preferred orientation of plagioclase neutron diffraction and u stage data abstract pole figures of anorthosite mylonite an 65 from san juan bautista california were determined with neutron diffraction using a 23 position sensitive detector this novel technique enables us to deconvolute the complex diffraction spectrum of this triclinic mineral into fifteen separate peaks hkl which are measured simultaneously all pole figures display strong preferred orientation with complicated triclinic distributions from which it appears that 001 poles are concentrated normal to the schistosity plane of the specimen the triclinic mineral is well suited to discuss some fundamental issues of texture representation if crystals are measured individually e g on the u stage positive and negative ends of directions can be unequivocally identified and the whole sphere rather than a hemisphere is necessary to represent the distribution of positive axes this is illustrated for a plagioclase rich amphibolite from orno huvud sweden

spectrally based remote sensing of river bathymetry this paper evaluates the potential for remote mapping of river bathymetry by 1 examining the theoretical basis of a simple ratio based technique for retrieving depth information from passive optical image data 2 performing radiative transfer simulations to quantify the effects of suspended sediment concentration bottom reflectance and water surface state 3 assessing the accuracy of spectrally based depth retrieval under field conditions via ground based reflectance measurements and 4 producing bathymetric maps for a pair of gravel bed rivers from hyperspectral image data consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate the remotely sensed signal must be dominated by bottom reflected radiance we developed a simple algorithm called optimal band ratio analysis obra for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong linear relationships between an image derived quantity x and flow depth d obra of simulated spectra indicated that water column optical properties were accounted for by a shorter wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer wavelength denominator band subject to strong absorption by pure water field spectra suggested that bottom reflectance was fairly homogeneous isolating the effect of depth and that radiance measured above the water surface was primarily reflected from the bottom not the water column obra of these data 28 of which were collected during a period of high turbidity yielded strong x versus d relations r2 from 0 792 to 0 976 demonstrating that accurate depth retrieval is feasible under field conditions moreover application of obra to hyperspectral image data resulted in spatially coherent hydraulically reasonable bathymetric maps though negative depth estimates occurred along channel margins where pixels were mixed this study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry copyright 2009 john wiley sons ltd

effects of lateral confinement in natural and leveed reaches of a gravel bed river snake river wyoming usa this study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques fusing lidar topography with image derived bathymetry over a large spatial extent 58 km of the snake river wy fused dem s from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment develop morphological sediment budgets and infer spatial gradients in bed material transport our study spanned two similar reaches that were subject to different controls on confining margin width natural terraces vs artificial levees channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic theeffects of tributaries also differed between the two reaches generally the natural reach featured greater confining margin widths and was depositional whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced although our remote sensing methods provided topographic data over a large area net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates we therefore focused on along channel spatial differences in bed material transport rather than absolute volumes of sediment to complement indirect estimates of sediment transport derived by morphological sediment budgeting we collected field data on bed mobility through a tracer study surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach we hypothesize that constriction by levees induced an initial phase of incision and bed armoring because levees prevented bank erosion the channel excavated sediment by migrating rapidly across therestricted braidplain and eroding bars and islands

remote measurement of river morphology via fusion of lidar topography and spectrally based bathymetry this study developed and evaluated a hybrid approach to remote measurement of river morphology that combines lidar topography with spectrally based bathymetry comparison of filtered lidar point clouds with surveyed cross sections indicated that subtle features on low relief floodplains were accurately resolved by lidar but that submerged areas could not be detected due to strong absorption of near infrared laser pulses by water the reduced number of returns made the active channel evident in a lidar point density map a second dataset suggested that pulse intensity also could be used to discriminate land from water via a threshold based masking procedure fusion of lidar and optical data required accurate co registration of images to the lidar and we developed an object oriented procedure for achieving this alignment information on flow depths was derived by correlating pixel values with field measurements of depth highly turbid conditions dictated a positive relation between green band radiance and flow depth and contributed to under prediction of pool depths water surface elevations extracted from the lidar along the water s edge were used to produce a continuous water surface that preserved along channel variations in slope subtracting local flow depths from this surface yielded estimates of the bed elevation that were then combined with lidar topography for exposed areas to create a composite representation of the riverine terrain the accuracy of this terrain model was assessed via comparison with detailed field surveys a map of elevation residuals showed that the greatest errors were associated with underestimation of pool depths and failure to capture cross stream differences in water surface elevation nevertheless fusion of lidar and passive optical image data provided an efficient means of characterizing river morphology that would not have been possible if either dataset had been used in isolation copyright 2011 john wiley sons ltd

magma mingling and melt modification between granitic pipes and host diorite guernsey channel islands within the northern igneous complex of guernsey cylindrical pipe intrusions 20 40 cm in diameter developed by buoyant emplacement of granite magma into overlying denser diorite magma the high viscosity of the partially crystallized magmas and lack of mechanical stirring inhibited physical mixing and mesoscopically sharp well defined interfaces developed the granitic pipes are surrounded by aureoles up to a metre in diameter which exhibit changes in bulk chemical composition and partial mineralogical re equilibration these formed in response to the modification of interstitial melt in the partially crystallized host resulting from residual melt migration and or melt interdiffusion across the pipe host interface such processes between partially crystallized magmas may in part provide an explanation for textural mineralogical and chemical compositional features commonly exhibited by mafic enclaves within granites

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

the copper gold and gold deposits of the neoproterozoic mara rosa magmatic arc central brazil mineral exploration in the neoproterozoic goias magmatic arc central brazil dates back to the beginning of the 1970s the goias magmatic arc extends for more than 1000 km in the western and northern parts of goias into tocantins and disappears under the phanerozoic parnaiba basin two main areas of neoproterozoic juvenile crust the arenopolis and the mara rosa arcs are identified they lie in the southern and northern sectors of the goias arc respectively and are relatively well studied the goias magmatic arc dominantly comprises tonalitic dioritic orthogneisses and narrow nne striking volcano sedimentary belts recent u pb zircon data indicate crystallization of the tonalite protoliths in two main episodes the older between ca 890 and 790 ma and the younger at 670 600 ma nd isotopic data indicate the very primitive nature of the original magmas with tdm model ages mostly within the interval between 0 9 and 1 0 ga and end t values between 3 0 and 4 6 in the chapada mara rosa area the supracrustal rocks form three individual nne belts known as the eastern central and western belts separated from each other by metatonalites metadiorites gold and cu au deposits of the mara rosa area occur in four main associations i au ag ba e g zacarias which are interpreted as stratiform disseminated volcanogenic deposits ii cu au e g chapada which has been interpreted either as volcanogenic or as a porphyry type deposit iii au only deposits e g posse interpreted as an epigenetic disseminated deposit controlled by a mesozonal shear zone and iv au cu bi e g the mundinho occurrence which are considered as vein type deposits controlled by magnetite rich diorites the gold and cu au deposits located within the goias magmatic arc can be spatially and temporally related to the magmatic evolution of a collisional belt or in other words to an orogenic gold deposit model these models are based on the continuous evolution of collisional plates which can be subdivided into four stages with distinct magmatic characteristics i subduction stage ii syntectonic collisional magmatism stage iii post tectonic collisional magmatism stage and iv post orogenic extension stage

the mara rosa arch in the tocantins province further evidence for neoproterozoic crustal accretion in central brazil the mara rosa volcano sedimentary sequence consists of several nne trending belts of metavolcanic metabasalts to metarhyolites and metasedimentary rocks micaschists quartzites cherts exposed over large areas of the tocantins province a neoproterozoic brasiliano orogenic region in the central part of brazil the supracrustal belts are separated by terrains dominated by metatonalites and metadiorites and intruded by several post orogenic granitic and dioritic bodies these volcano sedimentary and associated metaplutonic rock associations have been previously interpreted as a typical granite greenstone terrain of the archaean basement in this paper we present geochronological and isotopic data for rocks of the metavolcanic metaplutonic rock association samples of a felsic metavolcanic rock from the posse gold mine and a metatonalite yielded u pb zircon ages of 862 8 ma and 856 7 13 ma respectively these are interpreted as crystallization ages of the igneous protoliths titanites from the same metavolcanic rock sample yielded a concordant recrystallization age of 632 4 ma sm nd isotopes for these rocks indicate primitive compositions with nd t of 4 6 and 3 7 and tdm model ages of 1 0 ga a syn tectonic dioritic intrusion has an u pb crystallization age of 630 6 ma and nd t of 1 9 and tdm of 1 0 ga additional sm nd analyses on metasedimentary rocks and post orogenic granites of the mara rosa region yield tdm ages between 1 2 and 1 0 ga the isotopic data combined with preliminary trace element results suggest that the protoliths of the metavolcanic and metaplutonic rocks investigated were formed in an island arc system off the coast of the sao francisco congo continent at around 860 ma recrystallization and deformational ages of 630 ma may represent the timing of final ocean closure and continental collision the rock associations structural pattern geochronological and isotopic characteristics of the rocks from the mara rosa region are very similar to those of neoproterozoic arc terrains exposed 300 km to the southwest in the arenspolis area proving the regional importance of the neoproterozoic crustal accretion event in the central part of brazil

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

an introduction to remobilization information from ore body geometry and experimental considerations abstract mobilization involves the translocation and concentration of originally dispersed metallic constituents remobilization is the translocation resulting in modified concentration and distribution of pre existing metalliferous concentrations mobilization and remobilization proceed by chemical liquid state mechanical solid state and mixed processes the paradox of remobilization is that the more complete the process the more difficult becomes substantiation regional metamorphic remobilization is commonly invoked to explain the morphology of supposedly once stratiform massive sulphides and their feeder and alteration systems analysis of the principal dimensions of stratiform massive sulphides in non metamorphic and regionally metamorphosed deposits shows that whereas comparative morphology may be a guide to remobilization it does not constitute proof similarly feeder and alteration morphology suggests that geometric analysis may be of value in establishing mechanical remobilization but the more complex alteration distributions which exist could well lead to misinterpretation in highly deformed terranes ore composition internal structure and zonation influence the ore s capacity to be remobilized mechanical remobilization requires rheological divergence between sulphides and their host rocks experimental deformation of dry sulphides shows that most common sulphides pass through the brittle ductile transition before entering the field of regional metamorphism but that the strength order of sulphides silicates and carbonates remains dynamic until all are undergoing steady state flow within this context experimental strength orders support galena weakest experimental considerations indicate that during diagenesis and early prograde metamorphism the brittle ductile transition will result in widely distributed micro and mesoscale mechanical remobilization nevertheless there is usually insufficient gross behavioural contrast to engender discordant macroscale remobilization possible exceptions particularly in relation to thrusting are outlined but we conclude that macroscale mechanical remobilization during the brittle ductile transition is an uncommon occurrence experimental data were also examined relative to subsequent prograde to peak metamorphism and strength contrasts during decaying and retrogressive metamorphism because the largest strength difference between sulphides and the host sequence is in the lower part of the 350 650 c metamorphic range we contend that macroscale mechanical remobilization is more probable during prograde metamorphism in the 350 500 c interval we similarly believe that macroscale mechanical remobilization is more likely during deformation accompanying retrogressive cooling in the range 500 350 c and we note that it may also result from deformation exploiting the brittle ductile contrasts between silicate and sulphide rocks during the water deficient non retrogressive metamorphic decay cycle chemical mobilization and remobilization require the dissolution of base metals by metamorphic fluids the compositions of hydrothermal low grade metamorphic fluids and their precipitates in active geothermal systems show that the fluids can dissolve transport and form concentrations of base and precious metals similarly fluid inclusion compositions from low to medium grade metamorphic rocks show that such fluids can dissolve a few ppm of base metals in both cases low salinities and low dissolved base metal contents raise doubts over whether such metamorphic fluids can form ore grade base metal concentrations we submit that they can metamorphogenesis is favoured by high initial base metal concentrations preferential dissolution of sulphides over silicates and fluid dominated metamorphism as found in a multiple pass fluid system preferential dissolution of sulphides and the need for high water rock ratios are supported by theoretical considerations experimental work on mafic felsic and sedimentary source rocks and field based studies in the context of mobilization the work strongly implies that prograde metamorphic devolatilization and a mobile fluid phase have substantial ore forming capability retrograde revolatilization does not remobilization is more complex although favoured by high initial metal concentrations dissolution is inhibited by the low permeability of homogeneous low silicate massive sulphides and the consequent peripheral fluid channeling it is conversely enhanced by fine grainsize in discordant fluid focussing retro grade shear zones in all cases for remobilization to form a new ore body both fluid flow and the precipitation process must be focussed and efficient

volume effect of a gabbro amphibolite transition abstract specific gravities of a series of gabbroic rocks and their metamorphic equivalents are compared with their major element compositions using the gresens equation care was taken to assure a close parent daughter rock match by careful field control and by applying composition volume screening the study indicates that correct matching of protoliths with their metamorphic derivatives is the limiting factor deciding the accuracy of volume effect determinations the metamorphic transition is consistent with a constant sio2 tio2 al2o3 feo mgo model a small but well defined volume increase of 2 is indicated

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

plagioclase microfabrics in a ductile shear zone from the jotun nappe norway abstract gabbroic and anorthositic rocks from the jotun nappe are transected by small ductile shear zones in which a high grade paragenesis and a new foliation are formed most plagioclase grains show evidence of plastic deformation and have recrystallized by subgrain rotation and bulge processes to fine grained mylonite during these processes a plagioclase grain shape fabric was destroyed and with increasing strain a pre existing plagioclase crystal fabric was successively modified enhanced and finally obliterated this could be evidence of superplastic flow inverse pole figure analysis of the typical plagioclase crystal fabric in the shear zone indicates that 021 a could be an operative slip system and planes close to 132 could be possible slip planes

earth s copper resources estimated from tectonic diffusion of porphyry copper deposits improved estimates of global mineral endowments are relevant to issues ranging from strategic planning to global geochemical cycling we have used a time space model for the tectonic migration of porphyry copper deposits vertically through the crust to calculate earth s endowment of copper in mineral deposits the model relies only on knowledge of numbers and ages of porphyry copper deposits earth s most widespread and important source of copper in order to estimate numbers of eroded and preserved deposits in the crust model results indicate that 125 895 porphyry copper deposits were formed during phanerozoic time that only 47 789 of these remain at various crustal depths and that these contain 1 7 1011 tonnes t of copper assuming that other types of copper deposits behave similarly in the crust and have abundances proportional to their current global production yields an estimate of 3 1011 t for total global copper resources at all levels in earth s crust thus 0 25 of the copper in the crust has been concentrated into deposits through phanerozoic time and about two thirds of this has been recycled by uplift and erosion the amount of copper in deposits above 3 3 km a likely limit of future mining could supply current world mine production for 5500 yr thus quantifying the highly unusual and nonrenewable nature of mineral deposits

the role of exhumation in the temporal distribution of ore deposits we show here that the temporal age frequency distribution of ore deposits is controlled largely by exhumation the combination of burial uplift and erosion that exposes subsurface rocks and ore deposits exhumation rates calculated from modal ages and emplacement depths for epithermal porphyry copper and orogenic gold deposits of phanerozoic age are 167 158 and 63 m m y respectively these rates agree with rates estimated for continent scale terranes by numerous independent methods thus the scarcity of precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation archean and pale oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their phanerozoic counterparts suggesting that the precambrian deposits formed in greater numbers recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large scale changes in earth history

serpentinization of cumulate ultramafic rocks from the north arm mountain massif of the bay of islands ophiolite abstract partially serpentinized dunites and wehrlites comprise the bulk of the cumulate ultramafic unit at the north arm mountain massif of the bay of islands ophiolite complex newfoundland in a suite of 59 dunites and werhlites from the base of the unit the serpentinized portions consist of lizardite chrysotile brucite accessory magnetite the ratio of lizardite chrysotile to brucite 8 2 weight percent petrographic observations show that most serpentinization occurred at the expense of olivine only limited amounts of clinopyroxene were serpentized an estimated volume increase of 32 accompanied serpentinization of the peridotites reconstructions of the primary modal proportions of wehrlites made taking this volume increase into account contain an average of 6 more clinopyroxene and 6 less olivine than do modal reconstructions that ignore the volume increase mass balance calculations provide no clear evidence for appreciable metasomatism of al2o3 cao feo mgo or sio2 during serpentinization the presence of brucite the evidence that most serpentinization occurred at the expense of olivine and the lack of appreciable metasomatism suggest that the primary reaction that controlled serpentinization of the peridotites is 2mg 2 sio 2 3h 2 o mg 3 si 2 o 5 oh 4 mg oh 2 olivine added serpentine brucite

st john s island red sea a new geophysical model and its implications for the emplacement of ultramafic rocks in fracture zones and at continental margins abstract new gravity and magnetic data from the northern red sea reveal the extent of the large gravity anomaly 164 mgal and the presence of significant magnetic anomalies over st john s island spectral transformation and three dimensional potential field modelling delineate the surface configuration and vertical extent of the causative body and the enormous density contrast required 1 2 g cm 3 suggests that it is composed of unserpentinised peridotite density 3 4 g cm 3 to a depth of at least 8 km st john s island is uniquely located not only at a passive continental margin but also within a fracture zone at the transition from plate separation by seafloor spreading to extension by lithospheric attenuation this precludes several suggested mechanisms for the emplacement of ultramafic bodies in fracture zones thermal contraction serpentinite diapirism and changes in the poles of rotation do not seem possible mechanisms in this tectonic environment and the emplacement is most probably related to the spreading readjustment necessary to create a continent to continent fracture zone a post mesozoic age of emplacement associated with the onset of continental rifting and the rejuvenation of a pre existing continental fracture seems most probable

modification of a palaeoproterozoic porphyry like system integration of structural geochemical petrographic and fluid inclusion data from the aitik cu au ag deposit northern sweden the aitik cu au ag deposit in the gallivare area in northern sweden is sweden s largest sulphide mine with an annual production of 35 mt of ore and the biggest open pit operation in northern europ

modelling channel incision and alpine hillslope development using laser altimetry data this paper presents a new approach to simulate drainage basin evolution and demonstrates that high resolution elevation data can be used as useful tool for a dynamic simulation of alpine landscape development in which channel incision is incorporated in high spatial detail a vector channel incision model cim uses 1 m high resolution laser altimetry data for simulation of longitudinal profile development the cim is combined with a grid cell based hillslope erosion model to incorporate the hillslope response to incising bedrock rivers in a simulation of landscape evolution the combined simulation model is applied to a geologically diverse alpine catchment to simulate landscape development from reconstructed late glacial conditions towards the current situation the model is time efficient and realistically adapts to contrasting geological substrata while spatially and temporally variable incision values knick point recession and variable hillslope development result in a realistic simulation of post glacial landscape evolution high resolution elevation data in combination with dynamic geomorphological simulation models facilitate research of complex and difficult to access alpine terrain at greater detail than before it potentially paves the way for more efficient landscape evolution research and can contribute to increasing the understanding of the functioning of geo ecological systems

rapid late pleistocene incision of atlantic passive margin river gorges the direct and secondary effects of rapidly changing climate caused large rivers draining the atlantic passive margin to incise quickly into bedrock beginning about 35 000 years ago measured in samples from bedrock fluvial terraces 10 beryllium shows that both the susquehanna and potomac rivers incised 10 to 20 meter deep gorges along steep convex lower reaches during the last glacial cycle this short lived pulse of unusually rapid down cutting ended by 13 000 to 14 000 years ago the timing and rate of downcutting are similar on the glaciated susquehanna and unglaciated potomac rivers indicating that regional changes not simply glacial meltwater initiated incision

microstructures in feldspars from a major crustal thrust zone the grenville front ontario canada abstract samples collected across the nw grenville front in ontario canada have been used to document the change in feldspar microstructures produced during shearing under metamorphic conditions that range from upper amphibolite to lower greenschist grade the differential displacement across this 5 km thick section of the grenville front tectonic zone is at least 10 km at upper to mid amphibolite conditions both plagioclase and potassium feldspars behave plastically grainsize reduction occurs through grain boundary migration and or subgrain rotation and produces a core and mantle structure at middle to lower amphibolite grade grain size reduction is accomplished through grain boundary migration at lower amphibolite to upper greenschist grade grain size reduction occurs by the nucleation and growth of new grains with a different composition the abundance of intracrystalline deformation at this grade is inversely proportional to the amount of fine grained matrix in ultramylonite with a high matrix to porphyroclast ratio few intracrystalline strain features occur other than ubiquitous undulatory extinction myrmekite is well developed on the high stress boundaries in k feldspar at upper to mid greenshist conditions feldspars deform mainly by slip on synthetic shear fractures deformation twins undulatory extinction deformation bands and kink bands occur in plagioclase and perthite flames and myrmekite occur principally on high stress boundaries in k feldspar grain size reduction in feldspar is accomplished through cataclasis at middle to lower greenschist facies deformation in feldspars is dominated by antithetic fractures the transition from the dominance of synthetic to antithetic fractures is gradational below lower greenschist grade rocks deform by pervasive cataclasis of all minerals

relative elemental mobility during hydrothermal alteration of a basic sill isle of skye n w scotland in sconser quarry isle of skye a thin tertiary basic sill is cut by vertical veins which formed fluid conduits in a major meteoric hydrothermal system in order to study the relative mobility of different elements during hydrothermal metamorphism sill material adjacent to a large 6 mm wide vein was cut into slices and subjected to geochemical and isotopic analysis

structural controls on gold mineralisation and the nature of related fluids of the paiol gold deposit almas greenstone belt brazil chemical analyses suggest that the metavolcanic rocks of the almas greenstone belt agb tocantins state brazil have a continental affinity possibly related to a continental rift environment they were metamorphosed to amphibolite facies during a regional tectono metamorphic event dn retrogressed to greenschist facies assemblages and then hydrothermally altered within dextral strike slip shear zones dn 1 fracture sets related to dn 2 intersect sn 1 the paiol gold mine is one of several mineralised zones within metabasic and meta intermediate rocks of the agb it exploits shoots of sulphide au quartz mineralisation that occupy dilational zones approximately perpendicular to an elongation lineation ln 1 within mylonitic foliation sn 1 sn 1 s within the s c fabric the dilational zones probably formed due to dextral displacement on sinistrally en echelon c surfaces minor amounts of gold may have been introduced or remobilised during dn 2 coexisting primary and pseudosecondary fluid inclusions in mineralised quartz veins from ore shoots comprise a high salinity three phase type type ii and a lower salinity two phase type type i homogenisation temperatures for type ii inclusions range from 200 to 410 c and type i from 90 to 320 c the inclusions and their temperature ranges are believed to reflect heat exchange and some mixing between the two fluid types under relatively constant ambient temperatures but variable though broadly declining fluid temperatures this took place late in dn 1 in conjunction with greenschist facies retrogression and localised hydrothermally induced metasomatism

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

sense of shear in high temperature movement zones from the fabric asymmetry of plagioclase feldspars abstract a new method for determining the sense of shear in plagioclase bearing tectonites from the 010 orientation of plagioclase feldspar is presented the method is based on the asymmetry of the 010 plane with respect to the structural frame foliation and lineation and the dominant activity of the 010 slip plane in the high temperature plasticity of plagioclase feldspar using examples from the zabargad gneisses red sea the method is applied to plagioclases of an25 an45 and compared with other methods of shear sense determination quartz c axis fabrics and microstructural criteria

step by step error assessment in braided river sediment budget using airborne lidar data abstract sequential airborne lidar surveys were used to reconstruct the sediment budget of a 7 km long braided river channel in southeastern france following a 14 year return period flood and to improve its accuracy step by step data processing involved i surface matching of the sequential point clouds ii spatially distributed propagation of uncertainty based on surface conditions of the channel and iii water depth subtraction from the digital elevation models based on water depths measured in the field the respective influence of each processing step on sediment budget computation was systematically documented this showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget although dem of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget this step is crucial for the production of a comprehensive map of channel deformations a large independent data set of rtk gps checkpoints was used to control the quality of the lidar altimetry the results showed that high density 7 9 points m 2 airborne lidar surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel with a 95 confidence interval level of detection between 19 and 30 cm change detection from lidar data revealed that 54 of the pre flood active channel was reworked by the flood the braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions

chemical exchange in migmatites during cooling abstract the chemistry of the leucosome components in limited size migmatitic associations is generally believed to reflect the composition of the partial melt that could have been extracted to yield an anatectic magma several well documented studies of migmatites indicate that the distributions of some trace elements in leucosome melanosome pairs are inconsistent with equilibrium partial melting but are rather in agreement with chemical reequilibration during cooling in migmatites the liquid fraction does not leave the system this may induce an alteration of the chemical composition of the whole migmatite system by extensive chemical exchange between the liquid and the solid residue during cooling if this is the case the leucosome and melanosome components are not representative of the chemical composition of the liquid and solid residue respectively at the time of partial melting a rough evaluation of the residences time of the melt fractions in cooling in situ migmatitic bodies yields minimum estimates of 1 to 10 ma for such time spans the characteristics distances of diffusion distances of diffusion induced chemical transfer exceed the sizes of individual mineral grains which is consistent with a re equilibration process the release of latent heat of crystallization in cooling migmatitic systems and the presence of an interstitial liquid phase are critical in determining the extent and scale of chemical exchange the mechanism involves 1 reducing the cooling rate and 2 promoting the efficiency of chemical diffusion through the liquid phase thus some doubt is cast on the ability of small scale migmatitic systems to provide relevant information about chemical mass balance during partial crustal melting

strontium isotopic geochemistry of pan african brasiliano rocks chapada copper deposit goias brazil whole rock and mineral rb sr isochrons from the upper amphibolite grade metamorphic host rocks of the chapada copper deposit in goias brazil yield an age of 561 9 ma with a87sr 86sr initial i of 0 70414 0 00005 for the crystallization of pre metamorphic volcanic and igneous rocks and 532 1 ma for their metamorphism during the pan african brasiliano orogeny 700 450 ma a porphyritic diorite stock which intruded the host schists yields a mineral isochron age of 534 16 ma i 0 70415 0 00004 the low i values determined from these isochrons suggest that the host schists at chapada were derived from upper mantle or lower crust material and are characteristic of magmatic products associated with island arcs the early cambrian age of the host rocks at chapada contradicts the previously assigned mid proterozoic age and suggests that pan african brasiliano magmatic activity may have been more extensive in central brazil than previously thought

the gneiss of zabargad island deep crust of a rift abstract the gneisses of the zabargad island are in contact with lherzolites that were emplaced by mantle diapirism during the early rifting of the red sea the gneisses and the peridotites at their contact develop similar structures kinematics and common granulite metamorphism away from the contact the shear strain and associated recrystallizations decrease rapidly thus the zabargad gneisses are metamorphosed and deformed by the mantle diapiric intrusion this is confirmed by preliminary isotopic dates the gneisses have a tripartite polygenic composition of felsic granulites metagabbros and amphibolites the metagabbros and amphibolites are metamorphosed only by the mantle diapir intrusion which also induces a partial anatexis of the gneisses the felsic granulites record a proceeding high p granulite facies metamorphism they are assumed to represent screens of ancient continental crust

the santa rita gold deposit in the proterozoic paranoa group goias brazil an example of fluid mixing during ore deposition abstract the santa rita gold deposit central goias brazil is hosted by middle to upper proterozoic carbonate pelite sequences of the paranoa group that have been metamorphosed in the greenschist facies the ore is contained in pyrite bearing quartz carbonate veins the mineralization is structurally controlled by wnw ese high angle faults and fractures resulting from the reactivation of older ne sw lineaments pyrite is the sole sulphide and it shows growth zones enriched in co ni and as up to 4 wt hydrothermal alteration zones are enriched in co ni and as and are characterized by diffuse albitization carbonatization silicification and pyritization a fluid inclusion study on quartz from pyrite bearing quartz carbonate veins led to the identification of two fluids 1 a highly saline co 2 n 2 rich aqueous fluid with halite and sylvite daughter minerals and 2 a co 2 n 2 rich aqueous fluid with moderate salinity the two fluid types occur in the same quartz domain and display great variation in the degree of filling and notable dispersion of the microthermometric data on heating all the inclusions decrepitate between 200 and 300 c raman spectrometry detected high concentrations of n 2 in the gas phase with a co 2 n 2 molar ratio between 1 and 19 and a small proportion of ch 4 up to 2 mole the simultaneous entrapment of compositionally variable fluids in the system h 2 o co 2 n 2 nacl kcl allow us to propose a mechanism of heterogeneous trapping the entrapment may result from the mixing of a high salinity fluid h 2 o nacl kcl system with a carbonic fluid h 2 o co 2 n 2 system produced by the devolatilization process of carbonate and phyllitic host rocks considering the absence of spatially and temporally related igneous activity and the low p t regional metamorphism in the paranoa group the brines are inferred to result from leaching of evaporites occurring in the lower part of the paranoa lithostratigraphic column gold was probably initially transported as an aucl 2 complex t 300 c low ph moderate o 2 pyrite field stability as temperature decreased below 290 c the switch over process would lead to the predominance of au hs 2 in the fluid pyrite precipitated in this temperature interval the oscillatory zoning of the as co ni bearing pyrites indicates episodic fluctuation of the fluid composition such changes in fluid composition are favoured by a mechanism of fluid mixing by intermittent supplies in the hydrothermal system the proposed mechanism of heterogeneous trapping of two separate fluids in the system h 2 o co 2 n 2 nacl kcl and the resulting changes in the physicochemical conditions caused by the fluid mixing appears as a conspicuous process for the santa rita hydrothermal fluid evolution a model based on the existence of a proterozoic geothermal system involving the regional thermal gradient is proposed

major and minor element mobilization with implications for nicufe sulphide remobilization during retrograde metasomatism at the vammala mine southwest finland abstract granitic melt derived from migmatitic host rocks intruded a d 3 related fracture system in a 1 89 ga ni cu fe sulphide bearing peridotite sheet near vammala southwest finland zones of wall rock alteration mainly comprising amphibole phlogopite chlorite developed in the peridotite adjacent to the leucocratic dykes the minerals in the alteration zones and in the gneissic host rocks together with the production and intrusion of granitic melt are consistent with metamorphic conditions of at least 600 c and 4 5 kbar later hydration under condtions of lower temperature and pressure resulted in partial serpentinization of the peridotite and dykes this later transition precluded direct investigation of the earlier transition that developed the medium to high grade alteration zones in the peridotite at the interface with the leucocratic dykes because serpentinization was largely accommodated by volume increase rather than mass loss of mgo and sio 2 the relative concentrations of most components in the serpentinized peridotite should mirror those in the peridotite based on this contention two methods are used to document the composition volume behaviour of the transition from now serpentinized peridotite to alteration zones apparent transition and hence infer the mass balance trends of the igneous peridotite to alteration zone transition real transition the methods collectively suggest that in the alteration assemblages k 2 o rb 2 o p 2 o 5 tio 2 and al 2 o 3 form a group of relatively enriched components and that al 2 o 3 was particularly mobile an estimated volume increase of 10 10 accompanied serpentinization and a calculated volume decrease of 10 15 accompanied the apparent transition thus a volume increase of real transition for best fit volume factors gresens equation demonstrates that the apparent transition involved mass gains in sio 2 al 2 o 3 k 2 o p 2 o 5 and tio 2 and mass losses in feo mgo cao ni s and volatiles loss on ignition loi these amounting to net losses of 32 5 kg of volatiles and 10 8 kg of other components per 1000 kg of serpentinized peridotite the real transition involved similar relative gains and losses except for sio 2 gain slightly less mgo loss slightly more and loi loss negligible it respectively records inward transfer of components from a feldspar rich source to the peridotite and outward transfer to that source this is consistent with metasomatic exchange between the peridotite and the probably supra solidus granitic intrusions during the real exchange ni cu fe sulphides were retained and redistributed internally remobilized in the outer alteration zones but transferred into the dyke from the zone abutting it externally remobilized the same genetic interpretations probably apply to similar dyke and alteration systems in other ni cu fe sulphide deposits hosted in ultramafic rocks in southwest finland

an episode of rapid bedrock channel incision during the last glacial cycle measured with 10be we use 10 be to infer when how fast and why the susquehanna river incised through bedrock along the u s atlantic seaboard one of the world s most prominent and ancient passive margins although the rate at which large rivers incise rock is a fundamental control on the development of landscapes relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins exposure ages of fluvially carved bedrock strath terraces preserved along the lower susquehanna river demonstrate that even along a passive margin large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions such as the himalayas over eighty samples collected along and between three prominent levels of strath terraces within holtwood gorge indicate that the susquehanna river incised more than 10 meters into the appalachian piedmont during the last glacial cycle beginning 36 ka incision rates increased dramatically and remained elevated until 14 ka the northern half of the susquehanna basin was glaciated during the late wisconsinan however similar rates and timing of incision occurred in the unglaciated potomac river basin immedi ately to the south the concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision instead it appears that changing climatic conditions during the late pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion thus enabling a short lived episode of rapid incision into rock although this study has constrained the timing and rate of bedrock incision along the largest river draining the atlantic passive margin the dates alone cannot explain fully why or by what processes this incision occurred however cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate these results and the methods we employ provide valuable insights into the nature of bedrock channel incision not only along the susquehanna river and passive margins but also across a wide range of settings around the globe because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes comprehending when where and why rivers incise has important implications for the evolution of land scapes

identification of the scales of differential element mobility in a ductile fault zone two fundamentally different scales of element mobility have been identified in the upper amphibolite facies hunts brook fault zone of south central connecticut usa field relations mineral chemistry and 80 bulk rock analyses provide overwhelming evidence that the blastomylonitic schists and gneisses of the fault zone were derived from the enclosing granodioritic rope ferry orthogneiss two sample mass balance calculations between the rope ferry gneiss and fault rocks strongly suggest that the rope ferry gneiss was segregated into biotite rich schists and quartz plagioclase rich gneisses through the centimetre scale transfer of si al ca na ba and zr from schists to gneisses three and four sample mass balance calculations provide convincing evidence that al ca na and ba were lost and si and k gained by the entire fault zone both scales of metasomatism have been identified at two localities separated by 20 km implying that the metasomatic processes were pervasive throughout the fault zone from the mass balance calculations an apparent disparity in k mobility arises k appears to be gained by the entire fault zone but is immobile during the centimetre scale segregation this is because mass balance calculations can only detect differential element mobility differential element mobility requires that the mechanism of metasomatism produces chemical potential gradients therefore the identification of differentially mobile elements provides insight into the mechanisms of metasomatism the immobility of k during segregation of schists and gneisses implies that the segregation was not achieved through the extraction of partial melt however the element mobility is reconcilable with deformation driven metamorphic differentiation the gains of si and k and losses of ca na al and ba for the entire fault zone are also inconsistent with the intrusion or extraction of partial melt but may reflect the infiltration of a metasomatizing aqueous fluid

origin and geochemistry of the chapada cu au deposit goias brazil a metamorphosed wall rock porphyry copper deposit chapada is a large 134 x 10 6 metric tons low grade 0 44 cu 0 35 g metric tons au disseminated chalcopyrite pyrite deposit within a geologically complex pan african mobile belt in central goias state brazil mineralization is hosted largely by subhorizontal biotite schist with lesser amphibolite muscovite schist and feldspathic quartzite a foliated diorite is separated from the deposit by a shallow diping 40 m thick mylonite zone discontinuous lenses of mica amphibole schists within the deposit are considered hydrothermally altered equivalents of this diorite which have intruded geochemically related wall rocks such as the locally porphyritic amphibolite seen in the deposit previous assignment of a mid proterozoic age to chapada must be revised in view of our rb sr whole rock isochron which yields a pan african age of 561 or 9 m y for the host schists rare earth element patterns of chapada rocks have steep negative slopes with no eu anomalies petrochemical data and an 87 sr 86 sr initial i value of 0 70414 or 0 00005 indicate chapada host schists and diorite are similar to peraluminous calc alkaline andesites of magmatic arc affiliation mineralization occurred prior to upper amphibolite grade regional metamorphism at 532 or 1 m y as indicated by an rb sr mineral isochron as well as by sulfides paralleling foliation sulfide inclusions in metamorphic minerals and the presence of gahnite and zincian staurolite estimated conditions of peak metamorphism were 650 degrees or 20 degrees c 7 5 or 1 kb log f sub o 2 13 to 14 log f sub s 2 0 5 to 0 5 and a sub h 2 o 0 85 mineral zonations in and around chapada include a central magnetite rich zone a pyritic shell and peripheral pyrrhotite and sphene these mineral zonations and x fe of biotites reflect a gross zonation in oxygen and sulfur fugacities from high within the deposit to relatively low in peripheral rocks pyrite and chalcopyrite have delta 34 s values of 0 4 to 0 6 per mil k 2 o is enriched and cao and na 2 o are depleted in the host schists relative to the unaltered diorite within the deposit several major element abundances describe a symmetrical pattern about the center of the deposit the tonnage grade and ore mineralogy of the chapada deposit are comparable to those reported from porphyry copper deposits of island arc settings much of the gangue mineralogy at chapada is also typical of porphyry deposits and has survived metamorphism whereas the more aluminous original gangue minerals are now represented by such metamorphic minerals as kyanite and staurolite these similarities combined with the textural zoning and geochemical characteristics of the host rocks suggest that chapada is a metamorphosed porphyry copper deposit which hosts mineralization in both wall rocks and intrusive rocks

the chapada cu au deposit mara rosa magmatic arc central brazil constraints on the metallogenesis of a neoproterozoic large porphyry type deposit abstract the large chapada cu au deposit is situated in goias magmatic arc central brazil which is part of an accretionary orogen with tectonic evolution between ca 900 and 600 ma during the brasiliano orogeny with a current reserve proven and probable of 420 94 mt cu 0 29 and 479 84 mt au 0 25 g t or 3 83 moz au the chapada cu au deposit is an important example of a large tonnage low grade porphyry copper gold deposit of precambrian age in which the mineralization is disseminated and hosted mainly by biotite rich schists and gneisses in this work we propose a two stage genetic model for the chapada deposit that includes an early porphyry type cu au event overprinted by a shear zone hosted cu au event the first mineralization event represents a rare case of metamorphosed neoproterozoic porphyry type deposit which preserves distinct hydrothermal alteration mineralization zoning developed at the interface between equigranular 867 8 ma to porphyritic 884 15 ma medium to high kcalc alkaline dioritic rocks and mafic to intermediate metavolcanic and metapyroclastic rocks the e nd values are positive from 2 17 to 5 39 thus indicating the juvenile nature of the original rocks for both metavolcano sedimentary and plutonic rocks in this context kyanite rich rocks are interpreted as products of metamorphosed argillic hydrothermal alteration halo and occur as linear alignments oriented parallel to the mara rosa magmatic arc trend the potassic hydrothermal alteration halo which includes the main host rocks of the chapada deposit is characterized by biotite schist muscovite biotite schist amphibole biotite schist and biotite gneiss the ore is represented predominantly by platy deformed chalcopyrite and pyrite disseminations along foliation plans or axial surfaces of folds and to a lesser extent by small massive concentrations in fold hinges the ore shows a systematic oxide sulfide zonation including the peripheral pyritic shell and the central magnetite rich zone in general the geological context of the deposit lacks preserved stocks dykes and breccias while deformed a type quartz veins veinlets are abundant the second mineralization event represents an epigenetic shear zone hosted cu au mineralization associated with d n 1 and occurred between 630 and 580 ma during the late orogenic to post orogenic stage of the mara rosa magmatic arc which may be interpreted as i a shear zone hosted cu au remobilization ii an orogenic cu au mineralization or iii an intrusion related cu au mineralization in the latter case the mineralization could be related to the ilmenite bearing younger metadiorite 634 8 6 8 ma with disseminations of chalcopyrite pyrite and pyrrhotite the narrow range of pyrite and chalcopyrite 34 s values close to 0 between 2 90 and 0 76 indicates that both the porphyry copper gold mineralization and the epigenetic mineralization were generated by sulfur of magmatic origin

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

accuracy assessment of lidar derived dems of bedrock river channels holtwood gorge susquehanna river 1 we evaluate the accuracy of 1 m lidar derived dems of an exposed bedrock channel and use these high resolution terrain models to calculate erosional fluxes between four levels of strath terraces dated previously with 10be recent investigations into the timing rates and processes by which rivers incise their bedrock channels have greatly enhanced our understanding of landscape evolution however measuring channel geometries in 3 dimensions is difficult thus volumes of bedrock eroded during incision events are rarely considered although our analysis successfully demonstrates the proportionality between incision rates and erosional fluxes for terraces high above the channel floor in this gorge unusually high river flows on the date of acquisition inundated lower bedrock surfaces preventing accurate volume estimates to ensure optimal low flow lidar coverage for fluvial environments we discuss methods to improve the scheduling of data acquisition by using archived discharge records and predictive models based on real time data