raft tectonics the effects of residual topography below a salt de collement abstract some natural examples of thin skinned extensional structures resulting from gravitational gliding on passive margins which display complex listric growth fault patterns are not just controlled by the slope direction examples from the gulf of guinea are presented it is proposed that the inherited topography of the underlying basement can control the initiation of faults oblique to the gliding direction we carried out a series of small scale physical models in order to investigate the effects of residual topography beneath a de collement on faulting in the overlying rafted sedimentary cover the experimental results sustain the hypothesis of structural inheritance and their implications are discussed in the light of natural examples from the gulf of guinea

geology and tectonic development of the bras d or suspect terrane cape breton island nova scotia the bras d or terrane is defined in cape breton island and consists of four distinctive components i low pressure regionally metamorphosed aluminous and calcareous gneiss of the proterozoic bra

geophysical studies of the structure of the appalachian orogen in the atlantic borderlands of canada results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the appalachian orogen in eastern canada wide angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins high velocity lower crust attributed to underplating is found below the former laurentian continental margin in newfoundland and below the magdalen basin potential field data are used to trace the surface zones of the orogen from the northeast newfoundland shelf to cape breton but extrapolation to new brunswick and quebec is unclear because of late paleozoic basin development the central mobile belt of the orogen is only a few tens of kilometres wide in southwest newfoundland and cape breton but broadens substantially to around 200 km elsewhere reflection images show a strong deep crustal fabric that runs along the orogen with a margin that crosses into the avalon zone in southern newfoundland but coincides with the avalon gander zone boundary el

coupled magma chamber inflation and sector collapse slip observed with synthetic aperture radar interferometry on mt etna volcano 1 volcanoes deform dynamically due to changes in both their magmatic system and instability of their edifice mt etna features vigorous and almost continuous eruptive activity from its summit craters and periodic flank eruptions even though its shape is that of a large stratovolcano its structure features two rift systems and a flank collapse structure similar to hawaiian shield volcanoes we analyze european remote sensing ers satellite differential interferometric synthetic aperture radar insar data 1993 1996 for mt etna spanning its quiescence from 1993 through the initiation of renewed eruptive activity in late 1995 we use synthetic aperture radar sar data from both ascending and descending ers satellite tracks comparison of independent interferograms covering the first 2 years of the inflationary period shows a pattern consistent with inflation of the volcano calculation of the tropospheric path delay based on meteorological data does not change this interpretation interferograms from late summer 1995 1996 show no significant deformation joint inversion of interferograms from ascending and descending satellite tracks require both inflation from a spheroidal magmatic source located beneath the summit at 5 km below sea level and displacement of the east flank of etna along a basal decollement both sources of deformation were contemporaneous within the resolution of our data and suggest that inflation of the central magma chamber acted to trigger slip of etna s eastern flank these results demonstrate that flank instability and recharge of a volcano s magma system must both be considered toward understanding how volcanoes work and in their hazard evaluation

the enigma of the albian gap spatial variability and the competition between salt expulsion and extension the albian gap is a uniquely large up to 65 km wide and 450 km long enigmatic salt related structure in the santos basin offshore brazil it is located near the basin margin and trends ne i e subparallel to the brazilian coastline the gap is characterized by a near complete absence of albian strata above depleted aptian salt its most remarkable feature is an equivalently large equally enigmatic basinward dipping supra salt rollover that contains a post albian sedimentary succession that is up to 9 km thick owing to its unique geometry size and counter regional aspect the origin and evolution of the albian gap has been the centre of debate for 25 years this debate revolves around two competing models that is did it form as a result of thin skinned i e supra salt extension or progradational loading and salt expulsion the extension driven model states that the albian gap and overlying rollover formed as a result of post albian gravity driven extension accommodated by slip on a large counter regional listric normal fault the cabo frio fault conversely the expulsion driven hypothesis states that the albian gap was established earlier during the albian and that post albian deformation was controlled by differential loading vertical subsidence and basinward salt expulsion in the absence of significant lateral extension this study utilizes a large c 76 000 km2 dense 4 8 km line spacing depth migrated 2d seismic dataset that fully covers and thus permits for the first time a detailed quasi 3d structural analysis of the entire albian gap in this study we focus on 1 the evolution of base salt relief and the original salt thickness variations and 2 the geometry of the post albian rollover and its related faults and salt structures to constrain the kinematics of the albian gap and how this relates to the evolution of the base salt relief we also apply novel structural restoration workflows that incorporate flexural isostasy in addition to a detailed sequential reconstruction of the intra gap rollover sequences our results show that the geometry and kinematics of the albian gap vary along strike and that both post albian extension and expulsion play a significant role in its evolution basinward dipping growth wedges salt rollers and listric normal faults record extension whereas sigmoidal wedges halokinetic sequences and upturned near diapir flaps the latter two associated with large diapirs bounding the downdip edge of the gap record basinward salt expulsion and inflation where the albian gap is relatively wide 50 km these processes alternate and operate at approximately equal proportions our results are consistent with the amount of basinward translation inferred from the analysis of ramp syncline basins located downdip on the sao paulo plateau our results seemingly reconcile one of the longest running debates in salt tectonics as well as having more general implications for understanding the regional kinematics and dynamics of salt related structures in other salt basins in particular the controls on the development of large counter regional faults supplementary material uninterpreted versions of the seismic sections are available at https doi org 10 6084 m9 figshare c 5023088

basin scale salt tectonic processes of the laurentian basin eastern canada insights from integrated regional 2d seismic interpretation and 4d physical experiments

stratigraphic record of translation down ramps in a passive margin salt detachment abstract ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps on passive margins movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp this growth syncline gradually moves seaward down and then off the monocline as if on a conveyor belt this shift creates accommodation space for a new isopach thick to form just landward of the older one repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin kinematic forward models and restored cross sections from the kwanza basin angola show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors 1 the relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines 2 bathymetric scarps above basement ramps can create spectacular seaward dipping onlap surfaces 30 km long downdip adjoining ramps generate stacked interfering onlap surfaces 3 salt diapirs or anticlines are commonly shortened at the top of the ramp especially where this coincides with the base of the continental slope diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side this buffering can have a major control on the entire gravity spreading system containing the diapirs

contraction induced by block rotation above salt angolan margin gravity spreading above salt at passive margins is the major mode of deformation of post salt sediments whereas this process generally creates a structural zoning extensional upslope and contractional downslope discrepancies can however arise for example evidence of contractional deformation occurs in the extensional domain of the angolan margin to the south of the congo delta fan slope parallel seismic lines show grabens rollover and extensional diapirs conversely strike parallel seismic lines present inversion of early grabens apparently related to a regional scale decrease in sedimentary thickness away from the congo delta as the spreading rate and the characteristic spacing of structures are direct functions of sedimentary loading one can expect structural changes along strike due to sedimentary thickness variations this hypothesis was tested using spreading type experiments of brittle ductile models lying on top of an inclined rigid substratum the experiments simulate the progradation of a synkinematic sedimentary cover above salt with a lateral variation of sedimentation rate the models show that the spreading rate was higher in the thicker part early grabens initiated perpendicular to the slope direction where sedimentation rate was high they kept their orientation during spreading and formed purely extensional synsedimentary structures grabens rollovers and diapirs where sedimentation rate was low blocks separated by grabens rotated in a domino type fashion but this domain continued to extend in a slope parallel direction strike slip between blocks was entirely localised within the early grabens which inverted and formed anticlines structures obtained in experiments are directly comparable to those in seismic lines of the angolan margin in both the angolan margin examples and the laboratory experiments block rotation is interpreted as slope parallel strike slip shear zones due to lateral variations in spreading rate

how a complex basaltic volcanic system works constraints from integrating seismic geodetic and petrological data at mount etna volcano during the july august 2014 eruption the petrological part of this study was supported by the fir 2014 research grant to marco viccaro from the university of catania italy grant number 2f119b title of the project dynamics of evolution ascent and emplacement of basic magmas case studies from eruptive manifestations of eastern sicily

the provenance of middle jurassic sandstones in the scotian basin petrographic evidence of passive margin tectonics the tectonic and geomorphological evolution of the scotian margin and its hinterland is poorly known between late triassic rifting and the early cretaceous progradation of major deltas this study determined sedimentary provenance of middle jurassic mohican formation sandstones from three wells using heavy minerals and mineral chemistry indicator minerals such as xenotime altered ilmenite and varietal types of garnet and tourmaline are similar to those in hauterivian barremian sandstones in the western scotian basin which are almost exclusively derived from the meguma terrane the wells adjacent to the canso ridge have more zircon and less ilmenite indicating a greater contribution of polycyclic reworking but with an ultimate source in the meguma terrane zircon and ilmenite were likely derived in part from carboniferous sandstones in eastern mainland nova scotia and cape breton island any river drainage from the inboard terranes of the appalachians either was diverted through the fundy basin or entered the easternmost scotian basin where the mohican formation is 5 5 km thick along the linear continuation of the southwest grand banks transform such sediment did not reach the canso ridge suggesting that the cobequid chedabucto fault zone in orpheus graben was not a significant physiographic feature this tectonically controlled paleogeography in the middle jurassic is quite different from that during active rifting in the late triassic early jurassic middle jurassic quiescence was followed in the tithonian early cretaceous by renewed tectonic uplift associated with rifting of grand banks from iberia and labrador from greenland

jurassic evolution of the gulf of mexico salt basin we present a new hypothesis for the jurassic plate tectonic evolution of the gulf of mexico basin and discuss how this evolution influenced jurassic salt tectonics four interpretations some based on new data constrain the hypothesis first the limit of normal oceanic crust coincides with a landward dipping basement ramp near the seaward end of the salt basin which has been mapped on seismic data second the deep salt in the deep water gulf of mexico can be separated into provinces on the basis of position with respect to this ramp third paleodepths in the postsalt sequence indicate that salt filled the gulf of mexico salt basin to near sea level fourth seismic data show that postsalt sediments in the central louann and the yucatan salt basins exhibit large magnitudes of late jurassic salt detached extension not balanced by equivalent salt detached shortening in our hypothesis callovian salt was deposited in preexisting crustal depressions on hyperextended continental and transitional crust after salt deposition ended rifting continued for another 7 to 12 m y before sea floor spreading began during this phase of postsalt crustal stretching the salt and its overburden were extended by 100 to 250 km 62 155 mi depending on location sea floor spreading divided the northern gulf of mexico into two segments separated by the northwest trending brazos transform the eastern segment opened from east to west leaving the walker ridge salient in the center of the basin as the final area to break apart in some areas salt flowed seaward onto new oceanic crust first concordantly over the basement as a parautochthonous province then climbing up over stratigraphically younger strata as an allochthonous province

modelling of ground deformation and gravity fields using finite element method an application to etna volcano summary elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions which disregard topography elastic heterogeneities and density subsurface structures with this in mind we reviewed the expected gravity changes accompanying the 1993 1997 inflation phase on mt etna by setting up a fully 3 d finite element model in which we used the real topography to include the geometry and seismic tomography to infer the crustal heterogeneities the inflation phase was clearly detected by different geodetic techniques edm gps sar and levelling data that showed a uniform expansion of the overall volcano edifice when the gravity data are integrated with ground deformation data and a coupled fem modelling was solved a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

intracrystalline vorticity record of flow kinematics during shear zone reactivation abstract the vorticity axis of deformation of a shear zone is a rotational axis controlled by the relative movement of its boundaries when characterized it is a reliable tool to determine the ductile flow geometry monoclinic general monoclinic transpressive or triclinic and an asset to identify the kinematics of complex oblique collisions advancements in analysis of electron backscattered diffraction ebsd maps now permit inference of vorticity axes known as crystallographic vorticity axes cvas from the intragranular lattice orientation dispersion of strain bearing minerals however natural shear zones may preserve a record of multiple shear events with contrasting kinematics and it is not understood to which extent the quartz lattice may preserve a kinematic record through multiple deformation events herein we characterize the finite flow kinematic record produced during reactivation of the eastern highlands shear zone ehsz in an oblique collision within the canadian appalachians we integrate field and thin section observations quartz lattice preferred orientations ebsd maps and grain classification leading to a new method to determine and compare cva within relict and recrystallized quartz grains using this method we were able to conclude that the ehsz was reactivated in an heterogenous monoclinic flow environment

devonian carboniferous tectonics and basin deformation in the cabot strait area eastern canada the magdalen basin in the cabot strait bay st george area was a major depocenter for devonian carboniferous sediments in eastern canada structure within the basin is complex and is characterized by northeast and east trending mainly dextral strike slip faults associated with the bend in the appalachian orogenic belt known as the st lawrence promontory under the cabot strait two linear grabens parallel the major fault trends and preserve up to 6 km of devonian carboniferous sedimentary rocks comprising mainly coarse grained terrigenous clastics with a lower carboniferous transgressive episode recorded by marine carbonates evaporites and fine grained clastics several unconformities within the sedimentary succession record deformation associated with movement alo g the regional strike slip faults minor local unconformities are interpreted within the upper horton early visean upper barachois late westphalian and post pennsylvanian successions a major unconformity cuts out most of the namurian and westphalian section in the study area and can be correlated on a regional scale kinematic strain partitioning along the master cabot fault led to the development of doubly vergent compressional structures within a wrench borderland this was complicated by transpressive deformation at a restraining bend in the master fault and by deformation associated with overstepped ends of splays of the regional fault system the magdalen basin probably formed in an early phase of post acadian extension and was later reactivated by regional strike slip faults the presence of thick source and reservoir rocks as well as diverse trapping possibilities and a favorable burial and maturation history indicate that the cabot strait area has good potential for accumulating and preserving petroleum

the engines of gravity driven movement on passive margins quantifying the relative contribution of spreading vs gravity sliding mechanisms movement of gravity driven systems on passive margins is fuelled by the loss of gravitational potential energy two end member modes gravity spreading and gravity gliding are defined by whether the potential energy loss is due to deformation and movement towards the base of the system spreading or by movement parallel to the base of the system gliding most natural systems consist of a mixture of the two processes hitherto use of these concepts has been limited or equivocal due to lack of a quantitative measure in some cases characterisation of gliding vs spreading systems based on secondary attributes has resulted in controversy because there is a lack of consensus as to which of these are truly diagnostic this paper presents a new simple quantitative method based on vector analysis providing a numerical measure of the relative contribution of spreading vs gliding the method is applied to synthetic examples where deformation can be tracked and to natural examples where a valid palinspastic reconstruction is available the results confirm that most natural examples exhibit mixed mode behaviour and that some have been mischaracterized much of the angola margin is dominated by spreading the method can also provide an estimate of the absolute amount of gravitational potential energy released in the movement and the energy contribution made by gliding vs spreading determining the dominant process has implications for predicting the development of seafloor topography and stratal architecture

an accurate and efficient method for including the effects of topography in three dimensional elastic models of ground deformation with applications to radar interferometry topography has a large effect on the results predicted by elastic surface deformation models in regions of significant relief in some cases topography may have more influence on the predicted deformation field than do model source parameters we have developed an approximate analytical technique for including topographic effects that retains most of the computational simplicity of elastic half space models while providing an accurate representation of topographic effects we use a series expansion of the elastic half space solution with a small slope approximation yielding a set of higher order corrections the integrated effect of these corrections is evaluated using fourier methods we investigate the effectiveness of our method by comparing predicted results for a tilted triaxial ellipsoid with those predicted by finite element models the resulting displacements and displacement gradients are in good agreement with finite element results both for relatively smooth topography synthetically generated and for the greater relief in the vicinity of mount etna volcano we then compare the results of our method with those predicted by traditional elastic half space models using different reference elevations and with a previously proposed method of estimating topographic effects our new method provides a significantly better fit to the finite element results than do the other methods our method is able to accurately portray both the number and the horizontal pattern of fringes in a synthetic interferogram when compared with finite element results in particular the method accurately represents the broadening of fringes that is observed in regions of high relief as well as reproducing the location of the fringe center and the topographically induced deviation of the fringes from a regular pattern elastic half space models typically show a fringe center that is displaced with respect to the finite element results indicating that parameter inversions based on such a model would provide incorrect estimates of the horizontal source position the lack of topographically generated fringe distortions in elastic half space results would also likely lead to inaccuracies in the predicted magnitude and orientation of proposed deformation sources our new technique over comes these limitations and should be useful when evaluating either traditional geodetic results or the greater areal coverage provided by interferometric observations

salt tectonics along the atlantic margin of morocco abstract the moroccan salt basin appears to be very unique in the sense that it is not sedimentary loading but tectonic inversion which appears to drive the latest stages of salt related deformation in the central part of the basin the gravity potential to maintain salt tectonics is provided by the differential uplift of the atlas mountains located adjacent and striking almost perpendicular to the margin along the offshore part of the moroccan salt basin there are many play types most of them related to the triassic syn rift salt toe thrust anticlines at the basinwards edge of the salt basin form very large structures traps associated with salt tongues and diapirs define a more classical salt flank play numerous salt tongues sheets and canopy complexes provide for a gulf of mexico style subsalt play despite the numerous untested play types there have been only four deep water exploration wells drilled in the entire moroccan salt basin none of them having subsalt penetrations

radial gravitational gliding on passive margins abstract gravitational gliding of uppermost sediments down a passive margin is possible if there is a basal layer of evaporite or other soft material to allow detachment in examples from the gulf of mexico and the brazilian margin gliding has produced three main structural domains an uppermost domain of downdip extension an intermediate domain of rigid gliding and a lowermost domain of downdip contraction domain boundaries are established by changes in slope in this paper we examine three kinds of gravitational gliding depending on the paths followed by material particles in ideal parallel gliding particle paths are parallel straight lines trending downslope this should occur where the margin is perfectly straight in ideal radial gliding particle paths are radii of a circle and the margin is shaped like a circular cone natural margins will not have ideal shapes but divergent gliding will tend to occur off coastal salients convergent gliding off coastal re entrants a simple kinematic model based on ductile behaviour illustrates some essential features of radial gliding changes in radius during divergent gliding produce strike parallel extension during convergent gliding they produce strike parallel contraction vertical strains also differ divergent gliding produces an uppermost domain of strong vertical thinning balanced by extensions in all horizontal directions similarly convergent gliding produces a lowermost domain of strong vertical thickening balanced by contractions in all horizontal directions these deformed states cannot be restored by simple techniques based on section balancing we have done three experiments using analogue materials sand to model the brittle behaviour of sediments silicone putty to model the ductile behaviour of basal layers of evaporite the experiments were properly scaled to account for gravitational forces experiment i reproduced convergent gliding above a basement with a conical upper surface strike parallel contraction was responsible for radial folds on the lower slopes the lowermost domain had a complex fold pattern indicating contraction in all horizontal directions experiment 2 reproduced divergent gliding above a basement with a pyramidal upper surface strike parallel extension produced radial rifts on the upper slopes the uppermost domain had a complex polygonal pattern of normal faults indicating extension in all horizontal directions experiment 3 also reproduced divergent gliding but due to non uniform sediment thickness we have examined the many seismic profiles both downdip and alongstrike available for the brazilian margin alongstrike profiles show structures which we attribute to strike parallel strains around the santos re entrant syn sedimentary growthfolds indicate strike parallel contraction increasing downslope this argues for a mechanism of convergent gliding in contrast around the campos salient normal growth faults and associated salt rollers indicate strike parallel extension decreasing downslope this argues for a mechanism of divergent gliding the pattern of oil fields in the campos area including the giant marlim field seems to be closely controlled by divergent gravitational gliding and associated processes radial gliding should occur on other passive margins as well especially where the coastline is sinuous structures around the western gulf of of mexico seem to indicate convergent gliding at the scale of the entire gulf structures at a smaller scale around the mississippi delta seem to indicate divergent gliding

tectonic setting and regional correlation of ordovician silurian rocks of the aspy terrane cape breton island nova scotia interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of ordovician to silurian age are characteristic of the aspy terrane of northwestern cape breton island these rocks were affected by medium to high grade metamorphism and were intruded by synkinematic granitoid orthogneisses during late silurian to early devonian times they were intruded by posttectonic devonian granitic plutons and experienced rapid devonian decompression and cooling the chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic arc setting the volcanic rocks of the aspy terrane differ from many other silurian and silurian devonian successions in atlantic canada which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within plate settings and are somewhat younger than the aspy terrane sequences aspy terrane units are most similar to ordovician silurian volcanic and metamorphic units in southwestern newfoundland incl

deflation of mount etna monitored by spaceborne radar interferometry ground based measurements of volcano deformation can be used to assess eruptive hazard but require the costly and often hazardous installation and maintenance of an instrument network here we show that spaceborne radar interferometry which has already shown its utility in mapping earthquake related deformation1 can be used to monitor long term volcano deformation two families of synthetic aperture radar images acquired from ascending and descending orbits by the satellite ers 1 and looking at mount etna from opposite sides cover the time period from 17 may 1992 to 24 october 1993 and include the second half of etna s most recent eruption despite artefacts of the interferometric technique we can observe a volcano wide deflation which is an expected consequence of the eruption but which had not previously been appreciated we quantify it using a simple model based on the change of pressure in a sphere located in an elastic half space the modelled deformation increases linearly with time until the end of the eruption our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

the structure and evolution of sutures in allochthonous salt salt canopies formed by the coalescence of salt sheets are an integral part of the slope and deep water areas of many passive margin salt basins a suture separates the two coalesced salt sheets allosuture or two lobes from a single salt sheet autosuture including any trapped sediments autosutures can form in two ways an overriding autosuture is produced when part of a salt sheet overrides its neighbor in the direction of salt movement the overridden roof subsides into the salt sheet and these trapped sediments appear as intrasalt reflections on seismic data an encircling autosuture forms when two lobes of a salt sheet separate to bypass an obstacle and then rejoin on the downstream side of the obstacle encircling autosutures tend to be short and parallel to the dominant salt flow direction allosutures separate sheets sourced from two different feeders if neither salt sheet overrides the other the resulting suture is symmetric forming an upright zone of roof sediments trapped between the two sheets more typically one salt sheet is more vigorous generally the larger sheet or the one whose feeder is farther updip and overrides the other sediments trapped in an asymmetric allosuture are mostly from the roof of the overridden sheet the overriding sheet shears and extends the roof of the overridden sheet detaching it from the base of the canopy and obscuring its origin we present diagnostic criteria to distinguish between suture types and provide physical model examples of each this distinction between suture types is important because autosutures and allosutures have very different implications for canopy dynamics and evolution

detrital muscovite geochronology and the cretaceous tectonics of the inner scotian shelf southeastern canada1 2 geochronology of detrital muscovite from the lower cretaceous of the central scotian basin has shown predominant supply of meguma terrane detritus including muscovite with alleghanian mid carboniferous to permian ages from the inner scotian shelf in this study 87 detrital muscovite grains from five wells in the eastern scotian basin representing depositional ages from tithonian to early albian were dated by single grain 40ar 39ar techniques previous work shows that the provenance of this sediment was different from wells in the central scotian basin compared with the central scotian basin the muscovite age populations from the eastern scotian basin have more 20 versus 7 pre devonian ages derived from inboard terranes of the appalachians in both the central and eastern scotian basin most old grains are found in the tithonian and the aptian albian with fewer in the valanginian and almost none in the kimmeridgian and the hauterivian barremian these data suggest rapid unroofing of the megum

late proterozoic tectonic model for the avalon terrane in maritime canada the avalon terrane in maritime canada extends from cape breton island through northern nova scotia antigonish and cobequid highlands to southern new brunswick the terrane contains abundant late proterozoic volcanic rocks 570 680 m y old the geochemistry of the volcanic rocks of southern cape breton island and southern new brunswick indicates that they were erupted in a volcanic arc environment in both regions the mafic rocks display a remarkably similar compositional zonation which resembles the across arc variations observed in modern volcanic arcs the progressive compositional changes that include a transition from island arc tholeiites along the southeastern coasts to calc alkaline rocks inland to the northwest are probably due to a northwest dipping subduction zone with a trench located to the southeast in the antigonish and cobequid highlands continental tholeiites and calc alkaline volcanic rocks are interbedded and overlain by turbidites that have probably been deposited in a back arc or intra arc environment the superimposed positive gravity and magnetic anomalies that may be traced discontinuously from the grand banks through nova scotia collector anomaly and along the northern side of the gulf of maine to near boston probably represent late proterozoic ophiolitic remnants preserved by incomplete suturing along a late proterozoic plate boundary northeast trending segments are inferred to mark subduction zones and the e w portions could correspond to transform faults thus the present geographical distribution of the late proterozoic volcanic rocks is explained by a tectonic model involving a single subduction zone offset by two late proterozoic transform faults located approximately along the minas fault and the scatarie ridge

magnetic and gravity models across terrane boundaries in southern new brunswick canada regional magnetic and gravity map patterns combined with modeling of magnetic and gravity data constrained by measured magnetic susceptibility and density information are used to develop a better understanding of the three dimensional character of major lithostratigraphic subdivisions terranes in southern new brunswick models and long wavelength map patterns indicate that the boundaries between the caledonia brookville kingston and new river terranes are sub vertical or dip slightly to the southeast and that some map units in each terrane extend to depths ranging from 5000 8000 m the mascarene and st croix terranes are less well constrained than the more outboard terranes on the models in part because of limited physical property data but also because of the presence of the saint george batholith which obscures relationships among stratigraphic units the models are consistent with the mascarene terrane being a cover sequence over the boundary between the st croix and new river terranes the specific location and nature of which is now revealed by the geophysical models the terranes appear to be associated at depth with geophysically distinct bodies that are interpreted to correspond to the basements from southeast to northwest of avalon terrane sensu stricto brookville bras d or terrane and exploits gander composite terrane the latter gander basement underlies the kingston new river mascarene and st croix terranes

new artificial granular materials for analogue laboratory experiments aluminium and siliceous microspheres abstract laboratory tests have been carried out to determine the physical properties of high sphericity and low density fine grained dry granular materials in particular we tested hollow aluminium microspheres and hollow siliceous microspheres shear tests have been carried out with a casagrande apparatus for different values of normal stress from 12 27 to 491 8 kpa in order to determine the frictional properties of the microspheres diagrams of the shear stress against displacement have been used to describe the strength of the investigated materials at different confining pressures the shear tests show that hollow aluminium and siliceous microspheres successfully replicate the mechanical behaviour of weaker layers within natural sedimentary successions undergoing deformation the use of these artificial granular materials in specifically designed experiments indicated that they can be successfully used for constructing more natural multilayers in the laboratory

lithoprobe onshore seismic reflection transects across the newfoundland appalachians vibroseis seismic reflection data have been recorded to 18 s two way traveltime along three transects across the island of newfoundland the upper crust has both steep and subhorizontal reflectors consistent with a ramp flat style of deformation whereas the middle and lower crust are largely free of regional flats reflectors descend through ca 20 km of vertical section in the middle and lower crust to flatten into the moho or perhaps cut through it in places the moho is interpreted to be no younger than the dipping reflectors reflection fabrics interpreted to be indicators of dominantly mid ordovician to mid silurian strain show consistent orientations among the transects and divide the crust into two blocks a northwestern block is characterized by upper and middle crustal reflectors dipping mostly southeast at variable angles this block is underlain to the southeast by supposedly younger and dominantly northwesterly dipping reflectors that define a northwest tapering wedge shaped block floored

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

the impact of base salt relief on salt flow and suprasalt deformation patterns at the autochthonous paraautochthonous and allochthonous level insights from physical models

contrasting u pb ages from plutons in the bras d or and mira terranes of cape breton island nova scotia u pb dates from zircon titanite and monazite in plutons of the bras d or and mira terranes of southern cape breton island combined with 40ar 39ar and other radiometric age data indicate that th

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

tropospheric corrections of sar interferograms with strong topography application to etna the accuracy of spaceborne geodetic techniques including sar interferometry is limited by the time and spatial variation and altitude dependance of the propagation delay of electomagnetic waves in the lower troposphere particularly in mountainous areas in this paper we use a 1d model developed for tropospheric corrections of gps and doris measurements to correct sar data the differential tropospheric delay is computed at each pixel of the interferogram from ground temperature humidity and pressure using two empirical parameters calibrated from several radio soundings acquired in various latitude and climate conditions it is shown that with such a model given the 3300 meters topography of etna tropospheric variations can generate up to 4 phase rotations between the top and the bottom of the volcano in 16 out of the 20 interferograms processed with images acquired between august 1992 and october 1993 correction of the tropospheric effect reduces the number of fringes associated with the 1991 93 eruption from previous estimates the remaining deformation is consistant with a deforming source located at a depth of 14 1 km during the second half of the eruption the subsidence rate at the top of the volcano is roughly stable at 13 3 mm month these values are in good agreement with tiltmeter data collected on etna during the same period and with the estimated volume of erupted material no significant deformation can be observed during the last month of eruption inflation of the volcano seems to resume immediately after the end of the eruption at a rate of 3 mm month

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

geometry and kinematics of salt detached ramp syncline basins abstract ramp syncline basins rsbs are characterized by asymmetric depocentres formed by translation above salt detachments with basal steps recognition of these minibasins allows quantification of the magnitude and rates of overburden translation above a deforming salt layer 3d seismic data from the sao paulo plateau santos basin brazil image a series of rsbs formed above thick salt and distributed above and or basinward of pronounced base salt steps the rsbs are composed of landward dipping and gently folded sigmoidal strata recording 28 32 km of se directed translation during the late cretaceous and paleocene at an average rate of 0 8 0 9 mm year we present several examples of rsbs in addition to results from numerical forward models to analyse the 3d kinematics of rsbs and their interaction with base salt structures the rsbs form not only by translation above basinward dipping ramps but also over landward dipping ramps translation over stepped ramps generates stacked rsbs thickness maps show translation is higher at the centre of rsbs and that depocentres become progressively more affected by diapirism as they evolve this study presents the first analysis of the 3d kinematics of ramp syncline basins and the first documentation of their occurrence above thick salt in the santos basin brazil it applies realistic numerical models that treat the detachment as a volume of viscous material improving our understanding of these systems rsbs are important to understand slope and deep basin tectono stratigraphic architecture of supra salt units and can also guide the identification of pre salt structures thus contributing to the exploration of salt basins

lateral mobility of minibasins during shortening insights from the se precaspian basin kazakhstan abstract minibasin provinces are widespread and can be found in all types of salt tectonic settings many of which are prone to shortening previous studies of how minibasin provinces shorten assume that the salt between the minibasins is homogeneous and that the base of salt is flat or of low relief such that minibasins are free to move laterally here we investigate how minibasin provinces respond to shortening when the lateral mobility of the minibasins is restricted by intra salt sediment bodies in order to gain a greater understanding of the controls on the structural styles and modes of tectono stratigraphic evolution exhibited in minibasin provinces we examine a borehole constrained 3d seismic reflection dataset from the se precaspian basin onshore western kazakhstan the study area is characterised by large supra salt minibasins and an array of smaller intra salt sediment packages distributed between these larger minibasins we first outline the evidence of episodic shortening between the late triassic and present after the onset of supra salt minibasin subsidence next we document spatial variations in shortening style showing how these relate to the concentration of intra salt sediment packages finally we develop synoptic models showing how intra salt sediment packages influence both the lateral mobility of minibasins during shortening and the resultant structural style and we compare and contrast our findings with existing models and other natural examples of shortened minibasin provinces we conclude that minibasin provinces may have different degrees of lateral mobility depending on the presence or absence of intrasalt barriers and that these variations provide a first order control on basin shortening style and tectono stratigraphic evolution

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

3d kinematics of a thick salt layer during gravity driven deformation abstract we present the results of an interpretation of 2d and 3d seismic from offshore lebanon in which we identify a suite of 5 linearly distributed trails of fluid escape pipes with pockmarks at their upper terminus these features transect the thick messinian evaporites and root within prominent ne sw oriented pre salt folds the pipe trails are oriented orthogonal to the strike of the pre salt folds with a synchronous initial expulsion episode in each trail dated at 1 7 ma 0 3 ma approximately coeval with the onset of salt detached growth faulting along the basin margin each expulsion episode has been systematically offset to the nw away from the pre salt fold by the flow of the salt resulting in deformation of the fluid escape pipes in the salt the orientation of the pipe trails thus provides a direct kinematic indicator for the flow direction of the salt layer during early stages of gravity driven deformation of the salt and overburden concomitant with basin margin uplift and tilting the unidirectional nw oriented flow is recorded over a region of some 50 km width within the translational domain of the salt tectonic deformation synchronicity in the onset of fluid expulsion from overpressured reservoirs within the pre salt succession evidenced by these pipe trails and growth fault development at the basin margins implies that the pipe trails record the kinematics of the deforming salt layer throughout its post messinian phase of deformation the deformed pipe trails demonstrate a couette flow regime for the salt layer and document subtle changes in cumulative strain and velocity 2 4 mm yr 0 3 mm yr over distances of a few km it is proposed that this novel method of using fluid flow features as natural markers for the kinematics of deforming salt layers could be utilized in other parts of eastern mediterranean as well as other salt basins on earth

effects of topography on the interpretation of the deformation field of prominent volcanoes application to etna we have investigated the effects of topography on the surface deformation field of volcanoes our study provides limits to the use of classical half space models considering axisymmetrical volcanoes we show that interpreting ground surface displacements with half space models can lead to erroneous estimations of the shape of the deformation source when the average slope of the flanks of a volcano exceeds 20 tilting in the summit area is reversed to that expected for a flat surface thus neglecting topography may lead to misinterpreting an inflation of the source as a deflation comparisons of mogi s model with a three dimensional model shows that ignoring topography may lead to an overestimate of the source volume change by as much as 50 for a slope of 30 this comparison also shows that the depths calculated by using mogi s solution for prominent volcanoes should be considered as depths from the summit of the edifices finally we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at mount etna during its 1991 1993 eruption a three dimensional modeling calculation shows that the flattening of the deflation field near the volcano s summit is probably a topographic effect

northeastern extension and crustal expression of terranes from cape breton island nova scotia based on geophysical data the narrowest section of the appalachian orogen in atlantic canada from grenville age basement in the west to the avalon terrane in the east is preserved in cape breton island where components of four terranes display distinctive stratigraphic igneous metamorphic aeromagnetic and gravity characteristics the blair river complex of northwestern cape breton island is a fragment of grenvillian rocks that is similar to units in western newfoundland the aspy terrane is characterized by mid paleozoic granitic rocks and high pressure paragneisses and appears to continue across the cabot strait as the gander terrane of the hermitage flexure in newfoundland the bras d or terrane is composed of hadrynian to early cambrian low pressure metasedimentary units and dioritic to granitic plutonic rocks as indicated by aeromagnetic anomalies this terrane continues across the laurentian channel to the south coast of newfoundland where it may be terminated by the hermitage fault the avalon terrane of southeaster

displacements and tilts from dip slip faults and magma chambers beneath irregular surface topography surface displacements and tilts due to buried deformation sources are influenced by topography the leading order corrections due to topography of arbitrary profile but small slope are determined for dip slip faults edge dislocations and magma bodies lines of inflation in a two dimensional elastic medium the vertical displacement correction is simply the product of the topography and the horizontal normal strain due to the source in a flat half space the correction for a normal fault beneath an idealized basin and range topography is a slight increase in the uplift on the range side the effect of topography for a line of inflation beneath a symmetric volcano is to reduce the central uplift failure to account for topographic influences can bias estimates of source depth and geometry