paleozoic mesozoic tectono sedimentary evolution and magmatism of the egersund basin area norwegian central north sea abstract this study focuses on the tectonic evolution of the greater egersund basin in the norwegian central north sea with special emphasis on late paleozoic extensional tectonics following caledonian collapse and the variscan orogeny and the impact of the basement structural grain on this evolution the caledonian collapse likely resulted in development rejuvenation of the deepest e w trending structures depocenters by late devonian time thus a late devonian early carboniferous age can be assigned to the initial extension which was associated with the development of an e w striking basin system to be overprinted by n s extensional structures of similar age a phase of regional magmatism at the carboniferous permian transition 300 ma may be associated with a large igneous province centred on the skagerrak area faulting during late carboniferous early permian was minor within the study area as reflected by uniform sedimentary thicknesses of the uppermost carboniferous and lower permian sequences major normal faults mainly trending n s were active during a late permian early triassic rift phase affecting large parts of the central and northern north sea area a later phase of extension was initiated in late middle jurassic time and the egersund basin proper formed during the late jurassic early cretaceous the depocenters that developed during this phase was influenced by the deep late paleozoic sub salt structural grain including strike slip movements along the sorgenfrei tornquist zone later events include mild inversion along the northern flank of the egersund basin possibly as a late cretaceous response to far field alpine compression and cenozoic regional tilting

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

syn to post rift fault evolution in a failed rift a reflection seismic study in central cambay basin gujarat india the barmer and cambay basins india formed as rifts during the cretaceous to paleocene prior to seychelles india separation during late cretaceous both of the rifts failed subsequently and the seychelles separated from india along the current saurashtra mumbai continental margin we study the fault kinematics i e fault growth and linkages in the cambay tarapur block and comment on the fault evolution from syn to post rift stages we use fault plane topography throw length and throw depth plots to understand the kinematics of the fault planes throw length plots show the along strike linkage of faults the throw depth plots are used to understand the down and up dip linkage of the fault planes faults originating at the deccan traps level and faults confined only to post rift progressed as single fault planes along strike throughout their deformation history faults initiating within the syn rift started as multiple along strike segments and joined together as they grew along dip faults can be classified as i faults originating at deccan traps and reaching post rift ii faults originating within syn rift sediments and reaching post rift iii faults confined only within syn rift and iv faults confined only within post rift some of the syn rift faults also show spatially and temporally limited compression indicating their possible oblique slip nature the faults were normal slip or oblique slip during syn rift and thereafter they propagated as normal dip slip faults as analysed from fault plane topography showing strike perpendicular ridges such ridges may indicate only the last movement on the fault plane due to the presence of thick shale horizons in the syn rift many faults show soft linked segments along dip hydrocarbon occurrences in the shallow 1200 1600 m miocene sands can possibly be attributed to the normal faults controlling fluid flow into the reservoirs 282 words

isochores and 3 d visualization of rising and falling slat diapirs abstract diapir fall which was predicted by physical models has been identified in salt provinces such as the south atlantic margins the north sea and the paradox basin colorado utah however the 3 d geometry of falling diapirs and their country rock is still poorly understood 3 d visualization and isochore patterns from a physical model help elucidate this geometry the model initially comprised a unit of viscous silicone overlain by a prekinematic sand unit sand units representing brittle sediments were deposited episodically during gravity gliding and spreading regional extension triggered and eventually widened salt walls causing them to sag the 3 d visualization shows that regional hydrocarbon migration which tends to be seaward during diapir rise and landward during diapir fall can potentially be orthogonal to local migration along grabens at soft linked zones of relay ramps furthermore anticlinal culminations may form 1 in horsts that bend along strike and 2 adjoining the fork of y shaped salt walls sequential isochore maps of the overburden show how patterns of sedimentation deformation and underlying salt thickness changed through time isochores of prekinematic units record only strain thinned belts record early extension in contrast isochores of synkinematic units record mostly thickness variations due to deposition on actively deforming topography isochores above sagging diapirs identify the thickest part of crestal depocenters where the most rapid sagging occurred in regions of maximum extension near the unbuttressed downdip part of the gravity spreading system additionally asymmetric isochore patterns may reveal underlying half grabens or tilted symmetric grabens in relay systems overlying isochores may indicate which part of a salt wall rose to compensate for sagging elsewhere in the relay

geochemistry and origin of archaean quartz cordierite gneisses from the godthabsfjord region west greenland we report new data on the major minor and trace element compositions of metasedimentary quartzcordierite gneisses qcg an important member of the archaean malene supracrustal suite found throughout the godthabsfjord region of west greenland the analyzed qcg contain assemblages of quartz cordierite biotite garnet anthophyllite gedrite staurolite sillimanite plagioclase with abundant accessory zircon and minor rutile monazite and allanite and broadly resemble cordierite orthoamphibole rocks found in a great number of other metamorphic terrains chemically the qcg are characterized by 1 high but variable sio2 59 87 wt relative enrichments in mgo feo and al2o3 mg 0 35 0 85 and depletions in na2o k2o and especially cao 2 low concentrations of sc cr co ni and sr 3 high concentrations of y nb zr hf ta th u and ree rare earth elements with prominent negative eu anomalies in each case 5 high concentrations of ga 18 55 ppm with variable ga al ratios that are significantly higher than average crustal material low cr and ni together with enriched and fractionated ree displaying negative eu anomalies distinguish the malene qcg from published accounts of most other archaean sedimentary rocks furthermore all of the above mentioned trace element characteristics distinguish the qcg from ordinary malene clastic metasediments quartzites psammites and pelites suggesting a separate origin for the qcg these data point towards chemically evolved felsic igneous rocks being the source of the qcg consequently we propose that the malene qcg represent metamorphosed felsic volcaniclastic sediments that underwent hydrothermal alteration by heated seawater prior to metamorphism which resulted in gain of mg and fe loss of alkalis and lime and possibly eu and sr the overall trace element characteristics of the qcg elevated ga zr nb ree etc are features shared by a type granites and their volcanic equivalents such igneous rocks may represent the ultimate source material for the qcg protolith

early stage evolution of growth faults 3d seismic insights from the levant basin eastern mediterranean the geometry and kinematic evolution of small growth faults were analysed from a high resolution 3d seismic dataset located at the margins of the levant basin in the eastern mediterranean the 3d geometry segmentation history and throw distribution of one particular fault was reconstructed to evaluate and illustrate the changes in dimension and displacement distribution that occurred during the transition from purely blind propagation to propagation at the free surface the fault is considered to have grown by blind radial propagation of three main segments that hard linked prior to surface interaction the fault subsequently reached the seabed and continued to accrue displacement as a syn sedimentary fault most of the fault surface area formed during the blind propagation phase but most of the displacement was added during the syn sedimentary phase of the growth history with little increase in surface area the interaction of the fault with the free surface led to a change in the position of the point of maximum displacement as well as modifying the vertical throw distribution the amount of displacement added after this transition from blind fault to growth fault is discussed with respect to existing fault growth models

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

normal fault growth and fault related folding in a salt influenced rift basin south viking graben offshore norway abstract three dimensional seismic data were analysed to reconstruct the structural and stratigraphical development of a salt influenced rift basin and thus gain an understanding of the relationships between normal fault growth salt tectonics and the evolution of syn rift depocentres the sleipner basin south viking graben northern north sea is ca 30 km long by 8 km wide and is bound to the east by a major extensional fault zone sleipner fault zone two types of fault related fold are identified within the basin 1 a fault parallel monocline interpreted as an extensional forced fold which formed through the upward propagation of the sleipner fault zone through ductile evaporites of the zechstein supergroup and 2 three fault perpendicular salt cored anticlines that compartmentalise the basin into four sub basins and are related to displacement gradients along strike of the sleipner fault zone detailed seismic stratigraphic analysis of pre and syn rift stratal units reveals a complex interplay between fault growth and salt movement which strongly controlled the evolution of syn rift depocentres during the early syn rift a series of depocentres separated along strike by the fault perpendicular folds were offset into the axis of the basin ca 3 4 5 km to the west of the sleipner fault zone by the fault propagation fold later in the rift event the influence of the fault perpendicular folds depleted resulting in a larger interconnected depocentre that shifted into the immediate hangingwall of the fault as the surface of the fault propagation fold was breached the results of this study have implications for normal fault growth and sedimentary depocentre development in salt influenced rift basins and contribute to the general understanding of the controls on salt migration

structural style and early stage growth of inversion structures 3d seismic insights from the egersund basin offshore norway abstract high quality three dimensional 3d seismic reflection and borehole data from the egersund basin offshore norway are used to characterise the structural style and determine the timing of growth of inversion related anticlines adjacent to a segmented normal fault system two thick skinned normal faults which offset permian clastics and evaporites delineate the north eastern margin of the basin these faults strike nnw sse have up to 1900 m of displacement and are separated by an ese dipping c 10 km wide relay ramp both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the lower cretaceous succession at relatively shallow structural levels in the hangingwalls of these faults a series of open low amplitude fault parallel anticlines are developed these anticlines which are asymmetric and verge towards the footwalls of the adjacent faults are interpreted to have formed in response to mild inversion of the egersund basin the amplitude of and apparent shortening associated with the anticlines vary along strike and these variations mimic the along strike variations in throw observed on the adjacent fault segments we suggest that this relationship can be explained by along strike changes in the propensity of the normal faults to reactivate during shortening wider damage zones and lower angles of internal friction coupled with higher pore fluids pressures at the fault centre mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock seismic stratigraphic analysis of growth strata indicate that the folds initiated in the latest turonian to earliest coniacian c 88 6 ma and santonian c 82 6 ma the control on this c 6 myr diachroneity in the initiation of fold growth is not clear but it may be related to strain partitioning during the early stages of shortening anticline growth ceased in the maastrichtian and the inversion event is therefore interpreted to have lasted at least c 20 myr this study indicates that 3d seismic reflection data is a key tool to investigate the role that normal fault segmentation can play in controlling the structural style and timing of inversion in sedimentary basins furthermore our results highlight the impact that this structural style variability may have on the development of structural and stratigraphic hydrocarbon traps in weakly inverted rifts

supra salt normal fault growth during the rise and fall of a diapir perspectives from 3d seismic reflection data norwegian north sea abstract normal faulting and the deep subsurface flow of salt are key processes controlling the structural development of many salt bearing sedimentary basins however our detailed understanding of the spatial and temporal relationship between normal faulting and salt movement is poor due to a lack of natural examples constraining their geometric and kinematic relationship in three dimensions to improve our understanding of these processes we here use 3d seismic reflection and borehole data from the egersund basin offshore norway to determine the structure and growth of a normal fault array formed during the birth growth and decay of an array of salt structures we show that the fault array and salt structures developed in response to i late triassic to middle jurassic extension which involved thick skinned sub salt and thin skinned supra salt faulting with the latter driving reactive diapirism ii early cretaceous extensional collapse of the walls and iii jurassic to neogene active and passive diapirism which was at least partly coeval with and occurred along strike from areas of reactive diapirism and wall collapse our study supports physical model predictions showcasing a three dimensional example of how protracted multiphase salt diapirism can influence the structure and growth of normal fault arrays

displacement loss on growth faults due to sediment compaction compaction models of normal growth faults combined with displacement data from a natural growth fault cape egmont fault new zealand are used to quantify the loss of displacement arising from compaction in circumstances where growth faults are blanketed and buried by compacting sediment in both footwall and hangingwall comparison of imposed tectonic displacements with the preserved displacements indicates that although the thicknesses of sand shale sequences may decrease by up to c 55 due to compaction associated losses in displacement on growth faults are typically 70 and post faulting burial is large i e km scale

evolution of a salt related listric growth fault near the d 1 well block 5605 danish north sea displacement history and salt kinematics abstract the top chalk surface and the tertiary sediments of the danish north sea are cut by only a few major faults which are often related to or controlled by the mobile zechstein salt a single listric growth fault the d 1 fault and its adjacent area have been mapped in detail in order to unravel the fault geometry and kinematics the spatial distribution of displacements and lateral dimensions of the fault are used to examine the interaction between salt movements and the evolution of the fault the displacement distribution on the fault is systematic with contours of equal displacement forming concentric semi ellipses centred on the point of maximum displacement with displacement decreasing upwards and laterally approaching the displacement configuration for the upper part of an ideal simple blind fault furthermore within the volume surrounding the fault vertical displacement shows similar contour patterns for the hangingwall and footwall respectively the lateral displacement variation during fault growth and reconstructed displacement geometries indicate that footwall uplift was mainly a result of salt flow despite the complicated nature of salt dynamics the evolution of the d 1 fault resulted in a systematic fault displacement geometry within the rock volume surrounding the fault

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

growth fault rollover systems birth growth and decay growth fault rollover systems are extremely common structures of thin skinned extensional systems resulting from gravity gliding above salt their development is studied using laboratory experiments based on brittle ductile models where the sedimentary cover and synkinematic sediments are simulated using brittle sand and the underlying decollement layer by viscous silicone putty the experiments are compared to natural examples from seismic lines the experimental results are used to present the evolution of growth fault rollover systems these being the result of a finite amplitude instability with three distinct stages birth growth and decay each of these stages is identified with typical structures which can be recognized on seismic sections a discussion is presented on the interactions in time and space between synthetic and antithetic listric faults parallel and transverse to the direction of displacement

segmentation and growth of an obliquely reactivated normal fault abstract detailed kinematic analysis of a large 1800 m maximum displacement reactivated normal fault in the taranaki basin new zealand has been conducted using high quality 3d seismic data the parihaka fault is approximately north south striking in basement where it accrued late cretaceous to early eocene displacements in response to east west extension and was obliquely reactivated by nw se extension in the pliocene reactivation resulted in upward propagation newly formed segmentation and up dip clockwise rotation of the fault surface by up to 20 from the strike of the basement fault fault segmentation and map view soft linkage by relay zones in post miocene strata was synchronous with the formation of antithetic faults in late miocene strata at bends in the fault surface fault segment lengths antithetic faults and relay zone dimensions were formed geologically instantaneously during initial reactivation of the main fault at 3 7 3 4 ma i e within the first 10 of faulting rapid formation of pliocene fault segments is followed by displacement accumulation without an increase in fault segment length until eventual relay breaching when continued ramp rotation is unsustainable this evolutionary history is consistent with a model in which arrays of fault segments are from inception components of a single coherent structure

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

overburden deformation patterns and mechanisms of salt diapir penetration in the central graben north sea abstract active and passive diapirism control the deformation and geometry of hydrocarbon traps in the overburden and a more detailed understanding of this process will help reservoir prediction and hydrocarbon recovery cores studies of seven central graben diapirs indicate zechstein salt penetrated late cretaceous chalk by extreme tectonic thinning with high angle 70 to bedding normal faulting tensile fracturing and pressure solution attenuation of the chalk significantly weakens the overburden allowing buoyancy forces to dome up the overburden doming created enough topography for downslope sliding of chalk slabs on slip planes parallel to bedding or in the case of the kyle diapir for chaotic debris flows of lithified chalk significant extensional bedding parallel faults and slump folds are developed within palaeocene shale on the diapiric flanks inter granular slip in unconsolidated clastic material was probably the dominant deformation mechanism diapirs have penetrated the palaeocene clastic sediments by maintaining topographic relief so that unlithified sediment continually slid off the crest producing translated intact rafts up to several tens of metres in thickness

three dimensional visualization of salt walls and associated fault systems abundant three dimensional 3 d seismic data from salt provinces have been acquired over the past two decades these data have been interpreted partly using concepts based on analysis of two dimensional 2 d sections through physical and numerical models three dimensional computer visualization of physical models is a recent development that exploits the full potential of model data by displaying even highly irregular geological structures such as convolute salt contacts strata disrupted by salt tectonics discontinuous faults and bedding traces on fault surfaces we used computer visualization techniques to display and analyze a physical model simulating salt related structures produced during gravity spreading and gliding the visualization shows in realistic 3 d detail that 1 structures change seaward from tall steep sided diapirs to squat salt rollers 2 salt walls change markedly along strike and form branches and relays 3 subsidence of underlying salt ridges produces irregular turtle structure closures that tend to have multiple seals 4 links that laterally connect reservoirs in adjacent rafts are most common in upper stratigraphic copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received november 1 1995 revised manuscript received march 4 1996 final acceptance august 12 1996 2bureau of economic geology university of texas at austin austin texas 78713 additional full resolution color 3 d images and digital animations related to this paper are available free on the internet at http www utexas edu research beg mmedia agl96 mm 004 we wrote this paper while testing an unreleased version of the program earthvision and working with its creators at dynamic graphics inc to enhance the technology for visualizing complex brittle and ductile structures dynamic graphics inc especially raphael mayoraz provided invaluable technical support shing tzong lin provided unpublished cross sections of the physical model that he created under our supervision hongxing ge digitized the model data the research was funded by the following companies in the applied geodynamics laboratory consortium agip amoco anadarko arco vastar british petroleum chevron conoco dupont elf aquitaine exxon louisiana land and exploration marathon mobil petrobras phillips statoil texaco and total k prewitt and t weaver edited the figures t hentz edited the paper j farre r ray and b blake refereed the paper which is published by permission of the director of the bureau of economic geology university of texas at austin

the role of co2 in the chemical modification of deep continental crust compositional differences between granulite facies rocks and equivalent amphibolite facies rocks and the observation of co2 rich fluid inclusions in granulites have led to the suggestion that co2 must play a role in modifying the composition of deep continental crust how co2 effects this change has remained unclear using the thermodynamic properties of aqueous ions in a fluid of evolving co2h2o ratio it is possible to model the incongruent dissolution of feldspars under conditions appropriate for granulite facies metamorphism the results demonstrate that dissolution will be strongly enhanced at high co2h2o ratios with ion solubilities being na k ca this enhancement is compatible with the reported compositional contrasts between granulite and amphibolite facies rock but requires large fluid volumes to test the dissolution model a detailed field and petrologic study was conducted in a well exposed granulite facies terrane in west greenland strong correlation between fluid composition and bulk rock chemistry can be documented co2 rich regions contain rocks which consistently have low ana2oacao ratios while h2o rich regions consistently have high ana2oacao ratios magnetite rims on sulfide grains are ubiquitous in high co2 regions and are absent in high h2o regions and they provide evidence that co2 was introduced into the region these correlations and observations are predictable from the properties of the dissolution process these considerations along with observations regarding graphite petrogenesis provide strong arguments that the total fluid volume interacting with the rock during metamorphism was very large in some cases equaling or exceeding total rock volume such large fluid volumes can lead to significant compositional modification of the crust and will mask the original protolith chemistry such processes should lead to ca and al enriched na k s and si depleted residues in the deep crust

impacts of data sampling on the interpretation of normal fault propagation and segment linkage abstract throw distance t d and throw depth t z plots are widely used by researchers and industry to examine the growth of normal faults this study uses high quality three dimensional 3d seismic and outcrop information to review the effect of data sampling on the interpretation of normal fault growth the results show that the accuracy of t d and t z data and of resulting fault slip tendency and leakage factor analyses are dependent on the sampling strategy followed by interpreters and field geologists i e on a sampling interval fault length ratio for discrete structures in particular this work demonstrates that significant geometric changes in t d plots occur when a module error ei for the ratio is larger than 6 9 for faults of all scales and growth histories this implies that a minimum number of measurements should be gathered on discrete faults to produce accurate t d and t z plots and that the number of measurements is dependent on fault length with no prior knowledge of fault segmentation a value of 0 05 should be applied when interpreting faults to fulfil the pre requisite of a i

geochemistry of evaporite bearing series a tentative guide for the identification of metaevaporites literature on metasedimentary rocks indicates that former evaporites have been assumed where brines are present as fluid inclusions or minerals such as scapolite tourmaline and lazurite which are considered as evidence of equilibria with brines very few works take into account the chemical composition of rocks because chemical data on evaporite bearing sedimentary series are scarce

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

physiography of the ne margin of the permian salt basin new insights from 3d seismic reflection data three dimensional seismic reflection data from the egersund basin offshore norway image geomorphological features that record mid permian footwall degradation of basin bounding fault systems this ancient landscape was subsequently flooded during the pan european late permian transgression of the north permian salt basin and was fossilized beneath zechstein supergroup evaporites we provide the first conclusive evidence for pre zechstein normal faulting in the egersund basin indicating that extensional strain was shared between permian and late jurassic early cretaceous rift events supplementary materials uninterpreted versions of the seismic sections shown in figure 2 are available are available at www geolsoc org uk sup18678

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

mineralogy and genesis of cordierite anthophyllite rocks from the sulfide deposit of falun sweden abstract cordierite anthophyllite rocks from the aureole of the falun sulfide deposit are characterized by the assemblages cordierite anthophyllite garnet gahnite quartz dierite staurolite quartz and cordierite andalusite quartz metamorphic conditions are estimated to be 550 50 c 2 5 1 kbar bulk rock chemistry trace element concentration and the variance of the system as defined by the parageneses hint at an origin from acid rocks altered metasomatically at rather low temperatures to chlorite quartz muscovite and subsequently metamorphosed under essentially isochemical conditions

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

large scale circulation classification and its links to observed precipitation in the eastern and central tibetan plateau the relationship between the large scale circulation dynamics and regional precipitation regime in the tibetan plateau tp has so far not been well understood in this study we classify the circulation types using the self organizing maps based on the daily field of 500 hpa geopotential height and link them to the precipitation climatology in the eastern and central tp by virtue of an objective determining method 18 circulation types are quantified the results show that the large amount of precipitation in summer is closely related to the circulation types in which the enhanced and northward shifted subtropical high sh over the northwest pacific and the obvious cyclconic circulation anomaly over the bay of bengal are helpful for the indian summer monsoon and east asian summer monsoon to take abundant low latitude moisture to the eastern and southern tp on the contrary the dry winter in the central and eastern tibet corresponds to the circulation types with divergence over the central and eastern tp and the water vapor transportations of east asian winter monsoon and mid latitude westerly are very weak some circulation types are associated with some well known circulation patterns monsoons influencing the tp e g east atlantic pattern el nino southern oscillation indian summer monsoon and the mid latitude westerly and exhibit an overall good potential for explaining the variability of regional seasonal precipitation moreover the climate shift signals in the late 1970s over the eastern pacific north pacific oceans could also be reflected by both the variability of some circulation types and their correspondingly composite precipitations this study extends our understandings for the large scale atmospheric dynamics and their linkages with regional precipitation and is beneficial for the climate change projection and related adaptation activities in the highest and largest plateau in the world

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

volcanogenic cu pb zn bodies in granulites of the central arunta block central australia small unexploited copper lead zinc deposits characterized by a distinctive wall rock association of cordierite quartzite silica undersaturated rocks calc silicate rocks and impure marbles occur in quartzofeldspathic gneisses and mafic granulites of the strangways metamorphic complex central arunta block central australia available data support the hypothesis that these are metamorphosed volcanogenic ore bodies the chemical compositions of the quartzofeldspathic gneisses are comparable with those of less metamorphosed felsic igneous rocks particularly the felsic igneous rocks emplaced in the north australian orogenic province in the interval 1880 1800 ma and the mafic granulites are chemically similar to basalts olivine normative tholeiites the wall rock suite can be correlated from chemistry and lithological association with the suites of wall rocks found in unmetamorphosed volcanogenic ore deposits that the protolith of the cordierite quartzites may well have been leached tuff similar to the illite chlorite quartz tuff found in volcanogenic ore deposits is also shown by retrogression of the granulitefacies assemblage cordierite garnet ortho pyroxene biotite quartz in the cordierite quartzites to cordierite anthophyllite bearing assemblages and thence to chlorite muscovite quartz assemblages lenses of silica undersaturated rocks with spinel and less commonly sapphirine are interpreted as the metamorphosed equivalents of chlorite rich pods found within leached tuffs in volcanogenic ore deposits the wall rocks form sheet like bodies this suggests that they were deposited in relatively shallow water thus precluding the formation of massive sulphides

3d structure and evolution of folds during normal fault dip linkage understanding the 3d geometry and evolution of extension related folds is important because they may document the geometry and evolution of the associated faults influence sediment routing and accommodation development and may represent targets for hydrocarbon exploration or co 2 storage previous work on extension related folds has largely been restricted to a 2d plane of observation in this study we use 3d seismic reflection data from the gulf of suez egypt to determine the 3d geometry and evolution of fault parallel folds during dip linkage of a vertically segmented extensional fault array that is locally decoupled across a salt bearing interval the 3d geometry of individual faults in the array and adjacent hanging wall folds varies along strike rollover structures occur above listric faults whereas fault bend folds occur above faults that have a ramp flat ramp geometry quantitative analysis of fault fold attributes e g fold amplitude and the growth history of the fault array indicate that fault shape is controlled by the style of dip linkage which in turn is controlled by the lateral separation of sub and supra salt segments prior to linkage small lateral separation yields a relatively subtle change in the overall convexity of the listric fault whereas larger lateral separation results in a ramp flat ramp fault geometry with the layer parallel detachment lying within the salt this study provides a link between fault spacing style of dip linkage final fault shape and ultimately the style of hanging wall folding in mechanically layered stratigraphy our study indicates that 3d seismic reflection data have the ability to provide us with new 3d insights into the variability of and controls on the geometry and evolution of fault related folds

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

four dimensional analysis of the sembo relay system offshore angola implications for fault growth in salt detached settings subsurface mapping of several relay ramps from a raft related fault array in the lower congo basin offshore angola reveals a full spectrum of fault linkage styles a comprehensive three dimensional geometric and kinematic appraisal of a more complex relay system within the fault array the sembo relay system srs highlights differences with current structural models of relay ramp genesis evolution and breaching the srs is a rearward upper ramp breached relay system with a maximum fault overlap and spacing of 9500 and 3600 m 31 000 and 11 800 ft respectively this system is characterized by a structural geometry that becomes increasingly complex with depth as the relay system is gradually assimilated into the structural architecture of a separate and structurally deeper fault system a detailed kinematic appraisal of the srs indicates that the throw patterns on the frontal and rearward segments are intrinsically different throw backstripping reveals different initiation ages for the rearward and frontal segments of about 5 5 and 2 5 ma respectively mutual overlap is estimated to first occur about 2 5 ma at the 5 0 ma structural level with fault linkage and ramp breaching occurring subsequently the srs therefore represents a complex amalgamation of faults that have each developed independently at different times the genesis and evolution of the srs have been governed through time by both salt withdrawal and associated fault detachment histories in conjunction with increased congo fan progradation and sedimentation rates and phases of tectonic tilting of the underlying salt detachment surface

the influence of mechanically weak layers in controlling fault kinematics and graben configurations examples from analog experiments and the norwegian continental margin fault systems in extensional basins commonly display geometries that vary with depth reflecting depth and lithology dependent mechanical strength using an experimental approach we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle ductile sand silicone polymer sequences subject to single and polyphase deformation the experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature the latter being representative of decollement horizons experiments series 1 s1 using homogeneous and stratified quartz and feldspar sand produced asymmetric composite single grabens with diverse fault frequencies and fault styles for the graben margin faults for the mechanically stratified experiments with one decollement level series 2 contrasting graben configurations were produced in that the lowermost sequence was characterized by graben geometries of similar type to that of the s1 experiments whereas the sequence above the decollement was characterized by large fault blocks delineated by steepened or oversteepened faults the experiments with two decollements series 3 were displayed similarly but included graben geometries that widened upward with each level being characterized by independent fault systems the results can be used to explain strata bound fault patterns and depth dependent extension as seen in several places along the norwegian continental margin and elsewhere

metamorphic and tectonic evolution of granulites arunta block central australia petrographical and chemical evidence presented here indicate a prolonged metamorphic evolution of the granulite terrain in the northern strangways range arunta block central australia nsr in fig 1 beginning with migmatization followed by dry granulite metamorphism at high temperatures t and moderate pressures p estimated at 850 920 c 8 1 kbar1 this occurred at 1 800 myr refs 2 3 very shortly after deposition of the protolith4 a bimodal volcanic suite5 and associated sediments granulite metamorphism was followed by isobaric cooling during which there was an episode of pervasive but partial hydration later retrogression and hydration localized along shear zones occurred at the normal geothermal gradient in the kyanite stability field a tensional rift like regime best describes the geological environment in which the protolith formed was deeply buried metamorphosed with high heat flow and then remained in isostatic equilibrium metamorphic parageneses recording uplift may be matched with mid palaeozoic tectonic events in central australia if this correlation is correct the rocks of the northern strangways range may have remained deeply buried for 1 400 myr during which the shear zones were reactivated several times fig 2

the origin of retrograde shear zones in the napier complex implications for the tectonic evolution of enderby land antarctica abstract retrograde shear zones rszs in granulites at fyfe hills in the napier complex east antarctica formed during a late proterozoic or early palaeozoic reactivation event these rszs preserve a structural and metamorphic record of excavation from depth equivalents of 6 8 kbar 20 26 km to depth equivalents of 3 5 kbar 10 17 km excavation was essentially isothermal suggesting that the rszs formed in an allochthonous terrain during crustal thickening by low angle thrusting rehydration of the rszs was accompanied in part by large ion lithophile element enrichment and reduction in k rb features which are attributed to 1 the retrograde fluid having originated in continental crust that had not previously undergone granulite facies metamorphism and 2 the fluid having been introduced into the rszs by the intrusion of granitic dykes and pegmatites the saturation of these rsz pegmatites in components characteristically depleted in deep crustal and mantle sources such as boron and beryllium supports a low grade source for the retrograde fluid furthermore a rehydration mechanism involving intrusion of pegmatites suggests that the fyfe hills granulites are underlain by a significantly lower grade hydrous terrain

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays