are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

3d seismic imaging of the shallow plumbing system beneath the ben nevis monogenetic volcanic field faroe shetland basin seismic reflection data allow for the 3d imaging of monogenetic edifices and their corresponding plumbing systems this is a powerful tool in understanding how monogenetic volcanoes are fed and how pre existing crustal structures can act as the primary influence on their spatial and temporal distribution this study examines the structure and lithology of host rock as an influence on edifice alignment and provides insight into the structure of shallow sub volcanic monogenetic plumbing systems the anticlinal ben nevis structure located in the northerly extent of the faroe shetland basin ne atlantic margin was uplifted during the late cretaceous and early paleocene by the emplacement of a laccolith and a series of branching sills fed by a central conduit seismic data reveal that multiple intrusions migrated up the flanks of the ben nevis structure after its formation c 58 4 ma kettla equivalent and fed a series of scoria cones and submarine volcanic cones these monogenetic edifices are distributed around the crest of the ben nevis structure the edifices are fed from a complex network of sills and transgressive sheets involving lateral magma migration of tens of kilometres before extrusion at the surface this work highlights the importance of underlying basin structures in influencing the sites and development of subaerial monogenetic fields and the importance of lateral magma flow within volcanic systems supplementary materials the results of the statistical alignment analysis of the monogenetic edifices are available at https doi org 10 6084 m9 figshare c 3662809

mobilizing salt magma salt interactions 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

eolian sediment responses to late quaternary climate changes temporal and spatial patterns in the sahara abstract this paper presents a compilation of eolian based records of late quaternary climate changes in the sahara although the data are relatively sparse when viewed as a whole they reveal a general pattern of widespread eolian sediment mobilization prior to 11 000 cal years bp eolian sediment stabilization from 11 000 to 5000 cal years bp and a return to widespread eolian sediment mobilization after 5000 cal years bp furthermore an eolian based record from southern tunisia reveals the existence of millennial scale changes in eolian sediment behavior these millennial scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital milankovitch changes and they are also coincident with abrupt atmospheric and oceanic changes the general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late quaternary eolian sediment behavior in the sahara

seismic detection of fractures from injection illustrated through a field example detection of fractures using geophysical methods has proven elusive a significant amount of theory has been developed over the years however convincing applications of the theory to field data have been scarce in this article we show a clear example of seismic amplitude changes resulting from controlled fracturing from injection at the alpine field in alaska we use the ability of time lapse seismic 4d data to remove the background geology so that the seismic amplitude changes caused by the creation of fracture systems are clearly exposed around injectors

sill morphology and comparison of brittle and non brittle emplacement mechanisms magmatic sheet intrusions contribute significantly to the upper crustal magma transport network the emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation previous observations have highlighted the preponderance of brittle structures associated with shallow level sheet intrusions however recent studies have suggested that non brittle host rock behaviour also occurs particularly related to the formation of magma fingers during shallow level sill intrusion here we examine both brittle and non brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems non brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics purely brittle and non brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling incorporation of variable host material behaviours in numerical and analogue modelling tuned using direct field observations may consequently further our understanding of the controls on shallow level intrusion

diapiric growth within an early jurassic rift basin the tazoult salt wall central high atlas morocco the central high atlas morocco constitutes a diapiric province that hosts a complex array of elongated diapirs and minibasins that formed during the lower jurassic rift of the atlas basin this paper aims to study the structure and growth evolution of the tazoult diapiric wall located in the central high atlas by means of structural and sedimentological fieldwork integrated with remote sensing mapping the tazoult salt wall is a 20 km long x 3 km wide ne sw trending ridge that exposes upper triassic red beds and basalts along its core the succession flanking the salt wall ranges from hettangian to bajocian ages displaying spectacular sedimentary wedges in the se and nw flanks the hettangian early sinemurian carbonates mainly crop out as blocks embedded in the core rocks the 1 km thick pliensbachian platform carbonates display large subvertical flap structures along the flanks of the tazoult salt wall with unconformities bounding tapered composite halokinetic sequences in contrast the 2 5 km thick late pliensbachian aalenian mixed deposits form tabular composite halokinetic sequences displaying small scale hook halokinetic sequences passive diapirism resulted in the lateral extrusion of the evaporite bearing rocks to form an allochthonous salt sheet towards the adjacent se amezrai minibasin the bajocian platform carbonates partially fossilized the tazoult salt wall and thus constitute a key horizon to constrain the timing of diapir growth and discriminate diapirism from alpine shortening the pliensbachian carbonate platform evolved as a long flap structure during the early growth of the tazoult salt wall well before the onset of the alpine shortening

response of aeolian systems to holocene climatic and hydrologic changes on the northern margin of the sahara a high resolution record from the chott rharsa basin tunisia four millennial scale latest pleistocene to holocene climatic cycles are recorded by aeolian lacus trine strata along the southern margin of chott rharsa a playa situated within an active tectonic basin along the northern margin of the sahara desert in tunisia cycles are characterized by 1 a humid phase of dunefield stabilization and high lake levels and 2 an arid phase of playa desiccation and deflation with dunefield construction the cycles overall define a progressive drying trend and correlate well with a detailed chronology from morocco and with the sahara region in general for the latest pleistocene and early holocene climatic events appear more regional in nature for the later holocene an isolated outcrop of aeolian deposits dated at 86 ka bp argues for records of older cycles in the chott rharsa basin that were subsequently removed by long term deflation in the area

estimation of fracture parameters from reflection seismic data part iii fractured models with monoclinic symmetry existing geophysical and geological data indicate that orthorhombic media with a horizontal symmetry plane should be rather common for naturally fractured reservoirs here we consider two orthorhombic models one that contains parallel vertical fractures embedded in a transversely isotropic background with a vertical symmetry axis vti medium and the other formed by two orthogonal sets of rotationally invariant vertical fractures in a purely isotropic host rock using the linear slip theory we obtain simple analytic expressions for the anisotropic coefficients of effective orthorhombic media under the assumptions of weak anisotropy of the background medium for the first model and small compliances of the fractures all effective anisotropic parameters reduce to the sum of the background values and the parameters associated with each fracture set for the model with a single fracture system this result allows us to eliminate the influence of the vti background by evaluating the differences between t

strategic and rare elements in cretaceous cenozoic cobalt rich ferromanganese crusts from seamounts in the canary island seamount province northeastern tropical atlantic abstract thick ferromanganese fe mn crusts from four cretaceous seamounts the paps tropic echo and drago at the southern canary island seamount province cisp in the northeastern tropical atlantic were recovered along the flanks and summits from 1700 to 3000 m water depths cisp is composed of 100 seamounts and submarine hills is likely the oldest hotspot track in the atlantic ocean and is the most long lived of known hotspots globally the fe mn crusts grow on basalt sedimentary rock substrates below the northeastern tropical atlantic core of the oxygen minimum zone omz with a maximum thickness of 250 mm at a water depth of 2400 m the mineralogical and chemical composition of these fe mn crusts indicate a hydrogenetic origin the main mn minerals are vernadite with minor interlayered todorokite and asbolane buserite fe oxides are essentially ferroxyhyte and goethite the fe mn crusts show high average contents in fe 23 5 wt mn 16 1 wt and trace elements like co 4700 g g ni 2800 g g v 2400 g g and pb 1600 g g rare earth elements plus yttrium rey averages 2800 g g with high proportions of ce 1600 g g total platinum group elements pges average 230 ng g with average pt of 182 ng g two main types of growth layers form the crusts 1 a dense laminae of oxides with high contents in mn co and ni associated with vernadite and cu ni and zn associated with todorokite 2 botryoidal layers with high contents in fe ti v and rey associated with goethite the fe mn crusts from the cisp region show higher contents in fe v pb and rey but lower mn co ni and pges contents than pacific or indian ocean seamount crusts the oldest maximum age of initiation of crust growth was at 76 ma campanian late cretaceous using a combination of high resolution co chronometer and geochemical data along an electron probe micro analysis epma transect four stages in morphology chemical contents and growth rates can be differentiated in the the cenozoic crusts since 28 ma which we interpret as due to changes in the ventilation of the north atlantic omz and to the increase of saharian dust inputs an earliest growth period characterized by similar contents of fe and mn in the interval 27 8 24 45 ma late oligocene early miocene reflects slow precipitation related to a thick omz an intermediate laminated zone with higher contents of fe si and p high growth rates reaching 4 5 mm ma and precipitation of fe mn oxides during the interval 24 5 16 ma is related to periods of ventilation of the omz by intrusion of deep upwelling currents significant increase in fe contents at ca 16 ma correlates with the onset of incursions of northern component waters into the north atlantic finally since 12 ma the very low growth rates

igneous sill and finger emplacement mechanism in shale dominated formations a field study at cuesta del chihuido neuquen basin argentina seismic reflection data and field observations have revealed the presence of voluminous igneous sill complexes emplaced into organic rich shale formations in sedimentary basins worldwide damage and structures associated with sills have major implications for fluid flow through basins constraining the distribution of these structures requires a good understanding of the sill emplacement mechanism however most mechanical models of sill emplacement assume elastic host behaviour whereas shale is expected to deform inelastically this contradiction calls for new field observations to better constrain sill emplacement mechanisms in this paper we report on detailed field observations of spectacularly exposed fingers and a sill emplaced in shale at cuesta del chihuido in the neuquen basin argentina exceptional outcrop conditions allow detailed descriptions of both 1 the entire cross section of the intrusions and 2 the deformation structures accommodating intrusion propagation in the host rock all intrusions exhibit irregular blunt or rectangular tips the structures accommodating the tip propagation are systematically compressional including reverse faults folding and imbricate thrust system our observations suggest that the studied intrusions have propagated by pushing the host rock ahead as a viscous indenter our observations suggest that the viscous indenter model is probably a dominant mechanism of sill emplacement in shale

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

emplacement mechanisms of a dyke swarm across the brittle ductile transition and the geodynamic implications for magma rich margins abstract igneous dykes are the main magma transport pathways through the earth s crust and they are considered to contribute to tectonic extension in volcanic rifts dykes are typically considered to result from brittle fracturing even in the ductile crust a common assumption is that dyke orientation is controlled by tectonic stresses such that dykes in rifts are expected to be vertical and perpendicular to extension here we report on detailed field observations of a spectacularly well exposed dyke swarm to show that dykes were not systematically emplaced by purely brittle processes and that dyke orientation may differ from the dominant tectonic stress orientations the dyke complex formed near the brittle ductile transition during opening of the iapetus ocean and is now exposed in the scandinavian caledonides distinct dyke morphologies related to different emplacement mechanisms has been recognized 1 brittle dykes that exhibit straight contacts with the host rock sharp tips en echelon segments with bridges exhibiting angular fragments 2 brittle ductile dykes that exhibit undulating contacts rounded tips ductile folding in the host rock and contemporaneous brittle and ductile features 3 ductile dykes that exhibit rounded shapes and mingling between the soft ductile host rock and the intruding mafic magma the brittle dykes exhibit two distinct orientations separated by c 30 that are mutually cross cutting suggesting that the dyke swam did not consist of only vertical sheets perpendicular to regional extension as expected in rifts we were able to use the well exposed host rock layers as markers to perform a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex it accommodated for 100 extension but counter intuitively it also accommodated for 27 crustal thickening we infer that the magma influx rate was higher than the tectonic stretching rate implying that magma was emplaced forcefully as supported by field observations finally our observations suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle ductile transition and lead to a considerable weakening of the crust the interpretations presented here could potentially have large implications for surface topography and seismicity in active rifts and volcanic areas around the world

salt usually seals but sometimes leaks implications for mine and cavern stabilities in the short and long term abstract thick evaporite masses bedded and halokinetic dominated by the mineral halite are currently mined using conventional solution mining techniques after excavation the resulting salt cavities are sometimes used as subsurface storage vessels for hydrocarbons or various types of waste including low level nuclear waste there are plans being discussed to use purposed designed solution cavities in thick salt masses for the long term storage of high level nuclear waste if high level nuclear waste is ever to be safely stored in salt it will involve a need for the encasing salt not to leak over time frames measured in tens of thousands of years understanding how where and why accessible salt masses leak is the rationale for this review it is the first step in assessing it a particular site s salt geology is suitable for storage we know salt can act as an excellent longterm seal over hundreds of thousands of years as evidenced by its ability to hold back significant columns of highly overpressured fluids even in structurally complex settings but we also know that locally salt bodies do occasionally leak large volumes of fluid as evidenced by the loss of a number of salt mines to uncontrolled floods the rapid creation of solution dolines atop subcropping salt masses and to black salt haloes around highly pressurized hydrocarbon reservoirs these types of leakage are usually tied to the edges of a salt body being exposed to longterm crossflows of undersaturated pore waters or to the build up of internal pressure to levels that exceed lithostatic in fact most zones where a salt body is liable to leak or has leaked are indicated by anomalous textural or mineralogical features when compared to the regional character of the salt the time of leakage can be early eogenetic related to burial mesogenetic or related to uplift telogenetic if the salt mass is not entirely dissolved in the fluid crossflow then the remaining salt tends to re seal especially in zones of ongoing salt flow however if non salt sediment remains in the re annealed salt mass it will tend to retain permeability and when intersected in a salt mine or by a well bore it will flow fluid more problematic in terms of significant leakage are zones in contact with an aquifer external to the salt mass these anomalous areas can transfer large volumes of fluid for this reason active telogenetic anomalies in a salt mass are the most problematic in terms of both mine safety and waste storage identifying the type of salt anomaly the time in diagenesis when leakage occurred and proximity and volume of intersected fluids in the zone of leaking salt is fundamental to mine safety and reliable waste storage

emplacement and deformation of mesozoic gabbros of the high atlas morocco paleomagnetism and magnetic fabrics a paleomagnetic and magnetic fabric study is performed in upper jurassic gabbros of the central high atlas morocco these gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults these structures were reactivated as anticlines during the cenozoic compressional inversion gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization carried by magnetite which has been interpreted as a primary component this component shows an important dispersion due to postemplacement tectonic movements the absence of paleoposition markers in these igneous rocks precludes direct restorations a novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks paleomagnetic vectors are distributed along small circles with horizontal axes indicating horizontal axis rotations of the gabbro bodies these rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases due to the uncertainties inherent to this work the igneous bodies recording strong rotations interpretations must be qualitative the magnetic fabric is carried by ferromagnetic s s minerals mimicking the magmatic fabric anisotropy of magnetic susceptibility ams axes using the rotation routine inferred from paleomagnetic results result in more tightly clustered magnetic lineations which also become horizontal and are considered in terms of magma flow trend during its emplacement nw se parallel to the general extensional direction in the western sector and ne sw parallel to the main faults in the easternmost structures

discovery of lower cretaceous hydrothermal vent complexes in a late rifting setting southern north sea insights from 3d imaging we present data for 31 kilometre scale hydrothermal vent complexes and associated sand remobilization that have formed as a consequence of magmatic intrusions within salt strata southern north sea dutch sector this study uses 3d seismic data tied to three wells and artificial neural networks to describe conical and cylindrical vent structures located in the ne part of the broad fourteens basin the structures are composites of 58 subvertical pipes that form complexes and are 951 364 m in height and 487 426 m in diameter interactions of magma and fluids at depth triggered successive fluid pressure build ups in triassic sandstones resulting in upward propagated ruptures followed by the collapse of overlying deposits and the injection and extrusion of fluidized sand the relationship between vent tops and their overlying deposits indicates a mid hauterivian age unusual for volcanic activity in the north sea area this event could have a significant impact on hydrocarbon exploration as the hydrothermal vent complexes bypass a regional source rock and seal offering new migration routes and connectivity between potential reservoirs the intrusions also raise questions about the influence of transform tectonics on the focusing of volcanic activity during the late rifting phase of the north sea supplementary material tables of seismic attributes and the geometry of the vent complexes as well as a 3d visualisation of the vents are available at https doi org 10 6084 m9 figshare c 3571593

large salt accumulations as a consequence of hydrothermal processes associated with wilson cycles a review part 1 towards a new understanding abstract the formation of large salt deposits is observed especially in areas with a geological history of high tectonic activity over the last decade it has become a well established fact that heavy brines form and solid salts precipitate due to the thermodynamic and physico chemical properties of seawater at high temperatures and pressures encountered within hydrothermal systems this article reviews the modern theoretical and experimental research behind these findings and also describes geological settings that most likely cause brine and salt forming hydrothermal processes to occur this analysis has led to the identification of a set of specific conditions properties and processes referred to as conceptual elements that are used to explain the often complex processes of brine behavior that leads to hydrothermal formation of solid salt the main objective of this review is to present hydrothermal conditions known to occur during wilson cycles subduction collision and rifting e g zones of repeated tectonic unrest where brines commonly derived from seawater are concentrated into heavy brines and precipitate solid salts the internal heat of the earth and its interaction with deeply circulating seawater in hydrothermal systems and also the immense recycling of crustal materials including porous oceanic crust and serpentinite hydrated rocks via mantle processes may lead to the formation of salt accumulations it is also acknowledged that such brines and solid salts may often be stored sub surface for long time periods extending from one wilson cycle to another thus on the basis of this analysis it is cautiously suggested that large amounts of salts hidden inside subduction zones may appear on the surface during subsequent rifting and oceanization phases in part 2 of this review the conceptual elements which are described and discussed herein part 1 are applied to selected cases including the andean mountains the east african rift the red sea rift and other locations

seismic indicators of focused fluid flow and cross evaporitic seepage in the eastern mediterranean abstract we present for the first time a synthesis of the evidence of focused fluid flow in the eastern mediterranean providing an updated record that includes recent and past occurrences through the last ca 6 my of evolution of the basin we do this by adding the interpretation of a previously unpublished regional 2d seismic dataset to the existing occurrences of focused fluid flow reported in the literature our interpretation shows a high number 141 of focused fluid flow features which span the stratigraphic interval from late miocene to recent of these features 82 are at the seabed and 59 are buried the previous published record is more difficult to quantify but in comparison shows an overwhelming majority of seabed features with only rare examples of buried features the spectrum of the buried and seabed features covers pockmarks pipes mud volcanoes clastic intrusions and collapse structures clustering of the fluid flow features is observed at different times in specific areas including the nile cone and the levant herodotus cyprus and latakia basins with the buried record we are able to highlight the evolution of the leakage points through time focused fluid flow venting has been occurring since the onset of the messinian salinity crisis and the start of basinwide deposition of evaporites we focus in particular on seismic indicators of leakage through evaporites and of sub evaporitic source for fluids and remobilised sediments we also discuss the role of the evaporites as a seal to ascending fluids and in which circumstances they can be breached fluids and associated remobilised sediments are sourced from different intervals from the sub and supra evaporitic section and possibly within the evaporites only a minor proportion of the fluid flow features are certainly sourced from below the messinian evaporites and most of them are located in the nile levant eratosthenes areas the few examples of pathways that are able to cross thick undeformed and well preserved evaporites are typically correlated to overpressure release and hydrofracturing this confirms that the evaporites do act regionally as a very good seal as expected while fluids are able to cross the evaporites only in their most extreme expression i e in near lithostathic overpressure conditions this is confirmed by our observations made in the eastern mediterranean where in the presence of relatively undisturbed evaporites cross evaporite vertical fluid pathways are only observed at the high end of the flux pressure range and involve sediment remobilisation maps combining these different elements can be used to detect areas potentially more prone to breaching

cycles of passive versus active diapirism recorded along an exposed salt wall abstract although it has long been recognised that passive salt diapirism may encompass sub ordinate cycles of active diapirism where sedimentary overburden is periodically shed off the roof of the rising salt there has been very little study of this process around exposed salt halite diapirs however the late miocene pliocene sedom salt wall on the western side of the dead sea basin presents an opportunity for detailed outcrop analysis of diapiric salt and the associated depositional and deformational record of its movement during both passive and active phases of diapirism the sub seismic scale record of diapirism includes sedimentary breccia horizons interpreted to reflect sediments being shed off the crest of the growing salt wall together with exceptional preservation of rotated unconformities and growth faults areas of more pronounced dips directed towards the salt wall are capped by unconformities and interpreted to represent withdrawal basins within the overburden that extend for at least 1500 m from the salt margin elsewhere broad areas of upturn directed away from the salt extend for up to 1250 m and are marked by a sequence of rotated unconformities which are interpreted to bound halokinetic sequences the margins of the salt wall are defined by steep extensional boundary faults that cut upturned strata and have enabled rapid and active uplift of the salt since the holocene the sedom salt wall therefore charts the transition from passive growth marked by withdrawal basins growth faults and unconformities to more active intrusion associated with major boundary faults that enable the rapid uplift of overburden deposited on top of the salt to 100 m above regional elevations in the past 43 ka individual cycles of passive and active diapirism occur over timescales of

mechanics of two interacting magma driven fractures a numerical study to understand magma focusing from broad melting zones in the crust propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time dependent plane strain hydraulic fracturing model the source is assumed to generate a constant influx rate to feed the dike growth which is also aided by buoyancy effects in contrast to uncoupled model results the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights which might be produced either by previous magma intrusion or during nucleation the shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation with parameters given in dimensionless forms numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes in that dike interaction can produce a low stress field which is just above the tip of the shorter dike favorable to growth of the shorter dike the energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late time buoyancy viscosity propagation stage where considerable ascent occurs this growth behavior might provide the mechanism for simultaneous instead of sequential growth of various dikes in a single set

origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep sided salt structures egersund basin northern north sea the ingress of meteoric fluids into the crests of salt structures typically results in the formation of anhydrite dominated caprock the migration of connate fluids up the margins of salt structures has also been documented although the products related to this are rarely sampled in the deep subsurface we use 3d seismic reflection and borehole data to document the geometry and lithology of a salt diapir seismic data suggest that a weld is developed along the diapir stem although borehole data indicate that the stem consists of an inner c 1500 m thick halite dominated zone and an outer c 250 m thick anhydrite dominated sheath the anhydrite may have formed early in the basin history as a depositional anhydrite or crestal caprock an alternative interpretation is that the anhydrite represents lateral caprock which formed late in the basin history in response to the migration of nacl poor fluid up the margins of the diapir and dissolution of halite the possibility that lateral caprock may form adjacent to salt structures has implications for understanding the patterns and vigour of groundwater flow in sedimentary basins furthermore our study shows the margins of steep sided salt structures may be misidentified by several hundred metres if time migrated seismic reflection data are used

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

geomorphology of the central red sea rift determining spreading processes highlights the red sea rift overall morphology is typical for ultra slow spreading ridges distribution of various volcanic morphotypes correlates with mantle temperatures spreading perpendicular ridges indicate stable magma focusing over 8 12 my warm mantle under the rsr prohibits the occurrence of oceanic core complexes specific characteristics of the rsr morphology are related to its young age abstract continental rifting and ocean basin formation is occurring today in the red sea providing a possible modern analogue for the creation of mid ocean ridges yet many of the seafloor features observed along the axis of the red sea appear anomalous compared to ancient and modern examples of mid ocean ridges in other parts of the world making it unclear until recently whether the red sea is truly analogous recent work suggests that the main morphological differences between the red sea rift rsr and other mid ocean ridges are due to the presence and movement of giant submarine salt flows which blanket large portions of the rift valley and thereby the oceanic crust using ship based high resolution multibeam bathymetry of the central rsr between 16 5 n and 23 n we focus here on the rsr volcanic terrains not covered by salt and sediments and compare their morphologies to those observed along slow and ultra slow spreading ridges elsewhere regional variations in style and intensity of volcanism can be related to variations in volcanic activity and mantle heat flow the red sea oceanic seafloor shows typical features of mature ultra slow spreading mid ocean ridges such as 2nd order discontinuities overlapping spreading centres and magma focussing in the segment centres forming spreading perpendicular volcanic ridges of thick oceanic crust the occurrence of melt salt interaction at locations where salt glaciers blanket the neovolcanic zone and the absence of large detachment faults are unique features of the central rsr these features can be related to the young character of the red sea and may be applicable to all young oceanic rifts associated with plumes and or evaporites thus the rsr falls in line with ultra slow spreading mid ocean ridges globally which makes the red sea a unique but highly important type example for initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research

structural signatures of igneous sheet intrusion propagation cm acknowledges a junior research fellowship funded by imperial college london jdm acknowledges national science foundation grant ear 1654518 ken mccaffrey paul bons and sandy cruden are thanked for their constructive reviews

evaporite deposition and coeval volcanism in the fortuna basin neogene murcia spain abstract the neogene basins of the eastern betic mountains were placed in a marginal position with respect to the deep mediterranean basin during the tortonian to the messinian they contain thick gypsum anhydrite formations resulting from the upper miocene salinity crisis the evaporitic sedimentation reached its maximum extension and stratigraphic complexity in the fortuna basin which belongs to this geological setting five stratigraphic units are distinguished in the fortuna basin 1 lower gypsum 2 chicamo gypsum 3 chicamo diatomitic evaporitic cycles 4 ribera gypsum and 5 rambla salada gypsum units some of these units occur locally whereas others can be laterally correlated with those of the archena mula guadalentin corridor and lorca basins most of the gypsum units consist of nodular laminated secondary gypsum however primary selenitic laminated gypsarenites and fine grained microlenticular burrowed gypsum lithofacies are also present the evaporite units can also be characterized by the geochemical composition of the gypsum the sulphur and oxygen of the sulphate and the strontium isotopes which display a wide range of values the extreme values indicate precipitation from tertiary marine brines or from meteoric waters that recycled triassic sulphate anion and additional non marine contributions from country rocks and hydrothermal solutions the intermediate values are attributed to mixing between seawater and non marine parent brines the fortuna basin contains several outcrops of volcanic to subvolcanic igneous lamproites cabezos negros derramadores el tale these lamproites the so called fortunites crop out as individual domic volcanoes with lava flows cabezos negros or as intrusive subvertical dikes derramadores el tale there is good evidence of several magma sediment interactions that produced macro and microglobular peperitic lithofacies in the fortuna basin a peperite is produced when two liquids a hot magma and a fluidized water rich sediment interact and no mixing is possible due to the sharp contrast of viscosity between them this implies that the eruption was nearly coeval with the deposition of the host sediment that was water rich the latest evaporitic event rambla salada gypsum unit in the fortuna basin took place coevally to the emplacement of the cabezos negros dome and related lavic structures and the intrusion of the tale and derramadores dikes this paper illustrates the presence of peperitic lithofacies in the fortunites and discusses their implications in assigning an age to these evaporitic sediments which in turn allows us to date the evaporitic units of the fortuna lorca basins

the antiquity of the sahara desert new evidence from the mineralogy and geochemistry of pliocene paleosols on the canary islands spain abstract the sahara is the largest warm desert in the world but its age has been controversial with estimates ranging from miocene to holocene mineralogical and geochemical data show that paleosols of pliocene to mid pleistocene age on fuerteventura and gran canaria in the canary islands have developed in part from inputs of dust from africa these paleosols contain quartz and mica minerals that are abundant in african dust but are rare in the basaltic rocks that dominate the canary islands trace elements with minimal mobility sc cr hf th and ta as well as the rare earth elements show that paleosols have compositions that are intermediate between those of local rocks and african derived dust thus results reported here and in a recently published study by others indicate that 9 paleosols record delivery of african dust to the canary islands between 4 8 2 8 ma 3 0 2 9 ma 2 3 1 46 ma and 0 4 ma a long term paleosol record of african dust input agrees with deep sea records off the coast of western africa that imply increased dust fluxes to the eastern atlantic ocean at 4 6 ma it is concluded that the sahara desert has been in existence as an arid region dust source at least intermittently for much of the pliocene and continuing into the pleistocene

inelastic deformation during sill and laccolith emplacement insights from an analytic elastoplastic model numerous geological observations evidence that inelastic deformation occurs during sills and laccoliths emplacement however most models of sill and laccolith emplacement neglect inelastic processes by assuming purely elastic deformation of the host rock this assumption has never been tested so that the role of inelastic deformation on the growth dynamics of magma intrusions remains poorly understood in this paper we introduce the first analytical model of shallow sill and laccolith emplacement that accounts for elasto plastic deformation of the host rock it considers the intrusion s overburden as a thin elastic bending plate attached to an elastic perfectly plastic foundation we find that for geologically realistic values of the model parameters the horizontal extent of the plastic zone lp is much smaller than the radius of the intrusion a by modeling the quasi static growth of a sill we find that the ratio lp a decreases during propagation as 1 a 4 p with p the magma overpressure the model also shows that the extent of the plastic zone decreases with the intrusion s depth while it increases if the host rock is weaker comparison between our elasto plastic model and existing purely elastic models shows that plasticity can have a significant effect on intrusion propagation dynamics with e g up to a doubling of the overpressure necessary for the sill to grow our results suggest that plasticity effects might be small for large sills but conversely that they might be substantial for early sill propagation 2

igneous petroleum systems in the malargue fold and thrust belt rio grande valley area neuquen basin argentina abstract the rio grande valley neuquen basin argentina is a large oil field where voluminous igneous sill complexes are emplaced in different levels of the sedimentary sequence in a fold and thrust belt setting these sills are predominantly emplaced in organic rich units such as vaca muerta and agrio formations and are critical elements of the defined petroleum system as they affect the thermal maturity of the surrounding source rocks and also act as naturally fractured reservoirs in this contribution we integrated structural sections borehole data core descriptions petrophysical laboratory tests and organic geochemistry measurements to characterize the impact of the magmatism in the petroleum system of the rio grande valley oil field especially we focused in evaluating the impact of the sill complexes in hydrocarbon generation migration and accumulation our data shows that 1 intrusions are preferably emplaced in organic rich units 2 a large number of intrusions is observed in areas intensely deformed by imbricated thrusts 3 an increase in the number of intrusions drives stronger and more extensive maturation processes in the vaca muerta formation enhancing notably the cracking of kerogen to hydrocarbon within this unit 4 where the number of intrusions increases the concentration of total gas and methane also increases given that all sills are suitable reservoirs 5 igneous rocks provide a low resistance path for fluids flow and act as the main reservoirs in the study area 6 the reservoir quality of igneous intrusions is dominated by the combination of matrix and fracture framework properties 7 zeolites are the most common type of cement in these reservoirs 8 deep sills located in the vaca muerta formation produce larger volumes of hydrocarbons relative to shallower intrusive reservoirs the rio grande valley oil field offers a world class example of the implications of igneous complexes in hydrocarbon generation migration and accumulation in a compressive tectonic setting of fold and thrust belt

sills and gas generation in the siberian traps on its way to the surface the siberian traps magma created a complex sub volcanic plumbing system this resulted in a large scale sill emplacement within the tunguska basin and subsequent release of sediment derived volatiles during contact metamorphism the distribution of sills and the released sediment stored gas volume is however poorly constrained in this paper results from a study of nearly 300 deep boreholes intersecting sills are presented the results show that sills with thicknesses above 100 m are abundant throughout the upper part of the sedimentary succession a high proportion of the sills was emplaced within the cambrian evaporites with average thicknesses in the 115 130 m range and a maximum thickness of 428 m thermal modelling of the cooling of the sills shows that the contact metamorphic aureoles are capable of generating 52 80 tonnes of co2 m 2 with contributions from both marine and terrestrial carbon when up scaling these borehole results an area of 12 19 000 km2 is required to generate 1000 gt co2 this represents only 0 7 1 2 of the total area in the tunguska basin affected by sills emphasizing the importance of metamorphic gas generation in the siberian traps these results strengthen the hypothesis of a sub volcanic trigger and driver for the environmental perturbations during the end permian crisis this article is part of a discussion meeting issue hyperthermals rapid and extreme global warming in our geological past

the interplay between fluids folds and thrusts during the deformation of a sedimentary succession abstract in this paper field evidence is presented to support the idea that fluid pressures in excess of lithostatic pressure were operating during the initiation and reactivation of large thrusts and folds in the wenlock shales of llangollen north wales it is also argued that as major thrusts are reactivated and as major folds amplify into finite structures they in turn exert an influence on the subsequent migration and concentration of fluids within the deforming sedimentary succession