evolution of faulting and plate boundary deformation in the southern taranaki basin new zealand abstract faulting and folding in the southern taranaki basin constrain the evolution of the new zealand plate boundary since 80 ma sedimentary rocks up to 8 km thick record multiple phases of deformation which have been examined using 2d and 3d seismic reflection data resulting in fault displacement time curves and basin wide isopach maps with temporal resolutions of 5 10 myr and 1 4 myr pre and post 23 ma respectively three main phases of tectonic activity have been recognised late cretaceous and palaeocene extension 80 55 ma mainly oligocene and younger contraction and plio pleistocene 3 7 0 ma extension most of the largest faults e g cape egmont fault accrued displacement during the late cretaceous and were reactivated one or more times during subsequent episodes of deformation the oldest phase of extension occurred during gondwana break up and was ubiquitous throughout the basin contraction along the eastern boundary of the basin associated with the onset of hikurangi margin subduction commenced as early as late eocene the zone of contraction widened and migrated westward during the miocene with reverse faults and folds in westernmost parts of the basin formed in the late miocene 7 5 ma initiation and episodic widening of this zone of contraction may have been partly triggered by changes in the rate of plate convergence contraction is now mainly confined to the northern south island and has been succeeded to the north by plio pleistocene extension the present day transition zone between extension in the north and contraction in the south is defined by a wnw trending line across the basin the extension contraction transition migrated southward during the late miocene and pliocene consistent with steepening of the subducting plate and associated southward movement of the southern termination of the hikurangi subduction system

strike slip tectonics in the sw barents sea during north atlantic rifting swaen graben northern norway this study uses high quality three dimensional 3 d seismic data to investigate the occurrence of strike slip faults in the swaen graben sw barents sea the swaen graben is divided into two principal sub basins ssb1 and ssb2 the along strike and along dip displacement variations and scale relationships are analyzed for forty two 42 faults the displacement profiles for these faults are complex in the swaen graben showing clear evidence for polycyclic fault growth and marked syn sedimentary activity the observed variations in the displacement profiles indicate complex along strike segmentation linkage and mechanical interactions at distinct structural levels along dip displacement minima indicate fault reactivation by dip linkage importantly geometric evidence for strike slip faulting in the swaen graben includes the presence of extensional horsetail splay faults positive flower structures and minor transfer faults this study shows that the faults in the swaen graben developed under extensional regimes during late jurassic to early cretaceous rifting and were reactivated by regional stresses during the late cretaceous the two principal strike slip faults in the swaen graben reveal sinistral movement and are linked at a shallow depth by minor transfer faults at a relay zone our work further demonstrates the occurrence of late mesozoic strike slip movements in the sw barents sea which were induced by regional tectonics halokinesis and fault block rotation importantly strike slip faulting in the region extends perhaps into the cenozoic interacting with extension during the north atlantic rifting

experimentally determined si isotope fractionation between silicate and fe metal and implications for earth s core formation abstract stable isotope fractionation amongst phases comprising terrestrial planets and asteroids can be used to elucidate planet forming processes to date the composition of the earth s core remains largely unknown though cosmochemical and geophysical evidence indicates that elements lighter than iron and nickel must reside there silicon is often cited as a light element that could explain the seismic properties of the core the amount of silicon in the core if any can be deduced from the difference in 30 si 28 si between meteorites and terrestrial rocks if the si isotope fractionation between silicate and fe rich metal is known recent studies e g georg r b halliday a n schauble e a reynolds b c 2007 silicon in the earth s core nature 447 31 1102 1106 fitoussi c bourdon b kleine t oberli f reynolds b c 2009 si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core earth planet sci lett 287 77 85 showing sometimes subtle differences between 30 si 28 si in meteorites and terrestrial rocks suggest that si missing from terrestrial rocks might be in the core however any conclusion based on earth meteorite comparisons depends on the veracity of the 30 si 28 si fractionation factor between silicates and metals at appropriate conditions here we present the first direct experimental evidence that silicon isotopes are not distributed uniformly between iron metal and rock when equilibrated at high temperatures high precision measurements of the silicon isotope ratios in iron silicon alloy and silicate equilibrated at 1 gpa and 1800 c show that si in silicate has higher 30 si 28 si than si in metal by at least 2 0 these findings provide an experimental foundation for using isotope ratios of silicon as indicators of terrestrial planet formation processes they imply that if si isotope equilibrium existed during segregation of earth s core forming metal and silicate mantle there should be an isotopic signature of si in the core our experiments combined with previous measurements of si isotope ratios in meteorites and rocks representing the bulk silicate earth suggest that the formation of the earth s core imparted a high 30 si 28 si signature to the bulk silicate earth due to dissolution of 6 wt si into the early core

new ni and co metal silicate partitioning data and their relevance for an early terrestrial magma ocean abstract it is generally assumed that the abundances of the siderophile metal loving elements in the earth s mantle are the result of core formation in the early earth in the most popular model the low contents of siderophile elements in the earth s mantle are the result of metal silicate equilibration followed by metal accumulation at the base of a magma ocean this model is primarily based on the pressure dependence of ni and co metal silicate partition coefficients first determined by li and agee li j agee c b 1996 geochemistry of mantle core differentiation at high pressures nature 381 686 689 we have undertaken a further test of this hypothesis by performing a large number of additional partition experiments with the two key elements ni and co at a variety of temperatures and a pressure range extending from ambient pressure to 25 gpa 750 km depth in the earth the unexpected result of the new experiments is the recognition of two pressure regimes in the temperature and pressure dependences of ni fe and to a lesser extent of co fe exchange metal silicate partition coefficients k d ni fe and k d co fe the strong pressure and temperature dependences of k d ni fe and k d co fe at atmospheric pressure change below about 5 gpa to much weaker dependences at higher pressures as a consequence the pressure dependences of k d ni fe and k d co fe cannot be regressed with a single fit over the entire pressure range fits based on partition data obtained in this work and from the literature between 5 gpa and 25 gpa were extrapolated to pressures and temperatures to lower mantle liquidus conditions the co fe partition coefficients required to satisfy the present mantle composition is reached at about 35 gpa whereas the proper ni fe ratio requires 45 to 50 gpa at 55 gpa ni and co partition coefficients would be identical but the ni and co contents imposed on the earth s mantle by metal silicate equilibration would be too low this would exclude single stage magma ocean models for producing approximately chondritic ni co ratio in the earth s mantle however the accuracy of the experimental data obtained here and from the literature is not sufficient to unambiguously exclude single stage equilibration the results of this and other recent studies exclude that fe ni and co contents of the present upper mantle were established by metal silicate equilibration at upper mantle conditions

crystallization experiments on a gusev adirondack basalt composition until recently the snc meteorites represented the only source of information about the chemistry and petrology of the martian surface and mantle the mars exploration rovers have now analyzed rocks on the martian surface giving additional insight into the petrology and geochemistry of the planet the adirondack basalts analyzed by the mer spirit in gusev crater are olivine phyric basaltic rocks which have been suggested to represent liquids and might therefore provide new insights into the chemistry of the martian mantle experiments have been conducted on a synthetic humphrey composition at upper mantle and crustal conditions to investigate whether this composition might represent a primary mantle derived melt the humphrey composition is multiply saturated at 12 5 kbar and 1375 c with olivine and pigeonite a primary anhydrous melt derived from a chondritic mantle would be expected to be saturated in orthopyroxene not pigeonite in addition the olivine and pigeonite present at the multiple saturation are too ferroan to have been from a martian mantle as is understood now therefore it seems likely that the humphrey composition does not represent a primary anhydrous melt from the martian mantle but was affected by mineral melt fractionations at lower crustal pressures

a simple method of determining sand shale ratios from seismic analysis of growth faults an example from upper oligocene to lower miocene niger delta deposits a plot of fault throw vs depth is a simple geometric tool that graphically represents strata thickness variations in growth fault and growth fold settings and has previously been used to infer fault kinematics in this paper we use it as a prediction tool for lithological change employing only seismic data if growth faulting is a continuous process intervals of shale deposition are recorded by unthickened units while intervals of sand fill in topographic lows the throw vs depth plot easily allows depiction of unthickened and thickened sedimentary intervals from even rough seismic records and can therefore be used to predict sand shale ratios the method is here applied to a growth fault in the niger delta that affects oligocene to lower miocene deltaic deposits most shale intervals are identified and the sand shale ratios are predicted we suggest that the method can be a valuable tool in oil exploration

solidus and liquidus profiles of chondritic mantle implication for melting of the earth across its history abstract we investigated the melting properties of a synthetic chondritic primitive mantle up to core mantle boundary cmb pressures using laser heated diamond anvil cell melting criteria are essentially based on the use of x rays provided by synchrotron radiation we report a solidus melting curve lower than previously determined using optical methods the liquidus curve is found between 300 and 600 k higher than the solidus over the entire lower mantle at cmb pressures 135 gpa the chondritic mantle solidus and liquidus reach 4150 150 k and 4725 150 k respectively we discuss that the lower mantle is unlikely to melt in the d layer except if the highest estimate of the temperature profile at the base of the mantle which is associated with a very hot core is confirmed therefore recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra low velocity zones indicate either 1 a outer core exceeding 4150 k at the cmb or 2 the presence of chemical heterogeneities with high concentration of fusible elements our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion not only complete melting of the lower mantle would require excessively high temperatures but also below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought in addition magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 gpa as suggested by siderophile metal silicate partitioning data such high surface temperature regime where thermal blanketing is inefficient points out to a transient character of the magma ocean with a very fast cooling rate

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

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

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

3 d visualization and isochore analysis of extensional diapirs overprinted by compression palinspastic restorations elucidate geologic and hydrocarbon migration histories in salt provinces however salt dissolution and salt flow in and out of the section plane make it difficult to determine the shape of salt bodies before deformation which hampers accurate restorations three dimensional computer visualization of a physical model and analysis of isochores provide clues to the original shape of allochthonous salt bodies that were emplaced during extension and later compressed

relative ages of the moraines of the dalijia shan northwestern china abstract soils of presumed middle to late quaternary age were analyzed to determine if d l ratios d to l form of amino acids and or sand clast weathering could be used for relative age assignment the soils are formed in moraine diamicton crests that have been interpreted as equivalent with the mindel riss wurm sequence of the western alps i e middle to late quaternary however the soils all have similar morphologies inceptisols or weathered states suggesting they have similar ages while the soils contain alanine valine leucine phenylalanine glutamic acid and aspartic acid there are no apparent differences in d l ratios for any amino acid that would support major differences in age even comparing d l ratios of h2o with hcl rinsed samples leads to the conclusion that all post depositional amino acid isomeric conversions occurred over approximately the same time interval or presumably since the end of the last glaciation in this area

amino acid d l ratio distributions in two late quaternary soils in the afroalpine zone of mount kenya east africa abstract two soil profiles of late glacial and neoglacial age in the afroalpine belt of mount kenya were analyzed to determine if d l ratios d form to l form of each amino acid of amino acids could be used for relative age determinations and to assess biogeochemical contamination the two profiles are prominent stratigraphic markers used to differentiate late glacial 12500 yr bp from early neoglacial 1000 yr bp glacial deposits which are commonly located close within 50 m to one another aspartic acid alanine and to some degree leucine tend to increase with age across the a1 horizons in the sequence of soils studied d l ratios show an increase of both aspartic acid and alanine with the highest values in horizons immediately adjacent to the surface a1 horizons even though valine often behaves erratically a higher d l ratio in the a1 horizon of the younger profile may signal geobiochemical contamination the presence of phenylalanine and glutamic acid in the youngest a1 horizon and disappearance in the older horizons is similar to trends observed in other afroalpine profiles because the thermal regime and history of the soils and their effects on rates of racemization are not known with precision all age estimates are tentative

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

characterisation and palaeoclimate of a loess like permafrost palaeosol sequence in ne siberia abstract we studied a 15 m high loess like permafrost palaeosol sequence the tumara palaeosol sequence tps which developed on a middle pleistocene fluvio glacial terrace of the tumara river various analytical methods were applied to characterise the tps similar to typical loess palaeosol sequences e g in china europe etc pedogenetic clay formation mineral weathering and smaller grain sizes are interpreted as representing warmer and more favourable climatic conditions interglacials or interstadials soil organic matter som however reveals an unfamiliar inverse pattern high organic carbon contents c org 1 characterise the dark grey glacial palaeosols whereas lower contents c org 0 5 are found in the brown interglacial stadial palaeosols this can be explained with permafrost and water logging having inhibited som mineralisation during cold periods d l ratios of aspartic acid and lysine proved to be useful proxies for both som aging and palaeotemperature with amino acid racemization being enhanced in interglacial stadial palaeosols on the basis of the geochemical and grain size results further palaeoclimatically relevant proxies describing the palaoewind strength u ratio the mineral weathering chemical index of alteration rb k and the changing mineral input signal ba ti zr ti al were applied to the tps in combination with numeric dating results radiocarbon and luminescence and in the context of other northern hemispheric records the simple warm cold stratigraphy as derived from the palaeoenvironment climate proxies suggests that the tps represents the last 240 000 years

valence and metal silicate partitioning of mo implications for conditions of earth accretion and core formation abstract to better understand and predict the partition coefficient of mo at the conditions of the deep interior of earth and other terrestrial planets or bodies we have undertaken new measurements of the valence and partitioning of mo x ray absorption near edge structure xanes k edge spectra for mo have been measured in a series of fe bearing glasses produced at 1 bar and higher pt conditions high pressure experiments have been carried out up to 19 gpa in order to better understand the effect of pressure on mo partitioning and finally a series of experiments at very low f o 2 conditions and high si content metallic liquids has been carried out to constrain the effect of si on the partitioning of mo between metallic liquids and silicate melt the valence measurements demonstrate that mo undergoes a transition from 4 to 6 near iw 1 in general agreement with previous 1 bar studies on feo free silicate melts high pressure experiments demonstrate a modest pressure dependence of d mo metal silicate and combined with previous results show a significant decrease with pressure that must be quantified in any predictive expression finally the effect of dissolved si in fe rich metallic liquid is to decrease d mo significantly as suggested by previous work in metallurgical systems the effect of pressure temperature oxygen fugacity metallic liquid composition and silicate melt composition can be quantified by using multiple linear regression of available experimental data for mo our xanes results show that mo will be 4 at conditions of core formation so only experiments carried out at f o 2 of iw 1 and lower were used in the regressions application of predictive expressions to earth accretion shows that d mo decreases to values consistent with an equilibrium scenario for early earth core mantle the mo content of the primitive upper mantle pum can be attained by metal silicate equilibrium involving s c and si bearing metallic liquid and peridotite silicate melt along the peridotite liquidus near 45 gpa and 3600 c late in the accretion process this conclusion is insensitive to late giant impacts unless the degree of equilibration is very low

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

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

normal fault growth and linkage in the whakatane graben new zealand during the last 1 3 myr determination of fault growth rates and fault network evolution at time scales from 104 106 years has been hampered by a lack of a well constrained stratigraphic succession that provides a high fidelity record of fault development over these time periods here we show how seismic reflection data of different spatial resolutions can be used to constrain the linkage history and displacement rate variations of a single major fault we present data collected in the offshore whakatane graben bay of plenty new zealand where intense normal faulting occurs as a result of active back extension the focus of our study is the rangitaiki fault a linked segmented normal fault which is the dominant active structure in the graben the total linked fault length is c 20 km long and has a displacement of up to 830 130 m in the top 1 5 km of sediments the fault has been actively growing for the last 1 34 0 51 ma and has developed from isolated fault segments to a fully linked fault system initially the dominant process of fault growth was tip propagation with an average and maximum displacement rates of 0 52 0 18 mm yr 1 and 0 72 0 23 mm yr 1 respectively interaction and linkage became more significant as the fault segments grew towards each other resulting in the fault network becoming fully linked between 300 and 18 ka following fault segment linkages the average displacement rate of the fault network increased by almost three fold to 1 41 0 31 mm yr 1 while the maximum displacement rate increased to 2 72 0 61 mm yr 1 this is the first time that the growth rate of unlinked fault segments has been resolved and has been shown to be slower than in the subsequent linked fault system

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

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

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

experimental models of hangingwall deformation in ramp flat listric extensional fault systems abstract the results of three experimental models of ramp flat extensional fault systems are presented the experiments were constructed from sand and mica layers to form an anisotropic sequence that would respond to the imposed deformation by both faulting and folding the geometry of the underlying detachment controls the deformation in the hangingwall sequence ramp flat detachment geometries produce an upper roll over with a crestal collapse graben system a ramp syncline and fold reverse fault zone and a lower roll over with a crestal collapse graben system short ramp geometries produce only minor perturbations in a larger roll over structure as extension progresses the crestal collapse systems migrate and superimpose earlier systems the models of ramp flat extensional structures produce templates for the interpretation of natural ramp flat listric fault systems

the effect of melt composition on metal silicate partitioning of siderophile elements and constraints on core formation in the angrite parent body we present 275 new metal silicate partition coefficients for p s v cr mn co ni ge mo and w obtained at moderate p 1 5 gpa and high t 1683 1883 k we investigate the effect of silicate melt composition using four end member silicate melt compositions we identify possible silicate melt dependencies of the metal silicate partitioning of lower valence elements ni ge and v elements that are usually assumed to remain unaffected by changes in silicate melt composition results for the other elements are consistent with the dependence of their metal silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations using multiple linear regression we parameterize compiled metal silicate partitioning results including our new data and report revised expressions that predict their metal silicate partitioning behavior as a function of p t x fo2 we apply these results to constrain the conditions that prevailed during core formation in the angrite parent body apb our results suggest the siderophile element depletions in angrite meteorites are consistent with a cv bulk composition and constrain apb core formation to have occurred at mildly reducing conditions of 1 4 0 5 log units below the iron wustite buffer iw corresponding to a apb core mass of 18 11 the core mass range is constrained to 21 8 mass if light elements s and or c are assumed to reside in the apb core incorporation of light elements in the apb core does not yield significantly different redox states for apb core mantle differentiation the inferred redox state is in excellent agreement with independent fo2 estimates recorded by pyroxene and olivine in angrites

quantifying trace element disequilibria in mantle xenoliths and abyssal peridotites we apply a tool based on element distribution between orthopyroxene and clinopyroxene for quantifying rare earth element ree disequilibria in ultramafic rocks in the subsolidus state we present case studies of the ree contents of mineral cores in mantle xenoliths and abyssal peridotites using in situ analytical tools even when only mineral cores are measured to avoid enriched rims equilibrium is not always achieved on the mineral scale mineral cores in mantle xenoliths are closer to equilibrium than those in abyssal peridotites even though mantle xenoliths are known to be light ree contaminated from the host lava in the case of the abyssal peridotites 13 out of 14 are out of equilibrium with the least metasomatized most in disequilibrium and the most metasomatized closest to equilibrium we discuss hypotheses for these observations but regardless of what caused the disequilibria this tool allows one to see through the effects of secondary processes such as infiltration by fluid inclusions via cracks and diffusive exchange between minerals and melts fluids along grain boundaries the ease of making in situ ree measurements makes this tool formidable in identifying different generations of clinopyroxenes in ultramafic lithologies such data will complement the interpretation of isotopic and petrographic studies of continental and oceanic lithospheric mantle

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

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

the molybdenum isotopic compositions of i s and a type granitic suites this study reports mo isotopic compositions for fifty two palaeozoic granitic rocks with contrasting source affinities a i and s type from the lachlan fold belt lfb and the new england batholith neb both in se australia and three compositionally zoned plutons loch doon criffell and fleet located in the southern uplands of scotland the results show relatively large variations in 98mo for igneous rocks ranging from 1 73 to 0 59 with significant overlaps between different types no relationships between 98mo and 18o or asi alumina saturation index are observed indicating that mo isotopes do not clearly distinguish igneous vs sedimentary source types instead effects of igneous processes source mixing regional geology as well as hydrothermal activity control the mo isotope compositions in these granites it is found that mo is mainly accommodated in biotite and to a lesser extent in hornblende hornblende and fe3 rich minerals may preferentially incorporate light isotopes as reflected by negative correlations between 98mo and k rb and fe2o3 there is a positive correlation between initial 87sr 86sr and 98mo in i type granitic rocks reflecting the admixing of material from isotopically distinct sources granitic rocks from scotland and australia display strikingly similar curvilinear trends in 98mo vs initial 87sr 86sr despite the differing regional geology localized hydrothermal effects can result in low 98mo in granite as seen in three samples from loch doon and criffell which have anomalously light 98mo of 1 based on this study an estimate of 98mo 0 14 0 07 95 s e for the phanerozoic upper crust is proposed this is slightly heavier than basalts indicating an isotopically light lower crust and or a systematic change to the crust resulting from subduction of isotopically light dehydrated slab and or pelagic sediment over time

tungsten isotopic evidence for disproportional late accretion to the earth and moon examination of three lunar samples reveals that the moon s mantle has an excess of the tungsten isotope 182w of about 20 parts per million relative to the present day earth s mantle this suggests that the two bodies had identical compositions immediately following the formation of the moon and that the compositions then diverged as a result of disproportional late accretion of chondritic material to the earth and moon two papers published in this issue of nature present precise measurements of tungsten isotope composition in lunar rocks that are best explained by the earth and moon having had similar composition immediately following formation of the moon and then having diverged as a result of disproportional late accretion of material to the two bodies mathieu touboul et al found small 182w excess of about 21 parts per million relative to the present day earth s mantle in metals extracted from two kreep rich apollo 16 impact melt rocks while thomas kruijer et al measured tungsten isotopes in seven kreep rich whole rock samples that span a wide range of cosmic ray exposure ages and found a 182w excess of about 27 parts per million over the present day earth s mantle characterization of the hafnium tungsten systematics 182hf decaying to 182w and emitting two electrons with a half life of 8 9 million years of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant impact theory for the formation and evolution of the moon and for testing the late accretion hypothesis uniform terrestrial mantle like w isotopic compositions have been reported1 2 among crystallization products of the lunar magma ocean these observations were interpreted to reflect formation of the moon and crystallization of the lunar magma ocean after 182hf was no longer extant that is more than about 60 million years after the solar system formed here we present w isotope data for three lunar samples that are more precise by a factor of 4 than those previously reported1 2 the new data reveal that the lunar mantle has a well resolved 182w excess of 20 6 5 1 parts per million 2 standard deviations relative to the modern terrestrial mantle the offset between the mantles of the moon and the modern earth is best explained by assuming that the w isotopic compositions of the two bodies were identical immediately following formation of the moon and that they then diverged as a result of disproportional late accretion to the earth and moon3 4 one implication of this model is that metal from the core of the moon forming impactor must have efficiently stripped the earth s mantle of highly siderophile elements on its way to merge with the terrestrial core requiring a substantial but still poorly defined level of metal silicate equilibration

estimation of trace element concentrations in the lunar magma ocean using mineral and metal silicate melt partition coefficients this study uses experimentally determined plagioclase melt d values to estimate the trace element concentrations of sr hf ga w mo ru pd au ni and co in a crystallizing lunar magma ocean at the point of plagioclase flotation similarly experimentally determined metal silicate partition experiments combined with a composition model for the moon are used to constrain the concentrations of w mo ru pd au ni and co in the lunar magma ocean at the time of core formation the metal silicate derived lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle plagioclase melt derived concentrations for sr ga ru pd au ni and co are also consistent with prior estimates estimates for hf w and mo however are higher these elements may be concentrated in the residual liquid during fractional crystallization due to their incompatibility alternatively the apparent enrichment could reflect the inappropriate use of bulk anorthosite data rather than data for plagioclase separates

accretion and core formation on mars molybdenum contents of melt inclusion glasses in three snc meteorites abstract molybdenum cerium barium yttrium and rubidium contents of glasses in melt inclusions in three snc meteorites lew 88516 governador valadares and chassigny have been measured by ion microprobe ratios of mo ba and mo ce have been used to estimate the mo content of the primitive martian mantle 120 60 ppb abundances of five moderately siderophile elements ni co mo w and p and re in the martian mantle are consistent with metal silicate equilibrium between s bearing metallic liquid in a core 22 wt of the planet and peridotite melt at 75 kb 1620 c and oxygen fugacity 1 4 logfo2 units below the iw buffer this homogeneous accretion scenario is different than many heterogeneous accretion models for the earth but similar to recent studies suggesting homogeneous accretion in the presence of a deep terrestrial magma ocean

the influence of silicate melt composition on distribution of siderophile elements among metal and silicate liquids abstract liquid metal liquid silicate partitioning of fe ni co p ge w and mo among a carbon saturated metal and a variety of silicate melts magnesian tholeiitic siliceous aluminous aluminosiliceous basalts depends modestly to strongly upon silicate melt structure and composition low valency siderophile elements fe ni and co show a modest influence of silicate melt composition on partitioning germanium shows a moderate but consistent preference for the depolymerized magnesian melt high valency siderophile elements p mo and w show more than an order of magnitude decrease in metal silicate partition coefficients as the silicate melt becomes more depolymerized detailed inspection of our and other published w data shows that polymerization state temperature and pressure are more important controls on w partitioning than oxidation state for this to be true for a high and variable valence element implies a secondary role in general for oxidation state even though some role must be present equilibrium core segregation through a magma ocean of ultrabasic composition can provide a resolution to the excess abundances of ge p w and mo in the mantle but the mantle composition alone cannot explain the excess abundances of nickel and cobalt in chondritic proportions

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

the formation of nuggets of highly siderophile elements in quenched silicate melts at high temperatures before or during the silicate quench the highly siderophile elements hse are powerful tracers of planetary differentiation despite the importance of their partitioning between silicate and metal for the understanding of planetary core formation especially for the earth and mars there is still a huge discrepancy between conclusions based on different high temperature ht experimental studies these disagreements may be due to the presence of hse micro and nanonuggets in ht experiments the formation of these nuggets is still interpreted in different ways one hypothesis is that these hse nuggets formed during the quench of the silicate melt while another hypothesis supposes that these nuggets formed before the quench and represented artefacts of ht experiments the goal of this work is to clarify whether the presence of hse nuggets in silicate melts is linked to a quench effect or not understanding the formation of these hse nuggets represents thus a necessary step towards the resolution of the earth s core formation scenarios we performed new ht experiments 1275 2000 c at different oxygen fugacities fo 2 between ambient air up to 5 log units below the iron wustite buffer iw 5 for two different silicate compositions synthetic martian and terrestrial basalts mixed with a metallic mixture of pt au pd ru our 1275 1600 c experiments were contained in either olivine diopside or graphite crucible experiments at 2000 c were performed using a levitation method so no capsule was necessary our samples contained quenched silicate melts minerals olivine pyroxene spinel depending on the run a two phase metallic bead and nano and micro nuggets of hse our samples underwent fine textural structural and analytical characterizations the distribution of the nuggets was not homogeneous throughout the quenched silicate melt hse nuggets were present within crystals dendritic textures from the quenched silicate melt formed around hse nuggets which could be crystallized showing that the nuggets acted as nucleation sites during the quench thus they predated the quench finally these nuggets also had strong heterogeneities suggesting at least a two stage formation process under reducing conditions consequently our observations clearly show that these hse nuggets formed before the quench in the silicate melt our results agreed with previous studies which concluded that hse abundances in the earth s mantle require the late accretion of chondritic material subsequent to core formation however the effects of metallic si o h or the effect of pressure on the hse partitioning are still not fully understood further work to constrain these effects is to be encouraged to understand the earth s core formation

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

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

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

geometry of thin skinned tectonic systems in relation to detachment layer thickness in sedimentary basins characterizing features of both extensional and compressional thin skinned systems may be controlled by the thickness of the underlying mobile material within extensional fault arrays detachment layer thickness in conjunction with detachment dip controls variations in fault spacing and polarity because rigid fault blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels different styles of extensional fault array range from single polarity arrays with closely spaced faults thin detachment to arrays where the fault blocks rotate until the fault blocks separate from one another thick detachment departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks within contractional zones detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution thrusts occur where there is insufficient mobile material to sustain detachment fold growth the variations in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy applying this model to a salt basin an allochthon in the area of thickest salt may be characterized by updip raft tectonics and downdip detachment fold belts this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems

metal silicate partitioning of tungsten at high pressure and temperature implications for equilibrium core formation in earth abstract tungsten partitioning between liquid metal and liquid silicate d w from 1723 2673 k 0 5 18 gpa and over a wide range of metal and silicate compositions provides constraints on planetary core formation models we find that w partitioning is extremely sensitive to the carbon content of the metal alloy becoming about an order of magnitude more siderophile at carbon saturation activity composition corrections based on interactions between w c and fe c in metal solution shift calculated d w to more lithophile values and calculated oxygen fugacities fo2 to more oxidizing values than uncorrected data w exists as a highly charged cation in silicate solution displaying a mixture of oxidation states from 4 to 6 in experiments at fo2 of 0 5 2 log units below the iron wustite buffer at constant fo2 the average calculated valence decreases with pressure from 5 5 at 0 5 gpa to 4 at 11 18 gpa as a result of its high oxidation state w partitioning is strongly dependent on silicate melt polymerization and fo2 in contrast to some previous results we find that d w may decrease slightly in response to increasing temperature in the pressure range of our experiments pressure exerts a non monotonic effect d w increases with pressure up to 3 to 4 gpa but decreases at higher pressures previous models for the effects of pressure and temperature on w partitioning that conflict with our results appear to result from a conflation of the intensive parameters of pressure temperature and carbon content the mantle abundance of w could have been set by single stage metal silicate equilibration along the liquidus in a deep peridotite magma ocean at pressures from 20 50 gpa and at oxygen fugacities consistent with the mantle s present iron budget iw 2 to 2 5 equilibration at higher pressure is viable if the core forming metal contained a significant but not unreasonable abundance of carbon 2 wt recent continuous accretion models involving multi stage metal silicate equilibration in a deepening magma ocean with progressive oxidation of the silicate remain permissible given our new treatment of w partitioning data