the elatsite porphyry copper deposit in the panagyurishte ore district srednogorie zone bulgaria u pb zircon geochronology and isotope geochemical investigations of magmatism and ore genesis

structural and mechanical controls on intrusion related deposits of the tombstone gold belt yukon canada with comparisons to other vein hosted ore deposit types abstract intrusion related gold deposits at the clear creek scheelite dome and dublin gulch properties of the tombstone gold belt tgb yukon territory have dominantly e striking steeply dipping auriferous quartz extension veins within intrusions in adjacent metasedimentary rocks gold is hosted in subvertical nw to nnw striking sinistral faults as veins and breccias in e striking extension veins and locally in e to ene striking fault veins these structural relationships indicate low magnitude broadly e w directed shortening and n s extension during stock emplacement and gold mineralisation at 92 ma the lack of any deviation or deflection of the extension vein orientations in the country rocks with respect to their orientation within the stocks indicates consistent stress trajectories in both rock types these tgb deposits formed at 5 8 km depth where mean and differential stresses may be greater in magnitude than in shallower porphyry environments many porphyry systems feature magmatic related stresses that dominated the local stress field with more variable vein orientations the result conversely orogenic gold systems usually exhibit strong dimensionality in vein orientations fault hosted mineralisation in metasedimentary rocks of the tgb deposits in this study is comparable in geometry but generally smaller in size than in many orogenic gold systems intrusion related systems of the tgb exhibit intermediate structural styles of mineralisation that provide a useful bridge in understanding the diversity of mechanically controlled structural styles in otherwise mostly unrelated gold deposit types

characteristics of turbulent boundary layers over a rough bed under saw tooth waves and its application to sediment transport article i nfo a large number of studies have been done dealing with sinusoidal wave boundary layers in the past however ocean waves often have a strong asymmetric shape especially in shallow water and net of sediment movement occurs it is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves characteristics of the turbulent boundary layer under breaking waves saw tooth are investigated and described through both laboratory and numerical experiments a new calculation method for bottom shear stress based on velocity and acceleration terms theoretical phase difference and the acceleration coefficient ac expressing the wave skew ness effect for saw tooth waves is proposed the acceleration coefficient was determined empirically from both experimental and baseline k model results the new calculation has shown better agreement with the experimental data along a wave cycle for all saw tooth wave cases compared by other existing methods it was further applied into sediment transport rate calculation induced by skew waves sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by watanabe and sato watanabe a and sato s 2004 a sheet flow transport rate formula for asymmetric forward leaning waves and currents proc of 29th icce asce pp 1703 1714 moreover the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found

cuyania an exotic block to gondwana review of a historical success and the present problems abstract a review of the early history of the cuyania terrane and the numerous pioneering works of the past century provides the present robust framework of evidence supporting a derivation from laurentia travel towards gondwana as an isolated microcontinent and final amalgamation to the protomargin of western gondwana in middle to late ordovician times the major remaining uncertainties and inconsistencies such as the time of deformation and collision with gondwana the lack of evidence of famatinian derived zircons the effects of strike slip displacements proposed along the suture as well as the potential sutures defined by ophiolite assemblages are discussed the precise boundary along the northern and southern limits is not yet well defined the most suitable hypothesis based on present data is that cuyania originated as a conjugate margin of the ouachita embayment south of the appalachian platform during early cambrian times the subsequent travel toward the gondwana protomargin is clearly depicted by the changing faunal assemblages in the carbonate platform new geochemical and age data on k bentonites presented by several authors reinforce the strong connection between cuyania ash fall tuffs and famatina volcanics by 468 470 ma indicating cuyania and gondwana were in close proximity at that time extension related to flexural subsidence preceded by the drowning of the carbonate platform in early llanvirnian times is recorded by abrupt facies changes in the sedimentary cover during late llanvirnian and early caradocian times this episode marked the beginning of contact between cuyania and gondwana the subsequent evolution of the foreland basin indicates that deformation lasted until latest silurian early devonian times the time of collision is tracked by the cessation of arc related magmatic activity in the upper plate gondwana protomargin at about 465 ma in western sierras pampeanas and ages around 454 ma corresponding to syncollisional and postcollisional magmatism the age of the collision is also preserved in the lower plate cuyania where both angular unconformities in the sedimentary cover and the ages of peak of regional metamorphism in the basement rocks point to 460 ma as the most probable age for the beginning of the collision evidence from the upper plate is essentially identical with an age of 463 ma thermal gradients along this suture vary from 13 c km in the lower plate to 18 c km in the fore arc upper plate reaching more than 30 c km along the famatinian arc based on these data a llandelian caradocian age for the collision can be postulated on firm grounds deformation continued through most of the early paleozoic until amalgamation of the chilenia terrane by the late devonian

brittle failure mode plots for compressional and extensional tectonic regimes abstract equations governing different macroscopic modes of brittle rock failure extensional fracturing extensional shear fracturing compressional shear failure and reshear of existing faults can be represented on plots of differential stress vs effective vertical stress for a set of material properties such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions allowing easy evaluation of the physical controls on brittle rock failure and ready comparison of the fields occupied by the three failure modes in different tectonic settings they emphasize the relative ease in terms of differential stress and fluid pressure levels of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional aside from their relevance to general structural mechanics these generic failure plots have wide ranging application to understanding the initial development and progressive evolution of fault fracture systems both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings

strain fabric analysis applied to hydrothermal ore deposits emplaced during changing geodynamical conditions infiernillo and las picazas san rafael massif argentina abstract infiernillo and las picazas are two small hydrothermal ore deposits in the northern san rafael massif argentina they are genetically linked to the permian choiyoi volcanic province which reflects the transition from a convergent plate margin to an extensional regime calc alkaline early permian lower choiyoi magmatism was syntectonic with transpressional deformation of the san rafael orogeny whereas transitional late permian upper choiyoi sequences were emplaced under a transtensional regime during the post san rafael extension infiernillo is a cu mo porphyry type deposit hosted by pyroclastic rocks of the lower choiyoi it consists of a central quartz plug surrounded by a potassic and a phyllic halo and a set of peripheral polymetallic cu pb zn veins cropping out close to the alteration zone the las picazas deposit consists of a group of low sulfidation epithermal galena bearing veins hosted by early palaeozoic meta sediments strain fabric and available 2 d and 3 d kinematic analyses were performed in order to define the relationships between both deposits and the geodynamic scenario these data reveal that a porphyry emplacement at infiernillo occurred during the declination of the san rafael orogeny shortly before the change in stress regime and b las picazas low sulfidation epithermal veins were emplaced during the subsequent transtensional post san rafael regime these results prove that each ore deposit is linked to a different stress regime reflecting the change in geodynamical conditions that prevailed during the emplacement of the choiyoi volcanism thus strain fabric analysis at both ore deposits allows us to confirm that the tectonic regime is a major factor in controlling the mineralization style of hydrothermal ore deposits

age and origin of the paramillos de uspallata pb zn ag vein deposit in the cuyo basin argentina constraints from structural controls and isotopic evidence abstract the paramillos de uspallata deposit located in the cuyo rift basin is a pb zn ag vein deposit hosted by mesozoic triassic volcano sedimentary sequences in the present study new geological and isotopic data is used to constrain the age source and structural controls of the ore forming fluids the isotopic data suggest a middle cretaceous age for the mineralization and that mineralizing fluids were formed from a mixture of sources that includes the permian volcanic rocks from the basin basement and the triassic basalts with pb and sr isotopic composition typical of the upper crust regional structural analysis allowed to conclude that the veins formed within large scale reactivated structures that affect the basin basement local structural analysis showed that the mineralization was controlled by extensional and shear extensional wnw ese to nw se and shear e w trending structures kinematic analyses performed in the veins evidenced a transtensional environment with a ne extension direction and e w dextral shear in this scenario fluids were channeled by a strike slip faulting system connected with a deep weakness zone during the beginning of the andean orogeny this study provides new insights into the genesis and the geodynamic scenario of pb zn ag vein deposit

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

el morro caldera 33 10 s 66 24 w san luis argentina an exceptional case of fossil pre collapse updoming abstract volcanism at sierra del morro represents the final stages of the flat slab related magmatism in the easternmost san luis neogene volcanic belt this 80 km long nw wnw trending belt tracks the episodic inland migration of both magmatism and tectonic deformation since 18 ma the sierra del morro stands out in the eastern sierras pampeanas as a metamorphic block uplifted during the late miocene pleistocene by a combination of magma injection and tectonic deformation although sequences that preserve stages of basement updoming are not often preserved exposures in sierra del morro are exception in providing key evidence and insight into the involved processes based on the comprehensive study of volcanic stratigraphy and structures the reconstruction of the volcanic architecture has been carried out we infer a three stage evolution of the el morro caldera as follows 1 pre collapse updoming and volcanism 2 collapse caldera formation and 3 post caldera volcanism the ascent of magma is recorded in small tumescence sites strongly controlled by oblique transtensional wnw nw and ene striking brittle ductile megashear zones even though the area affected by tumescence was large magma injection progressed only locally at cerros guanaco and pampa metamorphic rocks were updomed and strongly brecciated whereas at sierra del morro magma was emplaced as pre collapse domes with associated block and ash flows ignimbrite caldera forming eruptions and post caldera lava domes and dykes the caldera is located in the intersection of two major oblique transtensional wnw nw and ene trending brittle ductile megashear zones where the highest positive dilatation occurred

suspension and near bed load sediment transport processes above a migrating sand rippled bed under shoaling waves the present study focuses on the fine scale flow and sand transport processes above onshore migrating ripples below skewed surface gravity waves in the shoaling zone a set of acoustic instruments was deployed in the shoaling region of the large scale wave channel at canal d investigacio i experimatacio maritima universitat poltiecnica de catalunya barcelona spain in order to provide high resolution velocity and sediment concentration profiles with an acoustic concentration and velocity profiler acvp measurements are analyzed relative to the positions of the measured nonmoving sand bed and the interface separating the suspension from the near bed load layer this interface is detected here by the application of a novel acoustic bed echo detection method furthermore the use of the dual frequency inversion proposed in the work of hurther et al 2011 allows for the calculation of the sediment concentration profile across both the suspension and near bed load layers the sand bed was covered by quasi two dimensional suborbital ripples migrating onshore as proposed by o donoghue et al 2006 the occurrence of quasi two dimensional ripples is attributed to the fine size sand of d50 250 mm used in the present study under full scale forcing conditions in order to determine the effect of shoaled wave skewness on the ripple vortex entrainment and sediment transport the instantaneous and mean measurements of the flow sediment concentration and sediment flux along the ripple profile are discussed in terms of 1 the occurrence of ripple vortex entrainment on either side of the ripple crest 2 the wave velocity phase lagging driven by the ripple vortex entrainment process and the turbulent bed friction effects in the wave boundary layer 3 phase lagging between velocity and maximum concentration and sediment flux events 4 the structure of bed friction and ripple driven turbulence across the suspension and the near bed load layers and 5 the streaming components the results on these aspects strongly support that the wave velocity skewness effect under shoaling waves is fairly similar to the one obtained in skewed oscillatory water tunnel flows furthermore it is found that the onshore oriented net bed load sediment transport is at the origin of the onshore ripple migration this flux is roughly twice as much as the opposite offshore oriented net suspension flux dominated by the ripple vortex entrainment processes

bed shear stress under skewed and asymmetric oscillatory flows abstract we present a new formulation to predict the bed shear stress under skewed asymmetric oscillatory flows with or without a co linear mean current extending the work of nielsen 1992 the nonlinearity of the oscillatory flow is incorporated through the use of two parameters the index of skewness or nonlinearity and the waveform parameter the new formulation is tested against the bed shear stress estimated from the log fit and momentum integral methods using oscillatory data from oscillating water tunnel experiments the new formulation and the momentum integral method agree well but differ from those with the log fit method possibly because both methodologies lead to different results for the phase lead between the bed shear stress and the free stream velocity the new bed shear stress formulation is incorporated in a quasi steady bedload formula and accurately reproduces net transport rates under non linear nonbreaking waves with and without an opposing current

s p conversion from the transition zone beneath tonga and the nature of the 670 km discontinuity summary using more than 300 recordings of deep tonga earthquakes from the warramunga seismic array central australia we have searched for short period s p conversions from the 670 km discontinuity arriving in the p wave codas the array seismograms were stacked and plotted in sections to optimize observation of s670p yielding the following results for the northern part of tonga 17 3 18 4 s s670p phases are observed with apparent conversion depths between about 660 and 680 km for the central part 20 2 22 3 s s670p is not clearly observed for the southern part 23 1 25 7 s s670p is observed for conversion depths between about 660 and 700 km intermittent occurrence of s p conversion may result from different characteristic source radiation patterns among the three sections overall uncertainties in conversion depths resulting from unmodelled lateral velocity variations and hypocentral location errors are perhaps a few tens of kilometres the s p rays must travel either within or very close to the subducted slab because of the source receiver slab dip geometry so we conclude that large 50 km deformations of the 670 km discontinuity do not occur beneath tonga our observations appear to be inconsistent with a chemical discontinuity at 670 km but are easily explained if the 670 km discontinuity is a strongly pressure dependent and perhaps moderately endothermic phase change in both the slab and surrounding mantle

hydrothermal alteration mapping using aster data in the infiernillo porphyry deposit argentina abstract the infiernillo cu mo porphyry deposit is located in the san rafael massif in southern mendoza province argentina it is hosted by and genetically related to lower permian gondwanan volcanic rocks which developed in a magmatic arc tectonic setting the alteration zone has an oval shape about 3 km 2 km in size with a nne ssw strike it consists of a small central quartz neck with appreciable hematite surrounded by an intense quartz injected zone with local pervasive potassic alteration outwards there is a well developed phyllic halo with intense bleaching which consists of pervasive and vein type silicification sericitization and pyritization cu and mo anomalies are approximately coincident and are located between the silicified zone and the phyllic halo in the outer part of the alteration zone small polymetallic veins with pyrite arsenopyrite galena and minor chalcopyrite sphalerite and electrum in quartz gangue crop out an advanced spaceborne thermal emission and reflection radiometer aster with three visible and near infrared vnir bands six shortwave infrared swir bands and five thermal infrared tir bands was used to characterize the infiernillo porphyry deposit alteration area a circular zoning pattern was clearly observed in the vnir swir band combination spectral analysis of the surface reflectance swir detected 2 20 and 2 26 m absorptions field data and sample spectroscopic analyses obtained using a ger 3700 spectral radiometer and a swir reflectance spectrometer portable infrared mineral analyzer pima showed a good correlation with the aster data the 2 20 m absorptions due to al hydroxyl reveal the presence of clay minerals al illite kaolinite and sericite whereas the 2 26 m absorption due to fe hydroxyl resulted from jarosite the field samples were also analyzed with a tir portable spectrometer micro ftir model 102 the tir was useful for detecting surface silica and potassic alteration through analysis of five band surface emissivity data aster images provided preliminary mineralogic information and geo referenced alteration maps at low cost and with high accuracy in this way aster has been proven to be a powerful tool in the initial steps of ore deposit exploration

separation of multiple stress events by fault striation analysis an example from variscan and younger structures at ogmore south wales the study of minor structures in carboniferous and triassic sedimentary rocks at ogmore by sea bridgend reveals that the observed microstructures are the consequence of successive brittle deformation events age relationships can be deduced from sets of structures consisting of conjugate faults oblique slip faults tension gashes and stylolites from which deductions can be made about the orientations of principal stresses corresponding to pre and post triassic events the demonstrable polyphase tectonic history at ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories the new technique based on the statistical procedure of cluster analysis involves the sorting of fault slip data into coherent dynamic setsasa preliminary stage of formal stress inversion the fault sets separated using this technique yield stresses which are similar to those deduced from field observations four stress configurations are distinguished of which two are pre triassic in age correlations with previously derived stresses are discussed

30 million years of permian volcanism recorded in the choiyoi igneous province w argentina and their source for younger ash fall deposits in the parana basin shrimp u pb zircon geochronology evidence abstract we present four shrimp u pb zircon ages for the choiyoi igneous province from the san rafael block central western argentina dated samples come from the yacimiento los reyunos formation 281 4 2 5 ma of the cochico group lower choiyoi section andesitic breccias dacitic to rhyolitic ignimbrites and continental conglomerates agua de los burros formation 264 8 2 3 ma and 264 5 3 0 ma and cerro carrizalito formation 251 9 2 7 ma upper choiyoi section rhyolitic ignimbrites and pyroclastic flows spanning the entire permian succession of the choiyoi igneous province a single zircon from the el imperial formation that is overlain unconformably by the choiyoi succession yielded an early permian age 297 2 5 3 ma while the main detrital zircon population indicated an ordovician age 453 7 8 1 ma the new data establishes a more precise permian age artinskian lopingian for the section studied spanning 30 ma of volcanic activity volcanological observations for the choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes capable of injecting enormous volumes of tephra in the troposphere stratosphere the new shrimp ages indicate contemporaneity between the choyoi succession and the upper part of the parana basin late paleozoic section from the irati up to the rio do rasto formations encompassing about 24 ma geochemical data show a general congruence in compositional and tectonic settings between the volcanics and parana basin permian ash fall derived layers of bentonites thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions thus we consider that the choiyoi igneous province was the source of ash fall deposits in the upper permian section of the parana basin data presented here allow a more consistent correlation between tectono volcanic permian events along the paleo pacific margin of southwestern gondwana and the geological evolution of neighboring paleozoic foreland basins in south america and africa

la peligrosa caldera 47 15 s 71 40 w a key event during the jurassic ignimbrite flare up in southern patagonia argentina pyroclastic and lava vent facies from the late jurassic el quemado complex are described at the southern lake ghio in the cordillera patagonica austral based on the comprehensive study of lithology and structures the reconstruction of the volcanic architecture has been carried out four ignimbrites and one rhyolitic lava unit affected by oblique slip normal faults have been recognized the evolution of la peligrosa caldera has been modeled in three different stages 1 initial collapse consisting of a precursory downsag subsidence related to a dilatational zone which controlled the location of the caldera 2 main collapse with the emplacement of large volume crystal rich ignimbrites and megabreccias under a progressive subsidence controlled by a pull apart structure related to a transtensional regime and 3 post collapse in which lava flows and associated domes were emplaced under an oblique extensional regime the caldera records a remarkable change from transtension to oblique extension which may represent an important variation in regional deformation conditions during jurassic times la peligrosa caldera may be considered a key event to understand the eruptive mechanisms of the flare up volcanism in the chon aike silicic province 2013 elsevier b v

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

direct evidence for the undulation of the 660 km discontinuity beneath tonga comparison of japan and california array data short period seismograms of tonga deep earthquakes recorded by japanese and californian seismic networks are stacked to identify the s p converted wave associated with the 660 km discontinuity the travel time difference between this s p converted wave and the direct p wave is used to constrain the depth of the 660 km discontinuity analysis of a total of 29 events produced a detailed topographical map of the discontinuity beneath the tonga subduction zone two events which exhibit clear s p conversions in both japan and california data are selected to show directly the depth variations of the 660 km discontinuity adjacent to the subducting slab the s p conversion points on the ray paths to japan are observed to be approximately 10 to 30 km deeper than the conversion points on those to california which represents direct evidence for a slab induced depression of the 660 km discontinuity

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

upper mantle discontinuity structure in the region of the tonga subduction zone we study the mantle structure below the southwest pacific in order to examine the geometry of the tonga slab at depth and its interaction with the 410 and 660 km discontinuities hereafter called the 410 and the 660 we utilize data from stations of both the lau basin ocean bottom seismogram experiment and island stations of the southwest pacific seismic experiment the tectonic complexity of this region containing both the tonga subduction zone and the associated lau back arc spreading center make it an ideal area to investigate the upper mantle discontinuities using a high resolution technique such as common conversion point stacking of receiver functions we produce a high resolution image of the upper mantle near the tonga subduction zone to show the interaction between the discontinuities and the subducting slab our results show the 410 uplifted by 30 km near the tonga slab and the 660 depressed by 20 to 30 km as expected for thermally controlled olivine phase transitions

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

discrete particle model for sheet flow sediment transport in the nearshore fully three dimensional discrete particle computer simulations of high concentration sheet flow transport in oscillatory flows quantify the effect of fluid acceleration on bed load transport in highly unsteady flows typical of nearshore marine environments a simple impulse momentum approach explains simulation results and forms the basis for adding an acceleration related term to widely used energetics sediment transport formulae transport predicted by the acceleration term becomes increasingly significant as wave shape approaches the sawtooth profile characteristic of surf zone bores simulations integrate f ma and a corresponding set of equations for the torques for each sphere normal and tangential forces between contacting particles are linear functions of the distance between sphere centers and the relative tangential displacement at the contact point respectively particle interactions are both inelastic and frictional pressure gradient forces generated by the passage of surface gravity waves drive fluid and particle motion in a stack of thin horizontal fluid layers that exchange momentum and exert fluid drag added mass and buoyancy forces on particles transport properties of the simulated granular fluid assemblage are robust to large variations in material properties of the particles simulated transport rates agree with available experimental data for unsteady transport of coarse sands the mode of bed load motion dispersion of bed load particles and particle segregation by size and density are qualitatively consistent with available particle scale observations of bed load transport of natural particles

upper mantle structure of the southwest pacific from regional waveform inversion we determine the upper mantle seismological structure of the southwest pacific by inverting complete regional seismograms recorded by the southwest pacific seismic experiment a deployment of 12 broadband seismographs in the fiji tonga and niue islands we first present a method to invert entire seismic waveforms for a laterally homogeneous velocity structure partial derivatives are computed using an efficient reflectivity code for differential seismograms randall 1994 and a conjugate gradient method is used to perform the nonlinear inversion band pass filtered 10 55 mhz vertical and radial component seismograms extending from the p arrival to the surface waves are used to constrain the structure waveforms are selected to provide regional distance 400 1500 km propagation paths predominantly within one of the tectonic regions of the southwest pacific source depths ranging from 10 to 240 km allow the deeper regions of the model to be resolved with relatively short path lengths results show extremely large lateral variability in the upper mantle structure of the southwest pacific the inactive south fiji basin shows upper mantle velocities much lower than those previously observed for the pacific lithosphere of a similar age the north fiji and lau basins containing active back arc spreading systems show upper mantle shear velocities as slow as 3 8 km s 1 the exceptionally low seismic velocities in the active back arc regions may represent the slowest upper mantle velocities in the world the velocity difference between the active back arc basins and the old pacific lithosphere immediately east of the tonga trench is maximum at 30 90 km depth with a variation of 18 indicating partial melting in this depth range velocity heterogeneity of 4 extends to a depth of 170 km velocity structure below 220 km depth is poorly resolved but there is some evidence of a 2 difference extending to depths of 350 km

9 processes of tectonism magmatism and mineralization lessons from europe abstract metallogenic provinces in europe range in age from the archaean to the neogene deposit types include porphyry copper and epithermal cu au volcanic hosted massive sulphide vms orogenic gold fe oxide cu au anorthosite fe ti oxide and sediment hosted base metal deposits most of them formed during short lived magmatic events in a wide range of tectonic settings many can be related to specific tectonic processes such as subduction hinge retreat accretion of island arcs continental collision lithosphere delamination or slab tear in contrast most sediment hosted deposits in europe evolved in extensional continental settings over significant periods of time in europe as elsewhere ore formation is an integral part of the geodynamic evolution of the earth s crust and mantle many tectonic settings create conditions conducive to the generation of water rich magma but the generation of ore deposits appears to be restricted to locations and short periods of change in temperature and stress imposed by transitory plate motions crustal influence is evident in the strong structural controls on the location and morphology of many ore deposits in europe crustal scale fault fracture systems many involving strike slip elements have provided the fabric for major plumbing systems rapid uplift as in metamorphic core complexes and hydraulic fracturing can generate or focus magmatic hydrothermal fluid flow that may be active for time spans significantly less than a million years once a hydrologically stable flow is established ore formation is strongly dependent on the steep temperature and pressure gradients experienced by the fluid particularly within the upper crust in europe significant fracture porosity deep in the crystalline basement 1 is not only important for magmatic hydrothermal systems but allows brines to circulate down through sedimentary basins and then episodically upward expelled seismically to produce sediment hosted base metal deposits and kupferschiefer copper deposits emerging research stimulated by geode can improve the predicting power of numerical simulations of ore forming processes and help discover the presence of orebodies beneath barren overburden

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

detailed structure and sharpness of upper mantle discontinuities in the tonga subduction zone from regional broadband arrays 1 recordings of deep tonga earthquakes from two arrays of 12 broadband seismographs each in the fiji and tonga islands are stacked and searched for reflections and conversions from upper mantle discontinuities in the tonga subduction zone the arrays operated as part of the seismic arrays in fiji and tonga saft experiment from july 2001 to august 2002 in comparison with the commonly used teleseismic approaches the short path lengths for the local data provide smaller fresnel zones and high frequency content for precise mapping of discontinuity topography and sharpness to enhance the low amplitude discontinuity phases s410p p660p and s660p deconvolved seismograms from each event array pair are aligned on the maximum amplitude of the direct p wave and subsequently slant stacked for the 410 km discontinuity the results show no systematic variations in depth with distance to the cold slab the 660 km discontinuity varies between 656 and 714 km in depth for the southern and central parts of the subduction zone the largest depths occur in the core of the tonga slab for the northern part two separate depressions of the 660 km discontinuity are observed these anomalies are interpreted as being induced by the active steeply subducting tonga deep zone and a subhorizontally lying remnant of subducted lithosphere from the fossil vityaz trench respectively interpreting the deflections of the 660 km discontinuity in terms of local temperatures implies a thermal anomaly of 800 k to 1200 k at 660 km depth except for the southern region where it may thicken the width of the depressed 660 km discontinuity region implies that the tonga slab seems to penetrate the 660 km discontinuity with little deformation waveform modeling suggests that both the 410 and 660 km discontinuities are sharp the 660 km discontinuity is at most 2 km thick in many parts of the region and a first order discontinuity cannot be precluded the 410 km discontinuity thickness shows somewhat more variability and ranges from 2 to 10 km outside the slab and is at most 10 km thick within the slab this suggests that the subduction process does not produce dramatic effects on the sharpness of the discontinuities

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

the role of magmatic and hydrothermal processes in the evolution of be bearing pegmatites evidence from beryl and its breakdown products beryl and euclase crystals from the mina do santino and the jacu pegmatites in the borborema pegmatite province in northeastern brazil contain several generations of melt and fluid inclusions which allow interpretation of p t x conditions responsible for beryl crystallization and for alteration of a primary pegmatitic mineral assemblage to a mixture of hydrothermal minerals euclase bertrandite kaolinite and quartz primary melt and fluid inclusions hosted by beryl were trapped simultaneously however their homogenization temperatures are significantly higher 870 900 c than the values previously reported for pegmatitic systems 712 c and should be treated with caution an isobaric drop of temperature resulted in the exsolution of a fluid a low salinity co2 enriched phase and a saline water rich phase were trapped in pseudosecondary inclusions in beryl at a pressure of 2 1 2 7 kbar and temperature of 390 480 c cooling of the country rocks below 400 c caused a ductile to brittle transition and allowed infiltration of cold groundwater which further decreased the temperature in the system to 190 240 c at the same time the pressure dropped from a lithostatic 2 1 2 7 kbar to a hydrostatic value 0 57 0 73 kbar consequently minerals deposited under magmatic conditions feldspars and beryl became unstable and a newly formed hydrothermal mineral paragenesis euclase bertrandite kaolinite and quartz overprinted the earlier one the hydrothermal fluids responsible for the alteration differ from the earlier exsolved fluids in having a lower salinity lower homogenization temperature the absence of co2 and the presence of ch4

seismic evidence for a thinner mantle transition zone beneath the south pacific superswell broadband seismograms recorded by the seismic stations deployed on oceanic islands in the south pacific for two deep earthquakes in 1998 are used to investigate the mantle transition zone structure beneath the south pacific where a large scale hot plume might ascend from the core mantle boundary cmb by stacking s waves reflected at the mantle transition zone discontinuities we find clear signals associated with the 410 km and 660 km discontinuities the transition zone thickness which is constrained from the travel time difference between the reflected waves from the 410 km and 660 km discontinuities is observed to be approximately 15 km thinner beneath the south pacific superswell than that beneath other regions the result suggests that the transition zone temperature beneath french polynesia is approximately 100 200 k higher than the surrounding mantle

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

pervasive seismic wave reflectivity and metasomatism of the tonga mantle wedge subduction zones play critical roles in the recycling of oceanic lithosphere and the generation of continental crust seismic imaging can reveal structures associated with key dynamic processes occurring in the upper mantle wedge above the sinking oceanic slab three dimensional images of reflecting interfaces throughout the upper mantle wedge above the subducting tonga slab were obtained by migration of teleseismic recordings of underside p and s wave reflections laterally continuous weak reflectors with tens of kilometers of topography were detected at depths near 90 125 200 250 300 330 390 410 and 450 kilometers p and s wave impedances decreased at the 330 kilometer and 450 kilometer reflectors and s wave impedance decreased near 200 kilometers in the vicinity of the slab and near 390 kilometers just above the global 410 kilometer increase the pervasive seismic reflectivity results from phase transitions and compositional zonation associated with extensive metasomatism involving slab derived fluids rising through the wedge

depression of the 660 km discontinuity beneath the tonga slab determined from near vertical scs reverberations the occurrence of the march 9 1994 mw 7 6 deep tonga earthquake during a temporary deployment of broadband seismographs provides an excellent opportunity to study the seismic discontinuity structure in the vicinity of a subducting slab near vertical scs reverberations from the 410 520 and 660 discontinuities are visible at 10 stations in the south pacific at frequencies between 0 003 0 033 hz without stacking we use a regional velocity model and ray theory to model the interval from scs to scs3 a grid search is then performed on the depth and impedance contrast at each of the seismic discontinuities to optimize the fit to both the underside and topside reflections stacked records indicate prominent discontinuities at 400 km and 665 km depth beneath and to the west of the slab and 410 km 500 km and 640 km to the east of the slab analysis of individual records suggests a local depression of 30 km in the 660 and a broadening of the transition zone directly beneath and to the west of the tonga slab in a region of possible near horizontal slab these results are consistent with a large cool region just to the west of the intersection of the tonga slab with the 660

matrix deformation in a basement involved fold and thrust belt a case study in the central andes malargue argentina abstract an analysis of the anisotropy of magnetic susceptibility ams is used to investigate the matrix strain record of weakly deformed clastic rocks including sandstones and shales along a cross section of the malargue fold and thrust belt mftb argentina we collected 339 oriented cores from the tres esquinas sandstones the red beds of the tordillo and neuquen formations as well as from shales silts of the mendoza group overall 90 of the magnetic fabrics are well defined and are related to the strain imprint of the layer parallel shortening among the tectonic related fabrics 40 show the development of a magnetic lineation at right angle of the shortening type ii 38 display an apparent loss of magnetic foliation type iii and 21 develops a magnetic foliation at right angle of the shortening type iv there is no lithological control on magnetic fabric typology despite contrasting ferromagnetic mineralogy between the red sandstones and dark shales thin section observations highlight the good match between the orientation of both the susceptibility ellipsoid and microstructure orientation which enables us to infer the preferred orientations of the petrofabric i e finite strain directions in this way two trends can be recognized in the study area shortening directions trending n110 in the north and trending n80 in the south in addition the spatial distribution of magnetic fabric typology and burial data suggests an atypical pattern of deformation from the foreland to hinterland such a pattern contrasts with previous studies in fold thrust belt settings suggesting that at the matrix scale the deformation even in a pre folding setting is compartmentalized and controlled by the occurrence of deep seated thrusts localized along inherited structures from the analysis of cross sections we can distinguish several domains each of them reflecting distinct states of matrix deformation

experimental simulation of shoreface nourishments under storm events a morphological hydrodynamic and sediment grain size analysis this study focuses on barred beach shoreface nourishments physically simulated in a wave flume the attack of a schematic storm on three different nourishments is analysed the apex and waning storm phases lead respectively to offshore and onshore sediment transports nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore the bar acts as a wave filter and reduces shore erosion lee effect in contrast nourishment on the beach face leads mostly to shore feeding and reconstruction feeder effect with successive nourishments the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates the surface grain size analysis reveals marked variations coarser sediments are sorted on the bar and the upper beach face these locations correspond to large wave dissipation zones during the storm apex

enechelon sigmoidal vein arrays hosted by faults abstract the morphology of enechelon sigmoidal veins generally supports an extension fracture origin for host fractures nevertheless a shear fracture origin has been proposed in some cases mainly on geometric arguments often without morphological support this study describes a system of sigmoidal enechelon quartz veins in a deformed greywacke which displays morphological evidence that the veins are hosted by faults the veins occur in the hinge zone of an upright horizontal antiform and their configuration is consistent with both faulting and vein opening occurring during folding the formation of close spaced vertical dextral faults transformed thick massive greywacke beds into a discontinuous multilayer structure of rock bridges between faults as the length to thickness ratio of the multilayer structure increased the deformation mechanism changed to one of rotation and bending of rock bridges along sinistral shear displacement zones resulting in sigmoidal openings between rock bridges morphological features which indicate that the host fractures are faults include 1 continuity of host fractures well past the tips of the sigmoidal veins and shear displacement of markers by unopened host fractures 2 pinnate extension veins emanating from host fractures particularly near terminations and 3 shear quartz fibres on host fractures basic kinematic analysis shows that shear displacement with opposite shear sense to the array must occur before sigmoidal forms develop as the curvature produces contractional jogs which are incompatible with vein opening recognition of these features may assist in determining the role of shear displacement on host fractures of sigmoidal enechelon vein arrays

implications of slab mineralogy for subduction dynamics phase relations among mantle minerals are perturbed by the thermal environment of subducting slabs both under equilibrium and disequilibrium metastable conditions such perturbations yield anomalies not only in seismic velocities but also in density the buoyancy forces arising from these density anomalies may exert several important effects they contribute to the stress field within the slab in a fashion consistent with observed patterns of seismicity they may affect subduction rates both by inducing time dependent velocity changes under equilibrium conditions and by imposing velocity limits through a thermal feedback loop under disequilibrium conditions they may affect slab morphology possibly inhibiting penetration of slabs into the lower mantle and allowing temporary stagnation of deflected or detached slabs latent heat release from phase transitions under disequilibrium conditions in slabs can yield isobaric superheating which may generate adiabatic shear instabilities capable of triggering deep seismicity 2001 elsevier science b v all rights reserved

strain fabric evolution within and near deformed igneous sheets the sudbury igneous complex canada abstract deformation structures differing in style and orientation within a given terrane are often attributed to distinct tectono metamorphic events however mechanical heterogeneities may locally cause strain perturbations that can have a profound effect on the geometry of such structures here we document highly variable orientations of planar structures metre to kilometre scale folds and shortening directions inferred from brittle fault analysis within the synclinal and layered sudbury igneous complex sic and its huronian host rocks nw se shortening during palaeoproterozoic deformation led to the formation of planar structures in the host rocks that are parallel to the ne sw striking contact of the southern sic during deformation local contact parallel shortening became more important than regional nw se shortening and generated contact orthogonal planar mineral fabrics and folds local contact parallel shortening is attributed to the shape change of the southern sic from a convex outward to a concave inward curvi planar geometry contact parallel shortening accounts for the formation of a previously unidentified kilometre scale buckle fold in the sic and respective axial planar mineral fabrics in huronian host rocks this buckle fold shares similar structural characteristics with known higher order buckle folds of the eastern sic we suggest that non cylindrical buckling and associated mineral fabric development accommodated the shape change of the sic this resulted in mutually perpendicular fabric orientations which are compatible with overall nw se shortening the original shape of the sic seems to have had a profound influence particularly on the geometry of metamorphic foliations our structural analysis supports earlier structural studies advocating that highly discordant planar strain fabrics can be generated by local strain perturbations near igneous sheets under uniform regional shortening

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

numerical modeling of fault controlled fluid flow in the genesis of tin deposits of the malage ore field gejiu mining district china a distinct element finite difference model based on geologic data from the tin polymetallic hydrothermal deposits of malage is constructed to simulate the geologic processes of fault controlled fluid migration during hydrothermal ore genesis the history of hydrothermal ore genesis is strongly affected by the interaction between fault deformation and fluid flow an injected fluid induces fault slip by lowering the effective stress across a fault the subsequent movement on the fault enhances the fault aperture which provides a channelway that both facilitates and focuses fluid flow the variation of fluid injection under certain stress conditions causes cyclic movement on faults this cyclic failure gives rise to pulsating fluid flow along the faults which may be responsible in part for the precipitation zoning of mineral deposits as an important structural condition for ore formation in any fault related mineralized region like malage the linking up of fracture networks not only allows appropriate long distance channels for fluid migration but also provides the appropriate conditions for ore deposition at particular structural sites this study indicates that different fluid flow patterns i e changes in fluid flow rate or velocity with time and space can reflect the variation of structural environment for instance the flow velocity is increased gradually over time on the relatively connected faults such as the northwest southeast trending fault and the western half of the east west trending yuanlao fault in the center of the malage ore field these are the main pathways for the ore forming fluids in the smaller secondary faults the flow velocity fluctuates more rapidly with time and space in some instances causing conditions that are favorable to mineral deposition the main ore deposition sites occur on the smaller secondary faults the detailed variation of fluid and aperture conditions modeled in this complex fault array can be related to the formation and location of mineral deposits both predictively and conceptually the modeling also demonstrates that the fault deformation and fluid flow are sensitive to the principal stress orientation if the orientation of sigma 1 is changed by more than 15 degrees there are very different results for the calculated fault motion pattern hydraulic aperture and fluid flow

deformation partitioning in flat subduction setting case of the andean foreland of western argentina 28 s 33 s 1 the andean foreland of western argentina 28 s 33 s corresponds to back arc deformations associated with the ongoing flat subduction of the nazca plate beneath the south american lithosphere in this paper short and long term tectonic regimes for this andean region are investigated and compared to nuvel 1 and the new gps derived velocity field for the andes mountains from this comparison it appears that 1 the slight convergence obliquity at the plate boundary is accommodated by the subduction zone itself precluding any deformation partitioning at lithospheric scale 2 clockwise rotation of 1 and p axes within the andean foreland of western argentina suggests that plio quaternary deformation partitioning may occur in the upper plate at crustal scale and 3 comparison of seismic rates of shallow deformations determined from moderate to large earthquakes localized between 22 s and 36 s shows that the amount of shortening is about the same 2 4 cm yr 1 between the forearcs of the 30 dipping slab segments and the back arc of the flat segment all together those observations are in close agreement with the idea that interplate coupling in flat subduction settings may play a key role in the present day transfer of plate boundary forces consequently the andean back arc of western argentina might be regarded as an obliquely converging foreland where plio quaternary deformations are partitioned between strike slip and thrust motions that are localized in the east verging thin skinned argentine precordillera and west verging thick skinned pampean ranges respectively

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

seismic evidence against a mantle chemical discontinuity near 660 km depth beneath izu bonin we analyze p wave codas from 12 deep izu bonin earthquakes recorded by hundreds of western united states seismograph stations for evidence of small amplitude phases caused by near source mantle discontinuities for nearly every event the dominant phase in the coda is the result of an s to p conversion from a nearly horizontal discontinuity ranging in depth from 650 to 690 km this is interpreted as a thermally depressed spinel to perovskite and magnesiowustite phase transition if the 660 km seismic discontinuity is also associated with a change in chemistry it would be dynamically depressed by a subducting slab we consistently see that there is no nearly horizontal discontinuity between 700 and 1000 km with shear wave velocity contrast exceeding 1 this observation places constraints on the properties of a postulated chemical discontinuity separating the upper and lower mantles

predicting gold rich epithermal and porphyry systems in the central andes with a continental scale metallogenic gis brgm s gis andes a comprehensive continental scale metallogenic information system for the entire andes cordillera is based on original syntheses structured into thematic layers the aim of developing the gis was to produce an integrated tool to understand ore deposit localization in the andes a fundamental question arising at the outset was whether the tool would be suitable for producing predictive mineral resource maps at the continental scale considering that previous predictive studies focus only on the regional scale the continental scale synthesis implied working with heterogeneous data in terms of distribution quantity quality and in particular accuracy the benefit is the ability to include uncommon parameters linked to the geodynamic evolution of the active margin and significant only at the continental scale in view of the particularities of the gis dataset an expert guided data driven approach was adopted for the multicriteria processing an approach that combined expert knowledge and the use of elementary statistics allowing to provide a link between the tectonic development of the whole andean margin and the spatial and temporal distribution of individual mining districts this study was purposely restricted to assessing the distribution of neogene gold in the central andes between lat 3 and 33 s thus a incorporating well constrained data on the present morphology of the convergent margin and b avoiding ambiguities in the less well constrained older history of the complex evolution of the andean margin five regional parameters were selected and were considered to have a significant influence on the neogene magmatic hydrothermal ore formation at continental scale the five parameters i host rock lithostratigraphy ii lithostratigraphic contacts iii structural discontinuities and iv depth and v dip of the wadati benioff zone modeled from seismic data had assigned favorability scores from 0 to 2 based on their associated metal content with respect to a set of identified neogene gold deposits the next step was to calculate favorability maps for each criterion that were combined to create an overall cumulative favorability map or predictive gold map verifying the predictive map against known gold deposits it was found that the cumulative favorability score of 4 out of 10 maximum located about two thirds of the known gold bearing epithermal and porphyry deposits and 95 of the metal content a cumulative favorability score of 5 reduced these figures to 50 of the deposits and 71 of the metal content and that of 6 relocated 24 of the deposits and 51 of the metal content in addition to verifying the method the predictive map outlines new potentially favorable gold areas and even indicates that some known districts could well host yet undiscovered mineralization

mechanism of slab thickening near 670 km under indonesia we examine a new data set of reliably relocated earthquakes deeper than 400 km under indonesia developed by schoffel and das 1999 the accuracy of this data allows us to demonstrate that the slab thickens shortens and weakens before penetrating below 670 km by shearing along conjugate fault planes on the upper and lower portions of the seismic zone we also show that the earthquakes in the lower portion of the wadati benioff zone width are generally fewer and smaller than those in the central portions with only 8 of the total moment released in the period 1976 1996 being due to earthquakes on the lower side

sediment transport under wave groups relative importance between nonlinear waveshape and nonlinear boundary layer streaming 1 sediment transport under nonlinear waves in a predominately sheet flow condition is investigated using a two phase model specifically we study the relative importance between the nonlinear waveshape and nonlinear boundary layer streaming on cross shore sand transport terms in the governing equations because of the nonlinear boundary layer process are included in this one dimensional vertical 1dv model by simplifying the two dimensional vertical 2dv ensemble averaged two phase equations with the assumption that waves propagate without changing their form the model is first driven by measured time series of near bed flow velocity because of a wave group during the sistex99 large wave flume experiment and validated with the measured sand concentration in the sheet flow layer additional studies are then carried out by including and excluding the nonlinear boundary layer terms it is found that for the grain diameter 0 24 mm and high velocity skewness wave condition considered here nonlinear waveshape e g skewness is the dominant mechanism causing net onshore transport and nonlinear boundary layer streaming effect only causes an additional 36 onshore transport however for conditions of relatively low wave skewness and a stronger offshore directed current nonlinear boundary layer streaming plays a more critical role in determining the net transport numerical experiments further suggest that the nonlinear boundary layer streaming effect becomes increasingly important for finer grain when the numerical model is driven by measured near bed flow velocity in a more realistic surf zone setting model results suggest nonlinear boundary layer processes may nearly double the onshore transport purely because of nonlinear waveshape

polymetallic pb zn cu ag au vein type deposits in brittle ductile transtensional shear zones eastern sierras pampeanas argentina age constraints and significance for the late paleozoic tectonic evolution and metallogenesis abstract this paper discusses new structural kinematic and geochronological data from polymetallic pb zn cu ag au vein type deposits hosted in the metamorphic basement of the southern sierras de cordoba a carboniferous age was established for the hydrothermal event between 329 and 315 ma late mississippian early pennsylvanian by the k ar fine fraction dating method of sericitic alteration related to metallic ore deposition in the las guindas and oro districts the obtained ages postdate the spatially associated devonian magmatism and overlap the a type early carboniferous magmatism defined for the eastern sierras pampeanas the presence of non exhumed granitic bodies at shallow depths possibly related to mineralization is supported by available geophysical and field evidence the strain fabric and 3 d kinematic analyses constitute first kinematic data for the carboniferous basement of the southern sierras pampeanas demonstrating that mineralization was controlled by nnw and ene trending brittle ductile transtensional shear zones that overprint the earlier high strain deformation fabrics of the basement transtensional deformation has accommodated large amounts of strike slip movements and subordinated extensional components the calculated kinematic axes indicate a coherent kinematic pattern of the mineralized systems in the two studied districts with a maximum extension direction oriented nne to ne and maximum shortening direction oriented wnw to nw this deformation regime active during mineralization point to a non compressive setting at the late mississippian early pennsylvanian boundary in line with other regional evidence we propose a distinctive carboniferous deformational phase in the eastern sierras pampeanas dominated by transtension this period would have occurred after the transition with the devonian compressional transpressional orogenic regime

laboratory and numerical study of dambreak generated swash on impermeable slopes new laboratory experiments have produced detailed measurements of hydrodynamics within swash generated by bore collapse on a steep beach the experiments are based on a dambreak rig producing a highly repeatable large scale swash event enabling detailed measurements of depths and velocities at a number of locations across the swash zone experiments were conducted on two beaches differentiated by roughness results are presented for uprush shoreline motion flow depths depth averaged velocity velocity profiles and turbulence intensity estimates of the time and spatially varying bed shear stress are obtained via log law fitting to the velocity profiles and are compared with the shear plate measurements of barnes et al 2009 for similar experimental conditions experimental results are compared with model predictions based on a nlswe model with momentum loss parameterised using the simple quadratic stress law in terms of the depth averaged velocity predicted and measured flow depths and depth averaged velocities agree reasonably well for much of the swash period but agreement is not good at the time of bore arrival and towards the end of the backwash the parameterisation of total momentum loss via the quadratic stress law cannot adequately model the swash bed shear stress at these critical times

discrimination criteria for assigning ore deposits located in the dinaridic palaeozoic triassic formations to variscan or alpidic metallogeny among the ore deposits located in the palaeozoic triassic formations of the dinarides siderite ankerite and barite mineralization hosted by carboniferous and lower permian sediments as well as polimetalic deposits in the mid bosnian schists mts mb coused a long standing dipute concerning there metallogenic affiliations

flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well sorted and graded sands oscillatory flow tunnel measurements of velocities and fluxes for sands in oscillatory sheet flow conditions are presented the experiments involved a range of well sorted and graded sands in two asymmetric flows velocities were measured using an ultrasonic velocity profiler uvp capable of measuring deep within the sheet flow layer velocity profiles are found to be similar for the same flow but different sand beds and display expected features of oscillatory boundary layer flow the near bed velocity leads the main flow velocity by approximately 21 and a small offshore directed current is generated near the bed measures of the boundary layer thickness are in good agreement with those predicted using an equation formulated for the boundary layer thickness over fixed beds velocity data have been combined with concentration data to produce time dependent sand flux profiles covering the sheet flow and suspension regions there are fundamental differences in the transport processes of sands of different size and grading caused by unsteady effects which dominate in the case of fine sand and are largely absent in the case of coarse sand 1 time averaged flux is onshore directed positive in the case of coarse sand and is confined to a region immediately above the bed in contrast time averaged flux in the case of fine sand extends high above the bed is offshore directed negative in the sheet flow layer and becomes onshore directed in the suspension layer 2 net transport in the case of coarse sand is directed onshore as the percentage of fine sand in the bed increases offshore transport becomes increasingly dominant as the percentage of fine sand increases 3 net transport in the suspension layer is onshore while net transport in the sheet flow layer may be onshore or offshore depending on sand size and grading

sigmoidal wall rock fragments application to the origin geometry and kinematics of en echelon vein arrays abstract wall rock fragments found within en echelon vein arrays may provide valuable information on the origin of vein systems shear zone kinematics and vein geometry these fragments are sigmoidal and comprise intact rock between adjacent veins or fragments enclosed within individual veins we present field examples of sigmoidal rock fragments within en echelon veins that grew as opening mode fractures in response to an applied simple shear by virtue of their unique shape and alignment of pre existing fabric we demonstrate how small wall rock fragments may be used as kinematic indicators as well as to predict geometries of individual veins and entire vein arrays such a tool may be especially useful in mining exploration where the precise boundaries of large veins are unknown or in stockworks where the rock is composed primarily of vein material

reverse osmosis contributing to metal zoning in porphyry type deposits a case study abstract representing the main source of copper in the world porphyry copper deposits have been widely studied different models have tried to explain the observed metal zoning but they did not completely explain it a permian cu mo porphyry deposit in the san rafael massif in argentina shows a similar metal zoning pattern to those described elsewhere however some particular features depart from the conventional cooling model based on data from this deposit and on theoretical background we present and discuss reverse osmosis as a complementary process which could have contributed to porphyry metal zoning during the phyllic stage the existence of potential energy gradients and the different relative rejection values for distinct ions make reverse osmosis a natural mineral concentration process at temperatures corresponding to those of porphyry phyllic halo formation and in presence of a phyllic clay membrane cu ag zn and pb would show a strong osmotic differentiation that could have led to the observed metal zoning

non linear shallow water modelling of bore driven swash description of the bottom boundary layer abstract the paper presents a simple approach to estimate the bottom shear stress in the swash zone by coupling the non linear shallow water equations with the momentum integral equation for the bottom boundary layer the approach allows not only the computation of the frictional dissipation term in the equations but also to have an insight into the flow structure in the water column during a swash event the numerical results have been compared with a new set of experiments involving a single dam break generated swash event three different grain sizes ranging from coarse sand to gravel have been tested in the laboratory a sensitivity analysis on the only calibration parameter of the model the bed roughness is presented and its optimal value is chosen the numerically predicted free surface depth averaged velocity and velocity profiles have been compared with the measured ones results are very good in the run up stage where also the bottom shear stress is well modelled in the backwash the frictional energy dissipation is better modelled for the gravel beach than for the coarse sand one results show that the simple model accurately predicts the flow parameters during the swash event also the velocity profiles are reasonably well predicted especially during the run up

dynamics of double subduction numerical modeling abstract double subduction is a geodynamic process in which two plates following each other are synchronously subducted double subductions are known for both modern izu bonin marianas and ryukyu arcs and ancient west himalaya collision zone plate tectonics however our knowledge about this process is limited to conceptual schemes and some restricted analogue experiments in order to fill this gap we performed 2d numerical experiments using a coupled petrological thermomechanical approach based on finite differences and marker in cell techniques combined with thermodynamic database for the mantle we investigated the influence of convergence rate intermediate plate length activation volume of the mantle dislocation creep and age of the lithosphere based on these experiments we conclude that a subduction rates at two zones running in parallel differ and vary in time even when the total convergence rate remains constant supremacy of either subduction zone depends on physical parameters such as i relative rates of the plates ii slab ages and iii length of the middle plate b subduction dynamics of the double subduction system involves several processes unknown in simple subduction systems such as i eduction i e un subduction ii subduction re initiation iii subduction flip triggered by shallow slab breakoff and iv turn over of detached slabs to up side down attitudes c simulated tomographic structures related to slab propagation account for both penetration and non penetration of the 660 km discontinuity non penetration is favored by i low convergence rate ii faster relative movement of the overriding plate iii young age of the subducting slab and iv up side down turn over of detached slab

thickness of the mantle transition zone beneath the south pacific as inferred from analyses of scs reverberated and ps converted waves abstract we study the thickness of the mantle transition zone beneath the south pacific in order to determine temperature anomalies associated with presumed hot plumes in the south pacific superswell the scs reverberation method is used to determine the average thickness between an event station pair and the velocity spectrum stacking vss method is used to determine the thickness near each station the thickness obtained by the scs reverberation method shows that the average thickness beneath the superswell is less than the globally averaged thickness by 6 km while the average thickness beneath the tonga fiji subduction is greater than the global average by 10 km the vss method shows nearly normal thickness beneath stations used in the superswell region we conclude that substantial thinning of the transition zone associated with presumed hot plumes occurs locally beneath the society hot spot as revealed by our previous ss precursor study and is not widespread beneath the whole area of the superswell

whole mantle shear structure beneath the east pacific rise we model broadband seismograms containing triplicated s s 2 and s 3 along with scs to produce a pure path one dimensional model extending from the crust to the core mantle boundary beneath the east pacific rise we simultaneously model all body wave shapes and amplitudes thereby eliminating depth velocity ambiguities the data consist of western north american broadband recordings of east pacific rise epr affiliate transform events that form a continuous record section out to 82 and sample nearly the entire east pacific rise the best fitting synthetics contain attenuation and small changes in lithospheric thickness needed to correct for variation in bounce point ages the 660 km discontinuity is particularly well resolved and requires a steep gradient 4 extending down to 745 km we find no discernible variation in apparent depths of the 405 and 660 km discontinuities over ridge orthogonal distances on the order of 1000 km or 20 ma lithosphere body waveform comparisons indicate that we can resolve discontinuity depths to less than 10 km providing an upper limit to transition zone topography these depth estimates in conjunction with the fan shot nature of the ray paths lower the detection limit from s 2 precursor analysis of the lateral length scale over which short wavelength topographic variation could occur and indicate the sub epr transition zone and upper mantle are remarkably homogeneous the lower mantle beneath the east pacific rise is well modeled by prem with the greatest variation occurring in scs reflecting strong heterogeneity along the core mantle boundary together these observations require that the east pacific rise spreading ridge cannot be actively supplied from the local lower mantle and that tomographically imaged lateral variation beneath the ridge likely reflects lateral smearing of outlying velocity gradients dynamically the transition zone therefore appears vertically decoupled from the overlying east pacific rise spreading system