valley scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes abstract high resolution topographic surveys using lidar and multibeam sonar can be used to characterize and quantify fluvial change this study used repeat surveys to explore how topographic change fluvial processes sediment budgets and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel cobble river a novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006 2008 to 2014 during this period which had four modest 3 5 year floods most sediment was laterally redistributed through bank erosion and channel migration erosion primarily occurred in the floodplain 97 000 m 3 terraces 80 000 m 3 and lateral bars 58 000 m 3 while deposition occurred in the adjacent pools 73 000 m 3 fast glides 48 000 m 3 and runs 36 000 m 3 in contrast significantly higher magnitude and longer duration floods from 1999 to 2006 2008 caused sediment to be displaced longitudinally with the upstream reaches exporting sediment and the downstream reaches aggrading the river maintained floodplain connectivity during both periods despite different processes dominating the type of connectivity larger floods promoted overbank scour and avulsion while smaller floods promoted bank erosion and lateral migration this study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics

a simple way to extract baddeleyite zro2 1 baddeleyite is a reliable geochronometer for dating the crystallization of mafic and other silica undersaturated intrusive rocks its high u and negligible initial pb content enable precise age determinations with statistical errors of a few million years or less the widespread use of baddeleyite for dating has however been limited by the low content of baddeleyite in many samples and by difficulties in isolating baddeleyite we have developed a new separation technique that utilizes differences in transport velocity among grains of varying size as they move across the deck of a water shaking table a small sample portion is loaded instantly on the table and only the finest and densest material remaining after similar to120 s is collected repeated recovery of sample portions yields a concentrate strongly enriched in baddeleyite and opaque minerals the latter is easily removed by a hand magnet the water based separation technique will improve yields of baddeleyite from samples processed on a water shaking table and is capable of recovering very fine grains as the entire separation is made in water problems arising from adhesive forces between minerals are minimized as is the risk of cross contamination no heavy liquids are necessary making separation quick uncomplicated and inexpensive

record of plate boundary metamorphism during gondwana breakup from lu hf garnet geochronology of the alpine schist new zealand

shear stress and hydrodynamic recovery over bedforms of different lengths in a straight channel abstractpools and riffles are common morphological features in rivers that are frequently used but poorly specified analogs in restoration design here straight two dimensional 2d bedforms are conceptualized as perturbations and flow recovery is measured in a laboratory flume with an array of ultrasonic doppler velocity profilers udvps the objectives are to 1 assess the variation of skin friction turbulent stresses and total stress 2 assess the role of topographical feedback on flow recovery and 3 compare flow recovery in isolated and bedforms in series the results show that the total shear stress and near bed turbulence greatly exceed the skin friction in decelerating flow and the pool and that hydrodynamic recovery tends to occur at length scales similar to geophysical scales despite potential negative feedback from the bed repeating short bedforms can push the flow to a more turbulent and laterally concentrated equilibrium condition implications for sediment entrainment thresholds e

petrology and ion microprobe u pb chronology applied to a metabasic intrusion in southern sweden a study on zircon formation during metamorphism and deformation the aker metabasite occupies a key position in a major tectonic lineament in southernmost sweden the protogine zone which coincides closely with the eastern boundary of the late mesoproterozoic sveconorwegian orogen of southwest scandinavia metamorphic reactions associated with the transformation from isotropic gabbro to foliated garnet amphibolite were identified from disequilibrium textures of which some involved release of zirconium zr and growth of metamorphic zircon ion microprobe dating of igneous zircon gave 1562 6 ma whereas metamorphic zircons yielded ages of 1437 21 1217 75 and 1006 68 ma the presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than younger metamorphic zircons suggest redistribution of zr into new zircon first by the breakdown of baddeleyite zro2 and later by the consumption of igneous phases containing trace amounts of zr several generations of metamorphic zircon and the presence of 1 56 and 1 22 ga mafic intrusions along the protogine zone call for a complex tectonic history probably reaching back to at least similar to1 56 ga growth of metamorphic zircon at similar to1 44 ga may relate to a regional compressional event the wnw trending deformational structures on both sides of the protogine zone may possibly relate to that event the similar to1 22 ga metamorphic zircons are coeval with the emplacement of numerous granitic syenitic and mafic intrusions along and parallel to the protogine zone the age around 1 0 ga finally marks sveconorwegian metamorphism for which thermobarometry of the aker garnet amphibolite suggests 1000 1200 mpa at 600degreesc 630degreesc thereafter significant relative uplift of the rocks to the west of the protogine zone occurred on nearly vertical north south trending deformation zones less

decompressed eclogites in the sveconorwegian grenvillian orogen of sw sweden petrology and tectonic implications relict eclogites and associated high pressure rocks are present in the eastern segment of the sw swedish gneiss region the tectonic counterpart of the parautochthonous belt of the canadian grenville these rocks give evidence of sveconorwegian eclogite facies metamorphism and subsequent pervasive reworking and deformation at granulite and amphibolite facies conditions the best preserved eclogite relics suggest a clockwise p t t history beginning in the amphibolite facies progressing through the eclogite facies decompressing and partially reequilibrating through the high and medium pressure granulite facies before cooling through the amphibolite facies textures demonstrate the former coexistence of the plagioclase free assemblages garnet clinopyroxene quartz rutile ilmenite garnet clinopyroxene kyanite rutile and garnet kyanite quartz rutile the former existence of omphacite is evidenced by up to 45 vol plagioclase expelled as small grains within large clinopyroxene matrix plagioclase is secondary and occurs expelled from clinopyroxene or in fine grained granulite facies reaction domains formed during resorption of garnet and kyanite garnet shows preserved prograde growth zoning with rimward increasing pyrope content decreasing spessartine content and decreasing fe fe mg ratio but is partly resorbed and reequilibrated at the rims p t estimates from microdomains with clinopyroxene plagioclase quartz garnet indicate pressures of 9 5 12 kbar and temperatures of 705 795 c for a stage of the granulite facies decompression the preservation of the prograde zoning suggests that the rocks did not reside at these high temperatures for more than a few million years and chemical disequilibrium and frozen reaction textures indicate heterogeneous reaction progress and overstepping of reactions during the decompression through the granulite facies together these features suggest a rapid tectonic exhumation the eclogite relics occur within a high grade deformation zone with wnw ese stretching and associated oblique normal sense top to the east sensu lato displacement suggesting that extension was a main cause for the decompression and exhumation probable tectonic scenarios for this deformation are sveconorwegian late orogenic gravitational collapse or overall wnw ese extension

disturbed radiometric ages and their bearing on interregional correlations in the sw baltic shield abstract rb sr whole rock and zircon u pb isotopic work is reported from the northern part of the region between the mylonite and protogine zones in the southern baltic shield three age determinations on polymetamorphic gneissic granites were carried out two of these yielded u pb upper intercept ages of 1650 and 1675 ma respectively which is approximately one hundred ma less than expected from the combined field evidence and earlier isotopic age determinations although the new discordias appear well defined various criteria suggest that the u pb isotope system was disturbed thus the rb sr system had been opened but nevertheless the rb sr errorchrones are consistent with the u pb upper intercept ages and an abraded zircon fraction suggests an older age than the unabraded fractions the third u pb age determination resulted in a poorly constrained discordia its upper intercept ranges between 1575 and 1605 ma depending on the number of fractions considered this paper tests a three stage model where the intrusion age is set identical to the 1780 ma intrusion age of the undeformed assumed protolith the first two analysed rocks are consistent with a model suggesting intrusion at 1780 ma followed by partial opening of the isotopic systems early 1200 ma and late 950 ma during the sveconorwegian orogeny an abraded fraction together with the time of the suggested last opening of the system 950 ma ago defines a two point discordia with an upper intercept age of 1745 ma this age is in close agreement with the assumed intrusion age the isotope data from the third gneissic granite cannot be fitted to this simple model it is concluded that the analysed rocks could belong to the granitoids of the transscandinavian igneous belt but if they do they were reworked during the sveconorwegian orogeny as a corollary it follows that the regions separated by the northern part of the protogine zone largely had a common pre sveconorwegain geological history another important implication is that the intrusion ages in the area between the mylonite and protogine zones are older than those of the trans labrador batholith in canada

valley width variation influences riffle pool location and persistence on a rapidly incising gravel bed river abstract decades of research have demonstrated that gravel bed rivers exhibit multiple spatial scales of landform nonuniformity landform features such as valley wall oscillations alluvial fans terraces river meanders point bars boulder clusters and logjams contribute to river corridor heterogeneity further studies have shown that the locations of riffles and pools in gravel bed rivers are closely associated with the spatial pattern of river corridor morphological variability these studies imply but do not directly test that persistence of riffles and pools through time is also conditioned by landform variability mechanistically it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing in such circumstances can variation in valley width influence channel morphology forcing riffle pool location and persistence to address this question research was performed on a valley confined wandering gravel bed reach of the regulated lower yuba river california usa that is incising from reduced sediment supply and flow regulation after a historic period of mining related valley sedimentation this study quantified stream planform change 1984 2006 and elevation change 1999 2006 using eight aerial photo sets and two digital elevation models and it qualitatively assessed channel change in older aerial photos going back to 1937 analysis revealed that the river has undergone rapid incision 0 11 m year and planform change in response to frequent floods yet eight riffles persisted in the same locations which coincided with the locally wide areas of the valley longitudinal profiles revealed that deep pools were associated with long valley constrictions geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

zircon coronas around fe ti oxides a physical reference frame for metamorphic and metasomatic reactions ilmenite in coronitic gabbros from the bamble and kongsberg sectors southern norway is surrounded by zircons ranging in diameters from a fraction of a micrometer to 10 m across the zircons are inert during subsequent metamorphism amphibolite to pumpellyite prehnite facies and metasomatism scapolitization and albitization and can be found as trails in silicates phlogopite talc chlorite amphibole albite and tourmaline in the altered rocks the trails link up to form polygons outlining the former oxide grain boundary this 3 dimensional framework of zircons is used to a recognize metasomatic origin of rocks b quantify the mobility of elements during mineral replacement c establish the growth direction of reaction fronts and to identify the reaction mechanism as dissolution reprecipitation zircon coronas on fe ti oxides have been described from a number of terrains and appear to be common in mafic rocks gabbros and granulites providing a tool for a better understanding of metasomatic and metamorphic reactions

kinematics of a major fan like structure in the eastern part of the sveconorwegian orogen baltic shield south central sweden abstract the n s trending so called protogine zone in the baltic shield of south central sweden is usually considered to mark a tectonic boundary between the rocks of the transscandinavian igneous belt tib in the east and the sveconorwegian orogen in the west detailed structural mapping in the karlskoga kristinehamn area has shown that an anastomosing network of ductile deformation zones with generally n s strike extends ca 40 km east of the traditional protogine zone furthermore the western boundary of this ductile deformation and the tib is not constrained in the kristinehamn area reconnaissance studies indicate that they both extend westwards towards the so called mylonite zone it is suggested that the eastern limit of the sveconorwegian orogen is located some 40 km east of the present boundary and that the protogine zone concept is obsolete the term sveconorwegian frontal deformation zone sfdz is proposed as a more appropriate alternative in southern sweden south of lake vattern and to correspond to a younger set of oblique ductile deformation zones with reverse and right lateral components of movement in the easternmost part of the orogen farther to the north ductile deformation zones older than the sfdz in the karlskoga kristinehamn area display a fan like geometry in an e w cross section with steep westerly dips in the eastern part of the section vertical dips farther west and moderate easterly dips in the western part of the section kinematic analysis indicates that dip slip movements predominate with a consistent top to the east sense of movement across the entire fan like structure in their present orientation deformation zones are characterized by reverse movements in the eastern part and normal movements in the western part of the structure between kristinehamn and the mylonite zone the main foliation is gently dipping to subhorizontal indicating that the regional structure is strongly asymmetric and that the fan like structure occurs close to the foreland of the orogen deformation zones are spaced to semi penetrative in the eastern part of the fan like structure whereas the deformation is more or less penetrative and the tib rocks are transformed to orthogneisses west of kristinehamn this east to west increase in bulk strain is in accordance with an increase in syn deformational metamorphic grade across the structure younger ductile deformation zones belonging to the sfdz are responsible for a major change in orientation of the older deformation zones in the easternmost part of the structure the fan like structure is best explained by models involving the interference of two separate tectonic events deformation occurred after 1 57 ga and prior to deposition of neoproterozoic and younger cover sedimentary rocks it is not yet clear whether the initial phase of deformation early sveconorwegian or older was related to the build up of an imbricate thrust stack in a compressional regime as favoured here or to regional e w extension the younger deformation phase was related to rotation of these older structures into the compressional late sveconorwegian sfdz

linking deformation migmatite formation and zircon u pb geochronology in polymetamorphic orthogneisses sveconorwegian province sweden absolute ages of migmatization in the polymetamorphic parautochthonous basement of the sveconorwegian province sweden have been determined using u pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses migmatite zircon was formed by recrystallization whereas dissolution reprecipitation and neocrystallization were subordinate the recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes it is backscatter electron bright u rich 800 4400 ppm with low th u ratios generally 0 01 0 1 unzoned or oscillatory ghost zoned and occurs as up to 100 m thick rims with transitional contacts to cores of protolith zircon protolith ages of 1686 12 and 1668 11 ma were obtained from moderately resorbed igneous zircon crystals generally th u 0 5 1 5 u 300 ppm in mesosomes protolith zircon is also present as resorbed cores in the leucosomes linkage of folding synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south vergent folding at 976 7 ma at a second locality similar recrystallized zircon rims in leucosome date pre sveconorwegian migmatization at 1425 7 ma an upper age bracket of 1394 12 ma for two overprinting phases of deformation upright folding along gently ssw plunging axes and stretching in ese was set by zircon in a folded metagranitic dyke lower age brackets for these events were set at 952 7 and 946 8 ma by zircon in two crosscutting and undeformed granite pegmatite dykes together with previously published data the present results demonstrate i tectonometamorphic reworking during the hallandian orogenesis at 1 44 1 42 ga resulting in migmatization and formation of a coarse gneissic layering ii sveconorwegian continent continent collision at 0 98 0 96 ga involving a emplacement of an eclogite unit b regional high pressure granulite facies metamorphism c southvergent folding subhorizontal east west stretching and migmatization all of which caused overprint or transposition of older mesoproterozoic and sveconorwegian structures the sveconorwegian migmatization and folding took place during or shortly after the emplacement of sveconorwegian eclogite and is interpreted as a result of north south shortening synchronous with east west extension and unroofing during late stages of the continent continent collision

tectonothermal evolution of high alumina rocks within the protogine zone southern sweden the protogine zone comprises a system of anastomosing deformation zones which approximately parallel the eastern boundary of the sveconorwegian 1200 900 ma province in south west sweden ages of granulite facies metamorphism in the sveconorwegian province require exhumation from c 30 to 35 km crustal depths after 920 880 ma 40ar 39 ar cooling ages are presented for muscovite from high alumina rocks formed by hydrothermal leaching associated with the protogine zone growth of fabric defining minerals was associated with a ductile deformational event muscovite from these rocks cooled below argon retention temperatures c 375 25 c at c 965 955 ma muscovite from granofels in zones of intense alteration indicates that temperatures 375 25 c were maintained until c 940 ma textural relations of al2sio5 polymorphs and chloritoid suggest that dated fabrics formed during exhumation the process of exhumation brittle overprint on ductile structures and hydrothermal activity along faults within the protogine zone tentatively are interpreted as the peripheral effects of initial neoproterozoic exhumation of the granulite region of south western sweden muscovite in phyllonites associated with the sveconorwegian thrust system cooled below argon retention temperatures at c 927 ma exhumation associated with this cooling could have been related to extension and onset of brittle ductile deformation superimposed on sveconorwegian contraction

seismic imaging in the frontal part of the sveconorwegian orogen south western sweden reflection seismic data have been acquired along a 17 km profile in the eastern frontal part of the sveconorwegian orogen south western sweden receiver spacing was 25 m and nominal shot spacing 100 m shots ranging in size from 0 5 to 1 0 kg were fired in 3 m deep shot holes the data image the structure of the upper part of the crust from depths of a few 100 m down to depths of approximately 10 km the profile crosses the central axis of an inferred fan like structure indicated from earlier detailed surface mapping results deformational fabrics within this structure dip approximately 15 40 e in the western part of the profile and 60 80 w in its eastern part the seismic data display a bivergent geometry with the central axis situated approximately 8 km east of a major fault protogine zone in earlier studies surface structural data predict the hinge axis to be located about 3 km farther east despite this discrepancy there is good general agreement with the structure inferred from the surface data the image obtained from the reflection seismic data establishes that the fan like structure is a major upper crustal feature the present data in combination with previous deep seismic data sets exclude a single stage extensional model with an east dipping extensional deformation zone protracting eastwards from the western part of the profile the combined seismic data provide support for a two stage compressional model for the development of the fan like structure with crustal thickening and stacking prior to 955 ma and later compression with a stronger horizontal component of displacement during 930 905 ma the latter gave rise to the development of the complex system of retrogressive deformation zones referred to as the sveconorwegian frontal deformation zone sfdz a tectonic analogy to the grenville front in the eastern part of north america the sfdz dips westwards may become listric at depth and possibly sole in a zone of lower crustal reflectivity west of the present profile the kinematics and geometry of the sfdz suggest that reverse displacements thrusting may be responsible at least in part for the exhumation of the medium to high grade rocks in the western part of the fan like structure both the seismic data and the surface structural geology show many similarities to the grenville front

pool spacing in forest channels field surveys of stream channels in forested mountain drainage basins in southeast alaska and washington reveal that pool spacing depends on large woody debris lwd loading and channel type slope and width mean pool spacing in pool riffle plane bed and forced pool riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing lwd loading whereas pool spacing in generally steeper step pool channels is independent of lwd loading although plane bed and pool riffle channels occur at similar low lwd loading they exhibit typical pool spacings of greater than 9 and 2 4 channel widths respectively forced pool riffle channels have high lwd loading typical pool spacing of 2 channel widths and slopes that overlap the ranges of free formed pool riffle and plane bed channel types while a forced pool riffle morphology may mask either of these low lwd loading morphologies channel slope provides an indicator of probable morphologic response to wood loss in forced pool riffle reaches at all study sites less than 40 of the lwd pieces force the formation of a pool we also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear cut forests have lower lwd loading and hence fewer pools than reaches in pristine forests

geomorphic mapping and taxonomy of fluvial landforms abstract fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes we identified 68 of these existing terms that describe truly distinctive landforms in which form is maintained under characteristic conditions and fluvial processes clear topographic definitions for these landforms to consistently identify and map them are lacking with the explosion of continuous high resolution topography and digital elevation models we have plenty of new basemaps in which these landforms are clearly visible but very few examples of manual or automated classification of fluvial landforms fluvial landforms are the building blocks of a river and are variously referred to as geomorphic units morphological units habitat units and channel units we present a tiered framework for describing geomorphic units with tier 1 differentiating units on the basis of their stage tier 2 separating shape e g concave convex or planar tier 3 using particular key attributes to narrow in on the likely specific geomorphic unit type and tier 4 differentiating those types on the basis of vegetative or roughness modifiers information on the assemblage and configuration of geomorphic units can be used to inform process based interpretations of the range of river behavior the accuracy and transferability of such analyses is fundamentally tied to the taxonomy we assign to these discrete building blocks in this paper we clarify the terminology and definitions relating to the identification and delineation of geomorphic units margins and structural elements we establish a set of procedures that can be used to manually map and identify these features the proposed framework provides a rigorous and repeatable approach to identification of topographically defined features of riverscapes we demonstrate the application of these systematic yet flexible procedures with a series of maps from rivers in differing valley settings

40ar 39ar geochronology across the mylonite zone and the southwester granulite province in the sveconorwegian orogen of s sweden abstract the crustal segment between the mylonite zone mz and the protogine zone in southern sweden the southwestern granulite province sgp is characterized by numerous occurrences of granulite and upper amphibolite facies rocks including migmatitic gneisses mafic granulites garnet amphibolites and charnockites the southwest part of the mylonite zone north of varberg marks a tectonic upper boundary of the sgp a 40 ar 39 ar study was initiated across the mylonite zone and within the sgp in order to constrain and compare the ages obtained from within the sgp with those obtained north of and within the mylonite zone 23 homblendes and one muscovite have been analyzed the results of these analyses indicate the following 1 hornblendes from within and near the mz yield 40 ar 39 ar hornblende ages of 915 ma these ages are interpreted to date the dynamic crystallization or cooling below 500 c of the deformation associated with the mz 2 away from the mz there is a distribution of ages between those which yield younger sveconorwegian ages of 931 934 ma and those which yield older sveconorwegian ages generally between 960 and 1007 ma the younger age may be associated with orogenic uplift while the older one may be associated with an earlier sveconorwegian crustal thickening event 3 the one muscovite age of 904 ma would indicate a late cooling rate of at least 6 15 c ma cooling rates of this magnitude may suggest that the final uplift of the sveconorwegian orogen was related to large scale crustal extension

significant decadal channel change 58 67 years post dam accounting for uncertainty in topographic change detection between contour maps and point cloud models abstract construction of digital elevation models dems and the subtraction of dems between different points in time as a method to determine temporal patterns of scour and fill is a highly valuable procedure emerging in geomorphology these dems of differences dods must be assessed for error in order to distinguish actual topographic change from uncertainty and surface error current methods include 1 uniformly excluding all values that fall below a minimum threshold 2 using a spatially variable approach such as the construction of minimum level of detection lod grids or 3 the creation of a fuzzy inference system although spatially variable methods for determining error have been more accurate in excluding noise without discarding large amounts of meaningful data a challenge remains in performing dods against preexisting contour based maps for which no original point data are available the goals of this study were to 1 develop a method that overcomes the unknown point density of contour and other historical data sets and allows for some assessment of dod uncertainty on the basis of information on topographic variability 2 perform comprehensive uncertainty analysis testing to understand the opportunities and constraints associated with this new method and 3 report and interpret the overall pattern and volume of decadal topographic change for a regulated river 67 years post dam in light of alternate conjectured mechanisms of post dam longitudinal profile adjustment the key feature of the new approach is the introduction of a high density artificial point grid that samples the topographic variability evident in the available historical data set the testbed used to develop and assess this new dod method was the 37 5 km lower yuba river california historical data consisted of 0 6 m contours from a 1999 survey while a more detailed point cloud was available for the most recent survey in 2006 2008 to evaluate uncertainty in the method this study applied seven different uncertainty metrics of varying strictness t 1 t 1 96 uniform 0 3 m exclusion t 1 plus uniform 0 3 m exclusion t 1 with lod minimum at 0 3 t 1 96 plus uniform 0 3 m exclusion and t 1 96 with lod minimum at 0 3 and two different dod adjustment methods exclusion and subtraction a stringent approach involving joint use of the contour half interval and the spatially distributed lod grid at a 95 confidence limit excluded 44 3 of the study area from spatial assessment of channel change and volumetric change computation this preferred approach yielded an estimated 2 518 million m 3 of total scour and 2 455 million m 3 of total fill in 7 9 years after considering different mapping epochs the net annual average export was 17 000 m 3 32 500 tons to the feather river and a river valley sediment yield of 2205 tons km 2 year this amount is 36 of the post dam annual yield of gravel and cobble to the upstream reservoir that blocks sediment conveyance into the study domain suggesting that the lowland system is still highly dynamic 67 years after the dam was built the scientific significance of this is that the response of rivers to dams can be far more long lasting and complex depending on the suite of cumulative societal impacts to rivers the ability to account for spatially explicit dod uncertainty i e data retention when uncertainty is low and data removal when uncertainty is high when comparing historic contour based and modern point cloud based dems will allow for more detailed and reliable dods and sediment budgets in these cases

relationships between mesoscale morphological units stream hydraulics and chinook salmon oncorhynchus tshawytscha spawning habitat on the lower yuba river california an expert based approach was used to identify 10 morphological unit types within a reach of the gravel bed regulated yuba river california that is heavily utilized by spawning chinook salmon oncorhynchus tshawytscha analysis of these units was carried out using two dimensional hydrodynamic modeling field based geomorphic assessment and detailed spawning surveying differently classified morphological units tended to exhibit discrete hydraulic signatures in most cases the froude number adequately differentiated morphological units but joint depth velocity distributions proved the most effective hydraulic classification approach spawning activity was statistically differentiated at the mesoscale of the morphological unit salmon preferred lateral bar riffle and riffle entrance units these units had moderately high velocity unit median 0 45 m s 1 and low depth unit median 0 6 m but each exhibited a unique joint depth velocity distribution a large proportion of redds 79 were associated with conditions of convective flow acceleration at riffle and riffle entrance locations in addition to reflecting microhabitat requirements of fish it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat

development of channel organization and roughness following sediment pulses in single thread gravel bed rivers large episodic inputs of coarse sediment sediment pulses in forested mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness a conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels channels exhibited self organizing behavior to various degrees based on channel gradient presence of large in channel wood or other forcing elements the size of the sediment pulse and the number of bed mobilizing flows since disturbance typical channel changes following a sediment pulse were initial decreases in water depth in variability of bed elevations and in the regularity of bed form spacing trajectories of change subsequently showed increased average water depth more variable and complex bed topography and increased uniformity of bed form spacing bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale two to five channel widths than in streams without such forcing mechanisms five to 10 channel widths channel roughness increased as bed forms developed

channel units in small high gradient streams on vancouver island british columbia descriptions and a classification are presented of channel units in very high gradient first order mountain channels bedrock cascades boulder cascades rapids chutes riffles glides and pools had distinct mean bed gradients of 0 49 0 45 0 20 0 12 0 09 0 06 and 0 03 respectively multiple pairwise comparisons showed that these gradients are significantly different except bedrock cascades were not different from boulder cascades and glides were not different from chutes riffles or pools channel width and entrenchment do not discriminate channel units in any consistent way but characteristic substrates occur constituent substrates of bedrock and boulder cascades are nominally apparent while chutes also are bedrock bound mixtures of boulders and cobbles constitute rapids while mixtures of cobbles and gravel constitute riffles glides and pools generally are composed of boulders cobbles and gravel in various proportions log steps sometimes delimit units particularly pools but wood is not a dominant element in these channels gradients of channel units in these small first order dominantly nonalluvial channels are significantly higher than correspondingly identified units in larger channels farther down the drainage system the reason for this distinction is supposed to be related to channel scale hence potential stream power

geospatial organization of fluvial landforms in a gravel cobble river beyond the riffle pool couplet abstract morphological units mu are landforms with distinct local form process associations at 1 10 channel widths scale that may be the fundamental building blocks describing the geomorphic structure of a river past research has disproportionately focused on the two mus of pool and riffle conjecturing that they are the central linked couplet in the process form association the goal of this study was to delineate and map spatially explicit fluvial landforms in two dimensional planview within a gravel cobble bed river using two dimensional hydrodynamic delineation and then to statistically examine mu geospatial patterns for indicators of deterministic geomorphic control this procedure is not discharge dependent like mesohabitat methods but gets at the geometry of underlying landforms statistical testing confirmed that eight delineated in channel mu types comprise a complex and diverse channel morphology in which pools and riffles are not directly coupled specifically gravel cobble river channels 1 exhibit nonrandom spatial organization of their longitudinally and laterally variable landform morphology 2 consist of a variety of mu types not just pools and riffles and 3 show distinct mu collocations and avoidances with riffles linked to chutes and runs while pools are linked to slackwaters and glides planview mu delineation with two dimensional hydrodynamic modeling provides a bottom up approach to understanding and linking channel morphology with ecosystem services and geomorphic processes and is being used to guide river management and rehabilitation strategies

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

prograde metamorphic zircon formation in gabbroic rocks the tale of microtextures u pb zircon dates of metagabbroic rocks such as eclogite mafic granulite and garnet amphibolite are used to constrain the timing of tectonometamorphic evolution in orogens worldwide for such interpretation however it is imperative to define at which stage of the p t evolution that zircon crystallization took place the prograde peak or retrograde stage in order to accurately interpret metamorphic zircon ages it is necessary to assess how the zircon crystallized or recrystallized as zircon can dissolve or grow under different metamorphic conditions zircon is robust to retrograde isotopic resetting under most crustal conditions but equilibrium zr mass balance models have suggested that zircon is largely produced during retrograde metamorphism this study takes a textural approach and identifies and reviews zircon forming textures and reactions in gabbro and metagabbro at different metamorphic grades ranging from subgreenschist to upper amphibolite and eclogite facies and at different stages of metamorphic recrystallization the textural relationships demonstrate that in metagabbro metamorphic zircon grows during the early stage of metamorphic recrystallization independent of pressure and temperature the mode of zircon formation is remarkably similar throughout different stages of metamorphic recrystallization and the most significant source of zr is igneous baddeleyite hence in contrast to the equilibrium mass balance model most zircon in metagabbro forms by prograde metamorphic reactions that consume igneous phases and not by late retrograde reactions and the onset of zircon forming reactions is governed primarily by the introduction of a hydrous fluid commonly accompanied by ductile deformation less

metamorphic zircon formation at the transition from gabbro to eclogite in trollheimen surnadalen norwegian caledonides a transition from gabbro to eclogite has been investigated at vinddoldalen in south central norway with the aim to link reaction textures to metamorphic zircon growth and to obtain a direct u pb zircon age of the metamorphic process in the different rocks of the transition zone zircon occurs as i igneous prismatic grains ii metamorphic polycrystalline rims and pseudomorphs after baddeleyite and iii as tiny 10 mu m bead like zircon grains textural relations suggest that type ii zircon formed by breakdown of baddeleyite in the presence of silica whereas fe ti oxides were the main zr source for the type iii zircon subsolidus liberation of zr and formation of bead zircon took place by oxyexsolution of titanomagnetite during fluid assisted metamorphism and by resorption of fe ti oxide in rock domains that were completely recrystallized to eclogite sims secondary ion mass spectrometry and tims thermal ionization mass spectrometry dating provides comparable u pb ages of magmatic zircon and baddeleyite baddeleyite tims yielded an age of 1457 11 ma for the gabbro emplacement bead type metamorphic zircon from eclogite gave 425 10 ma tims dating the metamorphic transition from gabbro to eclogite in the upper basement of the lower allochthon in the south central scandinavian caledonides less

riffle pool maintenance and flow convergence routing observed on a large gravel bed river abstract geomorphologists have studied and debated over the processes responsible for natural riffle pool maintenance for decades most studies have focused on small wadable rivers but they lack much description of overbank flood conditions or a spatially explicit characterization of morphodynamics in this study 1 m horizontal resolution digital elevation models were collected from a riffle pool run sequence before and after an overbank flood with a 7 7 year recurrence interval on the relatively large gravel bed lower yuba river california digital elevation model differencing was used to quantify the magnitude and pattern of flood induced morphodynamic change cross section based analysis and two dimensional hydrodynamic modeling of flows ranging from 0 147 to 7 63 times bankful discharge were completed to evaluate the hydraulic mechanisms responsible for the observed topographic changes one key finding was that riffle pool relief increased by 0 42 m confirming the occurrence of natural hydrogeomorphic maintenance spatially complex patterns of scour and deposition exceeding 0 15 m at the scale of subwidth morphological units were reasonably predicted by the two dimensional mechanistic model that accounts for convective acceleration the one dimensional cross section based method underperformed the two dimensional model significantly consequently multiple scales of channel non uniformity and a dynamic flow regime caused the observed maintenance of the pool riffle morphology through the mechanism of flow convergence routing proposed by macwilliams et al macwilliams m l wheaton j m pasternack g b kitanidis p k street r l 2006 the flow convergence routing hypothesis for riffle pool maintenance in alluvial rivers water resources research 42 w10427 doi 10 1029 2005wr004391

lead concentrations and isotopes in corals and water near bermuda 1780 2000 abstract the history of the oceanic anthropogenic lead pb transient in the north atlantic ocean for the past 220 yr is documented here from measurements of pb concentration and isotope ratios from annually banded corals that grew in coastal seawaters near bermuda and from seawater samples collected during the last 20 yr of the 20th century anthropogenic pb emissions in this area have been dominated by the industrialization of north america beginning in the 1840s the introduction of leaded gasoline beginning in the 1920s and its phase out that began in the mid 1970s the phase out of leaded gasoline was largely completed by the late 1990s coral pb concentrations occur at a constant low level of about 5 nmol pb mol ca 15 pmol kg in seawater from the late 1700s to 1850 from 1850 to 1900 there is a small increase rising to a plateau at 25 nmol pb mol ca 80 pmol kg in seawater in the 1930s until the late 1940s at which point pb concentrations rapidly increase to 60 nmol pb mol ca 200 pmol kg in seawater in the mid 1970s pb began to decline to 25 nmol pb ca 40 pmol kg in seawater by the end of the 20th century comparable to levels occurring in the early 20th century pb isotope ratios pb i r show maximum 206pb 207pb 1 21 and 208pb 207pb 2 49 in the middle of the 19th century we conclude that this signal is a reflection of the early dominance of upper mississippi valley pb ore in the united states as previously seen in the estuarine sediments of rhode island after 1900 pb i r decrease only slightly until the 1960s when there is a significant local maximum in the 1970s to 206pb 207pb 1 19 and 208pb 207pb 2 45 as low pb i r sources were phased out in the united states then as us leaded gasoline utilization decreased more rapidly than european pb gas utilization which has lower pb i r western north atlantic pb i r decreased to 206pb 207pb 1 17 and 208pb 207pb 2 44 their lowest values in the past two centuries

u pb and sm nd dating of high pressure granulite and upper amphibolite facies rocks from sw sweden abstract geochronological data from different radiometric systems on high grade metamorphic rocks in the southwest swedish granulite region southwestern sweden are generally analytically precise but sometimes in conflict with each other age data from seven samples on which a variety of radiometric methods have been applied are presented the age of peak metamorphism is determined by metamorphic zircons from two garnet amphibolites at c 975 ma using the conventional u pb isotope and pb pb evaporation methods titanites from the same type of rocks give ages of c 923 3 ma and 945 2 ma the sm nd data on mafic granulites and garnet amphibolites yield surprisingly young ages between 945 and 900 ma similar to previous sm nd ages these ages are comparable to or even younger than the 40 ar 39 ar hornblende ages that range between 1030 and 930 ma assuming that the sm nd systematics are entirely controlled by volume diffusion the closure temperature of the sm nd system in minerals from these rocks would be comparable to or lower than that of ar diffusion in hornblende i e around 500 c

complicated secondary textures in zircon record evolution of the host granitic rocks studies from western tauern window and otztal stubai crystalline complex eastern alps western austria abstract samples of metamorphosed and deformed granitic rocks were collected from two alpine complexes with well constrained metamorphic history western tauern window and otztal stubai crystalline complex zircon grains from these samples were investigated in situ by a combination of scanning electron microscope techniques cathodoluminescence cl imaging and raman spectroscopy the aims were to describe and interpret complicated secondary textures and microstructures in zircon based on cross cutting relationships between secondary microstructures reconstruct the sequence of processes affecting zircon crystals link the evolution of zircon with the history of the host rocks the results indicate that zircon in the sampled granitic rocks forms growth twins and multi grain aggregates which are unusual for this mineral moreover various secondary textures have been found in the sampled zircon often cross cutting each other in a single crystal these include distorted oscillatory cl zoning with inner zones forming inward penetrating cl bright embayments which are the evidence of dry recrystallization via annealing lattice recovery cl mosaicism with no preservation of growth zoning but abundant nano and micro scale pores and mineral inclusions which are the evidence of recrystallization by coupled dissolution reprecipitation and or leaching embayed zircon boundaries filled with apatite monazite epidote and mylonitic matrix indicating mineral fluid reactions resulting in zircon dissolution and fragmentation overgrowth cl dark rims which contain nano pores and point to transport and precipitation of dissolved zircon matter we conclude that zircon in our meta granites is sensitive to metamorphism deformation events and was reactive with metamorphic fluids additionally we have found evidence of crystal plastic deformation in the form of low angle boundaries and bent grain tips which is a result of shearing and ductile deformation of the host rock we suggest that the observed complicated secondary textures in zircon can be linked to the evolutionary stages of the host rocks such as magmatic crystallization prograde metamorphism peak of amphibolite facies metamorphism post peak cooling and exhumation formation of ductile shear zones and final cooling to 250 c

effects of lidar derived spatially distributed vegetation roughness on two dimensional hydraulics in a gravel cobble river at flows of 0 2 to 20 times bankfull abstract the spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented drawing on a lidar derived meter scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage dependent channel roughness this study developed a meter scale two dimensional hydrodynamic model of 28 3 km of a gravel cobble bed river corridor for flows ranging from 0 2 to 20 times bankfull discharge with and without spatially distributed vegetation roughness results were analyzed to gain insight into stage dependent and scale dependent effects of vegetation on velocities depths and flow patterns at the floodplain filling flow of 597 49 m 3 s adding spatially distributed vegetation roughness parameters caused 8 0 and 7 4 increases in wetted area and mean depth respectively while mean velocity decreased 17 5 vegetation has a strong channelization effect on the flow increasing the difference between mid channel and bank velocities it also diverted flow away from densely vegetated areas on the floodplain vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs for the river as a whole as discharge increases overall roughness increases as well contrary to popular conception

basin scale methods for predicting salmonid spawning habitat via grain size and riffle spacing tested in a california coastal drainage basin scale predictive geomorphic models for river characteristics particularly grain size can aid in salmonid habitat identification however these basin scale methods are largely untested with actual habitat usage data here we develop and test an approach for predicting grain size distributions from high resolution lidar light detection and ranging derived topographic data for a 77 km2 watershed along the central california coast this approach improves on previous efforts in that it predicts the full grain size distribution and incorporates an empirically calibrated shear stress partitioning factor the predicted grain size distributions are used to calculate the fraction of the bed area movable by spawning fish we then compare the movable fraction with 7 years of observed spawning data we find that predicted movable fraction explains the paucity of spawning in the upper reaches of the study drainage but does not explain variation along the mainstem in search of another morphologic characteristic that may help explain the variation within the mainstem we measure riffle density a proxy for physical habitat complexity we find that field surveys of riffle density explain 64 of the variation in spawning in these mainstem reaches suggesting that within reaches of appropriate sized gravel spawning density is related to riffle density because riffle density varies systematically with channel width predicting riffle spacing is straightforward with lidar data taken together these findings demonstrate the efficacy of basin scale spawning habitat predictions made using high resolution digital elevation models copyright 2016 john wiley sons ltd

objective identification of pools and riffles this paper presents a new technique for objectively identifying pools and riffles the technique is termed the bed form differencing technique and as its data base has bed elevations surveyed at a fixed interval along the channel these elevations are differenced and the difference or elevation change values are used to identify pools and riffles where the cumulative elevation change since the last bed form exceeds a certain tolerance value a new bed form is considered to exist the type of bed form being determined by the direction of the elevation change analysis of a small stream in western new york suggests that the most realistic pool riffle sequence is obtained where the tolerance value is 0 75 times the standard deviation of the difference values the bed form differencing technique can be used to identify bed forms other than pools and riffles such as ripples and dunes by simply modifying the surveying interval to reflect the scale of the bed forms

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

mapping hydraulic biotopes using terrestrial laser scan data of water surface properties for more than a decade habitat mapping using biotopes in channel hydraulically defi ned habitats has underpinned aquatic conservation in the uk through a providing baseline information on system complexity and b allowing environmental and ecological change to be monitored and evaluated the traditional method used is the subjective river habitat or corridor survey this has recently been revised to include the fl oodplain via georhs but issues still exist concerning development of a national database due to the labour intensive nature of the data collection subjectivity issues between samplers temporal changes the fuzzy nature of perceived habitats and habitat boundaries this paper takes an innovative approach to biotope defi nition using high resolution spatial data to defi ne water surface roughness for two representative reaches of the river south tyne cumbria and the river rede northumberland uk data was collected using a terrestrial laser scanner tls and hydraulic variability simply expressed through assigning a local standard deviation value to a set of adjacent water surface values statistical linkage of these data with biotope locations defi ned visually in the fi eld allowed complete mapping of the surveyed reach defi ning habitat and biotope areas to the fi ne scale resolution of the tls data despite issues of data loss due to absorption and transmission through the water the refl ected signal generated an extremely detailed and objective map of the water surface roughness which may be compared with known biotope locations as defi ned by visual identifi cation in the fi eld the tls accuracy achieved in the present study is comparable with those obtained using hyperspectral imagery with 84 of the pool glide marginal deadwater amalgamated biotope 88 of riffl es 57 of runs and 50 of the amalgamated cascade rapid biotope successfully plotted it is clear from this exercise that biotope distribution is more complex than previously mapped using subjective techniques and based upon the water surface roughness delimiters presented in this study the amalgamation of pools with glides and marginal deadwaters riffl es with unbroken standing waves and cascades with rapids is proposed

geochronology of eclogite facies metamorphism in the sveconorwegian province of sw sweden abstract decompressed eclogites in the sveconorwegian province sw sweden have been dated using u pb geochronology zircons are common as inclusions in garnet and kyanite and other minerals in the decompressed eclogites titanite inclusions are found exclusively in the core of garnets the mineral inclusions and the chemical zoning of the garnets suggest inital growth under prograde amphibolite facies conditions followed by eclogite facies metamorphism and subsequent decompression through the high pressure granulite and upper amphibolite facies the zircon and titanite thus formed prior to the eclogite stage of the p t path the age of the eclogite forming event was determined by ion probe dating of zircon inclusions in garnets the obtained age of 972 14 ma is the maximum age of the eclogitisation the age of the titanite inclusions in garnet is 945 4 ma this age is similar to other u pb ages of titanite in the region which suggest that the titanite has been isotopically reset and that the age reflects cooling the mode of occurrence textural relationships and the chemical homogeneity suggest that the zircons formed from zr released from magmatitic fe ti oxides and possibly amphiboles during breakdown of magmatic minerals at the onset of the sveconorwegian metamorphism spot analyses of complex zircons from a granitic dyke in the eclogite yielded an age of 1403 15 ma for magmatic cores and an age of 963 22 ma for metamorphic rims the older age is a minimum age of the eclogite protolith and correspond to the age of a generation of granites in the region the rim age is within error identical to the age of eclogite metamorphism the eclogite metamorphism in sw sweden is younger than its grenvillian counterparts in scotland canada and usa

two new geobarometers for garnet amphibolites with applications to southeastern vermont two new geobarometers for the assemblage garnet hornblende plagioclase quartz have been calibrated on the basis of the equilibrium 6 anorthite 3 tremolite 2 grossular 1 pyrope 3 tschermakite 6 quartz and its fe end member equivalent data representing 37 natural samples that equilibrated at conditions of 2 5 to 13 kbar and 500 to 800 c were fitted to the general equation rt in keq a bt p i c by using a weighted least squares method multiple correlation coefficients are high 0 98 and 0 97 lines of constant keqhave extremely shallow slopes in p t space 2 to 8 bars per degree suggesting that pressures may be deduced precisely even where temperatures are only poorly constrained typical analytical errors and temperature imprecisions propagate to very small errors in pressure about 500 bars caution is advised in applying the barometers outside the range of calibrant mineral compositions application of the calibrations to samples from southeastern vermont near the strafford chester and athens domes documents relatively high pressure metamorphism 7 to 10 kbar for these structures

tracing the 1271 1246 ma central scandinavian dolerite group mafic magmatism in fennoscandia u pb baddeleyite and hf isotope data on the moslatt and borgefjell dolerites between 1271 and 1246 ma dolerite dykes and sills of the central scandinavian dolerite group intruded into the fennoscandian shield during three distinct magmatic pulses they are distributed around five large magmatic complexes extending from sweden to western finland and record large scale intracratonic tensional stress coeval plutonism is observed in the westernmost terrane of the sveconorwegian orogen in southern norway but differs in the sense of a bimodal character and uncertain fennoscandian ancestry of the host terrane we report a u pb baddeleyite age of 1269 12 ma for a gabbronoritic member of an e trending set of dykes called the moslatt dolerites near lake vattern in southern sweden much farther to the south than any previously known central scandinavian dolerite group rock a similar age of approximately 1275 ma is obtained for a meta dolerite sheet in the borgefjell basement window in the scandinavian caledonides in mid norway the initial epsilon hf values for these two dykes are 3 9 and 10 1 respectively and correspond to the range of values for other occurrences of the central scandinavian dolerite group 4 7 to 10 3 they add to the evidence that the central scandinavian dolerite group is characterized by more positive epsilon values depleted source than other mafic proterozoic suites in fennoscandia these results extend the distribution of c 1270 1245 ma mafic magmatism in fennoscandia particularly when accounting for significant caledonian shortening the central scandinavian dolerite group and coeval bimodal magmatism in s norway may represent distal magmatic events related to a mesoproterozoic subduction along the western margin of fennoscandia rather than hotspot mantle plume activity as previously suggested

geochronological and geochemical constraints on the petrogenesis of middle paleozoic kwangsian massive granites in the eastern south china block abstract to achieve a better understanding of the kwangsian orogenic event of the eastern south china block this paper documents a set of new zircon u pb geochronological and hf isotopic data and whole rock elemental and sr nd isotopic analytical results for the representative massive granite intrusions across the jiangshan shaoxing fault the studied samples are classified into two groups representing the rocks from the cathaysia block to the east of the jiangshan shaoxing fault group 1 and those from the eastern yangtze block between the anhua luocheng and jiangshan shaoxing faults group 2 the group 1 samples gave the zircon u pb ages of 405 454 ma and e hf t values of 3 6 to 15 2 with hf model ages of 1 6 2 4 ga group 2 yielded the zircon u pb ages of 400 432 ma and e hf t values of 0 2 to 12 7 with hf model ages of 1 3 2 2 ga geochemically the group 1 samples a cnk 1 02 1 43 have relatively lower al 2 o 3 mgo cao p 2 o 5 and e nd t but higher k 2 o na 2 o than those of group 2 a cnk 0 93 1 44 both groups show similar chondrite normalized patterns of rare earth elements with eu eu values of 0 15 0 92 and strongly negative ba sr nb p and ti anomalies in primitive mantle normalized spider diagrams their e nd t values range from 11 1 to 8 0 for group 1 and 8 9 to 5 0 for group 2 generally similar to those of precambrian paragneiss and contemporaneous gneissoid granites in the eastern south china block our geochronological results indicate that the kwangsian massive granites in the eastern south china block were crystallized between 400 ma and 454 ma synchronous to the kwangsian gneissoid granites along the wugong and wuyi baiyun yunkai domains in the eastern south china block the synthesis of these whole rock geochemical and in situ zircon hf isotopic data suggests that both the group 1 and 2 granites across the jiangshan shaoxing fault were predominantly derived from a crustal source with some proportional metapelitic and metaigneous components from the precambrian basement the input of juvenile mantle derived magma is insignificant taking into account other available evidences it is proposed that the jiangshan shaoxing fault might be a pre existing boundary between the yangtze and cathaysia blocks which was reactivated during the middle paleozoic kwangsian orogenic event the massive granitic magmatism was probably resulted from the doubly crustal thickening and subsequent isostatic readjustment in an intracontinental tectonic regime

zircon growth during progressive recrystallization of gabbro to garnet amphibolite eastern segment sveconorwegian orogen the interpretation of whether a dated metamorphic zircon generation grew during the prograde peak or retrograde stage of a metamorphic cycle is critical to geological interpretation this study documents a case at herrestad in the eastern part of the 1 0 ga sveconorwegian province involving progressive metamorphic recrystallization of gabbro to garnet amphibolite and associated behaviour of zr bearing minerals in this case textures show that baddeleyite is by far the main source of zr for metamorphic zircon growth the amount of metamorphic zircon formed was primarily controlled by the degree of metamorphic recrystallization which in turn was controlled by deformation and the presence of a fluid as a transport medium zircon in the herrestad rocks shows a range of morphologies and internal textures at different degrees of metamorphic recrystallization igneous zircon occurs together with baddeleyite in coarse grained olivine free facies of the gabbro metamorphic polycrystalline zircon rims on baddeleyite and minute 5 m bead like zircon grains at fe ti oxide boundaries characterize the transition to coronitic metagabbro with increasing metamorphic recrystallization polycrystalline zircon rims grow at the expense of baddeleyite and the amount of minute bead like zircon increases forming strings of zircon beads with increasing distance from fe ti oxide grains the progressive breakdown of baddeleyite results in polycrystalline zircon aggregates that become denser and finally form single grains in completely recrystallized garnet amphibolite late magmatic zircon crystallized at 156765 ma whereas metamorphic zircon dates amphibolite facies metamorphic recrystallization at 97067 ma the herrestad case illustrates a general rule that the bulk zr budget in originally baddeleyite bearing rocks will rapidly become locked into metamorphic zircon during the first event of metamorphic recrystallization when silica and zr are released from the igneous minerals incomplete metamorphic recrystallization and partial preservation of baddeleyite however also allows later stages of zircon formation thus in incompletely reacted rocks the final result may be highly complex with microscale zircon of several age generations less

geochronologic evidence for a cold arc continent collision the taiwan orogeny abstract in order to constrain the tectonic consequences of the collision of the luzon arc with the se chinese continental margin during the neogene taiwan orogeny we assess the thermal history of the poly metamorphic para autochtthonous rocks of the continental margin in taiwan to accomplish this we report a new sims u pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology zircons extracted from the fenniaolin amphibolite near nanao taiwan in the contact aureole of a granodiorite are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on 1 their equant shape rather than the prismatic shape typical of magmatic zircon 2 their microcrystalline or micro saccharoidal aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging 3 their low concentrations of u most 206 pb 238 u age of 86 1 ma analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism we thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid cretaceous existing 40 ar 39 ar and rb sr cooling ages of both amphibole and muscovite at 80 ma e g lan 1990 lo and onstott 1995 show that the granodiorite and its contact aureole cooled rapidly from 700 to the crustal history reconstructed from these data shows that the regional gneissic terrane of the northern tananao complex may have been caused by coalescing contact aureoles of multiple mid cretaceous intrusions the nanao intrusive event and not by the neogene taiwan orogeny on the contrary the tananao rocks probably achieved middle greenschist conditions and 15 20 km depth in a forearc setting in the early cretaceous this intrusive event caused regional contact metamorphism at about 85 ma after which the passive margin setting preserved these rocks at mid crustal depths until the beginning of the taiwan orogeny 5 ma these depths 10 12 km and temperatures 200 250 c were high enough to account for the late miocene lower greenschist facies cleavages and the pliocene pleistocene fission track cooling ages without additional loading and heating from the taiwan orogeny

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

protolith ages and timing of deformation in the eastern marginal part of the sveconorwegian orogen southwestern sweden abstract u pb zircon and titanite ages from variably metamorphosed igneous rocks in the eastern marginal part of the sveconorwegian orogen eastern segment north of lake vanern sweden suggest that these rocks belong to the younger c 1 71 1 65 ga igneous suite of the c 1 85 1 65 ga transscandinavian igneous belt tib two porphyritic meta granites and one isotropic monzonite yield u pb zircon ages of 1661 27 1674 7 and 1674 7 ma respectively these ages support earlier interpretations that the eastern segment north of lake vanern contains tectonically reworked tib rocks and that there is no major lithological discontinuity either across the sveconorwegian frontal deformation zone or within the eastern segment igneous brown coloured titanites from five samples yield similar u pb ages as the zircons in contrast colourless and oblate shaped titanites from the western penetratively deformed parts of the eastern segment give concordant ages of 976 4 and 956 6 ma further to the east similar titanite from both a penetratively deformed meta granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late sveconorwegian lower intercept ages this type of titanite is interpreted to be syntectonic and formed during the upper greenschist east to amphibolite west facies fabric forming event in the eastern segment since the brown igneous titanites and the zircons share a common igneous origin and the single type of metamorphic titanites are either concordant or strongly discordant towards late sveconorwegian intercept ages it is inferred that no major tectonothermal event occurred between the time of tib emplacement and the late sveconorwegian tectonothermal reworking pre sveconorwegian palaeo to mesoproterozoic deformational and metamorphic events gothian which have been inferred west of and further south within the eastern segment appear to be absent in the northern part of this crustal unit

morphology of riffle pool sequences in the river severn england despite the occurrence of pool riffle sequences in many rivers there are few data concerning pool riffle unit morphology of many criteria proposed to identify pool riffle units only two methods can be regarded as objective and robust these are the zero crossing and the control point methods in this paper statistics are developed from the zero crossing method to describe the streamwise morphology of 275 riffles and 285 pools which form a near continuous 32 1km of the bed of the river severn in shropshire england yalin s theoretical relationship between pool riffle unit length i p and channel width w i p 3w applies to the river severn reach average riffle height h is a constant proportion of bankfull depth h typically h i 0 16h riffle height is a positive function of riffle length pool depth is a positive function of pool length however both riffle length and pool length increase more rapidly than the bed level amplitude such that long riffles or pools are relatively flat as channel gradient reduces bedforms flatten and become more asymmetric as riffle stoss sides and the proximal slope of pools lengthen at the expense of riffle lee sides and pool distal slopes the statistical relationships between riffle height length and water depth are similar to those for equilibrium subaqueous dunes the severn data are partially consistent with yalin s theoretical analysis relating riffle bedform length lr to water depth i e lr i i2i h wherein i i i 1 for steep near equilibrium bedforms but i i i 2 to 3 as the relative depth decreases and riffles become long low features a consideration of turbulence data indicates that the frequency of coherent turbulent flow structures associated with the riffle pool mixing length is of the order of 60 seconds the morphological and dynamic similarity of the river severn riffles with dunes raises intriguing questions with respect to self similar convergent organization of periodic alluvial bedforms and to bedform dynamic classification particularly

characterising physical habitats and fluvial hydromorphology a new system for the survey and classification of river geomorphic units geomorphic units are the elementary spatial physical features of the river mosaic at the reach scale that are nested within the overall hydromorphological structure of a river and its catchment geomorphic units also constitute the template of physical habitats for the biota the assessment of river hydromorphological conditions is required by the european water framework directive 2000 60 wfd for the classification and monitoring of water bodies and is useful for establishing links between their physical and biological conditions the spatial scale of geomorphic units incorporating their component elements and hydraulic patches is the most appropriate to assess these links given the weakness of existing methods for the characterisation and assessment of geomorphic units and physical habitats e g lack of a well defined spatiotemporal framework terminology issues etc a new system for the survey and characterisation of river geomorphic units is needed that fits within a geomorphologically meaningful framework this paper presents a system for the survey and classification of geomorphic units gus geomorphic units survey and classification system aimed at characterising physical habitats and stream morphology the method is embedded into a multiscale hierarchical framework for the analysis of river hydromorphological conditions three scales of geomorphic units are considered i e macro units units sub units organised within two spatial domains i e bankfull channel and floodplain different levels of characterisation can be applied depending on the aims of the survey broad basic and detailed level at each level different complementary information is collected the method is applied by combining remote sensing analysis and field survey according to the spatial scale and the level of description required the method is applicable to most of fluvial conditions and has been designed to be flexible and adaptable according to the objectives e g reach characterisation assessment monitoring and available data e g image resolution the method supports integrated hydromorphological assessment at the reach scale e g the morphological quality index mqi and therefore contributes to better establishing links between hydromorphological conditions at the reach scale characteristic geomorphic units and related biological conditions