microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

the origin of hematite in high grade iron ores based on infrared microscopy and fluid inclusion studies the example of the conceicao mine quadrilatero ferrifero brazil petrographic and textural analysis combined with fluid inclusion studies by infrared microscopy of high grade 65 fe hematite ore samples from the conceicao deposit in the northeastern part of the quadrilatero ferrifero brazil indicate a complex process of oxidation and mineralization during two orogenic events each developed under different conditions and involving distinct fluids the earliest mineralization formed massive magnetite rich orebodies under relatively reducing conditions in the early stages of the transamazonian orogeny magnetite was oxidized martitized with the development of porous hematite crystals hematite i possibly during this stage new hematite crystals were also formed from low temperature low to medium salinity fluids as indicated by two phase fluid inclusions the origin of these fluids is still uncertain but tentatively interpreted as being modified surface water the fluids were transported along normal faults and fractures during post tectonic collapse following the transamazonian orogeny 2 1 2 0 ga and creation of the dome and keel structural pattern of the quadrilatero ferrifero these solutions were also likely responsible for the initial oxidation of the iron formations and the development of hematite i subsequent uplifted hot basement rocks or post tectonic plutons were probable heat sources for the regional metamorphism and development of a granoblastic fabric of hematite ii grains in the iron formations and high grade orebodies however the ore was only partially recrystallized as several relics of the early magnetite martite and hematite are still preserved in the granular hematite ii crystals during the brasiliano pan african orogeny 0 8 0 6 ga high salinity fluids with temperatures varying from 120 to a maximum of approximately 350 c penetrated the iron formations along shear zones crystallizing initially tabular and thereafter platy hematite crystals hematite iii and specularite forming schistose orebodies quartz veins that cut across the ore and envelop specularite plates and ore fragments formed from late stage high temperature and low salinity fluids containing co2 these later fluids did not alter the ore each of these stages of mineralization produced orebodies with distinct features recurrent hydrothermal mineralization is thought to have been responsible for the development of giant high grade iron ore deposits in structurally favorable sites fold hinges with enhanced permeability and deep faults able to conduct the fluids to the surface repeatedly over time should be important targets for exploration of new resources

genesis of banded iron formations a definitive interpretation of the genesis of banded iron formations has long been sought the explanation presented here involves the interpretation of an active continental margin as the depositional environment of the minas supergroup in brazil with the results that the same environment could explain the origin of the caue itabirite a well known iron formation a model is proposed to cover the deposition of banded iron formations in this setting and also in that of a passive con tinental margin believed to be the two most important sites of precipitation of such ores in active margins during the powerful process of subduction the ocean lithosphere is cut by faults and fractures through which seawater gains access and hydrothermally leaches the brittle yet hot lower layers the process is analogous to that currently being studied near midocean ridges when iron and silica among other compounds are driven by thermal convection to the sea floor it occurs in present subductions as it occurred in past ones but in early precambrian time both hydrosphere and atmosphere were anoxic ferrous iron was soluble in seawater and the earth9s surrounding ozone layer had not yet been formed a plume of feo sio 2 rich seawater was concentrated above and along the trench covering the nearby cratonic border during the sunny hours of the day iron was oxidized into ferric hydroxide before precipitation most banded iron formations laid down in early precambrian time were subducted with their ocean plates and the only fraction preserved was that deposited above cratonic borders the break in iron formation deposition at the end of that era was due to seawater and atmosphere oxygenation which produced the ozone filtering layer around the earth and also caused extinction of marine anaerobic microorganisms banded iron formations deposited in active or passive continental margins may assist in the interpretation of the paleoenvironment of the regions where they occur attempts have been made to classify some well known precambrian iron formations based on this assumption

plate boundary observatory and related networks gps data analysis methods and geodetic products the geodesy advancing geosciences and earthscope gage facility global positioning system gps data analysis centers produce position times series velocities and other parameters for approximately two thousand continuously operating gps receivers spanning a quadrant of earth s surface encompassing the high arctic north america and caribbean the purpose of this review is to document the methodology for generating station positions and their evolution over time and to describe the requisite tradeoffs involved with combination of results gage gps analysis involves formal merging within a kalman filter of two independent loosely constrained solutions one is based on precise point positioning produced with the gps inferred positioning system orbit analysis simulation gipsy oasis software at central washington university cwu and the other is a network solution based on phase and range double differencing produced with the gps at mit gamit software at new mexico institute of mining and technology nmt the primary products generated are the position time series that show motions relative to a north america reference frame and secular motions of the stations represented in the velocity field the position time series themselves contain a multitude of signals in addition to the secular motions co seismic and post seismic signals seasonal signals from hydrology and transient events some understood and other not yet fully explained are all evident in the time series and ready for further analysis and interpretation we explore the impact of analysis assumptions on the reference frame realization and on the final solutions and we compare within the gage solutions and with others

in situ demonstration of a passive radio sounding approach using the sun for echo detection ice sheet contributions to sea level rise present one of the greatest challenges that our society will face in the next century however models predicting sea level rise due to ice melt lack critical information regarding processes at the base of ice sheets although radio echo sounders are powerful tools that are currently used to constrain subglacial conditions existing ice penetrating radar systems are too resource intensive in terms of cost power and logistics for multiyear deployment at a large scale to address this we present passive radio sounding as a low resource approach for observing ice sheets across a range of spatial and temporal scales while passive radar has been used for target tracking and military purposes it has never been used for the sounding of ice sheets some recent work has proposed using passive radio sounding of europa s icy shell using jupiter s decametric radiation we expand on this idea by evaluating and discussing challenges and opportunities for developing a passive radio sounder using the sun as an illuminator of opportunity for echo detection here our prototype instrument sits on the side of a cliff and measures the sun s direct and reflected path off the ocean surface we then use an autocorrelation based method to extract the amplitude and delay of the reflection this serves as the first in situ demonstration of an autocorrelation based passive sounder using a compact astronomical white noise signal

calibration of prism and avnir 2 onboard alos daichi the advanced land observing satellite alos nicknamed ldquodaichirdquo was successfully launched on january 24 2006 and it continues to work very well this paper describes the calibrations of two optical instruments onboard alos which are the panchromatic remote sensing instrument for stereo mapping prism and advanced visible and near infrared radiometer type 2 avnir 2 prism consists of three panchromatic radiometers and is used to derive a digital surface model dsm with high spatial resolution which is an objective of the alos mission avnir 2 has four radiometric bands from blue to near infrared which are used for investigating regional environment issues such as land use and land cover classifications and disaster monitoring in this paper we introduce the calibration and validation plan methodologies accuracy assessments of the standard products image quality evaluations for prism and avnir 2 and their results geometric calibration is important in generating a precise dsm by a stereo pair image of prism the relative geometric calibrations of both prism and avnir 2 are conducted by evaluating accuracies within one scene and evaluating sensor alignments as absolute calibration for absolute geometric accuracies we achieved 8 1 m for nadir looking images and 9 3 m for forward and backward looking images of prism we also achieved 114 2 m for avnir 2 prism is also radiometrically calibrated both relatively and absolutely prism relative radiometric calibration is accomplished by using acquired images over homogeneous targets such as oceans deserts ice and snow areas as well as nighttime observation simultaneously observed images with calibrated avnir 2 are used for absolute radiometric calibration by cross calibration the absolute radiometric accuracy of the prism nadir looking radiometer is similar to that of avnir 2

constraining the relative strengths of high grade metamorphic rocks using foliation refraction angles an example from the northern new england appalachians foliation refraction angles are used to estimate effective viscosity contrasts between metapelitic and metapsammitic layers in amphibolite facies metaturbidites in the presidential range of the white mountains in eastern new hampshire an early formed foliation developed during km scale nappe folding consistently displays larger bedding foliation angles in metapelitic units than metapsammitic units suggesting that the metapelitic units had higher effective viscosities during this deformation we collected bedding foliation angle measurements from a combination of outcrops and locally derived boulders to test the hypothesis that foliation refraction angles could be used to estimate the effective viscosity ratio between different rock types at high metamorphic grades our results show that the metapelitic layers were between 2 and 3 times more viscous than the metaspsammitic layers which we attribute to the presence of large up to 15 cm long abundant up to 30 vol effectively rigid andalusite porphyroblasts in the metapelitic layers we present a methodology for using foliation refraction angles to determine the effective viscosity ratios of different rock types address the practical limitations we encountered and suggest this method is an easy way of estimating the strength contrast between different rock types finally we hypothesize that metamorphism resulting in porphyroblast growth can strengthen large crustal volumes during orogenesis

quartz nanocrystals in the 2 48 ga dales gorge banded iron formation of hamersley western australia evidence for a change from submarine to subaerial volcanism at the end of the archean banded iron formations bif have recently been used as proxies for tracking the chemical changes associated with the transition from an anoxic to oxic atmosphere around 2 45 billion years ago known as the great oxidation event goe the timing of the goe has been ascribed to both the collapse of a methane greenhouse and a decreased overall demand for oxygen due to the production of more oxidizing gases associated with greater subaerial volcanism the latter is a byproduct of a period of high mantle plume activity and the formation of new continental crust between 2 51 to 2 45 ga here we report unique mineral evidence for momentary subaerial volcanism recorded in hematite rich layers of the 2 48 ga bif from dales gorge hamersley of western australia the bif contains euhedral quartz nanocrystals qnc which only occur on the surfaces or in cavities of hematite breccias exhibiting soft sediment features and an exogenous source these qncs with an average size of 170 100 nm are distinct to the amorphous chert in the bif mineral assemblage and have the smallest crystal sizes of well crystallized quartz ever reported we suggest that qncs represent pyroclastic materials that were transported as dust particles to the bif depositional setting although the analysis of one specific bif unit does not provide proof of changing modes of volcanism during the archean paleoproterozic transition this high resolution petrological study does confirm that subaerial volcanism existed at that time

detection of plumes at redoubt and etna volcanoes using the gps snr method abstract detection and characterization of volcanic eruptions is important both for public health and aircraft safety a variety of ground sensors are used to monitor volcanic eruptions data from these ground sensors are subsequently incorporated into models that predict the movement of ash here a method to detect volcanic plumes using gps signals is described rather than carrier phase data used by geodesists the method takes advantage of attenuations in signal to noise ratio snr data two datasets are evaluated the 2009 redoubt volcano eruptions and the 2013 2015 eruptions at mt etna snr based eruption durations are compared with previously published seismic infrasonic and radar studies at redoubt volcano snr based plume detections from mt etna are compared with l band radar and tremor observations to place these snr observations from redoubt and etna in context a model of the propagation of gps signals through both water water vapor and tephra is developed neither water nor fine ash particles will produce the observed attenuation of gps signals while scattering caused by particles 1 cm in diameter potentially could

on the structure of grain boundaries in tectonites abstract grain boundaries in several tectonites have been examined using high voltage and scanning transmission electron microscopy on a gross scale grain boundaries are observed to differ from the host crystal in exhibiting faster rates of preferential etching during ion beam thinning and faster rates of ionization damage during exposure to the electron beam grain boundary features can be grouped according to decreasing size as follows grain junction voids that can form linked networks of tubules arrays of isolated voids and inclusions along the grain boundary surface and a narrow grain boundary film of distorted crystal structure the presence of inclusions in voids and the propensity for electron damage along the boundary suggests that the former were initially fluid filled and that the latter may be hydrated initial microchemical analyses using stem indicate that no compositional difference exists between the grain boundaries and host crystals the overall complex grain boundary structure in tectonites suggests that the effective grain boundary width for intercrystalline diffusion is much greater than that proposed based on metals and that diffusion path lengths along grain boundaries are much less than the theoretical maximum the net effect is to greatly enhance deformation mechanisms dependent on intercrystalline mass transport

a phase altimetric simulator studying the sensitivity of earth reflected gnss signals to ocean topography this paper presents a simulation study on global navigation satellite system gnss reflections focusing on a phase altimetric method for ocean topography retrieval it examines carrier phase residuals of earth reflected gnss signals in preparation for the gnss reflectometry radio occultation and scatterometry experiment aboard the international space station geros iss the residuals sensitivity to ocean topography maximum of 2 m amplitude variation of global sea level is shown a trigonometric approach to determine the specular reflection point is proposed reflection events are simulated assuming different low earth orbit receivers and gnss type transmitters suitable events for phase altimetry are assumed between 5 and 30 elevation lasting between 10 and 15 min with ground tracks length of 3000 km typical along track footprints 1 s integration time have a length of about 5 km within the assumed elevation range the coherent footprint ellipse has a major axis between 1 and 6 km a master slave sampling is proposed to approximate large scale delay and doppler variations of the reflected signal slave channel relative to the direct signal master channel slave residuals of an example event are simulated to retrieve a small scale phase delay for ocean topography inversion the signal to noise ratio restricts the quality of the topography results height precision on sub decimeter level for 30 db snr is degraded up to a meter level for 20 db snr ionosphere free linear combination allows keeping the precision level troposphere refraction degrades precision particularly at the low elevation limit precision improves toward higher elevations the tolerance to ocean roughness decreases in the same way

geodesy using the swedish permanent gps network effects of snow accumulation on estimates of site positions we have observed variations at the several centimeter level in estimates of the vertical coordinate of site position the estimates are obtained from our analysis of data acquired from the swedish permanent global positioning system gps network the observed variations are strongly correlated with changes in the indirectly inferred accumulation of snow which we assume collects on the radomes and pillars the gps sites could not be observed directly due to their remoteness numerical simulations which assume a simple geometry for the snow cover are used to study the effects of snow accumulation on gps phase observables and hence on estimates of the vertical coordinate of site position obtained from these observables our results indicate that the variations in the vertical coordinate of site position can be fully explained by reasonable accumulations of snow which retard the gps signals and enhance signal scattering effects

a three stage structural evolution of the quadrilatero ferriifero consequences for the neoproterozoic age and the formation of gold concentrations of the ouro preto area minas gerais brazil abstract the quadrilatero ferrifero occurs in the southern part of the sao francisco craton brazil where three major proterozoic supracrustal units the rio das velhas minas and itacolomi supergroups are exposed together with archaean to palaeoproterozoic granito gneissic basement microtectonic and kinematic analyses have been undertaken in the area close to ouro preto in order to precise the tectonic evolution and to distinguish the tectonic features related to the transamazonian and brasiliano orogenies respectively 2000 and 600 ma three main tectonic events have been recognized the earlier event de is clearly expressed within basement rocks of the bacao complex and surrounding supracrustal units a stretching lineation le lineation roughly oriented n s can be observed numerous shear criteria such as drag folds and asymmetric pressure shadows indicate a top to the south sense of movement along the southern border of the bacao complex this event was developed within amphibolite facies conditions fact confirmed by quartz c axis fabrics this earlier deformation is related to plutonic activity and reactivation of the archaean basement expressed by the occurrence of scarce leucocratic granitoid rocks intruded within the bacao gneisses it is here attributed to the transamazonian orogeny in agreement with recent u pb dating 2000 ma the large scale folds i e mariana anticline dom bosco syncline which define the dominant structural geometry of the quadrilatero ferrifero were formed during this event the second tectonic event dm has been defined as a major thrusting towards the wnw related to the brasiliano cycle a well expressed stretching and mineral lineation oriented e w to nw se lm lineation and associated nw verging shear criteria characterize this event occurrence of muscovite biotite and more scarcely sillimanite indicate that deformation developed in upper greenschist lower amphibolite facies quartz c axis fabrics confirm the sense of shearing but the large scattering of several fabrics traduces a weak intensity of strain all supracrustal and gneiss formations were affected by the thrusting which is developed on a folded surface previously formed during the de event the third event dm is characterized by hangingwall down movement of the nappe pile in response to relaxation of the brasiliano compressional dm forces this event developed in greenschist facies is marked by the occurrence of metre scale drag folds sometimes associated to the development of a new lineation lm gold mineralization which occurs along the main mineralized contact located between the minas and rio das velhas supergroups is found within late veins which comprise large recrystallized quartz carbonate sulphide chlorite and tourmaline microscopic analysis and veins geometry allow us to conclude that the veins were emplaced mostly after the ductile dm deformation it is proposed that the veins were formed by filling of open cavities created during dm tectonics this study highlights that the northwest verging thrusting which is the main tectonic event of the quadrilatero ferrifero is only relevant of the brasiliano orogeny a model of structural evolution which involves plutonic activity at 2000 ma within the archaean bacao complex followed by neoproterozoic thrust tectonics brasiliano is proposed and discussed the age of gold concentration assumed to be achieved during the relaxation that occurred in response to the thrusting event is re interpreted and related to the late stage of the brasiliano tectonics

deformation induced silica redistribution in banded iron formation hamersley province australia abstract the formation of banded iron formations bif remains controversial despite their potential to provide key information on precambrian atmospheres and hydrospheres it is widely agreed that bif are chemical sedimentary rocks comprising alternating layers of iron oxides and chert formed from poorly known precursor phases many models address the chemical transformation of such precursor iron oxide phases into bif during compaction and diagenesis however the formation of chert and the influence of physical forces in this process have received less attention microstructural analysis of bif from the hamersley province western australia reveals that significant amounts of silica were redistributed by dissolution precipitation creep during both diagenesis and regional scale deformation this physicochemical process led to silica remobilisation and volume loss by stress induced dissolution of microcrystalline quartz in an aqueous fluid the dissolved solid phase was transported by diffusion and fluid flow along grain boundaries or within available porosity and then reprecipitated in low pressure zones leading to local volume increase these processes were further enhanced by rheological contrasts between different minerals resulting in significant variations of chert band thickness microstructural observations combined with quantitative microfabric analysis reveal domains of crystallographic preferred orientations cpo in quartz grains within chert layers the cpo fabrics record strain regimes e g pure and simple shear extension and shortening that modified quartz aggregates by dissolution precipitation creep providing new insights into the metamorphic and deformation history of bif we document microstructures that indicate that non coaxial deformation was active during diagenesis and subsequent deformation of the hamersley province bif further relatively undeformed chert layers may have been similarly affected by significant amounts of dissolution precipitation creep providing a possible explanation for the destruction of primary features we show that different generations of chert alternate on a micro scale suggesting that the role of deformation has been underestimated in many aspects of bif research the discovery of dissolution precipitation creep in low grade metamorphic bif provides a potential link between the physical and chemical processes that occur within these rocks after deposition in the hamersley province dissolution precipitation creep was active from the compaction or diagenesis stage and probably operated during all major extensional and compressional deformation events we also suggest that chert layers without cpo record the least overprint by diagenesis and as the most pristine form of bif should be targeted for future paleo environmental research

glacial lake inventory of bhutan using alos data methods and preliminary results the advanced land observing satellite alos is relatively new its optical sensors are capable of making high resolution digital surface models dsms for the first time the task of constructing a regional scale inventory of glacial lakes based on alos data has been undertaken this study presents the data processing methods and the results of validation and analysis on the alos based glacial lake inventory of bhutan in the himalaya the analysis based on gps measurements taken at metatshota lake in the mangde chu sub basin one of the glacial lakes assessed as presenting a potential flood danger shows a validation estimate of 9 5 m for the location of the alos based polygon with a root mean square of 11 7 m a comparison with digitized data from the international centre for integrated mountain development icimod shows that positioning and evaluation of terrain changes can be significantly improved using alos data preliminary analysis of the glacial lakes in four sub basins mo chu pho chu mangde chu and dangme chu reveals that the frequency distribution of lake sizes biases towards smaller lakes glacial lakes 0 01 0 05 km 2 in area account for 55 of the total number and occupy 13 of the total area together our results demonstrate the usefulness of high resolution alos data with accurate dsms for studying glacial lakes high priority must be given to continuously improving and updating the glacial lake inventory with high resolution satellite data

deformation partitioning during folding of banded iron formation abstract domainal electron and optical microscopy and c axis fabric analysis are utilized to document microstructures and the associated deformation partitioning between crystal plastic brittle and fluid assisted deformation mechanisms during folding of proterozoic banded iron formation a hematite quartz calcite multilayer from the quadrilatero ferrifero granite greenstone terrain southeastern brazil the operation of different mechanisms was partially determined by the contrasting rheologic response of these three minerals at greenschist facies metamorphic conditions fracturing was the main deformation process in hematite while solution transfer accounted for part of the deformation in both calcite and quartz notably there is strong interaction among the different deformation mechanisms which have influenced each other in various ways fracturing of hematite in hinge zones of folds caused opening of gaps which were sealed by direct precipitation of silica from the fluid phase as a consequence a chemical potential gradient between crystals and fluid phase was produced and quartz was dissolved to restore the thermodynamical crystal fluid equilibrium thus brittle deformation of hematite partially controlled solution precipitation creep in quartz heterogeneous access of fluid into the deforming medium also affected the deformation processes inhomogeneous deformation in the quartz calcite aggregates generated intergranular porosity and increased fluid access with solution transfer becoming dominant in these domains in contrast the relatively more homogeneous deformation in the pure quartz aggregates served to maintain well adjusted grain boundaries and reduced fluid access into the intergranular space such that these domains deformed uniformly by crystal plastic processes at relatively dry conditions

the role of deformation in the formation of banded iron formation hosted high grade iron ore deposits hamersley province australia abstract the hamersley province western australia hosts some of the world s largest iron ore deposits but despite decades of research their genesis is still extensively debated many iron ore deposits are hosted in complexly deformed archean to paleoproterozoic banded iron formations comprising thin chert and iron oxide bands interlayered with silicate rich shales and carbonates current iron ore genesis models have identified a strong structural control on ore formation linked to extensive hypogene and supergene fluid circulation along fault structures these fluid pathways facilitate the removal of vast amounts of gangue minerals leading to enrichment of the iron oxide residue to iron ore however the evolution of the associated structures has not yet been considered as a key element in ore genesis here we show through multiscale structural analyses that deformation not only forms suitable fluid channels but that folding and shearing also result in significant synkinematic removal of gangue minerals our multidisciplinary investigation of the structural evolution of the mount tom price deposit combines microtectonic field geology and 3d implicit modelling techniques to establish a link between deformation structures at various scales microscale shear bands and outcrop scale asymmetric parasitic folds share striking similarities in their evolution and their controlling mechanisms both features record substantial non coaxial deformation accompanied by volume changes due to stress induced silica remobilisation the closely spaced layering of rheologically different lithologies within hamersley province strata plays a crucial role in complex multilayer deformation which resulted in extensive strain partitioning our study suggests that deformation was of major significance in the upgrading of banded iron formation to iron ore and was active from the early stages of banded iron formation during diagenesis deformation structures also established a micro to deposit scale lateral and vertical fluid network which enabled infiltration by hypogene and supergene fluids during or after deformation these new insights have important implications for iron ore genesis models structural applications in the mine environment and for understanding complex multilayer deformation with volume loss

performance of aster and srtm dems and their potential for assessing glacial lakes in the lunana region bhutan himalaya to assess the potential volume of a glacial lake outburst flood glof more precisely than in previous studies we analyze ground survey data and remote sensing digital elevation models dems around glacial lakes in the lunana region bhutan based on a dem generated from differential gps ground surveys we first evaluate the relative accuracies of dems produced by the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm root mean square errors of the altitudinal difference between these dems and ground survey data were 11 0 m for aster and 11 3 m for srtm these errors are similar to those of previous studies we show that a topographical classification allows a better estimate of elevation on lakes ponds riverbeds and glaciers due to their flat surfaces while the relative accuracy is worse over moraines and hill slopes due to their narrow ridges and steep slopes using the optical satellite images and the ground survey data we re evaluate the glof volume in 1994 as 17 2 5 3 10 6 m 3 we show glof related information such as distance altitudinal difference and gradient at possible outburst points where the lake level is higher than the neighboring riverbed and or glacial lake

characterization of dry snow sub structure using gnss reflected signals abstract signals of global navigation satellite systems gnss bi statically reflected off pristine dry snow in dome concordia antarctica were collected during an experimental campaign with the aim of investigating the potential capabilities of these signals to remotely sense dry snow areas the data have been used to sense the sub surface structure of the snow by means of a new holographic observable the obtained reflected signals present interferometric patterns consistent with the coherent superposition of signals reflected in different layers of the snow sub structure down to a few hundred meters depth a forward model has been developed to compare the amplitude and phase behavior of the interferences with the data a new radio holographic observable is also defined to help identify the layer at which the internal reflections occur this work represents the first step towards the potential use of a space based gnss r mission for densely monitoring the depths of antarctica s thick dry snow and or complementing l band radiometric observations

passive radio frequency identification ranging a dense and weather robust technique for landslide displacement monitoring abstract ground deformation monitoring at a local scale requires accuracy along with dense spatio temporal resolution radio frequency identification rfid technology is proposed as an alternative to classical geodetic methods for monitoring displacements of a landslide passive rfid tags allow for a very dense resolution both in time and space at the scale of a 100 m long surface by deploying 19 passive rfid tags on a landslide for 5 months this study validates the technique by comparison with laser total station and wire extensometer data the accuracy of the rfid technique was 1 cm during normal weather and up to 8 cm during snow events the results demonstrate that rfid tag tracking can monitor landslide displacements with multiple sensors at low cost providing dense spatio temporal data this technique could potentially be used for other applications such as monitoring volcanic activity buildings unstable rocks or snow cover

geology of the gouap iron deposit congo craton southern cameroon implications for iron ore exploration abstract the ntem complex represents the northwestern edge of the archean congo craton in southern cameroon where numerous banded iron formation bif hosted iron deposits have been discovered the gouap iron deposit which is located on the western edge of the ntem complex is one of the recent discoveries of iron deposits in this area in this study geological mapping detailed drillcore logging and petrographical studies reveal that the gouap iron deposit comprises of two lithostratigraphic units namely the bif and the country rocks the bif unit consists of amphibole bif and amphibole pyrite bif whereas the country rocks unit is made up of gneisses garnet amphibole magnetite and amphibole garnet pyrite gneiss schists amphibole magnetite and garnet magnetite micaschist quartzites and dolerite sills the bifs are well interlayered and observed to be in sharp or gradational contacts to their associated country rocks the mineral assemblages of the bifs and wallrocks except the dolerites indicate that both units have been metamorphosed under amphibole facies conditions two main iron mineralization types are identified in the gouap deposit the soft iron type which is mainly located in the western and northern parts and the hard iron type mostly confined to the southern sector of the deposit the structural controls of the gouap iron deposit are better observed in drillcore samples other than on the outcrop scale there are three principal deformation events d1 d2 and d3 that led to the development of foliation folding and faulting respectively the iron mineralization are mostly concentrated on the f2 fold hinge zones and fractures that acted as passage ways for the circulation of meteoric water at surface we suggest that the following three major processes that led to the formation of the gouap deposit i the chemical precipitation of chert and iron oxide followed by sedimentation and diagenesis that formed chert magnetite bifs ii secondly the amphibolite facies metamorphism and deformation that formed quartz magnetite bifs which constitute the main iron ridge located on thicker zones of fold noses and iii finally the gouap bifs have been upgraded to medium grade iron ore due to supergene enrichment processes which are restricted to the modern land surface and locally reached deeper levels through fault and fracture zones the western and northern parts of the gouap deposit have been identified as potential exploration target areas for iron mineralization even though the iron formation processes of the gouap deposit are not yet completely understood and many questions remain unanswered regarding the genesis of the soft and hard iron mineralization these new insights have important implications on the exploration drilling strategies of this deposit

recommendations for the compilation of glacier inventory data from digital sources modern geoinformatic techniques allow the automated creation of detailed glacier inventory data from glacier outlines and digital terrain models dtms once glacier entities are defined and an appropriate dtm is available several methods exist to derive the inventory data e g minimum maximum and mean elevation mean slope and aspect for each glacier from digital intersection of both datasets compared to the former manual methods the new grid based statistical calculations are very fast and reproducible the major aim of this contribution is to help in standardizing the related calculations to enhance the integrity of the global land ice monitoring from space glims database the recommendations were prepared by a working group and also contribute to the european space agency project globglacier the document follows the former unesco manual for the production of the world glacier inventory published in 1970 identifies the potential pitfalls and describes the differences from the former methods of compilation the online background material for this paper see http www glims org contains example scripts for calculation of each parameter and will be updated when required

quartz cpo and kinematic analysis in deformed rocks devoid of visible stretching lineations an integrated ams and ebsd investigation abstract kinematic analysis of deformed rocks requires study of structures in a section parallel to the stretching lineation and perpendicular to the foliation i e xz section of the strain ellipsoid however presence of stretching lineation is more of an exception rather than a norm in naturally deformed rocks this raises challenges for kinematic studies in this study the authors advocate use of anisotropy of magnetic susceptibility ams to identify the three principal axes of ams ellipsoid k1 k2 k3 which are equated with principal axes of the strain ellipsoid x y z this helps identify x direction of strain ellipsoid in deformed rocks that lack visible stretching lineations it is proposed that a section prepared parallel to the k1k3 plane of a deformed rock can be treated as equivalent to xz section of strain ellipsoid thus making it possible to perform kinematic studies in a rock that did not have stretching lineation use of this method is demonstrated on massive metavolcanic rocks of hutti region dharwar craton south india which is replete with quartz veins that contain gold crystallographic preferred orientation cpo of quartz veins is measured using sem ebsd studies of thin sections prepared parallel to k1k3 plane of the host rock obtained data help recognize the presence of down dip sense of movement as well as strain partitioning within veins which are aspects that were not recognized in earlier studies it is concluded that integration of ams and sem ebsd studies will play an important role in kinematic studies in future

retrieval of significant wave height and mean sea surface level using the gnss r interference pattern technique results from a three month field campaign since 1993 when the european space agency esa proposed the use of global navigation satellite systems reflected signals for sea mesoscale altimetry a wide range of applications have appeared this paper focuses on the retrieval of significant wave height swh and the mean sea surface level mssl from a ground based experiment using the interference pattern technique ipt two different observables on the ipt are analyzed the oscillation frequency and the angle where coherency is lost the point where coherency in the reflection process is lost can be related to the rayleigh criterion for smooth surfaces and helps to determine the swh spectral analysis on the interference pattern helps to determine the mssl a three month field campaign was performed on the pont del petroli pier badalona spain to see how the reflected gnss signals were affected by coastal sea state and check previous assumptions results from this field experiment are shown confirming that the swh can be retrieved with accuracy of 6 cm and the mssl with 4 cm estimations of both parameters are obtained every 30 min approximately

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

prevention of outburst floods from periglacial lakes at grubengletscher valais swiss alps flood and debris flow hazards at grubengletscher near saas balen in the saas valley valais swiss alps result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost in order to prevent damage related to such hazards systematic investigations were carried out and practical measures taken the evolution of the polythermal glacier the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high resolution aerial photographs seismic refraction d c resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake the results indicate a maximum moraine thickness of 100 m extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub and periglacial permafrost following 19th 20th century retreat of the partially cold glacier tongue the safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex the water level of an ice dammed lake was lowered and a thermokarst lake artficially drained

a new way to detect volcanic plumes 1 detection of volcanic plumes especially ash laden ones is important both for public health and aircraft safety a variety of geophysical tools and satellite data are used to monitor volcanic eruptions and to predict the movement of ash however satellite based methods are restricted by time of day and weather while radars are often unavailable because of cost portability here a method is proposed to detect volcanic plumes using gps signal strength data the strengths and limitations of the method are assessed using gps data collected during the 2008 and 2009 eruptions of the okmok and mt redoubt volcanoes plume detections using this gps technique are consistent with independently collected seismic and radar data

a methodology to eliminate snow and ice contaminated solutions from gps coordinate time series 1 positions derived from continuously operating gps sites are used throughout the world for geophysical research these positions are estimated assuming that the gps signals have not been obstructed by either snow or ice on the gps antenna unfortunately in many regions of the world this assumption is not correct snow and ice attenuate and scatter the gps signal in a way that leads to significant positioning errors these positioning outliers are typically removed by assuming geophysical models of displacement in this study an algorithm is developed that uses signal strength data to determine when the gps signal has been impacted by snow or ice this information is then used to remove outliers in gps coordinate time series the signal strength based algorithm was tested on 6 years of data from the earthscope plate boundary observatory network the algorithm improves the precision of 10 of these coordinate time series with most of the improvement found for sites operating in alaska

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

the bif hosted high grade iron ore deposits in the archean koolyanobbing greenstone belt western australia structural control on synorogenic and weathering related magnetite hematite and goethite rich iron ore the koolyanobbing banded iron formation bif hosted iron ore deposits total premining resources 150 million metric tons mt indicated reserves 32 mt are located in the mesoarchean lower succession bif of the koolyanobbing greenstone belt younami terrane yilgarn craton in western australia in the koolyanobbing greenstone belt a deformation sequence that broadly correlates with the proposed deformation history of most greenstones belts within the southern cross domain includes d 1 structures mainly small scale f 1a and f 1b folds formed in a north south to northwest southeast compressional regime a ductile to brittle deformation sequence d 2 to d 4 generated during east west compression and a late stage brittle segmentation of bif and reactivation of faults attributed to d 5 the formation of the seven known medium 45 58 wt fe to high grade 58 68 wt fe magnetite martite specularite and goethite bearing orebodies can be subdivided into four archean stages and one weathering related upgrade from the permian and or mesozoic to recent times the archean ore forming stages comprise 1 early fe mg ca metasomatism causing local ferroan carbonate and ferroan talc alteration of the metamorphosed quartz magnetite bif protolith 2 sequential syn d 2a coaxial to syn d 4 transpressional tight folding driven removal of carbonate quartz and minor ferroan talc by solution and mechanical transfer producing residual enrichment of medium to high grade magnetite ore 3 magnetite mineralization in syn d 2b and syn d 4 breccias and fractures forming medium grade ore zones or overprint magnetite in bif and first stage magnetite ore and 4 mineralization of hydrothermal specularite and locally associated ferroan dolomite quartz alteration and local oxidation of magnetite in and near brittle d 4 faults fractures and reactivated f 1 and f 2a fold cores modern weathering related leaching of carbonate and minor quartz pseudomorphic goethite replacement of existing iron oxides and gangue and coeval or subsequent to oxidation in the vadose zone formed goethite martite ore with local relics of specularite or magnetite and or kenomagnetite the intensity and localization of this supergene modification is in most deposits at koolyanobbing controlled by existing hypogene magnetite specularite rich medium to high grade ore zones and or carbonate altered bif at depth the existence of high grade ore below the weathering horizons suggests the possibility of further concealed magnetite and or specularite rich orebodies within the deposits and region

detection of arctic ocean tides using interferometric gnss r signals 1 this paper evaluates the usage of reflected gps signals for earth observations to study changes of sea level and sea ice in remote sensing in a coastal setup 670 m above disko bay greenland signals with different carriers l1 and l2 were recorded a method is presented that analyses the interferometric phase between the reflected and the direct signals and derives the height of the reflecting surface the analysis includes a ray tracing and an estimation of signal coherence it is shown that coherent reflections are related to sea ice coverage absolute heights are derived with a time interval of 30 min the altimetric results show semidiurnal tides that are validated using the aodtm 5 tide model the residual height has a mean of 9 7 cm for l1 and 22 9 cm for l2 the dispersion is not significant but a significant tropospheric bias is detected with an error of up to 20 cm

an outline of shear sense analysis in high grade rocks ductile shear zones are important in tectonic reconstructions as a source of information on the relative motion of large crustal blocks or plates in the geological past methods to interpret fabric in ductile shear zones were mostly developed for low grade rocks where overprinting relations are usually well preserved however high grade shear zones are common and dominate in many precambrian terrains high grade shear zones should be analysed in a different way from low grade zones the plane on which shear sense markers should be observed the vorticity profile plane is more difficult to find than in low grade shear zones the most reliable shear sense markers in high grade shear zones are shear bands mineral fish mantled porphyroclasts sigmoids and asymmetric boudins 2006 published by elsevier b v on behalf of international association for gondwana research

breakdown of feldspar volume gain and lateral mass transfer during mylonitization of granitoid in a low metamorphic grade shear zone abstract in a low metamorphic grade shear zone from quadrilatero ferrifero southeastern brazil granitoid rocks have been transformed into phyllonites and mylonites via activation of crystal plastic processes in quartz and fluid assisted reaction softening in feldspars quartz deformed by basal a and prism a slip with concurrent subgrain rotation recrystallization breakdown of matrix plagioclase an 22 35 via mica producing softening reactions required cationic exchanges between ca na and k forming replacement perthites in the k feldspar megacrysts which occupy around 60 of the original rock volume subsequent breakdown of the perthitic plagioclase an 12 15 led to disruption of the megacrysts enabling strain accommodation that localized the mylonite and phyllonite zones domainal volume and mass balance calculations based on major and minor elements indicate only small positive changes in mass and volume around 15 in the whole system however accentuated differences ranging from mass and volume losses of 25 and 35 at the margins to gains of 85 and 95 in the centre respectively exist between the individual longitudinal subzones occupied by the different tectonite types this scenario indicates that deformation proceeded as a nearly isochemical process although with lateral mobility of major elements principally si al and k within the shear zone these results are different from those previously reported for other granitic mylonites most of them indicating volume losses in compressional tectonic settings it is suggested that the extensional tectonic framework attributed to the moeda bonfim shear zone where mass volume losses are in principle not required enhanced the access of fluid and consequent transport of components into the shear zone principally fe si and k producing the small gains of mass and volume observed

grain boundary microstructures in micaceous quartzite significance for fluid movement and deformation processes in low metamorphic grade shear zones observation by scanning electron microscopy of a sericitic quartzite from a low grade 1 cm wide shear band developed from an originally pure quartzite revealed a nonconnected intergranular porosity the isolated pores occur principally on quartz quartz grain boundaries pores surrounding isolated mica flakes show very irregular geometries reflecting a highly unstable disequilibrium crystal fluid interface but regular frequently crystallographic pore shapes predominate in other grain boundaries statistical analysis reveals that the pores are principally concentrated on grain boundaries oriented perpendicular to the two foliations developed within the shear band i e grain boundaries at 45 and 90 to the shear band boundaries indicating that the fluid phase occupied extensional sites relative to both the overall and local scale of one microlithon strain ellipsoids there is a strong spatial relationship between interfacial porosity and the presence of mica with the most porous grains occurrin

estimating snow water equivalent over long mountain transects using snowmobile mounted ground penetrating radar abstractthe water balance in alpine watersheds is dominated by snowmelt which provides infiltration recharges aquifers controls peak runoff and is responsible for most of the annual water flow downstream accurate estimation of snow water equivalent swe is necessary for runoff and flood estimation but acquiring enough measurements is challenging due to the variability of snow accumulation ablation and redistribution at a range of scales in mountainous terrain we have developed a method for imaging snow stratigraphy and estimating swe over large distances from a ground penetrating radar gpr system mounted on a snowmobile we mounted commercial gpr systems 500 and 800 mhz to the front of the snowmobile to provide maximum mobility and ensure that measurements were taken on pristine snow images showed detailed snow stratigraphy down to the ground surface over snow depths up to at least 8 m enabling the elucidation of snow accumulation and redistribution processes we estimated snow density an

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

can we measure snow depth with gps receivers 1 snow is an important component of the climate system and a critical storage component in the hydrologic cycle however in situ observations of snow distribution are sparse and remotely sensed products are imprecise and only available at a coarse spatial scale gps geodesists have long recognized that snow can affect a gps signal but it has not been shown that a gps receiver placed in a standard geodetic orientation can be used to measure snow depth in this paper it is shown that changes in snow depth can be clearly tracked in the corresponding multipath modulation of the gps signal results for two spring 2009 snowstorms in colorado show strong agreement between gps snow depth estimates field measurements and nearby ultrasonic snow depth sensors because there are hundreds of geodetic gps receivers operating in snowy regions of the u s it is possible that gps receivers installed for plate deformation studies surveying and weather monitoring could be used to also estimate snow depth

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

the genesis of the hope downs iron ore deposit hamersley province western australia the banded iron formation bif hosted hope downs high grade hematite ore deposits are situated within the marra mamba iron formation with subsidiary deposits in the brockman iron formation of the archean to proterozoic hamersley group of western australia the main orebody extends to 260 m below the surface and is unusually rich in martite pseudomorphous hematite after magnetite and poor in limonite and goethite compared to other ore deposits of the marra mamba iron formation the high grade hematite ore is mainly within the newman member but also occurs in parts of the nammuldi member together with low grade limonitic ore that becomes high grade after calcining karst erosion of the overlying wittenoom formation has produced steep sided buried valleys adjacent to the in situ orebodies that contain thick deposits 160 m of goethitic and sideritic sediments including remnants of robe pisolite formation bedded siderite hematite gravels red ochreous detrital material and enriched scree deposits that are additional sources of ore the ore consists of low phosphorous martite limonite goethite derived from chert free bif by supergene weathering no evidence of the complete carbonate replacement of chert has been found at hope downs nor were any traces of preexisting chert bands seen in the ore despite the abundance of chert bands in bif elsewhere a variety of textures and composition shown by cherty bif adjacent to the orebodies is described from which the origin of the chert free bif is inferred including sedimentary structures consistent with density current deposition a model is presented for the origin of the host iron formation and the ore deposits in which density currents transported reworked iron silicates and hydroxides in colloidal suspension onto an unstable sea floor the amorphous silica produced during diagenesis of al poor iron silicates formed the characteristic chert bands of bif but some of the hydrous amorphous silica was lost prior to lithification to form chert free bif weathering of the chert free bif produced the high grade hematite ore that is exposed today

texture microstructure and strength of hematite ores experimentally deformed in the temperature range 600 1100 c and at strain rates between 10 4 and 10 6 s 1 abstract polycrystalline hematite samples cored perpendicular and parallel to the foliation i e perpendicular and parallel to a weak c axis maximum respectively were deformed in triaxial compression experiments at confining pressures of 300 and 400 mpa temperatures t between 600 and 1100 c and strain rates between 10 4 and 10 6 s 1 the measured strength of hematite ranges from 890 to 67 mpa the grain size of the main starting material is up to 175 m grain boundaries are intensely serrated at t 800 c the grain boundaries become increasingly lobate and the number of r twins decreases dynamic recrystallization starts above 800 c and a foam structure with grain sizes up to 150 m develops at t 900 c neutron diffraction measurements show a distinct change of the preferred orientation texture in compression parallel to the foliation below 800 c a 300 maximum developed due to a m slip at 800 and 900 c a c axis maximum evolved probably due to c a slip the original texture is preferentially preserved but with lower densities at t 1000 c presumably caused by increasing diffusional flow processes perpendicular to the foliation only minor changes of the texture occurred the experimentally determined textures allow a better understanding of the natural preferred orientation of hematite ores the extrapolation of experimental strength data of hematite quartz and carbonates to geological conditions are compatible with field observations

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

constraints on snow accumulation and firn density in greenland using gps receivers data from three continuously operating gps sites located in the interior of the greenland ice sheet are analyzed traditionally these kinds of gps installations where the gps antenna is placed on a pole deployed into the firn are used to estimate the local horizontal speed and direction of the ice sheet however these data are also sensitive to the vertical displacement of the pole as it moves through the firn layer a new method developed to measure snow depth variations with reflected gps signals is applied to these gps data from greenland this method provides a constraint on the vertical distance between the gps antenna and the surface snow layer the vertical positions and snow surface heights are then used to assess output from surface accumulation and firn densification models showing agreement better than 10 at the sites with the longest records comparisons between the gps reflection method and in situ snow sensors at the dye 2 site show good agreement capturing the dramatic changes observed in greenland during the 2012 summer melt season the geocentric elevation of the snow surface can be inferred by subtracting the snow surface height estimates from the vertical position measurements it should be possible to use those surface elevation estimates to help validate elevation results obtained from satellite altimetry

the tectonic evolution of the quadrilatero ferrifero minas gerais brazil abstract the structural framework of the quadrilatero ferrifero is the result of two main deformational events the first is an extensional event of palaeoproterozoic age between 2 100 and 1700 ma the transamazonian event which resulted in the formation of archaean granite gneiss domes and the nucleation of regional synclines in the overlying rio das velhas and minas supergroups strata such regional synclines are continuous with each other and are bordered by structural granite gneiss highs at the contact between these units ductile brittle to ductile extensional shear zones are developed representing the dislocation surfaces of archaean blocks this tectonism is probably related to the evolution of a metamorphic core complex formed in the hinterland to the west of a transamazonian collision zone which structured the paramirim craton the second event is compressive and associated with the closure of the pan african brasiliano proto ocean 650 500 ma situated to the east of quadrilatero ferrffero qf during this event a west verging fold and thrust belt ftb developed causing inversion amplification translation and rotation of the basinal synclines the ftb affected mainly the eastern portion of qf and obliterated many of the tectonic features of the extensional event

major element distribution in archean banded iron formation bif influence of metamorphic differentiation the archean 2 8 ga banded iron formation bif of the bell lake region of yellowknife greenstone belt canada is recrystallized to metamorphic assemblages of the amphibolite facies this bif is characterized by centimetre scale fe rich and si rich mesobands in the si rich mesobands thin layers of magnetite microbands are developed in a quartz matrix the fe rich mesobands are composed mainly of ca amphibole hornblende fe mg amphibole grunerite and magnetite the metamorphic foliation locally cuts across the mesoband boundaries indicating the mesobanding was formed prior to peak metamorphism variations in mineral modal proportions between fe rich mesobands and microbands are diagnostic of depositional compositional differences between beds micro x ray fluorescence imaging reveals metamorphic differentiation within fe rich mesobands with segregation of fe mg amphibole and the incompatible element mn is concentrated at the margins of the fe rich mesobands during the amphibole forming reactions ti was relatively immobile during metamorphic segregation and its distribution provides a record of the original structures in the fe rich mesobands

proterozoic crustal extension and the generation of dome and keel structure in an archaean granite greenstone terrane archaean granite greenstone terranes1 3 in which narrow belts of greenstone ultramafic and mafic volcanics and overlying sedimentary rocks occur in association with broad provinces of granite granitic igneous rocks gneiss and migmatite have long puzzled geologists because of the lack of any clear modern analogues not only is there uncertainty about how the greenstone formed in the first place4 6 but there is continuing debate about how and when the terranes developed their distinctive structural and metamorphic architecture many granite greenstone terranes display a dome and keel geometry in which belts of supracrustal volcanic and sedimentary rocks occur as structural troughs wedged between dome shaped bodies of the granite gneiss migmatite complex a metamorphic aureole typically occurs in the supracrustals adjacent to their contact with the domes and the contact itself is a shear zone here we report the results of field studies of a granite greenstone terrane in brazil showing that this architecture originated during the proterozoic more than 500 million years after extrusion of the greenstone we suggest that the thermal regime and deformation kinematics necessary to create this architecture could be generated during an episode of crustal extension when hot basement rocks were transported upwards along a transcrustal normal fault system to the base of the supracrustals

using a ground based sar interferometer and a terrestrial laser scanner to monitor a snow covered slope results from an experimental data collection in tyrol austria in this paper we report on an experimental activity aimed at investigating the potential of two terrestrial remote sensing techniques namely ground based sar gb sar interferometry and terrestrial laser scanning in order to retrieve snow depth sd measurements in mountainous regions terrestrial laser scanning is a more consolidated technique based on the measurement of the optical near infrared reflectivity and it is affected by the surface of the snow layer a temporal data sequence allows us to estimate the absolute sd variation recent use of sar interferometry to evaluate snow mass characteristics is based on relating the measured interferometric phase shift to a change in the snow mass interferometric gb sar measurements and terrestrial laser scanner scans were collected together with pointwise conventional measurements of physical snow parameters during the winters of 2005 2006 and 2006 2007 the experiment was carried out in the wattener lizum a high alpine area at about 2000 m elevation north of the main ridge of the austrian alps in tyrol notwithstanding the difficulty of providing both lengthy data record in dry snow conditions and detailed knowledge of the observed snow characteristics the obtained results confirmed the presence of a clearly measurable interferometric phase variation in relation to the growing height of the snow layer a comparison of the sd maps obtained through the two techniques shows differences partly due to the different nature of the two observations

microstructures in a banded iron formation gua mine india this paper provides a detailed documentation of microstructures developed in the banded iron formation bif of gua mine located in the bonai synclinorium eastern india where the rocks have been subjected to three deformations d 1 to d 3 folded iron ores quartz strain fringes around rigid core objects and folded iron ore layers and refracted quartz veins are described from samples taken from d 2 folds in the banded iron formation orientations of microstructures are compared with mesoscopic structures to interpret the generations of ore minerals planar structures and the time relationship between deformation and development of different microstructures the mechanism of d 2 folding is worked out and its bearing on microstructure development is discussed the d 2 folds are inferred to have developed by a combination of tangential longitudinal strain in the competent layer flexural flow in the incompetent layers and flexural slip at the interface between layers of differing competence homogeneous flattening strain superposed the earlier strain which led to modification of the folds in the competent layer from class 1b to 1c this strain is quantified and is found to be higher in the limb than the hinge of a fold diffusive mass transfer by solution and bulging dynamic recrystallization in quartz are inferred as the dominant deformation processes during folding moreover based on comparison with published deformation microstructure maps the microstructures of the present study are estimated to have developed between 300 and 350 c temperatures at a strain rate of 10 14 10 12 s 1 which are geologically realistic conditions for naturally deformed rocks

inverse modeling of gps multipath for snow depth estimation part i formulation and simulations snowpacks provide reservoirs of freshwater the amount stored and how fast it is released by melting are vital information for both scientists and water supply managers gps multipath reflectometry gps mr is a new technique that can be used to measure snow depth signal to noise ratio data collected by gps instruments exhibit peaks and troughs as coherent direct and reflected signals go in and out of phase these interference fringes are used to retrieve the unknown land surface characteristics in this two part contribution a forward inverse approach is offered for gps mr of snow depth part i starts with the physically based forward model utilized to simulate the coupling of the surface and antenna responses a statistically rigorous inverse model is presented and employed to retrieve parameter corrections responsible for observation residuals the unknown snow characteristics are parameterized the observation parameter sensitivity is illustrated the inversion performance is assessed in terms of its precision and its accuracy and the dependence of model results on the satellite direction is quantified the latter serves to indicate the sensing footprint of the reflection

dome emplacement and formation of kilometre scale synclines in a granite greenstone terrain quadrilatero ferrifero southeastern brazil the quadrilatero ferrifero is a portion of the brazilian precambrian shield containing a granite greenstone terrain characterized by granite gneiss domes encircled by kilometre scale synclines integration of porphyroblast matrix microtextures c axis fabrics analysis and strain analysis with outcrop scale structural relationships indicates that the main phase of domes and synclines evolution occurred during the westerly directed 0 8 0 6 ga pan african brasiliano regional shortening this tectonic event has produced the single pervasive foliation observed in the folded supracrustal sequences of the quadrilatero ferrifero dip slip ductile shear zones developed at the dome supracrustal interface are synchronous with dome evolution during the pan african brasiliano deformation as indicated by contemporaneous growth of aureole porphyroblasts in the shear planes these shear zones facilitated steeply directed downward flow of country rock material around the granite gneiss domes the marked density contrast between granite gneiss material and the iron rich supracrustals provided a gravitationally favourable environment for downward wallrock flow variations in shear zone kinematics away from the domes combined with kilometer scale viscous drag contributed to produce kilometre scale synclines in the supracrustal rocks constrained between upward moving domes

deformation mechanisms in the mylonite ultramylonite transition abstract the deformation mechanisms and controls that operate in the mylonite ultramylonite transition are interpreted from microstructural observation the investigated mylonites and ultramylonites were derived from a granitic protolith which was deformed under greenschist facies conditions and in the presence of fluid in a regional scale shear zone from northwest argentina several deformation mechanisms were recognized to operate simultaneously in different domains of the microstructure at each particular stage of the microstructural evolution this continuously mobile deformation partitioning present throughout the microstructural evolution ceases abruptly in the ultramylonite stage where a stable state microstructure is achieved domainal quartz c axis fabrics indicate that quartz deforms by crystal plastic processes at the initial and intermediate stages of deformation but solution transfer processes become predominant in the ultramylonite stage plagioclase is progressively transformed into muscovite through retrograde softening reactions k feldspar is progressively transformed into fine grade aggregates via cataclastic flow and incipient recrystallization mica deforms by kinking and basal slip with progressive development of fine grained morphologically oriented aggregates plagioclase disappearance as well as the development of intrafolial microfolds characterize the transition between the mylonitic and ultramylonitic domains disruption of these microfolds is interpreted to represent the ultimate control on the localization of the ultramylonite bands

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

snow depth estimation based on multipath phase combination of gps triple frequency signals snow is important to the ecological and climate systems however current snowfall and snow depth in situ observations are only available sparsely on the globe by making use of the networks of global positioning system gps stations established for geodetic applications it is possible to monitor snow distribution on a global scale in an inexpensive way in this paper we propose a new snow depth estimation approach using a geodetic gps station multipath reflectometry and a linear combination of phase measurements of gps triple frequency l1 l2 and l5 signals this phase combination is geometry free and is not affected by ionospheric delays analytical linear models are first established to describe the relationship between antenna height and spectral peak frequency of combined phase time series which are calculated based on theoretical formulas when estimating snow depth in real time the spectral peak frequency of the phase measurements is obtained and then the model is used to determine snow depth two experimental data sets recorded in two different environments were used to test the proposed method the results demonstrate that the proposed method shows an improvement with respect to existing methods on average

three holocene and late pleistocene glacial stages inferred from moraines in the lingshi and thanza village areas bhutan abstract moraines formed by valley glaciers in lingshi area northwestern bhutan constitute three distinct stages with contrasts in the spatial distribution and size of moraines and surface features such as clasts soils and vegetation moraines in the thanza village area northern bhutan show three stages with similar characteristics to those in the lingshi area using morphostratigraphic criteria these three stages correlate with some glacial stages in the khumbu himal eastern nepal dates from moraines in the khumbu himal provide a tentative chronological sequence of these three stages valley glaciers in bhutan expanded during the following periods 1 the takaphu and raphsthreng stages are the little ice age and late holocene glacial advances 2 the jykhuje and tenchey stages represent the late glacial and or early holocene glacial advances and 3 the lingshi dzong and lunana stages are coincident with the last glacial period

snow depth density and swe estimates derived from gps reflection data validation in the western u s geodetic quality gps systems can be used to measure average snow depth in the 1000 m2 area around the gps antenna a sensing footprint size intermediate between in situ and satellite observations swe can be calculated from density estimates modeled on the gps based snow depth time series we assess the accuracy of gps based snow depth density and swe data at 18 gps sites via comparison to manual observations the manual validation survey was completed around the time of peak accumulation at each site daily snow depth derived from gps reflection data is very similar to the mean snow depth measured manually in the 1000 m2 scale area around each antenna this comparison spans site averaged depths from 0 to 150 cm the gps depth data exhibit a small negative bias 6 cm across this range of snow depths errors tend to be smaller at sites with more usable gps ground tracks snow bulk density is modeled using the gps snow depth time series and model parameters are estimated from nearby snotel sites modeled density is within 0 02 g cm 3 of the density measured in a single snow pit at the validation sites for 12 of 18 comparisons gps based depth and modeled density are multiplied to estimate swe swe estimates are very accurate over the range observed at the validation sites from 0 to 60 cm r2 0 97 and bias 2 cm these results show that the near real time gps snow products have errors small enough for monitoring water resources in snow dominated basins

monitoring crustal changes at volcanoes by seismic noise interferometry mt etna case of study abstract in this work we analysed the seismic noise recorded at mt etna by 18 stations during the interval 2007 2015 in the frequency band 0 1 0 3 hz chosen to avoid contamination from volcanic tremor variations in time of medium seismic velocity in the range 0 8 to 0 8 were found mostly affecting the stations located on the volcano summit and flanks based on the investigated frequency content the v v changes took place from the surface to a depth of 4 5 6 5 km to identify the source mechanism of the observed medium changes the variations were quantitatively compared by wavelet transform coherence with volcano tectonic and meteorological parameters a significant relationship with meteorological parameters with seasonal periodicity especially air temperature and snow loading was found probably caused by thermo elastic strain and increasing decreasing surface loading cycles moreover a sharp medium velocity decrease taking place in mid december 2009 and clearly time related to the largest volcano tectonic strain release phenomenon of the investigated period was also found such a velocity decrease was interpreted as resulting from ascent of fluids and gas exsolution taking place at the same time as the volcano tectonic swarm