reverse and normal drag along a fault an analysis of the theoretical displacement field around a single dip slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip we analytically model the heterogeneous part of the instantaneous displacement field of an isolated two dimensional mode ii fault in an infinite homogeneous elastic body in response to fault slip material on both sides of the fault is displaced and opposing circulation cells arise on opposite sides of the fault with displacement magnitudes increasing towards the center of the fault both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault normal drag develops there for low angles 30 408 and reverse drag for higher angles a comparison of the theoretical results with published models and natural examples reveals that the characteristics of normal and reverse fault drag are largely insensitive to the scale and rheology of the faulted rocks and that drag forces generated by frictional resistance need not be the primary cause of fault drag fault drag has some interesting geometric implications for normal and reverse fault terminology emphasizing the importance for discrimination of vertical separation and throw furthermore our results lead us to propose an alternative model for the formation of rollover anticlines above normal faults

release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

aptian albian palaeogeography of neo tethyan domain abstract the aptian albian interval 124 5 97 0 ma was a critical time both globally and for the tethyan domain in the tethyan domain it was the time when a united neo tethyan subduction zone became established between the future site of the alps and southeast asia and greatly accelerated the rate of north south convergence throughout the tethyan region a consequent widespread transgression on both laurasian and gondwanian margins deposited orbitolina limestones and associated clastics on wide continental shelf areas on the sea floor of the neo tethys ocean organic rich siliceous black shales radiolarites and turbidites with minor amounts of carbonates were deposited siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the neo tethyan realm and along their margins these areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves following the establishment of the north dipping subduction zone the laurasian passive margin was largely converted to an active one fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin land areas and continental basins were widespread on this margin in northern tibet china and indo china this was a consequence of the late triassic to early jurassic continental collissions and accompanied intracontinental convergence that lasted well into the cretaceous a detailed aptian albian facies map and a crude palinspastic palaeogeographic map of the entire tethyan realm are prepared in order to express the contrasts in sedimentation on laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in tethysides

copper isotopic signature of the tiegelongnan high sulfidation copper deposit tibet implications for its origin and mineral exploration we report the copper isotopic composition of cu sulfides in the tiegelongnan high sulfidation hs copper deposit tibet and investigate the possible application of cu isotopes to mineral exploration the copper isotopic values of samples from four drill holes display consistent progressive increase with depth to 400 m below surface with an overall variation of 65cu of up to 7 60 4 76 to 2 84 such a large range is very different from that observed in cu porphyry deposits which commonly exhibit a small 65cu range 1 with decreasing values with depth the large 65cu variation is likely of supergene origin and reflects strong leaching under oxidized conditions the systematic increase of 65cu with depth can be explained by the release of isotopically heavy cu at the top and its transport downward which is supported by the coupling of positive 65cu values with high cu grade and the occurrence of both negative and positive 65cu values in two drill holes mass balance consideration on the basis of cu isotopes can indicate mineralized zones which have been eroded or have not been found yet such mineralized targets if buried at depth could be located using cu isotopes

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

the subsidence history of conoco well 15 30 1 central north sea abstract the depth of deposition of the sediments from north sea well conoco 15 30 1 is determined using faunal and sedimentary evidence the effects of sedimentary load corrected for compaction and variations in water depth and sea level are removed to obtain the subsidence of the basement when covered by water only a crustal stretching and lithospheric thinning of 25 35 1 35 can account for both the initial fault controlled subsidence and the later uniform subsidence

working in complex areas new restoration workflow based on quality control 2d and 3d restorations when working in complex areas the explorationist needs to construct 3d models and to check their coherency coherence can be analyzed on the current geometry but could also be quantified through restoration to achieve this restoration i e the search for an initial geometry with a realistic deformation pathway between the initial and the final geometries appropriate tools are necessary these include classical cross section balancing surface unfolding and volumetric restoration in this paper we will describe a workflow to do quantitative structural geology in complex areas this includes the construction and quality control of the surfacic model the line balancing the cross section surface and multi surface restoration and the volumic restoration in addition to the quality control of the geometries the restoration allows us to compute strain tensors this can be done in the three types of restoration and visualized through ellipses and ellipsoids resp 2d and 3d that represent the main strain or stress vectors we shall discuss the relationship between these strain tensors and the expected fracture network in density as in direction

geochronology and geochemistry of late cretaceous igneous intrusions and mo cu w mineralization in the southern yidun arc sw china implications for metallogenesis and geodynamic setting abstract the sanjiang tethyan metallogenic domain stmd is an important part of the tethyan giant metallogenic belt the yidun arc is a part of the stmd in the eastern tibetan plateau recently four newly discovered mo cu w ore deposits related to granitic intrusions were found distributed along the north south strike in the southern yidun arc which are identified as the xiuwacu relin hongshan and tongchanggou deposits herein these four deposits formed along high angle north northwest or north west strike slip faults with vein type and porphyry type mo cu mineralization developed in the intrusions molybdenite re os and zircon u pb dating together with zircon hf isotopes and whole rock geochemistry of the intrusions were studied to discern the relationship between mineralization and magmatism metallogenesis and tectonic settings molybdenite from skarn type mineralization at the hongshan deposit has a re os isochron age of 81 2 2 6 ma mswd 1 3 n 5 consistent with previously published zircon u pb ages and re os ages of porphyry type mo mineralization these results indicate that the hongshan is a late cretaceous porphyry skarn cu mo deposit zircon u pb ages of the granitic intrusions in the xiuwacu relin and tongchanggou deposits varying from 87 4 ma to 82 7 ma combined with published molybdenite re os age spectrum 85 ma to 81 2 ma it is proposed that the mo cu w mineralization in the shangri la region is spatially temporally and probably genetically related to the late cretaceous granitic intrusions the relin hongshan and tongchanggou intrusions have high sio 2 65 2 70 0 wt sr 363 905 ppm sr y 22 72 and la yb 37 69 ratios and low y 11 6 17 0 ppm and yb 0 97 1 59 ppm which displayed adakitic affinities their low mgo 0 66 1 44 wt mg 25 46 variable negative zircon e hf t values 7 9 to 2 3 and proterozoic two stages hf model ages t dm2 1 13 1 62 ga suggest that they were probably dominantly derived from partial melting of thickened lower continental crust according to the tectonic evolution of the bangong meso tethys ocean during the late mesozoic the late cretaceous igneous event and mineralization in the yidun arc likely formed under a late or post collision extensional environment probably related to the collision between the lhasa and qiangtang terranes during the late cretaceous

orthorhombic fault fracture patterns and non plane strain in a synthetic transfer zone during rifting lennard shelf canning basin western australia abstract a complex series of faults occur within transfer zones normal to the wnw trending rifted northern margin of the canning basin western australia these zones controlled basinal fluid flow and the formation of some carbonate hosted mississippi valley type zn pb deposits along the basin margin during devonian to carboniferous rifting the study area has a regional fault geometry similar to a synthetic overlapping transfer zone surface and underground mapping in this transfer zone combined with 3d modelling indicate the faults and related extension fractures have an orthorhombic geometry the orthorhombic fault fracture mesh developed in response to three dimensional non plane strain in which the intermediate finite extension magnitude was non zero pre mineralisation marine calcite fill in the fault fracture mesh indicates that it formed early in the deformation history later deformation that overprints the zn pb mineralisation and fault fracture mesh was associated with a different maximum extension direction and this modified and reactivated the faults with both dip slip and oblique slip movement and tilting of earlier structures the orthorhombic geometry is not observed at a regional scale 10 10 km indicating probable scale dependant behaviour this study indicates that this transfer zone developed either by 1 strain partitioning with synchronous strike slip structures and adjacent zones of non plane extension or 2 by a component of non plane extension sub parallel to the basin margin followed by subsequent transtensional overprint of the system preferred model synthetic overlapping transfer zones are inferred to be key regions where orthorhombic fault geometries may develop

the calculation of bulk strain in oblique and inclined balanced sections abstract the calculation of bulk strain from balanced sections is a technique commonly used in the study of orogenic belts the validity of a balanced section is often enhanced by controls such as seismic and or borehole data the construction of a conventional vertical section perpendicular to orogenic strike i e in the transport direction may not allow control data to be directly incorporated into the section the control data can be projected into the plane of the section or alternatively the section may be constructed in an orientation such that it contains the available control data in the case of a vertical section constructed at an oblique angle to the transport direction the bulk strain value obtained is a minimum and can be corrected to the true value of bulk strain in the perpendicular vertical section by a simple trigonometric calculation if the section is perpendicular to strike but inclined at an angle to the vertical the correction of the bulk strain values is mathematically unique to the section this problem can be overcome by using a digitizing table in conjunction with a simple computer program the general case of a section both oblique to the strike direction and inclined to the vertical can be resolved by removing the effects of the inclination to produce a vertical oblique section from which the bulk strain can be obtained and corrected in realistic geological problems the oblique section will be a more common problem than the inclined section in both cases deviations of 10 and less introduce such small errors in the estimates of bulk strain that their effects can be ignored

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

chemical composition genesis and exploration implication of garnet from the hongshan cu mo skarn deposit sw china abstract in this study we present new mineral chemical data on the garnet from the hongshan cu mo deposit one of the largest skarn deposits in the sanjiang tethyan tectonic domain in sw china the aims are to unravel the formation mechanism of the oscillatory zoned garnet at hongshan and to explore possible applications using garnet trace element to distinguish different types of skarn deposits two generations of garnets i e poorly zoned garnet i grt i and the well zoned garnet ii grt ii are identified from the endoskarn and exoskarn at hongshan based on field and petrographic observations epma and la icp ms analyses show that grt i contains a narrow compositional range adr40 07 61 25 grs36 65 57 08 and chondrite normalized hree enriched and lree depleted patterns with minor positive eu anomalies in contrast grt ii shows a wide compositional range adr27 78 67 53 grs30 67 70 92 to almost pure andradite adr94 41 99 99 grs0 00 4 21 with interlayered al rich and fe rich zones in grt ii its al rich zone is chemically similar to grt i whereas its fe rich zone exhibits chondrite normalized lree enriched and hree depleted patterns with distinct positive eu anomalies the positive ree3 vs mg correlations and the poor ree3 vs y and ca correlations altogether indicate that the ree3 incorporated into garnet was co influenced by the menzerite type substitution mechanism c a 2 1 v i i i r e e 3 1 v i i i a l 3 1 v i m g 2 1 v i fluid chemistry and the physicochemical conditions of precipitation the higher u contents and hree enriched patterns of grt i suggest that it was formed under a relatively reducing and near neutral ph condition varying u contents and ree patterns across different oscillatory zones indicate that grt ii was probably formed under alternating physicochemical fluctuations led by repeating crack seal cycles in the hydrothermal system besides chemical data compilation suggests that the garnet from different types of skarn deposits has different compositions and can be used as mineral prospecting tools we suggested that discrimination plots such as eu vs v and ce vs u can distinguish cu skarn deposit from other skarn deposit types whilst the u vs w plot can discriminate between cu w w sn and w mo skarn deposits

miocene to recent cariaco basin offshore venezuela structure tectonosequences and basin forming mechanisms abstract the cariaco basin located 40 km off the central part of the coast of venezuela is the largest 4000 km 2 and bathymetrically deepest 1400 m bsl neogene fault bounded basin within the right lateral strike slip plate boundary zone that separates the caribbean and south american plates using subsurface geophysical data we test two previously proposed tectonic models for the age distribution and nature of east west striking strike slip faults and basin forming mechanism for the two main depocenters of the cariaco basin the earliest interpretation for the opening of the twin cariaco depocenters by schubert 1982 proposes that both depocenters formed synchronously by extension along transverse north south normal faults at a 30 km wide rhomboidally shaped pull apart basin between the right lateral east west striking and parallel san sebastian and el pilar fault zones a later model by ben avraham and zoback 1992 proposes that both depocenters formed synchronously by a process of transform normal parallel extension or rifting in a north south direction orthogonal to the east west striking and parallel strike slip faults we use more than 4000 km of 2d single and multi channel seismic data tied to 11 wells to map 5 tectono stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both cariaco depocenters evolved from paleogene to the present comparison of fault and isopach maps for dated horizons from paleogene to late neogene in age show three main phases in basin development 1 from middle miocene to pliocene the west cariaco basin formed as a rhomboidally shaped pull apart at a 30 km wide stepover between the northern branch of the san sebastian fault and the el pilar fault zone 2 during the early pliocene a new strike slip fault transected the west cariaco basin southern branch of the san sebastian fault and caused extension to cease and 3 during the early pliocene to recent a lazy z shaped pull apart formed along the curving connection between the southern branch of the san sebastian and el pilar fault zones

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

load strengthening versus load weakening faulting increases in shear stress along a fault during loading to failure cannot generally occur without changes in the normal stress across the fault n the fault loading parameter n n pf distinguishes situations of load strengthening n 0 where the frictional shear strength of faults increases as tectonic shear stress rises from load weakening environments n t6 0 where it decreases compressional faulting in tectonic regimes with v 3 is always load strengthening unless fluid pressure is rapidly increasing extensional faulting in regimes where v 1 is load weakening unless fluid pressure is dropping rapidly strike slip faulting in terrains where v 2 can be either load weakening or load strengthening the particular case where n 0 so that frictional shear strength stays constant during fault loading is a very special situation corresponding to direct shear load strengthening strike slip faulting appears to correlate with tectonic transpression and load weakening with transtension differing loading characteristics of faults in different tectonic regimes must induce varying patterns of cyclic fluid redistribution accompanying the seismic cycle with implications for earthquake recurrence and precursory groundwater phenomena

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

mechanics of wedge shaped fault blocks 2 an elastic solution for extensional wedges listric planar low angle and high angle normal faults are common in hanging walls of detachment faults an elastic model has been developed to evaluate the role of basal friction wedge geometry pore fluid pressure within the wedge and boundary conditions applied along the wedge rear in controlling the stress distribution in an extensional fault wedge this model assumes a stress free condition on the top and fractional sliding on the base of the wedge respectively a linear variation of stress components as a function of depth along the wedge rear and a uniform horizontal stress applied on the wedge toe the model predicts that 1 for the surface slope equal to zero a thin wedge favors development of high angle and planar faults whereas a thick wedge favors development of low angle and listric normal faults variation of pore fluid pressures along the basal detachment fault hardly affects the predicted fault geometry pore fluid pressure within the wedge is critical in controlling the state of stress in the wedge higher values of the internal pore fluid pressure promote low angle normal faulting and locally high angle reverse faulting 2 variation of surface slope and the uniform horizontal normal stress applied at the wedge toe does not affect the predicted fault geometry appreciably although the distribution of deviatoric stress magnitude changes for different cases and 3 listric normal faults are predicted in all computations and the fault curvature increases as the vertical gradient of the horizontal normal stress along the wedge rear the wedge angle surface slope dip angle and the internal pore fluid pressure increase the model provides a simple conceptual guide to deciphering the formation of complex fault geometries and cross cutting relationships as a function of mechanical parameters related to geologic processes and settings for example it provides an explanation for why low angle normal faults cut high angle normal faults in hanging walls of some detachment fault systems in the u s cordillera

tethys marginal sedimentary basins in western iran five sedimentary basins formed along the iranian margin of the southern tethys ocean during its evolution these basins record the opening and closing of the ocean basin and the collision of what is now arabia and iran the late paleozoic jurassic isfahan basin opened by continental rifting that began in the devonian and contains an early late paleozoic triassic passive margin sequence and a later clastic wedge phase the early cretaceous sanandaj basin is a forearc overlying the tectonized and subsided isfahan basin the latest cretaceous paleocene kermanshah basin is a remnant of the tethys ocean basin it initially lay along tectonic strike from the lengthening arabian iranian collision orogen to the southeast but was later incorporated into the orogenic foldbelt the late cenozoic zagros basin is a suture foreland basin that formed on the arabian plate as it attempted subduction beneath iran the paleogene tectonic setting of the kashan gavkhuni basin is in doubt but by mid tertiary time it was a foreland basin that lay landward of the collisional foldbelt and was nearly surrounded by other orogenic highlands that formed during convergence of other plates within and marginal to iran

structural evidence for the permo triassic tectonic evolution of the yidun arc eastern tibetan plateau abstract deformation across the yidun arc occurred as a two phase process i early triassic deformation of paleozoic sequences resulting from closure of the jinsha jiang suture and ii late triassic deformation of middle to late triassic rocks as a result of final basin closure deformation in the western yidun arc is dominantly west vergent a north south striking west directed thrust the jinsha thrust forms the boundary between the western yidun arc and the eastern qiangtang block the jinsha thrust incorporates within it ophiolitic material of the jinsha jiang suture and the structural geometry across the jinsha thrust suggests that early triassic subduction was east dipping along the jinsha jiang suture deformation within middle to late triassic sequences of the eastern yidun arc eastern qiangtang block and western songpan garze fold belt is thin skinned being restricted largely to a single generation of upright folds and associated thrusts late triassic westwards subduction underneath the combined western yidun arc qiangtang block resulted in arc volcanism in the eastern yidun arc coeval arc volcanics in the northern margin of the qiangtang block suggest that the suture along the northern margin of the qiangtang block may be correlated with the garze litang suture rather than the jinsha jiang suture

a systematic technique for the sequential restoration of salt structures abstract a method is described for the sequential restoration of cross sections in areas of salt tectonics where deformation is confined to the salt and higher layers the subsurface geometry evolves with time through the interaction of various processes sedimentation compaction isostatic adjustment thermal subsidence if present faulting and salt withdrawal diapirism the technique systematically calculates and removes the effects of each of these processes during specified time intervals defined by the interpreted horizons it makes no assumptions about salt kinematics and generally results in the area of the salt layer changing through time the method is described for restoration of extensional terranes but it is also suitable for areas of contractional salt tectonics with only minor modifications after converting an interpreted seismic profile to depth the top layer is stripped off and the underlying section is decompacted according to standard porosity depth functions a deep baseline unaffected by compaction or deformation is used to restore any isostatic compensation or thermal subsidence isostasy is calculated according to the airy model and differential sedimentary loading across a section is shown to be approximately balanced by changes in salt thickness so that the load is evenly distributed after these processes have been reversed the resulting geometry and the seismic data are used to create the sea floor template for structural restoration fault offsets are removed and the layers down to the top salt are restored to this template while the base salt remains fixed the resulting space between the restored top salt and the fixed base salt defines the restored salt geometry in addition the difference between the sea floor template and a fixed sea level provides a measure of the change in water depth ignoring eustatic changes in sea level the technique is applied to an interpreted seismic profile from the eastern green canyon ewing bank area of offshore louisiana the section is characterized by a variety of salt structures including salt rollers a diapiric massif a remnant salt sheet and a salt weld which are shown to have derived from an originally continuous salt sheet which has been modified by sedimentary loading early loading created vertical basin growth that was accommodated primarily by salt withdrawal and associated diapiric rise through the process of downbuilding once the salt weld formed continued sedimentation was accommodated by a lateral increase in basin size caused by down dip extension on listric growth faults

patterns in the copper isotope composition of minerals in porphyry copper deposits in southwestern united states cu isotope measurements of minerals from american southwest porphyry cu deposits reveal a positive relationship with the grade of cu and display spatial patterns we measured the cu isotope composition of 87 minerals contained within veins from drill core and hand specimen samples from three deposits the silver bell ray and morenci mines the overall range of cu isotope ratios varies from 13 5 to 8 3 per mil the deposits possess three different cu reservoirs in which each has unique cu isotope signatures where 65cu for leach cap minerals hypogene minerals supergene enrichment minerals the pattern exists in all three deposits and resulted from oxidative weathering of cu at surface and reprecipitation of cu at depth a rayleigh distillation model mimics the cu isotope patterns found in the leach cap and quantifies the degree of leaching a comparison of the isotopic composition of the three reservoirs among the three deposits reveals distinct differences the silver bell mine possesses leach cap minerals that are more depleted in 65cu and enrichment minerals that are more enriched in 65cu than both the morenci and ray mines a possible explanation for the difference among the deposits could indicate that the silver bell deposit experienced a greater degree of leaching than the ray and morenci deposits the comparative analysis of the cu isotope data reveals the exploration potential of using cu isotope fractionation in the supergene environments

tectonic evolution of the northumberland basin the effects of renewed extension upon an inverted extensional basin the northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time initial rifting is represented by a thick dinantian sedimentary fill but carboniferous extension is thought to have ceased by the early namurian in order to explain the development of certain facies patterns during the westphalian thermal subsidence phase of the evolution of the northumberland basin some syn depositional extensional fault movements are required at other times in the westphalian compaction induced subsidence was the dominant control on facies distribution a single phase of e w to se nw variscan compression commenced during or after late westphalian times and ceased prior to the intrusion of the whin sills and dykes subsequent permo mesozoic extension with a right lateral shear component re activated pre existing normal fault lines these later structures may be interpreted as being listric in form shallowing onto decollement surfaces within the carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin

internal structure of uppermost oceanic crust along the western blanco transform scarp implications for subaxial accretion and deformation at the juan de fuca ridge 1 the uppermost 2 km of oceanic crust created near the southern end of the juan de fuca ridge 60 mm yr full spreading rate is exposed in a tectonic window created along the north wall of the blanco transform fault a total of 27 submersible dives transect this escarpment over a distance of 30 km corresponding to 1 m y of spreading history in this exposure weakly deformed basaltic lavas grade downward into much more intensely fractured lavas cut by basaltic dikes lava flow surfaces dip persistently to the northwest toward the spreading center and the dikes dip southeast away from the spreading center the underlying sheeted dike complex is composed of subparallel dikes that dip moderately to the southeast discrete faults and more distributed cataclastic deformation zones separate the panels of sheeted dikes from one another disruption of the lava and dike units are interpreted as a result of dramatic subaxial vertical mass transport that created the accommodation space for the accumulation of a thickness of 1000 1500 m of basaltic lava the observed patterns of tilting of lavas and dikes imply subsidence beneath the region of active volcanism 3 km wide that is most rapid near the axis and diminishes quickly off axis deformation that accommodates this subsidence has generated extensive fracture porosity in the subaxial region that could strongly influence upper crustal hydrothermal pathways alteration history seismic properties and the distribution of subsurface biological communities

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

copper isotopic zonation in the northparkes porphyry cu au deposit se australia abstract significant systematic cu isotopic variations have been found in the northparkes porphyry cu au deposit nsw australia which is an orthomagmatic porphyry cu deposit copper isotope ratios have been measured in sulfide minerals chalcopyrite and bornite by both solution and laser ablation multi collector inductively coupled plasma mass spectrometry mc icp ms the results from both methods show a variation in 65cu of hypogene sulfide minerals of greater than 1 relative to nist976 significantly the results from four drill holes through two separate ore bodies show strikingly similar patterns of cu isotope variation the patterns are characterized by a sharp down hole decrease from up to 0 8 0 29 0 56 1 n 20 in the low grade peripheral alteration zones phyllic propylitic alteration zone to a low of 0 4 0 25 0 36 1 n 30 at the margins of the most mineralized zones cu grade 1 wt in the high grade cores of the systems the compositions are more consistent at around 0 2 0 19 0 14 1 n 40 the cu isotopic zonation may be explained by isotope fractionation of cu between vapor solution and sulfides at high temperature during boiling and sulfide precipitation processes sulfur isotopes also show an isotopically light shell at the margins of the high grade ore zones but these are displaced from the low 65cu shells such that there is no correlation between the cu and s isotope signatures fe isotope data do not show any discernable variation along the drill core this work demonstrates that cu isotopes show a large response to high temperature porphyry mineralizing processes and that they may act as a vector to buried mineralization

variation of copper isotopes in chalcopyrite from dabu porphyry cu mo deposit in tibet and implications for mineral exploration abstract the study presents copper cu isotope data of mineral separates of chalcopyrite from four drill core samples in the miocene dabu porphyry cu mo deposit formed in a post collisional setting in the gangdese porphyry copper belt southern tibet copper isotope values in hypogene chalcopyrite range from 1 48 to 1 12 displaying a large variation of up to 2 60 which demonstrates cu isotope fractionation at high temperature during hydrothermal evolution the majority of measured chalcopyrite isotopic compositions show a gradual increasing trend from 1 48 to 1 12 with the increase of drilling depth from 130m to 483m as the alteration assemblages change from potassic to phyllic similarly the other 65 cu values 65 cu 65 cu 63 cu sample 65 cu 63 cu standard 1 1000 of the chalcopyrite show a gradual increasing trend from 1 48 to 0 59 with the decrease of drilling depth from 130 m to 57 m as the alteration assemblages change from potassic phyllic through argillic to relatively fresh these observations suggest a genetic link between cu isotope variation and silicate alteration assemblages formed at different temperatures indicative of a rayleigh precipitation process resulting in the large variation of 65 cu values at dabu in general samples closest to the center of hydrothermal system dominated by high temperature potassic alteration are isotopically lighter whereas samples dominated by low temperature phyllic alteration peripheral to the center are isotopically heavier the predicted flow pathways of hydrothermal fluids are from no 0 to no 3 exploration line and the lightest 65 cu values are the most proximal to the hydrothermal source finally we propose that the northwest side of the no 0 exploration line has high potential for hosting undiscovered orebodies the pattern of cu isotope variation in conjunction with the features of silicate alteration in porphyry system can be used to trace the hydrothermal flow direction and to guide mineral exploration

copper and iron isotope fractionation during weathering and pedogenesis insights from saprolite profiles abstract iron and copper isotopes are useful tools to track redox transformation and biogeochemical cycling in natural environment to study the relationships of stable fe and cu isotopic variations with redox regime and biological processes during weathering and pedogenesis we carried out fe and cu isotope analyses for two sets of basalt weathering profiles south carolina usa and hainan island china which formed under different climatic conditions subtropical vs tropical unaltered parent rocks from both profiles have uniform 56 fe and 65 cu values close to the average of global basalts in the south carolina profile 56 fe values of saprolites vary from 0 01 to 0 92 in the lower reduced part and positively correlate with fe 3 fe r 2 0 90 whereas 65 cu values are almost constant by contrast 56 fe values are less variable and negatively correlate with fe 3 fe r 2 0 88 in the upper oxidized part where large 4 85 65 cu variation is observed with most samples enriched in heavy isotopes in the hainan profile formed by extreme weathering under oxidized condition 56 fe values vary little 0 05 0 14 whereas 65 cu values successively decrease from 0 32 to 0 12 with depth below 3 m and increase from 0 17 to 0 02 with depth above 3 m throughout the whole profile 65 cu positively correlate with cu concentration and negatively correlate with the content of total organic carbon toc overall the contrasting fe isotopic patterns under different redox conditions suggest redox states play the key controls on fe mobility and isotope fractionation the negative correlation between 56 fe and fe 3 fe in the oxidized part of the south carolina profile may reflect addition of isotopically light fe this is demonstrated by leaching experiments which show that fe mineral pools extracted by 0 5 n hcl representing poorly crystalline fe hydr oxides are enriched in light fe isotopes the systematic cu isotopic variation in the hainan profile reflects desorption and downward transport of isotopically heavy cu leaving the organically bound cu enriched in light isotope as supported by the negative correlation of 65 cu with toc r 2 0 88 the contrasting mostly positive vs negative cu isotopic signatures in the upper parts of these two profiles can be attributed to the different climatic conditions e g high rainfall at a tropical climate in hainan favors desorption and the development of organism whereas relatively dry climate in south carolina favors cu re precipitation from soil solutions and adsorption onto fe hydr oxides our results highlight the potential applications of fe and cu isotopes as great tracers of redox condition ancient climate and biological cycling during chemical weathering and pedogenic translocation

palinspastic reconstruction of structure maps an automated finite element approach with heterogeneous strain existing methods for the palinspastic reconstruction of structure maps do not adequately account for heterogeneous rock strain and hence cannot accurately treat features such as fault terminations and non cylindrical folds we propose a new finite element formulation of the map reconstruction problem that treats such features explicitly in this approach a model of the map surface with internal openings that honor the topology of the fault gap network is constructed of triangular finite elements both model building and reconstruction algorithms are guided by rules relating fault gap topology to the kinematics of fault motion and are fully automated we represent the total strain as the sum of a prescribed component of locally homogeneous simple shear and a minimum amount of heterogeneous residual strain the region within which a particular orientation of simple shear is treated as homogenous can be as small as an individual element or as large as the entire map for residual strain calculations we treat the map surface as a hyperelastic membrane a globally optimum reconstruction is found that unfolds the map while faithfully honoring assigned strain mechanisms closes fault gaps without overlap or gap and imparts the least possible residual strain in the restored surface the amount and distribution of the residual strain serves as a diagnostic tool for identifying mapping errors the method can be used to reconstruct maps offset by any number of faults that terminate branch and offset each other in arbitrarily complex ways

collision and rifting in the tethys ocean geodynamic implication abstract the tethys ocean was formed 250 m y ago when gondwana collided with laurasia since then and up to its closure about 40 50 m y ago the development of the ocean was dominated by repeated jumps of the spreading axes to the passive margin of gondwana splitting of microcontinents their transportation across the ocean and accretion to the active margin of eurasia it appears that jumps of the spreading centre and rifting of the passive margin coincided with periods of major collisions on the active margin several epochs of collision and rifting are described the late permian mid late triassic late jurassic early cretaceous end of the early cretaceous late eocene the simultaneous occurrence of rifting and collision has important geodynamic implications and it cannot be explained if only the forces applied to plate margins i e slab pull and ridge push are considered as the plate drying forces slab pull did not act in times of collision when the subduction zone was blocked by continental fragments and the ridge push creates compression but not extension on the passive margin it is suggested instead that the conveyor belt process of transportation of continental masses from the passive to the active margin of tethys was governed by north directed convective flow in the asthenosphere in times of collision when lithospheric plates were unable to move with the flow the latter created great tensile stresses in the overlying lithosphere that led to formation of rifts and then to new spreading centres

the ardeche palaeomargin of the south east basin of france mesozoic evolution of a part of the tethyan continental margin geologie profonde de la france programme abstract this paper incorporates the results of seismic and gravity investigations borehole data and studies of sedimentology biostratigraphy sequence stratigraphy and structural geology carried out in the framework of the deep geology of france programme the main purpose of the paper is to define the structure and to reconstruct the evolution of the ardeche palaeomargin of the south east basin of france from the stephanian to the end of the mesozoic the acquisition and processing of three seismic reflection profiles the drilling of two scientific boreholes ba1 and mm1 and subsequent structural modelling with the use of cross section balancing techniques applied to both the depth migrated seismic and geological sections provide new geometrical constraints which lead to the following hypothesis of the geodynamic evolution of the margin 1 1 late palaeozoic extension with the development of high angle basement faults asymmetrical permian half grabens pre extension sedimentary cover 2 2 during the middle triassic a pre rift stage with the creation of small fault blocks and in the late triassic the formation of an e w flexure 3 3 end lias early jurassic to middle jurassic formation of a major detachment in the carboniferous coal measures leading to complete decoupling of the mesozoic sedimentary cover from the basement this episode of extension coeval with the opening of tethys can be related to a phase of episodic rifting between the late sinemurian and the late bathonian i e during 30 ma 4 4 late jurassic to early cretaceous thermal subsidence with regional downwarping of the basement towards the east 5 5 after the late cretaceous the period of maximum burial pyrenean and alpine deformation in the south and east causing progressive uplift of the ardeche palaeomargin as much as two kilometres of mesozoic deposits subsequently being eroded from the section during the tertiary

coupled 63cu and 16o excesses in chondrites abstract recent developments in multiple collector magnetic sector icp ms inductively coupled plasma mass spectrometry have permitted the relative abundances of the two isotopes 63 and 65 of copper to be measured with unprecedented precision 40 ppm here we report cu isotopic variations among eight carbonaceous chondrites ccs from the ci cm co and cv groups and the presently ungrouped tagish lake and 10 ordinary chondrites ocs from the h l and ll groups the widest isotopic range of 0 8 per a m u is observed for the carbonaceous chondrites copper in carbonaceous chondrites becomes isotopically lighter with petrologic type in the order 1 to 3 but seems extremely homogeneous for each type the cu isotopic composition of tagish lake confirms its other characteristics that are intermediate between ci and cm in three of the groups ci cm co as well as for tagish lake 63 cu excess over terrestrial mantle abundances correlates well with 16 o excess for all four groups 63 cu excess also correlates remarkably well with elemental refractory volatile ratios e g ca mn for ordinary chondrites small differences exist between the h l and ll groups with cu becoming isotopically heavier in that order equilibrated and unequilibrated samples however exhibit the same cu isotopic signature within each group although the range of cu isotopic compositions in ordinary chondrites is smaller than in carbonaceous chondrites 63 cu excesses still correlate with 16 o excesses the observed trends of isotopic variation seem incompatible with a single stage fractionation process by either volatilization or low temperature metamorphism the correlations between 63 cu excesses and 16 o excesses suggest the presence of at least two and perhaps three isotopically distinct cu reservoirs in the early solar system 1 an earth like reservoir common to the ci and ll probably representing the main cu stock of the inner solar system 2 a reservoir present in all carbonaceous chondrites but most abundant in cv with large 63 cu and 16 o excesses this reservoir is probably hosted in refractory material and 3 possibly a third reservoir present in ordinary chondrites the oc trend may also be explained as a mixture of the first two cu reservoirs if its oxygen was first equilibrated with nebular gas the coexistence of 63 cu and 16 o excesses in the same component raises the issue of how volatile cu was preserved in refractory material a strong correlation between 63 cu 65 cu and ni cu ratios suggests that 63 cu excess may have originated as more refractory 63 ni t 1 2 100 yr upon irradiation of refractory grains by electromagnetic flares and particle bursts during the t tauri phase of the sun

fluid speciation controls of low temperature copper isotope fractionation applied to the kupferschiefer and timna ore deposits article i nfo mass balance amongreducedandoxidizedsolutionspeciesexertsastrongcontrol ontheisotopiccompositionof sulphide minerals we explore this issue for copper isotopic fractionation in sedimentary copper sulfide deposits through fluid speciation isotopic eh ph calculations based on the thermodynamic stability of copper chloride aqueous solution complexes and experimentally measured copper isotope fractionation factors applying these speciation diagrams to mc icp ms copperisotope data on the kupferschiefer sw partof thelubin sieroszowice copper district and timna s israel sediment hosted stratiform copper deposits ssc identifies differences in ore formation redox conditions timna valley copper sulfides have light cu isotopic compositions of 65 cu 2 04 0 44 2 relatively to srm 976 copper standard which are shown to correspond to eh values of 0 5 to 0 6 v at formation conditions t 40 c ph b6 these eh values indicate precipitation at relatively oxidized conditions where the cu i solution complex cucl3 2 i sb10 of the total solution species in contrast the kupferschiefer cu sulfides analyzed in this work dominantly show significantly higher 65 cu values 0 39 0 36 corresponding to eh values of 0 4 to 0 5 v at formation conditions t 100 c ph 6 3 in these eh conditions most copper in solution occurs as cucl3 2 complexes 80 the above observations are in accord with field relations showing that cu ii minerals dominate the timna system but cu sulfides are the major minerals of the kupferschiefer deposits fluid speciation isotopic calculations show that copper isotopes can be used as effective tracers of redox conditionsandthisapproach can bepotentiallyappliedtovarioushydrothermal oredeposits such as black smokers and volcanic hosted massive sulphide deposits and to other metallic isotope systems however the isotopic fractionation mayalso be strongly influenced by the types ofligand bondingofcopper ions and these effects need to be fully evaluated before the isotope geochemistry of copper ores can be fully understood

geochronology of the hongniu hongshan porphyry and skarn cu deposit northwestern yunnan province china implications for mineralization of the zhongdian arc abstract the hongniu hongshan porphyry and skarn copper deposit is located in the triassic zhongdian island arc northwestern yunnan province china single zircon laser ablation inductively coupled plasma mass spectrometry u pb dating suggests that the diorite porphyry and the quartz monzonite porphyry in the deposit area formed at 200 ma and 77 ma respectively a re os isotopic date of molybdenite from the ore is 78 9 ma which indicates that in addition to the known triassic cu au porphyry systems a late cretaceous porphyry cu mo mineralization event also exists in the zhongdian arc the quartz monzonite porphyry shows characteristics of a magnetite series intrusion with a high concentration of al k rb ba and pb low amount of ta ti y and yb and a high ratio of sr y average 26 42 the cretaceous porphyry also shows a strong fractionation between light and heavy rare earth elements average la yb n 37 9 which is similar to those of the triassic subduction related diorite porphyry in the hongniu hongshan deposit and the porphyry hosting the pulang copper deposit however in contrast to the older intrusions the quartz monzonite porphyry contains higher concentrations of large ion lithophile elements and co and lesser sr and zr therefore whereas the triassic porphyry cu au mineralization is related to slab subduction slab in an arc setting the quartz monzonite porphyry in the hongniu hongshan deposit formed by the remelting of the residual oceanic slab combined with contributions from subduction modified arc lithosphere and continental crust which provided the metals for the late cretaceous mineralization

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

listric versus planar normal fault geometry an example from the eisenstadt sopron basin e austria in a gravel pit at the eastern margin of the eisenstadt sopron basin a satellite of vienna basin austria neogene sediments are exposed in the hanging wall of a major normal fault the anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault the spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall subsequently in order to assess the 3d distribution and geometry of this fault system a series of parallel ground penetrating radar gpr profiles were recorded behind the outcrop wall both outcrop and gpr data were compiled in a 3d structural model providing the basis for a kinematic reconstruction of the fault plane using balanced cross section techniques however the kinematic reconstruction results in a geologically meaningless normal fault cutting down and up section additionally no evidence for a weak layer serving as ductile detachment horizon i e salt or clay horizon can be identified in stratigraphic profiles instead the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault with a maximum displacement in the fault centre decreasing towards the fault tips accordingly the observed deflection of markers in the hanging wall and in a nearby location in the footwall of the normal fault is interpreted as large scale fault drag along a planar fault that records a displacement gradient instead of a rollover anticline related to a listric fault

modelling of bed contours and cross sections adjacent to planar normal faults the geometry of beds in the volume surrounding a single blind planar fault depends on i the axial ratio of the fault surface ellipse ii the ratio between the maximum displacement and the maximum dimension of the fault surface iii the displacement distribution on the fault surface from the point of maximum displacement to zero displacement at the tip line loop fault surface displacement profile and iv the rate at which the displacement decreases to zero along a normal to the fault surface reverse drag displacement profile these relationships which are either known or can be estimated are incorporated in a computer model which generates structural contours on horizons intersected by a planar fault structural contour patterns also vary with the pre faulting dip and strike of beds the dip and strike of the fault and the level at which a bed intersects the fault surface when the boundary conditions are relaxed to include synsedimentary faults the ratio of hangingwall to footwall displacement varies systematically with fault dip a synthetic structural contour map is matched with that of an actual fault model isopachs based on simple depositional models are generated for synsedimentary units cross sections are generated for synsedimentary faults by sequential fault growth and sedimentary deposition and show features similar to actual cross sections the soft domino model is applicable primarily to dip slip tectonic faults with maximum displacements of up to about 5 km listric faults are not considered

subsidenz und tektonik des saar nahe beckens sw deutschland the saar nahe basin in sw germany is one of the largest permo carboniferous basins in the internal zone of the variscides its evolution is closely related to movements along the hunsruck boundary fault which separates the rhenohercynian and the saxothuringian zones recent deep seismic surveys indicate that the saar nahe basin formed in the hanging wall of a major detachment which soles out at lower crustal levels at about 16 km depth oblique extension along an inverted variscan thrust resulted in the formation of a half graben within more than 8 km of entirely continental strata accumulated the structural style within the basin is characterized by normal faults parallel to the basin axis and orthogonal transfer fault zones balanced cross section construction and subsidence analysis indicate extension of the orogenically thickened lithosphere by 35 subsidence modeling shows discontinuous depth dependent extension with laterally varying extension factors for crust and mantle lithosphere thus the offset between maximum rift and thermal subsidence can be explained by a zone of mantle extension shifted laterally with respect to the zone of maximum crustal extension

a mechanism for decoupling within the oceanic lithosphere revealed in the troodos ophiolite contrasting kinematic histories recorded in the sheeted dykes and underlying plutonic rocks of the troodos ophiolite provide a new perspective on the mechanical evolution of oceanic spreading centres the kinematic framework of the decoupling zone that partitions deformation between the sheeted dykes and plutonics contrasts with low angle detachment models for slow spreading ridges based on continental rift analogues a model for the generation of multiple horizontal decoupling horizons linked by planar normal faults demonstrates new possibilities for the kinematic and rheological significance of seismic reflectors in oceanic lithosphere

restoration in plan view of faulted upper cretaceous and oligocene horizons and its bearing on the history of salt tectonics in the campos basin brazil abstract in the campos basin atlantic margin of brazil cretaceous and tertiary sediments show abundant evidence for thin skinned deformation above a layer of aptian salt near the coast there is a domain of downslope extension further offshore a domain of donwslope contraction thus we attribute the domainal pattern to gravitational gliding on the salt layer gravitational gliding appears to be driven primarily by surface slopes each material particle tends to move in the direction of steepest slope if topography is irregular particle paths diverge or converge deformation then differs from a plane strain and vertical cross sections cannot be individually balanced or restored we have therefore developed a method for restoring non plane deformation in extensional domains assuming that blocks between faults are rigid we restore stratigraphic horizons in plan view by least squares minimization of distances across fault separations cut off lenses obtaining fields of finite horizontal displacements for selected areas in the extensional domain of the campos basin where divergent gravitational gliding has led to extension in various horizontal directions we have restored two stratigraphie markers an upper cretaceous and an oligocene horizon for each horizon displacement vectors diverge seawards forming a fanlike pattern with a degree of mirror symmetry nevertheless there are major differences between the upper cretaceous and oligocene patterns both for faults and for displacements we infer that this resulted from the development during the tertiary of a propagating deltaic front whose sediment load drove the divergent gravitational gliding and induced a new fault pattern

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

mechanical response to stratigraphic inhomogeneity during extension and surface expression of buried structures gulf of suez egypt abstract mechanical response of the stratigraphic succession to rifting in the gulf of suez egypt varies depending on the degree of competence of the rock units this mechanical stratigraphy has been documented by observational evidence from field surveys in the northern esh el mallaha and in the ras issaran area in conjunction with seismic reflection data complex response patterns to basement rooted block faulting is seen on several scales in both the prerift and synrift rocks the prerift section is divided into three major units based on mechanical response precambrian basement pre cenomanian nubian sandstone and cenomanian through eocene stable platform marine rocks brittle faulting in the basement propagates into the nubian sandstone by densely fracturing the latter parallel to the fault planes the overlying inhomogeneous cenomanian eocene section drapes and folds over underlying structural elements these rocks contain complicated structures due to the interlayering of thin brittle and ductile beds the incompetent units allow bedding parallel detachment and also flow into voids created during faulting or folding of the competent units the synrift section comprises three major stratigraphic units each of which reacts differently to block faulting these are the early miocene carbonate clastic section the middle late miocene evaporite section and the onshore pliocene recent clastic passive cover sequence in general the lower synrift rocks respond to deformation much like the cenomanian eocene units draping and folding due to interlayered brittle and ductile beds seismic reflection data indicate that the evaporite section is a major detachment zone with faults in underlying units dying out upwards as the ductile salts or anhydrites drape and flow structural response in this section is varied and complex the deformation of the evaporites breaks the overlying passive cover rocks with faults in the latter soling into the underlying ductile strate on gravel plains flanking the gulf of suez the neotectonic fault pattern and resulting topographic and drainage changes reflect underlying structures the faults breaking the passive cover sequence at the surface initially form en echelon traces with continued movement these coalesce into straight or curved often splaying fault traces where the evaporite section reaches a significant thickness the structures seen at the surface may be entirely decoupled from those of the prerift and early synrift sequences

the red sea 50 years of geological and geophysical research abstract the red sea displays lithosphere that is in transition from rifting to drifting and therefore provides enormous opportunity to understand incipient seafloor spreading development despite more than 50 years of extensive geological and geophysical research there remains significant conjecture concerning the timing of sea floor spreading initiation the extent of spreading along the axis of the red sea and the geodynamic processes responsible for the onset of crustal extension red sea tectonic models based on geological data are dominated by single stage rift models involving protracted stretching of continental crust followed by sea floor spreading at ca 5 ma and include both asymmetric and symmetrical extension models geophysical data suggest that an oceanic crust occurs beneath the red sea shelves although exactly how this crust has evolved remains undecided equally arguments have been made in favor of the sedimentary shelves forming on extended continental crust and that oceanic crust is restricted to the present day red sea axial valley however our synthesis shows that none of the models proposed so far is applicable to the entire red sea basin the distribution and timing of the red sea crustal extension and sea floor spreading may have been influenced by subduction related far field forces due to complex plate interactions along the northern edge of the arabian plate during early miocene our reassessment suggests that following the arrival of the afar plume the southern red sea underwent rapid extension culminating in the transition from rifting to seafloor spreading which stalled during the early miocene in the central red sea due to either slowing of the convergence between arabia and eurasia or the onset of the arabian plate passive margin collision with eurasia off axis magmatism is focused on the arabian margin and afar depression and has been episodically active since the miocene we consider a formation of the red sea as a hybrid process involving both active and passive rifting

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

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

zircon u pb geochronology and elemental and sr nd hf isotopic geochemistry of the daocheng granitic pluton from the yidun arc sw china abstract the garze litang suture zone located in the eastern part of the tethyan tectonic domain is notable for widespread late triassic granitic plutons which are genetically associated with the evolution of the paleo tethys ocean the daocheng granitic pluton in the eastern yidun arc sw china is located in the middle of the garze litang suture zone and has an outcrop area of 2800 km 2 in the present study we report zircon u pb ages and elemental and sr nd hf isotopic data for the daocheng granitic intrusion secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry u pb analyses on zircons yield consistent ages of ca 216 ma for three samples from the pluton all the daocheng granitic rocks are enriched in si sio 2 68 1 76 4 and large ion lithophile elements but depleted in high field strength elements e g nb ta and ti mineralogical and geochemical features indicate that these are high k and calc alkaline and i type granites they are characterized by relatively variable initial 87 sr 86 sr ratios 0 7059 0 7102 negative e nd t values 5 7 to 7 8 wide ranging e hf t values 9 8 to 3 4 and two stage hf model ages of 1 04 to 1 88 ga these isotopic signatures indicate that the source for the daocheng granite was probably derived from partial melting of a late paleoproterozoic to early mesoproterozoic mafic intermediate lower crust with a variably minor addition

copper isotopes trace the evolution of skarn ores a case study from the hongshan hongniu cu deposit southwest china abstract transition metal isotopes are sensitive geochemical tracers of ore genesis here we present mc icp ms analytical data of cu isotope compositions from the hongshan hongniu cu deposit in yunnan province the 65 cu values 65 cu 65 cu 63 cu sample 65 cu 63 cu nist976 1 1000 of seven whole rock quartz monzonite porphyries and twenty two chalcopyrite samples from the skarn ore bodies display relatively narrow ranges from 0 15 to 0 38 and from 0 02 to 0 77 respectively the overlap of 65 cu values indicates a genetic relationship between the quartz monzonite porphyry and skarn ore bodies we also evaluate the spatial and temporal variations of cu isotope compositions in the skarn ore bodies by comparison with some well documented porphyry deposits in the world the quartz monzonite porphyry shows compositional zoning with the inner domain enriched in heavy cu isotope and the skarn related to the porphyry depleted in heavy cu isotope the chalcopyrites that formed during the late stage of mineralization tend to be enriched in heavy cu isotope and this feature is analogous to porphyry deposits the 65 cu values of the quartz monzonite porphyry show typical features of hypogene mineralization suggesting a potential scope for deep exploration and development in this deposit

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

a new 3d geological model and interpretation of structural evolution of the world class rio tinto vms deposit iberian pyrite belt spain abstract a new 3d geological model and interpretation of structural evolution of the rio tinto world class vms deposit are presented in this work the rio tinto volcanogenic massive sulfide vms deposit is located in the spanish segment of the iberian pyrite belt and is hosted by felsic porphyritic volcanic rocks and tuffs computer generated 3d modeling of the different orebodies and host rocks has been carried out using data from around 3000 drill core logs allowing us to build 93 cross sections and 6 plants both 50 m spacing this has enabled us to recognize the geometry and relationships between the mineralization and the earliest carboniferous transtensional tectonics through the development of an extensional pull apart basin with two sub basins separated by the nw se trending eduardo fault the sub basins cerro colorado and san dionisio were limited by two e w strike slip faults the northern and southern faults and bounded in the east and west by the nw se trending nerva and western faults respectively the generated pull apart basin was first filled by a basaltic magmatism of mantle origin and later following the deposition of the intermediate complex sedimentary unit by rhyodacitic volcanic rocks of crustal origin the evolution of the subsiding basins caused the development of an e w oriented rollover anticline that affected these filling rocks as a result of a counterclockwise rotation of the stress axes the primitive pull apart basin evolved into a basin affected by e w transtensional sinistral shearing its northern and southern limits were favorable areas for increased hydrothermal fluid flow which gave way to the huge concentration of vms mineralization located near the limits the northern and to a lesser degree the southern extensional faults thus become channel areas for feeding and discharging of the vms and stockwork ores the main mineralizing period was related to this stage subsequently during the variscan transpressional phase the e w extensional faults were reactivated as inverse faults affecting the volcanic sequence of mafic to felsic composition and the intermediate complex sedimentary unit fault propagation folds developed above these faults affecting the massive sulfides the transition series and the culm flysch sediments with buttressing playing a significant role in the geometry of tectonically inverted structures the vms mineralization and cupriferous stockworks were folded and dismembered from the original conduits in the volcanic series and a dextral reactivation of the nw se trending faults also developed finally it should be emphasized that this new 3d geological model is an approach to provide a better insight into the 3d structure of the world class vms rio tinto deposit and could be a key point for further studies providing a new tool to increase knowledge of the vms mineralizations and exploration guidelines elsewhere in the ipb

a method for automatically determining normal fault geometry at depth a large number of methods have been described which relate the shape of a normal fault at depth to the shape of a sedimentary horizon in its hanging wall unfortunately the calculated fault geometry is strongly dependent upon the method used here arguments are put forward in favor of a general two dimensional kinematic model which assumes that the hanging wall deforms by a combination of arbitrarily inclined simple shear and differential compaction the method should be applicable to areas where it can be assumed that the fault plane does not change shape as deformation proceeds this assumption may not always be valid especially in the case of large scale basement extending normal faults fault geometry the inclination of simple shear and compaction parameters may all be determined from n beds using a simple inversion scheme based on the general method throughout it is assumed that hanging wall and footwall stratigraphies are accurately known though uncertainty in either could be included as a bounded variable within a formal inversion scheme the most important feature of the model is that it is testable it has first been tested on synthetic data using a range of fault geometries the results of such modeling are encouraging and imply that all unknown parameters including fault geometry can in general be uniquely determined provided that the geometries of two or more beds within the hanging wall are known the greater the number of beds used the greater the degree of confidence in the solution the method has also been applied to published sand box models with surprisingly good results ultimately it is hoped that the method can be applied routinely to depth converted seismic reflection data the preliminary applications presented here suggest that bulk antithetically inclined simple shear combined with differential compaction provide a good approximation for hanging wall deformation in the future the scheme will be generalized to allow for deformation in three dimensions other complexities such as horizontal and vertical variation in the degree of compaction could also be included although at this stage the data do not appear to justify them

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

the cu isotopic signature of granites from the lachlan fold belt se australia abstract this contribution reports our preliminary work to determine cu isotope ratios for various granite rocks and examine the cu isotope systematics within granite suites a chemical procedure modified from marechal marechal c n telouk p and albarede f 1999 precise analysis of copper and zinc isotopic compositions by plasma source mass spectrometry chemical geology 156 1 4 251 273 was used to separate cu from rock matrix quantitative recovery 100 6 1 6 with a low total procedural blank 2 65 0 66 ng for cu has been achieved allowing cu isotopic measurements on samples with as little as 10 ppm cu the cu isotope ratios 65cu relative to nist srm 976 of 32 rock samples ranging from mafic to felsic compositions from 3 batholiths 2 i type 1 s type from the lachlan fold belt in southeastern australia vary from 0 46 to 1 51 most of them cluster around zero with mean values for the i type and s type granites of 0 03 0 15 and 0 03 0 42 2 sigma respectively these data together with cu isotope ratios of two loess samples provide preliminary evidence that the baseline cu isotopic composition of the crystalline part of upper continental crust is close to zero the tight clustering of cu isotope ratios of rocks from the i type suites suggests that high temperature magmatic processes do not produce significant cu isotope fractionation however two granites with abnormally heavy cu isotope signatures up to 1 51 appears to be the result of localized hydrothermal alteration measurable variation in cu isotopic composition of the s type granite may reflect isotopic heterogeneity in the sedimentary source region as a result of redox processes or may be due to hydrothermal overprinting thus cu isotope geochemistry may be a useful tracer for studying hydrothermal alteration and source heterogeneity of granitic rocks

use of cu isotopes to distinguish primary and secondary cu mineralization in the canariaco norte porphyry copper deposit northern peru a significant proportion of the copper in the canariaco norte porphyry copper deposit in northern peru occurs in chalcocite and covellite rich veins and disseminations that exist from the surface to depths greater than 1 km the overall range of cu isotopic ratios of 42 mineral separates from canariaco varies from 8 42 to 0 61 with near surface chalcocite and fe oxides having isotopically depleted values compared to chalcocite covellite and chalcopyrite from deeper levels the majority 34 of 36 of measured cu sulfides have a typical hypogene copper isotope composition of 65cu 0 18 0 38 with no enriched isotopic signature existing in the canariaco norte sulfide data thus the copper isotope data indicate that most of the chalcocite and covellite formed from high temperature hypogene mineralization processes and that only a minor portion of the deposit is enriched by supergene processes the nonexistence of an enriched 65cu reservoir suggest the presence of an undiscovered lateral exotic cu occurrence that enriched 65cu that remained in solution during weathering regardless of the cause the comparative analysis of the cu isotope dataset reveals that little exploration potential for an extensive supergene enrichment blanket exists because the weathering history at canariaco norte was not conducive to preservation of enriched cu at depth beneath the leach cap

numerical simulation of rifting in the northern viking graben the mutual effect of modelling parameters numerous basin modelling studies have been performed on the viking graben in the northern north sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations in such modelling it is important to include lithospheric flexure the values derived for the lithospheric strength by these studies vary considerably i e up to a factor of 30 in this study which is based on new interpretation of a regional transect we show that both the estimated value of the effective elastic thickness and the derived b profile are dependent on the assumed value of the depth of necking the use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength and an overestimation of the thinning factors in the northern viking graben a necking depth at intermediate crustal levels gives results comparable to the observations extension by faulting is modelled to be a significant factor in conclusion rifting in the northern viking graben can be explained with various models of effective elastic thicknesses eet varying from 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking it is also shown that the development of the basin during the post rift phase cannot be explained by pure shear simple shear extension two mechanisms are proposed here to explain the post rift subsidence pattern namely intra plate stress and phase boundary migration the two extreme models for eet mentioned above 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking give very different responses to compressional stress the latter gives basically no response for realistic intra plate stress d 2004 elsevier b v all rights reserved

geologic structure of the uppermost oceanic crust created at fast to intermediate rate spreading centers abstract geological investigations of major fault scarps tectonic windows and dsdp odp drill holes provide direct views of the uppermost oceanic crust generated at fast to intermediate rate spreading centers these areas reveal a consistent upper crustal structural geometry with basaltic lava flows defining a pattern of downward increasing inward dip toward the spreading center at which they formed and dikes in the lavas and underlying sheeted dike complex showing a similar degree of outward dip widespread fracturing faulting and hydrothermal metamorphism accompanied magmatic construction these geological relationships can be interpreted in terms of dramatic asymmetrical subaxial subsidence of upper crustal rock units that diminishes across the very narrow few kilometers wide zone of lava accumulation and dike intrusion at the ridge axis this type of crustal structure is in accord with some existing models of spreading but augments these idealized views with more realistic geological

copper isotope systematics of the lucky strike rainbow and logatchev sea floor hydrothermal fields on the mid atlantic ridge in this paper we present the copper isotope signatures of black smoker sulfides massive sulfides and their alteration products and provide new insights into mineralization processes and applications of copper isotope geochemistry to sea floor hydrothermal systems on the mid atlantic ridge the hydrothermal systems studied include the lucky strike field at 37 17 n on a basaltic substrate and the rainbow and logatchev fields situated on ultramafic rock copper isotope variation in the hydrothermal precipitates was examined in conjunction with s isotopes and se and co concentrations the comparison between 65cu and se contents shows that subsurface precipitation of cu rich sulfides does not control significantly the 65cu values of the hydrothermal chimneys it appears that the major cause of copper isotope fractionation in hydrothermal systems up to 3 is the sea floor oxidation of primary copper sulfides enrichment in the heavy copper isotope can be explained by processes occurring at the sea floor such as hydrothermal reworking of previously altered sulfides by high temperature fluid massive sulfides characterized by negative 65cu values have undergone extensive recrystallization in these mineralogical assemblages isotopically heavy copper typical of altered sulfides has been leached and redeposited in the external zones or incorporated in hydrothermal fluids copper isotopes are therefore a promising tool for the study of supergene processes and the recycling of previously oxidized sulfides as well as a means of characterizing the degree of hydrothermal reworking of large sulfide deposits further studies of copper isotope fractionation under controlled laboratory experimental conditions are required to identify copper isotope fractionation during sulfide alteration in particular the possible biological mediation of copper isotope fractionation during sulfide oxidation may be an important direction for further studies

copper isotope characteristics of copper rich minerals from besshi type volcanogenic massive sulfide deposits japan determined using a femtosecond la mc icp ms the copper isotope ratios of chalcopyrite secondary malachite and native copper of metamorphosed besshi type volcanogenic massive sulfide vms deposits from two different mines japan were measured by femtosecond pulsed laser ablation multiple collector inductively coupled plasma mass spectrometry fs la mc icp ms the 65cu where 65cu 65cu 63cu sample 65cu 63cu nist srm976 1 1 000 values of chalcopyrite samples of both mines are relatively narrow 0 34 to 0 29 compared to those of previously reported chalcopyrite from modern submarine hydrothermal deposits at mid oceanic ridge settings 0 98 to 3 14 however the 65cu values of chalcopyrite are slightly different between the two mines this suggests that although metamorphic reequilibration may have reduced the original range of copper isotopes premetamorphic 65cu characteristics of both mines are generally preserved the chalcopyrite samples of one deposit might be significantly affected by dissolution during reworking processes after precipitation on the sea floor secondary malachite 65cu 2 63 2 97 and native copper 65cu 1 43 1 71 have higher 65cu values than chalcopyrite from the same deposit this variation is most reasonably explained in terms of a redox controlled isotope fractionation at low temperature conditions during secondary weathering processes involving the preferential incorporation of 65cu in secondary cu ii solutions it is also suggested that significant negative isotopic fractionations accompanying the reduction of cu ii solutions to native copper cu 0 occurred

structure and stratigraphy of the rukwa rift abstract combining recently acquired multifold seismic data with well and gravity information and field mapping a comprehensive picture of the structure and stratigraphy of the rukwa rift has emerged the rukwa rift lies between the tanganyika and nyasa malawi rifts in the western branch of the east african rift system in southwest tanzania the rukwa rift is a nw trending half graben basin that is 350 km long and 40 km wide unlike the neighboring tanganyika and nyasa rifts there is no evidence of half graben polarity reversals in the rukwa rift the nw trending boundary fault system lies on the northeastern side of the basin and comprises a series of listric faults most internal faults also show listric forms and trend n s oblique to the boundary fault the basal sedimentary section is the permo triassic karroo sequence this is overlain by the red bed sandstone sequence in which both mesozoic and tertiary fauna have been found the cenozoic lake bed sequence is the highest unit and covers nearly all of the present basin sediment thicknesses commonly reach 7 km and attain a maximum of 12 km at the southeastern end of the basin the lake bed sequence is the thickest unit in the main depocentre but the karroo sequence is often the thickest unit on the shoaling side of the half graben the rukwa rift is here interpreted to have evolved as a strike to oblique slip pull apart basin based on numerous indications of nw trending strike slip faulting

mesozoic intracontinental underthrust in the se margin of the north china block insights from the xu huai thrust and fold belt the xu huai thrust and fold belt located in the southeastern margin of the north china block consists mainly of thrust and folded pre mesozoic strata its geodynamic evolution and tectonic setting are topics of long debate this paper provides new evidence from geological mapping structural analysis and making balance cross sections with restoration of cross sections results suggest that this belt was subjected to two phase deformation including an early phase regional scale nw ward thrust and fold and a late phase extension followed by the emplacement of dioritic monzodioritic porphyrites dated at 131 135 ma and locally strike slip shearing according to the mapping field observations and drill hole data three structural units were distinguished namely 1 the pre neoproterozoic crystalline basement in the eastern segment 2 the nappe unit or the thrust and fold zone in the central segment which is composed of neoproterozoic to ordovician carbonate rocks and carboniferous permian coal bearing rocks about 2600 m thick and 3 the western frontal zone a major decollement fault has also been identified in the base of the nappe unit on which dozen meter to km scale thrust and fold bodies were commonly developed all pre mesozoic depositional sequences were involved into a widespread thrust and fold event six uncompetent rock layers with biostratigraphic ages nanjing university 1996 have been recognized and each uncompetent rock layer occurred mainly in the top of the footwall playing an important role in the development of the xu huai thrust and fold belt geometry of the major decollement fault suggests that the nappe unit of this belt was rooted in its eastern side near the tan lu fault zone two geological cross sections were chosen for structural balancing and restoration from the balanced cross sections ramp flat and imbricated faults as well as fault related folds were identified a shortening of 20 6 29 6 km was obtained from restoration of balanced sections corresponding to a shortening rate of 43 6 46 4 this shortening deformation was likely related to the se ward intracontinental underthrust of the north china block beneath the south china block during the mesozoic

spatiotemporal patterns of the late quaternary deformation across the northern chinese tian shan foreland abstract the investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt here we focus on the spatiotemporal patterns of the late quaternary deformation along the north piedmont of the chinese tian shan a mountain range formed by the ongoing india asia collision by using a terrace as the reference and applying the area conservation method the holocene shortening rate of the halaande anticline a fold of the distal structure belt iii in the foreland is estimated to 2 14 0 24 mm yr for the first time similarly we re calculate the holocene shortening rates of the other anticlines of belt ii iii using the magnitude of shortening documented by river terraces and the terrace formation ages published previously the summed holocene 103 year timescale shortening rates of individual anticlines along n s transects are 2 4 mm yr consistent with the late pleistocene 104 year timescale shortening rate but about 2 6 times higher than the long term 106 year timescale average shortening rate of 1 mm yr during the past several million years together with the shortening rates of individual anticlines at the 103 year 104 year and 106 year scales these observations imply that the deformation across the northern chinese tian shan foreland has accelerated since at least late pleistocene by summing the late quaternary rates of shortening in the southern chinese tian shan foreland 4 5 mm yr and the intermontane basins in the hinterland of the tian shan 2 mm yr the late quaternary rate of shortening across the tian shan range between longitude 83 e and 87 e amounts to 9 0 1 0 mm yr approximately matching the modern shortening rate of 8 mm yr derived from the gps measurements these results imply i that the deformation across the tian shan range and its foreland basins between longitude 83 e and 87 e could have not been changed significantly since at least late pleistocene ii that in the northern chinese tian shan foreland the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the holocene or even geodetic rate of deformation

copper isotope ratios in magmatic and hydrothermal ore forming environments multi collector inductively coupled plasma mass spectrometry now provides for precise and accurate measurements of cu isotope ratios copper minerals prepared by direct dissolution with and without chromatographic purification yield identical cu isotope ratios within analytic precision of about 0 04x 1r cu isotope ratios have been measured for copper minerals from worldwide magmatic and hydrothermal copper deposits and for several weathered deposits natural variations in d65cu values relative to nbs976 range over 9x chalcopyrite samples from mafic intrusions lie within a narrow range of about 1 5x and most cluster tightly between 0 10xand 0 20x this range lies within the broader black smoker chalcopyrite and iron meteorite ranges and possibly represents a bulk mantle cu isotope ratio most values for hydrothermal native copper from the michigan native copper district also show a narrow range just larger than 0 1xand suggest a common homogeneous source for cu in this large hydrothermal system later copper sulfide and arsenide minerals from this district range to values more than 2x lower than native copper ratios for chalcopyrite and bornite from moderate to high temperature porphyry skarn and replacement deposits as a group and within individual deposits exhibit a broad range of values variations of nearly 1xare observed over distances on the order of 1 m in some cases these variations may result from multiple mineralization events or copper remobilization during retrograde or later hydrothermal activity fractionations between chalcopyrite and bornite where they occur in the same sample or in related samples cluster near 0 4x suggesting equilibrium cu isotope fractionation between them at moderate temperatures in addition weathering of hydrothermal copper minerals produces a wide range of values in secondary copper phases in the supergene environment cuprite typically has higher values than associated native copper therefore redox states appear to exert a significant control over fractionation at low temperatures significant questions remain to be answered before the source of copper in hydrothermal environments can be fully addressed source reservoir cu ratios need to be determined and chemical and physical factors that control cu isotope fractionation must be quantitatively defined d 2003 elsevier b v all rights reserved

effects of layering and anisotropy on fault geometry the geometry and orientation of faults are examined using several field examples of small scale 1 with dihedral angles usually of about 50 as predicted by the coulomb theory of failure in layered rocks the geometry of faults varies with the orientation of layering with respect to the stress field where 1 is approximately normal to layering or anisotropy conjugate faults also develop symmetrically about 1 where rocks have interbedded layers with different mechanical behaviours however faults tend to initiate orthogonal to the more brittle layers i e originate as extension fractures sub parallel to 1 but oblique to the less brittle layers as the fault steps through the layering pull aparts are developed which may reduce the dihedral angle where 1 is oblique c 25 75 to anisotropy one set of faults is developed at a high angle to layering with another at a low angle usually showing a ramp flat geometry large dihedral angles up to 90 may result and 1 does not bisect this angle where 1 is approximately parallel to layering two cases can be recognized where 3 is approximately normal to layering faults with layer parallel flats and contractional ramps develop where 2 is approximately normal to layering conjugate faults develop which are symmetrical about 1 the geometry resembling that in isotropic rocks these observations are in agreement with rock deformation experiments which show the strong effect of anisotropy on fault orientation but the observations incorporate the effects of layering of materials with different deformation characteristics

variation in copper isotope ratios and controls on fractionation in hypogene skarn mineralization at coroccohuayco and tintaya peru hypogene chalcopyrite and bornite in copper skarn and related porphyry ore from coroccohuayco and tintaya peru have been analyzed for copper isotope ratios fifty six samples have a range in 65 cu values of 1 29 to 2 98 per mil relative to nist srm 976 using the sample standard bracketing technique to correct for machine drift and machine isotope fractionation effects the range of 65 cu values of vein hosted mineralization at coroccohuayco overlaps with disseminated mineralization in skarn ore but also extends to lower values the overlap of these ranges indicates that different mineralizing events in these deposits cannot be identified solely by their copper isotope compositions geologic and isotopic considerations of the samples analyzed in this investigation indicate that copper mineralization proximal to fluid sources including porphyries and principal fluid pathways tends to be isotopically lighter than more distal samples this suggests that important copper isotope fractionation occurred during mineralization and may have been the result of equilibrium fractionation and or indirect fractionation mechanisms related to the chemical characteristics of the hydrothermal fluid these fractionation mechanisms have produced copper isotope zonation over tens of meters in hypogene ore during the process of ore precipitation at coroccohuayco

the eastern iranian orocline abstract the eastern iranian range is seen as a large scale india eurasia collisional event and the subsequent amalgamation of the afghan and lut micro continents including the neo tethyan accretionary complexes and associated island arcs revised examination of the nature of tectono stratigraphic units distributed in both sides of the n s elongated eastern iranian orogen reveals two remarkable facts first from a general perspective it is structurally a giant parallel antiform in profile view second lithologically the most time equivalent comparable tectonic units from both northern and southern domains comprising the eastern iranian orogen are connectable follow the strike of hinge and limbs zones of the antiform and a m shaped disharmonic pattern in its core these characters are thought to be formed in response to two principal deformational phases resulting from two perpendicular stress directions the first was n s associated with the north dipping subduction of the tethyan oceanic lithosphere beneath the roughly ribbon shaped cimmerian supercontinent including the afghan and lut blocks before late eocene afterward the second was e w shortening originated by the westward escape of the afghan block as a consequence of the indian plate indentation into eurasia this orogen parallel stress was correspondingly accommodated by tens of degrees counter clockwise rotation of the lut block around a vertical axis the result of such shortening was oroclinal buckling and concomitant retreating of the subduction zone and closure of the sistan ocean a remaining wedge shaped part of the neotethys ocean formed by the ribbon curvature the development of the eastern iranian orogen already included the sistan suture zone an enormous mass of folded eocene flysch deposits with a general n s axial surface and some cretaceous ophiolitic remnants the plate scale buckling which was formed by this late stage orogenic event is hereby considered as an orocline call eastern iranian orocline lithosphere buckling around a vertical axis caused a large scale crustal folding coeval with the bending of its mantle part increasing the lithospheric thickness of the orocline compared to adjacent regions the syn orocline deformation associated delamination and resulting magmatic events took place in eastern iran during a short period of about 10 to 20 ma in the late paleogene the orocline hinge zone is occupied by the khorasan outer arc and the birjand core while its limbs are composed of the baluch inner arc and the southwestern and southeastern terminations of the lut and afghan blocks the eastern iranian orocline seems to be the middle segment of a triple bending belt with n s two opposite facing bend including afghan lut and sanandaj sirjan blocks this large curvature is possibly an example of secondary oroclines which was formed by collision related escape tectonics although the limited available kinematic data show a kind of progressive orocline

the pulang porphyry copper deposit and associated felsic intrusions in yunnan province southwest china the pulang porphyry copper deposit recently discovered in northwestern yunnan province china is located at the south end of the triassic yidun island arc to date 15 mineralized porphyry deposits have been defined in the pulang area and the copper resource is estimated to exceed 10 mt the pulang deposit as currently defined is made up of five ore bearing porphyry deposits covering an area of approximately 9 km2 intermediate acidic porphyritic intrusions composed of quartz diorite monzodiorite quartz monzonite and granodiorite are widespread in the pulang area the alteration zones identified with the porphyry deposits include silicic potassium silicate quartz sericite and propylitic zones the porphyry deposits have hornfels at the contact with slate sandstone and andesite re os ages of molybdenite and ar ar and k ar dating of biotite indicate that the pulang porphyry copper deposit formed during the indosinian tectonic episode with the main ore formation taking place from 216 to 213 ma late triassic norian however the whole process of hydrothermal activity including overprinting may have extended from 235 to 182 5 ma

identifying fault segments from 3d fault drag analysis vienna basin austria abstract the segmented growth of the markgrafneusiedl normal fault in the late miocene clastic sediments of the central vienna basin austria was investigated by construction of a detailed three dimensional 3d structural model using high resolution 3d seismic data the fault surface and marker horizons in the hanging wall and the footwall of the markgrafneusiedl fault were mapped and orientation displacement and morphology of the fault surface were quantified individual fault segments were identified by direct mapping of the deflection of the marker horizons close to the fault surface correlating the size of the identified segments with the magnitude of fault drag and displacement distribution showed that fault evolution progressed in several stages the proposed method allows the detection of segments that are not recorded by the magnitude of displacement or fault morphology most importantly detailed mapping of marker deflections in the hanging wall could help to constrain equivalent structures in the footwall which may represent potential hydrocarbon traps

yanshanian late mesozoic ore deposits in china an introduction to the special issue abstract the late jurassic cretaceous yanshanian orogeny or yenshan movement one of the most important tectonothermal events is first recognized in china especially eastern china this late mesozoic orogeny which was initiated most likely by a mesozoic tectonic switch strongly reworked or destructed the older continental lithospheres or cratonic keels that are manifested by alternating compressive and extensional deformation voluminous igneous rocks and a variety of characteristic magmatic hydrothermal mineral systems despite its first discovery and definition in yenshan yinshan area of north china craton the yanshanian orogeny probably is of global tectonic magmatic and metallogenic significance however there have been hot debates on the precise starting time accurate duration or time interval detailed processes and evolution linked to deep lithospheres tectonic nature and geodynamic mechanism s of the yanshanian orogeny which inevitably have hindered the understanding of the genesis mineralizing processes and geodynamic mechanism of the late mesozoic magmatic hydrothermal mineral systems this special issue captures some of the latest research results on the yanshanian ore deposits that are involved into a few main mesozoic metallogenic belts or provinces from northeast to southwest china including 1 the jiaodong peninsula metallogenic province in the north china craton 2 the middle lower yangtze river valley metallogenic belt in the central eastern china 3 the jiangnan and 4 the nanling metallogenic belts in the south china block 5 the southeastern china coast metallogenic belt and 6 the sanjiang metallogenic belt in southwest china through a multidisciplinary study this special issue re investigated and re evaluated the relationship between the late mesozoic magmatic hydrothermal mineral systems and the yanshanian tectonothermal events in the studied metallogenic belts or provinces a few important contributions to the topic in this special issue yanshanian metallogeny are summarized as followings 1 a new ore deposit type i e the intracontinental reactivation type has been suggested to interpret the genesis of those au polymetallic deposits that are hosted within older metamorphic rocks and related to the late mesozoic basin and range extensional settings 2 late mesozoic re activation of the preexisting structures by the yanshanian tectono thermal event s might be an important mechanism controlling the yanshanian large scale mineralization 3 a type granites formed by partial melting of the mesoproterozoic crust but with inputs from mantle derived melt are also favorable for sn mineralization in addition to s type and i type granites as previously recognized 4 calculated oxygen fugacities o 2 of granitic magmas based on chemical compositions of primary biotite have been confirmed to be effective proxy for distinguishing cu au mo w sn pb zn mineralized granites from barren granites 5 a significant epoch of w sn magmatic hydrothermal ore system at ca 145 135 ma has been identified in the southeastern china coast metallogenic belt and 6 in addition to traditional structural geology mineralogy petrology geochemistry and geochronology new analytical techniques e g cu isotopes and data treatment method e g bi dimensional empirical mode decomposition can be used to provide more constraints for deep exploration

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models

mesozoic plutons of the yidun arc sw china u pb geochronology and hf isotopic signature abstract the yidun arc is a triassic volcanic arc located between the songpan garze fold belt and the qiangtang block southwest china to constrain the age of a number of the major granitic plutons from the yidun arc laser ablation icp ms u pb analysis of zircon was conducted hafnium isotope data was also acquired through laser ablation multicollector icpms analysis of zircon with the aim of gaining insight into the age and nature of the source region of the plutons three age groups have been identified from seven granite samples early middle triassic 245 to 229 ma late triassic 219 to 216 ma and cretaceous 105 to 95 ma hafnium analysis shows the triassic granites to have negative and variable e hf values and mesoproterozoic 1 6 ga depleted mantle model ages which is interpreted to reflect derivation from an isotopically heterogeneous largely crustal source the cretaceous granite shows higher and less variable e hf values and slightly younger model ages 1 3 ga and is interpreted to be derived from melting of a more homogeneous crustal source a depleted mantle model age of 1 5 ga is calculated from the pooled triassic and cretaceous samples the source region for these magmas may be tentatively correlated with mesoproterozoic material of the yangtze craton which has been suggested to underlie the yidun arc however further work is necessary to demonstrate this suggestion