper, we use three-dimensional seismic data to characterize a succession with stacked MTDs (Abrolhos Formation), and to assess the distribution of undeformed stratigraphic packages (i.e. turbidites) with reservoir potential separating the interpreted MTDs. High-amplitude strata in less deformed areas of MTDs reflect their internal heterogeneity, as well as possible regions with a higher sand content. Separating MTDs, turbiditic intervals reach 100 ms Two-Way Travel Time (TWTT), with thicker areas coincident with the flanks of growing diapirs and areas of the basin where mass-wasting is less apparent. Turbiditic strata laterally grade into, or are eroded by MTDs, with transitional strata between MTDs and turbidites being also influenced by the presence of diapirs. MTDs show average thickness values ranging from 58 to 82 ms TWTT and constitute over 50% of Eocene-Oligocene strata along the basin slope. Low average accumulations of 58 ms TWTT in areas of high confinement imposed by diapirs suggest sediment accumulation upslope, and/or bypass into downslope areas. This character was induced by the high sediment input into the basin associated with coastal erosion and growth of the Abrolhos volcanic plateau. Our results suggest that significant amounts of sediment derive from the northwest, and were accumulated in the middle-slope region. Interpretations of (palaeo)-slope profiles led to the establishment of a model of margin progradation by deposition of MTDs, contrasting with the retrogressive erosional margins commonly associated with these settings.

- by Davide Gamboa
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- Marine Geology, Brazil, Salt Tectonics, Exploration Geophysics

Acad6mie des sciences / iditions scientifiques et mkdicales Elsevier SAS. Tous droits kserv6s. Oceanographic / Oceanograph (Ceologie marine / Marine Geo r ogy) Le cane sous-marin profond du Nil : principaux rhltats de la campagne Prismed... more

- by Jean Mascle
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- Salt diapir, Salt, Evaporites, Debris Flow

I review salt production as it occurs naturally, some methods of extraction, and historical evidence for its production and use in Saudi Arabia and Yemen. Ancient Israel was aware of such methods and produced salt, as did Mesopotamia. Evidence for trade routes from Saudi Arabia and Yemen to Israel, allowing for the possibility of salt trade, is reviewed. I conclude that Iron Age Judah and Israel produced their own salt, and did not import from Saudi Arabia and Yemen.

- by Barnea Levi Selavan
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- Archaeology, Saudi Arabia, Yemen, History of salt, Archaeology of salt
- by Antonio Vazquez
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- Geology, Stratigraphy, Subsidence, Sedimentary Basins

- by Tine Missiaen
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- Geophysics, Case Studies, Density, Concentration

An international research cruise named Iatá-Piuna took place on the São Paulo Plateau on May 2013 in the Campos and Espírito Santo basins, off Brazil. The cruise was carried ou on board the research vessel (R/V) Yokosuka that hosts the human operated vehicle (HOV) SHINKAI 6500. It aimed at finding chemosynthetic communities, composed of organisms capable of generating their own vital energy by metabolizing organic and inorganic compounds related to seeps. Identification of these organisms could provide information for understanding the origin of life, since they may resemble primitive organisms that existed in the initial stages of life on Earth. During Leg 2 (May 10-24, 2013), however, dives on the northern part of the São Paulo Plateau at the Espírito Santo Basin led to the discovery of a giant oil seep. The seep, ca. 3 nautical miles (ca. 5.6 km) in length is located along an outcrop of Eocene rocks on a salt-induced escarpment of the plateau and at a water depth of ca. 2700 m. The 200 m relief of the seafloor suggests that the seep takes place along an active fault system driven by salt diapirism. The oil was analyzed and identified as a severely biodegraded marine oil, generated by carbonate rocks within a minibasin located to the east of the escarpment. This represents valuable exploratory information because it proves that an active petroleum system is present in the context of minibasins associated with salt diapirism in the area.

- by Juliana Iemini
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- Geology, Geochemistry, Oceanography, Sedimentology

An international research cruise named Iatá-Piuna took place on the São Paulo Plateau on May, 2013 in the Campos and Espírito Santo basins, off Brazil. The cruise was carried ou on board the research vessel (R/V) Yokosuka that hosts the human operated vehicle (HOV) SHINKAI 6500. It aimed at finding chemosynthetic communities, composed of organisms capable of generating their own vital energy by metabolizing organic and inorganic compounds related to seeps. Identification of these organisms could provide information for understanding the origin of life, since they may resemble primitive organisms that existed in the initial stages of life on Earth. During Leg 2 (May 10–24, 2013), however, dives on the northern part of the São Paulo Plateau at the Espírito Santo Basin led to the discovery of a giant oil seep. The seep, ca. 3 nautical miles (ca. 5.6 km) in length is located along an outcrop of Eocene rocks on a salt-induced escarpment of the plateau and at a water depth of ca. 2700 m. ...

- by Nolan Maia Dehler
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- Geochemistry, Oceanography, Sedimentology, Brazil

ABSTRACTThe Murotomisaki Gabbroic Intrusion is a sill-like layered gabbro emplaced in sedimentary strata of Tertiary age in southwest Japan. The zoning (including resorption structures) and the compositional variations of plagioclase from throughout the intrusion were studied, and it was found that the zoning pattern may be classified into four types, which may well correlated with the hosting rock types, the mode of occurrences and their stratigraphic positions in the intrusion. The plagioclase zoning was successfully decoded, and the sequence of events that took place during the magmatic differentiation was deduced and further interpreted in the context of a stratified basal boundary layer slowly ascending in a solidifying magma body. It was shown that various layered structures – modal layering, podiform gabbroic pegmatites and anorthositic layers – observed in the Murotomisaki Gabbro were formed within the moving basal boundary layer by flushing of H2O-rich fluid and fractionate...

- by takashi hoshide
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- Earth Sciences, Salt diapir, Anorthosite, Magma Chamber

Iran has a various salt structures that their tectonic geomorphology is subject of this paper. Geologic situation of salt structures in Iran have determinate. According to age and geological setting of salt deposits that revealed by tectonic geomorphology methods, salt structure provinces of the Central and Southern Iran have been distinguished. Also, critical concepts of salt diapirism in the Southern Iran and Central Iran salt basins have explained. Therefore, Central Iran's salt diapirs have triggered by tectonic forces, but salt diapirism in the Southern Iran has triggered by halokinesis, then it has effected by tectonic forces, especially in Zagros fold and thrust belt.

- by Mehran Arian
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- Salt diapir

Formation of salt diapirs has been described to be due to upbuilding (i.e. Rayleigh-Taylor like instability of salt diapirs piercing through a denser sedimentary overburden) or syndepositional down-building process (i.e. the top of the salt diapir remains at the surface all the time). Here we systematically analyse this second end-member mechanism by numerical modelling. Four parameters are varied: sedimentation rate v sed , salt viscosity η salt , amplitude δ of the initial perturbation of the sedimentation layer and the wavenumber k of this perturbation. The shape of the resulting salt diapirs strongly depends on these parameters. Small diapirs with subvertical side walls are found for small values of v sed and η salt or large values of δ, whereas taller diapirs with pronounced narrow stems build for larges values of v sed and η salt or small values of δ. Two domains are identified in the four-parameter space, which separates successful down-building models from non-successful models. By applying a simple channel flow law, the domain boundary can be described by the non-dimensional law v sedcrit = C 1 1 2 δ 0 ρ sed k 2 k 2 +C 2 , where ρ sed is the sediment density scaled by the density contrast ρ between sediment and salt, the wavelength is scaled by the salt layer thickness h salt , and velocity is scaled by η salt /(h 2 salt ρg), where η salt is the salt viscosity and g is the gravitational acceleration. From the numerical models, the constants C 1 and C 2 are determined as 0.0283 and 0.1171, respectively.

- by Lukas Fuchs
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- Numerical Modelling, Salt diapir, Diapirism
- by Peter Klint K Jensen
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- Salt diapir, Subsurface temperature

The term cataclastic diapirism is proposed for the low-temperature extrusion of highly fractured rocks through more competent strata to produce domed topographies at the surface. The process is illustrated by reference to the geomorphology, neotectonics and microseismicity of the Pie de Palo, an elongated ridge in the western Sierras Pampeanas of Argentina composed of shattered and sheared Lower Palaeozoic rocks and subject to coseismic uplift. The Pie de Palo is conventionally interpreted as a fault-driven basement fold linked to low-angle eastward subduction of the Nazca plate beneath South America; the diapiric model implies instead that deformation is powered by regional compression from west-verging, near-surface, crustal shortening which results ultimately from Atlantic spreading.

- by Claudio Vita-finzi
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- Geology, Geomorphology, Plate Tectonics, Neotectonics

Several crater-like structures, up to 20 km wide and 300 m deep, have been identified by mapping of the top of the Oligocene-Miocene ooze formations in the Norwegian Sea (Fig. 1). The upper part of the ooze has been evacuated from the structures and emplaced in mounded, local accumulations of ooze sediments located stratigraphically above and geographically downslope relative to the evacuated structures. The structures are filled in by mass flow deposits belonging to the Plio-Pleistocene Naust Formation. Our conceptual model implies that the evacuation structures were triggered by mass flows which loaded ooze sediments at the sea floor or at shallow burial. The ooze was evacuated due to its low density which caused it to ascend to the surface of the mass flow.

- by Fridtjof Riis
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- Geology, Geophysics, Salt diapir, Conceptual Model
- by Amos Frumkin
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- Salt diapir, Dissolution, Notch, HAZARD

- by Masaaki Obata
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- Earth Sciences, Salt diapir, Anorthosite, Magma Chamber

Abstract The temperature field around salt diapirs has been calculated with a finite-element method, whose accuracy is estimated by comparing simulation results with analytical solutions. Temperature, anomaly, and heat flux are calculated in cross-sections through two-dimensional (2D) and axisymmetric (3D) structures. The anomalous temperature field extends to a lateral distance of about 3 diapir radii from the diapir center. At depth the anomaly disappears at about 2.5 times the depth to the base of the diapir.

- by Peter Klint K Jensen
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- Salt diapir, Subsurface temperature