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High-resolution bathymetric and shallow seismic data along the northeast Red Sea margin reveal a previously disregarded mechanism for carbonate platform drowning at a steepflanked rift basin. At the seafloor, salt extrusions highlight the influence of extensional salt tectonics, with a salt flow from the southern flank of the Al Wajh carbonate platform that likely originates from below. Salt-flow direction, morphology, and kilometer-sized slumps and rotated blocks indicate platform-margin disintegration and rafting of platform blocks toward the southwest. The outlines of several smaller detached or semi-detached carbonate platforms to the south of the main platform can be refitted to the larger platform margin by counter-moving the direction of mass wasting. Several platforms, reaching heights above the seafloor of up to 650 m, are partially or fully submerged in the mesophotic zone and appear to be in danger of drowning. We conclude that the southern outer rim of the Al Wajh platform is breaking apart owing to salt withdrawal, which indicates that carbonate platforms on top of salt sequences grow on mobile ground, leading to platform disintegration, basinward rafts, and the demise of broken-off, smaller pieces of platform. Salt displacement also controls the growth geometries of individual platform rafts, with keep-up reef growth (growth rate equal to sea-level rise) and drowning occurring in close spatial proximity. Therefore, the interplay between salt diapirism and platform growth is not limited to platforms growing on the apexes of diapirs and is more complex than previously thought. [ABSTRACT FROM AUTHOR]

We investigated the architecture of the greater Congo Basin, one of the largest and leastwell-studied sedimentary basins on any continent. Seismograms from a large number of M > 4.5 earthquakes within and surrounding the African plate were used to make event-tostation Rayleigh wave group velocity measurements between periods of 5 and 100 s. Group velocities for discrete periods across the basin, obtained by inverting the event-station measurements, were jointly modeled with gravity data to obtain a three-dimensional S-wave and density model of the basin. The model corroborates the existence of two previously suggested subbasins, one to the north and one to the south, each ~8 km deep and separated by an eastwest structural high. Our results favor a salt tectonics origin for the structural high but cannot rule out uplifted basement rock. The northern subbasin is offset to the west from the southern subbasin, consistent with previous studies suggesting sinistral motion along basement faults during periods of transpressional tectonics in late Neoproterozoic-early Paleozoic times. [ABSTRACT FROM AUTHOR]

Permian salt in the Hallstatt and neighboring salt structures of the Eastern Alps (Austria) crops out along with Triassic deep-water deposits that are at odds with the surrounding Triassic platform carbonates. The traditional interpretation of this juxtaposition is that the salt bodies were emplaced in the Late Jurassic as gravity nappes onto the carbonate platforms, in what has been considered to be the earliest orogenic event in the Eastern Alps. Here we describe for the first time a world-class outcrop of halokinetic sequences in Triassic platform carbonates flanking the Hallstatt diapir. Combining this with other outcrop evidence, we prove that the Hallstatt diapir grew passively during the Triassic, surrounded by carbonate platforms, and extruded to the seabed during the Jurassic. The development of the Hallstatt diapir in a platform setting disproves its emplacement as a gravity-driven nappe, proves the relevance of salt tectonics in the Mesozoic development of the Eastern Alps, and challenges the existence of a Late Jurassic Alpine orogenic event. [ABSTRACT FROM AUTHOR]

Passive-margin salt basins tend to be much more deformed than their nonsalt equivalents, but they are by no means all the same. We used seismic data to study the Salina del Bravo region, northeast Mexico, to investigate the ways in which margin configuration and postsalt uplift history can influence passive-margin salt tectonics. The Salina del Bravo area contains four main structural systems, all of which trend NNE across the entire region. These structures are the Bravo trough, Sigsbee salt canopy, Perdido fold-and-thrust belt, and BAHA high. Gravity-driven deformation did not begin until more than 130 m.y. after salt deposition, because of buttressing against the BAHA high. We suggest that deformation was ultimately triggered in the Cenozoic by Cordilleran uplift that tilted the margin seaward and created a major sediment source terrane. Sediments shed from the uplift expelled salt seaward to form the Sigsbee canopy. At the same time, tilted and loaded sediments were translated seaward on the Louann salt until they were buttressed against the BAHA high, forming the Perdido fold-and-thrust belt. A physical model was built to test this hypothesis. The model was able to reproduce most of the major structures in the region, suggesting that the hypothesis is reasonable. The Salina del Bravo region shows how a downdip buttress can inhibit gravity-driven salt deformation in passive-margin salt basins. Furthermore, the area also shows the importance of postsalt uplift, which can destabilize a margin through a combination of tilting and sedimentation. [ABSTRACT FROM AUTHOR]

The circum-Nile deformation belt (CNDB) demonstrates the interaction between a giant delta and a giant salt body. The semi-radial shape of the CNDB is commonly interpreted as the product of salt squeezing out from under the Nile Delta. We demonstrate, however, that this is not the dominant process, because the delta and its deep-sea fan do not reach the deep-basin salt. The distal part of the deep-sea fan overlies the edge of the salt giant, but squeezing this edge (<150 m thickness) should have had only little effect on the regional salt tectonics. Only on the easternmost side of the deep-sea fan, toward the Levant Basin, does the squeeze-out model work. Here, the delta front reaches the thick salt layer and differential loading promotes basinward salt flow, even upslope. On the western side of the delta, downslope gliding of the sediment-salt sequence toward the Herodotus Basin is driven by the elevation gradient toward the deepest part of the basin. Our analysis shows that salt squeezing by differential loading was previously overestimated in the Eastern Mediterranean and raises the need to carefully map the boundary of salt basins prior to any interpretation. This conclusion is especially relevant in young basins where deltas and shelves have not propagated far enough into the basin. [ABSTRACT FROM AUTHOR]

As a primary driving force, margin tilting is crucial for gravity-driven thin-skinned salt tectonics. We investigated how instant versus progressive margin tilting mechanisms influence salt tectonics using an analogue modeling setup where tilting rate could be controlled. Instant tilting resulted in initially high deformation rates, triggering widely distributed upslope extension and downslope contraction. Later, both the extensional and contractional domains migrated upslope as early extensional structures were successively deactivated, while deformation rates decreased exponentially. In contrast, progressive tilting led to downslope migration of the extensional domain by sequentially formed, long-lived normal faults. Contraction localized on a few, long-lived thrusts before migrating upslope. We attribute the distinct structural evolution of thin-skinned deformation, especially in the extensional domain, in the two tilting scenarios mainly to mechanical coupling between the brittle overburden and underlying viscous material. The coupling effect in turn is largely controlled by the deformation rate. By demonstrating the spatiotemporal variations of structural style and kinematic evolution associated with instant versus progressive tilting, we suggest that such variation is identifiable in nature and therefore can provide a new way to analyze margin tilting histories. [ABSTRACT FROM AUTHOR]

Minibasins are sagging synformal depocenters surrounded by upsurging ductile material. They are traditionally related to salt tectonics. The onshore Iranian Makran accretionary wedge exhibits closed minibasins developed onto a regional-scale olistostrome with a shaly matrix. Two-dimensional numerical experiments were carried out to investigate whether the growth of such minibasins above a shale-dominated unit is feasible and how the presence of a regional, shale-dominated olistostrome may affect the structural evolution of active accretionary wedges. Model results indicate that rapid mass-flow emplacement triggers thickening of the rear of the wedge while minibasins grow in a more frontal, tectonically quiet region. Further wedge growth leads to a jump forward of frontal accretion. Compared to the case history, this jump would explain the structural characteristics of the Coastal Makran in Iran. [ABSTRACT FROM AUTHOR]

The wide continental margin of southern Louisiana borders Paleozoic terranes that accreted to Laurentia before Jurassic rifting formed the Gulf of Mexico. It is unclear whether continental rifting here involved widespread or localized crustal extension, or how seafloor spreading in the Gulf of Mexico started. To improve our understanding of this rifting episode, we gathered marine seismic-refraction data along a 396-km-long transect from the continental shelf 50 km off the western Louisiana coast to the central ocean basin as part of the Gulf of Mexico Basin Opening (GUMBO) program. Using travel-time tomography, we imaged the compressional seismic-velocity structure from the shallow sediments to the uppermost mantle. In our geophysical model, the crust tapers in thickness from ~11 km near the Louisiana coast to ~8 km in the deep water of the central Gulf of Mexico. The compressional seismic velocity increases from 5.7 to 5.9 km/s in the shallow basement to 6.8-7.2 km/s above the Moho. The thickness and average wave speed of crust beneath the modern Louisiana coast and continental shelf suggest the presence of uniformly stretched continental crust that was intruded by mantle-derived melts during extension before continental breakup. South of the Sigsbee Escarpment, the crust is thinner with a higher seismic velocity, which is more consistent with thick oceanic crust. A comparison of our seismic-velocity model with coincident seismic-reflection data indicates that the voluminous Louann Salt was likely deposited on rifted continental crust shortly before the onset of seafloor spreading in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

The western Kuqa fold-thrust belt of Xinjiang Province, China, hosts a series of surface salt structures. Here we present preliminary analysis of the geometry, kinematics, and surface processes of three of these structures: the Quele open-toed salt thrust sheet, Tuzimazha salt wall, and Awate salt fountain. The first two are line-sourced, the third appears to be point-sourced, and all are active. The ~35-km-long, 200-m-thick Quele open-toed salt thrust sheet features internal folding, salt-lined transfer structures, dissolution topography, flanking growth strata, and alluvial fan/stream-network interactions. The ~10-km-long, 50-m-wide Tuzimazha salt wall marks a local topographic high, such that fluvial stream networks are deflected by the rising weak tabular salt body. The salt wall is also flanked by growth strata and normal faults. The ~2-km-long Awate salt fountain represents salt exhumation coincident with the intersection of multiple structures and a river. Therefore this salt body may respond to local structural and/or erosional variations, or it may play a key role determining such variations-or both. Activity along all three structures confirms that active deformation occurs from foreland to hinterland across the western Kuqa fold-thrust belt. Gradual lateral transition from bedded strata to flow-banded halite observed within the Quele open-toed salt thrust sheet implies that similar transitions observed in seismic reflection data do not require interpretation as diapiric cut-offrelationships. The surface salt structures of the western Kuqa fold-thrust belt display a variety of erosiontectonics interactions, with nuances reflecting the low viscosity and high erodibility of salt, including stream deflections, potential tectonic aneurysm development, and even an upper-crustal test site for channel flow- focused denudation models. [ABSTRACT FROM AUTHOR]

Salt sequences form an integral part of many sedimentary basins worldwide. Many of these basins have experienced igneous activity either syn- or post-deposition of the salt sequences. Despite this, little work has so far been undertaken to understand magma-salt interactions within the subsurface, and how aspects such as salt halokinesis may be influenced by igneous activity. Within this paper, we detail the first direct description of relationships and textures that are developed during intrusive igneous-salt interaction. We show that salt composition appears to play a dominant role in controlling where igneous intrusions invade laterally through salt sequences in a sedimentary basin. In particular, we illustrate that hydrous salts, such as carnallite, act as preferential horizons for lateral magma intrusion. This lithological control appears primarily related to the heating and subsequent dehydration reaction of carnallite, which causes the carnallite to behave as viscous fluidal horizons, resulting in the non-brittle emplacement of magma, and spectacular peperitic salt-magma mingling textures. We suggest that heating and transformation of carnallite and other hydrous salts into viscous fluidal horizons during igneous intrusion within a regional salt sequence may act as a possible trigger for contemporaneous halokinesis, by creating fluid-like viscous detachment layers. Over longer time scales, however, a solidified rigid boxwork of dikes and sills may create zones of increased mechanical strength that will locally inhibit further salt flow. [ABSTRACT FROM AUTHOR]

Three-dimensional seismic-reflection data are used to characterize the seismic expression and investigate the origin of two mass transport complexes (sensu Moscardelli and Wood, 2007) that are contained in two saltrelated minibasins on the São Paulo Plateau, offshore SE Brazil. The mass transport complexes contain numerous slide blocks, which are expressed on seismic data as broadly tabular packages of weakly deformed reflections. Individual slide blocks are up to 50 m thick and up to 1 km² in plan view. The slide blocks are flanked by laterally continuous reflections, which are interpreted as the seismic expression of either a thin mudstonedominated debrite deposit or a thin interval of hemi pelagic mudstones. The surface that bounds the base of the two mass transport complexes is planar, and this suggests that the associated gravity-flow event caused only limited erosion of the seafloor. The upper surfaces of the mass transport complexes are very rugose and onlapped by overlying strata, indicating that the slide blocks formed seabed relief of up to 20 m. The complexes occur at the base of a unit that thins toward the margins of the studied minibasins, and the slide blocks in the mass transport complexes decrease in size and density away from the saltcored structural high that separates the two minibasins. Based on its seismic stratigraphic context and the spatial distribution of the slide blocks that they contain, the mass transport complexes are interpreted to have been derived from the failure of the margins of the salt-cored high in response to a period of relatively rapid minibasin subsidence. The results of this study indicate that large volumes of sedimentary material may be derived from the margins of salt-related minibasins in relatively distal submarine settings. From a geohazard perspective, this observation is important because the risk associated with submarine slope failure, and the transport and emplacement of large blocks, is typically thought to be low in relatively distal, deepwater environments. [ABSTRACT FROM AUTHOR]

A succession of continental red beds in the Paleogene Carroza Formation, north-eastern Mexico, contains an assemblage of evaporite paleosols previously unknown in pre-Neogene strata that record the syn-depositional exposure of nearby diapiric evaporite and a climatic shift to increasing aridity. Carroza red beds were deposited in an ephemeral braided-fluvial system in a high-accommodation setting. Paleosols developed in nearly all depositional settings, including channels, crevasse splays, and fl oodplains, and contain salic/natric, gypsic, baritic, and calcic horizons. Calcic paleosols are limited stratigraphically to the lowermost part of the formation in oyster-bearing estuarine strata and yield upsection to evaporitic paleosols, thus providing a record of increasingly arid conditions as the Paleogene marine shoreline shifted eastward, toward the Gulf of Mexico Basin. The increase in aridity reduced vegetation and residuum thickness on the exposed diapiric salt, consequently increasing the influx of evaporitic minerals into the basin, and driving the development of salic/natric, gypsic, and baritic horizons in all depositional environments. Evaporitic paleosols of the Carroza Formation have characteristics similar to soils forming today in climates with annual precipitation ranging from <80 mm/yr to as much as 450 mm/yr, in apparent conflict with estimates of subhumid to subtropical conditions from Carroza fossil leaf data. Because evaporitic paleosols are persistent throughout the Carroza section, we infer that a combination of spring-fed, high water tables, augmented by flood-basin inundation from high-discharge seasonal fluvial flood events sustained perennial woodlands, and sodium-caused clay dispersion created poor drainage in topographically low parts of a rapidly subsiding salt-withdrawal basin. [ABSTRACT FROM AUTHOR]

Salt 'withdrawal' sedimentary minibasins, common features of salt tectonic provinces, are typically subcircular or polygonal, 10-30 km in diameter, and contain as much as 10 km of sediment above evaporite that has been expelled into surrounding diapiric structures. The early development of minibasins typically is not buoyancy driven (Rayleigh-Taylor instability) because thin sediment overburden is usually less dense than salt (strictly, halite) or other evaporites. We analyze an alternative mechanism that applies in compressional regimes involving sedimentation onto salt, lateral flow and shortening of sediment and salt to form viscous pressure ridges (VPRs) (the key process). Loading by sediment ponded between VPRs provides a positive feedback that grows the pressure ridges. We show using lubrication theory and numerical models that this mechanism quantitatively solves the enigma and grows minibasins until the compacting sediment is sufficiently thick and dense for Rayleigh-Taylor instabilities to take over. [ABSTRACT FROM AUTHOR]

A photogeologic and physical modeling study indicates that Hebes Chasma, Mars, formed by collapse of the megaregolith. Local heating facilitated drainage of ∼105 km³ of brines and entrained particulates through fractures in the chasma floor and into a regional aquifer. A megaregolith rich in salts and water is implied by massive, low-gradient allochthonous flows that terminate in deep pits and troughs, by emergent diapirs, and by arching of Hebes Mensa. These structures are consistent with plastic and viscous deformation but inconsistent with collapse of basalt flows and/or tephra. Spectral measurements confirm that hydrated sulfate salts are spatially associated with allochthonous flows from depth and light-toned deposits. Collapse features and flows are present in many other chasmata in Valles Marineris, suggesting that widespread salt tectonics and dissolution may have shaped the region. [ABSTRACT FROM AUTHOR]

Why do salt-floored minibasins subside? An almost universal explanation is that salt is forced from beneath the sinking basin by the weight of its sedimentary fill. This explanation is valid if the average density of the basin fill exceeds that of salt, which in the Gulf of Mexico needs at least 2300 m of siliciclastic fill to ensure enough compaction. However, most minibasins start sinking when they are much thinner than this. Some mechanism other than density inversion must explain the early history of these minibasins. Conventional understanding of minibasin subsidence is thus incomplete. Here, we identify five alternatives to density-driven subsidence of minibasins. (1) During diapir shortening, the squeezed diapirs inflate, leaving the intervening minibasins as bathymetric depressions. (2) In extensional diapir fall, stretching of a diapir causes it to sag, producing a minibasin above its subsiding crest. (3) During decay of salt topography, a dynamic salt bulge subsides as upward flow of salt slows, which lowers the salt surface below the regional sediment surface. (4) During sedimentary topographic loading, sediments accumulate as a bathymetric high above salt. (5) Finally, subsalt deformation affecting the base of salt may produce relief at the top of salt. Each mechanism (including density-driven subsidence) produces a different bathymetry, which interacts with sediment transport to produce different facies patterns in each type of minibasin. The particular mechanism for minibasin subsidence depends on the tectonic environment, regional bathymetry, and sedimentation rate. Their spatial variation on a continental margin creates provinces in which a given minibasin style is dominant. An appreciation of subsidence mechanisms should thus improve our understanding of minibasin fill patterns and allow genetic comparisons between minibasins. The mechanics of a minibasin sinking into fluid salt is in many ways analogous to a crustal basin sinking into a fluid asthenosphere. However, minibasins lack the complex rheologies, thermal histories, and compositional variations that make study of crustal basins so challenging. Minibasins are thus natural analogs and have the potential to elucidate fundamentals of subsidence mechanics. [ABSTRACT FROM AUTHOR]

A synthesis of deformation patterns within and around the Thaumasia Plateau, Mars, points to a new interpretation for regional deformation and the origin of Valles Marineris and associated outflow channels. The morphology of the Thaumasia Plateau is typical of thin-skinned deformation, akin to a "mega-slide," in which extensional deformation in Syria Planum and Noctis Labyrinthus connects via lateral zones of transtension and strike-slip--Claritas Fossae and Valles Marineris--to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the Coprates Rise and Thaumasia Highlands. However, the low regional slope (∼1°) results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the Tharsis volcanic province. Instead, we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and/ or mixtures of salts, ice, and basaltic debris would allow for weak detachments and largescale gravity spreading. We propose that the generally linear chasmata of Valles Marineris reflect extension, collapse, and excavation along fractures radial to Tharsis, either forming or reactivated as part of one lateral margin of the Thaumasia gravity-spreading system. The other, dextral, lateral margin is a massive splay of extensional faults forming the Claritas Fossae, which resembles a trailing extensional imbricate fan. The compressional mountain belt defined by the Coprates Rise and Thaumasia Highlands forms the toe of the "mega-slide." Topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below Syria Planum that could have provided further thermal energy and topographic potential for initiating regional deformation, either intrusively through inflation or extrusively through lava flow and/or ash fall emplacement. Higher heat flow during Noachian time, or geothermal heating due to burial by Tharsis-derived volcanic rocks, would have contributed to flow of salt deposits, as well as formation of groundwater from melting ice and dewatering of hydrous salts. We further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of Echus, Coprates, and Juventae chasmata at relatively uniform source elevations along the northern margin of the "mega-slide," where regional groundwater flow would have been directed toward the surface. Our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the Tharsis volcanic province, deformation of the Thaumasia Plateau, and the formation of Valles Marineris and associated outflow channels. [ABSTRACT FROM AUTHOR]

Regional 2D and 3D seismic data from the Levant Basin reveal the updip extensional component of thin-skinned gravity tectonics on this continental margin. Because of its youth (5-7 Ma), the earliest stages of deformation of this salt basin are preserved without the severe structural overprinting common on more mature, giant salt-tectonic systems. Extension detaches onto and within Messinian evaporites up to 1800 m thick. By structural restoration, we reconstruct the tectonic evolution of the Messinian evaporites using paleobathymetric constraints from wells and seismic profiles. This analysis suggests that the Mediterranean drawdown during the Messinian Salinity Crisis was ~800 m. The 10- to 15-km--wide extensional domain tracks the landward pinch-out of the mobile Messinian evaporites against an older Late Miocene scarp. Diachronous extension began in the center of the margin in the mid-Pliocene, then spread northward in the late Pliocene, then finally southward in the early Pleistocene. Extension continues today on many of the most landward faults. Extensional strain varies greatly along strike from <1 km to as much as 12-15 km. Comparing observations with four end-member conceptual models, we infer that both extension and seaward salt flow thinned the evaporite margin and its overburden. Both processes were triggered by a combination of uplift of the continental shoulder of the Dead Sea Rift and subsidence in the Mediterranean Basin. At least three factors controlled variations in extension: (1) degree of tilting of the salt wedge, related to the interplay of coastal uplift and basin subsidence; (2) presence of pre-Messinian canyons overlain by landward salients of salt; and (3) variations in evaporite facies and the proportion of siliciclastic admixture. [ABSTRACT FROM AUTHOR]

In the Northwest German Basin of Central Europe, Late Triassic interaction of normal faulting and salt diapirism during regional extension in subsalt basement locally initiated lateral flow of surface-piercing salt in namakiers (salt glaciers). Using seismic sections and variance attribute maps derived from high-resolution three-dimensional seismic data, we show that when a syndepositional fault cuts a near-emergent diapir crest, the caprock carapace was breached, opening a pathway for salt extrusion. The fault escarpment and the adjacent fault-induced depression allowed focused gravity-driven downward flow of salt across the land surface (a namakier) and its subsequent preservation and encasement in continental (arid redbed) sediments. Geodynamically there is an apparent distinction between the compressional setting of modern namakiers in the arid deserts of Iran and the fault-intersected extensional setting of stacked Keuper namakiers. Stacked namakiers preserved in thicknesses that are seismically resolvable are interpreted to indicate hyperarid conditions in Keuper time. The climate was typical of the highly continental Late Triassic Pangaean supercontinent as it rifted and sagged to form the incipient Atlantic Ocean. [ABSTRACT FROM AUTHOR]

A new Coniacian-early Santonian extensional salt tectonics event has been identified in the Cotiella thrust sheet of the central Spanish Pyrenees. We present a new interpretation of the Cotiella thrust system and describe exceptional outcrop examples of postrift, gravity-driven extensional growth faults. The thrust sheet contains three, kilometer-scale extensional faults with as much as 5.5 km of Coniacian-lower Santonian growth strata in their hanging walls. These postrift listric growth faults detached on the prerift Triassic evaporites on the uplifted and eroded southern flanks of Early Cretaceous rift basins. Early Alpine (late Santonian-Maastrichtian) contractional deformation reactivated and reversed the displacement on both the Early Cretaceous rift faults and some of the postrift- salt detachment faults. Hanging walls of the listric growth faults deformed into major antiforms, but the original extensional geometries are well preserved. Continued Alpine shortening incorporated these reactivated extensional fault systems into the thin-skinned thrust sheets of the southern Pyrenees. These postrift extensional structures account for significant thickness variations in the postrift succession and for along-strike changes in the styles of the thrust structures. The Late Cretaceous extensional salt tectonics is interpreted to result from gravity-induced northward sliding on the Early Cretaceous rift margin, toward the axis of the rift basin. The listric growth faults are similar to those found on the Gulf of Mexico margin, in the southern North Sea, and the South Atlantic margins. [ABSTRACT FROM AUTHOR]

This study addresses some aspects of the kinematics and structural setting of the Mediterranean Ridge accretionary complex, particularly those aspects related to the occurrence and distribution of Messinian evaporites. The approach is by (1) identification of the geometry of deformation through reprocessing of existing multichannel seismic reflection data from the Levantine Basin, aimed at the definition of the velocity field and depth imaging; (2) physical modeling in the laboratory, aimed at the study of the kinematics of shortening of sedimentary sequences detaching on viscous deco-elements; and (3) comparison between the results of the two approaches. We conclude that the thick Messinian sequence of the Levantine Basin is composed primarily of salt, so that the entire evaporitic sequence can be expected to behave as a viscous material. It follows that the main detachment of the post-Messinian wedge is located at the base of the Messinian salt layer. A viscous (salt) décollement would produce thrusting trending normal to the shortening direction, but boundary conditions affect structural trends even more than stress and/or movement direction. Both strain partitioning and the formation of major strike-slip faults within the post-Messinian wedge are prevented by the high angle of convergence between the African and Aegean plates as well as by the Iow intraplate friction. In addition, we show that curved and anastomosing thrust fronts are reflected in the cobblestone topography of the Mediterranean Ridge. We finally postulate that extension may occur in the central Mediterranean Ridge as a result of the geometry of the plate boundaries. This extension is considered as a possible cause of mud volcanism and mud diapirism. [ABSTRACT FROM AUTHOR]

Discusses the neoproterozoic allochthonous salt tectonics during the Lufilian orogeny in the Katangan Copperbelt in central Africa. Understanding of allochthonous salt sheets; Evidence for former evaporites; Salt-tectonic model for Shaba; Implications for ore genesis.