stratigraphic development of synkinematic deposits in a large growth fault system onshore brunei darussalam kilometre scale synsedimentary faults associated with well preserved sedimentary successions on both hanging wall and footwall sides are rarely seen in outcrop however one such example is found in a middle miocene deltaic sand shale sequence exposed along the jerudong anticline in onshore brunei darussalam integration of detailed outcrop information with regional geophysical subsurface data documents that 1 initiation of the jalan tutong growth fault was related to delta front instability and failure 2 sediment loading under shallow marine conditions maintained syndepositional faulting 3 growth fault abandonment coincided with a significant basinward shift of deposition and subaerial exposure high resolution analysis of facies characteristics stratal expansion and throw development within the studied growth sequence indicates that differential fault movement strongly influenced facies composition sedimentary geometry and bedding characteristics sandstone poor shelf to lower shoreface successions developed during periods of rapidly increasing fault movement whereas sandstone rich amalgamated upper shoreface deposits preferentially formed during intervals of constant or decreasing throw development the data and interpretations presented may help to focus attention on the complex interplay between tectonics and sedimentation associated with the growth and decay of deltaic faults by providing for the first time an outcrop based view on a feature documented in similar scale only by geophysical subsurface data

differential fault related early miocene sedimentation bayou hebert area southwestern louisiana well logs from the bayou hebert area in southwestern louisiana show that most of the differential sedimentation associated with one zone of contemporaneous faults cannot be attributed to simple expansion rather the lower miocene sequence on the downthrown side of the fault zone has grown principally by the episodic deposition of sedimentary units that have no correlative counterparts on the upthrown side such units range up to about 2 000 ft 600 m thick near faults and most are laterally discontinuous over distances of several kilometers the isolated downthrown intervals lie in different parts of the sequence at various places along the strike of the fault zone indicating lateral and temporal variation in subsidence rates in the downthrown block the intervals may represent times of erosion or sediment bypass updip of faults isolation of thick intervals on the downthrown block adds potential for unexpected reservoir units and may enhance the development of combination traps associated with contemporaneous faulting and deposition characteristic of growth faults overlapping of the tapered edges of multiple laterally adjacent intervals may also create potential for small flexural structures in the areas of overlap

franciscan subduction off to a slow start evidence from high precision lu hf garnet ages on high grade blocks lu hf analyses of garnet from metabasic amphibolite glaucophane schist and eclogite facies blocks from the franciscan complex give highly precise ages that allow us to place new constraints on the early thermal history of the franciscan subduction zone garnets yield 176 lu 177 hf ratios ranging from 1 5 to 28 with the highest ratios from garnets with high spessartine pyrope ratio sulphuric acid leaching sal of garnets revealed the presence of inclusions with significantly higher lu hf ratios than those of garnet itself most likely apatite their removal by sal brings the 176 lu 177 hf ratios in garnets down by as much as 40 this suggests that 176 lu 177 hf ratios of apparently pure garnets can be greatly overestimated due to the presence of such inclusions sm nd garnet analyses were dominated by inclusions mainly sphene and failed to provide precise and accurate age information the oldest lu hf ages are 168 7f0 8 and 162 5f0 5 ma on plagioclase bearing garnet amphibolite from panoche pass and the berkeley hills respectively which suggests initiation of the subduction zone at about 169 ma coeval with the formation of the tectonically overlying coast range ophiolite relatively high temperature conditions persisted for about 14 ma as indicated by 153 4f0 8 ma garnet growth recorded in epidote amphibolite and 157 9f0 7 in eclogite from ring mountain and jenner respectively a 146 7f0 7 ma age was obtained from garnet glacuophane schist metamorphosed at around 400 jc the sequence of ages from central and northern california shows a younging trend with decreasing metamorphic grade which supports previous suggestions that the high grade metamorphic blocks and slices resulted from progressive underthrusting and underplating in a cooling subduction system combining geothermometry with geochronological data allow us to estimate cooling rate along the subduction zone interface from amphibolite to blueschist facies conditions as ca 15 jc ma the thermal history requires high initial geothermal gradients within both the footwall and the hangingwall of the subduction zone and a relatively slow subduction rate of the order of 10 km ma during the initial stages of franciscan subduction such conditions are consistent with initiation of the subduction zone at or close to an oceanic spreading centre the data also suggest slow exhumation rates and significant residence time at depth of the earliest franciscan rocks

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

3d seismic analysis of gravity driven and basement influenced normal fault growth in the deepwater otway basin australia abstract we use three dimensional 3d seismic reflection data to analyse the structural style and growth of a normal fault array located at the present day shelf edge break and into the deepwater province of the otway basin southern australia the otway basin is a late jurassic to cenozoic rift to passive margin basin the seismic reflection data images a nw se 128 308 striking normal fault array located within upper cretaceous clastic sediments and which consists of ten fault segments the fault array contains two hard linked fault assemblages separated by only 2 km in the dip direction the gravity driven down dip fault assemblage is entirely contained within the 3d seismic survey is located over a basement plateau and displays growth commencing and terminating during the campanian maastrichtian with up to 1 45 km of accumulated throw vertical displacement the up dip normal fault assemblage penetrates deeper than the base of the seismic survey but is interpreted to be partially linked along strike at depth to major basement involved normal faults that can be observed on regional 2d seismic lines this fault assemblage displays growth initiating in the turonian santonian and has accumulated up to 1 74 km of throw our detailed analysis of the 3d seismic data constraints post cenomanian fault growth of both fault assemblages into four evolutionary stages 1 turonian santonian basement reactivation during crustal extension between australia and antarctica this either caused the upward propagation of basement involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement involved faults 2 continued campanian maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau nucleating a second vertically isolated normal fault array in the cover sediments 3 eventual hard linkage of fault segments in both fault arrays to form two along strike nw se striking fault assemblages and 4 termination of fault growth in the latest maastrichtian we document high variability of throw along strike and down dip for both fault assemblages thereby providing evidence for lateral and vertical segment linkage our results highlight the complexities involved in the growth of both gravity driven normal fault arrays such as those present in the niger delta and gulf of mexico and basement linked normal fault arrays such as those present in the north sea and suez rift with the interaction of an underlying and reactivating basement framework this study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales 2 km separation down dip

nature of the continent ocean transition on the non volcanic rifted margin of the central great australian bight a region of 50 120km width defines the continent ocean transition cot in the central great australian bight it is characterized by a thin apron of post break up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the cot and basement ridge modelled gravity and magnetic data and features interpreted from seismic data are consistent with aspects of extensional and break up models proposed for the west iberia margin many of the features and relationships observed beneath the outer margin of the central great australian bight can be explained by extension within a lithosphere scale pure shear environment involving four layers brittle upper crust and upper mantle and ductile lower crust and lower lithospheric mantle the cot is interpreted to be underlain by extended continental lithosphere thus the continentocean boundary is unequivocally defined between oceanic crust and the cot and appears to be associated with sea floor spreading magnetic anomaly 33 indicating that break up and sea floor spreading did not commence until c 83 ma early carnpanian time later than the currently accepted 95ma age the major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting the magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly but one that does not relate to break up and sea floor spreading

salt influenced normal fault growth and forced folding the stavanger fault system north sea abstract displacement ratio d r is the ratio between salt thickness t v and sub salt normal fault displacement d d r t v d and it is typically used to predict the degree of geometric and kinematic linkage between sub and supra salt fault populations and the overall structural style in salt influenced extensional settings however we currently lack natural examples of how d r and the underlying geological controls vary and how these may control the three dimensional geometry and evolution of salt influenced normal fault systems furthermore it is currently unknown if kinematic coherence in salt influenced extensional settings can be maintained over relatively long length scales 10 1 10 3 m and for relatively long timeframes and how this may impact the growth and geometry of large throw 500 m salt influenced normal fault systems in this paper we use a 3600 km 2 high quality 3d seismic reflection dataset and borehole data from the stavanger fault system sfs egersund basin eastern north sea basin to investigate i how pre rift salt thickness t v and sub salt fault throw t control the structural style and evolution of a basin bounding salt influenced normal fault system and ii the role salt plays in maintaining kinematic coherence in normal fault systems we demonstrate that i pre rift salt distribution t v specifically its presence in the proto footwall i e when t v 0 is the primary control on partitioning of faulting and forced folding along the fault system and the style of linkage i e hard or soft linkage between sub and supra salt fault populations and ii sub and supra salt fault populations represent brittle elements of a single geometrically and kinematically coherent structure the geometry and evolution of which is related to the ductile translation of strain on a scale up to 8 km and duration c 65 myr that believe is significantly greater and longer than previously documented

cenozoic magnetostratigraphy of the xining basin ne tibetan plateau and its constraints on paleontological sedimentological and tectonomorphological evolution abstract the xining basin is well known for its thick and continuous sequence of fine grained cenozoic sediments in addition it contains important xiejia fauna which define the xiejian stage of the early miocene in the standard chinese land mammal zonation and it also provides detailed histories of eolian dust deposition which document the aridification of asia monsoon evolution and the initiation of the yellow river in relation to the uplift of the tibetan plateau however the results of magnetostratigraphic dating of the fossil bearing sequence has yielded conflicting ages for the fauna and stratigraphy hindering the use of the sequence for addressing major paleoenvironmental and paleoclimatic issues here we review the paleontological lithological and magnetostratigraphic record of the xining basin and provide a new long and continuous high resolution magnetostratigraphy from the basin center the results show that the observed magnetic polarity zones from the various sections at different sites in the basin exhibit similar magnetic polarity patterns which can be readily correlated in terms of both magnetic polarity zonation and lithofacies in addition they show that the sedimentary sequence of the basin was sub continuously deposited from 54 ma to 4 8 ma the magnetostratigraphic correlations confirm previous constraint of the xiejia fauna in the late oligocene at 25 ma challenging the current chinese mammal land zonation for the early miocene and we suggest that it provides a superior record of eolian dust deposition and river incision in the late pliocene than previous studies there is a close match of the climatic proxy records of the xiejia section dated by magnetostratigraphy with the global climatic record which corroborates the paleomagnetic correlations the evolution of the sedimentary environment provided by the lithofacies demonstrates a complete cycle of basin formation and termination which records the eastern qilian shan experienced three main phases of uplifts slow episodic uplifts at 54 ma and 22 5 ma and a late rapid episodic uplifts at 8 7 ma and since 4 8 3 6 ma this tectonic uplift in the ne tibetan plateau was mostly nearly synchronous responses to the initial and continuing collision of india and asia since 50 5 ma

thin skinned extensional tectonics on a salt detachment northern kwanza basin angola abstract thin skinned extension on a salt detachment of a style known as raft tectonics characterizes deformation of the late aptian to recent section in the northern kwanza basin angola large rafts and intervening grabens are interpreted to have developed as a result of gravity gliding increased dip and gravity spreading asymmetrical loading of a sedimentary wedge major raft movement occurred primarily from the middle tertiary but some deformation appears to have started as early as late cenomanian or early turonian times individual grabens measure up to 70 km in length 15 km in width and nearly 3 km in depth and show switching polarities in the sense of thickening of the tertiary sedimentary infill graben geometries were controlled by syndepositional extension and the local availability of salt from the data examined which includes both seismic and well data the grabens appear to become younger from east to west reflecting basinward progression of the deformation as the age relationships could be related to insufficient sampling of strata deposited in complex sedimentation patterns they may have no relevance to the timing of the deformation the diachronous deformation is therefore speculative extension in the northern kwanza basin is estimated at 60 the outermost raft is translated 55 km westwards in addition to the extensional structures compressional folds thrust faults and salt structures mark the toe of the gravity gliding and spreading system all of the rafts lie within the african portion of the aptian salt basin on rifted continental crust and they are generally unrelated to structures below the salt biostratigraphy and lithostratigraphy indicate that the grabens formed on the shelf and upper slope from the middle eocene associated compressional features developed near the slope rise the unusual expression of raft tectonics is attributed to a combination of 1 the presence of a salt layer 2 a stable basement configuration that allowed quiescent accumulation of the raft sequence and 3 an increase in basin dip and sediment supply

counterclockwise p t t paths from amphibolites franciscan complex california relics from the early stages of subduction zone metamorphism overprinting mineral relationships in amphibolites from the franciscan complex california suggest metamorphic evolution from high temperature amphibolite facies to the blueschist facies with increasing p t ratio a counterclockwise p t t path early formed pargasitic amphiboles are both crosscut and rimmed by subcalcic hornblendes that are in turn cut or rimmed by sodic amphiboles some amphibolites are overprinted successively by eclogite and blueschist facies assemblages clinopyroxenes are zoned with increasing jadeite component from core to rim multiple generations of phengites are present in the same sample and are more si rich with each successive generation of growth garnets in eclogite overprinted amphibolites are zoned with an initial mgo increase away from the core to a maximum mgo zone followed by mgo decrease toward the rim garnets in other amphibolites show continually increasing mgo from core to rim several samples representative of the variety of franciscan amphibolites are describ

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

fractal analysis of tidal channels in the bahia blanca estuary argentina the fractal dimension d was estimated for nine tidal channels depicted in thematic mapper tm landsat 5 imagery to derive information about the degree of geomorphological control on a tidal channel network characteristic of the bahia blanca estuary argentina two methods box counting and contiguity were used to estimate fractal dimensions for each tidal channel all channels produced d values close to 1 meaning that they are self affine fractal features however these fractal dimensions do not represent the meandering pattern complexity characteristic of the tidal channels analysed although both methods allowed for estimation of d the contiguity method showed that three of the channels actually are not fractal but have sinusoidal characteristics a condition that was not detected by the former method

the effect of spatial heterogeneities on geomorphic expression in a model of basin evolution spatial variability is a basic component of all natural systems the system being studied here is the topography of an evolving drainage basin spatially heterogeneous erosivity within the drainage basin influences the structure of the drainage network the roughness of small scale features and the overall appearance of the simulated topography the presence of heterogeneities does not simply blur and smear analytical relationships the heterogeneities themselves introduce new structure to the organization of the drainage basin three measures the slope area relationship the cumulative area relationship and the hypsometric distribution are all systematically affected by spatial heterogeneity we will demonstrate how and why these relationships are affected and also how different structures in the heterogeneities themselves are manifested in the resulting simulated topography

precambrian blueschist terranes of the world blueschists are most common in post paleozoic orogenic belts higher geothermal gradients and a thinner lithosphere in the precambrian are widely thought to have disfavored blueschist formation however several precambrian blueschist belts have been reported from eurasia on the basis of established geologic and geochronologic constraints these belts are grouped as suspect possible and definite precambrian blueschists suspect ones include those in alaska in anglesey u k in the scandinavian caledonides and in yunnan china possible precambrian blueschist belts are those in delhi india in central china in heilongjiang china and in the urals and altai sayan tien shan u s s r definite precambrian blueschist terranes are those in western africa and in aksu china these blueschist belts are described with emphasis on the age constraints the recently investigated aksu blueschist terrane is presented as an example this high p t coherent blueschist greenschist terrane at aksu is unconformably overlain by a thick unmetamorphosed sedimentary sequence ranging in age from late sinian ca 600 800 ma through eocambrian to paleozoic the basal sinian conglomerates contain subrounded to rounded clasts of the underlying schist clearly demonstrating the pre sinian age of blueschist facies metamorphism characteristic features of the above mentioned blueschist belts include 1 1 the blueschist terranes are coherent and primary compositional lithological layers are well preserved melange belts are not common 2 2 protoliths include pelite sandstone bimodal volcanics limestone and small quantities of pillow basalt and pelagic sediment ultramafics are rare 3 3 the protoliths were subjected to multiple deformation and transitional blueschist greenschist facies metamorphism typical precambrian blueschist contains the assemblage crossitic amphibole epidote chlorite albite quartz actinolite rare lawsonite jadeitic pyroxene and aragonite have been described in few belts 4 4 the metamorphic facies series belongs to the high pressure intermediate type of miyashiro 1961 the precambrian blueschist and other pre mesozoic intracontinental blueschist of eurasia formed before rather than during final closure of intervening ocean basins between pairs of continents they do not usually mark the location of terminal sutures but are the result of earlier accretion and continental growth by subduction underplating and imbrication of accretionary wedges including both oceanic and continent derived elastics the rare preservation of precambrian blueschist is due to greenschist overprinting when the heat flow and geothermal gradient was high rather than reflecting lack of production their existence in china and africa demonstrates that requisite conditions for blueschist facies metamorphism existed at least 700 ma ago

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

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

lawsonite composition and zoning as tracers of subduction processes a global review abstract lawsonite is an abundant hydrous mineral in oceanic crust sediments and metasomatic rocks at depths of 45 to 300 km in most subduction zones but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism owing to the significance of lawsonite for water and element cycling in subduction zones occurrences of fresh lawsonite in blueschist and more rarely eclogite provide important opportunities to determine lawsonite composition zoning and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation in this review we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet omphacite in the rock matrix as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite facies rocks that lack matrix lawsonite as lawsonite blueschist is much more common than lawsonite eclogite we survey the composition of lawsonite in representative localities of blueschist including blueschist associated with eclogite lawsonite bearing epidote bearing and blueschist not associated with eclogite at current exposure levels included in this review are metabasaltic rocks silica and carbonate rich metasedimentary rocks metasomatic rocks and lawsonite rich veins this dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation and specifically of fluid rock interaction with implications for element cycling in subduction zones furthermore most exhumed lawsonite eclogite records slab surface conditions that correspond to the location where the slab mantle interface transitions from decoupled to coupled and therefore provides key insights into the thermal history and dynamics of subduction zones

australia s southern margin a product of oblique extension abstract recently developed detachment models of continental margin formation interpret the southern margin of australia to have formed when the lower plate australian margin was pulled out from beneath the upper plate antarctic margin data now available and summarised in this paper point very strongly to a generally nw se direction of initial continental extension for the southern margin in contrast to the widely held picture of simple n s rifting the evidence for this extension direction comes from the analysis of deep seismic data acquired by the bureau of mineral resources in 1986 in the central great australian bight gab the gravity field of the gab seismic and magnetic basement structures in the eyre sub basin polda trough ceduna depocentre and duntroon basin and from the analysis of the magnetic seafloor spreading anomalies produced during the slow first phase of drifting between australia and antarctica further it is now believed that the formation of the southern margin of australia can be described in terms of three phases of continental extension el to e3 and two phases of drifting d1 and d2 in summary these phases were as follows 1 e1 approximately 300 km of late jurassic or older to early cretaceous nw se oriented extension in the gab with strike slip motion in the nascent otway basin and along the tasmanian margin 2 e2 120 km of early cretaceous nne ssw oriented extension which formed the basins of southeastern australia otway bass gippsland and which probably produced a structural overprinting in the gab basin 3 e3 d1 minor continental extension and the first 500 km of slow drift between australia and antarctica on an azimuth of 165 wrenching on the tasmanian margin 4 d2 2600 km of fast drifting between australia and antarctica on a n s azimuth

quaternary slip history of the bare mountain fault nevada from the morphology and distribution of alluvial fan deposits analyses of alluvial fan sedimentation around bare mountain nevada indicate differential slip along the bare mountain fault during the pleistocene and holocene analyses show that the ratios of fan area to sediment source area and the degree of holocene sedimentation at the fan heads can be correlated with dip and displacement of the fault the well developed bajada and holocene deposits near the fan toes along the southwestern flank of bare mountain contrast with the location of holocene deposits near the fan heads and significantly smaller individual fan lobes on the eastern flank of the mountain adjacent to the bare mountain fault in addition ratios of fan area to source area along the eastern flank of the mountain decrease from north to south which we interpret to be caused by increased quaternary slip from north to south along the fault with relatively little holocene throw at tarantula canyon and maximum throw near wildcat peak the dip of the fault also changes from north to south with relatively shallow dip angles 45 to 50 at tarantula canyon and steeper 70 dips near wildcat peak geometric constraints dictate that for any given increment of horizontal extension vertical offsets will be smaller on those segments of the fault that have shallower dip angles on the basis of these observations we conclude that the recent slip rate of about 0 02 mm yr derived from trenching studies in the tarantula canyon fan should be considered a minimum value that may not represent the slip rate of the bare mountain fault as a whole

temporal and lateral variation in the development of growth faults and growth strata in western niger delta nigeria this study examines eight syndepositional faults and syntectonic sediments in five major fault blocks in western niger delta offshore nigeria on three dimensional seismic data the initiation lateral growth and retreat periods of activity and quiescence and decay of faulting around these blocks can be ascertained by analyzing a series of time structure and isopach maps the study area can be subdivided into three structural zones the first structural zone is a northwestern zone characterized by a major counterregional growth fault in the deep subsurface this deep seated structure is superposed by an array of younger regional growth faults displacing a kilometer thick sedimentary overburden that accumulated on the former footwall the second structural zone is a central to eastern zone that seems mostly unaffected by young deltaic faulting this zone is characterized by the thinnest sedimentary record of the study area the third structural zone is a southeastern zone that is dominated by a large listric backstepping master fault zone associated with a kilometer scale rollover system regional structural and stratigraphic analyses document an apparently strong relationship between syntectonic sedimentation and syndepositional fault activity in that phases of significant fault activity lateral fault growth and fault migration concur with major depositional phases in turn areas and intervals characterized by the least sediment accumulation also record the lowest fault activity however one particularity of the studied system is that it underwent at least one period of seaward fault progression that coincided with a backstepping of faulting on the landward side although the forward stepping of faulting near the delta front can be interpreted as the consequence of the progressive loading during delta progradation the contemporaneous backstepping of faulting further inboard likely reflects the sustained lateral growth of mature deltaic faults into previously undeformed proximal parts of the depocenter the results of this study thus document that although an apparent correlation with the superimposed depositional system exists on a regional scale inboard deltaic faults may persist to grow irrespective of sedimentary loading the recognition of such fault trends is particularly important for estimating the influence of late stage fault movement on hydrocarbon migration or the discovery of subtle fault controlled hanging wall reservoirs

a garnet zircon oxygen isotope record of subduction and exhumation fluids from the franciscan complex california tectonic blocks of high grade metamorphic rock hosted by the franciscan me lange commonly preserve textural and geochemical evidence for metasomatism and blueschist facies overprinting within a subduction zone these exhumation events can obscure information on the nature of subduction fluids at depth that might otherwise be preserved by these rocks in this tectonic setting cation and oxygen isotope zoning in garnets from eclogite and garnet hornblende rocks with minimal textural evidence of retrogression reveals separate prograde and retrograde fluid histories garnet cores preserve a homogeneous prograde oxygen isotope history with both high do 11o and low 4o values in different samples probably recording altered ocean crust protolith compositions multiple episodes of garnet resorption and regrowth record a dramatically changing bulk oxygen isotope ratio resulting in 6 7o neoformed garnet rims with sharp core rim boundaries in both samples matrix omphacite and hornblende are in profound oxygen isotope disequilibrium with garnet cores but are in equilibrium with garnet rims despite the appearance of overall textural equilibrium in thin section this cryptic metasomatism found in samples from different locations within the franciscan complex brings into question existing thermobarometry on non inclusion phases for this complex as well as interpretations based on whole rock geochemical data zircon ages and oxygen isotope equilibrium with late forming garnet are consistent with postmetasomatic formation of zircon the ability of garnet and zircon to record multiple fluid events and tie them to p t t fluid history is a powerful tool in gaining an improved understanding of the complex fluid environments within subduction zones

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

structural styles in the deep water fold and thrust belts of the niger delta the deep water niger delta includes two large fold and thrust belts products of contraction caused by gravity driven extension on the shelf that exhibit complex styles of thrusting these contractional structures formed above multiple detachment levels in the overpressured shales of the akata formation using the patterns of growth sedimentation fold shapes fault plane seismic reflections and combined conventional and shear fault bend folding theories we describe and model the structural styles and kinematics of the fault related folds and imbricate thrust systems that compose these belts individual fault related folds involving both forethrusts and backthrusts are characterized by long planar backlimbs that dip less than the associated fault ramps with upward shallowing of dips in growth strata above the backlimbs suggesting components of progressive limb rotation forelimbs are short compared to backlimbs but growth strata show more consistent dips that suggest a component of folding by kink band migration thus we employ a combination of classic and shear fault bend fold theories to describe these structures including the influence of a weak basal detachment zone in the overpressured shales we expand upon these theories to model the kinematics of imbricate thrust systems which display a complex history of thrusting related to spatial and temporal variations in deposition across the delta regional patterns of folded growth strata are used to define break forward break backward and coeval thrusting involving single and multiple detachment levels we define two main types of imbricate thrust systems type i system with a single basal detachment level and type ii imbricate system with multiple basal detachment levels which cause massive structural thickening of the akata formation and refolding of shallow thrust sheets through the sequential restoration of two regional cross sections across these systems we resolve the structural styles the timing and sequences of thrusting as well as the regional amounts of shortening all of which have important implications for hydrocarbon maturation and charge in the deep water niger delta

hanging wall fault kinematics and footwall collapse in listric growth fault systems we describe the structure of a listric growth fault system from se asia using high resolution 3 d seismic data the fault system shows systematic changes in geometry and kinematics that are sympathetic with along strike changes in the structure of the bounding fault where the position of the bounding fault remained fixed there is an overall landward decrease in the age of the hanging wall growth faults along strike three phases of footwall collapse caused by the active bounding fault stepping back into the footwall block were responsible for the punctuated stepwise landward migration of the rollover hinge and associated hanging wall growth faults during extension the migration of these hanging wall structures is similar to that predicted by simple analogue models with fixed detachment surfaces care should therefore be taken in defining kinematic models in areas where the geometry of the bounding fault is either poorly defined or unknown

the origin and evolution of complex transfer zones graben shifts in conjugate fault systems around the funan field pattani basin gulf of thailand abstract changes in dip province associated with conjugate fault sets produce complex transfer zones locally known as graben shifts between sets of convergent conjugate faults in the pattani basin 3d seismic data over a well developed graben shift geometry in the funan field area of the pattani basin has revealed details of the transfer zone development in map view the graben shift is seen as west dipping faults forming a wedge shaped incursion into a zone of east dipping faults the wedge boundaries trend ne sw and nw se at a high angle to the n s striking normal faults within the transfer zones faults only slightly overlap with their neighbours with individual faults tending to widen upwards the narrow regions of overlap indicate displacement transfer must occur between more widely separated faults not neighbouring faults the initial oligocene early miocene syn rift fault pattern appears to have been strongly influenced by pre existing basement trends as indicated by 1 the restriction of west dipping secondary faults to the present day area of the graben shift 2 the line of the ne sw boundary to the graben shift coinciding with fault segment linkage geometries in two major syn rift faults and 3 curvature of minor fault tips into the transfer zone the subsequent conjugate fault system developed during thermal subsidence shows that the dip asymmetry and map boundaries of the fault dip panels are strongly influenced by the syn rift fault geometry there is no indication of active strike slip faulting affecting the graben shift geometry fault displacement diagrams commonly show linkage between deeper and shallower displacement maxima indicating early late oligocene early miocene minor west dipping normal faults influenced the location and width of higher middle late miocene conjugate faults hence two stages of structural inheritance led to the middle late miocene graben shift geometry

sedimentation and shale tectonics of the northwestern niger delta front abstract the modern day slope and outer shelf of the niger delta are characterized by fault bounded sedimentary depocentres and intervening shale structures some of which are diapiric using two dimensional seismic reflection data and stratigraphic information from five wells the neogene history of a 70 30 km portion of the northwestern niger delta shelf and slope has been examined the shale structures were established by late miocene time probably in response to lateral shale withdrawal from beneath the advancing deltaic load combined with compressional uplift and folding of pro delta strata during pliocene and pleistocene time these structures were buried by the prograding delta and extensional growth faulting commenced stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period throughout the pliocene extension and subsidence were concentrated in a graben like depocentre bounded by both regional and counter regional growth faults during the early pleistocene subsidence on the regional growth fault ceased and growth was transferred to the counter regional growth fault set the geometry and history of the depocentre is analogous to salt related depocentres typical of the northern gulf of mexico and atlantic margins of brazil and angola to explain the history of the niger delta study area a model is proposed in which the miocene pleistocene sedimentary package has slid basinward breaking up during extension thereby creating seaward stepping depocentres examples from analogue modelling studies are used to suggest possible origins for the large counter regional growth faults

fault superimposition and linkage resulting from stress changes during rifting examples from 3d seismic data phitsanulok basin thailand abstract the phitsanulok basin thailand provides examples of changing fault displacement patterns with time associated with faults of different orientations in the northern phitsanulok basin three main stress states have been identified associated with late oligocene recent fault development 1 late oligocene late miocene approximately e w extension n s shmax main rift stage 2 late miocene pliocene transtension to tranpression e w to ne sw shmax late rift stage and 3 pliocene recent very minor faulting e w extension n s shmax post rift stage syn rift faults tend to strike n s but also follow ne sw and nw se trends and are basement involved the late miocene deformation produced a distinctly different type of fault population from the main rift fault set characterized by numerous small displacement tens of metres faults striking predominantly ne sw most of these faults are convergent conjugate sets aligned in discrete zones and nucleated within the sedimentary basin reactivation of main rift faults trends during the late rift stage favoured strike directions between 350 and 50 the displacement characteristics of three large faults within the basin show variations depending upon fault orientation the low angle 23 30 dip western boundary fault 7 km throw displays little discernible difference in the distribution of displacement on fault zone during the different stress states other than increases and decreases in displacement amount smaller faults exhibit a more selective reactivation history than the western boundary fault and are more informative about fault response to a varying stress field activation of the oblique ne sw striking ntm 1 initially produced a fault divided into three segments splaying into n s trends stress reorientation during the late rift stage finally linked ne sw striking segments the partial linkage of the fault zone at the time of oil migration resulted in the southwestern part of the ntm 1 fault sealing hydrocarbon bearing reservoirs whilst late linkage areas along the northeastern part failed to seal hydrocarbons the n s striking pto 1 fault shows early isolated fault segments linkage during syn rift motion then a more patchy distribution of displacement late in the fault history perhaps due to non optimal orientation of the fault to the regional stress field when compared with the ntm 1 fault the fault characteristics described indicate that where strong pre existing fabrics are present and varying stress regimes have occurred fault population characteristics and evolution of fault displacement can depart considerably from extensional fault populations associated with a single phase of extension

quantifying cretaceous cenozoic exhumation in the otway basin southeastern australia using sonic transit time data implications for conventional and unconventional hydrocarbon prospectivity in prospective basins affected by exhumation uncertainty commonly exists regarding the maximum burial depths of source reservoir and seal horizons one such basin is the otway basin an important gas province in southeastern australia which has witnessed several exhumation events here we present estimates of net exhumation magnitudes for 110 onshore and offshore petroleum wells based on the sonic transit time analyses of lower cretaceous fluvial shales our results show significant post albian net exhumation in the eastern onshore otway basin 1500 m 4920 ft and a generally minor net exhumation 200 m 655 ft elsewhere in the otway basin consistent with estimates based on thermal history data the distribution of net exhumation magnitudes in relation to mid cretaceous and neogene compressional structures indicates that exhumation was dominantly controlled by short wavelength basin inversion driven by plate boundary forces deeper burial coupled with high geothermal gradients in the onshore eastern otway basin and along the northern basin margin during the early cretaceous have rendered lower cretaceous source rocks mostly overmature with any remaining hydrocarbons from the initial charge likely to be trapped in tightly compacted reservoirs and or secondary fracture related porosity however the embrittlement of these reservoirs during their deeper burial may present opportunities for the development of low permeability plays through hydraulic fracturing where smectite clay minerals are illitized source rocks at near maximum burial at present day are at temperatures suitable for gas generation with key controls on prospectivity in these areas including the sealing potential of faulted traps and the relationship between charge and trap development

deep water niger delta fold and thrust belt modeled as a critical taper wedge the influence of elevated basal fluid pressure on structural styles we use critical taper wedge mechanics theory to show that the niger delta toe thrust system deforms above a very weak basal detachment induced by high pore fluid pressure the niger delta exhibits similar rock properties but an anomalously low taper sum of the bathymetric slope and dip of the basal detachment compared with most orogenic fold belts this low taper implies that the niger delta has a very weak basal detachment which we interpret to reflect elevated pore fluid pressure 0 90 within the akata formation a prodelta marine shale that contains the basal detachment horizon the weak basal detachment zone has a significant influence on the structural styles in the deep water niger delta fold belts the overpressured and thereby weak akata shales ductilely deform within the cores of anticlines and in the hanging walls of toe thrust structures leading to the development of shear fault bend folds and detachment anticlines that form the main structural trap types in the deep water fold belts moreover the low taper shape leads to the widespread development of backthrust zones as well as the presence of large relatively undeformed regions that separate the deep water fold and thrust belts this study expands the use of critical taper wedge mechanics concepts to passive margin settings while documenting the influence of elevated basal fluid pressures on the structure and tectonics of the deep water niger delta

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

fate of the subducted farallon plate inferred from eclogite xenoliths in the colorado plateau we present the first finding of the high pressure mineral coesite in lawsonite bearing eclogite xenoliths from the colorado plateau united states the presence of coesite in these xenoliths supports the hypothesis that the eclogite formed in a low temperature high pressure environment such as envisaged inside subducted oceanic lithosphere ion microprobe u pb dating of micrometer scale zircons in the eclogites yields ages ranging from 81 ma to 33 ma the two extremes in age likely indicating the age of crystallization during subduction related metamorphism and the age of recrystallization by the host magmatic event respectively these observations conclusively demonstrate that certain eclogite xenoliths from the colorado plateau originated as fragments of the subducted farallon plate which had been residing in the upper mantle since the late cretaceous this is the first conclusive evidence that any eclogite xenoliths can be directly linked to a known subducted plate

structural evolution of horst and half graben structures proximal to a transtensional fault system determined using 3d seismic data from the shipwreck trough offshore otway basin australia abstract using a three dimensional 3d seismic reflection dataset from the shipwreck trough offshore otway basin southern australia we aim to characterise and understand the structural evolution of the shipwreck fault zone sfz and associated extensional structures the sfz is a key structural element of the otway basin which is a nw striking upper jurassic cenozoic rift to passive margin basin that formed due to the breakup of australia and antarctica the sfz marks the transition from the major southern margin rift system to the west and the oceanic continental transform margin to the se the sfz formed and bounds the shipwreck trough on the eastern side and is interpreted as a n s striking transtensional fault zone representing the northern en echelon extension of the transform margin to the south the shipwreck trough is the downward thrown western side of the sfz and is host to an array of horst and half graben structures two of which contain the producing geographe and thylacine gas fields the shipwreck trough and sfz are imaged by the investigator 3d seismic dataset which has previously been studied to conduct 2d restorations and interpret the timing magnitude orientation and nature of the structural events of the shipwreck trough our study adds to this previous research by using spectral decomposition and coherence volumes to further characterise the sfz and associated igneous features basement structural elements and late cretaceous horst and half graben structures we have identified examples of releasing bend releasing jog and restraining jog structures along the sfz that are indicative of sinistral transtensional deformation and have highlighted areas of increased basement fault block relief which have driven extensional faulting in the cover we have also conducted throw distance and throw depth analysis on four horst and half graben structures and shown that the associated normal faults have had continuous late cretaceous growth with the structures being formed through incidental linkage of normal fault segments finally our two way time twt and isochronal mapping of the entire 3d survey shows the development of the late cretaceous rifting event in the shipwreck trough and highlights numerous other structural closures similar to and with close vicinity of the thylacine and geographe gas fields providing implications for prospectivity

growth and linkage of a complex oblique slip fault zone in the pearl river mouth basin northern south china sea abstract oblique slip faults are ubiquitous in sedimentary basins but have been largely neglected relative to their dip slip counterparts case studies of oblique slip faults are very limited in this study we used 3d seismic data tied to well control to investigate the geometry kinematic characteristics growth and linkage and tempo spatial evolution of a complex oblique slip growth fault zone in the pearl river mouth basin prmb of the northern continental margin south china sea scs the e w oriented 30 5 km long fault zone consists of two superimposed oblique slip fault systems the lower fault system is an integrated zig zag fault consisting of three ene wsw to e w striking right stepping sinistral en echelon fault segments which were hard linked by two nw se trending fault segments while the upper fault system is composed of nine wnw ese striking left stepping dextral en echelon component faults which had overlapping fault tips and were partly hard linked by breaching of the relay zones the lower and upper fault systems were activated in the eocene and the oligocene to pliocene which respectively correspond to the syn rift and post rift stages in the prmb the fault throws up to 288 m and activity rates up to 34 5 m ma of the upper fault system are overall much less than those of its lower counterpart reactivation of the lower syn rift fault system shows clear influence on the development of post rift en echelon fault segments a four stage evolution model of the oblique slip fault zone was presented

tectonic controls of the north anatolian fault system nafs on the geomorphic evolution of the alluvial fans and fan catchments in erzincan pull apart basin turkey abstract the erzincan pull apart basin is located in the eastern section of the north anatolian fault system nafs the tectonic evolution of this basin is mostly controlled by strike slip master faults of the nafs this study examines the topography structure relationships in an effort to evaluate the tectonic signatures in the landscape paying special attention to recent tectonic activity in the study the main focus is on the tectonic controls of the nafs on the geomorphic evolution of alluvial fans and fan catchments in the erzincan pull apart basin the observations of the amount of tilting of the alluvial fans and its relation with morphometric asymmetry factor af hypsometric integral hi fractal analysis of drainage networks d properties of the fan catchments provide valuable information about the tectonic evolution of the basin area the results of the analyses showed that the alluvial fan and fan catchment morphology in the pull apart basin are mainly controlled by the ongoing tectonic activity of the nafs the fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin and aggradation processes by causing channel migration channel incision and tilting the alluvial fans

ultrahigh pressure metabasaltic garnets as probes into deep subduction zone chemical cycling 1 we demonstrate an approach to examining the metamorphic history of subducting oceanic crust that can complement records of subduction zone chemical cycling derived from studies of igneous rocks produced at volcanic arcs by merging methods utilizing garnet zoning to establish prograde reaction histories with in situ high resolution trace element geochemistry and application to coesite bearing mafic eclogites representing subduction to depths beneath arcs we are able to directly identify geochemical manifestations of reactions contributing to element mobility in the subducting slab that are only inferred in studies of volcanic arcs or theoretical metamorphic models specifically we identify a prograde metamorphic reaction based solely on the zoning of geochemistry and mineral inclusions within garnet and infer that these features are a record of the breakdown of coexisting clinozoisite titanite and probable liberation of trace element laden fluid from the rock during prograde metamorphism we are then able to assign a specific depth interval for the reaction through calculation of the p t dependence of the reaction for these eclogites and comparison with a published p t trajectory because of the robust preservation of records of petrologic and geochemical processes by garnet this methodology is particularly suited for study of ultrahigh pressure uhp eclogites in which severe retrograde alteration generally related to exhumation commonly obscures prograde history

tectonic evolution of the penglai 7 6 structure and its implications for petroleum exploration in a releasing bend of a strike slip fault system tan lu fault zone east china abstract the penglai 7 6 pl7 6 structure is located on the tan lu fault zone a huge fault zone in east asia tectonism of the tan lu fault zone produced complex structural deformation and was an important factor in petroleum accumulation three dimensional seismic data were employed to document the structural geometry and evolutionary process of the pl7 6 structure and implications for petroleum exploration in a releasing bend of a strike slip fault system were discussed systematic analysis of the seismic data indicates that the main fault the bd2 fault of the tan lu fault system slipped right laterally during the cenozoic strike slip movement of the bd2 fault peaked during deposition of e 1 2 k to e 3 d 3 and decreased largely in intensity during e 3 d 1 2 deposition in the neogene and quaternary the bd2 fault was reactivated formation of the bodongnan low uplift is related to the connection between the bodongnan low uplift n and bodongnan low uplift s the bodongnan low uplift n is represented by an anticline produced by strike slip movement of the bd2 fault and the bodongnan low uplift s is represented by the relatively uplifted strata in the vicinity of an extensional fault the bd3 fault the pl7 6 structure developed above a releasing bend formed by the subsequent strike slip movement of the curved bd3 fault orientations of the shallow faults in the pl7 6 structure are not only associated with the lower bd3 fault but also controlled by the basement high unlike traditional releasing bends that are generally disadvantage to petroleum accumulation due to the lower structural elevation in the center the releasing bend in the pl7 6 structure is favorable for petroleum accumulation because of the three reasons 1 adjacent to generative kitchens 2 located on a regional structural high and 3 served by the releasing bend related faults acting as conduits for vertical petroleum migration

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

phosphate lu hf geochronology abstract igneous metamorphic and biogenic apatite contains lu and hf in proportions that make this mineral suitable for dating by the 176lu 176hf method we present a new method for separation of lu and hf from apatite that involves a single extraction column step for hf and a second exchange column step for lu this procedure allows rapid sample processing prior to analysis by mc icp ms results from the igneous gardiner skaergaard and khibina intrusions indicate that the closure temperature for the lu hf isotopic system in apatite is relatively high the lu hf isochron age of 60 ma for the skaergaard intrusion east greenland is older than the generally accepted emplacement age but does not appear to be a product of mixing a centimeter sized apatite from the otter lake area grenvillian province yields high and variable 176lu 177hf ratios showing that metamorphic apatite may in some cases allow for mono mineral dating the most important application of the method is undoubtedly its potential use for dating sedimentary formations although we find biogenic apatite in porous matrix highly susceptible to post depositional resetting of the lu hf isotopic system the preservation of a near depositional age for a shark tooth from the impermeable london clay and recent work on crystalline authigenic phosphorites earth planet sci lett 201 2002 203 show the lu hf system to be a promising tool for direct dating of sedimentary formations

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

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

deep seismic images and the tectonic framework of early rifting in the otway basin australian southern margin abstract the otway basin is one of a number of basins formed along australia s southern continental margin during the late jurassic early cretaceous rifting of australia from antarctica it lies on a transitional area of extended lithosphere between the margin to the west where continental separation took place close to the australian craton and the region to the east where separation failed to develop through bass strait but instead switched to the south of tasmania seven agso regional deep seismic profiles recorded during 1992 across onshore parts of the basin provide images of synrift basin bounding faults that dip predominantly towards the continent basin sequences in half graben rift segments at two way times greater than 4 s and mid crustal detachments with ramp and flat geometry at mid crustal levels when combined with industry seismic data trend variations on faults indicate that extensional strain direction varied along the rift system probably locally controlled by pre existing palaeozoic geology but consistent with general north south lithospheric extension basement highs between some of the rift segments are interpreted as accommodation or transfer zones multiple basin bounding faults in some places mirror features within basement and may indicate a component of local strike slip during early rifting the syn rift segments form part of the first stage early cretaceous failed rift system in the otway bass strait region crustal thickness is interpreted to be 31 km 10 3 10 5 s twt near the northern basin margin thinning to about 25 km 9 s twt 40 reduction in thickness of palaeozoic crust seaward of the tartwaup fault zone this fault zone and the timboon fault system farther east are interpreted to be headwall faults landward limit of a late cretaceous second stage rifting system along a lower plate margin which ultimately separated australia from antarctica

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico ii structure the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope

lawsonite lu hf geochronology a new geochronometer for subduction zone processes we present a new method for lu hf geochronology using lawsonite an index mineral of high pressure low temperature metamorphism the method uses common cation exchange chromatography to purify lu and hf from the sample and analysis by multicollector inductively coupled plasma mass spectrometry lawsonite 176 lu 177 hf ratios are elevated and are similar to other minerals commonly used in lu hf geochronology such as garnet or apatite we obtain an age of 145 5 2 4 ma for lawsonite blueschist facies metamorphism at ring mountain within the franciscan complex california the lawsonite type locality the age agrees well with published geochronology and thermochronology for the franciscan complex the new method provides a powerful tool to investigate processes and time scales of blueschist to eclogite facies metamorphism crust mantle recycling via subduction and the geodynamics of convergent margins

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

phengite based chronology of k and ba rich fluid flow in two paleosubduction zones subduction recycles aqueous fluids from slab and sediment to the mantle subduction zones are long lived but time scales for fluid rock interaction within subduction complexes are uncertain large ion lithophile elements potassium and barium were added to eclogite subducted basalt during high pressure temperature metamorphism via phengite crystallization from subduction zone fluids phengite grains from eclogite blocks and their metasomatic selvages yielded 40ar 39ar ages across grains and between samples that indicate 25 and 60 million years of fluid rock interaction in the samana complex dominican republic and the franciscan complex california respectively

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

the high pressure synthesis of lawsonite in the morb h2o system lawsonite is an important water reservoir in subducting oceanic crust below the amphibole dehydration depth 70 km to determine the maximum pressure stability of lawsonite in the morb1h2o system experiments were carried out using a 1000 ton uniaxial multi anvil apparatus spi 1000 mixtures of synthetic gel12wt h2o were used for the starting materials with the average morb composition experimental p t conditions were t 5 700 900 8c and p 5 5 5 13 5 gpa run durations were 12 and 24 h lawsonite was synthesized stably up to 10 gpa and t 700 8c in the stishovite stability field and 900 8c at 8 gpa and 750 8c at 5 5 gpa in the coesite stability field with a steep positive slope for the lawsonite out reaction the lawsonite out reaction in the coesite stability field changes to have a gentle negative slope in the stishovite stability field the reaction leading to the disappearance of lawsonite is a continuous reaction due to the compositional enlargement of garnet toward the grossular end member with increasing t and p lawsonite disappears when the tie line connecting grossular rich garnet with omphacitic clinopyroxene reaches the bulk composition on the conventional ac fm ternary diagram

balancing deformation in nw borneo quantifying plate scale vs gravitational tectonics in a delta and deepwater fold thrust belt system abstract recent gps measurements demonstrate that nw borneo undergoes 4 6 mm of plate scale shortening a year which is not accommodated by plate scale structures the only geological structure in nw borneo described to accommodate on going shortening is the baram delta system located on the outer shelf to basin floor delta toe fold thrust belts are commonly thought to be caused by margin normal compressional stresses generated by margin parallel upslope gravitational extension the baram delta system is divided into three neotectonic provinces 1 an inactive onshore and inner shelf region of inversion superimposed on an older extensional deltaic province 2 an outer shelf region of present day deltaic extension and 3 a compressional delta toe however it is uncertain whether compression in the delta toe area is purely driven by gravity i e shortening is less than upslope extension or if there is a component of regional shortening involved which can only be demonstrated if shortening is greater than upslope extension in order to quantify the balance between the shortening related to the upslope gravitational extension and the shortening related to the regional geodynamic framework in the baram delta system we have used a geomechanical code based on the finite element method and conservation of mass and momentum dynel 2d this enabled us to reconstruct the tectonic evolution of the delta and to demonstrate for the first time that the total shortening observed in the delta toe does not balance against the active extension in the delta top with the system exhibiting 1 8 shortening overall or 2 0 km this additional shortening is therefore attributed to plate scale shortening across nw borneo produced by far field compression using a convergence rate of 4 mm y 1 demonstrated by gps measurements the delta toe has accommodated far field compression only in the last 0 5 my

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

the franciscan complex california usa the model case for return flow in a subduction channel put to the test the model of return flow in a subduction channel rfsc is put to the test by opposing key assumptions of the model to an integrated review of field data petrology geochronology and structures of high p melanges of the franciscan subduction complex fsc to which rfsc has been first applied key assumptions are i the subduction channel sc is a low viscosity zone of finite width restrained by the rigid subducted and overriding plates ii forced return flow in the sc is associated with formation and km scale displacements of small tectonic blocks 1 km in a highly deformable matrix iii this results in apparently random distributions and close associations of blocks exhumed from different depths hence the block in matrix structures and exotic blocks in high p melanges would reflect the structural state at depth of the sc on the basis of the predictions ensuing from the key assumptions of the rfsc model on the rock record it is detailed why the actual record of the high p melanges of the fsc does not comply with this perception the record rather reflects recurring subduction underplating associated decollement erosion and mingling of high p rocks by sedimentary processes in the trench all occurring in an 80 m y lasting period distributed deformation of the melange matrix is unrelated to formation of apparently chaotic block in matrix structures since i creation subduction ascent and cooling of exotic blocks on counterclockwise p t paths predates deposition of the bulk of the metasediments constituting the matrix by 20 40 m y ii deformation of the matrix occurs during a second loop of high p metamorphism postdating creation and ascent of the exotic blocks by at least 20 40 m y iii the magnitudes of distributed deformation of the matrix are too low to cause juxtaposition of blocks different in p t paths against each other from km scale vertical distances instead narrow few tens of metres wide fault shear and decollement zones formed at locally high pore fluid pressures accumulate the major tectonic transport during high p metamorphism they bound several 100s of metres wide tabular tectonic bodies that are coherent sedimentary processes at the active continental margin formed the bulk of the melanges tectonically formed block in matrix structures within the shear and decollement zones are unrelated to juxtaposition of exotic blocks universal diagnostic criteria are developed to identify return rfsc as a mechanism that potentially amalgamates heterogeneous metamorphic terrains by using field data petrology and geochronology

dating subduction zone metamorphism with combined garnet and lawsonite lu hf geochronology studies of ancient and active subduction zones are critically important to understanding processes of interplate coupling crust mantle recycling and arc magmatism dating subduction metamorphism along prograde and retrograde paths in order to constrain such processes however has proved to be extremely difficult the complex thermal history of subduction systems poses significant challenges to low t geochronometers and subduction zone assemblages commonly lack suitable minerals for higher temperature geochronology garnet and lawsonite however are critical index minerals of high and low t subduction zone metamorphism and are well suited to lu hf geochronology in addition the closure temperature for lu hf in garnet and lawsonite should be sufficiently high that an age will date mineral crystallization and therefore the timing of subduction zone metamorphism the relative stability and timing of garnet and lawsonite formation will be controlled by the bulk composition peak metamorphic conditions and shape of the p t path experienced by a particular sample to test the influence of metamorphic conditions and p t path on lu hf geochronology garnet and lawsonite bearing samples were dated from rocks where lawsonite formed after garnet along a retrograde path stabilized prior to garnet along a prograde path and formed contemporaneously with garnet in the franciscan complex the ages of garnet epidote amphibolite garnet epidote blueschist garnet lawsonite blueschist and lawsonite blueschist range from c 166 130 ma and generally decrease with decreasing metamorphic grade consistent with previous studies garnet lawsonite blueschist eclogite formed along an apparent prograde path at ward creek records an apparent age of c 152 ma lower temperature lawsonite blueschist at ward creek however failed to provide a geologically significant date and likely reflects isotopic disequilibrium at low temperatures the apparent temperature time history from franciscan complex lu hf ages most likely reflects samples derived from various portions of the subduction zone or that were subducted and metamorphosed at different times in the thermal evolution of the subduction zone in the sivrihisar massif lawsonite eclogite and garnet lawsonite blueschist record distinctly different ages of 91 1 1 3 ma and 83 3 1 8 ma the different ages date the timing of high p metamorphism within each protolith and suggest that garnet lawsonite eclogite metamorphism pre dated garnet lawsonite blueschist metamorphism in these samples by c 8 ma the age of lawsonite eclogite metamorphism extends the timing of high p metamorphism and requires subduction initiation prior to 91 ma the results indicate that the lu hf system provides a reliable tool for dating the wide range in p t conditions of subduction zone metamorphism lawsonite dating in particular provides a reliable method by which to date low t retrograde and prograde metamorphism in the absence of garnet lawsonite may not be ideal for geochronology if sufficient garnet coexists in the mineral assemblage the lawsonite has very low t stability or if extremely fine grained hf phases such as zircon are present in lawsonite in poly metamorphic assemblages where the pressure and temperature can be estimated for separate garnet and lawsonite sub assemblages the age discrepancy between garnet and lawsonite may provide the ability to quantify the rates of heating or cooling and subduction or exhumation

temporal and spatial development of a gravity driven normal fault array middle upper jurassic south viking graben northern north sea abstract three dimensional seismic and well data from the south viking graben northern north sea basin is used to investigate the temporal and spatial development of a gravity driven normal fault array above an evaporite rich detachment two moderate throw 500 900 m middle to upper jurassic normal faults the gudrun and brynhild faults are developed within the study area both faults die out laterally and tip out upwards at different structural levels within the syn rift succession both faults terminate downwards into late permian evaporites zechstein group and do not offset pre evaporite basement units this thin skinned fault array developed in response to westwards tilting of the hangingwall of the south viking graben during late jurassic rifting and consequent westward gliding and extensional break up of units above the mechanically weak evaporite horizon isochron mapping and well based correlation of middle to upper jurassic syn rift units allow constraints to be placed on the temporal evolution of the fault array several stages of structural development are observed which document i a period of relatively minor early i e pre rift halokinesis ii variable spatial activity on individual faults within the array and iii the progressive upslope migration of active faulting within the array as a whole the progressive upslope migration of fault activity is interpreted to reflect progressive unbuttressing and extensional faulting of upslope post evaporite units the overall structural style and kinematic evolution identified here shares many characteristics with both rift raft tectonics documented in other rifts developed above an evaporitic sub stratum and raft tectonics described from passive margin basins containing thick mobile salt or shale intervals this style of fault array evolution differs from that observed in rifts lacking mobile layers at depth and highlights the importance of these units in the structural development of rifts

first 40ar 39ar ages from low t mafic blueschist blocks in a franciscan melange near san simeon implications for initiation of subduction abstractthe franciscan complex of california is a type example of an accretionary prism with widespread high p t subduction zone metamorphism low t fine grained lawsonite bearing mafic blueschists encased in a shale matrix melange near san simeon have been dated for the first time 40ar 39ar ages were obtained for phengite separated from four blocks and from an actinolitic rind on the margin of one of the blocks the three blocks with lawsonite epidote yield ages of between 154 and ma while the actinolitic rind yields an age of ma these ages are from the part of the franciscan complex west of the san andreas fault that moved northward at least 300 km with respect to the extensive franciscan exposures east of the fault the ages obtained in this study show that some fine grained low t lawsonite epidote franciscan blueschist blocks formed at the same time as coarse grained high t garnet epidote franciscan blueschist blocks these dated rocks indicate that both high and low t mafic blueschi

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

rare earth diffusion kinetics in garnet experimental studies and applications abstract we determined the diffusion coefficient of sm in almandine garnet as function of temperature at 1 bar and fo 2 corresponding to that of wustite iron buffer and to a limited extent that of a few other selected rare earth elements in almandine and pyrope garnets both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields the experimental diffusion profiles were analyzed by secondary ion mass spectrometry and in addition by rutherford back scattering spectroscopy for two samples transmission electron microscopic study of an almandine crystal that was diffusion annealed did not reveal any near surface fast diffusion path using reasonable approximations and theoretical analysis of vacancy diffusion the experimental data were used to develop an expression of rare earth element ree diffusion coefficient in garnet as a function of temperature pressure fo 2 ionic radius and matrix composition calculation of the closure temperature for the sm nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently modeling of the ree evolution in melt and residual garnet suggests that for dry melting condition the ree pattern in the melt should commonly conform closely to that expected for equilibrium melting however for much lower solidus temperatures that would prevail in the presence of a h 2 o co 2 fluid the concentration of light ree in the melt could be significantly lower than that under equilibrium melting condition a reported core and rim differences in the ree content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the ree zoning was a consequence of entrapment in a magma derived from an external source for 32 000 yr before the eruption

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

growth faults above shale seismic scale outcrop analogues from the makran foreland sw pakistan abstract the southern makran fold thrust belt pakistan displays unique outcrop examples of well exposed kilometre scale listric growth faults that displace miocene age deltaic growth strata by several hundreds of metres to kilometers the largest growth faults are counter regional landward dipping bounding major clastic depocentres exposed over areas 1000 km 2 stratal offset along these faults can exceed 1 5 km fault zone thicknesses range between ca 100 and 400 m and average fault thickness displacement ratios are around 1 10 high resolution satellite data show in unprecedented detail the faults and the stratigraphic architecture of associated growth sequences which comprise kilometre scale progradational clinoforms thick mudstone units and basinwards wedging sandstone shale deposits the true vertical thickness of the syn kinematic record is in places up to 8 km making the outcrop examples equivalent to major growth faulted successions known from seismic data of large deltas and at least an order of magnitude larger than other outcrop examples a comparison of the makran outcrops with seismic reflection examples offshore nw borneo reveals distinct similarities in the gross depocentre geometries and internal architecture the key control for growth faulting is interpreted to result from sedimentary loading with rapid sedimentary progradation causing the development of rollover synclines by differential compaction and fluid expulsion and counter regional growth faults preferentially forming on the basinward side of these synclines the data and interpretations presented can be used to assess the key parameters that contribute to the development of growth faults and growth successions above shale reinforcing structural and stratigraphic observations from seismic interpretation and modelling studies in demonstrating their occurrence in exposure

active normal faulting beneath a salt layer an experimental study of deformation patterns in the cover sequence scaled experimental models show that the presence of a viscous layer such as salt facilitates the development of extensional forced folds above active normal faults the geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer the thickness of the cover sequence the strength and ductility of the cover sequence and the magnitude and rate of displacement on the underlying master normal fault increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation alternatively increasing the viscosity of the viscous layer the thickness of the overburden and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults the model predicted deformation patterns closely resemble those observed in the gulf of suez the haltenbanken area of offshore norway and the jeanne d arc basin of the grand banks offshore southeastern canada

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